Nitrogen-doped titanium dioxide photocatalysts for visible response prepared by using organic compounds

In order to utilize visible light in photocatalytic reactions, nitrogen atoms were doped in commercially available photocatalytic TiO₂ powders by using an organic compound such as urea and guanidine. Analysis by X-ray photoelectron spectroscopy (XPS) indicated that N atoms were incorporated into two different sites of the bulk phase of TiO₂. A significant shift of the absorption edge to a lower energy and a higher absorption in the visible light region were observed. These N-doped TiO₂ powders exhibited photocatalytic activity for the decomposition of 2-propanol in aqueous solution under visible light irradiation. The photocatalytic activity increased with the decrease of doped N atoms in O site, while decreased with decrease of the other sites. Degradation of photocatalytic activity based on the release of nitrogen atoms was observed for the reaction in the aqueous suspension system.     

Modification of nano-TiO2 by doping with nitrogen and fluorine and study acetaldehyde removal under visible light irradiation

P25–TiO₂ nanoparticles were doped with fluorine, nitrogen, and their combination. Samples of N-doped, F-doped, and N–F-codoped TiO₂ were prepared by physical and chemical treatments. The products were characterized by X-ray diffraction, Fourier transform infrared, Brunauer–Emmett–Teller technique, and ultraviolet–visible diffuse reflectance spectroscopy. It was revealed that absorption spectra of N-doped, F-doped, and F–N-codoped TiO₂ were extended to the visible region wavelengths, and the photocatalytic experiments showed enhancement of acetaldehyde removal under visible light irradiation. The photocatalytic activity of the powders was evaluated through the process of acetaldehyde degradation under visible light scattering in a continuous stirred tank reactor. F–N-codoped nano-TiO₂ calcinated at 500 °C possessed the highest photocatalytic activity. The photocatalytic kinetic consumption of acetaldehyde was studied on N–F–TiO₂ powders under 80 W Hg lamp irradiation, and a Langmuir-type kinetic model was developed for the reaction with appropriate kinetic parameters.     

Preparation,characterization and photocatalytic activity of TiO2 codoped with yttrium and nitrogen

Nanocrystalline photocatalysts of TiO₂ codoped with yttrium and nitrogen were prepared by the sol–gel method and investigated by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), the Brunauer–Emmett–Teller (BET) surface area measurement, X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), respectively. Slight red-shifts of the Raman peak at 144 cm^?1 were observed in the doped samples after the incorporation of Y³⁺ and N^3? into the lattice of TiO₂. The N doping caused the improvement of visible light absorption because of the formation of the N 2p states isolated above the valence band maximum of TiO₂. Whereas, the absorption property of the pure or N doped TiO₂ was depressed after the introduction of Y. The photocatalytic activities of the samples were evaluated by monitoring the degradation of methylene blue (MB) solution. The codoped sample with N and 0.05 at.% Y exhibited an enhanced photocatalytic efficiency. It is suggested that the charge trapping due to the Y doping and the visible light response due to the N doping are responsible for the enhanced photocatalytic performance in this sample. However, the photocatalytic activity of the codoped TiO₂ was suppressed step by step as the Y doping level increased, which could be attributed to the formation of photogenerated charge carriers recombination centers at the Y substituting sites.     

Mn-doped TiO2 nanopowders with remarkable visible light photocatalytic activity

TiO₂ nanocrystalline powders with various Mn-doping levels were synthesized by the sol-gel process using tetrabutyl titanate and manganese nitrate as precursors. The crystal structure, morphology, doping concentration, optical absorption property, and elemental state of the obtained samples were analyzed. TEM results showed that the synthesized TiO₂ powders were anatase nanoparticles about 7 nm in size. EDX and XPS analyses proved the incorporation of Mn ions into the TiO₂ lattice. A remarkable red shift of the absorption edge was achievable by increased Mn content, leading to gigantically narrowed energy gap to permit absorption well into the infrared spectral region. The dramatic optical absorbance of the doped TiO₂ nanopowders in the visible spectral region led to strong photocatalytic activity under visible light illumination, which was observed by measuring the degradation of methylene blue. In contrast, little degradation was observed for the pure TiO₂ powder. The optimum Mn/Ti ratio was observed to be 0.2 at.% for photocatalytic applications.     

