Low temperature sonochemical synthesis of boron doped TiO2 nanoparticles with enhanced visible light induced photocatalytic activity

Abstract

A simple one-step sonochemical synthesis method for the preparation of boron doped TiO₂ (B-TiO₂) nanoparticles at low temperatures has been developed. The B-TiO₂ nanoparticles were synthesised through sonication of a solution of tetraisopropyl titanium and boric acid in ethanol at 70°C for 150 min. The as prepared B-TiO₂ sample was characterised using X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller surface area and ultraviolet–visible absorption spectroscopy. The average crystallite size of anatase B-TiO₂ is 6·2 nm. B doping of TiO₂ shifted the absorption edge towards higher wavelength. The band energy of B-TiO₂ was estimated as 2·74 eV. The photocatalytic activity of the as prepared photocatalyst was evaluated via the photodegradation of methylene blue dye. The results show that the B-TiO₂ nanoparticles prepared via the sonochemical method exhibit an excellent photocatalytic activity under simulated sunlight.     

Hydrogen production from sulphide wastewater using Ce3+–TiO2 photocatalysis

Cerium (Ce³⁺) doped TiO₂ powder was synthesized by a sol-gel method and characterized by Transmission Electron Microscope (TEM), X-ray Diffraction (XRD), UV–Vis Diffuse Reflectance Spectroscopy (UV-DRS), Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The Ce³⁺ doping strongly reduced the band gap of the TiO₂ from 3.2 eV (UV) to 2.7 eV (visible region). The photocatalytic activity of Ce³⁺ doped TiO₂ catalysts was evaluated by hydrogen production from sulphide wastewater under visible light illumination. The photocatalytic production of H₂ was studied in a batch recycle tubular photocatalytic reactor. The results show that 0.4% Ce³⁺–TiO₂ suspended in 500 mL of simulated sulphide wastewater irradiated at 150 W visible lamp produced maximum H₂ of 6789 μmol h^?1. It was noticed that the Ce³⁺ doped TiO₂ performs well than Nano TiO₂ and P25 TiO₂ photocatalysts.     

Facile synthesis of Ti3+ doped Ag/AgITiO2 nanoparticles with efficient visible-light photocatalytic activity

We successfully synthesized novel Ti³⁺ doped TiO₂ and Ti³⁺ doped Ag/AgITiO₂ nanoparticles with efficient visible-light photocatalytic activity for hydrogen production by facile one-step solvothermal method. The as-prepared Ti³⁺ doped TiO₂ nanoparticles displayed excellent visible-light absorption and visible-light driven hydrogen production activity (115.3 μmol g^?1 h^?1), while the commercial TiO₂ had no visible-light response. Moreover, the as-prepared Ti³⁺ doped Ag/AgITiO₂ nanoparticles in this experiment showed highly enhanced visible-light absorption and efficient visible-light driven activity for hydrogen (571.0 μmol g^?1 h^?1), which was 4.95 times as high as that of the as-prepared TiO₂ nanoparticles. And the surface areas of the as-prepared TiO₂ and Ti³⁺ doped Ag/AgITiO₂ catalysts were up to 138.829 m² g^?1 and 102.988 m² g^?1, much higher than that of the commercial TiO₂ (55.516 m² g^?1). Finally, the visible-light photocatalytic mechanism of the Ti³⁺ doped Ag/AgITiO₂ nanoparticles for hydrogen generation was also proposed in detail.     

Photocatalytic activity of TiO2 nanotube layers coated with Ag and Pt

Abstract

Abstract

Thin films of anatase TiO₂ nanotube arrays (TiO₂ NTs) were prepared in this study. Pt and Ag were coated on the TiO₂ NTs films, which intend to increase the photocatalytic activity under ultraviolet-visible (UV-vis) irradiation. The phase and structure of the films were investigated by X-ray diffraction and scanning electron microscopy. Photocatalytic activity was tested by UV-vis absorption spectroscopy and showed that UV-vis light absorption of the films was remarkably improved by coated Ag and Pt by 72% and 183% respectively. The photocatalytic activities of the films towards degraded methyl orange and HCHO were compared and were all found to follow the sequence Pt/TiO₂ NTs>Ag/TiO₂ NTs>TiO₂ NTs. It was also found that the kinetics of HCHO photocatalytic degradation by the films fits the first order reaction model better and has higher efficiency than that of the methyl orange photocatalytic degradation by the same films.     

