Fabrication of durable superhydrophobic epoxy/cashew nut shell liquid based coating containing flower-like zinc oxide for continuous oil/water separation

Superhydrophobic filters can be applied as cost-effective separation media to overcome oil contamination issues. In this study, superhydrophobic material based on natural resources was explored as a coating material for sustainable oil/water separation membranes. Epoxy (EP) cured with cashew nut shell liquid (CNSL, a bio-based curing agent) was coated on a stainless steel mesh (E-mesh) using a simple immersion technique. Different amounts of ZnO (0-60 wt%) were added to EP/CNSL to increase coating surface roughness. The highest water contact angle (WCA) of 149.2 degrees was measured for the E-mesh containing 60 wt% ZnO (E-ZnO-60 mesh). Modification of coated ZnO by immersion in acetic and stearic acid can create the flower-like morphology of ZnO (F-ZnO), which even further enhanced the coating hydrophobicity. The E-mesh containing 60 wt% F-ZnO (E-F-ZnO-60 mesh) showed superhydrophobicity with a WCA of 163.8 degrees. This high hydrophobicity was obtained after chemical and mechanical durability tests, indicating excellent coating stability. The continuous oil/water separation efficiency of E-F-ZnO-60 mesh was over 97% for 75 min after the mechanical stability testing. Based on these results, this durable superhydrophobic mesh showed promising cost-effective coating applications and oil/water separation medium.