Antimicrobial nanomaterials for water disinfection and microbial control: potential applications and implications

The challenge to achieve appropriate disinfection without forming harmful disinfection byproducts by conventional chemical disinfectants, as well as the growing demand for decentralized or point-of-use water treatment and recycling systems calls for new technologies for efficient disinfection and microbial control. Several natural and engineered nanomaterials have demonstrated strong antimicrobial properties through diverse mechanisms including photocatalytic production of reactive oxygen species that damage cell components and viruses (e.g. TiO2, ZnO and fullerol), compromising the bacterial cell envelope (e.g. peptides, chitosan, carboxyfullerene, carbon nanotubes, ZnO and silver nanoparticles (nAg)), interruption of energy transduction (e.g. nAg and aqueous fullerene nanoparticles (nC(60))), and inhibition of enzyme activity and DNA synthesis (e.g. chitosan). Although some nanomaterials have been used as antimicrobial agents in consumer products including home purification systems as antimicrobial agents, their potential for disinfection or microbial control in system level water treatment has not been carefully evaluated. This paper reviews the antimicrobial mechanisms of several nanoparticles, discusses their merits, limitations and applicability for water disinfection and biofouling control, and highlights research needs to utilize novel nanomaterials for water treatment applications.     

Self-organized vanadium and nitrogen co-doped titania nanotube arrays with enhanced photocatalytic reduction of CO2 into CH4

Self-organized V-N co-doped TiO₂ nanotube arrays (TNAs) with various doping amount were synthesized by anodizing in association with hydrothermal treatment. Impacts of V-N co-doping on the morphologies, phase structures, and photoelectrochemical properties of the TNAs films were thoroughly investigated. The co-doped TiO₂ photocatalysts show remarkably enhanced photocatalytic activity for the CO₂ photoreduction to methane under ultraviolet illumination. The mechanism of the enhanced photocatalytic activity is discussed in detail.     

Strategies to Optimize the Capacitive Behavior of Polypyrrole Electrodes

Polypyrrole (PPR) and composite PPR-multi-walled carbon nanotube (MCNT) electrodes for electrochemical supercapacitors were manufactured using new anionic additives for PPR polymerization. The analysis of the microstructure of PPR and PPR-MCNTs and electrochemical testing data provided information on the influence of the dopants on the mechanism of chemical polymerization and properties of nanostructured PPR and PPR-MCNT materials. The increase of the size and charge of the aromatic dopants resulted in decreasing PPR particle size, reducing agglomeration, and promoted the formation of PPR coatings on MCNTs. New additives allowed for the manufacturing of advanced electrodes with high active mass loading, excellent capacitance at high charging–discharging rates, and cyclic stability. A capacitance of 2.67 F cm^?2 at a potential variation rate of 100 mV s^?1 was achieved using composite PPR-MCNT electrodes. The electrodes were applied for the manufacturing of supercapacitor cells, which showed good electrochemical performance.     

Zirconia-multiwall carbon nanotubes dense nano-composites with an unusual balance between crack and ageing resistance

Yttria stabilized zirconia (Y-TZP) ceramics are used in a wide variety of applications, such as orthopaedic and dental implants. Y-TZP offers indeed a unique combination of biocompatibility and mechanical properties (high crack resistance for a ceramic). However, the major drawback of Y-TZP is their lack of stability: zirconia is prone to ageing, especially under humid atmosphere. Increasing the ageing resistance of Y-TZP led so far to a decrease of toughness and crack resistance. Here we show that the addition of a small volume fraction of multiwall carbon nanotubes (MWCNT) in a polycrystalline nano-structured Y-TZP sintered under specific conditions (Spark Plasma Sintering) leads to a material exhibiting a balance between ageing and crack resistance never reached before.     

Template assisted fabrication of TiO2 and WO3 nanotubes

Anodic aluminum oxide (AAO) templates with diameters of 200–500 nm were generated by anodizing a commercial aluminum (Al) substrate (99.7%) in 1 vol% phosphoric acid (H₃PO₄), with an applied voltage of 195 V. Titania and tungsten oxide nanotubes (NTs) were successfully grown on AAO template by the sol–gel process. Thermal gravimetric analyzer (TGA) curves showed that gel can be transfered to nanocrystalline particles after 19% weight loss of water molecule by evaporation. The results showed that the nanocrystalline TiO₂ NTs presented at 200 °C, and grains grew as temperature increased. At a temperature of 550 °C, the (101), (103), (004), (112), (200), (105), and (211) planes of anatase TiO₂ were detected clearly, whereas tungsten oxide NTs are amorphous after heat treatment at 200 °C or 300 °C. But the (110), (111), (002), (022), (222), and (004) planes of γ-WO₃ phase can be observed obviously after the heat treatment at 400 °C.     

