Hydrothermal Growth Method Research Articles

Studying the Effect of Seed-layers of Zinc Oxide Nanostructured Thin Film for Liquefied Petroleum Gas Sensor Application

Gas sensors are devices that can convert the concentration of an analyte gas into an electronic signal. Zinc oxide (ZnO) is one of the most important n-type metal oxide semiconductor which has been utilized as gas sensor for many years. In this work, ZnO nanostructured films were synthesized by a hydrothermal growth from ZnO seeds and used as a liquefied petroleum gas (LPG) sensor. At first ZnO seed layers were deposited on glass substrates by using spin coating method, then ZnO nanostructured were grown on these substrates by using hydrothermal growth method. The effect of seed layers of ZnO nanostructured on its structural, optical, and electrical properties was studied. These nanostructures were characterized by scanning electron microscopy, X-ray diffraction, optical spectroscopy, and sheet resistance measurement unit. The sensing performances of the synthetic ZnO nanostructures were investigated for LPG. XRD showed that all the ZnO nanostructures were hexagonal crystal structure. ZnO nanostructured thin film showed high sensitivity towards LPG gas. The sensitivity of the film is observed to increase with increase in number of seed layers. The sensitivity of the film was investigated by measured change in sheet resistance under with LPG gas.

Influence of the synthesis method on preferential clustering of Yb3+ in CaF2:Yb3+/Er3+ upconverting nanoparticles

Yb3+/Er3+ co-doped CaF2 upconverting nanoparticles have been synthesized by three preparation methods. Their 12 K absorption measurements exhibit signatures of preferentially formed Yb3+ clusters as the predominant centres along with a single ion cubic (Oh) centre. By changing the synthesis method from decomposition to co-precipitation and finally to hydrothermal, the ratio between negatively charged clusters and non-locally charge-compensated cubic centres decreases becoming similar to that in bulk crystals. For nanoparticles prepared by co-precipitation and decomposition the Er3+ 4S3/2,4F9/2 → 4I15/2 luminescence measured monitoring the heterogeneous Yb–Er cluster centres is insensitive to the excitation wavelength, giving a similar intensity when excited at around 10,204 cm−1 (980 nm) and 10,250 cm−1 (975 nm). However, for nanoparticles prepared by a hydrothermal growth method the intensity when excited at 10,250 cm−1 (975 nm), coinciding with the absorption maximum, is twice the yield when excited at 10,204 cm−1 (980 nm). By varying the optimum excitation wavelength and growth method, a factor of 102 times enhancement of the upconversion luminescence is achieved.

Cu2O/Ti3C2MXene heterojunction photocatalysts for improved CO2 photocatalytic reduction performance

Photocatalytic CO2 reduction has been viewed as a promising approach to relieve the energy crisis and green-house effect. Cheap and high performance cocatalyst is an effective approach to enhance the photocatalytic activity. Ti3C2Tx (MXene) is a new family of 2D layered materials, which can be served as an electron conductor. In this work, Cu2O/Ti3C2Tx heterojunction composites were prepared by in situ hydrothermal growth method. Cu2O/Ti3C2Tx with the different percentages of ultrathin Ti3C2Tx (2, 5, 10, 20 and 30 mg) nanosheet in the heterostructured catalysts are noted as CuTi-X (X = 2, 5, 10, 20, 30). As prepared CuTi-10 exhibits the highest photocatalytic CO2 reaction activity (17.55 μmol·g−1·h−1 for CO and 0.96 μmol·h−1·g−1 for CH4), which is 3.1 and 4.0 times higher than that of pure Cu2O (5.73 μmol·g−1·h−1 for CO and 0.24 μmol·g−1·h−1 for CH4, respectively). The advantage of the in situ growth endows the Cu2O/Ti3C2Tx heterojunction contact interface, which is conductive to the separation of photogenerated electrons-hole pairs. The main reason is analysed and can be attributed to that Ti3C2Tx can served as an electron acceptor due to its excellent conductive properties, rendering that more photo generated electrons attend the CO2 reduction reaction. This provides a strategy to construct the Cu2O/Ti3C2Tx heterojunction for photocatalytic CO2 reduction.

