| At present, more than seven million tons of dyes are annually produced in the world and are extensively used in different manufactures, thus large amount of effluents with dyes were discharged from the manufactures, which would cause long-term damaging effects on the environment upon which our society relies, because most synthetic dyes are toxic and even carcinogenic. Therefore, in the study, we have synthesized a new adsorbent by chemical modification and it was employed to remove acid orange 7 (AO7), from aqueous solution. Moreover, individual and interaction effects of the process variables in the adsorption reactions were investigated using experimental designs (BBD), and their corresponding maximum response values (i.e. the maximum adsorption ability of dye) were obtained by RSM. In addition, their adsorption kinetics and equilibrium data were also discussed by different kinetic and isotherm models, respectively. And we also discussed the isosteric heat of adsorption and activation parameters for the adsorption reaction. The details were given as follows:A novel low-cost bisorbent based on modified maize stalks (PEHA) was prepared by epichlorohydrin and pentaethylenehexamine (PEHA) as etherifying agent and crosslinking agent respectively. And the biosorbent was used for removing AO7. The effects of several important parameters (such as initial concentration of dye, temperature, pH, and adsorption time) on the removal of AO7 by PEHA-MS were evaluated using an optimal experimental design based on Box-Behnken Response Surface method. A quadratic model for predicting the optimum removal conditions was derived; and the obtained optimal parameters were C= 50 mg·L-1, T=25?, pH=2.3, and t=90 min; the experimental values (436.68 mg·g-1) for AO7 removal onto PEHA-MS were discovered at their optimal conditions, which were in good agreement with their corresponding maximum response value (444.42 mg/g). The results also implied that the concentration of dyes has the maximal contribution (69.58%) for removing it. Moreover, many kinetics and equilibrium isotherm models were investigated. In which, Sips, Freundlich, Redlich-peterson, Radke-Prausnit, Dubinin-Radushkevich and Toth isotherm models showed good fit (R> 0.99) to the equilibrium adsorption data. The results indicated that pseudo-second-order model present the best fit to the kinetic data. According to the results of liquid film, intraparticle diffusion and Boyd models, the adsorption processes of AO7 were controlled by the liquid film diffusion.In addition, the Arrhenius and Eyring equations were used to obtain the activation parameters such as activation energy (Ea), and enthalpy (?H#), entropy (?S#) and free energy (?G#) of activation for the adsorption system. The isosteric heat of adsorption (?HX) was also determined from the equilibrium information using the Clausius-Clapeyron equation. Thermodynamic parameters and isosteric heat of adsorption were calculated for the reactions, including ?G° (-10.47?-9.95 kJ·mol-1), ?H° (-15.43 kJ·mol-1),?S° (-16.64 J·mol-1·K-1), E (6.75?7.39 kJ·mol-1) and ?Hx (-21.39?-18.11 kJ·mol-1). Thermodynamic studies suggested the adsorption reaction was spontaneous and exothermic nature. According to these parameters, the adsorption mechanism of acid orange 7 removals onto PEHA-MS has a brief discussed, and study their regeneration ability and feasibility. |
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