Showing papers in "Applied Surface Science in 2012"

Abstract: The chemical structure of silver, nickel and bimetallic silver–nickel nanoparticles, i.e. Ag, Ni and AgNi NPs, with sizes ≤35 nm, obtained by derived seed-mediated growth method on transparent and conductive indium tin oxide (ITO) substrates, has been studied by a comparative X-ray photoelectron spectroscopy (XPS) analysis of Ag 3d, Ni 2p and O1s core levels in combination with X-ray diffraction and optical absorption spectroscopy in the visible range. XPS indicates that the surface of Ag NPs is not oxidized, while Ni NPs are clearly oxidized to nickel oxide and hydroxide. Absorptions at 384 and 600 nm in Ni optical spectrum are consistent with the presence of nickel in oxidized state; however the presence of metallic Ni 2p signal in Ni XPS spectrum indicates that a metallic nickel core is still present. In the case of bimetallic AgNi NPs, the XPS results are consistent with the presence of metallic silver core surrounded by NiO + Ni(OH) 2 shell. XPS spectra also show the presence of Ag 2 O at the interface between the Ag metallic core and the oxidized nickel shell. XRD patterns of AgNi and Ag NPs show the typical fcc structure of metallic silver, confirming the presence of Ag metallic core in AgNi NPs. The surface plasmon resonance peak (SPR) of AgNi NPs shows a blue shift to 375 nm with respect to the SPR of Ag NPs, located at 405 nm, reflecting the character of the oxidized nickel shell.

Abstract: Graphene oxide nanosheets (GOn)/PVDF nanocomposite films were prepared by solution casting method with various GOn contents. GOn were obtained via sonication of bulk graphite oxide in dimethylformamide (DMF). Due to the strong and specific interaction between carbonyl group ( C O) in GOn surface and fluorine group ( CF 2 ) in PVDF, the GOn were homogeneously dispersed and distributed within the matrix. The chosen approach for preparation and the high compatibility between GOn and PVDF result in the formation of purely piezoelectric β-polymorph at only 0.1 wt.% GOn content. Below that content a mixture of β and α-polymorph is observed. The Young's modulus and tensile strength of PVDF were respectively increased by 192% and 92% with the addition of 2 wt.% GOn. The thermal stability of PVDF polymer was also significantly increased with increasing of GOn loading. The as-obtained flexible nanocomposite films with such low GOn content can be used as active materials in the field of piezoelectric applications.

Abstract: Silver nanoparticles (Ag NPs) were produced on cotton fibers by reduction of [Ag(NH3)2]+ complex with glucose. Further modification of the fibers coated by Ag NPs with hexadecyltrimethoxysilane led to superhydrophobic cotton textiles. Scanning electron microscopy images of the textiles showed that the treated fibers were covered with uniform Ag NPs, which generate a dual-size roughness on the textiles favouring the formation of superhydrophobic surfaces, and the Ag NPs formed dense coating around the fibers rendering the intrinsic insulating cotton textiles conductive. Antibacterial test showed that the as-fabricated textiles had high antibacterial activity against the gram-negative bacteria, Escherichia coli. These multifunctional textiles might find applications in biomedical electronic devices.

Abstract: Cupric oxide (CuO) nanoparticles with an average size of 6 nm have been successfully prepared by an alcothermal method. The prepared CuO nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR) and UV–visible absorption spectroscopy. A strong sharp emission under UV excitation is reported from the prepared CuO nanoparticles. The results show that the CuO nanoparticles have high dispersion and narrow size distribution. The fluorescence emission spectra display an intense sharp emission at 365 nm and weak broad intensity emission at 470 nm. Picosecond fluorescence measurements of the nanoparticles suggest bi-exponential function giving time constants of τ 1 (330 ps, 94.21%) and τ 2 (4.69 ns, 5.79%). In neutral and alkaline solutions, Zeta potential values of CuO nanoparticles are negative, due to the adsorption of COO − group via the coordination of bidentate. At low pH the zeta potential value is positive due to the increased potential of H + ions in solution. Comparative UV–visible absorption experiments with the model amino acid compounds of positive and negative charges as arginine and aspartic acid, respectively confirmed the negative surface of CuO nanoparticles. The results should be extremely useful for understanding the mode of the interaction with biological systems. This binding process also affects the particle's behavior inside the body.

