Highly efficient Cd(II) removal from groundwater utilizing layered mixed metal oxides-graphitic carbon nitride composite with improved cycling stability

Abstract

Graphitic carbon nitride (GCN) and its mixed metal oxide (MMO) composites are synthesized via co-precipitation followed by the pyrolysis method using various ratios of calcium aluminium (Ca:Al) with GCN, to enhance the adsorption ability towards Cd(ii) present in wastewater. Synthesized composite materials were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface analysis, Fourier transforms infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. Due to its higher specific surface area (218.65 m 2 /g), the produced GCN and CaAl mixed metal oxide composite (GCN-MMO) exhibits improved adsorption ability towards Cd(II) ions. Approximately >99 % were adsorbed with Langmuir q max of 131.57 mg/g. An overall pseudo-second-order (PSO) model fitted the kinetics data well. The possible mechanisms were surface complexation and precipitation, outer-sphere complexation, and acid-base mechanism. Further, the groundwater application was studied, and it achieved adsorption below the maximum permissible limit of USEPA with excellent cycling stability. The findings of this study showed that GCN-MMO composite material may be useful for the adsorption of Cd(II) heavy metal from an aqueous solution. • Integration of graphitic carbon nitride and mixed metal oxide composites (GCN-MMO) by simple pyrolysis method. • A significant improvement in the Surface area and pore volume of the modified adsorbent. • GCN-MMO composite was able to reach the maximum permissible level for Cd(II) in drinking water, as set by the USEPA. • The Cd(II) removal was achieved via Lewis acid-base mechanism yielded 131.57 mg/g adsorption capacity. • The composite proved to be highly reusable for Cd(II) removal, exhibiting effective results for up to 5 cycles.