Removal of As(V) and Cr(VI) using quinoxaline chitosan schiff base: synthesis, characterization and adsorption mechanism

IF 4.3 2区 化学 Q2 CHEMISTRY, MULTIDISCIPLINARY
Huda E. Abdelwahab, Mohammed Elhag, Mohamed M. El Sadek
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引用次数: 0

Abstract

Elevated Arsenic and Chromium levels in surface and ground waters are a significant health concern in several parts of the world. Chitosan quinoxaline Schiff base (CsQ) and cross-linked chitosan quinoxaline Schiff base (CsQG) were prepared to adsorb both Arsenate [As(V)] and Chromium [Cr(VI)] ions. The thermo-gravimetric analysis (TGA), X-ray diffraction analysis (XRD), and Fourier-transform infrared spectroscopy (FTIR) were used to investigate the prepared Schiff bases (CsQ) and (CsQG). The UV–VIS spectra showed a shift in the wavelength area of the modified polymer, indicating the reaction occurrence, besides the variation of the shape and intensity of the peaks. The XRD patterns showed the incensement of the amorphous characteristic. On the other hand, the thermal stability of the modified polymers is better according to TGA studies; also, the morphology of the modified chitosan was investigated before and after crosslinking (CsQ and CsQG) using a scanning electron microscope (SEM) where the surface was fall of wrinkles and pores, which then were decreased after cross-linking. Contact time, temperature, pH, and initial metal ion concentration were all studied as factors influencing metal ion uptake behavior. The Langmuir, Temkin, Dubinin–Radushkevich, and Freundlich isotherm models were used to describe the equilibrium data using metal concentrations of 10–1000 mg/L at pH = 7 and 1 g of adsorbent. The pseudo-first-order and pseudo-second-order kinetic parameters were evaluated. The experimental data revealed that the adsorption kinetics follow the mechanism of the pseudo-second-order equation with R2 values (0.9969, 0.9061) in case of using CsQ and R2 values (0.9989, 0.9999) in case of using CsQG, demonstrating chemical sorption is the rate-limiting step of the adsorption mechanism. Comparing the adsorption efficiency of the synthesized Schiff base and the cross-linked one, it was found that CsQ is a better adsorbent than CsQG in both cases of As(V) and Cr(VI) removal. This means that cross-linking doesn’t enhance the efficiency as expected, but on the contrary, in some cases, it decreases the removal. In addition, the newly modified chitosan polymers work better in As(V) removal than Cr(VI); the removal is 22.33% for Cr(VI) and 98.36% for As(V) using CsQ polymer, whereas using CsQG, the values are 6.20% and 91.75% respectively. On the other hand, the maximum adsorption capacity (Qm) for As(V) and Cr(VI) are 8.811 and 3.003 mg/g, respectively, using CsQ, while in the case of using CsQG, the Qm value reaches 31.95 mg/g for As(V), and 103.09 mg/g for Cr(VI).

利用喹喔啉壳聚糖片基去除 As(V) 和 Cr(VI):合成、表征和吸附机理
在世界一些地区,地表水和地下水中砷和铬含量的升高是一个重大的健康问题。研究人员制备了壳聚糖喹喔啉席夫碱(CsQ)和交联壳聚糖喹喔啉席夫碱(CsQG),用于吸附砷酸盐[As(V)]和铬[Cr(VI)]离子。利用热重分析(TGA)、X 射线衍射分析(XRD)和傅立叶变换红外光谱(FTIR)对制备的希夫碱(CsQ)和(CsQG)进行了研究。紫外-可见光谱显示改性聚合物的波长区域发生了移动,表明发生了反应,此外,峰的形状和强度也发生了变化。XRD 图谱显示了无定形特征的增强。另一方面,根据 TGA 研究,改性聚合物的热稳定性更好;此外,使用扫描电子显微镜(SEM)研究了交联(CsQ 和 CsQG)前后改性壳聚糖的形态,发现其表面有皱纹和气孔,交联后皱纹和气孔减少。接触时间、温度、pH 值和初始金属离子浓度都是影响金属离子吸收行为的因素。使用 Langmuir、Temkin、Dubinin-Radushkevich 和 Freundlich 等温线模型来描述在 pH = 7 和 1 克吸附剂条件下金属浓度为 10-1000 mg/L 的平衡数据。评估了假一阶和假二阶动力学参数。实验数据显示,吸附动力学遵循伪二阶方程的机制,使用 CsQ 时的 R2 值为(0.9969,0.9061),使用 CsQG 时的 R2 值为(0.9989,0.9999),表明化学吸附是吸附机制的限速步骤。比较合成席夫碱和交联席夫碱的吸附效率,发现在去除 As(V) 和 Cr(VI) 的情况下,CsQ 的吸附效果都比 CsQG 好。这说明,交联并没有像预期的那样提高效率,相反,在某些情况下,交联还会降低去除率。此外,新改性的壳聚糖聚合物对 As(V) 的去除效果优于对 Cr(VI) 的去除效果;使用 CsQ 聚合物时,对 Cr(VI) 的去除率为 22.33%,对 As(V) 的去除率为 98.36%,而使用 CsQG 时,去除率分别为 6.20% 和 91.75%。另一方面,使用 CsQ 聚合物对 As(V) 和 Cr(VI) 的最大吸附容量(Qm)分别为 8.811 毫克/克和 3.003 毫克/克,而使用 CsQG 聚合物对 As(V) 的 Qm 值达到 31.95 毫克/克,对 Cr(VI) 的 Qm 值达到 103.09 毫克/克。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
BMC Chemistry
BMC Chemistry Chemistry-General Chemistry
CiteScore
5.30
自引率
2.20%
发文量
92
审稿时长
27 weeks
期刊介绍: BMC Chemistry, formerly known as Chemistry Central Journal, is now part of the BMC series journals family. Chemistry Central Journal has served the chemistry community as a trusted open access resource for more than 10 years – and we are delighted to announce the next step on its journey. In January 2019 the journal has been renamed BMC Chemistry and now strengthens the BMC series footprint in the physical sciences by publishing quality articles and by pushing the boundaries of open chemistry.
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