Patent Application
20240200228
Water splitting to form hydrogen and oxygen using solar energy in the presence of photocatalysts has been studied as a potential means of clean, large-scale fuel production. Hydrogen fuel production has gained increased attention with the concerns about global warming. Methods such as photocatalytic water splitting are being investigated to produce hydrogen, a clean-burning fuel. Water splitting holds particular promise since it utilizes water, an inexpensive renewable resource. Photocatalytic water splitting has the simplicity of using a catalyst and sunlight to produce hydrogen out of water.
In contrast to the two-step system of photovoltaic production of electricity and subsequent electrolysis of water, photocatalytic water splitting processes are performed by photocatalysts being in direct contact with water. The photocatalysts are either in homogeneous environments with respect to the water (photocatalysts suspended within the water) or are in a heterogeneous phase with respect to the water (photocatalysts bound to a surface in contact with the water). Examples of heterogeneous photocatalytic processes include that described in U.S. Pat. No. 10,744,495 and US2014/0174905. Whether homogeneous or heterogeneous, photocatalytic water splitting is more efficient than the two-step process of water electrolysis.
The prime measure of photocatalyst effectiveness is quantum yield (QY), which is:
QY (%)=(Photochemical reaction rate)/(Photon absorption rate)×100%.
This quantity is a reliable determination of how effective a photocatalyst is. Overall, the best photocatalyst has a high quantum yield and gives a high rate of gas evolution.
For a photocatalytic reaction, the quantum efficiency (QE) for photon-to-hydrogen conversion is the key parameter when evaluating the efficiency of renewable solar energy to hydrogen fuel systems. Almost all the reported photocatalytic water-splitting systems suffer from low QE in the visible-light region (e.g., rarely exceeding 3% at 420 nm), which largely hinders any potential practical applications.
The present invention relates to tantalum nitrides, in particular tantalum nitrides doped with one or more metals, and products containing or made from the tantalum doped with one or more metals, such as, but not limited to, a catalyst.
The present invention also relates to methods utilizing the tantalum doped with one or more metals, such as, but not limited to, methods to obtain hydrogen from solutions (e.g., aqueous solutions such as water) and methods for water splitting using the catalyst. The present invention further relates to methods of making the tantalum nitride doped with one or more metals and the catalyst.
Tantalum nitride (e.g., Ta3N5), an n-type semiconductor with a narrow bandgap (2.1 eV) and suitable energetic positions of conduction and valance bands straddling the water redox potentials, is a potential photocatalyst for producing sustainable hydrogen via solar photocatalytic water splitting. Despite a theoretically maximum solar-to-hydrogen (STH) energy conversion efficiency of 15.9%, the STH value achieved so far by overall water splitting (OWS) over Ta3N5 was only about 0.014%, and this was done by using nanorods grown on lattice-matched KTaO3. The apparently imbalanced water oxidation and reduction performance of Ta3N5 has long been an obstacle to the realization of OWS for this material. Compared with the water oxidation, photocatalytic water reduction activity of Ta3N5 has been always much poorer or even undetectable in some cases, though a variety of modifications (e.g., size minification, heterojunction, and surface modification) were considered and/or attempted but the progress thus far made is viewed as unsatisfactory. Hence, developing efficient strategies to substantially improve the water reduction activity of tantalum nitrides, such as Ta3N5 is still needed.
In addition, compositional modification of a photocatalyst material by doping with foreign ions has been considered to a certain degree and this doping has had an effect on photocatalytic performance. For Ta3N5, certain aliovalent metal ions, particularly Mg2+ (72 pm) and Zr4+ (72 pm) with similarly large ionic radius to Ta5+ (64 pm), were introduced into its crystal lattice, and this enhanced performance in photocatalytic/photoelectrochemical water oxidation and splitting to a certain extent. A lower photocurrent onset potential by the design of Mg—Zr co-doped Ta3N5 photoanode has been attempted. However, efficient photocatalytic water reduction, conceivably the bottleneck of this material for photocatalytic OWS, has not been well demonstrated by this doping method. On the other hand, impurities, such as MgO and Zr2ON2, were formed with Ta3N5, going against correctly catching the individual functionality of the dopant on single-phase Ta3N5. Variation in the number of different defect species (containing reduced Ta, oxygen impurity (ON), and nitrogen vacancy (VN)) arising from aliovalent doping has mainly been considered the reason for the activity enhancement. However, only part of them (mostly ON) have been directly detected. On the contrary, VN in Ta3N5 has never been directly captured and the nature of reduced Ta (Ta3+ or Ta4+ or both) was still controversial.
Moreover, the surface property that affects the cocatalyst loading and dispersion was very often ignored. All these have led to a poor mechanistic understanding of the doping-induced activity improvement, hindering further rational design and synthesis of active Ta3N5 photocatalysts that can overcome and/or improve the performance as a catalyst.
Accordingly, there is a need in the industry to provide improved nanoparticles and especially improved tantalum nitrides that find use, for instance, as catalyst and for use in methods for water splitting and/or other uses.
It is therefore a feature of the present invention to provide a novel tantalum nitride.
A further feature is to provide a single-phase tantalum nitride that is doped with one or more metals.
A further feature is a catalyst that is or includes the single-phase tantalum nitride that is doped with one or more metals.
An additional feature of the present invention is to provide a nanoparticle that is a tantalum nitride that is co-doped with one or two or more metals.
Another feature of the present invention is to provide a catalyst, such as for water reduction.
Another feature of the present invention is to provide a water splitting catalyst.
Another feature of the present invention is to provide a method to water split using nanoparticles such as in the form of a catalyst.
Another feature of the present invention is to provide methods of making the novel tantalum nitrides and catalysts.
Additional features and advantages of the present invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practice of the present invention. The objectives and other advantages of the present invention will be realized and attained by means of the elements and combinations particularly pointed out in the description and appended claims.
To achieve these and other advantages, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention relates to single crystalline nanoparticles that are tantalum nitride doped with at least one metal. The single crystalline nanoparticles can be a tantalum nitride that is co-doped with two metals. For instance, the two metals can be Zr and Mg. As an option, and preferably, the doped metal(s) reside as a cation(s) in a crystal lattice of the tantalum nitride.
