Facile Microwave-assisted Solvothermal Method Research Articles

Insights into the kinetics–morphology relationship of 1-, 2-, and 3D TiNb2O7 anodes for Li-ion storage

Understanding the influence of electrode material’s morphology on electrochemical behavior is of great significance for the development of rechargeable batteries, however, such studies are often limited by the inability to precisely control the morphology of electrode materials. Herein, nanostructured titanium niobium oxides (TiNb2O7) with three different morphologies (one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D)) were synthesized via a facile microwave-assisted solvothermal method. The influence of the morphological dimension of TiNb2O7 as electrode material on the electrochemical performance in Li-ion batteries (LIBs) and the underlying correlation with the electrochemical kinetics were studied in detail. 2D TiNb2O7 (TNO-2D) shows a superior rate capability and cycling stability, associated with improved kinetics for charge transfer and Li-ion diffusion, compared to the 1D and 3D materials. Operando X-ray diffraction measurements reveal the structural stability and crystallographic evolution of TNO-2D upon lithiation and delithiation and correlate the Li-ion diffusion kinetics with the lattice evolution during battery charge and discharge. Moreover, carbon-coated TNO-2D achieves enhanced rate capability (205 mAh·g−1 at 50 C) and long-term cycling stability (87% after 1000 cycles at 5 C). This work provides insights into the rational morphology design of electrode materials for accelerated charge transfer and enhanced fast-charging capability, pushing forward the development of electrode materials for high-power rechargeable batteries in future energy storage.

Enhanced Li storage properties of nickel oxalate microtubes with manganese doping and graphene oxide for lithium-ion batteries

Nowadays, metal oxalates with high discharge/charge capacities were chosen as new anode materials for batteries. Here, novel nickel oxalates microtubes with manganese doping and graphene Oxide (Ni0.8Mn0.2C2O4∙2 H2O/GO) are synthesized at low temperature through a facile microwave-assisted solvothermal method. The X-ray diffraction confirmed a formation of a pure binary compound of Ni0.8Mn0.2C2O4∙2 H2O/GO without contamination by other compounds of Nickel or Manganese. Furthermore, the formed product shows a good crystallinity and has a high surface area of 24.3 m2 g−1. With the assistance of graphene, the material delivers a high discharge capacity of 1781 mA h g−1. Even at high current densities of 5.0 and 10.0 A g−1, discharge capacities of 1138.1 and 891.0 mA h g−1 can be obtained. Encouraged by the superior rate performance, the long-term cycling performance at 10 A g−1 and 20 A g−1 was tested showing a discharge of 676.6 mA h g−1 after 300 cycles and 346.4 mA h g−1 after 1000 cycles. The remarkable electrochemical performance can be attributed to the doping of Mn in the structure of NiC2O4 ∙2 H2O and the contribution of graphene.

A microwave-assisted solvothermal method to synthesize BiOCl microflowers with oxygen vacancies and their enhanced photocatalytic performance

The photocatalytic performance of the catalysts are highly dependent on their morphology and the separation efficiency of photo-generated carriers. In this work, the self-assembled BiOCl microflowers with oxygen vacancies (OVs) were synthesized by facile microwave-assisted solvothermal method. The ethylene glycol was applied as solvent, reductant and soft templates of microflowers. As the preparation temperature increased from 100 ℃ to 160 ℃, the morphology of BiOCl was transformed from microflowers to nanosheets, and the concentration of OVs increased gradually. The photocatalytic performance of BiOCl was evaluated by photocatalytic degradation of Rhodamine B (RhB), Methylene blue (MB) and Ciprofloxacin (CIP) under visible light irradiation. It is indicated that the excessive OVs would inhibit the separation and migration of photo-generated carriers. Benefiting from the optimum OVs concentration and enhanced specific surface area, the BiOCl-100 microflowers exhibited a superior photocatalytic performance. The degradation constants for RhB, MB and CIP by BiOCl-100 were estimated to be 0.512, 0.022 and 0.022 min−1, which were 4.3, 1.7 and 5.5 folds higher than BiOCl-100-w nanosheets (with no OVs), respectively. This work demonstrated the superior photocatalytic performance of BiOCl microflowers with optimum OVs, which could be also applied to design of other highly efficient photocatalysts.

Microwave-Assisted Solvothermal Synthesis of Nanocrystallite-Derived Magnetite Spheres.

