Modified starch as a component of environmentally friendly polymer adsorbents − from synthesis and characterization to potential application in the removal of toxic C.I. Basic Yellow 2 dye

Abstract

Increasing global degradation of the aquatic environment is forcing the search for new and low-cost adsorbents of reduced toxicity, derived from natural and renewable sources. To meet these expectations, a new approach to adsorbent fabrication was developed.The study aimed to synthesize, characterize, and apply environmentally friendly adsorbents based on poly(ethylene glycol dimethacrylate-co-vinyl acetate) (EGDMA-VA) with unmodified/modified starch (St). The first step proposed a new mechanochemical method of starch modification using thiourea (T) and potassium dihydrogen phosphate (P). Then, the functionalized starch was used to obtain polymeric microspheres. The final step involves their application for the removal of toxic C.I. Basic Yellow 2 (BY2) dye. The pristine materials and adsorbents were characterized by ATR/FT-IR and XPS, DSC, SEM/EDX, porous structure, particle size distribution, tendency to swell, and pHpzc.Adsorption batch studies of BY2 as a function of time (1–60 min), initial dye concentration (1–25 mg/L, pH=8.3), temperature (298–328 K), and competing electrolyte (5–15 g/L Na2SO4) and surfactant (0.1–0.5 g/L CTAB) presence were carried out. The kinetic studies were analyzed using pseudo-first order, pseudo-second order, and intraparticle diffusion models. The equilibrium studies revealed that the Freundlich isotherm model (kF=5.62–6.56 mg1-1/n L1/n) described BY2-adsorbents systems rather than Langmuir, Temkin or Dubinin-Radushkevich. Thermodynamic parameters (ΔG°, ΔH°, and ΔS°) pointed to the exothermic nature of adsorption and its spontaneousness. Importantly, the starch-modified microspheres were regenerated, too.