Advanced oxidative degradation of sulfamethoxazole by using bowl-like FeCuS@Cu2S@Fe0 catalyst to efficiently activate peroxymonosulfate

CuFeS2 supported on dendritic mesoporous silica-titania for persulfate-assisted degradation of sulfamethoxazole under visible light

Sulfamethoxazole (SMX) is a prevalent sulfonamide antibiotic found in the environment, and it has a variety of detrimental effects on environmental sustainability and water safety. Recently, the combination of photocatalysis and sulfate radical-based advanced oxidation processes (SR-AOPs) has attracted a lot of interest as a viable technique for degradation of refractory pollutants. In this study, a visible light active CuFeS2 supported on dendritic mesoporous silica-titania (CuFeS2-DMST) photocatalyst was synthesized to improve the ability of TiO2 to activate persulfate (PS) by introducing CuFeS2 (Fe2+/Fe3+, Cu+/Cu2+ redox cycles). The CuFeS2-DMST/PS/Vis system demonstrated superior SMX degradation efficiency (88.9%, 0.0146 min-1) than TiO2 because of reduced e-/h+ recombination, excellent charge separation and mobility, and a greater surface area than TiO2. Furthermore, after four consecutive photocatalytic cycles, the system demonstrated moderate stability. From chemical quenching tests, O2●-, h+, 1O2, SO4●- and ●OH were found to be the main reactive oxidizing species. The formed intermediates during the degradation process were identified, and degradation mechanisms were proposed. This study proposes a viable technique for activating PS using a low-cost, stable, and high-surface-area TiO2-based photocatalyst, and this concept can be applied to design photocatalysts for water treatment.

Efficient degradation of ciprofloxacin in wastewater by CuFe2O4/CuS photocatalyst activated peroxynomosulfate

In this study, CuFe2O4/CuS composite photocatalysts were successfully synthesized for the activation of peroxynomosulfate to remove ciprofloxacin from wastewater. The structural composition and morphology of the materials were analyzed by XRD, SEM, TEM, and Raman spectroscopy. The electrochemical properties of the samples were tested by an electrochemical workstation. The band gap of the samples was calculated by DFT and compared with the experimental values. The effects of different catalysts, oxidant PMS concentrations, and coexisting ions on the experiments were investigated. The reusability and stability of the photocatalysts were also investigated. The mechanism of the photocatalytic degradation process was proposed based on the free radical trapping experiment. The results show that the p-p heterojunction formed between the two contact surfaces of the CuFe2O4 nanoparticle and CuS promoted the charge transfer between the interfaces and inhibited the recombination of electrons and holes. CuFe2O4-5/CuS photocatalyst has the best catalytic activity, and the removal rate of ciprofloxacin is 93.7%. The intermediates in the degradation process were tested by liquid chromatography-mass spectrometry (LC-MS), and the molecular structure characteristics of ciprofloxacin were analyzed by combining with DFT calculations. The possible degradation pathways of pollutants were proposed. This study reveals the great potential of the photocatalyst CuFe2O4/CuS in the activation of PMS for the degradation of ciprofloxacin wastewater.

Singlet oxygen-dominated peroxymonosulfate activation by layered crednerite for organic pollutants degradation in high salinity wastewater

Advanced oxidation processes have been widely studied for organic pollutants treatment in water, but the degradation performance of radical-dominated pathway was severely inhibited by the side reactions between the anions and radicals, especially in high salinity conditions. Here, a singlet oxygen (1O2)-dominated non-radical process was developed for organic pollutants degradation in high salinity wastewater, with layered crednerite (CuMnO2) as catalysts and peroxymonosulfate (PMS) as oxidant. Based on the experiments and density functional theory calculations, 1O2 was the dominating reactive species and the constructed Cu-O-Mn with electron-deficient Mn captured electron from PMS promoting the generation of 1O2. The rapid degradation of bisphenol A (BPA) was achieved by CuMnO2/PMS system, which was 5-fold and 21-fold higher than that in Mn2O3/PMS system and Cu2O/PMS system. The CuMnO2/PMS system shown prominent BPA removal performance under high salinity conditions, prominent PMS utilization efficiency, outstanding total organic carbon removal rate, wide range of applicable pH and good stability. This work unveiled that the 1O2-dominated non-radical process of CuMnO2/PMS system overcame the inhibitory effect of anions in high salinity conditions, which provided a promising technique to remove organic pollutants from high saline wastewater.

