The aqueous degradation of butylated hydroxyanisole by UV/S2O8(2-): study of reaction mechanisms via dimerization and mineralization

Remediation of diesel contaminated soil by using activated persulfate with Fe3O4 magnetic nanoparticles: effect and mechanisms

In this study, Fe3O4 magnetic nanoparticles (Fe3O4 MNPs) were assessed for their ability to enhance the activity of persulfate (PS). Various controlling factors including PS dosages, initial pH, water-soil ratio, ratio of Fe2+, and Fe3O4 MNPs to PS were considered in both the Fe2+/PS system and the Fe3O4 MNPs/PS system. Results showed that the Fe3O4 MNP-activated PS system exhibited high processing efficiency owing to the gradual release of Fe2+. This process occurred in a wide pH range (5-11), attributed to the synergistic action of sulfate radicals (SO4-·) and hydroxyl radicals (OH·) under alkaline conditions, effectively mitigating soil acidification. The ratio of Fe3O4 MNPs to PS and water-soil ratio significantly influenced the degradation rate with the highest petroleum hydrocarbon degradation rate exceeding 80% (82.31%). This rate was 3.1% higher than that achieved by the Fe2+/PS system under specific conditions: PS dosage of 0.05 mol/L, Fe3O4 MNPs to PS ratio of 1:10, water-soil ratio of 2:1, and initial pH of 11. Meanwhile, oxidant consumption in the Fe3O4 MNPs/PS system was halved compared to the Fe2+/PS system due to the slow release of Fe2+ and less ineffective consumption of SO4-·. Mechanistically, the possible degradation process was divided into three parts: the initial chain reaction, the proliferating chain reaction, and the terminating chain reaction. The introduction of Fe3O4 MNPs accelerated the degradation rate of pentadecane, heneicosane, eicosane, tritetracontane, and 9-methylnonadecane.

A comparative study on Fe(III)/H2O2 and Fe(III)/S2O82- systems modified by catechin for the degradation of atenolol

The processes of Fe(III) activated persulfate (PS) and H₂O₂ modified by catechin (CAT) had been shown to be effective in degrading contaminants. In this study, the performance, mechanism, degradation pathways and products toxicity of PS (Fe(III)/PS/CAT) and H₂O₂ (Fe(III)/H₂O₂/CAT) systems were compared using atenolol (ATL) as a model contaminant. 91.0% of ATL degradation was reached after 60 min in H₂O₂ system which was much higher than that in PS system (52.4%) under the same experimental condition. CAT could react directly with H₂O₂ to produce small amounts of HO^• and the degradation efficiency of ATL was proportional to CAT concentration in H₂O₂ system. However, the optimal CAT concentration was 5 μM in PS system. The performance of H₂O₂ system was more susceptible to pH than that of PS system. Quenching experiments were conducted indicating that SO₄^•- and HO^• were produced in PS system while HO^• and O₂^•- accounted for ATL degradation in H₂O₂ system. Seven pathways with nine byproducts and eight pathways with twelve byproducts were put forward in PS and H₂O₂ systems respectively. Toxicity experiments showed that the inhibition rates of luminescent bacteria were both decreased about 25% after 60 min reaction in two systems. Although the software simulation result showed few intermediate products of both systems were More toxic than ATL, but the amounts of them were 1-2 orders of magnitude lower than ATL. Moreover, the mineralization rates were 16.4% and 19.0% in PS and H₂O₂ systems respectively.

Fe3+-cysteine enhanced persulfate fenton-like process for quinclorac degradation: A wide pH tolerance and reaction mechanism

A green, high-efficiency, and wide pH tolerance water remediation process has been urgently acquired for the increasingly exacerbating contaminated water. In this study, a Fe³⁺/persulfate (Fe³⁺/PS) system was employed and enhanced with a green natural ligand cysteine (Cys) for the degradation of quinclorac (QNC). The introduction of Cys into the Fe³⁺/PS system widened the effective pH range to 9 with a superior removal rate for QNC. The mechanism revealed that the Fe³⁺/Cys/PS system can enhance the ability of degrading QNC by accelerating the Fe³⁺/Fe²⁺ redox cycle, maintaining Fe²⁺ concentration and thereby generating more HO^• and SO₄^•-. The impact factors (i.e., pH, concentrations of PS, Fe³⁺ and Cys) were optimized as well. This work provides a promising strategy with high catalytic activity and wide pH tolerance for organic contaminated water remediation.

Effective degradation of tetracycline via recyclable free-standing three-dimensional copper-based graphene as a persulfate catalyst

Water pollution by antibiotics is a serious and growing problem. Given this challenge, a free-standing three-dimensional (3D) reduced graphene oxide foam supported copper oxide nanoparticles (3D-rGO-Cu_xO) was synthesized using GO as a precursor and applied as an efficient persulfate activator for tetracycline (TC) degradation. The influences of Cu_xO mass, solution pH, persulfate dosage, and common anions on the TC degradation were investigated in detail. Analytical techniques indicated that the 3D-rGO-Cu_xO showed a cross-linking three-dimensional network structure, and Cu_xO particles with irregular shapes were uniformly loaded on graphene pore walls. The XPS and Auger spectra of Cu confirmed that Cu₂O was the main component in solid copper compounds. The addition of Cu_xO was vitally important for the activation of the oxidation system, and the removal rate reached 98% with a Cu_xO load of 7:1. The pH showed little influence on the activation effect on TC degradation. For common anions, Cl^- and CO₃^2- had little influence on the system, while humic acid had a great inhibitory effect. The EPR test and quenching experiment revealed that the active substances in the oxidative degradation process mainly include SO₄^-·, ·OH, ¹O₂, and reactive Cu(III). Additionally, the 3D-rGO-Cu_xO material proved highly stable according to the replicated test results and was promising for the remediation of antibiotic-contaminated water.

Humic Substance Photosensitized Degradation of Phthalate Esters Characterized by 2H and 13C Isotope Fractionation

The photosensitized transformation of organic chemicals is an important degradation mechanism in natural surface waters, aerosols, and water films on surfaces. Dissolved organic matter including humic-like substances (HS), acting as photosensitizers that participate in electron transfer reactions, can generate a variety of reactive species, such as OH radicals and excited triplet-state HS (³HS*), which promote the degradation of organic compounds. We use phthalate esters, which are important contaminants found in wastewaters, landfills, soils, rivers, lakes, groundwaters, and mine tailings. We use phthalate esters as probes to study the reactivity of HS irradiated with artificial sunlight. Phthalate esters with different side-chain lengths were used as probes for elucidation of reaction mechanisms using ²H and ¹³C isotope fractionation. Reference experiments with the artificial photosensitizers 4,5,6,7-tetrachloro-2',4',5',7'-tetraiodofluorescein (Rose Bengal), 3-methoxy-acetophenone (3-MAP), and 4-methoxybenzaldehyde (4-MBA) yielded characteristic fractionation factors (-4 ± 1, -4 ± 2, and -4 ± 1‰ for ²H; 0.7 ± 0.2, 1.0 ± 0.4, and 0.8 ± 0.2‰ for ¹³C), allowing interpretation of reaction mechanisms of humic substances with phthalate esters. The correlation of ²H and ¹³C fractions can be used diagnostically to determine photosensitized reactions in the environment and to differentiate among biodegradation, hydrolysis, and photosensitized HS reaction.

