Solar-driven PMS activation over Ag/Halloysite nanotubes onto floatable integrated device for pollutant degradation and coupled interfacial water evaporation

Abstract

The solar-driven photothermal photocatalytic contaminant degradation and water evaporation coupled technique is promising for practical wastewater treatment. This study developed photothermal HNTs@Ag/C-5 nanocomposites by polycondensation of tannic acid with silver and following carbonization to construct plasmonic silver nanoparticle onto halloysite nanotubes (HNTs). The incorporation of Ag onto HNTs enhanced electron-hole separation, enabling efficient activation of potassium peroxymonosulfate (PMS) under sunlight. A floatable integrated device was constructed by anchoring the catalyst to a melamine sponge via calcium ion-cross-linked sodium alginate. This device achieved 84.3 % degradation of carbamazepine (CBZ) in 90 min under light, with a reaction rate constant of 0.01685 min⁻¹, nearly four times higher than unmodified halloysite nanotubes. The photocatalytic PMS activation over HNTs@Ag/C-5 also show great potential for detoxifying other pharmaceutical compounds such as tetracycline (TC) and norfloxacin (NFX) in wastewater. Radical trapping and quenching experiments confirmed hydroxyl radicals (·OH) as the dominant reactive oxidative species in CBZ degradation. Additionally, the device functioned as a solar-driven photothermal evaporator, achieving an evaporation rate of 1.654 kg m⁻² h⁻¹. Reusability tests demonstrated consistent performance, with only a 4 % efficiency drop after multiple degradation cycles. This reported monolith evaporator affords possible opportunity for treating complex wastewater when harnessing the evaporation to obtain freshwater and synchronously degrade contaminant.