Search

Highlights: [•] Highly stable dispersion of monodisperse Ag nanoparticles (1–2nm) was obtained. [•] Poly-amino compounds were used as effective stabilizing agent in nonaqueous medium. [•] The robust one-step route is simple and highly reproducible. [ABSTRACT FROM AUTHOR]

Abstract: Highly stable dispersion of silver nanoparticles (Ag NPs) (1–2nm in diameter) having low size distribution was synthesized using a straightforward one-step synthesis method. Tetraethylenepentamine (TEPA), a kind of aliphatic amine, was utilized as stabilizing agent to prevent the aggregation of Ag NPs in nonaqueous medium. The successful formation of TEPA-stabilized Ag NPs was demonstrated by ultraviolet–visible spectroscopy (UV–vis), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). The mechanism of TEPA on the stabilization of Ag NPs is also discussed. This facile one-step synthesis route may provide a new perspective for creating other nanoparticles that have potential application in various nanotechnology fields. [Copyright &y& Elsevier]

Abstract: Water-soluble and highly stable dispersions of copper nanoparticles were obtained using a biomolecule-assisted synthetic method. Dopamine was utilized as both reducing and capping agent in aqueous medium. The successful formation of DA-stabilized copper particles was demonstrated by ultraviolet–visible spectroscopy (UV–Vis), transmission electron microscopy (TEM), Zeta potential measurement, and Fourier transform infrared spectroscopy (FT-IR). The mechanism of dopamine on the effective reduction and excellent stability of copper nanoparticles was also discussed. This facile biomolecule-assisted technique may provide a useful tool to synthesize other nanoparticles that have potential application in biotechnology. [Copyright &y& Elsevier]

Abstract: Single crystal silicon wafers (Si (100) ) were implanted with 110 keV Ar+ ions at a fluence of 1×1016 ions/cm2. Then the unimplanted and ion-implanted Si surfaces were coated with an amorphous carbon coating of 50±5 nm thick making use of vacuum vapor deposition. The microstructures of the unimplanted and Ar+ ion implanted Si wafers were analysed by means of transmission electron microscopy (TEM). The hardness and elastic modulus of the unimplanted and Ar+ ion implanted Si wafers were measured using a nano-indentation device. The adhesion strengths of the amorphous carbon coatings on the unimplanted and Ar+ ion implanted Si surfaces were determined making use of scratch test. The friction and wear behaviors of the samples were evaluated using a ball-on-disk reciprocating friction and wear tester. The morphologies of the wear and scratch tracks of the Si samples were observed using a scanning electron microscope (SEM). It was found that Ar+ ion implantation alone led to little effect on the friction and wear behavior of the Si sample. However, the amorphous carbon coating deposited on the Ar+ ion implanted Si surface showed much better friction-reducing and antiwear ability than that on the unimplanted Si surface. The formation of a mixed nano-crystal and amorphous silicon structure during the Ar+ ion implantation improves the ability of the amorphous carbon coating to resist plastic deformation, and hence increase the adhesion strength and antiwear-life of the amorphous carbon film. [Copyright &y& Elsevier]

Abstract: The effect of argon ion implantation on the nano-machanical properties of single crystal Si was examined making use of nano-indentation and nano-scratch tests. The morphologies of the scratched tracks of the unimplanted Si and that implanted at a moderate Ar+ fluence were observed on a scanning electron microscope, while the changes in the microstructure of the single crystal Si by Ar+ implantation were investigated on a transmittance electron microscope. It was found that the implantation of Si at a small or moderate fluence of Ar+ below 1×1015 ions/cm2 had little effect on the surface roughness and a minor effect on the surface nano-hardness. At the same time, the implantation of Si with Ar+ at a moderate fluence up to 1×1016 ions/cm2 led to a significant increase in the critical load. This was attributed to the desired changes in the microstructures of the single crystal Si by Ar+ implantation at a proper fluence. Namely, the Si surface implanted with Ar+ at a moderate fluence was composed of nano-sized polycrystalline Si uniformly distributed in amorphous Si matrix, which contributed to significantly increase the nano-scratch resistance and surface toughness of the single crystal silicon. It was suggested to implant the single crystal Si at an Ar+ fluence of 1×1016 ions/cm2 so as to acquire the optimized modification effect. [Copyright &y& Elsevier]

