Purifying water with silver nanoparticles (AgNPs)-incorporated membranes: Recent advancements and critical challenges

In the face of the growing global water crisis, membrane technology is a promising means of purifying water and wastewater. Silver nanoparticles (AgNPs) have been widely used to improve membrane performance, for antibiofouling, and to aid in photocatalytic degradation, thermal response, and electro-conductivity. However, several critical issues such as short antimicrobial periods, trade-off effects and silver inactivation seriously restrict the engineering application of AgNPs-incorporated membranes. In addition, there is controversy around the use of AgNPs given the toxic preparation process and environmental/biological risks. Hence, it is of great significance to summarize and analyze the recent developments and critical challenges in the use of AgNPs-incorporated membranes in water and wastewater treatment, and to propose potential solutions. We reviewed the different properties and functions of AgNPs and their corresponding applications in AgNPs-incorporated membranes. Recently, multifunctional, novel AgNP-incorporated membranes combined with other functional materials have been developed with high-performance. We further clarified the synergistic mechanisms between AgNPs and these novel nanomaterials and/or polymers, and elucidated their functions and roles in membrane separation. Finally, the critical challenges of AgNPs-incorporated membranes and the proposed solutions were outlined: i) Prolonging the antimicrobial cycle through long-term and controlled AgNPs release; ii) Overcoming the trade-off effect and organic fouling of the AgNPs-incorporated membranes; iii) Preparation of sustainable AgNPs-incorporated membranes; iv) Addressing biotoxicity induced by AgNPs; and v) Deactivation of AgNPs-incorporated membrane. Overall, this review provides a comprehensive discussion of the advancements and challenges of AgNPs-incorporated membranes and guides the development of more robust, multi-functional and sustainable AgNPs-incorporated membranes.

Polymer/Graphene Nanocomposite Membranes: Status and Emerging Prospects

Graphene is a unique nanocarbon nanomaterial, frequently explored with polymeric matrices for technical purposes. An indispensable application of polymer/graphene nanocomposites has been observed for membrane technology. This review highlights the design, properties, and promising features of the polymer/graphene nanomaterials and nanocomposite membranes for the pervasion and purification of toxins, pollutants, microbials, and other desired contents. The morphology, pore size, pore structure, water flux, permeation, salt rejection, and other membrane properties are examined. Graphene oxide, an important modified form of graphene, is also utilized in nanocomposite membranes. Moreover, polymer/graphene nanofibers are employed to develop high-performance membranes for methodological purposes. The adaptability of polymer/graphene nanocomposites is observed for water management and purification technologies.

Facile architecture of highly effective nanofibrous membrane adsorbent via electrospun followed by hydrothermal carbonization for potential application in dye removal from water

Rapid removal of toxic dye pollutants in water by conventional materials is ineffective and expensive that warrants the necessity for the architecture of hybrid nanofibrous membrane through layer by layer deposition using electrospinning method. In order to achieve this, here we demonstrated the electrospun fabrication of graphene/ferrocene intercalated polyacrylonitrile nanofibrous (GFPN) membrane through hydrothermal carbonization (HTC) method and studied its potential adsorption properties for the removal of environmental pollutants. An aqueous dispersion of graphene/ferrocene (1 mg/mL) stabilized by the polymeric backbone was prepared by the solvent homogenization method and electrospun to yield nanofibrous membrane and further characterized by several analytical and spectroscopic techniques. Raman and XPS investigations corroborated the intercalation of graphene/Fe decorated onto the nanofibrous network. Adsorption experiments found that the GFPN membrane achieved more than 90% removal of anionic Congo red (CR) dye within 30 min in the aqueous phase irrespective of the concentration and takes some additional time for attaining the equilibrium. The longevity and stability of the membrane was studied by conducting successive adsorption-desorption cycles for the regeneration of its adsorption properties. The de-coloration mechanism was comprehensively investigated through the mathematical approaches using the kinetic and intraparticle diffusion studies and confirmed with the experimental findings through IR and XPS spectroscopic techniques. In a nutshell, this work focuses on the fabrication of hybrid nanofibrous membrane and studied its adsorption properties through varying concentrations of dye (20 to 150 mg/L). Moreover, this work extensively explored the mechanism associated with the adsorption process and specifically emphasize the existence of combined phenomena during the process, i.e., anion-cation interactions, hydrogen bonding, and successive stages of intraparticle diffusion through the comparative elucidation of both theoretical and experimental approaches.

Electrospun Polyacrylonitrile (PAN) Templated 2D Nanofibrous Mats: A Platform toward Practical Applications for Dye Removal and Bacterial Disinfection

The fabrication of polymeric nanofibers and its potential versatility instigated to foster smart hybrid nanomaterials for the removal of environmental pollutants. In this pursuit, in this research work, polyacrylonitrile (PAN)-based two-dimensional (2D) nanofibrous mats with polyethyleneimine (PEI)/Fe and quaternary ammonium (QA)/Fe as hybrid fillers were prepared by the electrospinning process for the effective dye removal and bacterial disinfection. The characteristics of the fabricated nanomaterials were extensively explored by several analytical techniques such as field emission-scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and Brunauer-Emmett-Teller analysis. Magnetic and thermal properties were investigated by superconducting quantum interference device and thermogravimetric measurements. The kinetic and isothermal models affirmed the adsorption behavior of the PAN-PEI/Fe nanofibers, and further regenerative studies substantiated the sustainability of the mats for the removal of industrial dye effluents. Subsequently, the magnetic-QA-loaded PAN nanofiber mats exhibited bactericidal killing efficacy of 99 and 89.5% in both Staphylococcus aureus and green fluorescence protein expressing Escherichia coli bacterial models evaluated from the conventional quantitative bacterial colony-counting assay. Disk diffusion method and microscopic investigations corroborated the disinfection efficacy with zone of inhibitions of ∼23 and 33 mm, respectively. Interestingly, in vitro cell culture studies conducted in BHK-21 and NIH 3T3 cell lines demonstrated the cytocompatibility, and the in vivo toxicity investigations using the zebrafish models necessitated the real-time application of these nanofibrous mats. Therefore, the comprehensive study of the fabricated PAN-templated functionalized 2D nanofibrous mats affirmed to be competent for the remediation of industrial dye effluents and bacteria in water bodies.