The present invention further relates to single crystalline nanoparticles that are Ta3N5:Mg+Zr, or Ta3N5:Mg, or Ta3N5:Zr or any combination thereof.
The present invention further relates to a catalyst that includes the single crystalline nanoparticles of the present invention alone or optionally along with a co-catalyst(s). The co-catalyst can be distributed or dispersed on or used with the single crystalline nanoparticles. The co-catalyst can be a platinum metal (Pt) that is homogeneously distributed or dispersed on the single crystalline nanoparticles or mixed with the nanoparticles or used in combination with the nanoparticles.
Further, the present invention relates to a method to water split, and method includes the step of utilizing the catalyst (e.g., photocatalyst) in contact with water or other fluid.
The present invention also relates to a method to make the single crystalline nanoparticles of the present invention. The method can include impregnating a NaCl/Ta with MgCl2 or other first metal salt and ZrOCl2 or other second metal salt and then conducting nitridation under a flow of gas. The nitriding can be conducted under high temperatures such as, but not limited to, 900 deg C. or higher. The NaCl/Ta can be a NaCl-encapsulated Ta that can be obtained from a sodium/halide flame encapsulation method.
In addition, the present invention relates to a method to make a catalyst with a co-catalyst. The method includes the step of Pt loading of the single crystalline nanoparticles. The Pt loading can include or involve deposition of Pt by an impregnation-reduction method followed by deposition of more Pt by an in-situ photodeposition method. In lieu of Pt or in addition to Pt, other co-catalysts can be utilized, such as, but not limited to, other metals.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide a further explanation of the present invention, as claimed.
The present invention is directed to tantalum nitride nanoparticles that are doped with at least one metal, such as two metals or more than two metals. The nanoparticles can be a catalyst alone or be part of a catalyst. The catalyst can be used in various methods, such as methods to water split. The present invention is further directed to methods of making the tantalum nitride nanoparticles and the catalyst.
The tantalum nitride can be a n-type semiconductor, preferably with a narrow bandgap and/or suitable energetic positions of conduction and valance bands straddling the water redox potentials.
The nanoparticles of the present invention can be single crystalline nanoparticles doped with at least one metal. The nanoparticles of the present invention can be single crystalline tantalum nitride nanoparticles doped with at least one metal.
The nanoparticles can be monodispersed nanoparticles, such as single crystalline monodispersed nanoparticles.
The nanoparticles can be a tantalum nitride nanoparticle (e.g., single crystalline nanoparticle) doped with at least one metal (e.g., at least one metal, or at least two metals, or at least three or more metals).
As a more specific example, the nanoparticle can be single crystalline tantalum nitride nanoparticles co-doped with two metals. The two metals can be Zr and Mg.
Other examples of the one or more metals that can be used as the doped metal can be Li, Sc, Ti, Hf, Al, and/or Ga and/or any combinations thereof.
A specific example of a tantalum nitride is Ta3N5.
Other examples of tantalum nitride include, but are not limited to, Ta4N5, Ta5N6, Ta2N, and TaN and generally TaN, where x ranges from 0.1 to 3.
With respect to the doped metal or metals, preferably, the at least one metal (i.e., doped metal) reside as a cation(s) in a crystal lattice of the tantalum nitride.
More specific examples of a tantalum nitride (with doped metals) are Ta3N5:Mg+Zr, or Ta3N5:Mg, or Ta3N5:Zr or any combinations thereof.
And, as a further example, all of the Mg2+ and/or Zr4+ cations reside in the crystal lattice of Ta3N5.
The tantalum nitride can be Ta3N5:Mg+Zr alone. The tantalum nitride can be Ta3N5:Mg alone. The tantalum nitride can be Ta3N5:Zr alone. Each of these can be single crystalline nanoparticles. Each of these can have the Mg and/or Zr residing as cations in the crystal lattice of the Ta3N5.
When more than one tantalum nitride is present in the population of nanoparticles, the distribution between two or more different tantalum nitrides can be even or uneven. For instance, the Ta3N5:Mg+Zr can be present in the highest weight percent based on the total weight of all tantalum nitrides present.
The single crystalline nanoparticles of the present invention can exhibit single-phase X-ray diffraction (XRD) patterns associated with anosovite-type tantalum nitride, such as anosovite-type Ta3N5.
As an option, the single crystalline nanoparticles (such as Ta3N5:Mg+Zr, or Ta3N5:Mg, or Ta3N5:Zr) can be where EPR-active Ta4+ is not present (e.g., not present at −173.15° C.).
The single crystalline nanoparticles of the present invention can have a variety of shapes. For instance, the nanoparticles can have a shape such that the nanoparticles are considered monodispersed nanorod particles.
When nanoparticles are nanorod particles, the nanorod particles can have a length. The length can be from 50 nm to 500 nm, such as from 50 nm to 450 nm, from 50 nm to 400 nm, from 50 nm to 350 nm, from 50 nm to 300 nm, from 50 nm to 250 nm, from 50 nm to 200 nm, from 50 nm to 150 nm, from 75 nm to 500 nm, from 100 nm to 500 nm, from 125 nm to 500 nm, from 150 nm to 500 nm, from 175 nm to 500 nm, from 200 nm to 500 nm, from 225 nm to 500 nm, from 250 nm to 500 nm, from 275 nm to 500 nm, from 300 nm to 500 nm and the like. The length can be considered an average length.
When the nanoparticles are nanorods, the nanorods can have an aspect ratio (length/width) of at least 1.2 (e.g., at least 1.3, or at least 1.4, or at least 1.5, or at least 1.7, or at least 2 or at least 2.5, or at least 3, or at least 4 such as from 1.2 to 4 or higher, or from 1.3 to 4, or from 1.4 to 4 and the like).
When the tantalum nitride is Ta3N5:Mg+Zr, or Ta3N5:Mg, or Ta3N5:Zr or any combinations thereof, the tantalum nitride can have Mg-to-cation (e.g., Mg/(Ta+Mg+Zr)) and Zr-to-cation (e.g., Zr/(Ta+Mg+Zr)) ratios that are as high as 9.0 mol. % and 10.2 mol. %, respectively. Mg-to-cation ratio can be from 1 to 9 mol % or from 2 to 9 mol % or from 3 to 9 mol % or from 4 to 9 mol % or from 5 to 9 mol % or from 6 to 9 mol %. The Zr-to-cation ration can be from 1 to 10.2 mol %, from 2 to 10 mol %, from 3 to 10 mol %, from 4 to 10 mol %, from 5 to 10 mol %, from 6 to 10 mol %, from 7 to 10 mol %, or from 8 to 10 mol %.
