Patent Application
20250186983
In the modern study of light-matter interaction, a substantial number of efforts have been devoted to research on condensed matter. Generally, materials are categorized into conductors, semiconductors, and insulators, depending on the energy gap between the valence band and the conduction band. These materials behave differently under the illumination of light. With the assistance of thermal energy at a certain temperature, the electrons in conductors can be excited to higher energy levels, the electrons in semiconductors can be excited only when the light energy is higher than their band gap, while those in insulators cannot be exited. The excited electrons carrying the energy from the photons can deliver these energies to other matters to drive physical or chemical processes. Since the past few decades, studies of light-matter interactions have been of great interests, and academic products have benefited electronics, medical sciences, and chemical industries (Harrison, W. A. Electronic Structure and the Properties of Solids: the Physics of the Chemical Bond. Courier Corp., 2012; Cortie, M. B. et al., Chem. Rev. 2011, 111, 3713-3735; Dini, D. et al., Chem. Rev. 2016, 116, 13043-13233; Gonzilez-Urbina, L. et al., Chem. Rev. 2012, 112, 2268-2285; Hsu, S.-W. et al., Chem. Rev. 2018, 118, 3100-3120; Tadepalli, S. et al., Chem. Rev. 2017, 117, 12705-12763).
Nanoparticles present plenty of unique properties in thermodynamics, surface structures, optical responses, and so on. Their large surface energies and unique optical absorption properties are especially crucial to applications of metal and metal oxyhydroxide nanoparticles. As the size of the particle decreases, its mass-specific surface area increases tremendously. This higher surface area allows more active sites to interact with other substrates for the following physical or chemical processes. The high surface energy is also originated from their non-perfect surface structures. The high curvature of small nanoparticles creates plenty of surface defects and high-index facets. These highly unsaturated sites have a higher potential to adsorb other chemical species and may lower the activation energy of chemical reactions (Sergeev, G. B., 7—Size Effects in Nanochemistry. Ed. Elsevier Science: Amsterdam, 2006)
Nanoparticles also present some attractive optical properties. One of the well-known phenomena in some small noble metal nanoparticles is the localized surface plasmon resonances (LSPR). LSPRs result in strong absorption of a certain frequency of light in ultraviolet-to-visible light (UV-vis) region in silver (Ag), gold (Au), copper (Cu), and aluminum (Al) nanoparticles. This excitation can generate a great number of high-energy electrons at the excitation frequency, and these electrons can be injected into other adsorbed substrates to drive chemical processes. The utilization of ubiquitous solar energy and converting it into other forms of energy with high efficiency is highly favorable in accordance with the goal of overcoming the energy crisis and low-carbon production strategies (M. H. Nayfeh. “Optics in nanotechnology,” in Optics in Our Time. Springer, 2016).
Even though the synthesis of free-standing nanoparticles has been well-developed, the nanoparticles dispersed in liquid media are usually hard to purify and suffer from aggregation. Loading metal or metal oxyhydroxide nanoparticles onto support materials can not only increase their stability but also benefit the application through interaction between the nanoparticle and the support materials chemically or optically.
Thus, there is need in the art for ultrafine metal nanoparticles and methods of making such nanoparticles. The present invention satisfies this unmet need.
In one aspect, the present invention relates to a method of fabricating a nanoparticle material, the method comprising: providing silica nanospheres; dispersing the silica nanospheres in a first solvent; collecting and drying the silica nanospheres; dispersing the silica nanospheres in a second solvent and adding a metal precursor to create composite nanoparticles; collecting and drying the composite nanoparticles to create a nanoparticle material. In some embodiments, the silica nanospheres have diameters less than 1500 nm. In some embodiments, the step of dispersing the silica nanospheres in a first solvent further comprises the step of altering the pH of the first solvent to reach a value between 8 and 13. In some embodiments, the step of altering the pH of the first solvent comprises the step of adding a base or an acid to the first solvent. In some embodiments, the step of dispersing the silica nanospheres in a second solvent further comprises the step of altering the pH of the second solvent to reach a value between 5 and 14. In some embodiments, the step of altering the pH of the second solvent to reach a value between 5 and 14 comprises the step of adding an acid or a base to the second solvent.
In some embodiments, the metal precursor is selected from the group consisting of: manganese(II) nitrate hydrate (Mn(NO3)2·xH2O), Iron(II) chloride (FeCl2), cobalt(II) nitrate hexahydrate (Co(NO3)2·6H2O), nickel(II) nitrate hexahydrate (Ni(NO3)2·6H2O), copper(II) nitrate trihydrate (Cu(NO3)2·3H2O), ruthenium(III) chloride hydrate (RuCl3·xH2O), sodium tetrachloropalladate(II) hydrate (Na2PdCl4·xH2O), sodium hexachlororhodate(III) hydrate (Na3RhCl6·xH2O), tetrachloroauric(III) acid trihydrate (HAuCl4·3H2O), sodium tetrachloroplatinate(II) hydrate (Na2PtCl4·xH2O), potassium tetrachloroplatinate(II) hydrate (K2PtCl4·xH2O), sodium hexachloroplatinate (Na4PtCl6), potassium hexachloroplatinate (K4PtCl6), magnesium chloride (MgCl2), aluminum nitrate nonahydrate (Al(NO3)2·9H2O), zinc nitrate hexahydrate (Zn(NO3)2·6H2O), and combinations thereof. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution with less than 50.0 wt % of a metal precursor.
In some embodiments, the composite nanoparticles comprise metal nanoparticles with diameters less than 40 nm. In some embodiments, the step of collecting and drying the composite nanoparticles further comprises the step of reducing the composite nanoparticles. In some embodiments, the step of reducing the composite nanoparticles comprises the step of thermally reducing the composite nanoparticles. In some embodiments, the step of thermally reducing the composite nanoparticles comprises the step of contacting the composite nanoparticles with a flow of 5% H2/N2 gas. In some embodiments, the step of reducing the composite nanoparticles further comprises the step of coating the composite nanoparticles with a dielectric material coating. In some embodiments, the step dispersing the silica nanospheres in a second solvent, altering the pH of the second solvent, and adding a metal precursor the composite nanoparticles, comprises the step of anchoring the metal precursors to the surface of the silica nanospheres through metal-silane bonds.
