Preparation of CTAB-functionalized aqai stalk and its efficient application as adsorbent for the removal of Direct Blue 15 and Direct Red 23 dyes from aqueous media

In this work, a new adsorbent material based on the chemical modification of aqai stalk (AS) with hexadecyltrimethylammonium bromide (CTAB) was proposed, forming a new material called AS-CTAB. The characterization data from the AS-CTAB adsorbent indicated that the biomass was chemically modified by the surfactant. The prepared material was successfully used as an adsorbent for the removal of Direct Blue 15 (DB-15) and Direct Red 23 (DR-23) from aqueous solutions. For both dyes, adsorption followed the Avrami kinetic model. The kinetic data were better fitted using the nonlinear Avrami fractional model for both dyes. The contact time between the adsorbent and adsorbate was fixed at 180 and 30 min for DB-15 and DR-23, respectively. This remarkable difference of contact time between the dyes with AS-CTAB adsorbent was attributed to the difference in the physicochemical characteristics of the dyes such as size of the molecule, hydrophilic–lipophilic balance, and polar surface area (PA). The Liu isotherm model displayed <i>Q</i>_max of 394.2 and 454.9 mg g⁻¹ for DB-15 and DR-23, respectively, at 45°C. Since the AS-CTAB is not a porous material, electrostatic interaction was the main mechanism involved in the adsorption process for both dyes. The thermodynamic adsorption reaction was shown to be a spontaneous and endothermic process. The AS-CTAB adsorbent was also tested in the treatment of synthetic dye effluents and presented a removal of up to 95.41% of a simulated effluent containing several dyes and high saline concentration.

本研究提出了一种以十六烷基三甲基溴化铵（hexadecyltrimethylammonium bromide, CTAB）对阿瓜伊茎（aqai stalk, AS）进行化学改性制备的新型吸附材料，命名为AS-CTAB。对AS-CTAB吸附剂的表征数据表明，该生物质材料已被该表面活性剂成功化学改性。所制备的材料被成功用作吸附剂，用于去除水溶液中的直接蓝15（Direct Blue 15, DB-15）和直接红23（Direct Red 23, DR-23）。两种染料的吸附过程均符合阿夫拉米动力学模型，且非线性阿夫拉米分数阶动力学模型对两种染料的动力学数据拟合效果更优。吸附剂与吸附质的接触时间，针对DB-15固定为180 min，针对DR-23固定为30 min。二者接触时间的显著差异，归因于两种染料在分子尺寸、亲水亲油平衡值以及极性表面积（polar surface area, PA）等理化性质上的不同。在45℃条件下，刘等温吸附模型计算得到DB-15和DR-23的最大吸附容量（Q_max）分别为394.2 mg·g⁻¹和454.9 mg·g⁻¹。由于AS-CTAB并非多孔材料，静电相互作用为两种染料吸附过程的主要作用机制。吸附热力学分析表明，该吸附反应为自发且吸热的过程。AS-CTAB吸附剂还被应用于合成染料废水的处理实验，对含有多种染料及高盐浓度的模拟废水的染料去除率可达95.41%。