Using Al2O3 defect levels to enhance the photoelectrocatalytic activity of SnS2 nanosheets

Hexagonal SnS₂ nanosheets and Al₂O₃/SnS₂ composites were fabricated via a one-step hydrothermal synthesis method. The investigation indicates that hexagonal SnS₂ with diameters of 100–200 nm are well dispersed on the surface of Al₂O₃. The band gap of SnS₂ after coupling with 11 wt%-Al₂O₃ is reduced by 0.042 eV compared with the pure SnS_2. The composite with 11 wt%-Al₂O₃ shows the highest photocurrent density of 37 μA/cm² at 0.49 V (vs. Ag/AgCl) under visible light (λ>420 nm), which is approximately 1.2 times that of the pure SnS₂ nanosheets. Photoelectrocatalytic measurements demonstrate that an appropriate amount of Al₂O₃ can enhance the photoelectrocatalytic efficiency of SnS₂. The 11 wt%-Al₂O₃/SnS₂ composite (AOSS-11) can degrade 85.9% MB after 3 h under visible light illumination at an applied potential of 0.49 V (vs. Ag/AgCl). The highly effective photoelectrocatalytic activity of the Al₂O₃/SnS₂ composite is attributed to the efficient separation of photoinduced electron-hole pairs based on the defect levels. This work may provide a new design idea for constructing the effective SnS₂-based photocatalysts with other defective semiconductors.     

Enhanced optical,visible light catalytic and electrochemical properties of Au@TiO2 nanocomposites

Au@TiO₂ nanocomposites and pure TiO₂ were successfully used to know the effect of Au on TiO₂ and their comparative optical, visible light catalytic and electrochemical activities were investigated. Optical parameters such as band gap energy (E_g = 2.4 eV), absorption coefficient (α), refractive index (n) and dielectric constants (σ) have been determined using different methods. Visible light (λ = ～590 nm) catalytic activity of Au@TiO₂ nanocomposites was performed for reducing methyl orange (MO) under visible light irradiation. CV, EIS and DPV studies demonstrate that Au@TiO₂ nanocomposites exhibit redox behavior, charged its surface by accumulating electrons, store and release the electrons.     

Fabrication of SnO2/SnS2 hybrids by anchoring ultrafine SnO2 nanocrystals on SnS2 nanosheets and their photocatalytic properties

Ultrafine SnO₂ nanocrystals with sizes of ~4 nm have been successfully loaded on the SnS₂ nanosheets to fabricate SnO₂/SnS₂ hybrids via a facile hydrothermal method. The obtained samples are well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy, photoluminence (PL) and electrochemical impedance spectroscopy (EIS). The experimental results indicate that the SnO₂ nanocrystals of ~4 nm are well dispersed and intimately anchored on the SnS₂ nanosheets to form nanosized heterojunctions, which can be favorable to the separation of photo-generated holes and electrons. Consequently, the SnO₂/SnS₂ hybrids demonstrate obviously enhanced photocatalytic activities for reduction of Cr (VI) under visible light compared with both the bare SnO₂ and SnS₂.     

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.     

Simple self-assembly of SnS2 entrapped graphene aerogel and its enhanced lithium storage performance

In this work, SnS₂ nanoplates entrapped graphene aerogel has been successfully prepared by simple self-assembly of reduced graphene oxide obtained through mild chemical reduction. Structural and morphological investigations demonstrated that SnS₂ nanoplates are highly dispersed in the three dimensional (3D) porous graphene matrix. When served as anode material for lithium-ion batteries, the electrochemical properties of SnS₂/graphene aerogel (SnS₂/GA) were evaluated by galvanostatic discharge–charge tests, cyclic voltammetry and impedance spectroscopy measurement. Compared with pristine SnS₂, the SnS₂/GA nanocomposite achieved a much higher initial reversible capacity (1186 mAh g⁻¹), superior cyclic stability (1004 mAh g⁻¹ after 60 cycles, corresponding to 84.7% of the initial reversible capacity), as well as better rate capability (650 mAh g⁻¹ at a current density of 1000 mA g⁻¹). This significantly improved lithium storage performance can be attributed to the good integration of SnS₂ nanoplates with 3D porous graphene network, which can not only provide much more active sites and easy access for Li ions intercalation, but also prevent the aggregation of SnS₂ nanoplates and facilitate fast transportation of Li ions and surface electrons during the electrochemical process.     

