Microwave-assisted Hydrothermal Synthesis Method Research Articles

Structural, optical and temperature-sensing properties of LaOF:Yb3+, Tm3+ nanophosphor prepared by microwave-assisted hydrothermal synthesis

Luminescence thermometry forms a unique tool for remote temperature sensing by exploiting the variations in the luminescence properties of the probe. Thermometry based on the fluorescence intensity ratios (FIR) is a widely practiced approach due to them being a self-referenced measure. The quest for efficient temperature probes for thermometry led to the discovery of LaOF:Yb3+,Tm3+ upconversion nanoparticles, which were synthesized using a microwave-assisted hydrothermal synthesis method. Blue and near-infrared upconversion photoluminescence (UCPL) emission was observed under 980 nm laser excitation. The temperature-dependent UCPL was studied for their temperature sensing application. FIR of thermally coupled and non-coupled emission bands were calculated in the temperature range of 303 to 473 K. The thermometric characteristics such as absolute sensitivity, relative sensitivity and temperature uncertainty were also determined. The thermal stability of the UCNPs was established under continuous laser exposure operating at maximum power (2500mW). The reproducibility of the UCNPs was also determined by temperature cycling the UCNPs.

Photoreactive Carbon Dots Modified g-C3N4 for Effective Photooxidation of Bisphenol-A under Visible Light Irradiation

A series of carbon dots (CDs) modified g-C3N4 (xCDs/g-C3N4; x = 0.5, 1.0, and 1.5 mL CDs solution) was synthesized via the microwave-assisted hydrothermal synthesis method for the photooxidation of bisphenol-A (BPA) under visible light irradiation. The X-ray diffraction (XRD) analysis indicates that the CDs may have a turbostratic structure and the resulting photocatalysts have distorted crystal structure, as compared with pure g-C3N4. The high-resolution transmission electron microscope (HR-TEM) analysis revealed amorphous, mono-disperse, spherical CDs with an average particle size of 3.75 nm. The distribution of CDs within the matrix of g-C3N4 appear as small dark dot-like domains. The N2 adsorption-desorption analysis indicates that the nanocomposites are mesoporous with a density functional theory (DFT) estimate of the pore size distribution between 2–13 nm. The CDs quantum yield (QY) was determined to be 12% using the UV-vis spectral analysis, where the CDs/g-C3N4 has improved absorption in the visible region than g-C3N4. The higher BET surface area of CDs/g-C3N4 provided more adsorption sites and the ability to yield photogenerated e−/h+ pairs, which caused the 1.5 CDs/g-C3N4 to have better photocatalytic efficiency compared to the rest of the systems. The highest removal, 90%, was achieved at the following optimum conditions: BPA initial concentration = 20 mg L−1, catalyst dosage = 30 mg L−1, and pH = 10. The photooxidation process is mainly driven by photogenerated holes (h+) followed by •OH and O2•−. The synthesis of the 1.5 CDs/g-C3N4 system is simple and cost-effective, where this photocatalyst is highly stable and reusable versus other systems reported in the literature.

Multifunctional Smart ZnSe-Nanostructure-Based Fluorescent Aptasensor for the Detection of Ochratoxin A.

Herein, we present a comprehensive investigation of rationally designed zinc selenide (ZnSe) nanostructures to achieve highly negatively charged ZnSe nanostructures. A Microwave-assisted hydrothermal synthesis method was used to synthesize three types of ZnSe nanostructures, i.e., nanorods, µ-spheres and nanoclusters, as characterized by a zeta potential analyzer, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and BET, which were labeled as type A, B and C. Three different solvents were used for the synthesis of type A, B and C ZnSe nanostructures, keeping other synthesis conditions such as temperature, pressure and precursors ratio constant. Based on two heating time intervals, 6 and 9 h, types A, B and C were further divided into types A6, A9, B6, B9, C6 and C9. ZnSe nanostructures were further evaluated based on their fluorescent quenching efficiency. The maximum fluorescence quenching effect was exhibited by the ZnSe-B6 type, which can be attributed to its highly negative surface charge that favored its strong interaction with cationic dye Rhodamine B (Rh-B). Further, the optimized ZnSe-B6 was used to fabricate an aptasensor for the detection of a food-based toxin, ochratoxin-A (OTA). The developed aptasensor exhibited a limit of detection of 0.07 ng/L with a wide linear range of 0.1 to 200 ng/L.

