NaOH Etching Research Articles

Preparation of a Si/SiO2 -Ordered-Mesoporous-Carbon Nanocomposite as an Anode for High-Performance Lithium-Ion and Sodium-Ion Batteries.

In this work, an Si/SiO2 -ordered-mesoporous carbon (Si/SiO2 -OMC) nanocomposite was initially fabricated through a magnesiothermic reduction strategy by using a two-dimensional bicontinuous mesochannel of SiO2 -OMC as a precursor, combined with an NaOH etching process, in which crystal Si/amorphous SiO2 nanoparticles were encapsulated into the OMC matrix. Not only can such unique porous crystal Si/amorphous SiO2 nanoparticles uniformly dispersed in the OMC matrix mitigate the volume change of active materials during the cycling process, but they can also improve electrical conductivity of Si/SiO2 and facilitate the Li+ /Na+ diffusion. When applied as an anode for lithium-ion batteries (LIBs), the Si/SiO2 -OMC composite displayed superior reversible capacity (958 mA h g-1 at 0.2 A g-1 after 100 cycles) and good cycling life (retaining a capacity of 459 mA h g-1 at 2 A g-1 after 1000 cycles). For sodium-ion batteries (SIBs), the composite maintained a high capacity of 423 mA h g-1 after 100 cycles at 0.05 A g-1 and an extremely stable reversible capacity of 190 mA h g-1 was retained even after 500 cycles at 1 A g-1 . This performance is one of the best long-term cycling properties of Si-based SIB anode materials. The Si/SiO2 -OMC composites exhibited great potential as an alternative material for both lithium- and sodium-ion battery anodes.

Template-assisted sol–gel synthesis of porous MoS2/C nanocomposites as anode materials for lithium-ion batteries

Porous MoS2/C nanocomposites have been successfully via a sol–gel route with ammonium molybdatetetrahydrate ((NH4)6Mo7O24·4H2O) as molybdenum source, glucose as carbon source and tetramethyloxysilane (TMOS) as gelation accelerator, subsequently followed by high-temperature sulfuration and further NaOH etching to remove silica template derived from TMOS. The as-prepared MoS2/C nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR), and nitrogen adsorption–desorption, and the effect of molybdenum precursor mass on the synthesis of product was also investigated. The Mo and TMOS mass ratio obviously affects the gelation time, phase composition and morphology of the resultant product, and an appropriate Mo and TMOS mass ratio allows the formation of lamellar structure as well as perfect MoS2 phase. The as-prepared MoS2/C nanocomposite with Mo and TMOS mass ratio of 7:3 exhibits a BET surface area of 31 m2g−1 and a mesopore size of 20 nm, and demonstrates good electrochemical performances with 400 mA h g−1 specific reversible capacity after 60 cycles owing to the pore structure and synergistic effect between MoS2 and amorphous carbon.

Double-shell Fe2O3 hollow box-like structure for enhanced photo-Fenton degradation of malachite green dye

In this work we demonstrate the synthesis of novel Fe2O3 nanosheets with double-shell hollow morphology by replica molding from diatomite framework. The nanostructures of Fe2O3 nanosheets were examined by focused-ion-beam scanning electron microscopy (FIB/SEM), X-ray diffraction spectroscopy (XRD), Brunauer-Emmett-Teller (BET) specific surface area measurements and Fourier transform infrared (FT-IR) spectroscopy. The results reveal that (1) Pure Fe2O3 nanosheets were successfully obtained; (2) The double-shell Fe2O3 hollow structure achieved via the NaOH etching silica method was observed; (3) Fe2O3 nanosheets possessed uniformly distributed porous nanosheets. Such structural features enlarged the specific surface area of Fe2O3 nanosheets and led to more catalytic active sites. In the heterogeneous photo-Fenton reaction, the double-shell Fe2O3 hollow morphology exhibited excellent catalytic capability for the degradation of malachite green (MG) at circumneutral pH condition. Under optimum condition, MG solution was almost completely decolorized in 60 min (99.9%). The Fe2O3 nanosheets also showed good stability and recyclability, demonstrating great potential as a promising photo-Fenton catalyst for the effective degradation of MG dye in wastewater.

