Dominant Free Radical Research Articles

Degradation kinetics, influencing factors, and mechanisms of polycyclic aromatic hydrocarbons in a Fe3O4-nZVI Fenton-like system

To improve the catalytic performance of nano zero-valent iron (nZVI) in a Fenton-like system, Fe3O4 supported nZVI (Fe3O4-nZVI) was produced by the liquid-phase reduction method and co-precipitation method, then characterized by SEM, EDS, XRD, XPS, and VSM. Fe3O4-nZVI was used as the catalyst in a Fenton-like system to degrade polycyclic aromatic hydrocarbons (PAHs) such as naphthalene (Nap), phenanthrene (Phe), and pyrene (Pyr) in simulated wastewater. The results showed that under the optimization conditions, which were 25℃, 0.6g/L of Fe3O4-nZVI dosage, 3 of the pH in the reaction system, and 10-15mmol/L of the concentration of H2O2, the sequence of degradation efficiency in this system was Phe (99.76%)>Pyr (99.71%)>Nap (98.01%). The reused experiments on Fe3O4-nZVI showed that the degradation efficiency for PAHs remained above 87% after 4 reuses of Fe3O4-nZVI. These results indicated that nanoscale magnetic composites of Fe3O4-nZVI had excellent reactivity, stability, and reuse performance. The fitting parameters of kinetics showed that the degradation of PAHs in the Fenton-like system with the Fe3O4-nZVI catalyst fitted well with the Behnajady-Modirshahla-Ghanbery kinetic model. The radial quenching experiment proved that ·OH was the dominant free radical for the degradation of PAHs in the Fe3O4-nZVI Fenton-like system. Based on the degradation products of PAHs and the related literature, the possible degradation paths of the three PAHs in the Fe3O4-nZVI Fenton-like system were inferred. The above results could provide a reference and basis for the treatment of wastewater containing PAHs by Fe3O4-nZVI Fenton-like technology.

Long-Term Stable Dispersion of Multiwalled Carbon Nanotubes by Peroxydisulfate upon Ultrasonication Activation.

Poor dispersibility of carbon nanotubes greatly hinders their practical applications. Herein, a long-term stable dispersion of multiwalled carbon nanotubes (MWCNTs) in peroxydisulfate (PDS) is achieved. MWCNTs at 40mgL-1 are completely dispersed by PDS upon ultrasonication (US/PDS) within 64min and a stable dispersion is maintained at least 20 days. Mechanistically, US created defects on the nanomaterial and PDS-origin free radicals attacked these defects to introduce O-containing moieties (─OH and ─COOH). Interestingly, dispersion efficiency of MWCNTs by US/PDS initially at pH 7 and 3.8 is comparable, but lower than that initially at pH 12. Both •OH and SO4 •- are produced under alkaline condition, while SO4 •- is the dominant free radicals initially at pH 7 and 3.8 during the whole dispersion period. Stronger dispersion of MWCNTs initially at pH 12 resulted from greater amounts of O-containing moieties mainly in ─OH (46.32%) rather than ─COOH (24.19%) form. This differential more strongly promotes MWCNTs-water interaction via hydrogen bonding, thereby enhancing the dispersion. Notably, no significant mass loss of MWCNTs occurred during dispersion. Overall, the developed method achieves long-term stable dispersion of MWCNTs in a manner that can significantly extend their applications.

