Kronos Vlp7000 Research Articles

TiO2 P25 and Kronos vlp 7000 materials activated by simulated solar light for atrazine degradation

Abstract Photocatalysis-based technologies have been proposed for the treatment of wastewater containing atrazine (ATZ), a persistent and recalcitrant pollutant. This study aims to evaluate and compare the efficiency of TiO2 P25 and TiO2 modified with carbon (C–TiO2 Kronos vlp 7000) in the photocatalytic degradation of ATZ in aqueous systems. The experiments were performed in a tubular photochemical reactor equipped with a compound parabolic collector (CPC) irradiated by simulated solar light. The materials were characterized by X-ray diffraction, infrared spectroscopy, BET specific surface area, and diffuse reflectance spectroscopy. For TiO2 P25, ATZ removals varied in the range 86–100 % after 120 min of irradiation, although the total organic carbon (TOC) analyses indicated that no significant ATZ mineralization occurred (<20 %). C–TiO2 Kronos vlp 7000, on the other hand, was not able to completely remove ATZ after 120 min of irradiation. In this case, pesticide removals were 37–45 % over 120 min, while C–TiO2 performed better with regard to ATZ mineralization, with 38 % TOC removal. Given the low mineralization of atrazine, the intermediate compounds formed were identified for each photocatalytic material.

The overall assessment of simultaneous photocatalytic degradation of Cimetidine and Amisulpride by using chemical and genotoxicological approaches

Pharmaceutical Active Compounds (PhACs) are of particular interest among the emerging contaminants detected in the aquatic environment. Commonly, PhACs exist as complex mixtures in aquatic systems, causing potential adverse effects to the environment and human health than those of individual compounds. Based on the increasing interest in the contamination of water resources by PhACs, the photocatalytic degradation of Cimetidine and Amisulpride as a mixture in combination with their toxic and genotoxic effects before and after the treatment were evaluated for the first time. The toxic, genotoxic and cytotoxic effects were investigated using the Trypan Blue Exclusion Test and the Cytokinesis Block MicroNucleus (CBMN) assay in cultured human lymphocytes.The photocatalytic degradation of the PhACs was studied in ultrapure water and environmentally relevant matrices using UV-A and visible (Vis) irradiation and C–TiO2 (TiO2 Kronos vlp 7000) as photocatalyst. High removal percentages were observed for both compounds under UV-A and Vis irradiation in ultrapure water. In lake and drinking water a slower degradation rate was shown that could be attributed to the complex composition of these matrices. Scavenging experiments highlighted the significant role of h+ and O2●- in the degradation mechanisms under both irradiation sources. Oxidation, dealkylation and deamination were the main degradation pathways. Regarding the individual compounds, Amisulpride was found to be more cytotoxic than Cimetidine. No significant differences of the genotoxic effects during the treatment were observed. However, a slight increase in cytotoxicity was observed at the first stages of the process. At the end of the process under both UV-A and Vis light, non-significant cytotoxic/toxic effects were observed. Based on the results, heterogeneous photocatalysis can be considered as an effective process for the treatment of complex mixtures without the formation of harmful transformation products.

Study of Nanostructured TiO₂ Rutile with Hierarchical 3D-Architecture. Effect of the Synthesis and Calcinations Temperature.

