Au/Pd core-shell nanoparticles with varied hollow Au cores for enhanced formic acid oxidation

A facile method has been developed to synthesize Au/Pd core-shell nanoparticles via galvanic replacement of Cu by Pd on hollow Au nanospheres. The unique nanoparticles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, ultraviolet–visible spectroscopy, and electrochemical measurements. When the concentration of the Au solution was decreased, grain size of the polycrystalline hollow Au nanospheres was reduced, and the structures became highly porous. After the Pd shell formed on these Au nanospheres, the morphology and structure of the Au/Pd nanoparticles varied and hence significantly affected the catalytic properties. The Au/Pd nanoparticles synthesized with reduced Au concentrations showed higher formic acid oxidation activity (0.93 mA cm^-2 at 0.3 V) than the commercial Pd black (0.85 mA cm^-2 at 0.3 V), suggesting a promising candidate as fuel cell catalysts. In addition, the Au/Pd nanoparticles displayed lower CO-stripping potential, improved stability, and higher durability compared to the Pd black due to their unique core-shell structures tuned by Au core morphologies.     

Theoretical studies of preparation of core-shell nanoparticles by electrochemical metal deposition

In the present work we discuss the statistical mechanical framework for predicting the decoration of metallic nanoparticles using electrochemical methods, in thermodynamic equilibrium. It is found that depending on the interactions between the two metals, controlled decoration may be achieved for core-shell nanoparticles in undersaturation and oversaturation conditions. The concept of underpotential deposition is discussed for the case of nanoparticles, with the finding that this phenomenon may be size dependent.     

Sacrificial template synthesis of core-shell SrTiO3/TiO2 heterostructured microspheres photocatalyst

The core-shell SrTiO₃/TiO₂ heterostructure was obtained via a combined hydrothermal route and calcination treatment using amorphous spherical TiO₂ as both template and reactant. Adjusting the hydrothermal environments can control the morphology of the post-calcined sample when it is hydrothermally treated at 180 °C/3 h and 200 °C/6 h, respectively. Following the heat treatment at 700 °C/4 h, the obtained powder illustrates the core-shell heterostructure with a hierarchical surface, and the diameter of the microsphere is about 700 nm. This synthesizing route facilitates the formation of a concentration gradient of SrTiO₃ and TiO₂, and subsequently constructs a gradient energy level, which helps the samples exhibited an excellent de-colorize activity over the methylene blue. The possible formation mechanism of core-shell SrTiO₃/TiO₂ heterostructures was proposed to guide the further improvement of their photocatalytic activity.     

Synthesis and characterization of TiO2 nanoparticles

TiO₂ nanoparticles were synthesized by thermal decomposition of a precipitate obtained from a precursor solution of titanium isopropoxide (IV) and isopropyl alcohol. The as-prepared precipitate was heated at various temperatures and the obtained samples were morphologically, texturally and structurally characterized using TGA–DTA, gas adsorption, SEM, XRD and FTIR. The UV–vis radiation absorption and the photocatalytic activity also were verified. The TiO₂ sample heated at 300 °C shows the best results to be applied as blocker in solar skin protector.     

Fabrication, characterization and photocatalytic activity of Gd-doped titania nanoparticles with mesostructure

Gd³⁺-doped mesoporous TiO₂ (m-TiO₂) nanoparticles were synthesized via hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as surfactant-directing agent and pore-forming agent. The resulting products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), diffuse reflection spectra (DRS), and linear sweep voltammetry (LSV) etc. Experimental results indicate that different Gd³⁺-doping levels make great impact on the photocatalytic activity of the obtained m-TiO₂ nanoparticles and the 3.5 at.% Gd³⁺-doped m-TiO₂ nanoparticles calcined at 300 °C exhibit the optimal photoactivity on the degradation of Rhodamine B (RB), which is as nearly two times as that of the commercial photocatalyst P25. The mesoporosity, anatase wall as well as the cooperativity of ‘lattice Gd³⁺’ and ‘free Gd³⁺’ in the m-TiO₂ nanoparticles can be used to explain the observed high photoactivity of the doped m-TiO₂ nanoparticles.     

Spray drying of TiO2 nanoparticles into redispersible granules

We have demonstrated how titania nanoparticles can be spray-dried to produce redispersible granules. The evaluation of different dispersants using rheology, particle size and electrokinetic measurements showed that an anionic carboxylated polyelectrolyte, Dispex N40, was able to stabilize the primary aggregates of the titania nanoparticles with a size of about 180 nm at an addition of 2.4% dry-weight basis over a relatively large pH-range. Transmission electron microscopy showed that the commercial P-25 titania nanopowder could not be deagglomerated down to the individual crystallite size of 15-40 nm. Spherical granules with a size between 20 and 50 μm and a minimum amount of dusty fines could be produced by spray drying the aqueous titania dispersions in a configuration with internal bag filters. The granules could be completely disintegrated and redispersed in water by ultrasonication into a stable suspension with a size distribution that is identical to the as-received powder. The possibility to prepare redispersible nanoparticle granules by spray drying is a route to minimize the risk of airborne exposure and facilitate the handling of nanopowders.     

