Fe(VI) activation system mediated by a solar-driven TiO2 nanotubes electrode for CLQ degradation: Performances, mechanisms and pathways.

Ferrate (Fe(VI), FeO42-) has been widely used in the degradation of micropollutants with the advantages of high redox potential, no secondary pollution and inhibition of disinfection byproducts. However, the low transformation of Fe(V) and/or Fe(IV) by Fe(VI) and incomplete mineralization of pollutants limit their application. In this work, we designed a photo electric cell with TiO2 nanotubes (TNTs) and Pt serving as the anode and cathode to enhance the utilization of Fe(VI) (Fe(VI)-TNTs system). TNTs accelerated the generation of •OH via hVB+ oxidation of OH- and photogenerated electrons at Pt boosted the transformation of Fe(VI) to Fe(V) and/or Fe(IV), resulting in a 22.2 % enhancement of chloroquine (CLQ) removal compared to Fe(VI) alone. The results from EPR and quenching tests showed that Fe(VI), Fe(V), Fe(IV), •OH, O2•- and hVB+ coexisted in the Fe(VI)-TNTs system, among which Fe(V) and Fe(IV) were testified as the primary reactive substances accounting for 59 % of CLQ removal. The performance tests and recycling tests demonstrated that the Fe(VI)-TNTs system maintained excellent performance in an authentic water environment. The plausible degradation pathway of CLQ oxidized in the Fe(VI)-TNTs system was proposed with nine identified oxidation products via N-C cleavage, electrophilic addition and carboxylation processes. Based on the ECOSAR calculation, the constructed reaction system allowed a decrease in acute and chronic toxicity. Our findings provide a highly efficient and cost-effective strategy to enhance Fe(VI) application for micropollutant degradation in the future.

Degradation and dechlorination of trichloroacetic acid induced by an in situ 222 nm KrCl* excimer radiation.

Since the coronavirus disease 2019 (COVID-19) pandemic epidemic, the excessive usage of chlorinated disinfectants raised the substantial risks of disinfection by-products (DBPs) exposure. While several technologies may remove the typical carcinogenic DBPs, trichloroacetic acid (TCAA), their application for continuous treatment is limited due to their complexity and expensive or hazardous inputs. In this study, degradation and dechlorination of TCAA induced by an in situ 222 nm KrCl* excimer radiation as well as role of oxygen in the reaction pathway were investigated. Quantum chemical calculation methods were used to help predict the reaction mechanism. Experimental results showed that UV irradiance increased with increasing input power and decreased when the input power exceeded 60 W. Decomposition and dechlorination were simultaneously achieved, where around 78% of TCAA (0.62 mM) can be eliminated and 78% dechlorination within 200 min. Dissolved oxygen showed little effect on the TCAA degradation but greatly boosted the dechlorination as it can additionally generate hydroxyl radical (•OH) in the reaction process. Computational results showed that under 222 nm irradiation, TCAA was excited from S0 to S1 state and then decayed by internal crossing process to T1 state, and a reaction without potential energy barrier followed, resulting in the breaking of C-Cl bond and finally returning to S0 state. Subsequent C-Cl bond cleavage occurred by a barrierless •OH insertion and HCl elimination (27.9 kcal/mol). Finally, the •OH attacked (14.6 kcal/mol) the intermediate byproducts, leading to complete dechlorination and decomposition. The KrCl* excimer radiation has obvious advantages in terms of energy efficiency compared to other competitive methods. These results provide insight into the mechanisms of TCAA dechlorination and decomposition under KrCl* excimer radiation, as well as important information for guiding research toward direct and indirect photolysis of halogenated DBPs.

Comparison of ribavirin degradation in the UV/H2O2 and UV/PDS systems: Reaction mechanism, operational parameter and toxicity evaluation.

Residues in surface water of ribavirin, which used extensively during the COVID-19 pandemic, have become an emerging issue due to its adverse impact on the environment and human health. UV/H2O2 and UV/peroxydisulfate (PDS) have different degradation effects on ribavirin, and the same operational parameter have different effects on the two processes. In this study, the reaction mechanism and degradation efficiency for ribavirin were studied to compare the differences under UV/H2O2 and UV/PDS processes. We calculated the total rate constants of ribavirin with HO• and SO4 •- in the liquid phase as 2.73 × 108 and 9.39 × 105 M-1s-1. The density functional theory (DFT) calculation results showed that HO• and SO4 •- react more readily with ribavirin via H-abstraction (HAA). The nitrogen-containing heterocyclic ring is difficult to undergo ring-opening degradation. The UV/PDS process was more stable and performed better than the UV/H2O2 for the ribavirin degradation when the same molar oxidant dosage was applied. HO• plays an extremely important role in the degradation of ribavirin by UV/PDS. The reason for this phenomenon is the combination of the higher yield of HO• produced in the UV/PDS process and the faster reaction rate of ribavirin with HO•. The UV/H2O2 process is more sensitive to pH than UV/PDS. Alkaline condition can significantly inhibit the ribavirin degradation. The effects of natural organic matter (NOM) and ribavirin concentration were also compared. Eventually, the toxicity prediction of the product showed that the opening-ring products were more toxic than the parent compound.

Remediation technology towards zero plastic pollution: Recent advance and perspectives.

The rapid growth of plastic wastes exceeds efforts to eliminate plastic pollution owing to the outbreak of COVID-19 in 2020 and then aggravates inherent environmental threats to the ecosystem. The paper provided a short introduction relating to the hazards of plastic wastes on environment and a detailed statement about plastic toxicity on human. The article stated on plastic how to enter the body and cause harm for us step by step. Given the toxicity and harm of plastic wastes on human, the degradation of plastic wastes via the physical, chemical and biotic methodologies is looked back. The advanced physical techniques are introduced briefly at firstly. Additionally, evaluate on chemical method for plastic decomposition and review on biotic degradation of plastic. The reactive oxygen species and the enzymes play a crucial role in chemical and biotic degradation processes, respectively. The reactive oxygen species are derived from the activated state of oxides, and the enzymes that aid the microorganism to ingest plastic through its metabolic mechanism are secreted by the microorganism. Subsequently, the potential possibility of upcycling plastic is analyzed from two aspects of the technology and application. The innovative technology utilizes sunlight as driver-power of plastic upcycling. And the carbon capture, utilization and sequestration and the growth substrate provided the novel guided directions for plastic recycle. Lastly, the three suggestions on plastic waste management are expected to establish an economy and efficient plastic sorting system, and two engineering solutions on plastic recycle are to make a contribution for sustainable upcycling of plastic.