A simple approach for immobilization of gold nanoparticles on graphene oxide sheets by covalent bonding

Amino—functionalized gold nanoparticles with a diameter of around 5 nm were immobilized onto the surface of graphene oxide sheets (GOS) by covalent bonding through a simple amidation reaction. Pristine graphite was firstly oxidized and exfoliated to obtain GOS, which further were acylated with thionyl chloride to give acyl chloride bound GOS. Gold nanoparticles (AuNPs) were functionalized using 4-aminothiophenol in a single-phase system to introduce amino groups on their surface through the well-developed Au-S chemistry. Subsequently, amino groups of AuNPs were reacted with acyl chloride groups of GOS to form a novel hybrid material containing GOS and AuNPs. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy were used to study the changes in surface functionalities and demonstrate the successful immobilization of AuNPs on GOS surface. High resolution transmission electron microscopy (HR-TEM), field emission scanning electronic microscopy (FE-SEM), and atomic force microscopy (AFM) were employed to investigate the morphologies of prepared AuNPs and their distribution onto the GOS surface. Thermogravimetric analysis (TGA) was used to characterize the thermal stability of the samples on heating.     

Probing the diffusion of vacuum ultraviolet (λ = 172 nm) induced oxidants by nanoparticles immobilization

Vacuum ultraviolet (VUV, λ = 172 nm) patterning of alkyl monolayer on silicon surface has been demonstrated with emphasis on the diffusion of VUV induced oxygen-derived active species, which are accountable for the pattern broadening. The VUV photons photo-dissociates the atmospheric oxygen and water molecules into the oxygen-derived active species (oxidants). These oxidants photo-oxidize the hexadecyl (HD) monolayer in VUV irradiated regions (Khatri et al., Langmuir. 24 (2008) 12077), as well as the little concentration of oxidants diffuses towards the masked areas. In this study, we performed VUV patterning at a vacuum pressure of 10 Pa to track the diffusion pathways for the oxidants with help of gold nanoparticles (AuNPs; ? = 10 nm) immobilization. At VUV irradiated sites AuNPs are found as uniformly distributed, but adjacent to the pattern boundary we observed quasi-linear arrays of AuNPs, which are determined by diffusion pathways of the oxidants. The diffusion of oxidants plays vital role in pattern broadening. The site selective anchoring of AuNPs demonstrates the utility of VUV photons for the construction of functional materials with microstructural architecture.     

UV-laser-assisted liquid phase fluorination of PMMA

Polymethylmethacrylate (PMMA) substrate was covered with liquid 1,2,3,5-tetrafluorobenzene by spin coating. Then the sample was irradiated by a KrF-excimer laser (λ = 248 nm). Thus, fluorine is released from the fluorine-containing precursor diffusing into the polymeric substrate material where it is expected to substitute the hydrogen atoms of the polymeric molecule and form a water-repellent (hydrophobic) fluorinated polymer. After drying out the polymeric substrate, the sample surface was investigated by SEM, EDX, XPS and contact angle measurement method in order to determine the fluorine content and the wettability of the treated polymeric surface as well as the substitution sites inside the polymeric molecule. The measurements indicate some chemically bonded fluorine at the top of the sample layer. A UV-photochemical fluorination mechanism is proposed based on the XPS spectra evaluation.     

Luminescence and EPR studies of Eu doped BaAl12O19 blue light emitting phosphors

Europium doped BaAl₁₂O₁₉ powder phosphors have been synthesized by combustion process within few minutes. The phosphors have been characterized by XRD, SEM, FT-IR, EPR and PL techniques. The EPR spectrum exhibits an intense resonance signal at g=1.96 characteristic of Eu²⁺ ions. In addition to this two weak resonance signals have been observed at g=2.28 and g=4.86. The population of the spin levels (N) for the resonance signal at g=1.96 is calculated as a function of temperature. By post-treating the phosphor at 1350 °C under a reducing atmosphere, it is observed that the population of spin levels has been increased five times. The excitation spectrum shows a peak at 326 nm with a shoulder at 290 nm. Upon excitation at 326 nm, the emission spectrum exhibits a well defined broad band with maximum at 444 nm emitting a blue light corresponding to 4f⁶5d→4f⁷ transition. The luminescence intensity also has been enhanced to 60% by post-treating the phosphor at 1350 °C under a reducing atmosphere.     

