Study Of The Adsorption Of Methylene Blue In The Aqueous Solutions By Modified Polyaniline

Serious environmental problems are caused by a large amount of high chroma and toxicity dye wastewater.Among many treatment methods,adsorption method has the advantages of easy operation and rapid effects,so it is most widely used.In recent years,polyaniline has been a research hotspot as a new type of adsorbent,because of its good environmental stability and unique chemical structure.However,its adsorption capacity is not high resulting in limited application in water treatment,so it needs to be modified.In this paper,a high-speed and large-capacity methylene blue adsorbent,was prepared from polyaniline by simple oxidation modification.Firstly,a series of products with different adsorption properties were obtained through modification conditions,and characterized by UV-vis spectrum,XRD,SEM,N₂ sorption,XPS,FTIR and Zeta potentiometer.Secondly,the effects of external factors on the adsorption behavior were investigated,including initial concentration,contact time,pH,temperature and the other ions.Finally,the adsorption mechanism of methylene blue was analyzed by adsorption kinetic models,isotherm models and FTIR spectra of the materials before and after adsorption.The product was recorded OP at the optimum reaction condition,while the product without treatment by sodium persulfate was recorded as PANI for comparison.The main results are as follows:?1?The results of UV-vis spectra,XRD,SEM and N₂ sorption showed that,the reaction destroyed the relatively smooth surface of the original polyaniline,and interrupted the conjugated structure,resulting in the formation of porous structure.The characterization results of XPS,FTTR and Zeta potential indicated that,the relative oxygen content of OP increased from 12.49%to 22.2%,and the pH_zpc decreased from 4.5%to less than 2%,in comparison with PANI.It showed that sodium persulfate played an oxidizing role in the experimental process,as a result that the oxygen-containing functional groups on the surface were abundant and the negative charge was increasing.?2?The batch adsorption experiment results showed that,the adsorption conditions had a great influence on the adsorption.As for OP and PANI,the adsorption capacity of methylene blue could be promoted by increasing initial concentration,prolonging adsorption time and increasing pH value.In the solution,the presence of Na⁺and Mg²⁺had little effect on the adsorption effect,while the effect of Mg²⁺was greater than that of Na⁺.OP had faster and larger adsorption advantages than PANI.When the initial concentration of MB was 100mg/L,OP reached adsorption equilibrium just in about 5 minutes,while 4 hours for PANI.The maximum adsorption capacities of OP and PANI,were 551.89 and 168.06 mg/L at 45?,respectively,which were calculated by Langmuir model,close to the experimental values.When the initial concentration of MB was 300 mg/L,the total adsorption rates of the two materials were controlled by both external diffusion and intragranular diffusion.Though,the adsorption rate of OP was only affected by the external diffusion process when the initial concentration of MB was 100 mg/L.?3?The fitting results of adsorption model showed that,the adsorption process of OP was accorded with pseudo-second order kinetic model,while that of PANI accorded with Elovich model.OP conformed to Langmuir and Temkin isotherm model,while PANI applied Freundlich isotherm model.The adsorption mechanism was further explained.OP adsorption MB was a single layer?Langmuir isotherm mode?electrostatic interaction chemisorption?Temkin model?,while PANI?Elovich model,Freundlich isotherm model?was a heterogeneous multilayer adsorption.