The synthesis of magnetic particles triggers the interest of many scientists due to their relevant properties and wide range of applications in the catalysis, nanomedicine, biosensing and magnetic separation fields. A fast synthesis of iron oxide magnetic particles using an eco-friendly and facile microwave-assisted solvothermal method is presented in this study. Submicron Fe3O4 spheres were prepared using FeCl3 as an iron source, ethylene glycol as a solvent and reductor and sodium acetate as a precipitating and nucleating agent. The influence of the presence of polyethylene glycol as an additional reductor and heat absorbent was also evaluated. We reduce the synthesis time to 1 min by increasing the reaction temperature using the microwave-assisted solvothermal synthesis method under pressure or by adding PEG at lower temperatures. The obtained magnetite spheres are 200–300 nm in size and are composed of 10–30 nm sized crystallites. The synthesized particles were investigated using the XRD, TGA, pulsed-field magnetometry, Raman and FTIR methods. It was determined that adding PEG results in spheres with mixed magnetite and maghemite compositions, and the synthesis time increases the size of the crystallites. The presented results provide insights into the microwave-assisted solvothermal synthesis method and ensure a fast route to obtaining spherical magnetic particles composed of different sized nanocrystallites.

Micro/nano blocks of Ni/MnO composites synthesized by microwave-assisted solvothermal for supercapacitors

The micro/nano blocks of Ni/MnO composites were synthesized by a facile microwave-assisted solvothermal method. The results indicated that the morphology changed from irregular block to polyhedron and then to the sphere with the increase of ethylene glycol (EG) ratio in the solvent. The results indicated the specific capacitance of the obtained material increased as the EG ratio increased, but when the EG ratio exceeded 60%, the change of specific capacitance was not obvious (less than 5%). For the Ni/MnO material synthesized in pure EG, its specific capacitance reached 860 F/g at 1 A/g and the capacitance retention maintained 58% after 6500 cycles. The micro/nano structure of Ni/MnO material formed in EG solvent increased the surface area and provided more transfer channels for the electrolyte ion, which were all beneficial to improve the electrochemical properties. The high capacitance and good cycle stability especially after a period of cycles demonstrated the obtained Ni/MnO materials had a potential application for the supercapacitor electrode material.

Composition-controlled high entropy metal glycerate as high-performance electrocatalyst for oxygen evolution reaction

Direct growth of novel high entropy glycerate (HEG) on Ni foam using a facile microwave-assisted solvothermal method is demonstrated. The effect of adding Ti, V, Cu, Zn, and/or Mo into a baseline quinary-metal HEG, consisting of Cr, Mn, Fe, Co, and Ni, on the electrocatalytic performance is investigated. The quinary-metal HEG shows an overpotential of 307 mV at 50 mA cm−2 (η50). We demonstrate that the catalytic activity can only be enhanced via doping with desired metals. The additions of Ti, V, and Zn lead to enhanced electrocatalytic performances, exhibiting η50 of 254, 283, and 289 mV, respectively. The co-doping of Ti and Zn into the quinary-metal HEG results in a synergistic effect, giving robust catalytic activity with an ultra-low overpotential of 251 mV at 50 mA cm−2 and a low Tafel slope of 42.3 mV dec−1, and durable stability in 1 M KOH electrolyte for 60 h at different current densities of 10 and 100 mA cm−2. Also, phase transformation of the metal glycerate into metal (oxy)hydroxide during OER is investigated using various in situ and ex-situ analyses. Density functional theory (DFT) calculation validates the synergistic effect of addition of Ti and Zn in HEG system.

Exploring UiO-66(Zr) frameworks as nanotraps for highly efficient removal of EDTA-complexed heavy metals from water

Metal-organic frameworks (MOFs), an exciting class of porous crystalline materials, are suitable for adsorptive removal of toxic heavy metal-ethylenediaminetetraacetic acid (M-EDTA) complexes from wastewater. In this paper, water-stable UiO-66(Zr) with well-defined morphology was successfully synthesized through a facile microwave-assisted solvothermal method and employed as nanotraps for the efficient capture of the three M-EDTA complexes, Cu-EDTA, Pb-EDTA, and Ni-EDTA. The adsorption behaviors, effects of solution pH and co-existing anions, as well as the eluant and desorption were investigated. The obtained UiO-66(Zr) showed good stability and excellent uptake capacity of M-EDTA in a wide pH range (3.0–10.0). UiO-66(Zr) exhibited a higher removal efficiency of Cu-EDTA (57.56 mg/g), Pb-EDTA (120.6 mg/g), and Ni-EDTA (54.27 mg/g). Based on the overall analysis results, our findings show that EDTA-metal complex ions can be adsorbed inside UiO-66(Zr) mainly through the Lewis‐acid/‐base interactions and possible anion-π interaction with strong binding energies. Size-matching EDTA-metal complexes confined in the UiO-66(Zr) with flexible geometry would also contribute to the fast adsorption kinetics as well as the selective adsorption of different M-EDTA complexes.

