Flower-like CuO light traps as anti-wetting armor of Janus membrane for spraying wastewater treatment by photothermal membrane distillation

Current scientific advances in wastewater treatment have slowed the pressure on water access. Membrane distillation (MD) was a promising technology for wastewater treatment. However, for the treatment of the spraying wastewater containing high boiling point organic solutions, high energy dependence and membrane wetting by the water-soluble organics with high concentrations were the limitations of the MD process. Herein, Janus photothermal membranes (JPTM) were prepared by chemical plating and then surface oxidation under alkaline conditions. The flower-like CuO hydrophilic photothermal layer which acted as the light trap and anti-wetting armor was constructed on the PVDF hydrophobic membrane surface. In the process of photothermal membrane distillation, when the CuO hydrophilic photothermal layer contacted with feed solution, due to the arrangement of the hydrophilic hydroxyl heads of the organics on the hydrophilic photothermal layer, and the hydrophobic alkyl tails faced the water molecules and repelled them. The light was trapped in the hydrophilic photothermal layer and repeatedly refracted by the flower-like CuO. The flower-like CuO was further optimized by controlling alkali concentration. When the alkali concentration was 2.5 M, the photothermal conversion of JPTM with the moonflower-like CuO hydrophilic photothermal layer was up to 92.86%. When single component high boiling point organic solutions (BCS or DB) were treated by MD, under 1 sun irradiation (1 kW m−2), the permeate fluxes achieved 2.68 and 2.91 kg m−2 h−1 with over 98% removal of organics; Further, for the treating of spraying wastewater, it had a high permeate flux of 5.13 kg m−2 h−1, a photothermal efficiency of 90.79%, and a removal rate of 62%. The JPTM was a low-carbon technology to improve heat and mass transfer for wastewater treatment by photothermal membrane distillation.