Effect of the titania morphology on the Au/TiO2-catalyzed aerobic epoxidation of stilbene

We use a colloidal deposition method to prepare gold nanoparticles with similar size distributions centered at 3 nm over various anatase titania supports. All UV100, PC500 and AK350 titanias are loaded with similar amount of gold (1.0 ± 0.2 wt.%) which is in similar electronic and optical environments, as shown by X-ray photoelectron spectroscopy (XPS) and UV–vis. This allows us to assess the effect of the titania crystallization, morphology and chemical composition on the catalytic properties of gold in the aerobic epoxidation of trans-stilbene. We find that Au/UV100 is more active than Au/PC500 and Au/AK350 but that selectivities are similar on all materials. Epoxide yields on the other hand critically depend on the support functionalization and surface composition. TG–DTA characterization of the bare titania powders reveals indeed that AK350, which leads to the least active catalyst, is slightly less hydroxylated than PC500 and UV100. This indicates that surface titanol groups might be involved in the epoxidation of trans-stilbene. The presence of boron oxide on Au/UV100 (XPS), due to reaction of UV100 with the NaBH₄ reductant during the synthesis, is also thought to promote the epoxide-forming mechanism. This chemical promotion effect appears to compensate for the specific and beneficial gold–P25 interaction. As a result, Au/UV100 is more efficient than the reference Au/P25 catalyst for this reaction.     

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.     

Development of an amperometric immunosensor based on TiO2 nanoparticles and gold nanoparticles

A highly hydrophilic, non-toxic and conductive TiO₂ nanoparticles/gold nanoparticles bilayer films as immobilization matrix via self-assembly (SA) and deposition method was prepared on a gold electrode. Subsequently, positively charged horseradish peroxidase (HRP) was assembled onto the bilayer films, which provided an interface to assemble gold nanoparticles for immobilization of carcinoembryonic antibody (anti-CEA). Finally, HRP was used to block sites against non-specific binding. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were applied to characterize the electrochemical properties of the SA process. The CVs reduction current of the immunosensor decreases linearly in two concentrations ranges of CEA from 0.3 to 10 ng/ml and from 10 to 80 ng/ml with a detection limit of 0.2 ng/ml in presence of 0.7 mM H₂O₂ in analyte solution. Effects of deposition time, pH of working buffer, temperature and incubation time were also explored for optimum analytical performance by using the amperometric method. Moreover, the proposed immunosensor exhibited good accuracy, high sensitivity, long-term stability and made it to determine CEA in serum samples with satisfactory results.     

Catalytic oxidation of VOCs on Au/Ce-Ti-O

Ce_xTi_1−xO₂ oxides have been synthesised by sol–gel method with x varying from 0 to 0.3 and characterised by XRD and TPR. The structure of oxides changes with the Ce/Ti molar ratio. The presence of ceria in Ce-Ti oxides inhibits the phase transition from anatase to rutile. When x = 0.3 (Ce_0.3Ti_0.7O₂ sample), the solid presents an amorphous state. The TPR results indicate that the presence of Ti enhances the reducibility of cerium oxide species. Catalytic oxidation of propene is investigated on Ce-Ti oxides and the better conversion is obtained with Ce_0.3Ti_0.7O₂ but the CO₂ selectivity reaches 63% at 400 °C. Gold is then deposited on theses oxides to improve the catalytic activity. On the basis of characterisation data (H₂ TPR), it has been suggested that gold influences the reduction of the Ce-Ti oxide support and the catalytic activity to the propene oxidation. Thus, Au/Ce-Ti-O system catalysts are promising catalysts for propene oxidation.     

