Photocatalytic CO₂ reduction driven by green solar energy could be a promising approach for the carbon neutral practice. In this work, a novel defect engineering approach was developed to form the Sn_xNb_1−xO₂ solid solution by the heavy substitutional Nb-doping of SnO₂ through a robust hydrothermal process. The detailed analysis demonstrated that the heavy substitution of Sn⁴⁺ by a higher valence Nb⁵⁺ created a more suitable band structure, a better photogenerated charge carrier separation and transfer, and stronger CO₂ adsorption due to the presence of abundant acid centers and excess electrons on its surface. Thus, the Sn_xNb_1−xO₂ solid solution sample demonstrated a much better photocatalytic CO₂ reduction performance compared to the pristine SnO₂ sample without the need for sacrificial agent. Its photocatalytic CO₂ reduction efficiency reached ~292.47 µmol/(g·h), which was 19 times that of the pristine SnO₂ sample. Furthermore, its main photocatalytic CO₂ reduction product was a more preferred multi-carbon (C₂₊) compound of C₂H₅OH, while that of the pristine SnO₂ sample was a one-carbon (C₁) compound of CH₃OH. This work demonstrated that, the heavy doping of high valence cations in metal oxides to form solid solution may enhance the photocatalytic CO₂ reduction and modulate its reduction process, to produce more C₂₊ products. This material design strategy could be readily applied to various material systems for the exploration of high-performance photocatalysts for the solar-driven CO₂ reduction.

A highly porous nitrogen-doped carbon sphere (NPC) electrocatalyst was prepared through the carbonization of biomass carbon spheres mixed with urea and zinc chloride in N₂ atmosphere. The sample carbonized at 1000 ℃ demonstrates a superior oxygen reduction reaction (ORR) performance over the Pt/C electrocatalyst, while its contents of pyridinic nitrogen and graphitic nitrogen are the lowest among samples synthesized at the same or lower carbonization temperatures. This unusual result is explained by a space confinement effect from the microporous and mesoporous structures in the microflakes, which induces the further reduction of peroxide ions or other oxygen species produced in the first step reduction to water to have the preferred overall four electron reduction ORR process. This work demonstrates that in addition to the amount or species of its active sites, the space confinement can be a new approach to enhance the ORR performance of precious-metal-free, nitrogen-doped carbon electrocatalysts.

A novel arsenic adsorbent with hydrous cerium oxides coated on glass fiber cloth (HCO/GFC) was synthesized. The HCO/GFC adsorbents were rolled into a cartridge for arsenic removal test. Due to the large pores between the glass fibers, the arsenic polluted water can flow through easily. The arsenic removal performance was evaluated by testing the equilibrium adsorption isotherm, adsorption kinetics, and packed-bed operation. The pH effects on arsenic removal were conducted. The test results show that HCO/GFC filter has high As(V) and As(III) removal capacity even at low equilibrium concentration. The more toxic As(III) in water can be easily removed within a wide range of solution pH without pre-treatment. Arsenic contaminated ground-water from Yangzong Lake (China) was used in the column test. At typical breakthrough conditions (the empty bed contact time, EBCT = 2 min), arsenic researched breakthrough at over 24,000 bed volumes (World Health Organization (WHO) suggested that the maximum contaminant level (MCL) for arsenic in drinking water is 10 mg/L). The Ce content in the treated water was lower than 5 ppb during the column test, which showed that cerium did not leach from the HCO/GFC material into the treated water. The relationship between dosage of adsorbents and the adsorption kinetic model was also clarified, which suggested that the pseudo second order model could fit the kinetic experimental data better when the adsorbent loading was relatively low, and the pseudo first order model could fit the kinetic experimental data better when the adsorbent loading amount was relatively high.

Photocatalysts with the photocatalytic "memory" effect could resolve the intrinsic activity loss of traditional photocatalysts when the light illumination is turned off. Due to the dual requirements of light absorption and energy storage/release functions, most previously reported photocatalysts with the photocatalytic "memory" effect were composite photocatalysts of two phase components, which may lose their performance due to gradually deteriorated interface conditions during their applications. In this work, a simple solvothermal process was developed to synthesize Bi₂WO₆ microspheres constructed by aggregated nanoflakes. The pure phase Bi₂WO₆ was found to possess the photocatalytic "memory" effect through the trapping and release of photogenerated electrons by the reversible chemical state change of W component in the (WO₄)^2- layers. When the illumination was switched off, Bi₂WO₆ microspheres continuously produced H₂O₂ in the dark as those trapped photogenerated electrons were gradually released to react with O₂ through the two-electron O₂ reduction process, resulting in the continuous disinfection of Escherichia coli bacteria in the dark through the photocatalytic "memory" effect. No deterioration of their cycling H₂O₂ production performance in the dark was observed, which verified their stable photocatalytic "memory" effect.