Nanofluid-peroxydisulfate integrated volumetric solar interfacial evaporation system for water evaporation and organic pollutant removal

Solar evaporation exhibits significant potential for the treatment of high-salt organic wastewater. However, it's also confronted with challenges due to the accumulation of organic pollutants and salts in the concentrated wastewater following evaporation, which compromises the long-term stability of evaporation unit and complicates subsequent treatment processes. To address these challenges, a volumetric solar interfacial evaporation (V-SIE) system by integrating Fe₃O_{4 -}H₂O nanofluids and peroxydisulfate (PDS) were proposed in this study. In V-SIE system, Fe₃O₄ magnetic nanoparticles (NPs) were prepared as solar receivers to form a volume-absorbing solar energy interface and enhance evaporation efficiency. The results show that the evaporation rate was 1.412 kg/(m²·h) and the solar efficiency reached 93.75 % as the temperature rose to 57.2 ℃. Additionally, the high thermal conductivity of Fe₃O₄ facilitated the effective heat transfer to the fluid and provided sufficient thermal energy to activate PDS, thereby removing 99.3 % of Rhodamine B (RhB). Fe₃O₄ NPs effectively promoted the generation of reactive species including SO₄ ^·-, ·OH, O₂ ^·- and ¹O₂ from PDS and the four main stages including N-de-ethylation, chromophore cleavage, ring-opening, and mineralization were proposed as the possible degradation pathway of RhB. This study provides a reference for developing V-SIE system and highlights the positive effect of nanofluids in advanced oxidation processes.