The present invention also relates to TaNx:M1 or TaNx:M1+M2 or any combinations thereof, where x ranges from 0.1 to 3, M1 and M2 represent a metal cation (e.g., Mg, Zr, Li, Sc, Ti, Hf, Al, or Ga) and M1 and M2 are not the same.
As an option, the tantalum nitride (e.g., Ta3N5:Mg+Zr, or Ta3N5:Mg, or Ta3N5:Zr or any combinations thereof) can have minor segregated phases of MgO, Zr2ON2, NaTaO3 and/or ZrO2 not present (i.e., not detectable or 0%).
As an option, the tantalum nitride (e.g., Ta3N5:Mg+Zr, or Ta3N5:Mg, or Ta3N5:Zr or any combinations thereof) can be a tantalum nitride in the substantial or detectable absence of one or more of the following minor segregated phases: MgO, Zr2ON2, NaTaO3, and/or ZrO3. A ‘substantial absence’ being no detectable response within the XRD pattern of the tantalum nitride.
As an option, the tantalum nitride (e.g., Ta3N5:Mg+Zr, or Ta3N5:Mg, or Ta3N5:Zr or any combinations thereof) can have an atomic ratio of surface Ta in the form of Ta3N5 (N—Ta—N) that is over 90 at % (e.g., such as 91 at % or higher, or 92 at % or higher, or 95 at % or higher or from 91 at % to 99 at % or from 91 at % to 98 at %, or 92 at % to 98 at %, or 93 at % to 98 at %, or 94 at % to 98 at %).
As an option, the tantalum nitride (e.g., Ta3N5:Mg+Zr, or Ta3N5:Mg, or Ta3N5:Zr or any combinations thereof) can have an atomic ratio of surface Ta in the form of Ta“that is below 1 at % (e.g., 0.9 at % or lower, or 0.8 at % or lower, or 0.5 at % or lower, such as 0.001 at % to 0.9 at % or 0.01 at % to 0.5 at %). The atomic ratio of surface Ta in the form of Ta” can be undetectable or below 0.001 at %.
As an option, the tantalum nitride (e.g., Ta3N5:Mg+Zr, or Ta3N5:Mg, or Ta3N5:Zr or any combinations thereof) can have an atomic ratio of surface Ta in the form of TaOxNy (O—Ta—N) that is 2 at % or more. The atomic ratio can be from 2 at % to 5 at %. x and y here are such that the N/O is preferably greater than 2, or greater than 3, or greater than 4 or greater than 4.5 or greater than 4.8.
The crystalline particles of the present invention, such as a doped tantalum nitride, have a charge imbalance resulting in an oxygen-to-anion (O/N+O) molar ratio of 3.0% or higher or 4.0% or higher, such as from 3.0% to about 18% or from 5% to about 18%, or from about 7% to about 18%, or from about 10% to about 18% or from about 12% to about 18% or from 15% or higher.
As an option, the tantalum nitride (e.g., Ta3N5:Mg+Zr, or Ta3N5:Mg, or Ta3N5:Zr or any combinations thereof) can have a charge imbalance resulting in an oxygen-to-anion (O/N+O) molar ratio of 4.0% or higher (e.g., such as a molar ratio of from 5.0% to about 18%, or from 6.0% to 18%, or from 7.0% to 18%, or from 8.0% to 18%, or from 9.0% to 18%, or from 10% to 18% and the like).
As an option, the tantalum nitride (e.g., Ta3N5:Mg+Zr, or Ta3N5:Mg, or Ta3N5:Zr or any combinations thereof) can have a transient absorption (TA) kinetic profile of charged particles that is higher than undoped Ta3N5. The TA kinetic profile can be based on TA kinetic profiles of surviving electrons probed at 2000 cm−1 (5000 nm) under 470 nm excitation. The TA kinetic profile(s) for the nanoparticles of the present invention can be 5% or more, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, or 50% or more higher with respect to the delta absorbance and/or the decay time (ms). See
As an option, the tantalum nitride (e.g., Ta3N5:Mg+Zr, or Ta3N5:Mg, or Ta3N5:Zr or any combinations thereof) can have an evolved H2 with a rate (RH2) of at least 2 μmol/h where such rates are based on a Pt loading of 0.9 wt % Pt based on the total weight of the tantalum nanoparticles and the Pt particles having an average size of from about 2 mm to about 5 nm. The evolved H2 with a rate (RH2) can be from 10 μmol/h to 70 μmol/h or more, or from 2 μmol/h to 60 μmol/h, or from 2 μmol/h to 50 μmol/h, or from 2 μmol/h to 40 μmol/h, or from 2 μmol/h to 30 μmol/h, or from 2 μmol/h to 20 μmol/h, or from 2 μmol/h to 10 μmol/h, or from 5 μmol/h to 70 μmol/h, or from 10 μmol/h to 70 μmol/h, or from 15 μmol/h to 70 μmol/h, or from 20 μmol/h to 70 μmol/h, or from 25 μmol/h to 70 μmol/h, or from 30 μmol/h to 70 μmol/h, or from 35 μmol/h to 70 μmol/h, or from 40 μmol/h to 70 μmol/h.
As an option, the tantalum nitride (e.g., Ta3N5:Mg+Zr, or Ta3N5:Mg, or Ta3N5:Zr or any combinations thereof) can be a tantalum nitride in the substantial or detectable absence of one or more of the following defect species: a reduced species such as Ta3+ or Ta4+, or VN, or ON. A ‘substantial absence’ can be less than less than 15 at % or less than 10 at % or less than 5 at % or less than 2.5 at % or less than 1.5 at % or less than 1 at % or less than 0.5 at %. VN represents a nitrogen vacancy, and can be VN●●●, VN●●, VN● and VNØ. And, VN●●●, VN●●, VN● and VNØ represent the VN with zero, one, two and three trapped electrons, respectively, and that only VN●● and VNØ with unpaired electrons are possibly EPR-active. ON represents an oxygen impurity (examples include O2−).