Photocatalysis of carbamazepine via activating bisulfite by ultraviolet: Performance, transformation mechanism, and residual toxicity assessment of intermediates products

Carbamazepine (CBZ) as an extensively distributed emerging pollutant has menaced ecological security. The degradation performance of CBZ by UV driven bisulfite process was investigated in this work. The kinetics results indicated that CBZ was high-efficiently degraded by UV/bisulfite following a pseudo first-order kinetic model (K_obs = 0.0925 min^-1). SO₄^•- and •OH were verified as the reactive oxidants by EPR test and the radicals scavenging experiment using MeOH and TBA. SO₄^•- played a dominant role for CBZ degradation. The Density functional theory (DFT) and LC-qTOF-MS/MS clarified that hydroxylation, ketonation, ring opening reaction, and ring contraction were main transformation patterns of CBZ. As to influence factors, CBZ degradation was significantly hindered in presence of CO₃^2-, HPO₄^2- and NOM. Toxicological analysis derived from metabonomics suggested that the remarkable alteration of metabolic profile was triggered by exposure to intermediates mixture. CBZ intermediates interfered in several key metabolic pathways, including pentose phosphate, amino acids, lysine degradation, glycerophospholipid, glutathione, nucleotides and carbohydrate, which was alleviated after UV/bisulfite treatment. This work provided a meaningful support to potential risk of CBZ intermediates products, which shed light on the future application in eliminating drugs using UV /bisulfite.

Enhanced catalytic activity and stability of composite of cellulose film and nano zero-valent iron on Juncus effusus for activating peroxydisulfate to degrade Rhodamine B dye

In this study, a novel peroxydisulfate (PDS) activator (CF-nZVI-JE) was prepared via in-situ loading nano zero-valent iron (nZVI) on Juncus effusus (JE) followed with wrapping a layer of cellulose film (CF). The CF-nZVI-JE had the same 3D structure as the JE, being easy to separate from aqueous solution. The loaded nZVI existed single nanoparticles with a size of 60-100 nm except chain-type agglomeration of nanoparticles due to the stabilization of JE fibers. The activation performance of the CF-nZVI-JE for PDS was evaluated with Rhodamine B (Rh B) as a representative pollutant. Under the optimal activating conditions, the degradation rate of Rh B reached 99% within 30 min in the CF-nZVI-JE/PDS system. After five cycles, the degradation rate of Rh B was still over 85%, suggesting that the CF-nZVI-JE had good reusability. More interestingly, SO₄^·- and ·OH radicals were simultaneously detected in the CF-nZVI-JE/PDS system, but only SO₄^·- existed in the JE-ZVI/PDS system, suggesting the different activation mechanism. Meanwhile, the introduction of CF not only facilitated to the mineralization of Rh B but also significantly reduced the release amount of iron ions. Hence, the CF-nZVI-JE can be employed as a promising PDS activator for the treatment of organic wastewater.

Simultaneous removal of carbamazepine and Cd(II) in groundwater by integration of peroxydisulfate oxidation and sulfidogenic process: The bridging role of SO42

Heat-activated PDS oxidation (HAPO) has been widely used for in-situ chemical oxidation (ISCO) of micropollutants in groundwater, whereas the aesthetic demerit of additional SO₄^2- production is largely overlooked. In this study, the sulfidogenic process is used to offset the aesthetic demerit, and the production of SO₄^2- is then employed to recycle heavy metals. The innovative integration technology with PDS oxidation and sulfidogenic process via the bridging role of SO₄^2- was reported to remove micropollutants and heavy metals in groundwater simultaneously. HAPO could completely degrade CBZ, producing 400 mg/L SO₄^2- with the addition of 0.50 g/L PDS. Sulfate-reducing bacteria (SRB) utilize SO₄^2- generated from HAPO as the electron acceptor in the sulfidogenic process, removing and recycling Cd(II) via the precipitation of CdS. The SRB tolerance experiment revealed the viability of PDS oxidation coupled with the sulfidogenic process via the bridging role of SO₄^2-. Overall, the integration technology is a green and promising technology for simultaneous micropollutants removal and heavy metals recycling in groundwater.

Fate of typical organic halogen compounds in the coexistence of endogenic chlorine atoms and exogenic X. CHEMOSPHERE 2022;309:136761. [PMID: 36220428 DOI: 10.1016/j.chemosphere.2022.136761]

The transformation of halogenated organics in advanced oxidation processes (AOPs) has been extensively investigated. However, we currently know little about the fate of halogenated pollutants in the presence of exogenic halides (Cl^- or Br^-). Herein, the degradability, mineralization rate, and accumulation capacity of adsorbable organic halogen (AOX) for chlorophenols (2-chlorophenol (2-CP), 3-chlorophenol (3-CP), 4-chlorophenol (4-CP), and 2,4,6-trichlorophenol (TCP)) were compared in the Fe²⁺/persulfate (PS) process with the addition of exogenic halides. Results indicate that exogenic X^- can lead to a decrease in chlorophenols degradation and mineralization rate, undesirable accumulation of AOX, and generation of halogenated by-products which are more toxic than precursor chlorophenols. Results of kinetics modeling show that Cl₂^•- plays more important role than SO₄^•- with an addition of Cl^-, while SO₄^•-, Br₂^•-, and Br₂ are responsible for the effect of Br^-. As well, the effect of endogenic chlorine atoms on chlorophenols reveals that the degradability and AOX formation potential of 3-CP are highest while that of TCP are the lowest. This study demonstrates the significant influence of endogenic chlorine atoms and exogenic X^- on the fate of typical organic halogen compounds. Consequently, the X^- level and position/number of halogen atoms should be considered simultaneously when treating organohalogen compounds.

Visible-light-assisted peroxydisulfate activation over Ag6Si2O7/Cu(II)-modified palygorskite composite for the effective degradation of organic pollutants by radical and nonradical pathways

Photoassisted persulfate activation (PPA) is highly efficient oxidation process, but the eligible catalysts are scarce. Herein, a visible-light-responsive Ag₆Si₂O₇ was anchored on Cu(II)-exchanged attapulgite (Cu-Pal) via a facile precipitation-deposition method to construct a novel PDS activator. The synthesized catalyst was systemically analyzed by a series of characterization techniques. The results revealed that Ag₆Si₂O₇ nanoparticles were evenly dispersed on Cu-Pal to form heterojunction. 16%-Ag₆Si₂O₇/Cu-Pal, an optimal catalyst exhibited excellent catalytic performance and stability in the visible-light-assisted PDS activation for AR18 degradation. The influences of reaction parameters on this process were investigated. Under the optimal conditions ([catalyst] = 1.0 g L^-1, [PDS] = 3.9 mM, pH_i = 5.1), 50 mg L^-1 of AR18 was completely degraded within 30 min. More importantly, quenching experiments and EPR tests revealed that besides the common SO₄^•- and •OH, ¹O₂ and O₂^•- were generated as main reactive oxygen species in the PPA by 16%-Ag₆Si₂O₇/Cu-Pal. Moreover, it was found that surface hydroxyl groups of the catalyst and copper species incorporated in Pal could significantly influence PDS activation and ROS generation. Based on these results, together with PDS decomposition, fluorescent probe analysis, and XPS analysis of the used catalyst, the possible mechanisms of the PPA by 16%-Ag₆Si₂O₇/Cu-Pal were proposed. Finally, the versatility and practicability of the established PPA process were verified by degrading other organic contaminants and testing effects of the coexisting anions and water matrices on AR18 degradation. This study may provide new insights for designing and developing the efficient heterogeneous catalysis for wastewater treatment via persulfate-based AOP.

