Nutrient recovery and pollutant removal using carboxymethyl cellulose/ microfibrillated cellulose hydrogel: Templating effects of CaCO₃ nanoparticles

Cellulose-based hydrogel is an emerging adsorbent in pollution control, but the dense structure and the weak chemical interaction limit its adsorption capability and reusability. In this work, CaCO3 nanoparticles and the microfibrillated cellulose were incorporated into carboxymethyl cellulose (CMC) hydrogel beads to improve the removal of methylene blue (MB) and phosphate. CaCO3 nanoparticles were further removed using a chelating agent to create pores through templating. Scanning electron microscope, Fourier-transform infrared spectroscopy, and X-ray diffraction analysis showed that template removal was affected by the presence of microfibrillated cellulose. The intercalation of CaCO3 nanoparticles with the cellulose network improved the particle dispersion and pore interconnectivity. The MB and phosphate adsorption capacity of CMC hydrogel was improved to 237.48 mg/g and 121.58 mg/g, respectively. The chemical adsorption was described well using the pseudo-second-order kinetic model and Langmuir isotherm model. After 6 cycles, the adsorption capacity was maintained >90 %. The phosphate desorption was not affected by the initial concentration or phosphate loading according to the zero-order equation.