Alkali-free synthesis of a novel heterostructured CeO2-TiO2 nanocomposite with high performance to reduce Cr(VI) under visible light

In this study, a novel CeO₂-TiO₂ nanocomposite denoted as CeO₂-3TiO₂ was successfully synthesized via a facile one pot hydro-thermal method without alkali. It exhibits high photocatalytic reduction reactivity toward Cr(VI) under visible light. The photocatalytic reactivity of CeO₂-3TiO₂ is 18 times higher than that of pure CeO₂, 28 times higher than pure TiO₂, 15 times higher than the sample of simply mixed CeO₂ and TiO₂. The solution with Cr(VI) initial concentration of 2780 ppb can be fast photoreduced by CeO₂-3TiO₂ in 60 min under visible light to meet the criterion of U.S. Environmental protection Agency. Characterization results indicate CeO₂-3TiO₂ has the good crystal form of heterojunction structure, narrow pore size distribution, narrow energy gap and high photogenerated electron-hole separation efficiency. Based on the experimental results, a speculated photocatalytic mechanism was proposed.     

Highly active TiO2−x−yNxFy visible photocatalyst prepared under supercritical conditions in NH4F/EtOH fluid

A novel N and F co-doped TiO₂ (TiO_2−x−yN_xF_y) photocatalyst is prepared by treating the TiO₂ precursor in NH₄F/ethanol fluid under supercritical conditions. During photocatalytic degradation of methylene blue under visible light irradiation, the as-prepared TiO_2−x−yN_xF_y exhibits higher activity than the undoped TiO₂, N-doped TiO₂ (TiO_2−xN_x), and F-doped TiO₂ (TiO_2−yF_y). Based on the characterizations including XRD, Raman, FTIR, TEM, PLS, UV–vis DRS, N₂ adsorption–desorption isotherms, XPS and NH₃-TPD, the synergetic promotions of N- and F-dopants incorporated into the TiO₂ lattice are discussed based on the enhanced spectral response in visible region, oxygen vacancies, and surface acidic sites. Meanwhile, the supercritical treatment also promotes the activity owing to the increase in both the surface area and the crystallization degree of anatase, and the enhanced incorporation of N- and F-dopants into the TiO₂ lattice.     

Effect of the status of Sm on the properties of Sm contained N doped TiO2 photocatalysts

Nitrogen-doped TiO₂ (TiO_2?xN_y) nanoparticles with and without adding Sm³⁺ were synthesized by thermohydrolysis of TiCl₃. The samples were characterized by X-ray diffraction, specific surface area determination, UV–Vis diffuse reflectance spectroscopy. The photocatalytic activity of the sample was investigated by employing the oxidative destruction of nitric oxide as a probe reaction using a flow reactor. Although the doping of Sm³⁺ in the lattice of titania was not useful to improve the photocatalytic activity, loading of samarium oxides on the surface of titania resulted in an improvement of the photocatalytic activity of the nitrogen-doped TiO₂. The beneficial effect was explained by an increased separation efficiency of the photogenerated electron–hole pairs.     

Effect of dopant on ferroelectric,dielectric and photocatalytic properties of Co–La-doped dysprosium chromite prepared via microemulsion route

In the current study, pristine and a series of La and Co-doped dysprosium chromite (Dy_1-yLa_yCr_1-xCo_xO₃) nanoparticles have been fabricated via a facile microemulsion technique. The influence of doping was evaluated based on structural, ferroelectric, dielectric, and photocatalytic properties. The prepared nanoparticles were characterized by XRD, SEM, Raman, and UV–Vis techniques. XRD patterns confirm the synthesis of a monophase orthorhombic structure with space group Pbnm with an average crystalline size in the 18–37 nm range. The saturation polarization (Ps), remanence (Pr), and coercivity (Hc) were determined using a hysteresis loop, and it was observed that by increasing the concentration of dopants, the value of Ps and Pr were improved. According to the PL spectra, highly substituted materials had a low recombination rate and higher charge separation (e^? - h⁺), which was ultimately accountable for higher photocatalytic activity. The dielectric loss decreases with frequency and dopant concentration. The photocatalytic activity of Dy_1-yLa_yCr_1-xCo_xO₃ was investigated against Crystal Violet (CV) dye under sunlight irradiation. The Dy_1-yLa_yCr_1-xCo_xO₃ furnished a 70% dye degradation in 90 min, which is attributed to the tunned bandgap and efficient electron-hole pair separation and the photocatalytic activity under visible light making Dy_1-yLa_yCr_1-xCo_xO₃ a promising photocatalyst for dye removal from wastewater.     

