Microwave-assisted Solvothermal Synthesis Research Articles

Microwave-assisted solvothermal synthesis of Eu3+-doped CsY2F7 and RbY2F7 phosphorescent nanoparticles

We synthesized Eu3+-doped CsY2F7 and RbY2F7 nanoparticles (orthorhombic crystal structure, Pnna space group, No. 52) by the microwave-assisted solvothermal technique and investigated the influence of reaction temperature and fluoride ion concentration on the particles’ phase and crystal structure. Fluoride ions were added in excess of the stoichiometric amount to achieve the orthorhombic phase for CsY2F7 and to convert the cubic RbY3F10 to the orthorhombic RbY2F7. Mild synthesis conditions yielded nanoparticles with crystallites ranging in size from 19 to 37 nm and a combination of spherical, rod-like, and hexagonal shapes. Nanoparticles emit a strong orange and red light when excited into the Eu3+5L6 level, which is centered around 390 nm. The strongest emission peak is around 612 nm, which comes from the 5D0→7F2 electronic transitions. Emission intensity dependence on Eu3+ concentration revealed that nanoparticles can be heavily doped with Eu3+, up to 25 % with respect to Y3+. Emission decay measurements provided values of excited state lifetimes of 6.2 ms for the Cs(Y0.75Eu0.25)2F7 and 6.0 ms for the Rb(Y0.75Eu0.25)2F7.

Facile surfactant-free microwave-assisted solvothermal synthesis of Cu2Te1−xSx with enhanced thermoelectric performance

Cu2Te-based compounds show promise for thermoelectric applications, but their synthesis typically involves ball milling or melting-annealing processes. Here, we present a surfactant-free microwave-assisted solvothermal method for the controlled synthesis of Cu2Te1−xSx (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) nanostructures at 503 K within just 30 min. The substitution of sulfur promotes the formation of a hexagonal structure in Cu2Te1−xSx with x of 0.2 – 0.5, and inhibits phase transitions during heating. Moreover, the alloying of sulfur contributes to a reduction in hole concentrations toward the optimal range, resulting in enhanced power factors (e.g., 910 μW m−1 K−2 at 825 K for Cu2Te0.9S0.1) and reduced thermal conductivity (e.g., 0.53 W m−1 K−1 at 825 K for Cu2Te0.5S0.5). Ultimately, Cu2Te0.5S0.5 achieves a maximum dimensionless figure of merit of 0.80 at 825 K. This study offers a controllable solution-based strategy for synthesizing Cu2Te-based materials with tunable compositions and enhanced thermoelectric performance.

Fast and Facile Microwave Synthesis of Cubic CuFe2O4 Nanoparticles for Electrochemical CO2 Reduction

Electrochemical CO2 reduction is a promising strategy for the sustainable synthesis of carbon-based chemicals or fuels such as CO, or CH4.[1] Copper-based materials are of special interest due to their broad substrate scope. While copper itself is the first known metal catalyst able to directly yield CH4, CO, methanol, or C2+ products such as ethanol can also be obtained, e.g. from oxide derived catalysts.[2][3] Another interesting copper oxide is the spinel CuFe2O4, due to its versatile electronic and magnetic properties. Those can be tuned via variations in the cation distribution between octahedral and tetrahedral sites.[4] Changes in the cation distribution, or degree of inversion, can additionally lead to a structural transformation between the cubic and tetragonal form, due to the strong Jahn-Teller effect of Cu2+. Both degree of inversion and structure are strongly dependant on the synthesis conditions.[4]In this contribution we introduce a fast microwave-assisted solvothermal synthesis of cubic CuFe2O4. Very short synthesis times of 1 min and low temperatures of 120 °C in ethylene-glycol/water mixtures could be realised, without a loss of phase-purity and no necessity for subsequent thermal treatment.[5] The degree of inversion was found to decrease with increasing synthesis time, whereas the particle size and crystallinity was almost independent of the synthesis conditions. The influence of the synthesis conditions – and thus material properties – on the activity in electrochemical CO2 reduction to CO in 0.1 M KHCO3 was investigated. The best activity was obtained for CuFe2O4 with an intermediate degree of inversion of approx. 0.75, together with a large crystallite size and micro-strain. Since hydrogen was produced as the only side-product, CuFe2O4 can be an interesting candidate for the production of syngas.