In one aspect, the present invention relates to a nanoparticle material comprising silica nanospheres, wherein the silica nanospheres are coated with metal nanoparticles with diameters less than 40 nm. In some embodiments, the silica nanospheres comprise a dielectric material. In some embodiments, the dielectric material comprises a compound selected from the group consisting of silicon oxide (SiO2), aluminum oxide (Al2O3), tantalum pentoxide (Ta2O5), titanium oxide (TiO2), tungsten Oxide (WO3), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon nitride (SiN4), cerium oxide (CeO2), iron oxide (Fe2O3), lanthanum oxide (La2O3), hafnium oxide (HfO2), chromium oxide (Cr2O3), strontium titanate (STO), barium strontium titanate (BST), PLZT (lead zirconate titanate), lead magnesium niobate (PMN), and lead zirconate titanate (PZT), and combinations thereof. In some embodiments, the silica nanospheres have diameters less than 1500 nm. In some embodiments, the metal nanoparticles comprises a metal selected from the group consisting of: gold (Au), silver (Ag), copper (Cu), aluminum (Al), magnesium (Mg), iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), palladium (Pd), rhodium (Rh), platinum (Pt), manganese (Mn), zinc (Zn), molybdenum (Mo), tin (Sn), antimony (Sb), tungsten (W), rhenium (Re), iridium (Ir), and their combinations thereof. In some embodiments, the metal nanoparticles are anchored to the surface of the nanospheres through metal-silane bonds.
The following detailed description of various embodiments of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings illustrative embodiments. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities of the embodiments shown in the drawings.
The invention is in part based on silica nanospheres coated with metal nanoparticles which exhibit strong optical absorption in the visible spectral range. A general synthesis is reported wherein the metal nanoparticles are uniformly distributed among the surface of the silica nanospheres.
It is to be understood that the Figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for the purpose of clarity, many other elements found in polymer composites and methods of making. Those of ordinary skill in the art may recognize that other elements and/or steps are desirable and/or required in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein. The disclosure herein is directed to all such variations and modifications to such elements and methods known to those skilled in the art.
As used herein, each of the following terms has the meaning associated with it in this section. Unless defined otherwise, all technical and scientific terms used herein generally have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The articles “a” and “an” are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.
As used herein, the term “about” will be understood by persons of ordinary skill in the art and will vary to some extent depending on the context in which it is used. As used herein when referring to a measurable value such as an amount, a temporal duration, and the like, the term “about” is meant to encompass variations of 20% or +10%, more preferably +5%, even more preferably ±1%, and still more preferably ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods.
Throughout this disclosure, various aspects of the invention can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, and 6. This applies regardless of the breadth of the range.
In one aspect, the present invention relates to a nanoparticle material comprising nanospheres, wherein the nanospheres are coated with metal nanoparticles.
In some embodiments, the nanospheres are silica nanospheres. In some embodiments, the nanospheres comprises a dielectric material. In some embodiments, the silica nanospheres comprises a dielectric material. In some embodiments, the nanospheres comprise a metal oxide. In some embodiments, the dielectric material comprises inorganic elements such as silicon, zirconium, calcium, tungsten, cerium, iron, chromium, strontium, lead, magnesium, tin, titanium, yttrium, lanthanum, aluminum, hafnium, barium, tantalum, and the like. In some embodiments, the dielectric material comprises a metal oxide. In some embodiments, the dielectric material comprises a compound including, but not limited to, silicon oxide (SiO2), aluminum oxide (Al2O3), tantalum pentoxide (Ta2O5), titanium oxide (TiO2), calcium oxide (CaO), tungsten Oxide (WO3), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon nitride (SiN4), cerium oxide (CeO2), iron oxide (Fe2O3), lanthanum oxide (La2O3), hafnium oxide (HfO2), chromium oxide (Cr2O3), strontium titanate (STO), barium strontium titanate (BST), PLZT (lead zirconate titanate), lead magnesium niobate (PMN), lead zirconate titanate (PZT), other metal oxides, and combinations thereof. In some embodiments, the nanospheres are silane-functionalized.
In some embodiments the nanospheres comprise polymers such as thermoplastic elastomers, olefinic materials, polyolefin, polyurethane thermoplastic elastomers, polyamides, polyimides, synthetic rubbers, polytetrafluoroethylene (PTFE), polydimethylsiloxane (PDMS), polybutadiene, polyisobutylene, polystyrenes, polyurethanes, polychloroprene and silicones. Other dielectric materials include, but are not limited to: ceramics, glass, reinforced laminates such as polytetrafluoroethylene (PTFE) reinforced with glass, mica minerals and crystals, and non-conductive oxides.
In some embodiments, the nanospheres have diameters greater than 1 nm. In some embodiments, the nanospheres have diameters greater than 10 nm. In some embodiments, the nanospheres have diameters greater than 25 nm. In some embodiments, the nanospheres have a diameter greater than 50 nm. In some embodiments, the nanospheres have diameters greater than 100 nm. In some embodiments, the nanospheres have diameters greater than 200 nm. In some embodiments, the nanospheres have diameters greater than 300 nm. In some embodiments, the nanospheres have diameters greater than 400 nm. In some embodiments, the nanospheres have diameters greater than 500 nm. In some embodiments, the nanospheres have diameters greater than 750 nm. In some embodiments, the nanospheres have diameters greater than 1000 nm. In some embodiments, the nanospheres have diameters greater than 1200 nm. In some embodiments, the nanospheres have diameters greater than 1500 nm. In some embodiments, the nanospheres have diameters greater than 2000 nm.
In some embodiments, the nanospheres have diameters less than 5 nm. In some embodiments, the nanospheres have diameters less than 10 nm. In some embodiments, the nanospheres have diameters less than 25 nm. In some embodiments, the nanospheres have diameters less than 50 nm. In some embodiments, the nanospheres have diameters less than 100 nm. In some embodiments, the nanospheres have diameters less than 200 nm. In some embodiments, the nanospheres have diameters less than 300 nm. In some embodiments, the nanospheres have diameters less than 400 nm. In some embodiments, the nanospheres have diameters less than 500 nm. In some embodiments, the nanospheres have diameters less than 750 nm. In some embodiments, the nanospheres have diameters less than 1000 nm. In some embodiments, the nanospheres have diameters less than 1200 nm. In some embodiments, the nanospheres have diameters less than 1500 nm. In some embodiments, the nanospheres have diameters less than 2000 nm.
