Surface engineering of chitosan nanoparticles via polyamidoxime grafting and Response Surface Methodology...

Herein, we report the synthesis of polyamidoxime-functionalized chitosan-nanoadsorbent capable of efficiently removing hexavalent chromium (Cr(VI)) from aqueous media. Chitosan-nanoparticles were prepared by reverse-micelle method followed by vinyl-modification to incorporate grafting sites. Polyacrylonitrile was then grafted onto modified-nanoparticles by emulsion-graft polymerization followed by chemical-transformation to polyamidoxime (PAO-g-MCN). Gravimetric analyses revealed the maximum grafting-percentage of 183% under optimized reaction parameters comprising 5% monomer, 1.0% surfactant and 0.1% initiator. Chitosan-nanoparticles were characterized via DLS and UV-Visible spectroscopy to assess particle size distribution (167 nm) and characteristic absorption peak (254 nm). The structural and morphological characteristics of the bio-nanoadsorbent were examined using FTIR, XRD, FESEM, EDX and BET. Adsorption experiments were conducted to optimize the effects of contact time, pH and initial chromium concentration using Box-Behnken design within response-surface methodology framework. The experimental findings were investigated by the ANOVA showing that the model regression is acceptable. The R² determination coefficients were found to be 0.9781 for adsorption capacity and 0.9672 for %Removal signifying an excellent connection between predicted and experimental responses with optimal adsorption at pH = 4.5, time = 30 min, initial-concentration = 50 mg/L, adsorbate volume = 10 mL and adsorbent mass = 10 mg. The developed bio-nanoadsorbent exhibited a maximum adsorption-capacity of 320.47 mg g^-1, with experimental data best described by pseudo-second order and Langmuir isothermal-model, indicating monolayer chemisorption on homogeneous surface. The cyclic-reuse performance of PAO-g-MCN bio-nanoadsorbent was evaluated through nine cycles, which demonstrated that it maintained >90% removal-efficiency over five cycles indicating its promising durability and reusability. In conclusion, PAO-g-MCN demonstrates significant potential as an effective and environmentally friendly bio-nanoadsorbent for the remediation of Cr(VI) contaminated aqueous-systems.