Fabrication of Fe-doped TiO2 nanoparticles and investigation of photocatalytic decolorization of reactive red 198 under visible light irradiation

In this research, Fe-doped TiO₂ nanoparticles with various Fe concentrations (0. 0.1, 1, 5 and 10 wt%) were prepared by a sol–gel method. Then, nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray analysis (EDX), BET surface area, photoluminescence (PL) spectroscopy and UV–vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the nano-particles was evaluated through degradation of reactive red 198 (RR 198) under UV and visible light irradiations. XRD results revealed that all samples contained only anatase phase. DRS showed that the Fe doping in the titania induced a significant red shift of the absorption edge and then the band gap energy decreased from 3 to 2.1 eV. Photocatalytic results indicated that TiO₂ had a highest photocatalytic decolorization of the RR 198 under UV irradiation whereas photocatalytic decolorization of the RR 198 under visible irradiation increased in the presence of Fe-doped TiO₂ nanoparticles. Among the samples, Fe-1 wt% doped TiO₂ nanoparticles showed the highest photocatalytic decolorization of RR198 under visible light irradiation.     

Enhanced photocatalytic activity of graphene–TiO2 composite under visible light irradiation

Novel graphene–TiO₂ (GR–TiO₂) composite photocatalysts were synthesized by hydrothermal method. During the hydrothermal process, both the reduction of graphene oxide and loading of TiO₂ nanoparticles on graphene were achieved. The structure, surface morphology, chemical composition and optical properties of composites were studied using XRD, TEM, XPS, DRS and PL spectroscopy. The absorption edge of TiO₂ shifted to visible-light region with increasing amount of graphene in the composite samples. The photocatalytic degradation of methyl orange (MO) was carried out using graphene–TiO₂ composite catalysts in order to study the photocatalytic efficiency. The results showed that GR–TiO₂ composites can efficiently photodegrade MO, showing an enhanced photocatalytic activity over pure TiO₂ under visible-light irradiation. The enhanced photocatalytic activity of the composite catalysts might be attributed to great adsorptivity of dyes, extended light absorption range and efficient charge separation due to giant π-conjugation system and two-dimensional planar structure of graphene.     

Nitrogen doped TiO2 nanoparticles decorated on graphene sheets for photocatalysis applications

Nitrogen doped TiO₂ nanoparticles decorated on graphene sheets are successfully synthesized by a low-temperature hydrothermal method. The resulting GR-N/TiO₂ composites are characterized by X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-Ray photoelectron spectroscopy (XPS) and Transmission Electron Microscopy (TEM). The optical properties are studied using UV–visible diffuse reflectance spectroscopy (DRS), which confirms that the spectral responses of the composite catalysts are extended to the visible-light region and show a significant reduction in band gap energy from 3.18 to 2.64 eV. Photoluminescence emission spectra verify that GR-N/TiO₂ composites possess better charge separation capability than pure TiO₂. The photocatalytic activity is tested by degradation of methyl orange (MO) dye under visible light irradiation. The results demonstrate that GR-N/TiO₂ composites can effectively photodegrade MO, showing an impressive photocatalytic enhancement over pure TiO₂. The dramatically enhanced activity of composite photocatalysts can be attributed to great adsorption of dyes, enhanced visible light absorption and efficient charge separation and transfer processes. This work may provide new insights into the design of novel composite photocatalysts system with efficient visible light activity.     

Effective removal of organic pollution by using sonochemical prepared LaFeO3 perovskite under visible light

In the present work, LaFeO₃ perovskite was prepared via ultrasonic probe with power of 60 W and frequency of 18 KHz. LaFeO₃ nanorods were formed when sonication time was 20 min. In this research, green materials including corn, starch, and rice were used to control the size, morphology, and purity of final products. As-prepared LaFeO₃ nanostructures were used to purify water containing organic contaminants. LaFeO₃ nanostructures prepared by using corn, starch, and rice showed higher photocatalytic activity compare to LaFeO₃ nanostructures without natural capping agents. Using corn increased degradation efficiency by 65% under visible light. XRD results show that Fe₂O₃ appeared as an impurity when starch was used to prepare LaFeO₃ nanostructures. This impurity significantly boosts the degradation efficiency under UV light. Fe₂O₃ under UV light act as co-absorbent and boost efficiency by 43%. LaFeO₃ nanostructures were characterized by XRD, EDX, SEM, CV, BET, TEM, DRS and FT-IR.     

