SiO2 Nanorods Research Articles

Surface acoustic wave hydrogen sulfide gas sensors based on porous SnO2-SiO2 composite films

A SnO2-SiO2 composite fabricated with an EBE method was developed as the sensitive film for a room-temperature SAW H2S in this work. In this film, the SnO2 nanoparticels, acting as the active adsorption sites, were uniformly deposited on the slanted SiO2 nanorods array with a mesoporous structure. This structure is found to be beneficial for adsorption and diffusion of H2S gas molecules, thus leading to an excellent sensing performance of the sensor. The fabricated sensor exhibited a frequency response ranging from −180 Hz to −13550 Hz toward H2S with a concentration varying from 0.05 ppm to 10 ppm and a fast response, good selectivity and stability. In addition, the sensing mechanism of the sensor was revealed to be lied on the change in film mass during the adsorption process.

Extinction Behavior and Near-Field Enhancement of 3D Hybrid Nanostructures Consisting of Ag-Coated SiO2 Nanorods

Extinction Behavior and Near-Field Enhancement of 3D Hybrid Nanostructures Consisting of Ag-Coated SiO2 Nanorods

Rapid and ultrahighly sensitive ethanol sensing in p-type SrTi1‐xFexO3

Gas sensors based on p-type semiconducting metal oxides have recently received significant attention due to their superior gas selectivity compared to those based on n-type metal oxides. Nevertheless, p-type metal oxides-based gas sensors have limitations such as low sensitivity and slow response. Herein, we present highly sensitive and fast responding ethanol (C2H5OH) gas sensors that are composed of p-type SrTi1−xFexO3 (STF) with various Fe compositions deposited on vertically aligned SiO2 nanorods (NRs) with a larger surface-to-volume ratio than STF thin films. As the Fe content increases, the charge transfer energy between adsorbed oxygen species and transition cations decreases, and the amount of oxygen vacancy increases, This results in the acceleration of charge transfer and the generation of active sites. The fabricated STF on SiO2 NRs exhibited gas responses ranging from 74 to 528 for 50 ppm ethanol gas depending on the Fe content with fast response and recovery time, overcoming the low sensitivity and slow response of previously reported p-type gas sensors. The observed unprecedented synergistic effects of STF on SiO2 NRs for highly selective ethanol sensing establish a new perspective on quaternary p-type perovskites for selective gas sensing in which n-type metal oxides have been used.

Highly Reliable Threshold Switching Characteristics of Surface-Modulated Diffusive Memristors Immune to Atmospheric Changes.

Active cation-based diffusive memristors featuring essentially volatile threshold switching have been proposed for novel applications, such as a selector in a one-selector-and-one-resistor structure and signal generators in neuromorphic computing. However, the high variability of the switching behavior, which results from the high electroforming voltage, external environmental conditions, and transition to the non-volatile switching mode in a high-current range, is considered a major impediment to such applications. Herein, for the first time, we developed a highly reliable threshold switching device immune to atmospheric changes based on an ultraviolet-ozone (UVO)-treated diffusive memristor consisting of Ag and SiO2 nanorods (NRs). UVO treatment forms a stable water reservoir on the surface of SiO2 NRs, facilitating the redox reaction and ion migration of Ag. Consequently, diffusive memristors possess reliable switching characteristics, including electroforming-free, repeatable, and consistent switching with resistance to changes in ambient conditions and compliance levels during operation. We demonstrated that our approach is suitable for various metal oxides and can be used in numerous applications.

Adsorptive potential of ZnO/SiO2 nanorods prepared via the sol–gel method for the removal of Pb(II) and Cd(II) from petroleum refinery wastewater

AbstractBACKGROUNDThe adsorption technique is considered one of the most effective and economical methods for the removal of heavy metals, due to its excellent advantages of low cost, high efficiency and easy handling. This research looks into the possibility of using ZnO/SiO2 nanorods to remove Cd(II) and Pb(II) from refinery wastewater and their reusability.RESULTSZnO/SiO2 nanorods were synthesized via the sol–gel method. The analysis of ZnO/SiO2 shows the formation of a rod‐like structure and surface area of 33 m2 g−1 compared with the 0.3 and 8.620 m2 g−1 for ZnO and SiO2, respectively. Effects of adsorption contact time, adsorbent dosage and temperature were examined via batch adsorption. The result indicates that the ZnO/SiO2 rods exhibited higher adsorption removal efficiency of 85.06% and 84.12% for Pb(II) and Cd(II), respectively, compared to Pb(II) (80.00% and 74.25%) and Cd(II) (76.48% and 70.99%) using ZnO and SiO2 nanoparticles. A thermodynamic study indicates that the adsorption process was endothermic. The data from the adsorption isotherm were well fitted to the Langmuir isotherm. The pseudo‐second‐order kinetic model best described the adsorption process. An adsorption–desorption study indicated the adsorption to be concentration‐dependent and maintained up to 80.65% and 76.90% for Pb(II) and Cd(II) after the fourth regeneration cycle.CONCLUSIONSThese findings demonstrated that ZnO/SiO2 nanorods are a better nanoadsorbent for the removal of Pb(II) and Cd(II) than ZnO and SiO2 nanoparticles due to their high adsorptive potential and stability. © 2022 Society of Chemical Industry.