Abstract: AISI1045 steel was modified by laser heat-treatment and conventional heat treatment. The friction and wear behaviors of the steel specimens after various surface modifications sliding against SAE52100 steel under the lubrication of liquid paraffin containing sulphurized olefin were comparatively investigated on an Optimol SRV oscillating friction and wear tester. The worn surface morphologies of the modified steel specimens were analyzed using a scanning electron microscope. The elemental compositions and chemical states of some typical elements on the worn surfaces of the modified steel specimens were analyzed with an energy dispersive X-ray analyzer and X-ray photoelectron spectroscope, respectively. It was found that the laser heat-treated specimen showed the highest hardness and best wear-resistance. The laser heat-treated and conventionally heat treated AISI1045 steel specimens sliding against SAE52100 steel under the lubrication of liquid paraffin containing sulphurized olefin registered smaller friction coefficients than under the lubrication of liquid paraffin alone. This was partly attributed to the increased hardness of the modified specimens. The tribochemical reaction between the steel and the active elements in the additive was involved in the sliding of the modified steel specimens against SAE52100 steel ball under the boundary lubricating condition, with the formation of a surface protective film composed of various tribochemical products. This also contributed to improve the friction and wear behavior of the modified steel specimens. The steel specimens subject to different surface modifications showed differences in the wear mechanisms under the boundary lubricating condition as well. Namely, the tempered steel specimen was mainly characterized by plastic deformation and pitting, the quenched specimen by grooves and delaminating, and the laser heat-treated one by polishing and mild adhesion. [Copyright &y& Elsevier]

To enhance the interfacial interaction in silica-nanoparticle-filled polymer composites, an effective surface modification method was developed by grafting polystyrene onto the nanoparticles. That is, the silica surface was first treated with silane to introduce the methacryloxypropyl, followed by radical copolymerization with styrene via a dispersion polymerization method. Results of elemental analysis (EA), IR, XPS and TEM demonstrated that the desired polymer chains were covalently bonded to the surface of the silica nanoparticles. A percentage of grafting (PG) of 49.5% was achieved when 2.44 mmol AIBN was used as initiator. The resulting products could be used as nanocomposites directly, or the PS-grafted silica nanoparticles (PS-SNs) could be separated and used as nanofillers for polymers. [ABSTRACT FROM AUTHOR]

Nodular cast iron was modified by means of a laser micro-precision treatment. The surface roughness of the treated sample was determined with a profilometer. The friction and wear behavior of the modified specimens sliding against SAE-52100 steel under the lubrication of liquid paraffin (LP) containing various anti-wear and extreme pressure additives was investigated on an Optimol SRV oscillating friction and wear tester. The morphologies and elements distribution of the worn surfaces were observed with a scanning electron microscope and an energy dispersive X-ray analyzer, in an attempt to reveal the wear mechanisms of the surface-modified cast iron. The phase composition of the laser treated nodular cast iron was examined by means of X-ray diffraction. As the results, the friction coefficients for the laser treated cast iron are slightly higher than that for the untreated one. The wear volume loss of the treated cast iron specimen sliding against SAE-52100 steel under lubrication of LP containing various additives is only about 5–10% of that of the untreated one. The nodular cast iron specimens after laser surface modification show good surface shape and high rigidity. The substantial increase in the wear-resistance of the cast iron after laser treatment can be attributed to a significant increase in the surface hardness of the laser-modified layers and to the friction-reducing and wear-resistant action of the extreme pressure and anti-wear additives. [Copyright &y& Elsevier]

