Low-temperature Hydrothermal Method Research Articles

Synthesis of Ni2+ cation modified TS-1 molecular sieve nanosheets as effective photocatalysts for alcohol oxidation and pollutant degradation

Improvement of the charge separation of titanosilicate molecular sieves is critical to their use as photocatalysts for oxidative organic transformations. In this work, MFI TS-1 molecular sieve nanosheets (TS-1 NS) were synthesized by a low-temperature hydrothermal method using a tailored diquaternary ammonium surfactant as the structure-directing agent. Introducing Ni2+ cations at the ion-exchange sites of the TS-1 NS framework significantly enhanced its photoactivity in aerobic alcohol oxidation. The optimized Ni cation-functionalized TS-1 NS (Ni/TS-1 NS) provide impressive photoactivity, with a benzyl alcohol (BA) conversion of 78.9% and benzyl aldehyde (BAD) selectivity of 98.8% using O2 as the only oxidant under full light irradiation; this BAD yield is approximately six times greater than that obtained for bulk TS-1, and is maintained for five runs. The excellent photoactivity of Ni/TS-1 NS is attributed to the significantly enlarged surface area of the two-dimensional morphology TS-1 NS, extra mesopores, and greatly improved charge separation. Compared with bulk TS-1, Ni/TS-1 NS has a much shorter charge transfer distance. The as-introduced Ni species could capture the photoelectrons to further improve the charge separation. This work opens the way to a class of highly selective, robust, and low-cost titanosilicate molecular sieve-based photocatalysts with industrial potential for selective oxidative transformations and pollutant degradation.

Green synthesis of CNTs/Ni(OH)2 nanostructures for electrochemical supercapacitors

In this paper, the effects on specific capacitance and other electrical properties of supercapacitor electrodes synthesized with different hydrothermal growth time are discussed. Carbon nanotubes/nickel hydroxide hybrid electrodes were proposed via a low-temperature hydrothermal synthesis method. The concentration of nickel hydroxide set to 0.5 M and a hydrothermal reaction time of 30 min, exhibited a high specific capacitance of 912.22 F/g at a scan rate of 10 mV/s in a 3 M KOH electrolyte. The CNTs/ Ni(OH)2 also exhibited excellent charge/discharge property with 84% of its specific capacitance kept after 1000 cycles at the current density of 1 A/g.

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.

Enhanced ethanol sensing performances of hetero-assembly Zn1-xFexO/rGO nanocomposites

Nanocomposites of Zn1-xFexO/reduced graphene oxide (Zn1-xFexO/rGO, x = 0∼0.15) with carpet-like mesoporous structures have been simply synthesized via a low temperature hydrothermal method. FESEM and TEM results show that the hetero-assembly trend of Zn1-xFexO and rGO is much more striking than that of Zn1-xFexO self-assembly at 100 °C hydrothermal condition. The specific surface area and pore size tests indicate that rGO leads to the formation of slit holes with inclined panel structure, providing a large specific surface area for the nanocomposites. Mesoporous Zn0.89Fe0.11O has been proved to have the optimal gas response to ethanol at high operating temperatures, while Zn0.89Fe0.11O/rGO-10 (the content of rGO is 10 %) composite has a remarkable gas response (4.37) at low operating temperature and low ethanol concentration (160 °C, 2 ppm). In addition, the charge transport process and potential mechanism of gas response enhancement of Zn1-xFexO/rGO composite have been discussed in detail, and this may be ascribed to the combined effect of P-N junctions and the interfacial coupling between Zn1-xFexO and rGO.

Degradable porous nanoflower substrate-embedded microfluidic device for capture, release and in situ manipulation of cancer cells

