Synthesis and color properties of the TiO2@CoAl2O4 blue pigments with low cobalt content applied in ceramic glaze

The TiO₂@CoAl₂O₄ complex blue pigments with low cobalt content were synthesized through calcinations of the precursor obtained from coprecipitating Co²⁺ and Al³⁺ to form Co‐Al LDHs (layered double hydroxides) on the surface of TiO₂ particles. The structure and the properties of the synthesized pigments were characterized by XRD, SEM, TEM, UV‐Vis spectroscopy, XPS, and colorimeter. The precursors of the blue TiO₂@CoAl₂O₄ complex pigments were consisted of LDHs shell layer encapsulated TiO₂ microsphere. After calcinations at 1100°C, the LDHs shell layer were absolutely transformed to the spinel CoAl₂O₄, and the pigments presented a core‐shell structure and uniform sphere morphology (the diameter of microsphere was about 780 nm). The absorption bands at around 547, 584, and 624 nm in the Uv‐Vis absorption spectra of the TiO₂@CoAl₂O₄ complex pigments were corresponded to the characteristic absorption bands of the spinel CoAl₂O₄, revealed the pigments with a bright blue hue. In addition, as the mass ratio of CoAl₂O₄/TiO₂ increased to 0.4, the blue component of the pigments reached to 27.89 and slight color variation with the increase in the CoAl₂O₄ content in a range, possessed low cobalt content and exhibited a stabile performance in commercial low‐temperature ceramic glazes. The XGT results showed that the TiO₂@CoAl₂O₄ complex pigments with low cobalt content presented bright color in ceramic glaze. Especially, the synthesized pigments reduced the usage and toxicity of cobalt, which were efficiency for economy and environmental protection.     

Influence of crystallite size on color properties and NIR reflectance of TiO2@NiTiO3 inorganic pigments

Crystallite size may significantly impact optical properties of inorganic pigments. However, limited studies have so far been reported in this area. In this work, TiO₂@NiTiO₃ complex pigments were synthesized by precipitation-calcination method. Results showed that the increase in calcination temperature led to the formation of TiO₂@NiTiO₃ pigments with crystallite sizes from 29 to 82.6 nm but similar morphologies and aggregate particle sizes (around 1 μm). The yellow component (b*) significantly increased by 7 with crystallite size, but the integrated NIR reflectance decreased slightly (4.02%). Also, the characteristic absorption of NiTiO₃ pigments in NIR region declined the integrated NIR reflectance values.     

Structural analysis and characterization of doped spinel Co2−xMxTiO4 (M=Mg2+, Mn2+, Ni2+, Cu2+ and Zn2+) coated mica composite pigments

A new kind of composite mica pigments were prepared by coating Co_2−xM_xTiO₄ composite oxide nanoparticles onto mica, to investigate the effects of doping ions Mg²⁺, Mn²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ on the properties of the doped composite pearlescent pigments, such as the crystal structure, color and shading power. The structure, morphology, color and shading power of the coated pigments were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis spectrophotometer and CIE L*a*b* methods. SEM images of coated pigments showed that mica were coated uniformly with a single layer of dispersed nanoparticles. Research of the doped composite pigments showed that the doping ions had entered into the spinel crystal structure, forming a new kind of composite mica pearlescent pigments coated with Co_2−xM_xTiO₄. For the analysis of color and shading power of the pigments, doping of Ni²⁺ and Zn²⁺ can improve the color and shading power of the doped pigments, but the larger dosage of Zn²⁺ doping can weaken the color and shading power of the doped pigments. Doping of Mg²⁺, Mn²⁺ and Cu²⁺ metal ions can also weaken the color and shading power of the doped pigments.     