The effect of TiCl₄ hydrolysis temperature on the structural, textural and morphological properties of the resulting rutile and on the changes of these properties upon calcination was studied. The XRD, Raman spectroscopy, mercury porosimetry, BET, SEM and TEM studies have revealed that TiO₂ rutile has a hierarchical 3D-architecture. The obtained nanostructured rutile had a cauliflowerlike/ spherical morphology composed of fan-shaped nanofibers. Rutile samples were shown to have a heterogeneous pore structure including micro-, meso- and macropores with a BET surface area of 110-140 m₂/g. According to the mercury porosimetry, among mesopores and macropores the latter dominate in the samples. Elevation of the synthesis temperature from 50-70 to 80-90 °C decreased the fraction of macropores from 95 to 70%. The BET method showed that the samples synthesized at low temperatures (50-70 °C) contain 30-44% of micropores in the total amount of mesopores and micropores. The fraction of micropores decreases to 25-18% with a subsequent increase in the fraction of mesopores as the synthesis temperature is raised to 80-90 °C. As shown by a study of the samples upon calcination in the temperature range of 100-1000 °C, temperature is the key factor that produces changes in the crystallites size, nanofiber length and packing density, and 3D particle shape at different levels of the hierarchical system and determines features of the porous structure and morphological properties of nanostructured rutile. The assessment of photocatalytic activity in the oxidation of acetone vapor demonstrated that, regardless of the hydrolysis temperature, the synthesized samples of nanostructured rutile are able to oxidize acetone vapor to carbon dioxide and water. In the process, activity of the samples is comparable with that of commercial photocatalysts under UV light and is superior to the activity of commercial photocatalysts P25 (2-4 times) and TiO₂ KRONOS vlp 7000 (1.2-2 times) under visible light in dependence on the synthesis temperature.

Solar reclamation of wastewater effluent polluted with bisphenols, phthalates and parabens by photocatalytic treatment with TiO2/Na2S2O8 at pilot plant scale

Investigations of anthropogenic contaminants in fresh- and wastewater have shown a wide variety of undesirable organic compounds such as Endocrine Disruptors (EDs). As a result, wastewater treatments using innovative technologies to remove those organic compounds are required. In this paper, the photodegradation of six EDs in wastewater at pilot plant scale is reported. The EDs were bisphenol A, bisphenol B, diamyl phthalate, butyl benzylphthalate, methylparaben and ethylparaben. Commercial TiO2 nanopowders (P25, Alfa Aesar and Kronos vlp 7000) were used as photocatalysts. The operating variables (type and loading catalyst, effect of electron acceptor and pH) were previously optimized under laboratory conditions. The results show that the use of TiO2 alongside an electron acceptor like Na2S2O8 strongly enhances the degradation rate of the studied compounds compared with photolytic tests, especially P25. The oxidation rates of the EDs at pilot plant scale were calculated following the disappearance of the target compound as a function of fluence (H). The ED degradation followed a pseudo-first order kinetics in all cases. In our experimental conditions, the half-fluence (H50) varied from 79 to 173 J cm−2 (photolytic test), 10–117 J cm−2 (TiO2 vlp 7000) and 3–58 J cm−2 (TiO2 P25), for bisphenol B and butyl benzylphthalate, respectively. It is concluded that solar photocatalysis using the tandem TiO2/Na2S2O8 can be considered as an environmental-friendly tool for water detoxification and a sustainable technology for environmental remediation, especially in the Mediterranean Basin, where many places receive more than 3000 h of sunshine per year. Although the cost depends on the nature of the pollutant, the treatment cost was estimate to be about 150 € m−3 for photocatalytic treatment with TiO2 P25.

Effect of the Co-deposition of Pd and Pt on $$\hbox {TiO}_{2}$$ TiO 2 Photoactivity

$$\hbox {TiO}_{2}$$ was obtained by a simple sol–gel synthesis and subsequently modified by the addition of Pt and/or Pd particles on the surface by photodeposition. These photocatalysts were characterised by X-ray diffraction analysis, UV–Vis diffuse reflectance spectra, Brunauer–Emmett–Teller measurements, Fourier transform infrared spectroscopy, transmission electron microscopy, electron dispersive spectroscopy and X-ray photoelectron spectroscopy. Their photocatalytic activity was studied by following the degradation, mineralisation and detoxification of solutions of phenol, propanil and methylene blue. For comparison purposes, different commercial $$\hbox {TiO}_{2}$$ catalysts were also tested: Kronos vlp7000, Millenium PC100, Aeroxide P90 and Aeroxide P25. This latter catalyst was also modified with Pt and/or Pd. The degradation kinetics of all the pollutants in aqueous solutions satisfactorily followed the pseudo-first order according to the Langmuir–Hinshelwood model in conditions of low concentration values. It was found that the simultaneous photodeposition of Pt and Pd contributed to enhancing photoactivity more than the individual deposition of either Pt or Pd.