Ordered Self-supporting NiV LDHs@P-Nickel foam Nano-array as High-Performance supercapacitor electrode

Transition metal layered double hydroxides (LDHs) with amazing theoretical capacitance have caused remarkable interest as a potential supercapacitor electrode materials. However, the exerted low performance limits their further application. Nano-engineering technology was considered to be an effective strategy to further expose the pseudocapacitive properties of materials. Here, an ordered NiV LDHs@P-NF nanoarray was successfully constructed via phosphorized pretreatment and hydrothermal growth method. The as prepared NiV LDHs@P-NF electrode delivers an areal capacitance of 2.85 F cm−2 at the current density of 20 mA cm−2 and rarely decrease capacitance after over 5000 cycles at 50 mA cm−2. Furthermore, the asymmetric supercapacitor assembled with prepared NiV LDHs@P-NF as the positive electrode and activated carbon as the negative electrode was found to show a maximum energy density of 0.202 mWh cm−2 under a power density of 7.022 mW cm−2. This work suggests that the NiV LDHs@P-NF nano-arrays electrode can be regard as the remarkable candidate to improve the performance of the asymmetric supercapacitor.

Facile synthesis of defect-rich ultrathin NiCo-LDHs, NiMn-LDHs and NiCoMn-LDHs nanosheets on Ni foam for enhanced oxygen evolution reaction performance

Layered double hydroxides (LDHs) containing transition metals with unsaturated d-bands are ideal candidates for oxygen evolution reaction (OER). However, the bulk layers and congested interlayers block the active sites and avoid the electrolyte access to the internal space. In this work, we report a simple coprecipitation coupled with the hydrothermal method for the direct growth of bimetallic NiCo-LDHs (5.01 nm), NiMn-LDHs (3.45 nm) and trimetallic NiCoMn-LDHs nanosheets (1.26 nm) on Ni foam and these fabricated electrodes exhibit the superior performance for OER. Notably, the NiCoMn-LDHs nanosheets exhibit the lowest overpotential of 290 mV at 20 mA cm−2 and the smallest Tafel slope of 87 mV dec−1, reducing by 20–40 mV and 31–39 mV dec−1 in comparison with those of bimetallic NiCo-LDHs (310 mV, 118 mV dec−1) and NiMn-LDHs (330 mV, 126 mV dec−1). This excellent performance is attributed to the 2D structure of the nanosheets and an abundance of exposed active sites, especially oxygen vacancies. Additionally, NiCoMn-LDHs nanosheets exhibit the smallest charge transfer resistance (Rct) of 6.3 Ω and the largest electrochemical double layer capacitance (Cdl) of 5.52 mF cm−2 than those of the bimetallic NiCo-LDHs (11.0 Ω, 4.85 mF cm−2) and NiMn-LDHs (30.6 Ω, 3.00 mF cm−2). Furthermore, NiCoMn-LDHs nanosheets maintain good durability over 10 h and cyclic stability without distinct change. This work offers a facile strategy to design various types of bimetallic and trimetallic LDHs boosting for OER process.

Fabrication of Ag3PO4/TiO2@molecular sieve (MS) ternary composites with remarkably enhanced visible light-responded photocatalytic activity and mechanism insight

In this study, Ag3PO4/TiO2@molecular sieve (MS) ternary composites were fabricated via in-situ deposition and hydrothermal growth method for photocatalytic degradation of formaldehyde and sodium isobutyl xanthate (SIBX) under visible light irradiation. XRD, PL, UV–vis, UPS, SEM-EDS and XPS techniques were adopted to characterize the composite. The results show that the MS material was indexed as zeolite P and Ag3PO4–TiO2 hybrid structure could improve the absorption of visible light and greatly inhibit the recombination of photogenerated charge carriers by introducing 3 times TiO2. After evaluating the photocatalytic activity and kinetics model, it is found that photocatalytic activity is consistent with the apparent first-order kinetic model. The Ag3PO4/TiO2-3@MS ternary composite under visible light irradiation appears the highest removal rate with 97.9% of formaldehyde and 96.7% of SIBX, respectively. Furthermore, the reusability of the photocatalyst was investigated by successive reuse. After five reuses, the removal rates reached 97.3% and 94.6% within 105 min for formaldehyde and SIBX, respectively. At last, the proposed mechanism of the photocatalytic reaction and the degradation routes of formaldehyde and SIBX were systematically discussed.

