Synthesis of a novel clay/polyacrylic acid-tannic acid hydrogel composite for efficient removal of crystal violet dye with low swelling and high adsorption performance

Hydrogels are versatile materials with numerous applications; however, their potential in water treatment is hindered by their tendency to exhibit high swelling, degradation, and excessive water absorption. In this study, a hydrogel composed of natural clay, polyacrylic acid (PAA), and tannic acid (TA) was prepared with varying ratios of TA to control swelling ratio, reduce degradation and enhance adsorption efficiency for removal of cationic dye-contaminated wastewater. The effect of the TA ratio on the physical, chemical, and adsorption properties of prepared hydrogel (clay/PAA-TA) was studied by preparing a series of hydrogel composites and characterizing them using various techniques. The swelling ratio of pure PAA hydrogels was 7061%, but by incorporating TA into the polymer mixture, the swelling ratio decreased to less than 500%, with the lowest observed swelling of 250% occurring at a 5% tannic acid. In adsorption studies, the target pollutant was crystal violet dye (CV) and the pH effect, time effect, temperature and initial dye concentration for the adsorption CV dye were investigated using batch adsorption parameters. Adsorption studies showed that using 5% of TA is the optimal ratio to achieve the highest adsorption capacity of the prepared clay/PAA-TA to uptake CV dye. With an adsorption capacity of 444.5 mg/g, the Langmuir-Freundlich model suited the adsorption isotherm. The adsorption kinetics were best explained by the pseudo-first-order model. The results of thermodynamic studies indicated that the adsorption was spontaneous, favorable, and endothermic.