Water, among the most valuable natural resources available on earth, is under serious threat as a result of undesirable human activities: for example, marine dumping, atmospheric deposition, domestic, industrial and agricultural practices. Optimizing current methodologies and developing new and effective techniques to remove contaminants from water is the current focus of interest, in order to renew the available water resources. Materials like nanoparticles, polymers, and simple organic compounds, inorganic clay materials in the form of thin film, membrane or powder have been employed for water treatment. Among these materials, membrane technology plays a vital role in removal of contaminants due to its easy handling and high efficiency. Though many materials are under investigation, nanofibers driven membrane are more valuable and reliable. Synthetic methodologies applied over the modification of membrane and its applications in water treatment have been reviewed in this article.

Highly crystalline hierarchical TiO 2 nanostructures of morphology ranging from one-dimensional regular fibers, hollow tubes, porous rods and spindles were achieved from electrospun TiO 2 /composite fibers by annealing at temperatures ranging from 400 C, 500 C, 600 C, 700 C, and 800 C, with a ramp rate of 5 C min À1 , and at a pressure of 1 mbar. Crystallographic structure, crystallite size, surface morphology and surface area of annealed TiO 2 nanostructures were analysed by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and Brunauer-Emmett-Teller (BET) method. The analysis of post-annealing process on electrospun TiO 2 nanofibers showed an orderly change in the crystallographic phase transformation with corresponding change in their surface morphologies. XRD and HRTEM analysis confirmed the phase transformation of highly crystalline anatase phase to rutile with crystallite size varied from 11 nm to 36 nm upon tuning the annealing temperature. Interestingly, TiO 2 nanostructures annealed at 700 C showed the formation of biphasic TiO 2 hollow tubes with stoichiometry phase compositions of 45.74% anatase and 54.25% rutile. A possible formation mechanism was proposed based on series of temperature-dependent experiments. To evaluate the potential use of these TiO 2 nanostructures, dye sensitized solar cell (DSSC) was fabricated using the post-annealed TiO 2 nanostructures as photoanode. A higher conversion efficiency (h) of 4.56% with a short circuit current (J sc ) of 8.61 mA cm À2 was observed for highly ordered porous anatase TiO 2 nanorods obtained upon annealing at 500 C under simulated AM1.5 G (100 mW cm À2 ), confirming that surface area of TiO 2 resulted out of porous structure played dominant role.

Plenty of fresh water resources are still inaccessible for human use. Calamities such as pollution, climate change, and global warming pose serious threats to the fresh water system. Although many naturally and synthetically grown materials have been taken up to resolve these issues, there is still plenty of room for enhancements in technology and material perspectives to maximize resources and to minimize harm. Considering the challenges related to the purification of water, materials in the form of nanofiber membranes and nanomaterials have made tremendous contributions to water purification and filtration. Nanofiber membranes made of synthetic polymer nanofibers, ceramic membranes etc., metal oxides in various morphologies, and carbonaceous materials were explored in relation to waste removal from water. In this review, we have discussed a few key materials that have shown effectiveness in removing pollutants from waste water, enabling solutions to existing problems in obtaining clean drinking water.

In situ polymerization of poly (vinylidene fluoride) (PVDF) with hydroxyethylmethacrylate (HEMA) followed by electrospinning was employed to prepare electrospun nanofibrous membranes (ENMs), referred to as PVDF-PHEMA-ENMs. Enhanced hydrophilicity of the ENMs was observed after polymerization. A decrease in the fiber thickness resulted in a decrease in the pore size and 60% improvement in the flux. The fiber mat exhibited excellent microfiltration behavior after being coated with a surface-charged chitosan (CS) polymer, compared with its non-coated counterparts. Porosity, flux and protein adsorption studies were performed for these ENMs. A comparatively less reduced flux and better recovery ratio were observed for the PVDF-PHEMA-ENMs and CS-coated PVDF-PHEMA-ENMs due to hydrophilic pendant hydroxyl groups (from PHEMA) and/or CS groups, which can prohibit irreversible protein adsorption, on the ENM surfaces.

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