Microwave-assisted Hydrothermal Synthesis Research Articles

Microwave-Assisted Hydrothermal Synthesis of Hydroxyapatite Flakes as Substrates for Titanium Dioxide Film Deposition

This article describes the synthesis of hydroxyapatite (HAp) flakes through a microwave-assisted hydrothermal method. These flakes suggest possible applications as a substrate for depositing titanium dioxide (TiO2) films using chemical vapor deposition with metal–organic precursors (MOCVD). The results reveal the formation of crystalline hydroxyapatite characterized by a uniform morphology. Additionally, we demonstrated the successful deposition of TiO2 coatings on the hydroxyapatite flakes, resulting in a distinctive faceted prism morphology. Our findings affirm the effective synthesis of the HAp/TiO2 composite material. To further explore the material’s practical applications, we recommend assessing the photocatalytic activity of these composite membranes in future research.

Microwave-Assisted Hydrothermal Synthesis of Zinc-tin Based Nanoflower for the Adsorptive Removal of Cadmium from Synthetic Wastewater

The present study utilized zinc-tin nanoflowers (ZT-NFs) in a batch adsorption treatment process to effectively remove cadmium from synthetic wastewater. The batch adsorption strategy was optimized using the univariate approach to enhance the efficiency of the adsorption process. The dominant parameters examined in the optimization experiments were pH/volume of buffer solution, nanoflower amount, and sample agitation type/period. After determining the optimal batch adsorption conditions, equilibrium studies were performed by adding cadmium to synthetic wastewater at concentrations in the range of 1.0 – 40 mg/L. The quantification accuracy for cadmium was improved by developing the calibration plot with spiked sample matrix. The equilibrium data were subjected to mathematical modelling utilizing the Langmuir adsorption isotherm model. The calculated isotherm constants indicated a well-fitted isotherm model to the experimental data. The reported ZT-NFs-based adsorptive removal strategy was effectively employed to remove cadmium from synthetic wastewater.

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.

Microwave-Assisted Hydrothermal Synthesis, Characterization and Catalytic Performance of α-Bi2Mo3O12 in the Selective Oxidation of Propene

Microwave-Assisted Hydrothermal Synthesis, Characterization and Catalytic Performance of α-Bi2Mo3O12 in the Selective Oxidation of Propene

Microwave-Assisted Hydrothermal Synthesis of Na3V2(PO4)2F3 Nanocuboid@Reduced Graphene Oxide as an Ultrahigh-Rate and Superlong-Lifespan Cathode for Fast-Charging Sodium-Ion Batteries.

Na3V2(PO4)2F3 (NVPF) has been regarded as a favorable cathode for sodium-ion batteries (SIBs) due to its high voltage and stable structure. However, the limited electronic conductivity restricts its rate performance. NVPF@reduced graphene oxide (rGO) was synthesized by a facile microwave-assisted hydrothermal approach with subsequent calcination to shorten the hydrothermal time. NVPF nanocuboids with sizes of 50-150 nm distributed on rGO can be obtained, delivering excellent electrochemical performance such as a longevity life (a high capacity retention of 85.6% after 7000 cycles at 10 C) and distinguished rate capability (116 mAh g-1 at 50 C with a short discharging/charging time of 1.2 min). The full battery with a Cu2Se anode represents a capacity of 116 mAh g-1 at 0.2 A g-1. The introduction of rGO can augment the electronic conductivity and advance the Na+ diffusion speed, boosting the cycling and rate capability. Besides, the small lattice change (3.3%) and high structural reversibility during the phase transition process between Na3V2(PO4)2F3 and NaV2(PO4)2F3 testified by in situ X-ray diffraction are also advantageous for Na storage behavior. This work furnishes a simple method to synthesize polyanionic cathodes with ultrahigh rate and ultralong lifespan for fast-charging SIBs.