Atomic-level thick TiO2–CoTiO3 multilayer p-n junction with extended built-in electric field as efficient photoanode

Formation of p-n junction was an effective method to improve the photocatalytic performance due to its built-in electric field. However, the electric field was distributed only on the interface between two semiconductors, which was insufficient in comparison to the entire material. In this work, a multilayer TiO₂–CoTiO₃ p-n junction was designed and fabricated by atomic layer deposition. The charge transport and photoelectrochemical properties of multilayer TiO₂–CoTiO₃ films of various thicknesses are thoroughly investigated. The PL and electrochemical tests demonstrate that TiO₂–CoTiO₃ exhibits enhanced charge separation and transport. Additionally, the extra visible light response was achieved by introduction of CoTiO₃. Also, theoretical calculations indicate that the electrons prefer to immigrate from TiO₂ to CoTiO₃ in a multilayer TiO₂–CoTiO₃ structure. Benefited from the boosted light absorption and charge transfer, the multilayer TiO₂–CoTiO₃ composite film exhibits a significantly increased photocurrent, much higher than pure TiO₂ and a single TiO₂–CoO p-n junction. This multilayer p-n junction structure opens a rational and novel way for nanostructure construction in the energy conversion region.     

Codoping Ti in low Co-containing hibonite achieving excellent optical properties for near-infrared reflective pigment applications

To reduce carcinogenic cobalt content in pigments, a series of near-infrared reflective pigments based on CaAl_12-x-yCo_xTi_yO₁₉ (x = 0–0.5 and y = 0-(x+0.3)) were prepared via solid state reactions. Although the cobalt content in the pigment CaAl_11.7Co_0.1Ti_0.2O₁₉ is only 0.87% by mass, the resulting pigment still has excellent color properties (64.89, 3.88, ?40.30) and near-infrared reflectance (～70%). The structural information of the obtained pigments were analyzed by XRD refinement, and the results revealed that the doping concentration of titanium relative to cobalt significantly affected the coordination structure of cobalt in hibonite, which in turn apparently influenced the optical properties of the obtained samples. The actual cooling effect of the CaAl_11.7Co_0.1Ti_0.2O₁₉ coating was tested using a model house and the annual energy consumption was simulated by using EnergyPlus software. For a warm city (Haikou), using this CaAl_11.7Co_0.1Ti_0.2O₁₉ coating can reduce energy consumption for cooling by 24.75%.     

Synthesis and coloration of highly dispersed NiTiO3@TiO2 yellow pigments with core-shell structure

The highly dispersed NiTiO₃@TiO₂ yellow pigments with core-shell structure were prepared through calcinations of precursors obtained from the precipitation of Ni²⁺ on the surface of TiO₂ particles. The synthesized pigments were characterized by XRD, SEM, TEM, Uv–vis spectroscopy and colorimetry. The pigments were found to consist of TiO₂ core and outer ilmenite NiTiO₃ shell. The optical absorption of Ni²⁺ in octahedral coordination produced intense yellow colors. Compared with pure NiTiO₃, the NiTiO₃@TiO₂ pigments presented higher yellow and lower red hues, resulted in intense yellow colors. The particle size distribution of the prepared pigments and ζ potential measurement indicated that the NiTiO₃-0.75@TiO₂ pigments were uniform and well-dispersed in glycol solvents, and they form relatively more stable suspension than pure NiTiO₃ pigments. Meanwhile, these pigments were stable in commercial low–temperature ceramic glazes, possessed more brilliant yellowish colors than pure NiTiO₃ prepared by sol-gel method.     

Surface chemical structures of CoO x /TiO2 catalysts for continuous wet trichloroethylene oxidation

