Adsorption behavior of phosphate on lanthanum(III)-coordinated diamino-functionalized 3D hybrid mesoporous silicates material

An inorganic/organic hybrid adsorbent for phosphate adsorption was synthesized by introducing lanthanum (La) onto diamino modified MCM-41. The adsorbent was characterized by XRD, SEM, BET, TGA, and FTIR spectroscopy. A series of batch tests were conducted to investigate the influence of contact time, initial phosphate concentration, pH of the solution, and competitive ions on the phosphate adsorption capacity. The Langmuir and Freundlich models were used to simulate the sorption equilibrium, and the results indicated that the Langmuir model fitted the experiment data better than the Freundlich model. The maximum adsorption capacity calculated from the Langmuir model is 54.3 mg/g. For kinetic study, phosphate adsorption followed the pseudo-second-order equation well with a correlation coefficient greater than 0.99. Optimum pH value for the removal of phosphate was between 3.0 and 7.0. The presence of Cl(-) and NO(3)(-) has neglectable influence on the phosphate adsorption. F(-)and SO(4)(2-) have negative effects on the adsorption of phosphate. Phosphate on the spent adsorbent can be almost released by 0.01 M NaOH solution in 12 min.