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Hydrothermal synthesis as a commonly bottom-up growth method has considerable advantages for manufacturing thermoelectric nanomaterials with advanced thermoelectric properties. However, the hydrothermally synthesized thermoelectric nanostructures often show a low thermoelectric performance due to their low power factor. In this work, we report on using a hydrothermal method for the growth of n-type Bi2-xSbxSe3 nanoflakes with a fixed thickness of ∼16 quintuple-layers. The controlling of the stoichiometric composition, phase purity and crystallinity of the Bi2-xSbxSe3 nanoflakes are demonstrated by the X-ray diffraction, Raman spectroscopy, and high resolution transmission electron microscopy. We further prove that adding of antimony into Bi2Se3 compound mostly influences the in-plane vibration mode. The optical energy gap is sharply increased as the Sb content increases. The effect of the antimony incorporation on the electrical conductivity, Seebeck coefficient and power factor of Bi2-xSbxSe3 nanoflakes is systematically investigated. The Bi1.92Sb0.08Se3 sample is found to have the highest power factor ∼13.17 μW/cm.K2 at 470 K which is much higher than those published for other various nanostructured or bulk Bi2Se3 compounds. The results propose a great prospect for further enhancing the thermoelectric power factor of the Bi2Se3 nanostructures synthesized by this hydrothermal method. Taking into consideration the progress in Bi–Se compounds, the results of this work advocate the promise of Bi–Se nanostructures towards producing high performance thermoelectric devices.

Highly fluorescent Ag–In–S/ZnS (AIS/ZnS) core/shell quantum dots (QDs) with good crystallinity were synthesized via hydrothermal method with adding ZnS precursors directly into AIS cores initial solution. The influences of shell growth time and Zn/AgIn ratios on the crystal structure, composition and morphology were analyzed by using X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM), and the fluorescence properties of AIS/ZnS core/shell QDs were systematically investigated by absorption and photoluminescence (PL) spectra. In contrast with AIS cores, the AIS/ZnS core/shell QDs showed significantly improved yellow-orange emission with long PL lifetimes, as well as the maximum quantum yield (QY) increased from 21.6% to 45.7%. Moreover, bright white light was successfully generated from the AIS/ZnS QDs and Lu 3 Al 5 O 12 :Ce 3+ phosphors based white light-emitting diode (WLED). Under the forward bias current of 200 mA, the fabricated WLED exhibited a high luminous efficiency of 77.98 lm/W with the Commission Internationale de I'Eclairage (CIE) color coordinate of (0.32, 0.32), a color rendering index (CRI) of 85 and the correlated color temperature (CCT) of 6215 K, demonstrating the prospective application of obtained QDs in solid-state lighting devices.

In the present work, an oxidation-crystallization-reduction route in the hydrothermal systems has been demonstrated to be facile and feasible in the large-scale production of γ-MnOOH nanowires. The whole is green and cheap only using Mn2+ and polyvinylpyrrolidone without adding any oxide agent or template. The structure and morphology of the as-synthesized samples are characterized by X-ray diffraction, scanning electron microscopy, Transmission electron microscopy, Infrared active spectrum, Raman spectrum, thermogravimetry, cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. As anode of lithium-half cells, γ-MnOOH nanowires exhibit enhanced cycling performance and rate capacity in comparison with the previous reports. A high capacity of up to 393.9 mAh g−1 with a Coulombic efficiency of nearly 100% is obtained at 0.1C after 100 cycles, which presents a promising application as anode materials for lithium power batteries.

A one-pot hydrothermal synthesis was applied for growth of cobalt-doped TiO2 nanosheets (Co-TNs) having different quantities of cobalt on the reduced graphene oxide surfaces (Co-TNs/rGO (x)). The synthesized nanocomposites were characterized by a range of analyses including XRD, UV–Vis DRS, FESEM/EDX, elemental mapping, TEM, HRTEM and Raman spectroscopy. The visible light degradation of Tetracycline antibiotic (TC) by synthesized samples was investigated and the degradation percentage of TC was 60% by Co-TNs/rGO (0.152) (the optimal sample). Reusing the optimal photocatalyst after five successive cycles showed ∼7% decline in its activity for degrading of TC. Active species trapping experiments showed that OH radicals and h+ are the main active species in the degradation process. An artificial neural network (ANN) model was used to predict the photocatalytic removal of tetracycline antibiotic. The multilayered feed forward networks were trained by using a backpropagation algorithm; a three-layer network with 14 neurons in the hidden layer gave the optimal results. The relative importance of different parameters on the photoactivity of the as-obtained photocatalysts were evaluated.

Cobalt ferrite is an important magnetic material due to its high saturation magnetization and high energy product BH. CoFe2O4 nanoparticles can be synthesized by a variety of methods that often demand long synthesis times. Using the microwave-assisted hydrothermal method, single-phase CoFe2O4 with controlled crystallite size was rapidly obtained. The effect of a preheating step and mineralizing agent, i.e., NH4OH and KOH, was investigated. Exposure to microwave radiation ranged from 0.5 to 2 h. The formation of CoFe2O4 was confirmed by X-ray diffraction. The average crystallite size of CoFe2O4 nanoparticles was estimated between 5.2 nm and 21.3 nm by Rietveld refinement. The crystallite size depended on the preheating step and mineralizing agent used. Transmission electron microscopy images revealed that CoFe2O4 nanoparticles were nearly spherical when prepared with NH4OH but cubic and spherical when prepared with KOH. Both, hysteresis curves and Mossbauer spectra at room temperature, showed superparamagnetic behavior for samples with the smaller crystallite size. Samples with larger crystallites consisted of blocked particles and depicted an increase in the MR/MHmax ratio and coercive field, Hc. Distinct magnetic properties resulting from variations in the synthesis parameters yield different applications for nanostructured CoFe2O4.

