Microwave-assisted Hydrothermal Research Articles

Microwave-Assisted Hydrothermal Synthesis of Ru-doped Mn3O4 Nanoflowers for Biomedical Applications

Ruthenium-doped manganese oxide nanoflowers (denoted as Ru-Mn3O4 NFs) were synthesized via microwave-assisted hydrothermal (MW-HT) method. The prepared NFs were evaluated for antimicrobial, anti-inflammatory, anti-oxidant and hemolytic assays. Because of their unique physicochemical features, low cytotoxicity, excellent stability, exceptional antibacterial action, and significant interest in biomedical field. Various analytical techniques were used to assess the related phase constitution, elemental content, and surface morphology. The X-ray diffraction (XRD) patterns and field-emission scanning electron microscopy (FE-SEM) micrographs revealed that the Ru-Mn3O4 NFs had a tetragonal phase with a nanoflowers-like shape and Ru mainly existed as the metallic state. It has been found that Ru-Mn3O4 NFs hold higher microbial activities against various pathogens, making them ideal options for fighting bacterial infections.

The role of capping agents on the trapping levels structure and luminescent emission of SrMoO4 phosphors

In the present work, we investigate the thermoluminescence (TL) and optically stimulated luminescence (OSL) from strontium molybdate SrMoO4 powders designed with different capping agents. The samples were prepared through co-precipitation and processed in a Microwave-Assisted Hydrothermal (MAH) system. The structural, optical, and morphological characteristics were investigated using Raman, Fourier transform infrared spectroscopy (FTIR), DRX, ultraviolet-visible (UV–vis) absorption, and Scanning electron microscopy (SEM). The TL glow curves recorded from as-prepared and irradiated samples with beta particles reveal that their intensity and profile depend on the used capping agent. The trapping depth energy, determined from the TL glows curves, ranges from 1.02 to 2.23 eV for the as-prepared samples and from 0.9 to 2.33 eV for the irradiated phosphors. The residual TL spectra, registered from successive readouts, reveal that the thermal treatment shifts the glow curve to lower temperatures suggesting the formation of shallower trap states. The results reveal that the OSL signal and its behaviors with the radiation dose depending on the employed capping agent. The results show the TL and OSL signal's dependence on the structural properties and support the potential application of SrMoO4 powders as an OSL detector.

Using rice husk ash as a SiO2 source in the preparation of SiO2/Nb2O5 and SiO2/ZnS heterostructures for photocatalytic application.

This work presents the synthesis of SiO2/Nb2O5 and SiO2/ZnS heterostructures using the microwave-assisted hydrothermal (MAH) method, which is fast and has low temperature. The silica used in the synthesis was obtained by burning the rice husk without any pre- or post-treatments. The obtained samples were characterized using various techniques such as X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and UV-visible. The obtained silica was found to be amorphous, and the materials used for modification showed characteristic of the type of synthesis used. SEM images showed that Nb2O5 and ZnS interacted with the SiO2 surface, filling the voids. In the photocatalytic process, the heterostructures showed enhanced decolorization efficiency for dyes such as rhodamine B (RhB) and methylene blue (MB) compared to SiO2. For RhB, the silica decolorized approximately 24%, and for MB, it discolored approximately 27%; SiO2/Nb2O5 showed 91.24% decolorization efficiency for RhB and 72.77% MB, while SiO2/ZnS showed approximately 96% for RhB and 100% for MB. All samples were tested under the same conditions. This demonstrates that the use of rice husk residue not only improves the photocatalytic activity of heterostructures but also promotes the utilization of improperly discarded residues.