Zeolites as Adsorbents and Photocatalysts for Removal of Dyes from the Aqueous Environment

This study investigated the potential of zeolites (NH₄BETA, NH₄ZSM-5, and NaY) to remove two frequently used dyes, methylene blue (MB) and rhodamine B (RB), from an aqueous environment. The removal of dyes with zeolites was performed via two mechanisms: adsorption and photocatalysis. Removal of dyes through adsorption was achieved by studying the Freundlich adsorption isotherms, while photocatalytic removal of dyes was performed under UV irradiation. In both cases, the removal experiments were conducted for 180 min at two temperatures (283 K and 293 K), and dye concentrations were determined spectrophotometrically. Additionally, after photodegradation, mineralization was analyzed as chemical oxygen demand. A computational analysis of the structures of MB and RB was performed to gain a deeper understanding of the obtained results. The computational analysis encompassed density functional theory (DFT) calculations and analysis of two quantum-molecular descriptors addressing the local reactivity of molecules. Experimental results have indicated that the considered zeolites effectively remove both dyes through both mechanisms, especially NH₄BETA and NH₄ZSM-5, due to the presence of active acidic centers on the outer and inner surfaces of the zeolite. The lowest efficiency of dye removal was achieved in the presence of NaY zeolite, which has a lower SiO₂/Al₂O₃ ratio. A more efficient reduction was completed for RB dye, which agrees with the computationally obtained information about reactivity.

pH-dependent generation of radical and nonradical species for sulfamethoxazole degradation in different carbon/persulfate systems

The impacts of pH on purification efficiency can be phenomenal in advanced oxidation processes (AOPs), because solution pH affects persulfate (PS) activation processes. However, consensus has not been reached on the regimes of pH-regulated oxidation in persulfate-based AOPs (PS-AOPs). Particularly, the impacts of pH on carbon-catalyzed generation of radical and nonradical species remain unclear. In this work, we evaluated three typical carbonaceous materials including pyrolytic carbon (PC), activated carbon (AC), and carbon nanotube (CNT) to activate PS for sulfamethoxazole (SMX) degradation within a pH range from 4 to 9. The experiment revealed pH-dependent SMX removal in PC/PS, AC/PS, and CNT/PS, and the kinetics followed an order of pH 4 > pH 7 > pH 9. Solution pH simultaneously affected SMX adsorption and degradation, but the latter was more profound. Chemical quenching experiment, electrochemical measurement, kinetics calculation, and ATR-FTIR tests collectively revealed that high pH was not favorable for both radical and nonradical oxidation. In the PC/PS system, increased pH decreased the amount of phenolic -OH on PC surface, thereby restraining the generation of SO₄^•- and ^•OH due to the lack of electron donors. For AC/PS system, elevated pH hindered the interactions between AC and PS, thus suppressing the formation of surface-bound radicals. CNT/PS initiated an electron-transfer pathway, and increased pH reduced the oxidation potential of surface CNT-PS* complex, which was not favorable for nonradical oxidation of adsorbed pollutants. Therefore, outcomes of this work will advance the current knowledge on the intrinsic impacts of pH in PS-AOPs catalyzed by carbonaceous materials for wastewater purification.

Heat-activated persulfate for the degradation of micropollutants in water: A comprehensive review and future perspectives

This work is a critical review of the most important studies that have dealt with heat-activated persulfate to degrade persistent micropollutants in the last six years. The effect of the different operating parameters is discussed, wherein in all cases, the efficiency was favored at higher temperatures and oxidant concentrations. Particular emphasis was given to the effect of the aqueous matrix. Since heat activation is a homogeneous process based on the production of free radicals, in most of the studies presented, the removal of pollutants decreases as the complexity of the aqueous matrix increases except in cases where secondary oxidative species are produced that are selective with specific pollutants. It has also been observed that the change in toxicity usually follows the removal of the parent compound despite the formation of several by-products. Nowadays, combining different processes for the simultaneous activation of persulfate seems to be gaining ground. A hybrid process is an interesting strategy to reduce costs and increase efficiency, especially in real wastewater. In this light, the most interesting studies of hybrid systems for the destruction of micropollutants in recent years based on thermally activated persulfate are also summarized. Finally, some steps are proposed for future research towards the industrial application, including the study of chemical mixtures, the integrated toxicity assessment, the examination of simultaneous disinfection and decomposition of pollutants into real wastewater, the estimation of the required costs, and energy the combination of processes and their coupling with renewable sources, and the design of pilot plants and the scale-up of the hybrid processes.

Sulfur or nitrogen-doped rGO supported Fe-Mn bimetal - organic frameworks composite as an efficient heterogeneous catalyst for degradation of sulfamethazine via peroxydisulfate activation

In this work, sulfur/nitrogen modified reduced graphene oxide (S/N-rGO) was employed as both electron shuttle and support to fabricate Fe-Mn bimetallic organic framework@S/N-rGO hybrids (BOF@S/N-rGO) via a facile two-step solvothermal route. Compared with the transition metal ions (Fe²⁺/Mn²⁺), the classical metal oxide catalyst (Fe₂O₃ and Fe₃O₄) and nano zero-valent iron (nZVI), BOF@S/N-rGO catalyst can more effectively activate peroxydisulfate (PDS) with ultra-low concentration (0.05 mM) to degrade sulfamethazine (SMT). Quenching experiments, electron paramagnetic resonance (EPR) measurement and linear sweep voltammetry (LSV) showed that the activation pathways of PDS between the two catalysts were different. In BOF@N-rGO+PDS system, the degradation of SMT was mainly attributed to the oxidation of radicals including SO₄^•- and •OH, especially SO₄•- . However, in BOF@S-rGO+PDS system, in addition to the radical pathway, there are also non-radical pathways, namely ¹O₂ and direct electron transfer. Furthermore, the applicability of BOF@S/N-rGO used in the PDS-mediated advanced oxidation processes (AOPs) was systematically investigated in terms of the effects of operating parameters and coexisting substance (anions and humic acid (HA)), the degradation of other pollutants, as well as the stability and reusability of the catalyst. This study proved that BOF@S/N-rGO was a promising activator of PDS with ultra-low concentration for the degradation of SMT.

