Removal of high concentration p-nitrophenol in aqueous solution by zero valent iron with ultrasonic irradiation (US-ZVI)

Rapid removal of ultra-high-concentration p-nitrophenol in aqueous solution by microwave-enhanced Fe/Cu bimetallic particle (MW-Fe/Cu) system

Ultra-high-concentration PNP-contained wastewaters are produced sometimes due to the wide application of this nitrophenolic compound in the chemical industry. However, there is a lack of appropriate technologies to rapidly pretreat the ultra-high-concentration wastewater. Therefore, a new microwave-enhanced Fe/Cu bimetallic particles (MW-Fe/Cu) system was developed to rapidly remove ultra-high-concentration PNP. First, the priority of the determinative parameters was obtained by orthogonal experiment. Based on this result, the effects of initial pH, microwave power, Fe/Cu dosage and initial PNP concentration on PNP removal were optimized thoroughly. Under the optimal conditions (i.e. initial pH = 1.0, MW power = 385 W, Fe/Cu dosage = 30 g/L and initial PNP concentration = 4000 mg/L), four control treatment systems (i.e. MW-Fe⁰, heating-Fe/Cu, MW alone and Fe/Cu alone system) were set up to compare with the MW-Fe/Cu system. The results suggest that high PNP removal (more than 99% with 2.5 min, k₁/k₂ = 1.18/6.91 min^-1) and COD removal (26.6% with 5 min treatment) could be obtained by the MW-Fe/Cu system, which were much superior to those obtained using the MW-Fe⁰ (k₁/k₂ = 0.62/2.21 min^-1) and the heating-Fe/Cu system (k₁/k₂ = 0.53/1.52 min^-1). Finally, the determination of the intermediates of PNP degradation by HPLC indicated that the MW assistance process did not change the degradation pathway of PNP. This concludes that the new MW-Fe/Cu system was the promising technology for pretreatment of wastewater containing ultra-high-concentration toxic and refractory pollutants at a fairly short treatment time.

Immobilization and characterization of Fe(0) catalyst on NaOH-treated coal fly ash for catalytic reduction of p-nitrophenol

In this study, coal fly ash (CFA), i.e., an industrial waste product created in large quantities by thermoelectric power plants, was treated with sodium hydroxide to afford a novel Fe (0) catalyst supported on alkaline-treated CFA. The NaOH-treated CFA (NCFA) exhibited a morphological change from slick spheres to pointed, leaf-like spheres, which was accompanied by a noticeable increase in specific surface area from 1.2 to 7.5 m²/g. Sequential addition of an Fe(III) precursor and NaBH₄ solution to a suspension of NCFA resulted in the formation of Fe (0) particles on the surface of NCFA (Fe/NCFA). The catalytic activity of Fe/NCFA toward the reduction of p-nitrophenol (p-NP) was examined; among the Fe/NCFAs synthesized from different NCFAs (1, 3, and 7 M NaOH), the Fe/3 M NCFA sample displayed the highest activity owing to the highest Fe content on its surface, without leaching any toxic heavy metals. In addition, the effects of NaBH₄ concentration, Fe loading, and catalyst dosage on the catalytic reduction of p-NP by Fe/NCFA were comprehensively investigated. Finally, the recyclability and stability of Fe/NCFA were examined, demonstrating the complete reduction of p-NP over four continuous recycling cycles. The present results demonstrate the marked potential of CFA as a component in reactive catalysts for the removal of environmental pollutants from wastewater.

Effect of pH on Zero Valent Iron Performance in Heterogeneous Fenton and Fenton-Like Processes: A Review

Heterogeneous Fenton processes with solid catalysts have gained much attention for water and wastewater treatment in recent years. In the field of solid catalysts, zero valent iron (ZVI) is among the most applicable due to its stability, activity, pollutant degradation properties and environmental friendliness. The main limitation in the use of ZVI in heterogeneous Fenton systems is due to its deactivation in neutral and alkaline conditions, and Fenton-like processes have been developed to overcome this difficulty. In this review, the effect of solution pH on the ZVI-Fenton performance is discussed. In addition, the pH trend of ZVI efficiency towards contaminants removal is also considered in oxic solutions (i.e., in the presence of dissolved O₂ but without H₂O₂), as well as in magnetic-field assisted Fenton, sono-Fenton, photo-Fenton and microwave-Fenton processes at different pH values. The comparison of the effect of pH on ZVI performance, taking into account both heterogeneous Fenton and different Fenton-like processes, can guide future studies for developing ZVI applications in water and wastewater treatment.

