Synthesis and photocatalysis of hierarchical heteroassemblies of ZnO branched nanorod arrays on Ag core nanowires

In this paper, hierarchical heteroassemblies made of interwoven Ag core nanowires (NWs) covered by ZnO branched nanorods (ZnO BNRs) are successfully prepared on a large scale via a solution bottom-up strategy coupling with a templating method. Briefly, heteroepitaxial growth of ZnO nanorods (ZnO NRs) on ZnO seed-coated Ag NWs is first conducted to form fluffy worm-like heteroassemblies. Then, by templating these, ZnO BNRs with exposed high-energy (001) planes on Ag NWs are fabricated with preserved morphology through the second nucleation and growth processes. When evaluated with UV-induced photo-degradation of rhodamine B (RhB), the heteroassemblies of Ag NWs-ZnO BNRs exhibit high photocatalytic properties, due to the decisive roles of the synergistic effect of the unique metal-semiconductor heterojunction and the hierarchical fluffy worm-like morphologies as well as the (001) plane-dominant surface of ZnO BNRs which are attractive for highly efficient photocatalysis.     

In situ solid-state NMR studies of ethanol photocatalysis: characterization of surface sites and their reactivities

In situ solid-state NMR methodologies have been employed to investigate the photocatalytic oxidation of ethanol (C₂H₅OH) over two TiO₂-based catalysts, Degussa P-25 powder and a monolayer TiO₂ catalyst dispersed on porous Vycor glass. Two adsorption sites were observed for ethanol, a chemisorbed species identified as an ethoxide species, and a hydrogen-bonded species. The Ti-bound ethoxide was found to be the more photocatalytically reactive species. ¹³C magic-angle spinning (MAS) experiments revealed that long-lived intermediates, including acetaldehyde (CH₃CHO), acetic acid, formic acid, and acetate were observed under dry conditions and in the presence of molecular oxygen. Similar reaction intermediates form on the surfaces of both catalysts. ¹³C cross-polarization MAS experiments allowed us to identify and follow the evolution of surface-bound species during UV irradiation. Acetate, which forms from mobile acetic acid, appears to be bound to the non-irradiated surfaces of the powdered TiO₂ catalyst, and was also observed on the surface of TiO₂/PVG catalyst, and further degradation was not possible. The presence of molecular oxygen was found to be essential for photooxidation to proceed.     

In situ synthesis,structure, and properties of a dendritic branched nano-thickening agent for high temperature fracturing fluid

The aim of this work was to prepare a novel dendritic branched nano-thickening agent by free radical polymerization of acrylamide (AM), acrylic acid (AA), sodium p-styrene sulfonate, dimethyl diallyl ammonium chloride, and multiwalled carbon nanotubes. The as-synthesized nano-thickening agent was characterized by Fourier transform infrared, Raman spectra, transmission electron microscope, ¹H-NMR, and thermogravimetric analysis (TGA). Compared with the pristine polymer and partially hydrolyzed polyacrylamide (HPAM), thickening capacity, temperature resistance, and salt tolerance properties of the nano-thickening agent considerably improved, and the viscosity of 0.5% nano-polymer solution was 126.5 mPa·s. Additionally, the properties of the nano-gel prepared by nano-thickener, such as temperature and shear tolerance, viscoelasticity, sand carrying capacity, and gel breaking performance, were evaluated showing the satisfactory performance of the nano-gel under high temperature condition. The results indicated that the nano-thickener has potential applications in the field of oil and gas production. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48446.     