Mineralization of the antineoplastic drug carboplatin by heterogeneous photocatalysis with simultaneous synthesis of platinum-modified TiO2 catalysts

Photocatalytic oxidation of carboplatin, a platinum antineoplastic drug, has been investigated in aqueous heterogeneous solutions containing TiO2 photocatalysts. The current study, besides the photocatalytic degradation of the drug, examines the utilization of the photo-reduction process occurring on the surface of the catalyst, leading simultaneously to the photo-deposition and recovery of platinum. TiO2 photocatalytic process was evaluated for its ability to degrade the molecule of carboplatin and concurrently result in the synthesis of efficient platinum modified TiO2 catalysts. The degradation kinetic was studied under different operational conditions, such as type of photocatalyst, catalyst loading, initial pH and addition of electron acceptors. Three systems were evaluated namely, TiO2 P25 under UV-A and TiO2 Kronos vlp 7000 under UV-A or visible illumination, with respect to their activity for substrate degradation and mineralization and their ability to bind platinum on their surface during photocatalytic oxidation of the drug. The initial degradation rate (r0) decreased in the order TiO2 P25/UV-A > TiO2 Kronos vlp 7000/UV-A > TiO2 Kronos vlp 7000/visible light. For TiO2 P25/UV-A, the addition of 100 mg L−1 H2O2 increases slightly the initial mineralization rate, while degradation rates gradually decrease as photocatalysis takes place in neutral and alkaline pH. Phytotoxicity measurements, showed that heterogeneous photocatalytic oxidation in the presence of TiO2 P25 is capable of reducing the phytotoxicity of carboplatin. For TiO2 P25 and TiO2 Kronos vlp 7000 under UV-A illumination, photo-reduction and deposition of platinum is fully accomplished within 60 min of oxidation, while for TiO2 Kronos vlp 7000 in the presence of visible light, the percentage of platinum deposited on the surface of the catalyst reaches 40%. Platinum photo-deposition is feasible, employing TiO2 P25, even after the catalyst is reused. The synthesized platinum modified TiO2 P25, demonstrated higher photocatalytic efficiency in comparison to the bare one, leading to 100% degradation of the model pollutant malachite green and 40% DOC reduction, after 30 min of photo-oxidation.

Photocatalytic oxidation of six pesticides listed as endocrine disruptor chemicals from wastewater using two different TiO2 samples at pilot plant scale under sunlight irradiation

The photocatalyzed degradation of a mixture of six pesticides (malathion, fenotrothion, quinalphos, vinclozoline, dimethoate and fenarimol) with endocrine disrupting activity has been studied in sewage wastewater effluent under natural sunlight at pilot plant scale. The initial level of each pesticide was 0.30mgL−1. For this, two commercial TiO2 nanopowders (Degussa P25 and Kronos vlp 7000) were used as photocatalysts. The operational conditions (catalyst loading, effect of electron acceptor and pH) were previously optimized under laboratory conditions using a photoreactor. The results show that the use of TiO2 alongside an electron acceptor like Na2S2O8 strongly enhances the degradation rate of the studied pesticides compared with photolytic tests, especially Degussa P25. The photodegradation process followed pseudo-first order kinetics in all cases. In our experimental conditions, the necessary time necessary for 90% degradation (DT90) varied from 79 to 1270min (6–108min as normalized illumination time, t30W) for malathion and fenarimol, respectively for TiO2 vlp 7000 and 32–817min (t30W=3–69min) for the same pesticides, in the case of TiO2 P25. The results confirm the efficacy of the treatment to remove recalcitrant pollutants from wastewater using natural sunlight as renewable source.