Photocatalytic Properties of PbMoO4 Nanocrystals against Cationic and Anionic Dyes in Several Experimental Conditions

This paper reports easy and fast synthesis of PbMoO4 nanocrystals by microwave-assisted hydrothermal (MH) method at different synthesis times (1, 10, 30 and 60 min) at 100 °C. X-ray diffraction, Rietveld refinement and Raman spectroscopy confirm all characteristics of diffraction peaks and active vibrational modes of the pure scheelite structure (tetragonal, I41/a) for all synthesized PbMoO4 nanocrystals. The optical bandgap calculated directly from the samples is close to 3.5 eV. The images collected by scanning electron microscopy show particles with mean length from 159.90(8) nm to 303.02(3) nm with greater exposure of planes (111), (100), (011) and (110). The photocatalytic activity of PbMoO4 nanocrystals against RhB and RBBR dyes resulted in successful degradation in short time intervals using ultraviolet light, where the best performance was achieved for the PbMoO4-10 sample, which was 29.2 and 51.8 times more effective than photolysis. The contribution of oxidant species was monitored by radical scavengers, which confirms that holes (h+) are the main oxidative species in photodegradation of RhB and RBBR dyes, while reuse of the catalyst against RhB and RBBR dyes confirms high stability of the catalyst, although recycled four times.

Magnetodielectric Comparison Study Between Microwave and Conventional Sintered NiCuZn Ferrites

AbstractNi0.53Cu0.12Zn0.35Fe2O4 ferrite powder is synthesized using the microwave‐assisted hydrothermal (M‐H) technique. The synthesized powder is characterized using X‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The morphology of the powder particles is examined using field effective scanning electron microscopy (FESEM). The powder is then sintered using microwave and conventional methods at 910°C/1.5 h and 910°C/4 h, respectively. The grain size, bulk density, d.c. resistivity, and saturation magnetization of both the sintered samples are measured and compared. The dielectric properties of both the sintered samples are measured at frequencies ranging from 1 MHz to 1.8 GHz. The research indicates that the sintering process has an impact on the magnetodielectric performance of ferrites. The change in properties resulting by the sintering method is briefly reviewed.

Theoretical and experimental photocatalytic implications of Co ions upon the SrTiO3 lattice

SrTiO3 (STO) nanoparticles have been synthetized by the microwave-assisted hydrothermal (MAH) with the introduction of Co dopants in quotas of 0.5%, 1.0%,1.5% and 2.0% and the analytes were characterized by scanning electron microscopy (SEM), X-ray powder diffraction, Raman spectroscopy and UV/VIS techniques. The theoretical calculations have demonstrated that by the addition of Co ions the top of the valence band has been shifted to values above the potential energy for the formation of the OH– radical, a fact that indicates the defects as a hindrance to the conduction of the dye photo degradation steps. Although the band gap reduction being related to the amount of Co ions in the matrix the effect of recombination seemed to be augmented for the escalation of dopant material within the unit cell. The photocatalytic benchmark has demonstrated that the Co doping were directly related to the reduction on the reaction rate constant (k).

Synthesis of high-quality Na[sbnd]P1 zeolite from municipal solid waste incineration fly ash by microwave-assisted hydrothermal method and its adsorption capacity

The Si and Al in municipal solid waste incineration fly ash (MSWI FA) can be utilized for zeolite fabrication, which can improve the application value of the products. This study focuses on the fabrication of zeolite from MSWI FA by microwave-assisted hydrothermal (MH) treatment. The effects of magnetic stirring time, Na2SiO3 dosage, MH time, and NaOH solution concentration on the crystallization of zeolite NaP1 from MSWI FA are systematically analyzed. The synthetic products are analyzed through spectroscopic and mineralogical methods. The results show that zeolite NaP1 with high crystallinity (51.68 %) can be fabricated by magnetic stirring and MH treatment, and the cation exchange capacity (CEC) of the product can reach a value of 2.58 meq/g, which is approximately 133 times that of the CEC of MSWI FA. The Si/Al ratio plays a decisive role in the zeolite NaP1 synthesis, and a Na2SiO3 dosage of 30 wt% is adopted for zeolite NaP1 fabrication. A NaOH concentration of 1 M is sufficient for zeolite NaP1 synthesis. Additionally, the zeolite NaP1 content is found to obviously increase with increasing MH time from 0.5 h to 2 h. To demonstrate the feasibility of the method provided in this study, the optimal experimental condition is employed for various MSWI FAs, and zeolite NaP1 and analcime are fabricated successfully. The leachability of heavy metals for the synthetic products was evaluated, which met the requirements for pollution control. The BET surface area and total pore volume of zeolite NaP1 fabricated at optimal condition are 61.42 m2/g and 0.44 cm3/g, respectively. The adsorption capacity of zeolite NaP1 for Cu2+ ion and methylene blue are determined to be 84.65 mg/g and 84.55 mg/g, respectively, indicating zeolite NaP1 is a potential adsorbent for cation ion and dyes. This study provides an environmentally friendly scheme for the utilization of MSWI FA.