An earlier sample of 5% CoO _x /TiO₂ used for the wet oxidation of TCE at 310 K forca. 6 h has been characterized with a fresh catalystvia XRD and XPS measurements. The binding energy for Co 2p_3/2 of the fresh sample appeared at 781.3 eV, which was very similar to the chemical states of CoTiO _x such as Co₂TiO₄ and CoTiO₃, whereas the spent catalyst indicated a 780.3-eV main peak for Co 2p_3/2 with a satellite structure at a higher energy region. This binding energy was almost equal to that of Co₃O₄ among reference Co compounds used. The phase structure of Co₃O₄ was revealed upon XRD measurements for all the catalyst samples. Based on these XPS and XRD results, a surface chemical structure of CoO _x species existing with the fresh catalyst can be proposed to be predominantly Co₃O₄ encapsulated completely by very thin filmlike CoTiO _x consisting of Co₂TiO₄ and/or CoTiO₃, with a tiny amount of Co₃O₄ particles covered partially by such cobalt titanates which may be responsible to the initial catalytic activity. Those CoTiO _x overlayers on Co₃O₄ particles may be readily removed into the wet media within 1 h at 310 K based on our earlier study, thereby giving rapid increase in the catalytic activity for that period.     

Exploring the hindering mechanism of element Ti on the adherence of CoO-bearing one-coat enamel/steel

The effect of element Ti on adherence between a CoO-bearing single-layer enamel coating and steel was investigated. Falling-weights tests were carried out and cross-sections at interface of the enamel/substrate were analyzed with a scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). Results show that addition of TiO₂ reduced adherence of the enamel coating by hindering the formation of anchor-like alloy precipitates. The decrease of anchor points lies in the following three reasons: I. The diffusion path of Co²⁺ ions to the interface was lengthened because of the blocking effect of rutile and the FeTiO₃ crystals; II. Formation of CoTiO₃ crystals leads to a reduction of free Co²⁺ ions; III. Co–Fe precipitates form away from the enamel/substrate interface, as FeTiO₃ crystals provide extra surface for the nucleation of Fe–Co alloy precipitates.     

Replication Route Synthesis of Mesoporous Titanium–Cobalt Oxides and Their Photocatalytic Activity in the Degradation of Methyl Orange

Mesoporous Ti–Co oxides were synthesized via a replication route, using a 3-D wormlike mesoporous silica as template and tetra-tert-butyl orthotitanate (TBOT) and Co(NO₃)₂ as source materials. The prepared materials were characterized by X-ray diffraction (XRD), N₂-physisorption, TEM, EDS, and UV/Vis-DRS and found to possess a spherical morphology and a 3-D wormhole-like mesoporous structure, with the average pore size between 4.5 and 16.0 nm. The pore walls consisted mainly of a cobalt-incorporated anatase phase. The Co³⁺ ions were generated in the replicated mesoporous Co–Ti oxides, via the transfer of electrons from Co²⁺ to Ti⁴⁺ ions. The formation of cobalt-incorporated anatase phase and Co³⁺ ions were both favored by larger Co/Ti atomic ratios and by relatively low calcination temperatures. The specific surface area decreased and the mesopore sizes increased, with increasing Co/Ti atomic ratio or calcination temperature. The average crystal size of the anatase phase decreased with increasing Co/Ti atomic ratio but increased with increasing calcination temperature. The photocatalytic activity of the replicated mesoporous Co–Ti oxides in the degradation of methyl orange dye was investigated. It was observed that the photocatalytic activity increased with increasing Co/Ti atomic ratio and exhibited a maximum with increasing calcination temperature. With the exception of those prepared at too high calcination temperatures, the replicated mesoporous Co–Ti oxides were much more active than the pure titania. It is concluded that, in addition to a higher diffusion, the cobalt-containing anatase, as the active phase, and the Co³⁺ ions, as the active sites, are responsible for the high photocatalytic activity of the replicated mesoporous Co–Ti oxide.     

