Formation of electrically conductive hollow fiber membranes via crossflow deposition of carbon nanotubes – Addressing the conductivity/permeability trade-off

Multifunctional polysulfone composite membranes via constructing electrically conductive gradient and magnetic-core/electric-shell dual-gradient microstructures: A strategy to tackle multiple hazards

The rapid advancement of industries and technologies leads to the emergence of new pollutants such as dyeing wastewater and electromagnetic interference (EMI), and their efficient treatment poses great challenges for traditional materials and methods. Herein, a novel electrically conductive membrane (ECM) was fabricated on a large scale through the electric field-assisted membrane formation. Carbon nanotubes (CNTs) and carbon black (CB) were uniformly dispersed in dope solution by strong hydrogen bonding with suitable polyvinylpyrrolidone (PVP) molecules. They moved towards the coating layer upper surface under an electric field, forming electrically conductive gradient microstructures. Subsequently, a stable electrically conductive skin layer was generated due to the excellent film-forming ability of PVP, which hindered the loss of CNTs and CB into coagulating bath. The optimized membrane possessed a high electrical conductivity of 34.3 ± 0.7 S/m, and exhibited superior permeate fluxes (>515.6 L/m2 h·bar), dye rejections (>87.1 %) and flux recovery ratios (>91.5 %) in the electric-assisted filtration. Moreover, magnetic Fe3O4 nanoparticles were incorporated on the bottom surface and inside the pores by vacuum filtration, yielding an innovative magnetic-core/electric-shell dual-gradient microstructure. Electromagnetic wave went through an "absorption-multiple reflection/absorption-strong reflection-reabsorption/multiple reflection" process within the membrane, and then was consumed through the superposition of magnetic loss, polarization loss and conducting loss. Accordingly, the membrane displayed an EMI shielding efficiency of 23.6 ± 0.5 dB with a thickness of 0.2 mm at a low CB-CNTs loading of 20 wt%. This work provides a strategic framework for designing adaptable multifunctional membranes, bridging critical applications from wastewater remediation to next-generation electronic shielding technologies.

Production of Stable Electrically Conductive PVDF Membranes Based on Polydopamine-Polyethyleneimine-Assisted Deposition of Carbon Nanotubes

Electrically conductive membranes (ECMs) have emerged as a multifunctional separation technology that integrates membrane filtration with electrochemical reactions. Physical stability remains a critical challenge for ECMs synthesized by coating polymer membranes with conductive materials. In this article, polydopamine (PDA) and polyethyleneimine (PEI) were used to facilitate the synthesis of significantly more stable ECMs using poly(vinylidene fluoride) (PVDF) ultrafiltration membranes and carbon nanotubes (CNTs). Four different synthesis methods were compared in terms of the final surface stability and separation properties: (1) CNTs deposited on PEI-crosslinked PDA-coated PVDF membranes, (2) PEI-crosslinked CNTs deposited on PDA-coated PVDF, (3) PDA, PEI and CNTs sequentially deposited layer-by-layer on PVDF, and (4) PEI-crosslinked PDA deposited on CNT-coated PVDF. The results revealed that method 1 generated ECMs with the greatest physical stability, highest electrical conductivity (18,518 S/m), and sufficient permeability (395.2 L/(m2·h·bar). In comparison, method 2 resulted in membranes with the highest permeability (2128.5 L/(m2·h·bar), but with low surface conductivity (502 S/m) and poor physical stability (i.e., 53-75% lower peel-off forces compared to other methods). Overall, methods 1, 3, and 4 can be used to make highly conductive membranes with a 97-99% removal of methyl orange by electrochemical degradation at -3 V.

Fabrication of a Co-Mo-Based Metal-Organic Framework for Growth of Double-Walled Carbon Nanotubes

Double-walled carbon nanotubes (DWCNTs) make up a unique class of carbon nanotubes (CNTs) that are particularly intriguing for scientific research and are promising candidates for technological applications. A more precise level of control and greater yields can be achieved via catalytic chemical vapor deposition (CCVD), which involves the breakdown of a carbonaceous gas over nanoparticles. The addition of molybdenum to the system can increase the selectivity with regard to the number of walls that exist in the obtained CNTs. As reported herein, we have designed and synthesized a novel Co-Mo-MOF, [Co(3-bpta)1.5(MoO4)]·H2O (where 3-bpta = N,N'-bis(3-pyridyl)terephthalamide), and employed the Co-Mo-MOF as a bimetallic catalyst precursor for the CCVD approach to prepare high-quality DWCNTs. The Co-Mo-MOF was employed after being calcined in N2 and H2 at 1100 °C and decomposing into CoO, CoMoO4, and MoO3. Existing CoMoO4 is unaltered after reduction in H2 at 1100 °C, while CoO and MoO3 are converted into Co0 and MoO2, and more CoMoO4 is created at the expense of Co0 and MoO2 without clearly defining agglomeration. Finally, the interaction between metallic Co particles and C2H4 is what initiates the formation of DWCNTs. In-depth discussion is provided in this paper regarding the mechanism underlying the high selectivity and activity of Co-Mo catalysts in regulating the development and structure of DWCNTs. The DWCNTs also offer excellence performance when they are used as water purification agents and as selective sorbents. This work opens a feasible way to use MOFs as a way to produce MWCNTs, thus blazing a new trail in the field of MOF-derived carbon-based materials.