N-doped TiO2 Catalyst Research Articles

Effective sonophotocatalytic degradation of tetracycline in water: Optimization, kinetic modeling, and degradation pathways

Hybrid advanced oxidation processes (AOPs) are gaining interest in degradation of variety of recalcitrant compounds for water and wastewater treatment, due to possible synergistic effects. The present study systematically evaluated the degradation of tetracycline (TC) with a sonophotocatalytic process combining acoustic cavitation (sonocavitation) and photocatalysis based on N-doped TiO2 catalyst. The TC degradation rate constant was 2.4 × 10−2 min−1, i.e., much higher than individual sonocatalytic (0.5 × 10−2 min−1) and photocatalysis (0.6 × 10−2 min−1) processes at the optimized conditions. The synergy index was 2.14, which reveals a significant improvement in the process performance. Maximum TC degradations of 55.5 ± 1.8 % for photocatalysis, 66.4 ± 1.8 % for sonocatalysis, and 79.5 ± 0.3 % for sonophotocatalysis were observed for 10 mg L−1 initial TC concentration after 90 min of treatment. The photocatalytic experiments were extended further to 210 min to achieve a maximum degradation of 78.9 ± 0.2 % at the optimized condition. Scavenging experiments confirmed that hydroxyl radicals (•OH), electron holes (h+), and superoxide radical anions (O2−•) played a significant role in the degradation of TC. Further, the degradation intermediates for each process were identified and degradation pathways were proposed. Empirical kinetic models based on operational parameters were also developed and validated.

Enhanced formic acid electro-oxidation reaction over Ir,N-doped TiO2-supported Pt nanocatalyst

In this work, we prepared an Ir,N-doped TiO2 nanomaterial via a facile HNO3-assisted hydrothermal process that was used as an advanced support for nano-sized Pt nanoparticles (NPs) for the formic acid oxidation reaction (FAOR). The physical and electrochemical behaviours of the as-made Pt/Ir,N-doped TiO2 catalyst were systemically investigated through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscopes coupled with energy dispersive X-ray analysis (FE-SEM/EDX mapping), transmission electron microscopy (TEM), linear sweep voltammetry (LSV), Tafel slope, CO-stripping, and chronoamperometric (CA) test. The Pt NPs (ca. 3 nm) were anchored on the Ir,N-doped TiO2 support, being formed by a mixture of rutile and brookite with a particle size of several ten nanometers. Due to the small size and uniform distribution of Pt NPs, the Pt/Ir,N-doped TiO2 catalyst had an electrochemical surface area of 79.88 m2 g−1, which was greater than that of the commercial Pt/C (77.63 m2 g−1). In terms of the FAOR, the Pt/Ir,N-doped TiO2 catalyst showed a negative FAOR onset potential, high current density (11.85 mA cm−2), and superior CO-tolerance compared to the commercially available catalyst. Also, the as-made catalyst possessed high electrochemical durability after 3600 s for testing. The enhanced FAOR efficiency was assigned to the formation of a dual-doping effect and strong interplay between Pt and TiO2-based support, which not only improved the electron transfer but also weakened the adsorption of carbonaceous species, thereby boosting the reaction kinetics. This study could open up a facile but effective strategy to promote particular electrochemical applications.

Ultrasound-Assisted Synthesis of a N-TiO2/Fe3O4@ZnO Complex and Its Catalytic Application for Desulfurization

Ultrasound (US)-assisted synthesis of a N-doped TiO2 catalyst supported on magnetically separable Fe3O4@ZnO particles and its subsequent application for catalytic desulfurization were performed in the present work. The catalyst was also synthesized conventionally to compare the role of acoustic cavitation (US horn working at 20 kHz frequency) in improving the catalyst characteristics. The effects of different ultrasonic (US) power (80 W to 120 W) and duration (15 min to 75 min) were studied to elucidate the best operating conditions for obtaining the minimum particle size of the catalyst. Under optimal conditions of 80 W power and 30 min of time, a minimum particle size of 31.22 μm was obtained. The particle size for the conventionally synthesized catalyst was 806.4 µm, confirming that the particles were agglomerated in the absence of ultrasound. The synthesized catalyst was used for the desulfurization of thiophene to assess the performance of the catalyst, along with a comparative study between the conventionally synthesized catalyst and that obtained using the US-assisted approach. It was evident that the performance of the catalyst synthesized sonochemically was superior, as US enhanced the activity of the catalyst by reducing the particle size and achieving homogeneity. The desulfurization achieved using the sonochemically synthesized catalyst was 47% in 100 min at a 2 g/L catalyst dose and a 3 mL/L H2O2 dose. The desulfurization was only 25% using the conventionally synthesized catalysts under the same operating conditions. Overall, the present work demonstrates the advantages of US in improving the catalyst characteristics, as well as the successful application of catalyst in desulfurization.

