Facile preparation of reusable alginate g-C3N4 hydrogel beads for efficient photocatalytic removal of organic pollutants

g-C₃N₄ has shown great advantages in photocatalytic degradation of pollutants; however, its extensive application is limited by the problems of easy agglomeration and difficult recovery of powder materials. Taking advantage of the egg-box gel characteristics of alginate, g-C₃N₄ hydrogel beads with millimeter size which can be floated on liquid surface were prepared by a simple process. The study revealed that g-C₃N₄ hydrogel beads with a diameter of 2 mm showed excellent cationic dye adsorption performance. The hydrogel beads containing 50 mg g-C₃N₄ powder could completely adsorb methylene blue dye with a concentration of 10 mg/L within 30 min, then degrade the dye under visible-light irradiation. After 5 cycles of adsorption and degradation, the beads can still maintain good and stable properties. The outstanding ability of photocatalytic degradation is based on that once exposed to visible light, the hydrogel network of g-C₃N₄ hydrogel beads can reduce the recombination and promote carrier separation for the generated electron–hole pairs, furtherly, facilitating the O₂⁻ and ·OH induced by electrons and holes, respectively, to oxidize the adsorbed pollutants as CO₂ and H₂O. This strategy makes full use of the network structure of alginate, not only can g-C₃N₄ powder be uniformly locked inside the beads, improving the dispersion of the powder material; but also can open the porous network structure of the hydrogel during the adsorption and degradation process, gradually exposing the powder, and give full play to the excellent photocatalytic performance of g-C₃N₄ material while in contact with the pollutants, consequently, all laying foundation for its further industrial application.