Preparation and characterization of N–I co-doped nanocrystal anatase TiO2 with enhanced photocatalytic activity under visible-light irradiation

N–I co-doped TiO₂ nanoparticles were prepared by hydrolysis method, using ammonia and iodic acid as the doping sources and Ti(OBu)₄ as the titanium source. The prepared catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and ultraviolet–visible diffuse reflection spectroscopy (UV–vis DRS). XRD spectra show that N–I–TiO₂ samples calcined at 673 K for 3 h are of anatase structure. XPS analysis of N–I–TiO₂samples indicates that some N atoms replace O atoms in TiO₂ lattice, and I exist in I⁷⁺, I⁻ and I⁵⁺ chemical states in the samples. UV–vis DRS results reveal that N–I–TiO₂ had significant optical absorption in the region of 400–600 nm. The photocatalytic activity of catalysts was evaluated by monitoring the photocatalytic degradation of methyl orange (MO). Compared with P25 and mono-doped TiO₂, N–I–TiO₂ powder shows higher photocatalytic activity under both visible-light (λ > 420 nm) and UV–vis light irradiation. Furthermore, N–I–TiO₂ also displays higher COD removal rate under UV–vis light irradiation.     

Preparation and visible-light photocatalytic activity of In2S3/TiO2 composite

A novel In₂S₃/TiO₂ composite with visible-light photocatalytic activity was prepared by a chemical precipitation method and characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope and UV–vis diffuse reflectance spectroscopy. Under both UV- and visible-light irradiation, the In₂S₃/TiO₂ composite shows good photocatalytic activity to degrade methyl orange, ascribed to the absorption of visible light by In₂S₃ sensitizer and enhanced separation of photoinduced electron–hole pairs in the composite semiconductors.     

Visible-light-responsive Ag–Si codoped anatase TiO2 photocatalyst with enhanced thermal stability

To utilize visible light more efficiently and enhance the photocatalytic performance of TiO₂, Ag–Si/TiO₂ photocatalyst was synthesized via a two-step method. The obtained materials were characterized by XRD, Raman, TEM, HRTEM, BET, TG–DTA, XPS, ICP as well as UV–vis DRS. All photocatalyst materials held an anatase phase confirmed by XRD, Raman and HRTEM. The Ag–Si/TiO₂ photocatalysts possessed high thermal stability and the phase transformation was retarded to about 900 °C revealed by XRD and TG–DTA. The Ag–Si/TiO₂ particles synthesized via the nonaqueous method were highly monodispersed and the particles size became smaller compared to the un-doped TiO₂, resulting in the enlargement of surface area. In addition, UV–vis light absorption shifted to visible region after Ag doping. XPS results demonstrated that Si weaved into the matrix of TiO₂ and enriched in the surface layer, while Ag dispersed on the surface of TiO₂ particles. The Ag dopant suppressed the recombination of photogenerated electrons and holes, Si enlarged the surface of photocatalysts. Silver and silicon co-doping improved the visible photocatalytic activity, which was evaluated by Rhodamine B (RhB) degradation. The photocatalytic activity of the obtained Ag–Si/TiO₂ sample was much more higher than those of pure TiO₂ and Ag/TiO₂, reaching the maximum at the Ag and Si content of 0.5 mol% and 20.0 mol%, respectively. The improved visible photocatalytic activity may be attributed to the synergetic effects of codoping by silver and silicon.     

Photocatalytic effects for the TiO2-coated phosphor materials

This study investigated the photocatalytic behavior of the coupling of TiO₂ with phosphorescent materials. A TiO₂ thin film was deposited on CaAl₂O₄:Eu²⁺,Nd³⁺ phosphor particles by using atomic layer deposition (ALD), and its photocatalytic reaction was investigated by the photobleaching of an aqueous solution of methylene-blue (MB) under visible light irradiation. To clarify the mechanism of the TiO₂-phosphorescent materials, two different samples of TiO₂-coated phosphor and TiO₂–Al₂O₃-coated phosphor particles were prepared. The photocatalytic mechanisms of the ALD TiO₂-coated phosphor powders were different from those of the pure TiO₂ and TiO₂–Al₂O₃-coated phosphor. The absorbance in a solution of the ALD TiO₂-coated phosphor decreased much faster than that of pure TiO₂ under visible irradiation. In addition, the ALD TiO₂-coated phosphor showed moderately higher photocatalytic degradation of MB solution than the TiO₂–Al₂O₃-coated phosphor did. The TiO₂-coated phosphorescent materials were characterized by transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and X-ray photon spectroscopy (XPS).     

