Efficiency and stability evaluation of Cu2O/MWCNTs filters for virus removal from water.

Both multi-walled carbon nanotubes (MWCNTs) and metal or metal oxides have demonstrated virus removal efficacy in drinking water applications. In this study, MWCNTs were coated with copper(I) oxide (Cu2O) using three distinct synthesis procedures (copper ion attachment, copper hydroxide precipitation, and [Cu(NH3)4]2+ complex attachment) and virus removal efficacy (using MS2 bacteriophages) was evaluated. All synthesis procedures resulted in the presence of adsorbed, nanosized Cu2O particles on the MWCNTs, shown using X-ray diffraction. Further, transmission electron microscopy confirmed uniform copper(I) oxide distribution along the MWCNTs for all three materials. Virus removal efficacy was assessed for all three synthesised composites both before and after material conditioning (filtering for at least 24 h/280 mL/h), and accounting for additional MS2 inactivation in the permeate due to continued copper inactivation from dissolved/desorbed copper in permeate (time-control). Material conditioning influenced virus removal, with the first litres of water containing higher concentrations of copper than the sixth litres of water, suggesting excess or non-bonded copper species dissolve from filters. Higher copper dissolution was observed for water at pH 5 than at pH 7, which decreased with time. Copper dissolution most likely caused an associated decrease in copper adsorbed to MWCNTs in the filters, which may explain the observed lower MS2 removal efficacy after conditioning. Additionally, the time-control study (immediately after filtration as compared to 2 h after filtration) highlighted continued MS2 inactivation in the permeate over time. The obtained results indicate that the synthesis procedure influences virus removal efficacy for MWCNTs coated with copper oxides and that virus removal is likely due to not only virus electrostatic adsorption to the coated MWCNTs, but also through antiviral properties of copper which continues to act in the permeate. In conclusion, it is highly important to revise the methods of testing filter materials for virus removal, as well as procedure for virus concentration evaluation.

Insights into Pore Size Control in Cellulose Nanopapers Through Modeling and Experiments.

An easy way of controlling pore sizes during the preparation of cellulose nanopapers using nanofibrillated cellulose and different solvents, such as water, ethanol and acetone, was applied in this study. A possible mathematical model is also presented, that describes the occuring processes, which model is based on simple probability theory computations taking the number of possible hydrogen bonds into consideration. This model allows the better understanding of the solvent dependence of pore formation on a molecular level. For the comparison of the effects of solvents two different series of cellulose nanopapers were prepared. In the cases of both series, an aqueous nanofibrillated cellulose suspension was used for the fabrication of nanopapers, and different solvents were used for their modification. Based on scanning electron microscopy images and mercury intrusion porosimetry data it has been concluded, that using different solvents was a crucial point in controlling pore sizes. A theory about the swelling effects, as well as the formation and decomposition of nanofibrillated cellulose aggregates based on the hydrogen bonding abilities of the solvents, was proposed and proven in this paper. As-prepared nanocellulose papers can be excellent candidates for further applications as support materials (e.g., virus filtration).

Electrospun TiO(2) fiber composite photoelectrodes for water splitting.

This work has focused on the development of electrospun TiO2 fiber composite photoelectrodes for hydrogen production by water splitting. For comparison, similar photoelectrodes were also developed using commercial TiO2 (Aeroxide P25) nanoparticles (NPs). Dispersions of either fibers or P25 NPs were used to make homogenous TiO2 films on fluorine-doped SnO2 (FTO) glass substrates by a doctor blade (DB) technique. Scanning electron microscopy (SEM) analysis revealed a much lower packing density of the DB fibers, with respect to DB-P25 TiO2 NPs; this was also directly reflected by the higher photocurrent measured for the NPs when irradiating the photoelectrodes at a light intensity of 1.5AM (1 sun, 1000 W/m(2)). For a better comparison of fibers vs. NPs, composite photoelectrodes by dip-coating (onto FTO) TiO2 sol-gel (SG) matrixes containing an equal amount (5 or 20 wt %) of either fibers or P25 NPs were also investigated. It emerged that the photoactivity of the fibers was significantly higher. For composites containing 5 wt % TiO2 fibers, a photocurrent of 0.5 mA/cm(2) (at 0.23 V vs Ag/AgCl) was measured, whereas 5 wt % P25 NPs only provided 0.2 mA/cm(2). When increasing to 20 wt % fibers or NPs, the photocurrent decreased, because of the formation of microcracks in the photoelectrodes, because of the shrinkage of the sol-gel. The high photoactivity of the fiber-based electrodes could be confirmed by incident photon to current efficiency (IPCE) measurements. Remarkably, the IPCE of composites containing 5 wt % fibers was between 35% and 40% in the region of 380-320 nm, and when accounting for transmission/reflection losses, the absorbed photon to current efficiency (APCE) was consistently over 60% between 380 nm and 320 nm. The superior photoactivity is attributed to the enhanced electron transport in the electrospun fibers, with respect to P25 NPs. According to this study, it is clear that the electronic connectivity ensured by the sol-gel also contributes positively to the enhanced photocurrent.

TiO2-based nanopowders and thin films for photocatalytical applications.

TiO2-based nanopowders are elaborated by flame spray synthesis, FSS from organic precursors of titanium and chromium with the Cr content changing from 0 to 15 at.%. Well-crystallized nanopowders with high specific surface area SSA reaching 107 m2/g for undoped TiO2 and 177 m2/g for TiO2 + 15 at.% Cr are obtained. Thin films are deposited by rf reactive sputtering from metallic Ti and Ti-Cr targets in Ar + O2 flow controlled atmosphere. The adjustable area of Cr/Ti allows to obtain up to 16 at.% Cr in TiO2 thin films. X-ray diffraction, transmission electron spectroscopy, TEM, atomic force microscopy, AFM and optical spectrophotometry over the ultraviolet UV and visible VIS range of the light spectrum have been performed in order to characterize the nanomaterials. The particle size of nanopowders is within the range of 5-42 nm. Anatase is the predominating polymorphic form while the amount of rutile increases with Cr content to reach of about 25 wt.% at 15 at.% Cr. The post-deposition annealing of thin films in air at temperatures from 770 K to 1280 K modifies the phase composition, leads to irreversible transformation from anatase to rutile and affects the surface roughness. Structural and optical properties of TiO2-based nanopowders and thin films are compared. The effect of grain size and the level of chromium doping on the band gap E(g) is discussed. Photocatalytic activity of the nanopowders is tested for degradation of methylene blue, MB.

Isoelectric points of viruses.

Viruses as well as other (bio-)colloids possess a pH-dependent surface charge in polar media such as water. This electrostatic charge determines the mobility of the soft particle in an electric field and thus governs its colloidal behaviour which plays a major role in virus sorption processes. The pH value at which the net surface charge switches its sign is referred to as the isoelectric point (abbreviations: pI or IEP) and is a characteristic parameter of the virion in equilibrium with its environmental water chemistry. Here, we review the IEP measurements of viruses that replicate in hosts of kingdom plantae, bacteria and animalia. IEPs of viruses are found in pH range from 1.9 to 8.4; most frequently, they are measured in a band of 3.5 < IEP < 7. However, the data appear to be scattered widely within single virus species. This discrepancy is discussed and should be considered when IEP values are used to account for virus sorption processes.