Hydroxyapatite (HA) coatings were widely used to improve the poor corrosion resistance, the osteoinduction and osseointegration ability of biodegradable magnesium alloys as biodegradable implants. To further improve the performance of the HA coated biodegradable magnesium alloys, strontium (Sr) was introduced in the HA coating through hydrothermal methods to partially replace the calcium ions. The growth mechanism, electrochemical properties, degradation, and cytocompatibility of the Sr-doped HA coated ZK60 magnesium alloys were investigated in details. The results show that with the addition of Sr element, the shape of the fabricated HA turned from nanorods into nanowires and the morphology of the coatings changed from a flower-like structure to a network structure. The electrochemical and immersion tests showed that the Sr doping can enhance the corrosion resistance of the HA coatings. Moreover, BMSCs cell culture results suggested that the addition of the trace element Sr can promote the cell adhesion and proliferation of HA coated biodegradable Mg alloys. This work provides a simple and efficient way to fabricate nanowired HA coating on biodegradable Mg alloys with improved biocompatibility and osteogenity. The Sr-doped HA coatings on biodegradable Mg alloys have shown a great potential for the orthopedic application.

The porous NiO nanostructures have received considerable attention owing to high surface-to-volume ratio, low density and sufficient interior space for potential applications, such as gas sensing. The novel lotus-root slice NiO architectures were prepared via a facile hydrothermal method. The cetyltrimethylammonium bromide and urea played an important role for the formation of the lotus-root slice NiO. A possible formation mechanism has been proposed. The lotus-root slice NiO showed excellent gas-sensing performance to ethanol. Such unique architectures may open up an avenue to further enhance the gas-sensing performances of NiO nanostructures for future sensor applications.

A series of iron‒nickel‒cerium nanocatalysts were synthesized by the hydrothermal method in different metal molar ratios for the first time. These nanocatalysts were used in a fixed bed micro reactor for the Fischer‒Tropsch process and the catalytic activity and products selectivity were evaluated. The 60% Fe‒ 30% Ni– 10% Ce nanocatalyst was designated as optimal nanocatalyst due to the maximum yield of the light olefins. The catalytic performance of the optimum nanocatalyst was investigated in a wide range of the operating conditions such as temperature, H2/CO molar ratio, gas space velocity, and pressure. The obtained results indicate that the optimal operating conditions are the follows: T = 280 °C, H2/CO molar ratio = 1/1, GHSV = 1800 h−1, and P = 2 bar. The nanocatalysts were characterized by XRD, N2 physisorption, FE‒SEM, EDS, TGA, DSC, and TPR.

A novel highly ordered three-dimensional nanoflower-like α-Fe2O3/coal-based graphene (α-Fe2O3/CG) composite was fabricated through a simple and controllable hydrothermal synthesis strategy. The nanoflower-like α-Fe2O3/CG provides abundant mesoporous morphology, efficient conductive network and rapid electron transfer, as well as unique structural features that all contribute to improved electrochemical performance. Here, α-Fe2O3/CG composites have been investigated as advanced anode in the lithium-ion batteries. The electrochemical performance indicated that nanocomposite of α-Fe2O3/CG exhibited a high capacity (1000 mAh g−1) after 100 cycles at 0.2 A g−1. In addition, the as-designed composite exhibited excellent cycling stability and even at 5 A g−1, the specific capacity of it still can achieve 425 mAh g−1.

The oxygen reduction reaction (ORR) plays a significant role in energy conversion technologies such as metal-air batteries and fuel cells. The development of efficient ORR electrocatalyst is highly desirable to achieve the fast oxygen reduction. In this work, the bimetallic Cu and Co embedded nitrogen-doped carbon (CuCo-N/C) is fabricated as efficient electrocatalyst for ORR. The incorporation of Cu-precursor into Co-based zeolitic imidazolate frameworks (ZIF) is innovated here to synergistically enhance the activity of Co. Surprisingly, the addition of Cu can also increase the nitrogen content in the CuCo-N/C catalysts, which could generate more active sites and result in the improvement of ORR activity. The optimized CuCo-N/C catalysts exhibit superior ORR performance with a half-wave potential of 0.85 V (vs. RHE), a limiting current density of 5.61 mA cm−2 and enhanced long-term durability comparing with the state-of-the-art Pt/C catalysts. Benefiting from the unique structure, the as-made CuCo-N/C catalysts as electrode for Zn-air battery delivers excellent performance with a peak power density of 66.9 mW cm−2, a high open circuit voltage of 1.468 V, and a voltage degradation of about 1.4% after 12 h discharging, which is much better than that of Pt/C catalysts.

Polyhedral FeCo alloys with grain sizes of 1–2 μm were synthesized by using a low-temperature hydrothermal method. The effects of heating time and molar ratio on microstructure and electromagnetic absorption performances of the alloys were studied. Their growth follows the Ostwald ripening mechanism. At the given reaction time of 10 h, as the molar ratio of Fe:Co was varied from 3:7 to 4:6, morphology of the alloy particles was changed from flower-like to polyhedral shape. Specifically, the Fe6Co4 sample had superior impedance matching, while a strong dielectric resonance at about 10 GHz was observed in the complex dielectric constant imaginary part, thus resulting in significantly enhanced electromagnetic absorption performance. It exhibited an optimum reflection loss (RL) value of −52.20 dB at 10.48 GHz, with a sample thickness of 1.7 mm. Meanwhile, the RL of −10 dB was over the frequency range of 7.6–13.6 GHz, covering the Ku-band and the entire X-band. Most importantly, the matching thickness of all the samples was less than 2 mm. These results indicate that the FeCo alloy particles are suitable for electromagnetic absorbing materials at the C, X and Ku bands.