The tantalum nitride(s) of the present invention can be or serve as a catalyst alone or as an option, can be part of a catalyst. The tantalum nitride of the present invention as a catalyst can be used with one or more co-catalyst.
The catalyst of the present invention can be a photocatalyst. The photocatalyst can be active with various light waves or light regions, such as ultraviolet light and/or visible light (i.e., visible-light region).
The co-catalyst can be a metal co-catalyst. The co-catalyst can be platinum (Pt). The co-catalyst can be a metal such as, but not limited to, gold, platinum, cobalt, palladium, silver, nickel or any combinations thereof. The co-catalyst can be Cr2O3.
A co-catalyst such as a metal co-catalyst (e.g., Pt) can be used in combination with another co-catalyst, such as Cr2O3.
The tantalum nitride(s) of the present invention can be or serve as a catalyst alone, such as photocatalyst and optionally has the ability to split water without the assistance of cocatalysts.
The tantalum nitride(s) of the present invention can be or serve as a catalyst alone, such as photocatalyst and optionally has the ability to split water without using sacrificial reagents.
The tantalum nitride(s) of the present invention can be or serve as a catalyst alone, such as photocatalyst and optionally has the ability to split water under ultraviolet irradiation or under visible light.
The catalyst of the present invention comprises, consists essentially of, consists of, includes, or is single crystalline nanoparticles of the present invention.
The catalyst of the present invention can further comprise or include one or more co-catalysts.
The co-catalyst can be one or more metal-based or metal-containing or metal co-catalyst. As indicated, the co-catalyst can be platinum (Pt). The co-catalyst can be a metal such as, but not limited to, gold, platinum, cobalt, palladium, silver, nickel or any combinations thereof.
The co-catalyst can be distributed or dispersed on the nanoparticles, such as homogeneously distributed or dispersed on the single crystalline nanoparticles. In the alternative or additionally, the co-catalyst can be mixed with the nanoparticles or used in combination with the nanoparticles in any fashion.
The co-catalyst can be platinum (Pt) distributed or dispersed on the nanoparticles, such as homogeneously distributed or dispersed on the single crystalline nanoparticles.
Preferably, the co-catalyst, such as Pt, is evenly distributed on the surface of the single crystalline nanoparticles (e.g., a variance of ±10% by weight of Pt or other co-catalyst anywhere on the surface). As an option, no aggregation of the co-catalyst (e.g., Pt) or the aggregation of co-catalyst (e.g., Pt) with nanoparticles is detectable.
The catalyst can have a solar-to-hydrogen (STH) energy conversion efficiency of over 0.015%. For instance, the STH energy conversion efficiency can be from 0.015% to 0.1%, such as from 0.02% to 0.1%, or from 0.03% to 0.1% or from 0.04% to 0.1% or from 0.05% to 0.1% or from 0.06% to 0.1%.
The catalyst can have an H2 production that is over 5 μmol/h. The H2 production can be from 5 μmol/h to 13 μmol/h or 6 μmol/h to 13 μmol/h, or from 7 μmol/h to 13 μmol/h or from 8 μmol/h to 13 μmol/h and the like.
The catalyst of can have a higher photocatalytic water reduction activity than pristine Ta3N5 under visible-light irradiation. The higher activity can be 5% or more higher or 10% or more higher or 15% or more higher.
The catalyst can have an apparent quantum yield (AQY) at 420 nm of over 0.15% for photocatalytic H2 evolution reaction (HER). The AQY at 420 nm can be from 0.15% to 0.54% or from 0.2% to 0.54%, or from 0.3% to 0.54%.
The method to make the catalyst with co-catalyst includes or involves the co-catalyst loading (e.g., Pt loading) of the single crystalline nanoparticles.
The co-catalyst loading (e.g., Pt loading) can involve or include the deposition of one or more co-catalyst (e.g., Pt) by an impregnation-reduction (IMP) method. This method involves dispersing the tantalum nitride with a co-catalyst containing compound or co-catalyst precursor (e.g., Pt containing compound or Pt precursor such as H2PtCl6) to form a slurry which can be heated with hot water vapor such as steam until dry. The powder can be then heated at 250° C. for 1 h under a H2/N2 gaseous flow (H2: 20 mL/min; N2: 200 mL/min) so as to obtain the co-catalyst loaded tantalum nitride (e.g., PtIMP/Ta3N5).
The co-catalyst loading (e.g., the Pt loading) can involve or include the deposition of co-catalyst (e.g., Pt) by an in-situ photodeposition (PD) method. In this method, the co-catalyst precursor (e.g., Pt precursor) can be added to an aqueous solution containing the tantalum nitride nanoparticles. The co-catalyst (e.g., Pt) can be loaded onto the tantalum nitride nanoparticles in-situ under photocatalytic reaction conditions.
The co-catalyst loading (e.g., Pt loading) can be a combination of the IMP and PD methods. For instance, the co-catalyst loading (e.g., Pt loading) can be in a stepwise method. The IMP-PD stepwise method can involve the deposition of the co-catalyst (e.g., Pt) by IMP as the seed (first step) and further seed growth of the co-catalyst (e.g., Pt) by in-situ PD (second step).
In a combination of IMP and PD methods, the co-catalyst loading (e.g., Pt loading) by the photodeposition (PD) method can account for from 70% to 95% of total co-catalyst loading by wt % of co-catalyst (e.g., Pt loading by wt % Pt).
The catalyst of the present invention can be use in methods to split water or other fluids (such as an aqueous fluid, and where fluid refers to a liquid or gas) and thus produce, for instance, hydrogen (e.g., in the form of hydrogen gas or hydrogen protons). The method can form also oxygen (e.g., in the form of oxygen gas or oxygen molecules).
The aqueous fluid can be water. The aqueous fluid can be a water-based fluid. The aqueous fluid can be an alcohol.
The method can comprise or include applying energy to the water or aqueous fluid in the presence of the catalyst to drive the splitting of water molecules into protons (H+), electrons, and oxygen gas.
