With more and more attention to health, developing a simple and effective method for detecting phenolic compounds is an urgent and challenging task. In this context, Mn-doped CoP (referred to as Mn-CoP) with a nanocage interior architecture has been successfully constructed. The formation of a hollow structure exposes more active sites, while the incorporation of Mn ion reduces the charge transfer resistance and accelerates the charge transfer. Consequently, Mn-CoP effectively provides electrons to activate H2O2 and O2 producing OH center dot and O2 center dot-, demonstrating excellent peroxidase-like and oxidase-like activities. Given its strong oxidase-like activity, Mn-CoP enables a straightforward colorimetric assay for detecting hydroquinone using 3,3 ',5,5 '-tetramethyl benzidine (TMB) as colorimetric substrate. Interestingly, the developed colorimetric detection method exhibits a broad linear range and a low limit of detection (LOD) for hydroquinone, showing good potential for application even in real samples. Detailed analyses reveal that the doped Mn ions serve as Lewis acid sites directly reacting with the amino functional group in TMB. The Lewis acid-base reaction between Mn-CoP and TMB is crucial for the chromogenic reaction of TMB. Moreover, doping Mn ion to enhance the oxidase-like activity of the nanozyme is a simple and feasible modification strategy with universal applicability. This work provides a valuable reference for designing nanozymes with oxidase-like activity.

As a renewable energy carrier and an environmental-friendly oxidant, hydrogen peroxide (H2O2) has attracted widely attention. In comparison with conventional anthraquinone process, photocatalytic H2O2 generation is a sustainable, simple, safe, and green process, so there is a growing body of research on photocatalytic H2O2 generation. In this review, the progress and challenge of photocatalytic H2O2 generation are summarized, including the main mechanism of photocatalytic H2O2 synthesis, and design and modification principles of photocatalyst. Notably, the main issues facing photocatalytic H2O2 synthesis are low utilization of solar energy, high recombination rate of electron-hole pairs, poor selectivity of product, and easy decomposition of H2O2. To overcome these problems, various effective and feasible strategies are proposed, and the mechanisms, advantages and disadvantages of these strategies are also discussed. Furthermore, the environmental applications of photocatalytic H2O2 evolution are summarized in brief. More significantly, the challenges and future prospects about photocatalytic H2O2 production are proposed. In short, it is expected that this review can share some meaningful insights into photocatalytic H2O2 generation and provide some valuable references for future research.

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.

It is of great significance to establish an effective method for removing Cr(VI) from wastewater. Herein, Fe-doped g-C3N4 (namely Fe-g-C3N4-2) was synthesized and then employed as photocatalyst to conduct the test of Cr(VI) reduction. Notably, the embedding of Fe ion in g-C3N4 can offer the Fe2+/Fe3+ redox couples, so reducing the interfacial resistance of charge transfer and suppressing the recombination of photogenerated electrons and holes. The impurity energy levels will form in g-C3N4 after the introduction of Fe ion, thereby boosting the light absorption capacity of catalyst. Thus, Fe-g-C3N4-2 showed good performance in photocatalytic Cr(VI) reduction, and the reduction efficiency of Cr(VI) can reach 39.9% within 40 min. Different with many previous studies, current work unexpectedly found that the addition of p-benzoquinone (BQ) can promote the Cr(VI) reduction, and the reduction efficiency of Cr(VI) over Fe-g-C3N4-2 was as high as 93.2% in the presence of BQ (1.5 mM). Further analyses showed that BQ can be reduced to hydroquinone (HQ) by photogenerated electrons, and UV light can also directly induce BQ to generate HQ by using H2O as the hydrogen donor. The HQ with reducing ability can accelerate the Cr(VI) reduction. In short, current work shared some novel insights into photocatalytic Cr(VI) reduction in the presence of BQ. Future research should consider possible reactions between photogenerated electrons and BQ. For the UV-induced photocatalysis, the suitability of BQ as the scavenger of O2•‒ must be given carefully consideration.

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.