Effect of the seed layer on surface morphology and humidity sensing property of CoTiO3 nanocrystalline film

CoTiO₃ nanocrystalline film with enhanced humidity sensing property has been prepared via a two-step method. A nanostructured CoTiO₃ seed layer was firstly grown on silicate substrate by sol-gel process, and another CoTiO₃ layer was subsequently deposited on the seed layer by RF magnetron co-sputtering using TiO₂ and Co₂O₃ targets. The influence of seed layer on the microstructure and humidity sensing property of the CoTiO₃ film was investigated, it was found that the seed layer facilitates the intrinsic growth of CoTiO₃ grain and improves the crystallinity. Meanwhile, the surface morphology changes from brick-like grain type to a pebble-like pattern. The uniformity and alignment of the grains are both strongly related to the underneath CoTiO₃ seed layer. The as-prepared CoTiO₃ multilayer displayed enhanced humidity sensing properties such as the sensitivity to 95%RH reached to 41.9. The response time and recovery time was dramatically shortened, from 50 s for the seed layer to 5 s for the multilayer.     

Preparation of novel Ni/Co co-doping Fe3O4/TiO2 core–shell nanocomposites and their use in effective photocatalytic degradation of Amlodipine drug.

Ni/Co co-doping Fe₃O₄/TiO₂ magnetic core–shell nanocomposites (wt% varied amount of dopants) have been prepared by sol-gel method at low temperature. X-ray diffraction, Fourier transform infrared, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, inductively coupled plasma optical emission spectroscopy and vibrating sample magnetometry studies have been made to investigate the crystalline structure, morphology and magnetic properties of these composites. The prepared Ni/Co co-doping Fe₃O₄/TiO₂ nanocomposites exhibit high degree of crystallinity and suitable magnetic properties at room temperature. Their use has been made in effective photocatalytic degradation of Amlodipine a pharmaceutical contaminant under UV light irradiation at 365 nm. The results have shown that wt% amount of dopants, calcination time, calcination temperature and pH of the Amlodipine aqueous solution are important factors in degradation efficiency of Amlodipine. The optimal weight ratios of Ni and Co to Ti were 0.015%. The nanocomposites can be recovered from the aqueous system easily by using a magnet. Their photocatalytic degradation activity for Amlodipine drug remained 94.43% after five times of repetitive use.     

Low-temperature continuous wet oxidation of trichloroethylene over CoOx/TiO2 catalysts

TiO₂-supported metal oxides such as CoO_x, CuO_x, NiO_x and FeO_x have been used for catalytic wet oxidation of trichloroethylene (TCE) in a continuous flow type fixed-bed reactor system, and the most promising catalyst for this wet catalysis has been characterized using XPS and XRD techniques. All the supported catalysts gave relatively low conversions for the wet oxidation at 36 °C, except for 5 wt% CoO_x/TiO₂ which exhibited a steady-state conversion of 45% via a transient activity behavior up to 1 h on stream. XPS measurements yielded that a Co 2p_3/2 main peak at 779.8 eV appeared with the 5 wt% CoO_x/TiO₂ catalyst after the continuous wet TCE oxidation at 36 °C for ca. 6 h (spent catalyst) and this binding energy value was equal to that of Co₃O₄ among reference Co compounds used here, while the catalyst calcined at 570 °C (fresh catalyst) possessed a main peak at 781.3 eV, very similar to that for CoTiO_x species such as CoTiO₃ and Co₂TiO₄. Only characteristic reflections for Co₃O₄ were indicated upon XRD measurements even with the fresh catalyst sample. The simplest model, based on these XPS and XRD results, for nanosized Co₃O₄ particles existing with the fresh catalyst could reasonably explain the transient activity behavior observed upon the wet TCE oxidation.     

AgBr@Ag/TiO2 core–shell composite with excellent visible light photocatalytic activity and hydrothermal stability

AgBr@Ag/TiO₂ core–shell photocatalysts were fabricated by a facile green route. TiO₂ was uniformly coated on the surface of cubic AgBr, making AgBr@Ag/TiO₂ core–shell photocatalyst show excellent hydrothermal stability. Beneficial from that Ag nanoparticles and AgBr can respond to visible light and core–shell structure can effectively separate the photogenerated electrons and holes, AgBr@Ag/TiO₂ core–shell composites exhibited outstanding visible light photocatalytic activity for the degradation of acid orange 7. The activity of AgBr@Ag/TiO₂ is related to the thickness of TiO₂ shell, and the optimal shell thickness for obtaining the highest activity is 10 nm.     