Combined ultrasound with Fenton treatment for the degradation of carcinogenic polycyclic aromatic hydrocarbons in textile dying sludge

To develop an effective method to remove the toxic and carcinogenic polycyclic aromatic hydrocarbons (CPAHs) from textile dyeing sludge, five CPAHs were selected to investigate the degradation efficiencies using ultrasound combined with Fenton process (US/Fenton). The results showed that the synergistic effect of the US/Fenton process on the degradation of CPAHs in textile dyeing sludge was significant with the synergy degree of 30.4. During the US/Fenton process, low ultrasonic density showed significant advantage in degrading the CPAHs in textile dyeing sludge. Key reaction parameters on CPAHs degradation were optimized by the central composite design as followed: H₂O₂ concentration of 152 mmol/L, ultrasonic density of 408 W/L, pH value of 3.7, the molar ratio of H₂O₂ to Fe²⁺ of 1.3 and reaction time of 43 min. Under the optimal conditions of the US/Fenton process, the degradation efficiencies of five CPAHs were obtained as 81.23% (benzo[a]pyrene) to 84.98% (benz[a]anthracene), and the benzo[a]pyrene equivalent (BaP_eq) concentrations of five CPAHs declined by 81.22-85.19%, which indicated the high potency of US/Fenton process for removing toxic CPAHs from textile dyeing sludge.

Homogenous UV/periodate process in treatment of p-nitrophenol aqueous solutions under mild operating conditions

Aqueous solutions of p-nitrophenol (PNP) were treated with UV-activated potassium periodate (UV/KPI) in an efficient photo-reactor. Either periodate or UV alone had little effect; however, their combination led to a significant degradation and mineralization. The response surface methodology was employed for design of experiments and optimization. The optimum conditions for treatment of 30 mg/L of the substrate were determined as [KPI] = 386.3 mg/L, pH = 6.2 and T = 34.6°C, under which 79.5% degradation was achieved after 60 min. Use of 25 and 40 kHz ultrasound waves caused the degradation to enhance to 88.3% and 92.3%, respectively. The intermediates were identified by gas chromatography-mass spectroscopy analysis, leading to propose the reaction pathway. The presence of water conventional bicarbonate, chloride, sulfate and nitrate anions caused unfavorable effects in efficiency. Meanwhile, the kinetic study showed that PNP degradation follows a pseudo-first-order reaction and the activation energy was determined. The irradiation energy consumption required for one order of magnitude degradation was estimated as 11.18 kWh/m³. Accordingly, comparison with the previously reported processes showed the superiority of PNP treatment with the employed process.

Enhanced Nitrobenzene reduction by zero valent iron pretreated with H2O2/HCl

In this study a novel iron-based reducing agent of highly effective reduction toward nitrobenzene (NB) was obtained by pretreating zero valent iron (ZVI) with H₂O₂/HCl. During the H₂O₂/HCl pretreatment, ZVI undergoes an intensive corrosion process with formation of various reducing corrosion products (e.g., Fe²⁺, ferrous oxides/hydroxides, Fe₃O₄), yielding a synergetic system (prtZVI) including liquid, suspensions and solid phase. The pretreatment process remarkably enhances the reductive performance of ZVI, where a rapid reduction of NB (200 mg L^-1) in the prtZVI suspension was accomplished in a broad pH range (3-9) and at low dosage. Nitrosobenzene and phenylhydroxylamine are identified as the intermediates for NB reduction with the end-product of aniline. Compared with the virgin ZVI as well as another nanosized ZVI, the prtZVI system exhibits much higher electron efficiency for NB reduction as well as higher utilization ratio of Fe⁰. A rapid reduction of various nitroaromatics in an actual pharmaceutical wastewater further demonstrated the feasibility of the prtZVI system in real wastewater treatment.

Enhancing the efficiency of zero valent iron by electrolysis: Performance and reaction mechanism

Electrolysis was applied to enhance the efficiency of micron-size zero valent iron (mFe⁰) and thereby promote p-nitrophenol (PNP) removal. The rate of PNP removal by mFe⁰ with electrolysis was determined in cylindrical electrolysis reactor that employed annular aluminum plate cathode as a function of experimental factors, including initial pH, mFe⁰ dosage and current density. The rate constants of PNP removal by Ele-mFe⁰ were 1.72-144.50-fold greater than those by pristine mFe⁰ under various tested conditions. The electrolysis-induced improvement could be primarily ascribed to stimulated mFe⁰ corrosion, as evidenced by Fe²⁺ release. The application of electrolysis could extend the working pH range of mFe⁰ from 3.0 to 6.0 to 3.0-10.0 for PNP removal. Additionally, intermediates analysis and scavengers experiments unraveled the reduction capacity of mFe⁰ was accelerated in the presence of electrolysis instead of oxidation. Moreover, the electrolysis effect could also delay passivation of mFe⁰ under acidic condition, as evidenced by SEM-EDS, XRD, and XPS analysis after long-term operation. This is mainly due to increased electromigration meaning that iron corrosion products (iron hydroxides and oxides) are not primarily formed in the vicinity of the mFe⁰ or at its surface. In the presence of electrolysis, the effect of electric field significantly promoted the efficiency of electromigration, thereby enhanced mFe⁰ corrosion and eventually accelerated the PNP removal rates.