Controllable synthesis of branched ZnO/Si nanowire arrays with hierarchical structure

A rational approach for creating branched ZnO/Si nanowire arrays with hierarchical structure was developed based on a combination of three simple and cost-effective synthesis pathways. The crucial procedure included growth of crystalline Si nanowire arrays as backbones by chemical etching of Si substrates, deposition of ZnO thin film as a seed layer by magnetron sputtering, and fabrication of ZnO nanowire arrays as branches by hydrothermal growth. The successful synthesis of ZnO/Si heterogeneous nanostructures was confirmed by morphologic, structural, and optical characterizations. The roles of key experimental parameters, such as the etchant solution, the substrate direction, and the seed layer on the hierarchical nanostructure formation, were systematically investigated. It was demonstrated that an etchant solution with an appropriate redox potential of the oxidant was crucial for a moderate etching speed to achieve a well-aligned Si nanowire array with solid and round surface. Meanwhile, the presence of gravity gradient was a key issue for the growth of branched ZnO nanowire arrays. The substrate should be placed vertically or facedown in contrast to the solution surface during the hydrothermal growth. Otherwise, only the condensation of the ZnO nanoparticles took place in a form of film on the substrate surface. The seed layer played another important role in the growth of ZnO nanowire arrays, as it provided nucleation sites and determined the growing direction and density of the nanowire arrays for reducing the thermodynamic barrier. The results of this study might provide insight on the synthesis of hierarchical three-dimensional nanostructure materials and offer an approach for the development of complex devices and advanced applications.     

Growth and characterization of ZnO/ZnTe core/shell nanowire arrays on transparent conducting oxide glass substrates

ABSTRACT: We report the growth and characterization of ZnO/ZnTe core/shell nanowire arrays on indium tin oxide. Coating of the ZnTe layer on well-aligned vertical ZnO nanowires has been demonstrated by scanning electron microscope, tunneling electron microscope, X-ray diffraction pattern, photoluminescence, and transmission studies. The ZnO/ZnTe core/shell nanowire arrays were then used as the active layer and carrier transport medium to fabricate a photovoltaic device. The enhanced photocurrent and faster response observed in ZnO/ZnTe, together with the quenching of the UV emission in the PL spectra, indicate that carrier separation in this structure plays an important role in determining their optical response. The results also indicate that core/shell structures can be made into useful photovoltaic devices.     

In situ growth of vanadia-titania nano/micro-porous layers with enhanced photocatalytic performance by micro-arc oxidation

Micro-arc oxidation process was used to synthesize V₂O₅-TiO₂ porous layers for the first time. Surface morphology and topography of the layers were investigated by scanning electron microscope (SEM) and atomic force microscope (AFM). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques were also employed to evaluate phase structure and chemical composition of the layers. It was found that the V₂O₅-TiO₂ layers consisted of anatase, rutile, and vanadium pentoxide phases fraction of which varied with the applied voltage and the electrolyte concentration. It was also revealed that pore size and surface roughness increased with the applied voltage and the electrolyte concentration. Optical properties of the layers were studied by a UV-vis spectrophotometer, and the band gap energies of the MAO-grown pure TiO₂ and V₂O₅-TiO₂ layers were respectively calculated as 3.21 and 2.56 eV. Furthermore, the composite layers exhibited a significantly enhanced photo-activity when compared to pure TiO₂ layers. The photocatalytic reaction rate constants of degradation of methylene blue on the surface of the V₂O₅-TiO₂ layers under ultraviolet and visible irradiations were measured as 0.0228 and 0.0117 min⁻¹, respectively. As a consequence, micro-arc oxidation was deduced to be an appropriate and efficient method for synthesis of V₂O₅-TiO₂ porous layers.     

微支化聚丙烯酰胺的支化结构表征及热稳定性/流变性研究

以过硫酸铵(APS)和甲基丙烯酸二甲氨基乙酯(DMAEMA)为引发体系,在水溶液中采用常规自由基聚合制备了不同支化程度的聚丙烯酰胺(b-PAM).考察了微支化结构和支化程度对聚合物热稳定性和流变性的影响.结果表明,支化结构能够明显提高聚合物的热稳定性、抗剪切性和剪切稀释性以及粘弹性,且各项性能随着支化度的增加而增强.     