Preparation of metal ion (Fe and Ni) doped TiO2 nanoparticles supported on ZSM-5 zeolite and investigation of its photocatalytic activity

Metal ion doped TiO₂ nanoparticles supported on ZSM-5 zeolite (M-TiO₂/ZSM-5 composites, M = Fe or Ni) were synthesized by hydrothermal method. The prepared composites were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activities of composites were evaluated by degradation of yellow GX aqueous solution under ambient condition. Fe-TiO₂/ZSM-5 composite showed to be more efficient catalyst for degradation of dye molecules as compared with Ni-TiO₂/ZSM-5 and TiO₂/ZSM-5. Its higher photocatalytic activity is attributed to the effective separation of charge carriers that will be discussed in this paper in detail.     

Photocatalytic degradation of formaldehyde by nanostructured TiO2 composite films

Interest in the photocatalytic oxidation of formaldehyde from contaminated wastewater is growing rapidly. The photocatalytic activity of the nanocrystalline Fe³⁺/F^? co-doped TiO₂–SiO₂ composite film for the degradation of formaldehyde solution under visible light was discussed in this study. The films were characterised by field emission scanning electron microscopy (FE-SEM) equipped with energy-dispersive spectroscopy, X-ray diffraction (XRD), BET surface area, UV–Vis absorption spectroscopy, and photoluminescence spectroscopy. The FE-SEM results revealed that the Fe³⁺/F^? co-doped TiO₂–SiO₂ film was composed of uniform round-like nanoparticles or aggregates with the size range of 5–10 nm. The XRD results indicated that only the anatase phase was observed in the film. Compared with a pure TiO₂ film and a singly modified TiO₂ film, the Fe³⁺/F^? co-doped TiO₂–SiO₂ composite film showed the best photocatalytic properties due to its strong visible light adsorption and diminished electrons-holes recombination.     

Visible light absorption ability and photocatalytic oxidation activity of various interstitial N-doped TiO2 prepared from different nitrogen dopants

Nitrogen-doped TiO₂ was developed to enable photocatalytic reactions using the visible range of the solar spectrum. This work reports on the synthesis, characterisation and kinetic study of interstitial N-doped TiO₂ prepared by the sol–gel method using three different types of nitrogen dopants: diethanolamine, triethylamine and urea. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and UV–visible spectroscopy were used to analyse the titania. Different interstitial N-doped TiO₂ properties, such as absorption ability in the UV–visible light region, redshift in adsorption edge, good crystallisation and composition ratio of titania structures (anatase and rutile) could be obtained from different nitrogen dopants. Amongst investigated nitrogen precursors, diethanolamine provided the highest visible light absorption ability of interstitial N-doped TiO₂ with the smallest energy bandgap and the smallest anatase crystal size, resulting in the highest efficiency in 2-chlorophenol degradation. The photocatalytic activity of all N-doped TiO₂ can be arranged in the following order: TiO₂/diethanolamine > TiO₂/triethylamine > TiO₂/urea > un-doped TiO₂. The initial rate of 2-chlorophenol degradation using the interstitial N-doped TiO₂ with diethanolamine was 0.59 mg/L-min and the kinetic constant was 2.34 × 10⁻² min⁻¹ with a half-life of 98 min. In all cases, hydroquinone was detected as a major intermediate in the degradation of 2-chlorophenol.     