Premagnetization enhancing the reactivity of Fe0/(passivated Fe0) system for high concentration p-nitrophenol removal in aqueous solution

In order to strengthen the treatment efficiency of Fe⁰ based system for high concentration wastewater treatment, Fe⁰ particles were passivated by concentrated nitric acid, and a premagnetization Fe⁰/(passivated Fe⁰) system was setup for high concentration p-nitrophenol (PNP) removal in this study. The significant parameters of this system were optimized. Under the optimal conditions, the premagnetization Fe⁰/(passivated Fe⁰) system could obtain high k_obs value for PNP removal (0.100 min^-1) and COD removal (15.0% after 60 min) for high concentration PNP (500 mg/L) treatment. In addition, five control experiments were set up to confirm the advantage of the premagnetization Fe⁰/(passivated Fe⁰) system. The results suggest that passivated Fe⁰ particles could be stimulated better than Fe⁰ particles by premagnetization process, and the premagnetization Fe⁰/(passivated Fe⁰) systems is much superior to the other five control systems. Furthermore, the pathway for PNP destruction treated by 6 different systems was also proposed according to intermediates determination by High Performance Liquid Chromatography (HPLC) and UV-vis spectrum, and the carbon mass balance was demonstrated according to the COD and HPLC analyses. Finally, the characteristics of (premagnetization) Fe⁰ and passivated Fe⁰ was detected by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and vibrating sample magnetometer (VSM), and the mechanism of premagnetization effectively enhancing the reactivity of Fe⁰/(passivated Fe⁰) system (better than that of Fe⁰ system) was proposed. Consequently, the premagnetization for reactivity improvement of Fe⁰/(passivated Fe⁰) system is a promising technology to enhance the efficiency of this system for high concentration wastewater treatment.

Ultrasonic assisted synthesis of palladium-nickel/iron oxide core-shell nanoalloys as effective catalyst for Suzuki-Miyaura and p-nitrophenol reduction reactions

In this study, ultrasonic assisted synthesis of Pd-Ni/Fe₃O₄ core-shell nanoalloys is reported. Unique reaction condition was prepared by ultrasonic irradiation, releasing the stored energy in the collapsed bubbles and heats the bubble contents that leads to Pd(II) and Ni(II) reduction. Co-precipitation method was applied for the synthesis of Fe₃O₄ nanoparticles (NPs). Immobilized solution was produced by sonicating the aqueous mixture of Fe₃O₄ and mercaptosuccinic acid to obtain Pd-Ni alloys on Fe₃O₄ magnetic NP cores. The catalytic activity of the synthesized Pd-Ni/Fe₃O₄ core-shells was investigated in the Suzuki-Miyaura CC coupling reaction and 4-nitrophenol reduction, which exhibited a high catalytic activity in both reactions. These magnetic NPs can be separated from the reaction mixture by external magnetic field. This strategy is simple, economical and promising for industrial applications.

Exploring the mechanism and kinetics of Fe-Cu-Ag trimetallic particles for p-nitrophenol reduction

Preparation conditions of Fe-Cu-Ag trimetallic particles were optimized by single-factor and response surface methodology (RSM) batch experiments to obtain high-reactive Fe⁰-based materials for p-nitrophenol (PNP) removal. Under the optimal conditions (i.e., Fe⁰ dosage of 34.86 g L^-1, theoretical Cu mass loading of 81.87 mg Cu/g Fe, theoretical Ag mass loading of 1.15 mg Ag/g Fe, and preparation temperature of 52.1 °C), the actual rate constant (k_obs) of PNP reduction in 5 min was 1.64 min^-1, which shows a good agreement between the model prediction (1.85 min^-1) of RSM and the experimental data. Furthermore, the high reactivity of Fe⁰-based trimetals was mainly attributed to the plating order of transition metals (i.e., Ag and Cu). Furthermore, we propose a new theory that the pyramid trimetallic structure of Fe-Cu-Ag could improve the electron transport and create active sites with high electron density at the surface (Ag layer) that could enhance the generation of surface-bonded atomic hydrogen ([H]_abs) or the direct reduction of pollutant. Moreover, Fe-Cu-Ag trimetallic particles were characterized by SEM, EDS, and XPS, which also could confirm the proposed theory. In addition, the leached Cu²⁺(<10 μg L^-1) and Ag⁺ (below detection limits) in Fe-Cu-Ag system could be neglected completely, which suggests that Fe-Cu-Ag is reliable, safe, and environment friendly. Therefore, Fe-Cu-Ag trimetallic system would be promising for the removal of pollutants from industrial wastewater.