Microwave-assisted hydrothermal synthesis of NiO/Co3O4 nanosheets decorated on three-dimensional porous graphene for supercapacitors

Electrode material is the key part of capacitor, which seriously affects the electrochemical performance of supercapacitor. NiO/Co3O4 nanosheets decorated on three-dimensional porous graphene (NiO/Co3O4/3DGN) have been prepared though a microwave-assisted hydrothermal method. It is found that NiO can affect the crystallinity and morphology of Co3O4 in the composites. The composites possess excellent electrochemical performance with the special capacity of 1303.9 F g−1 (at 1 A g−1). The assembled NiO/Co3O4/3DGN//AC asymmetric supercapacitor device achieved an energy density of 18.8 Wh kg−1 at a power density of 750.4 W kg−1 and maintained 92.7% of the initial capacitance after 10,000 cycles. The excellent capacitance and rate capability of the composites can be attributed to its unique structural features. The large surface area and the rich porosity provide more activate sites and facilitate the fast diffusion of electrolyte during the charge/discharge process. The direct contact between NiO/Co3O4 nanosheets and 3DGN ensures effective charge transport.

Water-Tolerant Superbase Polyoxometalate [H2(Nb6O19)]6- for Homogeneous Catalysis.

Here, doubly protonated Lindqvist-type niobium oxide cluster [H2(Nb6O19)]6-, fabricated by microwave-assisted hydrothermal synthesis, exhibited superbase catalysis for Knoevenagel and crossed aldol condensation reactions accompanied by activating C-H bond with pKa >26 and proton abstraction from a base indicator with pKa=26.5. Surprisingly, [H2(Nb6O19)]6- exhibited water-tolerant superbase properties for Knoevenagel and crossed aldol condensation reactions in the presence of water, although it is well known that the strong basicity of metal oxides and organic superbase is typically lost by the adsorption of water. Density functional theory calculation revealed that the basic surface oxygens that share the corner of NbO6 units in [H2(Nb6O19)]8- maintained the negative charges even after proton adsorption. This proton capacity and the presence of un-protonated basic sites led to the water tolerance of the superbase catalysis.

Microwave-assisted hydrothermal synthesis of CeVO4 nanostructures: exploring their applicability in supercapacitor technologies

Microwave-assisted hydrothermal synthesis of CeVO4 nanostructures: exploring their applicability in supercapacitor technologies

Microwave-assisted hydrothermal synthesis of ZnO@ZrO2 nanohybrid for biomedical and photocatalytic applications

The present study was conducted to synthesize zinc oxide decorated on zirconium oxide (ZnO@ZrO2) nanohybrid synthesized through microwave-hydrothermal (MW-HT) method. Various analytical techniques were used to analyze the morphology, surface properties, constitution of hybrid, and elemental composition. Additionally, the anti-microbial activity of ZnO@ZrO2 nanohybrid was assessed against Gram-positive and Gram-negative pathogenic bacteria, hemolytic, anti-oxidant as well as anti-inflammatory assay. The hexagonal wurtzite phase of the ZnO was revealed by the XRD analysis. The experimental results reveal that the synergetic effect between the Zn and Zr active sites results an excellent biomedical activity. The ZnO@ZrO2 nanohybrid was successfully applied to the photocatalytic degradation of basic fuchsin (BF) dye within short period of time under visible light (VL) radiation. Moreover, the ZnO@ZrO2 nanohybrid exhibited an extraordinary performance for photocatalytic degradation of BF with a pseudo-first order rate constant (k) of ca. 0.1702 min−1, which was 2.5 and 1.8 fold compared to ZnO and ZrO2 photocatalysts. These results indicated that the ZnO@ZrO2 nanohybrid can be used as a potential biomaterial for bioengineering and photocatalytic applications.

Microwave-Assisted Hydrothermal Synthesis of {100} and {111} Faceted LiFeO2 Truncated Octahedra: Investigations on Volatile Organic Compound Sensing Performance.