Determination of photo-catalytic activity of un-doped and Mn-doped TiO2 anatase powders on acetaldehyde under UV and visible light

Titanium dioxide (TiO₂) photocatalytic powder materials doped with various levels of manganese (Mn) were synthesized to be used as additives to wall painting in combating indoor and outdoor air pollution. The heterogeneous photocatalytic degradation of gaseous acetaldehyde (CH₃CHO) on Mn-TiO₂ surfaces under ultraviolet and visible (UV/Vis) irradiation was investigated, by employing the Photochemical Static Reactor coupled with Fourier-Transformed Infrared spectroscopy (PSR/FTIR) technique. Experiments were performed by exposing acetaldehyde (~ 400 Pa) and synthetic air mixtures (~ 1.01 × 10⁵ Pa total pressure) on un-doped TiO₂ and doped with various levels of Mn (0.1-33% mole percentage) under UV and visible irradiation at room temperature. Photoactivation was initiated using either UV or visible light sources with known emission spectra. Initially, the photo-activity of CH₃CHO under the above light sources, and the physical adsorption of CH₃CHO on Mn-TiO₂ samples in the absence of light were determined prior to the photocatalytic experiments. The photocatalytic loss of CH₃CHO on un-doped TiO₂ and Mn-TiO₂ samples in the absence and presence of UV or visible irradiation was measured over a long time period (≈ 60 min), to evaluate their relative photocatalytic activity. The gaseous photocatalytic end products were also determined using absorption FTIR spectroscopy. Carbon dioxide (CO₂) was identified as the main photocatalysis product. It was found that 0.1% Mn-TiO₂ samples resulted in the highest photocatalytic loss of CH₃CHO under visible irradiation. This efficiency was drastically diminished at higher levels of Mn doping (1-33%). The CO₂ yields were the highest for 0.1% Mn-TiO₂ samples under UV irradiation, in agreement with the observed highest CH₃CHO decomposition rates. It was demonstrated that low-level (0.1%) doping of TiO₂ with Mn results in a significant increase of their photocatalytic activity in the visible range, compared to un-doped TiO₂. This elevated activity is lost at high doping levels (1-33%). Finally, the photocatalytic degradation mechanism of CH₃CHO on 0.1% Mn-TiO₂ surfaces under visible irradiation leading to low CO₂ yields is different than that under UV irradiation resulting to high CO₂ yields.     

Visible light photoelectrocatalysis with salicylic acid-modified TiO2 nanotube array electrode for p-nitrophenol degradation

This research focused on immersion method synthesis of visible light active salicylic acid (SA)-modified TiO₂ nanotube array electrode and its photoelectrocatalytic (PEC) activity. The SA-modified TiO₂ nanotube array electrode was synthesized by immersing in SA solution with an anodized TiO₂ nanotube array electrode. Scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), UV–vis diffuse reflectance spectrum (DRS), and Surface photovoltage (SPV) were used to characterize this electrode. It was found that SA-modified TiO₂ nanotube array electrode absorbed well into visible region and exhibited enhanced visible light PEC activity on the degradation of p-nitrophenol (PNP). The degradation efficiencies increased from 63 to 100% under UV light, and 79–100% under visible light (λ > 400 nm), compared with TiO₂ nanotube array electrode. The enhanced PEC activity of SA-modified TiO₂ nanotube array electrode was attributed to the amount of surface hydroxyl groups introduced by SA-modification and the extension of absorption wavelength range.     

Mesoporous Au/TiO2 composites preparation,characterization, and photocatalytic properties

In this work, mesoporous Au/TiO₂ composites have been synthesized and tested on photodegradation of methylene blue dye solution. Mesoporous TiO₂ prepared at 450 °C using triblock polymer F127 as structure-directing agent was applied as substrate, while various HAuCl₄ concentrations were used for Au loading through deposition-precipitation method using urea as precipitator and hydrogen reducing process. The influences of Au loading on the microstructures of mesoporous TiO₂ including degree of dispersion, particle size, surface area, light absorption, and band gap were studied with transmission electron microscopy (TEM), X-ray diffraction (XRD), diffuse reflection infrared Fourier transformed spectroscopy (DRIFT), N₂ adsorption–desorption isotherm analysis (BET), and UV–Vis diffuse reflectance spectra. With Au loading, the size of TiO₂ nanoparticles in Au/TiO₂ composites is similar as that of TiO₂ substrate. However, the degree of dispersion was greatly improved. Furthermore, an obvious surface plasmon resonance centered at 570 nm was found in UV–Vis diffuse reflectance spectra for Au/TiO₂ composites. Au loading also induced an obvious red shift of light absorption from UV region to visible region and strengthened both UV and visible light absorption in contrast to substrate. Photodegradation results verified that photocatalytic activity of mesoporous TiO₂ was improved by Au loading. 0.25%Au/TiO₂ composite showed the highest activity, which may be ascribed to its high surface hydroxyl content and the formed Schottky junction after Au loading. These results suggested that noble metal modification is a promising way to synthesize photocatalysts with both high activity and visible light sensitivity.     