Enhanced reactivity of microscale Fe/Cu bimetallic particles (mFe/Cu) with persulfate (PS) for p-nitrophenol (PNP) removal in aqueous solution

In this study, batch experiments were conducted to examine the enhanced reactivity of microscale Fe/Cu bimetallic particles (mFe/Cu) with persulfate (PS) for p-nitrophenol (PNP) removal in aqueous solution. The key operating parameters (i.e., theoretical Cu mass loadings (TML_Cu), mFe/Cu dosage, PS dose, initial pH and temperature) were optimized by the batch experiments, respectively. The experimental data were followed well the pseudo-first-order kinetic model. Result reveals that refractory PNP (500 mg L^-1) was effectively degraded by mFe/Cu-PS system with removal of 98.4% and k_obs of 1.91 min^-1 after only 3 min treatment under the optimal operating conditions. Moreover, compared with control experiments (i.e., mFe/Cu, microscale Fe⁰ with PS (mFe⁰-PS), and PS alone), mFe/Cu-PS system exerted better performance for PNP removal due to the strong synergistic effect between PS and mFe/Cu. According to the analysis results of degradation kinetics of PNP, COD (chemical oxygen demand) removal, UV-vis absorption spectra and the intermediates formed, the results reveal that the PNP removal by mFe/Cu-PS system was mainly attributed to reduction accompanied slight oxidation. And based on the analysis of surface characteristics of mFe/Cu particles, it is further demonstrated that PS could enhance the reactivity of mFe/Cu through rapid corrosion of iron surface and decrease of surface passivation of mFe/Cu surface when the low molar ratio of PS to mFe/Cu (i.e., 1:43) was used in this study. These results also illustrates mFe/Cu-PS can be as a high efficient pretreatment technology for the removal of toxic refractory PNP from wastewater.

Synthesis of a hierarchical structured NiO/NiS composite catalyst for reduction of 4-nitrophenol and organic dyes

The synthesis approach of the catalyst is simple and facile. The NiO/NiS catalyst is effective and universal towards reduction. NiS facilitates electron transfer for reduction reactions.

Facile green synthesis of functional nanoscale zero-valent iron and studies of its activity toward ultrasound-enhanced decolorization of cationic dyes

For the first time, an integrated green technology by coupling functional nanoscale zero-valent iron (NZVI) with ultrasound (US) was innovatively developed for the enhanced decolorization of malachite green (MG) and methylene blue (MB). The functional NZVI (TP-Fe) was successfully fabricated via a facile, one-step and environmentally-benign approach by directly introducing high pure tea polyphenol (TP), where TP contenting abundant epicatechin was employed as reductant, dispersant and capping agent. Note that neither additional extraction procedure nor protection gas was needed during the entire synthesis process. Affecting factors (including US frequency, initial pH, dye concentration, and reaction temperature) were investigated. Results show that TP-Fe exhibited enhanced activity, antioxidizability and stability over the reaction course, which could be attributed to the functionalization of TP on NZVI and the invigorating effect of US (i.e., improving the mass transfer rate, breaking up the aggregates of TP-Fe nanoparticles, and maintaining the TP-Fe surface activity). The kinetics for MG and MB decolorization by the TP-Fe/US system could be well described by a two-parameter pseudo-first-order decay model, and the activation energies of MG and MB decolorization in this new system were determined to be 21 kJ mol^-1 and 24 kJ mol^-1, respectively. In addition, according to the identified reaction products, a possible mechanism associated with MG and MB decolorization with the TP-Fe/US system was proposed.

