Synthesis and catalytic properties of novel POM@TiO2 composite materials

Donor–π-bridge–acceptor (D–π–A) type polyoxometalates (POMs) were self-assembled for the first time on the surface of titanium dioxide (TiO₂) nanoparticles through the layer-by-layer (LBL) method. The obtained composite materials POM@TiO₂ were characterized by Transmission electron microscopy (TEM), Fourier transform IR spectroscopy (FTIR), Raman spectrum and energy dispersive X-ray (EDX) spectroscopy. Catalytic properties of POM@TiO₂ were also investigated by treating organic pollutants (typically, removal of 40 mL 20 mg L^− 1 methylene blue (MB) by 10 mg POM@TiO₂ was up to 99.5% within 3 min under ambient conditions and the photodegradation efficiency was obviously higher than bare TiO₂ nanoparticles under irradiation).     

Kinetics of anatase transition to rutile TiO2 from titanium dioxide precursor powders synthesized by a sol-gel process

Kinetics of anatase transition to rutile TiO₂ from titanium dioxide precursor powders synthesized by a sol-gel process have been studied using differential thermal analysis (DTA), X-ray diffraction, transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano beam electron diffraction (NBED) and high resolution TEM (HRTEM). The DTA result shows residual organic matter decomposed at 436 K. The transition temperature for amorphous precursor powders converted to anatase TiO₂ occurred at 739 K. Moreover, the full anatase transition to rutile TiO₂ occurred at 1001 K. The activation energy of anatase TiO₂ formation was 128.9 kJ/mol. On the other hand, the activation energy of anatase transition to rutile TiO₂ was 328.4 kJ/mol. Mesoporous structures can be observed in the TEM image.     

Hydrothermal preparation of Ag-TiO2 nanostructures with exposed {001}/{101} facets for enhancing visible light photocatalytic activity

Nano-composite materials of Ag nanoparticles dispersed TiO₂ nanocubes with exposed {001}/{101} crystal faces were fabricated mainly via a flexible one-step method of hydrothermal treatment with different content of Ag from 1 up to 3 mol%. Prepared photocatalysts were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, UV–vis absorption spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. These analysis was carried out for understanding the contribution of different content of silver for enhancing the photocatalytic activity of TiO₂ nanocubes. Prepared silver nanoparticles had small particle size and grafted to the {101} crystal face of TiO₂ with the role of template control agent and linking agent. The photocatalytic performance of Ag-TiO₂ nanocubes were researched via Rhodamine B dye removal under visible light irradiation ( ≧420 nm). Ag-TiO₂ composite materials with the content of 2 mol% Ag showed the best photocatalytic activity for degradation of Rhodamine B, which was five times more than bare TiO₂ and associated with the localized surface plasmon resonance (LSPR) propelled effect. The mechanism by which silver enhanced the photocatalytic activity of TiO₂ was also demonstrated.     

Synthesis of phase- and shape-controlled TiO2 nanoparticles via hydrothermal process

The TiO₂ nanoparticles with anatase (5.7–12.7 nm), rutile (5.4–8.8 nm), mixed (4.4–8.6 nm) phase were individually prepared using the hydrothermal method. The structure and shape of the particles could be controlled by careful alterations of the hydrothermal conditions. Herein, the TiO₂ nanoparticles were successfully synthesized by employing Ti-isopropoxide as the titanium source into hydrochloric acid solution at mild conditions. The crystal structures such as anatase, rutile and mixed phase of TiO₂ nanoparticles were determined by means of concentration of hydrochloride. Especially, we observed that the rutile TiO₂ crystallites were grown into one-dimensional nanostructures, especially, nanowires, with increasing reaction time. The mechanism of the crystallization of the nanoparticles and the growth habit of TiO₂-rutile structure were discussed.     