Study of adsorption and degradation of dimethylphthalate on TiO2-based photocatalysts

This work studied the degradation and adsorption of dimethylphthalate (DMP) using various TiO2-based photocatalysts: TiO2 Aeroxide P25, Kronos vlp7000, Hombikat UV-100, Kemira 650 and a synthesized photocatalyst named SG750. As the photocatalysts with mixed anatase and rutile phases, P25 and SG750, showed greater activity than those of pure phase, an in-depth study was undertaken of these two catalysts in the adsorption and degradation of DMP. The degradation results were fitted with a high degree of correlation to the Langmuir-Hinshelwood model and those for adsorption to the Freundlich model. The Freundlich constants showed good correlation with FTIR observations of the DMP-P25 and DMP-SG750 interactions. These two photocatalysts were additionally modified by photodeposition with Pt and Au (0.5–1.5wt%) to study the effect of these metals on degradation and mineralization kinetics.

Study of the decomposition and detoxification of the herbicide bentazon by heterogeneous photocatalysis: Kinetics, intermediates and transformation pathways

Photocatalytic degradation and mineralization of the herbicide bentazon in aqueous solutions has been investigated. The pseudo-first order degradation kinetics was studied under different operational conditions, such as type of photocatalyst, catalyst loading, initial pH and addition of electron acceptors. The degradation rates proved to be strongly influenced by these parameters. Organic sulfur and nitrogen were only partially converted into inorganic in the presence of TiO2 P25 or TiO2 Kronos vlp 7000 and UV-A. The presence of H2O2 led to either enhancement or decrease of the initial degradation rates, depending on the type of catalyst employed. Intermediate products formed during photocatalytic treatment were identified by means of a high resolution LIT Orbitrap LC-ESI/MS system. 21 intermediates including dimers, hydroxy and/or keto bentazon derivatives, and further oxidized species were identified and detailed transformation pathways have been proposed. Acute toxicity profiles using marine bacteria Vibrio fischeri showed an increasing trend at the first stages of oxidation, implying the progressive formation of intermediates more toxic than the parent molecule, or synergistic effects among the transformation products. Thereafter, ecotoxicity was completely eliminated within 90min of irradiation under the investigated conditions. Phytotoxicity tests, carried out on the monocotyl Sorghum saccharatum and the dicotyls Sinapis alba and Lepidium sativum, showed similar responses of the three plant species to the photocatalytically treated samples, resulting to complete removal of phytotoxicity under the employed conditions.

Photooxidation of three spirocyclic acid derivative insecticides in aqueous suspensions as catalyzed by titanium and zinc oxides

Abstract The photocatalyzed degradation of tetramic (spirotetramat) and tetronic (spirodiclofen and spiromesifen) spirocyclic acid (ketoenol) derivative insecticides has been studied in aqueous suspensions using different semiconductor oxides. The photodegradation was studied by monitoring the change in compound concentration using HPLC-MS analysis and by the decrease in the dissolved organic carbon (DOC) content as a function of irradiation time. Laboratory scale experiments under UVA irradiation were performed to investigate the kinetics degradation of these compounds using different binary (ZnO, TiO2 and TiO2 Kronos vlp 7000) and ternary oxides (Zn2TiO4 and ZnTiO3) of zinc and titanium. Highest degradation rates were observed for ZnO and TiO2 P25 Degussa while with ternary oxides smaller photodecomposition rates were assessed, especially with ZnTiO3. New photocatalytic experiments were then performed under natural sunlight using ZnO, TiO2 P25 Degussa and TiO2 Kronos vlp 7000 leading nearly complete degradation of the studied insecticides when ZnO and TiO2 P25 Degussa were used. The photodegradation processes followed first-order reaction kinetics. Comparison of these catalysts showed that ZnO is the most efficient for the removal of these insecticides at constant volumetric rate of photon absorption in the photoreactor. The main photocatalytic intermediates (enol-derivatives) were detected during the degradation in all cases as a consequence of the cleavage of alkyl-oxygen bond of the parent compounds.

