Ag-Si Co-doped TiO2 photocatalyst synthesized via a nonaqueous method

Ag-Si/TiO2 photocatalysts were synthesized in a nonaqueous system at 140 degrees C, and then annealed at different temperatures. The obtained photocatalysts were characterized by XRD, TEM, BET, TG-DTA, XPS, as well as UV-vis DRS. The results showed that All Ag-Si/TiO2 held an anatase phase and high thermal stability and the phase transformation from anatase to rutile was retarded to about 900 degrees C. The Ag-Si/TiO2 particles were highly mono-dispersed and the particles size became smaller compared to TiO2. Additionally, UV-vis light absorption shifted to visible region after Ag doping. Si weaved into the matrix of TiO2, while Ag dispersed on the surface of TiO2 particles. The visible light photocatalytic activity was evaluated by Rhodamine B (RhB) degradation in an aqueous solution under visible light irradiation. It was found that the photccatalytic activities of the obtained Ag-Si/TiO2 samples were all higher than those of pure TiO2 and Ag/TiO2, reaching the maximum at the Ag and Si content of 0.5 mol% and 20.0 mol%, respectively. The enhanced visible photocatalytic activity may be attributed to the simultaneous effects of silver and silicon co-doping.     

Spectroscopic investigations of nanoporous SiO2 impregnated with Ag β-diketonates from supercritical solution of carbon dioxide

Porous materials based on SiO₂ containing nanoparticles of silver (NP Ag) are perspective objects for different medico-biological and optoelectronic applications. In the present work nanoporous glasses Vycor (pore size ∼4 nm) and synthetic opal matrices (OM, void size ∼40 nm) impregnated with β-diketonates of silver (Ag(hfac)COD) via solution of supercritical carbon dioxide were studied. Paramagnetic molecules Cu(hfac)₂ were used as spectroscopic probes permitting to obtain the information about the incorporation of similar organometallic molecules into these matrices. Spectra of absorption and electronic paramagnetic resonance (EPR) in the samples of porous SiO₂ containing Ag(hfac)COD were studied before and after heat treatment in air atmosphere. In both materials impregnated at temperature above 50 °C the absorption band at 420-430 nm (the plasmon resonance (PR) band)) typical for nanoparticles of metallic Ag is observed. This band increases in the intensity at heat treatment or at an increase in temperature of impregnation processing. Features of the formation of the PR band in each case depends on sizes and shape of voids in the samples as well as on conditions of heat treatment. The states of paramagnetic centers formed after Ag(hfac)COD introduction are analyzed.     

Magnesia supported Au and Ag catalysts for the preparation of few-layer graphene–metal nanocomposites: relationship between catalyst structure and the properties of graphene composites

Magnesia supported Au, Ag, and Au–Ag nanostructured catalysts were prepared, characterized, and used to synthesize few-layer graphene–metal nanoparticle (Gr–MeNP) composites. The catalysts have a mezoporous structure and a mixture of MgO and MgO·H₂O as support. The gold nanoparticles (AuNPs) are uniformly dispersed on the surface of the Au/MgO catalysts, and have a uniform round shape with a medium size of ~8 nm. On the other hand, the silver nanoparticles (AgNPs) present on the Ag/MgO catalyst have an irregular shape, larger diameters, and less uniform dispersion. The Au–Ag/MgO catalyst contains large Au–Ag bimetallic particles of ~20–30 nm surrounded by small (5 nm) AuNPs. Following the RF-CCVD process and the dissolution of the magnesia support, relative large, few-layer, wrinkled graphene sheets decorated with metal nanoparticles (MeNPs) are observed. Graphene–gold (Gr–Au) and graphene–silver (Gr–Ag) composites had 4–7 graphitic layers with a relatively large area and similar crystallinity for samples prepared in similar experimental conditions. Graphene–gold–silver composites (Gr–Au–Ag) presented graphitic rectangles with round, bent edges, higher crystallinity, and a higher number of layers (8–14). The MeNPs are encased in the graphitic layers of all the different samples. Their size, shape, and distribution depend on the nature of the catalyst. The AuNPs were uniformly distributed, had a size of about 15 nm, and a round shape similar to those from Au/MgO catalyst. In Gr–Ag, the AgNPs have a round shape, very different from that of the Ag/MgO catalyst, large size distribution and are not uniformly distributed on the surface. Agglomerations of AgNPs together with large areas of pristine few-layer graphene were observed. In Gr–Au–Ag composites, almost exclusively large bimetallic particles of about 25–30 nm, situated at the edge of graphene rectangles have been found.     