Growth of exposed crystal facets has received considerable attention because of their coordinatively unsaturated surface atoms and defect-related surface reactivities. Herein, LiFeO2 truncated octahedra exposed with 6 {100} facets and 8 {111} facets were prepared through a simple microwave-assisted hydrothermal method without using any additives, surfactants, and calcination processes. The detailed growth process revealed that the formation of LiFeO2 truncated octahedra occurred only at the optimized reaction temperature (180 °C), time (30 min), and reactant concentrations. The prepared LiFeO2 truncated octahedra showed excellent sensing responses toward aliphatic organic compounds compared to that against aromatic organic compounds and poor response to inorganic compounds. The response percentages of 150 ppm concentrations of acetone, ethanol, formaldehyde, and isopropyl alcohol are 81.84, 62.91, 62.68, and 69.41%, respectively, at a low operating temperature (100 °C). The presence of exposed facets with their coordinatively unsaturated Li/Fe surface atoms such as 5-fold {100}, 3-fold {111}, 3-fold {100}-{111}, 2-fold {111}-{111}, and 2-fold coordination with the O atom in the vertices facilitated more oxygen vacancies and led to improved surface reactivities as well as sensitivity.

Ultrafast in situ microwave-assisted hydrothermal synthesis of nanorods and soft magnetic colloidal nanoparticles based on MnFe2O4

This work presents for the first time one-step ultrafast (precursor-free) synthesis of 1D MnFe2O4 (MFO) nanorods and soft magnetic colloidal nanoparticles (NPs) using microwave-assisted hydrothermal (MAH) methods, with or without citric acid (CA) as a surfactant (in situ synthesis), respectively. The mechanism of growth of spinel MFO nanostructures during the MAH synthesis was studied by varying synthesis duration (3–6 h) and temperature (180–200 °C). An increase in both the duration and temperature improved the purity of the samples, up to 97%. On the other hand, a temperature increase by 20 °C notably shortened the formation time of MFO nanorods, which have an average diameter and length of less than 20 nm and 350 nm, respectively, as observed at 200 °C after 6 h. All the fabricated MFO NPs with spherical and rod-like morphologies manifested high saturation magnetization in the range of 54–64 emu/g. The chelation of lattice metal ions by CA resulted in the formation of a stable colloid comprising 100% pure spinel MFO NPs with a size of ≤32 ± 10 nm (mean ± SD) and featuring very soft magnetic properties. This colloid was generated by the MAH synthesis at 175 °C within 30 min. Notably, an increase in synthesis duration from 30 min to 3 h diminished MFO phase purity from 100% to 52% and saturation magnetization from 43.4 ± 0.7 to 33.9 ± 2.0 emu/g for CA-functionalized MFO NPs owing to CA degradation increasing during the in situ MAH synthesis with longer duration. This study indicates good potential of ultrafast MAH synthesis for the development of 1D magnetic spinel nanostructures with controllable morphology, size, magnetic properties, and colloidal stability, thereby offering a wide range of applications within the fields of adsorption, catalysis, electronics, and biomedicine.

Facile Microwave-Assisted Hydrothermal Synthesis of Copper Oxide Nanoneedle Arrays for Practical Biomedical Applications.

Copper oxide nanoneedle arrays (CuO NAs) have been widely used as antibacterial agents and in therapeutic applications because of their unique physicochemical features, low cytotoxicity, low cost, exceptional antibacterial action, and significant interest in biomedicine. Various analytical techniques were used to assess the related phase constitution, optical characteristics, elemental content, and surface morphology. The X-ray diffraction (XRD) patterns and field-emission scanning electron microscopy (FE-SEM) micrographs revealed that the CuO NAs had a monoclinic phase with a nanoneedle-like shape. Our findings may cover the progress of innovative and effective anti-bacterial capabilities based on CuO NAs, which have been shown to be effective against various pathogens, making them ideal options for fighting bacterial infections. Objective: This research aimed to synthesize CuO NAs using microwave-solvothermal (MW-ST) technology, explore their effectiveness, and assess their biological activity. The CuO NAs were synthesized using the MW-ST process, and their properties were assessed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), energy dispersive analysis (EDS), field emission transmission microscopy (FE-TEM), and ultraviolet-visible (UV-Vis) techniques. The biocompatibility of CuO NAs was determined through hemolytic assays, and their bioactivities like antioxidant and anti-inflammatory assays were also determined. The CuO NAs were successfully developed,and various analytical tools were used to characterize and validate their morphology, size, crystallinity, and elemental compositions. It has been shown in in-vitro investigations that a strong anti-inflammatory impact is demonstrated by the inhibition of protein denaturation with low hemolytic potential. As a result, CuO NAs have the potential to be an excellent choice for anti-inflammatory solicitations. CuO NAs were synthesized and characterized with various advanced techniques, revealing the formation of nanoneedles-like morphology. Based on the experimental findings, CuO NAs have the potential for anti-microbial, anti-oxidant, anti-inflammatory, and anti-hemolytic activities. However, additional in-vivo testing is essential to properly evaluate their efficiency and safety.

