Synthesis of Zn-doped TiO2 microspheres with enhanced photovoltaic performance and application for dye-sensitized solar cells

Zn-doped TiO₂ microspheres have been synthesized by introducing a trace amount of zinc nitrate hexahydrate to the reaction system. Scanning electron microscope (SEM), field-emission scanning electron microscope (FESEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) have been utilized to characterize the samples. Both surface photovoltage spectroscopy (SPS) technique based on lock-in amplifier and transient photovoltage (TPV) measurement reveal that the slight doping of Zn can promote the separation of photo-generated charges as well as restrain the recombination due to the strong interface built-in electric field and the decreasing of surface trap states. The photovoltaic parameters of dye-sensitized solar cells (DSSCs) based on Zn-doped TiO₂ are significantly better, compared to that of a cell based on undoped TiO₂. The relation between the performance of DSSCs and their photovoltaic properties is also discussed.     

In situ synthesis and enhanced visible light photocatalytic activity of C-TiO2 microspheres/carbon quantum dots

TiO₂ microspheres and TiO₂/carbon quantum dots (CQDs) composites with different CQDs contents were successfully synthesized via solvothermal and in situ hydrothermal method. The structure and morphology of the prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM). Results showed that carbon elements were successfully doped into the TiO₂ lattice (C-TiO₂) and CQDs were hybrid with C-TiO₂ microspheres. The X-ray photoelectron spectroscope (XPS), valence band XPS (VB-XPS) and UV–vis diffuse reflectance spectra (DRS) analyses revealed that carbon doped into TiO₂ microspheres could lead to local energy levels in the band structure and generate valence band tails to absorb visible light. The photocatalytic activities of these samples were evaluated by the photodegradation of Rhodamine B (RhB) under visible light irradiation. C-TiO₂/CQDs samples presented an enhanced photocatalytic performance compared with pristine TiO₂, which could be attributed to the present of CQDs, acting as adsorption sites for RhB molecules and charge separation centers to impede the recombination and prolong the life time of electron and hole pairs.     

A novel SiCN@TiO2 core–shell ceramic microspheres derived from a polymeric precursor

A novel core–shell ceramic microspheres, composed of a SiCN inner core and TiO₂ nanoparticles outer shell, were prepared via emulsion technique and polymer-derived ceramics (PDCs) method. The forming process of SiCN@TiO₂ core–shell ceramic microspheres were controlled by adjusting the ratio of raw material, curing temperature and pyrolysis temperature. The morphology, chemical composition and phase transformation were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). PVSZ@TiO₂ microspheres with good spherical structure and uniform-dispersed TiO₂ surface were fabricated at 200 °C with raw material ratio of 25%. After pyrolyzed at 1400 °C, the obtained SiCN@TiO₂ core–shell ceramic microspheres retained spherical structure. The XRD showed that the products were mainly composed of rutile TiO₂, SiC and Si₃N₄ crystalline phase, which were generated by polyvinylsilazane.     

Synthesis and Application in Solar Cell of Poly (3-Decylthiophene)/Titanium Dioxide Hybrid

A series of conducting polymer complexes of poly (3-decylthiophene) and titanium dioxide (PDT/TiO₂) in different proportions were synthesized. Scanning electron microscope (SEM) depicted the morphology of the samples, defining that TiO₂ was successfully coated by poly (3-decylthiophene) molecules. X-ray diffraction patterns (XRD) showed that the interplaner spacing of the composite samples was smaller than the pure TiO₂. X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) showed that there was chemical interaction between PDT and nano-TiO₂ in the complexes. Cyclic voltammetry (CV) showed that the energy gap of the PDT/TiO₂ composite was lower to 0.86 eV, which was the smallest when the proportion was 2:1. Ultraviolet-visible spectra (UV-vis) showed that optical performance was far superior to both PDT and TiO₂. A solar cell was sensitized by PDT/TiO₂, and a solar-to-electric energy conversion efficiency of 0.185% was obtained with the system.     

