Hydrothermal Bath Research Articles

Controlling Oxygen Vacancy Content by Varying Calcination Temperature to Enhance the Gas Sensing Performance of BiVO4 Material

Compared to gas sensors based on single metal oxide, gas sensors based on binary metal oxide semiconductors (MOS) offer a rich variety of structural types and hold great potential for excellent selectivity. Inspired by this, we synthesized BiVO4 powder through a stepwise reaction combining calcination with hydrothermal bath and investigated the influence of different calcination temperatures on its gas sensitivity performance. Our study revealed that BiVO4-600 exhibited optimal TEA gas sensing behavior at 225 °C, showing high response values (Ra/Rg = 43.4) and fast response/recovery times (15 s/52 s). Additionally, the sensor displayed high stability, repeatability, and exceptional selectivity. Preliminary research indicates that calcination temperature induces changes in the oxygen vacancy content of BiVO4, thus affecting its sensing performance.

Water diffusion kinetics study at different hydrothermal bath temperatures and subsequent durability studies of CNT embedded fibrous polymeric composites: Roles of CNT content, functionalization and in‐situ testing temperature

AbstractAlthough structural polymers like epoxy are extensively used in marine applications over metallic structures, environmental water tends to ingress into this polymer which may affect its long‐term durability. The extent of degradation caused by the absorbed water on polymeric composite's mechanical properties depends on the water diffusion mechanism, environmental temperature and subsequent reversible and irreversible chemical restructuring of the polymer. In this study, hydrothermal conditioning behavior of glass fiber reinforced epoxy (GE) composites with varying (0.1, 0.3, and 0.5) wt.% of pristine and functionalized carbon nanotubes (CNTs and FCNTs) was studied at 15°C (Low‐Temperature Hydrothermal Conditioning (LTHC)) and 50°C (Elevated‐Temperature Hydrothermal Conditioning (ETHC)) water baths. The changes in chemical bonding characteristics and glass transition temperature of GE composite due to above mentioned factors have been studied by Fourier transformed infrared spectroscopy and differential scanning calorimetry. The gravimetric analysis was employed to monitor the water uptake kinetics of the composites and flexural strength of conditioned composites after 50 days of conditioning and saturation was study to understand the effect of water sorption. Experimental results revealed that, FCNTs greatly hinders the water absorption through the interfaces at LTHC, as the equilibrium water content of 0.1FCNT‐GE composite was ~9.5% and ~3.0% and Diffusion coefficient was ~60.0% and ~15.5% lower than the GE and 0.1CNT‐GE composites, respectively at LTHC. At LTHC, the water saturated 0.1FCNT‐GE composites exhibited superior flexural strength than GE and 0.1CNT‐GE composites. At ETHC, generation of hygroscopic stresses and unfavorable stresses at the weak CNT/polymer interface adversely affected the 0.1CNT‐GE composites water resistance compared to 0.1FCNT‐GE composites with stronger FCNT/polymer interface. The extent of recovery in the flexural strength was evaluated by complete desorption of water‐saturated specimens. Finally, a fractography study was conducted to understand the variation in the well‐being of the glass fiber/polymer and nanotube/polymer interface due to mentioned varying factors.

Impact of Cultivar, Processing and Storage on the Mycobiota of European Chestnut Fruits

Sweet chestnut fruits are popular fruits commercialized as fresh or processed ready-to-eat products. The major post-harvest problems associated with stored chestnut fruits are fungal rots, which cause major losses in fruit quality. The aims of this work were to determine the incidence, abundance and diversity of rots and fungi in three chestnut varieties (Longal, Judia and Martaínha) of Portugal, collected from an industrial plant, and to identify the stages of storage and processing where fungi and rots are more significant. Thirty-three chestnut samples from the three varieties were collected from different stages of industrial processing. Nuts were internally and externally inspected for damage, infestation and infection, and internal fungi were isolated and molecularly identified. The variety Martaínha was identified as the least susceptible to fungal growth, while Longal was the most susceptible. A high diversity of fungi was detected and identified. The dominant fungi were Mucor racemosus, Penicillium spp. (the causal agents of green rots), Ciboria batschiana (black rot) and Botrytis cinerea (gray rot). Gnomoniopsis smithogilvyi, the causal agent of brown rot, was also frequently detected. Sterilization with hydrothermal bath was effective in the elimination or reduction of most of the rot-causing fungi. These results could serve as a baseline for better monitoring fungal development and chestnut decay, and to develop effective management measures to control post-harvest chestnut rots.