Enhanced activity for total benzene oxidation over SBA-15 assisted electrospun LaCoO3

A high surface area rhombohedral LaCoO3 perovskite (ELS-JX) was synthesized by SBA-15 assisted electrospinning combined with NaOH etching technology, and investigated for total benzene oxidation. LaCoO3 nanoparticles are confined in the self-assembled nanorods or scattered on the mesopores/surface of SBA-15, resulting in less aggregation of perovskite nanoparticles for ELS-JX. H2-TPR analysis and XPS measurements reveal that better low-temperature reducibility, higher Oads/Olatt and Co2+/Co3+ as well as larger amounts of surface exposed Co species of ELS-JX considerably enhance its catalytic activity for total benzene oxidation compared to sol-gel (SG) and SBA-15 free electrospinning (EL) method synthesized LaCoO3. Moreover, the results of O2-TPSR match well with the catalytic performances of SG, EL and ELS-JX. In addition, the presence of water vapor has a negative effect on benzene oxidation over the best performed ELS-JX.

Microstructural and surface modifications and hydroxyapatite coating of Ti-6Al-4V triply periodic minimal surface lattices fabricated by selective laser melting

Ti-6Al-4V Gyroid triply periodic minimal surface (TPMS) lattices were manufactured by selective laser melting (SLM). The as-built Ti-6Al-4V lattices exhibit an out-of-equilibrium microstructure with very fine α′ martensitic laths. When subjected to the heat treatment of 1050°C for 4h followed by furnace cooling, the lattices show a homogenous and equilibrium lamellar α+β microstructure with less dislocation and crystallographic defects compared with the as-built α′ martensite. The as-built lattices present very rough strut surfaces bonded with plenty of partially melted metal particles. The sand blasting nearly removed all the bonded metal particles, but created many tiny cracks. The HCl etching eliminated these tiny cracks, and subsequent NaOH etching resulted in many small and shallow micro-pits and develops a sodium titanate hydrogel layer on the surfaces of the lattices. When soaked in simulated body fluid (SBF), the Ti-6Al-4V TPMS lattices were covered with a compact and homogeneous biomimetic hydroxyapatite (HA) layer. This work proposes a new method for making Ti-6Al-4V TPMS lattices with a homogenous and equilibrium microstructure and biomimetic HA coating, which show both tough and bioactive characteristics and can be promising materials usable as bone substitutes.

Coupled chemical reactions in dynamic nanometric confinement: VII. Biosensors based on swift heavy ion tracks with membranes

ABSTRACTIn previous papers it was shown that the coupling of the two chemical reactions: {NaOH etchant – PET polymer} and {NaOH etchant – AgNO3 solution} within the dynamic confinement of etched swift heavy ion tracks eventually leads to the formation of tiny Ag2O membranes within these nanopores, thus separating the latter ones into two adjacent segments. It is shown here that the deposition of enzymes in these two segments transforms these structures into biosensors. In our earlier developed sensors with transparent etched ion tracks, we frequently used glucose oxidase as enzyme and glucose as analyte. In these cases, the enzymatic reaction within the tracks leads to a change in the pH value of the confined solution and hence also in the track conductivity, so these structures can be used for biosensing. When applying, for easy comparison, the same enzyme/analyte combination to the segmented sensor arrangement presented here, we find a striking improvement in detection sensitivity which points at a different biosensing mechanism due to intrinsic polarisation effects across the newly inserted membranes.

Effect of UV and gamma rays on bulk etching of the Pokalon track detector

Solid-state nuclear track detectors (SSNTDs) find applications in many fields of science and technology. Polycarbonates like CR-39 or Lexan are most widely used for such applications. Pokalon is a relatively new member of the polycarbonate family of SSNTDs. It has the same monomer as that of Makrofol. In the present work we have studied the bulk etching characteristics of Pokalon at different temperatures and normalities of NaOH etchant with and without magnetic stirring. The effect of UV and gamma irradiation on the bulk etch rate has also been studied. From the bulk etch rate values at different temperatures, we have determined the corresponding activation energies. Measurable enhancement of the bulk etch rates with accompanying reduction in the activation energies following UV and gamma irradiation suggests chain scission and bond breaking as possible mechanisms for these changes in the etching characteristics.

