Al2O3 Nanostructures Research Articles

Structural and Optical Properties of Al2O3 Nanostructures Prepared by Hot Water Treatment Method

Structural and Optical Properties of Al2O3 Nanostructures Prepared by Hot Water Treatment Method

Improved optical and electrical response by glancing angle synthesized Al2O3 nanorod array device

An Aluminum Oxide (Al2O3) nanorod (NR) array–based device has been synthesized upon an Al2O3 thin film (TF) by electron beam (E-beam) evaporation with a glancing angle deposition technique. The complete fabrication has been done inside a vacuum coating unit. The Al2O3 nanostructures have been fabricated on a silicon substrate. Field emission scanning electron microscopy and transmission electron microscopy show a vertically aligned Al2O3 NR array. From the Tauc plot, the optical band energies are estimated as 5 eV and 5.5 eV for the bare Al2O3 TF and Al2O3 NR/Al2O3 TF devices, respectively. Significant improvement has been observed in photosensitivity by 10 fold, detectivity by 4.2 fold, and noise equivalent power (NEP) by 16.5 fold for the Al2O3 NR/Al2O3 TF device compared with the Al2O3 TF. The Al2O3 NR/Al2O3 TF device exhibits a very fast photoswitching response (rise time = 0.15 s and fall time = 0.13 s). Therefore, the Al2O3 NR/Al2O3 TF device proves to be a prominent candidate for next-generation optoelectronic device applications.

Dye degradation, antimicrobial activity, and molecular docking analysis of carbon sphere and graphene oxide–doped aluminum oxide

In this research work, pristine and various concentrations (2.4 wt%) of graphene oxide (GO)/carbon sphere (CS)–doped Al2O3 nanostructures (NSs) were synthesized with the chemical sol–gel method. Aluminum oxide (Al2O3) exhibits quick recombination of electrons and holes with a low specific surface to limit catalytic and antibacterial activities. Al2O3 doped with CS is good in wastewater treatment and reduces the size of NSs. The incorporation of graphene oxide (GO) into Al2O3 at different concentrations (2 and 4 wt%) enhances both the structural and chemical stabilities of the resulting material while concurrently decreasing the number of charge carriers and reducing the band gap energy. This modified Al2O3-GO composite exhibits promising potential for utilization in dye degradation and antibacterial activity. A series of characterizations were performed to investigate the structural, morphological, and optical properties. The NSs exhibited excellent catalytic activity (CA) against rhodamine B (RhB) dye in acidic, basic, and neutral media. The antimicrobial activity was tested against Escherichia coli. Pairs of electrons and holes are the primary building blocks for the production of reactive oxygen species (ROS), which causes bacteria to die. The significant inhibition zones against E. coli were calculated to be approximately 5.65 mm when compared to ciprofloxacin. Moreover, in silico investigations have revealed the possible inhibitory impact of produced nanomaterials (GO/CS-doped Al2O3) on DNA gyrase and FabI enzymes of fatty acid biosynthesis.

Performance, Emission, and Catalytic Activity Analysis of AL2O3 and CEO2 Nano-Additives on Diesel Engines Using Mahua Biofuel for a Sustainable Environment.

Diesel engines are particularly harmful to the environment due to the high levels of pollution they release. This led to the discovery of a sustainable and environmentally friendly fuel source. Mahua oil transesterified into biofuel seems to be the most popular option. The possibilities for nano-additions to enhance engine performance while simultaneously lowering pollution levels are substantial. In this research, 20% by proportion mahua biodiesel (MAH B20) was mixed with varying concentrations of aluminum oxide (Al2O3) and cerium oxide (CeO2) nanoparticles, and their joint effects on a mono-cylinder diesel engine working at a speed of 1500 revolutions per minute (rpm) were evaluated. With the use of an ultrasonic bath, the nanoparticles and MAH B20 were blended at varying concentrations and a surfactant was added for stability. The investigations concluded that the combustion and emission properties of mahua biofuel were improved because of the higher volume to surface area ratio of the combined Al2O3 and CeO2 nanostructures. The best results are found when mahua biofuel is mixed with Al2O3 and CeO2 each at 100 parts per million (ppm). The blend MAH B20 AL100 CE100 exhibits reduced brake specific fuel consumption (BSFC) by 3.25%, increased brake thermal efficiency (BTE) by 1.39%, and reduced emissions of hydrocarbon (HC), oxides of nitrogen (NOX), and carbon monoxide (CO) by 30.73, 1.27, and 44.13%, respectively.