Coupling CoFe2O4 and SnS2 nanoparticles with reduced graphene oxide as a high-performance electromagnetic wave absorber

The reduced graphene oxide (RGO)/CoFe₂O₄/SnS₂ composites have been successfully synthesized by two-step hydrothermal processes. TEM results show that CoFe₂O₄ and SnS₂ nanoparticles with both diameters about 5–10 nm are well dispersed on the surface of graphene. Compared with RGO/CoFe₂O₄ composites, the as-prepared RGO/CoFe₂O₄/SnS₂ composites exhibit excellent electromagnetic (EM) wave absorption properties in terms of both the maximum reflection loss and the absorption bandwidth. The maximum reflection loss of RGO/CoFe₂O₄/SnS₂ composites is −54.4 dB at 16.5 GHz with thickness of only 1.6 mm and the absorption bandwidth with the reflection loss below −10 dB is up to 12.0 GHz (from 6.0 to 18.0 GHz) with a thickness in the range of 1.5–4.0 mm. And especially, they cover the whole X band (8.0–12.0 GHz), which could be used for military radar and direct broadcast satellite (DBS).     

Synthesis and properties of TiO2 added NiNb2O6 microwave dielectric ceramics using a simple process

TiO₂ added NiNb₂O₆ ceramics produced using a reaction-sintering process were investigated. Pure columbite NiNb₂O₆ could be obtained without TiO₂ addition. With 30 and 40 mol% TiO₂ addition, a phase with the same structure of Ni_0.5Ti_0.5NbO₄ formed. Grain growth is easier in pellets with 30 and 40 mol% TiO₂ addition than in the NiNb₂O₆ pellets. Microwave dielectric properties: ?_r = 20.7, Q × f = 19,800 GHz (at 9 GHz) and τ_f = ?31.9 ppm/°C were obtained for NiNb₂O₆ pellets sintered at 1300 °C/2 h. ?_r around 45, Q × f = 5400–7700 GHz (at 6 GHz) and τ_f ～ 73 ppm/°C were obtained in pellets with 30 mol% TiO₂ addition. ?_r around 50, Q × f = 3800–5700 GHz (at 6 GHz) and τ_f ～ 99 ppm/°C were obtained in pellets with 40 mol% TiO₂ addition.     

Low temperature sintering and microwave dielectric properties of TiO2 ceramics

The TiO₂ ceramics were prepared by a solid-state reaction in the temperature range of 920–1100 °C for 2 h and 5 h using TiO₂ nano-particles (Degussa-P25 TiO₂) as the starting materials. The sinterability and microwave properties of the TiO₂ ceramics as a function of the sintering temperature were studied. It was demonstrated that the rutile phase TiO₂ ceramics with good compactness could be readily synthesized from the Degussa-P25 TiO₂ powder in the temperature range of 920–1100 °C without the addition of any glasses. Moreover, the TiO₂ ceramics sintered at 1100 °C/2 h and 920 °C/5 h demonstrated excellent microwave dielectric properties, such as permittivity (Ɛ_r) value >100, Q × f  > 23,000 GHz and τ_f ≅ 200 ppm/°C.     