In situ hybridization and characterization of fibrous hydroxyapatite/chitosan nanocomposite

Nano‐fibrous hydroxyapatite/chitosan (HA/CS) composites with HA contents of 0–70 wt % were prepared by in situ hybridization with a preprepared chitosan film as semipermeable membrane to slow down the hybridization process. The phase composition, microstructure, and morphology of the composites were characterized by means of Fourier transform infrared spectroscopy, X‐ray diffraction, and high‐resolution transmission electron microscopy. It was found that the in situ prepared inorganic phase was hydroxyapatite nano‐fibers that were uniformly dispersed in the chitosan matrix. The average diameter of the fibers were about 3 nm, while the length of the fibers increases from 20 to 60 nm when the hydroxyapatite content increased from 10 to 70 wt %. The compressive strength and Young's modulus of these nano‐fibrous HA/CS composites increased with the increasing HA content and reached the highest values of 170 and 1.7 GPa, respectively, at the HA content of 50–70 wt %, which were much higher than the values of samples prepared by coprecipitation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Highly oriented growth of n-type ZnO films on p-type single crystalline diamond films and fabrication of high-quality transparent ZnO/diamond heterojunction

We present the results on the fabrication and characterization of high-quality transparent heterojunction between n-type ZnO film and p-type diamond single crystalline film on the substrate of diamond bulk single crystal. The results indicated that the current density of the fabricated p-n junction reaches 110 A/m² when the forward bias voltage is 2.5 V, and the turn-on voltage value is about 0.75 V and agreement with the expected value. Moreover, a good rectification characteristic and transparent in the visible light range was obtained in the device.     

In situ preparation of polyimide/titanium carbide composites with enhanced dielectric constant

A series of polyimide/titanium carbide (PI/TiC) composites with different TiC contents were prepared using the ultrasonic dispersion and in situ polymerization method. Atomic force microscopy (AFM), X‐ray diffraction (XRD), scanning electron microscope (SEM), mechanical, and electrometer were used to characterize the structure and properties of the obtained composites. The morphological study of composites by AFM and SEM showed that TiC particles had a homogeneous dispersion in polyimide matrix with nanoscale at low filler dosage (≤10% volume content). X‐ray diffractions (XRDs) indicated that the doping of TiC slightly reduced the packing density of polyimide and destructed the aggregation structure of polyimide molecules. Experimental results showed that the obtained PI/TiC composites exhibited appropriate mechanical properties and moderate electric breakdown strength. Dielectric investigation evidenced that the dielectric constant and the dielectric loss of these composites increased with the increase of the volume fraction of TiC particles. The composite with 20 vol% TiC particles showed a highest dielectric constant of 37 while retaining an appropriate dielectric loss of 0.026, as compared with the dielectric constant (3–4) of neat polyimide resin. In addition, the dielectric properties of the composites displayed good stability within a wide range of frequency. The results of this work demonstrate the potential use of a PI/TiC composite film in an embedded capacitor. POLYM. COMPOS., 125–130, 2016. © 2014 Society of Plastics Engineers     

In situ solvothermal synthesis and characterization of transparent epoxy/TiO2 nanocomposites

A solvothermal process was developed to in situ prepare epoxy (EP)/TiO₂ hybrid precursors. The chemical structure of samples was confirmed by X-ray and Fourier transformed infrared spectroscopy. Field emission scanning electron microscope micrographs of cured EP/TiO₂ hybrid composites showed that well-dispersed TiO₂ nanoparticles were successfully in situ formed in epoxy matrix through the solvothermal process. The thermogravimetic analysis, DSC, and gel content measurements showed that EP/TiO₂ hybrid precursors were fully cured with the glass transition temperature decreasing gradually. The effect of TiO₂ contents on optical and surface properties was investigated in detail. The results indicated that epoxy/TiO₂ nanocomposites exhibited excellent UV shielding effect and high visible light transparency. The contact angle of EP/TiO₂ nanocomposites, when the content of silane-coupling agent (KH560) was 5 g and the content of tetrabutyl titanate (TBT) was 3 g, can reach as high as 101°, which was 36° higher than that of pure EP, representing for the increase of hydrophobicity. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

