Synthesis and characterization of carbon nanotube membranes for water treatment

This work presents the synthesis and characterization of carbon nanotube (CNT) incorporated polyethersulfone (PES) membranes. Firstly, CNTs were prepared via a nebulized spray pyrolysis of toluene (carbon source) and ferrocene (catalyst) mixture at a temperature of 850 0C. The CNTs produced were then purified and functionalized by acid treatment to aid their interaction with the solvent and polymer during membrane preparation. Characterization techniques used for CNTs include scanning electron microscopy (SEM) analysis, Raman spectroscopy analysis, thermogravimetric analysis and X-ray photoelectron spectroscopy analysis. The outer diameters of CNTs measured from SEM micrographs using Image J software were in the range of 10 – 14 nm. TGA analysis revealed that the CNTs undergo complete thermal degradation after acid treatment; i.e. no catalyst particle residues were detected after 600 0C. Please click Additional Files below to see the full abstract

Water as the Pore Former in the Synthesis of Hydrophobic PVDF Flat Sheet Membranes for Use in Membrane Distillation

Although PVDF flat sheet membranes have been widely tested in MD, their synthesis and modifications currently require increased use of green and inexpensive materials. In this study, flat sheet PVDF membranes were synthesized using phase inversion and water as the pore former. Remarkably, the water added in the casting solution improved the membrane pore sizes; where the maximum pore size was 0.58 µm. Also, the incorporation of f-SiO2NPs in the membrane matrix considerably enhanced the membrane hydrophobicity. Specifically, the membrane contact angles increased from 96° to 153°. Additionally, other parameters investigated were mechanical strength and liquid entry pressure (LEP). The maximum recorded values were 2.26 MPa and 239 kPa, respectively. The modified membranes (i.e., using water as the pore former and f-SiO2NPs) were the most efficient, showing maximum salt rejection of 99.9% and water flux of 11.6 LMH; thus, indicating their capability to be used as efficient materials for the recovery of high purity water in MD

A review of shaped carbon nanomaterials

Materials made of carbon that can be synthesised and characterised at the nano level have become a mainstay in the nanotechnology arena. These carbon materials can have a remarkable range of morphologies. They can have structures that are either hollow or filled and can take many shapes, as evidenced by the well-documented families of fullerenes and carbon nanotubes. However, these are but two of the shapes that carbon can form at the nano level. In this review we outline the types of shaped carbons that can be produced by simple synthetic procedures, focusing on spheres, tubes or fibres, and helices. Their mechanisms of formation and uses are also described

Cyclodextrin-Based Nanofibers and Membranes: Fabrication, Properties and Applications

Cyclodextrin (CD)-based electrospun nanofibers have become critical role players in the water treatment arena due to their high porosities, small diameters, high surface area-to-volume ratio and other unique properties they exhibit. Investigations demonstrate that nanofibers containing CD molecules can be facially blended with other polymeric species and/or photocatalytic and magnetic nanoparticles to enhance their rates of adsorption, inclusion complexation and selective photodegradation. These properties make them excellent candidates for the removal of water pollutants. On the other hand, the electrospinning process has become the method of choice in the fabrication of various types of CD nanofibrous mats due to its versatility, cost-effectiveness and its potential for the mass production of uniform nanofibers. CDs and CD-derivatives have also found application in membrane technologies, particularly in mixed matrix and thin film composite membranes. CD-blended membranes display improved performances in terms of selectivity, rejection, permeation and flux with reduced fouling propensities and can be used for drinking water purification and removal of emerging micropollutants. This chapter critically reviews CD-based electrospun nanofibers looking at their production, characterization methods and various applications. The use of CDs as membrane materials and how they can be fully explored in water treatment are also investigated

From waste cooking oil to oxygen-rich onion-like nanocarbons for the removal of hexavalent chromium from aqueous solutions

Vegetable cooking oil is used in domestic and commercial kitchens owing to its ability to modify and enhance the taste of the food through the frying process. However, as the oil is used through several frying cycles, it changes colour to dark brown and acquires an unpleasant smell. At this point, the waste oil is usually discarded, thereby finding its way into freshwater streams due to poor disposal and thus becoming an environmental pollutant. To provide an alternative, ‘green’ route to waste oil disposal, herein we report on the metal-free synthesis of onion-like nanocarbons (OLNCs) made from waste cooking oil via flame pyrolysis. The OLNCs were then applied in the removal of hexavalent chromium ions from aqueous solutions. The as-synthesised OLNCs were found to have similar properties (size, quasi-spherical shape etc.) to those synthesised from pure cooking oils. The Fourier-transform infrared spectroscopy data showed that the OLNCs contained C-O-type moieties which were attributed to the oxygenation process that took place during the cooking process. The OLNCs from waste oil were applied as an adsorbent for Cr(VI) and showed optimal removal conditions at pH = 2, t = 360 min, Co = 10 mg/L and Q0max = 47.62 mg/g, superior to data obtained from OLNCs prepared from pristine cooking oil. The results showed that the OLNCs derived from the waste cooking oil were effective in the removal of hexavalent chromium. Overall, this study shows how to repurpose an environmental pollutant (waste cooking oil) as an effective adsorbent for pollutant (Cr(VI)) removal. Significance: • Waste cooking oil outperformed olive oil as a starting material for the production of OLNCs for the removal of toxic Cr(VI) from water. • The superior performance of the OLNCs from waste cooking oil was attributed to the higher oxygen content found on their surface and acquired through the cooking process. • Not only are the OLNCs produced from waste cooking oil effective in the removal of Cr(VI), but they can be used multiple times before replacement, which makes them sustainable

