环氧氯丙烷改性花生壳吸附亚甲基蓝的研究

Study on adsorption of methylene blue with epichlorohydrin modified peanut hull

主要研究了环氧氯丙烷改性花生壳对亚甲基蓝的吸附作用。考察了溶液pH值、亚甲基蓝初始质量浓度、吸附时间、温度等因素对改性花生壳吸附亚甲基蓝效果的影响。结果表明,当温度为298 K,亚甲基蓝初始质量浓度为100 mg/L时,在改性花生壳用量为2 g/L,溶液pH值为6.00,吸附时间为60min的条件下,亚甲基蓝吸附量最大,可达49.25 mg/g。在试验条件下,改性花生壳对亚甲基蓝的吸附符合拟二级动力学方程,吸附平衡符合Freundlich等温方程,吸附焓变ΔH>0,反应吉布斯自由能ΔG<0,表明该吸附过程为自发进行的吸热过程。

The aim of this paper is to introduce a new adsorbent mod- ified by the present author from the peanut hull chemically identified with epichlorohydfin in the alkaline medium. For our study purpose, we have done the experiments in a batch system to evaluate the ad- sorption capacity of methylene blue on the adsorbent. To make a clear account of the influence of such factors, such as pH value, initial dye concentration, adsorption time and temperature on the adsorption pro- cess, we have tested and analyzed the maximal adsorption capacity, which is up to 49.25 mg/g under the conditions of modified peanut hull dosage of 2 g/L, the pH of 6.00 and the adsorption time of 60 min at the temperature of 298 K and the initial concentration of methylene blue of 100 mg/L. The results of our experiments also in- dicate that the higher the temperature, the better the absorptive ca- pacity would be. The Freundlich isotherm model provides us with a better description for the adsorption equilibrium when compared to the Langmuir isotherm equation. Since the value of Freundlich constant, kF, tends to increase with the increasing temperature, peanut hull would be easy in absorbing the methylene blue. The highest kr has been reported as 36.48 at 318 K. In addition, we have also evaluat- ed the thermodynamic constants of the process. The positive values of the adsorption enthalpy and the negative values of the free energy in- dicate its spontaneous endothermic nature. Last of all, we have ex- amined the controlling mechanisms of the adsorption process, such as the kinetic equations of the mass transfer and chemical reaction, pseudo-first order and pseudo-second order so as to correlate the ex- perimental data, and in turn, found that the pseudo-second order e- quation can provide a better correlation of the adsorption data under which the chemical adsorption goes on. The results of our study re- veal that the peanut hull modified in this way with epichlorohydrin proves to be a low-cost adsorbent for the efficient removal of methy- lene blue from the aqueous solution.