甲基丙烯酸接枝改性玉米芯对Cd2+的吸附及机理

以甲基丙烯酸为单体、高锰酸钾/浓硫酸为引发体系对玉米芯进行接枝改性,成功引入羧基官能团,结合扫描电镜、红外光谱和zeta电位等分析手段研究了吸附条件对玉米芯吸附Cd²⁺过程的影响及其吸附机理。结果表明,吸附过程符合Langmuir模型和准二级动力学方程,改性玉米芯对Cd²⁺的吸附主要是化学吸附过程,吸附速率是颗粒内扩散速率和膜扩散速率共同影响的结果;在pH 7、投加量为5 g·L^-1、温度为30℃、吸附时间为6 h的条件下,接枝改性玉米芯和原玉米芯对Cd²⁺的最大吸附容量分别为28.00 mg·g^-1和5.96 mg·g^-1,提高了近4倍;玉米芯对Cd²⁺的吸附是一个自发的吸热反应,温度越高,自发程度越大;接枝改性玉米芯对Cd²⁺的吸附过程中,参与反应的主要官能团有羧基、羟基、酰胺基和甲基等,吸附Cd²⁺后的接枝改性玉米芯表面出现褶皱和白色小颗粒,孔隙消失,电负性增大。

Adsorption mechanism of Cd2+ ions in wastewater by corncob grafted with methacrylic acid

To modify corncob by graft copolymerization, the methacrylic acid and a potassium permanganate- sulfuric acid redox system were used as monomer and initiator, carboxyl groups was introduced successfully. Scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR) and zeta potential analysis were used to characterize corncob and the effects of adsorption conditions on the adsorption of Cd²⁺ in aqueous solutions and its mechanism analyzed. The results showed that the experimental data obtained could be represented with a Langmuir isotherm, the adsorption rate followed pseudo-second-order kinetics and the rate-controlling step was the chemical sorption. Under certain conditions the adsorption rate was affected by both intra-particle and film diffusion rates. The maximal adsorption capacities of Cd²⁺ for methacrylic acid grafted and crude corncobs were 28.00 mg·g^-1 and 5.96 mg·g^-1, respectively, indicating improvement of nearly 4 times (adsorption conditions: pH 7, the dosage 5 g·L^-1, temperature 30℃, adsorption time 6 h). The adsorption was a spontaneous endothermic process, the higher the temperature was, the greater the degree of spontaneous. During the process of adsorbing Cd²⁺, the groups on the surface of grafted corncob, including carboxyl, hydroxyl, amide and methyl groups could play important roles. It was found that there existed some wrinkles and white particles on the surface of grafted corncob after adsorbing Cd²⁺, and its porosity disappeared and electronegativity increased.