Engineered eco-friendly composite membranes with superhydrophobic/hydrophilic dual-layer for DCMD system

Considerable advancements have been made in the development of hydrophobic membranes for membrane distillation (MD). Nonetheless, the environmentally responsible disposal of these membranes poses a critical concern due to their synthetic composition. Herein, an eco-friendly dual-layered biopolymer-based membrane was fabricated for water desalination. The membrane was electrospun from two bio-polymeric layers. The top hydrophobic layer comprises polycaprolactone (PCL) and the bottom hydrophilic layer from cellulose acetate (CA). Additionally, silica nanoparticles (SiO₂ NPs) were electrosprayed onto the top layer of the dual-layered PCL/CA membrane to enhance the hydrophobicity. The desalination performance of the modified PCL-SiO₂/CA membrane was compared with the unmodified PCL/CA membrane using a direct contact membrane distillation (DCMD) unit. Results revealed that silica remarkably improves membrane hydrophobicity. The modified PCL-SiO₂/CA membrane demonstrated a significant increase in water contact angle of 152.4° compared to 119° for the unmodified membrane. In addition, PCL-SiO₂/CA membrane has a smaller average pore size of 0.23 ± 0.16 μm and an exceptional liquid entry pressure of water (LEPw), which is 3.8 times higher than that of PCL/CA membrane. Moreover, PCL-SiO₂/CA membrane achieved a durable permeate flux of 15.6 kg/m².h, while PCL/CA membrane showed unstable permeate flux decreasing approximately from 25 to 12 kg/m².h over the DCMD test time. Furthermore, the modified PCL-SiO₂/CA membrane achieved a high salt rejection value of 99.97% compared to a low value of 86.2% for the PCL/CA membrane after 24 h continuous DCMD operation. In conclusion, the proposed modified PCL-SiO₂/CA dual-layer biopolymeric-based membrane has considerable potential to be used as an environmentally friendly membrane for the MD process.