Facile preparation of magnetic chitosan/poly (vinyl alcohol) hydrogel beads with excellent adsorption ability via freezing-thawing method

Novel magnetic chitosan/poly (vinyl alcohol) hydrogel beads (MCPHBs) were prepared through a freezing-thawing method. FTIR, XRD, VSM, TGA and SEM were used to characterize the structure and morphology of MCPHBs. XRD and VSM results indicated that MCPHBs had enough response to meet the needs of magnetic separation even with only little amounts of magnetic nanoparticles. On the other hand, adsorption of methyl orange (MO) was studied. The adsorption capacity was mainly affected by pH value and initial dye concentration. The adsorption followed the pseudo-first-order reaction, which was well fitted with the Langmuir isotherm model. Maximum adsorption capacity of MO at pH 4.0 was up to 6.936 mg/g (with the dye concentration of 30 mg/L) and the adsorption of MO onto the gel beads was fast (reached equilibrium in less than 30 min). Furthermore, it was found that the MCPHBs could be regenerated and reused in alkaline solution. Therefore, the MCPHBs could be employed as low-cost alternatives for the removal of dyes.