Effective Adsorption–Desorption Kinetic Study and Statistical Modeling of Bentazon Herbicide Mediated by a Biodegradable β-Cyclodextrin Cross-Linked Poly(vinyl alcohol)–Chitosan Hydrogel

Indiscriminate use of pesticides to meet the global demand for food has contaminated groundwater and surface water, affecting the global environment. In view of this, it is imperative to find an economical solution to this critical issue. Herein, a novel β-cyclodextrin cross-linked poly(vinyl alcohol)–chitosan (PVA/CS/β-CD) hydrogel is reported for the adsorption of bentazon (BZ) herbicide. The properties of the PVA/CS/β-CD hydrogel, such as its surface morphology, surface area, thermal stability, and the presence of functional groups, have profound effects on the adsorption of BZ on its surface, and hence these have been investigated by FESEM, BET, TGA, and FT-IR analytical techniques. Several influential factors, viz., pH of the solution, temperature, initial concentration of BZ, contact time, and mass of the hydrogel, have been explored by the Box–Behnken design model and systematic batch studies. From the response surface methodology model, 13.45 mg of hydrogel was able to remove 93.71% of BZ from 10 mL of a 10 mg/L solution at pH 7.4 in 120 min, as assessed by systematic batch adsorption studies. The adsorption behavior of BZ on the PVA/CS/β-CD hydrogel was thermodynamically spontaneous and endothermic. The maximum adsorption capacity was 398.40 mg/g, which comes from the Langmuir isotherm and follows pseudo-second-order model. BZ-loaded PVA/CS/β-CD hydrogel can be recycled using methanol and shows good removal efficiency (>70%) for six consecutive adsorption–desorption cycles. Additionally, the BZ-adsorbed PVA/CS/β-CD hydrogel can be employed as a sustained release vehicle for BZ having long-term weedicide effects at diverse pH values in water.