Carbon dioxide (CO2) reduction to useful chemicals is of great significance to global climate and energy supply. In this study, CO2 has been photoelectrocatalytically reduced to formate at metallic Cu nanoparticles (Cu NPs) decorated Co3O4 nanotube arrays (NTs) with high yield and high selectivity of nearly 100%. Noticeably, up to 6.75 mmol·L(–1)·cm(–2) of formate was produced in an 8 h photoelectrochemical process, representing one of the highest yields among those in the literature. The results of scanning electron microscopy, transmission electron microscopy and photoelectrochemical characterization demonstrated that the enhanced production of formate was attributable to the self-supported Co3O4 NTs/Co structure and the interface band structure of Co3O4 NTs and metallic Cu NPs. Furthermore, a possible two-electron reduction mechanism on the selective PEC CO2 reduction to formate at the Cu–Co3O4 NTs was explored. The first electron reduction intermediate, CO2 ads•–, was adsorbed on Cu in the form of Cu–O. With the carbon atom suspended in solution, CO2 ads•– is readily protonated to form the HCOO– radical. And HCOO– as a product rapidly desorbs from the copper surface with a second electron transfer to the adsorbed species.

A novel Sb-doped SnO2 electrode featuring high oxygen evolution potential, excellent electrocatalytic performance, and long stabilitytoward electrochemical degradation of refractory organic pollutants was constructed by designing and regenerating the microstructure of the Ti substrate. Highly ordered TiO2 nanotubes (TiO2-NTs) with three-dimensional microstructure, large specific surface area and space utilization rate could be grown in situ on Ti substrate under controlled conditions, followed by being implanted with Sb-doped SnO2 through a surfactant-assisted, sol-gel method under vacuum environment. The amount of Sb-doped SnO2 and service lifetime for the constructed electrode (TiO2-NTs/SnO2) were 2.4 and 12 times as much asthose for a traditional Sb-doped SnO2 (SnO2) electrode. Moreover, the constructed electrode performed at higher oxygen evolution potential and exhibited superior electrochemical capability to that on SnO2 electrode. Compared with low TOC removal by the SnO2 electrode, the TiO2-NTs/SnO2 electrode could completely mineralize benzoic acid (BA) under the same condition. The mineralization current efficiency and the first-order kinetic constant for BA degradation at the TiO2-NTs/SnO2 electrode were 1 and 3.5 times greater than those observed for the SnO2 electrode.

Driven by the urgent demand of determining low level of 17β-estradiol (E2) present in environment, a novel and ultrasensitive photoelectrochemical (PEC) sensing platform based on anti-E2 aptamer as the biorecognition element was developed onto CdSe nanoparticles-modified TiO2 nanotube arrays. The designed PEC aptasensor exhibits excellent performances in determination of E2 with a wide linear range of 0.05-15 pM. The detection limit of 33 fM is lower than the previous reports. The aptasensor manifests outstanding selectivity to E2 while used to detect seven other endocrine disrupting compounds that have similar structure or coexist with E2. The superior sensing behavior toward E2 can be attributed to the appropriate PEC sensing interface resulting from the preponderant tubular microstructure and excellent photoelectrical activity, the large packing density of aptamer on the sensing interface, as well as the high affinity of the aptamer to E2. The PEC aptasensor was applied successfully to determine E2 in environmental water samples without complicate sample pretreatments, and the analytical results showed good agreement with that determined by HPLC. Thus, a simple and rapid PEC technique for detection low level of E2 was established, having promising potential in monitoring environmental water pollution.

In this article, ZnO nanorods (NRs) were grafted on Ti-based vertically aligned TiO 2 nanotubes (NTs) by a feasible seed-induced hydrothermal reaction. Through such a simple but interesting structure combination of the two semiconductors, a novel composite photocatalytic anode of ZnO NRs/TiO 2 NTs with high efficiency was accordingly obtained. In this coupling, ZnO NRs could grow to flowerlike clusters directly grafted on the tops of TiO 2 NTs, acting just like a large number of lead wires, outstretched from the trunk TiO 2 NTs. Thus, the grafted ZnO NRs could serve conveniently as favorable hole channels and receptors for the efficient separation of photoelectrons and holes, which resulted in a slight shift of the band gap absorption edges and consequently changed the band gap energy (Eg). Moreover, the graft amount would further make a certain impact on the Eg. With an appropriate graft amount, ZnO NRs/TiO 2 NTs exhibited broader optical absorption range and higher photocatalytic activity than pure TiO 2 NTs or ZnO NRs did. Under the illumination of 365 nm UV light, the photoelectric conversion efficiency was enhanced from 7.0% of pure TiO 2 NTs to 23.6% of ZnO NRs/TiO 2 NTs. In the photoelectrocatalytic oxidation application, ZnO NRs/TiO 2 NTs exhibited higher removal ability for bisphenol A (BPA). The kinetic constant was 21.4 × 10 -5 s -1 , almost 2.3 times faster than that on pure TiO 2 NTs. Also, the stability of ZnO NRs was promoted on TiO 2 NTs with a stable BPA cyclic removal percentage because the receipted holes on ZnO NRs could prevent ZnO from photocorrosion efficiently.

Integration of photoresponsive chromophores that initiate multistep catalysis is essential in dye-sensitized photoelectrosynthesis cells and related devices. We describe here an approach that incorporates a chromophore assembly surface-bound to metal oxide electrodes for light absorption with an overlayer of catalysts for driving the half-reactions of water splitting. The assembly is a combination of a core-twisted perylene diimide and a ruthenium polypyridyl complex. By altering the connection sequence of the two subunits in the assembly, in their surface-binding to either TiO or NiO, the assembly can be tuned to convert visible light into strongly oxidizing equivalents for activation of an electrodeposited water oxidation catalyst (NiCoO ) at the photoanode, or reducing equivalents for activation of an electrodeposited water reduction catalyst (NiMoS ) at the photocathode. A key element in the design of the photoelectrodes comes from the synergistic roles of the vertical (interlayer) charge transfer and lateral (intralayer) charge hopping in determining overall cell efficiencies for photoelectrocatalysis.

When zerovalent iron (ZVI) is used in reductive removal of contaminants from industrial wastewater, where dissolved oxygen (DO) competes with target contaminant for the electrons donated by ZVI, both the reactivity and the electron selectivity (ES) of ZVI toward target contaminant are critical. Thus, the reactivity and ES of two sulfidated ZVI (S-ZVI) samples, synthesized by ball-milling with elemental sulfur (S-ZVI) and reacting with NaS (S-ZVI), toward Cr(VI) under aerobic conditions were investigated. Sulfidation appreciably increased the reactivity of ZVI and the ratio of the rate constants for Cr(VI) removal by S-ZVI or S-ZVI to their counterparts without sulfur fell in the range of 1.4-29.9. ES of S-ZVI and S-ZVI toward Cr(VI) were determined to be 14.6% and 13.3%, which were 10.7- and 7.5-fold greater than that without sulfidation, respectively. This was mainly ascribed to the greater improving effect of sulfidation on the reduction rate of Cr(VI) than that of DO by ZVI. The improving effects of sulfidation on the performance of ZVI were mainly due to the following mechanisms: sulfidation increased the specific surface area of ZVI, the FeS layer facilitated the enrichment of Cr(VI) anions on S-ZVI surface because of its anions selective property and favored the electron transfer from Fe core to Cr(VI) at the surface because of its role as efficient electron conductor.

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