The key to heterogeneous photo-Fenton technology lies in the efficient generation of hydrogen peroxide (H2O2). Herein, a newly-designed ZnO/ZnIn2S4 composite with heterostructure is synthesized. Benefiting from the formation of built-in electric field, the recombination of photoinduced electrons and holes is suppressed and interfacial charge transfer resistance is reduced. Importantly, the embedding of ZnO in ZnIn2S4 can improve the hydrophobicity and create microscopic three-phase interface, thereby boosting the capture capability for O2 and providing the convenience for the occurrence of O2 reduction reaction. More interestingly, the existence of ZnIn2S4 in the ZnO/ZnIn2S4 composite can reduce the Gibbs free energy (ΔG) of key intermediate (OOH*) formation, which will accelerate the generation of H2O2. As a result, the ZnO/ZnIn2S4 composite displays excellent performance in photocatalytic H2O2 production, and the highest yield was about 897.6 μmol/g/h within 60 min under visible light irradiation. The transfer of photoinduced carriers follows the S-scheme type mechanism. The photogenerated holes can be captured by drug residues (i.e., diclofenac sodium) to accelerate H2O2 production, while generated H2O2 can combine with Fe2+ to construct photo-Fenton system for achieving the advanced degradation of diclofenac sodium, which was mainly related to the formation of OH•. Furthermore, generated H2O2 can be applied for performing the inactivation of pathogenic bacteria. In short, current work will provide a valuable reference for future research.

Photocatalytic two electron oxygen reduction reaction is considered to be a promising approach for green H2O2 production. Herein, for the first time, an intramolecular donor-acceptor (D-A) conjugated polymer was constructed in resorcinol-formaldehyde (RF) resin by embedding benzothiadiazole. As a typical electron deficient group, the introduction of benzothiadiazole can increase the specific surface area of RF and expose more active sites, and the hydrophobicity was also improved, thereby enhancing the affinity of RF to O-2. Owing to the potential difference between the electron donor and acceptor, the formation of a D-A conjugated polymer can provide a driving force to separate photoinduced charge, prolonging the lifetime of photogenerated charge and restraining the recombination of photogenerated electrons and holes. Furthermore, the light absorption ability of RF was enhanced after the introduction of benzothiadiazole. As expected, the catalyst (namely RF-BZ) exhibited excellent performance in photocatalytic H2O2 evolution, and the highest yield of H2O2 over RF-BZ can reach 2553.2 mu mol g(-1). More importantly, the thermodynamic analysis based on DFT calculations revealed that the introduction of benzothiadiazole can reduce the adsorption energy of O-2 over RF, and the Gibbs free energy of the rate-determining step for the two-electron oxygen reduction reaction was also reduced to 0.28 eV from 2.05 eV. In short, the current study provides a valuable reference for future research on photocatalytic H2O2 production.

It is of great significance for a clean energy system to develop novel non-noble catalysts toward the alkaline hydrogen evolution reaction (HER). Herein, CQDs-doped Ni(OH)2 nanosheets generated on nickel foam were fabricated by a feasible method using Ni-MOF as precursor. Notably, the alkali etching treatment can open the spatial structure of Ni(OH)2 and expose more active sites, thereby improving the electrocatalytic active surface area. Meanwhile, introduced CQDs can be acted as the charge carrier and accelerate the charge transfer. As a result, the Ni(OH)2-CQDs nanosheets showed excellent electrocatalytic performance in HER under alkaline condition, and an overpotential of 101 mV for OER over Ni(OH)2-CQDs/NF electrode can be realized at a current density of 10 mA/cm2. More significantly, embedding CQDs can effectively boost the photocatalytic activity of Ni(OH)2. Thus, light radiation can enhance the performance of Ni(OH)2-CQDs/NF electrode in HER, and the overpotential of Ni(OH)2-CQDs/NF electrode for HER can reduce to 90 mV under light irradiation. Furthermore, the Ni(OH)2-CQDs/NF electrode displayed great HER stability, and the possible mechanism of photo-assisted electrochemical HER was also proposed. All in all, current work will share some valuable insights into preparation and application of catalysts in HER.

A novel CeO2/Co3O4–Fe2O3@CC electrode derived from CeCo-MOFs was developed for detecting the endocrine disruptor bisphenol A (BPA). Firstly, bimetallic CeCo-MOFs were prepared by hydrothermal method, and obtained material was calcined to form metal oxides after doping Fe element. The results suggested that hydrophilic carbon cloth (CC) modified with CeO2/Co3O4–Fe2O3 had good conductivity and high electrocatalytic activity. By the analyses of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the introduction of Fe increased the current response and conductivity of the sensor, greatly increasing the effective active area of the electrode. Significantly, electrochemical test proves that the prepared CeO2/Co3O4–Fe2O3@CC had excellent electrochemical response to BPA with a low detection limit of 8.7 nM, an excellent sensitivity of 20.489 μA/μM·cm2, a linear range of 0.5–30 μM, and strong selectivity. In addition, the CeO2/Co3O4–Fe2O3@CC sensor had a high recovery rate for the detection of BPA in real tap water, lake water, soil eluent, seawater, and PET bottle samples, which showed its potential in practical applications. To sum up, the CeO2/Co3O4–Fe2O3@CC sensor prepared in this work had excellent sensing performance, good stability and selectivity for BPA, which can be well used for the detection of BPA.

