Porcupine quills-like-structures containing smart PVDF/chitosan hybrids for anti-fouling membrane applications and removal of hazardous VOCs

Abstract

The separation materials with enhanced transport and separation in membrane distillation (MD) and antifouling features were generated. The membranes were systematically characterized to understand how the covalent modification process, i.e., silanization and functionalization with chitosan, impacts the membrane performance. The material modification was done by the biomimicry of desert beetle (Stenocara gracilipes) armor and porcupine quills. The hydrophobic-hydrophilic structure of beetle armor was mimicked with the application of PVDF membrane as a hydrophobic surface and chitosan (CS) as hydrophilic nodes. By changing the experimental protocol, unique quill-like structure morphology was generated. The introduction of pristine and partially hydrophobized chitosan increased roughness significantly from 70 nm to 386 nm and 440 nm, causing contact angle improvement from 114.6° to 157.4° and 168.2°, respectively. Four times increment of transport was observed after adding CS. MD membranes with superior wetting resistance (critical surface tension ca. 20 mN m−1) were created by combining hierarchically structured membranes with re-entrant texture. The selection of fluorine-free modifiers allows the synthesis of environmentally friendly membranes and reduces the problem of bioaccumulation and acute toxicity occurring with long-chain fluorinated modifiers. Materials were tested in the air gap membrane distillation (AGMD) to remove hazardous volatile organic compounds from water. Data were analyzed by applying Hansen’s Solubility Parameters. Membranes were also applied for raw apple juice dewatering with fouling study during the osmotic MD process.