Enhancing the removal performance of Cd(II) from aqueous solutions by NaA zeolite through doped thiourea reduced GO which is trapped within zeolite crystals

Abstract In this study, thiourea reduced graphene oxide/NaA zeolite composite (tGO-Zeo) was successfully prepared by a facile two-step synthetic route and used as an efficient adsorbent for removal of Cd(II) from aqueous solution. Characterization of the composite material showed that tGO was entrapped within zeolite crystalline particles and intimately interacted with the zeolite framework. Furthermore, the presence of tGO considerably reduced zeolite crystal size and altered crystal morphology, turning cubic zeolite crystals of micrometer size into nanometer irregular particles. Batch adsorption experiment for Cd(II) removal was conducted and the adsorption performance of tGO-Zeo and Zeo (zeolite) were determined. It was shown that doped tGO significantly enhanced the adsorption capacity of zeolite by 31.54%. The adsorption mechanism differs for tGO-Zeo and Zeo, and tGO-Zeo has higher affinity for Cd(II). The adsorption capacity of tGO-Zeo with a tGO doping amount of 1.26% (wt%) was estimated to be 196 mg/g (1.74 mM/g) at 30 °C and superior to most previously reported zeolite based composites, which often contain large amounts of dopants. The effects of pH and ionic strength on adsorption suggest that ion exchange and coordination are responsible for Cd(II) adsorption by tGO-Zeo. Humic acid can slightly increase Cd(II) adsorption performance of tGO-Zeo, which may be due to tGO-Zeo—humic acid—Cd(II) complexes formation. Therefore, tGO-Zeo composite is a cost-effective and eco-friendly adsorbent for efficient removal of Cd(II) ions from aqueous solutions.