In this research work, nanowires were grown on brass (Cu - 37.2 wt% Zn) substrate by thermal oxidation process. The substrate was oxidized at temperature ranging from 350-600 °C in the presence of varying concentrations of O2 in N2 (1-100%) flown at a rate of 200 sccm. The oxidized brass surface was characterized by field emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray (EDX) spectroscope and transmission electron microscope (TEM). Four different types of morphological variations such as thin, thick with branches, circular-flake and flat-cone shape were observed during oxidation at different conditions. However, the prevalence of thin, thick morphology with branches was more prominent and found in all growth conditions. The length and diameter of the nanowires were varied from 1-30 µm and 50-500 nm, respectively whereas the length of the branches varied from 1-3 µm. The composition of the nanowires was ZnO possessing of hexagonal wurtzite structure. The selected area diffraction confirms that the nanowires grew along <1 1 0> directions. Based on the results, a stress induced based mechanism is proposed for the growth of ZnO nanowires on Cu - 37.2 wt% Zn substrate.
In this research, novel ultrafiltration nanocomposite membranes were prepared by incorporating self-synthesized nanoporous titanium dioxide (NTiO2) nanoparticles into polysulfone. The surface of the nanoparticle was treated with a silane-based modifier to improve its distribution in the host polymer. Atomic-force microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller, transmission electron microscopy, energy-dispersive x-ray spectroscopy, porosity and contact angle tests were conducted to characterize the properties of the particles as well as the fabricated nanocomposite membranes. The effects of the nanoparticle incorporation were evaluated by conducting ultrafiltration experiments. It was reported that the membrane pure water flux was increased with increasing NTiO2 loading owing to the high porosity of the nanoparticles embedded and/or formation of enlarged pores upon addition of them. The antifouling capacity of the membranes was also tested by ultrafiltration of bovine serum albumin fouling solution. It was found that both water flux and antifouling capacity tended to reach desired level if the NTiO2 added was at optimized loading.
Obtaining compositional homogeneity without compromising morphological or structural quality is one of the biggest challenges in growing ternary alloy compound semiconductor nanowires. Here we report growth of Au-seeded InxGa1-xAs nanowires via metal-organic vapour phase epitaxy with uniform composition, morphology and pure wurtzite (WZ) crystal phase by carefully optimizing growth temperature and V/III ratio. We find that high growth temperatures allow the InxGa1-xAs composition to be more uniform by suppressing the formation of typically observed spontaneous In-rich shells. A low V/III ratio results in the growth of pure WZ phase InxGa1-xAs nanowires with uniform composition and morphology while a high V/III ratio allows pure zinc-blende (ZB) phase to form. Ga incorporation is found to be dependent on the crystal phase favouring higher Ga concentration in ZB phase compared to the WZ phase. Tapering is also found to be more prominent in defective nanowires hence it is critical to maintain the highest crystal structure purity in order to minimize tapering and inhomogeneity. The InP capped pure WZ In0.65Ga0.35As core-shell nanowire heterostructures show 1.54 μm photoluminescence, close to the technologically important optical fibre telecommunication wavelength, which is promising for application in photodetectors and nanoscale lasers.
Working electrode (WE) fabrication offers significant challenges in terms of achieving high-efficiency dye-sensitized solar cells (DSCs). We have combined the beneficial effects of vertical nanorods grown on conducting glass substrate for charge transport and mesoporous particles for dye loading and have achieved a high photoconversion efficiency of (η) > 11% with an internal quantum efficiency of ∼93% in electrode films of thickness ∼7 ± 0.5 μm. Controlling the interface between the vertical nanorods and the mesoporous film is a crucial step in attaining high η. We identify three parameters, viz., large surface area of nanoparticles, increased light scattering of the nanorod-nanoparticle layer, and superior charge transport of nanorods, that simultaneously contribute to the improved photovoltaic performance of the WE developed.