MOF衍生的多孔ZnO/C、Ag/ZnO/C复合材料光催化性能研究

以金属有机骨架(MOF-5)为前驱体, 通过高温热处理和湿化学法获得ZnO/C和Ag/ZnO/C两种光催化复合材料。采用X 射线衍射(XRD)、扫描电子显微镜(SEM)、X射线能谱(EDS)和紫外-可见分光漫反射(UV-Vis DRS)等方法对所得样品的晶体结构、形貌特征、组成及光谱特性进行了表征。结果显示, 高温热处理保留了MOF-5的原始结构。ZnO/C比表面积为390 m²/g, 载银后比表面积仍达232 m²/g, 负载的银颗粒尺寸约30 nm。光催化降解实验表明ZnO/C和Ag/ZnO/C复合材料对亚甲基蓝(MB)都具有很高的降解效率, 均优于商业TiO₂。Ag/ZnO/C的光催化性能更好, 且具有较好的重复利用和稳定性。因此, 适度的高温碳化和掺杂贵金属是获得优良光催化性能的根本原因。     

Catalytic properties of silica/silver nanocomposites

The catalytic properties of silver nanoparticles supported on silica and the relation between catalytic activity of silver particles and the support (silica) size are investigated in the present article. The silver nanoparticles with 4 nm diameters were synthesized and were attached to silica spheres with sizes of 40, 78, 105 nm, respectively. The reduction of Rhodamine 6G (R6G) by NaBH4 was designed by using the SiO2/Ag core-shell nanocomposites as catalysts. The experimental results demonstrated that the catalytic activity of silica/silver nanoparticles depends on not only the concentration of catalysts (silver) but also the support silica size. Silver particles supported on small SiO2 spheres (approximately 40 nm) show high catalytic activity. Moreover, by making a comparison between the UV-vis spectra of the catalyst before and after the catalytic reaction, we found that the position of surface plasma resonance (SPR) peak of Ag nanoparticles changes little. The above results suggested that the size and morphology of silver particles were probably kept unchanged after the reduction of R6G and also implied that the catalytic activity of silver particles was hardly lost during the catalytic reaction.     

化学还原法制备纳米银粉及性能表征

在低温反应条件下,通过化学还原的方法以双氧水还原银氨配离子,制备了Ag纳米粉,并利用X射线衍射(XRD)、透射电子显微镜(TEM)对样品的成分、形貌、晶体结构、粒度及其分布进行性能表征;用红外吸收光谱(FT-IR)对结构组成进行定性分析;采用热失重分析(TGA)和差示扫描量热分析(DSC)研究了在热处理过程中的物相转变。结果表明:在所选择的实验条件下制备了类球形分布、分散性好的Ag纳米颗粒,其粒径主要分布在10￣50nm范围,平均粒径为26nm,晶体结构与相应的块体材料基本相同,为fcc结构,样品具有很强的吸附性。     

Oxidation of NiAl-Ag Alloys at 1000℃ in 0.1 MPa O2

Small amounts of silver have been added to the intermetallic compound NiAl with the purpose of improving its mechanical properties. Four ternary NiAl-Ag alloys containing 0.5, 1, 5 and 10 at. pct Ag, denoted as NiAl-0.5Ag, NiAl-1Ag, NiAl-5Ag and NiAl-10Ag, and the Ag-free NiAl have been oxidized at 1000℃ for 24 h in 0.1 MPa O2 to study the effect of the presence of silver on the oxidation behavior of NiAl. All the NiAl-Ag alloys are composed of a matrix of β-NiAl containing a dispersion of isolated particles of a second silver-rich phase. A continuous external layer of Al2O3 formed on all the alloys. In addition, the scales formed on NiAl-5Ag contained a thin and discontinuous layer of pure silver located at the alloy/Al2O3 interface, while those formed on NiAl-10Ag contained isolated particles as well as discontinuous layers of silver at various locations in the scale extending up to the gas/scale interface. The kinetic curves of all the alloys were generally composed of two main parabolic stages with smaller parabolic rate constants for the final stage. The addition of silver does not significantly affect the oxidation behavior of the NiAl intermetallic compound in all cases, as expected because silver is essentially present only as a second phase due to its very small solubility in β-NiAl.     

