Single atom catalysts (SACs) with the maximized metal atom efficiency have sparked great attention. However, it is challenging to obtain SACs with high metal loading, high catalytic activity, and ...good stability. Herein, we demonstrate a new strategy to develop a highly active and stable Ag single atom in carbon nitride (Ag‐N2C2/CN) catalyst with a unique coordination. The Ag atomic dispersion and Ag‐N2C2 configuration have been identified by aberration‐correction high‐angle‐annular‐dark‐field scanning transmission electron microscopy (AC‐HAADF‐STEM) and extended X‐ray absorption. Experiments and DFT calculations further verify that Ag‐N2C2 can reduce the H2 evolution barrier, expand the light absorption range, and improve the charge transfer of CN. As a result, the Ag‐N2C2/CN catalyst exhibits much better H2 evolution activity than the N‐coordinated Ag single atom in CN (Ag‐N4/CN), and is even superior to the Pt nanoparticle‐loaded CN (PtNP/CN). This work provides a new idea for the design and synthesis of SACs with novel configurations and excellent catalytic activity and durability.
A new Ag single atom in carbon nitride (Ag‐N2C2/CN) photocatalyst with Ag‐N2C2 configuration is developed. It affords fast charge transfer, high Ag loading, and good stability. Noteworthily, the Ag‐N2C2/CN exhibits much better hydrogen evolution activity than Ag‐N4/CN, and even superior to the platinum‐loaded CN.
•Functionalized phosphonium-based ILs (FPBILs) were synthesized by a simple method.•For the first time the FPBILs were used as catalysts for cycloaddition reaction.•The FPBILs show high catalytic ...activity and selectivity under mild conditions.•The structure of FPBILs has an influence on catalytic activity.
A series of novel functionalized phosphonium-based ionic liquids (FPBILs) were synthesized by a simple method, and first evaluated as catalysts for the synthesis of cyclic carbonates through the cycloaddition of CO2 to epoxides in the absence of co-catalyst and solvent. The FPBILs perform well in the cycloaddition reaction, especially the carboxyl-functionalized one. Over Ph3PC2H4COOHBr, the yield of propylene carbonate is 97.3% (TOF=64.9h−1) at 130°C and 2.5MPa in 3h. The synergistic effects of polarization induced by hydrogen bonding and nucleophilic attack of Br−anion account for the excellent performance. Furthermore, the FPBILs with moderate methylene chain length show superior catalytic activity. It is because they have both strong acidity and weak electrostatic interaction between phosphonium cation and halide anion. The strong acidity facilitates the ring-opening of epoxyl, and the weak electrostatic interaction enhances the nucleophilic attack capability of Br−. It is envisaged that the metal- and solvent-free process has high potential for the catalytic conversion of CO2 into value-added chemicals.
A facile impregnation combined with photo-deposition approach was adopted to deposit CdS nanoparticles on covalent-organic framework (CTF-1), which not only acted as supporter but also served as ...photocatalyst and electron-donor. The fast electron transfer rate and injection efficiency enabled the as-formed CdS-CTF-1 to show higher photocatalytic performance than CdS/CTF-1 prepared via solvothermal method.
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A facile and effective impregnation combined with photo-deposition approach was adopted to deposit cadmium sulfide (CdS) nanoparticles on CTF-1, a covalent triazine-based frameworks (CTFs). In this system, CTF-1 not only acted as supporter but also served as photocatalyst and electron donor. The performance of the obtained CdS deposited CTF-1 (CdS-CTF-1) nanocomposite was evaluated by H2 evolution reaction under visible light irradiation. As a result, CdS-CTF-1 exhibited high H2 production from water, far surpassing the CdS/CTF-1 nanocomposite, in which CdS was deposited via solvothermal method. The high activity of CdS-CTF-1 was attributed to the confined CdS nanoparticles with small size, leading to expose more active sites. In addition, time-resolved spectroscopy indicated that the superior performance of CdS-CTF-1 also can be ascribed to the fast electron transfer rate and injection efficiency (KET = 0.18 × 109 s−1, ηinj = 39.38%) between CdS and CTF-1 layers, which are 3.83 times faster and 4.84 times higher than that of CdS/CTF-1 nanocomposite. This work represents the first example on using covalent organic frameworks (COFs) as a support and electron-donor for fabricating novel CdS-COF nanocomposite system and its potential application in solar energy transformations.
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•Cu2O/BiVO4 photocatalyst was synthesized under mild conditions.•It shows high catalytic activity for the simultaneous removal of dyes and Cr(VI).•The degradations of cationic and/or ...anionic dyes operate under neutral condition.•A synergistic photoreduction–oxidation mechanism is proposed.
We synthesized Cu2O/BiVO4 composites by growing Cu2O nanoparticles on BiVO4 under mild condition. The optimized composite shows high photocatalytic efficiency in the simultaneous oxidation of organic dyes and reduction of Cr(VI) in neutral media. The XPS results confirm that the Cr(VI) adsorbed on Cu2O/BiVO4 was completely reduced to Cr(III). The photocatalyst can be used for the degradation of cationic or anionic dyes as well as a mixture of them under visible light irradiation. The photocatalytic activity of the composite can be ascribed to the heterojunctions between Cu2O and BiVO4, which facilitate the separation of photogenerated electrons and holes. The work demonstrates that the as-synthesized Cu2O/BiVO4 composite is a promising photocatalyst for the treatment of wastewater that contains organic dyes and Cr(VI) ions.