Cross-linked structure of self-aligned p-type SnS nanoplates for highly sensitive NO2 detection at room temperature

A highly sensitive NO2 gas sensor of p-type SnS operating at room temperature is developed using crosslinked SnS nanoplates self-formed only on SiO2 nanorods, without an additional patterning process.

Manganese oxide nanorod catalysts for low-temperature selective catalytic reduction of NO with NH3.

MnOx nanorod catalysts were successfully synthesized by two different preparation methods using porous SiO2 nanorods as the template and investigated for the low-temperature selective catalytic reduction (SCR) of NO with NH3. The catalysts were characterized by scanning electron microscopy, transmission electron microscopy, nitrogen adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, and NH3 temperature-programmed desorption. The results show that the obtained MnOx-P nanorod catalyst prepared by redox precipitation method exhibits higher NO removal activity than that prepared by the solvent evaporation method in the low temperature range of 100–180 °C, where about 98% NO conversion is achieved over MnOx(0.36)-P nanorods. The reason is mainly attributed to MnOx(0.36)-P nanorods possessing unique flower-like morphology and mesoporous structures with high pore volume, which facilitates the exposure of more active sites of MnOx and the adsorption of reactant gas molecules. Furthermore, there is a lower crystallinity of MnOx, higher percentage of Mn4+ species and a large amount of strong acid sites on the surface. These factors contribute to the excellent low-temperature SCR activity of MnOx(0.36)-P nanorods.

In situ DRIFTS and CO-TPD studies of CeO2 and SiO2 supported CuOx catalysts for CO oxidation

Gas adsorption-desorption processes on oxide supported metal catalysts are critical steps for understanding catalytic CO oxidation mechanism. This report investigates the support structure (shape and exposed crystal planes)-catalytic activity relationship of irreducible SiO2 and reducible CeO2 nanorods (NR) and nanocubes (NC) supported CuOx via various structural and surface characterization methods, including XRD, Raman spectroscopy, BET surface area, H2-TPR, CO-TPD, in situ DRIFTS, XPS, and HRTEM. Evidence is presented that both isolated Cu+/Cu2+ redox pair and lattice oxygen of oxide supports from different crystal planes (111, 011, and 001) of CeO2 play important role towards CO oxidation by supporting Langmuir–Hinshelwood mechanism. The Cu+/Cu2+ and Ce3+/Ce4+ species at CuOx-CeO2 interfaces can facilitate the charge and mass transfer between CuOx nanoclusters and CeO2 by electronic interaction which was highly promoted by reducible CeO2 NR support. In addition, CeO2 NR contains significantly higher amount of surface defects including oxygen vacancy, steps, voids, and lattice distortion on various crystal facets, which promote surface oxygen release of CeO2 and CO adsorption and oxidation on catalytically active sites at lower temperature. According to the CO oxidation results, the oxidized CuO/CeO2 NR sample showed 62.8% CO conversion at 100°C and up to 98.9% conversion at 397 °C.

FDTD simulation of Ag-decorated ZnO nanorods for optimization of 3D SERS substrates

Surface enhanced Raman spectroscopy (SERS) is becoming an effective method of detecting organic molecules, and three-dimensional (3D) SERS substrates are promising in practical applications. To optimizing 3D SERS substrates, the extinction spectra and local electromagnetic fields of Ag-decorated ZnO nanorods (Ag-ZnO-NR) were studied by a finite-difference time-domain (FDTD) method. The diploe local surface plasmonic resonance (LSPR) was found to split into high- and low-frequency two branches, in which the low-frequency mode is predominant in contributing to the Raman enhancement, while the ZnO-NR radius and Ag-layer thickness play important roles in tuning the LSPR frequencies. Both of high- and low-frequency LSPRs were enhanced with the increase in the Ag-ZnO-NR length while the intensity of local electromagnetic field depends on the Ag-ZnO-NR density. The FDTD results were discussed with a comparison to the experimental data obtained from flower-like Ag-ZnO-NR 3D SERS substrates. In addition, the extinction spectra of Ag nanotube and Ag-decorated TiO2 and SiO2 nanorods were calculated and the refractive index of dielectric materials was found to be capable of tuning the LSPR of 3D SERS substrates as well. The principle revealed in this work is helpful for design and optimization of 3D SERS substrates.