Synthesis of epitaxial pentasodium trioxoundecafluoro-trititanate with plate-like morphology on fluorine-doped tin oxide coated glass substrates

A route for synthesis of epitaxial pentasodium trioxoundecafluoro-trititanate (Na5(Ti3O3F11)) with plate-like morphology on fluorine-doped tin oxide coated glass substrates (FTO- glass) using the hydrothermal bath method is described and discussed, followed by the presentation of a systematic study of the physical properties of the samples. The samples are textured with a small amount of micron sized crystals existing among predominantly plate like structures of Na5(Ti3O3F11). These structures are attached to the F:SnO2 (FTO) layer due to their nucleation and growth on the substrate surface during the hydrothermal process. Additionally, an epitaxial relationship between the fluorine doped SnO2 layer and plate-like (Na5(Ti3O3F11)) exists: an alignment of planes along (111). Last of all, a set of unidentified vibrational Raman modes recorded from Na5(Ti3O3F11) plates grown on fluorine-doped tin oxide is presented.

Acetamide-assisted hydrothermal growth of NiCo double hydroxide on graphene modified Ni foam for high-performance supercapacitor

The free-standing hierarchical flower-like NiCo-double hydroxide/reduced graphene oxide composite (NiCo-DH/RGO) on Ni foam (NiF) was synthesized with a facile two-step method. First, the growth of partially reduced graphene oxide (PRGO) membrane on NiF was achieved via the direct reduction of graphene oxide (GO) by NiF, which acted as not only the reducing agent but also the current collector. Then, the growth of high mass-loading NiCo-DH on PRGO/NiF was realized with a hydrothermal process, in which acetamide plays a crucial role. The high mass-loading of NiCo-DH is due to the addition of acetamide into the hydrothermal bath, in which PRGO reacted with the solution, containing Ni(II), Co(II), acetamide and urea, to form a thick gelatinous membrane on Ni foam. During the hydrothermal process, PRGO was further reduced to RGO while both Ni(II) and Co(II) reacted with ammonium, released by the hydrolysis of urea, to form NiCo-DH. Used as the positive electrode of supercapacitor, NiCo-DH/RGO/NiF displays an ultrahigh areal capacity of 6.15 C cm−2 at 10 mA cm−2 and 94.6% capacity retention after 1000 GCD cycles at 10 mA cm−2. An asymmetric supercapacitor (ASC) is also assembled with NiCo-DH/rGO/NiF as the positive electrode and activated carbon (AC) as the negative electrode. The ASC exhibits a prominent energy density of 61.81 Wh kg−1 at a high power density of 842.63 W kg−1. It is especially worth noting that the ASC exhibited remarkable capacity retention of 84.53% even after 1000 GCD cycles at a current density of 10 mA cm−2.

Etching of ZnO nanorods by ZnO nanoparticles and adjustment of morphological and UV photodetection properties

Zinc oxide nanorods (NRs) were successfully synthesized on the seeded substrate by low-temperature hydrothermal method. The effect of adding ZnO nanoparticles (NPs) to hydrothermal bath on the structural, morphological, and electrical properties of the resulting NRs was systematically investigated. The NRs diameter and length decrease with increasing amount of NPs added to hydrothermal solution thereby confirmed NPs efficiently able to etch ZnO NRs. XRD analysis revealed that all the ZnO NRs have the hexagonal wurtzite structure with a preferential orientation along the c-axis. The I–V measurement illustrated a remarkable increment in electrical resistance of ZnO NRs due to morphological changes in the etched NRs. Photoconducting properties of ultraviolet (UV) detectors based ZnO NRs were also evaluated. It was observed that sensitivity of photodetectors increases to value of ~2 × 104 in NRs etched with 0.03 g/L NPs concentration.

