胺化改性木基吸附剂的制备及其吸附性能

Removal of lead ions from wastewater by amine-modified wood chips

以桐木木片为原料,通过氢氧化钠预处理脱除木片原料的部分木质素和半纤维素,再以环氧氯丙烷为交联剂、四乙烯五胺为接枝剂对其进行改性,制备了一种胺化改性木基吸附剂(APW),用于去除模拟废水中的铅离子。扫描电镜图像显示APW的细胞壁更为疏松,组分测定和X射线衍射(XRD)分析结果表明氢氧化钠预处理脱除了桐木木片中部分木质素和半纤维素。傅里叶变换红外光谱(FT-IR)和X射线光电子能谱(XPS)分析结果表明APW化学结构中出现胺基官能团;元素分析结果显示APW的氮含量(3.96%)较未处理桐木木片的氮含量(0.46%)明显提高,表明桐木木片胺化改性成功。吸附试验结果表明,APW对铅离子有良好的吸附能力,在45℃、pH 6、铅离子质量浓度为140 mg/L的模拟废液中,APW的吸附量为111.35 mg/g。动力学和等温线研究结果表明,APW吸附铅离子过程满足拟二级动力学模型,遵循Langmuir等温线模型和Freundlich等温线模型。胺化改性木基吸附剂具有成本低、制备简单、易于回收的优点,可用于水体中铅离子的高效去除。本研究避免了传统生物质高值化利用的组分分离,在保持生物质原本结构条件下,完成了胺化改性,有效降低了生物质高值化利用成本。

With the development of industries, heavy metal pollution has become increasingly severe problem. Adsorption method is one of the most effective methods in a wide variety of water pollution treatment methods. Wood is a kind of biomass adsorbents with great potential because of its wide sources, porous structure and a variety of active functional groups. In this study, amine-modified paulownia wood(APW) was used to prepare heavy metal ions absorbents for removing lead ions from wastewater. Firstly, the pores and reaction sites of wood chips were increased by the sodium hydroxide pretreatment, and then the active hydroxyl groups of main chemical components on wood chips were used as reaction sites, and amine groups were introduced through etherification and amination reactions to improve the adsorption capacity of wood-based adsorbents for removing lead ions. The Fourier transform infrared spectroscopy(FT-IR) and X-ray photoelectron spectroscopy(XPS) showed that amine functional groups appeared in the chemical structure of APW. The elemental analysis showed that the nitrogen content of APW(3.96%) was higher than the unmodified(0.46%) ones, indicating that the amination of wood chips was successfully achieved. The adsorption tests showed that APW had an excellent adsorption capacity for lead ions, and the adsorption reaction was easier to carry out when the temperature of wastewater increases and the pH was 5-6. The adsorption capacity of APW was 111.35 mg/g in the simulated waste solution at 45 ℃, pH 6 and lead ion mass concentration of 140 mg/L. The Quasi-first-order kinetic model and Quasi-second-order kinetic model were used to fit the lead ions adsorption process, and the results showed that the two models can fit this adsorption process successfully. However, the pseudo-second-order kinetic model showed higher correlation, which reflected that, although the adsorption process contained both physical adsorption and chemical adsorption simultaneously, the chemical adsorption played the major role. Both the Langmuir isothermal adsorption model and Freundlich isothermal adsorption model can well fit the adsorption process of lead ions by APW, indicating that the adsorption process of APW included single layer adsorption and multi-layer adsorption. This study avoided the traditional process of the component separation for high-value utilization of biomass. After the alkali extraction of wood chips, amination of wood chips was completed through a two-step reaction, which significantly improved the adsorption capacity of wood chips for lead ions. The amine-modified wood-based adsorbent has the characteristics of low cost, simple preparation, good adsorption performance and easy recycling. It can be used for the removal of lead ions in water, which is of great significance to the efficient utilization of wood chips for water purification and environmental protection.