Phosphate was generally applied as a buffer and its effect as a common water constituent has been extensively investigated in peroxymonosulfate (PMS)-contained advanced oxidation processes (AOPs), although its role remains controversial. In this study, it was surprisingly found that phosphate buffer solution (PBS) was readily to activate PMS at initial pH (pH0) of 7.0 and 8.0 with different activation pathways, and satisfactory removal efficiencies (>= 95 %) were achieved for all nine target organic refractory compounds (ORCs) especially at pH0 8.0, thus the catalytic contribution of PBS might be underestimated. Typical quenching methods, electron spin resonance (ESR) spectrum and density functional theory (DFT) calculations demonstrated that HPO42- and H2PO4- could effectively break the O-O bond of PMS, leading to the formation of different active radicals (i.e., sulfate radical, singlet oxygen, etc.) in the PBS/PMS system. The probable degradation pathway was elucidated. The toxicity of the intermediates was predicted and the biotoxicity of the treated solution was monitored. In addition, the PBS/PMS system could be well reused and maintained strong resistance and tolerance to most common inorganic ions (Cl- , NO3- , PO43- and SO42-) and natural organic matter (NOM). Overall, this work provides a promising metal-free PMS technique, highlights the overlooked roles of oxygen reactive species, and thereby deepens our understanding of PBS/PMS process in water purification.

Nonradical pathway-dominated peracetic acid (PAA) advanced oxidation processes (AOPs) with efficient degradation, strong adaptability and ecological safety, offer a promising strategy in antibiotic wastewater treatment. In this study, cobalt (Co) single-atom anchored g-C3N4 (CN) with low loading of Co, named CoCN catalyst, was successfully synthesized with a typical Co-N4 moiety and applied as a PAA activator for the oxidation of sulfadimethoxine (SDM) at a low-dose of PAA (0.04 mM). The experiments and theoretical calculations implied the formation of singlet oxygen (1O2), high-valent cobalt-oxo species (CoIV=O), surface reactive complex (CoCN-PAA*) and organic radicals (R-O center dot) during the oxidation process, and 1O2 was the dominant reactive species for the degradation of SDM. Mechanistic investigations revealed a novel nonradical pathway in PAA activation with the formation of CoCN-O* intermediate that favored 1O2 generation. The CoCN/PAA system exhibited favorable SDM degradation and detoxification, broad-spectrum degradation capability for various SAs, high durability in a continuous-flow fixed-bed reactor after 36-hour run, strong resistance to certain coexisting matter, and less than satisfied SDM removal in real water caused by the presence of HCO3-and natural organic matter (NOM). The study offers novel insights into the nonradical mechanism involved in cobalt single-atom catalyst-mediated PAA activation processes for water decontamination.

Peracetic acid (PAA)-driven advanced oxidation processes (AOPs) are increasing favored for water treatment due to their environmentally benignity and ease of activation. However, the development of low-cost and high-performance activators is still a primary challenge. In this study, Fe-doped g-C3N4 (Fe-N-C) was fabricated as an efficient peracetic acid (PAA) activator for sustainable degradation of emerging contaminants (ECs) like bisphenol A (BPA) with a removal efficiency of 97.8 %. Quite different from the reported non-radical involved catalytic studies, Fe-N-C-PAA complex (Fe(III)-OO(O)CCH3) was formed and served as the primary reactive species rather than high-valent iron-oxo species (FeV=O) and singlet oxygenation (1O2) for the oxidation of BPA on the basis of electron paramagnetic resonance (EPR) spectra, chemical quenching and probe tests, Raman spectroscopy, 18O isotope labeling tests, electrochemical analysis and density-functional theory (DFT) calculations in the Fe-N-C/PAA process. Satisfactory BPA removal efficiency can still be obtained with water matrices, in actual water, after 5 cycles of Fe-N-C, at the flow-through device with carbon felt for 120 h. BPA was successfully detoxified within 60 min and the probable degradation pathway of BPA was elucidated with the assistance of DFT calculations. The correlation between kobs and Hammett constants σ+ or half-wave potentials (φ1/2) of different organics implied that the contaminants with greater electron-donating capacity were more prone to be oxidized. This study advances the understanding of metal-PAA complex, offering novel insights into PAA activation using multiphase iron-based catalysts and their potential for practical environmental applications.