Effects of samarium dopant on photocatalytic activity of TiO<Subscript>2</Subscript> nanocrystallite for methylene blue degradation

Sm³⁺-doped TiO₂ nanocrystalline was synthesized by a sol–gel auto-combustion method and characterized by X-ray diffraction, Brunauer-Emmett-Teller method (BET), UV–vis diffuse reflectance spectroscopy (DRS), and also photoluminescence (PL) emission spectroscopy. The photocatalytic activity of Sm³⁺–TiO₂ catalyst was evaluated by measuring degradation rates of methylene blue (MB) under either UV or visible light. The results showed that doping with the samarium ions significantly enhanced the photocatalytic activity for MB degradation under UV or visible light irradiation. This was ascribed to the fact that a small amount of samarium dopant simultaneously increased MB adsorption capacity and separation efficiency of electron-hole pairs. The results of DRS showed that Sm³⁺-doped TiO₂ had significant absorption between 400 nm and 500 nm, which increased with the increase of samarium ion content. The adsorption experimental demonstrated that Sm³⁺–TiO₂ had a higher MB adsorption capacity than undoped TiO₂ and adsorption capacity of MB increased with the increase of samarium ion content. It is found that the stronger the PL intensity, the higher the photocatalytic activity. This could be explained by the points that PL spectra mainly resulted from surface oxygen vacancies and defects during the process of PL, while surface oxygen vacancies and defects could be favorable in capturing the photoinduced electrons during the process of photocatalytic reactions, so that the recombination of photoinduced electrons and holes could be effectively inhibited.     

Preparation and characterization of Bi-doped TiO2 and its solar photocatalytic activity for the degradation of isoproturon herbicide

Bi-doped TiO₂ catalyst was prepared by sol–gel method and was characterized by thermo gravimetric analysis (TGA), X-ray diffraction spectra (XRD), X-ray photo electronic spectroscopy (XPS), UV–Vis diffused reflectance spectra (DRS), photoluminescence spectra (PLS), transmission electron microscopy (TEM), energy dispersive analysis of X-rays (EDAX) and BET surface area. The photocatalytic activity of the catalysts were evaluated for the degradation of isoproturon herbicide under solar light irradiation. The UV–Visible DRS of Bi-doped TiO₂ showed red shift in optical absorption. The presence of Bi^3+δ+ species are playing a vital role in minimizing the electron hole recombination resulting higher activity compared to bare TiO₂.     

Photocatalytic degradation of dodecyl-benzenesulfonate over TiO2–Cu2O under visible irradiation

A series of TiO₂–Cu₂O mixed oxides were prepared by the hydrolysis of titanium butoxide and reduction of copper acetate with hydrazine. These composite oxides were characterized by X-ray diffraction (XRD), inductively coupled plasma spectrometry (ICP), high-resolution transmission electron microscopy (HRTEM), N₂ adsorption and UV–vis techniques. Photocatalytic degradation of dodecyl-benzenesulfonate (DBS) under visible irradiation was performed, and effects of composition of catalysts and reaction conditions were studied. It was observed that TiO₂–Cu₂O composite oxides exhibited better photocatalytic activity than Cu₂O or TiO₂ alone. Among these composite oxides, the 5%TiO₂–Cu₂O displayed the highest activity, and the degradation percentage of DBS and COD reached 97.3% and 65%, respectively. In addition, it was found that the decomposition of DBS followed the first-order kinetics and the adsorption of DBS followed the Langmuir model. Oxygen in solution played a vital role in the elimination of COD.     

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.     

