Highly efficient and continuous activation of O2 by a novel FexP-FeCu composite for water purification and insights into the activation mechanisms through DFT calculation.

Degradation of organic pollutants through O2 activation catalyzed by transitional metals is challenging without addition of external chemicals and input of energy. We prepare a novel Fe based catalyst by compositing carbon, iron phosphide (FexP), iron carbide (FexC), Fe0 and Cu NPs, which can continuously activate O2 to produce high amount of 1O2,·O2- and·OH radicals in a wide pH range. DFT calculation discloses that O2 molecules are dissociated into *O or exist as O-O in various configurations. The Fe-O2, Cu-O2 and FeP-O2 surfaces can react with H2O molecules to generate *OOH, *OH and/or OH-. The sorbed-O2 intermediates on FexC surface might be released as 1O2 or·O2-. The oxidative O2-sorbed surfaces and in-situ produced oxygen reactive species contribute to the efficient and pH-indenpendent degradation of organic pollutants. Cu NPs accelerate Fe2+/Fe3+ cycles and offer impetus to initiate O2 activation due to the potential difference between Fe and Cu. The recycling test and XPS results confirm that the mutual electron transferring among carbon, FexC, FexP, Fe and Cu maintains reactivity and stability of the catalysts.

One-pot molten salt method for constructing CdS/C3N4 nanojunctions with highly enhanced photocatalytic performance for hydrogen evolution reaction.

The construction of heterojunction photocatalysts for efficiently utilizing solar energy has attracted considerable attention to solve the energy crisis and reduce environmental pollution. In this study, we use the energy released from an easily-occurred exothermic chemical reaction to serve as the drive force to trigger the formation of CdS and C3N4 nanocomposites which are successfully fabricated with cadmium nitrate and thiourea without addition of any solvents and protection of inert gas at initial temperature, a little higher than the melting point of thiourea. The as-prepared CdS/C3N4 materials exhibit high efficiency for photocatalytic hydrogen evolution reaction (HER) with the HER rate as high as 15,866 µmol/(g∙hr) under visible light irradiation (λ > 420 nm), which is 89 and 9 times those of pristine C3N4 and CdS, respectively. Also, the apparent quantum efficiency (AQE) of CdS/C3N4-1:2-200-2 (CdS/C3N4-1:2-200-2 means the ratio of Cd to S is 1:2 and the reaction temperature is set at 200°C for two hours) reaches 3.25% at λ = 420 ± 15 nm. After irradiated for more than 24 hr, the HER efficiencies of CdS/C3N4 do not exhibit any attenuation. The DFT calculation suggests that the charge difference causes an internal electric field from C3N4 pointing to CdS, which can more effectively promote the transfer of photogenerated electrons from CdS to C3N4. Therefore, most HER should occur on C3N4 surface where photogenerated electrons accumulate, which largely protects CdS from photo-corrosion.

Hotpots and trends of covalent organic frameworks (COFs) in the environmental and energy field: Bibliometric analysis.

Covalent organic frameworks (COFs) have attracted extensive attention due to their low density, adjustable structure, functionalization, and good stability. This paper systematically and comprehensively describes to qualitatively and quantitatively the progress, trends, and hotspots of COFs in the environmental and energy fields from the perspective of bibliometrics. Herein, based on the Web of Science database, a total of 2589 articles from 2005 to October 6, 2020, were collected. Thereafter, co-occurrence, co-citation analysis, and cluster analysis were conducted using CiteSpace and VOSviewer software. The results indicated that COFs research shows the characteristics of rapid growth. The active countries were mainly USA, Germany, Japan, China, and India. More than half of the top 20 active institutions were from China. The research hotspots in this field were systematically elaborated, including synthesis, adsorption, catalysis, membrane, sensor, and energy storage. Research has shown that various COFs are reasonably designed, synthesized, and used in different applications. For example, when COFs are used for photocatalysis, groups containing photocatalytic active sites are integrated into COFs to improve photocatalytic activity. Finally, some challenges were proposed, that are beneficial to the rapid and balanced development of the COFs field. For instance, the preparation methods still need to be further improved for mass production and there is an imbalance in environmental applications such as fewer sensor and membrane applications. We believe that this study provides a comprehensive and systematic overview of the environmental and energy applications of COFs for future investigations.

Single-crystalline Fe7S8/Fe3O4 coated zero-valent iron synthesized with vacuum chemical vapor deposition technique: Enhanced reductive, oxidative and photocatalytic activity for water purification.

Well-defined core/shell type single crystalline Fe7S8/Fe3O4 coated α-Fe hybrids (Fe7S8/Fe3O4@Fe) are synthesized with vacuum chemical vapor deposition (CVD) technique. The CVD process triggers conversion of naturally formed Fe3O4 layer on the surface of commercial Fe nanoparticles from amorphous into single crystalline phase. The Fe7S8/Fe3O4 coat promotes the surface affinity of dissolved oxygen and targets and rapidly transfers electrons from the Fe core to targets, which decreases water splitting on Fe7S8/Fe3O4@Fe surface and endows Fe7S8/Fe3O4@Fe with ultra-strong reducibility and improved oxidative ability under different conditions. Different with the sulfurized ZVI prepared with hydrothermal or solvothermal method, the increase of reaction solution pH is retarded due to the relieved water splitting instead of releasing H+ via oxidation of S2-/S22- on the Fe7S8 coat. The cooperation of Fe7S8 with Fe3O4 and α-Fe not only improves the anti-oxidation ability of Fe7S8 coating but also broadens its band gap. By using Fe7S8/Fe3O4@Fe nanohybrids as photocatalysts, light irradiation accelerates the degradation of organic pollutants combined with enhanced mineralization efficiency. The Fe7S8/Fe3O4@Fe exhibits good performance when it is utilized to treat the influent from a municipal sewage treatment plant upon air aeration or under visible light and solar light irradiation.

Ball milling synthesis of covalent organic framework as a highly active photocatalyst for degradation of organic contaminants.

Facile, environmentally-friendly fabrication of high-yield and stable covalent organic framework (COF) materials has been a limitation to their large-scale production and application. In this work, ball milling was used to synthesize COF by mechanochemical reaction between 1,3,5-triformylphloroglucinol (Tp) and melamine (MA) at ambient temperature. Different routes (liquid-free, solvent-assisted and catalyst-assisted) and proportions of liquids (solvents or catalyst) were investigated. Two morphologies were obtained when various amounts of liquid were added during grinding. The two forms were interwoven thread-shaped and exfoliative thin ribbon-like structures. Further, visible-light photocatalytic (λ > 400 nm) performance and mechanism of the two structures of COFs were investigated. The exfoliative ribbon-like structures exhibited greater rates of photodegradation of phenol and retained 87.6% of initial photodegradation after being used four times. Addition of liquid catalyst not only improved crystallinity of the COF materials, but also enhanced rates of photocatalytic reactions. Photocatalytic activity of the exfoliative structure of TpMA synthesized by ball milling was comparable with that of the photocatalyst prepared by use of the solvothermal method, while time to prepare the catalyst was shortened by 36-fold and the amount of solvent used was reduced by 8-fold at room temperature. Mechanochemical synthesis is a promising potential tool for large-scale production of COFs, which will make greater use of COFs for degradation of pollutants.