METHOD FOR PRODUCING METALS WITH TEXTURED SURFACES

CROSS-REFERENCE TO OTHER APPLICATIONS

The current disclosure claims priority from US Provisional Application No. 63,577,197 filed Apr. 10, 2023 which is hereby incorporated by reference.

FIELD

The disclosure is generally directed at material chemistry and, more specifically, at methods for producing metals with textured surfaces.

BACKGROUND

Synthetic control over the nanoscale morphology of metal nanoparticles and extended metal surfaces enables the fine tuning of their physicochemical properties for various target applications which may result in improvements in catalytic activity and unusual optical effects leading to a broad range of associated applications. One technique that is currently used in colloidal metal nanoparticle synthesis is the formation of well-defined geometric shapes realized via the preferential stabilization of certain crystallographic facets by facet-specific ionic or molecular adsorbates. Higher order geometric complexity in metal nanoparticles can be achieved by using sacrificial metals as shape-directing agents enabling the formation of branches and other extruded features. Similarly, sacrificial metals or other inorganic and organic templating agents are used to create void-containing nanoparticles, such as nanocages, nanoframes, and mesoporous nanoparticles. The latter structures are a special category of nanoscale objects for catalysis, optics, and other applications. Specifically, mesoporous or void-containing nanoparticles have high surface-to-volume ratios and are rich in under coordinated surface atoms, which are characteristics desirable for many catalytic applications. Furthermore, nanoscale confinements and structures with nanoscale periodicity have been identified as promising catalyst design strategies for selective electrosynthesis due to their ability to modulate catalytic kinetics. In optics, nanoscale surface roughness, mesopores and voids can result in unusual plasmonic modes and non-linear optical effects, which are desirable for a variety of applications including medical applications of bioplasmonics.

One established technique to obtain mesoporous metal architectures is templated electrochemical deposition. This technique relies on the use of a sacrificial mesoporous template such as a metal, liquid crystal, or block copolymer, filled with a metal precursor that is subsequently reduced, followed by selective removal of the original template. The size of pores in these materials can be controlled in a wide range from microns down to two (2) nm. Alternatively, mesoporous metal nanoparticles have been prepared using chemical reduction of a metal precursor on block copolymer micellar templates, a combination of surfactants and block copolymers or surfactants and chiral co-surfactants. These chemical strategies are more powerful compared to electrochemical methods, as they rely solely on solution processing and do not require additional equipment. However, the disadvantages of these approaches include limited synthetic tuneability of the resultant morphologies and the reliance on highly specialized polymers or organic additives to obtain these structures. A limited mechanistic understanding of the nanotexture formation process has also restricted the tunability of morphologies achievable through these methods.

Therefore, there is provided a novel method for producing metals with textured surfaces.

SUMMARY

The disclosure is directed at a method and system for producing metals with textured surfaces. The metals may include metal nanoparticles, metal alloy nanoparticles, thin metal films, thin metal foils and/or extended metal surfaces.

In one embodiment, the disclosure is used to create texture or patterning in the form of grooves on a surface of the metal. The grooves may be of tunable depth within the metal and metal alloy nanoparticles, thin metal films, thin metal foils or extended metal surfaces. In some embodiments, a depth of the grooves can range from about a few atomic layers (subnanometer) to about tens of nanometers (and theoretically can reach 100+nm). In some embodiments, this may occur during the formation of nanoparticles and their method of synthesis related to the field of nanoparticle materials.

In some embodiments, surfaces of metal nanoparticles, thin metal films, metal foils or extended metal surfaces include a Turing-like pattern after undergoing a method of the disclosure (seen as a metal reduction) with highly concentrated suspensions of precursors in the presence of cationic surfactants of a specific, or predetermined, composition and specific, or predetermined, co-surfactants or other additives causing the surfactants to self-assemble into worm-like micelles under the reaction conditions. In some embodiments, the disclosure enables the creation of mesoporous metal particles and films with a pore gap size corresponding to a minimal or small distance between two micelles determined by their electrostatic repulsion.

In one aspect of the disclosure, there is provided a method of applying a texture to a metal surface including obtaining a cationic surfactant solution; adding an aqueous metal salt solution to the cationic surfactant solution to generate a reaction mixture; and adding an ascorbic acid to the reaction mixture to generate a textured metal.

In another aspect, the method further includes adjusting a pH level of the cationic surfactant solution. In yet another aspect, the method further includes adding a texturing metal before or after the reaction mixture is generated. In a further aspect, the texturing metal is at least one of metal seeds, nearly spherical metal nanoparticles, nanorods, metal foils, metal films or metal nanocubes. In yet a further aspect, the texturing metal is a same metal as a metal in the aqueous metal salt solution. In another aspect, the texturing metal is palladium, platinum, ruthenium, gold, silver, rhodium or ruthenium-silver alloy.

In a further aspect, the method includes adding a thin metal film into the reaction mixture. In another aspect, the method includes washing the thin metal film before it is added to the reaction mixture. In yet another aspect, the method includes collecting the textured metal. In a further aspect, the method includes washing the collected textured metal.

In another aspect, the method includes adjusting a temperature of the reaction mixture to a predetermined temperature. In an aspect, the method further includes agitating the reaction mixture for a predetermined period of time. In yet another aspect, obtaining a cationic surfactant solution includes mixing water with at least one of cetylpyridinium bromide (CPB), cetyltrimethyl ammonium chloride (CTAC), cetylpyridinium chloride (CPC), cetylpyridinium iodide (CPI) or cetyltrimethyl ammonium bromide (CTAB). In another aspect, the method includes synthesizing the texturing metal before adding the texturing metal to the reaction mixture.

In an aspect, the aqueous metal salt solution comprises at least two salts. In another aspect, obtaining a cationic surfactant solution includes mixing a cationic surfactant above a critical micelle concentration (CMC) with a liquid. In a further aspect, the method includes mixing a co-surfactant into the cationic surfactant solution. In yet another aspect, the method includes mixing sodium salicylate (NaSal) into the cationic surfactant solution. In yet a further aspect, the method includes centrifuging the reaction mixture to separate the textured metal from the reaction mixture

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached Figures.

FIG. 1a is a flowchart showing a method of synthetically applying patterning to metal nanoparticles, thin metal films and/or extended metal surfaces;

FIG. 1b is a flowchart showing another method of synthetically applying patterning to metal nanoparticles, thin metal films and/or extended metal surfaces.

FIGS. 2a to 2f are scanning electron microscope (SEM) images of palladium (Pd) nanocubes after having patterning synthetically applied at different pH levels;

FIG. 2g is a schematic diagram of a continuum of surfactant micelle structures;

FIG. 2h is a phase-like diagram showing an onset of patterning;

FIGS. 3a to 3c are transmission electron microscope (TEM) images of Pd nanocubes with shallow patterning;

FIGS. 3d to 3f are TEM images of Pd nanocubes with deep patterning;

FIG. 3g is a TEM image of self-seeded Pd nanoparticles;

FIG. 3h is a SEM image of self-seeded Pd nanoparticles;

FIG. 3i is a set of schematic images showing imprint formazation with increasing Pd content;

FIG. 4 is a phase-like diagram showing an onset of patterning;

FIGS. 5a to 5c are TEM images of nanoparticles synthesized in cetylpyridinium chloride (CPC);

FIG. 5d is a chart showing corrugation width distribution for the images of FIGS. 5a to 5c;

FIGS. 5e to 5g are SEM images of nanoparticles synthesized in CPC;

FIG. 5h is a chart showing corrugation width distribution for the images of FIGS. 5e to 5g;

FIGS. 6a to 6c are bright-field TEM images of Pd nanoparticles synthesized in CPC;

FIG. 6d is an SEM image of Pd nanoparticles with shallow patterning synthesized in CPC;

FIGS. 6e and 6f are dark-field TEM images of PD nanoparticles synthesized in CPC;

FIG. 6g is a bright-field TEM image of Pd nanoparticles synthesized in CPC;