Visible light enhanced the degradation of sulfadiazine with persulfate activated by Cu2O@zeolite

ABSTRACT Cu2O/ZL-10 was successfully fabricated as a good activator of PDS and photo-catalyst. The physicochemical characteristics of the prepared Cu2O/ZL-10 were investigated. Cu2O/ZL-10 was employed to activate PDS for the sulfadiazine (SDZ) degradation under visible light irradiation. In the Vis/Cu2O/ZL-10/PDS system, 91.98% degradation rate of SDZ and 51.8% TOC removal after 180 min reaction were obtained. The SDZ degradation rate was improved significantly by the increase of the doping amount of Cu2O, PDS concentration and Cu2O/ZL-10 addition while it decreased with the growth initial pH. Moreover, the SDZ degradation rate descend by only 0.9% after five cycles uses of Cu2O/ZL-10. Quenching experiments and EPR spectra demonstrated that the dominant free radicals of •O2 –, SO4 •– and •OH were generated for the SDZ degradation. It demonstrated that Cu2O/ZL-10 was an effective and promising catalyst for the simultaneous activation of PDS and the utilization of visible light to generate active species and photo-induced electron, respectively.

N, S, and Cl tri-doped carbon boost the switching of radical to non-radical pathway in Fenton-like reactions: Synergism of N species and defects

Heteroatom doping represents a promising strategy for enhancing the generation of singlet oxygen (1O2) during the activation of peroxymonosulfate (PMS) using carbon-based catalysts; however, it remains a formidable challenge. In this study, we systematically controlled the structure of metal-free carbon-based materials by introducing different heteroatoms to investigate their efficacy in degrading organic pollutants in water via PMS activation. The results of reactive oxygen species detection showed that the dominant free radical in the four samples was different: CN (•SO4- and •OH), CNS (•O2-), CNCl (1O2), and CNClS (1O2). This led to the transformation of active species from free radicals to non-free radicals. The tri-doped carbons with nitrogen, sulfur, and chlorine (CNClS) exhibited exceptional performance in PMS activation and achieved a remarkable degradation efficiency of 95% within just 6 min for tetracycline. Moreover, a strong linear correlation was observed between the ratio of pyridine-N/graphite-N and ID/IG with the yield of 1O2, indicating that N species and defects play a crucial role in CNClS as they facilitate the transition from radical to non-radical pathways during PMS activation. These findings highlight the possibility that adjustable tri-heteroatom doping will expand the Fenton-like reaction for the treatment of actual wastewater.

Monodispersed Co-N3 loaded carbon nitride mediated peroxymonosulfate activation for rapid degradation of trace urea via singlet oxygen

The removal of trace urea presents a significant challenge in the production of electronic-grade ultra-pure water (UPW). This study proposed a simple strategy to regulate the low-coordination of a single-atom cobalt catalyst (RyCo-CN0.20) for the efficient removal of trace urea via peroxymonosulfate (PMS) activation. The optimal R0.50Co-CN0.20 with low-coordination Co-N3 sites was constructed by in-situ reduction of NaBH4 and significantly enhanced the PMS activation. The removal efficiency of trace urea achieved 94 % within 5 mins. The kobs of trace urea degradation in R0.50Co-CN0.20/PMS system reached 0.4576 min−1, which was much higher than previous reported systems. Experiments of free radical quenching and electron paramagnetic resonance demonstrated that singlet oxygen species were the dominant free radical. The corresponding steady concentration of singlet oxygen species in the R0.50Co-CN0.20/PMS system was enhanced to be 16.361 × 10–6 μM, which was twice of Co-CN0.20/PMS. Density functional theory calculations revealed that the optimized electron distribution of the Co center in the Co-N3 sites processed a higher d band center (−1.08 eV) and richer electron transfer number (0.75 e−) compared with Co-N4 sites, hence realizing the stronger PMS activation. Continuous operation verified that R0.50Co-CN0.20/PMS could maintain the removal rate of trace urea above 80 % after 150 h operation. Moreover, R0.50Co-CN0.20/PMS in the pilot UPW production process effectively reduced the pollution caused by trace urea and ensured the quality of the terminal UPW (Total organic carbon <1 μg/L). This study provides a new approach for the removal of trace urea through PMS activation by low-coordination single-atom catalysts.

