A novel photocatalytic system coupling metal-free Carbon/g-C3N4 catalyst with persulfate for highly efficient degradation of organic pollutants

Degradation of PCDD/Fs from incineration of waste at low temperatures for resource utilization of fly ash

Municipal solid waste incineration fly ash (MSWIFA) is of great value in resource utilization. Harmless pretreatment is a crucial prerequisite for the resource utilization of MSWIFA. The detoxification process is a crucial step in the harmless pretreatment of MSWIFA. This includes polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), which are among the most toxic substances to humans and other living organisms. Low-temperature degradation technology has broad prospects in engineering applications due to the advantages of low technical difficulty and operating costs. This work conducts a pilot test on the degradation of 17 toxic PCDD/Fs in MSWIFA at low temperatures. The pilot test investigates the effects of reaction temperature and oxygen content on the degradation of PCDD/Fs in MSWIFA. Furthermore, based on the perspective of MSWIFA resource utilization, an analysis and a proposal are made to judge the degradation effect of low-temperature thermal treatment technology on PCDD/Fs in MSWIFA. Further, taking the soil sludge field as the application scenario, the application feasibility of MSWIFA after detoxification is analyzed. The flotation process markedly reduces both the carbon content and the levels of PCDD/Fs in MSWIFA. The hydrothermal method facilitates the degradation of dioxins in fly ash while introducing oxygen significantly lowers the reaction temperature required for fly ash treatment. This can enhance the degradation rate and reduce the demands on reaction equipment. The results indicate that the low-temperature thermal treatment technology can effectively degrade PCDD/Fs in MSWIFA, satisfying the requirements of some application scenarios. Notably, evaluating the effect of low-temperature thermal treatment technology on the degradation and detoxification of PCDD/Fs in MSWIFA should satisfy the residue requirements of different industries and achieve a certain detoxication efficiency.

Photocatalytic activation of peroxydisulfate by UV-LED through rGO/g-C3N4/SiO2 nanocomposite for ciprofloxacin removal: Mineralization, toxicity, degradation pathways, and application for real matrix

If trace amounts of antibiotics remain in the environment, they can lead to microbial pathogens becoming resistant to antibiotics and putting ecosystem health at risk. For instance, ciprofloxacin (CIP) can be found in surface and ground waters, suggesting that conventional water treatment technologies are ineffective at removing it. Now, a rGO/g-C3N4/SiO2 nanocomposite was synthesized in this study to activate peroxydisulfate (PDS) under UVA-LED irradiation. UVA-LED/rGO-g-C3N4-SiO2/PDS system performance was evaluated using Ciprofloxacin as an antibiotic. Particularly, rGO/g-C3N4/SiO2 showed superior catalytic activity for PDS activation to remove CIP. Operational variables, reactive species determination, and mechanisms were investigated. 0.85 mM PDS and 0.3 g/L rGO/g-C3N4/SiO2 eliminated 99.63% of CIP in 35 min and mineralized 59.78% in 100 min at pH = 6.18. By scavenging free radicals, bicarbonate ions inhibit CIP degradation. According to the trapping experiments, superoxide (O2•-) was the main active species rather than sulfate (SO4•-) and hydroxyl radicals (•OH). RGO/g-C3N4/SiO2 showed an excellent recyclable capability of up to six cycles. The UVA-LED/rGO-g-C3N4-SiO2/PDS system was also tested under real conditions. The system efficiency was reasonable. By calculating the synergistic factor (SF), this work highlights the benefit of combining composite, UVA-LED, and PDS. UVA-LED/rGO-g-C3N4-SiO2/PDS had also been predicted to be an eco-friendly process based on the results of the ECOSAR program. Consequently, this study provides a novel and durable nanocomposite with supreme thermal stability that effectively mitigates environmental contamination by eliminating antibiotics from wastewater.

New breakthrough in rapid degradation of lignin derivative compounds · A novel high stable and reusable green organic photocatalyst

The pulp and paper sectors are thriving yet pose significant environmental threats to water bodies, mainly due to the substantial release of pollutants. Lignin-derived compounds are among the most problematic of these contaminants. To address this issue, we present our initial results on utilizing organic semiconductor photocatalysis under visible light for treating lignin-derived compounds. Our investigation has been centered around creating a green and cost-effective organic semiconductor photocatalyst. This catalyst is designed using a structure of bagasse cellulose spheres to support PM6 (poly[(2,6-(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene))-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)-benzo[1,2-c:4,5-c']dithiophene-4,8-dione))]: MeIC (3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-cyclopentane-1,3-dione[c]-1-methyl-thiophe))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']-dithiophene)). This photocatalyst demonstrates remarkable efficiency, achieving over 91 % degradation of lignin-derived compounds. The superior photocatalytic performance is attributed to three main factors: (1) The ability of PM6 to broaden MeIC's absorption range from 300 to 800 nm, allowing for effective utilization of visible light; (2) the synergistic interaction between PM6 and MeIC, which ensures compatible energy levels and a vast, evenly spread surface area, promoting charge mobility and extensive donor/acceptor interfaces. This synergy significantly enhances the generation and transport of carriers, resulting in a high production of free radicals that accelerate the decomposition of organic materials; (3) The deployment of PM6:MeIC on biomass-based carriers increases the interaction surface with the organic substances. Notably, PM6: MeIC showcases outstanding durability, with its degradation efficiency remaining between 84 % and 91 % across 100 cycles. This study presents a promising approach for designing advanced photocatalysts aimed at degrading common pollutants in papermaking wastewater.

Heat and carbon co-activated persulfate to regenerate gentamicin-laden activated carbon: Performance, mechanism, and safety assessment

Activated carbon enriched with high concentrations of gentamicin (ACG) was generated in the production process of gentamicin. Inappropriate handling methods for ACG not only squanders carbon resource, but also seriously hinders achieving global carbon neutrality and hazardous to human health. In the present work, thermal and carbon co-activated persulfate method (TC-PS) was developed to regenerate ACG with degrading gentamicin. The results showed that ACG was effectively regenerated by TC-PS, restoring the adsorption performance for gentamicin. When the treatment temperature was 80 °C, the persulfate dosage was 20 mM and the initial pH was 3.0, the degradation efficiency of gentamicin reached 100%. The HO• and SO4•- were the major reactive species for gentamicin degradation. The possible degradation routes of gentamicin were proposed and the safety assessment indicated that the produced intermediates during the regeneration process of ACG by TC-PS have insignificant impact on the biological and ecological environment.

Using waste to treat waste: facile synthesis of hollow carbon nanospheres from lignin for water decontamination

Lignin, the most abundant natural material, is considered as a low-value commercial biomass waste from paper mills and wineries. In an effort to turn biomass waste into a highly valuable material, herein, a new-type of hollow carbon nanospheres (HCNs) is designed and synthesized by pyrolysis of biomass dealkali lignin, as an efficient nanocatalyst for the elimination of antibiotics in complex water matrices. Detailed characterization shows that HCNs possess a hollow nanosphere structure, with abundant graphitic C/N and surface N and O-containing functional groups favorable for peroxydisulfate (PDS) activation. Among them, HCN-500 provides the maximum degradation rate (95.0%) and mineralization efficiency (74.4%) surpassing those of most metal-based advanced oxidation processes (AOPs) in the elimination of oxytetracycline (OTC). Density functional theory (DFT) calculations and high-resolution mass spectroscopy (HR-MS) were employed to reveal the possible degradation pathway of OTC elimination. In addition, the HCN-500/PDS system is also successfully applied to real antibiotics removal in complex water matrices (e.g. river water and tap water), with excellent catalytic performances.