Study of Photocatalytic Properties of Ag/AgCl-Decorated Soybean Protein Knitting Fabric Against Acid Blue 260 Dye by Factorial Design

Photocatalytic materials have been the focus of several studies due to their excellent optical photoexcitation properties for waste treatment. However, their use promotes the generation of inorganic secondary waste, due to their nanometric grain size, which can cause several environmental hazards. The optimization and immobilization of such photocatalysts for treatment after the catalytic process have thus attracted much attention. In this work, Ag/AgCl nanoparticles were immobilized by hydrothermal treatment on soybean knitted fabric. The photocatalytic activity of the resulting Ag/AgCl-functionalized soybean knitted fabric was estimated based on the reduction of the concentration of Acid Blue 260 dye. The response surface factorial design methodology was applied, varying the Ag/AgCl concentration, nanocatalyst immobilization time, and hydrothermal process temperature, to analyze the individual effect of and interaction between the variables, besides establishing a mathematical model of the process. The photocatalytic results showed that addition of Ag/AgCl to the fabric favored its use and reuse for the degradation of the Acid Blue 260 dye. The mathematical model together with the response surfaces showed that the residence time in the hydrothermal bath was the most significant variable in terms of the dye reduction, favoring this advanced treatment method.

Raman spectroscopy characterisation of oriented bundles of single-crystal rutile-phase TiO2 nanorods prepared by hydrothermal bath deposition on transparent conducting substrates

Rutile-phase TiO2 rods prepared by hydrothermal bath deposition on F:SnO2 are in fact bundles of single-crystal TiO2 prismatic nanorods of ~ 4 nm diameter each. These bundles of rutile-phase TiO2 nanorods have tetragonal morphology and are strain-free (or the strain in all the samples is the same). Bundles of TiO2 that are oriented tetragonally with respect to the substrate’s surface, can be prepared for optimized growth times. It is observed that bundles of TiO2 nanorods act as single entities from the point of view of the Raman spectra (and thus lattice vibrations). Single prismatic nanorods of ~ 4 nm width, as observed via TEM, appear to act as “larger” crystals to the lattice phonons once stacked together to form large oriented bundles of TiO2. Hence, the phonon confinement effect cannot be observed because translational symmetry is preserved at the grain boundaries of the nanorods that make each TiO2 bundle. Moreover, an increase in the density of bundles growing preferentially in the [002] direction, perpendicular to the substrate surface, results in an unusual increase of room and low (77 K) temperature Raman band Eg/A1g intensity ratios.

Construction and electrochemical performances of the three-dimensional nano NiCo2O4

ABSTRACTBilayer NiCo2O4/NiCo2O4 nanosheet arrays on nickel foam (NF) are fabricated by a two-step solution-based method, which involves in hydrothermal process and chemical bath deposition. Compared with the monolayer NiCo2O4/NF electrode, the NiCo2O4/NiCo2O4/NF displays the unique micro-nanometer hierarchical and porours structure and has excellent pseudocapacitive behaviors in 6 M KOH, which exhibits high specific capacitances of 2363.64 F g−1 at a constant current density of 0.5 Ag−1, and 1454.55 F g−1 at the higher current density of 8 Ag−1, and shows a favourable cycling stability of 77.5% retention after 1000 cycles.

