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

Abstract

IntroductionNanotechnology, with tremendous versatility and unprecedented opportunities, has ubiquitously gained the recognition in enhancing the sustainability of membrane-based water treatment processes [1,2]. The promising synergistic effects of nano-and membrane technologies provide tangible ways to develop mixed-matrices with tunable functional features, which can make the membrane separation process more productive, energy-efficient, and environmental-friendly. Amongst the nanomaterials, the carbon nanotubes (CNTs) possess outstanding structural, mechanical and electronic properties that are exploited to develop high-performance mixed-matrix systems [3]. The importance of CNTs to the membrane scientists stems from its unique potential to result in a membrane with improved permeability [4,5] 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, M w : 35 kDa), confirm the potential of carboxylated CNTs in leading to development of high-performance mixed-matrix membranes.

Strategies in Forward Osmosis Membrane Substrate Fabrication and Modification: A Review

“…The recovered normalized flux was observed to be 6% higher than that of TFC membrane after physical cleaning. As underpinned in other studies, favorable membrane changes by CNTs have proven to improve the level of separation performance with great membrane stability [4,121,167].…”

“…Blending is by far the simplest and most efficient method to change the chemical and mechanical functionalities of the membrane [120], but for polymers, it has limited applicability, which is principally attributed to their limited miscibility of hydrophobic and hydrophilic polymers. Polymer blend is a process where two organic polymers blend in a homogeneous dope solution in the presence of a solvent and/or an additive under mild conditions [66,121,122]. It is conducted to obtain a membrane with desirable morphologies and performance by controlling both the thermodynamics of the casting solution and the kinetics of the demixing process.…”

“…In parallel to the development of TFN-FO membranes, prior findings have shown that incorporating nanomaterials into substrate have spawned noticeable improvements in permeability, water flux, salt rejection, and antifouling behavior [121,122,126,127]. The growing development of nanotechnology has brought considerable improvement to conventional polymeric membranes.…”

“…By virtue of their antimicrobial, high efficiency, potential energy savings, and ease of integration and scale-up, carbon-based nanomaterials, especially activated carbon, graphene oxides (GO), and carbon nanotubes (CNTs) in various derivatives, have seen an upward trend in a wide range of separation applications [4,111,[162][163][164]. Many researchers have joined efforts to unveil CNTs and GO potential applications by compositing in a substrate or active layer of membrane to produce TFC membranes with the ability to reduce ICP and fouling tendency along with enhanced hydrophilicity, permeability, and solute rejection [121,122,139,165,166]. Earlier, Choi et al [82] studied the efficiency of polyamide TFC supported on functionalized multiwalled CNT (MWCNT)-blended PES substrate for integrated seawater desalination and wastewater recovery through the FO process.…”