FIG. 6h is an SEM image of Pd nanoparticles with shallow patterning synthesized in CPC;

FIG. 7a is a SEM image of pattern formation on mixed facet nanoparticles;

FIG. 7b is an SEM image of cube-seeded patterning before patterned growth;

FIG. 7c is an SEM image of cube-seeded patterning after patterned growth;

FIGS. 7d to 7f are SEM images of octahedron-seeded patterning;

FIGS. 7g to 70 are SEM images of nanostructures obtained at different pH values and Na Sal fractions;

FIG. 7p is a SEM image of truncated Pd nanooctahedra patterned with wormlike micelles in the presence of NaSal at low Ph;

FIG. 7q is a SEM image of truncated Pd nanooctahedra patterned with wormlike micelles in the presence of NaSal at high Ph;

FIG. 7r is an SEM image of self-seeded Pd nanoparticles patterned at low pH in the presence of NaSal;

FIG. 7s is an SEM image of self-seeded Pd nanoparticles patterned at high pH in the presence of NaSal;

FIG. 7t is a SEM image of polycrystalline Pd foil patterned in the presence of NaSal;

FIGS. 8a to 8e are images of different examples of surface patterning;

FIGS. 8f to 8j are images of EDX maps of Au—Pd core-shell nanoparticles;

FIGS. 8k to 80 are images of EDX maps of Ru—Pd alloy nanoparticles;

FIG. 8p is a SEM image of Pt nanoparticles;

FIG. 8q is am SEM image of Au nanoparticles;

FIGS. 9a to 9f are electron microscopy images of Au—Pd core-shell nanoparticles synthesized in CPC;

FIGS. 10a to 10f are electron microscopy images of Pd—Ru alloy nanoparticles synthesized in CPC;

FIGS. 11a to 11g are electron microscopy images of Pd/Ag nanoparticles synthesized in CPC;

FIGS. 12a to 12c are electron microscopy images of patterned Pt nanoparticles using CTAB as surfactant;

FIGS. 13a and 13b are electro microscopy images of patterned Pt nanoparticles using CPI as surfactant;

FIGS. 14a to 14c are electron microscopy images of patterned Au nanoparticles;

FIG. 15 is a SEM image of synthesized Pd nanocubes;

FIGS. 16a to 16e are SEM images of Pd nanoparticles synthesized in CTAB;

FIGS. 17a to 17d are SEM images of Pd nanoparticles synthesized in CPB;

FIGS. 18a to 18f are SEM images of Pd nanoparticles synthesized in CTAC at different pH levels;

FIGS. 19a to 19e are electron microscopy images of Pd nanoparticles synthesized in CPC; and

FIGS. 20a to 20e are graphs showing catalytic performance of patterned Pd in thermal and electrocatalytic reactions;

DETAILED DESCRIPTION

The disclosure is directed at methods of producing metals with textured or patterned surfaces. Examples of metals that can be produced may include, but are not limited to, metal or metal alloy nanoparticles, metal films, extended metal surfaces or thin metal foils. In another embodiment, the disclosure is directed at synthetically applying mesoporous morphologies on metal surfaces, such as metal nanoparticle surfaces or extended metal surfaces and a method for formulating the same using a synthetic method or approach.

Turning to FIG. 1a, a flowchart showing a method for producing metals with textured surfaces is shown. In some embodiments, the metal may be a metal nanoparticle, a metal alloy nanoparticle, a thin metal film, a metal foil or an extended metal surface. An extended metal surface may refer to a stand-alone thin piece of metal and/or a metal film that has a metal surface that is exposed and where patterning may be applied.

Initially, a metal or metal nanoparticle on which a textured surface is to be applied is selected (100). In some embodiments, the metal may be metal nanoparticles, a thin metal film, a thin metal foil or an extended metal surface.

Depending on the selected metal in (100), an aqueous growth solution is selected, obtained or mixed (102). The selection of the components of the growth solution is based on the metal selected in (100) and/or a desired texture that is to be applied to a surface of the selected metal. In one embodiment, the growth solution includes a cationic surfactant above critical micelle concentration (CMC), a precursor metal salt and a mild reducing agent. In some embodiments, the metal in the precursor metal salt is the same metal as the selected metal. In some embodiments, the mild reducing agent may be molecular reductants such as, but not limited to, ascorbic acid and the like. In other embodiments, the aqueous growth solution may include pre-synthesized small metal nanoparticles that act as crystalline seeds.

The aqueous growth solution and the selected metal are then combined or synthesized together (104). In some embodiments, the selected metal may be placed in the aqueous growth solution.

During this synthesis process, the nanoparticles are colloidally stabilized by molecular assemblies of the cationic surfactant (such as, but not limited to, micellar structures, bilayers and the like). In a specific embodiment, an aqueous growth solution of a cationic surfactant above CMC along with the presence of hydrotropes (such as within the reducing agent) with a pre-desired pH level and a high concentration of metal halide salts produce an environment for controlling the structure of the molecular assemblies on the surface of growing nanoparticles to apply a pattern or texture to a surface of the nanoparticles beyond the formation of a stabilizing bilayer. This enables a bridging or combining of soft matter chemistry and metal crystal growth to enable the synthesis of metal nanoparticles or other metal foils or films with morphologically tunable patterned surfaces in accordance with an embodiment of the disclosure.

Turning to FIG. 1b, a flowchart showing a second embodiment of a method of synthetically applying patterning to metal nanoparticles is provided. As a result of a performance of the method, a set of metal nanoparticles having patterning on a surface are produced. In other embodiments, the synthetically applied patterning may be applied to thin metal films, extended metal surfaces and the like.

Initially, a synthesis of a texturing metal may be obtained (150). Examples of texturing metals include, but are not limited to, metal seeds, nearly spherical metal nanoparticles, nanorods, metal foils, metal films or metal nanocubes. Metal examples include, but are not limited to, palladium, platinum, ruthenium, gold, silver, Ruthenium-palladium alloy or silver-palladium alloy.

As will be described below, the texturing metal may or may not be included in the method for producing texture to a surface of a metal. The determination of whether to include or not include the texturing metal may be based on a desired texture that is to be applied to a surface of the metal. In some embodiments, such as with the production or generation of a mesoporous metal, there may not be a need or desire to include the texturing metal. In some embodiments, previously synthesized texturing metals may be obtained or the texturing metals may be synthesized from scratch via known methods. In some embodiments, these texturing materials may be used as part of the process for applying patterns or textures to metal nanoparticles or for producing textured nanoparticles as will be discussed in more detail below.

Independent from the texturing metal being obtained, a cationic surfactant is dissolved in a liquid (152) to produce, or obtain, a cationic surfactant solution. In some embodiments, the liquid is water while in other embodiments, the liquid may be a buffer solution. Examples of cationic surfactants, which may be seen as surfactants that have a positively charged functional group, include, but are not limited to, cetyltrimethyl ammonium bromide (CTAB), cetylpyridinium bromide (CPB), cetyltrimethyl ammonium chloride (CTAC), cetylpyridinium chloride (CPC), cetylpyridinium iodide (CPI) and the like. In some embodiments, multiple cationic surfactants can be mixed together in the cationic surfactant solution.

In some embodiments, the pH of the cationic surfactant solution is then adjusted (154) in order to control or change the effect of the texturing or patterning on the resulting nanoparticles that are produced or the thin metal film or foil. As the pH level affects the resultant texture on the metal, depending on the pH level of the initial cationic surfactant solution, the pH level may have to be adjusted. In some embodiments, the pH can be changed or adjusted by adding hydrochloric acid (HCl) or sodium hydroxide (NaOH) to the cationic surfactant solution although other acids or bases are contemplated.

