Photoactivity of TiO₂-Coated Pebbles

Abstract

Development of immobilized TiO2 photocatalysts for solar photocatalytic degradation of organic pollutants is a technological need. In the present study, Degussa P-25 TiO2 photocatalyst was coated on pretreated pebbles and the photoactivity of TiO2/pebbles is reported for the first time. Three types of pebbles, i.e., black (B), red (R), and white (W), and a mixture (M) having equal proportions of B, R, and W, were chosen. The pretreatment of pebbles constituted washing with deionized water or leaching with EDTA solution. Coating of TiO2 on the pretreated pebbles was carried out as per the previously made titania powder (PMTP) method. X-ray powder diffractograms (XRD) of powdered pebbles and analysis for various metals in washings and leachates using an inductively coupled plasma-optical emission spectrometer (ICP-OES) and an atomic absorption spectrophotometer (AAS) were carried out. Solar photocatalytic decolorization of reactive black 5 (RB5) and some other reactive dyes was tested using TiO2/pebbles in an open dish method. The percent decolorization of RB5 using TiO2/white washed pebbles (TiO2/WW) and TiO2/white leached pebbles (TiO2/WL) was 59% and 99%, respectively, at the end of 5 h of exposure to sunlight. In contrast, less than 28% decolorization was found with all the other TiO2/pebble systems. On the basis of the apparent first-order rate constants, the TiO2/WL was found 63−81 times more efficient when compared to the lowest efficiency TiO2/black leached (TiO2/BL) pebbles. The difference in photoactivity of various TiO2/pebble systems was rationalized in terms of interaction between metal oxides/ions native to pebbles and illuminated TiO2.

Fouling and Inactivation of Titanium Dioxide-Based Photocatalytic Systems

“…Furthermore, the MnO 2 / TiO 2 interface may increase the band gap energy, leading to a blue shift in the absorption edge and effectively reducing the absorption further. Similar effects were reported by Rao andChaturvedi[62] with P25 immobilized on pebbles made of minerals high in MnO 2 .…”

“…The effect of these ions on the structure or photocatalytic activity of TiO 2 has not been studied in these situations. quartz with significant amounts of FeOOH, and quartz/Fe oxide rich [118]. MnO 2 -rich pebbles showed significantly less activity than the others, presumably due to the effects of MnO 2 (as noted above) as well as the dissolution of small amounts of magnesium ions into solution.…”

Advances in Magnetically Separable Photocatalysts: Smart, Recyclable Materials for Water Pollution Mitigation

“…Immobilising the photocatalyst particles on solid supports such as glass, ceramics, polymers, zeolites, sand, etc. has been widely investigated and has successfully enabled easy separation of the photocatalyst [66][67][68][69][70][71]. However, in the process of attaining easy separation, the photocatalytic activity of the immobilised semiconductors decreased remarkably.…”

TiO2 Solar Photocatalytic Reactor Systems: Selection of Reactor Design for Scale-up and Commercialization—Analytical Review

“…Five coating cycles were conducted to obtain an adequate TiO2 coating. The coated pebbles were dried at 150 °C for eight hours [116]. The stability of the immobilized TiO2 is questionable since only drying was performed while firing of the coated pebbles at high temperatures is normally practiced to enhance TiO2 coat adherence to the support [39,41,42,117].…”