Comparison of microstructure,toughness, mechanical properties and work hardening of titanium/TiO2 and titanium/SiC composites manufactured by accumulative roll bonding (ARB) process

In this study, the effects of TiO₂ ceramic nanoparticles and SiC microparticles on the microstructure, mechanical properties and toughness of titanium/TiO₂ nanocomposite and titanium/SiC composite were investigated. To achieve this goal, TiO₂ and SiC ceramic particles were incorporated as the reinforcement in titanium through the ARB (accumulative roll bonding) process. By adding SiC ceramic particles, the mechanical properties of the composite and the nanocomposite were enhanced, while their toughness was decreased, as compared to TiO₂ nanoparticles. After applying 8 cycles of the ARB process, UTS in Ti/5 vol% SiC composite reached to about 1200 (MPa), as compared to that in Ti/0.5 wt% TiO₂ nanocomposite, which was about 1100 (MPa). Furthermore, toughness in the Ti/5 vol% SiC composite and the Ti/0.5 wt% TiO₂ nanocomposite was 60 and 29 J/m³, respectively. Finally, SEM and TEM images showed SiC microparticles clustering in Ti/SiC composite samples and a suitable distribution of TiO₂ nanoparticles in the Ti/TiO₂ nanocomposite. By adding TiO₂ nanoparticles, mechanical properties and work hardening coefficient were found to be increased, as compared to those of the monolithic samples. TiO₂ nanoparticles, after being distributed in the titanium matrix through the ARB process, caused pin dislocations. As clearly shown in TEM images, dislocation tangles around TiO₂ nanoparticles acted as the main mechanism improving the work hardening coefficient.     

Polyimide/nano-TiO2 hybrid films having benzoxazole pendent groups: In situ sol–gel preparation and evaluation of properties

Polyimide/titania (PI/TiO₂) nanocomposite films have been successfully fabricated through the in situ formation of TiO₂ within a PI matrix via sol–gel method. Poly(amic acid) (PAA), which is the precursor of PI, was successfully synthesized by mixing pyromellitic dianhydride (PMDA), with equimolar amount of a diamine monomer having a pendent benzoxazole unit and two flexible ether linkages in N,N-dimethylformamide (DMF) solvent. Tetraethyl orthotitanate [Ti(OEt)₄] and acetylacetone were then added to the resulted PAA. After imidization at high temperature, PI/TiO₂ hybrid films were formed. The structure and morphology of the hybrid nanocomposites with different titania contents (0 wt%, 5 wt%, 10 wt%, and 15 wt%) were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and transmission electron microscopy. The results indicate that the TiO₂ nanoparticles were homogeneously dispersed in the hybrid films. The thermogravimetric analysis of nanocomposites confirms the improvement in the thermal stability with the increase in the percentage of titania nanoparticle. Transmission electron microscopy showed that the nanoparticles with an average diameter of 25–40 nm were dispersed in the polymer matrix.     

Green sonochemical synthesis of cupric and cuprous oxides nanoparticles and their optical properties

Nanoparticles of cupric oxide (CuO) and cuprous oxide (Cu₂O) with various morphologies were synthesized by a green sonochemical process without any surfactants and templates. The Cu₂O nanoparticles with the truncated cubic, cubic octahedral and octahedral morphologies were prepared via the deoxidation of the CuO nanoparticles. The Cu₂O and CuO samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet visible absorption spectroscopy (UV–vis). The experimental results indicate that the molar ratio of sodium hydroxide to copper sulfate affects the morphology and size of the CuO and Cu₂O nanoparticles produced by the sonication. The band gap energy of CuO nanoparticles was 1.45–1.75 eV, the morphology had a great effect on the optical properties of CuO. The Cu₂O nanoparticles had broad emission peaks at the visible region, and the band gap energy was estimated to be 1.95–2.09 eV. The growth mechanisms of the CuO and Cu₂O nanoparticles are discussed.     

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.     

Chemical synthesis of TiO2 nanoparticles and their inclusion in Ni–P electroless coatings

The work addresses the preparation of Ni3P3TiO₂ nanocomposite coatings on mild steel substrate by the electroless technique. Nanosized TiO₂ particles were first synthesized by the precipitation method and then were codeposited (4 g/l) into the Ni3P matrix using alkaline hypophosphite reduced EL bath. The surface morphology, particle size, elemental composition and phase analysis of as-synthesized TiO₂ nanoparticles and the coatings were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive analysis of X-ray (EDAX) and X-ray diffraction (XRD). Coatings with 20 µm thickness were heat treated at 400 °C for 1 h in argon atmosphere. The morphology, microhardness, wear resistance and friction coefficient characteristics (ball on disc) of electroless Ni3P3TiO₂ nanocomposite coatings were determined and compared with Ni3P coatings. The results show that as-synthesized TiO₂ nanoparticles are spherical in shape with a size of about12 nm. After heat treatment, the microhardness and wear resistance of the coatings are improved significantly. Superior microhardness and wear resistance are observed for Ni3P3TiO₂ nanocomposite coatings over Ni3P coatings.     

