Adsorption performance of Ag/Fe₃O₄/ZrO₂ composite decorated with graphene toward methylene blue dye

Use of carbon-based materials, such as graphene, has drawn attention in the wastewater treatment field because of their high specific surface area. This property of graphene suggested that it had superior adsorption characteristics for removing contaminant dyes from aqueous solutions. Based on this precept, we wanted to enhance the adsorption ability of the Ag/Fe₃O₄/ZrO₂ photocatalyst by adding graphene, using the co-precipitation method for synthesis. The crystal structure of as-prepared specimen was characterized using X-ray diffraction, which confirmed the existence of tetragonal phase ZrO₂, cubic spinel phase Fe₃O₄ and cubic phase Ag. Unfortunately, the graphene characteristic peak could not be detected by X-ray diffraction (XRD). Thermal gravimetric analysis showed that mass degradation below 150 °C could be attributed to the loss of bound water from the surface of the ZrO₂. Mass degradation at 340 °C could be attributed to the combustion process of graphene, which indicated the presence of graphene in the prepared samples. The synthesized samples were utilized for the uptake of methylene blue (MB) as a model of an organic pollutant. The results that were obtained showed that the inclusion of graphene increased the ability of Fe₃O₄/ZrO₂ adsorption. Increases in the weight percentage of graphene increased the adsorption ability of the samples. The best adsorption occurred in alkaline pH conditions. The experimental data could be fitted better using the Langmuir model than it could using the Freundlich model. Finally, as-prepared samples showed good stability, even after four cycles of reuse.