Electrochemical Monitoring of Photoelectrocatalytic Degradation of 3,4‐Dichlorophenol Using TiO2 Thin Film Modified Graphite Electrode

A novel electrode was prepared by forming TiO₂ thin films using a commercially available TiO₂ powder (Degussa P25) on graphite plates for water photoelectrocatalytic decontamination. In addition to, for the first time the photoelectrochemical degradation of 3,4‐dichlorophenol was investigated. The effects of applied potential, pH, and initial 3,4‐dichlorophenol concentration on the photoelectrocatalytic (PEC) degradation of 3,4‐dichlorophenol using ultraviolet (UV) illuminated TiO₂/graphite (TiO₂/C) thin film electrode was examined and discussed. Also, direct photolysis (DP), electrochemical oxidation (EC), photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of 3,4‐dichlorophenol were compared. Results show that the best responses for PEC are obtained at applied potential 1.2 V versus reference electrode, pH 8.0 and initial 3,4‐dichlorophenol concentration 6.7 mg L^?1.     

Electrochemical monitoring of photoelectrocatalytic degradation of rhodamine B using TiO2 thin film modified graphite electrode

A commercially available TiO₂ powder (Degussa P25) has been used to prepare thin films on graphite plates. The photoelectrochemical degradation of rhodamine B was investigated using this photoelectrode. The effects of applied potential, pH, and initial rhodamine B concentration on the photoelectrocatalytic (PEC) degradation of rhodamine B using ultraviolet illuminated TiO₂/graphite (TiO₂/C) thin film electrode were examined and discussed. Also, direct photolysis, electrochemical oxidation, photocatalytic, and PEC degradation of rhodamine B were compared. Results show that the best responses for PEC are obtained at applied potential of 1.2?V vs. reference electrode, pH?4.0, and initial rhodamine B concentration of 4.2?mg?L^?1.     

Visible Light Photocatalytic Activity of Porphyrin Tin(IV) Sensitized TiO2 Nanoparticles for the Degradation of 4-Nitrophenol and Methyl Orange

A stable metalloporphyrin sensitized TiO₂ (Degussa P25) photocatalyst was prepared by using trans-dihydroxo[5,10,15,20-tetraphenylporphyrin]tin(IV) (SnP) as a sensitizer in a simple impregnation process. The solid diffuse reflectance ultraviolet-visible (UV-vis) spectrum of the SnP sensitized TiO₂ photocatalyst (SnP-TiO₂) indicated that there existed interaction between SnP and TiO₂. It was found that SnP-TiO₂ exhibited an enhanced visible light photocatalytic activity as compared with that over P25 for the degradation of 4-nitrophenol (4-NP) and methyl orange (MO) in aqueous solutions. The mechanism exploration showed that the degradation of MO and 4-NP experienced two different ways, that is, MO was photodegraded by reactive oxygen species and 4-NP was directly photodegraded by the excited state of SnP. Furthermore, it was found that the loading content of SnP had an important influence on the photocatalytic activity of TiO₂. The maximum photocatalytic efficiency was achieved when the contents of SnP were 25 mg and 30 mg per gram TiO₂ for MO and 4-NP, respectively. Importantly, SnP-TiO₂ was particularly stable and the photocatalytic activity was hardly decreased after being recycled seven times in the presence of oxygen, which could be attributed to the easy reductive regeneration of SnP.     

Photoelectrocatalytic degradation of ethylene by a combination of TiO2 and activated carbon felts

Postharvest loss of quality is an important problem in the food and horticultural product industry. One of the major factors contributing to loss of quality is the uncontrolled exposure of the products to small amounts of ethylene gas during storage. In this study we investigated the photoelectrocatalytic (PEC) degradation of ethylene gas at a temperature of 3 ± 1 °C and relative humidity of 90 ± 3% on an activated carbon felts (ACF)-supported photocatalyst titanium dioxide photoelectrode [TiO₂/ACF] or on a photoelectrode which had been modified by coating the ACF support with platinum [TiO₂/ACF-Pt]. The apparent pseudo-first-order kinetic model was used to describe the PEC degradation of ethylene. The key designing parameters for a PEC reactor affecting the degradation efficiency in terms of the rate constant of this model were studied, including the bias voltage and the light intensity. Degradation of ethylene by applying a bias voltage to the [TiO₂/ACF] |Nafion|[TiO₂/ACF] electrode-membrane assembly or to the [TiO₂/ACF-Pt] |Nafion|[TiO₂/ACF-Pt] electrode-membrane assembly enhanced the efficiency of photocatalytic (PC) degradation. The combination of the ACF support modified with platinum and the applied bias voltage were found to have an additive enhancement effect on the rate constant compared to PEC degradation carried out using the unmodified ACF support. With respect to the [TiO₂/ACF-Pt] |Nafion|[TiO₂/ACF-Pt] electrode-membrane assembly, a kinetic model was established using response surface methodology to describe the relationship between the rate constant and the affecting parameters. Optimized parameters were found to be a light intensity of 3.1 mW cm⁻² with a bias voltage of 47.5 V.     