Highly Efficient Ni-Phyllosilicate Catalyst with Surface and Interface Confinement for CO2 and CO Methanation

For the conventional Ni/SiO2 catalyst, it is a challenge to address the sintering problem of Ni particles, especially at high Ni loading. A series of Ni-phyllosilicate catalysts were prepared through the hydrothermal reaction of mesoporous SiO2 nanorods (SRs) and nickel nitrate, followed by an impregnation modification of CeO2. Hydrothermal temperature played an important role in the formation of nickel phyllosilicate. A small amount of Ni-phyllosilicate with a Ni content of 18.56 or 23.88 wt % was formed at a low hydrothermal temperature of 120 or 160 °C, and a large amount of nanosheet-like Ni-phyllosilicate with the Ni content as high as 31.65 wt % was obtained at a high hydrothermal temperature of 200 °C. The prepared Ni-phyllosilicate catalysts were beneficial to obtain Ni particles with small sizes (3.3–6.3 nm), even though they were reduced at 750 °C and possessed high Ni loadings (18.56–31.65 wt %) owing to the surface and interface confinement of nickel phyllosilicate. After the modification of CeO2 using an impregnation method, the CeO2 promoter could further reduce the Ni particle size and increase hydrogen and carbon dioxide uptakes. The CeO2-modified Ni-phyllosilicate catalyst (NPS-180-5C) was the best catalyst in this work, which could reach the thermodynamic equilibrium of CO methanation above 350 °C and exhibited high catalytic activity for CO2 methanation. In addition, for the 55 °C-100 h-lifetime test for CO2 methanation and 600 °C-6 h-100% steam treatment tests, NPS-180-5C also showed an excellent antisintering property and higher hydrothermal stability than the impregnated one (N/SR-Im) owing to its special structure and confinement effect as well as promotion of CeO2 species. In all, the CeO2-modified SR-derived Ni-phyllosilicate catalyst could not only effectively suppress the problem of easy sintering of metallic Ni particles on the conventional Ni/SiO2 catalysts but also exhibit high catalytic activity and hydrothermal stability, which was a promising catalyst for both CO2 and CO methanation reactions.

Surface-Confined Winding Assembly of Mesoporous Nanorods.

Bending and folding are important stereoscopic geometry parameters of one-dimensional (1D) nanomaterials, yet the precise control of them has remained a great challenge. Herein, a surface-confined winding assembly strategy is demonstrated to regulate the stereoscopic architecture of uniform 1D mesoporous SiO2 (mSiO2) nanorods. Based on this brand-new strategy, the 1D mSiO2 nanorods can wind on the surface of 3D premade nanoparticles (sphere, cube, hexagon disk, spindle, rod, etc.) and inherit their surface topological structures. Therefore, the mSiO2 nanorods with a diameter of ∼50 nm and a variable length can be bent into arc shapes with variable radii and radians, as well as folded into 60, 90, 120, and 180° angular convex corners with controllable folding times. Additionally, in contrast to conventional core@shell structures, this winding structure induces partial exposure and accessibility of the premade nanoparticles. The functional nanoparticles can exhibit large accessible surface and efficient energy exchanges with the surroundings. As a proof of concept, winding-structured CuS&mSiO2 nanocomposites are fabricated, which are made up of a 100 nm CuS nanosphere and the 1D mSiO2 nanorods with a diameter of ∼50 nm winding the nanosphere in the perimeter. The winding structured nanocomposites are demonstrated to have fourfold photoacoustic imaging intensity compared with the conventional core@shell nanostructure with an inaccessible core because of the greatly enhanced photothermal conversion efficiency (increased by ∼30%). Overall, our work paves the way to the design and synthesis of 1D nanomaterials with controllable bending and folding, as well as the formation of high-performance complex nanocomposites.