Improving sewage sludge dewaterability via heterogeneous activation of persulfate by Fe–Al layered double hydroxide: Role of generated SO4−•

In this study, Fe–Al layered double hydroxide (Fe–Al LDH) was prepared and applied to activate persulfate to condition sewage sludge and improve its dewaterability. The results showed that Fe–Al LDH activated persulfate to generate a large amount of free radicals, which attacked extracellular polymeric substances and reduced their content, disrupted microbial cells, released bound water, decreased sludge particle size, increased sludge zeta potential, and improved sludge dewaterability. After sewage sludge was conditioned with Fe–Al LDH (0.20 g/g total solids (TS)) and persulfate (0.10 g/g TS) for 30 min, the capillary suction time of the sludge dropped from 52.0 s to 16.3 s, while the moisture content of the sludge cake decreased from 93.2% to 68.5%. The dominant active free radical produced by the Fe–Al LDH-activated persulfate was SO4−•. The maximum Fe3+ leaching of the conditioned sludge was only 102.67 ± 4.45 mg/L, thus effectively alleviating the secondary pollution of Fe3+. The leaching rate of 2.37% was significantly lower than that of the sludge homogeneously activated with Fe2+ (738.4 ± 26.07 mg/L and 71.00%).

Magnetic nanoreactor Fe3O4@HNTs as heterogeneous Fenton-like catalyst for acid fuchsin degradation: Efficiency, kinetics and mechanism

Compared with traditional heterogeneous Fenton catalysis, iron-based catalysts with nano-confinement effect could significantly improve the effectiveness for organic pollutants degradation, due to the shorter migration distance and longer half-life of reactive oxygen species (ROS). Here, we encapsulated the Fe3O4 nanoparticles in the lumen of halloysite nanotubes (HNTs) by means of the electrostatic interactions to fabricate the Fe3O4@HNTs nanoreactor with an outstanding Fenton-like catalytic performance. The instrumental characterizations indicated that the Fe3O4 NPs successfully loaded on the inner wall of HNTs. An active dye acid fuchsin (AF) was chosen as the target pollution to evaluate the Fenton-like catalytic performance of Fe3O4@HNTs nanoreactor. The experimental results showed that the degradation efficiency of 50 mg L−1 AF could approach 100% in 120 min reaction time under almost neutral pHs. To have an insight into the Fenton-like mechanism of Fe3O4@HNTs nanoreactor, the comparisons of AF degradation in different systems, dominant free radicals, iron leaching concentration, H2O2 decomposition efficiency, and ·OH production efficiency were investigated in details. In addition, the degradation pathways of AF were also predicted based on the density functional theory, frontier orbit theory, and high performance liquid chromatography-quadrupole-time of flight mass spectrum (HPLC-QTOF-MS) technique.

Ascorbic acid promoted sulfamethoxazole degradation in MIL-88B(Fe)/H2O2 Fenton-like system

In this work, the presence of ascorbic acid (AsA) in MIL-88B(Fe)/H2O2 system was demonstrated to significantly increase the sulfamethoxazole (SMX) degradation efficiency. The SMX degradation rate in AsA/MIL-88B(Fe)/H2O2 system was 0.177 L/(mg∙min), which was 60 times that of the MIL-88B(Fe)/H2O2 system. Moreover, the study shows that AsA not only promotes SMX degradation in Fenton-like systems but also expands its pH application range. The effect of coexisting anions on the catalytic performance of the AsA/MIL-88B(Fe)/H2O2 system was also investigated. Then, reactive species were detected via quenching experiments, which indicated •OH as the dominant free radical contributing to SMX degradation. Meanwhile, ESR determinations confirmed the existence of •OH and O2 − • in AsA/MIL-88B(Fe)/H2O2 system. The high activity of the AsA/MIL-88B(Fe)/H2O2 system was attributed to the effective surface Fe(III)/Fe(II) cycle promoted by AsA, and a possible mechanism of the AsA/MIL-88B(Fe)/H2O2 system is proposed. The possible pathways for SMX and AsA degradation in the AsA/MIL-88B(Fe)/H2O2 system are proposed based on the identified intermediates and the ecotoxicity analysis was conducted by ECOSAR. Finally, experimental results using the actual surface water and groundwater revealed the excellent availability of AsA/MIL-88B(Fe)/H2O2 system in remediating SMX contaminated water. This study presents a novel, efficient Fenton-like system using AsA and iron-based metal-organic frameworks for sulfonamide removal from water.