Bacterial cellulose based TiO2-CdS nanocomposite gel with enhanced photocatalytic activity for adsorptive degradation of cationic dye

Dye released by industrial is one of the main known pollutants in wastewater, which is harmfully affected to the human health. Adsorptive method by absorbents and photocatalytic degradation technique are advanced technologies to remove dyes from wastewater. However, the single technique mentioned above has imperfections limiting its application. Herein, in order to integrate the two techniques and take both advantages, bacterial cellulose (BC) based titanium dioxide (TiO2)‑cadmium sulfide (CdS) nanocomposite gel was prepared by microwave-assisted solvothermal synthesis. The BC@TiO2-CdS nanocomposite gel was characterized by SEM, EDS, XRD, XPS, Raman spectral and TG, its photocatalytic mechanism was proved by PL. The results showed the TiO2-CdS nanophotocatalyst exhibited binary hierarchical structure and followed the Z-scheme type photocatalytic system. The Z-scheme heterojunction is advantageous for photo-generated charge separation and migration. The photocatalytic performance of BC@TiO2-CdS nanocomposite gel was evaluated by MB degradation under visible light irradiation. Due to synergistic effect of BC matrix and TiO2-CdS, the as-prepared BC@TiO2-CdS nanocomposite gel possesses enhanced photocatalytic activity with 94.47 % removal of methylene blue (MB) after 180 min visible light irradiation. Therefore, this work provides a facile route to fabricate bio-mass based efficient nanophotocatalytic material for pretreating the water pollution.

Microwave-assisted solvothermal synthesis of In-MIL-68 derived hollow In2O3 microrods for enhanced 1-pentanol sensing performance

The development of microbial volatile organic compounds (MVOCs) sensors is helpful due to the detection of toxic contaminants in foods, non-invasive disease diagnosis, and monitoring of contamination in industrial processes. Materials that are typically applied in the sensors field are semiconductor metal oxides (SMOx) since they have shown efficiency in identifying gases. Using metal-organic frameworks (MOFs) as precursors is an exciting approach to producing well-structured SMOx. Therefore, we report the preparation and characterization of In-MIL-68 (a MOF composed of terephthalic acid) derived hollow In2O3 microrods. The sensor material was obtained by the microwave-assisted solvothermal (MAS) method and subsequent calcination. We also show the application of the hollow In2O3 microrods as a 1-pentanol sensor for the first time. The sensor demonstrated exceptional sensitivity to this MVOC compared to other sensors reported in the literature, achieving a great response of 390 for 100 ppm of this compound at 350 °C.

Acetaminophen oxidation under solar light using Fe-BiOBr as a mild Photo-Fenton catalyst

Acetaminophen is an analgesic used as a first-choice treatment for pain and fever. When individuals consume acetaminophen, a portion of the drug is excreted through urine and can end up in wastewater. Water remediation from pharmaceuticals, such as acetaminophen, is required before reaching the environment. This work demonstrates that Fe–BiOBr using the solar photo-Fenton process eliminates acetaminophen at mild pH in aqueous media. Fe-BiOBr is produced using microwave-assisted solvothermal synthesis, and the formation of the BiOBr phase is confirmed with XRD. SEM and TEM demonstrated the flower-like morphology, in which crystallite size reduces as a function of the Fe loading. The chemical environment at the surface of Fe–BiOBr is investigated with XPS. The results are connected with Raman analysis, which suggests the presence of oxygen vacancies in Fe–BiOBr. Furthermore, the effect of Fe in BiOBr is assessed by determining the optical band gap with UV–Vis. The Fe-BiOBr functionality is assessed during acetaminophen degradation. Fe-BiOBr revealed excellent performance in degrading acetaminophen in the first minutes (Q = 10 kJ m−2) under natural sunlight. Results reveal that 1% Fe content in BiOBr can degrade acetaminophen and its main byproduct (30 min, Q = 50 kJ m−2) at pH 5 and using 0.25 gL-1 of catalyst. A synergistic mechanism between heterogeneous photocatalysis and Fenton processes with primary superoxide (•O2–) radical, followed by hydroxyl (•OH) radical and photogenerated holes (h+), is proposed. Our research contributes to the degradation of pharmaceuticals under mild conditions and sunlight irradiation.