Factors hindering the degradation of pharmaceuticals from human urine in an iron-activated persulfate system

This study investigated the degradation of clofibric acid (CFA), bezafibrate (BZF), and sulfamethoxazole (SMX) in synthetic human urine using a novel mesoporous iron powder-activated persulfate system (mFe-PS system), and identified the factors limiting their degradation in synthetic human urine. A kinetic model was established to expose the radical production in various reaction conditions, and experiments were conducted to verify the modeling results. In the phosphate-containing mFe-PS system, the 120 min removal efficiency of CFA decreased from 95.1% to 76.6% as the phosphate concentration increased from 0.32 to 6.45 mmol/L, but recovered to 90.5% when phosphate concentration increased to 16.10 mmol/L. Meanwhile, the increased concentration of phosphate from 0.32 to 16.10 mmol/L reduced the BZF degradation efficacy from 91.5% to 79.0%, whereas SMX removal improved from 37.3% to 62.9%. The mFe-PS system containing (bi)carbonate, from 4.20 to 166.70 mmol/L, reduced CFA and BZF removal efficiencies from 100% to 76.8% and 80.4%, respectively, and SMX from 83.5% to 56.7% within a 120-min reaction time. In addition, alkaline conditions (pH ≥ 8.0) inhibited CFA and BZF degradations, while nonacidic pH (pH ≥ 7.0) remarkably inhibited SMX degradation. Results of the kinetic model indicated the formation of phosphate (H2PO4·/HPO4·-) and/or carbonate radicals (CO3·-) could limit pharmaceutical removal. The transformation products (TPs) of the pharmaceuticals revealed more incompletely oxidized TPs occurred in the phosphate- and (bi)carbonate-containing mFe-PS systems, and indicated that H2PO4·/HPO4·- mainly degraded pharmaceuticals via a benzene ring-opening reaction while CO3·- preferentially oxidized pharmaceuticals via a hydroxylation reaction.

Ultrasensitive Bio-H2S Gas Sensor Based on Cu2O-MWCNT Heterostructures

Developing a respiratory analysis disease diagnosis platform for the H2S biomarker has great significance for the real-time detection of various diseases. However, achieving highly sensitive and rapid detection of H2S gas at the parts per billion level at low temperatures is one of the most critical challenges for developing portable exhaled gas sensors. Herein, Cu2O-multiwalled carbon nanotube (MWCNT) heterostructures with excellent gas sensitivity to H2S at room temperature and a lower temperature were successfully synthesized by a facile two-dimensional (2D) electrodeposition in situ assembly method. The combination of Cu2O and MWCNTs via the principle of optimal conductance growth not only reduced the initial resistance of the material but also provided an ideal interfacial barrier structure. Compared to the response of the pure Cu2O sensor, that of the Cu2O-MWCNT sensor to 1 ppm of H2S increased nearly 800 times at room temperature, and the response time decreased by more than 500 s. In addition to the excellent sensitivity with detection limits as low as 1 ppb, the Cu2O-MWCNT sensor was extremely selective with low-temperature adaptability. The sensor had a response value of 80.6 to 0.1 ppm of H2S at -10 °C, which is difficult to achieve with sensors based on oxygen adsorption/desorption mechanisms. The sensor was used for the detection of real oral exhaled breath, confirming its feasibility as a real-time disease monitoring sensor. The Cu2O-MWCNT heterostructures maximized the advantages of the individual components and laid the experimental foundation for future applications of highly sensitive portable breath analysis platforms for monitoring H2S.