The past few years have witnessed remarkable progress in solution-processed methylammonium lead halide (CH3NH3PbX3, X = halide) perovskite solar cells (PSCs) with reported photoconversion efficiency (η) exceeding 20% in laboratory-scale devices and reaching up to 13% in their large area perovskite solar modules (PSMs). These devices mostly employ mesoporous TiO2 nanoparticles (NPs) as an electron transport layer (ETL) which provides a scaffold on which the perovskite semiconductor can grow. However, limitations exist which are due to trap-limited electron transport and non-complete pore filling. Herein, we have employed TiO2 nanorods (NRs), a material offering a two-fold higher electronic mobility and higher pore-filing compared to their particle analogues, as an ETL. A crucial issue in NRs' patterning over substrates is resolved by using precise Nd:YVO4 laser ablation, and a champion device with η ∼ 8.1% is reported via a simple and low cost vacuum-vapor assisted sequential processing (V-VASP) of a CH3NH3PbI3 film. Our experiments showed a successful demonstration of NRs-based PSMs via the V-VASP technique which can be applied to fabricate large area modules with a pin-hole free, smooth and dense perovskite layer which is required to build high efficiency devices.
Upconversion (UC) of lanthanide-doped nanostructure has the unique ability to convert low energy infrared (IR) light to high energy photons, which has significant potential for energy conversion applications. This review concisely discusses the basic concepts and fundamental theories of lanthanide nanostructures, synthesis techniques, and enhancement methods of upconversion for photovoltaic and for near-infrared (NIR) photodetector (PD) application. In addition, a few examples of lanthanide-doped nanostructures with improved performance were discussed, with particular emphasis on upconversion emission enhancement using coupling plasmon. The use of UC materials has been shown to significantly improve the NIR light-harvesting properties of photovoltaic devices and photocatalytic materials. However, the inefficiency of UC emission also prompted the need for additional modification of the optical properties of UC material. This improvement entailed the proper selection of the host matrix and optimization of the sensitizer and activator concentrations, followed by subjecting the UC material to surface-passivation, plasmonic enhancement, or doping. As expected, improving the optical properties of UC materials can lead to enhanced efficiency of PDs and photovoltaic devices.
Inkjet-printable ink formulated with graphene oxide (GO) offers several advantages, including aqueous dispersion, low cost, and environmentally friendly production. However, water-based GO ink encounters challenges such as high surface tension, low wetting properties, and reduced ink stability over prolonged storage time. Alkali lignin, a natural surfactant, is promising in improving GO ink's stability, wettability, and printing characteristics. The concentration of surfactant additives is a key factor in fine-tuning GO ink's stability and printing properties. The current study aims to explore the detailed effects of alkali lignin concentration and optimize the overall properties of graphene oxide (GO) ink for drop-on-demand thermal inkjet printing. A meander-shaped temperature sensor electrode was printed using the optimized GO ink to demonstrate its practical applicability for commercial purposes. The sensing properties are evaluated using a simple experimental setup across a range of temperatures. The findings demonstrate a significant increase in zeta potential by 25% and maximum absorption by 84.3%, indicating enhanced stability during prolonged storage with an optimized alkali lignin concentration compared to the pure GO dispersions. The temperature sensor exhibits a remarkable thermal coefficient of resistance of 1.21 within the temperature range of 25 °C-52 °C, indicative of excellent sensitivity, response, and recovery time. These results highlight the potential of alkali lignin as a natural surfactant for improving the performance and applicability of inkjet-printable GO inks in various technological applications.
An ethanol gas sensor with enhanced sensor response was fabricated using Ni-doped SnO2 nanorods, synthesized via a simple hydrothermal method. It was found that the response (R = R 0/R g) of a 5.0 mol% Ni-doped SnO2 (5.0Ni:SnO2) nanorod sensor was 1.4 × 104 for 1000 ppm C2H5OH gas, which is about 13 times higher than that of pure SnO2 nanorods, (1.1 × 103) at the operating temperature of 450 °C. Moreover, for 50 ppm C2H5OH gas, the 5.0Ni:SnO2 nanorod sensor still recorded a significant response reading, namely 2.0 × 103 with a response time of 30 s and recovery time of 10 min. To investigate the effect of Ni dopant (0.5-5.0 mol%) on SnO2 nanorods, structural characterizations were demonstrated using field emission scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, x-ray diffraction (XRD) analysis, x-ray photoelectron spectroscopy and an ultraviolet-visible spectrometer. XRD results confirmed that all the samples consisted of tetragonal-shaped rutile SnO2 nanorods. It was found that the average diameter and length of the nanorods formed in 5.0Ni:SnO2 were four times smaller (∼6 and ∼35 nm, respectively) than those of the nanorods formed in pure SnO2 (∼25 and 150 nm). Interestingly, both samples had the same aspect ratio, ∼6. It is proposed that the high response of the 5.0Ni:SnO2 nanorod sensor can be attributed to the particle size, which causes an increase in the thickness of the charge depletion layer, and the presence of oxygen vacancies within the matrix of SnO2 nanorods.