An innovative approach to deposit ultrathin ZnO nanoflakes (2D) through hydrothermal assisted electrochemical discharge deposition and growth method

The functionality and structural properties of nanomaterials significantly depend on the synthesis method. This work explored a novel fast route to deposit ultrathin zinc oxide (ZnO) nanoflakes on a conical microprobe tip by combining the effect of hydrothermal, electrochemical, and electro-discharge deposition process. The experimental results indicate the formation of ZnO nanoflakes and show the variance of thickness (min≤10 nm)/morphologies at different electrochemical parameters. The impact of varying voltage potential and concentration was analyzed and discussed. A hydrothermally prepared precursor solution of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and hexamine ((CH2)6N4) was used as a growth solution. The crystallinity and phase purity were analyzed by XRD. The functional groups, molecular fingerprints, were recognized by FTIR. Further, the bandgap energy (3.262eV) was estimated by Mott-Davis relation in UV–Vis spectroscopy via Tauc plot.

Hierarchical flower-like zinc oxide nanosheets in-situ growth on three-dimensional ferrocene-functionalized graphene framework for sensitive determination of epinephrine and its oxidation derivative

Epinephrine (EP) is a significant neurotransmitter, energizes and maintains the various body systems and plays a pivotal role in the response to stressful conditions of blood pressure and blood sugar level. Herein, a novel epinephrine sensor based on the hierarchical flower-like zinc oxide nanosheets (flower-like ZnO) embedded into three-dimensional ferrocene-functionalized graphene framework (3D graphene@Fc) was successfully prepared, using a facile route of one-pot in situ hydrothermal growth method. Benefiting from the unique structural advantages, meanwhile integrated with synergistic effect of components, the flower-like ZnO/3D graphene@Fc exhibits excellent sensing performance for epinephrine with a wide linear range of 0.02 to 216 μM, a low detection limit of 0.0093 μM, high anti-interference and good cyclic stability. Interestingly, it is unexpectedly found that the flower-like ZnO/3D graphene@Fc has sensing ability for EP’s oxidized derivative (QA) during the oxidation process of EP, along with a linear range of 0.192 to 527 μM and a detection limit of 0.1 μM for QA. More importantly, acceptable recovery obtained from the real sample test, confirming the feasibility of this biosensor for practical application.

Carbon inserted defect-rich MoS2−X nanosheets@CdSnanospheres for efficient photocatalytic hydrogen evolution under visible light irradiation

Carbon -MoS2−x@CdS (C-MoS2−x@CdS) core-shell nanostructures with controlled surface sulfur (S) vacancies were prepared via a glucose assisted hydrothermal growth method. The glucose acted as a reducing agent of C-MoS2−X to partially reduce Mo4+ ions to Mo3+ and served as a carbon source to insert the amorphous carbon into the layered MoS2−X simultaneously. The presence of Mo3+ result in the surface S-vacancies, which can provide more additional active sites and enhance the photocatalytic performance. Moreover, the inserted carbon in layered MoS2−X enhanced the electron mobility and decreased the resistance electron transfer. Density functional theory (DFT) calculation confirmed that the surface S-vacancies and the amorphous carbon increase the projected density of states at the conduct band edge, which could enhance the photo-absorption and photo-responsibility. The result is consistent with the photocatalytic H2 production experiment. C2-10%MoS2−x@CdS presented a high H2 evolution rate of 61,494 μmol h−1 g−1 under visible light irrigation (λ ≥ 420 nm), which is 1.98 times and 158 times higher than that of sample without S-vacancies (10%MoS2@CdS) and pure CdS, respectively.