Control of refractive index by annealing to achieve high figure of merit for TiO2/Ag/TiO2 multilayer films

We modified the refractive index (n) of TiO₂ by annealing at various temperatures to obtain a high figure of merit (FOM) for TiO₂/Ag/TiO₂ (45 nm/17 nm/45 nm) multilayer films deposited on glass substrates. Unlike the as-deposited and 300 °C-annealed TiO₂ films, the 600 °C-annealed sample was crystallized in the anatase phase. The as-deposited TiO₂/Ag/as-deposited TiO₂ multilayer film exhibited a transmittance of 94.6% at 550 nm, whereas that of the as-deposited TiO₂/Ag/600 °C-annealed TiO₂ (lower) multilayer film was 96.6%. At 550 nm, n increased from 2.293 to 2.336 with increasing temperature. The carrier concentration, mobility, and sheet resistance varied with increasing annealing temperature. The samples exhibited smooth surfaces with a root-mean-square roughness of 0.37–1.09 nm. The 600 °C-annealed multilayer yielded the highest Haacke's FOM of 193.9×10⁻³ Ω⁻¹.     

Studies on chemical bath deposited SnS2 films for Cd-free thin film solar cells

Tin disulfide (SnS₂) is a simple binary metal chalcogenide and it has been proposed as a promising buffer material for Cd-free thin film solar cells. The present work explores the deposition of SnS₂ films by a facile chemical bath deposition at different deposition times in the range of 30–120 min. The effect of deposition time on the structural, optical and electrical properties was investigated. The as-grown SnS₂ films showed a hexagonal crystal structure with a high intensity (001) peak at 15.03°. The films showed shuttle shaped grains that were uniformly distributed across the surface of the substrate. The films showed an optical energy band gap in the range of 2.95–2.80 eV. PL spectra showed a strong emission peak in the wavelength range, 410–460 nm with the variation of deposition time. The SnS₂ films prepared at a deposition time of 90 min showed good crystallinity and morphology with low resistivity of 11.2 Ω-cm. A solar cell with device structure of Mo/SnS/SnS₂/i-ZnO/Al: ZnO/Ni/Ag was fabricated. The fabricated solar cell showed an efficiency of 0.91%, which validate the photovoltaic performance of SnS₂ films.     

Mixture behavior and microwave dielectric properties of (1 − x)Ca2P2O7–xTiO2

(1 − x)β-Ca₂P₂O₇–xTiO₂ were prepared by solid-state reaction. The mixture behavior and microwave dielectric properties were investigated using X-ray powder diffraction and a network analyzer, respectively. X-ray powder diffraction patterns showed that β-Ca₂P₂O₇ and TiO₂ existed in a mixture form, which was also confirmed by SEM analysis. It was shown that TiO₂, which has positive temperature coefficient of the resonant frequency (τ_f), compensated the negative τ_f of β-Ca₂P₂O₇ (−53 ppm/°C) through mixture formation. The variation of dielectric properties with a function of TiO₂ contents could be explained using mixture rule. In the 0.3 < x < 0.4 regions, τ_f value could be successfully reduced almost zero. In particular, at x = 0.3, good microwave dielectric properties was obtained: Q × f = 44,000, ɛ_r = 10.9, and τ_f = −11 ppm/°C.     

Raman spectra and extended X-ray absorption fine structure characterization of La(2−x)/3NaxTiO3 and Nd(2−x)/3LixTiO3 microwave ceramics