Structures and properties of the polyester nonwovens coated with titanium dioxide by reactive sputtering

Nanoscale titanium dioxide (TiO₂) films were deposited on the surface of polyester nonwovens by using direct current (DC) reactive magnetron sputtering. The effect of coating thickness on the surface structures and properties of TiO₂ coated fabrics was investigated by atomic force microscope (AFM), X-ray diffraction (XRD), energy dispersive X-ray analysis system (EDX), scanning electron microscope (SEM), and antistatic test in this article. The results indicated that the grain sizes of the sputtered clusters increased and the coating layer became more compact as film thickness was increased, but the crystal structure did not have any significant change. At the same time, the film mechanical properties and antistatic performance in general depended strongly on the film thickness which could lead to the optimum thickness for a particular application.     

Selective liquid-phase oxidation of toluene with molecular oxygen catalyzed by Mn-TiO2 under solvent-free conditions

In this paper, we reported the preparation, characterization, and catalytic performance of TiO₂ doped with Mn for the selective oxidation of toluene to benzyl alcohol and benzaldehyde without any solvent. The structure of the catalyst was determined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption–desorption analysis (Brunauer–Emmet–Teller [BET]), scanning electron microscope (SEM), transmission electron microscope (TEM), and mapping. The results demonstrated that the catalytic properties of Mn-TiO₂ were higher than those of pure Mn₃O₄ and TiO₂. The effects of reaction temperature, reaction time, oxygen pressure, and the amount of catalyst were studied. Under the optimal conditions, Mn-TiO₂ could afford 6.4% toluene conversion at a combined benzyl alcohol/benzaldehyde selectivity of 58.6%. Moreover, the catalyst can be repeated in the experiment for five times without significant loss of activity.     

Novel spindle-shaped nanoporous TiO2 coupled graphitic g-C3N4 nanosheets with enhanced visible-light photocatalytic activity

Highly efficient visible-light-driven heterojunction photocatalysts, spindle-shaped nanoporous TiO₂ coupled with graphitic g-C₃N₄ nanosheets have been synthesized by a facile one-step solvothermal method. The as-prepared photocatalysts were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption-desorption analysis and UV–vis diffuse reflectance spectrometry (DRS), proving a successful modification of TiO₂ with g-C₃N₄. The results showed spindle-shaped nanoporous TiO₂ microspheres with a uniform diameter of about 200 nm dispersed uniformly on the surface of graphitic g-C₃N₄ nanosheets. The g-C₃N₄/TiO₂ hybrid materials exhibited higher photocatalytic activity than either pure g-C₃N₄ or nanoporous TiO₂ towards degradation of typical rhodamine B (RhB), methyl blue (MB) and methyl orange (MO) dyes under visible light (>420 nm), which can be largely ascribed to the increased light absorption, larger BET surface area and higher efficient separation of photogenerated electron–hole pairs due to the formation of heterostructure. In addition, the possible transferred and separated behavior of electron–hole pairs and photocatalytic mechanisms on basis of the experimental results are also proposed in detail.     

Desulfurization of Model Fuels with Carbon Nanotube/TiO<Subscript>2</Subscript> Nanomaterial Adsorbents: Comparison of Batch and Film-Shear Reactor Processes

The effectiveness of carbon nanotube/TiO₂ (CNT/TiO₂) adsorbents to desulfurize model fuels containing various thiophenes was studied. The CNT/TiO₂ adsorbents were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR). Experiments carried out in the film-shear reactor and in a batch reactor were both very effective in removing various recalcitrant thiophenes (typically >80–90 % removal), but reactions in the film-shear reactor required far smaller TiO₂ concentrations to be effective (0.01–0.1 wt/vol% vs. 1–10 % in the batch experiments). The effectiveness of the film-shear reactor is attributed to its ability to intimately mix the fuels and the CNT/TiO₂ adsorbent. The CNT/TiO₂ nanomaterial could be regenerated by heating without loss of desulfurization ability.     