The effect of powder preparation method on the artificial photosynthesis activities of neodymium doped titania powders

The effects of nanostructure on the artificial photosynthesis activities of undoped and Nd doped titania (TiO₂) powders prepared by three different chemical co-precipitation methods were investigated. Substitutional/interstitial N and S doping was observed in powders due to the presence of high concentrations of HNO₃ (NP) and H₂SO₄ (SP) in the powder preparation media, respectively. Nd, N and S doping caused anatase/rutile phase transformation inhibition and crystallite size reduction in the nanostructure. Light absorption was significantly enhanced by Nd doping and the residual SO₄^2?/NO_x species in the nanostructure. Photocatalytic hydrogen production activity of Nd doped NP powder was 4 times greater than undoped NP powder at 700 °C and had a high purity (CO:H₂ ratio～0.00). CO was determined to be the main product in photocatalytic CO₂ reduction. NP powders had the highest CO yields and Nd doping enhanced CO production. The powders with high crystallite sizes and rutile weight fractions had the highest artificial photosynthesis activities.     

Pd loading,Mn+ (n=1, 2, 3) metal ions doped TiO2 nanosheets for enhanced photocatalytic H2 production and reaction mechanism

Pd nanoparticles (NPs) loading, main group metal ions doped TiO₂ nanosheets were prepared by a hydrothermal method, followed by photo-deposition of Pd. The samples were characterized, and their photocatalytic hydrogen production activities were tested in a methanol aqueous solution. The effects of cationic charge, radius and concentration of the doping ions (Na⁺, K⁺, Mg²⁺, Al³⁺) on the photocatalytic activities were investigated systematically. The photocatalytic reaction mechanism was discussed by considering the three aspects: specific surface area, light absorption and charge transfer/separation. The results show that the cation dopings significantly increased the photocatalytic activities of the TiO₂ nanosheets, which may be attributed to the enhanced UV-vis light absorption and accelerated charge transfer/separation of the catalysts. Particularly, the Pd/0.2%K⁺-TiO₂ possesses the highest photocatalytic H₂ production activity (76.6 μmol h^?1), which is more than twofold higher than that of the undoped Pd/TiO₂. The apparent quantum efficiency of hydrogen evolution system reaches 3.0% at 365 nm. The high activity of the Pd/K⁺-TiO₂ may be attributed to the lower electronegativity of K⁺, caused by the lower cationic charge or the larger cationic radius, compared to Na⁺, Mg²⁺ and Al³⁺. The doping metal cations with higher electronegativity may compete electrons with H⁺, which eventually partly depressed the reduction of H⁺ to H₂.     

In situ tuning of band gap of Sn doped composite for sustained photocatalytic hydrogen generation under visible light irradiation

The significance of Sn dopant on the photocatalytic performance of Iron/Titanium nanocomposite towards photocatalytic hydrogen generation by water splitting reaction is investigated. Iron/Titanium nanocomposite modified by Sn⁴⁺ dopant acts as a suitable photocatalyst for induced visible light absorption facilitating pronounced charge separation efficiency. Various characterization techniques reveal the heterojunction formation of hematite Fe₂O₃ with anatase - rutile mixed phase of TiO₂ employing Sn doping, where Sn⁴⁺ dopant accomplishes the phase transformation of anatase to rutile, entering into the TiO₂ lattice. This extended the lifetime of photogenerated charge carriers and enhanced the quantum efficiency of the photocatalyst. The band gap of the nanocomposite is tuned to ~2.4 eV, favoring visible light absorption. A hydrogen generation activity of 1102.8 μmol, approximately five times higher than the lone system (216.5 μmol) is achieved for the 5% Sn doped system for an average of 5 h. Heterojunctions of hematite with anatase-rutile mixed phase, generated as a consequence of tin doping facilitated the enhanced hydrogen generation activity of photocatalyst.     

