[Adsorption of Cd2+ ions in aqueous by diamine-modified ordered mesoporous SBA-15 particles]

Highly ordered channel structure SBA-15 was widely concerned as new adsorbents in environmental protection, in order to increase its heavy metal ions adsorption ability from aqueous solution, the diamine -modified porous silicate SBA-15 was synthesized by a hydrothermal grafting method and characterized by TEM, X-ray diffraction, FTIR and N2 adsorption-desorption. The SBA-15 and modified SBA-15 samples were used as sorbents to adsorb Cd(II) ions from aqueous solution. The effect of experimental parameters, such as pH, contact time, sorbent dosage and temperature were examined, and the maximum adsorption amount was also calculated. The results showed that under same conditions, the Cd(II) removal rate was higher for 2N-SBA-15 than that of the unmodified SBA-15. The adsorption process was controlled by system pH. The highest removal rate could reached about 95% after pH was higher than 4. Adsorption equilibrium was reached within 30 minutes,and more than 95% Cd2+ was adsorbed when 7.5-20 mg sorbent was added into 100 mL solution contained 25 mg x L(-1) Cd2+. The adsorption capacity increased from 94.73% to 98.22% with temperature increased from 25 degrees C to 35 degrees C. The Langmuir model can be used to describe adsorption isotherms. The adsorption capacity of Cd2+ was 0.9 mmol x g(-1) which is comparable to the adsorption capacity of various adsorbents reported in the literature, and 0.1 mol x L(-1) HCl could remove nearly 93% Cd2+ from 2N-SBA-15 particles. Based on the thermodynamic, pH, XPS and Zeta potential analysis results in this study, it could be concluded that the adsorption process was an endothermic and spontaneous reaction which contained physical adsorption, ion exchange and chelating reaction etc. The study indicated that the diamine -modified ordered mesoporous material SBA-15 is a potential sorbent which could be used for the aqueous Cd2+ removal.