The energy source can be solar energy. The energy source can be light energy. The energy source can be ultra-violet light. The energy source can be visible light. The energy source can be infrared (IR) energy. The energy source can be visible-light irradiation. The energy source can provide irradiation that is at least 20 mW/cm2 or at least 40 mW/cm2 or at least 60 mW/cm2 or at least 80 mW/cm2 or at least 100 mW/cm2.
The catalyst can be suspended or otherwise present in the water or aqueous fluid or other fluid.
The catalyst can be attached to a surface and in contact with the water or aqueous fluid or other fluid.
The water or aqueous fluid or other fluid can be moving or stationary relative to the catalyst.
The catalyst can be present in any amounts. For instance, when the catalyst is suspended in water or aqueous fluid or other fluid, the amount can be at least 0.15 g/150 ml fluid or at least 0.2 g/150 ml, or at least 0.5 g/150 ml or other amounts below or above any one of these ranges. Similar amounts can be used when the catalyst is fixed to a surface.
The present invention further relates to a method to make the nanoparticles of the present invention.
The method can comprise, consists of, consists essentially of, or include impregnating a tantalum powder (such as a salt encapsulated tantalum powder) (e.g., NaCl/Ta) with MgCl2 or other first metal salt and ZrOCl2 or other second metal salt and then conducting nitridation or nitriding under a flow of gas.
The salt-encapsulated tantalum powder, such as NaCl/Ta, can be a NaCl-encapsulated Ta from a sodium/halide flame encapsulation method.
The method for forming the starting tantalum can be a tantalum production process that includes or is sodium/halide flame encapsulation (SFE). Techniques employed for the SFE process which can be adapted for preparation of starting tantalum powder for the present invention are described in U.S. Pat. Nos. 5,498,446 and 7,442,227, which are incorporated in their entireties by reference herein. See, also, Barr, J. L. et al., “Processing salt-encapsulated tantalum nanoparticles for high purity, ultra-high surface area applications,” J. Nanoparticle Res. (2006), 8:11-22. An example of the chemistry employed for the production of metal powder by the SFE process of the '446 patent is as follows, wherein “M” refers to a metal such as Ta: MClx+XNa+Inert→M+XNaCl+Inert. Tantalum pentachloride is an example of a tantalum halide that can be used as the reactant MClx, and argon gas may be used as the Inert and carrying gas, in this chemistry. Initially, particles (e.g., Ta) are produced at the flame and grow by coagulation while the salt remains in the vapor phase. The salt condenses onto and/or around the Ta particles with heat loss, and uncoated core particles can be scavenged by the salt particles.
With respect to the nitriding step, the gas for the flow of gas can be a nitrogen containing gas, such as NH3. The flow rate of the gas can be 100 ml/min or more, 150 ml/min or more, or 200 ml/min or more.
The nitriding can be conducted at an elevated temperature, such as above 500 deg C. or higher, or 600 deg C. or higher, or 700 deg C. or higher, or 800 deg C. or higher, or 900 deg C. or higher, or at a temperature from 500 deg C. to 1,100 deg C., or from 600 deg C. to 1,100 deg C., or from 700 deg C. to 1,100 deg C., or from 800 deg C. to 1,100 deg C., or from 900 deg C. to 1,200 deg C.
The present invention will be further clarified by the following examples, which are intended to be purely exemplary of the present invention.
Ta Nanopowder Precursor. NaCl-contained Ta nanopowder (NaCl/Ta) and Ta nanopowder without NaCl (w/o NaCl/Ta), the precursors for Ta3N5 synthesis, were used and available from Global Advanced Metals USA, Inc. The NaCl/Ta material was mainly characterized with micron-sized NaCl crystals surrounded by aggregated spherical Ta nanoparticles (
Synthesis of Doped Ta3N5. 0.67 g of NaCl/Ta was well mixed with 92.1 μL of aqueous MgCl2 solution (2 M; Sigma-Aldrich BioUltra), 92.1 μL aqueous ZrOCl2 solution (2 M; Fujifilm Wako Pure Chemical Industries, Ltd.) and 300 μL of ultrapure H2O in an agate mortar. The feed molar ratio of Ta/Mg/Zr was about 7.5/1/1. After desiccating the mixture by mild heating at 60° C. and grinding for around 20 min, the solid was carefully loaded into an alumina crucible, and further heated to 900° C. with a ramping rate of 10° C./min and held at 900° C. for 3 h under a gaseous NH3 flow of 200 mL/min. After natural cooling to room temperature, the obtained sample was washed with hot water (70° C.), and then dried at 40° C. for 6 h under vacuum conditions. Ta3N5:Mg+Zr (feed molar ratio of Ta/Mg/Zr=7.5/1/1) was obtained. Ta3N5:Mg (feed molar ratio of Ta/Mg=7.5/1), Ta3N5:Zr (feed molar ratio of Ta/Zr=7.5/1) and Ta3N5 were synthesized using the same procedures adjusting the amount of MgCl2 solution and/or ZrOCl2 solution to achieve the desired molar ratios. Following the same procedure, but replacing the NaCl/Ta with the w/o NaCl/Ta, and adjusting the amount of MgCl2 solution and ZrOCl2 solution to achieve the desired molar ratios, the material Ta3N5:Mg+Zr (w/o NaCl) (feed molar ratio of Ta/Mg/Zr=7.5/1/1) was obtained. The materials Ta3N5:Mg+Zr, Ta3N5:Mg, Ta3N5:Zr, Ta3N5, and Ta3N5:Mg+Zr (w/o NaCl) are collectively the Doped Ta3N5.