Characterization of mesoporous VOx/MCM-41 composite materials obtained via post-synthesis impregnation

Spherical-particle MCM-41 was synthesized at room temperature, and, then, impregnated with aqueous solutions of NH₄VO₃ to produce variously loaded VO_x/MCM-41 composite materials. Bulk and surface properties of the materials thus produced were characterized by means of X-ray powder diffractometry (XRD), infrared spectroscopy (FTIR), N₂ sorptiometry and X-ray photoelectron spectroscopy (XPS). Results obtained indicated that subsequent calcination at 550 °C (for 2 h) of the blank and impregnated MCM-41 particles, results in materials assuming the same bulk structure of MCM-41, and exposing uniformly mesporous, high area surfaces (P_w = 2.0-2.3 nm; 974-829 m²/g), except for the material obtained at 20 wt%-V₂O₅ that was shown to suffer a considerable loss on surface area (down to 503 m²/g). XPS results implied that the immobilization of the VO_x species occurs via interaction with surface OH/H₂O groups of MCM-41, leading to the formation of vanadate (VO₃⁻) surface species, as well as minor V-O-Si and V₂O₅-like species. However, in all cases, the vanadium sites remained pentavalent and exposed on the surface.     

Preferential surface segregation of homopolymer and copolymer blend films

Surface film properties of the homopolymers polystyrene (PS), poly(methyl methacrylate) (PMMA), poly(butyl methacrylate) (PBMA) and the copolymer poly(methyl methacrylate)-co-poly(butyl methacrylate) (PMMA-co-PBMA) and their blends with PS have been examined by atomic force microscopy (AFM) and contact angle measurements. The total and the Lifshitz-van der Waals, acid and base components of the surface free energy together with the work of adhesion and its components, the cohesive energy density and the solubility parameters of the homopolymer, copolymer and blend films were determined. Films of about 3 μm were considered. The results are discussed in terms of surface migration mechanisms based on surface free energy and solubilities of the polymers in the solvent, toluene in this paper. AFM imaging and contact angles revealed surface enrichment at the air polymer interface of PBMA for both the PS/PBMA blend and the copolymer PMMA-co-PBMA, whereas the PS/PMMA and PS/PMMA-co-PBMA blend film surfaces show island-like phase-separated structure of typical size 27.4-86.5 nm in diameter and 6.9-15.6 nm in height for PS/PMMA, while for PS/ PMMA-co-PBMA film surface the typical size is 49.6-153.3 nm in diameter and 1.6-14.2 nm in height.     

The role of pulse time Toff on porous silicon as template for Au nanoparticles by using the integrated electrochemical technique

Gold nanoparticles (AuNPs) having variety of sizes and shape were prepared using the template synthesis approach. Porous silicon (PSi) was fabricated using the pulsed electrochemical anodization method at different pause times, T_off as template for gold deposition. Choosing suitable pulse parameter produces PSi with higher porosity and smaller crystallite size. SEM showed that the variation of T_off affects the pores formation and the growth of gold nanoparticles while EDX suggested the presence of Au inside the pores structure. Photoluminescence spectra showed emission enhancement and a blue shifted relative to porous silicon before deposited with AuNPs. XRD shows a high degree crystallinity of the samples and the presence of cubic gold with crystalline sizes was around 42 nm.     