Preparation, Characterization and Photocatalytic Activities of F-doped TiO2 Nanotubes

F-doped TiO₂ nanotubes were prepared by impregnation method. The prepared catalysts were characterized by XRD, TEM, and XPS. The photocatalytic activity of F-doped TiO₂ nanotubes was evaluated through the photodegradation of aqueous methyl orange. The experiments demonstrated that the F-doped TiO₂ nanotubes calcined at 300 °C possessed the best photocatalytic activity. Compared with pure TiO₂ nanotubes, the doping with F⁻ significantly enhanced the photocatalytic efficiency. The high photocatalytic activity was ascribed to several beneficial effects produced by F-doping: creation of oxygen vacancies, presence of Ti³⁺, and so on. An erratum to this article can be found at     

Effect of heat treatment on crystal phase and photocatalytic activity of Tm doped TiO2 nanoparticles

Abstract

Abstract

Tm doped TiO₂ nanoparticles have been synthesised by hydrolysis-precipitation method. The effect of heat treatment on the crystal phase and photocatalytic activity of Tm doped TiO₂ nanoparticles has been studied. The prepared samples were characterised by transmission electron microscopy, X-ray diffraction, Fourier transformed infrared and diffuse reflection spectrum analysis. The results show that Tm³⁺ doping can effectively inhibit the phase transformation from antase to rutile and decrease the crystallite size of nano-TiO₂ particles. There is an optimal Tm doping (1·4?mol.-%) after calcination at 550°C for the photocatalytic activity of methylene blue degradation.     

Prediction of a highly sensitive molecule sensor for SOx detection based on TiO2/MoS2 nanocomposites: a DFT study

First principles calculations within density functional theory have been carried out to investigate the adsorptions of SO_x (x?=?1, 2) molecules on TiO₂/MoS₂ nanocomposites in order to fully discover the gas sensing capabilities of TiO₂/MoS₂ composite systems. The van der Waals interactions were included to obtain the most stable geometrical structures of TiO₂/MoS₂ nanocomposites with adsorbed SO_x molecules. SO_x molecules preferentially interact with the doped nitrogen and fivefold coordinated titanium sites of the TiO₂ anatase nanoparticles because of their higher activities in comparison with the other sites. The results presented include structural parameters such as bond lengths and bond angles and energetics of the systems such as adsorption energies. The variation of electronic structures are discussed in view of the density of states and molecular orbitals of the SO_x molecules adsorbed on the nanocomposites. The results show that the adsorption of the SO_x molecule on the N-doped TiO₂/MoS₂ nanocomposite is energetically more favorable than the adsorption on the undoped one, implying that the nitrogen doping helps to strengthen the interaction of SO_x molecules with TiO₂/MoS₂ nanocomposites. These calculated results thus provide a theoretical basis for the potential applications of TiO₂/MoS₂ nanocomposites in the removal and sensing of harmful SO_x molecules.     

Ag nanoparticles loaded TiO2/MWCNT ternary nanocomposite: A visible-light-driven photocatalyst with enhanced photocatalytic performance and stability

A visible light active photocatalyst, Ag/TiO₂/MWCNT was synthesized by loading of Ag nanoparticles onto TiO₂/MWCNT nanocomposite. The photocatalytic activity of Ag/TiO₂/MWCNT ternary nanocomposite was evaluated for the degradation of methylene blue dye under UV and visible light irradiation. Ag/TiO₂/MWCNT ternary nanocomposite exhibits (~9 times) higher photocatalytic activity than TiO₂/MWCNT and (~2 times) higher than Ag/TiO₂ binary nanocomposites under visible light irradiation. The enhancement in the photocatalytic activity is attributed to the synergistic effect between Ag nanoparticles and MWCNT, which enhance the charge separation efficiency by Schottky barrier formation at Ag/TiO₂ interface and role of MWCNT as an electron reservoir. Effect of different scavengers on the degradation of methylene blue dye in the presence of catalyst has been investigated to find the role of photogenerated electrons and holes. Simultaneously, the Ag/TiO₂/MWCNT shows excellent photocatalytic stability. This work highlights the importance of Ag/TiO₂/MWCNT ternary nanocomposite as highly efficient and stable visible-light-driven photocatalyst for the degradation of organic dyes.     

