Amino phosphate on the surface of nanotitania as attractive group to improve the adsorptive properties for lanthanides removal: adsorption, kinetic, equilibrium, and thermodynamic studies

The present work focuses on the adsorption of La(III) from aqueous solutions by amino phosphate-functionalized nanotitania in a batch system. Surface modification was based on anchor group using chelating ligand, 2-aminoethyl dihydrogen phosphate. The effects of some important parameters including pH of solution, adsorbent dose, contact time, initial metal concentration, and temperature on the adsorption process were examined. The maximum adsorption of La(III) on the modified nanotitania was observed to occur at pH 6.0. Kinetic data showed that the adsorption process achieved equilibrium within 90 min and experimental data were fitted well by the pseudo-second-order model (R2>0.99). The equilibrium data were correlated with Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherm models. The results indicated that La(III) adsorption was well described by Langmuir isotherm model. The maximum adsorption capacity was 14.33 mg g−1 for La(III). According to the evaluated thermodynamic parameters at different temperatures, the adsorption was a spontaneous (ΔG0) process. The effect of interfering cations on the adsorption of La(III) was studied. The presence of Mg and Ca ions up to 150 mg g−1 caused no considerable lowering effect on the La(III) adsorption. The presence of Ce(III) with a concentration in the range of 30–70 mg L−1 led to decreasing adsorption of La(III) from 84 to 76%. In addition, regeneration of the modified nanotitania was performed using HNO3 (0.1 mol L−1) with efficiency greater than 84%.