A-site deficient perovskite compounds, La_(2?x)/3Na_xTiO₃ (0.02 ≤ x ≤ 0.5) and Nd_(2?x)/3Li_xTiO₃ (0.1 ≤ x ≤ 0.5) microwave ceramics, were investigated by Raman scattering. Nd_(2?x)/3Li_xTiO₃ (0.1 ≤ x ≤ 0.5) was also investigated by extended X-ray absorption fine structure (EXAFS) measurement. The Raman shifts of the E (239 cm^?1) and A₁ (322 cm^?1) modes of La_(2?x)/3Na_xTiO₃ were found to decrease with x. However, the E (254 cm^?1) and A₁ (338 cm^?1) of Nd_(2?x)/3Li_xTiO₃ were found to blueshift with x, which was caused by Li substitution. The redshift of the A₁ (471 cm^?1) phonon of Nd_(2?x)/3Li_xTiO₃ (0.1 ≤ x ≤ 0.3) indicates that O–Ti–O bonding forces lessen with Li concentration, which is consistent with the EXAFS result that Ti–O bond lengths increase for 0.1 ≤ x ≤ 0.3. For x > 0.3, the EXAFS result shows that Ti–O bond lengths decrease. Moreover, Ti–O bond lengths show strong correlation with the microwave dielectric constants of Nd_(2?x)/3Li_xTiO₃.     

Structural,thermal and electrical properties of Ti4+ substituted Bi2O3 solid systems

In the present study, the effect of TiO₂ doping on (1 ? x) Bi₂O₃ (x)TiO₂ (x = 0.05, 0.10, 0.15, 0.20) materials is investigated using X-ray diffraction (XRD), differential thermal analysis (DTA), ac conductivity, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). XRD results show the formation of single phase Bi₁₂TiO₂₀ at x ≥ 0.15 concentration of TiO₂. It is observed that, the lower concentration of TiO₂ leads to the formation of mixed phase. The x = 0.15 and x = 0.20 samples exhibit regular and uniform distribution of the grains as compared to x = 0.10 sample. The highest conductivity is observed for x = 0.15 specimen, e.g., 9 × 10^?7 S cm^?1.     

Low temperature sintering of ZnTiO3/TiO2 based dielectric with controlled temperature coefficient

Structure, microstructure and dielectric properties of ZnTiO₃ and rutile TiO₂ mixtures (ZnTiO₃ + xTiO₂ with x = 0, 0.02, 0.05, 0.1, 0.15 and 0.2) sintered using ZnO–B₂O₃ glass phase (5 wt.% added) as sintering aid have been investigated. For all compounds, the sintering temperature achieves 900 °C. The X-ray diffraction patterns indicate for x = 0.1 that the material is composed by three phases identified as ZnTiO₃ hexagonal, TiO₂ rutile and ZnO. The presence of ZnO is explained by the introduction of Ti into Zn site to form the (Zn_1−xTi_x)TiO_3+x solid solution in resulting the departure of ZnO from the ZnTiO₃ structure. The ZnTiO₃ + 0.15TiO₂ composition sintered at 900 °C with glass addition exhibits attractive dielectrics properties (ɛ_r = 23, tan(δ) < 10⁻³ and a temperature coefficient of the dielectric constant near zero (τ_ɛ = 0 ppm/°C)) at 1 MHz. It is also shown that the introduction of TiO₂ allows to tune the temperature coefficient of the permittivity. All these properties lead this system compatible to manufacture silver based electrodes multilayer dielectrics devices.     

Photocatalytic reduction of CO2 to energy products using Cu–TiO2/ZSM-5 and Co–TiO2/ZSM-5 under low energy irradiation

Copper or cobalt incorporated TiO₂ supported ZSM-5 catalysts were prepared by a sol–gel method, and then were characterized by XRD, BET, XPS and UV–vis diffuse reflectance spectroscopy. Ti^3 + was the main titanium specie in TiO₂/ZSM-5 and Cu–TiO₂/ZSM-5, which will be oxide to Ti^4 + after Co was doped. With the deposition of Cu or Co, the efficiency of the CO₂ conversion to CH₃OH was increased under low energy irradiation. The peak production rate of CH₃OH reached 50.05 and 35.12 μmol g^− 1 h^− 1, respectively. High photo energy efficiency (PEE) and quantum yield (φ) were also reached. The mechanism was discussed in our study.     