Comparison of sunlight-AOPs for levofloxacin removal: kinetics, transformation products, and toxicity assay on Escherichia coli and Micrococcus flavus

Levofloxacin (LFX) is a widely used antibiotic medication. Persistent traces of LFX in water and wastewater may induce bacterial resistance. Photon-driven advanced oxidation processes (AOPs) can assist in attaining complete abatement of LFX for environmental protection. This work benchmarks different solar AOPs based on hydroxyl radical (OH^•) and sulphate radical (SO₄^•-) chemistry. Other oxidant precursors, as radical sources, were used to selectively control the generation of either hydroxyl radical (i.e., H₂O₂), sulphate radical (i.e., peroxydisulphate (PDS)), or a controlled mixture ratio of both OH^•/SO₄^•- (i.e., peroxymonosulphate (PMS)). The influence of pH on degradation performance was evaluated using unbuffered and buffered solutions. Simulated irradiation/PMS process exhibited a strong pH-dependence attaining partial degradation of ca. 56% at pH 5 up to complete degradation at pH 7. Despite the similitudes on the abatement of target pollutant LFX in pristine solutions, only simulated irradiation/PDS treatment achieved effective abatement of LFX in wastewater samples given the higher selectivity of SO₄^•-. Toxicity tests were conducted with Escherichia coli (LMG2092) and Micrococcus flavus (DSM1790), demonstrating successful inhibition of the antibiotic character of polluted waters, which would contribute to preventing the development of resistant bacterial strains. Finally, a degradative pathway was suggested from the by-products and intermediates identified by LC-MS. Results demonstrate that the degradation of specific functional groups (i.e., piperazine ring) is associated with the loss of antibacterial character of the molecule.

Degradation of dyes by UV/Persulfate and comparison with other UV-based advanced oxidation processes: Kinetics and role of radicals

This study investigated the degradation of methylene blue (MeB), methyl orange (MeO), and rhodamin B (RhB) by the UV/Persulfate (UV/PS) process. The dye degradation in the investigated UV-based Advanced Oxidation Processes (UV/AOPs) followed the first-order kinetic model. The second-order rate constant of the dyes with •OH, SO₄^•-, and CO₃^•- were calculated and found to be: k_•OH,MeB = 5.6 × 10⁹ M^-1 s^-1, [Formula: see text]  = 3.3 × 10⁹ M^-1 s^-1, [Formula: see text]  = 6.9 × 10⁷ M^-1 s^-1; k_•OH,MeO = 3.2 × 10⁹ M^-1 s^-1, [Formula: see text]  = 13 × 10⁹ M^-1 s^-1, [Formula: see text]  = 4.4 × 10⁶ M^-1 s^-1; k_•OH,RhB = 14.8 × 10⁹ M^-1 s^-1, [Formula: see text]  = 5 × 10⁹ M^-1 s^-1, [Formula: see text]  = 1 × 10⁷ M^-1 s^-1. The steady-state concentrations of •OH and SO₄^•- (including other reactive species) were determined using both chemical probes and modeling methods (Kintecus® V6.8). In the UV/PS, the dye degradation depends on the pH of the solution with the order: k_dye (at pH of 7) > k_dye (in acidic conditions) > k_dye (in alkaline conditions). The presence of water matrices had different impacts on dye degradation: 1) The HCO₃^- and Cl^- promoted the degradation efficiency of one dye, but also inhibited the degradation of other dyes; 2) Humic acid (HA) inhibited dye degradation as it scavenged both •OH and SO₄^•-. The degradation of the dyes by UV/PS was also compared with the UV/Chlorine (UV/HOCl) and UV/H₂O₂ and it was established that: 1) In UV/PS and UV/HOCl, SO₄^•- and RCS contributed to dye degradation more than •OH, while •OH played a major role in dye degradation by UV/H₂O₂; 2) The calculated toxicity in UV/PS was the lowest probably due to the low toxicity of by-products; 3) For MeO and RhB, the UV/PS process is more beneficial for the total organic carbon (TOC) removal compared to that of the UV/HOCl and UV/H₂O₂ processes; 4) The UV/PS showed lower cost than the UV/HOCl and UV/H₂O₂ systems for MeO, and RhB degradation but higher cost for MeB removal.

The synergistic effect of calcite and Cu2+ on the degradation of sulfadiazine via PDS activation: A role of Cu(Ⅲ)

A system of Cu²⁺/calcite/PDS was constructed to degrade sulfadiazine (SDZ). Different from the traditional Cu-mediated activation, a low concentration of Cu²⁺ that met drinking water standards (≤ 1 mg/L) transformed into Cu(Ⅱ) solid in the presence of calcite, and then enhanced the degradation of SDZ via PDS activation over a pH range from 3 to 9. According to scavenger and chemical probe experiments, Cu(Ⅲ), rather than radicals (hydroxyl radicals and sulfate radicals) and singlet oxygen, was the predominant reactive species, which was responsible for the degradation of SDZ. Based on the results of XRD, ATR-FTIR, and CV curves et al., CuCO₃ was the main complex with high reactivity for PDS activation to form Cu(Ⅲ). Moreover, detailed degradation pathways of sulfadiazine were proposed according to the UPLC-ESI-MS/MS and their toxicity was predicted by ECOSAR. Besides, the real water matrix would not seriously affect the degradation of SDZ in the Cu²⁺/calcite/PDS system. In summary, this study reveals a new insight into the synergistic effect of Cu²⁺ and calcite on the SDZ degradation, and promotes an understanding of the environmental benefits of natural calcite.

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.

Vacancy-rich BiO2-x as a highly-efficient persulfate activator under near infrared irradiation for bacterial inactivation and mechanism study

This study, for the first time, developed a novel defective BiO_2-x based collaborating system, where the near-infrared light (NIR) irradiation (λ > 700 nm) initiated persulfate activation and photocatalytic bacterial inactivation simultaneously. Vacancy-rich BiO_2-x nanoplates possessed impressive NIR absorption and firstly realized persulfate activation under NIR irradiation. In this collaborating system, on one hand, the persulfate can be transformed into sulfate radicals through light/heat activation mode directly, which would be enhanced by the presence of vacancy-rich BiO_2-x owing to its outstanding light and heat absorption ability. On the other hand, the photogenerated electrons can further efficiently react with persulfate and form sufficient reactive sulfate radicals. The sulfate radicals, synergizing with other reactive species (O₂^-, h⁺, etc.), achieved a 7-log Escherichia coli inactivation within 40 min. The systematic investigation of inactivation mechanism revealed that the reactive species caused the dysfunction of cellular respiration, ATP synthesis and bacterial membrane, followed by the severely oxidative damage to the antioxidative SOD and CAT enzymes and the generation of carbonylated protein. The final leakage of DNA and RNA implied the lethal damage to the bacteria cells. This work provided a new insight into the persulfate associated NIR driven remediation technology of controlling microbial contaminants.

Degradation of rifamycin from mycelial dreg by activated persulfate: Degradation efficiency and reaction kinetics

Rifamycin mycelial dreg (RMD) is a biological waste, and its residual rifamycin (RIF) is potentially harmful to both the environment and human health. In this work, thermally activated persulfate (PDS) oxidative degradation of RIF in RMD was developed for the first time. The effects of reaction temperature, initial PDS concentration, and pH on RIF degradation in RMD were investigated, and the treatment conditions were optimized using response surface methodology (RSM). The results showed that 90 °C, 50 mg/g PDS, and pH = 5.3 were the optimal pretreatment conditions, and 100% degradation efficiency of RIF (734 mg/kg) was achieved. SEM and FTIR analyses confirmed that the RIF was destroyed and decomposed after the oxidation reaction. The possible degradation pathways of RIF in the thermally activated PDS system were discussed through HPLC/MS and ESR analyses. The intermediate product was identified, and the toxicity of the final product was predicted to be low or nontoxic. In this work, a degradation pathway of RMD was proposed by activating persulfate, which facilitates subsequent resource utilization and provides meaningful guidance for the practical treatment of antibiotic mycelium residue (AMR).