Facile Microwave-Assisted Synthesis of Functionalized Carbon Nitride Quantum Dots as Fluorescence Probe for Fast and Highly Selective Detection of 2,4,6-Trinitrophenol.

Functionalized carbon nitride quantum dots (CNQDs) are fabricated by moderate carbonization of L-tartaric acid and urea in oil acid media by a facile microwave-assisted solvothermal method. The obtained CNQDs are monodispersed with a narrow size distribution (average size of 3.5nm), and exhibit excellent selectivity and sensitivity of fluorescence quenching for 2,4,6-trinitrophenol (TNP) with a quenching efficiency coefficient Ksv of 4.75 × 104M-1. This sensing system exhibits a fast response time within 1min and a wide linear response range from 0.1 to 15μM. The limit of detection is as low as 87nM, which is comparable or lower than the other probes. The application of the developed probe to the detection of TNP in spiked water samples yields satisfactory results. The mechanism of fluorescence quenching is also discussed. Graphical Abstract An optical sensor based on functionalized carbon nitride quantum dots (CNQDs) were fabricated from L-tartaric acid and urea by a facile one-pot microwave-assisted solvothermal method, and were effectively utilized to the detection of 2,4,6-trinitrophenol (TNP) based on fluorescence (FL) quenching.

Rational design of hierarchical porous Fe3O4/rGO composites with lightweight and high-efficiency microwave absorption

The hierarchical porous flower-like Fe3O4/rGO composites were fabricated through facile microwave-assisted solvothermal method and annealing process. The flower-like Fe3O4 particles were in-situ grown on the rGO. The porous structure led to enhanced multiple reflections and scatterings, facilitating the increased propagation paths and the energy dissipation of electromagnetic wave (EMW). In addition, the construction of hierarchical heterostructure contributed to the strong interfacial polarization and dipole polarization. As a result, the obtained Fe3O4/rGO composites exhibited a minimum reflection loss (RLmin) value of −50.2 dB and a broad effective absorption bandwidth of 4.1 GHz at a matching thickness of only 1.5 mm. Therefore, this work provides a simple and flexible paradigm for the design and synthesis of hierarchical heterostructure as lightweight and high-efficiency EMW absorber.

Facile preparation of hydroxyl‑rich mesoporous magnesium silicate with excellent adsorption performance

The pollution of heavy metal ions and dyes in water pose a significant threat to the ecological environment and organismal health, and the development of effective adsorbents has attracted greatly attention. In the present work, hydroxyl‑rich mesoporous magnesium silicate (HMMS) with a high specific surface area of 472.9 m2/g was synthesized by a facile microwave-assisted solvothermal method for adsorption of Pb(II) ions and cationic dye methylene blue (MB) from water. HMMS particles were formed by the stack of nano-sized crystal and dense pores were formed between them. Adsorption experiments showed that HMMS exhibited fast adsorption speed and excellent adsorption capacity for Pb(II) ions (449.8 mg/g) and MB (467.3 mg/g). After six cycles, the adsorption performance of HMMS still remained above 92%. The adsorption data of HMMS for Pb(II) ions and MB were both well-fitted by the Langmuir isotherm model and pseudo-second-order kinetic model. Adsorption carried out at different initial pH values and FTIR analysis demonstrated that the adsorption mechanism of HMMS for Pb(II) ions and MB was the synergistic effect of electrostatic attraction and hydroxyl bonding. This work demonstrated that HMMS has significant potential in practical wastewater treatment.