Synthesis, Properties and Application of Titanium Dioxide Doped with Nitrogen. Its Effectiveness on Photo Degradation Glutathione-S-Transferase (GST) enzymes Pupae Instar of Aedes aegypti

The sol-gel method was used to create N-doped TiO2. From the characterization results, it was found that N-doped TiO2 using Titanium(IV) ammonia solution and calcination tetraisopropoxide 600 K provided the most appropriate properties for acting as the photo catalyst can be use as inhibitor of GST. SEM, AFM and XRD results indicated that this N-doped TiO2 catalyst had high crystallinity because its titania precursor was simply hydrolyzed completely so no organic contents blocked initial phase construction. SEM and AFM results demonstrated that its surface morphology was spherical like fluffy powders. Moreover, with increasing calcination temperature, its anatase-to-rutile phase transformation was retarded by the incorporated nitrogen. Elemental Analysis and UV-Vis/DR results also suggested that nitrogen could be dormant in the TiO2 lattice with strong bonds, causing the effect on the band gap structure by adding energy states nearly valence band of TiO2. All of these properties enhanced the photocatalytic activity of N-doped TiO2 under visible light. Regarding the photocatalytic activity, N-doped TiO2 with ammonia solution of titanium(IV), calcinated 600 K Tetraisopropoxide succeeded in degrading glutathione-S-transferase (GST) enzymes, with the highest efficiency. However, its photocatalytic activity was drastically decreased when it was calcined at higher temperature. Additionally, the plausible mechanism was also proposed in case of photo degradation of antioxidant content based on two detected intermediates by The association between ln Co/C and photo degradation period (h).

Photocatalytic degradation of flumequine by N-doped TiO2 catalysts under simulated sunlight

Flumequine (FLU) is one of the most used fluoroquinolone antibiotics in intensive aquaculture, however, it has become a typical pollutant in water environment at present due to inappropriate use. Therefore, it is necessary to develop facile techniques for efficient degradation of FLU. In this work, three N-doped TiO2 photocatalysts were synthesized for degradation of FLU. The obtained photocatalysts were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectrum and UV-Vis diffuse reflection spectra (UV-Vis-DRS). The XRD and XPS results from NH4NO3-doped catalyst (TiO2/AN) confirmed that NO3<sup>-</sup> ions were successfully incorporated into the lattice of TiO2. The TiO2/AN sample exhibited higher photocatalytic performance than other N-doped catalysts under simulated sunlight irradiation, and 100% removal efficiency of FLU was achieved after 4 hours of illumination. The photogenerated holes (h<sup>+</sup>) and hydroxyl radicals (<sup>•</sup>OH) are main reactive species involved in the photocatalytic degradation of FLU. Eight intermediates for photocatalytic degradation of FLU were detected and their toxicities to aquatic organisms were predicted. This study might have important implications for further research on the removal of fluoroquinolone antibiotics in wastewater.

Degradation of Phenol By Photolysis Using N-doped TiO2 Catalyst

Phenol (C6H5OH) is a common contaminant in wastewater. In certain concentrations, phenol can inhibit the activity of microorganisms and give adverse effects tohumanhealth, such as liver and kidney damage, perfect heart rate, and lower blood pressure. In this study, phenol was degraded with andwithoutN-doped TiO2under photolysis UV-light (10 Watts, λ = 365 nm) and visible-light (13 watt Philips, lux= 1400, λ = 465-640 nm)irradiation. The reductionof phenol concentrationwas measured by a UV-Vis spectrophotometer at a wavelength 200-400 nm. Some parameters such as catalyst dose, irradiation timesand type of light sources were studied. The XRD and DRS UV-Vis characterization confirmthat the nitrogen modified of titania catalyst potentially actives in visible-light. The N-doped TiO2is able to catalyze and improve the efficiency of phenol degradation in photocatalysissystem. Phenol with initialconcentration 8 mg/L was degraded by 33.89% and 30.51% without catalyst and increased to be 90.8% and 67.80%by additionof 15 mg N-doped TiO2catalyst under UV-light and visible-lightfor 210 minutes photolysis, respectively. From the results,irradiation using UV-light achieveshigherefficiency than visible-lightonphenol degradation.