Microwave-Assisted Hydrothermal Synthesis of Pure-Phase Sodalite (>99 wt.%) in Suspension: Methodology Design and Verification.

Despite numerous studies focused on the hydrothermal (HT) synthesis of fly ash zeolites (FAZs), this method still has many limitations, the main of which is the low yield of zeolites. Hydrothermally synthesized zeolites are typically multiphase and exhibit low purity, which limits their applicability. Pure-phase zeolites have been primarily prepared from filtrates after alkaline mineralization of fly ashes, not directly in suspension. In addition, the published methodologies have not been tested in a wider set of samples, and thus their reproducibility is not confirmed. The aim of the study is to propose a reproducible methodology that overcomes the mentioned limitations. The influence of the Si/Al ratio (1.3:1-1:2), the type and concentration of the activator (2/4 M NaOH/KOH/LiOH), the reagent (30% LiCl), the duration (24-168 h), and the temperature (50-180 °C) of the synthesis phases were studied. The sequence of the synthesis phases was also optimized, depending on the type of heat transfer. The fly ashes were analyzed by wavelength-dispersive X-ray fluorescence (WD XRF), flame atomic absorption spectrometry (F-AAS), and X-ray diffraction (XRD). The energy intensity of the synthesis was reduced through the application of unique microwave digestion technology. Both microwave and combined (microwave and convection) syntheses were conducted. FAZs were identified and quantified by XRD analysis. This study presents a three-stage (TS) hydrothermal synthesis of pure-phase sodalite in suspension. Sodalite (>99 wt.%) was prepared from nine fly ashes under the following conditions: I. microwave phase: 120 °C, 150 min, solid-to-liquid ratio (S/L) 1:5, Si/Al ratio 1:1.5, and 4 M NaOH; II. convection phase: 120 °C, 24 h, S/L 1:40, and the addition of 30 mL of 30% LiCl; and III. crystallization: 70 °C for 24 h. The formation of rhombododecahedral sodalite crystals was confirmed by scanning electron microscope (SEM) images.

Unraveling the impact of microwave-assisted techniques in the fabrication of yttrium-doped TiO2 photocatalyst

In this study, we investigate the role of microwave technology in the fabrication of yttrium-doped TiO2 through a comparative analysis of hydrothermal techniques. Microwave-assisted hydrothermal synthesis offers advantages, but a comprehensive comparison between microwave-assisted and conventional methods is lacking. Therefore, in our investigation, we systematically evaluate and compare the morphological, structural, and optical properties of yttrium-doped TiO2 samples synthesized using both techniques. The X-ray diffraction (XRD) patterns confirm the anatase tetragonal structure of the synthesized TiO2-Y systems, while the larger ion radius of yttrium (Y3+) compared to titanium (Ti4+) presents challenges for yttrium to incorporate into the TiO2 lattice. The X-ray Photoelectron Spectroscopy (XPS) revealed a significant difference in the atomic content of yttrium between the TiO2-Y systems synthesized using microwave-assisted and conventional methods. This finding suggests that the rapid microwave method is more effective in successfully doping TiO2 with rare earth metals such as yttrium. The photo-oxidation of carbamazepine (CBZ) using TiO2-Y systems demonstrated high efficiency under UV-LED light. Microwave-synthesized TiO2-Y demonstrates improved photo-oxidation efficiency of CBZ, attributed to enhanced absorption, charge transfer, surface area, and crystallite size. Overall, the microwave-synthesized TiO2-Y systems showed promising performance for the photo-oxidation of CBZ, with improved efficiency compared to conventional synthesis methods.