Photodegradation of acid yellow 23 BY Nb2O5 supported on eco-friendly glass foams

Photocatalytic processes are efficient techniques for decolorization of dye-contaminated water. However, efficient techniques for complete recovery of the spent catalysts, after the process, are required. Based on this need, the present study describes the synthesis of the composites of niobium(V) oxide (Nb2O5) supported on eco-friendly glass foams (GFs) as well as their applications as photocatalytic materials in the treatment of wastewater using Advanced Oxidation Processes (AOPs). The GFs decorated with different shapes of Nb2O5 particles (GF-Nb2O5) were synthesized using microwave-assisted hydrothermal (MAH) technique. The GF-Nb2O5 composites were utilized as photocatalysts for treatment of water containing Acid Yellow 23 (AY-23) dye. By varying the morphology (laminar, spherical or rods-shaped) and optical characteristics (optical band gap between 3.2 eV and 3.1 eV) of the Nb2O5, the particles of Nb2O5 formed were dependent on the time and temperature of synthesis. The sample synthesized at 160 °C and 15 min possessed microrod particles, which were coordinated in such a way to give a “microrod forest” that was capable of covering the support material. In addition, this sample degraded 91.1% of the AY-23 synthetic dye from water in 300 min. With such an exceptional performance, the growth of the Nb2O5 in this unique architecture could serve as an important driver for adopting the novel concept for the efficient treatment of dye-contaminated water. The results showed high possibility of applying GF-Nb2O5 for the effective treatment of dye-polluted water using AOPs, which eliminate catalyst separation step usually performed in the process.

Electrochemical performance of mixed-phase 1T/2H MoS2 synthesized by conventional hydrothermal v/s microwave-assisted hydrothermal method for supercapacitor applications

Mixed-phase 1T/2H MoS2 has been receiving immense attention as an electrode material for supercapacitors due to the synergistic effects of both the phases. Herein, we synthesized mixed-phase 1T/2H MoS2 via two different techniques: conventional hydrothermal (HT) and microwave-assisted hydrothermal (MHT) technique. The formation of MoS2 is confirmed through X-ray diffraction pattern, scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman-spectra, and X-ray photoelectron spectra. The electrochemical performance of the two samples is investigated using cyclic voltammetry (CV), Gravimetric charging-discharging (GCD) and electrochemical impedance spectroscopy (EIS). MoS2 synthesized via MHT method (MS-MW) and HT method (MS-HT) deliver capacitances of 421 F g−1 and 742 F g−1 at 5 mV s−1, respectively. The energy density of MS-HT (57 Wh kg−1) is almost double than that of MS-MW (30 Wh kg−1). MS-HT also exhibited remarkable capacitance retention of 91% over 1200 cycles, compared with MS-MW. The results demonstrate that MoS2 synthesized by the hydrothermal method delivers superior electrochemical performance.

Energy Densification of Groundnut Shell through Microwave-Assisted Hydrothermal Carbonization

Modern technology of microwave synthesis was utilized for hydrochar production from groundnut shell biomass. Hydrochar was produced at three different temperatures (180, 200, and 220°C) with 20 minutes of holding time and analyzed for the physicochemical characteristics. The yield of hydrochar and hydrocrude were in the range of 45 to 61 % and 51 to 56 % respectively. The maximum value of the higher heating value of 19.11 MJ/kg was obtained for hydrochar produced at 220°C, which is similar to the higher heating value of lignite (19 MJ/kg). The energy densification ratio of respective hydrochar was 1.13 with 51.77 % energy yield. The result implied that microwave-assisted hydrothermal carbonization was an energyefficient method to produce hydrochar. Hydrochar produced from groundnut shells was an eco-friendly, energy enriched product that can be used as a solid fuel.