Tin (IV) oxide (SnO2) nanostructures are regarded as one of the most popular materials for conventional gas sensors, due to their high surface area and fast response in regard to most reducing and oxidizing gases. However, their high operating temperature (>200 °C) leads to high power consumption and limits their applications. Here, a new nanocomposite fiber materials, consisting of undoped and doped (nickel and palladium) SnO2 nanorods, polyaniline (PANI), and polyhydroxy-3-butyrate (P3HB) are synthesized via the hydrothermal method,followed by an in situ polymerization and electrospinning technique. The as-synthesized nanocomposites are tested using ethanol gas at different operating temperatures: 25 °C (room temperature), 60 °C, and 80 °C. The results reveal that all samples began to show a response at 80 °C. Pd:SnO2/PANI/P3HB nanocomposite fiber sensors demonstrate a relatively higher response than that of SnO2/PANI/P3HB and Ni:SnO2/PANI/P3HB nanocomposite sensors. At 80 °C , the Pd:SnO2/PANI/P3HB nanocomposite sensor records a response (R0/Rg ) of 1610, with a response time (Tres) of 90 s and a recovery time (Trec ) of 9 min in relation to 1000 ppm ethanol gas in N2. The sensor also displays a good level of response (R0/Rg = 200) at a low concentration level (50 ppm) of ethanol gas. Structural and chemical characterizations indicate that the ethanol gas sensing performance of Pd:SnO2/PANI/P3HB nanocomposite fibers can mainly be attributed to the p-n heterojunction, fiber geometry, and one-dimensional structure of SnO2 and to the presence of the Pd catalyst. This bio-nanocomposite fiber has the potential to be a breakthrough material in biodegradable low temperature ethanol sensing applications.
Arrays of TiO2 nanotubes (TiO2 NTs) with grassy surfaces were observed on titanium foil anodised at 60 V in fluorinated ethylene glycol (EG) with added hydrogen peroxide (H2O2). The grassy surface was generated by the chemical etching and dissolution of the surface of the TiO2 NTs walls, which was accelerated by the temperature increase on the addition of H2O2 . Upon annealing at 600 °C, the grassy part of the TiO2 NTs was found to consist of mostly anatase TiO2 whereas the bottom part of the anodic oxide comprised a mixture of anatase and rutile TiO2. The TiO2 NTs were then used to reduce hexavalent chromium (Cr(VI)) under ultraviolet radiation. They exhibited a rather efficient photocatalytic effect, with 100% removal of Cr(VI) after 30 min of irradiation. The fast removal of Cr(VI) was due to the anatase dominance at the grassy part of the TiO2 NTs as well as the higher surface area the structure may have. This work provides a novel insight into the photocatalytic reduction of Cr(VI) on grassy anatase TiO2 NTs.
ZrO2 nanotubes (ZrNTs) were produced by anodisation of zirconium foil in H2O2/NH4F/ethylene glycol electrolyte. The as-anodised foils were then soaked in the anodising electrolyte for 12 h. Soaking weakens the adherence of the anodic layer from the substrate resulting in freestanding ZrNTs (FS-ZrNTs). Moreover, the presence of H2O2 in the electrolyte also aids in weakening the adhesion of the film from the foil, as foil anodised in electrolyte without H2O2 has good film adherence. The as-anodised FS-ZrNTs film was amorphous and crystallised to predominantly tetragonal phase upon annealing at >300 °C. Annealing must, however, be done at <500 °C to avoid monoclinic ZrO2 formation and nanotubes disintegration. FS-ZrNTs annealed at 450 °C exhibited the highest photocatalytic ability to degrade methyl orange (MO), whereby 82% MO degradation was observed after 5 h, whereas FS-ZrNTs with a mixture of monoclinic and tetragonal degraded 70% of MO after 5 h.
