Photocatalytic Activity of TiO

TiO2-WO3 photocatalysts were prepared in a vacuum evaporator by impregnation of TiO2 with WO2 dissolved in an H2O2 solution (30%) and followed by calcination at 400 and 600∘C. XRD analyses showed that at 400∘C monoclinic phase of WO3 was dominated whereas at 600∘C both monoclinic and regular phases of WO3 were present. Modification of TiO2 by WO3 caused increasing in the absorption of light to the visible range. TiO2 and photocatalysts modified with low amount of WO3 (1–5 wt.%) showed high adsorption of Acid Red (AR) on their surface and enhanced photocatalytic activity under UV irradiation. Under visible light irradiation, TiO2-WO3 photocatalysts prepared at 400∘C were more active for AR decomposition than those prepared at 600∘C suggesting that monoclinic phase of WO3 is more active under visible light than regular WO3. Although TiO2-WO3 photocatalysts appeared to be active under visible light for decomposition of AR, the UV irradiation was more efficient

Impact of TiO2 Surface Defects on the Mechanism of Acetaldehyde Decomposition under Irradiation of a Fluorescent Lamp

TiO2 was placed in heat-treatment at the temperature of 400–500 °C under flow of hydrogen gas in order to introduce some titania surface defects. It was observed that hole centers in TiO2 were created during its heat treatment up to 450 °C, whereas at 500 °C some Ti3+ electron surface defects appeared. The type of titania surface defects had a great impact on the mechanism of acetaldehyde decomposition under irradiation of artificial visible light. Formation of O•− defects improved both acetaldehyde decomposition and mineralization due to the increased oxidation of adsorbed acetaldehyde molecules by holes. Contrary to that, the presence of electron traps and oxygen vacancies in titania (Ti3+ centers) was detrimental for its photocatalytic properties towards acetaldehyde decomposition. It was proved that transformation of acetaldehyde on the TiO2 with Ti3+ defects proceeded through formation of butene complexes, similar as on rutile-type TiO2. Formed acetic acid, upon further oxidation of butene complexes, was strongly bound with the titania surface and showed high stability under photocatalytic process. Therefore, titania sample heat-treated with H2 at 500 °C showed much lower photocatalytic activity than that prepared at 450 °C. This study indicated the great impact of titania surface defects (hole traps) in the oxidation of acetaldehyde and opposed one in the case of defects in the form of Ti3+ and oxygen vacancies. Oxidation abilities of TiO2 seem to be important in the photocatalytic decomposition of volatile organic compounds (VOCs) such as acetaldehyde.This research was funded by the National Science Centre, Poland, grant nr 2020/39/B/ST8/01514

Increase of the Photocatalytic Activity of TiO by Carbon and Iron Modifications

Modification of TiO2 by doping of a residue carbon and iron can give enhanced photoactivity of TiO2. Iron adsorbed on the surface of TiO2 can be an electron or hole scavenger and results in the improvement of the separation of free carriers. The presence of carbon can increase the concentration of organic pollutants on the surface of TiO2 facilitating the contact of the reactive species with the organic molecules. Carbon-doped TiO2 can extend the absorption of the light to the visible region and makes the photocatalysts active under visible-light irradiation. It was proved that TiO2 modified by carbon and iron can work in both photocatalysis and photo-Fenton processes, when H2O2 is used, enhancing markedly the rate of the organic compounds decomposition such as phenol, humic acids and dyes. The photocatalytic decomposition of organic compounds on TiO2 modified by iron and carbon is going by the complex reactions of iron with the intermediates, what significantly accelerate the process of their decomposition. The presence of carbon in such photocatalyst retards the inconvenient reaction of OH radicals scavenging by H2O2, which occurs when Fe-TiO2 photocatalyst is used