In some embodiments, the metal nanoparticles comprise a metal. Exemplary metals include, but not limited to, gold (Au), silver (Ag), copper (Cu), aluminum (Al), magnesium (Mg), iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), molybdenum (Mo), tin (Sn), antimony (Sb), tungsten (W), rhenium (Re), iridium (Ir), palladium (Pd), rhodium (Rh), platinum (Pt), manganese (Mn), zinc (Zn), and their combinations thereof.
In some embodiments, the nanospheres are silica nanospheres. In some embodiments, the metal nanoparticles are anchored to the silica nanospheres through metal-silane bonds. In some embodiments, the metal nanoparticles are uniformly distributed on the nanospheres. In some embodiments, the metal nanoparticles are randomly distributed on the nanospheres. In some embodiments, the metal nanoparticles coat the nanospheres through a film-like coating. In some embodiments, the nanospheres coated with metal nanoparticles further comprise a dielectric material coating over the metal nanoparticles. In some embodiments, the dielectric material coating comprises a dielectric material such as those described above. In some embodiments, the dielectric material coating is a layer of silica. In some embodiments, there is a dielectric material coating between the nanospheres and the metal nanoparticles. In some embodiments, the dielectric material coatings described herein are less than 100 nm thick. In some embodiments, the dielectric material coatings described herein are less than 90 nm thick. In some embodiments, the dielectric material coatings described herein are less than 80 nm thick. In some embodiments, the dielectric material coatings described herein are less than 70 nm thick. In some embodiments, the dielectric material coatings described herein are less than 60 nm thick. In some embodiments, the dielectric material coatings described herein are less than 50 nm thick. In some embodiments, the dielectric material coatings described herein are less than 40 nm thick. In some embodiments, the dielectric material coatings described herein are less than 30 nm thick. In some embodiments, the dielectric material coatings described herein are less than 20 nm thick. In some embodiments, the dielectric material coatings described herein are less than 10 nm thick. In some embodiments, the dielectric material coatings described herein are less than 9 nm thick. In some embodiments, the dielectric material coatings described herein are less than 8 nm thick. In some embodiments, the dielectric material coatings described herein are less than 7 nm thick. In some embodiments, the dielectric material coatings described herein are less than 6 nm thick. In some embodiments, the dielectric material coatings described herein are less than 5 nm thick. In some embodiments, the dielectric material coatings described herein are less than 4 nm thick. In some embodiments, the dielectric material coatings described herein are less than 3 nm thick. In some embodiments, the dielectric material coatings described herein are less than 2 nm thick. In some embodiments, the metal nanoparticles comprise metal oxyhydroxides MOy(OH)Z. In some embodiments, the metal nanoparticles comprise metal oxides (MOy).
In some embodiments, the metal nanoparticles have diameters less than 200 nm. In some embodiments, the metal nanoparticles have diameters less than 100 nm. In some embodiments, the metal nanoparticles have diameters less than 90 nm. In some embodiments, the metal nanoparticles have diameters less than 80 nm. In some embodiments, the metal nanoparticles have diameters less than 70 nm. In some embodiments, the metal nanoparticles have diameters less than 60 nm. In some embodiments, the metal nanoparticles have diameters less than 50 nm. In some embodiments, the metal nanoparticles have diameters less than 40 nm. In some embodiments, the metal nanoparticles have diameters less than 30 nm. In some embodiments, the metal nanoparticles have diameters less than 20 nm. In some embodiments, the metal nanoparticles have diameters less than 10 nm. In some embodiments, the metal nanoparticles have diameters less than 9 nm. In some embodiments, the metal nanoparticles have diameters less than 8 nm. In some embodiments, the metal nanoparticles have diameters less than 7 nm. In some embodiments, the metal nanoparticles have diameters less than 6 nm. In some embodiments, the metal nanoparticles have diameters less than 5 nm. In some embodiments, the metal nanoparticles have diameters less than 4 nm. In some embodiments, the metal nanoparticles have diameters less than 3 nm. In some embodiments, the metal nanoparticles have diameters less than 2 nm. In some embodiments, the metal nanoparticles have diameters less than 1 nm.
In some embodiments, the metal nanoparticles have diameters greater than 200 nm. In some embodiments, the metal nanoparticles have diameters greater than 100 nm. In some embodiments, the metal nanoparticles have diameters greater than 90 nm. In some embodiments, the metal nanoparticles have diameters greater than 80 nm. In some embodiments, the metal nanoparticles have diameters greater than 70 nm. In some embodiments, the metal nanoparticles have diameters greater than 60 nm. In some embodiments, the metal nanoparticles have diameters greater than 50 nm. In some embodiments, the metal nanoparticles have diameters greater than 40 nm. In some embodiments, the metal nanoparticles have diameters greater than 30 nm. In some embodiments, the metal nanoparticles have diameters greater than 20 nm. In some embodiments, the metal nanoparticles have diameters greater than 10 nm. In some embodiments, the metal nanoparticles have diameters greater than 9 nm. In some embodiments, the metal nanoparticles have diameters greater than 8 nm. In some embodiments, the metal nanoparticles have diameters greater than 7 nm. In some embodiments, the metal nanoparticles have diameters greater than 6 nm. In some embodiments, the metal nanoparticles have diameters greater than 5 nm. In some embodiments, the metal nanoparticles have diameters greater than 4 nm. In some embodiments, the metal nanoparticles have diameters greater than 3 nm. In some embodiments, the metal nanoparticles have diameters greater than 2 nm. In some embodiments, the metal nanoparticles have diameters greater than 1 nm.
In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is less than 1%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is less than 2%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is less than 3%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is less than 4%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is less than 5%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is less than 6%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is less than 7%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is less than 8%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is less than 9%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is less than 10%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is less than 15%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is less than 30%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is less than 50%.
In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is greater than 1%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is greater than 2%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is greater than 3%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is greater than 4%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is greater than 5%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is greater than 6%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is greater than 7%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is greater than 8%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is greater than 9%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is greater than 10%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is greater than 15%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is greater than 30%. In some embodiments, the mass percentage of the metal nanoparticles in the nanospheres is greater than 50%.
