A microfluidic atmospheric-pressure plasma reactor for water treatment

A dielectric barrier discharge microfluidic plasma reactor, operated at atmospheric pressure, was studied for its potential to treat organic contaminants in water. Microfluidic technology represents a compelling approach for plasma-based water treatment due to inherent characteristics such as a large surface-area-to-volume ratio and flow control, in inexpensive and portable devices. The microfluidic device in this work incorporated a dielectric barrier discharge generated in a continuous gas flow stream of a two-phase annular flow regime in the microchannels of the device. Methylene blue in solution was used to investigate plasma induced degradation of dissolved organic compounds within the microfluidic device. The relative degradation rates of methylene blue were influenced by the residence time of the sample solution in the discharge zone, type of gas applied, channel depth and flow rate. Increasing the residence time inside the plasma region led to higher levels of degradation. Oxygen was found to be the most effective gas, with the spectra obtained using Liquid Chromatography-Mass Spectroscopy indicating the most significant degradation. By reducing the channel depth from 100 to 50 µm, the best results were obtained, achieving a greater than 97% level of methylene blue degradation. The microfluidic system presented here demonstrates proof-of-concept that plasma technology can be utilised as an advanced oxidation process for water treatment, with the potential to eliminate water treatment consumables such as filters and disinfectants

Plasma enhanced chemical vapour deposition of silica thin films

Atmospheric pressure chemical vapour deposition is an industrially significant process for forming functional thin films. There is a great opportunity for increased scientific understanding with the aim of improving current processes and helping to formulate new ones. This work is concerned with developing a methodology to assist this ongoing concern. A combination of spectroscopic and chemometric techniques are used to investigate several chemical vapour deposition processes. The first investigation concerns the spatial concentration mapping of key by-products during the thermal chemical vapour deposition of tin oxide films through the use of near infra red laser diode spectroscopy. This novel two dimensional characterisation of the process has identified reaction hotspots within the process, and has identified the redundancy of part of the exhaust mechanism. Subsequently, there has been improvements to the head design, and the operation of the process.The main thrust of the investigations are focussed towards the use of chemometric methods, such as experimental design and principal components analysis, in conjunction with a suite of spectroscopic measurement techniques, to analyse the plasma enhanced chemical vapour deposition of silica films. This work has shown the importance of active oxygen species on the chemistry. It has also been shown that the film properties are highly dependant on oxygen concentration in the reactor, and hence active oxygen species forming in the plasma. The identification of by-products in the silica deposition process has also been carried out for the first time. Finally, this work also presents the first rigorous studies of a new precursor for silica deposition, dichlorodimethylsilane.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Evaluation of a microfluidic atmospheric-pressure plasma reactor for water treatment

A dielectric barrier discharge (DBD) microfluidic plasma reactor, operated at atmospheric pressure, was studied for its potential to treat organic contaminants in water. The proposed microfluidic plasma reactor (MPR) allows in situ production of plasma in a continuous flow, operated under atmospheric pressure, for plasma-based water treatment. The MPR operates with glass as the dielectric barrier, where plasma is generated in the continuous gas flow stream of a gas-liquid two-phase annular flow regime in the microchannels. The microchannels have dimensions of 100 µm depth, 250 µm width and the plasma is generated in an approximately 21 cm length of microchannel arranged in a serpentine pattern. Methylene blue (MB) in solution was used as a model organic to investigate its degradation by plasma generated in the microchannels. The influence of discharge time, residence time and gas sources, i.e. air, argon and oxygen, on MB degradation was studied. The percentage degradation increased with lower liquid flow rates, with maximum degradation of MB achieved at a liquid flow rate of 35 µL/min and inlet gas pressure of 1 bar using oxygen as the working gas. Liquid chromatography/mass spectrometry analysis of the MB solution after treatment suggests degradation through fragmentation of MB. It is intended that the device will be used as proof of concept to introduce plasma technology as an advanced oxidation process for water treatment, with the potential to achieve total mineralization of dissolved organic materials and microbial inactivation, replacing water treatment chemicals and consumables

Interfacial Chemical Effects of Amorphous Zinc Oxide/Graphene

Research on the preparation and performance of graphene composite materials has become a hotspot due to the excellent electrical and mechanical properties of graphene. Among such composite materials, zinc oxide/graphene (ZnO/graphene) composite films are an active research topic. Therefore, in this study, we used the vacuum thermal evaporation technique at different evaporation voltages to fabricate an amorphous ZnO/graphene composite film on a flexible polyethylene terephthalate (PET). The amorphous ZnO/graphene composite film inherited the great transparency of the graphene within the visible spectrum. Moreover, its electrical properties were better than those of pure ZnO but less than those of graphene, which is not consistent with the original theoretical research (wherein the performance of the composite films was better than that of ZnO film and slightly lower than that of graphene). For example, the bulk free charge carrier concentrations of the composite films (0.13, 1.36, and 0.47 × 1018 cm−3 corresponding to composite films with thicknesses of 40, 75, and 160 nm) were remarkably lower than that of the bare graphene (964 × 1018 cm−3) and better than that of the ZnO (0.10 × 1018 cm−3). The underlying mechanism for the abnormal electrical performance was further demonstrated by X-ray photoelectron spectroscopy (XPS) detection and first-principles calculations. The analysis found that chemical bonds were formed between the oxide (O) of amorphous ZnO and the carbon (C) of graphene and that the transfer of the π electrons was restricted by C=O and C-O-C bonds. Given the above, this study further clarifies the mechanism affecting the photoelectric properties of amorphous composite films

