| Textile dyes and other industrial dyestuffs constitute the largest groups of persistent refractory organic pollutants, which represent an increasing environmental danger. It is important to develop efficient ways of treating dye-containing wastewater. In this work, the model compound Rhodamin B(Rh B) in aqueous solution was removed by homogeneous Fe(III)/PS and heterogeneous Fe2(Mo O4)3/PS system. The main objectives of this paper were to investigate the effects of parameters including Fe(III) and persulfate concentration, initial p H and inorganic salts on the process performance in homogeneous Fe(III)/PS system. In which the degradation kinetics and reaction mechanism were also proceed study research. Meanwhile, three aspects have been studied in heterogeneous Fe2(Mo O4)3/PS system as following: influence factors including initial p H and the dosage of catalyst and oxidizing agent, reuse and stability analysis of Fe2(Mo O4)3, catalytic mechanism. The potential degradation way of Rh B was proposed under the attack of sulfate radicals. The following results were achieved in this paper from the above experimental research and theoretical analysis:(1) Rh B degradation efficiencies were connected with the adding concentration of Fe(III) and persulfate and initial p H in homogeneous Fe(III)/PS system. Total Rh B(initial concentration 25 mg/L) removal was obtained within 60 min under Fe(III) and persulfate concentration 1 mmol/L with initial p H 3.0. The Rh B degradation was found to be first order kinetics based on dynamic simulation. The kinetic constant was proportional to Fe(III) and persulfate concentration, and in inverse proportion of Rh B initial concentration.(2) The effect of various inorganic anions on Rh B degradation was also evaluated under the optimal conditions in homogeneous Fe(III)/PS system. NO3- had little or no effect on Rh B degradation efficiencies. However, the anions Cl-, SO42- and H2PO4-caused a negative influence on the performance of the process in different extent. This was mainly because the complexation between anions and Fe(III), reducing the amount of available free iron ion in this system. Cl- could react with sulfate radicals quickly to generate chlorine radicals, whose oxidation was much lower than sulfate radicals and reduced Rh B degradation efficiencies. The inhibitory effect in the presence of SO42-was elucidated by a proposed formula using Nernst equation.(3) Fe2(Mo O4)3 was synthesized through calcinations after coprecipitation and characterized by X-ray diffraction(XRD), fourier transform infrared spectrometer(FTIR) and X-ray photoelectron spectroscopy(XPS). The use of 0.4 g/L catalysts and 4 mmol/L persulfate created a nearly complete removal of the added Rh B(10 mg/L) within 4 h. Fe2(Mo O4)3 catalyst was confirmed to have excellent reuse and stability by successive degradation experiments, and exhibited lowing iron leaching and no loss of catalytic performance.(4) Rh B was mainly removed under the attack of sulfate radicals by quenching experiments. According to the oxidation mechanism of sulfate radicals, combined with UV-vis spectra during Rh B degradation process and the formation of intermediate products, Rh B degradation was divided into three stages, which included damaging molecular conjugated structure, benzene ring destruction and mineralization.(5) The catalytic mechanism could be that Fe(III) was reduced into Fe(II) under some intermediate products with reducibility. Then generated Fe(II) could react with persulfate to produce sulfate radicals and Fe(III). Therefore, there was an oxidation reduction cycle of Fe(III)/Fe(II) in systems. In heterogeneous Fe2(Mo O4)3/PS system, the surface hydroxyl function and synergistic effect between Fe(III) and Mo O42- in catalyst could be contribute to catalytic activity. |
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