Insight into photo-fenton catalytic degradation of tetracycline by environmental friendly nanocomposite 1T-2H hybrid phases MoS2/Fe3O4/g-C3N4

Photogenerated charge recombination is a bottleneck in the field of photocatalysis. Polycrystalline materials may be an actual way to solve this problem. In this study, a novel 1T-2H hybrid phases MoS2/Fe3O4/g-C3N4 nanocomposite (MFG) was synthesized to improve the photo-Fenton degradation under visible light on tetracycline whose emergence in water environment had attracted great public attention. We got an insight into the photo-Fenton catalytic effect on tetracycline via detailed investigation and discussion. MFG was synthesized by calcination, hydrothermal and coprecipitation. The successful synthesis of 1T-2H hybrid phases MoS2 (HP–MoS2), as a polycrystalline material, was proved by XRD and XPS. After HNO3 treatment, the grain size of bulk g-C3N4 decreased obviously, and the photocatalytic effect was also improved. It showed stable performance and significant photo-Fenton catalytic activity when H2O2 was at low concentration. Especially, the best degradation efficiency of tetracycline had been more than 80% at 0.003M H2O2 within 30min. HCO3− had an obvious inhibition effect on the reaction compared with SO42−, Cl−, and NO3−, and a reasonable explanation was proposed that HCO3− reacts with •OH to form less reactive free radicals. Free radical quenching experiments and EPR proved that •OH and •O2− were the dominant free radicals. The LC-MS was employed to identified the intermediate products of TC. The synergistic effect of HP-MoS2 and acid-treated g-C3N4(HCN) improved the transfer efficiency of photogenerated charges and promoted the reduction of Fe3+, which accelerated the photo-Fenton reaction. Moreover, the reusability of the composite was observed up to four cycles and showed good recycling performance during the degradation of tetracycline.

Sulfate radicals induced from peroxymonosulfate on electrochemically synthesized TiO2-MoO3 heterostructure with Ti-O-Mo bond charge transfer pathway for potential organic pollutant removal under solar light irradiation.

Here, a novel method for synthesis of heterostructured TiO2-MoO3 (MT) nanosheets photocatalyst by utilizing a facile electrochemical method and examined it's photocatalytic activity by the degradation of tetracycline hydrochloride (TCH), a model of organic pollutants, in the presence of peroxymonosulfate (PMS) under solar light irradiation (SL) was reported for the first time. The influence of several factors on the degradation efficiency including the initial concentration of TCH, solution pH, catalyst dosage, PMS concentration, and the existence of inorganic anions was explored. The MT-15/PMS system displayed a promising photocatalytic performance and up to 97% of TCH was degraded in 90min the rate of the degradation reaction of MT-15/PMS was the highest (0.05299 min-1) compared to 0.00251, 0.00337, 0.00546, 0.00735, 0.01337min-1of TiO2-P25, TiO2-P25/PMS, MoO3, MoO3/PMS, and MT-15 respectively. The enhancement can be attributed to several reasons. First, the 2D morphology of the optimized heterostructure photocatalyst plays a significant role in providing much more active sites on its surface. Next, the boosted light absorption efficiency and higher photoproduced electron-hole pair separation ability, induced by the unique direct transformation of photogenerated electrons from the valance band of TiO2 to the conduction band of MoO3 via the Ti-O-Mo bond formed at the interface of MT heterostructure. Finally, the appropriate accessible reactive sites for the activation of PMS together with the synergistic effect between activation of PMS and photocatalytic processes eased the production of active species for the degradation of pollutants. Based on the scavenger experiments and EPR analysis, hydroxide and sulfate radicals were found to be the dominant free radical active species in the degradation process. Furthermore, the synergistic degradation reaction mechanism was proposed.

