Photocatalytic H₂ Evolution from Water–Methanol System by Anisotropic InFeO₃(ZnO)_m Oxides without Cocatalyst in Visible Light

Abstract

InFeO3(ZnO)m series of oxides are found to give unprecedented H2 evolution from water-methanol mixtures without using any cocatalysts. This family of compounds has an anisotropically layered structure in which Zn/FeOn polyhedra are sandwiched between InO6 octahedral layers. Local structure characterization by X-ray absorption spectroscopy reveals that Zn coordination changes from pentacoordinated to tetrahedral geometry across the series, whereas Fe geometry remains trigonal bipyramidal in all the compounds. This peculiar structure is conducive for a spatial separation of photogenerated charges reducing recombination losses. Band gap energies calculated from absorption spectra indicate potential visible light activity, and this may be due to the orbital mixing of Fe 3d and O 2p as revealed by pre-edge features of X-ray absorption spectra. Band positions are also advantageously placed for a visible light H2 generation and is indeed found to be the case in methanol-assisted water splitting with standardized hydrogen evolution of ∼19.5 mmol g(-1) h(-1) for all the catalysts.

Faceted Titania Nanocrystals Doped with Indium Oxide Nanoclusters As a Superior Candidate for Sacrificial Hydrogen Evolution without Any Noble-Metal Cocatalyst under Solar Irradiation

“…The saturation of the H 2 production rate is expected due to the steady−steady conditions, also reported by Narendranath et al during photoctalytic H 2 evolution from the water−methanol system using InFeO 3 (ZnO) m oxides without any cocatalyst. 53 A controlled experiment with pure titania nanoparticles (P-25) under similar experimental conditions showed little hydrogen evolution (0.2 μmol h −1 g −1 ). Under similar experimental conditions pure indium oxide nanoparticles did not show any hydrogen production.…”

Photocatalytic Activity of g-C3N4 Quantum Dots in Visible Light: Effect of Physicochemical Modifications

“…4−7 A suitable semiconductor photocatalyst for the H 2 evolution reaction should possess such a band gap that it can absorb light in the visible region of the solar spectrum. 7 More importantly, the reduction and oxidation potentials of water should fall within the valence band maxima and conduction band minima of the semiconductor, which should also be stable in the presence of water for the reaction to proceed. 8 Taking these factors into consideration, researchers have focused on finding effective and nontoxic transition metal free catalysts, and in the past few years, graphitic-carbon nitride (g-C 3 N 4 ) 9 has brought a revolution in this field.…”

“…Efficient conversion of solar to chemical energy by solar cells and utilization of solar energy in various photocatalytic processes have been premeditated to be some of the best solutions to the energy crisis and environmental pollutions these days. , Particularly, photocatalytic conversion of water to clean fuel H 2 in the presence of a semiconductor photocatalyst plays an important role in this aspect as it involves easily available and nontoxic energy sources . Consequently, the search for efficient semiconductor materials for the water splitting reaction using solar energy has become one of the “hot topics” of material science research in recent days. − A suitable semiconductor photocatalyst for the H 2 evolution reaction should possess such a band gap that it can absorb light in the visible region of the solar spectrum . More importantly, the reduction and oxidation potentials of water should fall within the valence band maxima and conduction band minima of the semiconductor, which should also be stable in the presence of water for the reaction to proceed …”

Homologous Compounds ZnnIn2O3+n (n = 4, 5, and 7) Containing Laminated Functional Groups as Efficient Photocatalysts for Hydrogen Production

“…33−35 Such a laminate arrangement of photocatalytic active segment (ZnO) and electrical conductive segment (In 2 O 3 ) brings these compounds promising applications in the field of photocatalysis and optoelectronics. 27,30,36 During previous investigations, encouraging results in terms of photocatalytic water splitting have been reported among these compounds, 37,38 yet detailed studies on the origin of their visible light absorption and associated photocatalytic activity are still lacking. In this work, we carried out an investigation on the optical and photocatalytic properties of three representative homologous compounds Zn n In 2 O 3+n (n = 4, 5, and 7).…”

“…It has been realized that a series of homologous compounds with general formula Zn n In 2 O 3 +n ( n = 3, 4, 5, ...) have demonstrated interesting optical and conductive properties. − Visible light absorbance (>400 nm) and high electrical conductivity (>2000 S/cm) are both achievable in these compounds. , Their crystal structures can be roughly viewed as layer-by-layer alternate stacking of ZnO unit (wurtzite structure) and In 2 O 3 unit (bixbyite structure) along the c direction. − Such a laminate arrangement of photocatalytic active segment (ZnO) and electrical conductive segment (In 2 O 3 ) brings these compounds promising applications in the field of photocatalysis and optoelectronics. ,, During previous investigations, encouraging results in terms of photocatalytic water splitting have been reported among these compounds, , yet detailed studies on the origin of their visible light absorption and associated photocatalytic activity are still lacking. In this work, we carried out an investigation on the optical and photocatalytic properties of three representative homologous compounds Zn n In 2 O 3 +n ( n = 4, 5, and 7).…”