In this paper, we proposed the growth of ZnCo2O4 on the surface of a Cu-supported Fe2O3-C composite coating by hydrothermal synthesis combined with post-annealing treatment. The Fe2O3-C coating demonstrates a three-dimensional (3D) network structure; and the loaded ZnCo2O4 exhibits a nanoflake morphology. The composite with ZnCo2O4 nanoflakes loaded on the surface of the Fe2O3-C network can directly serve as an integrated lithium-ion battery anode. It delivers a very stable high capacity of 952 mA h g−1 at a current density of 100 mA g−1 and a capacity of 684 mA h g−1 at a high current density of 1000 mA g−1. The Fe2O3-C network substrate is free of binders and conductive agents, and it has a large specific surface area, good electrical conductivity and high structural stability, which allows it to achieve the outstanding battery performance of the loaded hydrothermally produced ZnCo2O4.

Powders of ZnO and ZnO:M (M = Al3+ and Sr2+) with 1 and 4% of M nominal content were synthetized by a hydrothermal method in a diethanolamine (DEA) medium. The samples were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), micro-Raman and photoluminescence (PL). The powder particles were spherical with average radius decreasing from 1 μm down to 70 nm with increasing Al3+ nominal content but nearly independent on the Sr2+ nominal content. The XRD and micro-Raman results indicate that both Al3+ and Sr2+ mostly incorporated substitutionally into the ZnO lattice, giving rise to compressive and tensile strain, respectively, as a result of ionic radii differences. The PL spectra for ZnO:Al exhibit a dopant-induced contribution at ∼3.1 eV, which is not observed for ZnO:Sr, due to radiative transitions involving trapping of photocarriers at theoretically expected substitutional Al3+ donor states or at Zn interstitial defects. Fil: Marín Ramírez, Oscar Alonso. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Laboratorio de Física del Sólido; Argentina Fil: Soliz, Tania. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; Argentina Fil: Gutierrez, Jorge Andrés. Universidad del Quindío. Facultad de Ciencias Básicas y Tecnológicas; Colombia Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Departamento de Nanomateriales y Propiedades Dieléctricas; Argentina Fil: Figueroa, Carlos. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Laboratorio de Física del Sólido; Argentina Fil: Comedi, David Mario. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Laboratorio de Física del Sólido; Argentina

Nanocomposites of well-standing δ-MnO2 nanoplatelets on nitrogen-doped reduced graphene oxide (δ-MnO2/NRGO) were synthesized via a simple hydrothermal method. Herein, p-phenylenediamine serves as the molecule for “anchoring” δ-MnO2 on graphene oxide, as well as the nitrogen source. Especially, graphene oxide was functionalized with p-phenylenediamine firstly, which was used as the substrate for growing of uniform MnO2 nanostructures. δ-MnO2/NRGO nanocomposites were characterized by Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray Diffraction, Fourier Transform Infrared Spectroscopy, and X-ray Photoelectron Spectroscopy. The electrochemical performance of the as-synthesized nanocomposites was investigated, which displayed excellent specific capacitance (299.5 F g−1 at 5 mV s−1), superior cycle stability (97.8% retention after 8000 cycles) and good energy density (24.2 Wh kg−1 with the power density at 242 W kg−1). The improvement is primarily attributed to the specific nanostructure, as well as the doping of nitrogen which provides more active sites and promotes charge transferring.

Graphene promoted triphasic N/Ti3+-TiO2 (GNTT) heterostructures with different weight addition ratios of graphene have been assembled by a facile in-situ hydrothermal treatment of TiN and graphene oxide. The obtained GNTT photocatalysts are characterized by a collection of techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, and photoluminescence (PL), etc. It is demonstrated that graphene modified N/Ti3+ codoped TiO2 with ternary phases mixture of brookite, anatase and rutile can be obtained. Furthermore, the GNTT heterostructure photocatalysts exhibit an enhanced photoactivity for photocatalytic degradation of methyl blue, levofloxacin, and rhodamine B as compared with TiO2, N-doped TiO2, and N/Ti3+ codoped TiO2 (NTT). The reason for the improved photoactivity can be listed as follows: i) N and Ti3+ doping can severally form N2p impurity level above valance band (VB) and local states below the conduction band (CB) of TiO2, which contribute to the visible light response of TiO2; ii) the ternary heterophase junction can efficiently transfer and separate photogenerated electron-hole pairs; iii) graphene acts as an electron reservoir to trap and transport the electrons photogenerated from TiO2. The synergistic effect of these factors accounts for the photoactivity advancement of GNTT photocatalysts. This study develops a novel approach to improve the visible light utilization of TiO2 and facilitates their applications in the environment and energy issues.

Two new structural types of BaREGeO4(OH) and BaRE10(GeO4)4O8 (RE = Ho3+,Er3+) single crystals were synthesized via high-temperature and high-pressure hydrothermal synthesis. The BaREGeO4(OH) compounds were found to crystallize in the orthorhombic space group Pbca. BaHoGeO4(OH) is used as a representative of the family with cell parameters of a = 5.7175(2) A, b = 10.1556(5) A, c = 10.6189(9) A and V = 964.97(8) A3. The BaREGeO4(OH) structure contains a one-dimensional chain of rare-earth polyhedra linked through edge sharing of oxygen atoms. High density BaRE10(GeO4)4O8 crystals crystallize in the monoclinic space group C2/m and feature a sheet like arrangement of rare-earth oxide polyhedra with Keggin-like features. BaHo10(GeO4)4O8 is used as a representative of this structure type with cell parameters of a = 12.4533(8) A, b = 7.2008(5) A, c = 12.0034(8) A, β = 100.183(2)⁰ and V = 1059.43(12) A3. Barium polyhedra and isolated GeO4 units aid in connecting the rare earth oxide framework to extend it in three-dimensional (3-D) space. Characterization by single crystal X-ray diffraction and Raman and photoluminescence spectroscopies is reported.