Enhanced photocatalytic activity of ZnO nanorods by surface treatment with HAuCl4: Synergic effects through an electron scavenging, plasmon resonance and surface hydroxylation

In this research, we demonstrate an enhanced photocatalytic activity (PA) of ZnOR/Au composites compared to PA of plain ZnOR structures. The ZnOR were produced by a hydrothermal growth method and the surface treatment of the ZnOR crystals was carried out with HAuCl4 using a spin coating technique. In this study, methyl orange was chosen to evaluate the photocatalytic activity of the ZnOR and ZnOR/Au. The highest degradation efficiency of MO was achieved with ZnOR/Au layers. The XPS and wettability measurements have confirmed the increase in the amount of hydroxyl groups on the surface of the ZnOR/Au. Taking into account the physical and chemical characterizations of the samples, the enhanced photocatalytic activity of the ZnOR/Au composites has been attributed to the three main issues 1) an effective charge carries separation due to proper ZnO and Au bands alignment where the gold acts as an electron scavenger, 2) surface plasmon resonance from Au nanoparticles 3) increase of the hydroxylation of the ZnOR crystals surface after HAuCl4 interaction with ZnOR surface.

Nano-Flower Structure of Indium and Gallium doped Zinc Oxide Powder

Flower-like zinc oxide nanostructures have been successfully fabricated by various methods such as chemical vapor deposition, vapor phase transport deposition, thermal evaporation, hydrothermal, sol-gel and template growth methods. Zinc oxide doped with indium and gallium can demonstrate the potential utilization in electronic application for its semiconductor characteristic and the nanostructure of this doped material can enhance its property. In this study, indium and gallium doped zinc oxide nano-structures were prepared by ease method of hydrothermal process, which can well control the morphologies of zinc oxide nanostructure. The concentration percentage of dopants including indium and gallium were varied up to the limitation of synthesis. The dependence on doping content of indium and gallium on the particle morphologies and specific surface area of the samples was investigated systematically. The atomic arrangement and surface properties of synthesized samples were studied according to the measured results obtained by x-ray diffraction, x-ray photoelectron spectroscopy, field emission scanning electron microscope and Brunauer-Emmett-Teller measurement. According to the results, the obtained sample nanostructures are in the size of hundred nanometers with the shape in sheet-like and/or needle-like flower structures. However, the nano-flower structure is found to be disappeared beyond some specific high percentage of the dopant above 15%. The amount of doped indium and gallium are also found in XPS measurement and the substitution of doped atoms in zinc oxide crystal system are also showed in XRD investigation.

Experimental Investigations on the Thermal Diffusion Characteristics and Photoluminescence in Multiphase Micro Fluids Containing ZnO Micro Tubes and Fluorescein Dye-=SUP=-*-=/SUP=-

Scattering of light by disordered structures is normally detrimental to their applicability in many optoelectronic devices. However, some micro and nanostructures are useful in enhancing several optical and thermal properties like emission, heat diffusion etc. For this purpose, we have optimized the low temperature hydrothermal growth method for the ZnO micro tubes which leads to the growth of ZnO as mono dispersed micro tubes. Further, these samples were used to enhance the fluorescence efficiency of disordered media consisting of micro tubes of ZnO and fluorescein dye and to optimize the thermal diffusion of the mixture which will help us optimize the composition of these microscopic inclusions in designing a random lasing medium. Dual beam thermal lens method was used for this purpose. Keywords: thermal lens, thermal fluidics, thermal diffusivity, ZnO micro tubes, fluorescein.

In situ hydrothermal fabrication of visible light-driven g-C3N4/SrTiO3 composite for photocatalytic degradation of TC.

A series of g-C3N4/SrTiO3 (CN/SrTiO3) composites with the different mass ratio of g-C3N4 were prepared by facile in situ hydrothermal growth method, which was utilized to degrade tetracycline antibiotics (TC) under the visible light. The obtained samples were characterized by XRD, SEM, XPS, FT-IR, and UV-vis DRS. The photocatalytic performance was also investigated in detail. The obtained 20% CN/SrTiO3 composite is sixfold of the pure SrTiO3 and twofold of the pristine g-C3N4 under the visible light irradiation. This impressive performance of the heterojunction is ascribed to the effective restraint of the charge carrier recombination and expanded light absorption region. Moreover, the stability of the composite is also researched in detail. At last, a possible photocatalytic mechanism and charge carrier transfer pathway were further discussed.