Photocatalytic degradation of crystal violet on titanium dioxide/graphene aerogel doped sulfur

In this study, titanium dioxide/graphene aerogel doped sulfur (S-TiO2/GA) was successfully synthesized by the coprecipitation method with the precursors including titanium isopropoxide, graphene oxide, and thiourea. The S-TiO2/GA material was characterized by different advanced analysis methods. The doping between titanium dioxide (TiO2) and S increased the degree of anatase, reduced the bandgap energy, and enhanced the absorption and photoactivity of the S-TiO2/GA material. The degradation efficiency was evaluated via crystal violet (CV) under UV light illumination. The effects of five parameters such as (1) photocatalyst dosage, (2) pH, (3) CV concentration, (4) Adsorption time, and (5) irradiation time, were investigated by the Plackett-Burman and Box-Behnken models to select the optimal conditions for the CV degradation process of the S-TiO2/GA material. Besides, the mineralization of the S-TiO2/GA was evaluated via the total organic carbon parameter. The dominant free radical for the photodegradation of CV was also found. The aforementioned results also confirmed the promising applications of the material in environmental treatments.

Compound-specific isotopic analysis to characterize the photocatalytic reaction of TiO2 nanoparticles with diethyl phthalate

In this study compound-specific isotope analysis (CSIA) has been used to explore the degradation mechanism of nano titanium dioxide (TiO2) catalyzes photodegradation of diethyl phthalate (DEP). TiO2 is a popular photosensitizer with potential in waste water treatment and application in advanced oxidation processes. The degradation process of DEP can be described with a first-order kinetics in the applied concentration ranges. The larger degradation rate constant has been found at neutral conditions. The 13C and 2H isotope fractionation associated with the nano TiO2 catalyzes photodegradation of DEP at pH 3, 7 and 11 yield normal isotope effects. In the TiO2/UV/DEP and TiO2/H2O2/UV/DEP systems, the correlation of 13C and 2H fractionation (Λ) were calculated to be 2.7 ± 0.2, 2.8 ± 0.2 at pH 3, 2.2 ± 0.4, 2.5 ± 0.2, 2.3 ± 0.6 at pH 7 and 2.6 ± 0.3, 2.2 ± 0.3, 2.7 ± 0.2 and 2.3 ± 0.3 at pH11, respectively. The dominant free radical species in studied systems were explored by combining free radical quenching method and electron paramagnetic resonance analysis. The hydroxyl radicals have been found as the main radical species at all pH conditions studied. Furthermore, the 13C and 2H fractionation suggested that the addition of •OH on the benzene ring of DEP is the main conversion pathway. Therefore, CSIA is a promising technology for the identification of reaction pathways of DEP for example in water treatment systems.