Wireless Humidity Sensor for Smart Packaging via One‐step Laser‐Induced Patterning and Nanoparticle Formation on Metallized Paper

AbstractIn this work, a scalable and rapid process is developed for creating a low‐cost humidity sensor for wireless monitoring of moisture levels within packaged goods. The sensor comprises a moisture‐sensitive interdigitated capacitor connected to a planar spiral coil, forming an LC circuit whose resonant frequency is a function of environmental humidity. The sensor is fabricated on a commercially available metallized parchment paper through selective laser ablation of the laminated aluminum (Al) film on the parchment paper substrate. The laser ablation process provides a unique one‐step patterning of the conductive Al layer on the paper while simultaneously creating high surface area Al2O3nanoparticles within the laser‐ablated regions. The intrinsic humidity‐responsive characteristics of the laser‐induced Al2O3nanostructures provide the wireless sensor with a tenfold higher sensitivity to humidity than a similar LC resonant sensor prepared by conventional photolithography‐based processes on FR‐4 substrates. The frequency change of the sensor is observed to be a linear function within the range of 0−85% RH, providing an average sensitivity of −87 kHz RH−1with good repeatability and stable performance. Furthermore, the employment of scalable laser fabrication processes using commercially available inexpensive materials renders these technologies viable for roll‐to‐roll manufacturing of low‐cost wireless sensors for smart packaging applications.

Self-assembled multifunctional nanostructures for surface passivation and photon management in silicon photovoltaics

Abstract This work reports the fabrication and characterization of multifunctional, nanostructured passivation layers formed using a self-assembly process that provide both surface passivation and improved light trapping in crystalline silicon photovoltaic (PV) cells. Scalable block copolymer self-assembly and vapor phase infiltration processes are used to form arrays of aluminum oxide nanostructures (Al2O3) on crystalline silicon without substrate etching. The Al2O3 nanostructures are characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and spectroscopic ellipsometry. Injection-level dependent photoconductance measurements are used to determine the effective carrier lifetime of the samples to confirm the nanostructures successfully passivate the Si surface. Finite element method simulations and reflectance measurement show that the nanostructures increase the internal rear reflectance of the PV cell by suppressing the parasitic optical losses in the metal contact. An optimized morphology of the structures is identified for their potential use in PV cells as multifunctional materials providing surface passivation, photon management, and carrier transport pathways.

Effect of alumina nanoparticles on the antifouling properties of polycarbonate‐polyurethane blend ultrafiltration membrane for water treatment

AbstractIn this work, the flexibility of polycarbonate (PC) membrane was improved by using polyurethane (PU) additive. However, due to the hydrophobic nature of the PU polymer, alumina (Al2O3) nanoparticles were incorporated to PC‐PU blend membrane. The prepared membranes have been used in a submerged membrane system to eliminate humic acid molecules from polluted water in both the presence and absence of coagulant (polyaluminum chloride). The obtained results showed that introduction of PU into PC membrane diminished hydrophilicity and enhanced porosity. Moreover, the flexibility of the PC membrane remarkably improved. Introduction of 1.5 wt% Al2O3 to the PC‐PU blend membrane led to enhancement in both porosity and hydrophilicity. Results of morphological studies showed that in the presence of Al2O3 nanostructures, finger‐shaped voids seemed to elongate across the entire thickness of the prepared membrane. Atomic force microscopy images showed that incorporation of PU and Al2O3 to the PC membrane resulted in a smoother surface. The antifouling performance of membranes revealed that the PC‐PU/Al2O3 nanocomposite membrane possessed the most favorable antifouling features owing to its lowest surface roughness as well as highest hydrophilicity. For all membranes utilizing coagulant (PAC), the irreversible fouling ratio and the flux recovery ratio significantly diminished and increased, respectively.

