A novel carbon nanotube modified scaffold as an efficient biocathode material for improved microbial electrosynthesis

We report on a novel biocompatible, highly conductive three-dimensional cathode manufactured by direct growth of flexible multiwalled carbon nanotubes on reticulated vitreous carbon (NanoWeb-RVC) for the improvement of microbial bioelectrosynthesis (MES). NanoWeb-RVC allows for an enhanced bacterial attachment and biofilm development within its hierarchical porous structure. 1.7 and 2.6 fold higher current density and acetate bioproduction rate normalized to total surface area were reached on NanoWeb-RVC versus a carbon plate control for the microbial reduction of carbon dioxide by mixed cultures. This is the first study showing better intrinsic efficiency as biocathode material of a three-dimensional electrode versus a flat electrode: this comparison has been made considering the total surface area of the porous electrode, and not just the projected surface area. Therefore, the improved performance is attributed to the nanostructure of the electrode and not to an increase in surface area. Unmodified reticulated vitreous carbon electrodes lacking the nanostructure were found unsuitable for MES, with no biofilm development and no acetate production detected. The high surface area to volume ratio of the macroporous RVC maximizes the available biofilm area while ensuring effective mass transfer to and from the biofilm. The nanostructure enhances the bacteria-electrode interaction and microbial extracellular electron transfer. When normalized to projected surface area, current densities and acetate production rates of 3.7 mA cm-2 and 1.3 mM cm-2 d-1, respectively, were reached, making the NanoWeb-RVC an extremely efficient material from an engineering perspective as well. These values are the highest reported for any MES system to date

Silica-polyamide nanofriction in electrolyte solutions: insights into scaling of RO membranes

Understanding the phenomena governing silica scaling in reverse osmosis (RO) relies in part on properly measuring the forces acting on silica nanoparticles in high ionic strength environments, such as the concentration polarisation zone near membranes. Characterising these interactions is challenging, given the extremely small forces acting at nanoscale. In this work we develop an atomic force microscopy (AFM) based lateral force spectroscopy (LFS) approach to measure trends in friction force associated with interaction between silica nanoparticle surrogate probes and synthetic polyamide in NaCl, CaCl and MgCl solutions at ionic strengths resembling typical RO concentration polarisation zone. We found that, for silica-polyamide interactions, whenever electrolytes are involved, friction is reduced in comparison to the case of pure water. Further, Ca ions tend to increase friction coefficients relative to Na ions, while Mg ions have the opposite effect

Advanced microscopy of inorganic colloids sampled from consecutive stages of RO filtration

Understanding the phenomena governing silica scaling in reverse osmosis (RO) relies on properly characterising the water matrix. One of the challenges to characterising water samples is the presence of inorganic nanoparticles, which are difficult to detect and analyse. In this work we develop a straightforward approach for nanoparticle trapping, detection, visualisation and elemental analysis by means of electron microscopy. The new approach is applied to characterise samples from three consecutive stages of RO in a water treatment facility. Transmission electron microscopy grids are employed with and without carbon films, to capture nanoparticles. We find that film coated traps are more effective in collecting colloids, and the colloids collected are of similar size. For the waters tested, the nanoparticles are rich in silica and the number of particulates increases with the advancement of the RO process

Effect of alcohol-water exchange and surface scanning on nanobubbles and the attraction between hydrophobic surfaces

Atomic force microscopy (AFM) was used to examine how different alcohols affect the hydrophobic attraction between a hydrophobic silica colloidal probe and a hydrophobic silica wafer. The experiments were performed in water and in water after rinsing alcohol (methanol, ethanol, or 1-propanol) throughout the AFM system. In all three cases the range of the attractive force increased after alcohol–water exchange, with 1-propanol showing the largest increase in range followed by ethanol and methanol. Additionally, experiments were performed before and after scanning the flat substrate with the colloidal probe. The range of the attractive force substantially increased with increasing scanning area. The attraction was explained by nanobubble bridging with a capillary force model with constant bridge volume proposed. The bridge volume (constant during each of the force curve measurements), contact angle and rupture distance were also determined for different scan sizes. The correlation between the rupture distance and bridge volume agreed with the available prediction