Sonocatalytic degradation of diclofenac with FeCeOx particles in water

This paper studies the sonocatalytic degradation of diclofenac in water using FeCeO_x-catalyzed ultrasound. The effects of pre-adsorption and gas addition were investigated. Nitrogen adsorption/desorption, SEM, XRD, Raman and XPS analyses of FeCeO_x before and after sonication were characterized. The proposed mechanism was based on the microstructure changes of FeCeO_x and reactive-species-scavenging performances. The results show that FeCeO_x has excellent performance in catalyzing an ultrasonic system in water, and 80% of diclofenac was removed in 30min ([Diclofenac]=20mg/L, FeCeO_x amount=0.5g/L, pH=6, ultrasonic density=3.0W/cm³, ultrasonic frequency=20kHz, temperature=298K). The Fe, Ce, and O elements remained highly dispersed in the structure of FeCeO_x, and the solid solution structure of FeCeO_x remained stable after the reaction. Ce (III) was gradually oxidized to Ce (IV) and Fe (III) was gradually reduced to Fe (II) after the reaction, which indicates that Fe and Ce ions with different valences coexisted in dynamic equilibrium. The amount of oxygen vacancies in FeCeO_x significantly decreased after the reaction, which indicates that oxygen vacancy participated in the ultrasonic process. Singlet oxygen ¹O₂ was the primary reactive species in the degradation process, and the hydroxyl radicals OH and superoxide radical anion O₂^- also participated in the reaction. FeCeO_x had excellent chemical stability with negligible leaching ions in the ultrasonic process.

New insights into the activity of a biochar supported nanoscale zerovalent iron composite and nanoscale zero valent iron under anaerobic or aerobic conditions

To gain insight into the mechanism of p-nitrophenol removal using the biochar supported nanoscale zerovalent iron composite and nanoscale zero valent iron under anaerobic or aerobic conditions, batch experiments and models were conducted.

pH-dependent degradation of p-nitrophenol by sulfidated nanoscale zerovalent iron under aerobic or anoxic conditions

Sulfidated nanoscale zerovalent iron (S-NZVI) is attracting considerable attention due to its easy production and high reactivity to pollutants. We studied the reactivity of optimized S-NZVI (Fe/S molar ratio 6.9), comparing with pristine nanoscale zerovalent iron (NZVI), at various pH solutions (6.77-9.11) towards p-nitrophenol (PNP) under aerobic and anoxic conditions. Studies showed that the optimized extent of sulfidation could utterly enhance PNP degradation compared to NZVI. Batch experiments indicated that in anoxic S-NZVI systems the degradation rate constant increased with increasing pH up to 7.60, and then declined. However, in aerobic S-NZVI, and in anoxic or aerobic NZVI systems, it decreased as pH increased. It was manifested that anoxic S-NZVI systems preferred to weaker alkaline solutions, whereas aerobic S-NZVI systems performed better in acidic solutions. The highest TOC removal efficiency of PNP (17.59%) was achieved in the aerobic S-NZVI system at pH 6.77, revealing that oxygen improved the degradation of PNP by excessive amounts of hydroxyl radicals in slightly acidic conditions, and the TOC removal efficiency was supposed to be further improved in moderate acidic solutions. Acetic acid, a nontoxic ring opening by-product, confirms that the S-NZVI system could be a promising process for industrial wastewater containing sulfide ions.

Highly efficient removal of chromium(VI) by Fe/Ni bimetallic nanoparticles in an ultrasound-assisted system

Highly active Fe/Ni bimetallic nanocomposites were prepared by using the liquid-phase reduction method, and they were proven to be effective for Cr(VI) removal coupled with US irradiation. The US-assisted Fe/Ni bimetallic system could maintain a good performance for Cr(VI) removal at a wide pH range of 3-9. Based on the characterization of the Fe/Ni nanoparticles before and after reaction, the high efficiency of the mixed system could attribute to the synergistic effects of the catalysis of Ni(0) and US cavitation. Ni(0) could facilitate the Cr(VI) reduction through electron transfer and catalytic hydrogenation. Meanwhile, US could fluidize the Fe/Ni nanoparticles to increase the actual reactive surface area and clean off the co-precipitated Fe(III)-Cr(III) hydroxides to maintain the active sites on the surface of the Fe/Ni nanoparticles. Thus, compared with shaking, the US-assisted Fe/Ni system was more efficient on Cr(VI) removal, which achieved 94.7% removal efficiency of Cr(VI) within 10 min. The pseudo-first-order rate constant (kobs) in US-assisted Fe/Ni system (0.5075 min(-1)) was over 5 times higher than that under shaking (0.0972 min(-1)). Moreover, the Fe/Ni nanoparticles still have a good performance under US irradiation after 26 days aging as well as regeneration.

