Synthesis and Characterization of Co-Doped Brookite Titania Photocatalysts with High Photocatalytic Activity

Transition metal-doping could effectively extend the light response range of TiO _2 photocatalysts from the ultraviolet(UV)to the visible region.Co-doped brookite titanium dioxide(Co–TiO_2)photocatalysts were synthesized via the hydrothermal method with titanium tetrachloride as the raw material and cobalt chloride hexahydrate as the dopant.The prepared Co–TiO_2 photocatalysts were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),Raman spectroscopy,X-ray photoelectron spectroscopy(XPS)and UV–Vis diffuse reflectance spectroscopy(UV–Vis DRS).The photocatalytic activities of Co–TiO _2 photocatalysts were evaluated by photocatalytic degradation of isopropanol alcohol(IPA),a typical volatile organic compound(VOC),under visible light.The influences ofdifferent Co doping rates,initial concentrations of IPA gas and the amounts of photocatalyst addition were also studied.At the same time,the enhancement mechanism ofcobalt ions as a trap for photogenerated holes was discussed.Thus,we found the optimum doping rate,initial concentration of IPA gas and amount of photocatalyst to add.The results show that the mesoporous Co–TiO _2 photocatalysts possess smaller size particles,larger specific surface area,lower forbidden bandgap energy(Eg)and better photocatalytic activity than pure brookite TiO _2.When the doping of Co was 7% by mass,the initial concentration ofIPA gas was 1.0×10^(-6 )mol/L and the addition of Co–TiO_2 photocatalysts was 50 mg,the best photocatalytic activity was achieved.Furthermore,the degradation rate ofIPA was up to 91%,which shows great potential for waste water treatment.

Fabrication of Ni Nanoclusters-Modied Brookite TiO2 Quasi Nanocubes and Its Photocatalytic Hydrogen Evolution Performance

The development of low-cost, earth-abundant and highly-ecient cocatalysts is still impor- tant to promote the photocatalytic H2 evolution reaction over semiconductors. Herein, a series of Ni nanoclusters (NCs) modied brookite TiO2 quasi nanocubes (BTN)(marked as Ni/BTN) are fabricated via a chemical reduction process. It is found that the loading content and oxidation state of Ni NCs can signiticantly inuence the optical absorption, photocat-alytic activity, and stability of Ni/BTN composites. Among the resultant Ni NCs-loaded products, 0.1%Ni/BTN composite delivers the best H2 evolution activity (156μmol/h), which is 4.3 times higher than that of the BTN alone (36 mol/h). Furthermore, the Ni NCs with ultrane size (-2 nm) and high dispersity enable shorter charge transfer distance by quickly capturing the photoexcited electrons of BTN, and thus result in the improved activity even though the oxidization of some Ni NCs on BTN is harmful to the activity for H2 evolution due to the much lower electron capturing capability of NiO than metallic Ni. This study not only clari es that brookite TiO2 would be a promising high-ecient photo- catalyst for H2 evolution, but also reveals vital clues for further improving its photocatalytic performance using low-cost Ni-based cocatalyst.

Quasi-Spherical Brookite TiO_2 Nanostructures Synthesized Using Solvothermal Method in the Presence of Oxalic Acid

Brookite TiO_2,the latest TiO_2 photocatalyst,promises to be an interesting candidate for photocatalytic applications because of its unique physical and chemical properties. In this study,pure-phase brookite TiO_2 with a quasi-spherical nanostructure was successfully synthesized via a solvothermal method using tetrabutyl titanate(Ti(OC_4H_9)_4,TBOT) as the Ti source in the presence of oxalic acid. NaOH was used to regulate the pH of solution. The structure and morphology of the samples were then analyzed using multiple methods,such as X-ray diff raction(XRD),Raman spectroscopy,scanning electron microscopy(SEM),transmission electron microscopy(TEM),Brunauer–Emmett–Teller(BET) measurements and ultraviolet–visible diff use spectroscopy(UV–Vis). Photocatalytic activities of the as-synthesized brookite TiO_2 were evaluated by degrading aqueous methylene blue solution under UV light irradiation. The effect of thermal treatment temperature on photocatalytic activity of the samples was also investigated. The produced brookite TiO_2 nanopowders calcined at 500 °C for 2 h showed the highest photocatalytic activity,and the corresponding degradation rate of methylene blue(10 mg/L) reached 96.7% after 90 min of illumination. In addition,the formation mechanism of pure-phase brookite TiO_2 was investigated. It was found that the formation of pure-phase brookite TiO_2 in this study was ascribed to the combined action of oxalic acid and sodium hydroxide.