Controlled Citrate Oxidation on Gold Nanoparticle Surfaces for Improved Surface-Enhanced Raman Spectroscopic Analysis of Low-Affinity Organic Micropollutants

Surface-enhanced Raman spectroscopy (SERS) provides an ultrasensitive, fast, and inexpensive method for organic micropollutant analysis, but its applications are limited by the low affinity of most organic micropollutants toward plasmonic nanoparticle surfaces. Particularly, the citrate layer on gold nanoparticle (AuNP) surfaces exerts strong resistance to ligand exchange and prevents carboxylic and phenolic pollutants from entering SERS "hot spots". In this study, we aim to extend the application of SERS to low-affinity organic micropollutants by oxidative decomposition of the citrate layer on AuNP surfaces. The kinetics of citrate oxidation were carefully controlled using sulfate radicals that were slowly released from peroxydisulfate photolysis, which guarantees both the stability of AuNP colloid and generation of a high density of SERS hot spots for pollutant analysis. In situ Raman spectroscopic monitoring demonstrates that citrate is first oxidized to di- and monocarboxylate acids and subsequently displaced by guest ligands. This oxidation-induced ligand exchange has been applied for SERS analysis of various low-affinity organic micropollutants, including monochloro-substituted carboxylates and phenols, as well as a widely used herbicide 2.4-dichlorophenoxyacetic acid. This study substantially broadens the library of organic micropollutants for label-free SERS analysis and advances SERS toward a holistic analytical tool for water quality monitoring.

Visible light-promoted photocatalyst-free activation of persulfates: a promising strategy for C-H functionalization reactions

The employment of renewable energy resources is highly desirable according to the twelve principles of green chemistry. In this context, visible light promoted organic transformations have gained much attention from synthetic chemists due to the employment of renewable energy. However, the inability of the majority of organic molecules to absorb visible light encouraged the use of photocatalysts in visible light-mediated organic transformations. As a result, different types of photocatalysts like transition-metal containing photoredox catalysts, organophotoredox catalysts, heterogeneous photocatalysts, etc. have emerged over the years. On the other hand, persulphates (K₂S₂O₈, Na₂S₂O₈, and (NH₄)₂S₂O₈) have been widely used as oxidants in various oxidative organic transformations under thermal and photochemical conditions. The initial formation of an active persulfate radical anion from a persulfate anion is the crucial step for these oxidative transformations and the conversions under visible light are generally carried out employing different photocatalysts. Although numerous methodologies have been successfully developed employing these photocatalysts, the development of new processes under photocatalyst-free conditions are more preferable from the viewpoint of sustainable development. Persulphates could be very useful for various organic transformations through C-H functionalizations under photocatalyst-free visible light irradiation. In this review, we will exemplify the efficiency of persulphates in various oxidative organic transformations under visible light irradiation without the employment of any photocatalysts. The utilities and mechanistic pathways of the methodologies will also be highlighted.

Activation of persulfate by mesoporous silica spheres-doping CuO for bisphenol A removal

In the present work, mesoporous silica spheres-doping CuO (CuO/MSS) was prepared via a facile hydrothermal method. It acted as a peroxydisulfate (PDS) activator for the removal of bisphenol A (BPA). X-Ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) showed that CuO was successfully synthesized and silica spheres were doped in CuO. Nitrogen sorption isotherm showed that CuO/MSS, which had a high specific surface area and a narrow pore size distribution, exhibited a mesoporous structure. The effect of initial pH, PDS dosage, catalyst amount, and activation temperature was assessed. A removal efficiency of over 80% was observed after five consecutive cycles, suggesting the superior stability of the catalyst. X-ray photoelectron spectroscopy (XPS), radical quenching experiments, and electrochemical evaluation showed that BPA removal was dominated by the electron transfer among PDS, BPA, and the surface of CuO/MSS (non-radical pathway), while SO₄^·- and OH· radicals had a minor contribution (radical pathway). In addition, the degradation pathways of BPA were proposed according to the intermediates. Overall, this study indicates that CuO/MSS is a promising effective PDS activator to address the drawbacks of the classical Fenton process.

Application of sludge biochar combined with peroxydisulfate to degrade fluoroquinolones: Efficiency, mechanisms and implication for ISCO

Peroxydisulfate (PDS) is increasingly used for in situ chemical oxidation (ISCO) of organic pollutants in groundwater, but the efficient and applicable activator is still scarce. In this study, sludge-derived biochar (SDBC) was prepared by pyrolysis to activate PDS, which could effectively degrade the fluoroquinolone antibiotics (FQs, levofloxacin, enrofloxacin, norfloxacin and ciprofloxacin). Compared with pig manure and corn straw derived biochar, SDBC showed higher efficiency in PDS activation. Singlet oxygen (¹O₂) was identified as the major reactive species, and the surface-bonded radicals also contributed to the FQs degradation. The selective oxidation of FQs by ¹O₂ was first reported, which followed the trend of enrofloxacin ~ levofloxacin > norfloxacin ~ ciprofloxacin. The CO and Fe²⁺ on SDBC were the dominant reactive sites for PDS activating. Products analysis revealed that FQs degradation proceeds via the cleavage of the piperazine ring, breaking of the quinolone ring, decarboxylation, and defluorination. Moreover, the tertiary amine of N (4) on enrofloxacin was more reactive towards singlet oxygen than the secondary amine of N (4) on ciprofloxacin, inducing the faster degradation and de-toxicity of enrofloxacin in the reaction system. SDBC showed high reusability in PDS activation and negligible metals leachates were detected. The column study proved the efficiency of PDS/SDBC in groundwater remediation.

Knowledge extraction of sonophotocatalytic treatment for acid blue 113 dye removal by artificial neural networks

Removing decolorizing acid blue 113 (AB113) dye from textile wastewater is challenging due to its high stability and resistance to removal. In this study, we used an artificial neural network (ANN) model to estimate the effect of five different variables on AB113 dye removal in the sonophotocatalytic process. The five variables considered were reaction time (5-25 min), pH (3-11), ZnO dosage (0.2-1.0 g/L), ultrasonic power (100-300 W/L), and persulphate dosage (0.2-3 mmol/L). The most effective model had a 5-7-1 architecture, with an average deviation of 0.44 and R² of 0.99. A sensitivity analysis was used to analyze the impact of different process variables on removal efficiency and to identify the most effective variable settings for maximum dye removal. Then, an imaginary sonophotocatalytic system was created to measure the quantitative impact of other process parameters on AB113 dye removal. The optimum process parameters for maximum AB 113 removal were identified as 6.2 pH, 25 min reaction time, 300 W/L ultrasonic power, 1.0 g/L ZnO dosage, and 2.54 mmol/L persulfate dosage. The model created was able to identify trends in dye removal and can contribute to future experiments.