The hybrid architectures comprising different types of nano-structured WO3 particles were prepared via facile surfactant-and template-free hydrothermal synthesis process. We demonstrate that morphology of the fabricated hybrid nanomaterials can be manipulated but the phases of those nanomaterials are still monoclinic and hexagonal hybrid structure via tuning the proportion of the reagents. The synthesis mechanism and the gas-sensing properties of the harvested nanomaterials have also been investigated. The as prepared WO3 nano-particles with hybrid architectures exhibit excellent gas-sensing functions to ethanol gas at the optimal temperature as low as 350 °C under the low concentration of 35 ppm, rendering them a promising sensing material for the on-site detection of ethanol.

Spherical FePO4 and three-dimensional porous graphene (3DG) were prepared by hydrothermal synthesis, then LiFe0.98V0.02PO4/3DG/C composite was prepared by two-step sintering method based on FePO4/3DG. The structure, composition and morphology of the synthesis production were confirmed by X-ray diffraction (XRD), Raman spectra, Energy Dispersive Spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The electrochemical properties were studied by cyclic voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and charge/discharge tests. At a current density of 0.2C, the first charge/discharge specific capacities were 161.1 mAh/g and 159.1 mAh/g, and the corresponding capacity retention rates after 50 and 100 cycles was 99.5% and 99% respectively. In addition, LiFe0.98V0.02PO4/3DG/C composite had a better rate and cycle performance, as well as greater Li+ diffusion coefficient (DLi+) compared with LiFePO4/C and LiFePO4/3DG/C. Therefore, LiFe0.98V0.02PO4/3DG/C composite will become a potential cathode materials for lithium-ion (Li+) power batteries.

We demonstrate a facile hydrothermal synthesis of the interconnected porous NiCo2O4 nanosheets for hybrid supercapacitor applications. The as-synthesized NiCo2O4 nanosheets show a high specific capacitance of 3137 F g−1 at a current density of 2 A g−1, which is much greater than 1916 and 1251 F g−1 of Co3O4 and NiO, respectively. Interestingly, the total specific capacitance of the NiCo2O4 is almost close to the sum of the specific capacitance of the NiO and Co3O4. Furthermore, a hybrid supercapacitor is configured with the NiCo2O4 nanosheets and the nitrogen- and sulfur-codoped reduced graphene oxide as the positive and negative electrodes, respectively. This hybrid supercapacitor delivers a maximum energy density of 33.64 W h kg−1 at a power density of 1196 W kg−1 and excellent long-term cyclic stability over 12,000 charge/discharge cycles at the enlarged voltage window of 1.5 V. The remarkable supercapacitive performances of the hybrid device are attributed to the interconnected porous structure of NiCo2O4 nanosheets and three-dimensional continuous macropores of codoped reduced graphene oxides.

High-efficient photocatalyst based on Zn2SnO4/C/AgBr multi-component heterostructure was prepared via a two-step hydrothermal synthesis method followed by chemical deposition process. Morphological studies showed that ultra-fine AgBr nanoparticles with the size of 3–5 nm were in situ grown on the surface of the carbon layers attached to Zn2SnO4 nanocrystals. UV–vis characterization demonstrated that the co-modification of carbon and AgBr contributed to the dramatically improved light absorption ability of Zn2SnO4/C/AgBr nanocomposites. In the multi-component heterostructured photocatalyst, carbon functioning as a charge mediator plays a pivotal role in separating photogenerated electron-hole pairs efficiently. Zn2SnO4/C/AgBr photocatalysts exhibited a significant enhancement of visible-light photocatalytic performance toward the photodegradation of rhodamine B (RhB), resulting from the synergistic effect of the intensified visible-light absorption capacity and efficient photogenerated electron-hole pairs transfer. In addition, a proposed schematic mechanism for the significant enhancement of photocatalytic performance is as well put forward on the basis of the experimental results.

The novel chemical composition of pristine Mn1/3Ni1/3Co1/3MoO4 (MNC) and Mn1/3Ni1/3Co1/3MoO4 dispersed in various percentages of reduced graphene oxide (MNC/rGO) composites were prepared via the one-step hydrothermal method. X-ray diffraction (XRD) patterns showed pure crystalline phase CoMoO4 for the heat treated powder at 350 °C. Fourier Transform Infrared (FT-IR) spectra showed that the chemical band structure of Mn1/3Ni1/3Co1/3MoO4 corresponds to the strong vibrational bands of Mo O, Mo O and Mo O Mo bonds. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of Mn, Ni, Co, Mo, C and O elements and its valance in the MNC/rGO powder. Field Emission Scanning Electron Microscope (FE-SEM) images displayed the nanorods morphology of the MNC/rGO powders. High-resolution Transmission Electron Microscopy (HR-TEM) images showed the morphology of MNC nanorods wrapped with the reduced graphene oxide of the MNC/rGO composite. The MNC/rGO composite displayed the highest specific capacitances of 1750 F g−1 at 1 A g−1 in 3 M KOH. The MNC/rGO composite demonstrated a better cycling stability with a cycling efficiency of 85.5% after 5000 cycles at 10 A g−1. The high rate performances, good reversibility and capacity retention at a range of current densities were demonstrated the structural stability of the MNC/rGO composite. The high energy density of 38.8 W h kg−1 at a constant power density of 200 W kg−1was achieved for the MNC/rGO composite.

Epitaxial PbTiO3 films with a smooth and dense surface were fabricated by a promising hydrothermal synthesis on an Nb:SrTiO3(100) substrate. The resulting coated substrate was used to fabricate a Pt/PbTiO3/Nb:SrTiO3 heterostructure device. The device exhibited a multilevel storage capacity with an appropriate R OFF / R ON ratio and excellent endurance and retention. An electric conduction analysis indicated that the resistive switching behavior of the device was attributed to the trap controlled space-charge-limited current conduction that was caused by the oxygen vacancies in the PbTiO3 hydrothermal films. The modulation of the Pt/PbTiO3 Schottky-like junction depletion under an applied electric field is thought to be responsible for the resistive switching behavior of the device in the carrier injection-trapped/detrapped process.

