Effective adsorption of tannic acid by porous dual crosslinked soy protein isolate-alginate hybrid spheres from aqueous solution

Soy protein isolate-alginate hybrid spheres (SPIAHS) were prepared sequentially by using Ca2+ ions and glutaraldehyde as crosslinkers via the dual crosslinking method for tannic acid (TA) adsorption. SPIAHS samples before (SPIAHS-1) and after (SPIAHS-2) glutaraldehyde crosslinking were featured by SEM, FT-IR, XPS, etc. Adsorption performance for TA from aqueous solution by the SPIAHS-2 was explored under various experimental conditions, such as different initial pH, adsorbent dosage, temperature, etc. SPIAHS-2 manifested a maximal adsorption capacity of 1030 mg/g, being greater than most of the previously reported biosorbents. This result could be principally ascribed to the increased specific surface area, robust spheres of lamellar porous network structure, and richness of organic functional groups anchored on the SPIAHS-2 surface after glutaraldehyde crosslinking. Adsorption kinetics and isotherm investigations disclosed that TA adsorption onto SPIAHS-2 can be commendably depicted by the pseudo-second-order kinetic and obeyed single molecule layer adsorption of the Langmuir model. Moreover, the mechanism of TA adsorption was identified by the hydrogen bonding interaction between the oxygen and nitrogen functional groups of SPIAHS-2 and multiple hydroxyl groups of TA. The TA-loaded SPIAHS-2 could be regenerated and used repeatedly with relatively high adsorption capacity, showing great potential in wastewater treatment for TA removal.