秸秆及磁性秸秆吸附剂对废水中亚甲基蓝的去除行为及机理

Removal behavior and mechanism of methylene blue in aqueous solution by rice straw and rice straw-Fe_3O_4 composite

以水稻秸秆(RS)为对象,通过化学沉淀法负载Fe_3O_4以制备秸秆负铁(RS-Fe)复合材料.同时,采用MBET、SEM、FTIR、XRD、XPS、VSM技术对RS、RS-Fe进行表征,研究了秸秆及复合材料对溶液中亚甲基蓝(MB)的去除效果,考察了固液比、溶液初始pH值对亚甲基蓝吸附效果的影响,并结合吸附动力学、吸附等温线、仪器表征及官能团封闭实验探究其作用机理.结果表明,吸附剂投加量为4.0 g·L^(-1)较合适;pH在3.0～11.0内,RS对MB去除率均在90%以上,碱性条件下有利于亚甲基蓝的高效去除.RS和RS-Fe对亚甲基蓝的吸附符合拟二级动力学模型.RS对亚甲基蓝的去除符合Langmuir模型,而RS-Fe对亚甲基蓝的去除更适合用Freundlich模型描述.FTIR、XPS和官能团封闭实验分析表明,秸秆表面官能团能在亚甲基蓝吸附过程中发挥重要作用,其中,羧基和氨基更为重要.秸秆对亚甲基蓝的吸附机理包括静电作用、氢键和π-π作用.Fe_3O_4的引入减少了秸秆官能团数量,降低了对亚甲基蓝的吸附量,但能实现快速固液分离.因此,RS具有作为亚甲基蓝染料废水吸附剂的潜力.负铁RS有利于提升固液分离效果.

Rice straw-Fe3O4 composite (RS-Fe) was prepared through chemical precipitation and then characterized by MBET, SEM, FTIR, XRD, VSM, XPS techniques. RS and RS-Fe were used to remove methylene blue (MB) from aqueous solution. The effects of solid-to-liquid ratio and pH on MB removal were investigated. Adsorption kinetic, isotherm, instrumental analysis and functional groups blocking experiment were performed to reveal MB- adsorbing behavior and mechanism. The result indicated that the optimum S/ L ratio for MB removal was 4.0 g·L-1. MB removal rates of RS and RS-Fe were more than 90% and 60% respectively in the pH range of 3.0~11.0. MB removal was beneficial to alkaline environment. Pseudo-second order kinetic model could well describe the adsorption process of MB by RS and RS-Fe. MB-adsorbing isotherm of RS was fitted to Langmuir. However, Freundlich model could be suitable for MB removal of RS-Fe. FTIR, XPS and functional group blocking analysis indicated that functional groups in RS played an important role in the MB removal process, especially carboxyl and amino groups. The mechanism of MB removal by RS includes electrostatic interaction, hydrogen bond binding and π-π stacking. Introduction of Fe3 O4 in RS reduced the quantity of functional groups and then theamount of adsorbed MB decreased. Nevertheless, the existence of Fe3 O4 could realize fast separation of adsorbent and MB solution. Thus, RS has the potential to act as an adsorbent for dye removal and RS-Fe is in favor of solid-liquid separation.