Relative humidity sensor based on no-core multimode interferometer coated with Al2O3-PVA composite films

Abstract Herein, a simple relative humidity (RH) fiber sensor based on a multimode interferometer (MMI) with aluminum oxide nanoparticles (Al2O3 NPs) and polyvinyl alcohol (Al2O3-PVA) composite was fabricated and experimentally demonstrated. The sensor was fabricated by splicing a no-core fiber (NCF) segment between two single-mode fibers (SMF). The chemical etching method has been used with hydrofluoric (HF) acid to prepare diverse NCF diameters. This was proposed to expand the evanescent fields and enhance sensor sensitivity. A hydrophilic sensitive film based on Al2O3-PVA was coated on the surface of NC fiber using the cast-drop and evaporation technique. By altering the ambient humidity, water adsorption into the Al2O3 nanostructures occurs and therefore, the refractive index (RI) of the coated film varies inducing a 38.9 nm wavelength shift in the output spectra. The results showed that a maximum sensitivity of 0.587 nm/%RH has been achieved as the percentage of the RH increases from 30% to 100%. The simple fabrication and the high sensitivity of this sensor may prompt many potential applications in the fields of biology and chemistry.

Enhanced Catalytic Hydrogenation Performance of Rh-Co2O3 Heteroaggregate Nanostructures by in Situ Transformation of Rh@Co Core-Shell Nanoparticles.

In this work, poly(vinylpyrrolidone)-stabilized 3–5 nm Rh@Co core–shell nanoparticles were synthesized by a sequential reduction method, which was further in situ transformed into Rh-Co2O3 heteroaggregate nanostructures on alumina supports. The studies of XRD, HAADF-STEM images with phase mappings, XPS, TPR, and DRIFT-IR with CO probes confirm that the as-synthesized Rh@Co nanoparticles were core–shell-like structures with Rh cores and Co-rich shells, and Rh-Co2O3 heteroaggregate nanostructures are obtained by calcination of Rh@Co nanoparticles and subsequent selective H2 reduction. The Rh-Co2O3/Al2O3 nanostructures demonstrated enhanced catalytic performance for hydrogenations of various substituted nitroaromatics relative to individual Rh/Al2O3 and illustrated a high catalytic stability during recycling experiments for o-nitrophenol hydrogenation reactions. The catalytic performance enhancement of Rh-Co2O3/Al2O3 nanocatalysts is ascribed to the Rh-Co2O3 interfaces where the Rh-Co2O3 interaction not only prevents the active Rh particles from agglomeration but also promotes the catalytic hydrogenation performance.

Controlling fibroblast adhesion and proliferation by 1D Al2O3 nanostructures.

The fibrotic encapsulation, which is mainly accompanied by an excessive proliferation of fibroblasts, is an undesired phenomenon after the implantation of various medical devices. Beside the surface chemistry, the topography plays also a major role in the fibroblast-surface interaction. In the present study, one-dimensional aluminium oxide (1D Al2O3) nanostructures with different distribution densities were prepared to reveal the response of human fibroblasts to the surface topography. The cell size, the cell number and the ability to form well-defined actin fibres and focal adhesions were significantly impaired with increasing distribution density of the 1D Al2O3 nanostructures on the substratum.

Synthesis of Flower-Like Mesoporous γ-AlOOH and γ-Al2O3 Nanoarchitectures via an Ionic Liquid-Assisted Hydrothermal Route

In this work, flower-like [Formula: see text]-AlOOH and [Formula: see text]-Al2O3 nanoarchitectures with excellent surface and mesoporous properties were successfully synthesized in ionic liquid-assisted hydrothermal reaction system. The as-prepared suprastructures were characterized by several techniques, such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption/desorption measurement. The formation mechanism of flower-like [Formula: see text]-AlOOH mesoporous crystallites by ionic liquid-assisted hydrothermal process was proposed and discussed. Flower-like [Formula: see text]-Al2O3 nanostructures were obtained by calcining the as-prepared [Formula: see text]-AlOOH at 600∘C for 2[Formula: see text]h, preserving the same morphology.

Rice-like Ag/Al2O3 nanocomposites preparation from AlOOH nanostructures synthesized via a facile hydrothermal route for azo dyes photocatalytic degradation and Pb2+ adsorption

Herein, various morphologies of AlOOH (boehmite) nanostructures were successfully synthesized via a facile hydrothermal route. The obtained AlOOH nanostructures were utilized as a novel starting reagent with AgNO3 and cochineal powder for synthesizing Ag–Al2O3 nanocomposites via a thermal decomposition method. The prepared nanocomposites were applied as photocatalyst for decolorization of acid violet 7 as an azo dye under visible light irradiation. The results showed the rice-like sample (A3) has the highest photodegradation efficiency due to its more surface to volume ratio. Moreover, the synthesized AlOOH nanostructures were directly calcined to transform into rice-like Al2O3 nanostructures as an adsorbent for Pb2+ ions removing from aqueous medium. The rice-like Al2O3 (sample B3) as an adsorbent showed a remarkable adsorption capacity (250 mg/g) compared to other samples with different morphologies.