MOFs decorated sugarcane catalytic filter for water purification

MOFs nanoparticles decorated sugarcane-based cellulose hierarchical porous framework as a free-standing catalytic filter for water purification. • ZIF-67 are in-situ immobilized on sugarcane to achieve ZIF-67@SC catalytic filter. • The ZIF-67@SC shows high catalytic activity and treatment flux for MB degradation. • The amount of ZIF-67 loaded regulates the catalytic performance of ZIF-67@SC. • Dominant free radicals (SO 4 - · and ·OH) during MB degradation are verified. • Proof-of-concept continuous-flow water purification devices are demonstrated. Developing high-performance catalytic filter with both high removal efficiency and ultra-high flux, especially under gravity-driven conditions, is of great significance yet still a fundamental challenge in organic wastewater purification. Herein, a high-efficiency gravity-driven catalytic filter, ZIF-67 decorated sugarcane that is denoted as ZIF-67@SC sponge, is successfully constructed by the in-situ growing ZIF-67 nanoparticles inside the channels of biomass sugarcane skeleton. Pretreatment of cellulose fibers with alkali can set the nucleation sites for the ZIF-67 nanocrystals decoration on the sugarcane skeleton, which originates from the ion exchange between Co 2+ and Na + . The effect of the perforated plate structures of sugarcane on fluid obstruction and the widely distributed ZIF-67 nanoparticles can synergistically enhance the contraction between organic pollutants and ZIF-67 nanoparticles. The resultant ZIF-67@SC sponge therefore exhibits the superior removal efficiency up to 86.99 % for methylene blue (MB) in water with the water treatment flux of ∼ 2720 L m -2 h −1 under the activation of peroxymonosulfate (PMS). Importantly, the ZIF-67@SC sponge catalytic filter can be readily regenerated by a simple methanol washing, maintaining the removal efficiency of 82.09 % after even 10 continuous regeneration cycles. Furthermore, the ZIF-67@SC sponge catalytic filter can be facilely engineer as a continuous-flow catalytic reactor like a water purifier for high throughout wastewater purification. It’s believed that relying on the outstanding catalytic performance of metal–organic frameworks (MOFs) and the unique skeletons of sugarcane and other biomass materials, the present outcomes can be promising by extended to the large-scale water remediation.

Insights into the performance, mechanism, and ecotoxicity of levofloxacin degradation in CoFe2O4 catalytic peroxymonosulfate process

The catalysis effectiveness and influence factors of CoFe2O4 nanoparticles were investigated with peroxymonosulfate (PMS) as oxidant. Meanwhile, the degradation mechanism of levofloxacin (LVF) and the toxicity of its degradation products were analyzed. Efficient LVF degradation (95.4%) could be achieved within 30 min in CoFe2O4/PMS system with the optimum reaction conditions. The removal efficiency of LVF was decreased from 94.66% to 27.38% as the concentration of HCO3− increased from 0 to 20 mM, while increased to nearly 100% with 5 mM H2PO4− addition. The inhibition effect of Cl− on LVF removal decreased as the concentration of Cl− increased, and the addition of humic acid did not affect the final removal efficiency of LVF significantly. According to the results of degradation experiments and XPS analysis, both Co(II)/Co(III) and Fe(II)/Fe(III) redox pairs were involved in PMS catalysis, and Co(II)/Co(III) played a dominant role. SO4•− was the dominant free radical in CoFe2O4/PMS system for LVF degradation, and five possible degradation pathways were proposed based on the eleven degradation products. Compared with LVF, more toxic degradation products were generated in degradation pathways of decarboxylation and conversion of quinolone moieties, due to the coexisting of SO4•− and HO•. Meanwhile, the luminescence inhibition ratio of the reaction solution (23.5%) was still higher than the original LVF solution (21.4%) by the end of the experiment. Therefore, the degradation pathways that generate toxic products should be avoided or detoxification by the complete mineralization of LVF, which needs further research via the targeted optimization of CoFe2O4/PMS system.

Removal of Ciprofloxacin from Wastewater by Ultrasound/Electric Field/Sodium Persulfate (US/E/PS)

Ciprofloxacin (CIP), as a common antibiotic used in human clinical and livestock farming, is discharged into natural water bodies and its concentration has increased in the last years. Its stable chemical structure is difficult to remove by conventional techniques. Residual ciprofloxacin in the environment has become an emerging micropollutant that promotes the generation of resistance genes of bacteria and endangers ecosystem balance and human health. Removal of ciprofloxacin from water by the system of ultrasound/electric field/sodium persulfate (US/E/PS) was investigated. Firstly, CIP degradation affects by different oxidation methods, such as ultrasonic oxidation, electro-oxidation, and persulfate oxidation, and their four combined oxidation methods (ultrasound-activated persulfate oxidation, electro-activated persulfate oxidation, ultrasound-enhanced electro-oxidation, and ultrasound-enhanced electro-activated persulfate oxidation), on the target contaminants were compared. Secondly, the influences of parameters on the CIP degradation by an ultrasound-enhanced electro-activation-persulfate reaction system were investigated. Thirdly, the possible free radical species in the ultrasound-enhanced electro-activation-sulfate reaction system were identified and the dominant free radical species in the system were analyzed. Finally, the samples of CIP in the US/E/PS system were tested by liquid mass spectrometry, and the possible intermediate products and degradation path were speculated. The results indicate that the US/E/PS system is of great potential application value in the removal of organic pollution and environmental purification.