Feasibility of micropollutants removal by solar-activated persulfate: Reactive oxygen species formation and influence on DBPs

As a natural source of visible light and a type of renewable energy, solar energy is extensively used in the field of photochemistry. In this study, solar was employed to activate persulfate (PS) to degrade typical micropollutants. The removal kinetics of aspirin (ASA) and flunixin meglumine (FMME) in the solar/PS system were well fitted by pseudo-first-order models (R² > 0.99). In the system containing 1.0 mM PS activated by solar irradiation at a fluence of 1.14 × 10^-4 E·m^-2·s^-1, 72.6% and 97.5% of ASA and FMME were degraded, and the corresponding kinetic constants were 6.8-9.8 × 10^-2 and 1.6-9.8 × 10^-1 min^-1, respectively. Qualitative and quantitative analyses of the reactive oxygen species (ROS) indicated that sulfate radical (SO₄^·-) played a major role in degradation, with the maximum contributions of 77.7% and 88.8% for the degradation of ASA and FMME, whereas the maximum contributions of hydroxyl radical (·OH) were only 11.6% and 6.5%, respectively. The contributions of singlet oxygen (¹O₂) were less than 15% at pH 5.5, but increased to 25.6% and 45.5% at pH 8.5, respectively. Solar/PS pre-oxidation increased disinfection byproducts (DBPs) (95.8% for trihalomethanes (THMs) and 47.9% for haloacetic acids (HAAs) at pH 7.0) after chlorination in deionized water, and an opposite trend was found in systems coexisting with natural organic matter (NOM). Residual PS after oxidation resulted in a high aquatic toxicity, with an inhibition rate of 18.70% to algae growth. Economic analysis showed that the electrical energy per order values of the system ranged from 23.5 to 86.5 kWh·m^-3·order^-1, indicating that the solar/PS system shows promise for practical applications.

A novel Fe-rectorite composite catalyst synergetic photoinduced peroxymonosulfate activation for efficient degradation of antibiotics

Developing a low-cost and efficient photocatalysts activated peroxymonosulfate (PMS) for organic pollutants degradation are recognized as an importance way for dealing with environmental pollution. In this work, Fe-rectorite catalyst was synthesized by a simple impregnation-calcine method to synergetic photo activate PMS for antibiotics degradation. As expected, the Fe-rectorite/PMS/Light system exhibits superior catalytic performance for tetracycline (TC) removal, which achieving 96.4% removal rate of TC (30 mg/L) under light within 60 min. Fe-retorite has better degradation performance for TC than rectorite under photo-mediation. The enhancement of the degradation performance of TC by Fe-retorite can be attributed to the improvement of the separation efficiency of photogenerated electrons and holes in the rectorite by the loading of Fe₂O₃, and the accelerated active Fe(Ⅱ)/Fe(Ⅲ) cycle on the surface under photo-mediation. The large specific surface area and abundant hydroxyl groups of rectorite can also provide active sites for PMS activation. The quenching experiment and electron paramagnetic resonance (EPR) test were indicated that the h⁺, SO₄•^-, •OH, and O₂^-• all contributed to TC degradation. And the possible degradation pathway was proposed by LC-MS. This work helps induced a novel direction that design green, efficient, and recyclable heterogeneous catalysts to synergetic photoinduced PMS activation for enhanced degradation of TC.

Transformation of gemfibrozil by the interaction of chloride with sulfate radicals: Radical chemistry, transient intermediates and pathways

The radical chemistry of SO4·- is strongly affected by its interaction with chloride in natural waters, during which SO4·- can be converted to HO· and reactive chlorine species (RCS). This study investigated the effects of chloride on gemfibrozil (GFRZ) transformation via the UV/peroxydisulfate (PDS) process, elucidating the kinetics, degradation pathways and solution toxicity. The pseudo-first-order rate constants (k') of GFRZ by UV/PDS changed slightly from 1.0 × 10-3 s-1 to 9.3 × 10-4 s-1 as the chloride content increased from 0 to 10 mM because the increase in HO· and RCS levels compensated for the decrease in SO4·- concentration. However, the transformation pathways in the presence of chloride changed significantly. From the transient absorption spectra, we inferred that RCS and SO4·- attacked GFRZ mainly through hydrogen abstraction and/or electron transfer, while HO· interacted with the GFRZ aromatic ring by addition. Hydroxylation, carboxylation and cleavage products were enhanced in UV/PDS/Cl- compared to UV/PDS through the addition of HO· and the cleavage of CO bonds by RCS, and total organic chlorine (TOCl) was undetectable. Interestingly, the acute toxicity was lowest in UV/PDS/Cl-, with an inhibition percentage of 1% at 30 min. The higher inhibition percentages in UV/PDS (13%) and UV alone (53%) at 30 min likely resulted from the stronger capacity of HO· and RCS to oxidize aldehydes to carboxylic groups and cleave CO bonds, respectively, than that of SO4·-. This study provides a better understanding of contaminant transformation mechanisms under UV/PDS treatment at chloride levels present in natural waters.

Efficient removal of organic pollutants by a Co/N/S-doped yolk-shell carbon catalyst via peroxymonosulfate activation

Carbon-based catalysts with heteroatom doping and hollow structures are desired for advanced oxidation processes (AOPs). Herein, dual-shelled Co, N, and S codoped hollow carbon nanocages were developed by wrapping zeolitic imidazolate framework-67 (ZIF-67) with trithiocyanuric acid (TCA) and performing subsequent carbonization. The optimal composite catalyst (Co-NC-CoS) exhibited excellent catalytic performance toward different organic pollutants. Almost complete removal of 4-NP (60 mg/L^-1) was achieved within 20 min by 10 mg of catalyst and 0.2 g/L^-1 peroxymonosulfate (PMS). Moreover, the catalyst showed good stability and reusability. The effects of catalyst and PMS dose, pollutant concentration, pH and common anions were investigated, and reactive oxygen species (ROS) were studied by scavenger experiments and electron paramagnetic resonance (EPR) tests. The results show that multidoped atoms S, Co and N all contributed to the degradation system. Several lines of evidence suggested that S could change the catalytic process from Co³⁺/Co²⁺ to Co³⁺/Co²⁺/Co⁰ reduction due to its low redox potential. Degradation was achieved through both radical and nonradical pathways, where sulfate radicals (SO₄^·̶), hydroxyl radicals (^·OH) and singlet oxygen (¹O₂) were primary reactive species. Overall, this work may suggest that the novel multi heteroatom-doped catalysts with complex structures can be developed for environmental remediation.

Nitrogen-doped mesoporous carbon material (NCMK-3) as a catalyst for the removal of 4-chlorophenol during persulfate oxidation and its efficiency after reuse

Persulfate (PS) oxidation of 4-chlorophenol (4CP) is mostly catalysed by relatively expensive metal substrates. In this study, we investigated the influence of nitrogen-doped and non-doped mesoporous carbon materials (NCMK-3 and CMK-3) during persulfate (PS) oxidation of 4CP in water. Batch experiments were conducted such that PS was added to simulated contaminant mixture after 1 h agitation with NCMK-3 and CMK-3. Further, the experiment was carried out at different temperatures, pH ranges, concentrations of persulfate (PS), and different doses of NCMK-3, since it recorded better removal rates compared to CMK-3. The results revealed that NCMK-3 and CMK-3 aided the removal of 4CP from water during persulfate oxidation. When persulfate was added after an hour of equilibration with CMK-3 and NCMK-3, 83% and 92% of 4CP were removed within 20 min, respectively, whereas lower removal rates (≤40) were recorded in the absence of persulfate (PS). The removal rates of 4CP increased with an increase in temperature but reduced in the alkaline medium in the NCMK-3/PS system. The efficiency of the NCMK-3 reduced significantly after it was reused three times. Based on the results, NCMK-3 influences the activity of PS oxidation of 4-chlorophenol (4CP) and exhibited a synergistic effect in the removal of the organic contaminant from water.