Rapid Zeolization of Potassic Rocks by Means of a Microwave‐Assisted Hydrothermal Method

AbstractPotassic rocks are rapidly activated and converted to cancrinite (CAN) zeolites in NaOH solution via microwave‐assisted hydrothermal (MH) method. The conditions of zeolization process via MH method are optimized, and the mechanism is illustrated. The phase transition process of potassic rocks is obtained as follows: decomposition of the potassic rocks→zeolite sodalite→zeolite CAN. In this process, the microwave exerts a reinforcement effect by generating the cleavage cracks on the surface of potassic rocks and accelerating the dissolution and crystallization processes. The synthesized zeolite CAN exhibits the maximum adsorption capacity of 6.5 mg g−1 for methylene blue. In addition, the filtrate is further used to prepare linda type A (LTA) zeolites by conventional hydrothermal synthesis method. The synthesized zeolite LTA presents the cubic morphology with rounded corners, and its Ca2+ ion exchange capacity could reach 335.6 mg CaCO3 g−1.

Alkali influence on ZnO and Ag-doped ZnO nanostructures formation using the microwave-assisted hydrothermal method for fungicidal inhibition

This study reports on the effect of the alkali source in pure ZnO and Ag-doped ZnO samples formation quickly synthesized using the microwave-assisted hydrothermal (MAH) method. The flower-like morphology of ZnO and Ag-doped ZnO samples was controlled by the presence of ammonia under reaction conditions, which provided slower ZnO nucleation. In the presence of sodium hydroxide, the precursor species were instantaneously formed, promoting a rapid ZnO formation and the obtainment of Ag0 in the Ag-doped ZnO sample. The presence of Ag+ ions into ZnO wurtzite structure created defects, contributing to a local structural disorder, as observed by Raman spectra. All the samples studied herein presented antifungal activity for Saccharomyces cerevisiae, which was influenced because of the presence of Ag+ ions into ZnO lattice and the morphologies of the samples.

Preparation of Silicon Hydroxyapatite Nanopowders under Microwave-Assisted Hydrothermal Method.

The synthesis of partially substituted silicon hydroxyapatite (Si-HAp) nanopowders was systematically investigated via the microwave-assisted hydrothermal process. The experiments were conducted at 150 °C for 1 h using TMAS (C4H13NO5Si2) as a Si4+ precursor. To improve the Si4+ uptake in the hexagonal structure, the Si precursor was supplied above the stoichiometric molar ratio (0.2 M). The concentration of the TMAS aqueous solutions used varied between 0.3 and 1.8 M, corresponding to saturation levels of 1.5–9.0-fold. Rietveld refinement analyses indicated that Si incorporation occurred in the HAp lattice by replacing phosphate groups (PO43−) with the silicate (SiO4−) group. FT-IR and XPS analyses also confirmed the gradual uptake of SiO4− units in the HAp, as the saturation of Si4+ reached 1.8 M. TEM observations confirmed that Si-HAp agglomerates had a high crystallinity and are constituted by tiny rod-shaped particles with single-crystal habit. Furthermore, a reduction in the particle growth process took place by increasing the Si4+ excess content up to 1.8 M, and the excess of Si4+ triggered the fine rod-shaped particles self-assembly to form agglomerates. The agglomerate size that occurred with intermediate (0.99 mol%) and large (12.16 mol%) Si contents varied between 233.1 and 315.1 nm, respectively. The excess of Si in the hydrothermal medium might trigger the formation of the Si-HAp agglomerates prepared under fast kinetic reaction conditions assisted by the microwave heating. Consequently, the use of microwave heating-assisted hydrothermal conditions has delivered high processing efficiency to crystallize Si-HAp with a broad content of Si4+.