Abstract: Hydrothermal method was utilized to prepare reduced graphene oxide (RGO) and fabricate ZnO–RGO hybrid (ZnO–RGO) with zinc nitrate hexahydrate and graphene oxide (GO) as raw materials under pH value of 11 adjusted by ammonia water. During the process of reduction of GO, hydrothermal condition with ammonia provided thermal and chemical factors to synthesize RGO. The retained functional groups on RGO planes played an important role in anchoring ZnO to RGO, which was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy and photoluminescence spectra. The various mass ratios of zinc nitrate hexahydrate to GO used to prepare ZnO–RGO impacted significantly on the morphology of ZnO nanostructures such as nanoparticles and nanorods. And, the RGO sheets wrapped ZnO nanoparticles and nanorods very tightly. After the emission of photo electrons from ZnO, RGO in ZnO–RGO can effectively transfer the photo electrons to exhibit a high performance and reproducibility in photocatalytic degradation toward methylene blue (MB) absorbed on the surface of RGO through π–π conjugation.

Abstract: The present paper reveals the formation of cobalt ferrite (CoFe 2 O 4 ) thin film on stainless steel substrate by simple chemical route from an alkaline bath containing Co 2+ and Fe 2+ ions. The films are characterised for structural, surface morphological and FT-IR properties. The XRD and FT-IR studies revealed formation of single phase of CoFe 2 O 4 . The formation of nano-flakes-like morphology is observed from scanning electron microscope. The electrochemical behaviour of CoFe 2 O 4 film has been studied using cyclic voltammetry in 1 M NaOH electrolyte. The maximum specific capacitance of 366 F g −1 is obtained at the scan rate of 5 mV s −1 . Using AC impedance technique equivalent series resistance (ESR) value is found to be 1.1 Ω.

Abstract: In this paper, a novel approach was successfully developed for advanced catalyst Ag-deposited silica-coated Fe 3 O 4 magnetic nanoparticles, which possess a silica coated magnetic core and growth active silver nanoparticles on the outer shell using n-butylamine as the reductant of AgNO 3 in ethanol. The as-synthesized nanoparticles have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), Fourier transform infrared spectra (FT-IR), vibration sample magnetometer (VSM), and have been exploited as a solid phase catalyst for the reduction of p -nitrophenol in the presence of NaBH 4 by UV–vis spectrophotometry. The obtained products exhibited monodisperse and bifunctional with high magnetization and excellent catalytic activity towards p -nitrophenol reduction. As a result, the as-obtained nanoparticles showed high performance in catalytic reduction of p -nitrophenol to p -aminophenol with conversion of 95% within 14 min in the presence of an excess amount of NaBH 4 , convenient magnetic separability, as well as remained activity after recycled more than 6 times. The Fe 3 O 4 @SiO 2 –Ag functional nanostructure could hold great promise for various catalytic reactions.

Abstract: In this study, SnO 2 /ZnO/TiO 2 composite photocatalysts were successfully synthesized using sol–gel and solid-state methods. The as-prepared samples were characterized for the phase structure, optical absorption, thermal stability and surface property using X-ray diffraction (XRD), Raman spectroscopy, UV–vis diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The photocatalytic activity was tested with photodecomposition of Methyl Orange under both visible and UV light irradiations. The results indicated that the SnO 2 /ZnO/TiO 2 composite materials have an apparent visible light absorption, combining TiO 2 with SnO 2 and ZnO could promote the TiO 2 phase transition from anatase to rutile. The SnO 2 /ZnO/TiO 2 heterojunctions with the highest performance was the one prepared using Sn(Zn)/Ti molar ratio of 0.05. It was found that the enhanced photocatalytic activity could be attributed to the increased separation of the charge carriers, which therefore depress the charge pair recombination and prolonged the electron lifetime in the composite structure, and a large number of electrons could take part in the photoreaction. Based on the results of the present study, a tentative mechanism for the enhanced photocatalysis of the SnO 2 /ZnO/TiO 2 composite catalyst has been proposed.