Facile synthesis of α-MnO2 nanorods for high-performance alkaline batteries

Single-crystalline α-MnO₂ nanorods have been successfully synthesized by a novel hydrothermal method based on the redox reactions between the permanganate anion MnO₄^- and H₂O in mixture containing KMnO₄ and HNO₃. The products have been characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectrum (FT-IR) and Brunauer-Emmett-Teller (BET). The results prove that the grain size of α-MnO₂ nanorods with the surface area ∼95.2 m² g⁻¹ is homogeneous with diameters ranging from 10 to 20 nm. The electrochemical property of the material shows that compared with the commercial electrolytic manganese dioxide (EMD), the discharge capacity of the as-prepared α-MnO₂ nanorods is increased by 70.4%, 104.1% and 135.7% at different constant currents of 50, 250 and 500 mA g⁻¹, respectively.     

Collagen-grafted temperature-responsive nonwoven fabric for wound dressing

Polypropylene (PP) nonwoven fabric (NWF) was modified by direct current pulsed plasma followed by grafting with acrylic acid (AAc) to improve its surface hydrophilicity and to introduce carboxylic acid group on the surface for further conjugation with bioactive collagen biomolecule. To endow temperature-responsive property, PP-g-collagen NWF was further modified with poly(N-isopropylacrylamide) (PNIPAAm). Experimental results demonstrated that the amount of AAc and collagen grafted were 43.4 nmole/cm², and 35.9 μg/cm², respectively. The amount of PNIPAAm immobilized was 213 μg/cm². The physical properties, surface chemical composition, and microstructure of the NWFs were characterized. From animal study, modified NWFs were found to promote wound healing with bigraft PP-g-collagen-g-PNIPAAm NWF showing the best performance.     

Laser synthesis of nanostructures based on transition metal oxides

Nanostructures based on iron oxides in the form of thin films were synthesized while laser chemical vapor deposition (LCVD) of elements from iron carbonyl vapors (Fe(CO)₅) under the action of Ar⁺ laser radiation (λ_L = 488 nm) on the Si substrate surface with power density about 10² W/cm² and vapor pressure 666 Pa. Analysis of surface morphology and relief of the deposited films was carried out with scanning electron microscopy (SEM) and atomic force microscopy (AFM). This analysis demonstrated their cluster structure with average size no more than 100 nm. It was found out that the thicker the deposited film, the larger sizes of clusters with more oxides of higher oxidized phases were formed. The film thickness (d) was 10 and 28 nm. The deposited films exhibited semiconductor properties in the range 170-340 K which were stipulated by oxide content with different oxidized phases. The width of the band gap E_g depends on oxide content in the deposited film and was varied in the range 0.30-0.64 eV at an electrical field of 1.6 × 10³ V/m. The band gap E_g was varied in the range 0.46-0.58 eV at an electrical field of 45 V/m. The band gap which is stipulated by impurities in iron oxides E_i was varied in the range 0.009-0.026 eV at an electrical field of 1.6 × 10³ V/m and was varied in the range 0-0.16 eV at an electrical field 45 V/m. These narrow band gap semiconductor thin films displayed of the quantum dimensional effect.     

Magnetic structure and collective Jahn-Teller distortions in nanostructured particles of CuFe2O4

The aim of the present work is to compare the structural, the composition and chemical state of the surface and magnetic properties of different nanosized CuFe₂O₄ powders exhibiting collective Jahn-Teller effect. The samples under examination consist of edged nanosized particles (needle like) with average length 1300 ± 20 nm and diameter 300 ± 20 nm obtained after high temperature synthesis, and superparamagnetic (at room temperature) spherical particles (d = 6 ± 2 nm), obtained by soft chemistry techniques. The surface composition of the particles was investigated by X-ray photoelectron spectroscopy (XPS). Mössbauer spectroscopy (MöS), including at high magnetic field up to 5 T and 4.2 K, was used for characterization of cation distribution in the samples. The data yielded by the XPS and MöS analyses for spherical nanosized particles led us to the assumption for the existence of a Jahn-Teller effect gradient—from the B-sublattice on the surface to a compensation of the tetragonal distortion in the two sublattices in the core. The analysis of the contribution of the anisotropy energy in edged and spherical nanoparticles shows that it must be considered as an effective value reflecting the influence of the individual factors depending on the particle shape and surface.     

