SrTiO3 Photocatalyst Research Articles

Doping of fluorine into SrTiO3 by spray pyrolysis for H2 evolution under visible light irradiation

Fluorine doped SrTiO3 photocatalysts were prepared by spray pyrolysis with varying fluorine content, and were employed for the first time for hydrogen evolution from aqueous methanol solution under visible light irradiation. The doped fluorine ions were substituted for 6-coordinated oxygen ions in the lattice of SrTiO3, which led to the generation of extra electrons and oxygen deficiencies. The doping of fluorine resulted in the partial transformation of the band gap structure of SrTiO3 to Sr(Ti4+1−xTi3+x)O3−xFx, by reducing Ti4+ to Ti3+ to compensate for the charge balance in the host lattice. The doping of fluorine contributed to the photocatalytic activity for hydrogen evolution by forming an acceptor level by Ti3+ from the conduction band to the valence band, generating the free electrons in the lattice structure, discarding the hydroxyl group on the surface and increasing the BET surface area and pore volume of the photocatalyst. The hydrogen evolution rate exhibited a maximum value of 464.1μmolg−1h−1 (QE=0.74%) with induction period of 1h, when the amount of fluorine content doped into SrTiO3 was 4.0mol%.

Roles of Cr3+ doping and oxygen vacancies in SrTiO3 photocatalysts with high visible light activity for NO removal

The photocatalytic degradation of nitrogen monoxide (deNOx) in the gas phase was investigated in a continuous reactor using a strontium titanate-based semiconductor, CaAl2O4:(Eu, Nd)/Cr-doped SrTiO3, and CaAl2O4:(Eu, Nd)/oxygen vacancy-induced SrTiO3 catalysts. Cr doping and oxygen vacancies generation could narrow the band gap of SrTiO3 and affect the photocatalytic performance to varying degrees. The photocatalytic activity of SrTiO3 toward LED light (445nm)-induced photocatalytic deNOx can be greatly improved by the nonstoichiometric synthesis of SrTiO3, mainly due to oxygen deficiency generation. CaAl2O4:(Eu, Nd)/Cr-doped SrTiO3 composites possessed superiority in NO removal under persistent fluorescence irradiation (440nm) after the mercury lamp with wavelength larger than 290nm was turned off.

Elucidation of Rh-Induced In-Gap States of Rh:SrTiO3 Visible-Light-Driven Photocatalyst by Soft X-ray Spectroscopy and First-Principles Calculations

The occupied and unoccupied in-gap electronic states of a Rh-doped SrTiO3 photocatalyst were investigated by X-ray emission spectroscopy and X-ray absorption spectroscopy for different Rh impurity valence states and doping levels. An unoccupied midgap Rh4+ acceptor state was found 1.5 eV below the SrTiO3 conduction band minimum. Both Rh4+ and Rh3+ dopants were found to have an occupied donor level close to the valence band maximum of SrTiO3. The density of states obtained from first-principles calculations show that all observed spectral features can be assigned to electronic states of substitutional Rh at the Ti site and that Rh:SrTiO3 is an unusual titanate compound with a characteristic p-type electronic structure. The Rh doping results in a large decrease of the bandgap energy, making Rh:SrTiO3 an attractive material for use as a visible-light-driven H2-evolving photocatalyst in a solar water splitting reaction.

Preparation and photocatalytic activities of two new Zn-doped SrTiO3 and BaTiO3 photocatalysts for hydrogen production from water without cocatalysts loading

Abstract Sr2/3Zn1/3TiO3 (1) and Ba5/6Zn1/6TiO3 (2) with perovskite structure have been prepared by a facile sol–gel method, among which the A sites (Sr and Ba for 1 and 2, respectively) were partially replaced by zinc ions. The photocatalysts were characterized by powder X-ray diffraction, UV–vis diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The results of photocatalysis experiment showed that both 1 and 2 exhibited good activity for water reduction to form H2 without cocatalysts loading under ultraviolet light irradiation. Compared with pure SrTiO3 and BaTiO3, 1 and 2 showed remarkable improvement in H2 production efficiency, respectively. And the photocatalytic mechanisms of them were investigated by the theoretical method. This study demonstrated that the substitutional doping of appropriate ions could change the crystal and band structures and significantly promote electron transport in catalysts, which result in their good photocatalytic activities.

