Preparation Of CTAB-Fe₃O₄-Sepiolite And Study Of Its Performance On The Removal Of Congo Red In Water

With the flourishing development of synthetic dyestuff industry,the environmental problems caused by the massive discharge of dye wastewater were becoming more and more serious.As a kind of efficient and environment-friendly dye wastewater treatment method,adsorption method has also been widely studied at home and abroad,so it is very important to choose a suitable adsorbent.In this paper,with cheap clay mineral sepiolite as raw material,magnetic sepiolite and organic sepiolite were prepared by magnetic modification and organic modification respectively,while CTAB-Fe3O4-Sepiolite was prepared by magnetic modification and organic modification,the morphology and structure of three kinds of modified sepiolite and sepiolite original soil were characterized,and then the adsorption properties and removal mechanism were studied,the following conclusions were obtained:(1)The Congo red adsorption capacity of sepiolite,magnetic sepiolite,organic sepiolite and CTAB-Fe3O4-Sepiolite was increased in turn,55.07 mg/g,59.20 mg/g,296.80 mg/g and 500.27 mg/g,respectively.The adsorption capacity of the three modified sepiolite was 1.07 times of the sepiolite(magnetic sepiolite),5.39 times of the sepiolite(organic sepiolite)and 9.08 times of the sepiolite(CTAB-Fe3O4-Sepiolite).(2)The analysis of SEM,TEM,AFM,BET/BJH,XRD,XPS,PPMS,FT-IR can be concluded as below:SEM results showed that the surface of the magnetic sepiolite was rough,while the surface of the CTAB-Fe3O4-Sepiolite was smooth and loose.From the TEM result,it could deduce that Fe3O4 and CTAB were loaded on the surface of sepiolite from the inside to the outside,and form a three element composite system.AFM results showed that CTAB was covered on the surface of magnetic sepiolite with the form of cationic surfactant bimolecular layer;BET/BJH results showed that the specific surface area of sepiolite was 90.1196 m2/g,and its specific surface area increased to 138.8833 m2/g(magnetic sepiolite)by magnetic modification,and then the specific surface area reduced to 65.2057 m2/g(CTAB-Fe3O4-Sepiolite)by organic modification;XRD,XPS and PPMS characterization analysis confirmed that Fe3O4 was introduced to sepiolite surface by magnetic modification;FT-IR characterization analysis showed that organic modification had also introduced CTAB to sepiolite surface.(3)The best adsorption conditions of CTAB-Fe3O4-Sepiolite for Congo red were as shown below:T=30 ?,M=1 g/L,pH =3,t=5 h.The results of adsorption kinetics showed that the process of Congo red adsorption onto CTAB-Fe3O4-Sepiolite obeyed well with the pseudo-second-order kinetic model,the adsorption reaction was exothermic process,and low temperature was beneficial to adsorption,and the calculated activation energy was 2.38 kJ/mol,indicating that Congo red adsorption onto CTAB-Fe3O4-Sepiolite has the the characteristic of low activation energy,and the adsorption reaction was mainly controlled by physical adsorption.The adsorption thermodynamics results showed that the process of Congo red adsorption onto CTAB-Fe3O4-Sepiolite obeyed well with the Langmuir model.It was also proved that the adsorption reaction was also exothermic and conforms to preferential adsorption.It was shown that the process of Congo red adsorption onto CTAB-Fe3O4-Sepiolite was a spontaneous physichemisorption process.(4)Under the acid condition,it was found that the flocculation of Congo red itself will promote the adsorption and flocculation of the CTAB-Fe3O4-Sepiolite to Congo red,thus effectively improving the removal effect on Congo red.In the experiment,the initial pH value and initial concentration of the Congo red solution were found to have a larger effect on the removal rate,and the removal rate of CTAB-Fe3O4-Sepiolite to Congo red gradually increased from alkaline to acidity,and the experiments confirm that pH=3 was the best pH value(the removal rate of Congo red is above 99%).Under the condition of pH=3,the removal rate of CTAB-Fe3O4-Sepiolite for the medium and low initial concentration(200-2000mg/L)of Congo red solution decreased from 99.92%to 96.49%(negative correlation),while the removal rate of Congo red solution for high concentration(2000-4500mg/L)increased from 96.49%to 99.53%(positive correlation).(5)The adsorption mechanism of CTAB-Fe3O4-Sepiolite on Congo red was as shown below:it was mainly controlled by electrostatic attraction and chelation,according to the experimental data analysis:the adsorption process can be divided into two steps,the first step was the electrostatic attraction by CTAB,which adsorb Congo red from the solution to the surface of sepiolite,and then the second step was the chelation between Fe(III)center and the sulfonic group(-SO3)of Congo red,which made Congo red more stable on the surface of sepiolite.Under acid conditions(such as pH=3),the removal mechanism of CTAB-Fe3O4-Sepiolite to Congo red solution with different initial concentration ranges was also different,CTAB-Fe3O4-Sepiolite was mainly adsorption removal for the low medium initial concentration of Congo red solution(100-2000mg/L),and the flocculation removal was supplemented;The high concentration Congo red solution(2000-4500mg/L)was mainly flocculation removal,and adsorption removal was subsidiary.