Preparation and characterization of CeO2/TiO2 nanoparticles by flame spray pyrolysis

Nanocrystalline TiO₂, CeO₂ and CeO₂-doped TiO₂ have been successfully prepared by one-step flame spray pyrolysis (FSP). Resulting powders were characterized with X-ray diffraction (XRD), N₂-physisorption, Transmission Electron Microscopy (TEM) and UV-Vis spectrophotometry. The TiO₂ and CeO₂-doped TiO₂ nanopowders were composed of single-crystalline spherical particles with as-prepared primary particle size of 10-13 nm for Ce doping concentrations of 5-50 at%, while square-shape particles with average size around 9 nm were only observed from flame-made CeO₂. The adsorption edge of resulting powder was shifted from 388 to 467 nm as the Ce content increased from 0 to 30 at% and there was an optimal Ce content in association with the maximum absorbance. This effect is due to the insertion of Ce^3+/4+ in the TiO₂ matrix, which generated an n-type impurity band.     

Magnetically recyclable Ni1-xCdxCeyFe2-yO4-rGO nanocomposite photocatalyst for visible light driven photocatalysis

In this study, a magnetically recyclable Ni_1-xCd_xCe_yFe_2-yO₄-rGO (x, y = 0.05) (NCCF-rGO) nanocomposite photocatalyst has been prepared by following a facile in-situ co-precipitation method combined with ultra-sonication means. The as-synthesized magnetically separable NCCF-rGO nanocomposite photocatalyst efficiently degrades methylene blue (MB) dye in comparison to bare Ni_1-xCd_xCe_yFe_2-yO₄ (x, y = 0.05) (NCCF) nanoparticles (NPs) under visible light irradiation. The photo-degradation rate of MB with NCCF-rGO was ~9 times higher than NCCF nanoparticles (NPs). This enhanced photocatalytic performance of NCCF-rGO photocatalyst was due to the presence of reduced graphene oxide, which greatly help in production of photoactive species by reducing the rate of electro-hole pair recombination. The role of photoactive species that were responsible for the photocatalytic degradation of methylene blue has also been investigated. The as-synthesized NCCF-rGO photocatalyst expressed superb chemical stability and photocatalytic activity even after seven cycle runs. Moreover, the NCCF-rGO nanocomposite worked at all pH values and showed good acid resistance. In particular, the as-synthesized NCCF-rGO photocatalyst could be collected for the next cycle run by simply applying an external magnetic field. Hence, the NCCF-rGO nanocomposite could have potential use in organic dyes contained wastewater treatment.     

Preparation of transparent PVA/TiO2 nanocomposite films with enhanced visible-light photocatalytic activity

Polymer/semiconductor oxide nanocomposite films have been intensively investigated for various applications. In this work, we reported a simple hydrothermal method to fabricate highly transparent poly(vinyl alcohol)/titanium dioxide (PVA/TiO₂) nanocomposite films with enhanced visible-light photocatalytic activity. The as-prepared PVA/TiO₂ nanocomposite films showed high optical transparency in the visible region even at a high TiO₂ content (up to 40 wt.%). The determination of photocatalytic activity by photodegradation of methyl orange (MO) and colorless phenol showed that PVA/TiO₂ nanocomposite films exhibited enhanced visible-light photocatalytic activity and excellent recycle stability. This work provided new insights into fabrication of polymer/TiO₂ nanocomposites as high performance photocatalysts in waste water treatment.     

Preparation and photochemical properties of nanoparticles of ceria doped with zinc oxide

Abstract

Nanoparticles of CeO₂ doped with ZnO were syn thesised via soft solution chemical processes at 40°C and a final pH of 6. The particle size of CeO ₂decreased markedly after doping with ZnO. The solubility limit of ZnO in Ce_1-xZn_xO_2-x was determined to be x = 0·561. The oxidation catalytic activity of CeO₂ was effectively decreased by doping with ZnO. For the oxidation of phenol, the photocatalytic activity of ZnO doped CeO₂ was much lower than that of fine titania particles. ZnO doped CeO₂ showed excellent UV absorption and transparency in the visible region, in a similar manner to undoped CeO₂.     