Phenanthrene (PHE) and nitrate co-contamination widely exists in the groundwater. Anaerobic bioremediation of the two suffered from the slow removal rate and limited electron transfer within microbes. Herein electrical stimulation (ES) was proved to stimulate the simultaneous removal of PHE and nitrate anaerobically. High removal of PHE and nitrate (90.94 % and 100 %, respectively) was obtained within 24 h in the ES-bioreactor, two times higher than the control anaerobic bioreactor (32.16 %). ES-bioreactor exhibited a good PHE removal performance within initial PHE ranging from 5 to 25 mg/L. In ES-bioreactor, extracellular polymeric substances increased PHE bioavailability and acted as protective capsules. Nicotinamide adenine dinucleotide (NADH) and cytochrome C (cyt-C) facilitated the extracellular and intracellular electron exchange during PHE biotransformation. ES significantly selected Acetobacterium, PHE-degraders (f_Bacteroidetes_vadin HA17, Limnobacter and Stenotrophomonas) and electrogens (Clostrium_sensu_stricto_13) to participate in PHE decomposition. Acetobacterium decomposed complex organics to acetate, proving accessible substrates for electrogens to maintain an efficient electron flow. Enzymes regulating bacterial chemotaxis, flagellar assembly and carbohydrate metabolism were up-regulated with ES, suggesting the indispensable role of such enzymatic processes in ES-bioreactor. Overall, this work demonstrates ES can promote anaerobic bioremediation of PHE and nitrate in groundwater and, thus, opens up a new bioelectrochemistry application scenario.

Photocatalytic oxygen reduction is regarded as the cleanest approach for the production of hydrogen peroxide (H2O2). Herein, oxygen-modified graphite carbon nitride (g-C3N4) with nitrogen-defect (namely g-C3N4-ND4OM3) was synthesized by a feasible method. Owing to the existence of nitrogen vacancy and oxygen-containing functional group, the absorption bands derived from n & RARR; & pi;* and & pi; & RARR; & pi;* electronic transitions were enhanced, thereby enlarging the visible light response range of catalysts. Interestingly, nitrogen-defect can capture electron and effectively suppress the recombination of photoinduced electrons and holes. More importantly, the introduction of oxygen-containing functional groups can improve the hydrophilicity of g-C3N4, which was beneficial for the adsorption of dissolved oxygen. The electrostatic potential distributions of g-C3N4-based photocatalyst structural unit were also changed after introducing nitrogen vacancy and oxygen-containing functional group, and the electron-donating ability of g-C3N4 was improved. As a result, the evolution rate of H2O2 catalyzed by gC3N4-ND4-OM3 was as high as 146.96 & mu;mol/g/L under visible light irradiation. The photocatalytic H2O2 generation was completed through the direct 2-e  oxygen reduction. In short, current work will share novel insights into photocatalytic H2O2 generation over g-C3N4-based catalyst.

Photocatalytic technique is regarded as the cleanest approach for producing H2O2. Herein, two kinds of novel polyimide COFs decorated with CQDs (namely, MPa-COFs/CQDs and MNd-COFs/CQDs) were constructed by using the one-pot hydrothermal method. Due to the electron donor role of CQDs, the recombination of photoinduced electrons and holes was suppressed after the combination of polyimide COFs with CQDs. Importantly, the introduction of CQDs not only boosted the absorbing ability of polyimide COFs toward visible light but also reduced the impedance and improved the charge transfer efficiency. After CQDs were embedded into polyimide COFs, the surface hydrophilicity of catalysts was significantly improved, which provided convenience for the water oxidation reaction. Benefiting from the electron donor-acceptor interaction between polyimide COFs and CQDs, a step-by-step two-electron oxygen reduction reaction over polyimide COFs was enhanced. More interestingly, the embedding of CQDs can create a direct two-electron water oxidation reaction pathway, which played an important role in photocatalytic H2O2 generation. Meanwhile, H+ generated from water oxidation can also be used for the reduction of oxygen to form H2O2. Under the synergistic effects of water oxidation and oxygen reduction, as-prepared MPa-COFs/CQDs-2 displayed excellent performance in photocatalytic H2O2 generation, and its yield was as high as 540 μmol/g within 60 min. In short, the current work shared an effective strategy to improve the performance of polyimide COFs in photocatalytic H2O2 production.

Herein, Co-loaded hollow carbon sphere (namely Co-HCS-1) served as PMS activation mediator was synthesized. The construction of hollow structure can improve specific surface areas and offer more active sites, thereby reducing electron transfer resistance and increasing contact among PMS, pollutant and catalyst. Thus, the Co-HCS-1-mediated direct electron-transfer oxidation between PMS and pollutant was enhanced. After embedding Co-based nanoparticle in hollow carbon sphere, hollow carbon skeleton will provide spatial confinement for Co-based nanoparticle, which shortened mass transfer process. Thus, spatial confinement effect originated from Co-HCS-1 can accelerate the charge transfer between PMS and active sites of Co-HCS-1, thereby promoting O-O bond cleavage of PMS. As a result, the generations of radicals and high-valent metal complexes (namely Co-HCS-1≡Co4+) were boosted. Under the combined effects of electron-transfer oxidation, radicals and Co-HCS-1≡Co4+, developed Co-HCS-1/PMS system with good water stability can achieve the effective removal of various pollutants in very short time.