Electric-field assisted growth and mechanical bactericidal performance of ZnO nanoarrays with gradient morphologies

Abstract In response to the widespread bacterial threat, mechanical bactericidal nanostructures with various morphologies have been reported for years. However, the relationship between morphology and bactericidal properties is still yet to be elucidated due to the lack of a fair comparison under similar density of the nanostructures. For this purpose, an electrical-field assisted hydrothermal growth method were utilized to prepare the ZnO nanoarrays with similar array density (1.9×109 rod·cm2-2.4 ×109 rod·cm2) but gradient morphologies from hexagonal prism, hexagonal prismoid to hexagonal pyramid on stainless steel sheets. Moreover, in dark condition, a bactericidal activity was observed on the ZnO nanoarray surfaces within 30 min contact for both E. coli and S. aureus cells. The bactericidal rate was rapidly enhanced as the average tip width of the nanorods decreasing from 137 to 38 nm. These results suggest that the hexagonal pyramid ZnO nanoarrays have a rapid, efficient and broad-spectrum bactericidal activity, which could contribute to the next-generation aquatic pathogens control strategies.

Ordering and disordering of in situ grown MgAl-layered double hydroxide and its effect on the structural and corrosion resistance properties

A MgAl-layered double hydroxide (MgAl-LDH) protective film was developed on AA6082 substrates via the in situ hydrothermal growth method to obtain a distinct cauliflower-like LDH structure, and coated substrates were further heat-treated in air at temperatures from 100 to 250°C to further improve the corrosion resistance of MgAl-LDH by taking advantage of the LDH memory effect; also, the effect of calcination on MgAl-LDH structural stability and the corresponding corrosion resistance properties were investigated. The structural characterization of uncalcined and calcined LDH films were examined using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, and Fourier transform infrared spectroscopy. The corresponding corrosion protection efficiency of the developed coating was studied through potentiodynamic polarization experiments and by electrochemical impedance spectroscopy. Compared with uncalcined MgAl-LDH, the calcined film showed a relatively lower corrosion current density and a higher impedance value, especially after heat treatment at 250°C. The findings demonstrate that calcination strongly affects the oriented growth of the LDH and causes an increase in the surface area and contraction of the basal spacing, which in turn caused a compact structure that substantially influenced the LDH corrosion resistance properties.

Alternating Current‐Driven Oxide Powder Electroluminescent Device Employing Vertically Aligned ZnO Nanowire Array

A novel type of AC‐driven oxide powder electroluminescent (EL) device is demonstrated. The device is based on stable heterogeneous junctions between Mn2+‐activated zinc germanate (Zn2GeO4:Mn) oxide phosphor and a vertically aligned ZnO nanowire array. The ZnO nanowire array is synthesized on an ITO‐coated glass substrate via a hydrothermal growth method. A stable phosphor–nanowire junction is formed by simple drop‐coating of a Zn2GeO4:Mn oxide phosphor suspension on the nanowire layer followed by annealing at 400 °C for 3 h. Bright green light (≈20 cd m−2) with a wavelength of 535 nm from the as‐fabricated EL device is observed, and the as‐fabricated device shows excellent stability in air, maintaining a brightness of ≈10 cd m−2 for 15 days with less than 2.5% intensity loss. The electroluminescence emission mechanism is discussed in detail. This new and facile strategy to build an oxide powder EL device can enable cost‐effective, highly stable, and energy‐efficient devices for lighting or display applications.

Enhanced visible-light photoelectrochemical performance via chemical vapor deposition of Fe2O3 on a WO3 film to form a heterojunction

A heterojunction photoanode of Fe2O3 loaded on a WO3 film on a fluorine-doped tin oxide substrate (FTO-WO3/Fe2O3) was prepared via a simple hydrothermal and chemical vapor deposition (CVD) growth method. The photoanode showed higher photoelectrochemical (PEC) water-splitting activity than that of the pristine FTO-WO3 under simulated sunlight because of the synergistic effect of Fe2O3 and WO3. The as-synthesized material was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The photocurrent density was estimated by linear sweep voltammetry and further confirmed using intensity-modulated photocurrent spectra. Experiments demonstrated that the coated Fe2O3 enhanced the separation and migration efficiencies of the photoinduced electrons and holes, improving the PEC water-splitting properties. The FTO-WO3/Fe2O3 photoanode showed a 1.25 times enhancement in photocurrent density compared with FTO-WO3. This result suggests that facile chemical vapor deposition growth is an effective way to fabricate heterojunctions and improve the properties of WO3 photoanodes for PEC water-splitting applications.

