Methyl Orange adsorption by reuse of a waste adsorbent poly(AAc/AM/SH)-MB superabsorbent hydrogel: matrix effects, adsorption thermodynamic and kinetics studies

The traditional method for the treatment of used adsorbents is usually recovery for recycling or direct discarding them. In the present study, a more potential and economical method is described to reutilize a waste adsorbent. Poly(AAc/AM/SH) SAHs have proved to be a good adsorbent for cationic MB dye, and after adsorption, the SAHs were recovered for recycling. In this work, the waste MB dye loaded poly(AAc/AM/SH) SAHs were not recovered but directly applied to adsorb an anionic MO dye from another waste solution. The poly(AAc/AM/SH) SAHs after the MB dye adsorption were stable and suitable for MO dye adsorption for altered surface structures within a wide pH range. The various factors affecting the MO dye adsorption, including pH, contact time, ionic strength, initial concentration of the MO dye, and temperature, were systematically investigated. The equilibrium adsorption data fitted very well to the Langmuir adsorption isotherm and the maximum MO dye adsorption capacity reached to a high of 134 mg/g at 30°C. The thermodynamic parameters such as Δ<i>H</i>⁰, Δ<i>G</i>⁰, and Δ<i>S</i>⁰ for the MO dye adsorption processes onto the SAHs were also evaluated, and the obtained negative Δ<i>G</i>⁰ and Δ<i>H</i>⁰ values confirmed that the MO adsorption process was spontaneous as well as exothermic. The kinetic studies indicate that the MO dye adsorption process was well consistent with the pseudo-second-order kinetic model. The desorption studies showed that the regeneration of the poly(AAc/AM/SH)-MB SAHs adsorbent can be easily achieved.

传统废弃吸附剂的常规处理方式通常为回收复用或直接丢弃。本研究报道了一种更具潜力且经济的方法，用于对废弃吸附剂进行再利用。聚(丙烯酸/丙烯酰胺/巯基) SAHs（Poly(AAc/AM/SH) SAHs）此前已被证实是一种优良的阳离子亚甲基蓝（MB）染料吸附剂，吸附完成后可回收再利用。本研究中，负载了MB染料的废弃聚(丙烯酸/丙烯酰胺/巯基) SAHs并未进行回收处理，而是直接用于从另一废液中吸附阴离子甲基橙（MO）染料。经MB染料吸附后的该类SAHs结构稳定，且因表面结构发生改变，可在较宽pH范围内适配MO染料吸附。本研究系统考察了影响MO染料吸附的各类因素，包括pH值、接触时间、离子强度、MO染料初始浓度及温度。平衡吸附数据与朗缪尔（Langmuir）吸附等温模型拟合度极佳，在30℃下MO染料的最大吸附容量可达134 mg/g。本研究还评估了MO染料在SAHs上吸附过程的热力学参数，包括标准焓变(ΔH⁰)、标准吉布斯自由能变(ΔG⁰)及标准熵变(ΔS⁰)。所得负的ΔG⁰与ΔH⁰值证实，MO染料吸附过程为自发且放热的过程。动力学研究表明，MO染料吸附过程与准二级动力学模型高度吻合。脱附实验结果显示，负载MB染料的聚(丙烯酸/丙烯酰胺/巯基) SAHs吸附剂可轻松实现再生。