Synthesis and catalytic performance of SiO2@Ni and hollow Ni microspheres

Nickel (Ni) catalyst has been widely used in catalytic reducing reactions such as catalytic hydrogenation of organic compounds and catalytic reduction of organic dyes. However, the catalytic efficiency of pure Ni is low. In order to improve the catalytic performance, Ni nanoparticle-loaded microspheres can be developed. In this study, we have prepared Ni nanoparticle-loaded microspheres (SiO2@Ni) and hollow Ni microspheres using two-step method. SiO2@Ni microspheres with raspberry-like morphology and core–shell structure are synthesized successfully using SiO2 microsphere as a template and Ni2+ ions are adsorbed onto SiO2 surfaces via electrostatic interaction and then reduced and deposited on surfaces of SiO2 microspheres. Next, the SiO2 cores are removed by NaOH etching and the hollow Ni microspheres are prepared. The NaOH etching time does no have much influence on the crystal structure, shape, and surface morphology of SiO2@Ni; however, it can change the phase composition evidently. The hollow Ni microspheres are obtained when the NaOH etching time reaches 10 h and above. The as-synthesized SiO2@Ni microspheres exhibit much higher catalytic performance than the hollow Ni microspheres and pure Ni nanoparticles in the catalytic reduction of methylene blue. Meanwhile, the SiO2@Ni catalyst has high stability and hence it can be recycled for reuse.

Solvothermal synthesis of Bi2O3/BiVO4 heterojunction with enhanced visible-light photocatalytic performances**Project supported by the National Natural Science Foundation of China (Nos. 61306077, 21301060), the Fundamental Research Funds for the Central Universities (Nos. JB-ZR1109, JB-ZR1212), the National Science Foundation of Quanzhou City (No. 2014Z108), the Promotion Program for Young and Middle-aged Teachers in Science and Technology Research of Huaqiao University (No. ZQN-PY207),

Novel, three-dimensional, flower-like Bi2O3/BiVO4 heterojunction photocatalysts have been prepared by the combination of homogeneous precipitation and two-step solvothermal method followed by thermal solution of NaOH etching process. The as-obtained samples were fully characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, Brunauer-Emmett-Teller surface area, and UV—vis diffuse-reflectance spectroscopy in detail. The crystallinity, microstructure, specific surface area, optical property and photocatalytic activity of samples greatly changed depending on solvothermal reaction time. The photocatalytic activities of samples were evaluated on the degradation of methyl orange (MO) under visible-light irradiation. The Bi2O3/BiVO4 exhibited much higher photocatalytic activities than pure BiVO4 and conventional TiO2 (P25). The result revealed that the three-dimensional heterojunction played a critical role in the separation of the electron and hole pairs and enhancement of the interfacial charge transfer efficiency, which was responsible for the enhanced photocatalytic activity.

Hollow CuO microspheres with open nanoholes: Fabrication and photocatalytic properties

A kind of novel hollow CuO microspheres with open nanoholes was fabricated via a SiO2 template-assisted synthesis process under hydrothermal conditions in the present work. Sodium silicate acted as an alkaline medium as well as SiO2 precursor. Copper sulphate and glucose were used as copper source and reducing agent, respectively. The as-synthesized products consisted of Cu2O/SiO2 mixture, which was transformed completely into CuO/SiO2 after calcinations at 600 °C, and then SiO2 could be removed by NaOH etching. Eventually, a kind of hollow CuO microspheres with open nanoholes was attained. Results showed such microspheres were composed of numerous small CuO crystalline grains, and the productions of hollow inner structures and open nanoholes were from the imprints of SiO2 nanoparticle removal. Meanwhile, the effect of the amount of sodium silicate in the reaction was investigated, suggesting such CuO microspheres could be fabricated only if an enough amount was used. In addition, we also propose the possible formation mechanism of such nanostructures. These CuO microspheres exhibited a better photocatalytic activity on the degradation of methyl orange (MO) than commercial CuO powders (∼200 nm) under the identical conditions.

Multifunctional CuO nanowire embodied structural supercapacitor based on woven carbon fiber/ionic liquid–polyester resin

Novel structural supercapacitors based on CuO nanowires and woven carbon fiber (WCF) has been developed for the first time employing vacuum assisted resin transfer molding (VARTM) process. The growth of CuO nanowires on WCF is an efficient process and can be used in structural capacitors which can trigger the electric vehicle industries toward a new direction. The specific surface area of the carbon fiber was enhanced by NaOH etching (41.36m2g−1) and by growing CuO nanowires (132.85m2g−1) on the surface of the WCF. The specific capacitance of the CuO–WCF based supercapacitor was 2.48Fg−1, compared with 0.16Fg−1 for the bare WCF-based supercapacitor. The usage of ionic liquid and lithium salt improved the capacitance to 5.40 and 6.75Fg−1 with lowest ESR and Rp values of 133 and 1240Ω along with improving mechanical properties within an acceptable range. The energy and power densities were also increased up to 106.04mWhkg−1 and 12.57Wkg−1. Thus, this study demonstrated that growing CuO nanowires on the surface of WCF is a novel approach to improve multifunctionality that could be exploited in diverse applications such as electric cars, unmanned aerial vehicles (UAVs), and portable electronic devices.