Photocatalytic performance of S doped TiO2 in relation to processing conditions: calcination temperature and heating rate

Abstract

The effect of different heating profiles on the photocatalytic performance of sulphur doped TiO₂ photocatalysts is reported. The photocatalysts were synthesised by a sol–gel method using thiourea as the dopant precursor and characterised using X-ray diffraction, elemental analysis and reflection measurements. The degradation of dichloroacetic acid, under indirect sunlight and visible light irradiation, was used to determine the photocatalytic performance of the synthesised materials. A number of different commercial photocatalysts were used as comparative standards. In all the studied specimens, anatase TiO₂ was the dominant crystalline type. Additionally, compared with undoped TiO₂ and commercial standards, significant absorption into the visible region (400–470 nm) was observed for the modified TiO₂.     

Insights into the visible light photocatalytic activity of S-doped hydrated TiO2

Cationic doping of TiO₂ anatase with sulphur represents a facile method to improve catalytic and photocatalytic activity for hydrogen production and extend the action spectrum of TiO₂ into the visible light region. However, there is a lot of misunderstanding when trying to explain the experimental findings and suggest theoretical models. In the present computational research work, novel theoretical models are put forward representing fully hydroxylated small anatase nanoparticles with S(IV) and S(VI) doping in various surface positions and in the bulk. It was found that sulfur in the doped anatase nanoparticles preserves its typical coordination geometries of trigonal pyramid for S(IV) and tetrahedron for S(VI). Doping in the anatase surface is much more energetically favorable compared to doping in the bulk. Doping with S(IV) causes decrease of the band gap from 3.22 to 2.65 eV while S(VI) doping could decrease E_g only to 2.96 eV. Location of photogenerated electrons and holes depends strongly on the position of dopant atoms and their valent state. Contrary to some experimental works, no strong and extended visible light absorption bands could be found with cationic doped hydroxylated anatase nanoparticles. However, improved charges separation is observed indeed and causes improved photocatalytic hydrogen production.     

N‐doped titania powders prepared by different nitrogen sources and their application in quasi‐solid state dye‐sensitized solar cells

Nitrogen‐doped TiO₂ nanocrystalline particles are synthesized by a microwave‐assisted hydrothermal growth method using different amines (Dipropylamine, Diethanolamine and Ammonium hydroxide) as nitrogen sources. Characterization of the nanoparticles was performed with X‐ray diffraction, UV–vis diffuse reflectance spectroscopy, Field Emission Scanning Electron Microscopy and X‐ray Photoelectron Spectroscopy. The prepared N‐doped TiO₂ nanoparticles exhibit pure anatase phase with average diameter of 9 nm and reduced optical energy gap compared to undoped TiO₂. Immobilization of N‐doped and pure TiO₂ nanoparticles on SnO₂:F conductive glass substrates was successfully performed by using doctor‐blade technique and paste of the aforementioned nanoparticles. A series of N‐doped TiO₂ photoelectrodes with varying N dopant source and concentrations were fabricated for quasi‐solid state dye‐sensitized solar cells. The N‐doped solar cells achieve an overall conversion efficiency ranging from 4.0 to 5.7% while undoped TiO₂ showed 3.6%. The basic difference to the electrical performance of the cells is focused to the enhancement in the current density of N‐doped TiO₂‐based cells which was from 11% to 58% compared with undoped TiO₂ cells. Current densities were directly proportional with nitrogen doping level in TiO₂ lattice which differs depending on the amine source nature such as basicity differences, hydrogen bonding abilities and steric inherences. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of doping level on physical properties of antimony doped nanocrystalline tin oxide films fabricated using low cost spray technique