Microwave-induced band gap attenuation of novel manganese zinc aluminum sulfide kesterite nanomaterials for optimal photovoltaics

Recently, kesterite (copper zinc tin sulfide, CZTS) have emerged as a promising alternative active layer to cadmium telluride and copper indium gallium selenide for low-cost thin films for solar cell applications due to its high absorption coefficient, direct band gap, natural abundance, and low toxicity. The photovoltaic power conversion efficiency achieved with CZTS is still very low when compared to silicon, thereby hindering its commercialization. Developing new materials with improved optical and photovoltaic properties is, therefore, encouraged. Here, we report for the first time the microwave-assisted solvothermal synthesis of novel manganese zinc aluminum sulfide using chlorides, sulfates, nitrates and a mixture of chlorides, nitrates, and sulfates in ratio 1:1:1 as cation precursor salts. The influence of microwave reaction temperatures from 100 to 190 °C for 5–60 min were investigated on the crystal structure, morphology, composition, optical, and electrochemical properties. It has been found out that the microwave reaction temperature and time have potential effect on the overall reaction. The optimum temperature and time were found to be 190 °C for 5 min and 150 °C for 20 min for our studies. The obtained powder samples were analyzed using X-ray diffraction, Raman spectroscopy, energy-dispersive X-ray spectroscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared, ultraviolet-visible, cyclic voltammetry, and electrochemical impedance spectroscopy. Structural characterization using X-ray diffraction revealed that the samples synthesized with chlorides, nitrates, and mixtures of the precursor salts were all amorphous while samples synthesized with sulfate precursor salts have a kesterite crystal structure. Raman spectroscopy shows major intense peaks between 326 and 331 cm for all the nanomaterials which could be assigned to the Raman A mode of kesterite CZTS. The morphological features revealed spherical shapes with little agglomeration for all the synthesized materials except for that synthesized with sulfate precursor salts at 190 °C revealing a rod-like morphology with a width of 0.780–1.200 μm, a length of 1.90–2.5 μm and attached to the surface are agglomerated nanospheres. Small-angle X-ray spectroscopy revealed a core-shell shape for most of the nanomaterials with an average particle size between 10 and 100 nm. Electrochemical impedance spectroscopy revealed that electron transfer is faster in the nanomaterials synthesized with the chloride precursor salts at both temperatures studied. The band gap falls within the range of 1.2–1.7 eV. The nanomaterials presented in this study possess the desirable properties for application in photoelectrochemical and solar cells.

Microwave-assisted solvothermal synthesis of cube-shaped MOF-COF composites for copper detection and capture

A novel metal organic framework-covalent organic framework (IRMOF3-TzDa) composite was prepared by microwave-assisted solvothermal methods. The designed IRMOF3-TzDa was integrated with dual function of copper ion detection and removal, and characterized by FTIR, XRD, SEM, TEM and XPS et al. The adsorption capacity of Cu2+ by IRMOF3-TzDa was 86 mg g−1 by Langmuir isotherm model fitting. In a mixed metal ions solution, IRMOF3-TzDa demonstrated high adsorption selectivity to Cu2+. The strong affinity between IRMOF3-TzDa and Cu2+ and the rapid transfer of the π electrons of the material to the lowest unoccupied molecular orbital of Cu2+ provided the chance for Cu2+ fluorescence sensing by IRMOF3-TzDa. A linear range of 10–500 μM was obtained, with a limit of detection of 2.2 μM (n = 11) and a precision of 3.3% (50 μM, n = 9), respectively. Water samples were analyzed by the detection platform, with satisfactory recoveries of 94% to 107%. Benefiting from the high density of adsorption groups and excellent fluorescence properties, the facile synthetic MOF-COF composite provided an alternative material for copper ion removal and detection.

