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木质素基炭材料的制备及其对Cr(Ⅵ)的吸附机制研究

Preparation of Lignin-based Carbon Material and Adsorption Mechanism of Cr(Ⅵ) from Wastewater

  • 摘要: 以工业残渣玉米芯木质素(CL)为原料,利用磷酸、氢氧化钾和氯化锌分别对其活化制备木质素基炭材料PA-CL、PH-CL和ZC-CL,并将其应用于废水中重金属Cr(Ⅵ)的吸附。3种活化方法对比分析表明:磷酸活化工艺简单、环保、活化温度低,对Cr(Ⅵ)的吸附效率高于氢氧化钾、氯化锌活化样品。PA-CL在Cr(Ⅵ)初始质量浓度为50 mg/L、50℃、投加量为0.05 g时,吸附5 min,Cr(Ⅵ)去除率可达79.2%,40 min时达到96.5%,吸附效果较好。采用FT-IR、SEM等手段分析PA-CL的结构及形貌,Boehm滴定法测定炭材料表面官能团数量,结果表明:磷酸根基团被引入PA-CL样品表面,使得总酸度由原料木质素的2.54 mmol/g增大到3.20 mmol/g,有利于重金属Cr(Ⅵ)的吸附。PA-CL对Cr(Ⅵ)的吸附符合反应动力学准二级模型方程,平衡吸附量(qe)为390.625 mg/g,R2为0.991 0;吸附等温线符合Langmuir模型,不同温度下的R2均大于0.9,说明PA-CL对Cr(Ⅵ)的吸附为化学吸附过程占主导的单分子层吸附。

     

    Abstract: The industrial residue corncob lignin(CL) was used as raw material and activated by phosphoric acid, potassium hydroxide, and zinc chloride, respectively, to obtain lignin-based carbon materials, PA-CL, PH-CL and ZC-CL.And the carbon materials were used for adsorbing the chromium(Cr(Ⅵ)) ions from wastewater. Results showed that phosphoric acid activation process was simple, environmentally friendly and the activation temperature was low. And the phosphoric acid activated sample had higher adsorption efficiency for Cr(Ⅵ) than NaOH and Zncl2 activated samples. The removal efficiency of Cr(Ⅵ) by using PA-CL reached 79.2% in the first 5 min and 96.5% in 40 min with the initial Cr(Ⅵ) mass concentration 50 mg/L and adsorbent dosage 0.05 g at 50℃. The structural features of carbon material were analyzed by FT-IR and SEM and the functional groups on the surface of carbon materials were tested by the Boehm titration. The results showed that the phosphate group was introduced onto the surface of PA-CL and the total acidity increased to 3.20 mmol/g from 2.54mmol/g(original lignin), which was beneficial to adsorption of Cr(Ⅵ). The adsorption was described well with the pseudo-second-order model with qe of 390.6 mg/g and R2 of 0.991 0, for PA-CL. And the adsorption isotherm conformed to the Langmuir model with R2>0.9, which indicated that the adsorption of Cr(Ⅵ) on PA-CL was chemical adsorption-based monolayer adsorption.

     

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