Synthesis of zeolite SSZ-13 from coal gangue via ultrasonic pretreatment combined with hydrothermal growth method.

SSZ-13 zeolite has been widely used in catalysis and adsorption because of good hydrothermal stability and pore structure. However, long crystallization time is the main challenge limiting its industry application. As increased emissions and ineffective treatment, coal gangue not only occupies land, but also pollutes the waterbody and farmland. Using coal gangue as raw material to synthetize zeolite has been considered as an environmentally friendly and effective alternative to solve the issues of accumulation and pollution, which also improves the added value of coal gangue. The ultrasonic assistance has been proven to be one of the potential pretreatment methods to promote the dissolution of crystalline silicon aluminum and reduce the crystallization time of molecular sieve. In this work, SSZ-13 was synthesized by coal gangue via ultrasonic pretreatment combined with hydrothermal growth method. The ultrasonic frequency and power were 20 kHz and 120 W, respectively. The synthesized samples were characterized by XRD, SEM, EDS, BET. The results showed that the crystallization time was shorten to 18 h, which was about 12 h lower than the same conditions of conventional chemicals synthesis. Furthermore, the specific surface area of the synthesized sample was more than 620 m2/g, which also indicated over 95% NOx conversion across a broad range from 180 to 400 °C and over 94% NOx conversion at 200-400 °C after hydrothermal treatment 6 h. This study provides a reference for the environmentally friendly utilization of coal gangue and the low-cost rapid synthesis and application of SSZ-13.

All‐Solid‐State Asymmetric Supercapacitors with Metal Selenides Electrodes and Ionic Conductive Composites Electrolytes

AbstractAll‐solid‐state flexible asymmetric supercapacitors (ASCs) are developed by utilization of graphene nanoribbon (GNR)/Co0.85Se composites as the positive electrode, GNR/Bi2Se3 composites as the negative electrode, and polymer‐grafted‐graphene oxide membranes as solid‐state electrolytes. Both GNR/Co0.85Se and GNR/Bi2Se3 composite electrodes are developed by a facile one‐step hydrothermal growth method from graphene oxide nanoribbons as the nucleation framework. The GNR/Co0.85Se composite electrode exhibits a specific capacity of 76.4 mAh g−1 at a current density of 1 A g−1 and the GNR/Bi2Se3 composite electrode exhibits a specific capacity of 100.2 mAh g−1 at a current density of 0.5 A g−1. Moreover, the stretchable membrane solid‐state electrolytes exhibit superior ionic conductivity of 108.7 mS cm−1. As a result, the flexible ASCs demonstrate an operating voltage of 1.6 V, an energy density of 30.9 Wh kg−1 at the power density of 559 W kg−1, and excellent cycling stability with 89% capacitance retention after 5000 cycles. All these results demonstrate that this study provides a simple, scalable, and efficient approach to fabricate high performance flexible all‐solid‐state ASCs for energy storage.

Three-Dimensional Hierarchically Ternary Iron Tungsten Nitride Nanosheets with Slight Ratio of Nickel Modulation for Oxygen Evolution Reaction

Practical application of oxygen evolution reaction (OER) in energy conversion devices, such as water splitting and metal-air batteries, relies on the development of highly efficient and stable electrocatalysts and is still challengeable. Here, Nickel modulated ternary Iron tungsten nitride (Ni-FeWN[Formula: see text] nanosheets are synthesized through a facile hydrothermal growth method and subsequently nitriding process for boosting OER. A potential of 1.57[Formula: see text]V at the current density of 10[Formula: see text]mA/cm2 and Tafel slope (40[Formula: see text]mV/dec) are achieved on Ni-FeWN2, much lower than that on Ni-free FeWN2 and commercial IrO2. More importantly, Ni-FeWN2 nanosheets display high stability and electrocatalytic activity toward driving oxygen evolution efficiently in alkaline media.