Efficient visible-light-driven photocatalytic H2 production over Cr/N-codoped SrTiO3

Visible-light-response Cr/N-codoped SrTiO3 was prepared by a sol–gel hydrothermal method. The comparison studies indicate that Cr-doped and Cr/N-codoped SrTiO3 can be synthesized by this means, but not the N-doped SrTiO3. The theoretical calculations exhibit the defect formation energy of the Cr/N codoping into SrTiO3 is much smaller than that of the N doping into SrTiO3, illuminating that the incorporation of Cr can promote the N doping into the O sites in the SrTiO3. Compared to the Cr-doped SrTiO3, the Cr/N-codoped SrTiO3 photocatalyst shows the high photocatalytic activities for hydrogen production with the quantum efficiency of 3.1% at 420 nm, due to the smaller band gap and much less vacancy defects.

Synthesis of Nano-Sized SrTiO<sub>3</sub> Photocatalyst by Sol-Gel Method

A sol-gel processing technology was employed to synthesize fine SrTiO3 powder by using strontium nitrate (Sr(NO3)2) , butyl titanate (Ti(OC4H9)4) as precursors, citric acid (C6H8O6) as complexing agent and (ethylene) glycol (C2H6O2) as stabilizer. Prepared the precursors in liquid phase and then calcined the precursors to achieve nano-sized SrTiO3 powders. The microstructure and composition of the as-synthesized samples were characterized by X-ray diffraction (XRD), Scan Electron Microscopy (SEM), and the photocatalytic activity was studied. The results showed that all the SrTiO3 particles were identified as perovskite phase. The pH values, the content of the acetic acid, the heat treat temperature play important roles on the synthesis of the SrTiO3 photocatalyst. When the pH=1, n(Sr(NO3)2 ) : n(Ti(OC4H9)4) = 1 : 1, n(Sr(NO3)2 ) : n(C6H8O6)=1:1.7, the product has better rate of photodegradation for the Methylene Blue under the ultraviolet condition.

Surface-Alkalinization-Induced Enhancement of Photocatalytic H2 Evolution over SrTiO3-Based Photocatalysts

A strategy of reaction-environment modulation was employed to change the surface property of a semiconductor photocatalyst to enhance its photocatalytic performance. Surface alkalinization induced by a high alkalinity of the solution environment significantly shifted the surface energy band of a SrTiO(3) photocatalyst to a more negative level, supplying a strong potential for H(2)O reduction and consequently promoting the photocatalytic efficiency of H(2) evolution. This mechanism is also applicable for visible-light-sensitive La,Cr-codoped SrTiO(3) photocatalyst, which hence, could achieve a high apparent quantum efficiency of 25.6% for H(2) evolution in CH(3)OH aqueous solution containing 5 M NaOH at an incident wavelength of 425 ± 12 nm.

Reaction mechanism of visible-light responsive Cu(II)-grafted Mo-doped SrTiO3 photocatalyst studied by means of ESR spectroscopy and chemiluminescence photometry

The reaction mechanisms of visible-light responsive Cu(II)-grafted Mo-doped SrTiO3 (Cu(II)/MoSTO) photocatalyst and related photocatalysts were analyzed by means of ESR spectroscopy for detecting trapped carriers at 77K and chemiluminescence photometry for O2− and H2O2 in aqueous suspension. On the irradiation of visible light, the reduction of grafted Cu2+ ions was observed by ESR measurements for both Cu(II)/MoSTO and Cu(II)/STO (Cu(II)-grafted undoped SrTiO3) photocatalysts. One electron reduction product for O2, i.e., O2−, was detected in aqueous suspension by 442-nm irradiation for the Cu(II)-grafted samples. On the other hand, the amount of H2O2 detected as the two electron reduction product of O2 was a very small scale, indicating possible further reduction of H2O2 into H2O. From the ESR observations of crystalline defects, it was concluded that the Mo doping to increase visible-light response also increase the electron–hole recombination to some extent, while the Cu(II) grafting functioned as a trap of excited electrons to decrease the recombination.

Sol–gel hydrothermal synthesis of visible-light-driven Cr-doped SrTiO3 for efficient hydrogen production

Using a sol–gel hydrothermal method, we have synthesized Cr-doped SrTiO3 with a high specific surface area (19.3–65.4 m2 g−1, depending on the hydrothermal temperature). X-ray diffraction (XRD), UV-Vis diffuse reflectance spectra, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to investigate the Cr-doped SrTiO3. XRD analysis showed that Cr-doped SrTiO3 exhibited good crystallinity and the crystalline size calculated using Scherrer equation is about 20–30 nm. UV-Vis diffuse reflectance spectra showed that Cr doping can extend the absorption edge of SrTiO3 into visible region (540 nm). TEM images of Cr-doped SrTiO3 showed that the high temperature during the hydrothermal reaction will prompt the aggregation of primary particles into porous spheres. The porous structure was further certified by nitrogen physisorption results. By loading Pt (0.6 wt.%) nanoparticles as a cocatalyst, the as-prepared Cr-doped SrTiO3 photocatalyst exhibited high H2 evolution rate (82.6 μmol h−1) from 20% methanol solution under visible light irradiation, which is 3 times higher than that of the sample synthesized by solid state reaction. The high activity of the as-prepared Cr-doped SrTiO3 can be attributed to the high specific surface area and good crystallinity.