A novel high reflective glass-ceramic ink with Bi2Ti2O7 nanocrystals used for the photovoltaic glass backplane

Photovoltaic glass ink is a kind of ink used for the photovoltaic glass backplane to enhance the photoelectric conversion efficiency of solar cells. In this work, a novel kind of photovoltaic glass-ceramic ink, with Bi₂Ti₂O₇ nanocrystals precipitated from the low-melting glass for the first time in the short sintering process, was successfully designed and prepared to further improve the reflectance of near-infrared light. Bi₂Ti₂O₇ nanocrystals fill the gap between TiO₂ color pigments to a certain extent, which reduce the diffraction of light and greatly improve the reflectivity of the photovoltaic glass backplane to near-infrared light. In the near-infrared wavelength range (780–2500 nm), the average reflectance of photovoltaic glass ink with Bi₂Ti₂O₇ nanocrystals is 20.6% higher than that without Bi₂Ti₂O₇ nanocrystals. The maximum reflectance of photovoltaic glass-ceramic ink is 86.18%. Our research and findings have provided an important reference point for future development of photovoltaic glass inks.     

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.     

Structure and reactivity of titania-supported oxides: IV. Characterisation of dried vanadia/titania catalyst precursors

Temperature-programmed reduction and quantitative X-ray photoelectron spectroscopy (XPS) have been used to characterise dried precursors to V₂O₅/TiO₂ catalysts prepared either by wet impregnation with NH₄VO₃-oxalic acid solution or by grafting with either VOCl₃ or VO(OⁱBu)₃. Washed and unwashed low area anatase, and Degussa P-25 TiO₂, were used as supports. The reducibility, and the variation of the XPS V/Ti intensity ratio with V₂O₅ content, of the dried precursors made by grafting were almost the same as after calcination: the structure after drying is therefore not much changed by calcination. In dried precursors formed by wet impregnation, however, the vanadyl oxalato complex remains substantially intact, and during TPR it decomposes to VO_x species (mainly V^IIIO_x) probably with evolution of NH₃, CO, CO₂ and H₂O. The form of the variation of the XPS V/Ti ratio with V₂O₅ content is strange; after an initial increase, its value remains constant in the range of one to four VO_x monolayer equivalents, but it then increases abruptly before reaching a second constant value. A possible model is presented to account for this behaviour.     

Core–Shell Structure and Dielectric Properties of Ba0.991Bi0.006TiO3@Nb2O5–Co3O4 Ceramics

To meet the needs of future multilayer ceramic capacitors (MLCCs), thinner dielectric layers are necessary. To achieve this goal, the grain size and uniformity of the particles must be effectively controlled. In this study, we confirmed a core–shell particle structure by means of X‐ray diffraction, scanning electron microscopy, and energy‐dispersive spectroscopy. The dielectric properties of the ceramics were measured using an LCR meter. We found Ba_0.991Bi_0.006TiO₃ particles form a core that was coated with a homogeneous Nb₂O₅–Co₃O₄ layer (~9 nm). The relationship between core–shell structure and ε_r‐T curves of the Ba_0.991Bi_0.006TiO₃@Nb₂O₅–Co₃O₄ ceramics by different sintering temperature has been investigated. Dense, fine‐grained Ba_0.991Bi_0.006TiO@Nb₂O₅–Co₃O₄ ceramics were obtained by sintering at 1160°C. The ceramics met the X8R requirements, with a maximum dielectric constant of 2795, and a low dielectric loss at room temperature of 0.89%.     

