壳聚糖交联改性荔枝皮小球对Cr(Ⅵ)的吸附研究
Research on adsorption of hexavalent chromium onto chitosan cross-linked modified litchi pericarp
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摘要: 以NaOH 改性的荔枝皮和壳聚糖为原料,在适当的吸附时间、搅拌速率和pH 条件下,采用滴加成球的方法制备一种新型的重金属吸附剂——壳聚糖交联改性荔枝皮小球。通过其对Cr(Ⅵ)的吸附试验,研究了Cr(Ⅵ)溶液初始浓度、初始pH、吸附时间、壳聚糖交联改性荔枝皮小球的投加量对吸附量的影响;通过吸附动力学、吸附等温线、扫描电镜和红外光谱研究其吸附机理。结果表明:(1)壳聚糖交联改性荔枝皮小球对Cr(Ⅵ)的吸附最佳条件为:初始浓度为120 mg/L,初始pH 值为1,吸附溶液体积与壳聚糖交联改性荔枝皮小球投加量的比是100 mL∶0.2 g,吸附时间为240 min。(2)通过吸附动力学研究,发现其符合准二级动力学模型,基本符合准一级动力学模型。(3)通过吸附等温线研究,发现其符合Langmuir等温吸附模型,属于单分子层,在室温下,最大的吸附量可达到108.7 mg/g。(4)扫描电镜结果显示壳聚糖交联改性荔枝皮小球吸附前比吸附后表面粗糙,孔隙多。(5)通过红外光谱分析得出,壳聚糖交联改性荔枝皮小球中含有壳聚糖与改性荔枝皮中绝大多数的官能团,起主要吸附作用的官能团是羟基和酰胺基。Abstract: A new type metal adsorbent was successfully prepared by chitosan and litchi pericarp modified with NaOH,by the method of dropping into sphericity under the conditions of appropriate stirring time,stirring rate and suitable pH. Batch adsorption experiments were carried out to evaluate the effects of initial concentration of Cr(Ⅵ), initial pH,adsorption time and dosage of chitosan cross-linked modified litchi pericarp on the adsorption of Cr(Ⅵ). The adsorption kinetics,adsorption isotherm,scanning electron microscopy and infrared spectroscopy were analyzed. The results showed that the optimum of adsorption Cr(Ⅵ) on chitosan cross-linked modified litchi pericarp occurred at initial Cr(Ⅵ) solution concentration of 120 mg/L,initial pH at 1 and per 100 mL adsorption solution with 0.2 g chitosan cross-linked modified litchi pericarp for 240 mimutes. The kinetics of adsorption exhibited quasisecond- order behavior and basically coincided quasi-first-order model. The adsorption date was well described by Langmuir isotherm model. The adsorption was identified as monomolecular layer. The maximum adsorption capacity of Cr(Ⅵ) was 108.7 mg/g at indoor temperature. And scanning electron microcopy indicated that the chitosan cross-linked modified litchi pericarp had rougher surface and more porosities after adsorption. Besides,chitosan crosslinked modified litchi pericarp contained the vast majority of functional groups. Especially,hydroxyl and amide play an irreplaceable roles in adsorption of Cr(Ⅵ).