Optimization of microwave-assisted hydrothermal pretreatment and its effect on pyrolytic oil quality obtained by an auger reactor

Microwave-assisted hydrothermal (MHT) treatment of biomass has received significant attention owing to energy efficiency during internal energy transfer and the additional benefits to the hydrochar produced in terms of physicochemical composition. Therefore, this study proposes the combination of MHT pretreatment with the fast pyrolysis process, to evaluate and optimize the effect of this treatment on the quality of the hydrochar and, consequently, on the quality of the bio-oil. The optimization of MHT treatment using black spruce was carried out, followed by fast pyrolysis of the hydrochar produced under optimal conditions in an auger reactor at 550 °C to obtain a high-quality bio-oil. As a result, the pretreated biomass showed on the one hand a significant decrease in the ash content by 58% and 43% in the content of the extractives. While on the other hand, the obtained hydrochar showed an increase in the availability of cellulose by 18.5% as a consequence of the reduction in the content of hemicellulose. Accordingly, hydrochar showed an increase in thermal stability during pyrolysis and it produced a higher total bio-oil yield, increasing by 24%. Most importantly, the oil obtained showed a 35% reduction in moisture content. Chemical composition of the oil was qualitatively examined through GC-MS analysis. It was observed that the bio-oil showed a dramatic increase in the relative content of levoglucosan, by 127%. A bio-oil with the characteristics obtained would be a suitable candidate for use in boilers for heating purposes or chemical extraction.

Multifunctional environmental applications of ZnO nanostructures synthesized by the microwave-assisted hydrothermal technique

Herein, we explore the multifunctional potential of ZnO nanostructures obtained via the microwave-assisted hydrothermal (MAH) method using a single synthesis route in the presence of CTAB. The ZnO samples were characterized by X-ray diffraction (XRD), Infrared Spectroscopy, Field Emission Gun Scanning Electron Microscopy (FEG-SEM), Transmission Electron Microscopy (TEM), photoluminescence properties (PL), as well as their photocatalytic activity and gas sensing response. XRD indicated that the ZnO nanostructures are free from impurities and crystallize in the hexagonal structure. FEG-SEM and TEM showed that rod-like ZnO nanostructures were obtained. Photoluminescence results indicate that the commercial ZnO sample has a higher bandgap and a more disordered crystalline structure compared with the ZnO nanostructures. The nanostructures presented superior photocatalytic performance, reaching 50% rhodamine 6-G photodegradation in 17 min, while the commercial sample took 43 min to reach the same value. The sensor film prepared from the ZnO nanostructures showed a fast response time of 10 s to 20 ppm of CO. The photocatalytic and gas sensing performances of the nanostructured ZnO highlights the multifunctional character of the nanostructures prepared via the MAH method and their potential for environmental applications such as water purification and air monitoring.

Synthesis of Pure Phase NaP2 Zeolite from the Gel of NaY by Conventional and Microwave-Assisted Hydrothermal Methods

The gel of zeolite NaY has potential as a precursor of other zeolites. The particular interest in this work is to convert the gel of NaY to NaP2. We found that the pure phase NaP2 can be produced simply by the conventional hydrothermal (CH) method at 150 °C for 24 h. This NaP2 sample, named CH150, has an average particle size of 10.3 µm and an Si/Al ratio of 1.82. In the case of single crystallization via microwave-assisted hydrothermal (MH) method, various parameters were studied, including the crystallization temperature (90, 150, 175 °C) and time (15, 30, 45, 60 min). The samples were analyzed by X-ray diffraction and scanning electron microscopy. However, mixed phases of P1 and P2 or ANA were obtained from all samples. Another attempt was made by a double crystallization via MH method as followed: at 90 °C for 1 h, quickly cooled down to room temperature in the microwave chamber and aged for 23 h, and finally at 150 °C for 1 h. The sample, named MH90A150, has an average crystal size of 16.45 µm and an Si/Al ratio of 1.85. The high Al content of NaP2 in both samples (CH150 and MH90A150) could lead to interesting applications.

