High-performance mixed-matrix membranes with altered interfacial and surface chemistry through benign reinforcement of functionalized carbon nanotubes of different configurations

Abstract

Nanomaterials potentially minimize the inherent trade-off between productivity and selectivity of membranebased ultrafiltration (UF) process. A comparative study on the reinforcement effect of pristine carbon nanotubes (CNTs) of three different configurations, viz. single-walled (SWNT), double-walled (DWNT) and multi-walled (MWNT), and their carboxylated counterparts, onto a polysulfone (Psf) host matrix of mixed-matrix UF membranes is illustrated herein. The varying structural features of carboxylated CNTs, probed by XPS analysis, underpin the enrichment of CNTs with oxygen rich functionalities following the trend of MWNT > DWNT > SWNT. The membranes with enhanced hydrophilicity and altered electrokinetics substantiate the efficacy of facilitated reinforcement of functionalized CNTs over the pristine ones. Variations in surface topography and mechanical feature of the membranes elucidate that carboxylation influences the interfacial chemistry by enhancing the dispersion stability of MWNTs more profoundly than its configurational counterparts like SWNTs and DWNTs, and concurrently alters its distribution within the membranous matrix. The enhanced ultrafiltration performances, as achieved by twofold enhancement in solvent fluxes without compromise in the solute rejection capabilities (~89–90% toward PEG, Mw: 35 kDa), confirm the potential of carboxylated CNTs in leading to development of high-performance mixed-matrix membranes.

Keywords

• Polymer membranes
• carboxylation
• carbon nanotubes
• mixed-matrix
• ultrafiltration