Fast microwave-assisted solvothermal synthesis of Mn2O3 nanoparticles decorated on nitrogen-doped reduced graphene nanosheets for lithium-ion batteries

Fast microwave-assisted solvothermal synthesis of Mn2O3 nanoparticles decorated on nitrogen-doped reduced graphene nanosheets for lithium-ion batteries

Ultrafast microwave-assisted solvothermal synthesis and characterization of near-spherical CoSb3 nanopowders

Ultrafast microwave-assisted solvothermal synthesis and characterization of near-spherical CoSb3 nanopowders

Tuning the core-shell ratio in nanostructured CuS@In2S3 photocatalyst for efficient dye degradation

This work reports on a microwave-assisted solvothermal synthesis of CuS@In2S3 core-shell hybridized nanoparticles (Hy-NPs) at different weight ratios (wt%) of CuS to tune the heterojunction optoelectronic properties and evaluate the application for photocatalytic degradation of organic dyes. The photodegradation performance in terms of the efficiency and reaction kinetics shows that the 10 wt% CuS Hy-NPs presents the highest photoactivity in the degradation of two dye species, methylene blue (MB) and methyl orange (MO) when compared to 5 wt% CuS, 15% CuS Hy-NPs samples as well as the pristine CuS or In2S3 NPs. The structural and morphological studies combining the optical bandgap analysis suggest that the CuS amount used in the synthesis step plays an important role to forming the efficient heterojunction interfaces for charge carrier separation to inhibit the recombination of excited electron and hole pairs and the resultant apparent optical bandgap of the Hy-NPs. The 10 wt% CuS@In2S3 core-shell Hy-NPs demonstrate a lower optical band for a wide range visible light absorption and higher photocatalytic activity than that of the CuS NPs, In2S3 NPs, and the 5 wt% CuS, or 15 wt% CuS Hy-NPs. The findings in this work may offer an alternative simple and effective approach to designing and synthesizing metal chalcogenide heterojunctions for improving photocatalytic activity.

Revealing the effect of substitutional cation doping in the A-site of nanoscale APbI3 perovskite layers for enhanced retention and endurance in optoelectronic resistive switching for non-volatile bipolar memory devices.

The effect of substitutional cation doping in the A-site of the nanoscale APbI3 perovskite layer has been systematically investigated to achieve improvements in the charge-carrier dynamics and endurance of non-volatile bipolar (NVB) memory devices. We successfully adopted an energy-efficient, ultra-fast microwave-assisted solvothermal (MW-ST) synthesis route to prepare a sequence of APbI3 (A = MA+, FA+, MAFA+, CsMA+ and CsMAFA+) perovskite powders with morphological transitions from cube-like polyhedrons to mixed polyhedrons and rods within 10 minutes at 120 °C without requiring any inert-gas atmosphere under high-humid ambient conditions. As-prepared APbI3 powders were dissolved in DMSO:DMF, followed by the fabrication of a thin film via spin-coating. Upon annealing at 120 °C, the nanoscale self-assembled thin-film layer was formed. We observed that devices with the inorganic Cs+ cation with organic cations, (CsMAPI and CsMAFAPI) device showed improved endurance (3500 and 5000 cycles, respectively) and outstanding retention (60 000 s) owing to effective charge-carrier dynamics, compared to organic cation-based MAPI, FAPI and MAFAPI (1800, 1200 and 1300 cycles, respectively). Significantly, various cation-doped APbI3-powders obtained via the MW-ST method remained to be stable for up to 5-months under high-humid conditions. Thus, enhanced optoelectronic-memory performance studies could provide an opportunity for next-generation nanoscale ORSNVB-memory devices for artificial intelligence (AI) and Internet of Things (IoT) applications.