Herein, hollow carbon sphere (HCS) is constructed via hard template method for loading the Co 3 O 4 , and obtained catalyst (namely Co 3 O 4 /HCS) is then employed to activate peroxymonosulfate (PMS) for the removal of tetracycline (TC). Owing to high specific surface area and good conductivity of HCS, Co 3 O 4 modified with HCS exhibits low interface resistance and fast charge transfer rate. Meanwhile, hollow structure of HCS can provide spatial confinement effect for Co 3 O 4 and accelerate the mass transfer process between Co 3 O 4 and PMS. As predicted, peroxy bond break of PMS over Co 3 O 4 /HCS is significantly boosted compared with pure Co 3 O 4 , so reaction system can produce more SO 4 center dot - , OH center dot , 1 O 2 and high-valent metal complexes to conduct TC degradation. Importantly, Co 3 O 4 /HCS-mediated electron transfer process between PMS and TC is also involved in TC degradation. As a result, Co 3 O 4 /HCS shows excellent performance in TC degradation, and the highest removal efficiency of TC is more than 95 % within 10 min. Benefiting from the protective effect of HCS, only a small amount of Co ion is released from Co 3 O 4 /HCS during the reaction process. Besides, Co 3 O 4 /HCS possesses good reusability and anti -interference ability. In short, current work provides a promising catalyst for PMS activation to treat wastewater containing antibiotic.

It is of great significance to exploit simple and efficient methods for detecting hazardous substances in the fields related to food safety and environmental protection. Herein, for the first time, a newly-designed hollow Co-N/C nanocage with oxidase-like activity was synthesized via a feasible method. Benefiting from the construction of hollow structure and the introduction of carbon layer, the specific surface area of enzyme mimic was improved, so exposing more active sites. Importantly, hollow Co-N/C nanocage displayed an excellent performance in interfacial charge transfer, which provided convenience for the occurrence of chromatic reaction between enzyme mimic and TMB. As predicted, hollow Co-N/C nanocage can effectively oxidize colorless TMB to blue oxTMB in the absence of H2O2, and the analyses about catalytic mechanism suggested that both the redox couples of Co3+/Co2+ and O2•− were involved in the oxidation of TMB. Furthermore, a chromogenic sensing method for the detection of Na2SO3 and Cr6+ was exploited, and a broad linear range and a low LOD can be achieved. More interestingly, developed detection method still possessed good recovery even in real samples. In a word, current work will share novel insights into the design of enzyme mimics and the analyses on chromogenic mechanism.

In this study, a double p-n heterojunction based on g-C3N4@NiO/Ni@MIL-101 ternary composite was successfully prepared by a feasible method. Results suggested that the rational growth of NiO and MIL-101 on the surface of g-C3N4 can improve the absorption capacity for visible light. Importantly, the formation of double p-n heterojunction can effectively inhibit the recombination of photogenerated electrons and holes. Due to the significant Fermi level differences among NiO, MIL-101 and g-C3N4, the internal electric fields were established on the interface after constructing the composite, consequently reducing the electrical resistance and accelerating the transfer of photoinduced charge carriers. As expected, the g-C3N4@NiO/Ni@MIL-101 ternary composite with good stability had excellent photocatalytic performance in the degradation of emerging pollutants, and the removal efficiency of ibuprofen was as high as 95.6%, wherein •O2−, •OH and 1O2 were the major active species in the reaction system. Furthermore, developed photocatalytic oxidation system can also achieve the rapid inactivation of bacteria. Based on the synergistic effects of energy band position and double internal electric fields, the separation and transfer of photogenerated charge carriers followed a traditional type-II route. In short, current work not only constructed a promising photocatalyst, but also shared an effective strategy for boosting the photocatalytic activity.

Nowadays photocatalysis assisted advanced oxidation processes exhibited a great application prospects in pollution control. Herein, for the first time, a series of transition metal modified UiO-66-NH2 (namely Fe-UiO-66-NH2, Co-UiO-66-NH2 and Ni-UiO-66-NH2) were synthesized via a simple method. After that, these functional materials were employed as photocatalyst to activate PMS for degrading BPA under visible light irradiation. Significantly, prepared Fe-UiO-66-NH2 exhibited the highest photocatalytic activity among these samples. More importantly, proposed Fe-UiO-66-NH2/PMS/light oxidation system showed excellent degradation ability for various organic pollutants, including BPA, TC, OFX, IBP as well as SMX. Owing to the occurrence of d-d transitions after the coordination of transition metal ions, UiO-66-NH2 displayed the enhanced utilization efficiency of visible light. Furthermore, introduced Fe ion as a mediator could boost the charge transfer by the cluster-to metal way, thereby effectively inhibiting the recombination of photogenerated electrons and holes. In addition, embedding cluster-to-metal charge transfer in UiO-66-NH2 modified the band structure, and both SO4-center dot and (OH)-O-center dot were major active species in the photocatalytic reaction system. Developed Fe-UiO-66-NH2/PMS/light oxidation system with good stability also presented great antibacterial performance. To sum up, current work could provide some novel inspirations for designing the high-efficiency photocatalyst.