sol-gel法制备CeO2-TiO2/凹凸棒石复合材料的催化性能

以凹凸棒石(ATP)为载体,Ce(NO₃)₃·6H₂O和Ti(OBu)₄为原料,冰醋酸为抑制剂,采用溶胶-凝胶法制备CeO₂-TiO₂/ATP纳米复合材料。利用TG-DSC、TEM、XRD和N₂吸附/脱附仪对复合材料进行表征,考察铈钛摩尔比对所制备样品催化降解罗丹明B溶液性能的影响。结果表明,当Ce/Ti≥5/5时,具有立方萤石结构的氧化物颗粒以固溶体形式均匀分布在ATP表面,颗粒尺寸约5~10 nm;随Ti⁴⁺的进一步增加,样品中的CeO₂结晶不完全;当Ce/Ti<3/7时,样品中出现锐钛矿型TiO₂的分离相。适量的Ti⁴⁺掺杂能促进CeO₂产生较多的结构缺陷,有利于增加晶格氧空位的浓度,提高样品的催化活性。对罗丹明B的催化降解实验表明,当Ce/Ti=5/5时,样品的催化性能较好,对罗丹明B溶液的化学需氧量(COD)去除率可达96%以上。     

Synthesis of TiO2−xNy/Ag‐PbMoO4 Composite and Their Photocatalytic Activity Under Simulated Solar Light Irradiation

TiO_2?xN_y/Ag‐PbMoO₄ composite were synthesized by sonochemical method. The results revealed that the band‐gap energy absorption edge of TiO_2?xN_y/Ag‐PbMoO₄ composite was shifted to a longer wavelength as compared to TiO₂, TiO_2?xN_y, PbMoO_4, and Ag‐PbMoO₄. The TiO_2?xN_y/Ag‐PbMoO₄ composite showed the enhanced photocatalytic activity for degradation of indigo carmine dye (ICD) under simulated solar light irradiation. The TiO_2?xN_y/Ag‐PbMoO₄ composite exhibited the highest percentage (95.4%) of degradation of ICD and the highest reaction rate constant (0.0244 min^?1) in 2 h. The results suggested that a good combination of Ag and TiO_2?xN_y nanoparticles has great influence on the photocatalytic behavior of PbMoO₄.     

Photocatalytic hydrogen production by Au–MxOy (MAg,Cu, Ni) catalysts supported on TiO2

Au–M_xO_y (MAg, Cu, Ni) nanoparticles supported on TiO₂–P25 were prepared by the deposition–precipitation method and were evaluated for the photocatalytic water splitting reaction for hydrogen production, using a mixture of water–methanol (1:1). The combinations of Au–Cu₂O/TiO₂ and Au–NiO/TiO₂ effectively increased the hydrogen production (2064 and 1636 μmol·h^− 1·g^− 1) obtained by Au/TiO₂ (1204 μmol·h^− 1·g^− 1). The higher photoactivities achieved by Au–Cu₂O and Au–NiO nanoparticles deposited on TiO₂ were attributed to an enhancement of the electron charge transfer from TiO₂ to the Au–M_xO_y systems and the effect of surface plasmon resonance of gold nanoparticles.     

Preparation of TiO2/carbon nanotubes photocatalysts: The influence of the method of oxidation of the carbon nanotubes on the photocatalytic activity of the nanocomposites

A method for the preparation of efficient TiO₂/multi-wall carbon nanotubes nanocomposite photocatalysts by precipitation of anatase TiO₂ nanoparticles onto differently oxidized carbon nanotubes is presented. The precursor compound titanium(IV) bromide was hydrolyzed producing pure anatase phase TiO₂ nanoparticles decorated on the surface of the oxidized carbon nanotubes. The oxidative treatment of the carbon nanotubes influenced the type, quantity and distribution of oxygen-containing functional groups, which had a significant influence on the electron transfer properties, i.e., the photocatalytic activity of the synthesized nanocomposites. The results of C.I. Reactive Orange 16 photodegradation in the presence of all the synthesized nanocomposites showed their better photocatalytic activity in comparison to the commercial photocatalyst Degussa P-25.     

Specific features of the formation of oxyfluoride glass-ceramics in the SiO2-PbF2-CdF2-ZnF2-Al2O3-Er(Eu, Yb)F3 system

Oxyfluoride glasses of the composition 0.3SiO₂ · 0.15AlO_3/2 · (0.29 − z)CdF₂ · (0.18 + z)PbF₂ · 0.05ZnF₂ · 0.03Er(Eu, Yb)F₃ and the synthesis of the related glass-ceramic materials have been investigated. It has been demonstrated that heat treatment of the glasses is accompanied by the formation of a nanosized (16–25 nm) crystalline phase. X-ray powder diffraction analysis and measurement of spectral-luminescent characteristics have revealed that, during the phase decomposition induced in fluorosilicate glasses by rareearth ions, these ions gradually pass from the vitreous matrix into nanocrystals of the cubic modification and form, hypothetically, the β-Pb_{2 − y} Cd _y Er _x F_{2 + x} crystalline phase, in which the value of x is constant and equal to 0.2, whereas the value of y varies from 0 to 0.145 depending on the composition of the initial mixture.     