Comparison of supported TiO2 catalysts in the photocatalytic degradation of NOx

A comparison is made in this study of the effectiveness of various commercial catalysts in the oxidation of NOx by heterogeneous photocatalysis. The following catalysts were considered: Aeroxide TiO2 P25, Aeroxide TiO2 P90, Hombikat UV-100, Kronos vlp7000, CristalACTIV PC105, CristalACTIV PC500, Kemira 650 and Anatasa Aldrich. All catalysts were deposited by a dip-coating technique onto borosilicate 3.3 glass plates. Optimization of catalyst load showed no significant enhancement of photoactivity, in general, above a deposited mass of 1.16mgcm−2. Differences between photocatalyst activity were more apparent at longer illumination times. Photoactivity decreased in the presence of humidity and differences in the adsorbed products were detected. Photocatalyst activity was strongly influenced by specific surface area, with the best results obtained by the catalysts with the largest surface area, namely the PC500, Hombikat and Kronos. Photocatalyst stability was demonstrated in successive reuse cycles.

Kinetic Study of Acetaldehyde Degradation Applying Visible Light Photocatalysis

AbstractA commercially available TiO2 type (Kronos vlp 7000), doped with carbon and having an extended spectrum of light absorption wavelength, is investigated for photocatalytic degradation of a representative air pollutant, namely acetaldehyde, under visible light. The modeling of the studied system was carried out including the proposal of kinetic expressions for the contaminant degradation and generation of main intermediates based on the reaction mechanism, the mass balances in the reactor, and the lamps' superficial emission model to evaluate the radiation distribution in the reaction space. The predicted and experimental outlet concentrations of acetaldehyde and formaldehyde as main intermediate were found to be in good agreement obtaining a root mean square error equal to 13 %.

Study of the photocatalytic activity of Pt-modified commercial TiO2 for hydrogen production in the presence of common organic sacrificial agents

A detailed study is undertaken of the photocatalytic activity in hydrogen production of the commercial photocatalyst Kronos vlp7000 (KR) surface-modified with photodeposited platinum particles (2.1wt% Pt). The influence of different photocatalytic variables is studied: photocatalyst loading, suspension pH value and the nature and concentration of the sacrificial agent used. Optimum pH was found to be neutral or slightly acidic. The catalyst loading, which ranged between 0.5 and 2gL−1, had little effect on hydrogen production. In general, the results for the tested sacrificial agents in terms of hydrogen production were as follows (in descending order):methanol >ethanol >ethylene glycol >glycerol. In studies of reuse the commercial photocatalyst Kronos shows better perform in its photoactivity than the commercial photocatalyst Aeroxide TiO2 P25. Finally, studies were also undertaken of photoactivity under solar radiation in which promising results were obtained (5.5–18mLh−1).

TiO2 photocatalytic degradation of UV filter para‐aminobenzoic acid under artificial and solar illumination

AbstractBACKGROUNDThe presence of pharmaceutical and personal care products' (PPCPs) residues in the aquatic environment is an emerging issue due to their uncontrolled release, through grey water, and accumulation in the environment that may affect living organisms, ecosystems and public health. As a result, efforts are being made to develop methods to inactivate or eliminate this class of substance in the environment.RESULTSThe heterogeneous photocatalytic degradation of para‐aminobenzoic acid (PABA), one of the components that are present in many types of PPCPs, has been investigated in aqueous solutions using artificial and solar illumination. The effects of TiO2 P25 and TiO2 Kronos vlp 7000 and their concentration (0.25–1.5 g L−1), initial concentration of H2O2 (0.25–0.2 g L−1), pH of the solution (3–10), temperature (280–323 K), as well as the type of radiation (artificial, solar) on initial reaction rates were evaluated in a bench‐scale Pyrex reactor. Solar‐induced photocatalytic degradation of PABA was accompanied by the formation of several hydroxylated aromatic intermediates, while a decrease in the parent compound toxicity has been observed after treatment in the presence of TiO2 P25.CONCLUSIONAccording to the results presented in this study, the TiO2 photocatalytic process in the presence of artificial and solar illumination is an efficient methodology for PABA degradation and its toxicity reduction. © 2015 Society of Chemical Industry

Visible Light Photocatalytic Oxidation of Ethanol Vapor on Titanium Dioxide Modified with Noble Metals

The kinetics of photocatalytic oxidation of ethanol vapors under visible light ( $$ \lambda $$ > 420 nm) on the TiO2 modified with noble metal (Au and Ag) and ions (Pt, Pd and Ru) is studied. The effect of the modificator on the activity of Au/TiO2 and Pt/TiO2 photocatalysts is studied. The optimum metal content is ~1 wt.%. The quantum efficiency is calculated for all the samples. The photocatalytic activity of the studied samples is compared with activity of the commercial sample of Kronos vlp7000. The dependence of Ag/TiO2 catalytic activity on the silver ion reduction method is shown.