Synergistic modulation of power factor and thermal conductivity in Cu3SbSe4 towards high thermoelectric performance

Abstract In this study, we develop a synergistic modulation of the thermal conductivity and power factor of Cu3SbSe4-based materials through Sn and Zr or Hf co-doping by using a facile microwave-assisted solvothermal method. A series of Cu3Sb1-xMxSe4 (M = Zr or Hf, x = 0, 0.02, 0.04, 0.06 and 0.08) compounds are firstly synthesized through the microwave-assisted solvothermal method combined with spark plasma sintering (SPS) process. The effect of Zr and Hf doping on the thermoelectric properties of Cu3Sb1-xMxSe4 (M = Zr or Hf) has been investigated. With increasing the content of Hf and Zr, the thermal conductivity of Cu3Sb1-xMxSe4 (M = Zr or Hf) is obviously decreased to 0.518 Wm−1K−1 of Cu3Sb0.92Hf0.08Se4 and 0.433 Wm−1K−1 of Cu3Sb0.92Zr0.08Se4 at 623 K, respectively. In addition, Sn doping further improves the low electrical conductivity and boosts the power factor, yielding a peak zT value of ~0.82 of Cu3Sb0.91Sn0.03Hf0.06Se4 at 623 K, which is ~228% higher than that of the pristine Cu3SbSe4. Our work provides a new methodology for the decoupling of thermal and electrical properties of the Cu3SbSe4-based thermoelectric materials.

Revealing the effect of cobalt-doping on Ni/Mn-based coordination polymers towards boosted Li-Storage performances

In this work, a nickel-based coordination polymer is synthesized through a facile microwave-assisted solvothermal method. Cobalt ions are further introduced by a cation-exchange process to construct the nickel-cobalt bimetallic coordination structure. This bimetallic coordination polymer (Co–Ni-BTC) exhibits substantially improved cycling performance than the single nickel coordination polymer (Ni-BTC) and previous Ni/Co-based coordination polymers with various organic ligands for lithium ion batteries. A reversible charge capacity of 1051 mAh g−1 is achieved at 100 mA g−1 after 300 cycles for Co–Ni-BTC, which is more than 4 times as large as that for Ni-BTC (258 mAh g−1) after same cycle number. The superior lithium-ion storage performance of the Co–Ni-BTC can be ascribed to its regular and porous structure inherited from the coordinated interaction between nickel/cobalt and 1,3,5-benzenetricarboxylic acid (BTC) and a highly reversible Li-reaction with the coordination polymer. The cobalt-doping is found to activate the electrochemical activity of nickel ions and facilitate the ion/electron diffusion process. The similar beneficial effect of Co-doping can also be applied to the Mn-BTC coordination polymer. These observations may shed lights on the design and development of new coordination polymer electrodes with large reversible capacities.

Microwave-assisted one-pot synthesis of SnC2O4/graphene composite anode material for lithium-ion batteries

Currently, SnC2O4 is considered as one of the most promising anode materials for high-energy lithium-ion batteries (LIBs) because its charge capacity is higher than that of metal oxides. Herein, a facile microwave-assisted solvothermal method was employed to obtain SnC2O4/GO composites within only 30 min, which is time-efficient. The amount of SnC2O4 was increased to 95.3 wt% to improve the capacity of the composite. Pure SnC2O4 with a high specific surface area of 19.6 m2 g−1 without any other tin compound was used for fabrication. The SnC2O4/GO composite exhibited excellent electrochemical performance, with reversible discharge/charge capacity of 657/659 mA h g−1 after 100 cycles at 0.2 A g−1. Furthermore, at high current densities of 1.0 and 2.0 A g−1, the SnC2O4/GO composite anode exhibited high reversible discharge/charge capacities of 553/552 and 418/414 mA h g−1, respectively, after 200 cycles at room temperature. These improvements were likely obtained because SnC2O4 was well composited with graphene, which not only offered rapid electron transfer but also released the tension produced by the volumetric effect during repeated lithiation/delithiation. Cyclic voltammetry (CV) was also performed to further study the electrochemical reactions of SnC2O4/GO. The facile microwave-assisted solvothermal method used herein is considered as a highly efficient method to fabricate metal oxalate/graphene composites for use as anode materials in LIBs.

High thermoelectric performance of Cu3SbSe4 nanocrystals with Cu2-xSe in situ inclusions synthesized by a microwave-assisted solvothermal method.