Effects of oxygen and weak magnetic field on Fe(0)/bisulfite system: performance and mechanisms

The performance and mechanisms of 4-nitrophenol (4-NP) degradation by the Fe(0)/bisulfite system were systematically investigated for the first time. The evidences presented in this study verified that O2 was a crucial factor that affected the mechanism of Fe(0)/bisulfite-driven 4-NP degradation. In the Fe(0)/bisulfite/O2 system, Fe(0) acted as a supplier of Fe(2+) to catalyze bisulfite oxidation that induced a chain reaction to produce reactive radicals for 4-NP degradation. While under N2 purging condition, bisulfite worked as a specified reductant that facilitated the transformation of Fe(3+) to nascent Fe(2+) ions, which principally accounted for the reductive removal of 4-NP. The application of a weak magnetic field (WMF) efficiently improved the removal rate of 4-NP and did not alter the mechanisms in both Fe(0)/bisulfite/O2 and Fe(0)/bisulfite/N2 processes. The secondary radicals, HO(·), SO4 (·-), and SO5 (·-), were considered as the most possible active oxidants contributing to the oxidative removal of 4-NP and even partial mineralization under an oxic condition. Compared with anoxic conditions, the performance removal of 4-NP by the WMF-Fe(0)/bisulfite/O2 system showed less pHini dependence. To facilitate the application of WMF-Fe(0)/bisulfite/O2 technology in real practice, premagnetization of Fe(0) was employed to combine with bisulfite/O2 and proved to be an effective and applicable method for 4-NP removal.

Pretreatment of ultra-high concentrated wastewater from phthalonitrile resin manufacturing by chemical precipitation, reduction and oxidation

To remove the toxic and refractory pollutants in the phthalonitrile resin wastewater and improve its biodegradability, a combined process (i.e., CaCl2+AA+Fe/Cu/air) was developed to pretreat this wastewater obtained from a phthalonitrile resin manufacturing plant in southwestern China. First, CO3(2-) was precipitated and removed by adding CaCl2. Furthermore, its ultra-high concentrated NO2(-) (22.7±0.1 g/L) was reduced into N2 by adding amidosulphonic acid (AA). Meanwhile, two control experiments were setup to confirm the superiority of the combined process (i.e., CaCl2+AA). Subsequently, the wastewater was further treated by Fe/Cu/air process after the removal of CO3(2-) and NO2(-). The results suggest that the developed method not only could effectively remove the ultra-high concentrated CO3(2-) (>99%) and NO2(-) (>99%), but also could obtain high COD (58.8%) and colority (95.2%) removal efficiencies. Meanwhile, B/C ratio of this wastewater increased from 0.19 to 0.45, which suggests the biodegradability also was improved significantly. Finally, the high treatment efficiency was mainly attributed to the synergistic effects of CaCl2, AA and Fe/Cu/air. Therefore, the combined process is a promising pretreatment process for the ultra-high concentrated wastewater from phthalonitrile resin manufacturing.

Sulfentrazone dechlorination by iron-nickel bimetallic nanoparticles

The sulfentrazone dechlorination using bimetallic nanoparticles of Fe/Ni was studied. Different variables that could influence the sulfentrazone conversion were investigated, such as nitrogen atmosphere, pH and dosage of the nanoparticles and initial concentration of sulfentrazone. The best results were obtained using controlled pH (pH 4.0) and 1.0 g L(-1) of nanomaterials, resulting in 100 % conversion in only 30 min. Kinetic studies were also conducted, evaluating the influence of different nanoparticle dosages (1.0 to 4.0 g L(-1)), system temperatures (20 to 35 °C) and nickel levels in the composition of the nanomaterials (0.025 to 0.10 gNi/gFe). The mechanism of sulfentrazone conversion has changed due a direct reduction on the catalytic activity sites and indirect reduction by atomic hydrogen. Both mechanisms have followed pseudo-first order models. The conversion rate improved when the dosage of the nanomaterials, system temperature and nickel content in the composition of the nanocomposites were increased. Finally, the conversion products were elucidated by mass spectrometry and toxicity assays were performed using Daphnia Similis. The results showed that the dechlorination product is less toxic than sulfentrazone.

Comparative study on the characteristics, operational life and reactivity of Fe/Cu bimetallic particles prepared by electroless and displacement plating process

In this study, an electroless (electrode-less) copper plating technology was developed to prepare the high-reactive and robust iron–copper (Fe/Cu) bimetallic particles.

Treatment of wastewater derived from dinitrodiazophenol (DDNP) manufacturing by the Fe/Cu/O3 process

In this paper, the Fe/Cu bimetallic particles and ozone were combined to decompose or transform the toxic and refractory pollutants in dinitrodiazophenol (DDNP) wastewater.

