Facile Preparation of Tannic Acid–Poly(vinyl alcohol)/Sodium Alginate Hydrogel Beads for Methylene Blue Removal from Simulated Solution

A novel hydrogel bead [tannic acid (TA)-poly(vinyl alcohol) (PVA)/sodium alginate (SA)] with high strength prepared by biocompatible PVA, TA, and biocompatible SA via an instantaneous gelation method was applied to remove methylene blue (MB) from aqueous solution. The obtained TA-PVA/SA hydrogel beads were fully characterized by thermogravimetric analysis, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and so on. The adsorption performances of TA-PVA/SA hydrogel beads for MB were investigated by changing the factors of TA content, initial concentration, pH, adsorbent dosage, contact time, and temperature systematically. The maximum capacity of TA-PVA/SA hydrogel beads for MB removal was obtained to be 147.06 mg/g at 30 °C, whose capability was better than that without TA. After fitting the adsorbed data, it was basically consistent with the Langmuir isotherm and pseudo-second-order kinetic model. Thermodynamic studies indicated that MB removal was spontaneous and exothermic in nature. It is concluded that the low-cost TA-PVA/SA hydrogel beads as an easily recoverable adsorbent have a great potential on the removal of hazardous dyes from wastewater.