Transition metal oxides especially Fe2O3 has been widely considered as a potential electrode material for current commercial supercapacitors. However, the low electronic conductivity limits the obtained specific capacitance and cycle stability of supercapacitor devices. In the present work, 2D nano-circular-like α-Fe2O3 coupled reduced graphene oxide (rGO) composites have been synthesized for the first time via a simple, inexpensive hydrothermal process. Moreover, circular α-Fe2O3 nanoplates are well-dispersed on rGO layers, which can offer abundant active sites and effectively buffer the reunion of α-Fe2O3 nanocomposites during the electrochemical reactions. At an optimal ratio of 10 wt% GO, the as-prepared sample exhibits electrochemical performance with excellent specific capacitance of 621.3 F g−1 at 5 mV−1 and 533 F g−1 at 1 A g−1, which is better than that of pure α-Fe2O3. Most attractively, the specific capacitance is highly retained about 77% after 14000 cycles, revealing superior cycle ability.

BiFeO3 (BFO) samples with nearly perfect ferroelectric hysteresis loops were synthesized from chemical solution via hydrothermal route at 200 °C. However, for many applications, ceramic samples of reasonable bulk density (>80%) have to be sintered at temperature over 700 °C, which in this case results in a significant reduction in resistivity due to increased amounts of Fe2+. Interestingly, doping of a few percent Sb minimized such a problem and the sintered Sb:BFO ceramics retained a similarly high resistivity as samples cold-pressed from the chemical-solution synthesized powders. However, for cold-pressed samples, Sb:BFO actually had higher conductivity than undoped BFO. Temperature-dependent conductivity showed that cold-pressed samples of both undoped and Sb doped BFO had the similar activation energy of 1.0 eV, typical for electrons trapped in oxygen vacancies. After sintering, the activation energy of Sb:BFO remained almost unchanged, but the activation energy of undoped BFO changed to 0.4 eV, which is associated to electron hopping between Fe2+/Fe3+. X-ray photoelectron spectroscopy (XPS) showed a significant increase in Fe2+/Fe3+ ratio from 6.6/93.4 to 25.7/74.3 in undoped BFO after sintering, while for 1% Sb doped BFO the increase was much milder from 10.9/89.1 to 14.1/85.9. XPS also showed that Sb had single +3 oxidation state before sintering, but after sintering a fairly large portion of Sb5+ occurred. So, charge compensation for oxygen vacancies in undoped BFO was achieved dominantly by reduction of Fe3+ to Fe2+, while in Sb:BFO it was achieved more by cation vacancies.

In this work, the α-MnO2 and α-MnO2/activated carbon composite were prepared by a facile hydrothermal method. Effects of reaction time (1–12 h) and MnO2 loading (10–70%) on structure and electrochemical performances for materials were studied. Samples were analyzed by X-ray diffraction, scanning electron microscope, galvanostatic charge/discharge, cyclic voltammetry and Mott-Schottky testing. A growth model was used to describe the development mechanism of α-MnO2, and MnO2 samples prepared at 6–12 h displayed the actiniaria-shaped structure. The MnO2 electrode at 6 h exhibited the largest specific capacity of 629.2 C/g in K2SO4 electrolyte. After incorporation of carbon, the composite expressed low resistance and large carrier concentration than single MnO2. Due to good conductivity of carbon, the capacity of MnO2/carbon was up to 977.4 C/g (55.3% higher than MnO2). After 3000 cycles at 0.2 A/g, the MnO2/carbon exhibited higher capacity retention of 81.3% than 56.2% for MnO2. It indicated that the α-MnO2/activated carbon showed potential application as electrode material for supercapacitor.

ZnO and CuO have attracted considerable attention for their potential application in gas sensors. However, they also have some disadvantages, such as high operating temperature and poor sensitivity. Graphitic carbon nitride (g-C3N4) has been widely used as metal-free catalyst and catalyst support in gas sensing field due to its unique chemical stability and excellent substrate characteristics. In this study, a one-step hydrothermal method was developed for the preparation of a CuO-ZnO/g-C3N4 ternary composite. The as-prepared samples were characterized by using the XRD, SEM, TEM, FTIR, UV–vis and XPS techniques. The analysis results indicated that the ternary composite was synthesized successfully. The morphological analyses demonstrated that the flake-like CuO and ZnO nanoparticles were wrapped and connected by g-C3N4 nanosheet. The as-prepared CuO-ZnO/g-C3N4 exhibited obviously enhanced sensing properties to ethanol, which were 1.34 times and 2.17 times higher than that of CuO-ZnO and CuO, respectively. The improving gas sensing properties were related to the valid p-n junctions of CuO-ZnO and excellent substrate effect of g-C3N4 nanosheet.

Ultrathin hematite (α-Fe2O3) nanosheets with highly exposed (110) facets were prepared via hydrothermal synthesis by controlling the concentration of silicate anions and pH. With the increase in silicate anions and decrease in pH, the growth of the c-axis for α-Fe2O3 was inhibited, whereas the growth of the a-axis was facilitated, leading to the formation of ultrathin α-Fe2O3 nanosheets. The as-prepared ultrathin α-Fe2O3 nanosheets exhibited expanded surface area and increased exposed (110) facets, which can effectively adsorb the visible light and inhibit the recombination of the electron and hole pairs, leading to superior photocatalytic activity toward the degradation of p-NP. A possible mechanism was also suggested for the p-NP degradation.

