A novel insight into the microwave induced catalytic reduction mechanism in aqueous Cr(VI) removal over ZnFe2O4 catalyst

Reducing the molecular oxygen activation energy barrier by increasing Fe-O bonds to eliminate antibiotics and their resistance genes

Sulfamethoxazole (SMX) and its antibiotic resistance genes (ARGs) are potential threats to public health. Microwave catalytic technology is an efficient environmental remediation technology, and a reasonable design of the catalyst enables the system to achieve an ideal remediation effect under low microwave power. In this study, a microwave catalyst (FeCO-2) that activates molecular oxygen (O2) was designed on the basis of rational theoretical organization. Density functional theory (DFT) calculations were used to predict the catalytic performance of FeCO-2 in the microwave field. The mechanism of active substance generation and successful construction of the MW/FeCO-2 catalytic system were verified by experimental studies. The abundance of Fe-O bonds alters the electronic structure of the iron carbide material (Fe@C), adjusts the conduction band potential of the material, reduces the reaction energy barrier, facilitates exciton dissociation under microwave, and facilitate O2 activation. The application of the MW/FeCO-2 system was verified with secondary effluent from a farm wastewater treatment process: 90.62 % SMX and over 86.77 % of ARGs were removed within 15 min. This study provides a new technique to efficiently simultaneously eliminate antibiotics and their resistance genes. In addition, this study provides ideas for the construction of a microwave catalytic system and explains the mechanism of the microwave catalytic process.

A nitrogen-enriched strategy to accelerate the remediation of Cr(VI)-contaminated soil by iron-based materials in microwave fields

The existing remediation technologies for Cr(VI) contamination soil suffer from long processing times. Microwave catalysis is an efficient environmental remediation technology, and the reasonable design of microwave catalysts can enable a microwave catalytic system to rapidly complete the remediation of Cr(VI). In this study, a microwave catalyst, NRFC-3, with high microwave absorption performance and electron density was designed via a nitrogen enrichment strategy. Density functional theory (DFT) calculations verified that the electron density of the material was increased by nitrogen-enriched strategy. Under the experimental conditions, the electrons (e-) of NRFC-3 originate from "hot spots" and the current density is not lower than 3.78 × 109 e·g-1·s-1. In addition, the reduction of Cr(VI) in the MW/NRFC-3 system is feasible through DFT predictions, and this conclusion was experimentally verified. The MW/NRFC-3 system has a remediation efficiency of 100 % for Cr(VI)-contaminated soil within 25 min, significantly reduced the toxicity of Cr(VI) to the environment and humans, and had long-term stability. The potential application of the MW/NRFC-3 system was verified by remediation experiments on Cr(VI)-contaminated soils of different degrees. This study provides a new technology for the rapid and harmless treatment of Cr(VI)-contaminated soil.

A novel approach to modify Stenotrophomonas sp. D6 by regulating the salt composition in the growth medium: Enhanced removal performance of Cr(VI)

In this study, a novel and effective modified microbial reducing agent was developed to detoxify Cr(VI) from aqueous solutions. This was achieved by carefully controlling specific salt components in the growth medium. Based on the single-salt modification, several effective modified salts were selected and added to the medium for synergistic modification. The results showed that the synergistic modification with NH4Cl and KH2PO4 had the best detoxification effect on Cr(VI), reaching 98.5% at 100 mg/L Cr(VI), which was much higher than the 43.7% of the control (original Luria-Bertani medium). This enhancement was ascribed to the ability of NH4Cl and KH2PO4 to stimulate the growth of Stenotrophomonas sp. D6 promoted chromate reductase secretion. The protein content of the modified medium supernatant was significantly increased by 10.76% compared to that before modification. Based on the micro-characterization, the main process for the elimination of Cr(VI) is microbial reduction rather than biosorption. Most of the reduced Cr was found in the extracellular suspension, thereby suggesting that the primary reduction occurred outside the cells, whereas only a small fraction was detected intracellularly. Overall, this study provides a simple and effective method for microbial treatment of heavy metals in aqueous solutions.