In situ preparation,electrospinning, and characterization of polyacrylonitrile nanofibers containing silver nanoparticles

Silver nanoparticles were prepared from a polyacrylonitrile (PAN)/N,N‐dimethylformamide solution of silver nitrate (0.05–0.5 wt %) with light treatment (xenon arc) to reduce Ag⁺ ions into Ag⁰. The formation of silver nanoparticles in the PAN solution and the effect of treatment time on the numbers of silver nanoparticles, their average diameter and size distribution were investigated by UV–visible spectroscopy. In addition, the average size of silver nanoparticles and their shapes in colloidal solution were determined by transmission electron microscopy images and found to be on the order of 10 nm. The resulting solution was electrospun into PAN nanofibers. An increase in the salt concentration led to decreases in the nanofiber diameter and bead numbers (determined by scanning electron microscopy images) and an increase in the crystallinity (confirmed by X‐ray diffraction patterns). A continuous rate of silver release from the nanofiber web was monitored by the atomic absorption technique. These nanofibers showed strong antibacterial activity against Pseudomonas aeruginosa. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

TiO2、ZnO和CdS 的光催化甲基橙脱色比较

以甲基橙作为脱色对象，对二氧化钛、氧化锌和硫化镉的光催化现象进行了对比研究，发现他们都具有明显的光催化脱色效果，其中硫化镉的脱色效果最好。掺杂银后，各种光催化剂的脱色效果又都有明显的提高。此外还对氧化锌的寿命进行了测试。     

Dispersivity of modified ZnO and characterization of polyurethane/ZnO composites

The properties of inorganic nanoparticles/polymer composites depend on the dispersivity of nanoparticles in a polymer matrix. The effect of surface modification on the dispersivity of ZnO nanoparticles in a polyurethane (PU) resin matrix was investigated. The nanocomposites were characterized by scanning electron microscopy (SEM), thermogravimetric analysis, and X‐ray diffraction. The scanning electron micrographs show that ZnO nanoparticles (CDI–SA–APS–ZnO), which were modified by aminopropyltriethoxysilane (APS) and activated stearic acid (SA) by N,N′‐carbonyldiimidazole (CDI), can be homogeneously dispersed and had been encapsulated in the PU phase. The interfacial compatibility between ZnO nanoparticles and PU matrix was significantly improved by hydrophobically modifying ZnO nanoparticles with APS and SA. The tensile strength and elongation at break of PU/CDI–SA–APS–ZnO nanocomposites increased by 82 and 64% respectively, compared with the pure PU material. The thermal stability and ultraviolet‐shielding properties were also improved by incorporating ZnO nanoparticles into the PU matrix. POLYM. COMPOS., 35:237–244, 2014. © 2013 Society of Plastics Engineers     

Asymmetric structure and enhanced gas separation performance induced by in situ growth of silver nanoparticles in carbon membranes

Ion-exchanged sulfonated poly(aryl ether ketone), SPAEK with different counter-ions (H⁺, Na⁺ and Ag⁺) have been utilized as polymeric precursors to fabricate carbon membranes. The effects of the substituted metal ions in polymeric precursors on the separation properties of resultant carbon membranes were investigated. X-ray diffraction analysis reveals that the polymer chain packing is improved by the substituted metal ions. The silver doped SPAEK membrane demonstrates the smallest d-spacing due to the strong interactions between the silver ions and the polar groups within the polymeric matrix. The carbon membrane derived from Ag-SPAEK exhibits a more porous structure compared to that from ion-exchanged SPAEK membranes. The silver doping enhances the ideal gas permeability of carbonized membranes by 100 fold. On top of this, the H₂/N₂ selectivity increases from 100 to 220 while the CO₂/CH₄ selectivity jumps from 25 to 67. An interesting phenomenon was observed, which is the migration of silver nanoparticles and the subsequent accumulation in the bulk of membrane after carbonization. A possible mechanism to explain for this particle relocation is the Ostwald ripening. The special directional dispersion of metal nanoparticles in carbonaceous materials was investigated and discussed.     

