Efficient degradation of carbamazepine in a neutral sonochemical FeS/persulfate system based on the enhanced heterogeneous-homogeneous sulfur-iron cycle

Treatment of landfill leachate by combined use of ultrasound and photocatalytic process using fly ash as catalyst

Advanced oxidation processes, such as sonophotocatalysis and photocatalysis, have been proven to be interesting alternatives for the effective treatment of old landfill leachates. Since there is no specific information about which parameters help to improve the treatment efficiency when using fly ash (FA) in a sonophotoreactor, this research focuses on evaluating the use of an ultrasound process (US) combined with a photo-Fenton process, with FA as a catalyst for the first time. The removals of colour, chemical oxygen demand (COD), and aromatic compounds (UV 254) present in landfill leachates were studied using a factorial design, where the effect of different loads of FA (1, 1.5, and 2 g FA/L), pH (pH = 3, 6, and 8.9), and US frequency irradiation (576, 864, and 1138 kHz) on the efficiency of photo-Fenton was evaluated. The highest removals of COD (40.7%), colour (36.8%), and UV 254 (50.8%) were achieved adjusting the pH to 3, adding 2 g of FA/L, and applying 576 kHz of US frequency. It was found that pH is the parameter that has the highest effect on pollutant removal (95% confidence level). In addition, the removals of COD, colour, and UV 254 increased at lower pH values and US frequency. Also, the presence of Fe2O3, SiO2, and TiO2 in the FA under UV irradiation and ultrasound process, improved the removal of complex organic matter present in the landfill leachate, where HO• was the most important radical.

Sulfur-doped α-Fe2O3 as an efficient and recycled peroxydisulfate activator toward organic pollutant degradation: performance and mechanism

Sulfur (S)-doped α-Fe2O3 has been regarded as an excellent catalyst for eliminating organic pollutants in the photo-Fenton-like reaction. Yet, the synthetic complexity and extremely low activity in the dark Fenton-like reaction still need to be solved. In this study, magnetic α-Fe2O3 with sulfide was successfully fabricated via hydrothermal and calcination processes, for the first time, where thiourea acted as both S source and reducing agent, and then, it was applied for activating peroxydisulfate (PDS) to degrade organic contaminants. Important influencing factors were systemically investigated, and the results showed that this catalyst activating PDS was highly effective in the removal of organic pollutants in dark- and photo-Fenton-like reactions. In addition, the catalyst possessed good stability and recyclable ability. The structure of catalyst was analyzed by several characterizations, such as XRD and XPS. The results revealed that sulfide had an important effect on the structure and performance of α-Fe2O3. The detected mechanism indicated that the main reactive oxygen species were altered after switching from darkness to LED illumination. This work offered a promising method to rationally design for S/α-Fe2O3 in the environmental remediation.

Ultrasound enhanced destruction of tetracycline hydrochloride with peroxydisulfate oxidation over FeS/NBC catalyst: Governing factors, strengthening mechanism and degradation pathway

In this study, FeS/N-doped biochar (NBC) derived from the co-pyrolysis of birch sawdust and Mohr's salt was applied to evaluate the efficiency of catalyzed peroxydisulfate (PDS) oxidation for tetracycline (TC) degradation. It is found that the combination of ultrasonic irradiation can distinctly enhance the removal of TC. This study investigated the effects of control factors such as PDS dose, solution pH, ultrasonic power, and frequency on TC degradation. Within the applied ultrasound intensity range, TC degradation increases with increasing frequency and power. However, excessive power can lead to a reduced efficiency. Under the optimized experimental conditions, the observed reaction kinetic constant of TC degradation increased from 0.0251 to 0.0474 min-1, with an increase of 89%. The removal ratio of TC also increased from ∼85% to ∼99% and the mineralization level from 45% to 64% within 90 min. Through the decomposition testing of PDS, reaction stoichiometric efficiency calculation, and electron paramagnetic resonance experiments, it is shown that the increase in TC degradation of the ultrasound-assisted FeS/NBC-PDS system was attributed to the increase in PDS decomposition and utilization, as well as the increase in SO4•- concentration. The radical quenching experiments showed that SO4•-, •OH, and O2•- radicals were the dominant active species in TC degradation. TC degradation pathways were speculated according to intermediates from HPLC-MS analysis. The test of simulated actual samples showed that dissolved organic matter, metal ions, and anions in waters can undercut the TC degradation in FeS/NBC-PDS system, but ultrasound can significantly reduce the negative impact of these factors.

Hydroxyl radical dominated ibuprofen degradation by UV/percarbonate process: Response surface methodology optimization, toxicity, and cost evaluation

Ibuprofen (IBP) is a typical nonsteroidal anti-inflammatory drug with a wide range of applications, large dosages, and environmental durability. Therefore, ultraviolet-activated sodium percarbonate (UV/SPC) technology was developed for IBP degradation. The results showed that IBP could be efficiently removed using UV/SPC. The IBP degradation was enhanced with prolonged UV irradiation time, with the decreasing IBP concentration and the increasing SPC dosage. The UV/SPC degradation of IBP was highly adaptable to pH ranging from 4.05 to 8.03. The degradation rate of IBP reached 100% within 30 min. The optimal experimental conditions for IBP degradation were further optimized using response surface methodology. IBP degradation rate reached 97.3% under the optimal experimental conditions: 5 μM of IBP, 40 μM of SPC, 7.60 pH, and UV irradiation for 20 min. Humic acid, fulvic acid, inorganic anions, and natural water matrix inhibited the IBP degradation to varying degrees. Scavenging experiments of reactive oxygen species indicated that hydroxyl radical played a major role in the UV/SPC degradation of IBP, while carbonate radical played a minor role. Six IBP degradation intermediates were detected, and hydroxylation and decarboxylation were proposed as the primary degradation pathways. An acute toxicity test, based on the inhibition of luminescence in Vibrio fischeri, indicated that the toxicity of IBP during UV/SPC degradation decreased by 11%. An electrical energy per order value of 3.57 kWh m^-3 indicated that the UV/SPC process was cost-effective in IBP decomposition. These results provide new insights into the degradation performance and mechanisms of the UV/SPC process, which can potentially be used for practical water treatment in the future.

