Plasmonic black gold converts CO2 to methane using solar energy.

Localized surface plasmon resonance (LSPR) allows nanoparticles (NPs) to harvest light and concentrate it near the nanoparticle surface. Light energy is utilized in the generation of excited charge carriers as well as heat. Plasmonic catalysts used these energetic charge carriers (and the heat) to drive chemical reactions on their surface and allowed the discovery of novel and selective reaction pathways that were not possible in thermal catalysis. This review discusses the fundamentals of plasmonic catalysis and its application for CO2 conversion to fuel and chemicals. We first discussed the fundamentals of LSPR and the mechanism of plasmonic photocatalysis, using the concepts of the dielectric function, charge carrier generation, and relaxation pathways. We then reviewed various charge carrier-mediated activation of molecules (their chemical bonds) on the surface of plasmonic nanocatalysts and how the extraction of charge carriers played a critical role in plasmonic catalysis. The concept of multicomponent plasmonic catalysis, a hybrid catalyst by combining plasmonic metals (Cu, Au, Ag, Al, etc.) with nonplasmonic but active catalytic metals (Pt, Pd, Ru, Rh, etc.), in close proximity to each other, was then discussed. Photocatalytic CO2 reduction reactions using the examples of each of three major pathways, (i) direct transfer of hot charge carriers to the reactant molecules, (ii) providing heat to the reactant molecules by photothermal effect, and (iii) enhancing the photon absorption rate of reactant molecules by optical near-field enhancement close to the nanocatalyst surface, were discussed. In the last section, we reviewed plasmonic photocatalysts for dry reforming of methane (DRM) using CO2, which uses two greenhouse gases as feed to produce industrially significant syngas. Overall, the review is broadly divided into four sections: (1) Fundamentals of Plasmonic Nanomaterials, (2) Mechanism of Plasmonic Photocatalysis, (3) Plasmonic Photocatalysts for CO2 Reduction to Fuels and Chemicals, and (4) Plasmonic Photocatalysts for Methane Dry Reforming using CO2; with each section divided into several subsections.

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Active and stable metal-free heterogeneous catalysts for CO2fixation are required to reduce the current high level of carbon dioxide in the atmosphere, which is driving climate change. In this work, we show that defects in nanosilica (E′ centers, oxygen vacancies, and nonbridging oxygen hole centers) convert CO2to methane with excellent productivity and selectivity. Neither metal nor complex organic ligands were required, and the defect alone acted as catalytic sites for carbon dioxide activation and hydrogen dissociation and their cooperative action converted CO2to methane. Unlike metal catalysts, which become deactivated with time, the defect-containing nanosilica showed significantly better stability. Notably, the catalyst can be regenerated by simple heating in the air without the need for hydrogen gas. Surprisingly, the catalytic activity for methane production increased significantly after every regeneration cycle, reaching more than double the methane production rate after eight regeneration cycles. This activated catalyst remained stable for more than 200 h. Detailed understanding of the role of the various defect sites in terms of their concentrations and proximities as well as their cooperativity in activating CO2and dissociating hydrogen to produce methane was achieved.

We report a dendritic fibrous nano-silica supported gold nanoparticles (DFNS/Au) as peroxidase like artificial enzyme. This study indicates the unique role of fibrous morphology of DFNS for enhancement in enzymatic activity. A solvent dependent selectivity towards a two-electron oxidation product, TMB-diamine, has also been observed.