Removal of Cadmium (II) Ions by Beaded Materials of Mangosteen (Garcinia mangostana Linn) Modified with Magnesium Oxide (MgO) and Titanium Dioxide (TiO)

The mangosteen peels and metal oxides of magnesium oxide (MgO) and titanium dioxide (TiO) were used to synthesize mangosteen powder beads (MPB), mangosteen powder modified with MgO beads (MPMB), and mangosteen powder modified with TiO beads (MPTB) for adsorbing cadmium (II) ions. Their characterizations by BET, XRD, FESEM-FIB, EDX, FTIR, pH, adsorption performances of cadmium (II) ions, adsorbent reusability, adsorption isotherms, kinetics, and thermodynamic studies were investigated. The addition of MgO or TiO into mangosteen peels could increase the specific surface area and pore volume approximately 2 and 1.5 times, so MPMB and MPTB might adsorb cadmium (II) ions higher than MPB. They were amorphous structures and rough surfaces with irregular shapes. The peak and characteristics of MgO or TiO were also detected in MPMB or MPTB by XRD and FESEM-FIB techniques. Their main chemical compositions and functional groups were oxygen, carbon, O–H, C–H, C=O, and C–O. The pH values of MPB, MPMB, and MPTB were 4.42, 9.50, and 4.83, respectively. MPMB had a higher adsorption performance of cadmium (II) ions of 99.02% than MPB (87.11%) and MPTB (91.54%), and the q values of MPB, MPMB, and MPTB were 8.71, 99.02, and 18.31 mg/g, respectively. They could reuse more than four cycles with high adsorptions of cadmium (II) ions of more than 61%. Freundlich and pseudo-second-order kinetic models were good explanations for their adsorption patterns and mechanisms to be a chemisorption. Moreover, they were endothermic processes with favored adsorptions of cadmium (II) ions with increasing temperature.