Response of CR-39 to 0.9–2.5 MeV protons for KOH and NaOH etching solutions

In some circumstances passive detecting methods are the only or preferable measuring approaches. For instance, defining particles׳ energy profile inside the objects being irradiated with heavy ions and measuring fluence of neutrons or heavy particles in space missions are the cases covered by these methods. In this paper the ability of polyallyl diglycol carbonate (PADC) track detector (commercially known as CR-39) for passive spectrometry of proton particles is studied. Furthermore, the effect of KOH and NaOH as commonly used chemical etching solutions on the response of the detector is investigated. The experiments were carried out with protons in the energy range of 0.94–2.5MeV generated by a Van de Graaff accelerator. Then, the exposed track dosimeters were etched in the two aforementioned etchants through similar procedure with the same normality of 6.25N and the same temperature of 85°C. Formation of the tracks was precisely investigated and the track diameters were recorded following every etching step for each solution using a multistage etching process. The results showed that the proposed method can be efficiently used for the spectrometry of protons over a wider dynamic range and with a reasonable accuracy. Moreover, NaOH and KOH outperformed each other over different regions of the proton energy range. The detection efficiency of both etchants was approximately 100%.

Ionic Liquid as the C and N Sources to Prepare Yolk-shell Fe3O4@N-doped Carbon Nanoparticles and its High Performance in Lithium-ion Battery

Transition metal oxide is a promising anode material in lithium-ion battery, however it suffers from poor cycling performance due to its large volume change during charge/discharge process. Herein, we designed and fabricated a yolk-shell Fe3O4 composite nanoparticle with individual Fe3O4 nanoparticle as the yolk and N-coped carbon as the shell by using ionic liquid as the C and N sources. The individual Fe3O4 nanoparticle was firstly covered by a sacrificial SiO2 layer, then coated with N-doped carbon by one-step carbonization with ionic liquid (3-cyanopyridine/H2SO4). After removing the SiO2 layer by NaOH etching, yolk-shell Fe3O4@void@N-doped carbon was obtained. This unique structure would not only afford adequate void to accommodate the large volume change during charge/discharge process, but also improve the structural stability and electrical conductivity. Thus, Fe3O4@void@N-doped carbon showed a high reversible capacity and cycling life of 860mAhg−1 after 500 charge/discharge cycles at a current rate of 1000mAg−1, and excellent rate capacity of 180mAhg−1 even at 7000mAg−1.

An Experimental Study into the Effect of Damage on the Capacitance of Structural Composite Capacitors

This paper presents the work to characterise the effects of tensile induced matrix cracks on capacitance of structural composite capacitor materials. The study is based on earlier work within the field of multifunctional materials where mechanical and electrical properties have been characterised. Effects of damage on electrical properties have, however, not been covered by earlier studies. The structural capacitor materials were made from carbon fibre/epoxy pre-pregs as structural electrodes with thermoplastic PET as the dielectric separator. NaOH etching was used as a route for improved adhesion between the epoxy and PET to ensure matrix cracking in the CFRP electrodes occurred prior to delamination between the electrodes and the PET separator. A method to induce and measure the effect of the matrix cracks on electrical properties was successfully developed and used in this study. The method is based on a simple tensile test and proved to be quick and easy to perform with consistent results. The structural capacitor material was found to maintain its capacitance even after significant intralaminar matrix cracking in the CFRP electrodes from high tensile mechanical loads.

Mesoporous carbon-supported Pd nanoparticles with high specific surface area for cyclohexene hydrogenation: Outstanding catalytic activity of NaOH-treated catalysts

Extremely high specific surface area mesoporous carbon-supported Pd nanoparticle catalysts were prepared with both impregnation and polyol-based sol methods. The silica template used for the synthesis of mesoporous carbon was removed by both NaOH and HF etching. Pd/mesoporous carbon catalysts synthesized with the impregnation method has as high specific surface area as 2250m2/g. In case of NaOH-etched impregnated samples, the turnover frequency of cyclohexene hydrogenation to cyclohexane at 313K was obtained ~14 molecules∙site−1∙s−1. The specific surface area of HF-etched samples was higher compared to NaOH-etched samples. However, catalytic activity was ~3–6 times higher on NaOH-etched samples compared to HF-etched samples, which can be attributed to the presence of sodium and surface hydroxylgroups of the catalysts etched with NaOH solution.

