FeS redox power motor for PDS continuous generation of active radicals on efficient degradation and removal of diclofenac: Role of ultrasonic

LED illumination-assisted activation of peroxydisulfate by heterogeneous Cu2S under alkaline condition for efficient organic pollutants removal

The copper-based materials were considered as promising catalysts for the activation of peroxydisulfate (PDS), but the study on the Cu2S-activated PDS under LED illumination and alkaline condition was little reported. In this work, Cu2S, a simple and readily available heterogeneous catalyst, was employed to enhance the activation of PDS under alkaline condition through LED illumination. The results indicated that under LED illumination, the degradation rate of tetracycline (TC) during the first 15 min was 3.55 times higher than that of the darkness. A series of important influencing factors were optimized, including anions, humic acid and complex water matrices. The results showed that the Cu2S/PDS/LED system exhibited excellent adaptability. Besides, the Cu2S maintained a good stability. The quenching experiments and electron spin resonance analysis demonstrated that the electron transfer and singlet oxygen were two primary pathways for the degradation of TC, and also other species such as sulfate and hydroxyl radicals played important roles. Furthermore, X-ray photoelectron spectroscopy characterization and a series of experiments confirmed that the Cu+ was the primary catalytic active sites, while the reductive sulfur species could directly activate PDS and accelerate the circulation of Cu2+/Cu+. The toxicity test proved that the toxicity of TC was decreased after the degradation. This study not only highlighted the potential of the Cu2S/PDS/LED system for efficient TC degradation under alkaline condition but also provided new insight for the development of Cu-based catalytic technology.

CuFeS2/GAC particle combined with electrochemical activation of persulfates for efficient degradation of carbamazepine

Electrochemically activated persulfate is a potential advanced oxidation process due to its advantages of environmental friendliness, high efficiency, and convenient operation. An Fe-Cu-S granular activated carbon (CuFeS2/GAC, abbreviated as FCSG) particles electrode was developed and applied to degrade carbamazepine (CBZ) combined with electrochemical activation of persulfate (E-PDS-FCSG) in this work. Compared to two-dimensional electrochemical process (E-PDS), the three-dimensional (3D) E-PDS-FCSG process exhibited higher removal efficiency of CBZ and lower energy consumption. The removal efficiency of CBZ and power consumption increased by 96% and reduced by 67%, respectively. Over 98% of CBZ removal rate was reached within 25 min. Apart from the same free radicals in two-dimensional electrochemical process, both Fe2+ and Cu+ on the surface of three-dimensional particle electrodes can directly activate PDS to produce SO4•-, and the existence of S2- strengthens the circulation of Fe3+/Fe2+ and Cu2+/Cu+. Furthermore, FCSG particle electrode can not only directly enhance the activation of PDS, but also accelerate the electron transfer, and then effectively promoting reactive species generation. LC-MS analysis showed that the main degradation pathways of CBZ involved decarbonylation, deamination, dealkylation, ring opening and mineralization. Moreover, after five cycle experiments, over 80% of CBZ removal rate could be achieved, demonstrating that the E-PDS-FCSG system had excellent electrocatalytic performance and good stability. These findings indicate that FCSG is a promising material and could be used as a particle electrode for removing organic pollutants from water.

Efficient degradation of sulfonamides by introducing sulfur to magnetic Prussian blue analog in photo-assisted persulfate oxidation system

The peroxynitrite photocatalytic degradation system was considered a green, convenient, and efficient water treatment process, but not satisfying against some antibiotics, e.g. sulfonamides (SAs). To improve the photocatalytic degradation efficiency of SAs, sulfur was introduced to a magnetic Fe-MOF (Fe-metal organic framework) Prussian blue analog to achieve a heteroatomic material CuFeO@S, which was applied in heterogeneous visible light photo-assisted catalytic process with persulfate (PS) as an oxidant. The characterization results of CuFeO@S by XRD and XPS confirmed the presence of Fe3O4 (for magnetic separation), Cu+ (for activation of PS) and S2- (for narrowing the energy band and prolonging the lifetime of photo-generated electronics). Through systematic optimization of reaction conditions in CuFeO@S + PS + hv system, efficient degradation of four tested SAs was achieved in 30 min (removal rate of 97-100% for the tested 4 SAs). Moreover, the material could be magnetically recycled and reused for over 7 cycles with a removal rate of >90% for sulfamerazine. Furthermore, the removal rate of sulfamerazine in pond water reached 99% at a mineralization rate of about 34% (decrease in total organic matter), demonstrating its potential in the treatment of antibiotic-containing wastewater.

