A reusable, separation-free and biodegradable calcium alginate/g-C3N4 microsphere for sustainable photocatalytic wastewater treatment

Graphitic carbon nitride (g-C3N4) is a metal-free photocatalyst with the advantages of facile preparation, low cost and good photocatalytic performance. However, as an extensively studied powder catalyst, it is though difficult to be recycled and reused which requires attention urgently. In this study, we report a facile preparation of g-C3N4 hydrogel microspheres with the cross-link reactions between sodium alginate and calcium ions, which can be simply removed from liquid for reuse. The hydroxyl of calcium alginate enabled to boost the adsorption of organic pollutants as well as to boost the transfer and separation of photogenerated charge carriers. The g-C3N4 hydrogel microspheres showed remarkable performance in the control of organic pollutant contamination. The sample 25%-SACN had the best photocatalytic activity, which can remove 80.94% MB in 42 h. The total removal is 1.77 times as that of 0%-SACN. Meanwhile, it had good cycle stability and the catalytic performance did not decrease after 5-time usage. The used g-C3N4 hydrogel microspheres were also demonstrated to be biodegraded anaerobically to produce methane for energy recovery and recycling. The results and outcome of this paper might bring new inspiration for the study of easily reusable and sustainable photocatalysts for wastewater treatment.