Low temperature fabrication of Al2O3 nanostrips and their enhanced dielectric property

Under ambient conditions, Al2O3 nanostrips were obtained through economical and facile hydrothermal route followed by dehydration process. The average length and width of the rectangular nanostrips were found to be 74 nm and 36 nm, respectively. On account of the significance of hydrothermal preparation route Al2O3 nanostrips with a lower band gap of 4.19 eV were obtained in comparison to counter routes which result in the higher bandgap Al2O3 nanostructures. Owing to the low band gap, the resulting samples show enhanced dielectric constant and a decrease in dielectric loss as the frequency increases than the nanostructures obtained through other routes under such conditions. Furthermore using super-saturation ratio, the detailed fabrication mechanism of Al2O3 nanostrips throughout the hydrothermal process have been incorporated.

Carbon-nanotube-templated deposition of amorphous aluminum oxide with linear photo transmittance

Atomic layer deposition on free-standing carbon nanotube (CNT) sheets produced highly amorphous Al2O3 nanostructures. The hybrid sheets maintained amorphousness for Al2O3 at 700 °C and robustness as well by thermally decomposing the CNTs. Higher temperatures (above 1000 °C) induced crystalline transformations into γ- and α Al2O3 phases. As each amorphous structure could contribute an absorption peak, the hybrid sheets with a mixture of amorphousness interestingly showed a linear photo-transmittance/absorbance when increasing the wavelength from 200 to 800 nm.

Synthesis mechanisms, optical and structural properties of η-Al2O3 based nanoparticles prepared by DC arc discharge in environmentally friendly liquids

The staple topic of this work is synthesis of η-Al2O3 nanoparticles via direct current (DC) arc discharge in different carrier media. The effects of surrounding liquid environment on composition, crystal structure and optical properties of η-Al2O3 nanoparticles were studied. DC arc discharge was made between two pure aluminum electrodes in water, ethanol and methanol as environmentally friendly liquid carrier media. For all media a 40A electrical current was used for arc discharge. Scanning electron microscopy observations, X-ray diffraction and optical transmission spectroscopy, were employed for characterization of particles size, shape, crystal structure and optical properties respectively. X-ray diffraction results reveal the synthesis of pure η-Al2O3, Al/η-Al2O3 and a mixture of η-Al2O3 and γ-Al2O3 in water, ethanol and methanol respectively. The mean particle size for the nanoparticles in ethanol is 50nm. In deionised water and also in methanol, Al2O3 nanoparticles with mean size of 37nm were observed. Nanoparticles in ethanol and methanol, were completely precipitated within 48h. In all the liquid media, optical transmissions are the optical characteristics of Al2O3 and aluminum nanoparticles in accordance with the data obtained from X-ray diffraction. The lowering of the band gaps with respect to the bulk value of alumina due to some oxygen deficiency reveals gradual oxidation of nanoparticles in water. The composition and formation mechanisms of the nanoparticles are discussed based on the chemical nature of the liquids and the behaviour of carrier medium under DC arc discharge condition. This results demonstrate an environmentally friendly pathway for rapid mass production of η-Al2O3 and mixed-Al2O3 and γ-Al2O3 nanoparticles that is essential for catalytic application of Al2O3 nanostructures.

Design of Highly Efficient Pt-SnO2 Hydrogenation Nanocatalysts using Pt@Sn Core–Shell Nanoparticles

In this work, Pt-SnO2 heteroaggregate nanocatalysts were synthesized by in situ transformation of Pt@Sn core–shell nanoparticles and their catalytic performance for hydrogenation of various substituted nitroaromatics was investigated. The Pt@Sn nanoparticles were prepared by a one-step method, and the alumina-supported Pt@Sn nanoparticles were further transformed in situ into Pt-SnO2 heteroaggregate nanostructures by calcination. The structures of Pt@Sn and Pt-SnO2 nanomaterials were characterized, and FT-IR with CO probes, HRTEM, XRD, and XPS characterizations revealed that the as-synthesized Pt@Sn nanoparticles were core@shell-like structures with Sn-rich shells and Pt-rich cores and the obtained Pt-SnO2 heteroaggregate nanostructures consisted of close-contact pure Pt and SnO2 phases. The Pt-SnO2/Al2O3 nanostructures demonstrated a better catalytic performance for hydrogenation of various substituted nitroaromatics relative to individual Pt/Al2O3 nanocatalysts. Theoretical calculations suggested that P...