Synthesis of Cocatalyst Doped Ta3N5. Pt as the hydrogen evolution cocatalyst was loaded onto the surface of the Doped Ta3N5 by a stepwise process utilizing an impregnation-H2 thermal reduction (IMP) method followed by an in-situ photodeposition (PD) method. For the IMP method, Doped Ta3N5 was first well-dispersed in an aqueous solution containing the required amount of H2PtCl6 as the Pt precursor by sonication for 1 min. The slurry was further heated by hot water vapor under manual stirring using a glass rod until it turned dry. After heating the powder at 250° C. for 1 h under a H2/N2 gaseous flow (H2: 20 mL/min; N2: 200 mL/min), the sample PtIMP/Doped Ta3N5 was obtained with a Pt IMP loading of 0.1 wt %. Following, a required amount of H2PtCl6 was added to an aqueous reaction solution containing PtIMP/Doped Ta3N5 photocatalyst. Pt was loaded onto PtIMP/Doped Ta3N5 in-situ under photocatalytic reaction conditions. The Pt loading by PD method was 0.9 wt. %. The resulting catalysts were the Doped Ta3N5 loaded with a total of 1.0 wt % Pt; 0.1 wt % Pt by IMP and 0.9 wt % Pt by PD. The Doped Ta3N5 are designated as Pt/Ta3N5:Mg+Zr, Pt/Ta3N5:Mg, Pt/Ta3N5:Zr, Pt/Ta3N5, and Pt/Ta3N5:Mg+Zr (w/o NaCl)
Photocatalytic H2 Evolution Reaction. All photocatalytic reactions were carried out at 12° C. implemented by a cooling water system in a Pyrex top-illuminated reaction vessel connected to a closed gas-circulation system. 0.15 g of the Pt Cocatalyst Doped Ta3N5 were each well-dispersed in 150 mL aqueous methanol solution (130 mL H2O+20 mL MeOH) with a pH value of around 7. After completely degassing the reaction slurry by evacuation, a required amount of argon gas was introduced to create a background pressure of ca. 7 kPa, and the reactant solution was irradiated with a 300 W xenon lamp equipped with a cold mirror and a cut-off filter (L42, λ≥420 nm). The evolved gas products were analyzed by an integrated online thermal-conductivity-detector gas chromatography system consisting of a GC-8A chromatograph (Shimadzu) equipped with molecular sieve 5 Å columns, with argon as the carrier gas.
Single Crystal Characterization. The materials Pt/Ta3N5:Mg+Zr, Pt/Ta3N5:Mg, Pt/Ta3N5:Zr, and Pt/Ta3N5, were distinctly different than the Pt/Ta3N5:Mg+Zr (w/o NaCl) The Pt/Ta3N5:Mg+Zr, Pt/Ta3N5:Mg, Pt/Ta3N5:Zr, and Pt/Ta3N5 were monodispersed nanorod-like particles having about 50-200 nm in length as the major product (
Scanning electron microscopy (SEM) images were taken on a JOEL JSM-7600F field-emission (FE) SEM instrument operated at an acceleration voltage of 15 kV or a Hitachi SU8000 FESEM instrument operated at an acceleration voltage of 30 kV. (Scanning) transmission electron microscopy ((S)TEM) images, energy-dispersive X-ray spectrometry (EDS) mapping images and selected area electron diffraction (SAED) patterns were recorded using a JEOL JEM-2800 system. The cross-sectional sample for (S)TEM observation was made by Ar ion milling using a JOEL EM-09100IS ion slicer. Scanning-transmission electron microscopy coupled with energy dispersive X-ray spectrometry (STEM-EDS) mapping of the cross-section of Ta3N5:Mg+Zr (
All of this provided the conclusion that the prepared Ta3N5:Mg+Zr comprised of Mg- and Zr-co-doped single-crystalline Ta3N5 nanoparticles. No minor segregated phases such as MgO, Zr2ON2, NaTaO3 and ZrO2 were observed in the formed Ta3N5:Mg+Zr.
Defect Species Analysis. Reduced Ta species (Ta3+ and/or Ta4+), nitrogen vacancy VN (VN●●●, VN●●, VN● and VNØ) and oxygen impurity ON, are the defect species impacting the photocatalytic performance of Ta3N5, and were comprehensively detected mainly by X-ray photoelectron spectroscopy (XPS; for reduced Ta), electron paramagnetic resonance spectroscopy (EPR; for reduced Ta and VN) and combustion analysis (for ON). Note that VN●●●, VN●●, VN● and VNØ represent the VN with zero, one, two and three trapped electrons, respectively, and that only VN●● and VNØ with unpaired electrons are possibly EPR-active. X-ray photoelectron spectra (XPS) were acquired using a PHI Quantera II spectrometer with an Al Kα radiation source. All binding energies were referenced to the C Is peak (284.8 eV) arising from adventitious carbon. Electron paramagnetic resonance (EPR) spectra were recorded on an X-band ELEXSYS 500-10/12 CW-spectrometer (Bruker) using a microwave power of 6.3 mW, a modulation frequency of 100 kHz and an amplitude up to 5 G. Standard EPR tubes were each filled with 100 mg of the individual photocatalyst under Ar and measured at 20° C. The oxygen and nitrogen contents of the synthesized Ta3N5 were measured by an oxygen-nitrogen combustion analyzer (Horiba, EMGA-620W). Diffuse reflectance spectra (DRS) were acquired using an ultraviolet-visible-near-infrared spectrometer (V-670, JASCO) and further converted from reflectance into the Kubelka-Munk (K.-M.) function.
The background absorbance of different Ta3N5 at 600-800 nm region, arising from defect species, was compared in
One major defect species suppressed by doping was found to be Ta3+. This is the case because a Ta 4f7/2 component was identified with a binding energy of 23.6 eV in undoped Ta3N5 (
Time-resolved absorption (TA) spectroscopic measurements were carried out using a pump-probe system equipped with Nd:YAG laser (Continuum, Surelite I; duration: 6 ns) and custom-built spectrometers. Photogenerated charge carriers were probed from visible to mid-IR region: 20000-1000 cm−1 (500-10000 nm). In the visible-near IR region (20000-6000 cm−1), the probe light emitted from the halogen lamp was focused on the sample and the reflected light passing through the spectrometer equipped with monochromatic gratings was finally detected by Si photodetectors. In the mid-IR region (6000-1000 cm−1), the IR probe light coming from the MoSi2 coil was focused on the sample and the IR transmitted light was then introduced to a monochromatic grating spectrometer, allowing to monitor the photocarriers at broad band probe energies (up to 10 μm, 0.12 eV). The transmitted light was then detected by mercury-cadmium-telluride (MCT) detector (Kolmar). The time resolution of the spectrometer was limited to 1 us by the response of photodetectors. The output electric signal was amplified using AC-coupled amplifier (Stanford Research Systems (SR560), bandwidth: 1 MHz), which can measure responses from one microsecond-millisecond timescales. Laser pulses (470 nm, 1 or 0.1 mJ pulse−1) were used to excite the charge carriers on undoped and doped Ta3N5, with and without Pt cocatalysts.