It is still controversial whether peroxydisulfate (PDS) can be efficiently activated by Fe(3+ )to remove pollutants. Herein, based on the results of density functional theory (DFT) calculations, electrochemical analysis, electron paramagnetic resonance (EPR), chemical probe and quenching experiments, this work proposed some new insights on the selective degradation of organic recalcitrant contaminants (ORCs) by Fe3+/PDS process at acidic pH conditions. DFT calculations indicated that ORCs with lower potential differences (E PD < 3.5 eV) values are more likely to be efficiently degraded, and particularly the presence of electron-donating functional groups from contaminants can enhance degradation. Fe(IV) was not the main active species for the degradation of ORCs. Sulfate radical (SO4 center dot- ), hydroxyl radical ((OH)-O-center dot) and superoxide radical (O-2(center dot-)) played different roles on the removal of various ORCs. Surprisingly, electron transfer played an important role in the removal of specific ORCs. Moreover, the impacts of environmental factors such as natural organic matter (NOM) and common inorganic anions were evaluated. The reuse of Fe3+/PDS process and its practical application in natural water were also investigated. This study provides a proof-of-concept that can be applied for PDS remediation contaminated water, and these new observations highlight the underappreciated characteristics of specific ORCs and advance our understanding of the selective-oxidative Fe3+/PDS process.

In this study, oxygen-doped graphitic carbon nitride (g-C3N4), named O-g-C3N4, was successfully fabricated and characterized, and its performance in activating peroxymonosulfate (PMS, HSO5−) for the removal of phenol, 2,4-dichlorophenol (2,4-DCP), bisphenol A (BPA), rhodamine B (RhB), reactive brilliant blue (RBB) and acid orange 7 (AO7) was evaluated. The catalytic performance of O-g-C3N4 for AO7 removal increased by 14 times compared to g-C3N4. In the presence of 0.2 g L−1 O-g-C3N4, 3.5 mM PMS at natural pH 5.8, 96.4% of AO7 could be removed in 60 min, reduced toxicity of the treated AO7 solution was obtained, and the mineralization efficiency was 47.2% within 120 min. Density functional theory (DFT) calculations showed that the charge distribution changed after oxygen doping, and PMS was more readily adsorbed by O-g-C3N4 with the adsorption energy (Eads) of −0.855 kcal/mol than that of the pristine g-C3N4 (Eads: −0.305 kcal/mol). Mechanism investigation implied that AO7 was primarily removed by the sulfate radicals (SO4•−) and hydroxyl radicals (•OH) on the surface of O-g-C3N4, but the role of singlet oxygen (1O2) to AO7 elimination was negligible. The results of cyclic experiments and catalyst characterization after reaction confirmed the favorable catalytic activity and structural stability of O-g-C3N4 particles. Furthermore, the O-g-C3N4/PMS system was very resistant to most of the environmental impacts, and AO7 removal was still acceptable in natural water environment. This study may provide an efficient metal-free carbonaceous activator with low dosage for PMS activation to remove recalcitrant organic pollutants (ROPs).

Nowadays, the treatment of residual refractory organic contaminants (ROCs) is a huge challenge for environmental remediation. In this study, a potential process is provided by copper ferrite catalyst (CuFe2O4) activated peroxymonosulfate (PMS, HSO5- in the bicarbonate (HCO3-) enhanced system for efficient removal of Acid Orange 7 (AO7), 2,4-dichlorophenol, phenol and methyl orange (MO) in water. The impact of key reaction parameters, water quality components, main reactive oxygen species (ROS), probable degradation mechanism, rational degradation pathways and catalyst stability were systematically investigated. A 95.0% AO7 (C-0 = 100 mg L-1) removal was achieved at initial pH (pH(0)) of 5.9 +/- 0.1 (natural pH), CuFe2O4 dosage of 0.15 g L-1, PMS concentration of 0.98 mM, HCO3- concentration of 2 mM, and reaction time of 30 min. Both sulfate radical (SO4-center dot) and hydroxyl radical ((OH)-O-center dot) on the surface of catalyst were proved as the predominant radical species through radical quenching experiments and electron paramagnetic resonance (EPR) analysis. The buffer nature of HCO3 was partially contributed for the enhanced degradation of AO7 under CuFe2O4/PMS/HCO3- system. Importantly, according to C-13 nuclear magnetic resonance (NMR) and EPR analysis, the positive effect of bicarbonate may be mainly attributed to the formation of peroxymonocarbonate (HCO4-), which may enhance the generation of (OH)-O-center dot. The magnetic CuFe2O4 particles can be well recycled and the leaching concentration of Cu was acceptable (<1 mg L-1). Considering the widespread presence of bicarbonate in water environment, this work may provide a safe, efficient, and sustainable technique for the elimination of ROCs from practical complex wastewater.