Abstract: Mg–Fe–Cl Layered double hydroxides (LDHs) have been prepared using a method involving separate nucleation and aging steps with Mg/Fe = 3. The interlayer anions readily replaced by carbonate are characterized by X-ray diffraction (XRD) and FTIR. The effects of different parameters, such as pH, contact time, concentration of dye and temperature on the capacity and adsorption mechanism of Mg–Fe–CO 3 –LDH in removing an anionic dye (congo red, CR) from aqueous solution were separately investigated. The results show that Mg–Fe–CO 3 –LDH is particularly efficient in removing CR and the dye removal increases with decreasing pH. The adsorption of CR on Mg–Fe–CO 3 –LDH reached equilibrium after 15 min where 100 mg/L CR was removed. The equilibrium isotherm indicates that the adsorption of CR onto Mg–Fe–CO 3 –LDH fits to Langmuir and Freundlich equation as well. The adsorption data obtained from the Langmuir model gave good values of the determination coefficient and the saturated adsorption capacity of Mg–Fe–CO 3 –LDH for CR was found to be 104.6 mg/g. The regeneration study indicates that the prepared LDH could be used for several cycles. The thermodynamic parameters have been calculated, and the adsorption process was found to be spontaneous, endothermic in nature and follows a pseudo-second-order kinetic model.

Abstract: Graphene–CdS (G–CdS) composites were synthesized through a simple solvothermal method. The formed CdS nanospheres were homogeneously scattered on the surface of graphene sheets. Fluorescence quenching effect of the G–CdS composites indicated effective transfer of photo-excited electrons from CdS to graphene, suppressed the recombination of photo-generated electron–hole pairs, so that the enhanced visible light induced photodegradation activity for Rhodamine B (RhB) was achieved. Based on the high photocatalytic activity and well stability, the G–CdS composite containing 70% CdS can be expected to be a practical visible light photocatalyst.

Abstract: Active carbons have been prepared from corncob using chemical activation with phosphoric acid at 400 °C using varied ratio of impregnation (RI). Porous structure of carbons was characterized by nitrogen adsorption and scanning electron microscopy. Surface chemistry was studied by IR and potentiometric titration method. It has been shown that porosity development was peaked at RI = 1.0 (SBET = 2081 m2/g, Vtot = 1.1 cm3/g), while maximum amount of acid surface groups was observed at RI = 1.25. Acid surface groups of phosphoric acid activated carbons from corncob includes phosphate and strongly acidic carboxylic (pK = 2.0–2.6), weakly acidic carboxylic (pK = 4.7–5.0), enol/lactone (pK = 6.7–7.4; 8.8–9.4) and phenol (pK = 10.1–10.7). Corncob derived carbons showed high adsorption capacity to copper, especially at low pH. Maximum adsorption of methylene blue and iodine was observed for carbon with most developed porosity (RI = 1.0).

Abstract: In this work, we developed a concentrated ammonia-assisted hydrothermal method to obtain N-doped graphene sheets by simultaneous N-doping and reduction of graphene oxide (GO) sheets. The effects of hydrothermal temperature on the surface chemistry and the structure of N-doped graphene sheets were also investigated. X-ray photoelectron spectroscopy (XPS) study of N-doped graphene reveals that the highest doping level of 7.2% N is achieved at 180 °C for 12 h. N binding configurations of sample consist of pyridine N, quaternary N, and pyridine-N oxides. N doping is accompanied by the reduction of GO with decreases in oxygen levels from 34.8% in GO down to 8.5% in that of N-doped graphene. Meanwhile, the sample exhibits excellent N-doped thermal stability. Electrical measurements demonstrate that products have higher capacitive performance than that of pure graphene, the maximum specific capacitance of 144.6 F/g can be obtained which ascribe the pseudocapacitive effect from the N-doping. The samples also show excellent long-term cycle stability of capacitive performance.