Synthesis,characterization and photocatalytic activity of ZnO-SnO2 nanocomposites

Nanocomposites of coupled ZnO-SnO₂ photocatalysts were synthesized by the coprecipitation method and were characterized by X-ray diffraction, UV–vis diffuse reflectance spectroscopy, surface area analyzer and scanning electron microscopy. Their photocatalytic activity was investigated under UV, visible and solar light and evaluated using methylene blue (MB) as a model pollutant. The performance of the coupled ZnO-SnO₂ photocatalysts was found to be related to the Zn/Sn molar ratio and to the calcination conditions. The photocatalyst with a Zn/Sn molar ratio of 1:0.05 calcined at 600 °C for 2 h showed the maximum degradation rate of MB under different lights used. Its photocatalytic activity was found to be about two times that of ZnO and about 10 times that of SnO₂ which can be explained by the heterojunction effect. Charge separation mechanism has been studied.     

A simple ultrasono-synthetic route of PbSe-graphene-TiO2 ternary composites to improve the photocatalytic reduction of CO2

The present work investigates the photocatalytic reduction of CO₂ to CH₃OH with a PbSe-G-TiO₂ photocatalyst. A heterogeneous PbSe-G-TiO₂ nanocomposite was prepared via ultra-sonication and was characterized via XRD, SEM, HRTEM, Raman, XPS, and DRS measurements. The photocatalytic efficiencies of the prepared sample were further characterized by GC for the photoreduction of CO₂ to CH₃OH under UV and visible light. The prepared PbSe-G-TiO₂ ternary nanocomposites with an optimum GO loading of 6% exhibited outstanding photocatalytic activity (4.35 µmol g^?1 h^?1) after 48 hours of reaction. This indicated that the photocatalytic efficiency was mostly dependent on the weight ratio of graphene, sacrificial material Na₂SO₃/Na₂S, and the type of reactant. This work provides an accessible way to improve the response of a graphene-based TiO₂ photocatalyst to UV/visible light and to facilitate its application in environmental remediation.     

Nest-like structures of Sr doped Bi2WO6: Synthesis and enhanced photocatalytic properties

A series of Sr-doped Bi₂WO₆ with three-dimensional (3D) nest-like structures were synthesized through simple hydrothermal route and characterized by XRD, FESEM, TEM, XPS, UV-vis DRS, etc. Morphology observation revealed that the as-synthesized Bi₂WO₆ were self-assembled three-dimensional (3D) nest-like structures, which were constructed from nanoplates. UV-vis diffuse reflectance spectra indicated that the samples had absorption in both UV and visible light areas. Their photocatalytic activities were evaluated by photodegradation of rhodamine B (RhB) under UV and visible light irradiation (λ > 420 nm). The photocatalytic properties were enhanced after Sr doping. Samples subsequently thermal treated at 500 °C showed higher photocatalytic activities. The reasons for the differences in the photocatalytic activities of these nest-like Bi₂WO₆ microstructures were further investigated.     

Synthesis and photocatalytic oxidation properties of titania hollow spheres

The hollow spheres of anatase TiO₂ with higher photocatalytic activity have been fabricated by spherical CaCO₃ nanoparticles as a template, and titanium sulfate (Ti(SO₄)₂) as a precursor, and the CaCO₃ templates were dissolved subsequently in dilute HNO₃ solution. The TiO₂ hollow spheres samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N₂ adsorption-desorption isotherms. The characterization results indicate that as prepared TiO₂ hollow spheres sample was transformed to anatase phase in calcined at 400 °C, and the anatase TiO₂ hollow spheres have a higher specific surface area and show much better photocatalytic activity than commercial P25 in the photodegradation of Rhodamine B under the UV irradiation.     

Photocatalytic degradation of RhB over MgFe2O4/TiO2 composite materials

MgFe₂O₄/TiO₂ (MFO/TiO₂) composite photocatalysts were successfully synthesized using a mixing-annealing method. The synthesized composites exhibited significantly higher photocatalytic activity than a naked semiconductor in the photodegradation of Rhodamine B. Under UV and visible light irradiation, the optimal percentages of doped MgFe₂O₄ (MFO) were 2 wt.% and 3 wt.%, respectively. The effects of calcination temperature on photocatalytic activity were also investigated. The origin of the high level of activity was discussed based on the results of X-ray diffraction, UV-vis diffuse reflection spectroscopy, scanning electron microscopy, transmission electron microscopy, and nitrogen physical adsorption. The enhanced activity of the catalysts was mainly attributed to the synergetic effect between the two semiconductors, the band potential of which matched suitably.