Efficient degradation of tetracycline in wide pH range using MgNCN/MgO nanocomposites as novel H2O2 activator.

Currently existing Fenton-like catalysts were limited in wastewater treatment owing to their potential transition-metal poisoning, narrow applicable pH range and high dependence on external energy excitation. In this work, the MgNCN/MgO nanocomposites were firstly synthesized by a facile one-pot calcination of melamine and basic magnesium carbonate, and used as novel H2O2 activator for antibiotic removal. It was found that the MgNCN/MgO composite calcined at 550°C with the mass ratio of melamine to basic magnesium carbonate at 2:1, exhibited an excellent catalytic ability to tetracycline (TC) degradation in a wide pH range of 4-10 without any external energy input. More than 90% of TC (100 mL, 50 mg/L) could be degraded within 30 min by 10 mg of the nanocomposite in the presence of 0.2 mL of 30 wt% H2O2. Based on the experimental results, it was concluded that the Mg-N coordination between MgNCN and MgO in MgNCN/MgO nanocomposites activated H2O2 to produce primary singlet oxygen (1O2) and minor hydroxyl radicals (·OH), responding for TC degradation. In addition, the degradation pathways of TC were deduced by determining the generated intermediates during the degradation process. This work provided a novel idea for designing transition-metal-free catalysts for nonradical activation of H2O2 in the absence of external energy excitation.

Enhanced degradation of sulfamethoxazole by a novel Fenton-like system with significantly reduced consumption of H2O2 activated by g-C3N4/MgO composite.

Advanced oxidation processes (AOP) based on nonradicals have attracted growing attentions because nonradical systems require much less oxidants and have low susceptibility to radical scavengers. Herein, a novel Fenton-like system that utilizes nonradicals was explored. It was derived from g-C3N4/MgO activated H2O2, and can reduce the H2O2 stoichiometry from 0.94%-0.18% to 0.03%. Sulfamethoxazole (SMX), a widely used sulfonamide, was used as the model pollutant to evaluate the efficacy of the system. It was observed for the first time that organic pollutants can be degraded with singlet oxygen (1O2) through a nonradical pathway in the g-C3N4/MgOH2O2 system. The reduced H2O2 consumption was the net result of continuously-recycled H2O2 from the reactions between H2O2 and g-C3N4/MgO. Based on experimental results and theoretical calculations, the synthesis of g-C3N4 and MgO forms a N-Mg bond with strong ability to absorb electrons and the electron transfer of H2O2 to N-Mg bonding is accelerated, activation of H2O2 to generate 1O2. Experimental data showed that organic pollutants can be degraded rapidly over a wide pH range. Findings of this study point to a cyclical but stable Fenton-like system with reduced H2O2 requirement for cost-effective remediation and treatment of organic pollutants and toxic wastes.