Enhanced adsorption and visible-light-induced photocatalytic activity of hydroxyapatite modified Ag-TiO2 powders

In order to get a kind of materials with enhanced adsorption and photocatalytic performance, hydroxyapatite modified Ag-TiO₂ powders (Ag-TiO₂-HAP) were prepared by a facile wet chemical strategy. The powders were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis absorption spectroscopy, N₂ adsorption-desorption measurement (BET), photoluminescence spectroscopy (PL), etc. The photocatalytic activities were evaluated by photocatalytic oxidation decomposition of acetone in air under visible-light illumination. The results showed that the coupled system indicated a highest photocatalytic activity and photochemical stability under visible-light irradiation than all the other catalysts. The intensively improved visible-light-induced photocatalytic activity of the Ag-TiO₂-HAP hybrids could be attributed to its strong absorption in the visible-light region, low recombination rate of the electron-hole pair and large BET specific surface area.     

Preparation of highly efficient Al-doped ZnO photocatalyst by combustion synthesis

Novel Al-doped ZnO (AZO) photocatalysts with different Al concentrations (0.5–6.0 mol%) were prepared through a facile combustion method and followed by calcination at 500 °C for 3 h. The obtained nanopowders were characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM) combined with EDX, transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), UV–vis spectroscopy and photoluminescence spectroscopy. The XRD patterns of AZO nanopowders were assigned to wurtzite structure of ZnO with the smallest crystallite size about 11 nm consistent with the results from TEM. The doping of Al in ZnO crystal structure successfully suppressed the growth of ZnO nanoparticles confirmed by XRD patterns. The absorption spectra analysis showed that the optical band gap energy (E_g) for the AZO nanopowders were in the range of 3.12–3.21 eV and decreased with increasing of Al dopant. The photocatalytic activities of the samples were evaluated by photocatalytic degradation of methyl orange under visible light (λ ≥ 420 nm) and sunlight irradiation. The results showed that the AZO photocatalyst doped with 4.0 mol% Al exhibited five times enhanced photocatalytic activity compared to pure ZnO. The enhanced photocatalytic activity could be attributed to extended visible light absorption, inhibition of the electron–hole pair's recombination and enhanced adsorptivity of MO dye molecule on the surface of AZO nanopowders.     

Synthesis of large surface area LaFeO3 nanoparticles by SBA-16 template method as high active visible photocatalysts

Nanosized LaFeO₃ with large specific surface area has been successfully synthesized by an impregnation process, with mesoporous silica SBA-16 as hard template and corresponding metal nitrates as La and Fe resources, and the resulting LaFeO₃ is also characterized by thermogravimetry–differential thermal analysis (TG–DTA), X-ray diffraction (XRD), N₂ adsorption–desorptions, Brunauer Emmett Teller (BET) technique, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–visible diffuse reflection spectrum (UV–Vis DRS), and surface photovoltage spectroscopy (SPS). It is found that, compared with that prepared by the conventional citrate method, the as-prepared LaFeO₃ with 20-50 nm particle size has remarkable large specific surface area, even still with the surface area as large as about 85 m² g⁻¹ after calcination at 800 °C, which is attributed to its mesoporous structure as well as the small particle size. During the photocatalytic degradation of Rhodamine B solution under visible irradiation, all the LaFeO₃ samples obtained are superior to P25 TiO₂, and the activity becomes high with increasing calcination temperature. It is revealed that the excellent photocatalytic performance is mainly ascribed to the large surface area and high photogenerated charge separation rate.     