Synthesis and characterization of novel nontoxic BiFe1−xAlxO3/mica-titania pigments with high NIR reflectance

A series of novel nontoxic near-infrared (NIR) reflective pigments based on Al-doped BiFeO₃ coated mica-titania were synthesized by precipitation combined with sol-gel method. The pigments of the formula BiFe_1−xAl_xO₃/mica-titania (x = 0, 0.1, 0.2, 0.3, 0.4) were characterized by XRD, FE-SEM, TG-DTA, UV–vis–NIR spectrophotometer and CIE L^* a^* b^* color scales. The results illustrate that the BiFeO₃ nanoparticles are coated on the surface of mica-titania uniformly, and the doped BiFe_1−xAl_xO₃/mica-titania is similar to BiFeO₃/mica-titania composite in morphology. Furthermore, the absorption edge of composite pigments shift to shorter wavelength (533–495 nm) can be attributed to O_2p-Fe_3d charge transfer transitions and change the color of the pigments from brown to orange. Additionally, the NIR solar reflectance of the powdered pigments and pigmented coatings were measured. The results reveal that with the increase of progressive doping of Al³⁺ for Fe³⁺, the NIR solar reflectance of the pigments increase gradually and exhibit higher NIR solar reflectance (R* ≥ 47.8%) than the conventional pigment of similar color. Moreover, we also evaluated the thermal and chemical stability of the pigments. In conclusion, the pigments have the potential to be applied as “cool pigments”.     

Allochroic effect of praseodymium doped neodymium molybdate pigment synthesized by solid-state reaction

This paper was to synthesize praseodymium-doped neodymium molybdate allochroic pigments with different molar ratios of molybdenum (Mo), neodymium (Nd) and praseodymium (Pr) through solid-state reactions. The pigments synthesized were investigated by X-ray diffraction (XRD), selected area electron diffraction (SAED), thermogravimetry and differential thermal analysis (TG-DSC), diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS) and colorimeter. The results show that a pure neodymium molybdate (i.e., Nd₂MoO₆) can be formed after sintering at 1000 °C for 3 h, and praseodymium-doped neodymium molybdate can be synthesized after sintering at 1000 °C for 3 h due to praseodymium ions entering in the lattice of Nd₂MoO₆. The crystal structure in the pigment synthesized can transform from cubic to tetragonal depending on the molar ratio of neodymium/molybdenum and sintering procedure. The color properties of pigments were measured in color space CIEL*a*b* under different standard illuminants (i.e., solar-light (D65), incandescent light (A), cool white fluorescent lamp (F2), and three-band fluorescent lamp (F11)). The results show that the colors of the pigments vary under different illuminants. According to the color difference (ΔE) analysis, neodymium molybdate pigment exhibits a maximum color difference of 10.69, and the maximum color difference of praseodymium-doped neodymium molybdate pigment with doping content of 0.2 increases to 17.63 due to the Pr³⁺ ions substitution for Nd³⁺ ions in the lattice. In addition, the color difference of the pigments with allochroic effect was discussed based on the colorimetry. The color difference of the pigments is due to a high reflectance region at 540–550 nm and a low reflectance region at 380–500 nm.     

The effect of nano‐ and micro‐TiO2 particles on reflective behavior of printed cotton/nylon fabrics in vis/NIR regions

To match the reflectance profile of desert colors including brown, olive green, and khaki in the Vis/near IR (NIR) bands, several pigments were used to print cotton/nylon fabrics. The reflectances of printed fabrics were measured by using spectrophotometric technique. TiO₂ microparticle and nanoparticle powders were also added to the printing pastes to evaluate their effect of reflectance, light, rubbing, washing fastnesses, and colorimetric values of each sample. Tuning the reflectance behavior of each color was successfully managed using specific pigments along with TiO₂ particles. NIR reflectance of brown, khaki, and olive green printed fabrics was enhanced by presence of TiO₂ in printing formulations, which is in complete agreement with the Kubelka–Munk theory. NIR enhancing effect of TiO₂ particles was fast against rubbing, washing, and light exposures while it could significantly change the visible appearance of the printed patterns even at concentrations as low as 0.25 g/kg. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2012