Carbonate-induced enhancement of phenols degradation in CuS/peroxymonosulfate system: A clear correlation between this enhancement and electronic effects of phenols substituents

This study investigated the enhancement effects of dissolved carbonates on the peroxymonosulfate-based advanced oxidation process with CuS as a catalyst. It was found that the added CO₃^2- increased both the catalytic activity and the stability of the catalyst. Under optimized reaction conditions in the presence of CO₃^2-, the degradation removal of 4-methylphenol (4-MP) within 2 min reached 100%, and this was maintained in consecutive multi-cycle experiments. The degradation rate constant of 4-MP was 2.159 min^-1, being 685% greater than that in the absence of CO₃^2- (0.315 min^-1). The comparison of dominated active species and 4-MP degradation pathways in both CO₃^2--free and CO₃^2--containing systems suggested that more CO₃•^-/¹O₂ was produced in the case of CO₃^2-deducing an electron transfer medium, which tending to react with electron-rich moieties. Meanwhile, Characterization by X-ray photoelectron spectroscopic and cyclic voltammetry measurement verified CO₃^2- enabled the effective reduction of Cu²⁺ to Cu⁺. By investigating the degradation of 11 phenolics with different substituents, the dependence of degradation kinetic rate constant of the phenolics on their chemical structures indicated that there was a good linear relationship between the Hammett constants σ_p of the aromatic phenolics and the logarithm of k in the CO₃^2--containing system. This work provides a new strategy for efficient removal of electron-rich moieties under the driving of carbonate being widely present in actual water bodies.

Effective degradation of chloramphenicol in wastewater by activated peroxymonosulfate with Fe-rich porous biochar derived from petrochemical sludge

Excess sludge produced from biological wastewater treatment plant in petroleum industry is a kind of hazardous solid waste. Converting the sludge into biochar catalysts may help to reduce its environmental risk, recover resources and increase economic efficiency. However, the role of the sludge biochar in persulfate activation remains unclear, limiting its application in removing organic pollutants from water body. In this study, metal-rich petrochemical sludge was used to produce activated sludge biochar (ASC) via a two-step method of pyrolytic carbonization (400 °C-800 °C) and subsequent KOH activation (abbreviated as ASC 400-800). The physio-chemical properties of ASC 400-800 were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) and Raman. The chloramphenicol (CAP) removal performances of ASC 400-800/peroxymonosulfate (PMS) systems were evaluated. Results showed that porous sludge biochar was successfully prepared by the two-step method. At 800 °C, the specific surface area of ASC reached the highest value of 202.92 m2 g-1. At 600-800 °C, Fe3O4, Fe0, and graphitized carbon were formed in ASC. Among ASC 400-800, ASC 800 exhibited the best CAP removal performance in ASC 800/PMS system by adsorption combined with catalytic degradation. The optimal conditions identified for 0.31 mM CAP removal were ASC 800 2.0 g L-1, PMS 6.2 mM, and pH 2.0. SO4•-, •OH, and 1O2 may contribute to CAP degradation. The degradation pathways of CAP were proposed based on the identified degradation intermediates. Overall, this study confirmed that porous biochar derived from petrochemical sludge was an effective adsorbent or PMS catalyst to remove organic pollutants from wastewater.

Phenol degradation in iron-based advanced oxidation processes through ferric reduction assisted by molybdenum disulfide

In the iron-based advanced oxidation processes (AOPs), direct use of Fe^III can be more convenient than Fe^II but the reduction of Fe^III to Fe^II is a rate-limiting step. Introducing co-catalysts with abundant reducing sites to Fe-based AOPs can be an efficient way to accelerate the Fe redox process. Herein, molybdenum disulfide (MoS₂) was used to enhance the catalytic performance of Fe³⁺/persulfate (PS) for phenol removal. In the Fe³⁺/MoS₂/PS system, 99.6 ± 0.1% of phenol was removed in 60 min, comparable to that of the Fe²⁺/PS/MoS₂ system (99.1 ± 0.3%). With the help of MoS₂, 99.3 ± 4.2% of Fe³⁺ was transformed to Fe²⁺ in 10 min, and the Fe²⁺/Fe ratio was able to be maintained at 70.0 ± 1.4% after 60 min. The rapid and complete reduction of Fe³⁺ with MoS₂ made it possible to replace Fe²⁺ by Fe³⁺, which is easier to store, transport, and use. The decrease in XPS peak area percentage of Mo(IV) and the lower valent S after reaction revealed that MoS₂ acted as an electron provider in the Fe redox cycle. Quenching experiment results indicated that the phenol removal was highly depended on the surface-bound radicals, including both SO₄^•- and ^•OH. Those results have demonstrated that ferric salts can be directly used in the Fe-based AOPs and the redox cycle could be sustained with the assistance of MoS₂.