Graphene aerogels as efficient adsorbers of water pollutants and their effect of drying methods

Environmental accidents highlight the need for the development of efficient materials that can be employed to eliminate pollutants including crude oil and its derivatives, as well as toxic organic solvents. In recent years, a wide variety of advanced materials has been investigated to assist in the purification process of environmentally compromised regions, with the principal contestants being graphene-based structures. This study describes the synthesis of graphene aerogels with two methods and determines their efficiency as adsorbents of several water pollutants. The main difference between the two synthesis routes is the use of freeze-drying in the first case, and ambient pressure drying in the latter. Raman spectroscopy, Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and contact angle measurements are employed here for the characterisation of the samples. The as-prepared aerogels have been found to act as photocatalysts of aqueous dye solutions like methylene blue and Orange G, while they were also evaluated as adsorbents of organic solvents (acetone, ethanol and methanol), and, oils like pump oil, castor oil, silicone oil, as well. The results presented here show that the freeze-drying approach provides materials with better adsorption efficiency for the most of the examined pollutants, however, the energy and cost-saving advantages of ambient-pressure-drying could offset the adsorption advantages of the former case.

A Monitoring System for Carbon Dioxide in Honeybee Hives: An Indicator of Colony Health

Non-dispersive infra-red (NDIR) detectors have become the dominant method for measuring atmospheric CO₂, which is thought to be an important gas for honeybee colony health. In this work we describe a microcontroller-based system used to collect data from Senserion SCD41 NDIR sensors placed in the crown boards and queen excluders of honeybee colonies. The same sensors also provide relative humidity and temperature data. Several months of data have been recorded from four different hives. The mass change measurements, from hive scales, when foragers leave the hive were compared with the data from the gas sensors. Our data suggest that it is possible to estimate the colony size from the change in measured CO₂, however no such link with the humidity is observed. Data are presented showing the CO₂ decreasing over many weeks as a colony dies.

Static and Dynamic Optical Analysis of Micro Wrinkle Formation on a Liquid Surface

A spatially periodic voltage was used to create a dielectrophoresis induced periodic micro wrinkle deformation on the surface of a liquid film. Optical Coherence Tomography provided the equilibrium wrinkle profile at submicron accuracy. The dynamic wrinkle amplitude was derived from optical diffraction analysis during sub-millisecond wrinkle formation and decay, after abruptly increasing or reducing the voltage, respectively. The decay time constant closely followed the film thickness dependence expected for surface tension driven viscous levelling. Modelling of the system using numerical solution of the Stokes flow equations with electrostatic forcing predicted that wrinkle formation was faster than decay, in accord with observations.

Dynamic response of a thin sessile drop of conductive liquid to an abruptly applied or removed electric field

We consider, both theoretically and experimentally, a thin sessile drop of conductive liquid that rests on the lower plate of a parallel-plate capacitor. We derive analytical expressions for both the initial deformation and the relaxation dynamics of the drop as the electric field is either abruptly applied or abruptly removed, as functions of the geometrical, electrical, and material parameters, and investigate the ranges of validity of these expressions by comparison with full numerical simulations. These expressions provide a reasonable description of the experimentally measured dynamic response of a drop of conductive ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate.

Flow-induced delayed Freedericksz transition

We demonstrate that a compact manometer experiment allows direct observation of a delay to the classical electric-field-induced Freedericksz transition produced by flow in a highly dispersive nematic liquid crystal layer. The Ericksen-Leslie equations are used to show that a flow aligning torque generated in the nematic layer under Poiseuille flow competes with the orthogonal electric-field reorientation torque. This model fully reproduces the experimental results using only self-consistently determined viscosity values, and predicts a more generally applicable expression for the dependence of the delay E(c)∝sqrt[ζ/Δχ(e)] on the shear rate ζ and on the electric susceptibility anisotropy Δχ(e).