Mechanism and industrial application feasibility analysis on microwave-assisted rapid synthesis of amino-carboxyl functionalized cellulose for enhanced heavy metal removal.

The study presented the successful microwave-assisted (MW-assisted) preparation of a novel adsorbent derived from rice straw (RS-AC) and explored its adsorption performance toward heavy metal ions from water. The RS-AC was rapidly synthesized through pretreatment and one step grafting via the MW-assisted approach. The quantitative predictive correlations between target performance of RS-AC and process parameters were obtained through the response surface methodology (RSM). Meanwhile, the optimal preparation process conditions were determined: NaOH solution concentration, 20%; MW irradiation temperature for pretreatment, 100 and 150 °C; MW irradiation time for pretreatment and grafting, 10 and 60 min; EDTAD-RS mass ratio, 3. The RS-AC showed a good adsorption of different heavy metal ions from water (152.39, 55.46, 52.91, 35.60 and 20.11 mg g for Pb(Ⅱ), Mn(Ⅱ), Cd(Ⅱ), Cu(Ⅱ) and Ni(Ⅱ), respectively). The adsorption behaviors followed the Langmuir model and pseudo second-order kinetics model with a highly significant correlation. Also of note was that amino and carboxyl groups were successfully introduced on the rice straw based on characterization results. Furthermore, preparation mechanism was explored to reveal reasons why microwave irradiation could accelerate the preparation of the adsorbent; its adsorption process was dominated by electrostatic attraction and chelation. Finally, the study made the industrial application feasibility analysis of MW-assisted approach used for pretreatment and graft reaction of agro-waste biomass.