Vapor-phase selective hydrogenation of maleic anhydride to succinic anhydride over Ni/TiO2 catalysts

A series of supported Ni/TiO₂ catalysts were prepared by incipient wetness impregnation method under different calcination temperatures, and the as-prepared catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic properties of these Ni/TiO₂ catalysts were investigated in the vapor phase hydrogenation of maleic anhydride (MA) to succinic anhydride (SA). The results showed that the catalytic activity and the selectivity of the Ni/TiO₂ catalysts were strongly affected by the calcination temperature. The catalyst calcined at 1023 K showed a relatively higher SA selectivity of 96% at high MA conversion (96%) under the tested conditions (493 K and 0.2 MPa). The improvement of SA selectivity could be mainly assigned to the presence of suitable metal–support interaction, which can play a role in catalytic property of active nickel species as electron promoter. Besides, the change of surface properties of TiO₂ support with the increasing calcination temperatures, e.g., the decrease of Lewis acid sites, might also have some positive role in reducing the side-products like γ-butyrolacetone (GBL).     

Synthesis of a stable and porous Co–B nanoparticle catalyst for selective hydrogenation of cinnamaldehyde to cinnamic alcohol

The Co–B nanoparticle catalyst supported on TiO₂ for the selective hydrogenation of cinnamaldehyde to cinnamic alcohol was prepared by a modified electroless plating method. The as-prepared catalyst was characterized by X-ray diffraction and transmission electron microscope. The results showed that porous Co–B nanoparticles were distributed narrowly (40–45 nm) over the support. Compared with the Co–B nanoparticles prepared by chemical reduction of Co²⁺ ions with borohydride, the as-resulted Co–B nanoparticles were stable to be stored in air, and exhibited higher activity and selectivity of cinnamic alcohol in cinnamaldehyde hydrogenation.     

Additive treatment effect of TiO2 as supports for Pt-based electrocatalysts on oxygen reduction reaction activity

In this study, we investigated the additive treatment effect of TiO₂ as alternative support materials to common carbon black for Pt-based electrocatalysts on electrocatalytic activity for oxygen reduction reaction (ORR). The shape of TiO₂ was varied by hydrothermal treatment with various additives, such as urea, thiourea, and hydrofluoric acid. From the results of transmission electron microscopy (TEM) images and ultraviolet-visible spectroscopy (UV-vis) spectra, it was identified that the morphology of hydrofluoric acid (HF)-treated TiO₂ was changed into a round shape having lower aspect ratio than other samples, and its band gap was decreased. Notably, the electronic state of HF-treated TiO₂ support was changed into highly reduced (electron rich) state which led to the increase of ORR activity, compared to other samples treated with different additives or before treatment. The electrocatalytic characteristics changes after treatment with various additives were investigated by using X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), cyclic voltammograms (CV), and rotating disk electrode (RDE) techniques.     

Physical properties of V-doped TiO2 nanoparticles synthesized by sonochemical-assisted process

V-doped TiO₂ nanoparticles were synthesized by sonochemical process using titanium isopropoxide as a titanium source, vanadyl acetylacetonate as a dopant source. Sonication was conducted using sonic horn operated at 20 kHz for 20 min until the completely precipitated product was reached. The as-synthesized precipitates with various vanadium dopant (1–5 mol %) were calcined at 500–1000 °C for 4 h. The relevant physical properties of the nanoparticles were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM). The anatase phase TiO₂ nanoparticles can be synthesized by sonochemical process. Post calcinations process results in the anatase-to-rutile phase transformation and the enhancement in crystallinity with increasing temperature. The results also indicate good incorporation of V ions in TiO₂ lattices and significant effect of V dopant on alternation of interplanar spacing of TiO₂.     

Surface doping of TiO2 powders via a gas–melt reaction using thermal plasma as an excitation source

Surface doping is an effective method to engineer and functionalize powder materials without modulating the internal crystal structure. This study proposed a facile technique for surface doping via a gas–melt reaction using thermal plasma as an excitation source. Doping molten titania (TiO₂) particles with La was preliminarily explored owing to the broad photocatalytic applications of TiO₂. Scanning electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy, transmission electron microscope, diffuse reflectance spectroscopy, photoluminescence spectroscopy and Fourier transform infrared spectroscopy were adopted to characterize the morphology, phase composite, chemical state, fine structure, and optical property of the doped TiO₂ powder, respectively. Results indicated that molten TiO₂ doped with La solidified into spherical particles under the effect of surface tension. No modification of the internal crystal structure was indicated in the XRD patterns, except that the diffraction peak of rutile TiO₂ (110) shifted to low angles after surface doping with La. The obtained TiO₂ powder exhibited sensitivity to sunlight and near-infrared light, and a La/Ti atomic ratio of 19.4% was achieved. The diffusivity D_i of La in molten TiO₂ ranged from 10⁻⁸ m²/s to 10⁻⁷ m²/s, as determined from the gas–melt reaction.     