Self-calibrated optical luminescent thermometers were prepared based on Eu3+/Mn2+ co-doped Zn2GeO4 phosphors with controllable morphology via a facile hydrothermal synthesis process. The co-doped concentration of Eu3+ ions in Zn2GeO4:Mn2+ played important roles in the evolution of the morphology and the formation of the dual luminescent emission mode. Depending on different excitation wavelengths ranging from 260 to 360 nm, the dual emission centers located at about 534 nm and 612 nm were ascribed to d-d transition derived from 4T1-6A1 of Mn2+ ions and f-f transition originated from 5D0-7F2 of Eu3+ ions, respectively, which gave rise to the excellent self-calibrating temperature sensing functions. The related luminescent and sensing mechanism of the Eu3+/Mn2+ co-doped Zn2GeO4 phosphors are also proposed. The as-obtained Eu3+/Mn2+ co-doped Zn2GeO4 phosphors had a high relative sensitivity (Sr) of 1.96% oC−1 between 20 and 80 °C, as well as stable reusability, demonstrating its superiority as a ratiometric luminescent thermometer for temperature sensing applications.

Upconversion (UC) nanophosphors of Lu2TeO6:Yb3+/Er3+ as temperature sensing material have been successfully synthesized via hydrothermal method followed by a subsequent heat treatment process. The phase and micrographs of the as-prepared phosphors were characterized by XRD, SEM, and TEM. Results indicate that the phosphors of hexagonal Lu2TeO6:Yb3+/Er3+, formed after heat-treatment at 800 °C for 5 h, consist of rice-like nanoparticles with size mostly distributed less than 200 nm in length. Under the 980-nm NIR excitation, the tellurite nanophosphors exhibit strong green and red UC emissions. The optimum Yb3+ and Er3+ concentrations for UC luminescence are determined to be 10% and 1%, respectively. The possible energy transfer mechanism implicated in the nanophosphors is discussed based on the pump power dependence of UC emissions. Furthermore, temperature sensing ability of Lu2TeO6:Yb3+/Er3+ (10/1) is investigated by employing the temperature dependent fluorescence intensity ratio (FIR) of two emission bands (2H11/2/4S3/2 → 4I15/2) of Er3+ ion. The maximum sensitivity achieved in this developed material is as high as 0.0103 K−1 at 623 K. This work provides a new qualified UC nanomaterial for application in optical remote temperature sensing.

17 pags., 20 figs., 5 tabs., Nickel ferrite samples are currently investigated due to their potential technological applications. For this reason, the optimal synthesis conditions of nickel ferrite samples with small particle size were investigated here. First, a systematic study was carried out using urea as an additive, and varying reaction parameter such as the amount of urea added or the reaction temperature and time. For comparison purposes, another sample was synthesized using potassium hydroxide as an additive. The two pure nickel ferrite samples were coated with silica, functionalizing them with APTES and AEPMDS. X-rays, FTIR, Mössbauer spectroscopy, TEM and Ms vs. H and FC/ZFC curves were used for the characterization of samples and the evaluation of their properties. Square particles with an average size of 21.2 nm were observed in the TEM images of the sample synthesized with urea, while these are spherical of 6.2 nm in the sample prepared with potash. Their subsequent coating and functionalization give rise to an arrangement of particles within interlocking strands whose thickness increases with their size. Ms vs. H curves confirm the almost superparamagnetic behavior of all synthesized powders, although with a slight increase in the coercivity value of the samples prepared with urea. Preliminary tests carried out on the functionalized samples to evaluate the adsorption capacity in aqueous solution and their easy separation in presence of an external magnetic field, confirm that the sample synthesized with urea and functionalized with AEPDMS is the most efficient for the Cu ions removal., We thank the ICTS National Center for Electron Microscopy of the UCM for access. Funding Fundación Neurociencias y Envejecimiento (Madrid, Spain) has supported this work through project 359/2014 as well as MINECO (Spain) from Grant MAT2016–80182-R. We acknowledge financial support from Grant RTI2018–095303-B-C51 funded by MCIN/AEI/10.13039/501100011033 (Spain) and by “ERDF-A way of making Europe”, and from grant S2018-NMT-4321 funded by the Comunidad de Madrid (Spain) and by “ERDF-A way of making Europe”.

As a matrix material, NaYbF4 has attracted more and more attention due to its large absorption cross section and high energy transfer efficiency. In this study, lanthanide doped NaYbF4 upconversion (UC) nano-/micro-crystalline was carefully synthesized by hydrothermal method. The influence of kinds of external conditions, including reaction time, initial reaction solution pH value, organic solvents codoping, and Na+ concentration on crystalline phase, size, morphology and especially luminescent property are systematically studied and the possible formation mechanism based on PH values is emphatically proposed. The products of NaYbF4 with various morphologies range from nanospheres, microprisms, microdisks, hexagonal crown-capped shapes, hexagonal clam-like shapes and hexagonal flower-like shapes were successfully prepared. The results show that the up-conversion luminescence property is positively correlated with the slenderness ratio. Solvents codoping and Na+ concentration can greatly improve the luminescence property, especially for red emission. Impressively, the emission colors and intensities might be finely tuned through finely tuning the PH values, solvents co-doping and Na+ dosage. Furthermore, this study will be expected to contribute to the synthesis of various morphologies and improving the UC intensity of lanthanide doped crystals.

Aqueous zinc-ion batteries (AZIBs) are now vigorously explored as a class of novel and competitive candidates for large-scale energy storage in terms of high safety, eco-friendliness and low cost. In order to realize efficient Zn-storage with desirable cycling stability and rate capability, constructing suitable cathode materials that possess reliable host structure and fast Zn2+ diffusion kinetics makes a lot of sense. Herein, novel V2O5 nanofibers were facilely synthesized via a hydrothermal method and employed as a cathode material for AZIBs. By matching with aqueous Zn(CF3SO3)2 electrolyte, the cathode is able to achieve a specific capacity as high as 264.5 mAh g−1 at 200 mA g−1. Even conducted at a large current density of 2000 mA g−1, a considerable rate capability of 132.6 mAh g−1 can also be delivered. In addition, electrochemical reaction kinetics and ion diffusion mechanism were initially conducted to uncover the insights for efficient Zn-storage. This work is anticipated to offer feasible strategy for the design and fabrication of promising vanadium-based cathode materials for rechargeable AZIBs.