In one aspect, the present invention relates to a method of fabricating a nanoparticle material. Exemplary method 100 is shown in
In one embodiment, exemplary method 100 further comprises step 125, wherein the silica nanospheres are collected, washed with a solvent, and dried before moving to step 130. In some embodiments, the step of collecting and washing the silica nanospheres further comprises the step of centrifuging the silica nanospheres. Exemplary solvents and aqueous solvents for the first solvent and the second solvent are known in the art. In some embodiments, the second solvent is the same as the first solvent.
In some embodiments, the silica nanospheres that are provided have diameters greater than 1 nm. In some embodiments, the silica nanospheres that are provided have diameters greater than 10 nm. In some embodiments, the silica nanospheres that are provided have diameters greater than 25 nm. In some embodiments, the silica nanospheres that are provided have diameters greater than 50 nm. In some embodiments, the silica nanospheres that are provided have diameters greater than 100 nm. In some embodiments, the silica nanospheres that are provided have diameters greater than 200 nm. In some embodiments, the silica nanospheres that are provided have diameters greater than 300 nm. In some embodiments, the silica nanospheres that are provided have diameters greater than 400 nm. In some embodiments, the silica nanospheres that are provided have diameters greater than 500 nm. In some embodiments, the silica nanospheres that are provided have diameters greater than 750 nm. In some embodiments, the silica nanospheres that are provided have diameters greater than 1000 nm. In some embodiments, the silica nanospheres that are provided have diameters greater than 1200 nm. In some embodiments, the silica nanospheres that are provided have diameters greater than 1500 nm. In some embodiments, the silica nanospheres that are provided have diameters greater than 2000 nm.
In some embodiments, the silica nanospheres that are provided have diameters less than 10 nm. In some embodiments, the silica nanospheres that are provided have diameters less than 25 nm. In some embodiments, the silica nanospheres that are provided have diameters less than 50 nm. In some embodiments, the silica nanospheres that are provided have diameters less than 100 nm. In some embodiments, the silica nanospheres that are provided have diameters less than 200 nm. In some embodiments, the silica nanospheres that are provided have diameters less than 300 nm. In some embodiments, the silica nanospheres that are provided have diameters less than 400 nm. In some embodiments, the silica nanospheres that are provided have diameters less than 500 nm. In some embodiments, the silica nanospheres that are provided have diameters less than 750 nm. In some embodiments, the silica nanospheres that are provided have diameters less than 1000 nm. In some embodiments, the silica nanospheres that are provided have diameters less than 1200 nm. In some embodiments, the silica nanospheres that are provided have diameters less than 1500 nm. In some embodiments, the silica nanospheres that are provided have diameters less than 2000 nm.
In some embodiments, the step of dispersing the silica nanospheres in a first solvent, comprises the step of dispersing the silica nanospheres in an aqueous solvent. In some embodiments, the step of dispersing the silica nanospheres in a first solvent further comprises sonication of the first solvent comprising the silica nanospheres. In some embodiments, the step of dispersing the silica nanospheres in a first solvent, further comprises the step of adding a base or an acid to the first solvent. Dispersing the silica nanospheres in an aqueous solvent with a base or an acid ensures that the surface of the silica nanospheres are enriched in silanol groups.
In some embodiments, the step of dispersing the silica nanospheres in a first solvent, further comprises the step of altering the pH of the first solvent. In some embodiments, the step of dispersing the silica nanospheres in a first solvent, further comprises the step of altering the pH of the first solvent to reach a value between 8 and 13. In some embodiments, the step of altering the pH of the second solvent comprises the step of adding a base or an acid to the first solvent. Altering the pH of the first solvent ensures that the surface of the silica nanospheres is negatively charged and rich in —Si—O— groups. The step of altering the pH of the first solvent further results in the altering of the zeta potentials of the silica nanospheres. As the zeta potential becomes more negative, this indicates that there is an increased coverage of —Si—O— groups on the silica nanospheres.
In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value greater than 5. In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value greater than 6. In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value greater than 7. In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value greater than 8. In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value greater than 9. In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value greater than 10. In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value greater than 11. In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value between 6 and 14. In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value between 7 and 14. In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value between 8 and 13. In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value between 9 and 12. In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value between 10 and 12. In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value between 6 and 8. In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value between 8 and 10. In some embodiments, the step of altering the pH of the first solvent comprises the step of bringing the pH to a value of 11.1.
In some embodiments, the step of altering the pH of the first solvent comprises the step of adding a base or an acid to the first solvent. In some embodiments, the step of adding a base or an acid to the first solvent further comprises the step of heating the solvent. Exemplary bases include, but are not limited to, aqueous ammonia hydroxide (28-30 wt %), ammonium carbonate, ammonium bicarbonate, sodium hydroxide, potassium hydroxide, calcium hydroxide, urea, triethanolamine, triethylamine, sodium ammonium phosphate, ammonium sulfate, magnesium hydroxide, and the like.
Exemplary acids include, but are not limited to, nitric acid, 0.1M nitric acid, hydrochloric acid, phosphoric acid, acetic acid, perchloric acid, citric acid, tartaric acid, oxalic acid, sulfuric acid, formic acid, benzoic acid, sodium hydrogen phosphate, boric acid, acetohydroxamic acid, trichloroacetic acid, iodic acid, lactic acid, malic acid, and the like.
In step 130, the silica nanospheres are dispersed in a second solvent. In some embodiments, the second solvent is an aqueous solvent. In some embodiments, the step of dispersing the silica nanospheres in a second solvent further comprises the step of sonicating the second solvent. In some embodiments, the step of dispersing the silica nanospheres in a second solvent further comprises the step of altering the pH of the second solvent. In some embodiments, the step of altering the pH of the second solvent comprises the step of adding a base or an acid to the second solvent. Exemplary acids and bases are described above. In some embodiments, the step of adding a base or an acid to the second solvent further comprises the step of adding a metal precursor to the second solvent to create composite nanoparticles. In some embodiments, the step of adding a base or an acid to the second solvent further comprises the step of adding more than one metal precursor to the second solvent to create composite nanoparticles. In some embodiments, composite nanoparticles comprise metal oxyhydride/silica nanoparticles and have the general formula of MOy(OH)z/SiOx. In some embodiments, composite nanoparticles comprise nanospheres with metal nanoparticles coating the surface of the silica nanospheres. In some embodiments, composite nanoparticles comprise metal nanoparticles anchored to the surface of the silica nanoparticles through metal silane bonds. In some embodiments, the steps of dispersing the silica nanospheres in a second solvent, altering the pH of the second solvent, and adding a metal precursor to create composite nanoparticles, further comprises the step of anchoring the metal precursors to the surface of the silica nanospheres through metal-silane bonds.