Visible-light-active silver- , vanadium-codoped TiO<Subscript>2</Subscript> with improved photocatalytic activity

Optimized doped TiO₂ is necessary for efficient visible light harvesting and widening the applications spectrum of TiO₂-based materials. Titanium dioxide doped with silver and/or vanadium has been synthesized by one-pot hydrothermal method without post-calcination. Codoping induced visible light absorption while maintaining the photoactive anatase phase along with good crystallinity. Synthesized products are in nanometer range and possess high specific surface area. Having nearly spherical morphology, the particles are distributed and the particle size estimated from TEM observation is in accordance with the XRD results. Spectroscopic investigations reveal that the doped atoms successfully entered the TiO₂ lattice modifying the band structure. The narrowed band gap allows visible light photons for absorption, and the codoped samples displayed enhanced visible light absorption among the synthesized samples. Photodegradation performance evaluated under visible light irradiations showed that silver- , vanadium-codoped TiO₂ have the best visible light photocatalytic activity attributed to stable configuration, high visible light absorption, coupling between silver and vanadium and their optimal doping concentration.     

Photocatalytic activity of nitrogen doped rutile TiO2 nanoparticles under visible light irradiation

This work provides the design and synthesis of nitrogen doped rutile TiO₂ nanoparticles working as efficient photocatalysts under visible light irradiation. Nitrogen doped rutile TiO₂ nanoparticles are synthesized through the surface nitridation of rutile nanoparticles, which have been prepared in advance. The experimental results show that the nitrogen element is easily doped into the lattice of TiO₂ nanoparticles and its doping amount increases with the decrease of nanocrystallite size. The photocatalytic activity of the nanoparticles under visible light irradiation is correlated not only with the amount of doped nitrogen element but also with the morphology and crystallinity of nanoparticles.     

(N, F)-codoped TiO2 Nanocrystals as Visible Light-activated Photocatalyst

(N, F)-codoped anatase TiO₂ nanocrystals with active visible light response were prepared by using a simple sol-gel approach. X-ray photoelectron spectroscopy measurements suggested that the substitutional N and F species replaced the lattice oxygen atoms in TiO₂ nanocrystals. Such nanocrystals showed strong absorption from 400 to 550 nm, which was mainly induced by nitrogen doping. The phase transformation from anatase to rutile was hindered by fluorine doping at high calcination temperatures, which was verified by XRD patterns. The N2 adsorption-desorption isotherms revealed the absence of mesopores in these nanocrystals. The (N, F)- codoped TiO₂ nanocrystals showed satisfying photocatalytic activity on the photo-degradation of methylene blue under visible light.     

Photocatalytic activity of pulsed laser deposited TiO2 thin films in N2, O2 and CH4

We report on pulsed laser deposition of TiO₂ films on glass substrates in oxygen, methane, nitrogen and mixture of oxygen and nitrogen atmosphere. The nitrogen incorporation into TiO₂ lattice was successfully achieved, as demonstrated by optical absorption and XPS measurements. The absorption edge of the N-doped TiO₂ films was red-shifted up to ∼ 480 nm from 360 nm in case of undoped ones.The photocatalytic activity of TiO₂ films was investigated during toxic Cr(VI) ions photoreduction to Cr(III) state in aqueous media under irradiation with visible and UV light. Under visible light irradiation, TiO₂ films deposited in nitrogen atmosphere showed the highest photocatalytic activity, whereas by UV light exposure the best results were obtained for the TiO₂ structures deposited in pure methane and oxygen atmosphere.     