离子液体辅助N,S,F共掺杂纳米TiO2的制备与表征

以TiCl4、硫脲和离子液体([C6mim]+[BF4]-)为原料,采用微波催化水解法合成掺杂的纳米TiO2前驱体,在NH3/N2气氛中经程序升温煅烧处理制得N,S,F共掺杂TiO2光催化剂(N—S—F—TiO2)。采用X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、紫外-可见漫反射光谱(UV-Vis/DRS)等对该光催化剂的结构和性能进行表征。结果表明,该光催化剂为锐钛矿晶型,具有较高的纯度和结晶度,掺杂在TiO2晶体中形成Ti—O—N键,Ti—O—S键,Ti—S键,而F以TiOF2形态掺杂。在可见光区400～550nm具有强吸收,且在600～800nm出现一个较强的吸收带。实验表明,使用[C6mim]+[BF4]-与H2O的体积比为5/95所制得的光催化剂对甲基橙降解的催化活性最高,可见光照射200min降解率达95%。多掺杂的协同效应使得N—S—F—TiO2具有对可见光的强烈吸收和较高的可见光催化活性。     

Effect of Nb doping on morphology,crystal structure,optical band gap energy of TiO2 thin films

Nb–TiO₂ nanofibers and thin films were prepared using a sol–gel derived electrospinning and spin coating, respectively, by varying the Nb/Ti molar ratios from 0 to 0.59 to investigate the effect of Nb doping on morphology, crystal structure, and optical band gap energy of Nb–TiO₂. XRD results indicated that Nb–TiO₂ is composed of anatase and rutile phases as a function of Nb/Ti molar ratio. As the Nb/Ti molar ratio rose, the anatase to rutile phase transformation and the reduction in crystallite size occurred. The band gap energy of Nb–TiO₂ was changed from 3.25 eV to 2.87 eV when the anatase phase was transformed to rutile phase with increasing the Nb doping. Experimental results indicated that the Nb doping was mainly attributed to the morphology, the crystal structure, the optical band gap energy of Nb–TiO₂, and the photocatalytic degradation of methylene blue.     

Preparation, characterization, and photocatalytic properties of silver carbonate

Silver carbonate (Ag₂CO₃) short rods were prepared using a precipitation method. It was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflective spectra (DRS) and photocatalytic degradation of organic pollutants and destruction of E. coli measurements. The results of DRS suggested that the optical transition of Ag₂CO₃ was indirectly allowed, and its band gap was determined to be 2.08 eV. The prepared Ag₂CO₃ displayed a high activity towards degradation of phenol and MB under visible light. The total organic carbon (TOC) value decreased during the photocatalytic process, which suggests that phenol was truly photodegraded. The stability of Ag₂CO₃ was greatly improved when Na₂CO₃ was added into the photocatalytic system. In addition, Ag₂CO₃ displayed enhanced photocatalytic activities for the destruction of E. coli due to its photogenerated electron-hole pairs.     

Characterization of NaTaO3 synthesized by ultrasonic method

NaTaO₃ perovskite-like materials were synthesized using sodium acetate and tantalum ethoxide as precursors in an ultrasonic bath at room temperature. The pristine sample was thermally treated at 600 °C and characterized using XRD, N₂ physisorption, DRS, SEM and TEM techniques. The structural characterization by X-ray powder diffraction revealed that the crystallization of the NaTaO₃ phase prepared at 600 °C showed agglomerates sizes in the micrometric scale, as confirmed by scanning electron microscopy (SEM). On the other hand, well-defined NaTaO₃ particles in the nanometric scale were determined using TEM. It was found that, for the treated sample, the band gap and BET area was 3.8 eV and 9.5 m² g^?1, respectively. The annealed perovskite, deposited onto ITO glass, presented an important variation in the open circuit potential transient during UV light irradiation in neutral solution, compared with its counterpart prepared by solid-state method. These intrinsic properties, given by the preparation route, might be appropriate for increase its photocatalytic activity.     

Synthesis,characterization of Cr-doped TiO<Subscript>2</Subscript> nanotubes with high photocatalytic activity

Cr-doped TiO₂ nanotubes (Cr/TiO₂ NTs) with high photocatalytic activity were prepared by the combination of sol–gel process with hydrothermal treatment. XRD, TEM and UV–vis DRS techniques were employed for microstructural characterization. TEM images show that Cr/TiO₂ NTs are in good tubular structure and have diameter of about 10 nm. The Cr doping induces the shift of the absorption edge to the visible light range and the narrowing of the band gap. The photocatalytic experiment reveals that the photocatalytic performance of TiO₂ NTs can be improved by the doping of chromium ions.     