Circulating tumor cell (CTC) detection has become a powerful tool for early diagnosis of metastasis and precise monitoring of cancer progression. While existing microchips have achieved promising progress on CTC capture, facile release and in situ regulation of CTC from devices for downstream analysis have rarely been realized. Herein, we demonstrated a porous nanoflower substrate (PNFS)-embedded microfluidic device that integrated multiple functionalities of effective CTC capture, in situ intracellular delivery, and nondestructive CTC release on a single device. The core of the device, PNFS, consisting of hierarchical Zn-phosphate composite structure on a nanoporous membrane, was produced by converting from micro/nano-fabricated ZnO nanostraws by low-temperature hydrothermal method and could be degraded via sodium citrate solution treatment for 20 min. Cancer cells could be captured on the PNFS with high efficiency up to 93.9 ± 1.7% after specific antibody conjugations, and be non-destructively released from the PNFS by using biocompatible sodium citrate to rapidly dissolve the PNFS at room temperature. In addition, the degradable PNFS was integrated with a microfluidic electroporation device, allowing in situ intracellular molecular delivery into the captured cells for cell modifications, where such reengineered cells could be further released for subsequent applications. This device promises to be a versatile and efficient platform for CTC analysis, with great potential for the futuristic cell-based cancer diagnostics and therapies.

Thin Film of TiO2–ZnO Binary Mixed Nanoparticles as Electron Transport Layers in Low-Temperature Processed Perovskite Solar Cells

Organic–inorganic hybrid perovskite solar cells have become one of the highly promising candidates for photovoltaic technologies because of their low processing cost, rapid-growing power conversion efficiency and easy preparation process. Electron transfer layer (ETL) plays an important role in exciton separation and charge transport for perovskite devices. A TiO2–ZnO binary mixed nanoparticle (NP) ETL, which can be prepared in low-temperature hydrothermal method, was proposed. By analyzing the XRD and SEM, the incorporation of mixed NPs thin film improved the interfacial stability of ZnO/perovskite and prevented the perovskite layer from being decomposed as compared to the pure ZnO NPs thin film. Furthermore, UV spectrum and EIS results show that TiO2–ZnO mixed NP ETL has high transmittance and maintains good electrical properties of pure ZnO NPs basically. Finally, the efficiency of perovskite device based on TiO2–ZnO mixed NP ETL was improved to 15%. Our research provides a simple way for the application of ZnO in PCSs.

Hydrothermally synthesized nano-carrots ZnO with CeO2 heterojunctions and their photocatalytic activity towards different organic pollutants

In current study, ZnO, CeO2, and a series of ZnO/CeO2 nano-composites with different Zn/Ce molar ratios (2:1, 4:1, 6:1, 8:1 and 10:1) are synthesized using a low-temperature hydrothermal method by varying synthesis processing time. X-ray diffraction pattern confirms the presence of hexagonal wurtzite ZnO and cubic CeO2 in synthesized ZnO/CeO2 nano-composites. The shape and morphology of ZnO/CeO2 nanostructures are uncovered by using field emission scanning electron microscope which shows the dispersion of CeO2 nanoparticles on the surface of ZnO nano-carrots. UV–Visible absorption spectra show a slight red shift in the absorption edge of binary oxides relative to pure oxide. X-ray photoelectron spectroscopy is examined to evident the formation of binary nano-composites and to predict the elemental states present in synthesized materials. All samples are employed for photocatalytic degradation of organic dye; rhodamine B (RhB) and a pesticide; triclopyr (TC) under UV light irradiation. The ZC-8 (Zn/Ce = 8:1) nano-composite possesses the highest photodegradation activity for the removal of RhB and TC among all the synthesized nano-composites. The photocatalytic removal of RhB and TC by varying the synthesis conditions such as time duration, pH, and molar ratio is also demonstrated. Furthermore, the role of active species in degradation process is also studied by performing radical scavenging assay. These photodegradation characteristics of ZnO/CeO2 nanostructures are valuable for environmental purification in various fields.

Holmium (Ho)-coated ZnO nanorods: an investigation of optoelectronic properties

In this work, ZnO nanorods were synthesized by a simple and low-temperature hydrothermal method. Their surfaces were coated by Holmium using the drop-coating deposition technique. The morphology and the structural measurements showed that Holmium has coated completely the surface of ZnO; nanorods have hexagonal structure and their average diameter is about 500 nm, length up to 4 µm. The absorption properties result showed that Ho coated ZnO has an intense absorbance in the ultra-violet region and the optical band gap energy (Eg) of Ho-coated ZnO was calculated and was found to be 3.35 eV. The photoluminescence (PL) spectrums of nanostructures were analyzed to survey the effect of Ho coating on the optical luminescence properties of ZnO, finding that the ZnO nanorods have a strong visible emission centered around 560 nm, while Ho-coated ZnO nanorods have luminescence peaks in the UV and visible region. The excitations wavelength effect revealed that the blue emission can be excited by energies lower than the band gap of ZnO (3, 37 eV). Thus, it indicates that the Ho-coated ZnO nanorods can increase the absorption of UV light, which may hold great promise for the development of the optoelectronic applications.

