Synthesis of cellulose hydrogel by utilizing agricultural waste and zeolite for adsorption of copper metal ions

Metal contamination in water is a widespread ecological problem that can lead to various health hazards. Copper is one of the common contaminants in water whose concentrations continue to elevate due to high industrial activities. To date, adsorption can be considered an efficient method for removing metals, with one direction of development being the synthesis of green adsorbents. This work demonstrated the utilization of cellulose from waste to synthesize adsorbent for copper. Rice husk is utilized as the cellulose source for preparing hydrogel, and then incorporation of zeolite was done to enhance the surface area and porosity. Adsorbent preparation was performed by first dissolving rice husk cellulose in NaOH/urea to form cellulose gel. Then, zeolite was incorporated at a mass ratio of cellulose-to-zeolite of 4:2. Finally, a crosslinking agent was added to obtain the hydrogel composite. The presence of exfoliated clay particles in the hydrogel matrix was revealed through scanning electron micrograph imaging. The additional functional groups due to the addition of zeolite particles in the hydrogel were analyzed using the Fourier transform infrared spectroscopy technique. The resulting hydrogel composites were applied for the removal of Cu2+ from water. The effect of pH level, contact time, and coexisting metal ions on adsorption effectiveness was investigated. X-ray photoelectron spectroscopy analysis was performed to get insight into the adsorption mechanism. Adsorption kinetics reveals that adding zeolite allows more rapid adsorption of Cu2+; based on the pseudo-first-order parameter, the rate is increased from 2 × 10−3 to 7 × 10−3 min−1 and the adsorption equilibrium was reduced from 20 to 8 h. However, incorporating zeolite contrarily affected the adsorption capacity, where it was decreased from 17.05 to 10.77 mg g−1 for the adsorption process at 30 °C. This work presents a novel approach to upcycling agrowaste, offering a sustainable solution for mitigating metal contamination in water.