Epoxy Polyamide Composites Reinforced with Silica Nanorods: Fabrication, Thermal and Morphological Investigations

Efficient improvement of the toughness of epoxy resin has been a bottleneck for growing their appropriateness for advanced application. In this study, thermoplastic polyamide and copolymer composites of thermosetting epoxy resins (DGEBA) were developed via the solution casting method. Polyamide acted as a part of the copolymer as well as a curing agent. Silica nanorods (SiO2 nanorods) were dispersed into the mixture to achieve blends of epoxy/polyamide reinforced silica nanocomposite with various weight ratio viz. 0 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt% and 11 wt%. The as-prepared epoxy/polyamide reinforced SiO2 nanocomposites were examined by scanning surface micrograph (SEM), Fourier-transform infrared (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) techniques. The obtained results show that the modified epoxy/polyamides have better toughness than that of pristine epoxy/polyamide polymers. FTIR confirmed the interaction among SiO2 nanorods with epoxy/polyamide. The SEM analysis showed well dispersion of SiO2 nanorods in the epoxy/polyamide blend coating, which demonstrated that this method could effectively avoid agglomeration of the inorganic nanoparticles. In conclusion, this study provides an effective approach to harvest epoxy/polyamide/SiO2 nanocomposite from diverse methods and minerals materials.

Facile Synthesis of Core-Shell Structured SiO2@Carbon Composite Nanorods for High-Performance Lithium-Ion Batteries.

Recently, SiO2 has attracted wide attention in lithium-ion batteries owing to its high theoretical capacity and low cost. However, the utilization of SiO2 is impeded by the enormous volume expansion and low electric conductivity. Although constructing SiO2/carbon composite can significantly enhance the electrochemical performance, the skillful preparation of the well-defined SiO2/carbon composite is still a remaining challenge. Here, a facile strategy of in situ coating of polydopamine is applied to synthesis of a series of core-shell structured SiO2@carbon composite nanorods with different thicknesses of carbon shells. The carbon shell uniformly coated on the surface of SiO2 nanorods significantly suppresses the volume expansion to some extent, as well as improves the electric conductivity of SiO2. Therefore, the composite nanorods exhibit a remarkable electrochemical performance as the electrode materials of lithium-ion batteries. For instance, a high and stable reversible capacity at a current density of 100 mA g−1 reaches 690 mAh g−1 and a capacity of 344.9 mAh g−1 can be achieved even at the high current density of 1000 mA g−1. In addition, excellent capacity retention reaches 95% over 100 cycles. These SiO2@carbon composite nanorods with decent electrochemical performances hold great potential for applications in lithium-ion batteries.

Preparation of monodisperse SiO2 nanorods with hollow structure and parameters affecting the length-diameter ratio

Monodisperse SiO2 nanorods with hollow structure were prepared using FeOOH as a template. Powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption isotherms were utilized to characterize the products. With a FeCl3 concentration of 0.1 M, the average length and width of the prepared hollow SiO2 nanorods were 397 nm and 116 nm, respectively, and the average length-diameter ratio was calculated as 3.4. The average size of the nanopores of the amorphous SiO2 shell were measured as 2.5 nm. Furthermore, increasing the concentration of Cl− ions improved length-diameter ratios of the FeOOH nanorod template and hollow SiO2 nanorods.

Hollow PtPd Nanorods with Mesoporous Shells as an Efficient Electrocatalyst for the Methanol-Oxidation Reaction.

Tailoring the morphology and composition of platinum-based electrocatalysts is of significant importance for the development of highly efficient direct methanol fuel cells. Herein, we report a dual-templating method for the design of hollow PtPd nanorods with mesoporous shells (mPtPd HNRs). We found that F127 micelles favored the formation of mesoporous structures and that SiO2 nanorods served as a hard template for the creation of cavities. The well-developed mesopores, hollow structures, and bimetallic composition of the mPtPd HNRs afforded a sufficient number of active sites to facilitate the electrochemical oxidation of methanol, thereby leading to enhanced activity and stability. This strategy allowed for the reliable preparation of mesoporous hollow platinum-based electrocatalysts with desired compositions and morphologies for catalytic applications.

SnS2 Nanograins on Porous SiO2 Nanorods Template for Highly Sensitive NO2 Sensor at Room Temperature with Excellent Recovery.

