Facile Fabrication of Photocatalyst-Immobilized Gel Beads with Interconnected Macropores for the Efficient Removal of Pollutants in Water

A novel strategy is developed for the facile fabrication of photocatalyst-immobilized gel beads with interconnected macropores for the efficient removal of pollutants in water via visible photocatalysis. In this study, a graphitic carbon nitride nanosheet (CNNS) is selected as the photocatalyst and calcium alginate (CaAlg) is used as the gel matrix. The interconnected macropores inside the gel beads, which are beneficial to the efficient mass transfer of pollutants, are generated using bubbles as templates. Air bubbles are wrapped in a pre-gel aqueous solution containing sodium alginate (NaAlg), CNNS, sodium dodecyl sulfate (SDS), and sodium bicarbonate (NaHCO3) by vigorously stirring the solution, and then, the foamy solution is dripped into calcium chloride/acetate acid (CaCl2/CH3COOH) mixed aqueous solution. The rapid crosslink of Ca2+ with alginate turns the droplets into gel beads, and meanwhile, the macropores inside droplets become interconnected because of the rapid generation of CO2 gas upon the reaction between NaHCO3 and excess CH3COOH. Effects of the formulations of pre-gel solutions, including NaAlg, CNNS, NaHCO3, and SDS contents, on the structures and photocatalytic performances of gel beads are investigated systematically. Demonstrated by removing a model pollutant rhodamine B (RhB) from water, CNNS-immobilized CaAlg gel beads with interconnected macropores exhibit excellent photocatalytic performances under visible light. About 99% of RhB in water can be removed efficiently within 30 min under visible light using the as-prepared gel beads. Importantly, the proposed gel beads can be easily recycled with stable photocatalytic performances. The proposed novel strategy for fabricating photocatalyst-immobilized gel beads with interconnected macropores is highly promising and is of great reference value for the fabrication of macroporous gel beads for various applications.