Photocatalytic H₂ Evolution Using Different Commercial TiO₂ Catalysts Deposited with Finely Size-Tailored Au Nanoparticles: Critical Dependence on Au Particle Size.

One weight percent of differently sized Au nanoparticles were deposited on two commercially available TiO2 photocatalysts: Aeroxide P25 and Kronos Vlp7000. The primary objective was to investigate the influence of the noble metal particle size and the deposition method on the photocatalytic activity. The developed synthesis method involves a simple approach for the preparation of finely-tuned Au particles through variation of the concentration of the stabilizing agent. Au was deposited on the TiO2 surface by photo- or chemical reduction, using trisodium citrate as a size-tailoring agent. The Au-TiO2 composites were synthetized by in situ reduction or by mixing the titania suspension with a previously prepared gold sol. The H2 production activities of the samples were studied in aqueous TiO2 suspensions irradiated with near-UV light in the absence of dissolved O2, with oxalic acid or methanol as the sacrificial agent. The H2 evolution rates proved to be strongly dependent on Au particle size: the highest H2 production rate was achieved when the Au particles measured ~6 nm.

Photocatalytic reduction of Cr(VI) over titania suspensions

The photocatalytic reduction of hexavalent chromium over titania suspensions was investigated using a 9W UV-A lamp as the irradiation source. Experiments were carried out at acidic conditions, with varying chromium and photocatalyst concentration. Commercially available titania powders were tested, predominantly Evonik P-25 (70:30 anatase:rutile), as well as Kronos vlp7000 and Millenium PC-100 (100% pure anatase). Four different organic substrates (phthalate, methanol, ethanol, propanol) were employed as sacrificial electron donor at varying initial concentrations.Reduction is strongly favoured at acidic conditions with complete conversion of 10mgL−1 Cr(VI) being achieved after 60min at pH=2.5 in the presence of 2gL−1 TiO2 P-25 and 50mgL−1 methanol. The role of electron donors is equally important as the respective extent of reduction is only 30% in the absence of a hole scavenger. At lower Cr(VI) concentrations, the reduction appears to obey first order kinetics (as evidenced measuring initial rates and computing kinetic constants), but it shifts to lower reaction orders at higher concentrations. All four organics can promote Cr(VI) reduction with phthalate being slightly more effective than the alcohols. Kronos vlp7000, whose surface area is about 3–5 times greater than the other two, results in the higher reduction rates.

Photocatalytic degradation of cylindrospermopsin under UV-A, solar and visible light using TiO2. Mineralization and intermediate products

Cyanobacteria (blue-green algae) are considered an important water quality problem, since several genera can produce toxins, called cyanotoxins that are harmful to human health. Cylindrospermopsin (CYN) is an alkaloid-like potent cyanotoxin that has been reported in water reservoirs and lakes worldwide. In this paper the removal of CYN from water by UV-A, solar and visible light photocatalysis was investigated. Two different commercially available TiO2 photocatalysts were used, i.e., Degussa P25 and Kronos-vlp7000. Complete degradation of CYN was achieved with both photocatalysts in 15 and 40min under UV-A and 40 and 120min under solar light irradiation, for Degussa P25 and Kronos vlp-7000 respectively. Experiments in the absence of photocatalysts showed that direct photolysis was negligible. Under visible light irradiation only the Kronos vlp-7000 which is a visible light activated catalyst was able to degrade CYN. A number of intermediates were identified and a complete degradation pathway is proposed, leading to the conclusion that hydroxyl radical attack is the main mechanism followed. TOC and inorganic ions (NO2−, NO3−, SO42− and NH4+) determinations suggested that complete mineralization of CYN was achieved under UV-A in the presence of Degussa P25.

