Development of a versatile experimental setup for the evaluation of the photocatalytic properties of construction materials under realistic outdoor conditions.

The interest on outdoor photocatalytic materials is growing in the last years. Nevertheless, most of the experimental devices designed for the assessment of their performance operate at controlled laboratory conditions, i.e., pollutant concentration, temperature, UV irradiation, and water vapor contents, far from those of real outdoor environments. The aim of the present study was the design and development of an experimental device for the continuous test of photocatalytic outdoor materials under sun irradiation using real outdoor air as feed, with the concomitant fluctuation of pollutant concentration, temperature, and water vapor content. A three-port measurement system based on two UV-transparent chambers was designed and built. A test chamber contained the photoactive element and a reference chamber to place the substrate without the photoactive element were employed. The third sampling point, placed outdoors, allowed the characterization of the surrounding air, which feeds the test chambers. Temperature, relative humidity (RH), and UV-A irradiance were monitored at each sampling point with specific sensors. NO x concentration was measured by a chemiluminescence NO x analyzer. Three automatic valves allowed the consecutive analysis of the concentration at the three points at fixed time intervals. The reliability of the analytical system was demonstrated by comparing the NO x concentration data with those obtained at the nearest weather station to the experimental device location. The use of a chamber-based reaction system leads to an attenuation of NO x and atmospheric parameter profiles, but maintaining the general trends. The air characterization results showed the wide operating window under which the photoactive materials should work outdoors, depending on the traffic intensity and the season, which are reproduced inside the test chambers. The designed system allows the measurement of the photoactivity of outdoor materials or the comparison of several samples at the same time. The suitability of the system for the evaluation of the DeNO x properties of construction elements at realistic outdoor conditions was demonstrated. The designed experimental device can be used 24/7 for testing materials under real fluctuations of NO x concentration, temperature, UV irradiation, and relative humidity and the presence of other outdoor air pollutants such as VOCs, SO x , or NH3. The chamber-based design allows comparing a photocatalytic material with respect to a reference substrate without the photoactive phase, or even the comparison of several outdoor elements at the same time.

Photocatalysis for continuous air purification in wastewater treatment plants: from lab to reality.

The photocatalytic efficiency of TiO(2)-SiMgO(x) plates to oxidize H(2)S was first evaluated in a flat laboratory reactor with 50 mL min(-1) synthetic air containing 100 ppm H(2)S in the presence of humidity. The use of the photocatalyst-adsorbent hybrid material enhanced the photocatalytic activity in terms of pollutant conversion, selectivity, and catalyst lifetime compared to previous H(2)S tests with pure TiO(2) because total H(2)S elimination was maintained for more than 30 operating hours with SO(2) appearing in the outlet as reaction product only after 18 h. Subsequently, the hybrid material was successfully tested in a photoreactor prototype to treat real polluted air in a wastewater treatment plant. For this purpose, a new tubular photocatalytic reactor that may use solar radiation in combination with artificial radiation was designed; the lamp was turned on when solar UV-A irradiance was below 20 W m(-2), which was observed to be the minimum value to ensure 100% conversion. The efficient distribution of the opaque photocatalyst inside the tubular reactor was achieved by using especially designed star-shaped structures. These structures were employed for the arrangement of groups of eight TiO(2)-SiMgO(x) plates in easy-to-handle channelled units obtaining an adequate flow regime without shading. The prototype continuously removed during one month and under real conditions the H(2)S contained in a 1 L min(-1) air current with a variable inlet concentration in the range of tens of ppmv without release of SO(2).

Revisiting the hydrothermal synthesis of titanate nanotubes: new insights on the key factors affecting the morphology.

Recently, titanate nanotubes have attracted a significant deal of interest, but the mechanism of formation as well as some structural aspects of these materials is still under debate. In this context, the main goal of the present study is to identify the key factors affecting the morphology of the titanate nanostructures during hydrothermal synthesis in order to increase the homogeneity and control, as finely as possible, the dimensions of the nanotubes. Previous studies also analyzed the influence of synthesis conditions but, unlike other works, the simultaneous assessment of the influence of parameters such as the phase and crystal size of the TiO(2) used as precursor, and the time and temperature of the hydrothermal treatment has been now analyzed under the same experimental context. The characterization of the prepared materials by means of TEM, XRD, N(2) adsorption isotherms and Raman spectroscopy was performed to establish correlations between the structural features and the preparation conditions. In this research, special attention has been paid to study the non-washed materials, which most of the previous studies have excluded from characterization. After hydrothermal treatment amorphous particles with different morphologies are isolated before acidification, which seems to be a crucial stage in controlling nanotube formation. Besides, the obtained data indicate that some characteristics of the nanotubes, such as the degree of conversion, the homogeneity and crystallinity of the structures or the aspect ratio, can be easily selected by adjusting the synthesis parameters.