Dyes Removal By Adsorption On Carbon Nanotubes Decorated With Magnetic Iron Oxide And Digestion Through Microwave

Dyeing wastewater is one of industrial effluents difficult to be treated with high organic contents and color strength which is resulted from dyes.Approximately two percent of dyes are discharged directly in industrial effluent during production,which is a threat not only to the environment but also to human beings.Using carbon nanotubes as substrates,carbon nanotubes decorated with magnetic iron oxide?m-MWCNTs?were prepared by chemical co-precipitation for removal of soluble dyes from aqueous solution.Dyes adsorbed on m-MWCNTs were disintegrated through microwave radiation,after adsorbents separation from aqueous solution by magnetic separation.The m-MWCNTs composite was characterized.Effects of dyes adsorption on m-MWCNTs and microwave degradation of dyes,kinetic and thermodynamic of adsorption were studied.The mechanisms of dyes adsorption on m-MWCNTs and dyes regeneration by microwave radiation were discussed.The work provided a new advanced treatment technology of dyeing wastewater with low concentration pollutants.The m-MWCNTs composite was characterized by scanning electron microscopy?SEM?,energy dispersive X-ray spectroscopy?EDS?,Fourier transform infrared spectroscopy?FTIR?,X-ray diffractometer?XRD?,vibrating-sample magnetometer?VSM?,specific surface area and porosity,respectively.The result showed that magnetic iron oxides,magnetite Fe₃O₄and maghemite?-Fe₂O₃,were loaded on MWCNTs,the saturation magnetization of m-MWCNTs was 21.20 emu/g at room temperature,and specific surface area and pore volume of m-MWCNTs were 240.87 m²/g and 1.3281 cm³/g,respectively.The adsorptive capacity of m-MWCNTs was examined using Cationic Red GTL?R-GTL?,Reactive Blue 19?B-19?,Acid Turquoise Blue A?B-A?and Direct Fast Turquoise Blue FBL?B-FBL?as adsorbates.Optimal adsorption conditions were obtained:reaction time of 30?min,agitation speed of 200 rpm,every dye concentration of 100?mg/L,m-MWCNTs dosage of 0.6 g/L for R-GTL,0.8 g/L for B-19,0.3 g/L for B-A and 1.5 g/L for B-FBL,normal p H 6.58 for R-GTL,p H 6.54 for B-19,p H 6.39 for B-A and p H 6.95 for B-FBL.Under these conditions,the removal rates of R-GTL,B-19,B-A and B-FBL were high to 99.34%,99.59%,99.32%and 93.27%,respectively.In addition,temperature and p H have sight effect on removal of different dyes using m-MWCNTs.The increase of the dosage can improve the dye removal rate,but after reaching a certain value,the removal rate tends to be stable;for R-GTL,B-19 and B-A,when the initial concentration is less than 100 mg/L,the dye removal rate was close to 100%,and when it gradually increased from 120 mg/L to200 mg/L,the removal rate decreased;for B-FBL,the removal rate decreased slightly with the increase of the initial concentration of the dye,but the adsorption amount of the four dyes increased with the increase of the initial concentration;from 100 rpm to 125 rpm,the dye removal rate increased significantly,and thereafter,the effect was not significant.The dye removal rate increases rapidly with time,then increases slowly,and finally remains stable.The presence of heavy metal ions Cu²⁺,Cd²⁺,Hg²⁺and Pb²⁺had no obvious effect on R-GTL adsorption of,and promoted the adsorption of B-19 and B-A.For B-FBL,Cu²⁺and Cd²⁺promoted adsorption,while Hg²⁺and Pb²⁺inhibited adsorption.And the composite was effective on dyes adsorption from both aqueous solution with different heavy mental ion and containing various dyes.It made microwave degradation of dyes more complete that increasing microwave time under the same microwave power or increasing power at a fixed time.Microwave degradation of dyes had a good effect at microwave energy consumption of a certain level.The removal rates of R-GTL,B-19,B-A and B-FBL on m-MWCNTs after m-MWCNTs suffering first microwave radiation were 89.76%,94.10%,86.11%and 89.63%,respectively.When the proess of dyes adsorption on m-MWCNTs following with dyes microwave regeneration ran four cycles,the removal rates of dys on m-MWCNTs after microwave radiation were above 87%.The experimental data of four dyes adsorption on m-MWCNTs were fitted using pseudo-first-order kinetic model,pseudo-second-order kinetic model,liquid film diffusion model and intraparticle diffusion model.The Results showed that the pseudo-second-order kinetic model fitted adsorption processes well.Langmuir,Freundlich and Temkin equations were used to analysis the experimental data of m-MWCNTs for four dyes.The adsorption isotherms of R-GTL,B-19,B-A and B-FBL were well fitted by Freundlich and Temkin model,Freundlich model,Freundlich model and Langmuir model,respectively.Thermodynamics analysis revealed that four dyes adsorption on m-MWCNTs were spontaneous,and R-GTL and B-19 adsorptions were exothermic processes with decreased entropy,B-A and B-FBL adsorptions were respectively a exothermic process with increased entropy and a endothermic process with increased entropy.Four dyes adsorption on m-MWCNTs was mainly physisorption,and chemisorption also existed.Hydrogen bonds and dipole bonds took effects in adsorption of R-GTL and B-FBL on m-MWCNTs;van der Waals force,hydrogen bonds and dipole bonds took the role in the adsorption of B-19 by m-MWCNTs.