Supercritical hydrothermal synthesis is a promising technology to produce nano-ZrO2 due to its simple craft, short reaction time and low cost. In this paper, nano-ZrO2 particles with an average particle size of 5.66 – 35.43 nm were successfully prepared by supercritical hydrothermal method. Meanwhile, the influences of reaction temperature, pressure, time, precursor concentration and pH value on the particle size distributions and surface topographies of nano-ZrO2 were investigated under different conditions. Reaction time and precursor concentration were strong influencing factors of particle sizes and distributions. The reaction mechanisms of different crystal forms were controlled by pH value of the precursor. Under acidic conditions, soluble [Zr4(OH)8(H2O)16] 8+ was produced due to the hydrolysis of precursors, and the appearance of abundant monoclinic nucleus was triggered subsequent condensation of [Zr4(OH)8(H2O)16] 8+. In-situ crystallization dominated the crystallization process and the tetragonal phase was formed by the rearrangement of the precursor structures. The intermediate product Zr(OH)3NO3 was detected under high pH conditions.

Pomegranate-like Fe2O3@C nanoparticles on carbon cloth (CC) as an anode for lithium-ion batteries are synthesized via a combination of dip-coating and hydrothermal synthesis. The spontaneous crosslinking reaction between sodium alginate (SA) and Fe3+ first creates a chelate compound, and then the SA-Fe3+ chelate is converted to Fe2O3@C nanoparticles after a simple hydrothermal treatment. The Fe2O3@C nanoparticles exhibit pomegranate-like morphology with an average diameter of 118 nm and are composed of smaller Fe2O3@C secondary nanoparticles of 13.7 nm. Such a hierarchical nanostructure can increase the accessible surface area of the Fe2O3@C/CC electrode, leading to enhanced electrochemical efficiency for the Li+ insertion/deinsertion reaction. Furthermore, by carefully controlling dip-coating time, the Fe2O3@C nanoparticles are individually and uniformly distributed on the CC surface, which supplies expansion space for Li+ insertion and protects the electrode from structural cracks. Owing to these structural characteristics, the Fe2O3@C/CC anode material shows superior electrochemical properties for lithium-ion batteries. The first discharge capacity is as high as 1006 mAh g−1 at the current density of 0.2 A g−1, and it remains up to 1091 mAh g−1 after 100 charge/discharge cycles, implying a stable cycling ability.

Ni-Co-Cu alloy nanoparticles were synthesized using a hydrothermal method from the low nickel matte. The effects of synthetic parameters such as hydrothermal temperature, pH value of precursor solution, added amount of PVP and reaction time on the chemical compositions, micromorphology and magnetic properties of the prepared products were systematically investigated by X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), High-resolution TEM (HRTEM) and Vibrating sample magnetometer (VSM). It is indicated that the size of as-prepared Ni-Co-Cu alloy nanoparticles decreased with the increasing of reaction temperature (150 °C-180 °C), pH value (10.0–12.0) and the added amount of PVP (0–1.0 g mL−1). Under the optimal experimental conditions, pure Ni-based alloy (Ni0.95Co0.03Cu0.02) which exhibited good magnetic properties with the saturation magnetization (Ms) value of 48.72 emu g−1 and the coercivity (Hc) value of 126.39 Oe, respectively, was achieved. Moreover, the main impurity ions, such as Fe ions in the leaching solution of low nickel matte, have no effect on the purity of as-prepared alloy nanoparticles. This paper may provide a new way for the synthesis of alloys from natural minerals for the first time.

A ternary MoO3/TiO2/Ti3C2Tx composite was successfully prepared through in-situ oxidation of Ti3C2Tx and loading of MoO3 nanoparticles by one-pot hydrothermal method. The obtained ternary composite was characterized by X-ray diffraction, XPS, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It could be clearly found that the TiO2 nanoparticles and MoO3 nanoparticles were well dispersed on the Ti3C2Tx, larger TiO2 nanoparticles were attached on the edges of Ti3C2Tx layers and smaller MoO3 nanoparticles were dispersed between Ti3C2Tx layers. The nanoparticles extremely increase specific surface area of MoO3/TiO2/Ti3C2Tx composite to 33.6 m2 g−1, and 9.8 m2 g−1 for as-prepared Ti3C2Tx powder. Electrochemical properties testing results showed a specific capacitance of 162 F g−1 at a scan rate of 2 mV s−1 in the potential range from −1 V to −0.3 V with 1 mol L−1 KOH as electrolyte during the cyclic voltammetry (CV) cycles, which is superior to the performance of pure 2D layered Ti3C2Tx. Also, the as-prepared ternary composites exhibited good specific capacitance retention of 91% after 8000 cycles. It is confirmed that the three components of ternary composites could make the integrated electrochemical behavior display and lead to a resulting capacitor with enhanced performance. The significant enhancement in electrochemical performance of the ternary composites can be attributed to the synergistic effect and cooperation of TiO2 and MoO3 nanoparticles dispersed on the Ti3C2Tx sheets.

In order to further improve electrocatalytic ability of MoS2 counter electrode(CE) in fiber-shaped dye sensitized solar cells(FDSSCs), Ni element was introduced and Ni-Mo-S nanosheet array was prepared by a simple one-step hydrothermal process. By utilizing synergetic effects between two transition metals and more catalytically active edges in Ni-Mo-S nanosheet array, lower series transfer resistance(Rct) at the interface of CE/electrolyte in the electrochemical impedance spectra (EIS) measurement and higher cathodic peak current in the cyclic voltammetry (CV) measurement were obtained when compared with MoS2, indicating Ni-Mo-S processed superior electrocatalytic activity to MoS2. As a result, power conversion efficiency of Ni-Mo-S based FDSSC(6.3%) was found to be higher than MoS2-based FDSSC (4.2%), comparable to Pt based FDSSC(6.4%).

