Highly selective photocatalytic CO_(2) reduction to ethylene in pure water by Nb_(2)O_(5) nanoparticles with enriched surface –OH groups under simulated solar illumination

Photocatalytic CO_(2) reduction to valuable chemical compounds could be a promising approach for carbon-neutral practice.In this work,a simple and robust thermal decomposition process was developed with ammonium carbonate((NH4)2CO3)as both precipitation agent and sacrificial template to produce fine Nb_(2)O_(5) nanoparticles with the rich existence of surface hydroxyl(–OH)groups.It was found by density functional theory(DFT)calculations and experiments that the rich existence of the surface–OH groups enhanced the adsorption of both reactants(CO_(2) and H_(2)O molecules)for the photocatalytic CO_(2) reduction on these fine Nb_(2)O_(5) nanoparticles,and the highly selective conversion of CO_(2) to the high-value chemical compound of ethylene(C_(2)H_(4),~68μmol·g^(−1)·h^(−1) with~100%product selectivity)was achieved under simulated solar illumination without usage of any sacrificial agents or noble metal cocatalysts.This synthesis process may also be readily applied as a surface engineering method to enrich the existence of the surface–OH groups on various metal oxide-based photocatalysts for a broad range of technical applications.

Dehydroxylation action on surface of TiO_2 films restrained by nitrogen carrier gas during atomic layer deposition process

A strong influence of nitrogen gas on the content of surface hydroxyl groups of TiO2 films by atomic layer deposition（ALD） was investigated by X-ray photoelectron spectroscopy（XPS）, contact angle measuring system, and UV–Vis spectrophotometer. XPS spectra of O 1s indicate that the content of surface hydroxyl groups is varied when using N2 as carrier gas. The results of water contact angles and optical reflection spectra show that the content variation of surface hydroxyl groups influences the wetting properties and optical reflectivity of TiO2 films. A surface reaction model is suggested to explain the ALD reaction process using N2 as carrier gas.

Thermal-, photo- and electron-induced reactivity of hydrogen species on rutile TiO_2(110) surface: Role of oxygen vacancy

Interaction of hydrogen with TiO2 plays a vital role in TiO2-based photocatalysis and thermal catalysis. In this work, we compared thermal-, photo-, and electron-induced reactivity of various types of hydrogen species on a rutile TiO2（110） surface formed by atomic H exposure at 320 and 115 K by means of thermal desorption spectroscopy, X-ray photoelectron spectroscopy and low energy electron diffraction. Atomic H interaction with rutile TiO2（110） at 115 K forms surface TiààH hydride, surface hydroxyl group, and chemisorbed water. Upon heating, surface TiààH hydride reacts to produce H2 while surface hydroxyl groups react to form both water and H2. Atomic H interaction with rutile TiO2（110） at 320 K strongly reduces TiO2 due to the continuous formation and desorption of water and forms surface hydroxyl groups and likely subsurface/bulk hydrogen species. Upon heating, hydrogen forms as the only gas-phase product and its desorption activation energy decreases with the subsurface/bulk reduction extent of rutile TiO2（110）. Surface Ti-H hydride exhibits photo-induced reactivity while both surface TiààH hydride and surface hydroxyl group exhibit electro-induced reactivity. These results have important implications for understanding the hydrogen-involved thermal and photo reactions on TiO2-based catalysts.

Insight into phase structure-dependent soot oxidation activity of K/MnO_(2) catalyst

In the present study,two nanosized MnO_(2)with β and δ phase structures and potassium loaded MnO_(2)catalysts with varied K loading amounts (denoted as K/MnO_(2)) were prepared.Temperature programmed oxidation and isothermal reactions in loose contact modes were employed to examine the soot oxidation activity of the as-prepared catalysts.Characterization results show that as compared with β-MnO_(2),δ-MnO_(2)has larger surface area and higher content of hydroxyl groups.Upon K loading,abundant hydroxyl groups in δ-MnO_(2)effectively sequestrate K cation to form bound K species and free K species are available only at K loading above 3.0 wt.%.In contrast,the majority of K species present as free state in β-MnO_(2)even at a K loading of 1.0 wt.%due to its very low hydroxyl group content.The O_(2)temperature-programmed desorption (O_(2)-TPD) demonstrates that the catalysts with free K species exhibit strong ability in activating gaseous O_(2),whereas the catalysts only having bound K display minor O_(2)activation capability.As a result,despite of slightly lower activity of β-MnO_(2)than δ-MnO_(2),the K/β-MnO_(2)catalysts exhibit substantially higher activities than K/δ-MnO_(2)catalysts with identical K loadings.The finding in this study clearly demonstrates that for MnO_(2)based catalysts,the enhancement of catalytic activity for soot oxidation is highly K loading amount dependent and the dependency is strongly associated with the phase structure of MnO_(2).