Tunable hydrophobicity and roughness on PVDF surface by grafting to mode – Approach to enhance membrane performance in membrane distillation process

Applying the "grafting to" process made it possible to generate hybrid materials based on the PVDF with precisely adjusted chemistry and roughness. The materials consist either of one additional layer of grafted silanes (chemistry tuning) or two, where sandwich-like structure via stable covalent settlement of multi-walled nanotubes MWCNT (roughness tuning) were generated. The selection of silane modifiers with differentiated hydrophobicity allowed to adjust the surface chemistry. The introduced hydrophobicity resulted in contact angle enhancement from 110° ±1.2° to 155°±1.2°. However, the tuned roughness was in the range of 111 ± 6 nm and 612 ± 22 nm. The covalent attachment of MWCNT accomplished the best enhancement in membrane performances (155%). All membranes were tested in long-term stability tests (60 days) and multiple runs (8 × 45 h), revealing their minor reduction in flux and maintaining introduced hydrophobicity and roughness. The modified separation materials possessed improved mechanical, thermal, and chemical stability. Membranes were highly effective in desalination during the membrane distillation process and successfully applied for VOCs removal from water. All samples were thoroughly characterized, taking material, physichochemical, mechanical, and thermal properties into account.