Synthesis of a zeolite-a/MOF-5 composite for the defluoridation of groundwater

Consumption of excessive F^- from groundwater harms human health and can cause bone and dental fluorosis. To reduce the excessive F^- concentration from groundwater, a novel zeolite-A/MOF-5 (Z-A/MOF-5) composite was synthesized through the solvothermal method. The phase structure, functional group, weight loss, morphology, and elemental composition were characterized by using PXRD, FT-IR, TGA, SEM, and EDX, respectively. The surface charge of the Z-A/MOF-5 composite showed a positive surface up to a pH value of 8.1, which is accessible for the defluoridation of groundwater. The defluoridation efficiency of the Z-A/MOF-5 adsorbent was activated by optimizing defluoridation conditions. The maximum defluoridation efficiency (88.20%) and capacity (11.025 mg g^-1) were recorded at a pH of 3, 1.2 g L^-1 of adsorbent dose, 6 h of contact time, and 10 mg L^-1 initial concentration of F^- (<i>C</i> _o) at ambient temperature. However, the defluoridation efficiency of the Z-A/MOF-5 composite still maintained its efficiency (85.50%) up to a pH of 7, which is applicable for the defluoridation of groundwater. The defluoridation data were well fitted with the Freundlich isotherm model and pseudo-second-order kinetics, confirming that defluoridation mainly proceeds <i>via</i> chemisorption on the heterogeneous surface of the Z-A/MOF-5 composite. The defluoridation performance of the Z-A/MOF-5 composite was tested on real water samples having 12.25 and 8.5 mg L^-1 F^- <i>C</i> _o taken from Ziway and Kenteri towns, Ethiopia, that reduced the concentration of F^- to 1.48 and 0.82 mg L^-1, respectively. Interestingly, the recyclability study showed defluoridation efficiencies of 88.20%, 87.90%, 86.80%, 85.60%, 82.00%, and 70.10% for the 1^st, 2^nd, 3^rd, 4^th, 5^th, and 6^th runs, respectively. Consequently, the synthesized composite is a promising adsorbent for practical application.