Tuning the composition of porous resin-templated TiO2 macrobeads for optimized photocatalytic performance

TiO2 in the form of macroscopic beads was prepared by resin templating. Anion-exchange macroporous resin beads were treated with a synthesis gel containing titanium isopropoxide, iso-propanol and diluted (0-5 wt.%) tetrapropylammonium hydroxide (TPAOH) aqueous solutions. The Ti-resin composite obtained was calcined at 600 °C to remove the resin. The presence of TPAOH in the precursor solution was essential for producing intact TiO2 beads. The use of 1-1.5 wt.% TPAOH resulted in anatase beads, whereas further increase in the TPAOH content promoted the anatase to rutile phase transformations. Decreasing the heating rate used during calcination also resulted in changes in the TiO2 composition from pure anatase (16 °C min-1 heating rate) to anatase with rutile impurities (0.5 °C min-1 heating rate). The photocatalytic activity of the TiO2 beads was evaluated for the degradation of acetone under ultraviolet irradiation. A high activity was displayed by the TiO2 samples composed of anatase with rutile impurities, whereas the activity was lower for pure anatase samples or samples containing mainly rutile. The TiO2 beads showed higher rates of charge carrier generation and slower charge trapping/recombination rates compared to a reference Cristal ACTiV™ PC500. In addition, the TiO2 beads could be used in at least five consecutive catalytic cycles without any in-between cycle treatment, without significant changes in their activity

Transceiver Design Concept for Cellular and Multispot Diffusing Regimes of Transmission

<p>A number of attempts have been made in an effort to combine the advantages of line-of-sight and diffuse configurations for indoor optical wireless communications via sophisticated combinations of elements that are characteristic for these architectures. A different approach has been followed in the present investigation, namely, developing a transceiver capable of operating in both configurations. It is proposed that the transceiver design be based on the utilization of two-dimensional arrays of infrared light-emitting devices and photodetectors. Basic design parameters of transceiver optics are derived from considerations about link blockage and system compliance with the unique features of line-of-sight and diffuse methods of transmission.</p

Optical wireless multi-spot diffusing: a MIMO configuration

Optical (infrared) wireless communications links offer an attractive solution for indoor applications. To enable terminal mobility and reduce temporal dispersion, we use a configuration known as Multi-Spot-Diffusing (MSD), which is a Multi-Input, Multi-Output (MIMO) architecture. In this configuration, a transmitter generates multiple narrow beams that get uniformly spread over a reflection surface accessible to a service area. A multi-branch receiver with each branch having access to a diffusing spot (generated by transmitter) combines signals on its branches. This scheme creates multiple virtually ideal communications channels between a base station and terminals. This paper considers issues involved in the design of a transmitter-based holographic spot array generator. The generator produces equally-spaced diffusing spots on the room ceiling and/or walls. To overcome power limitation set by eye safety requirements, a receiver optical concentrator is proposed. Furthermore, to improve receiver signal-to-noise ratio, an optical filter that rejects optical noise is needed. Thus, functionally receiver branch optical front-end consists of an optical concentrator and an optical band-pass filter. A single holographic optical element, capable of performing both functions is proposed. Link performance is investigated by providing equivalent link model and comparing probability of error for a bare and a holographic receiver. From performance evaluations, our results show that it is possible to achieve an increase of 11 dB in the SNR and improve power budget by reducing the path loss by over 6 dB.Conference PresentationConference PaperPublishe

Receiver alignment dependence of a GA controlled optical wireless transmitter

A genetic algorithm controlled multispot transmitter is demonstrated to be capable of optimizing the received power distribution for single element receivers in fully diffuse mobile indoor optical wireless systems. By dynamically modifying the intensity of individual diffusion spots, the transmitter is capable of compensating for changes in receiver alignment, user movement and surface reflectivity characteristics, with negligible impact to bandwidth and RMS delay spread. The dynamic range, referenced against the peak received power, can be reduced by up to 27% when the room is empty, and up to 26% with user movement and variable receiver alignment. Furthermore, received power perturbation, induced by user movement, is reduced from 10% to 2.5%. This method shows potential for providing a highly adaptable solution of overcoming channel variability whilst also reducing receiver complexity

Cell cultures in biocompatibility assessment of new materials for bone implants

The extended life expectancy and the increasing number of overweight people place bone diseases among the most serious health and social problems of our time. To meet this challenge there is a need for advanced new ma­terials for bone implants that maximally resemble the properties and behaviour of natural bones as well as ex­perimental designs to evaluate their biological activity. The aim of our study was to assess the cytocompatibili­ty of different classes of scaffolds for bone implants, including fine calcium phosphate powders, composite ma­terials, cements, and bacterial cellulose-based materials. Murine (bone marrow cells, cell cultures from bone ex­plants, BALB/c 3T3 and L929 fibroblasts) and human (Lep-3 and MRC-5 fibroblasts) cells were used as model sys­tems in our investigations. The effect of the materials on cell viability and proliferation was evaluated in direct (the cells were seeded on the material surface) and/or indirect (the cells were cultured in a medium where the ma­terials were incubated for various periods of time) experiments by the MTT test (the gold standard for cytotox­icity assessment), neutral red uptake cytotoxicity assay, double staining with acridine orange and propidium io­dide, SEM, Comet assay, Annexin V (FITC assay, alkaline phosphatase activity assay, alizarin red staining. The results obtained revealed that: the cell cultures used as model systems in our investigations have different advan­tages and disadvantages and provide complementary information on the biological activity of materials. Some of the examined scaffolds show promising biocompatibility and require additional studies on their osteoinductivi­ty and osteoconductivity