Abstract: The adsorption method was used for fluoride removal from aqueous solution by Apatitic tricalcium phosphate. In this study, response surface methodology was employed for the removal of fluoride. Experiments were carried out as per Box–Behnken surface statistical design with four input parameters namely adsorbent dose (0.1–0.3 g), initial concentration (30–60 mg L−1), temperature (20–40 °C) and pH (4–11). Contact time (90 min) was taken as a fixed input parameter. Regression analysis showed good fit of the experimental data to the second-order polynomial model with coefficient of determination (R2) value of 0.966 and Fisher F-value of 10.28. Applying the method of the desirability function, optimization of adsorbent dose (29 g), initial concentration (60 mg L−1), T (40 °C) and pH (4) gave a maximum of 82.34% fluoride removal white desirability of 0.916 by Apatitic tricalcium phosphate. Dynamic adsorption data were applied to pseudo-first-order and pseudo-second-order rate equations. Pseudo-second-order kinetic model well expressed fluoride adsorption onto Apatitic tricalcium phosphate. According to the correlation coefficients, the adsorption of fluoride on the Apatitic tricalcium phosphate was correlated well with the Langmuir and Freundlich models.

Abstract: In the present work, a nickel sulfate bath containing SiC submicron particles between 100 and 1000 nm was used as the plating electrolyte. The aim of this work is to obtain Ni–SiC metal matrix composites (MMCs) reinforced with submicron particles on steel surfaces with high hardness and wear resistance for using in anti-wear applications such as dies, tools and working parts for automobiles and vehicles. The influence of the SiC content in the electrolyte on particle distribution, microhardness and wear resistance of nano-composite coatings was studied. During the electroplating process, the proper stirring speed was also determined for sub-micron SiC deposition with Ni matrix. The Ni films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The depositions were controlled to obtain a specific thickness (between 50 and 200 μm) and volume fraction of the particles in the matrix (between 0.02 and 0.10). The hardness of the coatings was measured to be 280–571 HV depending on the particle volume in the Ni matrix. The tribological behaviors of the electrodeposited SiC nanocomposite coatings sliding against an M50 steel ball (O 10 mm) were examined on a tribometer. All the friction and wear tests were performed without lubrication at room temperature and in the ambient air (with a relative humidity of 55–65%). The results showed that the wear resistance of the nanocomposites was approximately 2–2.2 times more than those of unreinforced Ni.

Abstract: Cu-doped ZnO thin films were fabricated on glass substrates by the sol–gel dip-coating method. All samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The grain size and film thickness of the Cu-doped ZnO thin film decreased as a function of the Cu concentrations. All prepared films showed a very high transmittance above 89% in the visible region (400–800 nm). Two oxidation states of Cu in +1 and +2 were identified in the ZnO thin film by X-ray photoelectron spectroscopy (XPS). Their photocatalytic activities were investigated by the degradation of methylene blue (MB) dye under blacklight fluorescent tubes. The film prepared from the Zn2+ solution containing 0.5 mol% of copper ions had the highest photocatalytic activity. The photocatalytic degradation of methylene blue solution as a function of the initial concentrations was evaluated according to the Langmuir–Hinshelwood model. The reaction rate (k) and adsorption equilibrium constant (K) over 1 cm2 of 0.5 mol% Cu-doped ZnO thin film are 15.92 μM h−1 and 0.049 μM−1, respectively.

Abstract: In the present study, Fe3O4/graphene nanocomposite was prepared by solvothermal method and characterized by transmission electron microscope, Fourier transform infrared spectrometer and vibration sample magnetometer. Effects of different factors, including initial solution pH, agitation time and adsorbate concentration, on adsorption capacity of Fe3O4/graphene nanocomposite for aniline and p-chloroaniline were investigated. Experimental results demonstrated aniline and p-chloroaniline could be effectively removed from aqueous solution by Fe3O4/graphene nanocomposite within 60 min without adjusting solution pH. The adsorption of aniline and p-chloroaniline onto Fe3O4/graphene nanocomposite obeyed pseudo-second-order kinetic model and Freundlich isotherm model. The saturation magnetization of the Fe3O4/graphene nanocomposite was about 120 emu g(-1), which ensured the convenient magnetic separation after adsorption. (C) 2012 Elsevier B. V. All rights reserved.

