Fabrication of novel starch-based composite hydrogel microspheres combining Diels-Alder reaction with spray drying for MB adsorption

Herein, magnetic starch-based composite hydrogel microspheres (SCHMs) were produced via a Diels-Alder reaction during spray drying. The adsorption behavior of SCHMs for methylene blue (MB) was investigated systematically. The adsorption process could be described by Langmuir isothermal model and pseudo-first-order kinetic model with R 2 > 0.95 and R 2 > 0.98, respectively, resulting from its dominating physical adsorption. The thermodynamic studies showed the adsorption was spontaneous and the nature of adsorption was endothermic due to that the free energy ∆G was a negative value and the enthalpy ∆H was a positive value. The absorbent had good reusability with 90.5% of removal efficiency after 5 cycles. In addition, the effects of concentration, pH and temperature on the adsorption of MB by SCHMs were optimized using the Box-Behnken Design and response surface methodology. The order of three factors affecting the adsorption capacity of SCHMS is initial pH > initial concentration > temperature. Due to their safe, non-toxic and easily recycled advantages, SCHMs have the potential to be applied to water treatment in the future.