In this work, we developed a facile method to prepare FeOOH directly deposited on the Ni foam through one-pot hydrothermal route. The as-prepared FeOOH/Ni foams (FN) were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). Electrochemical performances of the as-prepared FN as electrodes were also evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectrometry (EIS) in 1 M KOH aqueous solution. The results indicate that the flocculent amorphous FeOOH flakes homogeneously grown on the surface of Ni foams construct a three-dimensional (3D) porous structure, which not only provides easy penetration of liquid electrolyte, facilitating fast electron transfer and ion diffusion, but also alleviates the volume change of FN electrodes during the charge-discharge process. The optimized FN electrode exhibits a high specific capacitance of 1300 F/g at a current density of 2 A/g, and excellent capacitance retention of 91% after 2000 cycle tests at a current density of 4 A/g. This work would open an avenue for designing high-performance amorphous electrode materials for supercapacitors.

3D hierarchical porous MoS2 microspheres assembled by nanosheets were successfully fabricated via a facile yet efficient hydrothermal process using an assistance of CTAB as soft template which had significant effects on the final morphology of MoS2 products. The possible formation mechanism of the harvested porous MoS2 microspheres were preliminarily presented on the basis of the experimental results. Moreover, the gas sensing properties of the samples were investigated. The hierarchical porous MoS2 microspheres are found to exhibit an excellent gas response capability, good response-recovery properties, reproducibility and selectivity, which provides further evidence that assistance CTAB is critical for governing the morphology and properties of the MoS2.

Composite C@NiCo2O4 hollow microspheres (HSs) as electrode material were prepared via a two-step strategy of hard-template induced hydrothermal synthesis and calcination, in which SiO2@RF (resorcinol–formaldehyde resin, RF) sphere and hexamethylenetetramine (HMT) were used as hard template, and precipitant; Ni(NO3)2·6H2O and Co(NO3)2·6H2O as nickel and cobalt source, respectively. The resultant samples are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) patterns, XPS and N2 adsorption and desorption. The prepared C@NiCo2O4 material possess large specific surface area of 127.61 m2 g−1 and porous structure. The electrochemical measurements show that the C@NiCo2O4 exhibit a large specific capacitance of 404 F g−1 at the current density of 1 A/g, a good cyclic stability with a capacitance retention of 87.1% after 1000 cycles of charge–discharge and a low resistance.

Nitrogen doped graphene oxide (NG) modified WSe2 nanorod composites (WSe2/NG) were prepared by a hydrothermal synthesis route. The synthesized samples were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy(DRS) and elemental analysis. Using methylene blue (MB) as a target organic dye, WSe2/NG nanocomposites exhibited significant enhancement in photocatalytic degradation of MB under visible light irradiation compared with WSe2. That was mainly attributed to the strong adsorption of MB, excellent electrical conductivity and charge separation features of the NG, leading to effectively restrained electron-hole pair recombination of WSe2 nanorods. Among the hybrid photocatalysts, WSe2/50NG (50 wt% of NG) exhibited the highest photocatalytic activity with a rate constant of 0.0572 min−1 for the degradation of the MB in aqueous solution under visible light irradiation, and the removal efficiency reached 99.3% which was 2.4 times higher than that of WSe2. In addition, WSe2/NG also showed higher stability and good reusability.

High quality N-doped Bi2WO6 nanoparticles were synthesized using a two-step microwave-assisted and hydrothermal method. The morphological, structural, compositional and optical properties of the samples were investigated using a scanning electron microscope, N2 adsorption/desorption, X-ray diffraction, X-ray photoelectron spectroscopy, UV-VIS diffuse reflectance and photoluminescence. The photocatalytic activity of the samples was studied using visible light irradiation of rhodamine B. Our results show that this two-step synthesis and N-doping are both helpful in enhancing the photocatalytic activity of Bi2WO6 nanoparticles, and that N-doping plays a more important role than the two-step synthesis. The best photocatalytic activity can be achieved by the N-doping of N:Bi = 0.5% (atomic ratio), which is mainly due to the greatest decrease in recombination rate of photogenerated electron-hole pairs obtained with this doping content. In addition, the photocatalytic mechanism study indicated that the photogenerated holes are the dominant active species in the photocatalytic process.

The Y2WO6:Yb3+/Er3+ crystals were synthesized by the hydrothermal method. The needle-shaped morphology is controllably formed and a number of crystals aggregate as spheres by adding the surfactant of sodium dodecylbenzenesulfonate (SDBS) into the reaction system. The crystal structure, morphology and upconversion luminescence properties of the Y2WO6:Yb3+/Er3+ crystals are conducted on the basis of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), FTIR and emission spectra. The different emission intensity ratio of the red and green bands is observed for the Y2WO6:Yb3+/Er3+ precursors under different heat treatments. The different intensity ratio are illustrated according to the upconversion mechanism.

A MoS2-coated CoS2 composite has been prepared successfully via a one-step hydrothermal method. This CoS2@MoS2 hybrid material has a distinct morphology with few-layer MoS2 wrapping the CoS2 nanoparticles. Serving as a supercapacitor electrode, the obtained CoS2@MoS2 hybrid material exhibits a remarkable specific capacitance of 1038 F/g, a high rate capability of 71.7%, and excellent cycling stability of 84.76% retention after 10000 cycles. The superior electrochemical properties of the CoS2@MoS2 nanocomposite are attributed to the synergistic effects between the layered MoS2 and conductive CoS2.