Achieving high thermoelectric performance through carrier concentration optimization and energy filtering in Cu3SbSe4-based materials

The previous works commonly adjust the carrier concentration through acceptor doping, but at the same time, the decrease of the Seebeck coefficient limits the further improvement of electrical properties in Cu3SbSe4-based materials. In this work, a microwave-assisted hydrothermal synthesis method was used to synthesize Cu3SbSe4/TiO2 hollow microspheres. Part of TiO2 participates in the reaction, replaces the Sb site of Cu3SbSe4 to form holes, and the rest is dispersed in the matrix in the form of the second phase. The first-principles calculations reveal that the doping of Ti significantly changes the band structure and phonon spectrum, thereby regulating carrier concentration while increasing phonon scattering. In addition, experimental results show that the energy filtering effect generated by the extra-mixed TiO2 nano particles, which suppresses the decrease of Seebeck coefficient by acceptor doping. Consequently, the highest average power factor 897.5 μW m−1 K−2 and the zT peak value of 0.70 can be obtained in Cu3SbSe4/6%TiO2 sample at 298–623 K. This work provides a new sight to improve the thermoelectric properties in Cu3SbSe4 through carrier concentration regulation and nano-phase composition.

Fabrication and characterization of La2O3–Fe2O3–Bi2O3 nanopowders: Effects of La2O3 addition on structure, optical, and radiation-absorption properties

In this study, we fabricated and characterized six new nanopowders representing variations of La2O3–Fe2O3–Bi2O3, i.e., 100Bi2O3, 30Fe2O3–70Bi2O3, 3La2O3–27Fe2O3–70Bi2O3, 7La2O3–23Fe2O3–70Bi2O3, 10La2O3–20Fe2O3–70Bi2O3, and 20La2O3–10Fe2O3–70Bi2O3 (represented by 100B, 30F70B, 3L27F70B, 10L20F70B, and 20L10F70B, respectively). These nanopowders were prepared by the microwave-assisted hydrothermal synthesis method. Saponin extract from soapnuts was used as the nanoparticle capping agent. The structural, optical, and gamma radiation characteristics were measured, calculated, and analysed, respectively. The chemical structures of the nanocomposites influenced their optical and radiation shielding characteristics. The optical bandgaps of the 100B, 30F70B, 3L27F70B, 7L23F70B, 10L20F70B, and 20L10F70B nanopowders were 3.16, 3.13, 3.43, 3.45, 3.46, and 3.58 eV, respectively. The ranges of the mass attenuation coefficients of the nanopowders were computed, using XCOM, to be 0.0412–5.1624, 0.0401–4.5406, 0.0401–4.5285, 0.0401–4.5129, 0.0401–0.5015, and 0.0400–4.4156 cm2/g, respectively, and the ranges of mass energy absorption coefficients were found to be 0.0232–1.7525, 0.0228–1.5484, 0.0228–1.5598, 0.0288–1.5746, 0.0228–1.5853, and 0.0227–1.6192 cm2/g, respectively, for photon energies in the range of 0.1–10 MeV. The order of the dose rate trend was as follows: 30F70B < L27F70B < 7L23F70B < 10L20F70B < 20L10F70B. Analysis of the photon interaction parameters showed that the synthesized nanopowders could function well as fillers in radiation-shielding matrices.

Microwave-assisted hydrothermal synthesis of NiMoO4 nanorods for high-performance urea electrooxidation

A large surface area with high active site exposure is desired for the nano-scaled electrocatalysts fabrication. Herein, taking NiMoO4 nanorods for example, we demonstrated the advantages of the microwave-assisted hydrothermal synthesis method compared to the traditional hydrothermal approaches. Both monoclinic structured NiMoO4 in the nanorods morphology are found for these samples but it is more time-saving and efficient in the Ni-Mo synergism for the catalyst obtained by microwave-assisted hydrothermal syntheses method. When evaluated for urea oxidation, the current density can reach 130.79 mA/cm2 at 1.54 V, about 2.4 times higher than that of the counterpart catalyst (54.08 mA/cm2). Moreover, largely improved catalytic stability, catalytic kinetics and rapid charge transfer ability are found on the catalyst obtained by the microwave-assisted approach. The high catalytic performance can be attributed to the high surface area and active site exposure of NiMoO4 nanorods formed by microwave irradiation. Considering the less time, facile synthesis condition and efficient components synergism, the microwave-assisted hydrothermal synthesis method might work better for the nanostructure electrocatalysts fabrication.