Nano-silver mediated polymerization of pyrrole: synthesis and gas sensing properties of polypyrrole (PPy)/Ag nano-composite

Thermal polymerization of pyrrole was performed using silver nitrate as source of silver ions followed by its conversion to Polypyrrole (PPy)/Ag nano-comoposites without using any external oxidizing agent or solvent. The formation of PPy was monitored by UV-Visible absorption spectroscopy showing a band at approximately 464 nm. XRD measurement confirmed characteristic peaks for face centered cubic (fcc) silver and presence of PPy at 2 theta of approximately 23 degrees suggesting the formation of PPy/Ag nanocomposite. Transmission electron microscopy (TEM) images showed non-aggregated spherical Ag nano-particles of about 5-10 nm. PPy/Ag thick film acts as a NH3 sensor at 100 degrees C, a H2S sensor at 250 degrees C and CO2 sensor at 350 degrees C. The thick films showed capability to recognize various gases at different operating temperature.     

Electrical properties of silver paste prepared from nanoparticles and lead-free frit

Recently, PbO containing glass systems in commercial silver paste have been used due to their low glass transition temperature, good thermal and electrical properties. However, PbO is a hazardous material to both health and the environment. In this study, Pb-free silver paste was prepared by mixing commercial silver powder and silver nanoparticles. The commercial powder has an average particle size of 1.6 microm. The silver nanoparticles with particles size of 20-50 nm were synthesized by a chemical reduction method using surfactant. Pb-free frit was added into the mixed silver powder as the amounts of 3, 6 and 9 wt%. Using the obtained paste, thick films were fabricated by a screen printing on alumina substrate and the films were fired at temperature from 400 to 550 degrees C. The films had thickness of 6-11 microm and sheet resistivity of about 4-11 microomega cm.     

沉淀法与水热法合成载银羟基磷灰石及其抗菌性能

采用沉淀法与水热法合成了纳米棒状载银羟基磷灰石(Ag-HA)颗粒。研究不同合成方法和载银量时Ag-HA晶体结构、形貌及抗菌性能。结果表明:水热法合成的Ag-HA长径比高、分散性好,产物结晶度高、晶粒尺寸大,晶胞参数更小。沉淀法70℃时,Ag-HA平均晶粒尺寸为(22.7±0.7)nm;水热法180℃时,平均晶粒尺寸为(50.7±0.9)nm。银的引入会增大产物晶粒尺寸及晶胞参数,当载银量为1.30%时,平均晶粒尺寸为(53.7±0.9)nm,晶胞参数a=0.9465nm,c=0.6970nm。产物与大肠杆菌(E.coli)和金黄色葡萄球菌(S.aureus)共培养后结果显示,Ag-HA对两种实验菌均表现出良好的杀菌性能,不同载银量Ag-HA在1,3,6,12,24h后的杀菌率均为100%。     

Tungsten film as a hard and compatible carrier for antibacterial agent of silver

Silver-containing tungsten (W–Ag) films for antibacterial applications were deposited on glass, silicon, and 316L stainless-steel substrates by magnetron sputtering with the silver target current of 0–2.0 A. The addition of silver improves adhesion of the films on glass substrate due to the reduced residual stress in the films. SEM and EDX analyses reveal Ag-rich tiny dots (~?20 nm) at the surface of W–Ag films with high silver contents. In XRD patterns, silver peaks are present for the samples deposited at 1.5 and 2.0 A, and tungsten grain size is decreased from?~?23 to 10 nm by silver addition. XPS analysis shows that tungsten is slightly oxidized (WO₃) at the top surface of the film, and silver presents mainly in metallic state. The low Ag/W ratios and the small surface roughness (<?8 nm) indicate that silver segregation at the film surface is not obvious. Microhardness of the samples with ≤?6.7 at.% silver is nearly seven times that of the stainless steel (~?250 HV). The coated samples are hydrophobic tested by contact angle measurement. The potentiodynamic polarization and the soaking test simulating the inflammatory state show that even corrosion occurs and silver addition decreases corrosion resistance of the films. The antibacterial ratio of the coated samples increases with silver content, being 91% at 4.2 at.% silver content tested by agar plate counting method. In agar disk diffusion assay, no inhibition zone is observed for all samples. The antibacterial property of the W–Ag films is localized, long-lasting, and reusable, which would be beneficial for their potential biomedical and environmental applications.     

The existence of non-labile sodium in polycrystalline sodium beta alumina

Experiments were carried out to measure the rate and extent to which silver and potassium ions exchange with the sodium ions in Monofrax sodium beta alumina (1.32Na₂O·11Al₂O₃) and high soda polycrystalline sodium beta alumina (nominal stoichiometry of 1.80Na₂O·11Al₂O₃). Ion exchange in molten nitrate melts at 350°C is complete within about 10 hours for 1–2 mm sized Monofrax beta alumina crystals. For the polycrystalline samples, however, exchanges with both silver and potassium reach limiting values of about 87% for silver and 84% for potassium after 50–80 hours. This is interpreted on the basis of second phases present in the polycrystalline samples and the apparent existence of non-labile sodium within the beta alumina grains.     