Growth mechanism and photocatalytic activity of chrysanthemum-like anatase TiO2 nanostructures

Chrysanthemum-like hierarchical anatase TiO₂ nanostructures self-assembled by nanorods have been successfully fabricated by a simple solvothermal route without using template materials or structure-directing additives. The products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Raman spectrometer system (Raman), UV–vis absorption spectroscopy (UV–vis) and N₂ adsorption–desorption measurement. The results indicate that synthesized chrysanthemum-like hierarchical anatase TiO₂ nanostructures have a spherical shape with an average diameter of 1.5 μm and they are composed of nanorods with a width of about 30 nm and a length of about 300 nm. The pore distribution of the sample exhibits two kinds of pores. Such mesoporous structure of the sample might be extremely useful in photocatalysis because they possess efficient transport pathways to the interior and supplies higher specific area for more pollutant molecules to be absorbed. In addition, the synthesized TiO₂ nanostructures show enhanced photocatalytic activity compared with commercial P25 for the degradation of RhB under UV light irradiation, which can be attributed to their special hierarchical structure and high light-harvesting capacity.     

Photocatalytic activities of N-doped nano-titanias and titanium nitride

TiO₂ doped with various loadings of nitrogen was prepared by nitridation of a nano-TiO₂ powder in an ammonia/argon atmosphere at a range of temperatures from 400 to 1100 °C. The nano-TiO₂ starting powder was produced in a continuous hydrothermal flow synthesis (CHFS) process involving reaction between a flow of supercritical water and an aqueous solution of a titanium salt. The structures of the resulting nanocatalysts were investigated using powder X-ray diffraction (XRD) and Raman spectroscopy. Products ranging from N-doped anatase TiO₂ to phase-pure titanium nitride (TiN) were obtained depending on post-synthesis heat-treatment temperature. The results suggest that TiN started forming when the TiO₂ was heat-treated at 800 °C, and that pure phase TiN was obtained at 1000 °C after 5 h nitridation. The amounts and nature of the Ti, O and N at the surface were determined by X-ray photoelectron spectroscopy (XPS). A shift of the band-gap to lower energy and increasing absorption in the visible light region, were observed by increasing the heat-treatment temperature from 400 to 700 °C.     

Influence of CeO2 addition on crystal growth behavior of CeO2–Y2O3–ZrO2 solid solution

Nanopowders with cubic fluorite-type structure as well as uniform distribution in particle size were synthesized by hydrothermal method in the ternary oxide zirconia–yttria–ceria system with ceria content of 0–25 mol%. X-ray diffraction (XRD), thermogravimetric analysis/differential scanning calorimeter (TG/DSC), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (Raman), specific surface area (S_BET) and high resolution transmission electron microscopy (HRTEM) were applied to characterize the structure, thermal decomposition, morphological characteristic and crystal growth of the produced powders. Qualitative analyses indicate that the as-synthesized nanoparticles are single-phase crystallites with an average particle size of 4–9 nm. The specific surface area, lattice parameter and microstrain are closely related to Ce⁴⁺ concentration. Moreover, activation energy of crystal growth is significantly dependent on the dopant (CeO₂) concentration. It firstly increased and then decreased with increasing dopant concentration, and the maximum value was observed at the dopant concentration of 5 mol%.     