Cerium molybdate nanocrystals: Microstructural, optical and gas-sensing properties

Metal molybdate compounds have attracted considerable attention due to their technological applications. Herein, we demonstrate the controllable synthesis of cerium molybdate (Ce2(MoO4)3) nanocrystals via the co-precipitation method followed by microwave-assisted hydrothermal (MAH) treatment at 150 °C during different times (15, 30 and 60 min). The effect of MAH treatment time on the microstructural, optical, and ozone gas-sensing properties of these nanocrystals was investigated. X-ray diffraction (XRD) and Raman spectroscopy measurements revealed that the samples presented a single-crystalline phase with scheelite-type tetragonal structure. Field emission gun scanning electron microscopy (FEG-SEM) images showed that the MAH conditions favored changes in the Ce2(MoO4)3 nanocrystal morphology. Photoluminescence (PL) measurements indicated a significant enhancement of PL emission with MAH time, suggesting an increase in the intrinsic defects formed during the MAH treatment. The gas-sensing performance of cerium molybdate nanocrystals towards sub-ppm ozone levels was also investigated. The experiments revealed complete recovery and good repeatability as well as good sensor response, which was improved in the sample synthesized at longer MAH time.

A novel synthesis route to obtain magnetic nanocrystalline cobalt ferrite with photo-Fenton activity

A novel unconventional coprecipitation procedure (UCP) followed by a simple and fast microwave-assisted hydrothermal (MAH) treatment was used to synthesize a new nanocrystalline magnetic cobalt ferrite (CoFe2O4/MAH) with photo-Fenton activity. The Co-ferrite nanoparticles were obtained at room temperature in the absence of surfactants and their photo-Fenton activity was evaluated through lignin degradation. It was found that microwave hydrothermal treatment is mandatory to obtain magnetic and photoactive Co-ferrite. According to XRD Rietveld refinements and FTIR, the photoactivity was mainly attributed to the Co2+ cation migration from octahedral to tetrahedral sites in the ferrite structure during the MAH treatment, leading, consequently, to a higher Fe3+ incorporation at octahedral sites, which strongly participate in the photo-Fenton degradation mechanism. The magnetic property of the CoFe2O4/MAH ferrite nanoparticles was confirmed by magnetometry and provided an easy catalyst separation.

Photocatalytic properties of the CeO2‐xTiO2 and TiO2‐xCeO2 (x = 10, 30, and 50 mol%) heterostructures obtained by a MAH

AbstractIn this work, CeO2‐TiO2 heterostructures were submitted to the microwave‐assisted hydrothermal (MAH) method at 140°C for 30 minute, and varying the CeO2 and TiO2 percentages as 10, 30, and 50 mol%. The heterostructures were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer‐Emmett‐Teller methodology (BET), and UV‐Vis diffuse reflectance spectroscopy (UV‐Vis). The photocatalytic properties were estimated varying the concentration of methylene blue (MB) dye. The diffractograms indicate the formation of TiO2 anatase and CeO2 phases, without the formation of secondary phases. TEM images indicate the formation of nanocubes and nanospheres for CeO2 and TiO2, respectively. BET analysis indicates that CeO2 has the largest surface area (62.80 m2.g−1), and TiO2‐10%CeO2 heterostructure has a low surface area (26.13 m2.g−1). The addition of TiO2 to CeO2 increases the photocatalytic activity from 32% to 80% for CeO2 and CeO2‐50%TiO2, respectively. In contrast, the addition of CeO2 significantly decreases the photocatalytic activity of TiO2 from 98.9% to 50% for TiO2 and TiO2‐50%CeO2, respectively. Reuse tests showed that the TiO2‐xCeO2 samples maintain the photocatalytic response in subsequent cycles while the CeO2‐xTiO2 samples have an increase in the response.

Enhanced magnetic performance of BiFeO3 by cerium substitution

Micrometre-sized pure BiFeO3 (BF) and Ce-doped Bi0.9Ce0.1FeO3 (BCF) powders were synthesized by using conventional hydrothermal (H) and microwave assisted hydrothermal (MH) methods. The BF-H and BCF-H show obviously enhanced weak ferromagnetic characteristic, in which the BCF-H exhibits excellent magnetic performance, with significantly increased maximum magnetization of ∼3.6 emu/g (under 50 kOe magnetic field) and remanent magnetization of ∼0.268 emu/g at room temperature. The superior magnetic property of BCF-H could be attributed to the suppression of spiral structure and the modulation of canting angle of spins in antiferromagnetic sublattices.