In some embodiments, the metal precursors are in the form of metal salts. In some embodiments, the metal precursors are water soluble. In some embodiments, the metal precursors are in the form of aqueous solutions. Exemplary metal precursors include, but are not limited to, manganese(II) nitrate hydrate (Mn(NO3)2·xH2O), Iron(II) chloride (FeCl2), cobalt(II) nitrate hexahydrate (Co(NO3)2·6H2O), nickel(II) nitrate hexahydrate (Ni(NO3)2·6H2O), copper(II) nitrate trihydrate (Cu(NO3)2·3H2O), ruthenium(III) chloride hydrate (RuCl3·xH2O), sodium tetrachloropalladate(II) hydrate (Na2PdCl4·xH2O), sodium hexachlororhodate(III) hydrate (Na3RhCl6·xH2O), tetrachloroauric(III) acid trihydrate (HAuCl4·3H2O), sodium tetrachloroplatinate(II) hydrate (Na2PtCl4·xH2O), potassium tetrachloroplatinate(II) hydrate (K2PtCl4·xH2O), sodium hexachloroplatinate (Na4PtCl6), potassium hexachloroplatinate (K4PtCl6), magnesium chloride (MgCl2), aluminum nitrate nonahydrate (Al(NO3)2·9H2O), zinc nitrate hexahydrate (Zn(NO3)2·6H2O), and combinations thereof.
Different metal precursors require different pH values for successful deposition on silica nanospheres and thus altering the pH of the second solvent ensures that successful deposition occurs between the metal precursor and the silica nanospheres.
In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value greater than 5. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value greater than 6. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value greater than 7. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value greater than 8. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value greater than 9. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value greater than 10. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value greater than 11. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value between 5 and 14. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value between 6 and 14. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value between 7 and 14. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value between 8 and 13. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value between 9 and 12. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value between 10 and 12. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value between 6 and 8. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value between 8 and 10. In some embodiments, the step of altering the pH of the second solvent comprises the step of bringing the pH to a value of 11.1.
In some embodiments, the step of adding a metal precursor to the second solvent comprises adding more than one type of metal precursor to the second solvent. In some embodiments, the step of adding more than one type of metal precursor to the second solvent comprises adding two metal precursors with metal ratios between 1:99 and 99:1. In some embodiments, the step of adding more than one type of metal precursor to the second solvent comprises adding two metal precursors with metal ratios between 1:50 and 50:1. In some embodiments, the step of adding more than one type of metal precursor to the second solvent comprises adding two metal precursors with metal ratios between 1:20 and 20:1. In some embodiments, the step of adding more than one type of metal precursor to the second solvent comprises adding two metal precursors with metal ratios between 1:10 and 10:1. In some embodiments, the step of adding more than one type of metal precursor to the second solvent comprises adding two metal precursors with metal ratios between 1:5 and 5:1. In some embodiments, the step of adding more than one type of metal precursor to the second solvent comprises adding two metal precursors with metal ratios between 1:4 and 2:1. In some embodiments, the metal precursors comprise metals described above. In some embodiments, the step of adding a metal precursor to the second solvent further comprises the step of heating the second solvent.
In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing less than 1.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing less than 2.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing less than 3.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing less than 4.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing less than 5.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing less than 6.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing less than 7.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing less than 8.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing less than 9.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing less than 10.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing less than 15.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing less than 30.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing less than 50.0 wt. % of metal.
In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing greater than 0.1 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing greater than 1.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing greater than 2.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing greater than 3.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing greater than 4.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing greater than 5.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing greater than 6.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing greater than 7.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing greater than 8.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing greater than 9.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing greater than 10.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing greater than 15.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing greater than 30.0 wt. % of metal. In some embodiments, the step of adding a metal precursor comprises the step of adding an aqueous metal precursor solution containing greater than 50.0 wt. % of metal.
In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 200 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 100 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 90 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 80 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 70 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 60 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 50 nm. In some embodiments, the composite nanoparticles created in step 140 comprise metal nanoparticles with diameters less than 40 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 30 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 20 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 10 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 9 nm. In some embodiments, the composite nanoparticles created in step 140 comprise metal nanoparticles with diameters less than 8 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 7 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 6 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 5 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 4 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 3 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 2 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters less than 1 nm.
In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 200 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 100 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 90 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 80 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 70 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 60 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 50 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 40 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 30 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 20 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 10 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 9 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 8 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 7 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 6 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 5 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 4 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters than 3 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters than 2 nm. In some embodiments, the composite nanoparticles created in step 130 comprise metal nanoparticles with diameters greater than 1 nm.
In step 140, the composite nanoparticles are collected and dried to create a nanoparticle material. In some embodiments, the step of collecting and drying the composite nanoparticles further comprises the step of centrifuging and washing the composite nanoparticles. In some embodiments, the step of collecting and drying the composite nanoparticles further comprises the step of reducing composite nanoparticles. Reducing the composite nanoparticles reduces the metal oxyhydroxide nanoparticles on the silica spheres by reducing the metal oxyhydroxide nanoparticles to their metallic state. In some embodiments, the step of reducing the composite particles alters the size of the metal nanoparticles to a diameter described above.
In some embodiments, the step of reducing the composite nanoparticles comprises the step of thermally reducing the composite nanoparticles. In some embodiments, the step of thermally reducing composite nanoparticles is done at a temperature above 50° C. In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature above 100° C. In some embodiments, the step of thermally reducing composite nanoparticles is done at a temperature above 200° C. In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature above 300° C. In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature above 400° C. In some embodiments, the step thermally reducing the composite nanoparticles is done at a temperature above 500° C. In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature above 600° C. In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature above 700° C. In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature above 800° C.
In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature below 50° C. In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature below 100° C. In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature below 200° C. In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature below 300° C. In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature below 400° C. In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature below 500° C. In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature below 600° C. In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature below 700° C. In some embodiments, the step of thermally reducing the composite nanoparticles is done at a temperature below 800° C.