Nanostructured transition metal chalcogenide embedded on reduced graphene oxide based highly efficient biosensor for cardiovascular disease detection

Herein, we report nanostructured metal chalcogenide (molybdenum tetraselenide, nMo3Se4) embedded on reduced graphene oxide (rGO) based electrochemical immunosensor for cardiovascular disease biomarker [cardiac troponin I (cTnI)] detection. The nanostructured molybdenum tetraselenide-reduced graphene oxide (nMo3Se4-rGO) was synthesized via low temperature hydrothermal method and further functionalization was carried out using 3-aminopropyltriethoxy silane (APTES). Deposition of functionalized nanostructured material (APTES/nMo3Se4-rGO) was conducted onto hydrolysed indium tin oxide (ITO) coated glass platform by using electrophoretic deposition (EPD) technique at a DC potential of 15 V for 60 s. The APTES/nMo3Se4-rGO/ITO platform was then immobilized with monoclonal anti-cardiac troponin I (anti-cTnI) via EDC-NHS chemistry and bovine serum albumin (BSA) was employed for blocking of non-specific sites. The morphological and functional characterization of synthesized materials and fabricated electrodes were characterized by X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy, Fourier transmission infrared spectroscopy and Atomic force microscopy. The electrochemical characterization and biosensing performance of the fabricated bioelectrodes was investigated by cyclic voltammetry studies. The fabricated biosensing (BSA/anti-cTnI/APTES/nMo3Se4-rGO/ITO) platform shows wider linear detection range [1 fg mL−1–100 ng mL−1] with higher sensitivity [36.2 μA log (mL ng−1) cm−2] and remarkable lower detection limit [1 fg mL−1]. We believe that our fabricated biosensor has potential for the detection of cTnI biomarker and towards the better understanding of cardiovascular disease.

Preparation of ZnO-AZO Core-Shell Nanoarrays and Its Application in Dye Sensitized Solar Cells

High quality one-dimensional ZnO nanometer array (ZnO NAs) was synthesized by low-temperature hydrothermal method. The length and diameter of ZnO NAs was regulated by controlling hydrolysis time (Th) and the concentration of hydrolysate, and the surface was modified by aluminum-doped ZnO (AZO) to obtain ZnO/AZO core-shell nanometer array, which was used as the photoanode of dye-sensitized solar cells. The ZnO NAs provide a direct and stable channel for charge transfer. The electron recombination caused by reaction of the acid dye and ZnO photoanode have reduced as adding AZO shell, and increased the array surface roughness to improve the load of dye molecules. As a result, the DSSC of composite film has a hig power conversion efficiency of 1.75%.

Hydrothermally synthesized UV light active zinc stannate:tin oxide (ZTO:SnO2) nanocomposite photocatalysts for photocatalytic applications

This study was carried out for the simple synthesis of zinc stannate (Zn2SnO4, ZTO): tin oxide (SnO2) nanocomposite photocatalyst in order to investigate the photodegradation of Rhodamine B (RhB) dye molecules under the UV light irradiation. For this purpose, nanocomposite photocatalysts were prepared via a low temperature hydrothermal method. Pure ZTO nanoparticles were also synthesized for the comparison purpose of the photocatalytic activity. Formation of the ZTO:SnO2 nanocomposites could be easily controlled by tuning of the hydrothermal reaction temperature. The structural properties of ZTO:SnO2 nanocomposites and ZTO nanoparticles were schematically characterized by XRD, XPS and FTIR. Morphological investigation was performed via SEM and TEM. Band structure and optical properties were investigated with UV–Vis spectroscopy and PL analyses. It was found that ZTO:SnO2 nanocomposites keep hexagonal ZTO nanoparticles and SnO2 nanorods together and have more surface defects than that of the ZTO nanoparticles. The degradation of RhB dye molecules in the presence of ZTO:SnO2 nanocomposites reached to 62.0% degradation after first 60 min and 94.5% after 240 min. The photocatalytic rate constant of the ZTO:SnO2 nanocomposites (k = 0.0111 min−1) was two times higher than that of the pure ZTO nanoparticles (k = 0.00527 min−1). In addition, ZTO:SnO2 nanocomposites exhibited very high stability in the cycling degradation test with 90.1% RhB degradation even after ten times cycling run.

