5 research outputs found
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Biomimetic Structure and Optical Property Control of Monometallic and Bimetallic Inorganic Nanoparticle Catalysts
Inorganic colloidal nanoparticles are known for their efficient catalytic reactivities, owing to their relatively small size and enhanced surface-to-volume ratio. Furthermore, the suitable selective incorporation of secondary metals can generate diverse bimetallic nanoparticles, further enhancing catalytic abilities through synergistic effects. Among synthesis approaches, peptide-based methods have demonstrated excellent ability in fabricating stable monometallic and bimetallic nanoparticles under facile and sustainable conditions. Furthermore, certain bio-synthesis approaches can achieve atom-level control over the morphologies and functionalities of nanoparticles. By utilizing the relatively weak and flexible non-covalent interactions between the peptide amino acids and the inorganic metal surfaces, the post-manipulation of peptide conformation on the metal surface becomes feasible. This could be accomplished through remote stimuli by incorporating a photoresponsive moiety, such as azobenzene, into the peptide sequence. This conformational alternation of the bio-capping ligands also provides a pathway for finely controlling nanoparticle catalysts. In this dissertation, to investigate control over nanoparticle morphologies, optical properties, and subsequent catalytic applications, the exploration of various surface capping ligands was employed in two parts. Initially, two Au@Pt Core@Shell nanocatalysts were fabricated using two Au-binding peptide sequences, AuBP2 and AgBP1, respectively. These stable bimetallic nanosystems confirm peptides’ fine-level control over morphology and subsequent enhanced catalytic hydrogenation ability across various substrates. Next, biohybrid photoswitchable capping ligands, peptide-azobenzene, were employed for the post-modulation of the inorganic surface. These demonstrate a new composition of photoswitchable peptide-capped Pt nanocatalyst system and the heterogeneous monolayer-capped Au nanoparticles
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Effect of a Mixed Peptide Ligand Layer on Au Nanoparticles for Optical Control of Catalysis
Inorganic colloidal nanoparticles are known for their efficient catalytic reactivities due to their enhanced surface-tovolume ratio. As an alternative to conventional synthetic methods, bioinspired approaches can sustainably generate stable colloidal nanoparticles where their reactivity can be tuned by the biomolecular overlayer structure. Recent studies have shown that incorporation of light-activated photoswitches into material-binding peptides could be used to optically and reversibly switch the biomolecular overlayer structure on Au nanoparticle surfaces, which has significant ramifications on the material catalytic reactivity. In this contribution, we demonstrate that the optical photoswitching capability and catalytic reactivity in these materials are highly dependent upon the composition of the biomolecular overlayer. For this, mixed monolayer-capped Au nanoparticles were prepared where the ratio of the parent material-binding peptide and the peptide with photoswitch included were varied. Key trends related to the photoswitching capability of the peptides and their overall reactivity were identified, where slower reactivity was noted for materials prepared using only the photoswitchable peptide. Taken together, these results demonstrate that the composition of the overlayer structure on Au nanoparticles is highly important in tuning the overall optical, photoswitching, and catalytic properties of these materials and can be used to refine the properties of the structure for their intended application
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Substrate Effects on Remote Optical Control of Pt Nanoparticle-Driven Olefin Hydrogenation
Bioinspired approaches for materials synthesis and application are emerging as potentially sustainable approaches to achieve functional structures with selectively controlled properties (e.g., turn-on catalysis). An attractive avenue to allow for selective functionality is optical stimulation; however, the ability to make nanomaterials light responsive for many applications remains challenging. One approach is to incorporate photoswitches into the surface-adsorbed ligands which can stimulate a surface structural change that could have implications on the catalytic reactivity driven by the underlying metallic nanoparticle component. Herein we demonstrate the ability to drive optical switching of surface ligand overlayer structures on peptide-capped Pt nanoparticles. To this end, incorporation of an azobenzene unit into the surface-adsorbed peptide allows for the ability to optically reconfigure the ligand overlayer structure. This change results in direct manipulation of the catalytic properties of the Pt materials for olefin hydrogenation, which demonstrated changes in reactivity not only between different reagents but also between the different ligand structures. Such results present information that could be used in the design of ligand interface structures to trigger specific reactivity control for a variety of reactions and materials for sustainable catalysis
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Biomimetic Control over Bimetallic Nanoparticle Structure and Activity via Peptide Capping Ligand Sequence
The controlled design of bimetallic nanoparticles (BNPs) is a key goal in tailoring their catalytic properties. Recently, biomimetic pathways demonstrated potent control over the distribution of different metals within BNPs, but a direct understanding of the peptide effect on the compositional distribution at the interparticle and intraparticle levels remains lacking. We synthesized two sets of PtAu systems with two peptides and correlated their structure, composition, and distributions with the catalytic activity. Structural and compositional analyses were performed by a combined machine learning-assisted refinement of X-ray absorption spectra and Z-contrast measurements by scanning transmission electron microscopy. The difference in the catalytic activities between nanoparticles synthesized with different peptides was attributed to the details of interparticle distribution of Pt and Au across these markedly heterogeneous systems, comprising Pt-rich, Au-rich, and Au core/Pt shell nanoparticles. The total amount of Pt in the shells of the BNPs was proposed to be the key catalytic activity descriptor. This approach can be extended to other systems of metals and peptides to facilitate the targeted design of catalysts with the desired activity
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Z-Contrast Enhancement in Au-Pt Nanocatalysts by Correlative X-ray Absorption Spectroscopy and Electron Microscopy: Implications for Composition Determination
The properties of bimetallic nanoparticles (BNPs) vary widely as a function of their composition and size distributions. X-ray absorption line structure analysis is commonly used to characterize their structure, but its application to elements that are close to each other in the periodic table is hampered by poor Z-contrast. We trained an artificial neural network to recognize the partial coordination numbers in AuPt NPs synthesized via peptide templating using their X-ray absorption near-edge structure spectra. This approach, combined with scanning transmission electron microscopy analysis, revealed unique details of this prototype catalytic system that has different forms of heterogeneities at both the intra- and inter-particle levels. Our method based on the enhancement of Z-contrast of metal species will have implications for compositional studies of BNPs