椰壳生物碳吸附Cd(II)的性能和机制

Cd(II)Adsorption Efficiency and Mechanism by Coconut Shell Biochar

将椰子壳在高温缺氧条件下热解制备了椰壳生物碳(coconut shell biochar,CSBC),用于吸附水中的Cd(II)。通过红外光谱分析(fourier transform infrared spectroscopy,FTIR)、X射线衍射(X-ray diffraction,XRD)、X射线光电子能谱(X-ray photoelectron spectroscopy,XPS)、X射线能谱(energy dispersive spectroscopy,EDS)等方法对CSBC以及CSBC-Cd(II)进行了表征,研究了CSBC对Cd(II)的吸附机理。考察了Cd(II)溶液pH、初始浓度、吸附时间对CSBC吸附Cd(II)性能的影响。结果表明:pH对CSBC吸附Cd(II)有显著的影响,pH=5为最佳吸附条件;CSBC吸附Cd(II)的动力学和热力学数据分别符合Pseudo-second-order model模型和Langmuir模型,吸附过程以化学吸附为主,拟合的饱和吸附量为29.36 mg/g。吸附机理为:Cd(II)与CSBC表面的CO_(3)^(2-)生成CdCO_(3)和Cd(OH)_(2)沉淀,以及O—H、C—O、C C、C O、COO-等活性官能团与Cd(II)形成配合物。可见CSBC是一种有应用前景的Cd(II)吸附剂。

Biochar is successfully synthesized by pyrolyzing coconut shell under an high temperature and oxygen-limiting condition for adsorption of Cd(II)in water.The results of physico-chemical characterization obtained for the CSBC loaded with Cd(II)fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),X-ray photoelectron Spectroscopy(XPS),and energy Dispersive spectroscopy(EDS)allowed to propose the mechanism of adsorption.The effects of pH,Cd(II)initial concentration,and adsorbent time on the adsorption of Cd(II)by CSBC are studied.The results show that the pH is a strong impact on the adsorption of Cd(II)by CSBC,a pH value of 5 is selected as the optimum value and uses throughout the following experiments.The pseudo-second-order model and Langmuir model better describe the adsorption of Cd(II)on CSBC,hence chemisorption acts as the rate-controlling step and the maximum adsorption capacity of 29.36 mg/g.The main adsorption mechanisms are that Cd(II)generated CdCO_(3) and Cd(OH)_(2) precipitation with CO_(3)^(2-) on CSBC surface,and the active functional groups(O—H、C—O、C C、C O、COO-)formed complexes with Cd(II).It is clear that CSBC is a promising Cd(II)adsorbent.