Removal of total petroleum hydrocarbons from oil-based drilling cuttings by a heat activation persulfate-based process

Oil-based drilling cuttings (OBDC) are typical hazardous wastes generated during shale gas extraction. In this study, two persulfate-based advanced oxidation processes (AOPs), heat/PMS and heat/PDS, have been used to treat OBDC. The results showed that for the heat/PMS process, within a certain range, the oxidant dosage, temperature, and reaction time were significantly positively correlated with the degree of total petroleum hydrocarbon (TPH) removal. When these parameters were increased from their initial values to 3.57 mmol/g, 70°C, and 80 min, respectively, TPH removal rates increased significantly, by 20.95%, 18.68%, and 16.41%, respectively. However, further increases in these parameters had little effect on the TPH removal rate. Similar observations were made for the heat/PDS process. There are other differences between the two processes, including that the heat/PDS process required less oxidant to reach an effective activation state than the heat/PMS process, but required a higher temperature and a longer reaction time. Fourier-transform infrared spectrometry and gas chromatography-mass spectrometry have shown that both processes could effectively remove the light components of linear paraffins contained in OBDC. The heat/PMS process performed significantly better than the heat/PDS process in removing aromatic hydrocarbons and long-chain alkanes. Scanning electron microscopy, energy-dispersive spectrometry, and X-ray diffraction analysis implied that the elemental and mineral compositions of OBDC were not significantly modified by reaction in the heat/PMS and heat/PDS processes. This study may provide theoretical support for the technological development of heat activation and persulfate-based AOPs to remove TPH from OBDC.

Lab-scale transport and activation of peroxydisulfate for phenanthrene degradation in soil: A comprehensive assessment of the remediation process, soil environment and microbial diversity

Electrokinetic transport followed by electrical resistance heating activation of peroxydisulfate is a novel in situ soil remediation method. However, the strategy of electrokinetic transport coupled with electrical resistance heating and the comprehensive evaluation of restored soil need to be further explored. In this study, a lab-scale simulation device for in situ electrokinetic transport coupled with electrical resistance heating activation of peroxydisulfate was constructed to monitor the transport and transfer of peroxydisulfate, target pollutants, and process parameters, and the physicochemical properties and bacterial community of treated soil were evaluated. The results showed that adding 10 wt% peroxydisulfate to both the anode and cathode resulted in the optimized transfer rate and cumulative concentration of peroxydisulfate under electrokinetics. After 8 h, the cumulative concentration of peroxydisulfate reached 66.15- 166.29 mmol L-1, which was attributed to the migration of a large amount of S2O82- from the cathode to the soil under electromigration. Additionally, the anodic interfacial electric potential was improved, which was more conducive to electroosmotic transport of peroxydisulfate from the anode chamber. By alternating electrokinetic transport and electrical resistance heating activation of peroxydisulfate for two cycles, the phenanthrene degradation efficiency in four evenly distributed wells between electrodes reached 75.4 %, 87.6 %, 92.3 %, and 94.4 %. With slight variations in soil morphology and structure, the electrokinetic transport coupled with electrical resistance heating activation of peroxydisulfate elevated the soil fertility index. The abundance and diversity of bacterial communities in treated soil recovered to above the original soil level after 15 days. Our findings may support the application of electrokinetic transport coupled with electrical resistance heating activation of peroxydisulfate as a promising green ecological technology for the in situ remediation of organic-contaminated soil.

Simultaneous oxidation of roxarsone and adsorption of released arsenic by FeS-activated sulfite

The conventional oxidation-adsorption methods are effective for the removal of roxarsone (ROX) but are limited by complicated operation, toxic residual oxidant and leaching of toxic metal ions. Herein, we proposed a new approach to improve ROX removal, i.e., using the FeS/sulfite system. Experimental results showed that approximately 100% of ROX (20 mg/L) was removed and more than 90% of the released inorganic arsenic (As(V) dominated) was adsorbed on FeS within 40 min. This FeS/sulfite system was a non-homogeneous activation process, and SO₄^·-, ·OH and ¹O₂ were identified as reactive oxidizing species with their contributions to ROX degradation being 48.36%, 27.97% and 2.64%, respectively. Based on density functional theory calculations and HPLC-MS results, the degradation of ROX was achieved by C-As breaking, electrophilic addition, hydroxylation and denitrification. It was also found that the released inorganic arsenic was adsorbed through a combination of outer-sphere complexation and surface co-precipitation, and the generated arsenopyrite (FeAsS), a precursor to ecologically secure scorodite (FeAsO₄·2H₂O), was served as the foundation for further inorganic arsenic mineralization. This is the first attempt to use the FeS/sulfite system for organic heavy metal removal, which proposes a prospective technique for the removal of ROX.