Joint synthesis of Zeolite A-LDH from mineral industry waste

Abstract This study evaluated the use of waste from the copper concentration process and kaolin processing for the combined synthesis of Zeolite A and layered double hydroxide (LDH). The synthesis occurred in two stages: synthesis of LDH by coprecipitation and submersion in a hydrothermal bath and then the addition of metakaolin for the synthesis of Zeolite A. The synthesized ZA-LDH sample was characterized by X-ray diffraction (XRD), scanning electron microscopy coupled with X-ray energy dispersive spectroscopy (SEM-EDS), N2 physisorption and point of zero charge (PZC). X-ray diffraction detected phases of high structural order, quantified by the Rietveld method in 90.57 Zeolite A, 9.21 pyroaurite and 0.22 anatase (% mass). In adsorption tests, the ZA-LDH showed greater efficiency in dye removal than commercial zeolite.

Hydrothermal synthesis of nanostructured Cr-doped hematite with enhanced photoelectrochemical activity

Using the easily applicable hydrothermal method Cr-doped hematite thin films have been deposited polycrystalline on conductive glass substrates. The hydrothermal bath consisted of an aqueous solution containing a mixture of FeCl3·6H2O and NaNO3 at pH = 1.5. The samples were introduced in an autoclave and heated for a fixed time at a fixed temperature and then annealed in air at 550 °C. The concentration of the incorporated Cr atoms (Cr4+ ions) was controlled by varying the concentration of the Cr(ClO4)3 precursor solution, varied from 0% to 20%. All samples followed morphological and structural studies using field-emission scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction. Chronoamperometry measurements showed that Cr-doped hematite films exhibited higher photoelectrochemical activity than the undoped films. The maximum photocurrent density and incident photon conversion efficiencies (IPCE) were obtained for 16 at.% Cr-doped films. This high photoactivity can be attributed to both the large active surface area and increased donor density caused by Cr-doping in the α-Fe2O3 films. All samples reached their best IPCE at 400 nm. IPCE values for 16 at.% Cr-doped hematite films were thirty times higher than that of undoped samples. This high photoelectrochemical performance of Cr-doped hematite films is mainly attributed to an improvement in charge carrier properties.

Comparative study on the photocatalytic properties of Ag3PO4 fabricated by different methods

A comparative study was carried out on the photocatalytic properties depending on Jodifferent morphologies of Ag3PO4 fabricated by different methods, i.e. as precipitated, oil bath heat treatment, hydrothermal, and microwave-assisted hydrothermal. The crystal structures of the prepared samples were analyzed by X-ray diffraction. The different morphologies of Ag3PO4 synthesized by different methods were observed from SEM micrographs. The micrographs show that the as-precipitated Ag3PO4 sample has smaller grain morphology whereas samples synthesized by other methods have distinct large-grain morphologies. Sharp-edged rhombic dodecahedron, cubic and polyhedral Ag3PO4 crystals were observed that were synthesized by microwave-assisted hydrothermal and hydrothermal methods. However, sharp-edged polyhedral Ag3PO4 crystals were not observed from the oil bath heat-treatment method. The optical properties of the different samples were measured by using UV–Vis diffuse reflectance spectroscopy. The samples fabricated by the microwave-assisted hydrothermal process showed better photocatalytic decoloring of methylene blue than those prepared by the hydrothermal and oil bath heat-treatment methods.