Visible-light-induced degradation of formaldehyde over titania photocatalyst co-doped with nitrogen and nickel

Titanium isopropoxide, ammonium carbonate and nickelous nitrate were used as the sources of titanium, nitrogen, and nickel to prepare titania photocatalyst co-doped with nitrogen and nickel by means of the modified sol-gel method. The photocatalyst was characterized by X-ray diffraction (XRD), UV-vis diffusive reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM). The prepared N-Ni co-doped photocatalyst showed optical absorption in the visible light area and exhibited excellent photocatalytic ability for the degradation of formaldehyde under visible light irradiation. The effects of annealing temperature and component on the phase composition and photocatalytic activity were investigated. The results demonstrated that nitrogen atoms was weaved into the structure of titania and led to the response to visible light. However, nickel atoms existed in the form of Ni₂O₃, dispersed on the surface of TiO₂, suppressed the recombination of photo-induced electron-hole pairs, raised the photo quantum efficiency, and led to the enhancement of photocatalytic performance. The increase of photoactivity was attributed to the synergistic effects of co-doping.     

Optical and photocatalytic properties of novel heterogeneous PtSe2–graphene/TiO2 nanocomposites synthesized via ultrasonic assisted techniques

Novel material PtSe₂–graphene/TiO₂ nanocomposites were successfully synthesized through a facile ultrasonic assisted method. The prepared composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) with an energy dispersive X-ray (EDX),transmission electron microscopy (TEM), Raman spectroscopic analysis, UV–vis absorbance spectra and UV–vis diffuse reflectance spectra (DRS) analysis were obtained. The catalytic behavior was investigated through the decomposition of rhodamine B (Rh.B) as a standard dye. Enhanced photocatalytic activities were observed by increasing the weight% of graphene in the PtSe₂–graphene/TiO₂ nanocomposites. We observed that the coupling of TiO₂ with PtSe₂–graphene alter the optical properties by observing a precise band gap in the visible range.     

Nonlinear optical absorption in Bi3TiNbO9 thin films using Z-scan?technique

Bi₃TiNbO₉ (BTN) thin films with layered perovskite structure were fabricated on fused silica by pulsed laser deposition. The XRD pattern revealed that the films are single-phase perovskite and highly (00l) textured. Their fundamental optical constants, such as band gap, linear refractive index, and linear absorption coefficient, were obtained by optical transmittance measurements. The dispersion relation of the refractive index vs. wavelength follows the single electronic oscillator model. The nonlinear optical absorption of the films was investigated by single beam Z-scan method at a wavelength of 800 nm with laser duration of 80 fs. We obtained the nonlinear absorption coefficient β=1.44×10⁻⁷ m/W. The results show that the BTN thin films are promising for applications in absorbing-type optical devices.     

Structural refinement,optical and ferroelectric properties of microcrystalline Ba(Zr0.05Ti0.95)O3 perovskite

For this study, a microcrystalline Ba(Zr_0.05Ti_0.95)O₃ (BZT) powder was prepared by a high energy ball milling method followed by calcination at 1100 °C for 4 h. The calcined powder was structurally characterized by X-ray diffraction and Rietveld refinement data, which showed that this material has a perovskite-type tetragonal structure with a space group of (P4mmm). The micro-Raman spectrum revealed local lattice distortions due to distorted octahedral [TiO₆] clusters. The temperature and frequency-dependent dielectric study of the BZT ceramic showed normal phase transition behavior. The ferroelectric property was studied by a P–E hysteresis loop. Optical band gap was investigated by ultraviolet–visible (UV–vis) absorption spectroscopy at room temperature. The UV–vis spectrum indicated that the BZT powder has an optical band gap of 3.15 eV.     