Development of Visible-Light-Driven TiO<sub>2</sub> and SrTiO<sub>3</sub> Photocatalysts Doped with Metal Cations for H<sub>2</sub> or O<sub>2</sub> Evolution

This review paper represents photocatalytic properties of metal cation-doped TiO2 (rutile) and SrTiO3 photocatalysts for O2 evolution from an aqueous silver nitrate solution and H2 evolution from an aqueous methanol solution under visible light irradiation. Photocatalytic activities for the O2 evolution of Cr/Sb and Rh/Sb-codoped TiO2 are strongly dependent on the codoping ratio and the amount of doped chromium and rhodium. The codopant controls the oxidation number of doped chromium and rhodium. Rh-doped SrTiO3 in which the doped Rh species possesses a reversible redox property is active for the H2 evolution reaction under visible light irradiation. Overall water splitting under visible light irradiation proceeds with Z-scheme photocatalyst systems consisting of the Rh-doped SrTiO3 as a H2 evolution photocatalyst combined with BiVO4 as an O2 evolution photocatalyst and an Fe3+/Fe2+ electron mediator.

Theoretical and experimental study of La/Ni co-doped SrTiO3 photocatalyst

Abstract The effects of Ni and La co-doping on the electronic structure of SrTiO 3 were investigated by theoretical (DFT) and experimental work. The calculation results revealed that doping sites of La and Ni impurities had a great influence on geometric structure and electronic properties of SrTiO 3 . Pure SrTiO 3 and doped SrTiO 3 were synthesized through citrate sol–gel method. The as-synthesized photocatalysts were characterized by XRD, UV–visible absorption spectroscopy and nitrogen adsorption, and employed to degrade methylene blue. La/Ni co-doped SrTiO 3 exhibited the highest activity. The experimental results were in good agreement with the calculation results.

Photo-electrochemical Lithium Insertion Characteristics of Carbon Nanotubes Modified with SrTiO3 Photocatalyst

Perovskite-type SrTiO3 nanoparticles were synthesized by direct hydrolysis-precipitation method and were employed to modify the surface of the carbon nanotubes to form a SrTiO3/CNTs composite. The photo-electrochemical lithium insertion characteristics of the SrTiO3/CNTs composite under xenon light irradiation were investigated. The results show that the light irradiation has little influence on the specific capacity of the CNTs electrode. However, for the SrTiO3/CNTs electrode irradiated by light, the lithium insertion capacity reaches about 251 mAh/g, much higher than that without light irradiation (170 mAh/g). Cyclic voltammetry test reveals that the light irradiation can remarkably increase the reaction currents of lithium insertion and extraction. This may be attributed to the photo-excited intercalation of Li-ions into the CNTs by the SrTiO3 photocatalyst when irradiated by light.

Synthesis and characterization of chromium doped SrTiO3 photocatalyst

SrTiO3 and chromium doped SrTiO3 (SrTi(1−x)CrxO3) photocatalysts were synthesized by the polymeric precursor method using citric acid and ethylene glycol. Single phase SrTiO3 and SrTi(1−x)CrxO3 nano-size powder were produced at 450 °C. A new band gap in the visible light range was formed by chromium doping in SrTiO3. The absorption of visible light is of practical importance for the application of SrTiO3 as a photocatalyst.

Nickel and either tantalum or niobium-codoped TiO2 and SrTiO3 photocatalysts with visible-light response for H2 or O2 evolution from aqueous solutions

TiO2 (band gap = 3.0 eV) and SrTiO3 (band gap = 3.2 eV) codoped with nickel and either tantalum or niobium ions showed photocatalytic activities for O2 evolution from an aqueous silver nitrate solution and H2 evolution from an aqueous methanol solution under visible light irradiation (lambda > 420 nm). The visible-light responses were due to the charge-transfer transition from the electron donor levels formed by the 3d orbitals of doped Ni2+ to the conduction bands of the host materials. Codoping of a tantalum or niobium ion made the absorption intensity in the visible light region strong for TiO2 doped with nickel ions, resulting in the enhancement of the photocatalytic activity for O2 evolution under visible light irradiation. SrTiO3 codoped with nickel and tantalum showed higher activity for H2 evolution than SrTiO3 doped with only nickel. This is due to the fact that codoped Ta5+ ions played a role in charge compensation, resulting in the suppression of the formation of Ni3+ ions, which are expected to trap photogenerated electrons.