Smart pathways for the photocatalytic degradation of sulfamethoxazole drug using F-Pd co-doped TiO2 nanocomposites

We report the doping of TiO2 with fluorine (F) and palladium (Pd) to synthesize F-Pd co-doped TiO2 nanocomposites via a microwave-assisted hydrothermal synthesis method as a smart pathway to achieve efficient photocatalytic degradation of sulfamethoxazole (SMX) using both a solar simulator and direct sunlight irradiation. SMX is an emerging persistent drug that might have toxic effects on aquatic organisms because of its antibiotic-resistance. The F-Pd co-doped TiO2 nanocomposites produced in this work have an outstanding extension effect on the photocatalytic activity of TiO2 to the visible and near infrared regions; thus, showing efficient photocatalytic degradation of SMX and floatation of fluorinated products. TEM images shows that the particles of the F-Pd co-doped TiO2 nanocomposites have average particle sizes ranging between 5−25 nm. The band gap of the F-Pd co-doped TiO2 shifted down to 0.54 eV which is a significant shift from the band gap of TiO2 i.e., 3.26 eV. Thus, the photodegradation of 94.4 % of SMX was achieved within 20 min and 98.8 % after 70 min under direct sunlight irradiation. In addition, more than 42.5 % of SMX was degraded by F-Pd co-doped TiO2 nanocomposites with 3 % and above of Pd after just 5 min of adsorption in the dark. By doping TiO2 with F and Pd, three processes were thus achieved: 1) photocatalytic degradation, 2) fluorination of the degraded products and 3) floatation as fluoropolymer. These three processes, therefore, present one of the smart pathways to provide an efficient water treatment system for wastewater.

Mercaptopropionic acid-capped Mn-doped ZnS quantum dots and Pb2+ as sensing system for rapid and sensitive room-temperature phosphorescence detection of sulfide in water

As a kind of serious concern environmental toxic pollutants, sulfide is widely used in various industrial processes, and generated from the process of biological metabolism. However, the sensitive, rapid and effective detection of sulfide still remains challenge. In this paper, a simple and rapid room-temperature phosphorescence (RTP) method for the detection of sulfide with a high selectivity and sensitivity was proposed by using mercaptopropionic acid (MPA)-capped Mn-doped ZnS quantum dots (QDs) and Pb2+ as a sensing system. Highly water-soluble MPA-capped Mn-doped ZnS QDs with phosphorescence emission property were successfully synthesized by microwave-assisted hydrothermal synthesis method. We discovered that the as-prepared QDs displayed effectively phosphorescence quenching to Pb2+ in pH 11.5 borax-NaOH buffer solution, then demonstrated remarkable phosphorescence recovery after the addition of sulfide to the QDs-Pb2+ system. Therefore, based on the phosphorescence "off-on" behavior of MPA-capped Mn-doped ZnS QDs, a simple, sensitive and selective phosphorescence method for rapid detection of sulfide was successfully developed. The quenching and recovery of the phosphorescence of MPA-capped Mn-doped ZnS QDs have been studied in detail. Under the optimized conditions, the recovered degree of RTP intensity had a very good linear relationship with sulfide concentration in the range of 2 × 10−7–80 × 10−7 mol L−1 with a correlation coefficient of 0.9982, and a lower detection limit of 6.89 × 10−8 mol L−1. The relative standard deviations for eleven times repeated detections of 5 × 10−6 and 8 × 10−6 mol L−1 sulfide were 3.24% and 4.50%, respectively. The proposed method could effectively avoid the interferences of common anions, fluorescence substances and scattering light. Furthermore, it was successfully applied to detect sulfide in real water samples with satisfactory results, and the recoveries were in the range from 94.2% to 107.1%. This work will provide the basis of method for the development of fast and on-line monitoring sensors of small molecule pollutions in water.

Au Supported TiO&lt;sub&gt;2&lt;/sub&gt;-Nanofibers as Novel Catalysts for Glycerol Oxidation

Composites of Au supported on the TiO2-nanofibers (Au/NF-TiO2) were synthesized and tested in glycerol oxidation processes. TiO2-nanofibers were prepared by a microwave-assisted hydrothermal synthesis method. Chemical deposition method was used for nanofibers modification with Au nanoparticles. Oxidation of aqueous glycerol solutions by molecular oxygen in the presence of Au/NF-TiO2 nanocomposites was performed. It was found that Au/NF-TiO2 composites are catalytically active in alkaline glycerol water solutions. The main product of glycerol catalytic oxidation was glyceric acid, by-products were – tartronic, lactic, glycolic, oxalic, acetic and formic acid. It was shown that Au/NF-TiO2 catalysts’ activity and selectivity depend on Au weight loading, glycerol/Au molar ratio, oxygen pressure and NaOH initial concentration. The best result was achieved using the 0.5 wt%Au/NF-TiO2 catalyst: selectivity by glyceric acid was 76% with glycerol conversion 100%.

