Functionalized cellulose nanocrystals extracted from date pits as agricultural waste for the efficient remediation of molybdenum from groundwater: Performance and mechanistic studies

Abstract

The adsorption technique has proven to be an excellent option for treating contaminated water. This work was designed to investigate the efficient remediation of molybdenum (Mo(VI)) from groundwater by using a novel adsorbent composed of date pits (DP) modified by manganese oxide/cellulose nanocrystal (CNC) composite (MnO2/CNC@DP). The physicochemical properties of the adsorbent were examined by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope with energy-dispersive X-ray spectroscopy techniques (SEM/EDX), X-ray diffraction (XRD), and transmission electron microscopy (TEM) to study the functional group on the adsorbent surface, surface morphology and chemical composition, and the crystallinity behavior. The performance of prepared (MnO2/CNC@DP) toward Mo(VI) was studied using synthetic solutions and real groundwater samples. Also, the effect of pH, temperature, and initial Mo concentration on the adsorption process was investigated. Moreover, various adsorption isotherm models were calculated, and the thermodynamics of adsorption was studied. The recovery experiments for Mo(VI) saturated MnO2/CNC@DP were conducted by using acidic and alkaline solutions. At the optimum pH of 2, the adsorption capacity increased with increasing the initial concentration of Mo(VI), and Qmax was 30 mg/g at 35 °C. The removal of Mo(VI) from real groundwater was 88.42% The negative values of Gibbs energy (ΔG°) demonstrated that the adsorption is spontaneous, and the experimental data followed the Langmuir isotherm model. Moreover, Mo(VI) can be desorbed from the MnO2/CNC@DP surface by using 1.0M HCl. The proposed mechanisms for the adsorption of Mo(VI) by MnO2/CNC@DP were dominated by electrostatic attraction and inner-sphere complexation. As a result of the research, MnO2/CNC@DP is a promising adsorbent with a high potential for removing Mo(VI) from groundwater. Furthermore, This research provides new knowledge into the modification of date pits using different metal oxides/cellulose nanocrystal particles. Furthermore, the results suggest an excellent chance of employing the efficiently produced adsorbent MnO2/CNC@DP for sustainable groundwater treatment from additional contaminants.