Nano-structured gold catalysts supported on CeO2 and CeO2-Al2O3 for NOx reduction by CO: effect of catalyst pretreatment and feed composition

Gold catalysts supported on ceria and ceria-alumina were studied in NOx reduction by CO. Gold was loaded using deposition-precipitation method. The ceria-alumina (20 wt% alumina) support was synthesized by co-precipitation. The average size of gold and ceria nano-particles was bellow 10 nm. It was established that the type of pretreatment do not have a substantial effect on the catalytic activity. The presence of O2 in the feed leads to a high conversion of CO to CO2 but no NO conversion was registered. Both NO and CO conversion was increased adding H2 to the feed. The catalytic activity became higher upon adding higher amount of H2. Supplementary to the main reaction parallel reactions took place. Bellow 200 degrees C N2O formation and at 250 degrees C and above the NH3 formation was detected. At around 200 degrees C it was established 100% selectivity to N2. The addition of water to the feed influenced positively the CO conversion and did not influence negatively the conversion of NO. The selectivity to N2 at around 200 degrees C remained 100% independent of the presence of moisture. Alumina in the mixed support prevents the sintering of both gold and ceria nano-particles. The results obtained make the catalysts containing gold supported on ceria-alumina promising for practical application.     

Huge increase of therapeutic window at a bioactive silver/titania nanocomposite coating surface compared to solution

A silver containing coating used in the human body, e.g., on an implant should be both effectively antimicrobial and non-cytotoxic to human cells. It is generally believed that the biologic effect originates from silver ions released from the coating. Nanocomposites with well controlled Ag filling factor were prepared by co-sputtering, and the silver surface concentration and the silver release were determined by XPS and ICP-MS, respectively. Here we show that only a small therapeutic window exists for dissolved silver but the therapeutic window is largely increased at the surface. While the toxicity observed for mammalian cells in contact with the bioactive Ag/TiO₂ nanocomposite surface and for silver ions in solution is rather similar the antimicrobial activity is drastically enhanced at the surface. A model is proposed to explain the strong increase of the antimicrobial activity at the surface. The present results not only question well-established tests for antimicrobial activity but they are also important for the design of antimicrobial coatings, e.g., for biomedical devices.     

Synthetic control of large-area, ordered silver nanowires with different diameters

Silver (Ag) nanowires with different diameters (28, 38, 55, 80, 200 nm) have been successfully fabricated into the anodic alumina membranes (AAMs) by direct-current electrochemical deposition technique. X-ray diffraction and selected area electron diffraction analysis show that the as-synthesized samples have preferred (220) orientation independent of the nanowire diameters. Transmission electron microscopy and field-emission scanning electron microscopy investigation reveal that the large-area and highly ordered Ag nanowire arrays with smooth surface and uniform diameter are synthesized, and they have the high aspect ratio. The formation mechanism of the silver nanowires is also discussed. The nanowire arrays with different diameters may have potential applications in the future nanodevices.     

Reducing resistance and curing temperature of silver pastes containing nanowires

Low temperature silver pastes can be widely applied on thin-film switch, flexible printing line and touch screen. In this article, we investigated printability and conductivity of silver pastes with silver wires of different diameters and content, and the conductivity of the silver pastes cured at different temperatures filled with different types silver powders and silver wires. The sheet resistance of silver pastes cured at 100 °C with Ag1 powders and Ag2 powders filled with 10 wt% silver wires of 100 nm diameters is 21.93?±?1.63 and 23.16?±?1.44 Ω/□, which is lower than the same samples cured at 135 °C without silver wire fillers. Tap density of Ag1 and Ag2 powders mixed with silver nanowires is higher than that of Ag3 powders mixed with nanowires, due to a higher filling ratio of Ag1 and Ag2 powders with silver nanowires. SEM results show silver pastes filled with Ag1 and Ag2 powders formed network when silver nanowires were added.     