Preparation of nitrogen co-doped SiO2/TiO2 thin films on ceramic with enhanced photocatalytic activity under visible-light irradiation

In this study, we have successfully deposited N-doped SiO₂/TiO₂ thin films on ceramic tile substrates by sol–gel method for auto cleaning purpose. After dip coating and annealing process the film was transparent, smooth and had a strong adhesion on the ceramic tile surface. The synthesised catalysts were then characterised by using several analytical techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscope (AFM) and UV-vis absorption spectroscopy (UV-vis). The analytical results revealed that the optical response of the synthesised N-doped SiO₂/TiO₂ thin films was shifted from the ultraviolet to the visible light region. The nitrogen substituted some of the lattice oxygen atoms. The surface area of co-doped catalyst increased, and its photocatalytic efficiency was enhanced. The photocatalytic tests indicated that nitrogen co-doped SiO₂/TiO₂ thin films demonstrated higher than of the SiO₂/TiO₂ activity in decolouring of methylene blue under visible light. The enhanced photocatalytic activity was attributed to an increasing of the surface area and a forming of more hydroxyl groups in the doped catalyst.     

Enhanced H2 Generation of Au‐Loaded,Nitrogen‐Doped TiO2 Hierarchical Nanostructures under Visible Light

Hierarchical N‐doped TiO₂ nanostructured catalysts with micro‐, meso‐, and macroporosity are synthesized by a facile self‐formation route using ammonia and titanium isopropoxide precursor. UV–vis diffuse reflectance spectra confirm the red shift and band gap narrowing due to the doping of N species in the TiO₂ nanoporous catalyst. Hierarchical macroporosity with fibrous channel patterning is observed and well preserved even after calcination at 800 °C, indicating thermal stability, whereas micro‐ and mesoporosity are lost after calcination at 500 °C. The photocatalytic activity of hiearchical N doped TiO₂ catalysts loaded with Au is evaluated for H₂ production reaction in visible light. The enhanced photocatalytic activity is attributed to the combined synergetic effect of N doping for visible light absorption, micro‐ and mesoporosity for an increase of effective surface area and light harvestation, and hierarchical macroporous fibrous structure for multiple reflection and effective charge transfer.     

Visible-light photocatalysis in nitrogen-carbon-doped TiO2 films obtained by heating TiO2 gel-film in an ionized N2 gas

To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Nitrogen and carbon doping TiO₂ films were obtained by heating a TiO₂ gel in an ionized N₂ gas. The as-synthesized TiO_2−x−yN_xC_y films have shown an improvement over titanium dioxide in optical absorption and photocatalytic activity such as photodegradation of methyl orange under visible light. The process of the oxygen atom substituted by nitrogen and carbon was discussed. Oxygen vacancy induced by the formation of Ti³⁺ species and nitrogen and carbon doped into substitution sites of TiO₂ have been proven to be indispensable for the enhance of photocatalytic activity, as assessed by UV-Vis Spectroscopy and X-ray photoemission spectroscopy.     

Effect of V doping concentration on the electronic structure,optical and photocatalytic properties of nano-sized V-doped anatase TiO2

V-doped TiO₂ with V/Ti ratio of 1–5% has been synthesized by hydrothermal method and then characterized by XRD, TEM, BET specific surface area, XPS and UV–vis. absorption spectra. The photocatalytic activity of the as-synthesized samples was investigated by the degradation of methylene blue in aqueous solution under visible light irradiation. Density functional theory (DFT) based calculations were performed to investigate the mechanism of band gap narrowing, the shift of light absorption edge, the location of V in the TiO₂ lattice and the variation in electronic and optical properties of TiO₂ with the increase of V doping concentration. Irrespective of the V doping concentration, TEM images indicate that all the doped samples were composed of equiaxed spherical anatase TiO₂ particles with good crystallinity and uniform particle size distribution. Both the experimental results from XPS survey and the theoretical calculation argue that the doped V replaces the lattice Ti and form substitutional impurity. The visible light absorption can be optimized by adjusting the V doping concentration. Among the doped samples with different V doping concentrations, the sample with V/Ti ratio of 2% depicts better visible light photocatalytic activity due to the enhanced visible light absorption and improved separation of electron–hole pairs.     

