A facile approach of thin film coating consisted of hydrophobic titanium dioxide over polypropylene membrane for membrane distillation

In this work, the hydrophobic modification of TiO₂ nanoparticles (HTiO₂) was carried out by reacting with dodecylphosphonic acid (DDPA) and hexylamine solution. A facile approach of the self-assembly technique was used for the coating of hydrophobic HTiO₂ layer over the microporous polypropylene (PP) membrane. The self-assembled layer was formed between the interface of trimesoyl chloride (TMC) (in hexane) and trimethylamine (in water) solutions. The high porosity for the coated membranes ascribed to the self-assembled trimesic acid (TMA) layer and its potential to generate open and loosely packed, two-dimensional hydrogen-bond networks on the membrane surface. The dispersion of HTiO₂ was accomplished in the TMC in hexane leading hydrophobic and porous surfaces than the neat PP membrane. The initial average pore size of the PP membrane was reduced from 0.4 µm to 0.2 µm with a coating of 2.0 wt% of HTiO₂. The new membranes showed high reliability, high rejection, and water flux during the real seawater desalination tested in direct contact membrane distillation (DCMD) configuration. The maximum transmembrane permeate flux of 45.4 kg/m²h with >98% salt rejection was obtained for the coating layer with 2.0 wt% HTiO₂ at 80ºC demonstrating the future potential application towards seawater desalination.