In-vitro anticancer and antimicrobial activities of PLGA/silver nanofiber composites prepared by electrospinning

In the present work, a series of 0, 1 and 7 wt% silver nano-particles (Ag NPs) incorporated poly lactic-co-glycolic acid (PLGA) nano-fibers were synthesized by the electrospinning process. The PLGA/Ag nano-fibers sheets were characterized using SEM, TEM and DSC analyses. The three synthesized PLGA/silver nano-fiber composites were screened for anticancer activity against liver cancer cell line using MTT and LDH assays. The anticancer activity of PLGA nano-fibers showed a remarkable improvement due to increasing the concentration of the Ag NPs. In addition to the given result, PLGA nano-fibers did not show any cytotoxic effect. However, PLGA nano-fibers that contain 1 % nano silver showed anticancer activity of 8.8 %, through increasing the concentration of the nano silver to 7 % onto PLGA nano-fibers, the anticancer activity was enhanced to a 67.6 %. Furthermore, the antibacterial activities of these three nano-fibers, against the five bacteria strains namely; E.coli o157:H7 ATCC 51659, Staphylococcus aureus ATCC 13565, Bacillus cereus EMCC 1080, Listeria monocytogenes EMCC 1875 and Salmonella typhimurium ATCC25566 using the disc diffusion method, were evaluated. Sample with an enhanced inhibitory effect was PLGA/Ag NPs (7 %) which inhibited all strains (inhibition zone diameter 10 mm); PLGA/Ag NPs (1 %) sample inhibited only one strain (B. cereus) with zone diameter 8 mm. The PLGA nano-fiber sample has not shown any antimicrobial activity. Based on the anticancer as well as the antimicrobial results in this study, it can be postulated that: PLGA nanofibers containing 7 % nano silver are suitable as anticancer- and antibiotic-drug delivery systems, as they will increase the anticancer as well as the antibiotic drug potency without cytotoxicity effect on the normal cells. These findings also suggest that Ag NPs, of the size (5–10 nm) evaluated in the present study, are appropriate for therapeutic application from a safety standpoint.     

Investigation of nanostructured oxides: synthesis, structure and properties

The process of forming three-component nanocrystalline fibers and powders of zirconia, yttria and alumina is studied depending on the component ratio and heat treatment temperature. It has been found that in the investigated system at 500-600 degrees C a nanocrystalline triple solid solution is formed, which exists up to 1200 degrees C. Beyond the above temperature, the triple solid solution decomposes into individual components. Specific regularities of changes in the crystalline structure and size of nanograins of oxides of triple solid solutions in the ZrO2(Y2O3)-Al2O3 system are established depending on the composition and thermal action. The structure--crystallite size--physical-chemical property relationship is also considered. The proposed synthesis method enables preparing nanocrystalline fibers and powders with a high degree of dispersion and reactive activity, whose use in composite materials and ceramics improves their service properties.     

Preparation and characterization of aminosilane-modified silicate supported with silver for antibacterial behavior

The objective of the study was to develop and evaluate aminosilanes-modified silicate impregnated with silver (Ag) nanoparticles, in which Ag dispersion is stabilized, to create a composite that protects against biological warfare agents. A composite based on Ag and organically modified silicate (Ormosil) was prepared by an in situ reduction method, in which silver nitrate, tetraethoxysilane (TEOS) and 3-(2-aminoethylaminopropyl)trimethoxysilane (AES) acted as precursor, linker and colloidal suspension stabilizer, respectively. The physical properties of the Ormosil hybrid and Ormosil/Ag composite were examined using NMR, ESR, SEM, TEM, and TGA spectroscopy, the results of which indicated that Ag was incorporated in the Ormosil matrix after impregnation. Morphological analysis by TEM showed the resulting Ag nanoparticles to be spherical and of a mean size of less than 50 nm. The antibacterial effects of the Ormosil hybrid and the Ormosil/Ag composite were assessed by the zone of inhibition and plate-counting methods, and an excellent antibacterial performance was discovered.     

Effect of test atmosphere composition on high-temperature oxidation behaviour of CoNiCrAlY coatings produced from conventional and ODS powders

Abstract

The oxidation behaviour of free-standing CoNiCrAlY coatings produced by low-pressure plasma spraying using conventional powder and oxide dispersion strengthened (ODS) powder containing 2 wt. % Al-oxide dispersion was investigated. Thermogravimetric experiments at 1100 °C in Ar-20%O₂ and Ar-4%H₂-2%H₂O showed lower oxidation rates of the ODS than the conventional coating. In the latter material the scale growth was enhanced by extensive Y-incorporation of Y/Al-mixed oxide precipitates in the scale and apparently by Y-segregation to oxide grain boundaries. In the ODS coating the alumina dispersion bonded Y in the form of Y-aluminate thereby effectively suppressing scale ‘overdoping’. SEM/EBSD studies of all alumina scales revealed a columnar grain structure with the lateral grain size increasing approximately linearly with depth from the oxide/gas interface. For both coatings the alumina scale growth was slower in Ar–H₂–H₂O than in Ar–O₂. The result is believed to be related to a lower oxygen potential gradient and to slower grain boundary diffusion in the scale forming in H₂/H₂O containing gas.