Visible Light-Promoted Plasmon Resonance to Induce “Hot” Hole Transfer and Photothermal Conversion for Catalytic Oxidation

Abstract

Titanium dioxide (TiO2) semiconductor photocatalysts were photosensitized to the visible spectrum with gold nanospheres (AuNSs) and gold nanorods (AuNRs) to study the ethanol photo-oxidation cycle, with an emphasis toward driving carbon–carbon (C–C) bond cleavage at low temperatures. The photocatalysts exhibited a localized surface plasmon resonance (SPR) that was harnessed to drive the complete photo-oxidation of formic acid (FA) and ethanol (EtOH) via augmented carrier generation/separation and photothermal conversion. Contributions of transverse and longitudinal localized SPR modes were decoupled by irradiating AuNSs–TiO2 and AuNRs–TiO2 with targeted wavelength ranges to probe their effects on plasmonically assisted photocatalytic oxidation of FA and EtOH. Photocatalytic performance was assessed by monitoring the yield of gaseous products during photo-oxidation experiments using a gas chromatography–mass spectrometry–multiple headspace extraction (GC–MS–MHE) analysis method. The complete oxidation of EtOH to CO2 under visible-light irradiation was confirmed by GC–MS–MHE for both AuNSs and AuNRs on TiO2 at room temperature. Photothermal and local field enhancements were found to aid in selectively cleaving the C–C bond in EtOH to form FA, while FA was further oxidized to CO2 by plasmon-induced electron transfer mechanisms. Under visible-light (>420 nm) irradiation, carrier generation/separation, and photothermal conversion was achieved, resulting in the photogenerated “hot” holes driving the photo-oxidation primarily on the gold nanoparticles. Specifically, plasmonic enhancement by AuNR–TiO2 enhances EtOH oxidation, providing a method to selectively cleave C–C bonds.

Plasmonic Au–Pd Bimetallic Nanocatalysts for Hot-Carrier-Enhanced Photocatalytic and Electrochemical Ethanol Oxidation

“…via light-energy conversion enables the generation of energy-dense fuels and electrical power [1][2][3]. Directed harvesting of solar energy can be facilitated by photocatalytic processes augmented by plasmon-mediated chemistry [3][4][5][6][7][8]. Plasmonic nanostructures (Au, Ag) exhibit localized surface plasmon resonance (SPR), the coherent oscillation of conduction electrons coupled to strong local electric fields.…”

“…Plasmonic nanostructures (Au, Ag) exhibit localized surface plasmon resonance (SPR), the coherent oscillation of conduction electrons coupled to strong local electric fields. Landau damping of the SPR (1-100 fs) promotes excitation of energetic, or "hot", charge carriers [3,8,9], in addition to increasing light absorption, enhancing far-field light scattering, and inducing charge separation in semiconductors [3,6,[8][9][10]. Ohmic relaxation of "hot" electrons (100 fs to 1 ps) results in local thermal dissipation (100 ps to 10 ns) that can aid in activating adsorbed reactants and accelerating surface kinetics [3,9,10].…”

“…Ohmic relaxation of "hot" electrons (100 fs to 1 ps) results in local thermal dissipation (100 ps to 10 ns) that can aid in activating adsorbed reactants and accelerating surface kinetics [3,9,10]. Emerging multifunctional photocatalysts incorporate both plasmonic and catalytic active materials for chemical conversion [3,[5][6][7][8][9][10][11][12][13][14][15][16]. Coupling of plasmonic metals to semiconductors as a photosensitization strategy has demonstrably facilitated hot-carrier generation/separation [6,7,11,12].…”

“…Emerging multifunctional photocatalysts incorporate both plasmonic and catalytic active materials for chemical conversion [3,[5][6][7][8][9][10][11][12][13][14][15][16]. Coupling of plasmonic metals to semiconductors as a photosensitization strategy has demonstrably facilitated hot-carrier generation/separation [6,7,11,12]. Bimetallic nanocatalysts with a plasmonic component interact strongly with resonant photons, generating hot carriers at catalytically active noble metal sites to promote chemical transformations and enhance product selectivity [16][17][18].…”

Plasmon-generated hot holes for chemical reactions

“…The plasmon-generated hot holes can also drive the oxidation of organic molecules, such as alcohol [94][95][96][97][98] and formic acid [99][100][101][102][103][104][105], at the plasmon-semiconductor interfaces, making plasmonic heterostructures promising in green synthesis of organic molecules.…”