Synergistic activation of persulfate by FeS@SBA-15 for imidacloprid degradation: Efficiencies, activation mechanism and degradation pathways

In this work, FeS supported SBA-15 mesoporous silica catalyst (FeS@SBA-15) was synthesized successfully, characterized and first applied to persulfate (PS) activation for the degradation of imidacloprid in wastewater. The as-prepared 3.5-FeS@SBA-15 presented an impressive imidacloprid removal efficiency of 93.1% and reaction stoichiometric efficiency (RSE) of 1.82% after 5 min, ascribed to the synergetic effects of improved FeS dispersion and abundant surface sites by SBA-15. Electron paramagnetic resonance spectra and quenching experiments proved that both SO4·- and ·OH were produced in FeS@SBA-15/PS system, and SO4·- played a dominant role in the degradation process. The S2- can accelerate the cycling of Fe(III)/Fe(II) during activation and increase the steady-state concentration of Fe(II). More importantly, the constructed heterogeneous system exhibited an efficient and stable catalytic activity over a wide range of pH (3.0-9.0), temperature (283K-313K), inorganic ion (NO3-) and humic acid (1-20 mg/L). Moreover, the density functional theory calculations were conducted to predict the potential reaction sites of imidacloprid. Based on eighteen identified intermediates, four main degradation pathways were proposed: hydroxylation, dechlorination, hydrolysis, and the ring cleavage of the imidazolidine. ECOSAR analysis indicated hydroxylation and dechlorination played a key role in the detoxification of the formed compounds. These findings would provide new insights into the application of FeS@SBA-15 catalyst in wastewater treatment and the removal mechanism of imidacloprid from wastewater.

Promoted elimination of metronidazole in ferrous ions activated peroxydisulfate process by gallic acid complexation

We applied gallic acid (GA) as the complexing agent to stabilizing the regeneration of Fe²⁺ during the Fe²⁺/peroxydisulfate (PDS) Fenton-like reaction for promoting the removal of metronidazole (MTZ). This research evaluated the elimination of MTZ by optimizing the dose of GA and Fe²⁺ and pH condition. MTZ removal reached 83% at the GA: Fe²⁺ molar ratio of 1:1 (30 μM) and initial pH 5 and 6.2 after 120 min, and the kinetics showed two degradation phases (k_obs1 = 0.09636 for the rapid stage and k_obs2 = 0.01056 for the slow stage). The Fe²⁺ and GA complexes could expand the range of pH applicability and effectively stabilize the regeneration of Fe²⁺, which ultimately promoted the decontamination of MTZ. Sulfate radical (SO₄^.-), hydroxyl radicals, and singlet oxygen were proved to exist in this ternary system and contribute to MTZ removal, and SO₄^.- played the dominant role. Furthermore, the possible pathways and mechanisms for MTZ degradation were proposed, and the simulation result indicated that the toxicity of degradation intermediates of MTZ were declined. The GA assisted Fe²⁺/PDS system provided an improved promising advanced oxidation process for organic wastewater disposal.

Enhanced SO2 Resistance of Cs-Modified Fe-HZSM-5 for NO Decomposition

Direct decomposition of NO into N2 and O2 is an ideal technology for NOx removal. Catalyst deactivation by sulfur poisoning is the major obstacle for practical application. This paper focuses on strengthening the SO2 resistance of metal-exchanged HZSM-5 catalysts, by investigating the metals, promoters, preparation methods, metal-to-promoter molar ratios, Si/Al ratios and metal loadings. The results show that in the presence of SO2 (500 ppm), Fe is the best compared with Co, Ni and Cu. Cs, Ba and K modification enhanced the low-temperature activity of the Fe-HZSM-5 catalyst for NO decomposition, which can be further improved by increasing the exchanged-solution concentration and Fe/Cs molar ratio or decreasing the Si/Al molar ratio. Interestingly, Cs-doped Fe-HZSM-5 exhibited a high NO conversion and low NO2 selectivity but a high SO2 conversion within 10 h of continuous operation. This indicates that Cs-Fe-HZSM-5 has a relatively high SO2 resistance. Combining the characterization results, including N2 physisorption, XRD, ICP, XRF, UV–Vis, XPS, NO/SO2-TPD, H2-TPR and HAADF-STEM, SO42− was found to be the major sulfur species deposited on the catalyst’s surface. Cs doping inhibited the SO2 adsorption on Fe-HZSM-5, enhanced the Fe dispersion and increased the isolated Fe and Fe-O-Fe species. These findings could be the primary reasons for the high activity and SO2 resistance of Cs-Fe-HZSM-5.