Abstract: The preparation of Ag doped ZnO nanoparticles conducted through the method of laser-induction is presented in this work. The Ag/ZnO nanoparticles attained from various weight percentages of added AgNO 3 relative to ZnO were applied under visible-light irradiation for evaluating the heterogeneous photocatalytic degradations of methylene blue (MB) solutions. It was shown that the catalytic behavior of Ag/ZnO nanoparticles in the visible-light range is notably improved through the Ag deposition onto ZnO nanoparticles by the method of laser-induction with a maximum effectiveness of 92% degradation. The properties of the nanoparticles were characterized by the employments of UV–vis spectroscopy (UV–vis), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and selected-area electron diffraction (SAED).

Abstract: An attempt to improve hydrophilicity and anti-fouling properties of PVDF membranes, a novel amphiphilic zwitterionic copolymer poly(vinylidene fluoride)-graft-poly(sulfobetaine methacrylate) (PVDF-g-PSBMA) was firstly synthesized by atom transfer radical polymerization (ATRP) and used as amphiphilic copolymer additive in the preparation of PVDF membranes. The PVDF-g-PSBMA/PVDF blend membranes were prepared by immersion precipitation process. Fourier transform infrared attenuated reflection spectroscopy (FTIR–ATR) and X-ray photoelectronic spectroscopy (XPS) measurements confirmed that PSBMA brushes from amphiphilic additives were preferentially segregated to membrane–coagulant interface during membrane formation. The morphology of membranes was characterized by scanning electron microscopy (SEM). Water contact angle measurements showed that the surface hydrophilicity of PVDF membranes was improved significantly with the increasing of amphiphilic copolymer PVDF-g-PSBMA in cast solution. Protein static adsorption experiment and dynamic fouling resistance experiment revealed that the surface enrichment of PSBMA brush endowed PVDF blend membrane great improvement of surface anti-fouling ability.

Abstract: The Fe-TiO2 photocatalysts synthesized by a sol–gel method have the mesoporous structure with a narrow pore size distribution, large pore volume and high surface area. The incorporated Fe3+ substitutes the octahedrally coordinated Ti4+ in the TiO2 lattice to extend the absorption of TiO2 to visible light region and promote the formation of electron–hole pair. Additionally, the separation and transportation efficiency increase with the doping of Fe3+ increasing from 0.1% to 0.7%, while decreases remarkably with the doping concentration increasing from 0.7% to 1.5%. The Fe-TiO2 shows excellent photocatalytic performance for toluene degradation under visible light irradiation. The optimal Fe/Ti ratio is 0.7%. Partial deactivation of the photocatalytic activity was observed after 20 consecutive reaction runs. From the in situ DRIFTS experiment, the deactivation reason can be attributed to the formation of stable intermediates, such as benzaldehyde and benzoic acid, which occupied the active sites on the surface of the photocatalyst. The adsorbed benzaldehyde and benzoic acid can be removed with heat treatment at 653 K for 3 h and the deactivated photocatalyst can be regenerated completely.

Abstract: Surface modification by a titanium coating layer onto a tungsten carbide surface by electrical discharge coating (EDC) was studied by considering a titanium coating modification as well as the completeness of the tungsten carbide surface. This was carried out by electrical discharge machining (EDM). The tungsten carbide material was produced using a fluid dielectric oil, which was mixed with titanium powder. The current and duty cycles were varied resulting in a change in the titanium coating layer thickness. Also, an analysis of the chemical composition using energy dispersive spectroscopy (EDS) revealed that a titanium coating layer was formed causing the hardness of the titanium surface to be close to that of tungsten carbide. The completeness of the surface was evaluated using scanning electron microscopy (SEM) and a small number of microcracks were found on the surface since the microcracks were filled and substituted by titanium powder and carbon (a hydrocarbon) that decomposed from the dielectric that acted as a combiner (TiC). Also, the high concentration of carbon increased the amount of Ti and C combination and TiC was formed, which enhanced the surface hardness of the coated layer to 1750 HV. The surface roughness of the coated layer decreased and this reduced the formation of microcracks on the surface workpiece.

