Development of robust dual functioning PPy-based photothermal membranes for simultaneous freshwater and salt...

Photothermal membranes driven by solar energy represent a promising approach for sustainable and cost-effective desalination and wastewater treatment. Solar energy's renewability and low environmental impact drive its adoption in desalination technologies. In this work, chemical vapor deposition polymerization (CVDP) is used to deposit high-performance polypyrrole (PPy) coatings on two different fabric types: woven and nonwoven, enabling broad-spectrum solar light absorption and efficient thermal conversion for enhanced water evaporation. This study investigated the efficacy of different oxidizing agents in initiating the CVDP process and in depositing PPy layer on the substrate surface, for use as a photothermal membrane to harvest freshwater and salt from different saline wastewater samples. The goal is to achieve efficient polymerization, targeting pyrrole usage as low as 15 μL for perfect PPy deposition. Among the investigated oxidizing agents, copper chloride and ammonium persulfate yielded the most effective performance in producing PPy-coated photothermal membranes. These membranes demonstrated superior light absorption and achieved surface temperatures of 63 °C and 60 °C under simulated 1 sun illumination (1 kW m^- 2), showing facilitated enhanced water evaporation rates of 0.95 and 0.93 kg m^- 2 h^- 1, respectively. Meanwhile, a a water evaporation rate of 2.91 kg m^- 2 h^- 1 under 3 sun illumination was obtained. Furthermore, the developed robust photothermal membranes tested against different saline solutions, including NaCl, CuSO₄.5H₂O, and FeCl₃ for simultaneous water evaporation and salt harvesting under solar simulator. A developed A4-size photothermal membrane from non-woven fabric was tested using actual brine water sample under natural sunlight for one week. The used photothermal membranes showed the recyclability and durability during the tests.