Fe0 and Fe0 fully covered with Cu0 (Fe0 + Fe/Cu) in a fixed bed reactor for nitrate removal

To develop a cost-effective, feasible and robust technology for nitrate removal by chemical degradation, a Fe⁰ and Fe⁰ fully covered with Cu⁰ (i.e., Fe⁰ + Fe/Cu) fixed reactor was set up in this study.

Mineralization of ammunition wastewater by a micron-size Fe0/O3 process (mFe0/O3)

A micron-size Fe⁰/O₃ process (mFe⁰/O₃) was set up to mineralize the pollutants in ammunition wastewater, and its key operational parameters (e.g., initial pH, ozone flow rate, and mFe⁰ dosage) were optimized by the batch experiments, respectively.

Efficient degradation of trichloroethylene in water using persulfate activated by reduced graphene oxide-iron nanocomposite

Graphene oxide (GO) and nano-sized zero-valent iron-reduced graphene oxide (nZVI-rGO) composite were prepared. The GO and nZVI-rGO composite were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR), energy-dispersive spectroscopy (EDS), and Raman spectroscopy. The size of nZVI was about 6 nm as observed by TEM. The system of nZVI-rGO and persulfate (PS) was used for the degradation of trichloroethylene (TCE) in water, and showed 26.5% more efficiency as compared to nZVI/PS system. The different parameters were studied to determine the efficiency of nZVI-rGO to activate the PS system for the TCE degradation. By increasing the PS amount, TCE removal was also improved while no obvious effect was observed by varying the catalyst loading. Degradation was decreased as the TCE initial concentration was increased from 20 to 100 mg/L. Moreover, when initial solution pH was increased, efficiency deteriorated to 80%. Bicarbonate showed more negative effect on TCE removal among the solution matrix. To better understand the effects of radical species in the system, the scavenger tests were performed. The •SO4(-) and •O2(-) were predominant species responsible for TCE removal. The nZVI-rGO-activated PS process shows potential applications in remediation of highly toxic organic contaminants such as TCE present in the groundwater. Graphical abstract Persulfate activated by reduced graphene oxide and nano-sized zero-valent iron composite can be used for efficient degradation of trichloroethylene (TCE) in water.

Comparative study on the reactivity of Fe/Cu bimetallic particles and zero valent iron (ZVI) under different conditions of N2, air or without aeration

In order to further compare the degradation capacity of Fe(0) and Fe/Cu bimetallic system under different aeration conditions, the mineralization of PNP under different aeration conditions has been investigated thoroughly. The results show that the removal of PNP by Fe(0) or Fe/Cu system followed the pseudo-first-order reaction kinetics. Under the optimal conditions, the COD removal efficiencies obtained through Fe(0) or Fe/Cu system under different aeration conditions followed the trend that Fe/Cu (air)>Fe/Cu (N2: 0-30 min, air: 30-120 min)>control-Fe (air)>Fe/Cu (without aeration)>Fe/Cu (N2)>control-Fe (N2). It revealed that dissolved oxygen (DO) could improve the mineralization of PNP, and Cu could enhance the reactivity of Fe(0). In addition, the degradation of PNP was further analyzed by using UV-vis, FTIR and GC/MS, and the results suggest that Fe/Cu bimetallic system with air aeration could completely break the benzene ring and NO2 structure of PNP and could generate the nontoxic and biodegradable intermediate products. Meanwhile, most of these intermediate products were further mineralized into CO2 and H2O, which brought about a high COD removal efficiency (83.8%). Therefore, Fe/Cu bimetallic system with air aeration would be a promising process for toxic refractory industry wastewater.

Effective removal of nemacide fosthiazate from an aqueous solution using zero-valent iron

In this study, the removal of fosthiazate in an aqueous solution using zero valent iron (ZVI) and the related removal reaction mechanism were investigated. The results indicate that the dissipation of fosthiazate adheres to a pseudo-first order reaction law. The apparent rate constant of fosthiazate removal could be improved by increasing the ZVI dosage, control temperature and initial pH. The observed pseudo-first-order degradation rate constants (Kobs) of fosthiazate removal using ZVI were varied in the different electrolyte solutions, and were determined as follows: Kobs (MgSO4) < Kobs (KCl) < Kobs (Control) <Kobs (NaCl) < Kobs (CaCl2) < Kobs (NaNO3) < Kobs (Na2SO4). In addition, the effects of Fe(2+) and Fe(3+) ions on the fosthiazate removal were also investigated, and the fosthiazate removal efficiencies were measured as 1.3% and 5.7% with Fe(2+) and Fe(3+), respectively. The characterizations of ZVI before/after the reaction were employed to gain insight into the reaction mechanism. Finally, the main degradation products were investigated by means of an Agilent 1100 LC/MSD Ion Trap.