为研究氧掺杂石墨相氮化碳活化过一硫酸盐降解水中橙黄Ⅱ的效能和反应机理,通过一步合成法将氧掺杂至石墨相氮化碳(g-C3N4),制备了新型无金属的环保氧掺杂g-C3N4(O-g-C3N4)催化剂,并采用场发射扫描电子显微镜(FESEM)、X射线衍射仪(XRD)、傅立叶变换红外吸收光谱仪(FTIR)、Zeta电位仪和X射线光电子能谱仪(XPS)对O-g-C3N4催化剂的形貌、结构和成分进行了表征,研究了 O-g-C3N4催化剂活化过一硫酸盐(PMS)体系(即O-g-C3N4/PMS体系)对水中橙黄Ⅱ(AO7)的降解效果、影响因素和反应机理.结果表明:成功将氧原子引入到g-C3N4基体中,O-g-C3N4催化剂保持了 g-C3N4的主体结构;O-g-C3N4/PMS体系反应1 h对70 mg/L AO7的去除率可达到96.4％,是g-C3N4/PMS体系的14.9倍;AO7的去除效果随着反应体系中O-g-C3N4和PMS用量的增加而提升,随着反应体系温度的升高而增加,反应体系在初始pH值为3.00～9.00范围内均能很好地去除AO7;反应体系中的硫酸根自由基(SO4·-)和羟基自由基(HO·)尤其是O-g-C3N4催化剂表面的SO4·-和HO·对AO7的降解起主要作用.

CoFe2O4 (Cobalt ferrite, CF) nanoparticles were prepared, well characterized and applied as efficient solid catalyst in catalytic ozonation, named CF/O3 process, for the removal of emerging organic contaminants (EOCs). The degradation and mineralization of clofibric acid (CA) in CF/O3 process were dramatically enhanced in comparison with those under the O3 system. Surface hydroxyl groups (HGs) were considered as an important factor for ozone decomposition and the reactive oxygen species (ROS) on the catalyst surface were mainly responsible for CA elimination. The contribution and formation of ROS, including hydroxyl radicals (?OH), especially superoxide radicals (O2?? ), singlet oxygen (1O2), and hydrogen peroxide (H2O2) were evaluated, and a rational mechanism was elucidated accordingly. Probable degradation pathway of CA was proposed according to the organic intermediates identified. The acute toxicity of the treated solution increased during the first 15 min and then declined rapidly and nearly disappeared as the reaction proceeded. In addition, acceptable catalytic performance of CF/O3 can be obtained for the treatment of other EOCs and the treatment of natural surface water spiked with CA. This work presents an efficient and promising catalytic ozonation technique for the elimination of EOCs in complex water matrices.

Cobalt ferrite CoFe2O4 catalyst was fabricated and systematically investigated as an efficient peroxymonosulfate (PMS, HSO5-) activator for the degradation of recalcitrant organic contaminants (ROCs) in water treatment. Both SO4 center dot- and (OH)-O-center dot on the surface of catalyst were unveiled to be primarily responsible for bisphenol A (BPA) degradation by a comprehensive study using electron paramagnetic resonance (EPR), radical scavengers and quantification of SO4 center dot-, and the negligible contribution of singlet oxygen (O-1(2)) was also observed. BPA degradation was accelerated in the presence of humic acid, and it increased first but then decreased with the further addition of fulvic acid. Moreover, the presence of chloride and bicarbonate ions can enhance both BPA and TOC removal. The toxicity of the target aqueous solution ascended slowly at the early stage but then declined dramatically and almost vanished as the reaction proceeded. The removal efficiencies of other typical ROCs (clofibric acid, 2,4-dichlorophenol, etc.) and the decontamination of natural surface water spiked with BPA were also evaluated. This CoFe2O4/PMS process could be well applied as a safe, efficient, and sustainable approach for ROCs remediation in complex wastewater matrix.