Abstract Although Janus membranes have been fabricated for the separation of oil/water mixtures, simplifying the construction processes is still a thorny challenge. In this work, a facile and easily scale-up approach based on in situ mussel-inspired chemistry is reported for the first time to prepare the Janus membrane with unidirectional oil/water separation. Here, the poly (vinylidene fluoride)/polydopamine/polyethylenimine (PVDF/PDA/PEI) membranes on the polyester non-woven fabric were fabricated via non-solvent induced phase separation (NIPS) technique. In the coagulation bath, the reactive oxygen species (ROS) produced by CuSO 4 /H 2 O 2 improved the formation of the hydrophilic PDA/PEI on the top surface of the membrane. The hydrophobic bottom surface was received after the membrane was stripped from the supporting fabric. Scanning electronic microscopy (SEM), confocal laser scanning microscopy (CLSM), attenuated total reflectance Fourier transform infrared spectrometer (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometer (EDS) were used to characterize the membrane. The Janus membrane showed asymmetric wettability with 152.2° underwater oil contact angle of F-T5 and 153.3° underoil water contact angle of B-T5. Furthermore, by this in situ mussel-inspired chemistry, the Janus membrane showed excellent water and oil separation, antifouling performance and stability, which can potentially be used for unidirectional oil/water separation. Highlights • A facile approach based on in situ mussel-inspired chemistry is used to prepare Janus membrane. • The Janus membranes were fabricated via non-solvent induced phase separation (NIPS) technique. • The Janus membrane showed excellent water and oil separation performance. • The Janus membrane provides a new method for oil and water separation field. [ABSTRACT FROM AUTHOR]

Dual pH- and thermo-responsive polysulfone (PSf) membranes with three-dimensionally interconnected networks are fabricated by introducing poly(acrylic acid- co - N -isopropylacrylamide) (P(AA-NIPAm)) into the membrane surfaces and pore walls during membrane formation via a vapor-liquid induced phase separation (V-LIPS) process. After introducing the copolymers of P(AA-NIPAm), the fabricated membranes exhibit impressive open network pores on the surfaces, meanwhile their cross-sectional structure turns from classical asymmetric finger-like structure into bi-continuous nanopores throughout the whole thickness of membrane, due to high solution viscosity and low mass transfer rate of VIPS process. Furthermore, pure water permeation tests show that the pure water permeation ( L p ) and the molecular weight cutoff (MWCO) of the fabricated PSf/P(AA-NIPAm) membranes increases sharply as the solution pH decreases from 12.5 to 1.5 and the feed temperature increases from 25 to 50 °C, attributing to the increasing pore size. With the decreasing mass ratio of AA to NIPAm, the pH-responsive coefficient decreases, while the temperature- responsive coefficient increases. In particular, for the fabricated membrane with the mass ratio of AA to NIPAm of 3 to 2, L p changes from ∼16.0 to ∼821.4 L m −2  h −1  bar −1 and MWCO increases from ∼223.1 to ∼1493.2 kDa, as the filtration experiments are operated with feed pH and temperature of 12.5/25 °C and 1.5/50 °C respectively. The results proposed in this study provide a novel mode for design and development dual responsive porous membranes in situ, which will enable good separation of various materials and expand the scope of membrane applications. [ABSTRACT FROM AUTHOR]

The preparation of thermo-responsive polymeric porous membranes with well-defined morphology and high mechanical strength is still a great challenge. In our work, high strength and self-supporting polysulfone/poly(N-isopropylacrylamide) (PSf/PNIPAm) membranes with tuning wormlike network morphology and thermo-responsibility were successfully prepared via the approach combining in situ cross-linking polymerization with vapor-liquid nonsolvent induced phase separation (V-LIPS). With increasing the NIPAm concentration and the exposure time during the VIPS process, the wormlike networks self-assembled on the membrane surfaces, and their diameter rapidly increased to ~ 63 nm in 60 s. As a result, the pore size/porosity of the membranes increased and the membrane hydrophilicity improved, leading to high water flux with a maximum value of ~ 222 L m −2 h −1 at 23 °C. Furthermore, the permselectivity of the fabricated membranes exhibited strong and fully reversible thermo-responsive character as feed temperature ranged from 23 to 50 °C, in which the thermo-responsive coefficient was as high as ~ 3.7 after viscosity correction and the size distribution of silver nanoparticles in the filtrates narrowed down sharply. In addition, the fabricated membranes with wormlike network morphology exhibited the maximum tensile strength of ~ 6 MPa and elongation at break of ~ 33%, which are much higher than the block copolymers based membranes with the similar morphology. The approach provided here opens a new and simple way to prepare high strength PSf membranes with tuning network morphology and thermo-responsive permselectivity in large scale, and which is expected to be expanded to fabricate other polymeric microporous membranes. [ABSTRACT FROM AUTHOR]

