Research On Degradation Of Organic Dye Wastewater Via Hydrogen Peroxide Catalyzed By Magnetic Nanobeads

Organic dye wastewater is a major pollutant from the production process of textile industry,with features of high colority,variable pH value,poor degradability and great uncertainty.Many methods for the treatment of organic dye wastewater have been developed,but there are still limitations such as hard separation and high cost.Aiming at these problems,in this article,a series of catalytic magnetic nanobeads were prepared specially to improve the traditional treatment techniques for the degradation of organic dye wastewater via hydrogen peroxide?H2O2?.Centered on the application of magnetic nanobeads on wastewater treatment,our work was carried out mainly from the following aspects:i)their catalytic performances;ii)the influencing factors and the corresponding optimization;and preliminarily iii)the catalytic mechanism.Firstly,a highly magnetic Fe₃O₄ nanonucleus was produced by modifying the literature coprecipitation method,then was functionalized by tetraethoxysilane and successively by3-aminopropyltriethoxysilane to give better-dispersed magnetic nanobeads Fe3O4@SiO2 or Fe₃O₄@SiO₂-NH₂,respectively.Here,strong magnetism is necessary for easy separation and regeneration,good dispersity is necessary for wide application,and theoretically,these functionalized nanobeads are believed to possess good catalytic performances which are crucial for the degradation of dye wastewater.The structure,surface and magnetism of these nanoparticles were studied by X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FTIR?,scanning electron microscope?SEM?,transmission electron microscope?TEM?and vibrating sample magnetometer?VSM?.Then,all preparation conditions were optimized in order to acquire nanoparticles with small size,strong magnetism and excellent dispersity.Results were as follows:i)for the magnetic nanonucleus Fe3O4,the average particle size was around 11 nm,the magnetic strength reached the strongest as high as 56eum/g,and the dispersion stability in EtOH was above 8 d;ii)for the nanobeads Fe₃O₄@SiO₂,the size was around 80 nm,the magnetic strength remained stronger as high as 30 eum/g,and the dispersion stability in EtOH was lengthened to 12 d;iii)for Fe₃O₄@SiO₂-NH₂,size still around 80 nm,magnetic strength still as strong as 25 eum/g,whereas stability in EtOH reached the longest of 14 d.All these nanoparticles have enough dispersity and magnetism as expected,and taken both into account,the nanobeads Fe₃O₄@SiO₂ might be most suitable for the further catalytic degradation research work.Thus,secondly,using the ultraviolet-visible spectroscopy?UV-vis?,Fe₃O₄@SiO₂ was chosen to catalyze the oxidative decomposition of Basic Fuchsine?BF?by H2O2 in simulated dye wastewater.Based on this favorable result,studies were deeply put forward to investigate possible factors that might influence the catalytic degradation.That is,the conditions of BF decomposition via H₂O₂ oxidation under Fe₃O₄@SiO₂ catalysis,were further optimized.Results showed,when C_Fe3O4@SiO2=0.15 g/L,C_H2O2=0.9 mol/L,C_0?BF?=10 g/L,at room temperature and pH>5.Similarly,altering the organic dye into Malachite Green?MG?without changing anything else.Likewise,further experiments gave the optimum conditions for MG degradation:C_Fe3O4@SiO2=0.12 g/L,C_H2O2=1mol/L,C_0?BF?=10 g/L,at room temperature and pH>5,After recycling for 5 times,the discoloration rate of both BF and MG wastewater within 5 min could still keep as high as 90%and 80%,respectively.Herein,the mechanism of these two catalytic degradations could be preliminarily discussed upon multi-angled analyses of all the optimum data.Firstly,a pseudo-first order kinetic model was setup for the degradation process,and was suitable for the following two conditions-at the presence/absence of Fe₃O₄@SiO₂.Furthermore,the reason that magnetic nanobeads exhibited good catalytic properties on the oxidative decomposition of organic dyes under hydrogen peroxide,might be attributed to the following points:i)Fe₃O₄@SiO₂ could effectively adsorb dye molecules due to its inherent high specific surface,which could support larger reaction areas as well as more collision opportunities between dye and H₂O₂molecules;ii)Fe₃O₄@SiO₂ could form a Fenton system together with H₂O₂ by releasing a few ferrous ions,which could accelerate the decompostion of H₂O₂ and thus catalyze its oxidative degradation of organic dyes.This probably makes it a promising catalyst to be widely applied for the treatment of triphenylmethane organic dye wastewater in a variety of environments.