Preparation Of Dye Adsorbent From Straw-based Materials And Its Adsorption Mechanism

In this article,three straw sorbents with good adsorption effect were prepared by treating corn straw with tartaric acid,citric acid and malic acid.Scanning electron microscope(SEM)and BET specific surface area were used to analyze the microstructure of corn stalk pith before and after modification.The surface group conversion and crystal structure of corn stalk pith before and after modification were studied by Fourier infrared spectroscopy(FT-IR),X-ray diffraction(XRD)and X-ray diffraction photon spectroscopy(XPS).The adsorption mechanism of three carboxylic acid modified corn stalk pith to methylene blue dye and the adsorption of malic acid modified corn stalk pith methylene blue and crystal violet binary mixture system were also studied.The conclusions are as follows:1.Corn stalks were divided into corn leaves,corn husks and corn stalk pith,and modified with enzymes(cellulase,hemicellulase)and polycarboxylic acids(tartaric acid,citric acid and malic acid).The results show that polycarboxylic acid has the best modification effect on corn stalk pith(hereinafter referred to as CSP).the best conditions for esterification were 0.5M,140℃,2h(tartaric acid modification);1.0M,120℃,2h(citric acid modification);1.5M,120℃,2h(malic acid modification).2.Characterization analysis indicated that tartaric acid,citric acid and malic acid were successfully grafted onto the surface of CSP,making the surface of CSP rougher,conducive to dye adsorption,and reducing the crystallinity of cellulose in CSP.Carboxylic acid modification brought carboxyl and hydroxyl groups to the surface of CSP,making the surface of a large number of negative charges,and having a good adsorption effect on the cationic dyes methylene blue and crystal violet.In addition,there were hydrogen bonds,π-πinteractions and van der Waals forces.3.The modified CSP surface was negatively charged,and the pH increased to promote adsorption.The addition rate increased the removal rate(the maximum removal rate of CSP modified by citric acid was 90.2%),but the adsorption capacity would decrease accordingly.Kinetics and isotherm results indicated that the pseudo-second-order kinetics and Langmuir model are more consistent with the adsorption process.The adsorption process was mainly monolayer chemisorption,and the fitted maximum adsorption capacities were 204.08 mg/g(tartaric acid modification,298.15 K),458.72 mg/g(modified with citric acid,308.15 K),406.50 mg/g(modified with malic acid,298.15 K).4.The single and binary mixed adsorption of methylene blue and crystal violet by malic acid modified CSP showed that the adsorption process was also in accordance with pseudo-second-order kinetics and Langmuir model,but crystal violet inhibited the adsorption of methylene blue.The maximum adsorption capacities fitted were 434.8 mg/g(single methylene blue,298.15 K),621.1 mg/g(single crystal violet,283.15 K),344.8 mg/g(mixed methylene blue,318.15 K)and 496.5(mixed crystal violet,318.15 K).The adsorption process was also inhibited by NaCl,NaNO2,NaNO3,NaSO4 and Na2HPO4.Figure 33 table 15 reference 112...