In some embodiments, the step of conducting a thermal reduction of the composite nanoparticles comprises the step of contacting the composite nanoparticles with a flow of H2 gas. In some embodiments, the step of conducting a thermal reduction of the composite nanoparticles comprises the step of contacting the composite nanoparticles with a flow of 5% H2/N2 gas. In some embodiments, the flow rate of the 5% H2/N2 gas is controlled to a desirable flow rate.
In some embodiments, the step of reducing the composite nanoparticles further comprises the step of coating the composite nanoparticles with a dielectric material coating. In some embodiments, the dielectric material coating comprises a dielectric material described above. In some embodiments, the dielectric material coating is less than 100 nm thick. In some embodiments, the dielectric material coating is less than 90 nm thick. In some embodiments, the dielectric material coating is less than 80 nm thick. In some embodiments, the dielectric material coating is less than 70 nm thick. In some embodiments, the dielectric material coating is less than 60 nm thick. In some embodiments, the dielectric material coating is less than 50 nm thick. In some embodiments, the dielectric material coating is less than 40 nm thick. In some embodiments, the dielectric material coating is less than 30 nm thick. In some embodiments, the dielectric material coating is less than 20 nm thick. In some embodiments, the dielectric material coating is less than 10 nm thick. In some embodiments, the dielectric material coating is less than 9 nm thick. In some embodiments, the dielectric material coating is less than 8 nm thick. In some embodiments, the dielectric material coating is less than 7 nm thick. In some embodiments, the dielectric material coating is less than 6 nm thick. In some embodiments, the dielectric material coating is less than 5 nm thick. In some embodiments, the dielectric material coating is less than 4 nm thick. In some embodiments, the dielectric material coating is less than 3 nm thick. In some embodiments, the dielectric material coating is less than 2 nm thick.
The invention is now described with reference to the following Examples. These Examples are provided for the purpose of illustration only, and the invention is not limited to these Examples, but rather encompasses all variations that are evident as a result of the teachings provided herein.
Ultrafine metal nanoparticles (ufMNPs) with sizes below 5 nm represent a class of widely used catalysts due to their high surface-to-volume ratios and profound electron dislocation upon interaction with surface adsorbates. In addition to traditional thermal catalysis, ufMNPs can absorb photoenergy to generate hot electrons that can transfer energy to surface adsorbates and promote surface reactions. Hot electron generation originates from the decay of excited surface plasmons, and the efficiency of generating high-energy hot electrons becomes higher with the decrease in nanoparticle size. Nevertheless, the light absorption power of ufMNPs lowers as the nanoparticles become smaller, preventing the ufMNPs from being used as efficient photocatalysts. Integrating ufMNPs with light antenna materials has been demonstrated to be a promising solution to improve the optical absorption power of the ufMNPs. Metal nanoparticles with strong localized surface plasmon resonances (LSPRs) (e.g., Au, Ag, Cu, and Al nanoparticles) and dielectric spheres with strong optical surface scattering resonances represent two types of light antenna, which can concentrate the incident photoenergy to enhance electric fields near the antenna's surface locally. Using plasmonic metal nanoparticle antennae usually requires delicate synthesis to create a dielectric separation layer with a precise thickness of 1-5 nm between the antenna nanoparticles and catalyst ufMNPs. A thick separation layer decays the electric field significantly for the ufMNPs, while a too thin separation could cause a charge flow between the antenna nanoparticles and the ufMNPs. In contrast, the catalyst ufMNPs can be directly dispersed on dielectric spheres without suffering from weakened electric fields and interparticle charge flow, allowing the ufMNPs to benefit the antenna effect fully. For example, nanoparticles made of noble metals and compounds loaded on silica spheres with diameters in the range of 200-1200 nm have been shown to exhibit enhanced optical absorption, particularly in the visible spectral range compared to the freestanding nanoparticles, along with characteristic absorption peaks determined by the surface scattering resonance bands of the silica spheres. It is necessary to develop a general method to load ufMNPs of varying compositions on silica spheres to maximize the antenna effect in boosting the photocatalytic performance of the ufMNPs (Hartland, G. V. et al., ACS Energy Letters 2017, 2, 1641-1653; Stewart, S. et al., Chemical Science 2021, 12, 1227-1239; Wei, Q. et al., Advanced Materials 2018, 30, 1802082; Besteiro, L. V. et al., The Journal of Physical Chemistry C 2016, 120, 19329-19339; Brongersma, M. L. et al., Nature Nanotechnology 2015, 10, 25-34; Rasamani, K. D. and Sun, Y., The Journal of Chemical Physics 2020, 152, 084706; Yuan, Y. et al., Science 2022, 378, 889-893; Yuan, L. et al., ACS Nano 2022, 16, 17365-17375; Swearer, D. F. et al., Proceedings of the National Academy of Sciences 2016, 113, 8916-8920; Zhang, N. et al., Nature Photonics 2016, 10, 473-482; Rasamani, K. D. et al., Nano Futures 2018, 2, 015003; Dai, X. et al., ChemNanoMat 2019, 5, 1000-1007; Wei, Q. et al., Nano-Micro Letters 2020, 12, 41; Wei, Q. et al., The Journal of Physical Chemistry C 2022, 126, 17997-18005; Dai, X.; Sun, Y., Nanoscale Horizons 2024. DOI 10.1039/D3NH00506B).