Visible-light-active freestanding zirconia (ZrO2) nanotube (FSZNT) arrays were fabricated by a facile electrochemical anodization method in fluoride containing ethylene glycol electrolyte added to it was 1 vol% of potassium carbonate (K2CO3) at 60 V for 1 h. Poor adhesion at the metal∣oxide interface was induced by K2CO3 leading to the formation of FSZNT flakes. The effect of the crystal structures of the FSZNTs e.g., amorphous, amorphous/tetragonal, and tetragonal/monoclinic was investigated towards the photocatalytic reduction of 10 ppm hexavalent chromium, Cr(VI) at pH 2 under sunlight. The results demonstrate the amorphous FSZNTs exhibited the highest Cr(VI) removal efficiency than the crystalline FSZNTs (95% versus 33% after 5 h). The high photocatalytic activity of the amorphous FSZNTs can be attributed to enhanced Cr(VI) adsorption, high visible light absorption, and better charge carrier separation. The low photocatalytic activity of the crystalline FSZNTs annealed at 500 °C was mainly attributed to poor Cr(VI) adsorption, low visible light absorption, and less photoactive monoclinic-ZrO2.
Self-organized, 23 μm-thick anodic TiO2 nanotube (TNT) arrays were formed in sodium hydroxide/fluoride/ethylene glycol (EG) electrolyte at 60 V for 60 min. The presence of sodium hydroxide (NaOH) in the fluoride/EG electrolyte accelerates the formation of the TiO2 nanotube arrays. The anodic film was then decorated with silver nanoparticles (Ag NPs) by the photodeposition process and used as a photoanode in a rear-side-illuminated dye-sensitized solar cell. The Ag NPs decorated TNT arrays, with the former having diameters of 10-30 nm formed from 0.2 M of Ag-precursor solution and exhibiting the highest photoconversion efficiency (η) of 3.7% and a short-circuit current density of 12.2 mA cm(-2) compared to η = 3% and short-circuit current density of 9.1 mA cm(-2) for a sample without Ag NPs. The increase in η is thought to be due to the surface plasmon resonance and excess electrons from the nanoparticles.
The length of titania nanotubes formed by anodization of 0.1 mm thick titanium foil was found to be a strong function of the pH of the electrolyte. The longest nanotubes were formed by using an electrolyte consisting of 1 M Na(2)SO(4) plus 5 wt% NH(4)F with pH 7. At this pH, after 30 min of anodization, 3 microm length nanotubular titania arrays with top diameters of approximately 50 nm and bottom diameters of 100 nm were produced. No acid was added to this electrolyte. The formation of titania nanotubes in neutral pH systems was therefore successful due to the excess NH(4)F in the electrolyte which increases the chemical dissolution process at the metal/oxide interface. Since the pH of the electrolyte at the top part of the nanotubes is kept very high, the dissolution of the nanotubes at the surface is minimal. However, the amount is adequate to remove the initial barrier layer, forming a rather well-defined nanoporous structure. All anodized foils were weakly crystalline and the transformation to anatase phase was achieved by heat treatment at temperatures from 200 to 500 degrees C for 1 h in air. Annealing at temperatures above 500 degrees C induce rutile phase formation and annealing at higher temperatures accelerates the diffusion of Ti(4+) leading to excessive growth and the nanotubular structure diminishes.