As an example, in one embodiment where texture or patterning is applied to a surface of metal nanoparticles, the texture or pattern morphology for the resulting nanoparticles may change from linear wormlike micelles to highly branched micellar networks or less branched structures in between based on a pH level of the cationic surfactant solution. Examples of different texture and texture morphology that have been achieved using the method of the disclosure with respect to PH level and a cationic surfactant solution made from CPC during palladium (Pd) nanocube synthesis are shown in the images of FIGS. 2a to 2f. More specifically, FIGS. 2a to 2f are scanning electron microscope (SEM) images of Pd nanocubes in CPC with a low H₂PdCl₄concentration at different pH as indicated under each image. FIG. 2g provides a schematic diagram of surfactant micelle structures based on imprints observed in the SEM images of FIGS. 2a to 2f. FIG. 2h is a chart showing an onset of texturing or patterning (zone A) and zones of texturing or patterning (Zone B) and no texturing or patterning (Zone C) in the pH—qualitative degree of counterion dissociation (a—the fraction of halide ions (here, Cl⁻ or Br⁻) dissociated from the micelle) parameter space.

An aqueous metal salt solution is then added to the cationic surfactant solution (156). In one embodiment, the aqueous metal salt solution is added to the cationic surfactant solution as the cationic surfactant solution is undergoing a vigorous stirring or agitation. In some embodiments, the metal that is selected or used in metal salt solution is the metal on which the texture is applied as nanoparticles are formed out of the metal. Examples of metal salt solutions include, but are not limited to, Hydrogen chloropalladate (H₂PdCl₄), Hexachloroplatinic acid (H₂PtCl₆), Chloroauric acid (HAuCl₄), Ruthenium chloride (RuCl₃), silver nitrate (AgNO₃), and their mixtures. In other embodiments, a metal salt can be added to the cationic surfactant solution and then dissolved within the solution. In further embodiments, the metal salt may be selected from transition metals in the 5th or 6th periods of the periodic table.

If desired or necessary, the synthesized texturing metal can then be added to the cationic surfactant solution (158). In one embodiment, synthesized metal nanocubes (from (150)) are added to the cationic surfactant solution to generate or produce shallow patterning on the surface of the produced nanoparticles or nanocubes. Examples of shallow patterning or texturing on a surface of Pd nanocubes are shown in FIGS. 3a to 3c which are transmission electron microscope (TEM) images where FIGS. 3a and 3c are bright field images and FIG. 3b is a dark field image.

In another embodiment, synthesized metal cubic seeds (from (150)) are added to the cationic surfactant solution to generate or produce deep patterning on the surface of the generated nanoparticles or nanocubes. Examples of deep patterning or texturing on a surface of a metal nanoparticle are shown in the TEM images of FIGS. 3d to 3f where FIGS. 3d and 3f are bright field images and FIG. 3e is a dark field image.

In other embodiments, no synthesized texturing metal is added to the cationic surfactant solution whereby fully mesoporous nanoparticles with texturing on their surface are generated. FIG. 3g is a TEM image of self-seeded Pd nanoparticles and FIG. 3h is an SEM image of self-seeded Pd nanoparticles with texturing that are produced via one of the methods of the disclosure. FIG. 3i provides a schematic diagram of imprint or patterning formation with increasing Pd²⁺.

Ascorbic acid is then be added to the cationic surfactant solution to produce a reaction mixture (160). The addition of the ascorbic acid assists to convert metal ions in the solution into a reduced metal form. A temperature of the cationic surfactant solution may then be adjusted, such as to around 45° C., and the reaction mixture agitated or stirred for a predetermined period of time (162). It is understood that selection of the temperature and the period of time is based on at least one of the components of the reaction mixture, a desired texturing or patterning or the selected metal.

The resulting nanoparticles (which include a synthetically applied texturing or patterning on their surface) that are generated or produced are then collected (164). In one embodiment, the nanoparticles can be collected by centrifugation and then washed with a liquid, such as, but not limited to, water.

As will be understood, while the flowcharts of FIGS. 1a and 1b may be interpreted as actions being taken in a consecutive and independent manner, it is understood that multiple actions may be combined into a single action. For example, the cationic surfactant solution may be mixed with the ascorbic acid before the patterning metal is added to the solution. Also, it is understood that the actions may not need to be taken in the order as described and may be performed with a different timing without affecting the scope of the disclosure.

In one specific embodiment, the method of the disclosure can be used to synthetically apply a pattern or texture to a surface of a metal foil. The metal foil is initially selected (100) for the application of texture to its surface. In some embodiments, the metal foil may be washed, such as with HCl and water, to clean its surface. A pre-mixed aqueous growth solution can then be obtained (102). In the current embodiment, the pre-mixed aqueous growth solution includes a cationic surfactant with a metal salt dissolved in a liquid. In some embodiments, multiple different metal salts may be used. In some embodiments, two different metal salts are used. The aqueous growth solution may be vigorously agitated or stirred and the temperature raised to about 45° C. before or after the addition of the metal foil (104). Ascorbic acid is then added to produce a reaction mixture and the reaction mixture left overnight to enable the components of the reaction mixture to react with each other and for the texturing or patterning to be applied to the surface of the metal foil. After a reaction time period has elapsed, synthetically patterned metal foil or film is then collected and washed, such as with water and methanol, and prepared for further use or application.

In another specific embodiment, the method of the disclosure can be used to produce a core-shell patterned nanoparticle. In this embodiment, a cationic surfactant (with a co-surfactant) is dissolved in water and heated to about 45° C. to produce a cationic surfactant solution. After five minutes, a metal salt is added. After another five minutes, metal cubic seeds can be added to the solution followed by ascorbic acid to produce a reaction mixture. In the current embodiment, the metal of the cubic seeds is different than the metal of the nanoparticle. After a period of reaction, core-shell patterned nanoparticles can be then collected from the solution for further use or application.

In another specific embodiment, the method of the disclosure can be used to synthesize seed-mediated growth of Pd nanocubes by reducing H₂PdCl₄with ascorbic acid in a aqueous growth solution of CTAB above its critical micelle concentration (CMC) with the results schematically shown in FIGS. 16a to 16e which are SEM images of Pd nanoparticles synthesized in CTAB with a high concentration of Pd precursor and seeded with Pd cubic seeds. A pH level of the growth solution is shown beneath each figure. In this example, two dynamic processes co-exist in the container in which the experiment was performed.

Firstly, CTA⁺ species formed spherical, rod, or wormlike micelles, micellar networks or micellar bilayers are combined or mixed with different concentrations of salts and hydrotropes in the CTAB solution. The CTA⁺ micelle structures include hydrophobic tails tucked inside the micelle and positively charged quaternary ammonium heads exposed on the surface, rendering the micelles positively charged and existing in dynamic equilibrium with the Br⁻ counterions. Secondly, the growing Pd nanocrystals with chemisorbed halide ions (Cl⁻, Br⁻) carry a negative charge on their surface, which can be electrostatically compensated for in the electrical double layer either by the surfactant micelles or by hydronium ions, considering that the reaction medium is acidic (pH=2).

If there are strong interactions between the preformed micelles (e.g., wormlike) and the growing nanoparticles, imprints of these micelles appearing on the surface of the nanoparticles are expected as a result of metal growth in the gaps between them, however, it was found that this was not the case, suggesting that this interaction is not sufficiently strong. In order to promote the attraction between wormlike micelles and the Pd nanoparticle surface, the interaction between the hydronium ions and the halide-bound Pd nanoparticle surface was reduced or minimized to favour the surface interaction with the preformed micelles.

In a series of experiments at different pH ranging from 2 to 10.1 (with several results shown in FIGS. 16a to 16e), it was determined that at pH ≥9.6, the nanoparticle surface looked like an imprint of a micellar network. FIG. 16a shows the results where a pH level of the solution is 3.5 and FIG. 16e shows the results where a pH level of the solution is 9.6. In addition to the lower hydronium concentration, the interaction between the micelles and the nanoparticle surface could be attributed to the hydrogen bonding between the metal-bound halide ions and the HO⁻ species leading to a higher negative surface charge, and, therefore, increased electrostatic attraction of the surface to the positively charged micelles.

