Mo-Based Heterogeneous Interface and Sulfur Vacancy Synergistic Effect Enhances the Fenton-like Catalytic Performance for Organic Pollutant Degradation

Doping and defects in carbon nitride cause efficient in situ H2O2 synthesis to allow efficient photocatalytic sterilization

In situ photocatalytic synthesis of H2O2 for disinfection has attracted widespread attention because it is a clean and environmentally friendly sterilization method. Graphitic carbon nitride has been used as a very selective photocatalyst for H2O2 generation but has some limitations (e.g., insufficient light absorption, rapid electron-hole recombination, and slow direct two-electron reduction processes) that prevent efficient H2O2 production. In this study, potassium-doped graphite carbon nitride with nitrogen vacancies (NDKCN) was prepared using a simple method involving a thermal fusion salt and N2 calcination, which possessed an ultrathin nanosheet structure (1.265 nm) providing abundant active sites. Synergistic effects caused by nitrogen vacancies and K+ and I- doping in the NDKCN photocatalyst gave the NDKCN a good ability to absorb light, undergo fast charge transfer, and give a high photoelectric current response. The optimized photocatalytic H2O2 yield of the NDKCN was 780.1 μM·g-1·min-1, which was 10 times the yield of the pristine g-C3N4. Tests involving quenching reactive species, electron spin resonance, and rotating disk electrodes indicated that one-step two-electron direct reduction on the NDKCN caused excellent H2O2 generation performance. The ability to efficiently generate H2O2 in situ gave NDKCN an excellent bactericidal performance, and 7.3 log10 (colony-forming units·mL-1) of Escherichia coli were completely eliminated within 80 min. Scanning electron microscopy images before and after sterilization indicated the changes in bacteria caused by the catalytic activity. The new g-C3N4-based photocatalyst and similar rationally designed photocatalysts with doping and defects offer efficient and simple in situ H2O2 sterilization.

Sulfur Vacancies in Pyrite Trigger the Path to Nonradical Singlet Oxygen and Spontaneous Sulfamethoxazole Degradation: Unveiling the Hidden Potential in Sediments

Pharmaceutical residues in sediments are concerning as ubiquitous emerging contaminants. Pyrite is the most abundant sulfide minerals in the estuarine and coastal sediments, making it a major sink for pharmaceutical pollutants such as sulfamethoxazole (SMX). However, research on the adsorption and redox behaviors of SMX on the pyrite surface is limited. Here, we investigated the impact of the nonphotochemical process of pyrite on the fate of coexisting SMX. Remarkably, sulfur vacancies (SVs) on pyrite promoted the generation of nonradical species (hydrogen peroxide, H2O2 and singlet oxygen, 1O2), thereby exhibiting prominent SMX degradation performance under darkness. Nonradical 1O2 contributed approximately 73.1% of the total SMX degradation. The SVs with high surrounding electron density showed an advanced affinity for adsorbing O2 and then initiated redox reactions in the sediment electron-storing geobattery pyrite, resulting in the extensive generation of H2O2 through a two-electron oxygen reduction pathway. Surface Fe(III) (hydro)oxides on pyrite facilitated the decomposition of H2O2 to 1O2 generation. Distinct nonradical products were observed in all investigated estuarine and coastal samples with the concentrations of H2O2 ranging from 1.96 to 2.94 μM, while the concentrations of 1O2 ranged from 4.63 × 10-15 to 8.93 × 10-15 M. This dark-redox pathway outperformed traditional photochemical routes for pollutant degradation, broadening the possibilities for nonradical species use in estuarine and coastal sediments. Our study highlighted the SV-triggered process as a ubiquitous yet previously overlooked source of nonradical species, which offered fresh insights into geochemical processes and the dynamics of pollutants in regions of frequent redox oscillations and sulfur-rich sediments.

Electronic structure regulation of Fe single atom coordinated nitrogen doping MoS2 catalyst enhances the Fenton-like reaction efficient for organic pollutant control

An efficient cathode for a Fenton-like reaction based on hydrogen peroxide (H2O2) has significant implications for the potential application of the advanced oxidation process. However, the low H2O2 selectivity and efficient activation remain challenging in wastewater treatment. In the present study, a single Fe atom doped, nitrogen-coordinated molybdenum disulfide (Fe1/N/MoS2) cathode that exhibited asymmetric wettability and self-absorption molecular oxygen was successfully prepared for pollutant degradation. The X-ray absorption near-edge structure and extended X-ray absorption fine structure of Fe1N3 in the Fe1/N/MoS2 catalyst were determined. The electronic structure demonstrated favorable H2O2 selectivity (75%) in a neutral solution and the cumulative hydroxyl radical concentration was 14 times higher than the pure carbon felt. After 10 consecutive reaction experiments, the removal ratio of paracetamol still reached 97%, and the catalytic performance did not decrease significantly. This work deeply understands the catalytic mechanism of Fenton-like reaction between single Fe atom and MoS2 double reaction sites, and proves that the regulation of the electronic structure of Fe single atom is an effective strategy to improve the activity of Fenton-like reaction.

Nanocatalysts for modulating antitumor immunity: fabrication, mechanisms and applications

Immunotherapy harnesses the inherent immune system in the body to generate systemic antitumor immunity, offering a promising modality for defending against cancer. However, tumor immunosuppression and evasion seriously restrict the immune response rates in clinical settings. Catalytic nanomedicines can transform tumoral substances/metabolites into therapeutic products in situ, offering unique advantages in antitumor immunotherapy. Through catalytic reactions, both tumor eradication and immune regulation can be simultaneously achieved, favoring the development of systemic antitumor immunity. In recent years, with advancements in catalytic chemistry and nanotechnology, catalytic nanomedicines based on nanozymes, photocatalysts, sonocatalysts, Fenton catalysts, electrocatalysts, piezocatalysts, thermocatalysts and radiocatalysts have been rapidly developed with vast applications in cancer immunotherapy. This review provides an introduction to the fabrication of catalytic nanomedicines with an emphasis on their structures and engineering strategies. Furthermore, the catalytic substrates and state-of-the-art applications of nanocatalysts in cancer immunotherapy have also been outlined and discussed. The relationships between nanostructures and immune regulating performance of catalytic nanomedicines are highlighted to provide a deep understanding of their working mechanisms in the tumor microenvironment. Finally, the challenges and development trends are revealed, aiming to provide new insights for the future development of nanocatalysts in catalytic immunotherapy.

Electrocatalytic degradation of p-nitrophenol on metal-free cathode: Superoxide radical (O2•-) production via molecular oxygen activation

Although metal-free electrodes in molecular oxygen-activated Fenton-like wastewater treatment technologies have been developed, the reactive oxygen species (ROS) generation mechanisms are still not sufficiently clear. As a typical example of refractory phenolic wastewater, p-nitrophenol (PNP) has been widely studied. This study demonstrated the critical role of superoxide radicals (O2•-) in PNP degradation by metal-free electrodes through electron spin resonance (ESR), ROS quenching, and density functional theory (DFT) tests. The most superior metal-free electrode exhibited a mass activity of approximately 133.5 h-1 gcatalyst-1. Experimental and theoretical studies revealed the mechanism of O2•- generation via oxygen activation, including one- and three-electron transfer pathways, and found that O2•- mainly attacked the nitro group of PNP to degrade and transform the pollutant. This study enhances the mechanistic understanding of metal-free materials in the electrochemical degradation of refractory pollutants.