High-Yield and Selective Photoelectrocatalytic Reduction of CO₂ to Formate by Metallic Copper Decorated Co₃O₄ Nanotube Arrays

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, CO_2 ads^•–, was adsorbed on Cu in the form of Cu–O. With the carbon atom suspended in solution, CO_2 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

Immobilization-Free Photoelectrochemical Aptasensor for Atrazine Based on Bifunctional Graphene Signal Amplification and a Controllable Sulfhydryl-Assembled BiOBr/Ag NP Microinterface

Immobilization-free sensors (IFSs), with no requirement of fixing the recognition element to the electrode surface, have received increasing attention due to their unique advantages of reusable electrodes, not being limited by the load of the recognition element, and not being easily changed to the structure of the probe. In the present work, an effective visible light-driven immobilization-free photoelectric aptasensor for ultrasensitive detection of atrazine (ATZ) was proposed based on a reusable BiOBr/Ag NP substrate electrode with ultrafast charge transfer. Controllable thiols were used as conditioning agents for the photoelectric signal. The ingeniously designed bifunctional graphene can act as not only a molecular “bridge” for the ATZ aptamer through a strong π–π stacking effect, obtaining a graphene–aptamer complex, serving as a homogeneous recognition element, but also a switch for signal modulation for quantitative detection of target substances. Benefiting from the synergistic effect of the above-mentioned factors, the proposed sensor is capable of ultrasensitive and highly selective detection of ATZ in real water samples with a low detection limit of 1.2 pM and a wide linear range from 5.0 pM to 10.0 nM. Furthermore, it shows high stability, good selectivity, and strong anti-interference ability. Thus, this work has provided a fresh perspective for designing advanced immobilization-free photoelectric sensors and convenient detection of environmental pollutants

Selective Electrocatalytic Degradation of Odorous Mercaptans Derived from S–Au Bond Recongnition on a Dendritic Gold/Boron-Doped Diamond Composite Electrode

To improve selectivity of electrocatalytic degradation of toxic, odorous mercaptans, the fractal-structured dendritic Au/BDD (boron-doped diamond) anode with molecular recognition is fabricated through a facile replacement method. SEM and TEM characterizations show that the gold dendrites are single crystals and have high population of the Au (111) facet. The distinctive structure endows the electrode with advantages of low resistivity, high active surface area, and prominent electrocatalytic activity. To evaluate selectivity, the dendritic Au/BDD is applied in degrading two groups of synthetic wastewater containing thiophenol/2-mercaptobenzimidazole (targets) and phenol/2-hydroxybenzimidazole (interferences), respectively. Results show that targets removals reach 91%/94%, while interferences removals are only 58%/48% in a short time. The corresponding degradation kinetic constants of targets are 3.25 times and 4.1 times that of interferences in the same group, demonstrating modification of dendritic gold on BDD could effectively enhance electrocatalytic target-selectivity. XPS and EXAFS further reveal that the selective electrocatalytic degradation derives from preferential recognition and fast adsorption to thiophenol depending on strong Au–S bond. The efficient, selective degradation is attributed to the synergetic effects between accumulative behavior and outstanding electrochemical performances. This work provides a new strategy for selective electrochemical degradation of contaminants for actual wastewater treatment

A Femtomolar Level and Highly Selective 17β-estradiol Photoelectrochemical Aptasensor Applied in Environmental Water Samples Analysis

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

Enhanced Reactivity and Electron Selectivity of Sulfidated Zerovalent Iron toward Chromate under Aerobic Conditions

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^bm) and reacting with Na₂S (S-ZVI^Na2S), 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^bm or S-ZVI^Na2S to their counterparts without sulfur fell in the range of 1.4–29.9. ES of S-ZVI^bm and S-ZVI^Na2S 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_<i>x</i> layer facilitated the enrichment of Cr­(VI) anions on S-ZVI surface because of its anions selective property and favored the electron transfer from Fe⁰ core to Cr­(VI) at the surface because of its role as efficient electron conductor