In situ pegylated (PEGylated) microporous membranes have been extensively reported using poly(ethylene glycol) (PEG)-based polymers as blending additives. Alternatively, free standing PEGylated polysulfone (PSf) membranes with excellent hydrophilicity and antifouling ability were directly fabricated from polysulfone/poly(ethylene glycol) methyl ether methacrylate (PSf/PEGMA) solutions after in situ cross-linking polymerization without any treatment via vapor induced phase separation (VIPS) process for the first time. The microstructures and performances of the resulting membranes shifted regularly by adjusting exposure time of the liquid film in humid air. With increasing exposure time, plenty of worm-like networks formed and distributed on membrane surfaces, meanwhile cross-sectional morphology changed from asymmetric finger-like microporous structure to symmetric cellular-like structure, resulting in better mechanical stability. As the exposure time raised from 0 to 5 min, the surface coverage of carboxyl groups increased from ∼1.1 to 4.0 mol%, leading to the decrease in water contact angle from ∼63 to 27° and the increase in water flux from ∼110 to 512 L m −2  h −1 . In addition, at prolonged exposure time, increasing hydrophilic PEG chains migrated to membrane surfaced and repelled the adsorption and deposition of protein, resulting in better antifouling ability. The findings of this study offer a facile and high efficient strategy for flexible design and fabrication of the in situ PEGylated membranes with desirable structures and performances in large scale. [ABSTRACT FROM AUTHOR]

Graphene quantum dots (GQDs) have attracted tremendous research interest due to the unique properties associated with both graphene and quantum dots. Here, a new application of GQDs as ideal electrode materials for supercapacitors is reported. To this end, a GQDs//GQDs symmetric micro-supercapacitor is prepared using a simple electro-deposition approach, and its electrochemical properties in aqueous electrolyte and ionic liquid electrolyte are systematically investigated. The results show that the as-made GQDs micro-supercapacitor has superior rate capability up to 1000 V s−1, excellent power response with very short relaxation time constant ( τ0 = 103.6 μs in aqueous electrolyte and τ0 = 53.8 μs in ionic liquid electrolyte), and excellent cycle stability. Additionally, another GQDs//MnO2 asymmetric supercapacitor is also built using MnO2 nanoneedles as the positive electrode and GQDs as the negative electrode in aqueous electrolyte. Its specific capacitance and energy density are both two times higher than those of GQDs//GQDs symmetric micro-supercapacitor in the same electrolyte. The results presented here may pave the way for a new promising application of GQDs in micropower suppliers and microenergy storage devices. [ABSTRACT FROM AUTHOR]

In this study, the electrochemical properties of graphene nanosheet (GNS) electrodes are evaluated in depth by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques in [Et4N]BF4/acetonitrile electrolyte, [BPy]BF4/acetonitrile electrolyte, [BMIM]BF4/acetonitrile electrolyte and [P4,4,4,4]BF4/acetonitrile electrolyte, respectively. The electrochemical results exhibit that GNSs show good supercapacitive properties in these aforementioned four non-aqueous electrolytes, especially in [Et4N]BF4/acetonitrile electrolyte. It is also observed that the rate performance and the specific capacitance of GNS electrode increase in the order of [P4,4,4,4]BF4/acetonitrile ＜ [BMIM]BF4/acetonitrile ≈ [BPy]BF4/acetonitrile ＜ [Et4N]BF4/acetonitrile in these four non-aqueous electrolytes. The reasons are attributed to the difference of the relative ionic size and the discrepancy in the functional group among these four non-aqueous electrolytes, which result in the differences of equivalent series resistance, charge transfer resistance, and rate performance. In addition, the GNS electrode shows excellent stability in these four non-aqueous electrolytes after 1500 repeating charge–discharge cycles. These results may provide valuable information to explore new electrolytes and illustrate the exciting potential for high performance supercapacitors based on GNSs. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, five types of waste tea-leaves, which come from five of the most typical tea in China, are first used to prepare activated carbons (ACs) by high-temperature carbonization and activation with KOH. The resulting ACs show typical amorphous character, and display porous structures with high specific surface areas ranging from 2245m2 g−1 to 2841m2 g−1. As the electro-active electrode materials, the as-made five ACs exhibit ideal capacitive behaviors in aqueous KOH electrolyte, and the maximal specific capacitance is as high as 330Fg−1 at the current density of 1Ag−1. Furthermore, they all show excellent electrochemical cycle stability with ∼92% initial capacitance being retained after 2000 cycles. The desirable capacitive performances enable the waste tea-leaves to act as a new biomass source of carbonaceous materials for high performance supercapacitors and low-cost energy storage devices. [Copyright &y& Elsevier]