钛基TiO2纳米管阵列电极的光电催化性能

应用电化学阳极氧化法在纯Ti基底上制备高度有序的TiO2纳米管阵列,考察了Ti/TiO2光阳极的光电化学响应.以苯酚溶液为目标污染物,研究Ti/TiO2电极的光电催化性能,并与光催化性能进行比较.结果表明,该电极光电催化性能优于光催化性能.施加0.6 V电压时,光电催化性能最好.电化学阻抗谱分析显示,光电催化和光催化降解过程的速控步骤均为表面反应步骤,外加偏压减小了界面电荷转移阻抗,提高了光生载流子的分离效率.     

Solvothermal preparation of copper(II) porphyrin-sensitized mesoporous TiO<Subscript>2</Subscript> composites: enhanced photocatalytic activity and stability in degradation of 4-nitrophenol

Four new copper(II) porphyrins CuPp(1, 2, 3, 4) with a different number of peripheral ester groups were synthesized and used to sensitize the mesoporous TiO₂ under solvothermal condition, and accordingly, four mesoporous CuPp(1, 2, 3, 4)/TiO₂ composites were obtained. These composites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, BET nitrogen adsorption–desorption isotherms (BET), UV–vis diffuse reflectance spectroscopy (UV–vis-DRS), and Fourier-transform infrared spectroscopy (FT-IR). The results showed the crystal structure and morphology of mesoporous TiO₂ were not affected by the porphyrin existence on its surface. The photocatalysis properties of mesoporous TiO₂ and CuPp(1, 2, 3, 4)/TiO₂ have been evaluated by conducting the photocatalytic degradation of 4-nitrophenol (4-NP) under visible-light irradiation, and the result showed their higher photocatalytic activities and the order is: CuPp(4)/TiO₂ > CuPp(3)/TiO₂ > CuPp(2)/TiO₂ > CuPp(1)/TiO₂ ? TiO₂. The probable reasons are their large surface area and different number of peripheral groups in CuPp, which separate electron–hole pairs efficiently. The repetition test of CuPp(1, 2, 3, 4)/TiO₂ composites demonstrated that they still maintained superior photocatalytic activity over six recycles.     

Assessment of operating parameters for photocatalytic degradation of a textile dye by Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/clinoptilolite nanocatalyst using Taguchi experimental design

In the current study, a nanophotocatalyst doped with of TiO₂ and Fe₂O₃ nanoparticles supported on Iranian clinoptilolite was synthesized and characterized by XRD, XRF, SEM, and EDX analyses. The results suggested the successful loading of TiO₂ and Fe₂O₃ nanoparticles onto the surface of clinoptilolite. The SEM images confirmed the average size of nanoparticles deposited on zeolite, which was about 20–40 nm. Furthermore, application of the synthesized photocatalyst in photocatalytic degradation of Acid Black 172 dye was studied using the Taguchi method and the chosen parameters were as follows: pH (2–7), dye concentration (50–200 mg/l), irradiation time (30–120 min), and catalyst dosage (0.5–1.5 g/l). The results indicate that dye concentration, pH, and irradiation time are respectively the most effective factors in these experiments while with the minimum dosage of the catalyst (0.5 g/l), up to 90 % removal efficiency could be achieved. The optimum value for each parameter was pH = 2, dye concentration = 50 mg/l, catalyst dosage = 1 g/l and irradiation time = 60 min, and the dye removal efficiency reached up to 100 % at these optimal conditions. Furthermore, after five-times recycling and reusing the catalyst, the efficiency of the photocatalytic degradation was reduced from 91.5 to 65.9 %, which is still an acceptable value.     