The result of defect species study described above was further supported by the transient absorption (TA) kinetic profiles of charge carriers probed at 2000 cm−1 (5000 nm) on a microsecond timescale (
aMeasured by ICP-AES; ICPS-8100, Shimadzu
bMeasured by the N—O combustion analyzer
Ta Nanopowder Precursor. NaCl-contained Ta nanopowder (NaCl/Ta), the precursor for Ta3N5 synthesis, was used and available from Global Advanced Metals USA, Inc. The NaCl/Ta material was mainly characterized with micron-sized NaCl crystals surrounded by aggregated spherical Ta nanoparticles (
Synthesis of Doped Ta3N5. 0.67 g of NaCl/Ta was well mixed with 92.1 μL of aqueous MgCl2 solution (2 M; Sigma-Aldrich BioUltra), 92.1 μL aqueous ZrOCl2 solution (2 M; Fujifilm Wako Pure Chemical Industries, Ltd.) and 300 μL of ultrapure H2O in an agate mortar. The feed molar ratio of Ta/Mg/Zr was about 7.5/1/1. After desiccating the mixture by mild heating at 60° C. and grinding for around 20 min, the solid was carefully loaded into an alumina crucible, and further heated to 900° C. with a ramping rate of 10° C./min and held at 900° C. for 3 h under a gaseous NH3 flow of 200 mL/min. After natural cooling to room temperature, the obtained sample was washed with hot water (70° C.), and then dried at 40° C. for 6 h under vacuum conditions. Ta3N5:Mg+Zr (feed molar ratio of Ta/Mg/Zr=7.5/1/1) was obtained. The material Ta3N5:Mg+Zr is the Doped Ta3N5.
Synthesis of Cocatalyst Doped Ta3N5. Pt as the hydrogen evolution cocatalyst was loaded onto the surface of the Doped Ta3N5 by a stepwise process utilizing an impregnation-H2 thermal reduction (IMP) method followed by an in-situ photodeposition (PD) method. For the IMP method, Doped Ta3N5 was first well-dispersed in an aqueous solution containing the required amount of H2PtCl6 as the Pt precursor by sonication for 1 min. The slurry was further heated by hot water vapor under manual stirring using a glass rod until it turned dry. After heating the powder at 250° C. for 1 h under a H2/N2 gaseous flow (H2: 20 mL/min; N2: 200 mL/min), the sample PtIMP/Doped Ta3N5 was obtained. Samples were prepared with Pt IMP loadings of 0 wt %, 0.05 wt %, 0.1 wt %, and 0.2 wt %. Following, a required amount of H2PtCl6 was added to an aqueous reaction solution containing PtIMP/Doped Ta3N5 photocatalyst. Pt was loaded onto PtIMP/Doped Ta3N5 in-situ under photocatalytic reaction conditions (PD method). The Pt loading by PD method was 0.9 wt. %. The resulting catalysts were the Doped Ta3N5 loaded with a total of 0.9 wt % Pt (0% IMP/0.9% PD); 0.95 wt % Pt (0.05% IMP/0.9% PD); 1.0 wt % Pt (0.1% IMP/0.9% PD); and 1.1 wt % Pt (0.2% IMP/0.9% PD). Similar to above, as comparison examples, Doped Ta3N5 with 1.0 wt. % Pt by the IMP method and Doped Ta3N5 with 1.0 wt. % Pt by the PD method were also prepared.
Examination of the catalyst samples found the stepwise process produced more evenly distributed Pt on the surface of the catalyst. Particularly, deposition of 1.0 wt. % Pt by a stepwise method (0.1% IMP/0.9% PD) provided a more even distribution of Pt nanoparticles with small sizes (around 2 mm-5 nm) and less aggregation (
Photocatalytic H2 Evolution Reaction. All photocatalytic reactions were carried out at 12° C. implemented by a cooling water system in a Pyrex top-illuminated reaction vessel connected to a closed gas-circulation system. The Pt Cocatalyst Doped Ta3N5 were each well-dispersed in 150 mL aqueous methanol solution (130 mL H2O+20 mL MeOH) with a pH value of around 7. After completely degassing the reaction slurry by evacuation, a required amount of argon gas was introduced to create a background pressure of ca. 7 kPa, and the reactant solution was irradiated with a 300 W xenon lamp equipped with a cold mirror and a cut-off filter (L42, λ≥420 nm). The evolved gas products were analyzed by an integrated online thermal-conductivity-detector gas chromatography system consisting of a GC-8A chromatograph (Shimadzu) equipped with molecular sieve 5 Å columns, with argon as the carrier gas. The rate of hydrogen produced was found to be Ta3N5:Mg+Zr 0.1% PtIMP/0.9% PtPD>>Ta3N5:Mg+Zr 0.05% PtIMP/0.9% PtPD>Ta3N5:Mg+Zr 1.0% PtIMP≈Ta3N5:Mg+Zr 0% PtIMP/0.9% PtPD>Ta3N5:Mg+Zr 1.0% PtPD≈Ta3N5:Mg+Zr 0.2% PtIMP/0.9% PtPD (
Ta Nanopowder Precursor. NaCl-contained Ta nanopowder (NaCl/Ta), the precursor for Ta3N5 synthesis, was used and available from Global Advanced Metals USA, Inc. The NaCl/Ta material was mainly characterized with micron-sized NaCl crystals surrounded by aggregated spherical Ta nanoparticles (
Synthesis of Doped Ta3N5. 0.67 g of NaCl/Ta was well mixed with 92.1 μL of aqueous MgCl2 solution (2 M; Sigma-Aldrich BioUltra), 92.1 μL aqueous ZrOCl2 solution (2 M; Fujifilm Wako Pure Chemical Industries, Ltd.) and 300 μL of ultrapure H2O in an agate mortar. The feed molar ratio of Ta/Mg/Zr was about 7.5/1/1. After desiccating the mixture by mild heating at 60° C. and grinding for around 20 min, the solid was carefully loaded into an alumina crucible, and further heated to 900° C. with a ramping rate of 10° C./min and held at 900° C. for 3 h under a gaseous NH3 flow of 200 mL/min. After natural cooling to room temperature, the obtained sample was washed with hot water (70° C.), and then dried at 40° C. for 6 h under vacuum conditions. Ta3N5:Mg+Zr (feed molar ratio of Ta/Mg/Zr=7.5/1/1) was obtained. The material Ta3N5:Mg+Zr is the Doped Ta3N5.