Laser synthesis of semiconductor nanostructures with narrow band gap

Semiconductor nanostructures with narrow band gap were synthesized by means of laser chemical vapor deposition (LCVD) of elements from iron carbonyl vapors [Fe(CO)₅] under the action of Ar⁺ laser radiation (λ_L = 488 nm) on the Si substrate surface. The temperature dependence of the specific conductivity of these nanostructures in the form of thin films demonstrated typical semiconductor tendency and gave the possibility to calculate the band gap for intrinsic conductivity (E_g) and the band gap assigned for impurities (E_i), which were depended upon film thickness and applied electrical field. Analysis of deposited films with scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrated their cluster structure with average size not more than 100 nm. Semiconductor properties of deposited nanostructures were stipulated with iron oxides in different oxidized phases according to X-ray photoelectron spectroscopy (XPS) analysis.These deposited nanostructures were irradiated with Q-switched YAG laser (λ_L = 1064 nm) at power density about 6 × 10⁷ W/cm². This irradiation resulted in the crystallization process of deposited films on the Si substrate surface. The crystallization process resulted in the synthesis of iron carbide-silicide (FeSi_2−xC_x) layer with semiconductor properties too. The width of the band gap E_g of the synthesized layer of iron carbide-silicide was less than for deposited films based on iron oxides Fe₂O_3−x (0 ≤ x ≤ 1).     

Immobilization of immunoglobulin G in a highly oriented manner on a protein-A terminated multilayer system

In this study, we have fabricated a multilayer system consisting of 3-glycidoxypropyldimethylmethoxysilane (GPDS), poly(dimethylsiloxane) bis 3-aminopropyl terminated (PDMS) and protein-A on a silicon wafer surface for oriented immobilization of immunoglobilin G (IgG). The multilayer system with a different component in each layer was characterized by ellipsometry, contact-angle goniometer, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) and fluorescence microscopy. The epoxy-terminated monolayer was formed by the chemisorption of GPDS molecules on the hydroxylated silicon surface. The PDMS film about 4.5 nm thick was produced on the GPDS-monolayer by the chemical reaction between the amine groups at the end of PDMS chain and the epoxy groups of GPDS molecules. By introducing the PDMS chains, the hydrophilic character of GPDS-monolayer decreased. Study of the time dependence of polymer grafting showed that the chemisorption of GPDS is fast, whereas at least 16 h is needed to generate the homogeneous PDMS layer. For immobilization of IgG molecules in a highly oriented manner, protein-A molecules were first chemically bound to an ultrathin (∼4.5 nm) PDMS reactive polymer layer and later used to capture IgG. It was shown that the existence of protein-A in the multilayer system has a strong influence on the binding properties of IgG not only in the efficiency of binding, but also in its specificity. In conclusion, the multilayer system with protein-A has the potential to be further developed into an efficient immunoassay protein chip.     

Covalent functionalization of silicon nitride surfaces by semicarbazide group

The paper reports on the covalent attachment of semicarbazide functional groups onto hydrogen-terminated silicon-rich silicon nitride (Si_xN₄; 4 < x < 5) surface under photochemical conditions. UV-irradiation (254 nm) of the surface coated with a thin film of tert-butyl 2-[(allylamino)carbonyl]hydrazine-carboxylate yields an organic monolayer covalently attached to the surface via Si-C bonds and terminated with t-Boc-protected semicarbazide moieties. Removal of the protecting group produces a reactive semicarbazide-terminated monolayer. The photo-induced reaction was investigated by means of X-ray photoelectron spectroscopy (XPS) and contact angle measurements.     