Effects of Chromium Dopant on Ultraviolet Photoresponsivity of ZnO Nanorods

Structural and optical properties of bare ZnO nanorods, ZnO-encapsulated ZnO nanorods, and Cr-doped ZnO-encapsulated ZnO nanorods have been investigated. Encapsulated ZnO nanorods were grown using a simple two-stage method in which ZnO nanorods were first grown on a glass substrate directly from a hydrothermal bath, then encapsulated with a thin layer of Cr-doped ZnO by dip coating. Comparative study of x-ray diffraction patterns showed that Cr was successfully incorporated into the shell layer of ZnO nanorods. Moreover, energy-dispersive x-ray spectroscopy confirmed presence of Cr in this sample. It was observed that the thickness of the shell layer around the core of the ZnO nanorods was at least about 20 nm. Transmission electron microscopy of bare ZnO nanorods revealed single-crystalline structure. Based on optical results, both the encapsulation process and addition of Cr dopant decreased the optical bandgap of the samples. Indeed, the optical bandgap values of Cr-doped ZnO-encapsulated ZnO nanorods, ZnO-encapsulated ZnO nanorods, and bare ZnO nanorods were 2.89 eV, 3.15 eV, and 3.34 eV, respectively. The ultraviolet (UV) parameters demonstrated that incorporation of Cr dopant into the shell layer of ZnO nanorods considerably facilitated formation and transportation of photogenerated carriers, optimizing their performance as a practical UV detector. As a result, the photocurrent of the Cr-doped ZnO-encapsulated ZnO nanorods was the highest (0.6 mA), compared with ZnO-encapsulated ZnO nanorods and bare ZnO nanorods (0.21 mA and 0.06 mA, respectively).

Nitrogen-Doped Carbon Cloth for Supercapacitors Prepared via a Hydrothermal Process

This paper reports a facile means of fabricating nitrogen-doped carbon cloth (CC) via a hydrothermal process in the presence of hydrazine and ammonia. The resulting N-doped CC can be used directly as an electrode for a supercapacitor, requiring no polymeric binder or current collector. X-ray photoelectron spectroscopy (XPS) revealed that the surface of oxidized CC was nitrogen-doped concurrently with reduction; in other words, the oxygen-containing groups were replaced with nitrogen species of different types depending on the composition and temperature of the hydrothermal bath. The highest areal capacitance was estimated to be 136 mF cm−2 at a current density of 0.5 mA cm−2 for a N-doped CC electrode treated at 160°C, while the capacitance remained at 81% of its original value when the applied current density was increased from 0.5 to 15 mA cm−2. We explored the role of different nitrogen species in the capacitive process based on a combination of XPS and electrochemical measurements. High hydrothermal temperatures and the presence of NH3 yielded pyridinic nitrogen atoms, leading to fast electron transfer during charge/discharge cycles.

Photocatalytic Activity of One-Pot Synthesized Reduced Graphene Oxide – Zinc Oxide Nanocomposites

In this research, reduced graphene oxide/zinc oxide nanocomposites (rGO/ZnO) were synthesized at different pHs (9, 10, 11 and 12) by using one-pot hydrothermal bath method., The obtained nanocomposites characterized by using X-ray diffractometer, Fourier transform infrared, Raman, scanning electronic microscope and diffuse reflection spectroscopy techniques. Photocatalytic activity of nanocomposites were evaluated by monitoring the photodegradation of 4-nitrophenol (4-NP) in water exposed to ultraviolet and visible light irradiation. The morphological and structural results have been shown that at pHs of 9 and 10, the ZnO nearly aggregated nanoparticle are crystalized, while at higher pHs (11 and 12), the preferential growth of ZnO in the form of nanorods is seen. Comparative studies on photocatalytic performance of the nanocomposites shows that ZnO nanorods have better photocatalytic activities than the others.

Hydrothermally Synthesized CuO Powders for Photocatalytic Inactivation of Bacteria

Various morphologies of monoclinic CuO powders were synthesized by hydrothermal treatment of copper nitrate, copper acetate or copper sulfate. The synthesized samples were characterized by scanning electron microscopy, X-ray di ractometry, the Fourier transform infrared spectroscopy, and di use re ectance spectrophotometry. Antibacterial activity of the samples was studied against Escherichia coli bacteria in dark and under visible light irradiation. Although the di erent precursors yielded the same band gap energies (≈1.6 eV) for the synthesized CuO samples, they resulted in various morphologies (hierarchy of stabilized micro/nanostructures), speci c surface areas, concentrations of OH-surface groups, and visible light photocatalytic performances. The CuO nanorods synthesized from nitrate hydrothermal bath not only exhibited a considerable e ective surface area, but also showed the highest concentration of absorbed OH-groups and subsequently, the strongest (photo)catalytic antibacterial properties (≈37 and 94% inactivation of the bacteria in dark and under visible light irradiation, respectively).