Room temperature Mössbauer characterization of ferrite with spinel structure

Cobalt ferrite (CoFe2O4) nanoparticle were obtained by different synthesis methods: coprecipitation (CO), ultrasonically assisted coprecipitation (US-CO), coprecipitation followed by mechanochemical treatment (MC-CO), microemulsion (ME) and microwave assisted hydrothermal synthesis (MW-HT). The structure and cation distribution are investigated by XRD diffraction analysis and Raman spectroscopy. The parameters such as chemical shift, quadruple splitting and hyperfine field and site occupancy of Fe3+ were determined by M?ssbauer spectroscopy. The 57Fe-M?ssbauer spectr? of the CoFe2O4 ? w?r? measured at room temperature in ? 12 mm s-1 Doppler velocity range. The 57Fe-M?ssbauer spectr? of the CoFe2O4 samples w?r? fitted with the extended Voigt-based fitting method.

Nano-ZnS photocatalytically active both under UV and solar radiation: A comparison of conventional and microwave-assisted hydrothermal syntheses with various reaction conditions

Influence of reaction conditions on properties of nano-ZnS was investigated. The nano-ZnS was synthesized from ZnCl2 and Na2S via conventional hydrothermal (H) and microwave-assisted hydrothermal (M) method with reaction times 90, 150, 210 min and 10, 20, 30 min, respectively. For all reaction times, three nZn:nS molar ratios (1:1; 1.5:1; 2:1) were tested. Samples were characterized by XRPD, FTIR, Raman microspectroscopy, UV–VIS and SEM. Photocatalytic activity (PA) was determined on Acid orange 7 under UV radiation (λ = 365 nm), and for selected samples also under the sunlight. After 360 min of UV radiation, PA 96% (H; 210 min; 1:1, 1.5:1 or 2:1) and 92% (M; 30 min; 1.5:1 or 2:1) was reached. Under the sunlight, PA 96% (H; 210 min; 2:1) and 92% (M; 20 min; 2:1) was achieved after 120 and 540 min, respectively. M-synthesized nano-ZnS is promising for outdoor applications not requiring a fast PA effect.

Comparative microwave- and conventional oven-assisted hydrothermal syntheses of BaTiO3 nanoparticles for improved electroceramics

Barium titanate (BT) nanoparticles were prepared using both microwave- and conventional oven-assisted hydrothermal syntheses with varying reaction times (1 h, 3 h, and 6 h). In the case of the conventional oven-assisted hydrothermal syntheses, 16 h, 24 h, 48 h and 72 h reaction times were also studied. Structural and morphological evolution of BT particles were investigated. Microwave-assisted hydrothermal synthesis allowed for the rapid formation of nearly pure barium titanate (BT) phase in just 1 h at 200 °C. On the other hand, using a conventional oven as the heat source required at least 6 h of synthesis to achieve a similar material. When the different BT powders were pelletized and sintered at 1300 °C, ceramics with over 95 % density were obtained. The room-temperature (RT) dielectric permittivity exceeded 1750 for BT particles prepared over 6 h using both heating methods. However, a significant distinction emerged when comparing the piezoelectric coefficient (d33) values. The BT pellet obtained through the sintering of BT synthesized in the conventional oven for 6 h exhibited a notably higher d33 value, approximately 171 pC/N, as opposed to the 146 pC/N value observed in BT ceramics resulting from the microwave synthesized powders. Among the ceramic BT variations, the one derived from the best-crystallized tetragonal BT particles (CON_72h) displayed the lowest d33 value at 79 pC/N. These findings underscore the immense potential of microwave- and conventional oven-assisted hydrothermal syntheses in the sustainable production of BT nanomaterials, which can then be sintered to enable the preparation of ceramics with enhanced ferroelectric and piezoelectric properties.