Abstract: In this work, polyacrylonitrile (PAN)-based carbon fiber were chemically modified with H 2 SO 4 , KClO 3 and silane coupling agent (γ-aminopropyltriethoxysilane, APS), and carbon fiber reinforced phenolic matrix composites were prepared. The structural and surface characteristics of the carbon fiber were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), laser Raman scattering (LRS) and Fourier transform infrared spectroscopy (FTIR). Single fiber mechanical properties, specific surface area, composite impact properties and interfacial shear strength (ILSS) were researched to indicate the effects of surface modification on fibers and the interaction between modified fiber surface and phenolic matrix. The results showed that carbon fiber surface modification by oxidation and APS can strengthen fiber surface chemical activity and enlarge the fiber surface area as well as its roughness. When carbon fiber (CF) is oxidized treatment, the oxygen content as well as the O/C ratio will be obviously increased. Oxygen functional groups increase with oxidation time increasing. Carbon fiber treated with APS will make C O R content increase and O C O content decrease due to surface reaction. Proper treatment of carbon fiber with acid and silane coupling agent prove an effective way to increase the interfacial adhesion and improve the mechanical and outdoor performance of the resulting fiber/resin composites.

Abstract: The purpose of this in vitro study was the evaluation of the bond strength of the adhesives/composite resin to Poly Ether Ether Ketone (PEEK) based dental polymer after using different surface conditioning methods. PEEK blanks were cut into discs. All disc specimens were polished with 800 grit SiC paper and divided into 6 main groups. Main groups were divided into 2 subgroups. The main groups of 32 specimens each were treated as follow: (1) control specimens (no treatment), (2) piranha solution etching, (3) abraded with 50 μm alumina particles and chemical etching, (4) abraded with 110 μm alumina particles and chemical etching, (5) abraded with 30 μm silica-coated alumina particles and chemical etching, (6) abraded with 110 μm silica-coated alumina particles and chemical etching. Plexiglas tubes filled with a composite resin (RelyX Unicem) were bonded to the specimens. The adhesives used were Heliobond and Clearfil Ceramic Primer. Each specimen was stored in distilled water (37 °C) for 3 days. Tensile bond strength was measured in a universal testing machine and failure methods were evaluated. Abraded surface with 50 μm alumina particles followed by etching with piranha solution lead to the highest bond strength of 21.4 MPa when Heliobond like adhesive was used. Tribochemical silica coated/etched PEEK surfaces did not have an effect on the bond strength. Non-treated PEEK surface was not able to establish a bond with composite resin. The proper choice of adhesive/composite resin system leads to a strong bond. Conclusion Airborne particle abrasion in combination with piranha solution etching improves the adhesive properties of PEEK.

Abstract: Shot peening, apart from its various projected effects, modifies also the surface state of treated components in terms of surface irregularities. Bearing in mind that both the macroscopic and the microstructure surface characteristics strongly affect the mechanical structures’ functionality, it is essential to carefully study the surface state of treated components. To assess the surface roughness evolution induced by shot peening, a 3D finite element model of the process is used to investigate surface topography alterations as a function of peening parameters and processing time. Discrete data obtained from the numerical simulations are subsequently elaborated to calculate the conventional roughness parameters. The results obtained from the numerical simulations, correspond quite well with the roughness values measured experimentally on shot peened specimens. It is indicated that the developed numerical model provides an efficient estimation of surface characteristics of shot peened specimens, in terms of surface roughness parameters and thus can be used to properly select the peening parameters considering the eventual surface roughness.