Limited by the electrostatic interaction, the oxidation reaction of cations at the anode and the reduction reaction of anions at the cathode in the electrocatalytic system nearly cannot be achieved. ...This study proposes a novel strategy to overcome electrostatic interaction via strong complexation, realizing the electrocatalytic reduction of cyanide (CN−) at the cathode and then converting the generated reduction products into nitrogen (N2) at the anode. Theoretical calculations and experimental results confirm that the polarization of the transition metal oxide cathodes under the electric field causes the strong chemisorption between CN− and cathode, inducing the preferential enrichment of CN− to the cathode. CN− is hydrogenated by atomic hydrogen at the cathode to methylamine/ammonia, which are further oxidized into N2 by free chlorine derived from the anode. This paper provides a new idea for realizing the unconventional and unrealizable reactions in the electrocatalytic system.
Electrostatic interaction could severely inhibit the selective conversion of ions. This work proposes a strategy to overcome electrostatic interaction via strong complexation, realizing the preferential hydrogenation of cyanide at the cathode, and then oxidizing the reduction products into nitrogen at the anode. The controlled mass transfer of ions provides more possibilities for their selective conversion in the electrocatalytic system.
The recent development of heterogeneous catalysts for the synthesis of valuable organic carbonates from CO
2 through various synthetic routes has been reviewed. The supported ionic liquids are worthy ...of further research. The mechanisms of acid–base or electrophile–nucleophile catalysis proposed in the literature will be valuable for the design and fabrication of high-performance catalysts.
In this review article, we report the recent developments of heterogeneous catalysts for the synthesis of cyclic and dimethyl carbonates from CO
2 through various routes. The synthesis of cyclic carbonates via cycloaddition of CO
2 to epoxides is one of the few processes that have been commercialized. Compared to the many effective homogeneous catalysts, the heterogeneous catalysts have the advantages of being superior in stability and reusability. However, of the reported catalysts including metal oxides, zeolites, smectite, supported organic bases, metal complexes, and ionic liquids, none can be considered as highly active and selective under mild conditions. Also, heterogeneous catalysts used in other routes do not perform satisfactorily. The supported ionic liquids have attracted much more attention and are worthy of further research for the cycloaddition reaction. We predict that the mechanisms of acid–base or electrophile–nucleophile catalysis proposed in the literature will be valuable for the design and fabrication of high-performance catalysts.
Indirect electrochemical oxidation by hydroxyl radicals is the predominant degradation mechanism in electrolysis with a boron-doped diamond (BDD) anode. However, this electrochemical method exhibits ...low reactivity in removal of hydrophilic aromatic pollutants owing to mass transfer limitation. In this study, the combination of ultraviolet light and BDD electrolysis could increase the degradation rate of hydrophilic aromatic pollutants by approximately 8–10 times relative to electrolysis alone. According to the results of the scavenging experiments and identification of benzoic acid oxidation products, surface-bound hydroxyl radical (•OH(surface)) was the primary reactive species degrading aromatic pollutants in the BDD electrolysis process, whereas freely-diffusing homogeneous hydroxyl radical (•OH(free)) was the major reactive species in the UV-assisted BDD electrolysis process. Cyclic voltammetry revealed that UV light decomposed H2O2 formed on the BDD anode surface, thus retarding O2 evolution and facilitating •OH(free) generation. This work also explored the potential application of UV-assisted BDD electrolysis in removing COD from bio-pretreated landfill leachate containing high concentrations of hydrophilic aromatic pollutants. This study shed light on the importance of the existing state of •OH on removal of pollutants during BDD electrolysis, and provided a facile and efficient UV-assisted strategy for promoting degradation of hydrophilic aromatic pollutants.
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••OH(surface) is the primary reactive species in BDD electrolysis process.•Hydrophobic organics are easier to be degraded with BDD electrolysis than hydrophilic ones.•UV shifts .•OH(surface) to •OH(free) in UV-assisted BDD electrolysis.•Degradation of hydrophilic organics is dramatically enhanced in UV-assisted BDD electrolysis.•Bio-pretreated landfill leachate is amenable to UV-assisted BDD electrolysis.
A strategy was developed to couple photocatalytic oxidation with photocatalytic reduction technology to realize one-pot conversion of MB into hydrocarbons for the first time. In this approach, ...organic pollutants were first decomposed into CO2 by photodegradation and then the as-obtained CO2 was converted into CH3OH, C2H5OH, and CH4 through photocatalytic reduction of CO2 under solar spectrum irradiation by using GQDs/V-TiO2 catalysts. The experimental results show that 5%GQDs/V-TiO2 has the best photocatalytic activity and the product rates of CH3OH, C2H5OH, and CH4 are 13.24, 5.65, and 0.445 μmol g–1 h–1, respectively. The corresponding apparent quantum efficiency is 4.87% at 420 nm. The one-pot conversion of MB into hydrocarbons was demonstrated by a series of experiments. The photocatalytic mechanisms of one-pot conversion of MB into hydrocarbons were proposed to explain the detailed photocatalytic process.
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