Eosin-Y and N3-Dye sensitized solar cells (DSSCs) based on novel nanocoral TiO2: A comparative study

Titanium oxide (TiO₂) nanocorals containing nanopolyps have been synthesized by a cost effective hydrothermal route directly on fluorine doped tin oxide (FTO) coated conducting glass substrates. The morphological features and physical properties of TiO₂ films were investigated by field-emission scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, Fourier transform Raman spectroscopy, room temperature photoluminescence spectroscopy and X-ray photoelectron spectroscopy. The surface morphology revealed the formation of TiO₂ corals having nanosized (30–40 nm) polyps. Further, we have studied its dye sensitized solar cell performance by using Eosin-Y and N3-Dye. The results indicate that the photoconversion efficiency of N3-Dye is 66% compared to that of Eosin-Y. The highest solar energy conversion efficiency of 2.37% was observed for N3-Dye loaded DSSCs.     

Fabrication of chain-like TiO2 hollow microspheres with enhanced photocatalytic activity

TiO₂ hollow microspheres (TiO₂-HMSs) have attracted much attention due to their low density, high photoreactivity and easy recovery. However, fabrication of TiO₂-HMSs is time-consuming and costly. In this paper, effect of H₂O₂ on the formation of chain-like TiO₂-HMSs was studied using (NH₄)₂TiF₆ as titanium source and urea as neutralizer through a one-pot hydrothermal reaction strategy. The prepared TiO₂-HMSs were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscopy (SEM). The photocatalytic activity of TiO₂-HMSs was evaluated by photocatalytic degradation of an anionic dye X3B under UV irradiation. It was found that the presence of H₂O₂ not only influences the nucleation, but also enhances the hollowing process of TiO₂-HMSs by accelerating the “inside-outside” mass transfer. TiO₂-HMSs prepared in the presence of H₂O₂ showed enhanced photocatalytic activity due to the synergistic effects of well crystallization and hollow structures.     

Supported TiO2/silica gel as an efficient and inexpensive catalyst for nonsolvent liquid-phase oxidation of cyclohexylamine to cyclohexanone oxime

A benign approach is proposed for the highly efficient synthesis of cyclohexanone oxime through nonsolvent liquid-phase oxidation of cyclohexylamine with dioxygen over supported TiO₂/silica gel. The as-prepared catalyst was characterized by Brunauer–Emmett–Teller (BET), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD) analyses. The results indicate that titanium active sites could be grafted on silica gel supports as catalytic centres. Various parameters such as reaction time and reaction temperature were systematically optimized; the results showed that supported 20%TiO₂/silica gel exhibited the best catalytic effect with 63.2% of amine conversion and 86.3% of selectivity to CHO. A possible pathway is proposed for cyclohexylamine oxidation over supported TiO₂/silica gel. The method developed in this study using dioxygen as the oxidant and inexpensive TiO₂/silica gel as an efficient catalyst has incredible industrial application potential for green synthesis of cyclohexanone oxime.     

Improvement of photostability and thermal stability of PVC by carbon quantum dots loaded on TiO2

Titanium dioxide (TiO₂) has a strong oxidation effect when absorbing ultraviolet light. Therefore, when TiO₂ is used as a light stabilizer in polyvinyl chloride (PVC), it will cause the photodegradation of PVC. Herein, carbon quantum dots (CQDs) coated TiO₂ composite (TiO₂@CQDs) was prepared by a one-step hydrothermal method. The prepared TiO₂@CQDs were characterized by transmission electron microscopy (TEM), UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The photostability of PVC film containing TiO₂@CQDs was investigated via photodegradation conductivity test, weight loss rate test, and ultraviolet aging test. Due to the down-conversion effect of CQDs under ultraviolet light, its existence can alleviate the photoaging of PVC. In addition, the thermal stability of PVC containing TiO₂@CQDs was studied by conductivity tests and oven thermal aging tests. The presence of CQDs significantly improved the thermal stability of PVC. Meanwhile, the HCl absorption capacity of CQDs could reach 30.8 mg/g_cat. According to the DFT calculations, this high absorption capacity is attributed to the HCl immobilization effect via forming hydrogen bonds between HCl and the keto oxygen, carboxyl keto oxygen in CQDs. The hydroxyl group in CQDs could also combine ZnCl₂ by forming a coordination bond.     

