Enhanced photocatalytic CO2 reduction with defective TiO2 nanotubes modified by single-atom binary metal components.

A binary component catalyst consists of single atoms (SAs- Pt and Au) anchored on self-doped TiO2 nanotubes (TNTs), was developed for photocatalytic CO2 reduction. The defects introduced TNTs substrate was stabilized with atomic Pt and Au via strong metal support interactions (MSI), due to which, the covalent interactions facilitated an effective transfer of photo-generated electrons from the defective sites to the SAs, and in turn an enhanced separation of electron-hole pairs and charge-carrier transmission. The Pt-Au/R-TNTs with 0.33 wt% of SA metals, exhibited a maximum of 149 times higher photocatalytic performance than unmodified R-TNT and a total apparent quantum yield (AQY) of 17.9%, in which the yield of CH4 and C2H6 reached to 360.0 and 28.8 µmol g-1 h-1, respectively. The metals loading shifted the oxidation path of H2O from •OH generation into O2 evolution, that inhibited the self-oxidization of the photocatalyst.

Synthesis of Z-scheme g-C3N4-Ti(3+)/TiO2 material: an efficient visible light photoelectrocatalyst for degradation of phenol.

In this study, a photocatalytic material g-C3N4-Ti(3+)/TiO2 nanotube arrays was prepared by a facile and viable approach involving a heat treatment followed by an electrochemical reduction step, and it was characterized using instrumental techniques such as X-ray diffraction pattern, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and UV-vis diffuse reflectance spectra. The photocatalytic efficiency of the as-prepared samples towards treating aqueous solution contaminated with phenol was systematically evaluated by a photoelectrocatalytic method and found to be highly dependent on the content of the g-C3N4. At the optimal content of g-C3N4, the apparent photocurrent density of g-C3N4-Ti(3+)/TiO2 was four times higher than that of the pristine TiO2 under visible-light illumination. The enhanced photoelectrocatalytic behavior observed for g-C3N4-Ti(3+)/TiO2 was ascribed to a cumulative impact of both g-C3N4 and Ti(3+), which enhances the photoresponsive behavior of the material into the visible region and facilitates the effective charge separation of photoinduced charge carriers.

Enhancement of S(IV)-Cr(VI) reaction in p-nitrophenol degradation using rice husk biochar at neutral conditions.

In this study, biochar R550, obtained from rice husk charred at 550 °C, was used to detoxify Cr(VI) and organic pollutant p-nitrophenol (PNP) with the cooperation of sulfite, simultaneously. Cr(VI) was mainly reduced by sulfite, and the reduction was accelerated by biochar. Also, the reactive oxygen species formed in-situ as a result of enhanced oxidation of sulfite with Cr(VI)/R550 system and the activation of O2 by R550, led to the degradation of PNP. Production of the radicals viz., SO3-, SO4- and OH was followed by Electron Paramagnetic Resonance (EPR) study, and the predominant role of SO4- towards PNP degradation was confirmed by radical quenching tests. The reaction completed biochar sample was undergone the X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FTIR) spectral analysis, which suggested that the carboxyl group of the biochar triggered and enhanced the reactivity of Cr(VI) via coordination linkage, which in turn activated the sulfite and converted the SO32- into SO4- to a higher extent by overcoming the undesirable transformation of SO32- to SO42-. Such results could also be verified by the other three biochar (Oxi-R550, H-R550, and R800). The results of the present study shed light on the mechanism of biochar mediated sulfite activation process by Cr(VI) and also assured the viability and green approach of the technique in detoxifying the industrial effluents containing Cr(VI) and organic pollutants.

Electrochemical degradation of PNP at boron-doped diamond and platinum electrodes.

The electrochemical degradation of p-nitrophenol (PNP) at boron-doped diamond (BDD) and platinum (Pt) anodes was studied by varying the parameters such as Cl(-) concentration, pH of aqueous medium and applied current density. The results obtained were explained in terms of in situ concomitant generation of hydroxyl radicals and chloride based oxidant species. The degradation of PNP was highly promoted in low concentration of NaCl electrolyte (less than 0.10 M), on contrary, the mineralization efficiency was poor at both BDD and Pt anodes with the NaCl concentration up to 0.20 M, which was ascribed to the formation of refractory chlorinated organic compounds. A maximum of 100% and 70% of COD removal was achieved in 5h of electrolysis period using both BDD and Pt anodes under similar experimental conditions. Kinetic study indicated that the degradation of PNP at BDD and Pt anodes followed pseudo-first-order reactions, and the reaction rate constant (k(s)) of the former was observed to be higher than that of the latter. Besides COD, conversion of PNP into various intermediate compounds and their degradations were also monitored. The mechanisms for PNP degradation at BDD and Pt anodes were proposed separately by considering the nature of respective intermediate species and their concentrations.