WO_3/ZnO的制备及其光催化降解甲基橙研究

以ZnSO4·7H2O、WO3和C2H2O4为起始原料,采用直接沉淀法制备了复合光催化剂WO3/ZnO。以甲基橙为研究对象,800W氙灯为光源,研究了催化剂煅烧温度、催化剂用量、WO3含量以及甲基橙初始浓度对其催化性能的影响。结果表明,WO3含量为15%,460℃煅烧3h所得的WO3/ZnO效果较好,在浓度为10mg/L的甲基橙溶液中加入WO3/ZnO1g/L,光照90min后脱色率可高达97.98%,且重复使用6次后脱色率仍在82%以上,表明WO3/ZnO复合光催化剂具有较好的催化性能和稳定性。     

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.     

Synthesis,characterization and photocatalysis of AgAlO2/TiO2 heterojunction with sunlight irradiation

A novel photocatalyst AgAlO₂/TiO₂ with a p–n heterojunction structure was synthesized through the method that combined sol–gel and ion exchange. The as-synthesized samples were characterized by XRD, SEM and UV–vis. The photocatalytic activity of as-synthesized sample was evaluated and the possible mechanism was discussed. As-synthesized AgAlO₂/TiO₂ (in mass ratio of 90/10) exhibited remarkably high photocatalytic activity of 97.8% in decomposing formaldehyde under sunlight irradiation for 90 min. Our work provided a basic experimental process for AgAlO₂/TiO₂ heterojunction and explored the connection between p–n heterojunction and photocatalysis, which will possess a broad prospect in terms of the applications in improving indoor air quality.     

Innovative preparation of bacterial cellulose/silver nanocomposite hydrogels: In situ green synthesis,characterization, and antibacterial properties

In this study, an innovative in situ green strategy was applied to prepare bacterial cellulose/silver nanocomposites using green tea as a substrate for the fermentation of Acetobacter xylinum bacteria and a reducing agent for the in situ synthesis of silver nanoparticles. The samples were analyzed by different characterization tests including field emission scanning electron microscopy (FESEM), X-ray diffraction analysis (XRD), UV–vis spectroscopy, atomic absorption spectroscopy, and ATR. The results indicated the excellent antibacterial activities with 100% bacterial reduction percentage and inhibition zones of 2.6 and 2.8 cm against S. aureus and E. coli, respectively. Moreover, water absorption percentage and vertical wicking measurements supported the hydrogel properties of the prepared bio-cellulose/silver nanocomposites. Finding of this research suggested the potential of the proposed green route for preparing antibacterial BC which can be regarded as a candidate for future wound healing applications.     

In situ preparation of graphene‐ZnO composites for enhanced graphite exfoliation and graphene‐nylon‐6 composite films

An effective method for the fabrication of graphene‐ZnO nanoparticle (GZN) composites has been developed. GZN composites with high electrical conductivity (18,607 S/m) are prepared in situ from graphite‐ZnO composites. The GZN composites also exhibit visible‐light absorption and enable the effective exfoliation of graphite. The presence of the ZnO nanoparticles assists the exfoliation of graphite and enables the preparation of solutions of highly dispersed and concentrated graphene sheets (2.7 mg/mL) that exhibit high electrical conductivity without reduction (40,404 S/m). A solution of graphene sheets was used to produce a graphene‐nylon‐6 film with an excellent Young's modulus (3 GPa) and a high tensile strength (109 MPa). An exclusive mechanism was proposed for the improvement of mechanical properties of the nylon‐6 composite film. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45034.