Structure and property of mesoporous molybdenum/carbon co-doped brookite titania

Phase-pure brookite TiO2 was prepared by hydrothermal method using Ti(SO4)2 as precursor. From the point of energy compensation, molybdenum/carbon co-doped brookite TiO2 photocatalysts were prepared in the presence of dissolved glucose and ammonium molybdate. The samples were characterized by thermoanalysis, UV-vis diffuse reflectance spectroscopy (UV-vis/DRS), X-ray diffractometry (XRD), nitrogen adsorption and transmission electron microscopy (TEM). The photocatalytic activities of the as-prepared samples were tested on the photodecoloration of rhodamine B (Rh B) under simulated solar-light irradiation. The wavelength of light adsorption of co-doped samples is red shifted and the intensity of light adsorption increases highly in visible-light region compared with the single-doped samples. Thermal stability of brookite phase is improved greatly after co-doping, indicating that the co-doping facilitates the phase stabilization. Co-doping can improve the photodecoloration activity of composite brookite TiO2.

Internalization of Foreign Ions into Meta-stable Lattices:a Case Study of Transition-metal-doped Brookite

The connections between the building units of meta-stable lattice were generally considered to be easily disturbed during the doping process, causing serious hindrances blocking the development of functional doped materials. In this work, the synthesis of doped brookite, a typical meta-stable phase of TiO2, has been explored novelly by in-situ adding of cations of VIIIB and IB,IIB elements in the 3rd period（Fe, Co, Ni, Cu, Zn） during the urea-lactate aided low-basicity hydrothermal process. The results showed that only Cu-doped brookite could be successfully synthesized with trace amount of copper intensively internalized into the brookite lattice, while the other dopants lead to the formation of anatase TiO2. Extensive characterizations indicated a two-step doping process, where copper ions were firstly dispersed in an amorphous layer on the lattice surface and then they were internalized into brookite lattice. Cu-doped brookite exhibited significantly enhanced photocatalytic activity in the phenol degradation under visible light compared to bare brookite. The enhancement of catalytic performance was assigned to the impurity band gap and the reduction of charge carriers＇ recombination introduced by the internalization of Cu ions. The investigation reported herein contributes to the understanding of complex ion-doping effects on the structures of meta-stable materials, and provides hints for obtaining other functional doped materials.

Synthesis of brookite-typed titania from titanium chloride solution

The brookite-phase TiO_2 was prepared by a hydrothermal synthesis of titanium chloride solution. The thermolysis time and the pH value of the solution were controlled during the synthesis. X-ray diffraction experiments showed that TiO_2 powders partially containing the brookite-phase were successfully obtained. A great amount of OH-in the reaction solution was found to be important to obtain the brookite phase because the intermediate complex leading to the brookite phase consumes more OH- than other phases like the rutile.

Morphology and photocatalytic performance of nano-sized TiO_2 prepared by simple hydrothermal method with different pH values

pH value is a key factor in the preparation of nano-sized TiO2 with hydrothermal method. Using Ti（SO4）2 as the titanium source, H2O2 as the complexing agent, NaOH and HCl as the pH value regulator, nano- sized TiO2 powder with various morphologies and sizes was synthesized. Changes in morphology, size and phase type with pH values of samples were characterized by X-ray diffraction （XRD） and transmission electron micro- scopy （TEM） measurements. Results show that under the present preparation conditions, TiO2 powder is an anatase phase with pH value less than 11, but is more likely to be a brookite phase with pH value more than 11. With the increase in pH value from 1 to 11 in hydrothermal envi- ronment, nano-sized anatase TiO2 gradually grows up in all directions. {001 }, { 101 } and { 100} groups of crystal plane are the exposed crystal planes of nano-sized anatase TiO2 for the （004）, （101） and （200） facets found in high-reso- lution TEM image. The photocatalytic performance of nano-sized TiO2 with different morphologies was com- pared by measuring their photocatalytic degradation rates for methylene blue under ultraviolet light. Results show that anatase TiO2 prepared under the alkalescenthydrothermal environment （pH = 9, 11） has a better pho- tocatalytic degrading performance. Different sizes and phases of nanoscaled TiO2 powders with different photo- catalytic performances can be prepared by the control of pH value of hydrothermal solutions.