Sol-gel synthesis of new TiO2/activated carbon photocatalyst and its application for degradation of tetracycline

A new efficient photocatalyst consisting of TiO₂-activated carbon composite (TiO₂/AC) was synthesized by sol-gel process and applied to decomposition of tetracycline (TC). Its properties and catalytic activity were evaluated in comparison with bare TiO₂ and P25, based on several characterization techniques and TC photodegradation kinetic studies. The results showed TiO₂/AC has better structural and electronic features for photocatalysis; S_BET of 129 m² g^–1, exclusively anatase phase, crystal size of 8.53 nm and band gap energy of 3.04 eV. The catalytic activity of the material was evaluated based on photodegradation kinetic studies of TC from aqueous solution (with initial concentration=50 mg L⁻¹ and catalyst dosage=1.0 g L⁻¹). Non-linear kinetic model of pseudo-first order were fitted to the resulting experimental data. The apparent first-order rate constant (k_app=42.9×10^–3 min^–1) and half-life time (t_1/2=16.1 min) determined for TiO₂/AC were better than those for P25 and bare TiO₂. TC degradation by-products were investigated by HPLC-MS, showing TC was completely degraded after 75 min, producing fragments with m/z smaller than 150.     

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.     

Effect of TiO2 on hydrodenitrogenation performances of MCM-41 supported molybdenum phosphides

The effect of TiO₂ on the hydrodenitrogenation (HDN) performance of MoP/MCM-41 was investigated using quinoline and decahydroquinoline as the model molecules. The catalysts were characterized by XRD, CO chemisorption, TEM, TPR and pyridine FT-IR. Addition of TiO₂ enhanced the C–N bond cleavage activity of MoP/MCM-41 but inhibited its dehydrogenation activity. A maximum HDN activity was observed when the TiO₂ loading was 5 wt%. The characterization results indicated that introduction of TiO₂ did not affect the formation of MoP phase. The TiO₂-containing catalysts possessed higher CO uptake than MoP/MCM-41, but no significant differences in the acid properties and particle size distributions were observed for all the catalysts. XPS results revealed a surface enrichment of TiO₂ in Ti-containing catalysts and small amount of these surface TiO₂ can be partially reduced to Tiⁿ⁺ (n < 4). It is suggested that these Tiⁿ⁺ (n < 4) species may be responsible for the promoting effect of TiO₂ on the HDN performance of MoP/MCM-41.     

Mixture behavior and microwave dielectric properties of (1 − x)CaWO4–xTiO2

The microwave dielectric characteristics and mixture behavior of (1 − x)CaWO₄–xTiO₂ ceramics prepared with conventional solid-state route were studied using a network analyzer and X-ray power diffraction, respectively. The CaWO₄ compound had good properties (low permittivity and high quality factor) for microwave applications, but it had a high negative temperature coefficient of resonant frequency (τ_f = −53). Hence, in order to tune the dielectric properties, (1 − x)CaWO₄–xTiO₂ were prepared for different values of x. X-ray powder diffraction and SEM analysis revealed that CaWO₄ and TiO₂ coexisted as a mixture. The mixture formation and dielectric properties could be explained by mixture rule. In particular, at x = 2.6, good microwave dielectric properties were obtained: Qf = 27,000, ɛ_r = 17.48, and τ_f = ∼0 ppm/°C.     

Improvement of the dielectric properties of rutile-doped Al2O3 ceramics by annealing treatment

The microwave dielectric properties of alumina (Al₂O₃) ceramics were studied. The objectives were to improve the large negative temperature coefficient of the resonant frequency (τ_f) of Al₂O₃ ceramics and to obtain a relatively large quality factor (Qf) through the addition of rutile (TiO₂), which has a large positive τ_f, and an annealing treatment. A near-zero τ_f (+1.5 ppm/°C), excellent Qf (148,000 GHz) and ɛ_r (12.4) were obtained in 0.9 Al₂O₃–0.1 TiO₂ ceramics sintered at 1350 °C for 2 h, followed by annealing at 1100 °C for 12 h in air.