Synthesis of NaNbxTa1−xO3/g-C3N4 composite photocatalyst for enhanced removal of organic dye

Water pollution has received much attention and constructing efficient catalysts to photodegrade the pollutants is a promising method. Herein, we reported that a novel composite catalyst, NaNbxTa1−xO3/g-C3N4, exhibited high efficiency to degrade the model pollutant, methylene blue (MB), in ultraviolet light. The optimal catalyst was NaNb0.75Ta0.25O3/g-C3N4 (1:9), which degraded 99.6% of MB (10 mg/L) after 180 min of reaction. The superior photocatalytic activity was attributed to the formation of the Z-scheme heterojunction, which could suppress the recombination of the photogenerated electron-hole pairs and protect the high redox potentials simultaneously. Hydroxyl radicals (.OH) and superoxide radicals (.O2-) were found to be the dominant active free radicals in the reaction process and a possible photocatalytic mechanism over the catalyst was proposed accordingly. This work provides an efficient direction to fabricate composite photocatalysts and helps to overcome the shortcomings of a single catalyst.

Enhanced effects of reducing agent on oxalate chelated Fe(II) catalyzed percarbonate system for benzene degradation

Abstract The addition of hydroxylamine hydrochloride (HAH), ascorbic acid (ASC), sodium ascorbate (SAS) to the OA-Fe(II)/SPC system could promote the generation of HO• by accelerating Fe(II)/Fe(III) recycles and H2O2 decomposition. The enhancement of HAH on HO• generation surpasses ASC and SAS in the OA-Fe(II)/SPC system. The generation of O2•− was also enhanced by HAH, ASC and SAS, and more significant promotion of O2•− generation was observed with ASC and SAS addition. More effective benzene removal was achieved in an OA-Fe(II)/SPC system with suitable HAH, ASC and SAS addition, compared to the parent system. Excessive HAH, ASC or SAS had a negative effect on benzene removal. Results of scavenger tests showed that HO• is indeed the dominant free radical for benzene removal in every system, but the addition of HAH, ASC and SAS increased the contribution of O2•− to benzene degradation. HAH, ASC and SAS enhanced OA-Fe(II)/SPC systems could be well utilized to acidic and neutral conditions, while HCO3−, high concentration of HA and alkaline conditions were not favorable to benzene removal. Moreover, the addition of HAH, ASC and SAS are conducive to benzene removal in actual groundwater, and HAH was the optimal reducing agent for the enhancement of the OA-Fe(II)/SPC system.

Novel Fe0-C/S(IV) system: Toward the interaction between Fe0-C internal electrolysis and sulfite for p-nitrophenol degradation