Synthesis of Cocatalyst Doped Ta3N5. Pt as the hydrogen evolution cocatalyst was loaded onto the surface of the Doped Ta3N5 by a stepwise process utilizing an impregnation-H2 thermal reduction (IMP) method followed by an in-situ photodeposition (PD) method. For the IMP method, Doped Ta3N5 was first well-dispersed in an aqueous solution containing the required amount of H2PtCl6 as the Pt precursor by sonication for 1 min. The slurry was further heated by hot water vapor under manual stirring using a glass rod until it turned dry. After heating the powder at 250° C. for 1 h under a H2/N2 gaseous flow (H2: 20 mL/min; N2: 200 mL/min), the sample PtIMP/Doped Ta3N5 was obtained with a Pt IMP loading of 0.1 wt %. Following, a required amount of H2PtCl6 was added to an aqueous reaction solution containing PtIMP/Doped Ta3N5 photocatalyst. Pt was loaded onto PtIMP/Doped Ta3N5 in-situ under photocatalytic reaction conditions. The Pt loading by PD method was 0.9 wt. %. The resulting catalysts was the Doped Ta3N5 loaded with a total of 1.0 wt % Pt; 0.1 wt % Pt by IMP and 0.9 wt % Pt by PD and is designated as Pt/Ta3N5:Mg+Zr. This catalyst was the same as in Example 1.
Synthesis of Coated Cocatalyst Doped Ta3N5. Cr2O3 was coated onto the surface of the Pt/Ta3N5:Mg+Zr using a photo-reduction method. K2CrO4 was dissolved in an aqueous methanol solution followed by the addition of the Cocatalyst Doped Ta3N5. Irradiating the solution reduced the K2CrO4(Cr6+) to Cr2O3 (Cr3+) forming a Pt/Cr2O3 core-shell nanostructure of a uniform thin layer of Cr2O3 on the Pt. The resulting Coated Cocatalyst Doped Ta3N5 is labeled as Cr2O3/Pt/Ta3N5:Mg+Zr or Pt@Cr2O3/Ta3N5:Mg+Zr.
The formation of a Pt/Cr2O3 core-shell nanostructure was demonstrated by the TEM analysis (
Photocatalytic H2 Evolution Reaction. The hydrogen evolution activity of Cr2O3/Pt/Ta3N5:Mg+Zr was compared against the uncoated Pt/Ta3N5:Mg+Zr. Note, the only difference between these two materials is the addition or absence of the Cr2O3 layer. Photocatalytic reactions were carried out at 12° C. implemented by a cooling water system in a Pyrex top-illuminated reaction vessel connected to a closed gas-circulation system. The Cr2O3/Pt/Ta3N5:Mg+Zr and Pt/Ta3N5:Mg+Zr were each well-dispersed in 150 mL aqueous methanol solution (130 mL H2O+20 mL MeOH) with a pH value of around 7. After completely degassing the reaction slurry by evacuation, a required amount of argon gas was introduced to create a background pressure of ca. 7 kPa, and the reactant solution was irradiated with a 300 W xenon lamp equipped with a cold mirror and a cut-off filter (L42, λ≥420 nm). The evolved gas products were analyzed by an integrated online thermal-conductivity-detector gas chromatography system consisting of a GC-8A chromatograph (Shimadzu) equipped with molecular sieve 5 Å columns, with argon as the carrier gas.
The Cr2O3/Pt/Ta3N5:Mg+Zr catalyst demonstrated a consistent high level of hydrogen production compared against the Pt/Ta3N5:Mg+Zr (
Apparent quantum yield (AQY) measurement. Under the H2 Evolution Reaction conditions, the AQY for H2 evolution was measured. The light source was a 300 W Xe lamp (MAX-303 Compact Xenon Light Source, Asahi Spectra) with bandpass filters of 420, 460, 500, 540, 580, 620, and 660 nm central wavelengths (full-width at half-maximum=15 nm), respectively. The number of incident photons was measured using a LS-100 grating spectroradiometer (EKO Instruments Co., Ltd.), and the AQY was 31 calculated according to the equation below.
AQY (%)=[2×nH
where nH
The AQY for photocatalytic H2 production over Pt@Cr2O3/Ta3N5:Mg+Zr was measured as a function of the irradiation wavelength (
The present invention includes the following aspects/embodiments/features in any order and/or in any combination:
The present invention can include any combination of these various features or embodiments above and/or below as set forth in sentences and/or paragraphs. Any combination of disclosed features herein is considered part of the present invention and no limitation is intended with respect to combinable features.
The disclosure herein refers to certain illustrated examples, it is to be understood that these examples are presented by way of example and not by way of limitation. The intent of the foregoing detailed description, although discussing exemplary examples, is to be construed to cover all modifications, alternatives, and equivalents of the examples as may fall within the spirit and scope of the invention as defined by the additional disclosure.
The entire contents of all cited references in this disclosure, to the extent that they are not inconsistent with the present disclosure, are incorporated herein by reference.
The present invention can include any combination of the various features or embodiments described above and/or in the claims below as set forth in sentences and/or paragraphs. Any combination of disclosed features herein is considered part of the present invention and no limitation is intended with respect to combinable features.
Other embodiments of the present invention will be apparent to those skilled in the art from consideration of the present specification and practice of the present invention disclosed herein. It is intended that the present specification and examples be considered as exemplary only with a true scope and spirit of the invention being indicated by the following claims and equivalents thereof.
This application claims the benefit under 35 U.S.C. § 119(e) of prior U.S. Provisional Patent Application No. 63/184,816, filed May 6, 2021, which is incorporated in its entirety by reference herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/027562 | 5/4/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63184816 | May 2021 | US |