Anodic aluminium oxide (AAO) is a self-organised nanopore that has been widely studied due to the ease of its synthesization and pore properties manipulation. However, pore growth behaviour under different geometrical surfaces is rarely studied, particularly on the effect of combined curved surfaces towards pore growth properties, which is crucial in designing unique porous platform for specific applications. This paper reports study on the decisive effect of curvature surfaces on development of pore structure and properties at a constant potential. In this work, AAO grown on treated convex and concave surfaces were analysed in terms of pore quantity, pore diameter, interpore distance, pore length and other parameters of pore bottom geometry in conjugation with observation of pore cessation, bifurcation, bending and tapering. The unique formation of tapered pore was observed and described. Major factors deciding pore properties under curved surfaces were identified and discussed. We introduced a new parameter for surface quantification known as central inscribed angle, which was identified to be the central factor which decides pore growth behaviour under a curvature. Here, we observed a different trend in growth rate of pores under different curvatures, which oppose the commonly accepted convex > planar > concave pattern. Levelling height was later identified to be the decisive factor in determining growth rate of pores under a curvature at different geometrical location. These findings open up possibility to precisely control and tailor the growing path and pore structures of AAO simply via anodising an Al sheet under combined curvature surfaces, which could be beneficial for future novel applications.
Two-dimensional materials have attracted intensive attention recently due to their unique optical and electronic properties and their promising applications in water splitting and solar cells. As a representative layer-structured of transition metal dichalcogenides, MoS2has attracted considerable devotion owing to its exceptional photo and electro properties. Here, we show that the chemical vapour deposition (CVD) growth of MoS2on Si photocathode and graphene/Si photocathode can be used to prepare photoelectrocatalysts for water splitting. We explore a bottom-up method to grow vertical heterostructures of MoS2and graphene by using the two-step CVD. Graphene is first grown through ambient-pressure CVD on a Cu substrate and then transferred onto SiO2/Si substrate by using the chemical wet transfer followed by the second CVD method to grow MoS2over the graphene/SiO2/Si. The effect of the growth temperatures of MoS2is studied, and the optimum temperature is 800 °C. The MoS2produced at 800 °C has the highest photocurrent density at -0.23 mA cm-2in 0.5 M Na2SO4and -0.51 mA cm-2in 0.5 M H2SO4at -0.8 V vs. Ag/AgCl. The linear sweep voltammetry shows that MoS2in 0.5 M H2SO4has about 55% higher photocurrent density than MoS2in Na2SO4due to the higher protons (H+) in the H2SO4electrolyte solution, which are sufficiently charged to reduce to H2and, therefore hydrogen evolves more rapidly where the photocurrent density and hydrogen generation can be enhanced. MoS2/graphene/SiO2/Si (MGS) has -0.07 mA cm-2at -0.8 V vs. Ag/AgCl of photocurrent density, which is 70% lower than that of bare MoS2because MGS is thicker compared with MoS2. Thus, MoS2has potential as a photocatalyst in photoelectrochemical water splitting. The structure and the morphology of MoS2play an important role in determining the photocurrent performance.
The phytochemicals found inCaralluma pauciflorawere studied for their ability to reduce silver nitrate in order to synthesise silver nanoparticles (AgNPs) and characterise their size and crystal structure. Thunbergol, 1,1,6-trimethyl-3-methylene-2-(3,6,9,13-tetram, Methyl nonadecanoate, Methyl cis-13,16-Docosadienate, and (1R,4aR,5S)-5-[(E)-5-Hydroxy-3-methylpent were the major compounds identified in the methanol extract by gas chromatography-mass spectrum analysis. UV/Vis spectra, Fourier-transform infrared spectroscopy, x-ray diffraction, scanning electron microscope with Energy Dispersive Xâray Analysis (EDAX), Dynamic Light Scattering (DLS) particle size analyser and atomic force microscope (AfM) were used to characterise theCaralluma paucifloraplant extract-based AgNPs. The crystal structure and estimated size of the AgNPs ranged from 20.2 to 43 nm, according to the characterization data. The anti-cancer activity of silver nanoparticles (AgNPs) synthesised fromCaralluma paucifloraextract. The AgNPs inhibited more than 60% of the AGS cell lines and had an IC50 value of 10.9640.318 g, according to the findings. The cells were further examined using fluorescence microscopy, which revealed that the AgNPs triggered apoptosis in the cells. Furthermore, the researchers looked at the levels of reactive oxygen species (ROS) in cells treated with AgNPs and discovered that the existence of ROS was indicated by green fluorescence. Finally, apoptotic gene mRNA expression analysis revealed that three target proteins (AKT, mTOR, and pI3K) were downregulated following AgNP therapy. Overall, the findings imply that AgNPs synthesised from Caralluma pauciflora extract could be used to treat human gastric cancer.
