Oxidation of polyvinyl alcohol by persulfate activated with heat,Fe, and zero-valent iron

The oxidation of polyvinyl alcohol (PVA) by persulfate (S₂O₈²⁻) activated with heat, Fe²⁺, and zero-valent iron (Fe(0)) was investigated via batch experiments. It was hypothesized that elevated temperature and the addition of Fe²⁺ or Fe(0) into a persulfate-water system could enhance the oxidation of PVA by activated persulfate. Increasing the temperature from 20 to 60 °C or 80 °C accelerated the oxidation rate of PVA, which achieved complete oxidation in 30 and 10 min, respectively. At 20 °C, the addition of Fe²⁺ or Fe(0) to the persulfate-water system significantly enhanced the oxidation of PVA. The optimal persulfate-to-Fe²⁺ or Fe(0) molar ratio was found to be 1:1. Complete oxidation of PVA was obtained by Fe(0)-activated persulfate in 2 h. Synergistic activation of persulfate by heat and Fe²⁺ or Fe(0) was also shown to enhance the oxidation of PVA in the persulfate-water system. By using GC–MS analysis, an oxidation product of PVA was identified as vinyl acetic acid (C₄H₆O₂), which is readily biodegradable. Our results suggest that the oxidative treatment of PVA by activated persulfate is a viable option for the pretreatment of PVA-laden wastewater to enhance its biodegradability.     

Indirect electrochemical synthesis of active oxygen in dilute sulfate solutions

Anodic oxidation of dilute solutions of sodium sulfate was developed to generate oxidants into aqueous solutions with a diaphragm electrolyzer, which consisted of titanium anodes covered with mixed oxides of iridium, ruthenium and tin, a titanium cathode, and Teflon cation-exchange membrane. An electronic device was created for continuous self-purification of cathode surface from hardness salt deposits. The anodic products of electrolysis were molecular oxygen and sodium persulfate. It should be noted that sodium persulfate was the only active oxidant. The synthesized anolyte was tested for its oxidizing activity towards certain metabolites and toxicants. Disinfecting properties of anolyte were detected towards gram-positive and gram-negative bacteria. The comparison of redox potentials of commercial samples of persulfate and the synthesized anolyte showed that the redox potential value for the anolyte is much higher than for solutions with the same concentration of commercial persulfate.     

Photo-fenton and UV photo degradation of naphthalene with zero- and two-valent iron in the presence of persulfate

An initial set of 12 kinetic experiments was carried out to remove naphthalene from an aqueous effluent by photo-Fenton involving Fe⁰ and Fe²⁺ at two different concentrations of H₂O₂ (150 and 300?mg?L^?1) and three different pHs (3, 5, and 7) (2²×3¹ experiments). The rate constants (k) for the reaction of naphthalene degradation by involving Fe²⁺ as reactant were in general higher than those with Fe⁰, but the use of Fe²⁺ increased the concentration of naphthalene at equilibrium (C_e) when compared with the same response obtained with Fe⁰ at analogous conditions. A second set of twelve kinetic experiments of photo-Fenton degradation was also performed with persulfate as additive at the conditions already reported, but at a constant concentration of H₂O₂ of 150?mg?L^?1 (2¹×3¹ experiments with NaCl +2¹×3¹ experiments without NaCl). In almost all the runs in which only the source of iron was varied, k from the kinetic data involving Fe²⁺ was higher than that involving Fe⁰, but no difference was observed in terms of C_e that was always zero. The addition of persulfate to treat the effluent either containing or not containing salt enhanced the chemical kinetics, and shifted the equilibrium toward the full removal of naphthalene. A final set of nine experiments of UV photo degradation of naphthalene by involving persulfate without iron, with Fe⁰ and Fe²⁺ in the pH range from 3 to 7 (3² experiments) mainly showed that the use of H₂O₂ may be avoided to remove rapidly and completely naphthalene from wastewater.     

Photochemical reduction of molecular weight and number of double bonds in natural rubber film

Natural rubber (NR) can be degraded depending on various factors such as heat, mechanical force, chemical reaction, and light. Light is a very interesting factor because it can cause the NR to degrade under low temperature and pressure. The photo-degradation of NR films was carried out to investigate the effects of the light and the temperature on the reduction of the weight-average molecular weight (Mw) and the double bonds in the NR films. The NR films, with and without catalysts, titanium dioxide (TiO₂), and potassium persulfate (K₂S₂O₈), were exposed to light from a mercury light bulb at 7,000 and 36,000 lux, and at the temperature of 25 °C and 80 °C for 192 hrs. After exposure, the Mw of the NR films was analyzed by gel permeation chromatography (GPC). Changes in the Mw were used to construct a kinetic model for the process, (1/Mw)=(1/Mw₀)+(kt/2M₀) where k is the rate constant, and M₀ is the Mw of the monomer unit. The linear relationship between 1/Mw and time suggested pseudo first-order processes with random scission. The Mw distribution information from the GPC was used to calculate the number of double bonds in the NR films. The trend of the double bonds reduction curves was quite similar to the result obtained from the calculation from the FTIR spectra. This indicated that this calculation method might possibly be another alternative way to obtain the number of double bonds in the NR.     

