Microfluidics combined with ionic gelation method for production of nanoparticles based on thiol-functionalized chitosan to adsorb Hg (II) from aqueous solutions

This work aimed at producing nanoparticles (NPs) based on thiol-functionalized chitosan (CS) using capillary microfluidic (MF) device combined with ionic gelation method to adsorb mercury ion [Hg (II)] from aqueous solutions. In this line, CS was functionalized with epichlorohydrin/cysteaminium chloride (2.73 M ratio) followed by fabricating NPs via MF and bulk mixing (BM) methods. To characterize the morphology, zeta potential, functionality, structure, and magnetic property of the samples, a series of tests such as SEM, TEM, DLS, FTIR, XRD, and VSM were carried out, respectively. The obtained results showed that MF technique was able to produce NPs with a diameter as small as 18 ± 3 nm, and a uniform shape compared to BM method. Thiol groups (−SH) functionalization on CS surface was confirmed by appearing a characteristic peak at 2579 cm−1. Also, the XRD patterns indicated the appropriate synthesis of Fe3O4 (magnetite), and no change in the structure of CS NPs in the presence of magnetite. Moreover, adding the magnetite to thiol-functionalized CS NPs led to suitable saturation magnetization about 26 emu/g to facilitate their separation using a magnetic field. To evaluate the performance of the nanoadsorbent, it has been exposed to Hg (II) in an aqueous solution which in turn the parameters optimization for the adsorption was done via Box-Behnken design (BBD) method, exhibiting the effect of adsorbent dose and the initial concentration of Hg (II) was much more significant than that of pH. Different concentrations of total dissolved solids up to 1000 mg/L had no adverse impact on the adsorption process confirmed by EDAX spectra. The least value of RMSE (5.023) and χ2 (0.3) were observed for Redlich-Peterson, Radke-Prausnitz, and UT isotherms. Maximum adsorption capacities calculated using Langmuir and UT models were 1192 mg/g and 1126 mg/g, respectively. Thermodynamic studies demonstrated that the nature of the adsorption process was spontaneous and endothermic. Recovery of nanoadsorbent was successfully carried out using HCl 0.5 mol/L. The adsorption studies revealed that the prepared nanoadsorbent is promising candidate used in mercury removal from a real wastewater potentially.