The most common method used in the chemical industry is the impregnation method, which is based on the loading of metal precursors onto the support material, followed by treatments to obtain final products. The loading can be conducted in both dry and wet conditions. For example, to load platinum (Pt) precursors onto porous silica supports, one can mix a certain amount of Pt precursor solution with silica powder with thorough mixing or disperse silica powder in a larger amount of precursor solution followed by solvent evaporation. The obtained metal-loaded powders are fully dried in the oven, and metal or metal oxyhydroxide can be obtained by treating the sample with hydrogen gas or air. Since this method relies on the adsorption of metal precursors in the pores in support materials, the obtained nanoparticle morphology is hard to be controlled. If the study is related to the effect of nanoparticle sizes, morphologies and crystallinity, nanoparticles can be synthesized separately in the solution phase, followed by loading onto the surface of support materials through adsorption or other surface interactions (e.g., electrostatic interactions). Furthermore, in order to obtain stronger interaction between the loaded metal species and the support, the metal ions can be loaded first to the support followed by a separate reduction process. The support materials are usually functionalized by organic linkers, on which one side is grafted to the support, and the other side can interact with free-standing metal ions. The interaction between the metal ion and the support prepared using this method is more direct since no surfactant is involved, and can result in higher thermal stabilities during the application (Deng, L. et al., Chem. Commun. 2017, 53, 6937-6940; Chen, H. et al., ChemCatChem 2019, 11, 3542-3551; Khdary, N. H.; Ghanem, M., RSC Adv. 2014, 4, 50114-50122; Hutchings, G. J. and Vedrine, J. C. Heterogeneous Catalyst Preparation; Springer Ser. Chem. Phys. 2004, 215-258; van de Water, L. G. A. et al., J. Am. Chem. Soc. 2005, 127, 5024-5025; Zhang, Q. et al., Metal Sites in Zeolites: Synthesis, Characterization, and Catalysis. Chem. Rev. 2022; Muthuchamy, N. et al., RSC Adv. 2015, 5, 76170-76181; Pei, Y. et al., Surf. Sci. 2016, 648, 299-306; Grigoropoulou, G. et al., Colloids Surf., A 2008, 320, 25-35; Ding, Y. et al., Appl. Catal., B 2017, 203, 372-380; Rice, D. et al., ACS Omega 2018, 3, 13028-13035).
Loading ufMNPs on silica spheres is currently realized through either electrostatic assembly of negatively charged colloidal ufMNPs on silane-functionalized silica spheres or in-situ reduction of metal ion precursors in the presence of colloidal silica spheres. Despite the success in loading ufMNPs of some noble metal elements, the quality and composition scope of the ufMNPs are yet to improve significantly. For instance, the former electrostatic assembly strategy is limited by the difficulty in synthesizing high-quality colloidal ufMNPs nanoparticles made of a wide range of compositions, particularly non-noble metals, in an aqueous (and/or ethanolic) solution phase, which is necessary for dispersing the surface-functionalized silica spheres. In addition, the organic silane reagents used for surface functionalization of the silica spheres and the capping agents used for synthesizing ufMNPs could adversely influence thermal stability and catalytic performance. These surface organic species may undergo thermal/photocatalytic decomposition, particularly in gas-phase reactions, to pollute the catalytic reaction products. The latter in-situ reduction strategy often suffers from the simultaneous homogeneous and heterogeneous nucleation that leads to nonuniform loading, broad size distribution, and agglomeration of ufMNPs. Although excluding surface species in the resulting composite particles favors thermal stability and catalysis, uniformly controlled deposition of metal contents on silica spheres is still challenging (Li, D. et al., ACS Catalysis 2012, 2, 1358-1362; Lee, I. et al., Nano Research 2011, 4, 115-123; Carneiro, L. et al., Catalysis Science & Technology 2016, 6, 8166-8176; Li, X. et al., RSC Advances 2015, 5, 69962-69969; Ataee-Esfahani, H. et al., Chemical Communications 2011, 47, 3885-3887; Gude, K. et al., The Journal of Physical Chemistry C 2010, 114, 6356-6362).
Herein is a general synthesis protocol involving two steps, i.e., uniform deposition of metal hydroxide on silica nanospheres (SiOx NSs) with a controlled manner at appropriate solution pH values followed by a thermal reduction in forming gas (5% H2+95% N2) at elevated temperatures (
The method produces highly monodisperse SiOx NSs with an average diameter of 346.8 nm (
The SiOx NSs with rich —Si—O− groups are utilized to anchor metal ions through surface acid-base reaction between metal cations and hydroxide anions (
Under these conditions, precious metal ions [Ru(III), Rh(III), Pd(II), Pt(II), Au(III)], 3d block transition metal ions [Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II)], 3p block metal ions [Al(III)], 3s block metal ions [Mg(II)], and their combinations are successfully loaded onto the surface of SiOx NSs, confirmed by inductively coupled plasma-optical emission spectrometry (ICP-OES). The resulting composite particles of SiOx NSs with thin MOy(OH)z coverage are characterized with TEM imaging (
The loaded MOy(OH)z can also react with H2 to be reduced at elevated temperatures, i.e., 250 or 550° C., producing ufMNPs. The latter group of MOy(OH)z are deposited as individual NPs, even with spatial distribution on the SiOx NSs, and small in size, ensuring that the following reduction of MOy(OH)z NPs transforms them into uniformly distributed ufMNPs. Reducing the thin layers of MOy(OH)z of the former group with appropriate reaction kinetics removes 0 and OH to shatter the film into evenly dispersed ufMNPs on the SiOx NSs. Depending on the chemical property of a metal element, its corresponding MOy(OH)z may not be reduced or completely reduced at a mild temperature. The composite particles of SiOx NSs with ufMNPs is denoted as ufMNPs/SiOx in the following contents. Typical TEM images of the ufMNPs/SiOx composite particles are shown in
Because of the small sizes of the ultrafine NPs formed from the thermal reduction of MOy(OH)z on SiOx NSs, the mass percentages of the ultrafine NPs in the composite particles are low (i.e., 1 to 2 wt. %). A synchrotron x-ray beam with a high flux has been used to examine these composite particles in order to record signals from the low-loading ultrafine NPs with decent signal-to-noise ratios. Wide-angle x-ray scattering (WAXS) patterns are collected to analyze the crystalline structures and compositions of the ultrafine NPs.