Colossal permittivity in (In1/2Nb1/2)xTi1−xO2 ceramics prepared by a glycine nitrate process

(In + Nb) co-doped TiO₂ nanoparticles with very low dopant concentrations were prepared using a glycine nitrate process. A pure rutile—TiO₂ phase with a dense microstructure and homogeneous dispersion of dopants was achieved. By doping TiO₂ with 1.5% (In + Nb) ions, a very high dielectric permittivity of ε′ = 42,376 and low loss tangents of tanδ = 0.06 (at room temperature) were achieved. The large conduction activation energy at the grain boundary decreased with decreasing dopant concentration. The colossal permittivity was primarily attributed to the internal barrier layer capacitor (IBLC) effect. The dominant effect of interfacial polarization at the non–Ohmic sample–electrode contact was observed when the dopant concentration was ≤1.0 mol%. Interestingly, the sample–electrode contact and resistive–outer surface layer effects, i.e., surface barrier layer capacitor (SBLC) effect, has also an effect on the colossal dielectric response in (In + Nb) co-doped TiO₂ ceramics.     

Sol–gel reverse micelle preparation and characterization of N-doped TiO2: Efficient photocatalytic degradation of methylene blue in water under visible light

A series of N-substituted titanium (IV) 2-ethyl-1,3-hexanediolate Ti(C₃₂H₆₈O₈) precursor were synthesized by the sol–gel reverse micelle (SGRM) method. The ethylene diaminetetraacetic acid (Na₂EDTA) has been used as a source of nitrogen n species. The obtained solids were calcined at 500 ?C for 1 h to obtain photoactive phases. The effect of nitrogen content (N/Ti = 0.025; 0.03; 0.05 atomic ratios) is examined. The materials were characterized by XRD, BET, TG/DTA and UV–vis reflectance spectroscopy (DRS). Photocatalytic decolourisation of methylen blue (MB) in aqueous solution was carried out using nano, doped TiO₂. Experimental results revealed that N/Ti = 0.05 atomic ratio N-doped TiO₂ required shorter irradiation time for complete decolourisation of MB than pure nano TiO₂ and commercial (Degussa P-25) TiO₂.     

Conductivity improvement of CuCrO2 nanoparticles by Zn doping and their application in solid-state dye-sensitized solar cells

Undoped and Zn-doped CuCrO₂ nanoparticles were synthesized by sol–gel method as promising wide band gap p-type semiconductor materials for solid-state dye-sensitized solar cells (DSSCs). We studied the influence of Zn dopant concentration on structural, electrical and optical properties of CuCrO₂ nanoparticles. The X-ray diffraction data indicated that the delafossite-to-spinel ferrite phase transition occurs by increasing the amount of Zn doping. The average nanoparticle size was determined about 40 nm. A minimum value of electrical resistivity of 5.7 Ω cm was obtained for doping concentration of 5%. Having optimized the Zn-doped CuCrO₂ nanoparticles, solid-state DSSCs were fabricated using undoped and Zn-doped CuCrO₂ (5%) as solid electrolytes. As the photoanode layer, the vertically aligned TiO₂ nanorod arrays were grown on FTO glass using a hydrothermal method. Compared with undoped CuCrO₂, the Zn-doped nanoparticles exhibited an improvement in photovoltaic properties. The overall efficiency enhancement of 39% was obtained for the dopant concentration of 5%. The improved power conversion efficiency is attributed to the lowered electrical resistivity and enlarged work function of Zn-doped CuCrO₂ nanoparticles.     

Sol–gel hydrothermal synthesis of bismuth–TiO2 nanocubes for dye-sensitized solar cell

Bismuth–TiO₂ nanocubes were synthesized via a facile sol–gel hydrothermal method with titanium tetraisopropoxide as the precursor. The influence of the bismuth on the size, morphology, crystallinity and optical behavior of TiO₂ nanocubes were investigated. The samples were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), field emission scanning electron microscopy (FESEM) and UV–visible spectroscopy (UV–vis). Photovoltaic behavior of dye-sensitized solar cells (DSSCs) fabricated using Bi–TiO₂ nanocubes was studied. The DSSCs had an open-circuit voltage (V_oc) of 590 mV, a short-circuit current density (J_sc) of 7.71 mA/cm², and the conversion efficiency (η) of 2.11% under AM 1.5 illumination, a 77% increment as compared to pure TiO₂ nanocubes.     