Step-scheme BiVO4/WO3 heterojunction photocatalyst under visible LED light irradiation removing 4-chlorophenol in aqueous solutions

In the present study, photodegradation of 4-chlorophenol (4-CP) using a step-scheme BiVO₄/WO₃ heterostructure under visible LED light irradiation (Vis LED) from aqueous solutions was investigated. The photocatalyst was synthesized through the hydrothermal process and characterized physically and chemically via X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray (EDX), and Brunnauer-Emmett-Teller (BET) techniques. The effects of the operational parameters i.e., solution pH, contact time, nanocomposite dosage, and initial 4-CP concentration were evaluated. Results indicated that BiVO₄/WO₃/Vis LED process has higher efficiency in 4-CP degradation than BiVO₄/Vis LED, WO₃/Vis LED, and BiVO₄/WO₃ systems. At BiVO₄/WO₃ concentration of 0.125 g/L, initial pH of 7, and initial 4-CP concentration of 25 mg/L, complete degradation of 4-CP (>97%) was achieved in reaction time of 60 min. The phenol, chlorobenzene, catechol, 4-chlorocatechol, 5-chloro-1,2,4-benzenetriol, hydroquinone, hydroxyhydroquinone, p-benzoquinone, o-benzoquinone, formic acid, acetic acid, and oxalic acid were identified as the major intermediates of 4-CP degradation. In optimal condition, 67.5% and 88.5% of TOC and COD removal rates were obtained in 120 min contact time, respectively. The degradation of 4-CP was pseudo-first-order kinetics. Through the use of tert-Butyl alcohol (TBA) and ethylenediamine tetraacetic acid (EDTA) as radical scavengers, hydroxyl radicals and holes were identified as the main active species in photocatalytic degradation. Also, a tentative pathway for 4-CP degradation using the Vis LED/BiVO₄/WO₃ process was proposed.

UV-induction of photolytic and photocatalytic degradation of fumonisins in water: reaction kinetics and toxicity

Although fumonisins are toxic and carcinogenic mold products that contaminate feed, food, and water, their photodegradation has not yet been reported. In this work, the efficiency of photolysis (UV, UV/H₂O₂, and UV/[Formula: see text]) and photocatalysis (TiO₂ (Degussa P25/Wackherr) and ZnO) for the degradation of fumonisins in an aqueous medium were investigated. In the case of fumonisin B₁ (FB₁) optimal conditions in terms of pH, the initial concentrations of H₂O₂/[Formula: see text] for UV, UV/H₂O₂, and UV/[Formula: see text] treatments were investigated. The photocatalytic degradation using TiO₂ Wackherr as catalyst at natural pH (about 8) proved to be the most efficient treatment for removal of FB₁ and FB₃. Namely, during the first 30 min of irradiation, 99% of FB₁ (1.39 μM) was degraded, while FB₃ (0.425 μM) was completely removed during the first 20 min of irradiation. In the case of FB₂ (0.687 μM), UV/[Formula: see text] was the most efficient treatment, and complete removal occurred in the first 90 min of irradiation. All applied treatments for fumonisins removal have followed pseudo-first-order kinetics under the relevant experimental conditions. Toxicity of fumonisins and their mixtures formed during photodegradation were investigated using mammalian cell lines (BHK, H-4-II-E, Neuro-2a, and MRC-5). The BHK cell line was the most sensitive to fumonisins, especially FB₂ and FB₃, and its photodegradation mixtures.

Oxidative Degradation of Tetracycline by Magnetite and Persulfate: Performance, Water Matrix Effect, and Reaction Mechanism

This study presents a strategy to remove tetracycline by using magnetite-activated persulfate. Magnetite (Fe3O4) was synthesized at high purity levels-as established via X-ray diffractometry, transmission electron microscopy, and N2 sorption analyses-and tetracycline was degraded within 60 min in the presence of both magnetite and persulfate (K2S2O8), while the use of either substance yielded limited degradation efficiency. The effects of magnetite and persulfate dosage, the initial concentration of tetracycline, and the initial pH on the oxidative degradation of tetracycline were interrogated. The results demonstrate that the efficiency of tetracycline removal increased in line with magnetite and persulfate dosage. However, the reaction rate increased only when increasing the magnetite dosage, not the persulfate dosage. This finding indicates that magnetite serves as a catalyst in converting persulfate species into sulfate radicals. Acidic conditions were favorable for tetracycline degradation. Moreover, the effects of using a water matrix were investigated by using wastewater treatment plant effluent. Comparably lower removal efficiencies were obtained in the effluent than in ultrapure water, most likely due to competitive reactions among the organic and inorganic species in the effluent. Increased concentrations of persulfate also enhanced removal efficiency in the effluent. The tetracycline degradation pathway through the magnetite/persulfate system was identified by using a liquid chromatograph-tandem mass spectrometer. Overall, this study demonstrates that heterogeneous Fenton reactions when using a mixture of magnetite and persulfate have a high potential to control micropollutants in wastewater.

Complete arsenite removal from groundwater by UV activated potassium persulfate and iron oxide impregnated granular activated carbon

Removal of toxic arsenite [As(III)] from the contaminated surface and groundwater is essential for human health. However, direct arsenite removal is difficult compared to arsenate [As(V)]. Therefore, the peroxidation of arsenite to arsenate is vital for its effective removal from water. Herein, we investigated the removal efficiency of arsenic from groundwater by oxidizing it with UV activated potassium persulfate (KPS) and subsequently adsorbing it on iron oxide impregnated granular activated carbon (FeO/GAC). A batch experiment was carried out to determine the adsorption kinetics and thermodynamics. Further, the effects of the adsorbent mass (FeO/GAC), C/Fe molar ratio, pH, arsenic concentration, competing anions, and humic acid in arsenic adsorption was studied. The characterization of FeO/GAC adsorbent was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), and zeta potential measurements. Using the UV activated KPS and FeO/GAC, a ∼100% removal amount was achieved for 10 ppm of the arsenic solution in 1 h. Also, the effect of pH showed the highest removal efficiency in the pH range of 6.0-7.0 and it decreased dramatically at higher and lower pH values. The groundwater collected from Cheongyang in South Korea was spiked with 10 ppm of the arsenic (III) and more than 82% removal of arsenic was achieved in 90 min even in the presence of natural contaminants. Therefore, the results suggest that the UV activated KPS with FeO/GAC provides an effective method for treating highly-arsenic-contaminated water sources and this may be a viable alternative method over the existing methods.