Effect of a galvanostatic treatment on the preparation of highly ordered TiO2 nanotubes

This work is intended to define an optimal methodology of preparation of highly ordered TiO₂ nanotube arrays by a 60 V anodization in a glycol ethylene solution. The effect of the presence of an initial superficial oxide on the sample, before operating the anodization growth, has been analysed. The best result has been obtained by a galvanostatic oxide growth on the titanium sheet, before the anodization process. The photoconversion efficiency was measured and we have obtained a maximum value of 12.97%, strictly in line with the literature. We have also underlined the necessity to operate a heat treatment using only dry atmosphere.     

Thermopower of Carbon Nanotubes in a Magnetic Field

Abstract

The thermopower of a quantum nanotube in magnetic field was investigated. We obtained the convenient analytic formula for the thermopower. The temperature dependence of the thermopower is studied and the influence of the magnetic field on the thermopower is examined. Oscillations in the thermopower were investigated.     

Production of a biomimetic apatite nanotube mesh via biotemplating a polymer nanofiber mesh

Here, we report the preparation of hydroxyapatite nanotubes for specific use as bone regeneration material. The nanofiber mesh of a polymer (polycaprolactone) used as a template was mineralized within solutions via a biomimetic process. A subsequent heat-treatment (over 500 °C) completely eliminated the inner polymer, resulting in preserving the surface mineral phase in the form of nanotubes. The nanotubes had diameters of hundreds of nanometers with nonwoven mesh, replicating the initial nanofiber template. Furthermore, the nanotubes revealed a phase of poorly crystallized apatite, mimicking biological bone mineral. The developed biomimetic apatite nanotubes may be useful for bone regeneration as a new type of biomaterial.     

Microporous polyacrylate matrix containing hydrogen bonded nanotubular assemblies

We report the straightforward photo-polymerization of polyacrylate films containing bis-urea based self-assembled nanotubes. The obtained materials are characterized by gas adsorption measurements, 129Xe NMR spectroscopy and WAXS. The presence of the bis-ureas is shown by butane adsorption (at 273 K and ambient pressure) to be responsible for the formation of a significant microporosity. This porosity is however not detected by the classical argon adsorption procedure (at 77 K and low pressure). This effect is attributed to the contraction of the material at low temperature and pressure, and may be of general concern for other organic porous materials. One of the potential advantages of the present materials is that the porosity results from the self-assembled nanotubes and should therefore be independent of the matrix mechanical properties. It should in particular be possible to adjust the flexibility of the matrix by changing the monomer composition.     

Multiwalled Carbon Nanotubes for Heterogeneous Nanocatalytic Ozonation

Multiwalled carbon nanotubes functionalized by plasma oxygen (CNTs) have been used as heterogeneous catalysts for the ozonation of methyl orange (MO) dye (CI 13025) in aqueous solutions. It was found that the addition of CNTs significantly enhanced the dye decolorization as compared to ozone alone or when activated carbon was used at the same dose as CNTs. Both the initial ozone concentration and catalyst dosage enhanced the removal of MO. However, ozone gas concentrations higher than 6 g/m³ NTP did not further improve the decolorization rates. The removal efficiency of MO increased with pH in the range 2 to 3, while a reverse trend was observed when the pH increased from 3 to 9. The addition of a radical scavenger resulted in only a limited change in the decolorization rates suggesting that molecular ozone was the main pathway by which MO decolorization occurred in solution. However, under favorable conditions for MO attraction to CNT surface (pH = 3), the decolorization rate has significantly increased. At higher pH than the pKa value of MO (3.47) and the point of zero charge of CNT (3.87), a condition that favors the electrostatic repulsion of MO from CNT, the rates were reduced in the presence of CNT as compared to ozone alone possibly due to loss of part of the supplied ozone in un-useful parallel reactions.