Efficiency and Mechanism of Ciprofloxacin Hydrochloride Degradation in Wastewater by Fe3o4/Na2S2O8

ABSTRACT

The nanosized Fe₃O₄ catalyst was synthesized via a modified reverse coprecipitation method and characterized by means of a scanning electron microscope (SEM) and an X-ray diffraction (XRD) analysis instrument. The degradation efficiency and reaction rate of Fe₃O₄ in activating sodium persulfate used to degrade ciprofloxacin were determined from the catalyst dosage, oxidant concentration, and initial pH. The results showed that under the optimum conditions of a catalyst dosage of 2.0 g·L^?1, a sodium persulfate concentration of 1.0 g·L^?1, and an initial pH of 7, the degradation rate of ciprofloxacin was 93.73%, the removal rate of total organic carbon was 78%, and the first-order reaction constant was 0.06907 min^?1 within 40 min. It was also demonstrated that the reactive oxygen species in the Fe₃O₄/sodium persulfate catalytic system were mainly composed of SO₄^– and supplemented by OH· and HO₂· using probe compounds such as ethanol, tertiary butanol, and benzoquinone.     

Persulfate oxidation of MTBE- and chloroform-spent granular activated carbon

Activated persulfate (Na₂S₂O₈) regeneration of methyl tert-butyl ether (MTBE) and chloroform-spent GAC was evaluated in this study. Thermal-activation of persulfate was effective and resulted in greater MTBE removal than either alkaline-activation or H₂O₂-persulfate binary mixtures. H₂O₂ may serve multiple roles in oxidation mechanisms including Fenton-driven oxidation, and indirect activation of persulfate through thermal or ferrous iron activation mechanisms. More frequent, lower volume applications of persulfate solution (i.e., the persulfate loading rate), higher solid/solution ratio (g GAC mL⁻¹ solution), and higher persulfate concentration (mass loading) resulted in greater MTBE oxidation and removal. Chloroform oxidation was more effective in URV GAC compared to F400 GAC. This study provides baseline conditions that can be used to optimize pilot-scale persulfate-driven regeneration of contaminant-spent GAC.     

Applicability of boron-doped diamond electrode to the degradation of chloride-mediated and chloride-free wastewaters

The degradation of diphenylamine (DPA) in aqueous solution by persulfate is investigated. Effects of pH, persulfate concentration, ionic strength, temperature and catalytic ions Fe(3+) and Ag(+) on the degradation efficiency of DPA by persulfate are examined in batch experiments. The degradation of DPA by persulfate is found to follow the pseudo-first-order kinetic model. Increasing the reaction temperature or persulfate concentration may significantly accelerate the DPA degradation. Fe(3+) and Ag(+) ions can enhance the degradation of DPA, and Ag(+) ion is more efficient than Fe(3+) ion. However, the increase of either the pH value or ionic strength will decrease the rate of DPA degradation. N-Phenyl-4-quinoneimine, N-carboxyl-4-quinoneimine, 4-quinoneimine and oxalic acid are identified as the major intermediates of DPA degradation, and a primary pathway for the degradation of DPA is proposed. The degradation of DPA in surface water, groundwater and seawater is also tested by persulfate, and more than 90% of DPA can be degraded at room temperature in 45min at an initial concentration of 20mgL(-1).     

Fe掺杂g⁃C3N4光催化活化过硫酸钠降解偶氮染料

以硝酸铁为铁源,通过浸渍法制备Fe?C₃N₄复合材料。采用FT?IR对Fe?C₃N₄材料进行了表征分析。结果表明,Fe掺杂不改变g?C₃N₄的骨架结构,可以增加g?C₃N₄材料的光催化性能。以橙黄II为目标污染物,在可见光下Fe?C₃N₄催化活化过硫酸钠降解偶氮染料,考察了过硫酸钠物质的量、Fe?C₃N₄质量浓度、橙黄II质量浓度及pH对降解效果的影响,并对反应进行了动力学研究,分析了所制备的催化材料的稳定性。结果表明,在Fe?C₃N₄质量浓度为2.0 g/L、过硫酸钠与污染物物质的量比为1 200∶1和pH=3的条件下,降解效果最好,降解率为77.8%;Fe?C₃N₄/过硫酸钠体系对偶氮染料的降解满足准二级动力学方程;Fe?C₃N₄材料具有可重复利用性。     

A granular adsorbent-supported Fe/Ni nanoparticles activating persulfate system for simultaneous adsorption and degradation of ciprofloxacin

In this work, Fe/Ni nanoparticles were produced through Fe(II) and Ni(II) reduction by NaBH_4 and they were stabilized by a kind of prepared granular adsorbent(Fe/Ni@PGA). Fe/Ni@PGA as an environment-friendly activator was used to activate persulfate(PS) for the removal of ciprofloxacin from aqueous solution. Fe/Ni@PGA was systematically characterized via Brunauer–Emmett–Teller(BET) method, X-ray diffraction(XRD), scanning electron microscopy(SEM), and Fourier transform infrared spectroscopy(FTIR). The effects of PS concentration, initial solution pH, Fe/Ni@PGA dosage, initial ciprofloxacin concentration, reaction temperature, anions, and natural organic matters on the removal of ciprofloxacin by Fe/Ni@PGA/PS were analyzed. The removal efficiency of ciprofloxacin by Fe/Ni@PGA/PS was 93.24% under an initial pH of 3.0, PS concentration of 10 mM, Fe/Ni@PGA dosage of 0.1 g, and reaction temperature of 30℃. Fe/Ni@PGA could still exhibit high catalytic activity after nine cycles of regeneration. The removal mechanisms for ciprofloxacin by the Fe/Ni@PGA/PS system were proposed. In summary, the Fe/Ni@PGA/PS system could be applied as a promising technology for ciprofloxacin removal.