As the electrostatic attraction between the metal nanoparticle surface and the micellar structures is a function of the metal surface and the micellar structures being sufficiently charged to attract to one another. Therefore, pH-related changes in the surface charge of the micelles are to be considered concomitantly with the changes in the charge of the metal particle surface described above. Specifically, for cetylpyridinium cationic micelles, increasing pH causes a restructuring of spherical micelles into wormlike structures and then into branched micellar networks. In terms of the ability to electrostatically interact with other objects, while a charged spherical micelle interacts with an oppositely charged surface through a point contact, a wormlike micelle, and especially a branched micellar network can interact with the surface through an extended area, acting as an electrostatic analogue of a polydentate ligand. In experiments, branched imprints on metal surfaces at a high pH were observed and the absence of any imprints at lower pH is consistent with the ability of branched micellar networks to electrostatically bind to the surface more efficiently than smaller micellar structures.

Once it was determined and observed that imprints could be established, attempts to obtain imprints of different micellar structures in a controllable way were tested. In the experiments, differently shaped CTAB micelles within a wide pH range were tested, however, as explained above, when the pH<9.6 (when CTAB is used as a surfactant), there was limited or insufficient interaction between the micelles and the metal nanoparticle surface to cause pattern formation. It is understood that a desired pH level of the solution is based on the cationic surfactant being used for the cationic surfactant solution as shown in the phase diagram of FIG. 2h. To overcome this, it was determined that the addition of, or use of, other cationic surfactants could be used to apply synthetically patterning to a surface of the nanoparticles. These surfactants include, but are not limited to, cetylpyridinium bromide (CPB), cetyltrimethyl ammonium chloride (CTAC), and cetylpyridinium chloride (CPC). The nature of the cationic surfactant head group and the counterion determines the degree of counterion dissociation (a) in the resultant micelles, and, therefore, their resulting charge. In the surfactant series CTAB-CPB-CTAC-CPC, a increases, meaning that the charge on the corresponding micelles increases in the same order. Thus, replacing CTAB with a higher a surfactant reduces or overcomes the problem of insufficient electrostatic interaction between the surfactant micelles and the surface of the nanoparticles due to the micelles being more charged.

In further experiments, when CTAB with replaced with CPC during Pd nanocubes synthesis, a variety of structural imprints of the nanoparticle surface determined by the reaction pH, corresponding to linear wormlike micelles, highly branched micellar networks, and less branched structures in between were observed. Therefore, it can be seen that in some embodiments, a combination of adjusting a pH level of a cationic surfactant solution along with a selection of a predetermined cationic surfactant for use in a cationic surfactant solution enables the synthetic application of patterning to a nanoparticle surface. These are shown in more detail in FIGS. 2a to 2g. When CTAC or CPB were used as the cationic surfactant, the pH at which the onset of patterning initiated progressively increased, but was below that for the CTAB system, which is consistent with the a trend. This is schematically shown in FIGS. 17a to 17d which are SEM images of Pd nanoparticles synthesized in CPB with a high concentration of Pd precursor and seeded with Pd cubic seeds and FIGS. 18a to 18f which are SEM images of Pd nanoparticles synthesized in CAC with a high concentration of Pd precursor and seeded with Pd cubic seeds. The phase-like diagram in the pH-a coordinates of FIG. 2h displays the observed trends.

In the above experiments, only a few nm of Pd was deposited on the pre-synthesized seeds. In other experiments, the depth control of the observed patterns, such as, but not limited to, corrugated patterns, using the method of the disclosure were observed. Based on the obtained electron microscopy images, the width of the wormlike micelles was about 1.7±0.3 nm (based on ≥150 measurements). It was observed that the depth of the corrugations or patterning exceeded the diameter of the wormlike micelles initially adsorbed to the substrate using the method of the disclosure. This is shown in more detail in FIGS. 3a to 3f, FIGS. 5a to 5c, FIGS. 5e to 5g, FIGS. 6a to 6h and FIGS. 19a to 19e. More specifically, FIGS. 5a to 5c are TEM images of Pd nanoparticles synthesized in CPC with a high concentration of Pd precursor at a pH level of 3 and FIGS. 5e to 5g are SEM images of Pd nanoparticles synthesized in CPC with a high concentration of Pd precursor at a pH level of 2.9 (FIG. 5e), 3.0 (FIGS. 5f) and 24 (FIG. 5g). FIGS. 6a to 6c and 6g are bright-field TEM images of Pd nanoparticles synthesized in CPC and a low concentration of Pd precursor at a pH of 3.5, FIGS. 6e and 6f are dark-field TEM images of the same and FIGS. 6d and 6h are SEM images of Pd nanoparticles with shallow patterning synthesized in CPC. FIGS. 19 and 19d are SEM images of Pd nanoparticles synthesized in CPC using small Pd cubic seeds and a high concentration of Pd precursor at a pH level of 2.4 while FIGS. 19b and 19 are bright-field TEM images of the same and FIG. 19c is a dark field TEM image of Pd nanoparticles with deep patterning synthesized in CPC. As can be seen in these Figures, the increase in amount of deposited Pd results in the formation of deeper corrugations.

In addition, when self-seeded synthesis of Pd nanoparticles in a CPC-based growth solution was performed, it was observed that the resultant structures are fully mesoporous due to the patterning or corrugations extending to the centers of the nanoparticles, indicating that the pattern formation process coincided with nanoparticle growth as soon as the seeds were formed (FIGS. 3g and 3h). This was attributed to the formation of deep patterning or corrugations to the dynamic nature of the micelles when they electrostatically interact with the growing metal particles, as schematically illustrated in FIG. 3i. More specifically, once the micelles are attracted to the halide-bound metal surface, the gaps between them (associated with the electrostatic repulsion of the positively charged micelles) begin to fill with Pd due to gradual Pd²⁺ precursor reduction. In the process of Pd growth, the initially centrosymmetric cross-sections of the micelles begin to grow outward forming micellar bilayer due to the attraction of the positively charged head groups to the negatively charged growing Pd features stabilized by chemisorbed halide ions. As this restructuring of the initial micelles affect the equilibrium in the system, the micelles from the solution merge with the developing bilayers in the gaps between the growing Pd features, resulting in periodic lamella-like structures in the forming grooves.

It was then investigated whether imprint formation was facet-specific, considering that the surface density of chemisorbed halide ions is different on different facets. To this end, polyhedral Pd nanoparticles enclosed by a mixture of well-defined {111} and {100} facets were used. It was determined that pattern formation in the CPC surfactant system was preferential on the {100} facets, while {111} facets remained mostly intact (FIG. 7a). The presence of wormlike micelles in the medium was evident from the observed patterning of the {100} facets, thus, the absence of their imprints on the {111} facets could be attributed either to a weaker interaction of the micelles with this particular facet, or to the restructuring of the micelles on them. To understand facet-specific patterning, Pd growth on facet-specific seeds was studied. It was observed that nanocubes solely enclosed by {100} surfaces and octahedra enclosed by {111} surfaces as shown in FIGS. 7b to 7f where FIGS. 7b and 7c are SEM images of cube-seeded patterning before (FIG. 7b) and after (FIG. 7c) patterned growth and FIGS. 7d to 7f are SEM images of octahedron-seeded patterning before (FIG. 7d) and after thin Pd layer growth (FIG. 7e) and thick Pd layer growth (FIG. 7e).