Abstract

Antimony doped nanocrystalline tin oxide (SnO₂∶Sb) films have been fabricated using a low cost and simple fabrication technique using a perfume atomiser. The X-ray diffraction patterns of the antimony doped tin oxide (ATO) films show that the films are polycrystalline with tetragonal cassiterite structure having (110) plane parallel to the surface of the substrate. The preferred orientation remains constant for all the doping levels (0·5–3·0 at-%) and the degree of preferred orientation increases with increasing doping concentration in the starting solution. The intensity of the (110) plane steadily increases as the doping concentration of antimony increases. The fine quality of AFM images show that the films have homogeneous and uniform surface. The sheet resistance is found to decrease with increasing antimony doping level, attain a minimum value (6·34 Ω sq^?1) when the doping concentration is 2·5 at-% and then increase for further doping.     

Effect of Ag/N codoping on photoactivity of TiO2 thin film

Abstract

Nano Ag/N–TiO₂ films with porous hadites as carriers have been successfully prepared by a modified sol–gel process. The performance of the films was characterised by X-ray diffraction, UV-vis and energy dispersive X-ray spectroscopy. The photocatalytic activities and sterilisations of the films were estimated with the waste water contained oil and the fresh cocci as polluted models. The experiments showed that the codoping of Ag and N modified observably the photocatalytic activity of TiO₂. The degradation rate of Ag/N–TiO₂ films on oil in water and bacteria was three times more than pure TiO₂ films on porous hadites. The porous hadites loaded Ag/N–TiO₂ films may be used for waste water processing, sterilisation and filtering.     

Modification of the photocatalytic properties of self doped TiO2 nanoparticles for hydrogen generation using sunlight type radiation

Synthetic approaches/methodologies can change the properties of nanoparticles significantly. In this study, the photocatalytic property of self (Ti³⁺) doped TiO₂ nanoparticles was modified by synthesizing through different routes. Solvothermal (T-Sol), sonochemical (T-Son) and polyol (T-Pol) methods were employed to prepare TiO₂ nanoparticles and the photocatalytic activities of these samples were compared with that of the sample prepared by precipitation using ammonia solution (T-Ppt). All samples had particle size below 30 nm except T-Son, where small nanoparticles existed as large spherical agglomerates with size around 500 nm. Surface area and porosity measurements of these different TiO₂ samples showed a significant dependency on the synthesis method. UV–Visible absorption spectra showed the onset of absorption at ∼440 nm for all samples due to the presence of defect levels originating from anion vacancies. Photocatalytic activity for hydrogen generation decreased in the order T-Sol > T-Son > T-Pol > T-Ppt and the observed activity is correlated with their physical properties such as surface area and crystallinity. The hydrogen yield was highly enhanced by the addition of Pd metal as co-catalyst on the surface of TiO₂ photocatalysts. Present experiments clearly demonstrate the importance of synthesis route to improve the photocatalytic activity of TiO₂.     

Photocatalytic reduction of Cr(VI) in aqueous titania suspensions exposed to concentrated solar radiation

Abstract

A laboratory scale parabolic trough collector has been tested for photocatalytic reaction application to wastewater treatment under different reaction conditions. The photocatalytic reduction of Cr(VI) to Cr(III), using TiO₂ suspensions under solar irradiation, has been investigated. The influence of reaction conditions has been illustrated using an organic additive (citric acid) in varying doses and also by performing the reaction at different pH values and doses of TiO₂. An attempt has also been made to investigate the reuse performance of the photocatalyst. The rate of reduction was found to increase steadily with increasing concentration of organic additive, TiO₂ dose and decreasing pH. Complete reduction of Cr(VI) to Cr(III) was achieved in 2 h and very low catalyst concentration at pH 2. The reuse studies showed that the catalyst can be used 2–3 times for lower Cr(VI) concentrations.     