Au@Void@TiO2 yolk–shell nanostructures as catalysts for the promotion of oxidation reactions at cryogenic temperatures

A new gold–titania catalyst has been developed for cryogenic oxidations based on a yolk–shell nanoarchitecture. The synthesis of those structures involves the sequential deposition of a sacrificial silica layer and a titania shell around well-defined gold nanoparticles followed by removal of the silica via NaOH etching. The resulting catalyst contains an amorphous titania shell with sodium titanate and silicon impurities that proved critical for the cryogenic activity; removal of those via HCl treatment kills most of the catalytic conversion. Oxidation of carbon monoxide is possible with this Au@Void@TiO2 catalyst at temperatures as low as 120K, by a mechanism different than the one operative at room temperature that involves a weakly-adsorbed CO species with a CO stretching frequency of 2162cm−1, possibly at Au–TiO2 interfacial sites.

Tailored synthesis of C@TiO2 yolk–shell nanostructures for highly efficient photocatalysis

Composite nanostructures with well-defined characteristics are often advantageous catalysts for highly efficient photocatalytic processes. Here, we report the tailored synthesis of C@TiO2 yolk–shell nanostructures and their photocatalytic applications in the degradation of organic dyes. The conductive carbon core serves as an electron-sink to promote the separation of electron–hole pairs photo-excited in the TiO2 shell, improve their lifetime, and enhance the photocatalytic performance of the system. The yolk–shell nanostructures were synthesized through a sol–gel coating of TiO2 on resorcinol-formaldehyde (RF) resin spheres followed by silica-protected calcination and ultimately NaOH etching to remove the silica layer and produce C@TiO2 yolk–shell nanostructures. In order to improve the crystallinity of the TiO2 shell, post-processing including acid treatment and re-calcination was also carried out. The resulting yolk–shell structures have many desirable properties for photocatalytic applications including the existence of a conductive core, well-maintained structural integrity, uniform particle dimensions, favorable mesoscale porosity, tunable crystallinity, and controllable crystalline phase of TiO2. As a result, we have been able to optimize the structure and property of the composite photocatalysts and achieve superior photocatalytic performance to commercial P25-TiO2 catalysts.

Field emission characteristics of diamond nano-tip array fabricated by anodic aluminum oxide template with nano-conical holes

Different sizes and periods of diamond nano-tip arrays are fabricated by anodic aluminum oxide (AAO) template with nano-conical holes. Before the anodic oxidation process, 99.5% Al sheets are annealed and electro-polished. AAO templates with nano-conical holes are obtained by continuously changing voltages from 40 to 160V in 0.3M oxalic acid at the temperature of −3°C. The aluminum pore of AAO is then removed by the wet etching solution of CuCl and HCl. Diamond nano-particles of diameters of 4–12nm are adhered to the AAO template as the nucleation sites by Polyethylenimine method. The diamond nano-tip arrays are deposited on the template by microwave plasma chemical vapor deposition with the mixture gas of methane and argon. The diamond nano-tip array of different sizes and periods are obtained after the AAO template is completely removed by NaOH etching. The ratio of nano-tip spacing to the pitch-height (pitch-height ratio) ranges from 1 to about 2.5. The diamond nano-tip array with the smallest spacing-height ratio of 1 by the AAO template with nano-conical holes has the highest field enhancement factor (β) of 4885 and the lowest turn-on field of about 2.63V/μm.

Synthesis of hierarchical hollow electrospun TiO2 nanofibers

In this study, we synthesized hierarchical hollow (HH) TiO2 nanofibers (NFs) using a simple single-spinneret electrospinning and etching process to form TiO2–SiO2 hybrid nanofibers (HNFs). The latter were prepared from a starting sol–gel solution consisting of titanium(IV) tert-butoxide and SiO2 nanoparticles (NPs) which were commercially available rather than prepared in situ. The SiO2 NPs were well dispersed in the TiO2–SiO2 HNFs, and the obtained TiO2 NFs after removal of the SiO2 NPs by NaOH etching showed hierarchically well-developed hollow structures. In the photocatalytic degradation of Rhodamine B, the HH TiO2 NFs showed significantly enhanced photocatalytic characteristics compared to pristine TiO2 NFs.

Model Membrane-Free Li-S Batteries for Enhanced Performance and Cycle Life.

The success of the rechargeable Li-S cell is limited in part by the dissolution of lithium-polysulfide in the electrolyte. Remarkably, it is found that removal of the conventional membrane separator in a Li-S cell improves sulfur utilization and cycling performance, whether the sulfur is initially contained in the cathode or electrolyte. An optimized cell design yields discharge capacities as high as 980 mA h g-1 after 100 cycles.