Nanosilica-polyacrylic acid superabsorbent hydrogel derived from fast concentration gradient method for remediation of Congo red wastewater

This study presents a novel composite superabsorbent hydrogel (SAH) synthesized from nanosilica and polyacrylic acid, demonstrating exceptional efficacy in removing Congo Red dye from wastewater. Utilizing a fast concentration gradient method, we achieved the synthesis of nanosilica with a high specific surface area of 380 m²/g, a total pore volume of 0.81 cm³/g, and a mean pore diameter of 17 nm. The modified nanosilica particles are well-dispersed, with around 83.5 % of the particles falling within the 20-35 nm size range. The resulting composite hydrogel exhibited a swelling ratio of 165 % after 135 min immersion in water. Remarkably, the hydrogel achieved over 98.5 % dye removal efficiency at a sorbent dosage of 3 g/L and a contact time of 1 h at pH 7. The maximum monolayer capacity obtained from the Langmuir isotherm was 555.56 mg/g. Additionally, it maintained a dye removal efficiency of 71.6 % after five regeneration cycles, highlighting its potential for sustainable wastewater treatment applications. The possible mechanisms for the removal of Congo Red dye involve electrostatic interactions and hydrogen bonding between the dye molecules and silica nanoparticles or hydrogel, facilitated by functional groups such as hydroxyl, carboxylic, and amino groups. This research not only advances the understanding of hydrogel properties but also introduces an innovative approach to enhance the performance of nanosilica-based adsorbents in environmental remediation, marking a significant contribution to the field of wastewater management.