Influence of Redox Couple on the Performance of ZnO Dye Solar Cells and Minimodules with Benzothiadiazole-Based Photosensitizers.

ZnO-based dye-sensitized solar cells exhibit lower efficiencies than TiO2-based systems despite advantageous charge transport dynamics and versatility in terms of synthesis methods, which can be primarily ascribed to compatibility issues of ZnO with the dyes and the redox couples originally optimized for TiO2. We evaluate the performance of solar cells based on ZnO nanomaterial prepared by microwave-assisted solvothermal synthesis, using three fully organic benzothiadiazole-based dyes YKP-88, YKP-137, and MG-207, and alternative electrolyte solutions with the I-/I3 -, Co(bpy)3 2+/3+, and Cu(dmp)2 1+/2+ redox couples. The best cell performance is achieved for the dye-redox couple combination YKP-88 and Co(bpy)3 2+/3+, reaching an average efficiency of 4.7% and 5.0% for the best cell, compared to 3.7% and 3.9% for the I-/I3 - couple with the same dye. Electrical impedance spectroscopy highlights the influence of dye and redox couple chemistry on the balance of recombination and regeneration kinetics. Combined with the effects of the interaction of the redox couple with the ZnO surface, these aspects are shown to determine the solar cell performance. Minimodules based on the best systems in both parallel and series configurations reach 1.5% efficiency for an area of 23.8 cm2.

Study of CaTiO3–ZnS heterostructure obtained by microwave-assisted solvothermal synthesis and its application in photocatalysis

We report herein the assembly of a calcium titanate (CTO)-zinc sulfide (ZnS) heterostructure through a microwave-assisted solvothermal (MAS) method and its respective characterizations to evaluate its material properties and applicability in heterogeneous photocatalysis. The CTO-ZnS heterostructure comprises a mixture of the orthorhombic crystalline phase of CTO and the cubic crystalline phase of ZnS. Scanning electron microscopy (SEM) images have revealed that the CTO consists of mesocrystals assembled from agglomerated microcubes. After applying a ZnS coating, it was possible to identify the formation of a cloud of particles around parts of the CTO mesocrystals, thus forming the heterostructure. The presence of ZnS on the CTO surface allowed for greater emission of photoluminescence, resulting in improved efficiency for photocatalytic applications. Photodegradation tests on Rhodamine B (RhB) dye in the presence of CTO, ZnS, and CTO-ZnS revealed that the heterostructure led to more extensive photocatalytic degradation (50.5%) within 30 min than CTO (10%). Moreover, the degradation efficiency over the CTO-ZnS increased to 95.7% after 180 min, indicating that the ZnS coating served to increase the degree of discoloration over time. These satisfactory results demonstrate that CTO-ZnS is a promising photocatalyst capable of accelerating the degradation of organic dyes, thus contributing to the decontamination of water resources. Scavenger tests revealed holes (h+) to be the main active species in the photocatalytic process with CTO, whereas electrons (e−), h+, and hydroxyl radicals (HO*) are all involved in the mechanism with both CTO-ZnS and ZnS.

Microwave-Assisted Solvothermal Synthesis of Mo-Doped TiO2 with Exceptional Textural Properties and Superior Adsorption Kinetics.

Assigned to their outstanding physicochemical properties, TiO2-based materials have been studied in various applications. Herein, TiO2 doped with different Mo contents (Mo-TiO2) was synthesized via a microwave-assisted solvothermal approach. This was achieved using titanium (IV) butoxide and molybdenum (III) chloride as a precursor and dodecylamine as a surface directing agent. The uniform effective heating delivered by microwave heating reduced the reaction time to less than 30 min, representing several orders of magnitude lower than conventional heating methods. The average particle size ranged between 9.7 and 27.5 nm and it decreased with increasing the Mo content. Furthermore, Mo-TiO2 revealed mesoporous architectures with a high surface area ranging between 170 and 260 m2 g−1, which is superior compared to previously reported Mo-doped TiO2. The performance of Mo-TiO2 was evaluated towards the adsorption of Rhodamine B (RhB). In contrast to TiO2, which revealed negligible adsorption for RhB, Mo-doped samples depicted rapid adsorption for RhB, with a rate that increased with the increase in Mo content. Additionally, Mo-TiO2 expressed enhanced adsorption kinetics for RhB compared to state-of-the-art adsorbents. The introduced synthesis procedure holds a grand promise for the versatile synthesis of metal-doped TiO2 nanostructures with outstanding physicochemical properties.