Evaluation of the photocatalytic activity of TiO2 based catalysts for the degradation and mineralization of cyanobacterial toxins and water off-odor compounds under UV-A, solar and visible light

Research on the development of new TiO2 based photocatalysts has been receiving increased attention due to the ability of TiO2 to degrade a great variety of organic compounds upon UV-A irradiation. In order to evaluate the photocatalytic performance of the new synthesized materials, it is essential to follow specific procedures during the photocatalytic process. Special care should be given on light intensity, presence of oxygen, catalyst loading, initial concentration of substrate, adsorption, pH, different irradiation wavelength, mineralization, intermediate products and toxicity. In this study, catalysts such as commercially available materials (Degussa P25, Kronos vlp-7000) and home prepared materials (N-TiO2, GO–TiO2 and Ref-TiO2) have been tested for their photocatalytic ability on the degradation and mineralization of the cyanobacterial toxin microcystin-LR and off-odor causing compounds (geosmin, 2-methylisoborneol) under UV-A, solar and visible light irradiation. Also, the identification of intermediate products and their toxicity under different experimental conditions for microcystin-LR was studied. Our results showed that in all cases of the compounds Degussa P25 was the better performing catalyst under UV-A light irradiation. Under solar light, all compounds were effectively degraded with the doped materials (N-TiO2, GO–TiO2, Kronos vlp-7000) showing better photocatalytic performance than theirs undoped material (Ref-TiO2). As far as concerning visible light irradiation, only the visible light activated materials showed some photocatalytic activity (N-TiO2, Kronos vlp-7000). It was also showed in order to have reproducible evaluation results on the photocatalytic performance of several catalysts (intra and inter-laboratory), a careful selection of experimental parameters is required.

Action spectra of P25 TiO2 and a visible light absorbing, carbon-modified titania in the photocatalytic degradation of stearic acid

The photonic efficiencies of films of Evonik (formerly Degussa) P25 TiO2 and carbon-modified TiO2 Kronos VLP 7000 samples are reported as a function of excitation wavelength (300–430nm; FWHM∼7.5nm), i.e. the action spectra, for the degradation of stearic acid, a model organic for the photocatalytic destruction of solid surface organic pollutants. For each of these semiconductor photocatalysts, at 365nm (FWHM=18nm), the dependence of the rate of degradation of stearic acid, upon the irradiance, I, is determined and the rate is found to be proportional to I0.65 and I0.82 for P25 and Kronos titania, respectively. Assuming this relationship holds at all wavelengths, the action spectra for two different semiconductor photocatalysts is modified by plotting, (RSA (rate of stearic acid destruction, units: molecules cm−2s−1)/Iθ) vs. wavelength of excitation (λexcit), and both differ noticeably from those of the original (unmodified) action spectra, which are plots of (RSA/I=photonic efficiency, ξ) vs. λexcit. The shape of the modified action spectrum for P25 TiO2 is consistent with that reported by others for other organic mineralisation reactions and correlates well with diffuse reflectance data for P25 TiO2 (Kubelka–Munk plot), although there is some evidence that the active phase, in the photodegradation of stearic acid, is the anatase form present in P25. The unmodified and modified action spectra of the beige Kronos VLP 7000 TiO2 compound exhibits little or no activity in the visible i.e. (λexcit>400nm) and a peak at 350nm. The Kronos powder contains a yellow/brown conjugated, extractable, organic sensitiser which has been identified by others as the species responsible for its reported photocatalytic visible light activity. But, irradiation of the Kronos powder film, with and without a stearic acid coating, in air, using UVA or visible light, bleaches rapidly (<60min) most, if not all, of the little colour exhibited by the original Kronos powder. The photobleached form of the Kronos has a similar action spectrum to that of the unbleached form, which, in turn, appears very similar to that of P25 titania, at wavelengths >350nm. It is proposed that the difference between the Kronos and P25 powder films at wavelengths <350nm is due to a photodegradation-resistant, previously unidentified (but extractable using MeCN) UV-absorbing organic species in the former which screens the titania particles at these lower wavelengths. The implications of these observations are discussed briefly.