In the case of the cubic seeds, the overall particle geometry remained cubic after patterned layer growth (as shown in FIG. 7c). In contrast, when a thin layer of Pd was deposited on the octahedral seeds, it was observed that selective deposition of Pd on the edges and vertices of the nanoparticles, while the faces remained relatively free of patterns (as shown in FIG. 7e). With increasing amounts of deposited Pd, the octahedral shape definition began to be lost and the preferential growth of Pd on the {100} facets became more evident (as shown in FIG. 7f). Based on these observations, it was determined that the interactions of the surfactant micelles with the {111} cannot be weaker than with the {100} surface, as otherwise the less surfactant-covered surface would be more readily accessible to Pd²⁺ species and, therefore, grow faster. Furthermore, it was determined that {111} surfaces have a higher density of chemisorbed halide ions compared to {100} surfaces, further supporting that the electrostatic interaction of the surfactant wormlike micelles with the {111} surface should not be weaker than that with {100} surface. Thus, a micellar restructuring at the {111} surface appears to be more likely, and considering a higher density of chemisorbed halide species on these surfaces compared to {100}, this restructuring might be facilitated by a higher surface charge density on the metal surface than on the wormlike micelles, as explained below. Analogously to the deep groove formation mechanism (as schematically shown in FIG. 3i), it was determined that the wormlike micelles undergo a similar transition in micelle morphology resulting in the formation of a flat micellar bilayer on the Pd {111} surface, which has a higher packing parameter compared to a wormlike micelle, and, therefore, better matches the surface density of the negatively charged surface-bound halide ions. In contrast, on the {100} surfaces, the wormlike micelles have a sufficiently high surface attraction to obstruct some of the Pd surface, but do not have a sufficient drive to restructure into a flat bilayer due to a lower halide density on {100} than on {111}. Compared to the dense continuous bilayer on the {111} surface, the wormlike micelles on the {100} facets have gaps due to intermicellar repulsion, providing more accessible metal surface sites for Pd²⁺ deposition, which explains the preferential patterned growth of {100} facets in these systems. The micellar transformations associated with this facet-specific behaviour and the deep groove formation illustrate that the surface environment of the metal nanoparticles can also act as a micellar restructuring trigger, further highlighting the complex dynamic nature of the solutions containing surfactant micelles and growing metal nanoparticles. Importantly, these observations highlight that the electrostatic interactions between the micelles and the metal surface must be within a specific window to cause surface patterning, otherwise the micelles would not obscure metal deposition and the metal would deposit evenly on the surface without forming a pattern, and not too strong, otherwise the micelles would undergo transition in micellar morphology on the surface and lose their templating characteristics. Importantly, when the facet-specific behaviour of the patterning mechanism is not desirable (e.g., when {111} facets must be patterned), it can be overcome by introducing an additional synthetic parameter.

In addition to the pH trigger, co-surfactants may be used to induce structural transformations of surfactant molecular assemblies. In one embodiment, sodium salicylate (NaSal) can be used to induce wormlike micelle formation in cationic surfactants. In experiments, NaSal was used in different amounts (CPC: NaSal ratios) and it was determined that the onset pH for patterning can be shifted to lower values with increasing NaSal content (as schematically shown in FIGS. 7g to 7o). FIGS. 7g to 70 are SEM images of nanostructures obtained at different pH values and nasal fractions.

In these experiments, a large amount of Pd was deposited on 15-nm cubic Pd seeds and the patterning facet selectivity observed. While in the CPC solution at pH=1.9 in the absence of NaSal the formation of octahedral particles enclosed by {111} facets is favoured (FIG. 7g). The addition of NaSal resulted in the formation of small {100} planes with wormlike micelle imprints (FIG. 7m); at pH=2 where non-patterned mixed-facet ({111}, {100}) particles were observed in the absence of NaSal, its addition caused the formation of slightly truncated patterned cubic particles (FIG. 7n). In the latter case, the truncations corresponding to {111} facets also show some patterning (FIG. 7n), in contrast to what was observed at a lower NaSal concentration (FIG. 7k) or in the absence of NaSal. The effect of the addition of NaSal indicated that it promoted interactions between the micelles and the nanoparticle surface over the micelle restructuring. This behaviour can be explained by the integration of NaSal into the micellar structures, making them denser due to the expulsion of water molecules from the micellar Stern layer and more structurally integrated due to the formation of strong ionic pairs between CP+ and Sal- and, therefore, increasing their structural stability against restructuring into micellar bilayer. Thus, adjusting both pH and the NaSal concentration enables modulating patterning in a broader range, as illustrated in FIGS. 7p to 7s. More specifically, the addition of NaSal enabled facet-nonselective patterning of truncated Pd nanooctahedra, while the pattern morphology was controlled by pH (FIGS. 7p and 7q). In the case of self-nucleated growth of Pd nanoparticles, the addition of NaSal at low pH enables well-defined wormlike micelle patterning (FIG. 7r), a higher pH in the presence of NaSal leads to imprints corresponding to micellar networks (FIG. 7s). It was also demonstrated that the introduction of a polycrystalline Pd foil into the Pd growth solution improved for surface patterning results the formation of the characteristic mesoscale surface corrugations on this extended metal surface (FIG. 7t).

As discussed below with respect to further experiments, the applicability of the disclosure to other material compositions and structures was tested. First, it was tested whether synthetically applying patterning to Pd can be induced when Pd layers are grown on other metals, by introducing Au nanoparticles. As outlined in procedure 9 below, the method of the disclosure was used to synthetically apply patterning to Au—Pd nanoparticles during core-shell nanoparticle formation with characteristic patterns. This is shown in more detail in FIGS. 8a to 8e and FIGS. 9a to 9f. FIGS. 8a to 8e are SEM images of Au—Pd core-shell nanoparticles where FIG. 8a is a SEM image, FIG. 8b is a dark-field TEM image, FIG. 8c is a mixed EDX map image, FIG. 8d is a image of Pd and FIG. 8e is an image of Au. FIGS. 9a to 9f are electron microscopy images of Au—PD core-shell nanoparticles synthesized by a reduction of Au and Pd in the patterning conditions in CPC where FIGS. 9a and 9d are SEMI images, FIGS. 9b and 9e are bright-field TEM images and FIGS. 9c and 9f are dark-field TEM Images.

In other experiments, different Pd-based alloys were tested to determine if the disclosure could synthetically apply patterning to these different Pd-based alloys. The alloys that were used were Pd: Ru (20:1 atomic ratio) alloy nanoparticles and Pd: Ag (1:1 atomic ratio) alloy nanoparticles.

Results for the Pd: Ru alloy are shown in FIGS. 8f to 8j and FIGS. 10a to 10f. FIG. 8f is an SEM image, FIG. 8g is a dark-field TEM, FIG. 8h is a mixed EDX map image, FIG. 8i is a image of Pd and FIG. 8j is an image of Ru and FIGS. 10a to 10f are electron microscopy images of the PdRu alloy nanoparticles synthesised by a co-reduction of Ru and Pd in the patterning conditions in CPC with FIGS. 10a and 109 being SEM images, FIGS. 10b and 10e being bright-field TEM images and FIGS. 10c and 10f being dark-field TEM images.

Results for the Pd: Ag alloy are shown in FIGS. 8k to 8o and FIGS. 11a to 11g. FIG. 8k is a SEM image. FIG. 8l is a dark-field TEM image, FIG. 8m is a mixed EDX map, FIG. 8n is an image of Pd and FIG. 8o is an image of Ag. FIGS. 11a to 11g are electron microscopy images of the PdAg nanoparticles synthesised by a co-reduction of Ag and Pd in the patterning conditions in CPC where FIGS. 11a and 11e are SEM images, FIGS. 11b, 11c and 11f are bright-field TEM images and FIGS. 11c and 11g are dark-field TEM images. Using the synthesis conditions improved or optimized for the Pd-micelle surface, patterned mesoporous nanoparticles of these materials were generated, produced or obtained.