Application of FeS-activated persulfate oxidation system for the degradation of tetracycline in aqueous solution

Tetracycline (TC), an antibiotic used to treat bacterial infectious diseases, is easily transferred to environmental matrixes and then sparks environmental concerns. In this study, TC was selected as a target pollutant to investigate the degradation performance of persulfate (PS) based advanced oxidation processes (AOPs) using FeS as the activator (FeS/PS). The results showed that with optimal PS and FeS concentrations of 1 mM and a pseudo-second-order rate constant (k₂) of 3.45 L mmol^-1 min^-1, 91.39% of TC, was effectively removed within 60 min. From the perspective of degradation rate, apart from CO₃^2-, TC decompositions by FeS/PS were hardly disturbed by the coexistence of different concentrations of Cl^-, NO₃^-, SO₄^2-, and humin acid. The degradation of TC under the O₂ bubbling, N₂ bubbling, and light-proof conditions also had limited effects on these AOPs. In addition, FeS exhibited excellent stability and recyclability when used as a PS activator for TC removal. The PS activated by old FeS and used FeS showed nearly identical performances on TC removal compared with the fresh FeS. It is suggested that homogeneous and heterogeneous reactions are jointly responsible for TC oxidation by FeS/PS. With the contributions of the generated, highly reactive SO₄^-•, and, in particular, •OH, TC enabled the mineralization of inorganic products eventually. Therefore, FeS/PS is highly recommended as an alternative AOPs in the future for TC-contaminated wastewater purification.

Deep oxidation of norfloxacin by the electrochemical enhanced heterogeneous catalytic oxidation: The role of electric field and reaction optimization

In this study, electrochemical (EC_G-G: graphite anode and cathode, EC_I-G: iron anode and graphite cathode) enhanced heterogeneous activation of peroxymonosulfate (PMS) by CoFe₂O₄ nanoparticles for the degradation of norfloxacin (NOR) in water was investigated. Although a higher NOR removal efficiency was achieved in EC_I-G/CoFe₂O₄/PMS system, the generation of Fe³⁺ had resulted in the deposition of iron mud and affect the recovery of CoFe₂O₄. Under the optimum reaction conditions of CoFe₂O₄/PMS system, the final removal efficiency of NOR did not show significant difference in EC_G-G/CoFe₂O₄/PMS system (96.0%) and CoFe₂O₄/PMS system (95.5%), but the value of apparent rate constant significantly increased in EC_G-G/CoFe₂O₄/PMS system (0.21 min^-1) compared with CoFe₂O₄/PMS system (0.11 min^-1). Similar NOR degradation pathways were obtained in these two systems, and the TOC removal efficiency in EC_G-G/CoFe₂O₄/PMS system (28.8%) is almost as low as CoFe₂O₄/PMS system (26.0%). Therefore, it can be proposed that the applied electric field through active electrodes can accelerate the reaction of heterogeneous catalytic oxidation, but does not participate much in NOR degradation. However, the TOC removal efficiency (30 min) could be reached 68.7% as the mass ratio of PMS to CoFe₂O₄ increased to 5:1 (250 mg L^-1: 50 mg L^-1). The EC_G-G/CoFe₂O₄/PMS system is a promising low-cost technique for efficient mineralization of antibiotics in wastewater.

Surface facet Fe2O3-based visible light photocatalytic activation of persulfate for the removal of RR120 dye: nonlinear modeling and optimization

Photocatalytic activation of persulfate (PS) is recently emerged as an energy-efficient and environmentally sustainable approach for pollutants degradation, which enables to leverage the strengths of low-cost solar energy and heterogeneous catalysis. Herein, we investigated the photocatalytic decomposition of reactive red 120 (RR120) dye using PS-activated Fe₂O₃ nanoparticles and elucidated the effect of their facets, α-Fe₂O₃ (001), β-Fe₂O₃ (100), and γ-Fe₂O₃ (111). β-Fe₂O₃ not only boosted the charge carrier separation but also provided more active sites for PS activation resulting in 6- and 3.5-fold higher photocatalytic activities compared to α-Fe₂O₃ and γ-Fe₂O₃, respectively. Response surface methodology and artificial neural network coupled with genetic algorithm models were utilized to optimize and foresee Fe₂O₃/PS system under visible light. Almost 100% color removal and 82% organic removal were observed under the optimum conditions at 20 mg/L RR120, 22 mg/L β-Fe₂O₃, 18 mg/L PS, and pH: 3. Scavenger test indicated that both sulfate and hydroxyl radicals are responsible for the observed RR120 removal. Although cell viability test indicated that cytotoxicity of wastewater is not significantly reduced after treatment. All the results proposed that β-Fe₂O₃/PS at relatively low doses has a great potential to decompose and mineralize recalcitrant dyes in wastewater under invisible light.