The WAXS pattern of SiOx NSs in the measured range exhibits three broad peaks corresponding to their amorphous phase. The strong SiOx signals may not be completely subtracted, particularly for the ultrafine NPs with amorphous phases showing weak WAXS. For example, the ultrafine NPs containing Mn, Fe, and Co do not present any sharp (or narrow) WAXS peaks but only broad peaks similar to SiOx NSs, indicating that the ultrafine NPs are in the format of amorphous phase and made of oxides. Even though the reduction temperatures applied are perceived to be able to reduce the metal to the metallic state, the presence of oxides rather than metals in these ultrafine NPs could be ascribed to the diffusion of oxygen atoms into the lattice of metal nanoparticles during transportation of the samples to the beamline, resulting in the loss of long-range ordering of metal atoms. Therefore, these three samples are labeled as MOy/SiOx composite particles in
The ultrafine NPs derived from the MOy(OH)z containing Cu exhibit a WAXS pattern showing a set of fcc peaks, but the lattice constant matches that of Cu2O rather than Cu. The result indicates that the temperature of 250° C. is not high enough to reduce Cu(II) in the MOy(OH)z NPs to zero-valence Cu. The Cu2O ultrafine NPs (
Diffuse reflectance spectroscopy (DRS) of the composite particles of SiOx NSs loaded with MOy(OH)z and derived ufMNPs is studied in the ultraviolet-visible (UV-vis) spectral range using a spectrometer equipped with an integrating sphere. The DRS spectrum of a sample can accurately represent its optical absorption property by eliminating the interferences of light scattering. For example, the as-synthesized SiOx NSs and those with rich —Si—O− surface groups show the DRS spectra with essential no signal in the examined spectral range (300-800 nm) (
Although two peaks are always observed in the DRS spectrum for each sample with broadband absorption, the relative intensities of these two peaks (or the ratio of peak intensity for these two peaks) are not always similar for all samples because different supported NPs or films (i.e., light absorber) exhibit different intrinsic DRS spectra. For example, the composite particles containing the freshly deposited MnOy(OH)z NPs exhibit a more intense DRS peak at the short wavelength (
The DRS spectra of SiOx NS-supported ufMNPs made of other metals (e.g., Ni, Rh, Pd, Pt, Au) exhibit much stronger signals than the corresponding MOy(OH)z NPs, particularly at the long wavelengths (
The success of the strategy of
The strategy depicted in
Synthesis of Silica Spheres: The synthesis relied on the controlled hydrolysis of tetraethyl orthosilicate (TEOS) and condensation of the hydrolyzates. In a typical synthesis, 24.60 mL of ammonium hydroxide solution (28-30 wt. % in water, Fischer Scientific) was added to a mixture of 45.45 mL of deionized (DI) H2O and 120 mL of isopropanol (Fisher Scientific) at room temperature. Under magnetic stirring at a rate of 400 rpm, the solution was then heated to 40° C. by a heating jacket equipped with a J-type thermocouple. To this solution, 10.88 mL of TEOS (98%, Sigma-Aldrich) was then injected. The temperature of 40° C. and magnetic stirring were maintained throughout the synthesis for 6 h. The resulting SiOx NSs were collected by centrifugation and washed with ethanol. The collected SiOx NSs were dried overnight in an oven at 60° C. (Stöber, W. et al., Journal of Colloid and Interface Science 1968, 26, 62-69).
Enrichment of Surface —Si—O− Group on SiOx NSs: One gram of the dried SiOx NSs was dispersed in 200 mL of DI H2O with the assistance of ultrasonication in a 500 mL three-neck round-bottom flask. Monitored by a pH meter (Apera Instruments PH700), to the dispersion was dropwise added 28-30 wt. % aqueous ammonia hydroxide or 0.1 M nitric acid solution until the pH value reached 11.10. Under magnetic stirring at a rate of 400 rpm, the dispersion was heated up to 100° C. followed by refluxing for 24 h. After the dispersion was cooled down to room temperature, the resulting SiOx NSs were collected by centrifugation and washed once with ethanol. The collected SiOx NSs were dried at room temperature.
Deposition and Reduction of MOy(OH)z on SiOx NSs: Forty milligrams of the treated SiOx NSs were dispersed in 20 mL of DI H2O with the assistance of ultrasonication. To this dispersion, 10 mM of aqueous ammonium hydroxide solution was added dropwise, followed by heating to the desired temperature. The optimized reaction conditions for each metal precursor are listed in Table S1. A 0.1-mL aqueous metal precursor solution containing 1 wt. % of metal was injected into the dispersion (2 wt. % for Au). The color change started in 15 s, indicating the deposition of metal ions on the SiOx NSs. After 1 h of continuous aging, the MOy(OH)z/SiOx composite particles were collected by centrifugation and washed with DI H2O and ethanol. The sample was then dried at room temperature in the ambient environment. Thermal reduction of MOy(OH)z was carried out in a tube furnace. In a continuous flow of 5% H2/N2 gas (i.e., forming gas) at a rate of 30 mL/min the sample powder was heated to an appropriate temperature at a ramping rate of 10° C./min. The reaction was maintained at the set temperature for 2 h followed by cooling to room temperature while the forming gas continuously flowed in the tube.
Characterization: Scanning electron microscopy (SEM) images were obtained using a field-emission microscope (FEI Quanta FEG 450) operated with an acceleration voltage of 10 kV at a high vacuum mode. Transmission electron microscopy (TEM) images were taken using JEOL JEM-1400 microscope operated at 120 kV. Zeta-potential (ζ) of colloidal nanoparticles was measured with a zeta potential analyzer (Malvern Instruments Ltd., Zetasizer Nano-ZS). The synthesized ufMNP/SiOx composite particles were examined with synchrotron wide-angle x-ray scattering (WAXS), which was carried out at the beamline 12-ID-B of Advanced Photon Source (APS), Argonne National Laboratory (ANL). The wavelength of the x-ray was 0.9322 Å, corresponding to a photon energy of 13.3 keV. The composite powders were packed and sealed in Kapton® tubes, which were shipped to and measured at the beamline. The scattering signals were collected using an imaging plate detector with a resolution of 2048×2048 pixels. The sample-to-detector distance (180 mm) was calibrated by fitting the WAXS pattern of a standard CeO2 sample. The recorded two-dimensional (2D) scattering patterns were reduced to one-dimensional (1D) curves using the Fit2D software, along with the background subtraction and intensity normalization. Ultraviolet-visible absorption spectra were analyzed with a UV-vis spectrophotometer (Thermo Scientific, Evolution 220), and DRS spectra were obtained with the same instrument equipped with an integrating sphere detector.
The disclosures of each and every patent, patent application, and publication cited herein are hereby incorporated herein by reference in their entirety. While this invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this invention may be devised by others skilled in the art without departing from the true spirit and scope of the invention. The appended claims are intended to be construed to include all such embodiments and equivalent variations.
The present application claims priority to U.S. Provisional Application No. 63/607,247, filed Dec. 7, 2023, which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63607247 | Dec 2023 | US |