In this study, an innovative redox system concerning Fe0-C internal electrolysis combined with sulfite (S(IV)) was first developed for p-nitrophenol (PNP) removal. The effects of different influencing factors including the Fe0/C mass ratio, sulfite concentration, initial pH value and aeration rate were comprehensively investigated in batch experiments. Satisfactorily, the maximum removal and mineralization of PNP reached 92.5% and 59.9%, respectively, in the Fe0-C/S(IV) system. Fe0-C composites with nanosized zero-valent iron anchored on activated carbon had great potential to release Fe2+ and initiate the activation of S(IV). During the reactions, transformation from Fe3+ to Fe2+ was realized, which was attributed to complexation. Significantly, the surface complexation occurred in the diffusion boundary because of the active iron species (Fe(II)–OH) generated on Fe0-C composites, having a remarkable activation effect on S(IV). Furthermore, the reactivity of Fe0-C composites was maintained through the associated effects of the complexation, acid etching and oxidation erosion caused by S(IV). In the end, quenching and ESR experiments illustrated that HO and SO4− were the dominant free radicals, combined with the subordinate participation of SO3− and SO5−. Reduction and oxidation collaborated efficiently to degrade PNP, and Fe0-C internal electrolysis and S(IV) mutually promoted each other in the process, which fully motivated strong the potential of this Fe0-C/S(IV) system to deal with toxic and refractory wastewater.

A new synthesizing method of TiO2 with montmorillonite: Effective photoelectron transfer to degrade Rhodamine B

Montmorillonite (MMT), with many excellent features, such as nano-layered structure, ion exchange ability and high hydrophilicity, could be considered as a kind of modified materials, so it is widely applied in many fields. In this study, novel photocatalyst material-TMC, is synthesized via the method of filling cations, accomplishing with prepared by loading TiO2 on the surface of MMT, which is proposed to remove Rhodamine B (Rh-B) via photocatalytic degradation. In the preparing process, the negative potential of MMT plays an important role in uniformly distributing TiO2 as well as limiting the size of distributed particles. Meanwhile, obtaining more oxygen vacancies could be attributed to optimal by screen calcination temperature. In addition, the specific surface area of TMC is measured to be three times larger than that of single TiO2. Furthermore, coupled with UV-DRS, FT-IR, XPS and PL, it is confirmed that Ti-O-Si bonds have been formed, and the narrowest bandgap (2.79 eV) is formed with the sample that calcinated at 450 °C. Meanwhile, the positions of conduction band and valence band with TMC contribute that it reaches higher Fermi level as compared with single TiO2. In addition, the negative potential (on the surface of MMT) acts as effectively extending the recombination time between electrons (e-) and holes (h+), so that the transferred photoelectrons can directly form O2− to degrade Rh-B that adsorbed on the surface of MMT. Finally, the main free radical scavenging experiment is conducted to indicate that O2− and OH are the dominant free radicals that involve in photocatalytic process, and the degradation pathways for Rh-B are speculated with characterization of HPLC-MS.

Synergistic Reaction Mechanism of Cu0@Fe3O4 Activated PMS for Degradation of p-nitrophenol

A Cu0/PMS system mainly relies on the leaching of copper ions to degrade the pollutants and adapt to the narrow pH range (<7). To solve this defect, we studied the properties and reaction mechanism of Cu0@Fe3O4 magnetic core-shell material, which was successfully prepared using co-precipitation method, taking PNP as the target pollutant. The results showed that: ① a degradation rate of 96% can be achieved within 60 min for 5 mg ·L-1 PNP, 200 mg ·L-1 Cu0@Fe3O4, and 0.5 mmol ·L-1 PMS at a natural pH value (5.65); ② the Cu0@Fe3O4/PMS system can be regarded as a heterogeneous reaction system because TCu, TCu+, and iron leaching were almost negligible; ③ on comparing the performance of the Cu0@Fe3O4/PMS system and Cu0/PMS system in the pH range of 3 to 11, it was discovered that the method by which Cu0 activates the PMS to degrade the PNP was successfully changed by coating a layer of Fe3O4. The Cu0@Fe3O4/PMS system has a good degradation performance towards PNP in the pH range of 5-9; ④ SO-4 · and HO · existed in the reaction system, and their contribution rates to the reaction system were 34% and 60% ; HO · was the dominant free radical; ⑤ A bimetallic synergy exists between Fe and Cu. The presence of Cu(Ⅰ) can promote the reduction of Fe(Ⅲ) to Fe(Ⅱ), thereby forming a good redox cycle and improving the durability of the reaction system.