Green approach for the synthesis of a acrylonitrile hyperbranched polymer/chitosan composite for the removal of diclofenac from water: determination of optimal conditions using statistical experiment design†

Abstract

Acrylonitrile hyperbranched polymer/chitosan composite (AC–Hyp/CS) material was synthesized for the removal of diclofenac. In this method, a hyperbranched polymer was prepared by crosslinking an acrylonitrile monomer to obtain a host with a large surface area (AC/Hyp). To improve the functional sites of AC/Hyp, it was functionalized with chitosan (AC–Hyp/CS), which led to excellent removal efficiency. The physiochemical characterization of AC–Hyp/CS was carried out using FTIR, XPS, PXRD, DLS, TGA-DTA and SEM coupled with EDS. The uptake of diclofenac by AC–Hyp/CS was optimized through RSM in combination with BBD. Four factors, namely, AC–Hyp/CS dose (0.002–0.0180 g), concentration of diclofenac (10–30 mg L⁻¹), solution pH (2–6) and contact time (20–100 min), were considered to examine influencing parameters that resulted in the excellent removal efficiency. A high value of R² (0.9969) confirmed the excellent agreement of equilibrium data to the quadratic model. The obtained results suggested that 0.01 g AC–Hyp/CS was sufficient to eliminate 99.6% diclofenac from 20.0 mL (20.0 mg L⁻¹) solution at pH 4. Isothermal investigation suggested that the Langmuir isotherm model was administrated well with equilibrated data as it showed appropriate R² values (0.9814–0.9908) and low values of error functions (SSE: 0.002–11.742, χ²: 1 × 10⁻⁵–0.048 and RMSD: 0.0447–3.426). The adsorption capacity (maximum) obtained from the Langmuir model was 200 mg g⁻¹. The high values of R² (0.9878–0.9982) and low values of error functions (SSE: 0.160–1.343, χ²: 0.004–0.0534, RMSD: 0.40–1.158) of the pseudo-second-order kinetic model confirmed that the absorption was chemisorption. Diffusion-based kinetic studies revealed that both diffusion processes (film and intraparticle) participated in this sorption. Adsorption/desorption cycling test suggested that the composite exhibited excellent reusability characteristics up to 7 cycles, which confirmed that AC–Hyp/CS could be an effective sorbent for elimination of diclofenac from aqueous environments.