Kannan Chellapandian, Sundaram Thiravium, Palvannan Thayumanavan
Department of Chemistry, Periyar University, Salem 636011, Tamilnadu, India.
J Hazard Mater. 2008 Aug 30;157(1):137-45. doi: 10.1016/j.jhazmat.2007.12.116. Epub 2008 Jan 17.
The conventional adsorbents like activated carbon, agricultural wastes, molecular sieves, etc., used for dye adsorption are unstable in the environment for long time, and hence the adsorbed dyes again gets liberated and pollute the environment. To avoid this problem, environmentally stable adsorbent of silica and alumina should be employed for malachite green adsorption. The adsorbents were characterized by Fourier transformed infrared spectroscopy (FT-IR) to confirm the tetrahedral framework of silica and non-tetrahedral framework of alumina. The adsorption equilibrium of dye on alumina and silica were 4 and 5h, respectively, this less adsorption time on alumina might be due to the less activation energy on alumina (63.46 kJ mol(-1)) than silica (69.93 kJ mol(-1)). Adsorption increased with increase of temperature on silica, in alumina, adsorption increased up to 60 degrees C, and further increase of temperature decreased the adsorption due to the structural change of non-tetrahedral alumina in water. The optimum pH for dye adsorption on alumina was 5 and silica was 6. The dye adsorptions on both adsorbents followed pseudo-second-order kinetics. The adsorption well matched with Langmuir and Freundlich adsorption isotherms and found that adsorption capacity on alumina was more than silica. The thermodynamic studies proved that the adsorption was endothermic and chemisorptions (DeltaH degrees >40 kJ mol(-1)) on alumina and silica. Recovery of dye on alumina and silica were studied from 30 to 90 degrees C and observed that 52% of dye was recovered from alumina and only 3.5% from silica. The less recovery on silica proved the strong adsorption of dye on silica than alumina.
用于染料吸附的传统吸附剂，如活性炭、农业废弃物、分子筛等，在环境中长时间不稳定，因此吸附的染料会再次释放并污染环境。为避免此问题，应采用环境稳定的二氧化硅和氧化铝吸附剂来吸附孔雀石绿。通过傅里叶变换红外光谱（FT-IR）对吸附剂进行表征，以确认二氧化硅的四面体结构框架和氧化铝的非四面体结构框架。染料在氧化铝和二氧化硅上的吸附平衡时间分别为4小时和5小时，氧化铝上吸附时间较短可能是因为其活化能（63.46 kJ mol(-1)）低于二氧化硅（69.93 kJ mol(-1)）。在二氧化硅上，吸附量随温度升高而增加；在氧化铝上，吸附量在60℃时达到最高，温度进一步升高时，由于水中非四面体氧化铝的结构变化，吸附量降低。染料在氧化铝上吸附的最佳pH值为5，在二氧化硅上为6。两种吸附剂对染料的吸附均符合准二级动力学。吸附与朗缪尔和弗伦德里希吸附等温线拟合良好，且发现氧化铝的吸附容量大于二氧化硅。热力学研究证明，在氧化铝和二氧化硅上的吸附是吸热的且为化学吸附（ΔH°>40 kJ mol(-1)）。研究了在30至90℃下从氧化铝和二氧化硅上回收染料的情况，发现从氧化铝上回收了52%的染料，而从二氧化硅上仅回收了3.5%。二氧化硅上回收率较低证明染料在二氧化硅上的吸附比在氧化铝上更强。