Synthesis and characterization of N-doped TiO2/ZrO2 visible light photocatalysts

Zirconia and nitrogen-doped TiO₂ powder was synthesized using a polymer complex solution method for the preparation of an enhanced visible light photocatalyst. The produced catalysts were characterized via the Brunauer, Emmett, and Teller method (BET), X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectra, and UV–Vis spectrophotometry analyses. The N-doped TiO₂/ZrO₂ photocatalyst showed a high specific surface area and small crystal sizes. The XPS spectra of the N-doped TiO₂/ZrO₂ sample indicated that nitrogen was doped into the TiO₂ lattice and enhanced the photocatalytic activity. The UV–Vis absorption spectra of the N-doped TiO₂/ZrO₂ sample noticeably shifted to the visible light region compared to that of the TiO₂. The photocatalytic activities of the prepared catalysts were evaluated for the decomposition of gaseous NO_x under UV and visible light irradiations. The photocatalytic activities of N-doped TiO₂/ZrO₂ were much greater than those of commercial Degussa P25 in both the UV and visible light regions. The high photocatalytic activity can be attributed to stronger absorption in the visible light region, a greater specific surface area, smaller crystal sizes, more surface OH groups, and to the effect of N-doping, which resulted in a lower band gap energy.     

Preparation N-F-codoped TiO2 nanorod array by liquid phase deposition as visible light photocatalyst

An efficient method for the preparation of N-F-codoped visible light active TiO₂ nanorod arrays is reported. In the process, simultaneous nitrogen and fluorine doped TiO₂ nanorod arrays on the glass substrates were achieved by liquid phase deposition method using ZnO nanorod arrays as templates with different calcination temperature. The as-prepared samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectra measurements. It was found that calcination temperature is an important factor influencing the microstructure and the amount of N and F in TiO₂ nanorod arrays samples. The visible light photocatalytic properties were investigated using methylene blue (MB) dye as a model system. The results showed that N-F-codoped TiO₂ nanorod arrays sample calcined at 450 °C demonstrated the best visible light activity in all samples, much higher than that of TiO₂ nanoparticles and P25 particles films.     

NO treated TiO2 as an efficient visible light photocatalyst for NO removal

In this study, we report that nitrogen doped TiO₂ could be achieved via thermal treatment of Degussa P25 TiO₂ in NO atmosphere directly (P25-NO). The samples were characterized with XRD, XPS, and FT-IR. The characterization results suggested that nitrogen species were interstitially doped in P25-NO during the NO thermal treatment process. In comparison with P25, the P25-NO exhibited significantly enhanced photocatalytic activities under visible light irradiation (λ > 420 nm) for gaseous NO removal. On the basis of electronic band structure theory, we proposed a possible mechanism for the enhanced visible light driven photocatalytic oxidation process over the interstitial N doping P25-NO samples. This work could not only deepen understanding of the enhanced photoactivity originated from interstitial N doping in TiO₂, but also provide a facile route to prepare nitrogen doped TiO₂ for environmental and energy applications.     

Theoretical and experimental study on the electronic structure and optical absorption properties of nitrogen-doped nanometer TiO2

Nitrogen-doped nanosized TiO₂ powders were prepared by using sol–gel technology while ammonium chloride, triethylamine and ammonia solution were taken as nitrogen precursors separately. Triethylamine with small bonding energy of N–C can introduce more nitrogen content into titania crystal than ammonium chloride and ammonia solution at the same initial molar concentration. The doping nitrogen atoms suppress the growth of titania crystal and the phase transformation, and increase the c-axis lattice parameter as well. UV–vis absorption studies confirmed that the spectral responses of nitrogen-doped TiO₂ powders were shifted to the visible light region. The optimum nitrogen content in our experiments is 14.1% (mol), the absorption edge of which shift to 480 nm. The ab initio calculations support the conclusion that the doping of nitrogen can decrease the energy gap by mixing the N 2p states with O 2p states. The theoretical lattice parameters and optimum nitrogen content agree well with the experimental results.     