A potential advanced oxidation process is provided by SBA-15 supported cobalt (Co/SBA-15) activated peroxymonosulfate (PMS, HSO5-) in the ultrasound (US) enhanced system, named Co/SBA-15/PMS/US process, for the elimination of refractory organic contaminants (ROCs) in water. This process exhibited favorable behavior with 95.5 % C.I. Acid Orange 7 (AO7) degradation using 5 mM PMS, 0.5 g/L Co/SBA-15 catalyst, 190 W US power at initial pH of 6.0 after 90 min reaction. Co/SBA-15 particles remained satisfied catalytic activity and stability with very low level of cobalt release in 10 successive cycles. The scavenge tests and electron paramagnetic resonance (EPR) result as well as the cobalt leaching concentration revealed that the reactive radicals (SO4 center dot- and (OH)-O-center dot) on catalyst surface were primarily responsible for AO7 oxidation, and a rational mechanism was elucidated accordingly. The presence of chloride ions and bicarbonate could improve AO7 removal. The probable pathway of AO7 degradation was proposed based on the intermediates identified. This Co/SBA-15/PMS/US process could be well applied for the destruction of other typical ROCs (bisphenol A, clofibric acid, and rhodamine B) and the treatment of lake and river water spiked with AO7, and this study may provide an efficient PMS technique for the remediation of ROCs in water.

Visible (Vis) light (>= 420 nm) response ZnFe2O4 photocatalyst was successfully fabricated via a facile reduction-oxidation method and its catalytic activity was demonstrated by the pronounced Orange II decolorization under Vis/ZnFe2O4/PS (persulfate, S2O82-) process. The reaction kinetics, degradation mechanism, catalyst stability, and mineralization as well as the toxicity, were detailed investigated. On the basis of the effects of radical scavengers, the sulfate radical (SO4 center dot-) is regarded as the predominant reactive oxidants for the Orange II decolorization, while the hydroxyl radical ((OH)-O-center dot) is also involved. A possible pathway is proposed according to the intermediates determined by GC-MS. The ZnFe2O4 catalyst maintained high activity and stability with very low iron and zinc leaching during the repeated experiments. At initial pH 6.0, the total organic carbon (TOC) and chemical oxygen demand (COD) removal efficiencies at 300 min were 50.5% and 78.6%, respectively, using 0.5 g/L. ZnFe2O4 dosage, 1.0 g/L, persulfate, and a 150 W visible light lamp. Toxicity experiments with activated sludge implied that the toxicity of the treated solution increased at the first stage but then declined as the reaction proceeded. (C) 2016 Elsevier B.V. All rights reserved.

The removal of Orange II by activation of persulfate (S2O8(2-), PS) using synthesized Fe/SBA-15 in the electrochemical (EC) enhanced process was reported in this study. The reaction rate constants, degradation mechanism, catalyst stability, and evolution of mineralization and toxicity were detailed investigated. On the basis of radical scavenger results, both the sulfate radicals (SO4(-)) and hydroxyl radicals (OH) were responsible for the degradation of Orange II. A possible pathway is suggested to describe the degradation of Orange II according to the degradation intermediates identified. The results showed that the Fe/SBA-15 catalyst maintained strong reusability and stability with a low level of iron leaching. In addition, favorable mineralization efficiency in terms of COD removal efficiency (75.4%) and TOC removal efficiency (46.3%) was obtained when the reaction time was prolonged to 24h. The toxicity experiments implied that the toxicity of the treated solution ascended at the first 30min but then dropped to almost zero eventually. This study provides a proof-of-concept that can be applied widely for the PS remediation of contaminated water.

Granular activated carbon (GAC) supported cobalt catalyst (Co-GAC) was prepared and used as heterogeneous catalyst for the activation of peroxydisulfate (PS, <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="tdwt_a_923194_ilm0001.gif"></inline-graphic>) under UV irradiation. The effects of some important reaction parameters such as PS concentration, catalyst addition, reaction temperature, and initial pH on the degradation of Acid Orange 7 (AO7) at neutral pH were investigated. Results showed that the decolorization efficiency by Co-GAC/PS process is enhanced in the presence of UV irradiation. The decolorization efficiency increased with the increase of PS concentration, catalyst addition, and reaction temperature, but decreased with the increase of initial pH. The decolorization efficiency was 96.2% and the chemical oxygen demand removal efficiency was 38.5% when initial pH value was 7, PS concentration was 1.0g/L and catalyst dosage was 0.8g/L.