Effect of calcination temperature on structural,vibrational, optical,and rheological properties of zirconia nanoparticles

ZrO₂ nanoparticles (NPs) were prepared by a simple, versatile, and an efficient methodology based on microwave. The synthesized NPs were calcined at temperatures ranging from 100 °C to 600 °C. The samples were characterized by X-ray powder diffraction (XRD), transmission electron microscope (TEM), FT-IR spectroscopy, Far-IR spectroscopy, Raman spectroscopy, and UV-vis absorption spectroscopy. The results clearly showed the presence of purely monoclinic phase of zirconia when the calcination temperature exceeds 400 °C. The experimental results showed that the viscosity of zirconia NPs in ethylene glycol (EG) increases with increasing the particle volume fraction and decreases with increasing temperature.     

Structure and luminescence properties of Eu3+ doped TiO2 nanocrystals and prolate nanospheroids synthesized by the hydrothermal processing

We report on a new approach to the synthesis of Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids. They were synthesized by shape transformation of hydrothermally treated titania nanotubes at different pH and in the presence of Eu³⁺ ions. The use of nanotubes as a precursor to the synthesis of Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids opens the possibility of overcoming the problems related to molecular precursors. The shapes and sizes of the nanotubes, Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids were characterized by transmission electron microscopy (TEM) technique. Crystal structures of the resultant powders were investigated by X-ray diffraction (XRD) analysis. The percentage ratio of Eu³⁺ to Ti⁴⁺ ions in doped nanocrystals was determined using inductively coupled plasma atomic emission spectroscopy. The optical characterization was done by using fluorescence and ultraviolet-visible reflection spectroscopies. An average size of faceted Eu³⁺ doped TiO₂ nanocrystals was 13 nm. The lateral dimensions of Eu³⁺ doped TiO₂ prolate nanospheroids varied from 14 to 20 nm, while the length varied from 40 to 80 nm, depending on precursor concentrations. The XRD patterns revealed the homogeneous anatase crystal phase of Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids independently of the amount of dopant. A postsynthetic treatment (filtration or dialysis) was applied on the dispersions of the doped nanoparticles in order to study the influence of the dopant position on photoluminescence (PL) spectra. In the red spectral region, room temperature PL signals associated with ⁵D₀ → ⁷F_J (J = 1–4) transitions of Eu³⁺ were observed in all samples. The increased contribution of dopants from the interior region of dialyzed nanocrystals to photoluminescence was confirmed by the increase of R value.     

Effect of carbon doping on WO3/TiO2 coupled oxide and its photocatalytic activity on diclofenac degradation

The improved photocatalyst carbon-doped WO₃/TiO₂ mixed oxide was synthesized in this study using the sol–gel method. The catalyst was thoroughly characterized by X-ray diffraction (XRD), diffuse reflectance UV–vis spectroscopy, N₂ adsorption desorption analysis, scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic efficiency of the prepared materials was evaluated with respect to the degradation of sodium diclofenac (DCF) in a batch reactor irradiated under simulated solar light. The progress of the degradation process of the drug was evaluated by high-performance liquid chromatography (HPLC), whereas mineralization was monitored by total organic carbon analysis (TOC) and ion chromatography (IC). The results of the photocatalytic evaluation indicated that the modified catalyst with tungsten and carbon (TWC) exhibited higher photocatalytic activity than TiO₂ (T) and WO₃/TiO₂ (TW) in the degradation and mineralization of diclofenac (TWC>TW>T). Complete degradation of diclofenac occurred at 250 kJ m⁻² of accumulated energy, whereas 82.4% mineralization at 400 kJ m⁻² was achieved using the photocatalytic system WO₃/TiO₂-C. The improvement in the photocatalytic activity was attributed to the synergistic effect between carbon and WO₃ incorporated into the TiO₂ structure.     

Synthesis and characterization of mesoporous anatase TiO2 nanostructures via organic acid precursor process for dye-sensitized solar cells applications

Titania (TiO₂) nanoparticles have been synthesized using organic precursor technique. The titania nanoparticles were characterized. The results indicated that the prepared titanium oxalate and citrate precursors were transformed to anatase TiO₂ phase at temperature 400 °C for 2 h. Dye-sensitized solar cells were assembled using the prepared nanocrystalline TiO₂ with large surface area. The specific surface area S_BET was 80.9 and 78.6 m²/g using oxalic and citric acids, respectively. The power efficiency was 3.5 and 2.4%. A brief discussion on the possible reasons behind the low power conversion efficiency observed for these type of solar cells was reported.