Microwave-assisted hydrothermal synthesis of autoclaved bricks from municipal solid waste incineration fly ash and coal fly ash (MSWIFA) and its carbon emission

In this study, the feasibility of manufacturing low-carbon autoclaved municipal solid waste incineration fly ash and coal fly ash (MSWI-FA) bricks from MSWI fly ash and coal FA with microwave-assisted hydrothermal synthesis was investigated. To facilitate the experiment, block samples were prepared. The effects of microwave pre-treating parameters on the performance of block samples were investigated. Mechanisms of microwave pre-treating were studied. The effects of microwave pre-treating were further investigated by micro-analyses of synthesized block samples. Environmental impacts were discussed from heavy metal solidification/stabilization and CO2 emission. The results showed that the optimal microwave parameters were 30 min and 385 W. With microwave pre-treating, Al-substituted tobermorite crystallites were generated in raw material mixtures. For block samples, more Al-substituted tobermorite crystals were observed, and lower total pore volume and pore diameter were found. The solidification/stabilization rates of Cu, Pb, and Zn increased by 163.20%, 24.89%, and 78.77%, respectively, and CO2 emission could be reduced up to 53.40%.

Microwave-assisted hydrothermal synthesis of lithium ion-sieve for adsorption of lithium ion in coal gangue leaching solution

A two-step method involving microwave-assisted hydrothermal synthesis and solid-phase calcination was employed to prepare the Li1.6Mn1.6O4 (LMO) precursor. Material characterization demonstrated the structural stability of LMO even after acid pickling, resulting in the creation of the ion-sieve H1.6Mn1.6O4 (HMO) with the most notable Li+ adsorption capacity of 29.45 mg·g−1. The adsorption isotherm of HMO adhered to the Langmuir isothermal model (R2 = 0.9929), indicating a smooth and monolayer adsorption process. Simultaneously, the adsorption kinetics of HMO was consistent with the pseudo-second-order kinetic model (R2 = 0.9911), indicative of chemisorption. Upon undergoing five adsorption-desorption cycles, HMO's adsorption capacity remained above 22.32 mg·g−1. Evaluation of the distribution coefficient (Kd) and the separation factor (αMeLi) for HMO in both coal gangue leaching solution and simulated salt lake brine highlighted its exceptional selectivity. Notably, HMO achieved a remarkable 99.9% adsorption rate in the coal gangue leaching solution. These outcomes underscore the efficacy of the synthesized HMO in highly selective Li+ recovery from both coal gangue and salt lake brine, additionally emphasizing the potential of coal gangue as a valuable lithium resource with significant prospects for future development and utilization.

Facile synthesis of high surface area of p-n Co3O4-In2O3 heterostructure-based sensor for improved xylene detection at low temperature

This study reports on the gas sensing properties of Co3O4 – n-type semiconducting metal oxides (Co-nSMOs) heterostructures, i.e., Co3O4-In2O3 (Co-In), Co3O4-CeO2 (Co-Ce), Co3O4-SnO2 (Co-Sn) and Co3O4-ZrO2 (Co-Zr) synthesized by microwave-assisted hydrothermal synthesis. Structural studies confirmed the formation of Co-nSMO heterostructures. Electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) showed that the Co-In possesses higher surface defects compared to its counterparts. The Co-nSMOs sensors were evaluated towards benzene, toluene, ethylbenzene, and xylene (BTEX) compounds, acetone, and NO2. Amongst the tested sensors, the Co-In heterostructure showed superior selectivity and a response of 36.6 to 100 ppm xylene at an optimum effective temperature of 150 °C. The sensor further showed good sensitivity and a low limit of detection of 0.2 ppm. Moreover, the Co-In-based sensor stored for 5 months, demonstrated excellent long-term stability toward xylene vapour in dry air and under 40 % relative humidity environment. The improved performance was due to the enriched facilitation of surface oxygen adsorption, which resulted in the enhanced catalytic influence of Co3O4 for oxidizing xylene vapour. Additionally, the performance was also associated with the higher surface area, mesoporous behaviour, and biggest pore volume which offered plentiful energetic sites for redox reactions, and synergistic combination of Co3O4 and In2O3 at the nanoscale p-n heterojunction. The xylene sensing mechanisms associated with improved performance were deliberated in detail. These results demonstrated that the Co-In could be utilized to monitor xylene with trivial interference from RH.