Preparation of TiO 2

This study examined the photocatalytic degradation of phenol and azo dyes such as Reactive Red 198 and Direct Green 99 by photocatalysis over amorphous hydrated titanium dioxide (TiO2 · H2O) obtained directly from the sulphate technology installation modified in gaseous ammonia atmosphere. The photocatalysts were used in the solution and coated on the glass plate after sandblasting. The highest rate of phenol degradation in the solution was obtained for catalysts calcinated at 700°C (6.5% wt.), and the highest rate of dye decolorization was found for catalysts calcinated at 500°C and 600°C (ca. 40%–45%). Some TOC measurements of dye solutions were performed to check the rate of mineralization. On the glass plate, the decomposition of DG99 on TiO2/N 500 contrary to TiO2-P25 proceeded completely after 120 hours of visible light irradiation. The prolongation of the time of irradiation did not enhance DG99 degradation on TiO2-P25. The decomposition of the Direct Green 99 on TiO2/N 500 coated on the glass plate covered with liquid glass took place up to 24 hours of irradiation. The liquid layer on the glass plate which was covered with the photocatalyst reduced its activity. The nitrogen doping during calcinations under ammonia atmosphere is a new way of obtaining a photocatalyst which could have a practical application in water treatment system under broadened solar light spectrum as well as self-cleaning coatings

Impact of paint matrix composition and thickness of paint layer on the activity of photocatalytic paints

Silicate, acrylic and latex photocatalytic paints were analyzed in regards to impact of paint matrix composition and paint layer’s thickness on performance in two photocatalytic tests. These included performances in photocatalytic decomposition of benzo[a]pyrene (BaP) and assessment of photocatalytic activity through use of smart ink test. Silicate photocatalytic paints displayed lower photocatalytic activity in comparison to acrylic and latex photocatalytic paints in both tests, despite the similar content of nanocrystalline TiO2. Measurements of depth of UV light penetration through the paints layer were performed and it appeared, that more porous structure of coating resulted in deeper penetration of UV light. In the case of acrylic paint, the thickness of the photocatalytic layer was around 9 μm, but for silicate paint DR this thickness was higher, around 21 μm

High performance fluidized bed photoreactor for ethylene decomposition

Removal of C2H4 in the air was carried out in the continuous flow reactor with the photocatalytic bed (expanded polystyrene spheres coated by TiO2 or SiO2/TiO2) under irradiation of UV light. Continuous flow of a gas stream through the reactor was realised at the static bed and under bed fluidization. The required flow of a gas stream through the reactor for bed fluidisation was 500–700 ml/min, whereas for the static bed the flow rate of 20 ml/min was used. Fluidized bed reactor appeared to be much more efficient in ethylene removal than that with the stationary bed. It was caused by the increased speed of C2H4 mass transfer to the photocatalyst surface and better utilization of the incident UV light. In the fluidized bed reactor calculated rate of C2H4 degradation was around 10 μg/min whereas in the stationary state 1.2 μg/min only

Photocatalytic Decomposition of Acetaldehyde on Different TiO2-Based Materials: A Review

Purification of air from the organic contaminants by the photocatalytic process has been confirmed to be very perspective. Although many various photocatalysts have been prepared and studied so far, TiO2 is still the most commonly used, because of its advantageous properties such as non-toxicity, relatively low cost and high stability. Surface modifications of TiO2 were extensively proceeded in order to increase photocatalytic activity of the photocatalyst under both UV and visible light activations. The intention of this review paper was to summarize the scientific achievements devoted to developing of TiO2-based materials considered as photocatalysts for the photocatalytic degradation of acetaldehyde in air. Influence of the preparation and modification methods on the parameters of the resultant photocatalyst is reviewed and discussed in this work. Affinity of the photocatalyst surfaces towards adsorption of acetaldehyde will be described by taking into account its physicochemical parameters. Impact of the contact time of a pollutant with the photocatalyst surface is analyzed and discussed with respect to both the degradation rate and mineralization degree of the contaminant. Influence of the photocatalyst properties on the mechanism and yield of the photocatalytic reactions is discussed. New data related to the acetaldehyde decomposition on commercial TiO2 were added, which indicated the different mechanisms occurring on the anatase and rutile structures. Finally, possible applications of the materials revealing photocatalytic activity are presented with a special attention paid to the photocatalytic purification of air from Volatile Organic Compounds (VOCs)