Ga-doped ZnO self-assembled nanostructures obtained by microwave-assisted hydrothermal synthesis: Effect on morphology and optical properties

Highly homogeneous gallium doped ZnO assembled nanostructures comprised by thin hexagonal platelets showing a striking preferred orientation along the ab plane have been obtained by an ultra-fast and eco-friendly microwave-assisted hydrothermal synthesis method. Although the incorporation of gallium into the ZnO lattice is found to be relatively low, namely ≤1 mol.%, the gallium nitrate addition plays a key role in the size and morphology of the obtained ZnO nanostructures. The observed morphology is attributed to the selective adsorption of the gallium species on the basal planes of ZnO, which inhibits the growth along the ± [0001] direction. Additionally, the optical band-gap and the fluorescence emission are modified upon gallium addition. The observed changes in the optical properties are ascribed to both the decreased crystal size and to the gallium incorporation into the ZnO structure, which lead to the modification in the energy levels.

Microwave-assisted hydrothermal synthesis of NH4V3O8 microcrystals with controllable morphology

Water-free NH4V3O8 microcrystals have been successfully synthesized by a microwave-assisted hydrothermal synthesis method. The products were characterized by means of X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis, cyclic voltammetry, and galvanostatic cycling. The results show phase-pure products whose particle size and morphology can be tailored by varying the reaction conditions temperature, time, and initial pH value. For instance, at low pH (2.5⿿3) flower-like agglomerates with primary particles of 20⿿30μm length are found, while at pH 5.5 single microplates with hexagonal outline (30⿿40μm) prevail. The electrochemical studies show reversible lithium de-/intercalation into the layered NH4V3O8 host structures with a maximum initial discharge capacity of 378mAhg⿿1 at 10mAg⿿1. However, there is no clear effect of the materials⿿ morphology on their electrochemical performance.

Microwave-assisted synthesis of BiFeO3nanoparticles with high catalytic performance in microwave-enhanced Fenton-like process

Synthesis of BiFeO3using microwave-assisted hydrothermal synthesis method.

A high-voltage lithium-ion battery prepared using a Sn-decorated reduced graphene oxide anode and a LiNi0.5Mn1.5O4 cathode

This paper describes the preparation and characterization of a high-voltage lithium-ion battery based on Sn-decorated reduced graphene oxide and LiNi0.5Mn1.5O4 as the anode and cathode active materials, respectively. The Sn-decorated reduced graphene oxide is prepared using a microwave-assisted hydrothermal synthesis method followed by reduction at high temperature of a mixture of (C6H5)2SnCl2 and graphene oxide. The so-obtained anode material is characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and electron diffraction spectroscopy. The LiNi0.5Mn1.5O4 is a commercially available product. The two materials are used to prepare composite electrodes, and their electrochemical properties are investigated by galvanostatic charge/discharge cycles at various current densities in lithium cells. The electrodes are then used to assemble a high-voltage lithium-ion cell, and the cell is tested to evaluate its performance as a function of discharge rate and cycle number.

Microwave-Assisted Hydrothermal Synthesis of Ni-Mg Layered Silicate Clays

The synthesis of Ni-containing layered silicate clays from the lizardite-nepouite series (1:1) and kerolite-pimelite series (2:1) with random distribution of octahedral cations was feasible with the microwave-assisted hydrothermal synthesis method. These series were obtained from co-precipitated gels with Si 2 Mg 3-x Ni x O 7 .nH 2 O and Si 4 Mg 3-x Ni x O 11 .nH 2 O (x = 0, 0.5, 1, 1.5, 2, 2.5, and 3) compositions. Syntheses were performed at 220°C during 48 hours under equilibrium water pressure using microwave furnace. X-ray diffraction revealed pure 1:1 and 2:1 synthesized phyllosilicates for the lizardite and the kerolite series, respectively. Fourier transform infrared spectroscopy in both near and mid infrared regions revealed a random distribution of Ni cations in the octahedral sheet of 1:1 and 2:1 silicate clays, that is a good requirement for material applications, especially for the synthesis of metallic catalysts.