Investigating on photocatalytic performance of CuO micro and nanostructures prepared by different precursors

In this paper, various morphologies of copper oxide (CuO) were synthesized from acetate, sulfate, and nitrate precursors using hydrothermal bath method. The photoluminescence spectra revealed that CuO-Ni sample contains the strongest surface defect peak which can be related to its highest active surface area. The Fourier transform infrared (FT-IR) results showed that the concentration of the surface OH− group on the samples varies considerably according to CuO-Ac > CuO-Ni > CuO-Su. From structural results, it could be observed that all the samples crystallized into a monoclinic crystal structure. The photocatalytic activity of CuO samples was evaluated by the catalytic oxidation of methylene blue in the presence of hydrogen peroxide. Concerning the nearly same optical band gap for the samples, the best photocatalytic performance of CuO-Ni nanorods was assigned to its highest active surface area and surface hydroxyl groups.

Absorption kinetics and swelling stresses in hydrothermally aged epoxies investigated by photoelastic image analysis

The present work proposes an experimental optical methodology able to measure the transient swelling stresses induced by the water uptake ageing of polymers. In particular, the work describes the implementation of a Photoelastic technique to quantify internal stresses arising during the hydrothermal ageing of cast epoxy samples. The material investigated is a model DGEBA/DDS epoxy system. Curing and post-curing cycles have been optimised in order to obtain a fully cured, high Tg, and completely stress free initial condition. Rectangular beam samples were then left in a hydrothermal bath at 90 °C, and regularly monitored by gravimetric and photoelastic analyses. The quantitative evolution of stresses induced by water ingress was obtained by a Photoelastic Stress Analysis technique applied during water absorption, and successive desorption in controlled conditions. The evolution of stresses is correlated with gravimetric data, allowing to gain a new insight to investigate the complex swelling and diffusion kinetics of water ingress into thermoset polymer networks.

Effect of Zinc Nitrate Concentration on Formation of AuNPs by Sacrificial Templated Growth Hydrothermal Approach and its Properties in Organic Memory Device

This paper describes a novel fabrication technique to grow gold nanoparticles (AuNPs) by using the sacrificial templated growth hydrothermal reaction approach. The effect of zinc nitrate Zn (NO3)2 concentration in the hydrothermal reaction on the formation of AuNPs was studied by varying the concentration from 0.01 M, 0.05 M, 0.1 M and 0.2 M. The increase of Zn (NO3)2 concentration lead to formation of smaller size and lower area density of AuNPs. XRD analysis proved the formation of AuNPs by using this approach. From scanning electron microscope images, the sample with 0.1M of Zn (NO3)2 concentration showed better AuNPs distribution. In order to investigate the memory properties of AuNPs embedded in organic insulator, polymethylsilsesquioxane (PMSSQ) was spin coated as insulator layer between the AuNPs. I-V and C-V characteristics showed hysteresis properties that indicated charge storage capability of AuNPs embedded organic insulator. AuNPs grown on 300°C annealed ZnO template in 0.1M of Zn (NO3)2 hydrothermal bath produced the best memory properties whereby 54 of electron charges has been stored per AuNPs in C-V measurement.

P-Type dye-sensitized solar cell based on nickel oxide photocathode with or without Li doping

Abstract Nickel oxide (NiO) nanostructures are synthesized using a microwave-assisted hydrothermal method. The hydrothermal bath has a solution of nickel salt mixed with precipitating agent. During the synthesis the microwave temperature, the concentration of nickel salt and precipitating agent along with the pH of the reaction solutions are changed and different morphologies of nickel oxide are obtained. The resulting nickel oxide nanostructures are characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller method and X-ray photoelectron spectroscopy. Thus formed NiO has been used as a photocathode in dye-sensitized solar cell. Lithium doped NiO showed better IPCE as well as solar to electrical conversion efficiency than the undoped NiO.