Photocatalytic Activities of Noble Metal Ion Doped SrTiO3 under Visible Light Irradiation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

04/02140 INSEDELF: method of studying separation in liquid-liquid phase application to water-diesel fuel emulsions: Schulz, P. et al. Fuel, 2004, 83 (1), 137–142

A sol–gel method with the aid of structure-directing surfactant was successfully used to synthesize mesoporous-assembled SrTiO3 nanocrystal photocatalysts by using strontium nitrate (Sr(NO3)2) and tetraisopropyl orthotitanate (TIPT) as precursors. Anhydrous ethanol (EtOH), ethylene glycol (EG), or EtOH/EG was selected as a solvent, while laurylamine hydrochloride (LAHC), cetyltrimethylammonium bromide (CTAB), or cetyltrimethylammonium chloride (CTAC) was used as a structure-directing surfactant. The photodegradation of methyl orange by SrTiO3 was found to be affected by the crystallinity, specific surface area, and pore characteristic. The mesoporous-assembled structure with a high pore uniformity of SrTiO3 plays the most important role affecting the photocatalytic activity of the SrTiO3 photocatalyst. The SrTiO3 with the mesoporous-assembled structure and narrow pore size distribution synthesized at a calcination temperature of 700 °C, a heating rate of 1 °C min−1, a LAHC-to-TIPT molar ratio of 0.25:1, and using an EtOH solvent provided the highest photocatalytic degradation activity, which was much higher than that of the non-mesoporous-structured commercial SrTiO3.

Photocatalytic Activities of Noble Metal Ion Doped SrTiO3 under Visible Light Irradiation

Mn-, Ru-, Rh-, and Ir-doped SrTiO3 possessed intense absorption bands in the visible light region due to excitation from the discontinuous levels formed by the dopants to the conduction band of the SrTiO3 host. Mn- and Ru-doped SrTiO3 showed photocatalytic activities for O2 evolution from an aqueous silver nitrate solution while Ru-, Rh-, and Ir-doped SrTiO3 loaded with Pt cocatalysts produced H2 from an aqueous methanol solution under visible light irradiation (λ > 440 nm). The Rh(1%)-doped SrTiO3 photocatalyst loaded with a Pt cocatalyst (0.1 wt %) gave 5.2% of the quantum yield at 420 nm for the H2 evolution reaction.

H2 evolution from an aqueous methanol solution on SrTiO3 photocatalysts codoped with chromium and tantalum ions under visible light irradiation

SrTiO3 photocatalysts doped with chromium ions showed photocatalytic activities for H2 evolution from an aqueous methanol solution under visible light irradiation. However, it had a long induction period. Codoping of niobium or tantalum ions with chromium ions shortened the induction period, and increased the photocatalytic activities in respect of the H2 evolution. The photocatalytic activities of chromium- and chromium/tantalum-doped SrTiO3 were improved when they were pretreated at 773K in the hydrogen reduction atmosphere. Codoping of tantalum ions suppressed the formation of Cr6+ ions and oxygen defects which would work as nonradiative recombination centers between photogenerated electrons and holes, resulting in the shortening of induction periods and the improvement of photocatalytic activities.

A new photocatalytic water splitting system under visible light irradiation mimicking a Z-scheme mechanism in photosynthesis

Abstract We studied the water splitting into H2 and O2 using two different semiconductor photocatalysts and a redox mediator, mimicking the Z-scheme mechanism of the photosynthesis. It was found that the H2 evolution took place on a Pt–SrTiO3 (Cr–Ta-doped) photocatalyst using an I− electron donor under the visible light irradiation. The Pt–WO3 photocatalyst showed an excellent activity of the O2 evolution using an IO3− electron acceptor under visible light. Both H2 and O2 gases evolved in the stoichiometric ratio (H2/O2=2) for more than 250 h under visible light using a mixture of the Pt–WO3 and the Pt–SrTiO3 (Cr–Ta-doped) powders suspended in NaI aqueous solution. It is for the first time that the stoichiometric water splitting occurred over oxide semiconductor photocatalysts under the visible light irradiation. We proposed a two-step photo-excitation mechanism using a pair of I−/IO3− redox mediators. The quantum efficiency of the stoichiometric water splitting was ca. 0.1% at 420.7 nm.