Abstract: Sorption of uranium (VI) from aqueous solutions onto Multiwalled Carbon Nanotubes (MWCNTs) has been studied under varying experimental conditions of initial uranium concentration, contact time, pH, and temperature, to assess the kinetic and equilibrium parameters. The optimum pH for sorption of uranium (VI) onto MWCNTs was 5. The kinetic data were fitted with pseudo-first-order, pseudo-second-order, and intra-particle diffusion models. The sorption process was well described by pseudo-second-order kinetics. The uranium sorption data were fitted by the Langmuir, Freundlich, and Dubinin–Radushkevich equilibrium models to obtain the characteristic parameters of each model. The Langmuir isotherm was found to best represent the measured sorption data. According to the evaluation using the Langmuir model, the maximum sorption capacity of uranium (VI) ions onto MWCNTs increased with temperature, from 24.9 to 39.1 mg g −1 when the temperature was increased from 298 to 318 K. The calculated sorption thermodynamic parameters including Δ G °, Δ H °, and Δ S ° indicated the spontaneous nature of uranium sorption onto MWCNTs. The results suggest that MWCNTs are suitable materials for preconcentration and solidification of uranium (VI) species from aqueous solutions.

Abstract: Inspired by the bio-adhesive proteins secreted by mussels for attachment to almost all wet substrates, a facile method involving oxidative polymerization of dopamine was proposed to prepare highly hydrophilic carbon black (CB) particles. A self-assembled polydopamine (PDA) ad-layer was formed via the oxidative polymerization of dopamine on the surface of CB simply by dipping the CB into an alkaline dopamine solution and mildly stirring at room temperature. The process is simple, controllable, and environment-friendly. The surface composition and structure of the CB were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The surface morphology of the CB was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the PDA ad-layer was successfully deposited on the CB surfaces. The PDA-functionalized CB (CB-PDA) gave a stable colloidal dispersion in water. Contact angle measurement results indicated that the hydrophilicity of CB was significantly improved after dopamine modification. TGA results confirmed that the modified CB maintained good heat resistance. The method provided a facile route to prepare hydrophilic CB having terminal hydroxyl groups.

Abstract: Multiwall carbon nanotubes (MWNT) with three medium diameters (20–22, 9–13, and 6–8 nm) and different morphology were chemically oxidized using concentrated nitric acid, mixture of nitric and sulfuric acids (“melange” solution) and mixture of sulfuric acid and hydrogen peroxide (“piranha” solution). Influence of MWNT type and structure as well as type of oxidizer on the surface composition and structure of nanotubes after oxidation was investigated. Acid–base titration, X-ray photoelectron spectroscopy and thermal gravimetric analysis were used for quantitative and qualitative investigation of surface group composition of initial and oxidized nanotubes. Amount of oxygen-containing groups on the surface of oxidized MWNT depends on the type of initial MWNT. It was found that ratio of different oxygen containing groups is less dependent on the type of oxidizer. Electrophysical properties of initial and oxidized nanotubes were investigated in temperature range 4–293 K and main types of electrical conductivity were determined. It was shown that oxidation results in decrease in electrical conductivity of all samples with simultaneous change in the conductivity mechanism. Dispersive behavior of initial and oxidized nanotubes in different commonly used solvents was investigated. It was shown that oxidation leads to the improvement of sedimentation stability of MWNT in polar solvents.

Abstract: The high temperature self-lubricating wear-resistant NiCr/Cr3C2–30%WS2 coating and wear-resistant NiCr/Cr3C2 coating were fabricated on 0Cr18Ni9 austenitic stainless steel by laser cladding. Phase constitutions and microstructures were investigated, and the tribological properties were evaluated using a ball-on-disc wear tester under dry sliding condition at room-temperature (17 °C), 300 °C and 600 °C, respectively. Results indicated that the laser clad NiCr/Cr3C2 coating consisted of Cr7C3 primary phase and γ-(Fe,Ni)/Cr7C3 eutectic colony, while the coating added with WS2 was mainly composed of Cr7C3 and (Cr,W)C carbides, with the lubricating WS2 and CrS sulfides as the minor phases. The wear tests showed that the friction coefficients of two coatings both decrease with the increasing temperature, while the both wear rates increase. The friction coefficient of laser clad NiCr/Cr3C2–30%WS2 is lower than the coating without WS2 whatever at room-temperature, 300 °C, 600 °C, but its wear rate is only lower at 300 °C. It is considered that the laser clad NiCr/Cr3C2–30%WS2 composite coating has good combination of anti-wear and friction-reducing capabilities at room-temperature up to 300 °C.

