Application of Geopolymers Modified with Chitosan as Novel Composites for Efficient Removal of Hg(II), Cd(II), and Pb(II) Ions from Aqueous Media

In the present paper, two amorphous aluminum silicates (i.e. geopolymers) were synthesized via the interaction of 23.57 mmol of sodium metasilicate pentahydrate with 5.18 or 10.35 mmol of aluminum chloride hexahydrate. The synthesized geopolymers using 5.18 and 10.35 mmol of aluminum chloride hexahydrate were abbreviated as G1.25 and G2.50, respectively. Also, the synthesized geopolymers were modified with chitosan as novel composites. The synthesized composites using G1.25 and G2.50 were abbreviated as G1.25/Ch and G2.50/Ch, respectively. Besides, the synthesized geopolymers and their chitosan composites were characterized using different tools such as XRD, FT-IR, SEM, and EDX. Moreover, the synthesized geopolymers and their chitosan composites were utilized as efficient adsorbents for the removal of Hg(II), Cd(II), and Pb(II) ions from aqueous media. The Langmuir isotherm and pseudo-first-order kinetic model were more consistent with the removal of metal ions from aqueous media. Furthermore, the adsorption processes were spontaneous, exothermic, and chemisorption. In the case of Hg(II), the maximum adsorption capacity of G1.25, G2.50, G1.25/Ch, and G2.50/Ch were 131.93, 140.85, 166.67, and 173.91 mg/g, respectively. In the case of Cd(II), the maximum adsorption capacity of G1.25, G2.50, G1.25/Ch, and G2.50/Ch were 118.34, 134.95, 159.49, and 166.11 mg/g, respectively. In the case of Pb(II), the maximum adsorption capacity of G1.25, G2.50, G1.25/Ch, and G2.50/Ch were 102.15, 118.91, 128.21, and 156.01 mg/g, respectively.