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.

O and S co-doping induced N-vacancy in graphitic carbon nitride towards photocatalytic peroxymonosulfate activation for sulfamethoxazole degradation.

Doping-induced vacancy engineering of graphitic carbon nitride (GCN) is beneficial for bandgap modulation, efficient electronic excitation, and facilitated charge carrier migration. In this study, synthesis of oxygen and sulphur co-doped induced N vacancies (OSGCN) by the hydrothermal method was performed to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) antibiotic degradation and H2 production. The results from experimental and DFT simulation studies validate the synergistic effects of co-dopants and N-vacancies, i.e., bandgap lowering, electron-hole pairs separation, and high solar energy utilization. The substitution of sp2 N atom by O and S co-dopants causes strong delocalization of HOMO-LUMO distribution, enhancing carrier mobility, increasing reactive sites, and facilitating charge-carrier separation. Remarkably, OSGCN/PMS photocatalytic system achieved 99.4% SMX degradation efficiency and a high H2 generation rate of 548.23 µ mol g-1 h-1 within 60 min and 36 h, respectively under visible light irradiations. The SMX degradation kinetics was pseudo-first-order with retained recycling efficiency up to 4 catalytic cycles. The results of EPR and chemical scavenging experiments revealed the redox action of reactive oxidative species, wherein 1O2 was the dominant reactive species in SMX degradation. The identification of formed intermediates and the SMX stepwise degradation pathway was investigated via LC-MS analysis and DFT studies, respectively. The results from this work anticipated deepening the understanding of PMS activation by substitutional co-doping favoring N-vacancy formation in GCN lattice for improved photocatalytic activity.

Defect Engineering Modulated Iron Single Atoms with Assist of Layered Clay for Enhanced Advanced Oxidation Processes.

Single-atom catalysts (SACs) feature maximum atomic utilization efficiency; however, the loading amount, dispersibility, synthesis cost, and regulation of the electronic structure are factors that need to be considered in water treatment. In this study, kaolinite, a natural layered clay mineral, is applied as the support for g-C3 N4 and single Fe atoms (FeSA-NGK). The FeSA-NGK composite exhibits an impressive degradation performance toward the target pollutant (>98% degradation rate in 10 min), and catalytic stability across consecutive runs (90% reactivity maintained after three runs in a fluidized-bed catalytic unit) under peroxymonosulfate (PMS)/visible light (Vis) synergetic system. The introduction of kaolinite promotes the loading amount of single Fe atoms (2.57 wt.%), which is a 14.2% increase compared to using a bare catalyst without kaolinite, and improved the concentration of N vacancies, thereby optimizing the regulation of the electronic structure of the single Fe atoms. It is discovered that the single Fe atoms successfully occupied five coordinated N atoms and combined with a neighboring N vacancy. Consequently, this regulated the local electronic structure of single Fe atoms, which drives the electrons of N atoms to accumulate on the Fe centers. This study opens an avenue for the design of clay-based SACs for water purification.

Flexible construct of N vacancies and hydrophobic sites on g-C3N4 by F doping and their contribution to PFOA degradation in photocatalytic ozonation.

N vacancies, hydrophobic sites and electron rich zone were simply regulated by doping F into g-C3N4 (CN) to accelerate photocatalytic ozonation of PFOA. Activity of F-CN was superior to that of CN, with 74.3% PFOA removal by F-CN/Vis/O3 but only 57.1% by CN/Vis/O3. Experimental results and theory simulations suggested that the photogenerated hole (hvb+) oxidation with the help of N vacancies was vital for PFOA degradation. N vacancies on both CN and F-CN would trap O atom of PFOA and seize electron from α -CF2 group, which made PFOA more easily to be oxidized. Doping of F narrowed band gap, lowered the valence band position and enhanced the oxidation potential of hvb+. The hydrophobic sites would accelerate the mass transfer of O3 and PFOA, enhance O3's single electron reduction with ecb- to generate hydroxyl radicals (•OH) and reduce the recombination of hvb+-ecb-. Under the joint function of hvb+, N vacancies and •OH, PFOA degradation in F-CN/Vis/O3 proceeded through the gradually shortening of perfluoroalky chain and loss of CF2 unit. The acute and chronic toxicity of generated short-chain perfluorocarboxylic acid toward fish, green algae daphnid were predicted by ECOSAR. And the toxicity change of solutions was examined by luminescent bacteria.