Acetylene Hydrogenation on Au-Based Catalysts

Hydrogenation of acetylene has been investigated on Au/TiO₂, Pd/TiO₂ and Au-Pd/TiO₂ catalysts at high acetylene conversion levels. The Au/TiO₂ catalyst (avg. particle size: 4.6 nm) synthesized by the temperature-programmed reduction-oxidation of an Au-phosphine complex on TiO₂ showed a remarkably high selectivity to ethylene formation even at 100% acetylene conversion. Au/TiO₂ prepared by the conventional incipient wet impregnation method (avg. particle size: 30 nm), on the other hand, showed negligible activity for acetylene hydrogenation. Although the Au catalysts showed a high selectivity for ethylene, the acetylene conversion activity and catalyst stability were inferior to the Pd-based catalysts. Au-Pd catalysts prepared by the redox method showed high acetylene conversions as well as high selectivity for ethylene. Interestingly Au-Pd catalysts prepared by depositing Pd via the incipient wetness method on Au/TiO₂ showed very poor selectivity (comparable to mono-metallic Pd catalysts) for ethylene. High-resolution transmission electron microscopy (TEM) studies coupled with energy dispersive X-ray spectroscopy (EDS) showed that while the redox method produced bimetallic Au-Pd catalysts, the latter method produced individual Pd and Au particles on the support.     

Photoactive behavior of polyacrylonitrile fibers based on silver and zirconium co‐doped titania nanocomposites: Synthesis,characterization, and comparative study of solid‐phase photocatalytic self‐cleaning

Silver and zirconium co‐doped and mono‐doped titania nanocomposites were synthesized and deposited onto polyacrylonitrile fibers via sol–gel dip‐coating method. The resulted coated‐fibers were characterized by X‐ray diffraction (XRD), scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, diffuse reflectance spectroscopy, thermogravimetric analysis, and BET surface area measurement. Photocatalytic activity of the TiO₂‐coated and TiO₂‐doped coated fibers were determined by photomineralization of methylene blue and Eosin Y under UV–vis light. The progress of photodegradation of dyes was monitored by diffuse reflectance spectroscopy. The XRD results of samples indicate that the TiO₂, Ag‐TiO₂, Zr‐TiO₂, and Ag‐Zr‐TiO₂ consist of anatase phase. All samples demonstrated photo‐assisted self‐cleaning properties when exposed to UV–vis irradiation. Evaluated by decomposing dyes, photocatalytic activity of Ag–Zr co‐doped TiO₂ coated fiber was obviously higher than that of pure TiO₂ and mono‐doped TiO₂. Our results showed that the synergistic action between the silver and zirconium species in the Ag‐Zr TiO₂ nanocomposite is due to both the structural and electronic properties of the photoactive anatase phase. These results clearly indicate that modification of semiconductor photocatalyst by co‐doping process is an effective method for increasing the photocatalytic activity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Facile synthesis of well-defined CeO2 hollow spheres with a tunable pore structure

Herein, SiO₂@CeO₂ composite microspheres were successfully prepared via a hydrothermal assisted layer-by-layer self-assembly method employing colloid SiO₂ as the template, which was fabricated by a typical Stöber method. Monodispersed CeO₂ hollow spheres with a narrow size distribution were achieved after etching colloid SiO₂ templates through NaOH. The resultant samples were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscopy (TEM), Fourier translation infrared spectroscopy (FT-IR), X-ray photoelectron spectrum (XPS), and Nitrogen adsorption–desorption isothermal. Specifically, the shell thickness and the mesoporous structure of the hollow sphere can be easily controlled by changing the concentration of cerium source.