In this study, a visible (Vis) light response photocatalyst was synthesized via a simple reduction-oxidation method. The structure, morphology and optical properties of the catalyst were well characterized. The absorption capability of ZnFe2O4 in visible-light region was demonstrated by the high rate of Orange II decolorization under Vis/ZnFe2O4/H2O2 process. Guided by studies to explore the effects of radical scavengers and to quantify the yield of hydroxyl radical ((OH)-O-center dot) production, (OH)-O-center dot on the surface of the catalyst was found to be the dominating reactive species for the Orange II removal. Moreover, ZnFe2O4 maintained high activity, crystallinity and extremely low iron and zinc leaching during repeated experiments. The intermediate products were identified by GC-MS and a possible pathway is accordingly proposed to elucidate the mechanism of Orange II degradation by (OH)-O-center dot. In addition, high extent of mineralization was obtained as the chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiencies were 86.6% and 60.4%, respectively, within 60 min reaction. The toxicity tests with activated sludge indicated that the toxicity of the solution increased during the first 30 min but then decreased significantly as the oxidation proceeded. (C) 2015 Elsevier B.V. All rights reserved.

Mesoporous silica SBA-15 supported iron and cobalt (Fe-Co/SBA-15) was prepared and used as catalyst in the ultrasound (US) enhanced heterogeneous activation of peroxymonosulfate (PMS, HSO5(-)) process. The effects of some important reaction parameters on the removal of Orange II by US/Fe-Co/SBA-15/PMS process were investigated. The results indicated that the removal rate of Orange II was not significantly affected by the initial pH, and it increased with the higher PMS concentration, reaction temperature, Fe-Co/SBA-15 dosage and ultrasonic power. Furthermore, sulfate radicals (SO4(-)) were assumed to be the dominating reactive species for the Orange II decolorization. Moreover, the Fe-Co/SBA-15 catalyst showed high activity during the repeated experiments. The intermediate products were identified by GC-MS, thereby a plausible degradation pathway is proposed. In addition, the chemical oxygen demand (COD) removal efficiencies at 2 and 24h were 56.8% and 80.1%, respectively and the corresponding total organic carbon (TOC) removal efficiencies were 33.8 and 53.3%. Finally, toxicity tests with activated sludge showed that the toxicity of the solution increased during the first stage and then decreased significantly with the progress of the oxidation.

Bimetallic Fe-Co/GAC (granular activated carbon) was prepared and used as heterogeneous catalyst in the ultrasound enhanced heterogeneous activation of peroxydisulfate (PS, S2O(2-)8) process. The effect of initial pH, PS concentration, catalyst addition and stirring rate on the decolorization of Acid Orange 7 (AO7) was investigated. The results showed that the decolorization efficiency increased with an increase in PS concentration from 0.3 to 0.5 g/L and an increase in catalyst amount from 0.5 to 0.8 g/L. But further increase in PS concentration and catalyst addition would result in an unpronounced increase in decolorization efficiency. In the range of 300 to 900 r/min, stirring rate had little effect on AO7 decolorization. The catalyst stability was evaluated by measuring decolorization efficiency for four successive cycles.

The removal of Acid Orange 7 by zero-valent iron (Fe-o) activated sodium persulfate (Na2S2O8, PS) in the presence of ultrasonic irradiation (US) was performed in this study. The effects of persulfate concentration, zero valent iron addition, ultrasonic power and initial pH on the decolorization rate of Acid Orange 7 were investigated. The results showed that the decolorization rate increased with an increase in persulfate concentration from 0.1 to 0.5 g/L, an increase in zero valent iron amount from 0.1 to 0.5 g/L, and an increase in ultrasonic power from 40 to 60 W. But further increase in persulfate concentration, zero valent iron addition and ultrasonic power would result in an unpronounced increase of decolorization rate. The optimal initial pH for decolorization was found as 5.8. The maximum decolorization efficiency of 96.4% was achieved within 20 min with persulfate concentration of 0.3 g/L, zero valent iron concentration of 0.5 g/L, initial pH value of 5.8 and ultrasonic power of 60 W. (C) 2013 Elsevier B.V. All rights reserved.

Activated-carbon-supported iron oxides were prepared and used as a catalyst in an integrated ultrasound/heterogeneous Fenton process for the decolorization of Crystal Violet. A synergistic effect was observed when ultrasound was combined with the heterogeneous Fenton process. The decolorization efficiency increased with the increasing power density and catalyst dosage, but decreased with the increase of initial pH value. There exists an optimal hydrogen peroxide concentration for decolorization. Catalyst stability was evaluated by measuring iron leaching in solution. The decolorization efficiency was 88% under the optimal conditions. Toxicity test with Daphnia magna showed that the acute toxicity of dye solution decreased significantly after the treatment by the heterogeneous sono-Fenton process.