Degradation of 2-Nitrophenol by Dielectric Barrier Discharge System: The Influence of Carbon Doped TiO<Subscript>2</Subscript> Photocatalyst Supported on Stainless Steel Mesh

This study investigated the degradation of 2-nitrophenol (2-NP) in aqueous solution by dielectric barrier discharge (DBD) system alone and its combination with supported TiO₂ photocatalysts. The TiO₂ photocatalyst supported on a stainless steel mesh was synthesised using sol–gel solution of 8% polyacrylonitrile (PAN)/dimethylformamide/TiCl₄ followed by pyrolysis in the furnace under N₂ atmosphere at temperatures of 300, 350, or 400 °C for 3 h holding time. The supported catalysts were characterized for their morphologies, functional groups, crystallinity, surface areas and elemental chemical states by high resolution scanning electron microscope (HRSEM), Fourier transform infrared, X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, and X-ray photoelectron spectroscopy. The influence of solution pH on the degradation of 2-NP was investigated. The residual concentration of 2-NP and the intermediate compounds were quantified and identified using high-performance liquid chromatography coupled with mass spectrometry (HPLC–MS). The concentration of the dissolved ozone, hydrogen peroxide and hydroxyl radicals generated by the DBD in the presence or absence of a catalyst was monitored using ultraviolet–visible spectroscopy and photoluminescence spectroscopy. The HRSEM, HRTEM, XRD and BET analysis revealed that the optimal thermal conditions to obtain well supported uniformly grown, highly active crystalline TiO₂ catalysts with high specific surface area was 350 °C at a 3 h holding time in N₂ atmosphere with a flow rate of 20 mL/min. The supporting procedure simultaneously carbon doped the photocatalyst. The DBD system alone without catalysts successfully mineralised 58.6% of 2-NP within 60 min while combined DBD/supported TiO₂ nanocrystals achieved 77.5% mineralisation within the same treatment time. The increase in mineralisation rate was attributed to the existence of a synergistic effect between the DBD system and the supported catalysts. 2-NP degradation proceeded via hydroxylation, nitration and denitration using DBD alone and combined DBD/Supported TiO₂ photocatalyst. Catechol, hydroquinone, hydroxyl-1,4-benzoquinone, 2-nitrohydroquinone, and 2,4-dinitrophenol were identified as major intermediate products. The order of production of free reactive species by DBD alone and combined DBD with supported photocatalyst was OH° > H₂O₂ > O₃.The results showed that the combined system was more than effective than DBD alone for the degradation of the 2-NP in aqueous solution.     

Kinetics and mechanism of photocatalytic degradation of metobromuron by TiO2 in simulated sunlight

The kinetics of photocatalytic degradation of metobromuron in aqueous solution, with TiO₂ as photocatalyst under simulated sunlight irradiation, have been systematically investigated. The single-variable-at-a-time method and the central composite design based on response surface methodology were used to study the individual and synergistic effects of several classical conditions on the efficiency of photocatalysis. Three different conditions, TiO₂ concentration, pH, and initial concentration of metobromuron, were found to independently determine the efficiency of degradation. The optimum degradation conditions were: TiO₂ concentration 3.00 g/L, pH 7.88, and initial concentration of metobromuron 60.23 μM. In addition, a mechanism of degradation of metobromuron is tentatively proposed on the basis of the experimental results and theoretical calculation of frontier electron densities and point charges. The results suggest that substitution of the Br atom, addition of ·OH radicals, and the cleavage of urea side chain are the predominant degradation pathways during the initial stage of photocatalytic degradation.     

