新型除镉吸附剂MPWS制备条件的优化与机理
Optimization of Preparation Condition and Preparation Mechanism for MPWS as Noval Adsorbent to RemoveCd(Ⅱ)
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摘要: 为了提高小麦秸秆(WS)对废水中Cd(Ⅱ)的吸附性能,采用氢氧化钠(NaOH)、L-半胱氨酸(L-Cys)、碳二亚胺盐酸盐(EDC·HCl)、N-羟基琥珀酰亚胺(NHS)对WS进行化学改性,制备出新型吸附剂巯基丙酰化小麦秸秆(MPWS). 以含Cd(Ⅱ)水样为考察对象,利用Plackett-Burman试验、最陡爬坡试验和响应面法的中心复合设计(CCD)对MPWS的制备条件进行优化,借助表征方法探讨了MPWS的制备机理,考察了WS、化学预处理小麦秸秆(CWS)、MPWS对Cd(Ⅱ)的吸附性能. 结果表明:①由响应面法建立的二次项回归方程P值为0.0002,表明模型非常显著. ②当WS粒径为30目(0.60 mm)、化学预处理试剂NaOH溶液浓度为0.07 mol/L、EDC·HCl与L-Cys物质的量比为0.099:1、NHS与EDC·HCl质量比为0.5:1、L-Cys与CWS质量比为4:1、反应介质pH为11、反应温度为40 ℃、反应时间为2.39 h时,该条件下制备的MPWS对水样中Cd(Ⅱ)去除性能最优,MPWS投加量为10 g/L对应Cd(Ⅱ)的去除率为84.55%,与模型预测值84.80%的相对偏差仅为-0.29%. ③MPWS制备机理为巯基丙酰基被接枝到WS结构中,发挥了其对Cd(Ⅱ)螯合吸附作用. ④秸秆对Cd(Ⅱ)的吸附性能为MPWS>CWS>WS,表明WS经化学预处理、接枝改性可提升吸附Cd(Ⅱ)的性能,当MPWS投加量为20 g/L时,Cd(Ⅱ)的去除率可达95.56%. 研究显示,通过响应面法优化MPWS制备条件的试验方法可行,经巯基丙酰基改性后可有效提升小麦秸秆对Cd(Ⅱ)吸附性能.Abstract: To improve the adsorption capacity of wheat straw (WS) for Cd(Ⅱ) in water sample, a novel adsorbent, named mercaptopropionyl wheat straw (MPWS), was prepared by chemically modifying WS by sodium hydroxide (NaOH), L-cysteine (L-Cys), carbondiimide hydrochloride (EDC·HCl) and N-hydroxysuccinimide (NHS). The optimal preparation condition of MPWS was determined by using Plackett-Burman experiment, steepest ascent experiment, and central composite design (CCD) of response surface method. The synthesis mechanism of MPWS was characterized, and the adsorption performances of WS, CWS (chemically pretreated wheat straw) and MPWS for Cd(Ⅱ) were also investigated. The results showed that: (1) the P value of the quadratic regression equation established by response surface method was 0.0002, indicating that the model was highly significant; (2) When the particle size of WS was 30 mesh (0.60 mm), the concentration of NaOH solution was 0.07 mol/L, the molar ratio between EDC·HCl and L-Cys was 0.099:1, the mass ratio between NHS and EDC·HCl was 0.5:1, the mass ratio between L-Cys and CWS was 4:1, the pH value in reaction medium was at 11, the reaction temperature was at 40 ℃, and the reaction time was 2.39 h, MPWS prepared under these conditions had the best removal performance of Cd(Ⅱ) in water sample. Furthermore, at 10 g/L of MPWS dosage, the experimental value of the Cd(Ⅱ) removal rate was 84.55%. It was close to 84.80% of predicted value, and the relative deviation was -0.29%; (3) The mercaptopropionyl groups was introduced into the structure of WS, and the chelation and adsorption for Cd(Ⅱ) by MPWS were well performed; (4) The order of adsorption capacity for Cd(Ⅱ) was MPWS>CWS>WS, suggesting that the adsorption capacity for Cd(Ⅱ) was enhanced by modifying WS with chemical pretreatment and graft modification. When the dosage of MPWS was 20 g/L, the removal rate of Cd(Ⅱ) by MPWS could reach 95.56%. These results show that response surface method can be used to optimize the preparation condition of MPWS, and the adsorption performance for Cd(Ⅱ) can be effectively improved by modifying WS with the mercaptopropionyl groups.
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