Other materials such as Pt was also tested and the method of the disclosure was used to synthetically apply patterning to Pt nanoparticles. The results are shown in FIG. 8p which is an SEM image of Pt nanoparticles with patterning applied to a surface. It was noted that the reduction of Pt required an elevated reaction temperature such that it is understood that the reaction temperature for different embodiments of the disclosure may be different. For Pt, the reaction temperature was 80° C. instead of 45° C. as in may of the other reactions in CTAB. The final Pt nanoparticles showed the imprint of highly intertwined micellar network. In other experiments, it was found that Pt line-like patterning can be achieved by replacing CTAB with CPI (cetylpyridinium iodide) as shown in FIGS. 12a to 12c, which can be ascribed to the higher affinity of I⁻ to Pt. FIGS. 12a to 12c are electron microscopy images of patterned Pt nanoparticles synthesised in a low concentration regime with CTAB as a surfactant with FIG. 12a being a TEM image and FIGS. 12b and 12c being HRTEM images.

It was also determined that the disclosure could be used to synthetically apply patterning to Au (as shown FIG. 8q which is an SEM image of Au nanoparticles). For Au, this interaction can be facilitated by adding a small fraction of aniline ([CPC]: [aniline]=20:1) into the reaction mixture. In this case, aniline acts as a bridging agent between the metal surface and the micelles, due to high affinity of nitrogen lone pair to Au and the integration of the aniline ring into the micellar structure due to TT-TT stacking of the aromatic components of the molecules.

In other testing, the catalytic properties of the patterned surfaces were investigated using the patterned or corrugated Pd nanocubes that were produced using the method of the disclosure as a test material. First, the thermocatalytic performance in the formic acid dehydrogenation reaction to that of non-patterned Pd nanocubes was compared with the results shown in FIG. 20a. It was determined that the activation energy of the reaction decreased by more than a factor of two (from 72 to 32 KJ mol⁻¹), indicating that the corrugated surface has a higher intrinsic catalytic activity in this reaction. This behaviour can be attributed to more efficient hydrogen desorption properties of this material. To further assess hydrogen desorption properties of the corrugated Pd surfaces, electrodes including patterned and non-patterned Pd foils were tested with the results shown in FIG. 20b which is a hydrogen desorption voltammograms in 0.5 M H₂SO₄during CVs in a potential range from 0.8 V to −0.3 V vs RHE at a scan rate of 20 mV s⁻¹on a pristine polycrystalline Pd foil and a patterned polycrystalline Pd foil. The patterning of the surface resulted in a 4.2-fold increase in the amount of desorbed hydrogen and a shift of 35 mV in the onset and 100 mV in the peak potential in this process, indicating superior hydrogen desorption properties, relevant for hydrogen production and a broad range of dehydrogenation reactions.

Comparisons between electrocatalytic performance of corrugated nanocubes to non-patterned nanocubes and branched Pd nanoparticles that are rich in undercoordinated surface sites were also performed. Based on the broad peak observed in the CO stripping analysis (FIG. 20c), corrugated Pd nanoparticles have a more complex surface structure enclosed by high-index facets, compared to even branched Pd nanoparticles. FIG. 20c is a CO stripping voltammograms on different Pd structures (non-patterned cubes, branched nanoparticles and patterned cubes).

The electrodes comprised of corrugated Pd nanoparticles showed higher currents (FIGS. 20d and 20e) and longer current stability (FIG. 20e) compared to the two controls (non-patterned nanocubes and branched nanoparticles), indicating higher activity and selectivity of the patterned material towards CO₂reduction to formate and suppression of competing CO formation, which leads to catalyst poisoning and, consequently, decrease in current over time. FIG. 20d is a CO₂electroreduction voltammogram and FIG. 12e is a chronoamperometry in 0.5 M KHCO₃at −0.2 V corresponding to non-patterned cubes, branched nanoparticles and patterned cubes.

Further details of experiments using the method of the disclosure are described below. Some of the procures described below provide more details to the description above. It is understood that in the following, specific volumes, measurements of time, temperatures and weights are taught, however, it would be understood that these are specifically selected experimental values and not meant to be limiting to the scope of the disclosure.

In performing the experiments, patterning metals in the form of Pd cubic seeds and seed-mediated Pd nanocubes were synthesized. For the Pd cubic seeds (seen as procedure 1), Pd seeds were added to a cationic surfactant solution that was prepared using 45.6 mg of CTAB dissolved in 10 mL of de-ionized (DI) water. The cationic surfactant solution was stirred vigorously in a 95° C. oil bath for 10 minutes followed by the addition of 250 μL of 20 mM H₂PdCl₄and 200 μL of 0.1 M AA. After 10 minutes, the Pd seed solution was transferred to a 30° C. bath and left undisturbed for about 1 hour.

The Pd nanocubes were generated via a seed-mediated synthesis procedure using the Pd cubic seeds produced using procedure 1. In the following description, this will be referred to as procedure 2. Initially, a cationic surfactant solution including 900 mg of CTAB in 6.12 mL of DI water was placed in a 45° C. bath and stirred vigorously. After 5 minutes, 1.92 mL 0.1 M H₂PdCl₄was added dropwise at an approximate rate of 2 mL/min. After a further 10 minutes, 6 mL of Pd cubic seeds and 3 mL of 1 M AA were added. The solution was then left to react with moderate stirring in a bath at 45° C. for 4 hours. The Pd nanocubes that were produced were left undisturbed at room temperature for about 2 hours to precipitate, collected, re-dispersed in water and washed twice in centrifuge at 3000 g for about five minutes.

For the synthesis of Pd nanocubes, the Pd cubic seeds of procedure 1 were used without further purification. For all other syntheses, or experiments, described below, the Pd cubic seeds were distributed in a set of 1.7 mL centrifugation tubes (1 mL of the seed solution per tube) then washed with water twice at 14000 g for 15 minutes and 11000 g for 11 minutes before the seeds in each tube were re-dispersed in 20 μL of water.

Collection of the synthetically patterned nanoparticles was performed after each experiment. In order to collect the synthetically patterned nanoparticles, the nanoparticles were washed in order to remove unwanted residue on a surface of the nanoparticles. This washing process is referred to as procedure 3 in the discussion below. After each experiment was completed, the nanoparticles were collected by centrifugation at a specified speed and the supernatant discarded. The precipitated nanoparticles were then re-dispersed in 1.5× volume of the reaction mixture (e.g. if aliquot volume was 1 mL, then 1.5 mL of DI water was used) and centrifuged at conditions specified for each reaction (washing #1). After the wash was completed, the supernatant was discarded and the precipitate was re-dispersed in 0.5× volume of the reaction (e.g. if aliquot volume was 1 mL, then 0.5 mL of DI water was used) and centrifuged at the conditions specified for each reaction (washing #2). This was repeated if further washings were required. The resulting precipitated nanoparticles were re-dispersed in 50 μL of DI water for every 1 mL of the initial reaction volume for imaging by a SEM or TEM.

In one experiment in accordance with the method of the disclosure, seed-mediated synthesis of Pd nanoparticles in CTAB/CPB/CTAC/CPC at different pH was performed. This may be referred to as procedure 4. In order to perform Pd nanoparticle growth at different pH, 492 mg of CPC (or an equimolar mass of another cationic surfactant, i.e., 440 mg CTAC, or 552 mg CPB, or 500 mg CTAB) was dissolved in 5 mL of DI water followed by the slow addition (˜ 2 mL/min) of 240 μL of 0.1 M H₂PdCl₄under vigorous stirring. After 5 minutes, the concentrated equivalent of 2 mL of Pd cubic seeds (a produced in procedure 1) was added to the reaction mixture followed by the addition of 375 μL of 1 M AA. A PH meter was immersed into the reaction mixture, and the pH was adjusted either by the slow addition of 1 M HCl or 1 M NaOH depending on the cationic surfactant). At a predetermined pH, the aliquot of the reaction mixture was taken and placed in a thermomixer to react at 45° C. under stirring at 1000 rpm for a period from 5 minutes to 6 hours depending on the surfactant and pH. The resulting Pd nanoparticles were collected by centrifugation and washed with DI water 2 times (CPC, CTAC) or 3 times (CPB, CTAB) at 3500 g for 10 minutes (such as described above with respect to procedure 3).