Micro arc oxidized HAp-TiO2 nanostructured hybrid layers-part I: Effect of voltage and growth time

Micro arc oxidation was employed to grow hydroxyapatite-TiO₂ nanostructured porous composite layers. The layers were synthesized on the titanium substrates in the electrolytes consisting of calcium acetate and sodium β-glycerophosphate salts under different applied voltages for various times. SEM and AFM investigations revealed a porous structure and rough surface where the pores size and the surface roughness were respectively determined as 70-650 nm and 9.8-12.7 nm depending on the voltage and time. Chemical composition and phase structure of the layers were evaluated using EDX, XPS, and XRD methods. The layers consisted of the hydroxyapatite, anatase, α-TCP, and calcium titanatephases with a varying fraction depending on the growth conditions. The hydroxyapatite crystalline size was also determined as ∼42 nm. The sample fabricated under the voltage of 350 V for 3 min exhibited the most appropriate Ca/P ratio (∼1.60) as well as the highest amount of the hydroxyapatite phase. This sample had a fine surface morphology and a high pores density.     

Self-assembled monolayers of flufenaminate anions on mild steel surface formed in aqueous solution

Adsorption of derivative of phenylanthranilic acid - flufenamic acid (FFA) on the “oxide-free” and oxidized surface of mild steel in neutral borate buffer solution was studied by ellipsometry and XPS. Anodic polarization curves reveal that complete suppression of the anodic dissolution of iron is achieved at FFA concentration C_in = 3.8 mM. Besides, adding FFA substantially shifts the pitting potential from 0.06 V to 0.67 V. Ellipsometric studies have shown that at the applied potential −0.65 V, when the surface is free from the oxide layer, FFA forms monomolecular layer. To characterize the surface layers formed after exposing the sample in 5 mM FFA solution the XPS was used to assess the composition and the thickness of the layers. Using the intensities of the Fe 2p, Fe 3p, N 1s, F 1s, O 1s and C 1s and analyzing the angle resolved XPS data the FFA molecules have been shown to form monomolecular layer in which FFA is (vertically or slightly inclined) anchored by iron cations through oxygen atoms of carboxyl group to the surface and the fluorine atoms of CF₃ groups form the utmost layer. Similar orientation is also assumed for FFA molecules adsorbed on the oxidized iron surface. It seems that the layer formed by FFA or similar molecules may serve a robust interface for grafting other substances on such a functionalized surface.     

Hf1−xSixOy dielectric films deposited by UV-photo-induced chemical vapour deposition (UV-CVD)

Hf_1−xSi_xO_y is an attractive candidate material for high-k dielectrics. We report in this work the deposition of ultra-thin Hf_1−xSi_xO_y films (0.1 ≤ x ≥ 0.6) on silicon substrate at 450 °C by UV-photo-induced chemical vapour deposition (UV-CVD) using 222 nm excimer lamps. Silicon(IV) and hafnium(IV) organic compounds were used as the precursors. Films from around 5 to 40 nm in thickness with refractive indices from 1.782 to 1.870 were grown. The deposition rate was found to be of 6 nm/min at a temperature of 450 °C. The physical, interfacial and electrical properties of hafnium silicate (Hf_1−xSi_xO_y) thin films were investigated by using X-ray photoelectron spectroscopy, ellipsometry, FT-IR, C-V and I-V measurements. XRD showed that they were basically amorphous, while Fourier transform infrared spectroscopy (FT-IR), clearly revealed Hf-O-Si absorption in the photo-CVD deposited Hf_1−xSi_xO_y films. Surface and interfacial properties were analysed by TEM and XPS. It is found that carbon content in the films deposited by UV-CVD is very low and it also decreases with increasing Si/(Si + Hf) ratio, as low as about 1 at.% at the Si/(Si + Hf) ratio of 60 at.%.     