Local structure and photocatalytic activity of B2O3–SiO2/TiO2 ternary mixed oxides prepared by sol–gel method

The local structure and the photoactivity of B₂O₃–SiO₂/TiO₂ ternary mixed oxides (SiO₂ content was fixed as 30 at.% with respect to TiO₂) was investigated by using XRD, FT-IR, BET, UV-vis spectra, and electron paramagnetic resonance (EPR) measurement. In FT-IR analysis, boron was incorporated into the framework of titania matrix with replacing Ti---O---Si with Si---O---B or Ti---O---B bonds. Also, paramagnetic species such as O⁻ and Ti³⁺ defects were formed by the boron incorporation. In SiO₂/TiO₂ mixed oxides, a blue shift in the light absorption band was observed due to the quantization of band structure. All B₂O₃–SiO₂/TiO₂ samples had pure anatase phase and no rutile phase was formed even though the calcination temperature was over 900 °C. Incorporating boron oxides of more than 10% enlarges the grain size of anatase phase and causes a red shift of the light absorption spectrum. The surface area was monotonically decreased with increasing the content of boron content. As a result, the photoactivity of B₂O₃–SiO₂/TiO₂ ternary mixed oxides was greatly influenced by the content of boron oxide. The highest photoactivity (g moles/min l) was obtained when the boron content was 5% and seven times higher than that of silica/titania binary mixed oxide. In addition, the specific photoactivity (g moles/m² l) was maximum still at 5%. It was concluded that the large reduction of surface area, the change of band structure, and more formation of bulk Ti³⁺ sites are responsible for the deterioration in the photoactivity of B₂O₃–SiO₂/TiO₂ ternary mixed oxides when the content of boron is over 10%, although their crystallinity was enhanced by increasing the calcination temperature with keeping anatase phase.     

Construction of spherical NiO@MnO2 with core-shell structure obtained by depositing MnO2 nanoparticles on NiO nanosheets for high-performance supercapacitor

The 3D spherical NiO@MnO₂ composites grown on Ni foam with core-shell structure were prepared by a hydrothermal process followed by a chemical bath deposition process, and then the mechanism improving the electrochemical performance of NiO by MnO₂ modification were investigated by the first-principles calculations for the first time. This core-shell structure promotes an efficient contact between electrolyte and active materials, and the distinct architecture can offer fast transfer channels of ion and electrons. The initial capacitances of NiO, NiO@MnO₂ (deposition time of MnO₂ is 20 min), NiO@MnO₂ (deposition time of MnO₂ is 30 min) and NiO@MnO₂ (deposition time of MnO₂ is 60 min) at 10 A g⁻¹ are 931.6, 1064.4, 1227.2 and 766.8 F g⁻¹, respectively. After 10000 cycles, the reversible capacitances attenuate to 352.8, 661.0, 1089.4 and 616.6 F g⁻¹, respectively. NiO@MnO₂ (deposition time of MnO₂ is 30 min) shows the most excellent reversible capacitance at each cycle and the highest retention rates after 10000 cycles among all samples. The first-principles calculation confirms that a strong interfacial interaction between NiO and MnO₂ can be generated, and then the atomic relaxations at the interface are rather small due to the well-matched interface and epitaxial bonding, resulting in a relatively small interfacial polarization of NiO@MnO₂ composites during cycling. The outstanding rate capability and cycle performance of NiO@MnO₂ (deposition time of MnO₂ is 30 min) electrode are attributed to the synergistic effect and particular 3 D architectures.     

Synthesis and properties of PS-PEO core-shell amphiphilic dendrigrafts

Water-soluble amphiphilic dendrigrafts constituted of a hydrophobic polystyrene core and a hydrophilic poly(ethylene oxide) shell have been prepared via a ‘grafting onto’ procedure from polystyrene dendrigraft precursors. The introduction of the surrounding hydrophilic shell was achieved through cyclic trans-acetalization between ω-acetal functionalized branches of the polystyrene precursor and PEO grafts bearing a α-bis(hydroxymethyl) chain end (A₂-PEO). Yields of grafting are strongly affected by the increase of the degree of polymerization of the reactive PEO grafts (respectively, 100, 87, and 38% with A₂-PEO20, A₂-PEO100 and A₂-PEO150). However, paradoxically, only the use of A₂-PEO100 or A₂-PEO150 as reactive grafts affords water-soluble dendrigrafts due to higher PEO weight content (respectively, 41 and 36%). The dimensions and the shape of the PS_core-PEO_shell polymers were investigated in solution (THF and water) by dynamic light scattering and in the dry state by TEM and AFM.     