Abstract: s The commercial pure magnesium was coated by micro arc oxidation method in different aqueous solution, containing sodium silicate and sodium phosphate. Micro arc oxidation process was carried out at 0.060 A/cm2, 0.085 A/cm2 and 0.140 A/cm2 current densities for 30 min. The thickness, phase composition, morphology, hardness, adhesion strength and wear resistance of coatings were analyzed by eddy current, X-ray diffraction (XRD), scanning electron microscope (SEM), micro hardness tester, scratch tester and ball-on disk tribometer, respectively. The average thicknesses of the micro arc oxidized coatings ranged from 27 to 48 μm for sodium silicate solution and from 45 to 75 μm for sodium phosphate solution. The dominant phases formed on the pure magnesium were found to be a mixture of spinel Mg2SiO4 (Forsterite) and MgO (Periclase) for sodium silicate solution and Mg3(PO4)2 (Farringtonite) and MgO (Periclase) for sodium phosphate solution. The average hardnesses of the micro arc oxidized coatings were between 260 HV and 470 HV for sodium silicate solution and between 175 HV and 260 HV for sodium phosphate solution. Adhesion strengths and wear resistances of coatings produced in sodium silicate solution were higher than those of the ones in sodium phosphate solution due to high hardness of coatings produced in sodium silicate solution.

Abstract: Undoped and Mg-doped ZnO thin films were deposited on Si(1 0 0) and quartz substrates by the sol–gel method. The thin films were annealed at 873 K for 60 min. Microstructure, surface topography and optical properties of the thin films have been measured by X-ray diffraction (XRD), atomic force microscope (AFM), UV–vis spectrophotometer, and fluorophotometer (FL), respectively. The XRD results show that the polycrystalline with hexagonal wurtzite structure are observed for the ZnO thin film with Mg:Zn = 0.0, 0.02, and 0.04, while a secondary phase of MgO is evolved for the thin film with Mg:Zn = 0.08. The ZnO:Mg-2% thin film exhibits high c -axis preferred orientation. AFM studies reveal that rms roughness of the thin films changes from 7.89 nm to 16.9 nm with increasing Mg concentrations. PL spectra show that the UV–violet emission band around 386–402 nm and the blue emission peak about 460 nm are observed. The optical band gap calculated from absorption spectra and the resistivity of the ZnO thin films increase with increasing Mg concentration. In addition, the effects of Mg concentrations on microstructure, surface topography, PL spectra and electrical properties are discussed.

Abstract: To explore the novel application of boron nitride nanotube (BNNT), we have investigated the structural, magnetic and electronic properties of CO and NO molecules adsorption on transition metals (TM = V, Cr, Mn, Fe, Co or Ni) doped (8,0) BNNT using first-principle calculations. The combining processes of all gas adsorption on TM-doped BNNT are exothermic, accompanying with larger formation energies and charges transfer showing that both CO and NO molecules present strong chemical interaction with the TM-doped BNNT, and the adsorption of NO is more stable than that of CO. The presence of CO molecule almost does not change the magnetic properties of the TM-BNNT systems. But the adsorption of NO gas on different sites of different TM doped BNNT has different magnetic moment. The adsorption of CO and NO molecules on TM-doped BNNTs leads to different electronic structure properties of BNNTs. Therefore, the TM-doped BNNT can be used as CO and NO gas sensor manufacturing raw materials, and it may be a potential material for nanodevice applications.