Photocatalytic degradation of triazine dyes over N-doped TiO2 in solar radiation

Photocatalytic degradation of the reactive triazine dyes Reactive Yellow 84 (RY 84), Reactive Red 120 (RR 120), and Reactive Blue 160 (RB 160) on anatase phase N-doped TiO₂ in the presence of natural sunlight has been carried out in this work. The effect of experimental parameters like initial pH and concentration of dye solution and dosage of the catalyst on photocatalytic degradation have also been investigated. Adsorption of dyes on N-doped TiO₂ was studied prior to photocatalytic studies. The studies show that the adsorption of dyes on N-doped TiO₂ was high at pH 3 and follows the Langmuir adsorption isotherm. The Langmuir monolayer adsorption capacity of dyes on N-doped TiO₂ was 39.5, 86.0, and 96.3 mg g^?1 for RY 84, RR 120, and RB 160, respectively. The photocatalytic degradation of the dyes follows pseudo first-order kinetics and the rate constant values are higher for N-doped TiO₂ when compared with that of undoped TiO₂. Moreover, the degradation of RY 84 on N-doped TiO₂ in sunlight was faster than the commercial Aeroxide^® P25. However, the P25 has shown higher photocatalytic activity for the other two dyes, RR 120 and RB 160. The COD of 50 mg l^?1 Reactive Yellow-84, RR 120 and RB 160 was reduced by 65.1, 73.1, and 69.6 %, respectively, upon irradiation of sunlight for 3 h in the presence of N-doped TiO₂. The photocatalyst shows low activity for the degradation of RY 84 dye, when its concentration was above 50 mg l^?1, due to the strong absorption of photons in the wavelength range 200–400 nm by the dye solution. LC–MS analysis shows the presence of some triazine compounds and formimidamide derivatives in the dye solutions after 3 h solar light irradiation in the presence of N-doped TiO₂.     

Electrochemically promoted photocatalytic oxidation of nitrite ion by using rutile form of TiO2/Ti electrode

The photocatalytic oxidation of nitrite ion in a NaCl aqueous solution using the rutile form of TiO₂/Ti as the working electrode was studied. Experimental results indicate that the rutile form of TiO₂/Ti film electrode has excellent photoactivity by applying a bias potential and irradiation simultaneously. The incident photo-to-current conversion efficiency (IPCE) of this working electrode is a function of the applying bias potential. The photocurrent efficiency of nitrite ion oxidation was 33–40% at a pH of about 7. The oxidation rate of the nitrite ion in brine wastewater using the rutile form of TiO₂/Ti electrode can be estimated by photocurrent measurements. The applying bias potential, light power and pH value were the major factors affecting the oxidation rate and the photocurrent efficiency of nitrite ion oxidation, while the concentrations of nitrite ion was minor.     

Enhancement of photoelectric catalytic activity of TiO2 film via Polyaniline hybridization

A Polyaniline (PANI)/TiO₂ film coated on titanium foil was successfully prepared using the sol-gel method followed by a facile chemisorption. Compared with pristine TiO₂, the photocatalytic (PC) and photoelectrocatalytic (PEC) degradation rates of 2,4-dichlorophenol (2,4-DCP) with the PANI/TiO₂ film were enhanced by 22.2% and 57.5%, respectively. 2,4-DCP can be mineralized more effectively in the presence of PANI/TiO₂ film. The best PEC degradation efficiency of 2,4-DCP with the PANI/TiO₂ film was acquired at an external potential of 1.5 V with a layer of 1 nm thick PANI. The PANI/TiO₂ film was characterized by Raman spectra, Fourier transform infrared spectra (FT-IR), Auger electron spectroscopy (AES), and electrochemical analysis. These results indicated that there was a chemical interaction on the interface of PANI and TiO₂. This interaction may be of significance to promote the migration efficiency of carriers and induce a synergetic effect to enhance the PC and PEC activities.     

A new acidic Ti sol impregnated kaolin photocatalyst: synthesis, characterization and visible light photocatalytic performance

In this study, a photocatalyst with visible light photocatalytic activity was obtained using raw materials, including commercial TiO₂, sulfuric acid, and calcined kaolin (CK). The photocatalyst was prepared via a dissolving/impregnating process, in which acidic Ti sol was obtained by initially dissolving TiO₂ particles in sulfuric acid, and then using the sol as impregnant for the CK. The prepared photocatalyst had wide spectral region and narrow band gap. In addition, the impregnation can create acid sites on the obtained composite surface and consequently improve the activity. A series of tests was performed to characterize the properties of the prepared samples. The visible light photocatalytic degradation of methyl orange (MO) in an aqueous solution was used as a probe reaction to evaluate the photocatalytic activities of the obtained samples. Under visible light irradiation, approximately 80 % of MO (with initial concentration of 20 mg/m³) was degraded in 3 h on the photocatalyst prepared by impregnating CK in acidic Ti sol, which was obtained using approximately 60 % H₂SO₄ solution followed by calcination at 400 °C. The acidity of the photocatalyst is the main factor that affects the catalytic activity of the photocatalytic degradation of MO.     