Persulfate-enhanced degradation of ciprofloxacin with SiC/g-C3N4 photocatalyst under visible light irradiation

SiC/g-C₃N₄ composite (SCN) showed the potential for photocatalytic degradation of synthetic dyes, it is deserved to study whether it is effective for the photocatalytic degradation of ciprofloxacin (CIP). In this work, persulfate-enhanced CIP degradation was investigated with SCN under visible light irradiation. The results showed that the degradation efficiency of 10 mg L^-1 CIP could reach 95% for 30 min under the conditions of 0.4 g L^-1 SCN, 2 mM persulfate (PS) and solution initial pH 6. The degradation process abided by pseudo first-order kinetic equation, and the observed rate constant (k_obs) with SCN/PS (0.132 min^-1) was 13 times of that with SCN (0.0102 min^-1), and twice of that with g-C₃N₄/PS (0.0649 min^-1). The quenching experiments and electron paramagnetic resonance analysis indicated that O₂^-· and ¹O₂ played the main role and other active species (e.g., h⁺, SO₄^-· and ·OH) also participated in CIP degradation. The possible degradation pathways were proposed through identifying the intermediate products, and the main reactions may include the ring opening of piperazine, decarbonylation, decarboxylation and defluorination. Bacterial toxicity test showed that the toxicity of the reaction solution decreased dramatically after 30 min degradation. Overall, this work could provide an efficient and environmentally friendly technology for eliminating CIP.

Aquaculture drug degradation in persulfate by PANI-based microparticles controlled via ultrasonic field: Forced motion of "burning hot micromotors"

The triphenylmethane derivative malachite green (tpm_MaG) despite repeated prohibitions but is frequently detected in aquatic environment and draws emerging attention because of the potential poisonous effects. The polyaniline/persulfate with ultrasound catalysis (US/PANI-PS) was developed for tpm_MaG removal. The effects of 12 factors and the optimization by response surface methodology (RSM) for tpm_FG removal were evaluated based on the pseudo-first-kinetics (k_obs). From free radical inhibition, the ratios of active species in US/PANI-PS (δ₁₁ = 0.355, δ₁₂ = 0.593) were close to that in US-PS (δ₂₁ = 0.346, δ₂₂ = 0.586) and different to that in PANI-PS and PS systems. A possible degradation pathway (hydroxylation, N-demethylation, deamination, and open-benzene ring) was explored by gas chromatography-mass spectrometer (GC/MS) and high performance liquid chromatography-mass spectrometer (HPLC-MS). The designed reactor involving the US-driven PANI was simulated by acoustic-piezoelectric interaction. From cavitation calculations, the estimated effective-mean temperature at bubble-water interface had little increasing (from 704 K to 711 K) after adding the PANI, however, the adsorption capacity of tpm_MaG in reactive zone decreased from 0.0891 μM to 0.0787 μM. The mechanism (PANI hot turbo-micromotors) with US/PANI-PS was proposed. The tpm_MaG was removed with a low treatment cost of 2.81 $⋅m^-3 (the EE/O value 18.29 kWh⋅m^-3) by US/PANI-PS, presenting a cost-effective treating process. The reusability tests and characterizations (contact angle, X-ray diffraction (XRD), and scanning electron microscope (SEM)) further confirmed the stability of PANI.

Mechanisms of persulfate activation on biochar derived from two different sludges: Dominance of their intrinsic compositions

Sludge-derived biochar (SDBC) has been regarded as persulfate (PS) activator during the remediation of organic contamination. However, the complexity of sludge composition makes it difficult to predict the activity of SDBC and the efficacy of PS. To improve the understanding of how the composition of sludge regulated activity of its parent SDBC towards PS activation, we used two SDBCs derived from different sludges with significantly different organic compositions and metals. Results indicated the higher content of organic and nitrogen content in sludge led to higher polymerization and condensation of carbon layer and more moieties in SDBC1, whereas more Fe species (e.g. Fe-O, Fe²⁺ and Fe³⁺) formed in SDBC2. According to the results of phenol (PN) degradation in SDBC/PS, the apparent rate constants (k_obs) of SDBC2-700 (0.0037 min^-1) was 2 folds higher than that of SDBC1-700 (0.0016 min^-1), whereas the SDBC1-500 (6.0 ×10^-4 min^-1) exhibited higher k_obs than that of SDBC2-500 (4.9 ×10^-4 min^-1). The difference of PS activation by different SDBCs mainly relied on generated reactive oxygen species (ROS). The persistent free radicals (PFRs) and Fe species acted as redox sites for generated ROS, which were depended on the organic compositions and involved metals in used sludges.

The oxidative degradation of Caffeine in UV/Fe(II)/persulfate system-Reaction kinetics and decay pathways

In this study, the degradation of caffeine was investigated by UV/Fe²⁺ /persulfate (PS) process. Caffeine (CAF) degradation in sole-UV, UV/Fe²⁺ , UV/PS, and Fe²⁺ /PS systems was also conducted to examine the contribution of isolated processes to CAF degradation. The effects of pH levels, the concentration of Fe²⁺ and PS, inorganic anions, and initial concentration of CAF on the performance of UV/Fe²⁺ /PS process were evaluated. Radical competitive reactions indicated both hydroxyl radicals and sulfate radicals played important roles in CAF degradation in UV/Fe²⁺ /PS system. Nine intermediates, among which three were detected for the first time, were identified by ultra-performance liquid chromatography/electrospray-time-of-flight mass spectrometry (UPLC/ESI-TOF-MS) and SPME (solid-phase microextraction)/GC/MS. The possible degradation pathways of CAF were proposed, among which demethylation, hydroxylation, the oxidation of olefinic double bond, and the cleavage of pyrimidine ring and imidazole ring were involved in the degradation of CAF in UV/Fe²⁺ /PS system. PRACTITIONER POINTS: Caffeine degradation by UV/Fe²⁺ /PS process was investigated. Caffeine degradation did not follow a simple pseudo-first order kinetics Chloride ions promoted CAF degradation. The anions NO₃ ^- , SO₄ ^2- , and H₂ PO₄ ^- exerted a negative influence on caffeine degradation. Nine intermediates were detected, and decay pathways were proposed.

Microwave photo-oxidation with diverse oxidants for Congo red degradation: effect of oxidants, degradation pathway and economic analysis

The present study investigated the efficacy of microwave photo-oxidation (MWPO) process with two oxidants i.e. persulphate (PS) and hydrogen peroxide (H₂O₂) for degradation of Congo red (CR). The result indicated a CR degradation efficiency of 98% and 96.8% with PS and H₂O₂, respectively, in 30 min of reaction with corresponding PS dosage of 50 mg/L and H₂O₂ dosage of 180 mg/L. The COD removal efficiency with the two oxidants were 97.7% and 94.9%, respectively. Higher dosages of oxidant and CR reduced the efficiency of the process in both the cases due to self-quenching. Effect of pH and initial CR concentration on CR removal efficiency also has been studied. Degradation of CR followed pseudo-first-order kinetics with a removal rate constant of 0.12/min and 0.09/min, respectively, with PS and H₂O₂. The main mechanism of CR degradation was cleavage of the benzene-benzene bond, cleavage of benzene-N bond and hydroxylation. Economic analysis of the MWPO process indicated an energy consumption of 18.3 kWh/g of CR removal and 18.4 kWh/g of COD removal. The process was effective in the rapid degradation and mineralization of high concentration of CR within 30 min.