Abstract: Two kinds of ordered mesoporous carbon (OMC), hexagonal mesoporous carbon CMK-3 and cubic mesoporous carbon CMK-8, are prepared by a hard template nanocasting method. Afterwards, nitric acid modification is conducted to explore the influence of surface functional groups on the supercapacitive characteristics of the OMC electrodes. The electrochemical performances of CMK-3, CMK-8, acid-modified CMK-3 (H-CMK-3) and acid-modified CMK-8 (H-CMK-8) electrodes are investigated in three-electrode cells using alkaline (2M KOH), acidic (2M H2SO4) and neutral (2M Na2SO4) aqueous media. After nitric acid modification, the capacitive performances of two OMCs are improved in KOH, decreased in H2SO4, but showed no change in Na2SO4. The correlations among the change of surface functional groups after acid modification, electrolyte category and the capacitive performance of the OMCs are studied in detail. It can provide a guideline for proper usage of OMC-based materials for the next generation of supercapacitors. [Copyright &y& Elsevier]

Abstract: Highly ordered, three-dimensional (3D) cubic mesoporous carbon CMK-8 is prepared by a facile nanocasting approach using cubic mesoporous silica KIT-6 as starting template. Afterwards, in order to increase the active sites of surface electrochemical reactions and promote the wettability in aqueous electrolyte, a chemical surface modification is carried out on the CMK-8 by nitric acid treatment. Two electrodes are prepared from the CMK-8 and the acid-modified CMK-8 (H-CMK-8) and used as the active materials for supercapacitors. The unique 3D mesoporous network combined with high specific surface area makes the nano-channel surfaces of the CMK-8 carbon favorable for charging the electric double-layer, resulting in that the CMK-8 and the H-CMK-8 electrodes both show well supercapacitive properties. Furthermore, the specific capacitance of the CMK-8 can be further improved by acid treatment, so that the H-CMK-8 exhibits the largest specific capacitance of 246Fg−1 at a current density of 0.625Ag−1 in 2M KOH electrolyte. Also, the two carbon electrodes both exhibit good cycling stability and lifetime. Therefore, based on the above investigations, such CMK-8 carbon, especially H-CMK-8 carbon can be a potential candidate for supercapacitors. [Copyright &y& Elsevier]

Abstract: Amorphous-carbon (a-C) films were deposited on a single-crystal silicon substrate by vacuum vapor deposition system and these amorphous carbon films were implanted with 110keV C+ at fluences of 1×1017 ions/cm2. The effect of ion mixing on the surface morphology, friction behavior and adhesion strengths of amorphous carbon films was examined making use of atomic force microscopy (AFM), ball-on-disk reciprocating friction tester, nano-indentation system and scanning electron microscope (SEM). The changes in chemical composition and structure were investigated by using X-ray photoelectron spectroscopy (XPS). The results show that the anti-wear life and adhesion of amorphous carbon films on the Si substrates were significantly increased by C ion implantation. The Sil bonding across the interface plays a key role in the increase of adhesion strength and the anti-wear life of amorphous carbon film. The friction and wear mechanisms of amorphous carbon film under dry friction condition were also discussed. [Copyright &y& Elsevier]

