Preparation Of Mulberry Twigs-based Adsorbent And Study For Its Adsorption Properties

Waste ramulus mori from sericulture process was modified chemically by succinic acidto prepare efficient adsorbents for removal of cationic dyes and heavy metal ions. Responsesurface methodology （RSM） was employed to optimize the preparation conditions oframulus mori-based adsorbent. Design Expert software was using to establish quadraticregression model which was used to predict the adsorption capacity for ramulus mori-basedadsorbent of methyl blue and to determine the optimum preparation conditions of ramulusmori-based adsorbent. The surface morphology and molecular structure of ramulusmori-based adsorbent were characterized.The adsorption properties of cationic dyes andheavy metal ions onto ramulus mori-based adsorbent were studied.The competitiveadsorption between heavy metal ions and cationic dyes were investigated. In addition, thedesorption behavior and reuse of adsorbent were also preliminarily studied. RSM resultsshow that quadratic regression model can simulate the relationships between adsorptioncapacity and independent variables, including microwave power, irradiation time, materialratio （mass ratio of succinic acid to ramulus mori）, reaction temperature and reaction time. Amicrowave power of745W, irradiation time of7min, ratio of succinic acid to mulberry twigpowder of1.0, reaction time of78min and reaction temperature of137℃were found to beoptimal for preparation of the adsorbent.The characterization results prove that it is possible to adsorb heavy metal ions and dye ontothe different parts of material as a result of irregularities of the surface and a wealth of pores,through observing the surface of ramulus mori-based adsorbent. Through qualitativeanalysis results of functional groups combining with FTIR to confirm that a large number ofcarboxyl groups was introducing to ramulus mori-based adsorbent. Using Boehm titration todetermine the content of acidic functional groups and titration results demonstrate: Carboxylcontent> Lactone group content> Phenolic hydroxyl content, the specific surface aera of1.6933m2/g and isoelectric point of4.2.In the range of pH5-9, the prepared adsorbent have excellent adsorption capacity forcationic dyes and the removal rates of NR, MB and CV were97.19%,92.57%and85.11%,respectively. The adsorption data of NR, MB and CV is better fitted to Langmuir and D-Risotherm than the Freundlich and Temkin isotherm. The monolayer capacity are in the orderof NR> MB> CV. At25℃, the maximum adsorption capacity of Neutral red, Methyleneblue and Crystal violet were126.58,123.46and114.92mg/g, respectively. The mean free energy of adsorption for NR, MB and CV were found to be in the range of8-16kJ/mol,indicating chemical ion exchange mechanism.The adsorption results of heavy metal ions indicate that the removal rate of Cu²⁺, Cd2with initial concentration of50mg/L are more than97%, and that of Pb²⁺, Zn²⁺are about90%. The equilibrium time of Cu²⁺is20min, and that of Cd²⁺, Pb²⁺, Zn²⁺is30min.Adsorption capacities increases with the increasing of pH value.The adsorption isotherm ofheavy metals ions is L type.The adsorption assumes monomolecular layer and carries outeasily. The adsorption capacities of heavy metal ions increase in the order of Pb²⁺> Cu²⁺>Cd²⁺>Zn²⁺. The adsorption of heavy metal ions can be simulated by thepseudo-second-order kinetics model and is governed by electrostatic attraction. Theadsorption is endothermic.The results also showed that competitive adsorption phenomenon exist between ontonly cationic dyes but also heavy metal ions. The priority order of adsorption of cationicdyes onto ramulus mori-based adsorbent is: Neutral red> Methylene blue> Crystal violetand that of heavy metal ions is Cd²⁺> Cu²⁺>Pb²⁺> Zn²⁺. Cationic dyes and heavy metal ionscan be desorbed from adsorbent by0.1M HCl. Desorption efficiency can reach to90%andthe regenerated adsorbent can be reused.