Photocatalytic degradation of Direct Yellow-27 by photolysis with UV-light and solar irradiation Using N-doped TiO2

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Novel one-step synthesis of nitrogen-doped TiO2 by flame aerosol technique for visible-light photocatalysis: Effect of synthesis parameters and secondary nitrogen (N) source

For the first time, nitrogen-doped TiO2 was successfully synthesized by a novel single-step flame spray pyrolysis (FSP) method. Our X-ray photoelectron spectroscopy results illustrate that the nitrogen was effectively doped into the crystal structure of TiO2 in our as-synthesized N-TiO2 catalysts predominantly in the form of interstitial nitrogen (Ti–O−N) rather than substitutional nitrogen (Ti–N). The shift of the (1 0 1) plane anatase diffraction peaks to lower angles in our N-doped TiO2 catalysts compared to pristine TiO2 revealed the distortion and strain in the crystal structure instigated by the incorporation of the nitrogen atoms. The growth or expansion of crystal lattice can be attributed to the larger atomic radius of respective nitrogen atoms (r = 1.71 Å) compared to oxygen (r = 1.40 Å). Our single-step rapid aerosol synthesis method directs the nitrogen atoms mainly occupy interstitial positions in TiO2 lattice. The increase in the primary nitrogen content does not impact the bandgap energies (from 2.54 eV to 2.53 eV), whereas increase in the secondary source monotonically decreased (from 2.95 eV to 2.47 eV) the bandgap energies. This observed lowering of the band-gap energy for the flame made N-doped TiO2 materials implies that the nitrogen doping in TiO2 by aerosol method is highly effective in extending the optical response of TiO2 in the visible region. The nitrogen atoms incorporation into the crystal structure of titania alters the electronic band structure of TiO2, resulting to a new mid-gap energy state N 2p band formed above O 2p valance band. This occurrence narrows the band gap of TiO2 (from 3.07 to ∼2.47 eV) in our N-doped TiO2 and shifts the optical absorption to the visible region.

Single-step rapid aerosol synthesis of N-doped TiO2 for enhanced visible light photocatalytic activity

For the first time, nitrogen-doped TiO2 was successfully synthesized by a novel single-step flame aerosol method. Our XPS and EDX results illustrate that the nitrogen was effectively doped into the crystal lattice of TiO2 in our as-synthesized N-TiO2 catalysts predominantly in the form of interstitial nitrogen (Ti−O−N) rather than substitutional nitrogen (Ti−N). The shift of the (101) plane anatase diffraction peaks to lower angles in our N-doped TiO2 catalysts compared to pristine TiO2 revealed the distortion and strain in the crystal lattice instigated by the incorporation of the nitrogen atoms. The growth or expansion of crystal lattice can be attributed to the larger atomic radius of respective nitrogen atoms (r = 1.71 Å) compared to oxygen (r = 1.40 Å). Our single-step rapid aerosol synthesis method directs the nitrogen atoms mainly occupy interstitial positions in TiO2 lattice. This occurrence narrows the band gap of TiO2 (from 3.12 to ~2.51 eV) in our N-doped TiO2. The lowering of band-gap energy for our flame-made N-doped TiO2 materials indicates that the nitrogen doping in TiO2 by aerosol method is highly effective in achieving a red-shift on adsorption to potentially make use of the energy of visible light. The presence of high amount interstitial nitrogen would modify the band structure and suppress the recombination efficiency of the photogenerated electron–hole pairs, resulting in enriched photocatalytic ability of TiO2 under solar environment or visible irradiation. The incorporation of nitrogen atoms into the lattice structure of TiO2 modifies the electronic band structure of titania, which leads to a new mid-gap energy state N 2p band formed above O 2p valance band. The photocatalytic degradation of phenol as a probe reaction was used to evaluate the photocatalytic properties of the as-synthesized N-doped materials under visible light.