In order to develop high performance chemoresistive gas sensors for Internet of Everything applications, low power consumption should be achieved due to the limited battery capacity of portable devices. One of the most efficient ways to reduce power consumption is to lower the operating temperature to room temperature. Herein, we report superior gas sensing properties of SnS2 nanograins on SiO2 nanorods toward NO2 at room temperature. The gas response is as high as 701% for 10 ppm of NO2 with excellent recovery characteristics and the theoretical detection limit is evaluated to be 408.9 ppb at room temperature, which has not been reported for SnS2-based gas sensors to the best of our knowledge. The SnS2 nanograins on the template used in this study have excessive sulfur component (Sn:S = 1:2.33) and exhibit p-type conduction behavior. These results will provide a new perspective of nanostructured two-dimensional materials for gas sensor applications on demand.

Enhancing GaN LED Efficiency through Nano-Gratings and Standing Wave Analysis.

Based on our recent work, this paper reviews our theoretical study on gallium nitride (GaN) light-emitting-diode (LED). The focus of the paper is to improve LED light extraction efficiency through various nano-grating designs. The gratings can be designed at different locations, such as at the top, the middle, and the bottom, on the LED. They also can be made of different materials. In this study, we first present a GaN LED error-grating simulation model. Second, nano Indium Tin Oxide (ITO) top gratings are studied and compared with conventional LED (CLED) using standing wave analysis. Third, we present results related to a patterned sapphire substrate (PSS), SiO2 Nanorod array (NR), and Ag bottom reflection layer. Finally, we investigate the nano-top ITO grating performance over different wavelengths to validate our design simulation, which focusing on a single wavelength of 460 nm.

Synthesis of Numerous Edge Sites in MoS2 via SiO2 Nanorods Platform for Highly Sensitive Gas Sensor.

The utilization of edge sites in two-dimensional materials including transition-metal dichalcogenides (TMDs) is an effective strategy to realize high-performance gas sensors because of their high catalytic activity. Herein, we demonstrate a facile strategy to synthesize the numerous edge sites of vertically aligned MoS2 and larger surface area via SiO2 nanorod (NRs) platforms for highly sensitive NO2 gas sensor. The SiO2 NRs encapsulated by MoS2 film with numerous edge sites and partially vertical-aligned regions synthesized using simple thermolysis process of [(NH4)2MoS4]. Especially, the vertically aligned MoS2 prepared on 500 nm thick SiO2 NRs (500MoS2) shows approximately 90 times higher gas-sensing response to 50 ppm NO2 at room temperature than the MoS2 film prepared on flat SiO2, and the theoretical detection limit is as low as ∼2.3 ppb. Additionally, it shows reliable operation with reversible response to NO2 gas without degradation at an operating temperature of 100 °C. The use of the proposed facile approach to synthesize vertically aligned TMDs using nanostructured platform can be extended for various TMD-based devices including sensors, water splitting catalysts, and batteries.

Spatial Isolation of Carbon and Silica in a Single Janus Mesoporous Nanoparticle with Tunable Amphiphilicity.

Like surfactants with tunable hydrocarbon chain length, Janus nanoparticles also possess the ability to stabilize emulsions. The volume ratio between the hydrophilic and hydrophobic domains in a single Janus nanoparticle is very important for the stabilization of emulsions, which is still a great challenge. Herein, dual-mesoporous Fe3O4@mC&mSiO2 Janus nanoparticles with spatial isolation of hydrophobic carbon and hydrophilic silica at the single-particle level have successfully been synthesized for the first time by using a novel surface-charge-mediated selective encapsulation approach. The obtained dual-mesoporous Fe3O4@mC&mSiO2 Janus nanoparticles are made up of a pure one-dimensional mesoporous SiO2 nanorod with tunable length (50-400 nm), ∼100 nm wide and ∼2.7 nm mesopores and a closely connected mesoporous Fe3O4@mC magnetic nanosphere (∼150 nm diameter, ∼10 nm mesopores). As a magnetic "solid amphiphilic surfactant", the hydrophilic/hydrophobic ratio can be precisely adjusted by varying the volume ratio between silica and carbon domains, endowing the Janus nanoparticles surfactant-like emulsion stabilization ability and recyclability under a magnetic field. Owing to the total spatial separation of carbon and silica, the Janus nanoparticles with an optimized hydrophilic/hydrophobic ratio show spectacular emulsion stabilizing ability, which is crucial for improving the biphasic catalysis efficiency. By selectively anchoring catalytic active sites into different domains, the fabricated Janus nanoparticles show outstanding performances in biphasic reduction of 4-nitroanisole with 100% conversion efficiency and 700 h-1 high turnover frequency for biphasic cascade synthesis of cinnamic acid.

Ultrasensitive immunoassay based on fluorescent SiO2 nanorods

Ultrasensitive immunoassay based on fluorescent SiO2 nanorods