Electrospun chitosan-based nanobres for removal of phenols from drinking water

Chitosan-based nanofibres were synthesized using a fibre electrospinning technique and tested for the removal of 3-methyl- 4-nitrophenol from aqueous solutions. The downside of chitosan-based materials is swelling. In this study, it was found that the addition of polyisoprene not only improved the electrospinning ability of chitosan but also reduced the swelling of the nanofibres by 50%. the adsorption studies of 3-methyl-4-nitrophenol on the chitosan-based nanobres were conducted in a batch process. e nanobres were found to remove up to 90% of 3-methyl-4-nitrophenol with an adsorption reduction capacity of 12% at each cycle of reusability test. The reduction capacity was associated with the chemical interaction of the adsorbate and the adsorbent. this indicated that the nanofibres can effectively remove 3-methyl-4-nitrophenol from water for at least 3 cycles. the adsorption efficiency improved as the degree of cross-linking was reduced and the adsorption mechanism followed the Freundlich isotherm suggesting that the adsorption of 3-methyl-4-nitrophenol occurred in different layers on the surface of the nanofibres. e degree of crosslinking of the electrospun nanobres with glutaraldehyde was found to affect the adsorption capacity. Nanofibres with different degrees of crosslinking were used to study the effect of pH, adsorbent dose, and initial concentration.Keywords: 3-methyl-4-nitrophenol, adsorption, chitosan nanofibres, the degree of cross-linking, removal efficienc

Synthesis of robust flexible polyethersulfone ultrafiltration membranes supported on non-woven fabrics for separation of NOM from water

This work describes the synthesis of structurally robust ultrafiltration (UF) polyethersulfone (PES) membranes supported on three different types of non-woven fabrics (NWFs) prepared using a simple phase inversion method. The NWF supported membranes exhibited high mechanical strength compared to the unsupported PES membranes modified with polyvinyl pyrrolidone (PVP) due to the strength provided by the NWFs. The tensile strength of the supported PVP modified membranes was ~7 MPa compared to ~2 MPa observed for the PVP modified unsupported UF membranes. The use of the NWFs clearly provides robustness to the modified membranes. The membrane surfaces became hydrophilic with addition of PVP and the pore sizes increased with an increase in PVP concentration (scanning electron microscopy (SEM) results). The rejection of humic acid (as a model NOM compound) was 98% for PES on NWF1, while PES membranes supported on NWF2 and NWF3 gave rejections of 94% and 96%, respectively; all with good fouling resistance. This work demonstrates that the use of a NWF support allows for the modification of the surface of the membranes without compromising the overall strength of the membranes, but more importantly the ability of the membranes to reject HA while exhibiting high resistance to fouling

Photocatalytic Nanofiber Membranes for the Degradation of Micropollutants and Their Antimicrobial Activity: Recent Advances and Future Prospects

This review paper systematically evaluates current progress on the development and performance of photocatalytic nanofiber membranes often used in the removal of micropollutants from water systems. It is demonstrated that nanofiber membranes serve as excellent support materials for photocatalytic nanoparticles, leading to nanofiber membranes with enhanced optical properties, as well as improved recovery, recyclability, and reusability. The tremendous performance of photocatalytic membranes is attributed to the photogenerated reactive oxygen species such as hydroxyl radicals, singlet oxygen, and superoxide anion radicals introduced by catalytic nanoparticles such as TiO2 and ZnO upon light irradiation. Hydroxyl radicals are the most reactive species responsible for most of the photodegradation processes of these unwanted pollutants. The review also demonstrates that self-cleaning and antimicrobial nanofiber membranes are useful in the removal of microbial species in water. These unique materials are also applicable in other fields such as wound dressing since the membrane allows for oxygen flow in wounds to heal while antimicrobial agents protect wounds against infections. It is demonstrated that antimicrobial activities against bacteria and photocatalytic degradation of micropollutants significantly reduce membrane fouling. Therefore, the review demonstrates that electrospun photocatalytic nanofiber membranes with antimicrobial activity form efficient cost-effective multifunctional composite materials for the removal of unwanted species in water and for use in various other applications such as filtration, adsorption and electrocatalysis

Environmentally benign chitosan-based nanofibres for potential use in water treatment

Chitosan (CS)-based nanocomposite materials are highly prone to swelling when in contact with water. It is therefore essential to modify them to enhance their resistance to swelling, in order to be applicable in water treatment. In this study, the CS-based nanofibres were prepared using the electrospinning technique. The nanofibres were prepared from a polymer blend of CS, and other polymers (polyacrylamide (PAA) and polyethylene glycol (PEG)) added in small optimized quantities to enhance the ability to electrospun CS. Elastic polyisoprene (PIP) and functionalized multi-walled carbon nanotubes (f-MWCNTs) were incorporated in the electrospinnable solution blend of CS, PAA and PEG to reduce the swelling behaviour of the CS-based nanofibres and to improve their mechanical strength and thermal properties. PIP did not only improve the morphology of the resulting nanofibres but also reduced their swelling behaviour by twofold. The addition of f-MWCNTs was found to improve the tensile strength of the nanofibres by twofold, relative to nanofibres with no f-MWCNTs. The thermal degradation of the nanofibres was improved by a magnitude of 50 degrees C. Antibacterial silver (Ag) and iron (Fe) nanoparticles (NPs) were embedded on the nanofibres for their possible use in disinfection processes. These NPs have demonstrated a potential to kill bacteria in water and, therefore, the prepared nanofibres can be used in disinfection water treatment processes with reduced swelling capacity