In a further experiment, seed-mediated synthesis of patterned nanoparticles in CPC was performed where a pattern thickness was controlled. This may be referred to as procedure 5. As shown in FIG. 4, a phase-like diagram indicating the onset of patterning based on pH with respect to a total concentration of Pd precursor in the reaction mixture parameter space is provided where Zone B represents an inset of patterning, Zone A is a zone of patterning and zone C is a zone of no patterning.

In order to synthesize patterned Pd nanocubes with shallow patterning, the Pd nanocubes produced in procedure 2 were used as seeds Firstly, the Pd nanocubes were washed and re-dispersed in 2 mL of 50 mM CPC to obtain a stock solution of Pd nanocubes. 492 mg CPC was then dissolved in 5 mL of DI water and placed in a 45° C. oil bath for about 5 minutes followed by the slow addition (˜ 2 mL/min) of 20 μL of 0.1 M H₂PdCl₄and 12.5 μL of 1 M NaOH under vigorous stirring. After 5 minutes, 100 μL of the Pd nanocube stock solution was added to the reaction mixture followed by the addition of 75 μL of 1 M AA. The reaction was left to proceed for 30 minutes at 45° C. under moderate stirring. The formed patterned Pd nanocubes were collected by centrifugation and washed 2 times at 3500 g for 5 minutes (such as via procedure 3). The results are shown in FIGS. 2a to 2c and FIG. 5.

In order to synthesize patterned Pd nanoparticles with deep patterning, cubic seeds (such as the ones produced in procedure 1) were used. A cationic surfactant solution including 492 mg CPC dissolved in 5 mL of DI water placed in 45° C. oil bath for 5 minutes followed by the slow addition (˜ 2 mL/min) of 240 μL of 0.1 M H₂PdCl₄and 25 L of 1 M NaOH under vigorous stirring. After 5 minutes, the concentrated equivalent of 2 mL of Pd cubic seeds was added to the reaction mixture followed by the addition of 375 μL of 1 M AA. The reaction was left to proceed for 30 minutes. The formed patterned nanoparticles were collected by centrifugation and washed 2 times at 3500 g for 5 minutes. The results are shown in FIGS. 2d to 2f and FIGS. 6a to 6h.

In a further experiment, self-nucleated synthesis of patterned nanoparticles in CPC was performed. This may be referred to as procedure 6. In order to synthetically apply patterning to Pd nanoparticles with a throughout patterning (such as schematically shown in FIGS. 2g and 2h), 492 mg of CPC was dissolved in 5 mL of DI water and placed in an oil bath at 45° C. After 5 minutes, 240 μL of 0.1 M H₂PdCl₄was added dropwise at the rate of ˜ 2 mL/min under vigorous stirring followed by the addition of 100 μL of 1 M NaOH. After another 5 minutes, 375 μL of 1 M AA was added, and the reaction was left to proceed for 30 minutes at 45° C. under moderate stirring. The resulting Pd nanoparticles were collected by centrifugation and washed with water 3 times at 7200 g for 10 minutes (such as described above with respect to procedure 3.

In yet another experiment, seed-mediated and self-nucleated synthesis of patterned nanoparticles in CPC in the presence of NaSal was performed. This may be referred to as procedure 7.

In order to synthetically apply patterning to Pd nanoparticles in this experiment. 492 mg of CPC was dissolved in 5 mL of DI water and placed in 45° C. oil bath for 5 minutes. As the experiment was performed multiple times, 87 μL (˜9:1 CPC: NaSal) or 175 μL (˜9:2 CPC: NaSal) of 1.875 M NaSal solution was added dropwise. After 5 minutes, 240 μL of 0.1 M H₂PdCl₄was slowly added (˜ 2 mL/min) along with 1 M HCl for pH adjustment. After another 5 minutes, the concentrated equivalent of 2 mL of Pd cubic seeds was added to the reaction mixture followed by the addition of 375 μL of 1 M AA. The reaction was left to proceed for 1-4 hours depending on pH. The formed patterned nanoparticles were collected by centrifugation and washed 2 times at 3500 g for 5 minutes.

For the self-nucleated synthesis of fully mesoporous nanoparticles, 492 mg CPC was dissolved in 5 mL of DI water and placed in 45° C. oil bath for 5 minutes. 175 μL (˜9:2 CPC: NaSal) of 1.875 M NaSal solution was then added dropwise. After 5 minutes, 240 μL of 0.1 M H₂PdCl₄was slowly added (˜ 2 mL/min) along with 100 μL 1 M NaOH for pH adjustment (to obtain the imprint of micellar networks) or without additives for pH adjustment (to obtain well-defined patterning). After another 5 minutes, 375 μL of 1 M AA was added. The mixture or reaction mixture was left to proceed for 1 hour. The formed patterned nanoparticles were collected by centrifugation and washed 3 times at 7200 g for 10 minutes.

In another experiment, the patterning of Pd foil was performed. This may be referred to as procedure 8. A Pd foil was immersed in 10% HCl for 5 minutes, washed with DI water, and immersed in a solution containing 98.4 mg CPC in 1 mL water, 48 μL of 0.1 M H₂PdCl₄, and 35 μL of 1.875 M NaSal for 1 hour under vigorous stirring at 45° C. 75 μL of 1 M AA was then added to the solution. The patterning growth reaction was left to proceed overnight. The obtained patterned foil (as shown in the SEM image of FIG. 7t) was then washed with water and methanol so that it could be examined or used for another application.

In another experiment, synthesis of Au/Pd core-shell patterned nanoparticles was performed. This may be referred to as procedure 9. In order to synthetically apply patterning to Au/Pd core-shell nanoparticles, 492 mg of CPC was dissolved in 5 mL of DI water and placed in an oil bath at 45° C. followed by the addition of 87 μL of 1.875 M NaSal. After 5 minutes, 120 μL of 0.1 M H₂PdCl₄and 120 μL of 0.1 M HAuCl₄were added dropwise at the rate of ˜ 2 mL/min under vigorous stirring. After another 5 minutes, the concentrated equivalent of 2 mL of Pd cubic seeds was added to the reaction mixture followed by the addition of 375 μL of 1 M AA and the reaction was left to proceed for 1 hour. The resulting nanoparticles were then collected and washed. Images of the resulting nanoparticles are shown in FIGS. 8a to 8e and FIGS. 9a to 9f.

In yet a further experiment, synthesis of Pd—Ru alloy nanoparticles was performed. This may be referred to as procedure 10. In order to synthetically apply patterning to Pd—Ru alloy nanoparticles, 492 mg of CPC was dissolved in 5 mL of DI water and placed in 45° C. oil bath. After 5 minutes, 120 μL of 0.1 M H₂PdCl₄and 120 μL of 0.1 M RuCl₃were added dropwise at the rate of ˜ 2 mL/min under vigorous stirring. After another 5 minutes, the concentrated equivalent of 2 mL of Pd cubic seeds was added to the reaction mixture followed by the addition of 375 μL of 1 M AA and the reaction was left to proceed for 1 hour. The resulting nanoparticles were collected by centrifugation and washed with water 2 times at 3500 g for 10 minutes. Images showing the resulting nanoparticles are shown in FIGS. 8f to 8j and FIGS. 10 to 10f.

In another experiment, the synthesis of Pd—Ag alloy nanoparticles was performed. This may be referred to as procedure 11. In order to synthetically apply patterning to Pd—Ag alloy nanoparticles. 492 mg of CPC was dissolved in 5 mL of DI water and placed in 45° C. oil bath. After 5 minutes, 120 μL of 0.1 M H₂PdCl₄and 120 μL of 0.1 M AgNO₃were added dropwise at the rate of ˜ 2 mL/min under vigorous stirring. After another 5 minutes, the concentrated equivalent of 2 mL of Pd cubic seeds was added to the reaction mixture followed by the addition of 375 μL of 1 M AA and the reaction was left to proceed for 1 hour. The resulting nanoparticles were collected by centrifugation and washed with water 2 times at 3500 g for 10 minutes. Images showing the resulting nanoparticles are shown in FIGS. 8k to 80 and FIGS. 11a to 11g.

