Effects of various alcohol sacrificial agents on hydrogen evolution based on CoS2@SCN nanomaterials and its mechanism.

Visible light induced photocatalysis converted solar energy to chemical energy in the form of hydrogen. g-C3N4 modified by thermal oxidation etching, doped S, and nonprecious metal cocatalyst CoS2 (CoS2@SCN) were used for photocatalytic hydrogen production. And then the charge transfer behavior and mechanism of various alcohol sacrificial agents on hydrogen evolution was analyzed by optical characterization, impedance analysis, Mott-Schottky, and photocurrent tests. The relationship between the structure and catalytic performance was also explored using characterization methods. The results showed that CoS2 significantly improved the light absorption of g-C3N4, and carrier migration and separation. And when the sacrificial agent was triethanolamine, the nanocomposite CoS2@SCN exhibited best catalytic performance with the highest hydrogen activity of 223.6 µmol g-1 h-1, the minimum volume in-phase charge transfer resistance with 55.19 Ω and the maximum photocurrent and photocurrent density with 5.5 µA cm-2 and 0.63 mA cm-2. The more negatively charged surface of organic alcohols were, the easier they were to react with holes, thus enhanced charge transfer and hydrogen production efficiency. This report provides guidance for the selection of hydrogen producing sacrificial agents and preparation of highly charge-efficient catalysts. And it also provides a theoretical basis for hydrogen production from wastewater and environmental remediation.

Comparison of visible light driven H2O2 and peroxymonosulfate degradation of norfloxacin using Co/g-C3N4.

As common advanced oxidation processes, Fenton-like and peroxymonosulfate (PMS) processes have received enormous attention due to their high efficiency in the pollutants degradation. In this study, the Co/g-C3N4 photocatalyst was prepared by facial calcination strategy and used to evaluate the behavior of the Co/g-C3N4/H2O2 and Co/g-C3N4/PMS systems for norfloxacin (NOR) photocatalytic degradation under visible light irradiation. The composite photocatalysts exhibited better performance compared to that of pure g-C3N4 due to the efficient separation of electron-hole pairs and visible light absorption. The Co/g-C3N4/PMS system possessed better photocatalytic performance than the Co/g-C3N4/H2O2 system, where the degradation ratio of NOR and removal ratio of total organic carbon (TOC) were 96.4% and 54%, respectively, in 10 min. The photocatalytic mechanism was investigated using reactive species trapping experiments and electron spin-resonance spectroscopy (ESR). ⋅OH and SO4⋅- were the dominant reaction species in the Co/g-C3N4/H2O2 and Co/g-C3N4/PMS systems, respectively. According to the analysis of the NOR degradation path, SO4⋅- could attack the C-H bond on the piperazine ring or quinolone group of NOR, which resulted in it more active and accelerating the destruction of NOR with SO4⋅- and ⋅OH. The destruction of the quinolone group was the main pathway in the H2O2 process, while the destruction of the piperazine ring was the main pathway in the PMS process. In sum, the Co/g-C3N4/PMS process had a higher photocatalytic activity and economic applicability.

Single-Atom Cobalt Catalysts for Electrocatalytic Hydrodechlorination and Oxygen Reduction Reaction for the Degradation of Chlorinated Organic Compounds.

Electrochemical reduction-oxidation processes with the aid of cathode catalysts are promising technologies for the decomposition of organic compounds. High-efficiency and low-cost catalysts for electrochemical reductive dechlorination and two-electron oxygen reduction reaction (ORR) are vital to the overall degradation of chlorinated organic compounds. This study reports electrochemical dechlorination using a single-atom Co-loaded sulfide graphene (Co-SG) catalyst via atomic hydrogen generated from the electrochemical reduction of H2O and electrolysis of hydrogen. The Co-SG electrocatalyst exhibited a remarkable performance for H2O2 synthesis with a half-wave potential of 0.70 V (vs RHE) and selectivity over 90%. The high electrochemical performance was achieved for bifunctional electrocatalysis with regard to the smaller overpotentials, faster kinetics, and higher cycling stability compared to the noble metal-based electrocatalysts. In this study, 2,4-dichlorobenzoic acid was well degraded and the TOC concentration was effectively reduced. This work introduces the preparation of a new active site for high-performance single-atom catalysts and also promotes its application in the electrochemical degradation of chlorinated organic pollutants.