Mechanisms for removal of p-nitrophenol from aqueous solution using zero-valent iron

Batch experiments were conducted to examine mechanisms for removal of p-nitrophenol (PNP) from aqueous solution using zero-valent iron (ZVI). Removal of PNP using ZVI was mainly attributed to three mechanisms: degradation, precipitation and adsorption. A complete removal of 30 mg L(-1) PNP with ZVI dosage of 1000 mg L(-1) achieved within 30 min at pH 3. The PNP removal rate in the acidic solutions was significantly suppressed at higher pH. The modified Langmuir-Hinshelwood kinetic model could successfully describe the PNP removal process using ZVI at different pH conditions. Total organic carbon (TOC) removal efficiencies were found to be almost independent of pH. While the TOC removal at lower pH was profoundly affected by the reductive and/or oxidative degradation, the adsorption was favorable at higher pH. The effect of dissolved oxygen on PNP removal was investigated at pH 3 where a maximum contribution of oxidative degradation could be expected. The PNP removal in the anoxic system purged with nitrogen gas was quick as well as that in the system being open to the air. However, the TOC removal under the anoxic condition was negligible as compared with that in the oxic system. The profiles of the intermediates formed during the PNP degradation indicated that the reductive degradation was predominant in the initial phase of the removal and subsequently the oxidative degradation occurred.

The reactivity of well-dispersed zerovalent iron nanoparticles toward pentachlorophenol in water

In order to prevent the aggregation of nanoparticles (NPs), surface modification or the addition of a stabilizer are used for stabilization. However, the real reactivity of NPs is still unclear because of the surface coating. For different physical dispersion methods, the particle stabilization for nanoscale zerovalent iron (NZVI) particles and their reactivity are studied. The particle properties of different preparations and their reactivity toward one polychlorinated aromatic compound, pentachlorophenol (PCP), with different electrolytes are also evaluated. Ultrasonication (US) with magnetic stirring disperses NZVI and Pd/Fe NPs well in water and does not affect the surface redox property a lot under the operating conditions in this study. The well-suspended NZVI cannot dechlorinate PCP but adsorption removal is observed. Compared to shaking, which gives limited removal of PCP (about 43%), Pd/Fe NPs remove 81% and 93% of PCP from water in the US and the US/stirring systems, respectively, which demonstrates that a greater surface area is exposed because of effective dispersion of Pd/Fe NPs. As the Pd doping increases, the dechlorination kinetics of PCP is improved, which shows that a catalyst is needed. With US/stirring, chloride ions do not significantly affect the removal kinetics of PCP, but the removal efficiency increases in the presence of nitrate ions because PCP anions were adsorbed and coagulated by the greater amount of iron (hydro)oxides that are generated from the reduction of nitrate on Pd/Fe. However, bicarbonate ions significantly block the adsorption and reaction sites on the Pd/Fe NP surface with US/stirring. The US/stirring method can be used to evaluate the actual activity of NPs near the nanoscale. The use of Pd/Fe NPs with US/stirring removes PCP from water effectively, even in the presence of common anions expect a high concentration of bicarbonate.

Enhancement of the advanced Fenton process by weak magnetic field for the degradation of 4-nitrophenol

A superimposed WMF could significantly improve the oxidative ability of Fe⁰/H₂O₂ and widen its applicable pH range.

Ultrasound enhanced heterogeneous activation of peroxymonosulfate by a bimetallic Fe-Co/SBA-15 catalyst for the degradation of Orange II in water

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

Biotoxicity evaluation of coking wastewater treated with different technologies using Japanese medaka (Oryzias latipes)

The potential biotoxicity to the environment should be addressed during wastewater treatment. In this study, biotoxicity of coking wastewater effluent from MBR, Fenton, electro-Fenton and coagulation treatment processes was evaluated using embryos and larvae of Japanese medaka (Oryzias latipes). The acute toxicity based on 96-h larval mortality as well as the chronic toxicity based on embryo hatching, larvae swim-up failure, growth, and sexual ratio were determined. The results showed that different treatment processes have various biotoxicity levels. The acute toxicity of Fenton and electro-Fenton effluents was much higher than that of MBR and coagulation. For the chronic toxicity, the effluent of the Fenton/electro-Fenton process displayed lower embryo hatching, larvae survival and growth in comparison with the effluents of MBR and coagulation. No endocrine disruption was detected in MBR, Fenton and electro-Fenton effluents, but was contained in the coagulation effluent. The biotoxicity test indicated that the effluent of MBR was very safe for the environment. The toxicological indices were necessary for ecological safety maintenance in the industrial wastewater treatment.