Microwave assisted growth of SAPO-34 on β-SiC foams for methanol dehydration to dimethyl ether

SAPO-34 layers were successfully grown on β-SiC foam with medium specific surface-area, using microwave-assisted hydrothermal synthesis method (MAHyS) for applications as a structured catalyst. Preliminary investigations on SAPO-34 phase purity were conducted to select the appropriate concentrations and protocol to grow pure SAPO-34 on SiC foams. SAPO-34/SiC foam composite was obtained via microwave-assisted synthesis route. X-ray diffraction (XRD) was used to confirm the formation of the composite. Microwave irradiation time, number of coating cycles and pretreatment of the SiC support with zeolite precursor and the template solution were studied to optimize the growth and coverage of SAPO-34 crystals on the SiC foam surface. SAPO-34 crystals with cubic morphologies having 7μm average size were obtained after 6h microwave irradiation at 180°C. However, multi coating steps were required to obtain full coverage of SAPO-34 crystals. Template pretreatments of the host material (SiC foams) significantly improved the loading of crystals on the support surface. Full coverage of SAPO-34 on SiC foams was obtained after 3 times of coatings, which is mostly attributed to the template layer formed on the foam surface that induced the heterogeneous nucleation on the support. The SAPO-34/SiC foam structured catalyst exhibited excellent selectivity and stability in methanol dehydration to dimethyl ether, which was carried out in a fixed bed reactor.

Synthesis and Characterization of Manganese Oxide/CNTs Composites as Electrochemical Capacitor Electrode Materials

Manganese oxide (MnO2)/Carbon nanotubes(CNTs) composites were prepared by a home-made microwave heating equipment. The crystal structure, microstructure, electrochemical properties were characterized by XRD and SEM, the discharge capacity and cycling performance were compared. The results show a birnessite-type MnO2 coating can be prepared. In this paper, a microwave-assisted hydrothermal synthesis method was used to synthesize the MnO2/CNTs composites. MnO2 content increases with the increasing of microwave power, which result in the specific capacitances of as-perpared materials increase

Microstructure and CO gas sensing property of Au/SnO2 core–shell structure nanoparticles synthesized by precipitation method and microwave-assisted hydrothermal synthesis method

Au/SnO2 core–shell structure NPs were prepared by a precipitation method and a microwave hydrothermal synthesis method, and their CO responses were measured by a high resistance meter. It was found that the CO response of the sample prepared by the precipitation method was extremely low, 0.18, with comparison to the one by the hydrothermal synthesis method, 0.965. Microstructures achieved by two-dimensional TEM characterization showed that both samples maintained the similar core–shell structures with their sizes ranging between 30 and 50nm, as the core consists of Au NP and the shell consists of SnO2 NPs. The average grain sizes of SnO2 NPs of precipitation method and hydrothermal synthesis method were measured as 5.2nm and 8.3nm, respectively. The thickness and the porosity variation of SnO2-shell layers were characterized further by three-dimensional electron tomography, and correlated with the sensing properties. It was found that the porosity within SnO2-shell layers prepared by the precipitation method was lower than the one prepared by the hydrothermal synthesis method. Since Au NP could act as the catalyst for CO oxidation reaction, high porosity within SnO2-shell layers would have lead the accessibilities of Au NP to the CO gas molecules and resulted high CO responses.

Preparation of Visible-Light-Driven Silver Vanadates by a Microwave-Assisted Hydrothermal Method for the Photodegradation of Volatile Organic Vapors

A variety of visible-light-driven silver vanadates, including α-AgVO3, β-AgVO3, and α-Ag3VO4, were synthesized using a microwave-assisted hydrothermal synthesis method. UV−vis spectroscopy indicated that each of the silver vanadate particles obtained in the study had strong visible-light absorption with associated band gaps in the range of 2.2−2.5 eV. The α-Ag3VO4 crystalline sample with rich hydroxyl functional groups on the surface exhibited the highest degree of photocatalytic activity. The reaction rates of the photodegradation of isopropanol (IPA) and benzene vapors were approximately 8 times higher than those of P25 under visible-light irradiation. Furthermore, the active sites at which catalysts play a role as proton donors (Brønsted acidity) in the photodegradation of VOC were characterized by the temperature-programmed desorption (TPD) method in conjunction with the diffuse reflectance infrared Fourier transform (DRIFT) technique. In addition, the photocatalytic activities of microwave-assisted hydrothermal samples were higher than those of samples produced by conventional hydrothermal techniques. This was due to an increase in the specific surface area and additional hydroxyl functional groups on the surface. These results demonstrate that the microwave-assisted hydrothermal method is an efficient technique for the fabrication of visible-light-responsive silver vanadates with outstanding performance in the photocatalysis of VOCs.