Photocatalytic sponges for wastewater treatment, carbon dioxide reduction, and hydrogen production: a review

Water pollution and the energy demand are calling for sustainable technologies such as photocatalysis, yet actual methods are difficult to upscale due to the poor recovery and reusability of nanocatalysts. This issue could be solved by using photocatalytic sponges, which display high surface area and reusability. Here we review the applications of photocatalytic sponges for wastewater degradation, disinfection, carbon dioxide reduction, and hydrogen production. Photocatalytic sponges are fabricated by templating, dip coating, sol–gel, polymerization, electrospinning, and freeze drying. Remarkable results include the monolithic microreactor with Ag/AgCl coated on a polydopamine-modified melamine sponge, which exhibits a 100% methylene blue degradation in 15 min, with a reusability of five cycles. An hydrogen production rate of 11.33 mmol h⁻¹ g⁻¹ was obtained with the pyridazine-doped graphitic carbon nitride with nitrogen defects and a spongy structure.