Sol–gel preparation and characterization of Ag and Mg co-doped nano TiO<Subscript>2</Subscript>: efficient photocatalytic degradation of C.I. Acid Red 27

In this study, we successfully prepared pure, mono-doped, and Ag, Mg co-doped TiO₂ nanoparticles using the sol–gel method, with titanium tetraisopropoxide as the Ti source. The prepared samples were characterized by X-ray powder diffraction (XRD), specific surface area and porosity (BET and BJH) measurement, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, photoluminescence, and energy dispersive X-ray spectroscopy techniques. The XRD data showed that the prepared nanoparticles had the same crystals structures as the pure TiO₂. Also, DRS results indicated that the band gap of co-doped photocatalyst was smaller than that of the monometallic and undoped TiO₂ and that there was a shift in the absorption band towards the visible light region. Furthermore, the photocatalytic activity of the prepared catalysts was evaluated by the degradation of C.I. Acid Red 27 in aqueous solution under visible light irradiation. The results showed that Ag (0.08 mol%), Mg (0.2 mol%) co-doped TiO₂ had the highest photoactivity among all samples under visible light. It was concluded that co-doping of the Ag and Mg can significantly improve the photocatalytic activity of the prepared photocatalysts, due to the efficient inhibition of the recombination of photogenerated electron–hole pairs. The optimum calcination temperature and time were 450 °C and 3 h, respectively.     

Photocatalytic Degradation of Styrene in Aqueous Solution: Central Composite Design Optimization

In this study, the response surface methodology was first applied to optimize the photocatalytic degradation of styrene in aqueous phase under UV/TiO₂ system. Twenty experiments were done by adjusting three parameters (styrene concentration, TiO₂ dose, and pH) at five levels. Optimal experimental conditions for arbitrary aqueous styrene concentration (115 mg L^?1) were found: initial pH 7 and TiO₂ loading 2 g L^?1 with photocatalytic degradation efficiency of 79.2%. Furthermore, the main degradation intermediate produced was identified by GC/MS. The total organic carbon results revealed that the photocatalysis process could be effectively mineralized. Kinetics of the photocatalytic reaction followed a pseudo-first-order model.     

High temperature stability and photocatalytic activity of nanocrystalline anatase powders with Zr and Si co-dopants

TiO₂ nanopowders doped by Si and Zr were prepared by sol–gel method. The effects of Si and Zr doping on the structural, optical, and photo-catalytic properties of titania nanopowders have been studied by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and UV–Vis absorption spectroscopy. XRD results suggest that adding impurities has a significant effect on anatase phase stability, crystallinity, and particle size of TiO₂. Titania rutile phase formation in ternary system (Ti–Si–Zr) was inhibited by Zr⁴⁺ and Si⁴⁺ co-doped TiO₂ in high temperatures (500–900 °C) and 36 mol% anatase composition is retained even after calcination at 1,000 °C. The photocatalyst activity was evaluated by photocatalytic degradation kinetics of aqueous methylen orange under visible radiation. The results show that the photocatalytic activity of the 20 %Si and 15 %Zr co-doped TiO₂ nanopowders have a larger degradation efficiency than pure TiO₂ under visible light.     

Construction of Er3+:YAlO3/RGO/TiO2 Hybrid Electrode with Enhanced Photoelectrocatalytic Performance in Methylene Blue Degradation Under Visible Light

Much attention has been paid on doping TiO₂ to narrow its band gap to promote the absorption of visible light and restrain the recombination of electron–hole pairs to improve its efficiency in photoelectrocatalysis (PEC) under visible‐light irradiation. However, the oxidation potential energy of photo‐induced holes for the modified catalysts by visible‐light excitation is lower than that without modification by UV excitation. In this work, we synthesized a co‐coupled TiO₂ electrode (denoted ERT) with the Er³⁺:YAlO₃ and reduced graphene oxide (RGO), achieving the synergetic effect of visible‐light‐to‐UV up‐conversion and response and great electron transfer ability. The effects of external bias voltage, electrolyte concentration and pH on the PEC activity were studied with the methylene blue (MB) as the target pollutant. The results indicated that PEC by the ERT electrode showed the highest MB removal compared with those by the electrodes coupled with RGO or Er³⁺:YAlO₃ alone. In addition, the kinetic rate constant of the PEC process using the ERT electrode was higher than the sum of those of the photocatalytic and electrocatalytic processes. The optimal conditions for PEC by the ERT electrode were an external bias voltage of 1.0 V, 0.1 mol L^?1 Na₂SO₄ and pH = 10.     