(Ag,Sn) co-doped Cu3SbSe4 nanocrystals are obtained via a facile microwave-assisted solvothermal method, and their thermoelectric properties are investigated in the temperature range from 300 K to 623 K. Sn-doping on Sb sites dramatically increases the carrier concentration and thus the electrical conductivity, promoting the thermoelectric power factor. Further alloying with Ag on Cu sites strongly suppresses the lattice thermal conductivity close to the glass limit. Aside from point defect scattering, such reduction in lattice thermal conductivity largely relies on the formation of Cu2-xSe nanoinclusions, which serve as additional scattering centers for phonons. Overall, the sample with the nominal composition of Cu2.8Ag0.2Sb0.95Sn0.05Se4 reaches a minimum lattice thermal conductivity of 0.27 W m-1 K-1 and a maximum zT of 1.18 at 623 K, which is the best result for the Cu3SbSe4-based materials in the same temperature region. Our results demonstrate that the microwave-assisted synthesis method is capable of fabricating Cu based ternary compounds with high thermoelectric performance.

A facile microwave-assisted fabrication of fluorescent carbon nitride quantum dots and their application in the detection of mercury ions

A facile microwave-assisted solvothermal method was used to prepare fluorescent carbon nitride quantum dots (CNQDs) using oleic acid as the reaction media at moderate reaction temperature in a short time (5min). Citric acid monohydrate and urea were used as the precursors. The as-prepared CNQDs were characterized by multiple analytical techniques. The CNQDs exhibited an uncommon excitation wavelength-dependent fluorescence with two maximum emission peaks at 450 and 540nm. The CNQDs with a quantum yield of 27.1% could serve as an effective fluorescent sensing platform for label-free sensitive detection of Hg2+ ions with a detection limit of 0.14μM. This method was also applied to the detection of Hg2+ ions in tap water samples.

CuS Nanotubes:Microwave-Solvothermal Synthesis and Photocatalytic Property

Copper sulfide (CuS) nanotubes assembled by nanoparticles were successfully synthesized by reaction thiourea with Cu(OH)2nanowire precursor which was obtained using CuCl2and NaOH as raw materials in the solvent ethylene glycol at 80 °C by a facile microwave-assisted solvothermal method. The forming influencing factors of CuS nanotubes were investigated. One of the advantages of this method is that the preparation of CuS nanotubes can well duplicate the shape of the nanowire precursor, thus the simplicity and low cost can be achieved. The products are characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The photocatalytic property of the CuS samples was also investigated.

Rapid microwave-assisted synthesis of hierarchical ZnO hollow spheres and their application in Cr(VI) removal

A rapid one-pot synthesis of hierarchical ZnO hollow spheres consisting of nanoparticles was realized by a facile microwave-assisted solvothermal method using ethanol as the solvent. According to the time-dependent observation of the formation process, a tentative mechanism based on ethyl acetate bubble-templating self-assembly of ZnO nanoparticles was proposed for the formation of the ZnO hollow spheres. Compared with the conventional heating, the microwave irradiation resulted in a significantly shortened reaction time (within 30 min) and considerably improved quality of the ZnO hollow spheres, such as narrower size distribution and more regular morphology, owing to the high heating rate and thus the accelerated reaction rate. It was shown that the microwave-assisted synthesis of ZnO nanostructures with tunable morphologies can be realized by judicious selection of appropriate solvents. The obtained ZnO hollow spheres exhibited an excellent adsorption capacity towards Cr(VI) ions in water because of their high surface area for adsorption and a good ability to preserve the accessible surface.

Microwave-assisted architectural control fabrication of 3D CdS structures

A facile microwave-assisted solvothermal method was developed for the controlled synthesis of novel 3D CdS structures. Dendrite-, star-, popcorn- and hollow sphere-like CdS structures could be obtained by changing the reaction conditions including the reaction temperature and the amounts of reagents and solvents. The products were examined by using X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman and photoluminescence spectroscopy. Results revealed that the final structures were related to the solvent properties such as surface tension and viscosity. The degree of supersaturation is also responsible for the morphology variation and it can be adjusted by the reaction temperature. The CdS products with different morphologies exhibited interesting shape-dependent optical properties and photocatalytic activities.

Hierarchically Nanostructured α-Fe2O3 Hollow Spheres: Preparation, Growth Mechanism, Photocatalytic Property, and Application in Water Treatment

α-Fe2O3 hierarchically nanostructured hollow spheres assembled by nanosheets were prepared by thermal decomposition of a precursor which was obtained using FeCl3·6H2O, NaOH, and sodium dodecylbenzenesulfonate in the solvent ethylene glycol by a facile microwave-assisted solvothermal method. The growth process of the precursor was investigated. The products were characterized by X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. Because of the unique hierarchically nanostructured hollow structures composed of nanosheets, the photocatalytic property and potential application in water treatment of the α-Fe2O3 samples were also investigated.