Adsorption of Cr(V) from aqueous solution using eggshell-based cobalt oxide- zinc oxide nano-composite

Abstract

In the present work, eggshell-based zinc oxide-cobalt oxide (ES-ZC) nanocomposite was synthesized and used for removal of Cr(VI) from an aqueous solution. The synthesized nanocomposite was characterized using SEM, FTIR, and XRD. The specific surface area of the nanocomposite was also measured using BET and its point of zero charge was determined using a standard method. The effects of adsorption process parameters (adsorption time, pH of solution, adsorbent dose, and initial Cr(VI) concentration) on the response (percent Cr(VI) removal) were investigated using a batch adsorption system. The Cr(VI) adsorption percentage increases with adsorbent dosage. The Cr(VI) adsorption percentage rapidly increases as adsorption time increases from 30 to 90 minutes, however, further increases in adsorption time does not significantly affect the Cr(VI) removal performance. The optimum pH for Cr(VI) adsorption was observed at 2.0, however, a further increase in pH results in a reduction of Cr(VI) removal. Similarly, the initial Cr(VI) concentration negatively affects its removal percentages. The effects of the adsorption process parameters were investigated and optimum Cr(VI) adsorptions were obtained using Response Surface Methodology (RSM) applying Central Composted Design (CCD). The optimum Cr(VI) percent removal obtained by RSM was 94.8% at adsorption time of 90 minutes, pH of 2, adsorbent dose of 1.5 g/L, and initial concentration Cr(VI) of 45 mg/L. The experimental Cr(VI) percent removal at this condition was 93.5 % showing its agreement with the predicted value. . This shows the model can sufficiently estimate the percent of Cr(VI) removal. Moreover, the adsorption kinetics was correlated with pseudo-second-order with R2 value of 0.989. Further, Langmuir isotherm model better fits the current adsorption process with R2 value of 0.999.