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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.
Hu et al. (2018) studied this question.