In yet another experiment, synthesis of patterned Pt nanoparticles was performed. This may be referred to as procedure 12.

In order to synthetically apply patterning to Pt nanoparticles, 500 mg of CTAB was dissolved in 5 mL of DI water and placed in 80° C. oil bath. After 5 minutes, 240 μL of 0.1 M H₂PtCl₆was added dropwise at the rate of ˜ 2 mL/min under vigorous stirring. After another 5 minutes, the concentrated equivalent of 2 mL of Pd cubic seeds 1 was added to the reaction mixture followed by the addition of 375 μL of 1 M AA and the reaction was left to proceed for 4 hours. The resulting nanoparticles were collected by centrifugation and washed with water 2 times at 3500 g for 10 minutes. Images of the resulting nanoparticles are shown in FIGS. 12a to 12c.

In order to synthetically apply patterning to Pt nanoparticles in diluted solutions, 91 mg of CTAB (for intertwined patterning) or 112 mg of CPI (for line-like patterning) was dissolved in 5 mL of DI water and placed in 80° C. oil bath. After 5 minutes, 24 μL of 0.1 M H₂PtCl₆was added dropwise at the rate of ˜2 mL/min under vigorous stirring. After another 5 minutes, the concentrated equivalent of 0.2 mL of Pd cubic seeds was added to the reaction mixture followed by the addition of 37.5 μL of 1 M AA and the reaction was left to proceed for 4 hours. The resulting nanoparticles were collected by centrifugation and washed with water 2 times at 3500 g for 10 minutes. Images of the resulting nanoparticles are provided in FIG. 8p and FIGS. 13a and 13b. FIGS. 13a and 13b are electron microscopy images of patterned Pt nanoparticles synthesised in a low concentration regime with CPI as a surfactant where FIG. 13a is a high magnification SEM image and FIG. 13b is a low magnification SEM image.

In another experiment, synthesis of patterned Au nanoparticles was performed. This may be referred to as procedure 13. In order to synthetically pattern Au nanoparticles, 0.1 M aqueous solution of CPC was premixed with aniline in a 20:1 ratio using vortex for 3 minutes until no phase separation was observed and the resultant was equilibrated overnight to ensure full integration of aniline in the CPC micelles. Then, 1 mL of CPC-aniline solution was mixed with 3 mL of water and 50 μL of 50 mM HAuCl₄under moderate stirring. After 5 minutes, 150 μL of 50 nm Au spheres²redispersed in CPC: aniline solution with the concentration of 1 mg/mL were added as seeds followed by the addition of 800 μL of 1 M AA. The reaction then was moderately shaken for 10 minutes, and the resulting nanoparticles were collected by centrifugation and washed with water 2 times at 3000 g for 10 minutes. Images of the resulting nanoparticles are shown in FIG. 8q and FIGS. 14a to 14c. FIGS. 14a to 14c are electron microscopy images of patterned Au nanoparticles in CPC-aniline medium where FIG. 14a is a TEM image and FIGS. 14b and 14c are HRTEM images.

As outlined above, as a result of these experiments and the success in synthetically applying patterning to different metal nanoparticles, thin metal films and/or extended metal surfaces, different catalytic applications were possible. Pd patterned nanoparticles with deep patterning, Pd nanocubes, and/or Pd branched nanoparticles (BNPs)³were washed as described and redispersed in water to obtain an ink concentration of approximately 2.5 mg/100 μL. The obtained ink then was deposited in 20 μL aliquots on 0.6 cm²of carbon paper until even coverage is achieved. The supported catalyst was dried and washed with MeOH.

Further details with respect to the catalytic testing of patterned and non-patterned Pd nanoparticles in formic acid dehydrogenation are now provided. In order to compare the performance of patterned and non-patterned Pd nanoparticles in the dehydrogenation of formic acid, 2.9 mL of solution containing 0.0905 M formic acid and 0.647 M sodium formate was placed in 4 mL vial with cap that was equipped with septa. A Pd catalyst that was deposited on Toray paper was immersed in the solution, the cap was sealed with Teflon tape, vial was covered with aluminum foil and placed in the preheated thermomixer for 30 minutes. A portion of the headspace was taken using 1 ml syringe and injected into gas chromatograph to evaluate the rate of H₂production. The percentage of H₂in the sample was determined by the comparison of the H₂peak area in the sample and in a standard containing 1% H₂in Ar. H₂production rate was calculated as:

$H_{2 production rate} = \frac{V_{headspace} \times H_{2} % \times 0.01 \times p}{R T \times t}$

where V_headspaceis a reaction headspace volume, p is pressure, R is gas constant, T is temperature, t is reaction time. H₂production rate was also normalized by the catalyst geometric surface area. Reaction rate constant was calculated as:

$k = \frac{H_{2 production rate}}{[{HCO}_{2}^{-}]}$

where [HCO₂] is a concentration of formate. Then the In (k) was plotted as a function of T⁻¹. The slope of the obtained line is equal to -Ea/R, where Ea is the activation energy for formic acid dehydrogenation.

For the electrochemical hydrogen desorption testing of patterned and non-patterned Pd foils, H₂desorption from the patterned and non-patterned Pd foils was analysed by performing cyclic voltammetry (CV) in undivided electrochemical cell in 0.5 M H₂SO₄in the potential rage from 0.8 V to −0.3 V vs RHE at the scan rate of 20 mV s⁻¹.

For the electrochemical CO stripping experiments on patterned and non-patterned Pd nanocubes and BNPs. CO stripping was performed in an undivided electrochemical cell. First, 0.5 M H₂SO₄electrolyte was enriched with CO by purging the system for 30 seconds, then the potential of 0.1 V vs RHE was applied for 40 minutes. At the 20-minute mark, argon delivery in solution was enabled to remove the excess CO from the electrolyte. CO stripping was conducted by CV in the potential range from 0.2 to 1.4 V vs RHE at a scan rate of 20 mV s⁻¹.

For the electrochemical CO₂reduction experiments using patterned and non-patterned Pd nanocubes and BNPs. The performance of patterned Pd nanoparticles, non-patterned Pd nanocubes, and branched Pd nanoparticles in electrochemical CO₂reduction to formate was studied in a divided (H-type) electrochemical cell equipped with a cation exchange membrane. CVs were performed in the CO₂-saturated solution of 0.5 M KHCO₃in the potential range from 0.2 V to −0.6 V vs RHE at the 20 mV s⁻¹scan rate. Chronoamperometry (CA) was performed in the CO₂-saturated solution of 0.5 M KHCO₃under a constant CO₂flow at 20 sccm rate under a constant applied potential (−0.2 V vs RHE) until a charge of 60 C was passed or until the catalyst became inactive (which manifested in a significant current decay, as in the case of Pd nanocubes). To evaluate the Faradaic Efficiency (FE) of formate, aliquots of the reaction mixture were diluted tenfold and analysed by ion chromatography using Metrohm Eco IC equipped with an anion column (Metrosep A Supp 5-150/4.0) using a solution containing 3.2 mM Na₂CO₃(>99.5%, ACP Chemicals) and 1 mM NaHCO₃(>99.7% VWR) in the Milli-Q water as an eluent. The FE of formate was calculated as:

$FE = \frac{n_{i} \times V \times C \times F}{Q \times M_{w}}$

where n_iis the number of the electrons transferred (n_i=2), F is the Faraday constant, C is the concentration of formate in the analyte in ppm, V is the total volume of the anolyte, Q is the total charge passed, and Mw is the molecular weight of formate.

In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments. However, it will be apparent to one skilled in the art that these specific details may not be required. In other instances, well-known structures may be shown in block diagram form in order not to obscure the understanding.

The above-described embodiments are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope, which is defined solely by the claims appended hereto.

METHOD FOR PRODUCING METALS WITH TEXTURED SURFACES

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