Fabricated superhydrophobic three-dimensional rambutan-like-β-NiOOH @sponge skeletons for multitasking oil–water separation

In this paper, oleophilic and superhydrophobic sponges were successfully constructed via a one-pot low temperature hydrothermal method anchoring three-dimensional rambutan-like-β-NiOOH microspheres into sponge skeletons and lauric acid modification. The constructed modified three-dimensional rambutan-like-β-NiOOH @sponge (the static contact angle of 153.5°) possessed outstanding oil sorption capacity (separation efficiency is nearly 99%) towards the various organics/oils and excellent recyclability after 30 cycles of adsorption-squeezing. Importantly, modified three-dimensional rambutan-like-β-NiOOH @sponge is capable of separating surfactant-stabilized water-in-oil emulsions and can be utilized for continuous oil-water separation with the aid of a peristaltic pump. This is mainly due to the fact that the three-dimensional hierarchical rambutan-like micronano structure formed by self-assembly with high specific surface area provides a large number of hydrophobic interfaces to improve the hydrophobic properties of sponges. This work presents a new strategy for the designs multitasking oil-water separation materials.

Delafossite CuGaO2 as promising visible-light-driven photocatalyst: synthesize, properties, and performances

3R-delafossite CuGaO2 sample with high crystallinity and single phase was prepared by simple low-temperature hydrothermal method. The fundamental physicochemical properties of 3R-delafossite CuGaO2 were systematically studied by density functional theory calculations and experimental characterization. Through a series of characterization, analysis, (photo)electrochemical and photocatalytic activity testing, the as-prepared CuGaO2 samples exhibit the potential for hydrogen production and high photocatalytic degradation for tetracycline hydrochloride (TCH). Furthermore, CuGaO2 photoelectrode exhibits long-term stability and large photocurrent density. These observations suggest that 3R-delafossite CuGaO2 is a potential promising photocatalyst driven by visible-light. Finally, possible breakthrough directions of 3R-delafossite CuGaO2 photocatalyst are discussed.

Photoelectrochemical Performance and Charge Transport Kinetics of CuO Nanocone Arrays

CuO nanocone arrays were grown in situ on an FTO substrate with thicknesses of 70–600 nm via a low-temperature hydrothermal synthesis method. Their morphological, optical, photoelectrochemical, and photocatalytic performances, were studied, as well as their charge transport photoelectric conversion kinetics. The photocurrent and photocatalytic degradation rate of CuO nanocone arrays increased when the nanocone length increased from 70 to 250 nm, and continued to decrease thereafter. Electrochemical impedance spectroscopy (EIS) indicated that charge separation and transfer were improved with a higher CuO/electrolyte interface area and longer CuO nanocones. But recombination also gradually increased with an increasing CuO nanocone length. Intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS) spectra showed an increased transport time constant τIMPS with a thicker CuO array, suggesting a more difficult hole transfer with a longer transport path. In contrast, a lower recombination time constant τIMVS was observed in thicker CuO arrays, implying a more severe charge recombination, meaning that electron and hole recombination was inhibited in longer nanocones. Moreover, hole transport kinetics indicated that the low hole diffusion length was less than 50 nm, and was the likely cause of the limited photoelectric conversion in CuO nanocone arrays.

Enhanced photoresponse in ZnO nanorod array/p-GaN self-powered ultraviolet photodetectors via coupling with CuO nanostructures

ZnO nanorod arrays (ZnO NRAs) coupled with coral-like CuO nanostructures (CuO CLNs) were prepared by low-temperature hydrothermal method. Self-powered ultraviolet (UV) photodetectors (PDs) based on ZnO NRAs/CuO CLNs/p-GaN heterostructure were fabricated via a direct-contact method. Under UV illumination (1.46 mW cm−2), the ratios of photocurrent to dark current (Iphoto/Idark), photo-responsivity and specific detectivity for the ZnO NRAs/CuO CLNs/p-GaN heterojunction self-powered PD were estimated to be 1143, 1.44 mA W−1 and 5.9 × 1010 cm H z 1 /2/W at 0 V, which were about ∼187, ∼104 and ∼153 times greater than those of the ZnO NRAs/p-GaN self-powered PD, respectively. Moreover, the PD displayed faster response time, excellent stability and repeatability by coupling with CuO CLNs. The mechanism of the enhanced photoresponse performance was discussed through the energy band diagram.