Water purification using solar energy: effect of sulphur on photocatalytic properties of TiO2

Abstract

The present work considers the effect of sulphur on several properties of titanium dioxide (TiO₂) including electronic structure, defect disorder and photocatalytic properties. While the reports on the mechanism of sulphur incorporation into the TiO₂ lattice are conflicting, there is a consensus that sulphur leads to reduction of band gap and enhanced photocatalytic performance. The latter effect suggests that light absorption, which is determined by an electronic structure, plays the key role in the conversion of the light energy into the chemical energy that is required for photocatalytic decomposition of organic contaminants in water. Analysis of the reported data suggests that different processing procedures result in different doping mechanisms. It is argued that most of the experimental data reported so far are not well defined and, therefore, are not compatible. Consequently, the progress in the science of photocatalysis requires collection of empirical data that are well defined.     

Photocatalytic hydrogen production by reforming of methanol using Au/TiO2, Ag/TiO2 and Au-Ag/TiO2 catalysts

Abstract

We have investigated polyvinylalcohol stabilized Au and Ag based nanoparticles supported on titania prepared via sol immobilisation for the anaerobic, ambient temperature reforming of methanol with water for the photocatalytic production of hydrogen. The catalytic activity of the Au/TiO₂ catalysts was strongly affected by the metal loading and calcination temperature. Here, we report the preparation and use of supported Au–Ag nanoparticles, based on either the co-reduction or the consecutive reduction of the two metals. Au–Ag supported catalysts were more active than monometallic Au and Ag catalysts and the preparation methodology had a pronounced effect in terms of catalytic activity of the Au–Ag catalysts. In fact, using a consecutive reduction where Au was firstly reduced followed by reduction of Ag gave materials which exhibited the highest catalytic performance.     

Hierarchical spheres assembled from large ultrathin anatase TiO2 nanosheets for photocatalytic hydrogen evolution from water splitting

We report the synthesis of TiO₂ hierarchical spheres (THS) with large specific surface area via a facile one-pot solvothermal method. The as-prepared THS are self-assembled by ultrathin TiO₂ nanosheets with thickness of several nanometers and they show a uniform spherical morphology with an average size of 500–700 nm. However, the as-prepared light yellow THS exhibit inferior photocatalytic activity for hydrogen evolution from water splitting due to the poor crystallization of TiO₂ and the existence of oxygen vacancies. Significantly, a subsequent thermal treatment improves the crystallinity of THS, reduces the oxygen vacancies, and thereby enhances the photocatalytic performance. It demonstrates that the sample annealed at 550 °C (THS550) exhibits the highest photocatalytic activity, about 5 times higher than that of commercial TiO₂ nanoparticles (CTiO₂). Moreover, the THS550 sample loaded with 1 wt% Pt exhibits an hydrogen evolution rate as high as 17.9 mmol h^?1g^?1, and the corresponding apparent quantum efficiency has been determined to be 28.46% under 350 nm light irradiation.     

Visible‐light response photocatalytic water splitting over CdS/TiO2 and CdS–TiO2/metalosilicate composites

In this work, we have synthesized two different phases of CdS nanoparticles, CdS/TiO₂ composites and their supported form on ZSM‐5 type metalosilicates (ferrisilicate and aluminosilicate) as CdS–TiO₂/metalosilicate composites. The photocatalytic performance of these samples was evaluated by monitoring the amount of hydrogen evolved from water under visible‐light irradiation. The supported composites of TiO₂–CdS/metalosilicate exhibited a higher photocatalytic activity in the photocatalytic water splitting than that of CdS/TiO₂ composites under visible‐light irradiation, suggesting an important role of support. Metalosilicate as a support, which can offer a very high surface area, provides effective and homogenous dispersion of the CdS/TiO₂ composite on the external surface or within the pores of metalosilicate and inhibits agglomeration of the formed composite. We observed that using the solvothermal method for the synthesis of CdS and the hydrothermal method for the synthesis of CdS/TiO₂ or CdS–TiO₂/metalosilicate results in the enhancement of the photocatalytic activity of these composite compared with other procedures, which has been reported previously. We have realized that the support of the CdS/TiO₂ composite on ferrisilicate enhances the photocatalytic activity; however, using aluminosilicate as a support results in the abatement of the photocatalytic activity in comparison with the unsupported composite. This can be attributed to the presence of partially occupied ‘d’ orbitals in the electronic configuration of Fe³⁺ in the structure of ferrisilicate which can interact with TiO₂ molecular orbitals. This interaction leads to the effective distribution of the composite on the support and the decreasing crystallite size of the composite and then enhancement of the photocatalytic activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Light-induced confined growth of amorphous Co doped MoSx nanodots on TiO2 nanoparticles for efficient and stable in situ photocatalytic H2 evolution