Synthesis of iron-doped TiO2 nanoparticles by ball-milling process: the influence of process parameters on the structural,optical, magnetic,and photocatalytic properties

Titanium dioxide (TiO₂) absorbs only a small fraction of incoming sunlight in the visible region thus limiting its photocatalytic efficiency and concomitant photocatalytic ability. The large-scale application of TiO₂ nanoparticles has been limited due to the need of using an ultraviolet excitation source to achieve high photocatalytic activity. The inclusion of foreign chemical elements in the TiO₂ lattice can tune its band gap resulting in an absorption edge red-shifted to lower energies enhancing the photocatalytic performance in the visible region of the electromagnetic spectrum. In this research work, TiO₂ nanoparticles were doped with iron powder in a planetary ball-milling system using stainless steel balls. The correlation between milling rotation speeds with structural and morphologic characteristics, optical and magnetic properties, and photocatalytic abilities of bare and Fe-doped TiO₂ powders was studied and discussed.     

Fabrication of the CN co-doped rod-like TiO2 photocatalyst with visible-light responsive photocatalytic activity

The CN co-doped TiO₂ nanorods were synthesized by the vapor transport method of water molecules, and urea was used as the carbon and nitrogen source. The samples were characterized by X-ray diffraction and photoelectron spectroscopy analysis. The scanning electron microscope images showed that as-prepared TiO₂ powders were nanorods, which were formed by the stacking of nanoparticles with a uniform size around 40 nm. The degradation of methylene blue with the prepared nanorods demonstrated the photocatalytic activities of TiO₂ under visible light are improved by doping with C and N elements. The main reasons were discussed: doping with C and N elements could enhance the corresponding visible-light absorption of TiO₂. On the other hand, doping C and N could create more oxygen vacancies in the TiO₂ crystals, which could capture the photogenerated electrons more effectively. Thus, more photogenerated holes could be left to improve the photocatalytic activity of TiO₂.     

Novel method for doping nano TiO2 photocatalysts by chemical vapour deposition

Highly active photocatalytic Fe-doped nano TiO₂ was successfully synthesised by chemical vapour deposition (CVD) method using FeCl₃ as Fe source. CVD was carried out by evaporating FeCl₃ at 350°C in nitrogen flow during 30–90?min. The amount of Fe incorporated into TiO₂ framework is adjusted by the amount of FeCl₃ used and the evaporation time. The obtained sample was characterised by X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), energy dispersive X-ray spectroscopy (EDS), UV-Vis, Fourier transform-infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). Photocatalytic activities of the samples were tested in photocatalytic decomposition of 2-propanol in liquid phase using visible light instead of UV light irradiation. Non-doped TiO₂ and high Fe loading TiO₂ samples showed very low photocatalytic activity, whereas the low Fe loading TiO₂ sample exhibited high photocatalytic activity under visible light. The high photocatalytic activity of this sample was rationalised by the existence of defects (Ti–OH groups) as the active sites.     

Preparation of boron-doped TiO2 films by autoclaved-sol method at low temperature and study on their photocatalytic activity

A series of uniform and transparent boron-doped TiO₂ films were synthesized from autoclaved-sol without organic solvent at low temperature. As-prepared B-TiO₂ films with two layers were characterized by XRD, DRS, XPS and AFM. The photocatalytic characteristics were measured based on the degradation of Rhodamine B (RhB) solution under visible or UV light. The results indicated that the anatase phase was the main crystal form of the films, containing a small amount of brookite. The presence of boron caused a red shift in the absorption band of TiO₂ films. The doped boron was mainly presented in the form of B₂O₃, O-Ti-B and O-Ti-B bonds, confirming that autoclaved-sol synthesis at low temperature allowed for incorporation of boron atoms into the TiO₂ matrix. Transmission of the films was about 90% in the visible region. The 10% (atom) B-TiO₂ film exhibited the best photocatalytic activity both in visible and UV light.