Synthesis of Ti1−xSnxO2 nanosized photocatalysts in reverse microemulsions

The preparation of Ti_1−xSn_xO₂ nanocrystalline photocatalysts in reverse microemulsions is reported in this work. The obtained materials have been characterised by total reflection X-ray fluorescence (TXRF), X-ray diffraction (XRD) and Raman and UV–vis spectroscopies. Very good accordance between calculated and obtained compositions is observed. Undoped TiO₂ prepared in this way crystallises in the anatase phase. Tin-doped anatase is formed with x < 0.05, while both anatase and rutile phases crystallise when x ≥ 0.05. When both phases coexist, a preferential doping of rutile seems to occur. When x = 0.10, a multiphase mixture containing TiO₂(anatase), TiO₂(rutile) and SnO₂ was formed. No significant modification of the band gap is found in any case. The photocatalytic activity of the obtained catalysts is compared employing the trichloroethylene photocatalytic degradation as a test reaction. The beneficial effect of Sn⁴⁺ in the activity of TiO₂ appears to be related to the formation of anatase–rutile mixtures, leading to the highest specific photocatalytic activity in the sample of composition Ti_0.93Sn_0.07O₂, with anatase:rutile ratio close to 3.     

Carbon-based TiO2-x heterostructure nanocomposites for enhanced photocatalytic degradation of dye molecules

Application of brown titanium dioxide (TiO_2-x) and its modified composite forms in the photocatalytic decomposition of organic pollutants in the environment is a promising way to provide solutions for environmental redemption. Herein, we report the synthesis of effective and stable TiO_2-x nanoparticles with g-C₃N₄, RGO, and multiwalled carbon nanotubes (CNTs) using a simple hydrothermal method. Among all the as-synthesized samples, excellent photocatalytic degradation activity was observed for RGO-TiO_2-x nanocomposite with high rate constants of 0.075 min^?1_, 0.083 min^?1 and 0.093 min^?1 for methylene blue, rhodamine-B, and rosebengal dyes under UV–Visible light irradiation, respectively. The altered bandgap (1.8 eV) and the large surface area of RGO-TiO_2-x nanocomposite impacts on both absorption of visible light and efficiency of photogenerated charge electron (e^?)/hole (h⁺) pair separation. This resulted in enhanced photocatalytic property of carbon-based TiO_2-x nanocomposites. A systematic study on the influence of different carbon nanostructures on the photocatalytic activity of brown TiO_2-x is carried out.     

Effect of doping on dielectric and optical properties of barium hexaferrite: Photocatalytic performance under solar light irradiation

A series of Co-doped and Cr-doped Ba_1-xCo_xFe_12-yCr_yO₁₉ nanoparticles (NPs) were synthesized via the microemulsion route. The effects of Co and Cr substitution on the structural, dielectric, optical, and photocatalytic properties of the NPs were investigated. The Ba_1-xCo_xFe_12-yCr_yO₁₉ NPs were characterized using Fourier-transform infrared spectroscopy, X-ray diffraction analysis, scanning electron microscopy, Raman scattering, and dielectric measurements. The Ba_1-xCo_xFe_12-yCr_yO₁₉ NPs were obtained in a single phase with an average crystallite size of 18 nm. The dielectric constant of the NPs decreased, while the dielectric loss and tangent loss increased with increasing dopant (Co and Cr) contents. The photocatalytic activities (PCAs) of the Ba_1-xCo_xFe_12-yCr_yO₁₉ and BaFe₁₂O₁₉ NPs were appraised by carrying out the degradation of CV (crystal violet) dye under solar light irradiation. The doping improved the PCA of BaFe₁₂O_19, and up to 64.23% of the CV dye could be degraded within 60 min under visible light irradiation. The Ba_1-xCo_xFe_12-yCr_yO₁₉ NPs showed great potential for application as an economic photocatalyst as they required solar light irradiation for the degradation of CV.