Direct Synthesis of Urchin-Like N-doped TiO2 Microstructures with Enhanced Photocatalytic Properties

ABSTRACTN-doped urchin-like TiO2 (NUT) with enhanced photocatalytic properties was prepared through a surfactant-free solvothermal treatment approach using carbamide as nitrogen precursor. The prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and UV-Vis diffuse reflectance spectroscopy. Effects of different carbamide contents on the crystal phase and the photocatalytic performance of the prepared samples were discussed. XPS results showed that N doping into TiO2 formed Ti-N-O structure. SEM results showed the change of morphology after superfluous doping. N doping can form a new impurity energy level in TiO2 forbidden band and provide a favourable nucleation for TiO2 catalyst. In addition, 0.1 M NUT showed the highest photocatalytic activity among all the prepared samples upon degradation of rhodamine B under sunlight irradiation. The mechanism of organic pollutants degradation on the surface of prepared phtocatalytic was also discussed. N-doped TiO2 catalysts showed enhanced photocatalytic properties than the pure TiO2 materials which could be attributed to the synergistic effect of the special superstructure and lower energy requirement for electron transport due to N doping in the TiO2 catalyst.

Kinetics of photodegradation of alizarin green in an acoustic fluidized bed using TiO2 catalyst

The kinetics of photodegradation of alizarin green (AG) in an acoustic fluidized bed was investigated using Degussa P25 catalyst and N-doped TiO2 catalyst, respectively. The effects of initial concentration of AG, catalyst amount, initial pH value and liquid flow rate on the photodegradation rates were the main goal of present study. The degradation rate increased with increasing amount of photocatalyst, pH value and liquid flow rate, reached a maximum and then decreased. The degradation rate decreased with increasing initial concentration. According to the Langmuir–Hinshelwood model, the disappearance of the AG followed pseudo-first-order kinetics. Experimental results showed that AG can be degraded effectively by Degussa P25 catalyst and N-doped TiO2 catalyst in an acoustic fluidized bed reactor. N-doped TiO2 catalyst has high and significant photocatalytic activity and in comparison with Degussa P25 catalyst was photocatalyst.

Facile template-free one-pot fabrication of TiO2@C microspheres with high visible-light photocatalytic degradation activity

TiO2@C microspheres were fabricated through facile template-free one-pot hydrothermal reaction, in which ferrocene was first simultaneously used as carbon source and structure directing agent. The composite obtained have been characterized by X-ray powder diffraction, field emission scanning electron microscopy, diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and nitrogen adsorption–desorption isotherms. The results show that the peripheries of the microspheres are stacked by several TiO2 particles. The band gap energy the as-prepared sample is estimated to be 2.26eV. All carbon species in the composite are modified on the surface of the photocatalyst. The as-prepared TiO2@C microspheres exhibited higher visible-light photocatalytic activity for the degradation of organic pollutants (Congo red and 4-nitrophenol) than that of N-doped TiO2 catalyst. The •OH radicals formed in the process of photocatalytic degradation were also detected through fluorescence technique.

Enhanced H2 production activity under solar irradiation over N-doped TiO2 prepared using pyridine as a precursor: a typical sample of N-doped TiO2 series

A series of N-doped TiO2 photocatalysts were synthesized by simple hydrolysis method using titanium isopropoxide and pyridine precusors. XRD studies of all the catalysts showed a single anatase phase and TEM results confirmed that the particles obtained by this procedure are of nano size and in the range of 3–5 nm. UV–vis DRS of N-doped TiO2 catalysts clearly show an enhanced absorption in the visible light region, and the band gaps are seen decreasing as the content of doped nitrogen increases. The formation of oxynitride linkages is evidenced by the FTIR results. Further the XPS analysis confirms the presence of Ti-O-N linkage, and the binding energy values indicate that the doped nitrogen is either interstitial or chemisorbed. The photocatalytic activity of N-doped TiO2 catalysts is evaluated for hydrogen production in methanol: water mixture under solar light irradiation and 0.5 wt% N-doped TiO2 has shown a stable and high activity, 3500 μ mol/h/g.cat. The enhanced hydrogen production activity of N-doped TiO2 catalysts is attributed to the high surface area of the catalysts containing doped nitrogen mostly at the interstitial positions and enhanced visible light absorption.

Kinetics of ethyl paraben degradation by simulated solar radiation in the presence of N-doped TiO2 catalysts