Synthesis of samarium- and nitrogen-co-doped TiO2 by modified hydrothermal method and its photocatalytic performance for the degradation of 4-chlorophenol

Sm- and nitrogen-co-doped TiO₂ (Sm-N-TiO₂) catalysts were prepared via the modified hydrothermal method using tetrabutyl titanate as the precursor and calcination at 200 °C. The microstructure of the sample was characterized by X-ray diffraction (XRD), ultraviolet-visible diffuse reflection spectroscopy (UV-vis-DRS), Fourier transform infrared (FTIR) spectra and X-ray photoelectron spectroscopy (XPS). The average particle size was ca. 16.0 nm as calculated from XRD patterns. Sm-N-TiO₂ nanocrystalline showed strong visible-light response and high photocatalytic activity for 4-chlorophenol degradation under irradiation by visible-light (400-500 nm). The high visible-light photocatalytic activity of the obtained Sm-N-TiO₂ might result from the incorporation of nitrogen atoms in TiO₂, which extended the spectral response to the visible region, and Sm₂O₃ facilitated the excited electron transfer and hence suppressed efficiently the recombination of photoproduced electron-hole.     

S掺杂对锐钛矿相TiO2电子结构与光催化性能的影响

采用基于第一性原理的平面波超软赝势方法研究了掺杂不同价态S的锐钛矿相TiO₂的晶体结构、杂质形成能、电子结构及光学性质.计算结果表明硫在掺杂体系中的存在形态与实验中的制备条件有关;掺杂后晶格发生畸变、原子间的键长及原子的电荷量也发生了变化,导致晶体中的八面体偶极矩增大; S 3p态与O 2p态、Ti 3d态杂化而使导带位置下移、价带位置上移及价带宽化,从而导致TiO₂的禁带宽度变窄、光吸收曲线红移到可见光区.这些结果很好地解释了S掺杂锐钛矿相TiO₂在可见光下具有优良的光催化性能的内在原因.根据计算结果分析比较了硫以不同离子价态掺杂对锐钛矿相TiO₂电子结构和光催化性能影响的差别. 关键词： 2')" href="#">锐钛矿相TiO₂ S掺杂 第一性原理 光催化性能     

碳-锌共掺杂锐钛矿相TiO2 电子结构与光学性质的第一性原理研究

近年来的理论和实验研究表明,通过不同离子共掺杂TiO₂是减小其禁带宽度的一种有效方法.本文采用基于第一性原理的平面波超软赝势方法研究了C和Zn共掺杂TiO₂的能带结构、态密度和光学性质.计算结果表明C-Zn共掺杂导致导带相对Fermi能级发生了明显的下降,同时在TiO₂的导带下方与价带上方形成了新的杂质能级,使TiO₂的禁带宽度变小, TiO₂的光学吸收带边产生红移. 杂质能级可以降低光激发产生的电子-空穴对的复合概率, 提高TiO₂的光催化效率. 此外, 掺杂后TiO₂在可见光区的吸收系数有明显增加, 能量损失也明显减小.     

Low-temperature preparation of F-doped TiO2 film and its photocatalytic activity under solar light

A novel and simple method for preparing F-doped anatase TiO₂ (defined as FTO) film with high photocatalytic activity was developed using titanium-n-butoxide and NH₄F as TiO₂ and fluorine precursors under mild condition, i.e. low temperature (lower than 373 K) and ambient pressure. The prepared samples were characterized by XRD, SEM, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectrum (DRS), photoluminescence spectrum (PL) and TG-DSC analysis. The photocatalytic activity was evaluated by decomposing X-3B under artificial solar light. The results showed that the crystallinity of TiO₂ was improved by F-doping. F⁻ ions can prevent the grain growth, and the transformation of anatase to rutile phase was also inhibited. The doped fluorine atoms existed in two chemical forms, and the ones incorporated into TiO₂ lattice might take a positive role in photocatalysis. Compared with surface fluorination samples, FTO film exhibited better photocatalytic activity. The high photocatalytic activity of FTO may due to extrinsic absorption through the creation of oxygen vacancies rather than the excitation of the intrinsic absorption band of bulk TiO₂. Furthermore, the FTO can be recycled with little photocatalytic activity depression. Without any further treatment besides rinsing, after 6 recycle utilization, the photocatalytic activity of FTO film was still higher than 79%.