| Over the years,owing to the rapid development of modern cities,heavy industries such as industry,papermaking,dyes,and metallurgy have also been rapidly rising and developing.This has seriously led to the gradual increase in emissions of heavy metals and organic dyes,causing significant pollution to the natural environment and ecosystems,and endangering the safety of biological life.Attapulgite clay(ATP)is a green and harmless inorganic nanomaterial with good adsorption properties for pollutants,due to its large specific surface area and numerous pores on the ATP structure.However,natural attapulgite clay is relatively poor adsorption capacity and imperfect adsorption effect due to the presence of accompanying minerals and impurities.Chitosan(CTS),as a natural and renewable alkaline polysaccharide with abundant resources,has unique characteristics such as biocompatibility,biodegradability,non-toxicity,and environmental friendliness.It also contains a large number of active groups such as hydroxyl and amino groups on the polymer chain,which can chelate and adsorb heavy metal ions and organic dyes.In view of this,this study organically modified attapulgite clay by adding hexadecyltrimethylammonium bromide(CTAB)to obtain CTAB-ATP adsorbent,and then introduced chitosan to composite with it to prepare CTAB-ATP/CTS composite adsorbent.The adsorption experiments were carried out with Ni(Ⅱ),Pb(Ⅱ),Cr(Ⅵ),rhodamine B and methylene blue as the target pollutants to inspect the recycling and regeneration of the composite agent,there is still some left the influence of the composite agent adsorption under different requirements.Based on the characterization of the structure of CTAB-ATP/CTS composite adsorbent,and combined with adsorption kinetics and thermodynamics,the adsorption mechanism was analyzed.The specific research results are as follows:(1)The attapulgite clay was purified and acid activated using a water washing method and an acetic acid solution with a mass fraction of 8%.Subsequently,the acid activated attapulgite clay was modified with cetyltrimethylammonium bromide(CTAB)to obtain a CTAB-ATP adsorbent.The CTAB-ATP/CTS composite adsorbent was obtained by combining the prepared CTAB-ATP adsorbent with chitosan using acid soluble ultrasound method.During the preparation process of the composite experiment,a single factor controlled experiment was used to study the effects of ultrasonic dispersion time,different mass ratios,and acetic acid acidification concentration on the adsorption performance of the composite adsorbent.(2)The composition and morphology of ATP raw soil,CTAB-ATP adsorbent,and CTAB-ATP/CTS composite adsorbent were analyzed and characterized by SEM,FT-IR,XRD,and BET.The results indicate that CTAB can open the pores and increase the channel radius of ATP.Chitosan has also been effectively loaded onto CTAB-ATP,and the surface roughness of the loaded adsorbent has increased,resulting in many folds and pore structures.A large number of active adsorption groups have been introduced,resulting in a larger specific surface area and unchanged crystal structure.It can provide many different active adsorption sites to improve adsorption performance.(3)The effects of time,p H,initial concentration of adsorbate,temperature and dosage on the adsorption properties of ATP native soil,CTAB-ATP and CTAB-ATP/CTS composite adsorbents for Ni(Ⅱ),Pb(Ⅱ),Cr(Ⅵ),rhodamine B and methylene blue were studied through single factor experimental analysis.It was found that the CTAB-ATP/CTS composite adsorbent exhibited superior adsorption performance for the adsorbate ions tested.The adsorption effect of CTAB-ATP/CTS composite adsorbent on objective contaminants is greatly affected by the p H value of the system.The adsorption of Ni(Ⅱ),Pb(Ⅱ)and rhodamine B is carried out under weak acidic conditions,while the adsorption of Cr(Ⅵ)must be carried out under strong acidic conditions,and the adsorption effect on methylene blue under alkaline conditions is much better than that under acidic conditions.The adsorption rate and dose of the adsorbent show a linear positive correlation,while the initial concentration of the adsorbent shows a linear negative correlation.Therefore,the selection of prerequisite conditions for adsorption should comprehensively consider economic cost and adsorption efficiency to avoid unnecessary resource consumption.(4)The regeneration performance of CTAB-ATP/CTS composite adsorbent was studied through desorption cycle regeneration experiments.The results indicate that CTAB-ATP/CTS composite adsorbent can effectively cycle and adsorb Ni(II),Pb(II),and Cr(VI)three times,but the regeneration performance is poor.This is because its adsorption quality mainly depends on chemical adsorption,making desorption and desorption difficult;Rhodamine B and methylene blue can be effectively recycled and adsorbed for 4 times.This is because the adsorbate is mainly physically adsorbed.The main force of Vander Waals is small,the desorption and desorption are easy to control,and the adsorbent is easy to recycle.(5)Through the fitting analysis of adsorption data results by pseudo first order,pseudo second order,Weber Morris mathematical models and Langmuir,Freundlich,Temkin thermodynamic adsorption isotherm models,it is comprehensively found that the adsorption process of CTAB-ATP/CTS composite adsorbent for Ni(Ⅱ),Pb(Ⅱ),Cr(Ⅵ),rhodamine B and methylene blue is consistent with the pseudo second order model and Temkin model.The internal membrane diffusion and intra particle diffusion control the adsorption rate together.Based on the comprehensive characterization of the adsorbent structure and experimental results,it is inferred that the adsorption process of CTAB-ATP/CTS composite adsorbent for Ni(II)and Pb(II)is mainly dominated by chemical adsorption,with the adsorption mechanism focusing on chemical sedimentary accretion and electrostatic interaction,at the same time accompanied by some physical adsorption.The adsorption process of CTAB-ATP/CTS composite adsorbent for Cr(VI)is dominated by chemical adsorption,and the adsorption mechanism is the coordination effect of external functional groups and electrostatic effect,accompanied by physical adsorption of some parts.The adsorption process of CTAB-ATP/CTS composite adsorbent for rhodamine B and methylene blue focuses on physical adsorption,and the adsorption mechanism focuses on van der Waals force,electrostatic attraction and cation exchange,accompanied by some chemical adsorption. |
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