Vertically standing MoS2 nanoflakes are favourable in applications such as energy storage devices, hydrogen evolution reactions, and gas sensors due to their large surface area and high density of exposed edges. In this work, we report the effect of Mo vapor concentration on the morphology of vertical MoS2 nanoflakes prepared by chemical vapor deposition at atmospheric pressure. A series of MoS2 samples were grown under different Mo vapor concentrations by varying the separation distance (x) between the MoO3 source and the substrate. Field emission scanning electron microscopy showed the sample grown at x = 1 cm had a high density of vertical flakes (7 vertical flakes µm-2) with an average flake length of ~770 nm and thickness of ~10 nm. As x increased to 4 cm, the average flake length was reduced to ~150 nm while the flake orientation changed from vertical to lateral. That is, high Mo vapor concentration favours the formation of large and vertical MoS2 nanoflakes. However, oversupply of Mo vapor results in significantly thicker flakes. Raman spectra of all samples showed two main peaks at 380 and 407 cm-1 that correspond to the E12g and A1g vibrational peaks of MoS2. As x decreased from 4 to 1, the peak intensity ratio (E12g/A1g) reduced from 0.58 to 0.42, suggesting greater dominance of vertical flakes at low x. X-ray diffraction data showed a prominent peak at 14.4°, which corresponded to the (002) diffraction peak of 2H MoS2. Transmission electron microscopy verified the flakes consist of eight layers with an interlayer spacing of 0.62 nm. Based on hydrogen evolution reaction measurements, samples with thin flakes have high catalytic activity. This work highlights the importance of optimizing Mo vapor concentration to obtain a high density of thin, large, and vertically standing MoS2 nanoflakes.
Different Ti substrates, such as particles (as-received and ball milled), plate and TEM grid were oxidized for the growth of one dimensional (1D) TiO2nanostructures. The Ti substrates were oxidized for 4 h at temperatures of 700 °C-750 °C in humid and dry Ar containing 5 ppm of O2. The effects of residual stress on the growth of 1D TiO2nanostructures were investigated. The residual stress inside the Ti particles was measured by XRD-sin2ψtechnique. The oxidized Ti substrates were characterized using field emission scanning electron microscope equipped with energy dispersive x-ray spectroscope, transmission electron microscope, x-ray diffractometer and x-ray photoelectron spectroscope. Results revealed that humid environment enhances the growth of 1D TiO2nanostructures. Four different types of 1D morphologies obtained during humid oxidation, e.g. stacked, ribbon, plateau and lamp-post shaped nanostructures. The presence of residual stress significantly enhances the density and coverage of 1D nanostructures. The as-grown TiO2nanostructures possess tetragonal rutile structure having length up to 10μm along the 〈1 0 1〉 directions. During initial stage of oxidation, a TiO2layer is formed on Ti substrate. Lower valence oxides (Ti3O5, Ti2O3and TiO) then form underneath the TiO2layer and induce stress at the interface of oxide layers. The induced stress plays significant role on the growth of 1D TiO2nanostructures. The induced stress is relaxed by creating new surfaces in the form of 1D TiO2nanostructures. A diffusion based model is proposed to explain the mechanism of 1D TiO2growth during humid oxidation of Ti. The 1D TiO2nanostructures and TiO2layer is formed by the interstitial diffusion of Ti4+ions to the surface and reacts with the surface adsorbed hydroxide ions (OH-). Lower valence oxides are formed at the metal-oxide interface by the reaction between diffused oxygen ions and Ti ions.
High porous ZnO nanoflakes were successfully prepared using microwave assisted hydrothermal method. The presence of aluminum changes the environment of preparation reaction which controlled the crystallographic orientation. The unique morphology and properties of ZnO nanoflakes may due to the effect of microwave irradiation and the ambient condition. The approach is very simple and rapid that grows around 3 μm ZnO within 30 minutes. The mechanism of the construction of unique ZnO nanoflakes growth using the present approach will be proposed. Hence, the prospective performance of ethanol vapor sensing for the rapid growth of ZnO porous nanostructures was investigated.