Effect of substrate temperature on the morphology, structural and optical properties of Zn1−xCoxO thin films

Zn_1−xCo_xO thin films with c-axis preferred orientation were deposited on sapphire (0 0 0 1) by pulsed laser deposition (PLD) technique at different substrate temperatures in an oxygen-deficient ambient. The effect of substrate temperature on the microstructure, morphology and the optical properties of the Zn_1−xCo_xO thin films was studied by means of X-ray diffraction (XRD), atomic force microscopy (AFM), UV-visible-NIR spectrophotometer, fluorescence spectrophotometer. The results showed that the crystallization of the films was promoted as substrate temperature rose. The structure of the samples was not distorted by the Co incorporating into ZnO lattice. The surface roughness of all samples decreased as substrate temperature increased. The Co concentration in the film was higher than in the target. Emission peak near band edge emission of ZnO from the PL spectra of the all samples was quenched because the dopant complexes acted as non-radiative centers. While three emission bands located at 409 nm (3.03 eV), 496 nm (2.5 eV) and 513 nm (2.4 eV) were, respectively, observed from the PL spectra of the four samples. The three emission bands were in relation to Zn interstitials, Zn vacancies and the complex of V_O and Zn_i (V_OZn_i). The quantity of the Zn interstitials maintained invariable basically, while the quantity of the V_OZn_i slightly decreased as substrate temperature increased.     

Thickness measurement of a thin hetero-oxide film with an interfacial oxide layer by X-ray photoelectron spectroscopy

The general equation T_ove = L cos  θ ln(R_exp/R₀ + 1) for the thickness measurement of thin oxide films by X-ray photoelectron spectroscopy (XPS) was applied to a HfO₂/SiO₂/Si(1 0 0) as a thin hetero-oxide film system with an interfacial oxide layer. The contribution of the thick interfacial SiO₂ layer to the thickness of the HfO₂ overlayer was counterbalanced by multiplying the ratio between the intensity of Si⁴⁺ from a thick SiO₂ film and that of Si⁰ from a Si(1 0 0) substrate to the intensity of Si⁴⁺ from the HfO₂/SiO₂/Si(1 0 0) film. With this approximation, the thickness levels of the HfO₂ overlayers showed a small standard deviation of 0.03 nm in a series of HfO₂ (2 nm)/SiO₂ (2-6 nm)/Si(1 0 0) films. Mutual calibration with XPS and transmission electron microscopy (TEM) was used to verify the thickness of HfO₂ overlayers in a series of HfO₂ (1-4 nm)/SiO₂ (3 nm)/Si(1 0 0) films. From the linear relation between the thickness values derived from XPS and TEM, the effective attenuation length of the photoelectrons and the thickness of the HfO₂ overlayer could be determined.     

Synthesis, characterization and analytical applications of Ni(II)-ion imprinted polymer

Ion recognition-based separation techniques have received much attention because of their high selectivity for target ions. In this study, we have prepared a novel ion imprinted polymer (IIP) to remove nickel ions with high selectivity. The imprinted polymer was prepared by copolymerization of 2-hydroxy ethyl methacrylate (HEMA) with nickel vinylbenzoate complex in the presence of ethylene glycol dimethacrylate (EGDMA) as a crosslinker. The polymerization was carried out in bulk with free radical initiation using 2-methoxy ethanol as a solvent and porogen. The adsorbed nickel was completely eluted with 15 mL of 1 M HCl. Control polymer was also prepared by similar experimental conditions without using imprint ion. The above synthesized polymers were characterized by surface area measurements, FT-IR, microanalysis and SEM analysis. The adsorption capacity of IIP and CP was found to be 1.51 and 0.65 mmol g⁻¹, respectively. The optimal pH for quantitative enrichment was 6.5. Nature of eluent, eluent concentration and eluent volume were also studied. The relative selectivity factor (α_r) values of Ni(II)/Zn(II), Ni(II)/Cu(II) and Ni(II)/Co(II) were 78.6, 111.1 and 91.6, respectively. Five replicate determinations of 30 μg L⁻¹ of Ni(II) gave a mean absorbance of 0.067 with a relative standard deviation of 1.06%. The lowest concentration determined by GTA-AAS below which the recovery becomes non-quantitative is 6 μg L⁻¹. IIP was tested for removal of Ni(II) from sea water sample.