Ethyl paraben (EP), an emerging micro-pollutant representative of the parabens family, has been subject to photocatalytic degradation under simulated solar radiation at a photon flux of 1.3·10−4 E/(m2 s). Six nitrogen-doped titania catalysts synthesized by annealing a sol–gel derived TiO2 powder under ammonia flow and their un-doped counterparts, calcined in air at different temperatures in the range 450–800 °C, were compared under solar and visible light and the most active one (N-doped TiO2 calcined at 600 °C) was used for further tests.Experiments were performed at EP concentrations between 150 and 900 μg/L, catalyst loadings between 100 and 1000 mg/L, pH between 3 and 9, different matrices (ultrapure water, water spiked with humic acids or bicarbonates, drinking water and secondary treated wastewater) and hydrogen peroxide between 10 and 100 mg/L. For EP concentrations up to 300 μg/L, the degradation rate can be approached by first order kinetics but then shifts to lower order as the concentration increases. The rate increases linearly with catalyst loading up to 750 mg/L and hydrogen peroxide up to 100 mg/L. Near-neutral (pH = 6.5–7.5) and alkaline conditions (pH = 9) do not affect degradation, which is reduced at acidic pH. The presence of humic acids at 10–20 mg/L impedes degradation due to the competition with EP for the oxidizing species and this is more pronounced in actual wastewater matrices.UPLC-ESI-HRMS and HPLC-DAD were employed to follow EP concentration changes, as well as identify and quantify transformation by-products during the early stages of the reaction. Five such products were successfully detected and, based on their concentration–time profiles, a reaction network for the degradation of EP is proposed. Hydroxyl radical reactions appear to prevail during the initial steps as evidenced by the rapid formation of hydroxylated and dealkylated intermediates.

A systematic study on visible-light N-doped TiO2 photocatalyst obtained from ethylenediamine by sol–gel method

N-doped titania is prepared using ethylenediamine as the nitrogen source by a sol–gel method. The preparation conditions, such as the volume ratio of ethylenediamine to sol, and the heat temperature on the nitrogen doping are systematically examined. UV results indicate the N-doped TiO2 catalysts have enhanced absorption in the visible light region, and exhibit high activities on the visible light photocatalytic reactions to the hydrogen production and methyl orange degradation. X-ray diffraction (XRD) and FT-IR results reveal that N species have been incorporated into the TiO2 lattice at a high N-doping level. N-doped titania prepared with an ethylenediamine to sol volume ratio of 1:1 and sintering temperature of 500°C performed the highest hydrogen production rate (2.98mmolg−1h−1) and best methyl orange degradation performance. A conceivable structure change of N-doped TiO2 sintered at different temperature was proposed.

Photocatalytic degradation of p,p′-DDT under UV and visible light using interstitial N-doped TiO2

1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (or p,p′-DDT) is one of the most persistent pesticides. It is resistant to breakdown in nature and cause the water contamination problem. In this work, a major objective was to demonstrate the application of N-doped TiO2 in degradation and mineralization of the p,p′-DDT under UV and visible light in aqueous solution. The N-doped TiO2 nanopowders were prepared by a simple modified sol–gel procedure using diethanolamine (DEA) as a nitrogen source. The catalyst characteristics were investigated using XRD, SEM, TEM, and XPS. The adsorption and photocatalytic oxidation of p,p′-DDT using the synthesized N-doped TiO2 under UV and visible light were conducted in a batch photocatalytic experiment. The kinetics and p,p′-DDT degradation performance of the N-doped TiO2 were evaluated. Results show that the N-doped TiO2 can degrade p,p′-DDT effectively under both UV and visible lights. The rate constant of the p,p′-DDT degradation under UV light was only 0.0121 min−1, whereas the rate constant of the p,p′-DDT degradation under visible light was 0.1282 min−1. Under visible light, the 100% degradation of p,p′-DDT were obtained from N-doped TiO2 catalyst. The reaction rate of p,p′-DDT degradation using N-doped TiO2 under visible light was sixfold higher than that under UV light. According to Langmuir-Hinshelwood model, the adsorption equilibrium constant (K) for the N-doped TiO2 under visible light was 0.03078 L mg−1, and the apparent reaction rate constant (k) was 1.3941 mg L−1-min. Major intermediates detected during the p,p′-DDT degradation were p,p′-DDE, o,p′-DDE, p,p′-DDD and p,p′-DDD. Results from this work can be applied further for the breakdown of p,p′-DDT molecule in the real contaminated water using this technology.