Synthesis and characterization of PMMA grafted ZnO nanoparticles

ZnO nanoparticles were synthesized by homogeneous precipitation. To reduce the aggregation among ZnO nanoparticles, an effective surface modification method was proposed by grafting polymethyl methacrylate (PMMA) onto the ZnO particles. That is, the surface of ZnO nanoparticles was firstly treated with a KH570 silane coupling agent, which introduces functional double bonds onto the surface of ZnO nanoparticles, followed by radical grafting polymerization in non-aqueous medium. The obtained nanocomposite was characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetry (TG), sedimentation test, scanning electron microscopy (SEM), and X-ray powder diffraction (XRD). Results of FT-IR and TG showed that the desired polymer chains have been covalently bonded to the surface of ZnO nanoparticles. It was found that the increasing monomer concentration could increase the grafting percentage and hence promote the dispersibility. The application of some surfactant is also helpful for dispersion. The viscous properties of nano-suspensions were investigated. The ZnO/PS nanocomposite was prepared by adding PMMA-grafted ZnO into styrene monomer, followed by radical grafting polymerization. The resulted nanocomposite was characterized by TG, DSC (differential scanning calorimetry) and XRD, and the testing results indicated that thermal behaviors of PS were obviously changed.     

对称性降低的SiO2/Au核壳结构纳米粒子的制备及其表面等离子共振特性

通过直流溅射镀膜的方法制备了SiO2/Au核壳结构复合纳米粒子,对其结构形貌以及表面等离子共振吸收特性进行了表征.所得到的金复合纳米粒子呈不完全包裹的帽状结构,其等离子共振吸收峰会随着内核粒径及金壳层的厚度不同而在近红外光区产生数百纳米波长范围的移动.这种对称性降低的核壳结构复合粒子敏感的光学特性在近红外光等离子共振领域有应用价值.     

Effect of Au in Cs2.5H1.5PVMo11O40 and Cs2.5H1.5PVMo11O40/Au/TiO2 catalysts in the gas phase oxidation of propylene

The catalytic study of the gas phase oxidation of propylene has been carried out using heteropolyacids modified with gold. In addition, TiO₂ was used as the main support for heteropolyacids and gold. Propylene oxidation was performed under different reaction conditions and in all the cases water was introduced owing to the beneficial effect in the formation of oxygenated products. It was found that deposition methods of Au onto heteropolyacid and heat pre-treatment procedure significantly affected the activity and the distribution of the products: sol immobilization promoted the total oxidation, whereas impregnation method the selective oxidation mainly to acrolein and acetic acid, depending on other reaction conditions. Depositing Cs_2.5H_1.5PVMo₁₁O₄₀ salt onto a preformed 1.5%Au/TiO₂ a significant increase towards the formation of oxygenated products was observed at the expense of total combustion. In particular, acrolein was produced in a synergistic manner. FT-IR, XRD, XPS and TPR techniques were used for catalyst characterization.     

Electrorheological response behavior of H2Ti2O5@MoS2@SiO2 core-shell nanoparticles

In this paper, a novel H₂Ti₂O₅@MoS₂@SiO₂ ternary composite material was prepared by a combination of dual hydrothermal method and controlled hydrolysis method, in which H₂Ti₂O₅ nanotubes are tightly combined with hierarchical molybdenum disulfide, and the unique structure of titanate nano whiskers, including the loosely bound alkali metal ions between the titanate layers with high dielectric constant and the large aspect ratio, which induce active response to the electric field. Flower-like molybdenum disulfide provides electrical conductivity, and silicon dioxide as a insulative coating layer can suppress excessive the electrical conductivity of the two-dimensional material. The morphological evolution was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results of showed that the sheet-shaped molybdenum disulfide coated with curved H₂Ti₂O₅ nanotubes showed a honeycomb structure with uniform size. Silicon oxide acts as a cladding layer to increase the thickness of the flakes. The existence of H₂Ti₂O₅, molybdenum disulfide and silicon dioxide is confirmed by X-ray powder diffractometer (XRD) and Fourier transform infrared spectroscopy (FT-IR). The prepared product was confirmed by XPS, BET test and electrorheological rheometer. Core/shell nanoparticles not only exert the active response characteristics of titanate nanoparticles and molybdenum disulfide to electric field, but also inherit the excellent characteristics of a core-shell structure produced by the interface polarization and the synergistic effect of the polar groups on the surface of the two-dimensional material further enhance the electrorheological effect.     

核-壳结构ZnO/TiO2复合材料的制备及其光催化性能研究

采用电化学阳极氧化法制得结构规则、有序的TiO2纳米管,以TiO2纳米管为基质,在一定水热条件下合成核-壳结构的TiO2/ZnO复合纳米材料。利用X射线衍射(XRD)、扫描电镜(SEM)、紫外-可见光谱(UV-VIS DRS)等分析手段对所得材料的结构、形貌及光催化性能进行分析和表征。实验结果表明:TiO2/ZnO复合纳米材料的光催化性能较单一TiO2、ZnO纳米材料有所提高。当前驱体溶液加入量为20 mL,甲基橙溶液初始pH为3时,TiO2/ZnO复合纳米材料的光催化效率最高。