Diamond-like carbon/nanosilica composite films have been deposited on silicon substrates, making use of the electrolysis of methanol–dimethylethoxydisilane (DDS) solution at low temperature. The electrodeposited composite films were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy, respectively. Moreover, the growth mechanism of the composite films in liquid phase was discussed as well. As the results, the films are diamond-like carbon films containing polycrystalline SiO2 nanoparticles. The introduction of DDS contributes to promote the growth of the carbon films and leads to the formation of the crystalline SiO2 grains. [Copyright &y& Elsevier]

Aligned amorphous Si nanowires (SiNWs) were synthesized directly from Si substrates with the assistance of a new carbon-based network polymer, poly(phenylcarbyne), during the heat-treatment in Ar atmosphere at 1120 °C. A core/shell structure of SiNWs wrapped with Au nanoparticles was simply fabricated as well. The analytic results of the morphology and microstructure confirmed the orientation and the amorphous nature of the SiNWs, and the high dispersion of Au nanoparticles on the surface of the SiNWs without any aggregation. The formation of the SiNWs was explained on the basis of the reaction of carbon with the native silica layer covering Si substrates. [Copyright &y& Elsevier]

AISI 1045 steel was permeated with boron and co-permeated with boron and lanthanum by means of solid permeation technique. The tribological behavior of boron and lanthanum co-permeated AISI-1045 steel under dry sliding in air was investigated and compared with that of the boron permeated and tempered AISI-1045 steel specimens with a reciprocal friction and wear tester. The cross-section of the permeated and co-permeated coatings and the morphologies of the worn surface and wear debris were examined by means of scanning electron microscopy, and the chemical states of the wear debris examined by means of X-ray photoelectron spectroscopy. Then the wear mechanisms of the permeated and co-permeated layers were discussed. As the results, boron and lanthanum co-permeated specimen shows much better wear resistance than the boron permeated and tempered specimens under a load of 20 to ∼100 N and a frequency of 20 to ∼60 Hz. However, the permeation has little effect on the coefficient of friction, but liquid paraffin is significantly reducing coefficient of friction. The treated specimens contain Fe2B phase and exhibit more compact structure and higher hardness, and the corresponding wear debris is smaller than that of the tempered ones. The surface layers of the boron-permeated and the boron and lanthanum co-permeated specimens show some kind of solid lubricity and hence prevent the direct metallic contact of the frictional pair, thus the improved wear-resistance is reached. Moreover, Fe2B and B2O3 in the surface layers of the boron-permeated and boron and lanthanum co-permeation specimens restrain wear during the friction process, with the generation of iron oxide and boron oxide. This leads to wear of the specimens at extended test duration. [Copyright &y& Elsevier]

Cellulose acetate (CA) is a low cost and readily available material widely used in forward osmosis (FO) membranes. However, the performance of pure CA membranes is not good enough in salt separation and the traditional modification methods are generally multistep and difficult to control. In this paper, we reported high performance cellulose acetate (CA) composite forward osmosis (FO) membranes modified with polyvinyl alcohol (PVA) and polydopamine (PDA). PVA was first cross-linked onto the surface of CA membranes, and then PDA was coated with a rapid deposition method. The membranes were characterized with respect to membrane chemistry (FTIR and XPS), surface properties comprising wettability (by water contact angle), and osmosis performance. The modified membrane coated by PVA and PDA shown better hydrophilicity and exhibited 16.72 LMH osmotic water flux and 0.14 mMH reverse solute flux with DI water as feed solution and 2.0 M NaCl as draw solution and active layer facing the feed solution. This simple and highly effective modification method makes it as an excellent candidate for further exploration for FO. [ABSTRACT FROM AUTHOR]

A new application of graphene quantum dots (GQDs) as an ideal electrode material for supercapacitors is explored by X.‐B. Yan and co‐workers. On page 4111 they build a GQD//GQD symmetric micro‐supercapacitor and a GQD//MnO2 asymmetric supercapacitor. Both devices show excellent rate capabilities, exceptionally high‐frequency responses, and long‐term cycle stability. [ABSTRACT FROM AUTHOR]