UV-assisted degradation of propiconazole in a TiO2 aqueous suspension: identification of transformation products and the reaction pathway using GC/MS

Photocatalytic degradation of propiconazole, a triazole pesticide, in the presence of titanium dioxide (TiO₂) under ultraviolet (UV) illumination was performed in a batch type photocatalytic reactor. A full factorial experimental design technique was used to study the main effects and the interaction effects between operational parameters in the photocatalytic degradation of propiconazole in a batch photo-reactor using the TiO₂ aqueous suspension. The effects of catalyst concentration (0.15–0.4 gL^?1), initial pH (3–9), initial concentration (5–35 mg L^?1) and light conditions were optimised at a reaction time duration of 90 min by keeping area/volume ratio constant at 0.919 cm² mL^?1. Photocatalytic oxidation of propiconazole showed 85% degradation and 76.57% mineralisation under UV light (365 nm/30 Wm^?2) at pH 6.5, initial concentration 25 mg L^?1 and constant temperature (25 ± 1 °C). The Langmuir–Hinshelwood kinetic model has successfully elucidated the effects of the initial concentration on the degradation of propiconazole and the data obtained are consistent with the available kinetic parameters. The photocatalytic transformation products of propiconazole were identified by using gas chromatography–mass spectrometry (GC/MS). The pathway of degradation obtained from mass spectral analysis shows the breakdown of transformation products into smaller hydrocarbons (m/z 28 and 39).     

Investigations on the Phase Transformation,Optical Characteristics,and Photocatalytic Activity of Synthesized Heterostructured Nanoporous Bi2O3–TiO2

Fine‐powdered, heterostructured, nanoporous Bi₂O₃–TiO₂ (BTO) was synthesized by a green approach using ultrasonication, with the mole ratio Bi/Ti of 1:1 and calcined at different temperatures. The physical and optical properties of the mixed oxides were investigated. The phase structure, as identified by X‐ray diffraction (XRD), showed the appearance of new phases as a function of the calcination temperature. Morphological examinations indicated the formation of a nanoporous structure with a drastic change in morphology at the calcination temperature of 850°C from a globule to a rod‐shaped structure, which further got transformed to a rocky appearance at 1200°C. Doping with Bi₂O₃ led to the lowering of the bandgap of TiO₂ from 3.25 to 2.5 eV. A BTO nanocatalyst calcined at 450°C exhibited promising photocatalytic activity for the degradation of quinalphos (QP) (92%) after a time interval of 100 min under visible light and at the optimum pH 8. The kinetics of degradation of QP showed that it follows a pseudo‐first‐order path with a rate constant 0.01267 min^?1. The synthesized BTO mixed oxide showed profound improvement in photocatalytic activity in the visible region as compared to TiO₂.     

Study on the Photodegradation of Salicylic Acid in Different Vehicles in the Absence and in the Presence of TiO2

In this work, the direct photolysis of salicylic acid, generally used as keratolytic agent in many dermatological products and as preservative in cosmetics, was investigated. The photodegradation of the acid under UVB irradiation was evaluated in different vehicles, such as water solutions at different pH, propylene glycol/water, and ethanol/water mixtures, sodium dodecyl sulphate solutions, and O/W emulsions prepared with Montanov 68 and Amphysol K as emulsifiers. The increase of pH enhanced the photodegradation of salicylic acid while the different vehicles protected the acid from the action of UVB radiations. However, the best protection was observed dissolving the acid in the lipid core of O/W emulsions, which probably removes the active from the polar environment that can promote the photolysis. The photocatalytic activity of TiO₂ on the degradation of salicylic acid also was evaluated. TiO₂ frequently is used as sunscreen in many cosmetic preparations. Salicylic acid and the pigment can be contained in the same solar formulation; hence, it can be interesting to study their interaction under UVB. TiO₂ enhanced the photodegradation of salicylic acid in all the media previously reported and its photocatalytic activity was influenced by the pH and by the components of the vehicles.