季铵型树脂的合成及其对水中溴酸根及前驱物溴离子的吸附性能与机制

Synthesis of quaternary ammonium resin and mechanisms for adsorption of bromate and its precursor bromine ion from water

水中的溴离子(Br^(-))和溴酸根离子(BrO_(3)^(-))由于难挥发、易溶解、稳定性好而难以除去,因此,制备了一种对较低浓度的Br^(-)和BrO_(3)^(-)都有良好吸附去除效果的季铵碱树脂(Quaternary ammonium base resin,QABR)并表征了其物化结构.同时,考察了初始浓度、QABR投加量、溶液pH、离子强度、吸附接触时间和吸附温度等因素对QABR吸附Br^(-)和BrO_(3)^(-)性能的影响.结果表明,在0.05~4.00 mmol·L^(-1)浓度范围内,在298 K、pH=7.0时QABR对Br^(-)和BrO_(3)^(-)的吸附能力最佳,其最大吸附量分别为1.78 mmol·g^(-1)和1.65 mmol·g^(-1);QABR对Br^(-)和BrO_(3)^(-)的吸附均与Langmuir等温吸附模型一致(R^(2)>0.99),其吸附过程符合拟二级动力学(R2>0.99);热力学分析表明,QABR对Br^(-)和BrO_(3)^(-)的吸附过程是吸热的、自发的过程.FTIR和XPS表征证实QABR吸附Br^(-)和BrO_(3)^(-)的作用位点是季铵基氮,pH对吸附的影响及理论计算结果证实离子交换作用是QABR吸附Br^(-)和BrO_(3)^(-)的主要推动力,而静电作用是次要的.QABR对Br^(-)的吸附量优于多种常用商品树脂,饱和吸附了Br^(-)或BrO_(3)^(-)的QABR能被0.50 mmol·L^(-1)NaOH有效洗脱且具有良好的重复再生使用性能.

The bromide and bromate anions are difficult to remove from waters due to their non-volatility,high solubility,and chemical stability.Here we describe the synthesis and characterization of a Quaternary ammonium base resin(QABR)that possesses excellent adsorption performance for the bromide and bromate anion from their minor-polluted water.Experimental conditions for batch adsorption were evaluated,including the initial concentration,QABR dosage,solution pH,ionic strength,adsorption contact time and adsorption temperature.The results show that the adsorption isotherm of QABR follows the Langmuir isotherm model(R^(2)>0.99),with the maximum adsorption capacity of 1.78 mmol·g^(-1)for Br^(-)and 1.65 mmol·g^(-1)for BrO_(3)^(-)in the concentration range of 0.05 to 4.00 mmol·L^(-1)at pH 7.0 and 293 K,and its adsorption process is well described by the pseudo-secondorder kinetics(R~2>0.99).The thermodynamic parameters indicate that the adsorption is spontaneous and endothermic.The analysis of FTIR and XPS confirms that the quaternary ammonium nitrogen is the adsorption site of Br^(-)and BrO_(3)^(-)on QABR.Furthermore,the pH effect on adsorption and the quantum chemistry calculation reveal the ion-exchange interaction represents the main adsorption mechanism,whereas the electrostatic interaction is less important.Br^(-)and BrO_(3)^(-)could be efficiently desorbed from the loaded QABR by 0.50 mmol·L^(-1)NaOH,and the resin could be recycled with acceptable adsorption performance.Also,its removal of Br^(-)from water was better than several commercial resins in the comparison.