Amorphous molybdenum sulfide (a-MoS_x) prepared by in situ photoreduction method with an abundance of exposed active sites has been identified as an efficient cocatalyst for catalyzing photocatalytic H₂ evolution reaction (HER). However, the intrinsic activity of the a-MoS_x cocatalyst toward HER is low due to the unfavorable electronic structures of the active sites. Herein, we report a facile light-induced method for the confined growth of transition metal (TM) doped MoS_x (a-TM-MoS_x) cocatalysts on TiO₂ nanoparticles and their catalytic activity for in situ photocatalytic HER. It is found that doping Co into a-MoS_x can greatly enhance the activity of resulted a-Co-MoS_x cocatalyst for photocatalytic H₂ evolution over TiO₂ among the transition metal dopants (Co, Ni, Fe, Cu, Zn) tested. The most efficient a-Co-MoS_x cocatalyst (Co/Mo = 1/4 and 4 mol% loading) loaded TiO₂ (TiO₂/a-Co-MoS_x) shows a H₂ evolution rate of 133.8 μmol h⁻¹, which is 3.3 times higher than that of a-MoS_x loaded TiO₂ (TiO₂/a-MoS_x). Moreover, the TiO₂/a-Co-MoS_x photocatalyst shows excellent recycling H₂ evolution stability. The characterization results reveal that a-Co-MoS_x cocatalyst can not only effectively capture the photogenerated electrons of TiO₂ to greatly enhance the separation efficiency of photogenerated charges but also significantly reduce the overpotential of HER due to the formation of highly active “CoMoS” sites, thus synergistically enhancing the catalytic activity of TiO₂/a-Co-MoS_x. Moreover, the light-induced growth of a-Co-MoS_x on TiO₂ is found to readily couple with the in situ photocatalytic HER. Therefore, this work provides a simple and efficient strategy for designing high-performance a-MoS_x-based cocatalysts for stable in situ photocatalytic H₂ evolution.     

The structure and photocatalytic studies of N-doped TiO2 films prepared by radio frequency reactive magnetron sputtering

N-doped TiO₂ films were prepared by a radio frequency reactive magnetron sputtering (RF-MS) deposition method from an undoped TiO₂ target in a mixture of Ar/N₂ atmosphere on heated quartz glass substrates. The structures and properties of the N-doped were studied by XRD, Raman, XPS, TEM, ultraviolet (UV)-vis and PL spectroscopy. By analyzing the structures and photocatalytic activities of undoped and N-doped TiO₂ films under ultraviolet and visible light irradiation, the probable photocatalytic mechanism of N-doped TiO₂ films was investigated. Because many oxygen defects are caused in films by nitrogen doping, it is presumed that nitrogen doping and oxygen defect induced the formation of new states closed to the valence band and conduction band, respectively. The cooperation of nitrogen and oxygen defects leads to a significant narrowing of the band gap and greatly improves the absorption in the visible light region. It is found that the degradation efficiencies of N-doped TiO₂ films greatly decreased under ultraviolet irradiation, but slowly improved under visible light irradiation, compared with the undoped TiO₂ film. It is suggested that the N-doped TiO₂ films are formed for the nitrogen to occupy oxygen defect sites directly. The doped nitrogen ions and oxygen defects act as recombination centers that reduce the lifetime of photo-induced electrons and holes, thereby resulting in the decrease of photocatalytic activity under ultraviolet light illumination.