Marina Ratova

Structural formation and photocatalytic activity of magnetron sputtered titania and doped-titania coatings.

Titania and doped-titania coatings can be deposited by a wide range of techniques; this paper will concentrate on magnetron sputtering techniques, including “conventional” reactive co-sputtering from multiple metal targets and the recently introduced high power impulse magnetron sputtering (HiPIMS). The latter has been shown to deliver a relatively low thermal flux to the substrate, whilst still allowing the direct deposition of crystalline titania coatings and, therefore, offers the potential to deposit photocatalytically active titania coatings directly onto thermally sensitive substrates. The deposition of coatings via these techniques will be discussed, as will the characterisation of the coatings by XRD, SEM, EDX, optical spectroscopy, etc. The assessment of photocatalytic activity and photoactivity through the decomposition of an organic dye (methylene blue), the inactivation of E. coli microorganisms and the measurement of water contact angles will be described. The impact of different deposition technologies, doping and co-doping strategies on coating structure and activity will be also considered.

Deposition of Visible Light Active Photocatalytic Bismuth Molybdate Thin Films by Reactive Magnetron Sputtering

Bismuth molybdate thin films were deposited by reactive magnetron co-sputtering from two metallic targets in an argon/oxygen atmosphere, reportedly for the first time. Energy dispersive X-ray spectroscopy (EDX) analysis showed that the ratio of bismuth to molybdenum in the coatings can be effectively controlled by varying the power applied to each target. Deposited coatings were annealed in air at 673 K for 30 min. The crystalline structure was assessed by means of Raman spectroscopy and X-ray diffraction (XRD). Oxidation state information was obtained by X-ray photoelectron spectroscopy (XPS). Photodegradation of organic dyes methylene blue and rhodamine B was used for evaluation of the photocatalytic properties of the coatings under a visible light source. The photocatalytic properties of the deposited coatings were then compared to a sample of commercial titanium dioxide-based photocatalytic product. The repeatability of the dye degradation reactions and photocatalytic coating reusability are discussed. It was found that coatings with a Bi:Mo ratio of approximately 2:1 exhibited the highest photocatalytic activity of the coatings studied; its efficacy in dye photodegradation significantly outperformed a sample of commercial photocatalytic coating.

Deposition of Visible Light-Active C-Doped Titania Films via Magnetron Sputtering Using CO2 as a Source of Carbon

Doping of titanium dioxide with p-block elements is typically described as an efficient pathway for the enhancement of photocatalytic activity. However, the properties of the doped titania films depend greatly on the production method, source of doping, type of substrate, etc. The present work describes the use of pulsed direct current (pDC) magnetron sputtering for the deposition of carbon-doped titania coatings, using CO2 as the source of carbon; ratios of O2/CO2 were varied through variations of CO2 flow rates and oxygen flow control setpoints. Additionally, undoped Titanium dioxide (TiO2) coatings were prepared under identical deposition conditions for comparison purposes. Coatings were post-deposition annealed at 873 K and analysed with scanning electron microscopy (SEM), X-ray diffreaction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The photocatalytic properties of the thin films were evaluated under ultraviolet (UV) and visible light irradiation using methylene blue and stearic acid decomposition tests. Photoinduced hydrophilicity was assessed through measurements of the water contact angle under UV and visible light irradiation. It was found that, though C-doping resulted in improved dye degradation compared to undoped TiO2, the UV-induced photoactivity of Carbon-doped (C-doped) photocatalysts was lower for both model pollutants used.

Magnetron Sputter-Coated Nanoparticle MoS2 Supported on Nanocarbon: A Highly Efficient Electrocatalyst toward the Hydrogen Evolution Reaction

The design and fabrication of inexpensive highly efficient electrocatalysts for the production of hydrogen via the hydrogen evolution reaction (HER) underpin a plethora of emerging clean energy technologies. Herein, we report the fabrication of highly efficient electrocatalysts for the HER based on magnetron-sputtered MoS2 onto a nanocarbon support, termed MoS2/C. Magnetron sputtering time is explored as a function of its physiochemical composition and HER performance; increased sputtering times give rise to materials with differing compositions, i.e., Mo4+ to Mo6+ and associated S anions (sulfide, elemental, and sulfate), and improved HER outputs. An optimized sputtering time of 45 min was used to fabricate the MoS2/C material. This gave rise to an optimal HER performance with regard to its HER onset potential, achievable current, and Tafel value, which were −0.44 (vs saturated calomel electrode (SCE)), −1.45 mV s–1, and 43 mV dec–1, respectively, which has the highest composition of Mo4+ and sulfide (MoS2). Electrochemical testing toward the HER via drop casting MoS2/C upon screen-printed electrodes (SPEs) to electrically wire the nanomaterial is found to be mass coverage dependent, where the current density increases up to a critical mass (ca. 50 μg cm–2), after which a plateau is observed. To allow for a translation of the bespoke fabricated MoS2/C from laboratory to new industrial applications, MoS2/C was incorporated into the bulk ink utilized in the fabrication of SPEs (denoted as MoS2/C-SPE), thus allowing for improved electrical wiring to the MoS2/C and resulting in the production of scalable and reproducible electrocatalytic platforms. The MoS2/C-SPEs displayed far greater HER catalysis with a 450 mV reduction in the HER onset potential and a 1.70 mA cm–2 increase in the achievable current density (recorded at −0.75 V (vs SCE)), compared to a bare/unmodified graphitic SPE. The approach of using magnetron sputtering to modify carbon with MoS2 facilitates the production of mass-producible, stable, and effective electrode materials for possible use in electrolyzers, which are cost competitive to Pt and mitigate the need to use time-consuming and low-yield exfoliation techniques typically used to fabricate pristine MoS2.