Двухэтапный синтез структурированных микросистем из наностержней оксида цинка с использованием ультразвукового спрей-пиролиза и низкотемпературного гидротермального метода

The features of a two-stage synthesis of structured microsystems based on zinc oxide nanorods using ultrasonic spray pyrolysis and a low-temperature hydrothermal method with suppression of nucleation in the bulk of the solution are presented. It is shown that the use of two-stage synthesis provides control over the size and aspect ratio of nanorods. It is proposed to control the concentration of intrinsic surface defects by measuring the photocurrent with irradiation through narrow-band interference light filters.

Low-temperature hydrothermal synthesis of hierarchical flower-like CuB2O4 superstructures

We report for the first time the fabrication of hierarchical ordered superstructure CuB2O4 with flower-like morphology via a one-step, low temperature hydrothermal method. The tetragonal structure of CuB2O4 was determined by X-ray diffraction and high-resolution transmission electron microscopy. Optical measurements attested of the quality of the fabricated CuB2O4 and high temperature X-ray diffraction confirmed its thermal stability up to 600 ?C. The oriented attachment growth and the hierarchical self-assembly of micrometer-sized platelets producing hierarchical superstructures with flower-like morphology are designed by pH of the hydrothermal solution. The excellent band gap, high thermal stability and hierarchical structure of the CuB2O4 are promising for the photovoltaic and photocatalytic applications.

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.

W-doped nanoporous TiO2 for high performances sensing material toward acetone gas

W-doped TiO2 with nanoporous structure was synthesized by a one-step low temperature hydrothermal method using TiOSO4 and (NH4)6H2W12O40•xH2O as titanium and tungsten sources. Structure, morphology, specific surface area and chemical state of samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). W-doped nanoporous TiO2 samples were used as sensing materials of indirect-heating sensors and their gas-sensing performances were studied to detect acetone. The experimental results show that 7.5% W-doped nanoporous TiO2 can adsorb more oxygen molecules on the surface and provide large amount of active reaction sites on interface to profit reaction between material and gas molecules. The gas sensor based on 7.5% W-doped nanoporous TiO2 exhibits good gas-sensing performances, including high gas response value, shortened response/recovery time and good reproducibility, which make it a promising candidate in acetone detection. Apart from these, the mechanism related to the advanced properties was also investigated and presented.

Hollow porous prismatic graphitic carbon nitride with nitrogen vacancies and oxygen doping: a high-performance visible light-driven catalyst for nitrogen fixation.

Hollow porous prismatic graphitic carbon nitride with nitrogen vacancies and oxygen doping was successfully constructed using dicyandiamidine as the only raw material via a facile two-step strategy of a low-temperature hydrothermal method followed by a subsequent calcination process. The as-obtained graphitic carbon nitride showed a hollow prismatic morphology with loose spongy-like walls, a hierarchical pore structure, and a specific surface area of 220.16 m2 g-1. Such graphitic carbon nitride exhibited an ultrahigh nitrogen fixation rate of 118.8 mg L-1 h-1 gcat-1 under visible light irradiation and showed excellent stability during the reactions. A possible mechanism for photocatalytic nitrogen fixation on the catalyst was proposed as follows: under visible-light irradiation, graphitic carbon nitride with nitrogen vacancies and oxygen doping underwent charge separation to generate electron-hole pairs, and then the photogenerated electrons on the conduction band were quickly transferred to the nitrogen vacancy induced mid-gap state; consequently, the trapped electrons reacted with the activated nitrogen on the nitrogen vacancies to produce ammonia. The significant enhancement in the photocatalytic nitrogen fixation performance of graphitic carbon nitride can be attributed to its unique hollow prismatic morphology with a loose porous structure, fully exposed active sites of nitrogen vacancies, more negative conduction band, suitable visible-light response and the efficient separation of photogenerated electron-hole pairs.