Fluorine ion induced phase evolution of tin-based perovskite thin films: structure and properties

To study the effect of fluorine ions on the phase transformation of a tin-based perovskite, CsSnI3 x(F)x films were deposited by using thermal vacuum evaporation from a mixed powder of SnI2, SnF2 and CsI, followed by rapid vacuum annealing. The color evolution, structure, and properties of CsSnI3 xFx films aged in air were observed and analyzed. The results showed that the colors of the films changed from black to yellow, and finally presented as black again over time; the unstable B-g-CsSnI3 xFx phase transformed into the Y-CsSnI3 xFx phase, which is then recombined into the Cs2SnI6 xFx phase with the generation of SnO2 in air. Fluorine dopant inhibited the oxidation process. The postponement of the phase transformation is due to the stronger bonds between F and Sn than that between I and Sn. The color changing process of the CsSnI3 xFx films slowed that the hole concentrations increased and the resistivities decreased with the increase of the F dopant ratio. With the addition of SnF2, light harvesting within the visible light region was significantly enhanced. Comparison of the optical and electrical properties of the fresh annealed CsSnI3 xFx films showed that the band gaps of the aged films widened, the hole concentrations kept the same order, the hole mobilities reduced and therefore, the resistivities increased. The double layer Cs2SnI6 xFx phase also showed ‘p’ type semi-conductor properties, which might be due to the incomplete transition of Sn2+ to Sn4+, i.e. Sn2+ provides holes as the acceptor

First Results from a Broadband Search for Dark Photon Dark Matter in the 4444 to 52 μ52\,\mueV range with a coaxial dish antenna

We present first results from a dark photon dark matter search in the mass range from 44 to 52 $\mu{\rm eV}$ ($10.7 - 12.5\,{\rm GHz}$) using a room-temperature dish antenna setup called GigaBREAD. Dark photon dark matter converts to ordinary photons on a cylindrical metallic emission surface with area $0.5\,{\rm m}^2$ and is focused by a novel parabolic reflector onto a horn antenna. Signals are read out with a low-noise receiver system. A first data taking run with 24 days of data does not show evidence for dark photon dark matter in this mass range, excluding dark photon - photon mixing parameters $\chi \gtrsim 10^{-12}$ in this range at 90% confidence level. This surpasses existing constraints by about two orders of magnitude and is the most stringent bound on dark photons in this range below 49 $\mu$eV.Comment: 7 pages, 4 figure

2D nanosheet molybdenum disulphide (MoS2) modified electrodes explored towards the hydrogen evolution reaction

We explore the use of two-dimensional (2D) MoS2 nanosheets as an electro-catalyst for the Hydrogen Evolution Reaction (HER). Using four commonly employed commercially available carbon based electrode support materials, namely edge plane pyrolytic graphite (EPPG), glassy carbon (GC), boron-doped diamond (BDD) and screen-printed graphite electrodes (SPE), we critically evaluate the reported electro-catalytic performance of unmodified and MoS2 modified electrodes towards the HER. Surprisingly, current literature focuses almost exclusively on the use of GC as an underling support electrode upon which HER materials are immobilised. 2D MoS2 nanosheet modified electrodes are found to exhibit a coverage dependant electrocatalytic effect towards the HER. Modification of the supporting electrode surface with an optimal mass of 2D MoS2 nanosheets results in a lowering of the HER onset potential by ca. 0.33, 0.57, 0.29 and 0.31 V at EPPG, GC, SPE and BDD electrodes compared to their unmodified counterparts respectively. The lowering of the HER onset potential is associated with each supporting electrodes individual electron transfer kinetics/properties. The effect of MoS2 coverage is also explored. We reveal that its ability to catalyse the HER is dependent on the mass deposited until a critical mass of 2D MoS2 nanosheets is achieved, after which its electrocatalytic benefits and/or surface stability curtail. The active surface site density and turn over frequency for the 2D MoS2 nanosheets is determined, characterised and found to be dependent on both the coverage of 2D MoS2 nanosheets and the underlying/supporting substrate. This work is essential for those designing, fabricating and consequently electrochemically testing 2D nanosheet materials for the HER

The Effect of Construction Operations on Interests in Land

As construction materials are fixed to land or the structure of an existing building, they lose their identity as personal property and become part of the land itself. This basic proposition threatens to elevate the interest of the ultimate owner of the land, the freeholder, above the proprietors of temporally shorter estates in land, as the freeholder will ultimately stand to benefit from the works. English law has therefore developed a series of doctrinal rules in order to balance the different interests of freeholders, leaseholders, those with a security interest in the land, and the interests of participants in the construction project itself. Despite its doctrinal and practical significance, however, there is no unitary academic study analysing how construction operations affect different legal interests in the land. The thesis identifies the extent to which English law has a doctrinal framework that is consistent, with an identifiable doctrinal rationale, and formally certain and ascertainable, when it sets the balance between different interests in construction operations and legal interests in the land. It first considers the effect on interests in real property at the point of physical affixation of materials to the land. It then considers the effect of transfers of value on interests in land both in a contractual and extra-contractual framework. It finally looks at the impact on legal interests in occupation in the post-construction phase. The thesis concludes that English land law has arrived at a number of balances between the different interests in the land comprising the site which are capable of being formally ascertained and which have, for the most part, an identifiable rationale. There are, however, considerable doctrinal tensions between freehold and leasehold interests in the occupation phase of a building which require re-examination.Society of Construction Law