Role of chlorophyll in Spirulina on photocatalytic activity of CO2 reduction under visible light over modified N-doped TiO2 photocatalysts

The combination of TiO2 nanoparticles and chlorophyll molecules is promising to provide potential new composite materials for improving photocatalytic CO2 reduction by merging the ability and features of both material types. In this research, the visible light reactive N-doped TiO2 (N–TiO2) catalysts were synthesized using a simple sol–gel method, and chlorophyll in Spirulina was consequently loaded onto the N-doped TiO2 catalysts (Sp/N–TiO2) in an attempt to enhance the photocatalytic efficiency. The effects of nitrogen and chlorophyll in Spirulina, and their loading amount on CO2 photoreduction with water under visible light of Sp/N–TiO2 catalysts were investigated. The activities of catalysts were in the order undoped TiO2<N–TiO2<Sp/N–TiO2. The addition of Spirulina was found to significantly improve the photocatalytic stability and C2+ (C2H4 and C2H6) product selectivity. The 0.5Sp/10N–TiO2 catalyst exhibited approximately 21.3 times and 1.9 times higher total production yield compared with undoped TiO2 and 10N–TiO2, respectively. This outstanding photocatalytic activity could be attributed to the enhancement in visible light harvesting, the surface oxygen vacancies (VO) facilitating reactants adsorption and dissociation, and the synergistic effect between N–TiO2 and chlorophyll in Spirulina.

Important role of surface fluoride in nitrogen-doped TiO2 nanoparticles with visible light photocatalytic activity.

Nitrogen-doped TiO2 nanoparticles have been synthesized using sol-gel methods and subsequently fluorinated at room temperature by aging in acidic solutions of NaF. The nanoparticles were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, UV-vis, and IR diffuse reflectance spectroscopy. After aging at room temperature in NaF solutions, the Ti-OH groups on the surface of the TiO2 nanoparticles were replaced by Ti-F bonds, which resulted in a decrease of the point of zero charge from pH 5.4 to 2.8. Most importantly, the nitrogen dopants were retained after the fluorination process, and the amorphous nanoparticles were partially converted into the anatase phase. Annealing the photocatalysts resulted in a decrease of both the nitrogen and fluoride atomic concentration. Diffuse reflectance spectra show an increase in absorbance above 400 nm after annealing the F,N-doped TiO2, which suggests the formation of color centers. The photoactivity of the F,N-doped and N-doped TiO2 catalysts were evaluated by monitoring by the decolorization of methylene blue with visible light. Mass spectrometric analysis revealed that methylene blue undergoes successive demethylation, and more importantly, the rate of decolorization depends on the fluoride concentration. These results show the importance of a two-step synthesis method to independently control the nitrogen and fluoride concentration.

Effect of oxygen, moisture, and temperature on the photo oxidation of ethylene on N-doped TiO2 catalyst

N-doped TiO2 catalyst synthesized by a sol–gel method was used for the photocatalytic oxidation of ethylene under visible-light illumination. Key parameters affecting the oxidation rate including feed composition (ethylene, oxygen, and water vapor), visible-light intensity, and reaction temperature were investigated. Results revealed that the reactivity of ethylene was greatly enhanced by increasing temperatures, light intensity, ethylene, and oxygen concentration. Feed ethylene concentrations ranging from 100 to 900ppmv were stoichiometrically oxidized to CO2 under all experimental conditions. The positive effect of ethylene oxidation at higher temperature can be ascribed to unfavorable adsorption of water on catalysts and an increase in the heterogeneous catalytic reactions. The presence of water vapor exhibited both inhibiting and activating capabilities on the photocatalytic oxidation reactions of ethylene. A Langmuir–Hinshelwood (L–H) expression displaying an explicit temperature dependence was proposed to simulate the entire set of rate data, i.e., r=Iαk′exp-EaRTKe′exp-ΔHe/RTTCe1+Ke′exp-ΔHe/RTTCe+Kw′exp-ΔHw/RTTCwKo2′exp-ΔHo2/RTTCO21+KO2′exp-ΔHo2/RTTCO2. Based on the L–H model, the adsorption enthalpy of ethylene, water vapor, and oxygen on N-doped TiO2 catalyst were −2.61, −12.09, and −3.81kcalmol−1, respectively.

Photodegradation of benzene, toluene and xylenes under visible light applying N-doped mixed TiO2 and ZnO catalysts

N-doped TiO2/ZnO catalysts were prepared by sol–gel technique and calcined at 380 and 500°C. Its photocatalytic activity was evaluated in the photodegradation of benzene, toluene and xylenes (BTX) under visible-LED light and compared with the undoped TiO2/ZnO activity. The amount of doped nitrogen was found to be 0.64at%. Concentrations of BTX were analysed by gas chromatography applying the headspace technique. The NTiO2/ZnO catalyst calcined at 500°C led to reductions of benzene, toluene and xylenes concentrations greater than 80wt% after 120min of irradiation. The photocatalytic reactions followed the first order kinetics.