Dual-vacancy engineered CoWO4/CdIn2S4 heterojunction aerogel for photothermal conversion and water purification

H 2 /Ar etching created O/S vacancies at CWO/CIS interface, narrowing bandgap for full-spectrum absorption. • H 2 /Ar etching enhanced photothermal conversion via non-radiative recombination, channeling charge relaxation to heat. • CWO/CIS-H 2 Ar aerogel achieves 2.29 kg m −2  h −1 , 88.9% efficiency at 1 sun, outperforming single and unetched composites. • This evaporator shows excellent photothermal conversion and strong potential for wastewater treatment. Solar-driven interfacial evaporation represents a green technology for efficient photothermal conversion and wastewater treatment. In this work, we propose a novel dual-defect engineering strategy coupled with heterojunction construction to design a solar evaporator. Specifically, a CoWO 4 /CdIn 2 S 4 (CWO/CIS) heterojunction was first fabricated via a hydrothermal method, followed by controlled H₂/Ar etching at 600 °C for 3 h to simultaneously introduce oxygen and sulfur vacancies. The resulting defect-rich heterojunction was then integrated with sodium alginate to construct a three-dimensional porous aerogel evaporation system. H 2 /Ar etching introduced dual vacancies on the material surface, which synergistically narrowed the bandgap (from 2.02 eV to 1.90 eV) and broadened the full-spectrum light absorption range. More importantly, the etching process optimized the heterojunction interfacial contact by creating defect-mediated charge transfer channels, thereby significantly promoting photogenerated carrier separation and migration while suppressing electron-hole recombination, a key advantage over conventional heterojunction designs. These combined effects substantially enhanced the photothermal conversion efficiency. Under one sun irradiation, the optimized CWO/CIS-H 2 /Ar-aerogel achieved an evaporation rate of 2.29 kg m −2  h −1 in pure water with a corresponding photothermal conversion efficiency of 88.9%, substantially outperforming both the individual components and the non-etched composite. The evaporator demonstrated stable evaporation performance across diverse water matrices, including seawater, river water, heavy metal-ion wastewater, and tetracycline-contaminated water. Notably, it effectively removed heavy metal ions and organic pollutants such as tetracycline, rhodamine B (RhB), and methyl orange (MO). This work provides a novel defect-heterojunction synergistic strategy for developing high-performance solar-driven water evaporation systems, offering new insights into the rational design of photothermal materials with tailored electronic structures for water purification applications. Download: Download high-res image (160KB) Download: Download full-size image