Adsorption, Kinetic and Thermodynamic Studies for Mercury Extraction from Water Samples Using Mesoporous Silica

Abstract

Mercury is recognized internationally as an important pollutant since mercury and its compounds are persistent, bioaccumulative and toxic, and pose human and ecosystem risks. A critical aspect of mercury cycling is its bioaccumulation, mainly as methylmercury, along the contaminated water with mercury resulting in high risk of human. Adsorption of mercury from water samples on mesoporous silica, mercaptopropyl functionalysed-SBA-15 (MP-SBA-15) and diethylenetriamine functionalysed-SBA-15 (DETA-SBA-15) has been studied. SBA-15 was prepared by using Pluronic P123, PEO20PPO70PEO20 and tetraethylorthosilicate. Surface modification of SBA-15 was carried out by MP-TMS or DETA-TMS to produce MP-SBA-15 or DETA-SBA-15, respectively. SBA-15 and functionalised SBA-15 materials were characterised for BET surface area, pore size and pore volume. The adsorption kinetics and adsorption isotherms of functionalised SBA-15 for mercury were investigated. Results revealed that the adsorption kinetics were fitted by a pseudo-second-order reaction model and the adsorption thermodynamic parameters ΔH°, ΔS° and ΔE° were 42.08 kJ/mol, 210.3 J/mol.K and 7.20 kJ/mol, respectively for DETA-SBA-15; 101.85 kJ/mol, 397.7 J/mol.K and 23.28 kJ/mol, respectively for MP-SBA-15. Langmuir and Freundlich isotherm models were also applied to analyse the experimental data and to predict the relevant isotherm parameters. The best interpretation for the experimental data was given by the Langmuir isotherm equation. The results indicate that the structure of the materials affects the adsorption behavior. These materials show a potential for the application as effective and selective adsorbents for Hg(II) removal from water.