Novel and solvent-free cochineal-assisted synthesis of Ag–Al2O3 nanocomposites via solid-state thermal decomposition route: characterization and photocatalytic activity assessment

Herein, silver–alumina nanocomposites have been synthesized via simple, novel, solvent-free and template-less solid-state thermal decomposition using cochineal powder as novel starting reagent for the first time. AgNO3 and Al(OH)3 were utilized as silver and aluminum source, respectively. The prepared Ag–Al2O3 nanostructures were characterized extensively by means of X-ray diffraction, energy-dispersive X-ray analysis, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and UV–Vis spectroscopy. Effect of reaction time, temperature and cochineal powder on morphology and particle size of prepared products was investigated. The results exhibited that in presence of cochineal powder, as-prepared nanostructures show very high degree of purity and uniformity. In other words, because of remarkable antioxidant properties of cochineal, it prevents silver nanoparticles from sintering and oxidizing. The silver–alumina nanocomposite were evaluated as photocatalyst for the Rhodamine B degradation using visible light irradiation and showed significant photocatalytic efficiency.

Charge optimized many-body (COMB) potential for Al2O3 materials, interfaces, and nanostructures

This work presents the development and applications of a new empirical, variable charge potential for Al2O3 systems within the charge optimized many-body (COMB) potential framework. The potential can describe the fundamental physical properties of Al2O3, including cohesive energy, elastic constants, defect formation energies, surface energies and phonon properties of α-Al2O3 comparable to that obtained from experiments and first-principles calculations. The potential is further employed in classical molecular dynamics (MD) simulations to validate and predict the properties of the Al (1 1 1)–Al2O3 (0 0 0 1) interface, tensile properties of Al nanowires, Al2O3 nanowires, Al2O3-covered Al nanowires, and defective Al2O3 nanowires. The results demonstrate that the potential is well-suited to model heterogeneous material systems involving Al and Al2O3. Most importantly, the parameters can be seamlessly coupled with COMB3 parameters for other materials to enable MD simulations of a wide range of heterogeneous material systems.

A simple technique for the facile synthesis of novel crystalline mesoporous ZrO2–Al2O3 hierarchical nanostructures with high lead (II) ion absorption ability

In this study, a simple evaporation-induced self-assembly process for the facile synthesis of crystalline ZrO2–Al2O3 hierarchical nanostructures was reported. The synthesized hierarchical nanostructures display a long ranged ordered mesoporous structure, and demonstrated excellent adsorption properties for Pb (II) ions removal due to its larger surface-to-volume ratio. Characterization by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller (BET) analysis reveal that the as-synthesized nanostructures possess large BET surface area (278m2g−1), relatively large pore size (12.99nm) and high pore volume (0.925cm3g−1). The Pb (II) ions adsorption processes conformed to the pseudo-second order kinetics and the Langmuir adsorption isotherm was suitable in describing the lead removal processes where the equilibrium time for the Pb (II) ions adsorption on the ZrO2–Al2O3 nanostructures was 30min. These crystalline mesoporous ZrO2–Al2O3 hierarchical nanostructures possess a maximum adsorption capacity of 110.49mgg−1 for Pb (II) and hence are an attractive adsorbent for the removal of heavy metal ion from water. In addition, our synthesized ZrO2–Al2O3 hierarchical nanostructures also display good reusability properties.

Growth and mechanism of one-dimensional Al2O3 nanostructures grown by chemical vapor deposition from an Al powder source

Alumina (Al2O3) nanostructures were grown in a horizontal Al2O3 tube furnace by chemical vapor deposition (CVD) using an aluminum (Al) powder source without catalysts at temperatures ranging from 1100 to 1400°C and pressures ranging from 0.01 to 53.32kPa. As the temperature and pressure were increased, the nanostructure size increased and in particular, increasing pressure resulted in various changes in morphology. Here we present a morphology diagram of the one-dimensional Al2O3 nanostructure growth to illustrate different growth features at various temperatures and pressures. Moreover, we suggest that the Al2O3 nanostructure deposition mechanism was affected by the liquid source droplet and film morphology as the temperature and pressure changed in the absence of catalysts.