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.

Facile microwave-assisted solvothermal synthesis of rod-like aluminum terephthalate [MIL-53(Al)] for CO2 adsorption

To alleviate environment issues derived from CO2 emission, developing effective and economical methods for CO2 capture has attracted much attention for decades. Metal-organic frameworks possess high porosity and stability, which is favorable to the adsorption of small molecules. Herein, an aluminum-based MOF, aluminum terephthalate [MIL-53(Al)], was synthesized with H2O and N,N′-dimethylformamide as co-solvent via microwave-assisted method for CO2 adsorption. The parameters including pre-mixing mode, microwave temperature, microwave power and reaction time were varied to study their influences on crystal structure, morphology and CO2 adsorption capacity of MW-MIL-53(Al). Wherein, MW-MIL-53(Al) prepared with pre-mixing mode of stirring at 130 °C, 200 W and 3 h presents high crystallinity and rod-like morphology. The synthesized MW-MIL-53(Al) possesses relatively high BET surface area (961 m2/g), pore volume (0.46 cm3/g) and thermal stability (up to 480 °C), and its CO2 adsorption capacity is 2.16 mmol CO2/g adsorbent under 25 °C and 0.1 MPa, which is higher than CS-MIL-53(Al) synthesized via conventional solvothermal method at 130 °C for 48 h.

Microwave-assisted solvothermal synthesis of hollow mesoporous SiOC ceramics in NaOH solution

Hollow SiOC ceramics were prepared by a microwave-assisted solvothermal method, and only mesopores were formed in NaOH solution. Increasing the microwave temperature and NaOH concentration not only increased the oxygen-enriched units and reduced the Si–C bonds of precursors, but also enhanced the etching effect in the interior SiOC ceramics. The specific surface area of SiOC ceramics increased with increasing solvothermal temperature and decreased with increasing NaOH concentration. In addition, the effect of synthesis temperature on the formation of hollow SiOC ceramics is more significant than that of NaOH concentration. Although the free C content is reduced, the microwave solvothermal synthesis results in the formation of graphitic C in SiOC ceramics. The surface CO is formed at the cost of some C–OH as the microwave temperature increases, which increases the amorphous C content of SiOC ceramics.

Microwave-assisted solvothermal synthesis of mesoporous rod-like manganese oxalate as a high-performance anode for lithium-ion batteries

Microwave-assisted solvothermal synthesis of mesoporous rod-like manganese oxalate as a high-performance anode for lithium-ion batteries

Molybdenum Carbide-Reduced Graphene Oxide Composites as Electrocatalysts for Hydrogen Evolution

The development of cost-effective, highly efficient, and stable electrocatalysts to replace expensive platinum-like metal catalysts remains a great challenge for the hydrogen evolution reaction (HER). In this study, we report a facile, microwave-assisted solvothermal (MWSV) synthesis of molybdenum carbide (Mo2C) nanoparticles and molybdenum carbide-reduced graphene oxide (Mo2C-RGO) nanocomposites at elevated temperatures. The optimized Mo2C-RGO nanocomposite catalysts show excellent HER performance in acidic media. When GO is added, the onset potential and Tafel slope of the nanocomposite catalyst are 120 mV and 85 mV/dec, respectively. The catalysts also exhibit good stability in an acidic environment. This improvement of the carbide catalyst is attributed to highly accessible active reaction sites, efficient mass/charge transportation, and enhanced conductivity of the hybrid structure.