Microwave Solvothermal Synthesis Research Articles

Microwave solvothermal synthesis of Component-Tunable High-Entropy oxides as High-Efficient and stable electrocatalysts for oxygen evolution reaction

Transition-metal-based high-entropy oxides (HEOs) are appealing electrocatalysts for oxygen evolution reaction (OER) due to their unique structure, variable composition and electronic structure, outstanding electrocatalytic activity and stability. Herein, we propose a scalable high-efficiency microwave solvothermal strategy to fabricate HEO nano-catalysts with five earth-abundant metal elements (Fe, Co, Ni, Cr, and Mn) and tailor the component ratio to enhance the catalytic performance. (FeCoNi2CrMn)3O4 with a double Ni content exhibits the best electrocatalytic performance for OER, namely low overpotential (260 mV@10 mA cm−2), small Tafel slope and superb long-term durability without obvious potential change after 95 h in 1 M KOH. The extraordinary performance of (FeCoNi2CrMn)3O4 can be attributed to the large active surface area profiting from the nano structure, the optimized surface electronic state with high conductivity and suitable adsorption to intermediate benefitting from ingenious multiple-element synergistic effects, and the inherent structural stability of the high-entropy system. In addition, the obvious pH value dependable character and TMA+ inhibition phenomenon reveal that the lattice oxygen mediated mechanism (LOM) work together with adsorbate evolution mechanism (AEM) in the catalytic process of OER with the HEO catalyst. This strategy provides a new approach for the rapid synthesis of high-entropy oxide and inspires more rational designs of high-efficient electrocatalysts.

Synthesis, Characteristics, and Effect of Zinc Oxide and Silver Nanoparticles on the In Vitro Regeneration and Biochemical Profile of Chrysanthemum Adventitious Shoots.

Studies on nanoparticles' effects on plants are relevant for horticulture. This study aimed to test the influence of zinc oxide submicron particles (ZnO SMPs), zinc oxide nanoparticles (ZnO NPs), and zinc oxide nanoparticles combined with silver nanoparticles (ZnO+1%Ag NPs) applied at 100 and 500 mg·L-1 on the regeneration and biochemical activity of adventitious shoots in Chrysanthemum × morifolium (Ramat.) Hemsl. 'UTP Burgundy Gold' and 'UTP Pinky Gold'. The original microwave solvothermal synthesis and characteristics of the ZnO samples were described. Internodes were cultured on the MS medium with 0.6 mg∙L-1 6-benzylaminopurine (BAP) and 2 mg∙L-1 indole-3-acetic acid (IAA). In 'UTP Burgundy Gold', the highest shoot regeneration efficiency was obtained for 100 mg·L-1 ZnO SMPs and 500 mg·L-1 ZnO NPs treatments (6.50 and 10.33 shoots per explant, respectively). These shoots had high or moderate chlorophyll and carotenoid contents. In 'UTP Pinky Gold', the highest shoot number was produced in the control (12.92), for 500 mg·L-1 ZnO SMPs (12.08) and 500 mg·L-1 ZnO NPs (10.42). These shoots had increased chlorophyll (a+b)-to-carotenoid ratios. In 'UTP Pinky Gold', the ZnO SMPs and ZnO NPs affected the anthocyanins biosynthesis, whereas ZnO + 1%Ag NPs decreased the phenolics accumulation. These results are important for the improvement of chrysanthemum micropropagation.

Enhancing Dispersion of Yttria-Stabilized Tetragonal Zirconia Nanopowders with Microwave Solvothermal Synthesis

Yttria stabilized tetragonal zirconia (Y0.08Zr0.94O2, YSZ) nanopowders were successfully synthesized by microwave solvothermal method (MSM). The synthesizing temperature, holding time and mineralizer concentration were optimized. The crystallization and particle distribution of as-prepared YSZ nanopowders were identified by DSC/TG, XRD, FESEM, TEM, FTIR, DLS, and BET. The dispersion of YSZ nanopowders dried by different methods and modified by polyethyleneimine (PEI) was analyzed and discussed. The results show that the PEI modified samples have the best dispersion, and the dispersion of freeze-dried samples is better than that of traditional dried ones. The particle size of the PEI modified samples calculated from the surface area determined by BET is 15.7 nm, which is consistent with that determined by TEM (16.5 nm), but slightly smaller than that calculated by the Scherrer formula according to XRD (22.3 nm). This may be attributed to the different testing principles in these methods.

(K, Na)NbO3 lead-free piezoceramics prepared by microwave sintering and solvothermal powder synthesis

Low temperature and short processing time are favorable for fabricating (K, Na)NbO3 (KNN) lead-free piezoelectric ceramics with a drawback of easy alkali metal volatilization during the powder synthesis and sintering processes. This study revealed that microwave sintering (MS) in addition to microwave solvothermal synthesis (MSS) of powder can lead to short-time fabrication of KNN ceramics with high density and fine grains. It was found that when the concentration of KOH/NaOH exceeds 1 M, KNN powder with single perovskite structure can be synthesized successfully by MSS method, which can be densified by MS to a high relative density close to 97% at 1050 °C even using 2/9 shorter time than conventional sintering (CS) at the same temperature. Importantly, the MSed KNN ceramics show better piezoelectric and ferroelectric properties than CSed counterparts. Without any dopants, the piezoelectric coefficient (d33) of the MSed pure KNN ceramics is 132 pC/N, and the remnant polarization (Pr) is 26.3 μC/cm2. The results show that the MS method is a promising method for preparing KNN-based ceramics.

Dental Implant Healing Screws as Temporary Oral Drug Delivery Systems for Decrease of Infections in the Area of the Head and Neck.

BackgroundPeriimplantitis is continuously one of major threats for the uneventful functioning of dental implants. Current approaches of drug delivery systems are being more commonly implemented into oral- and maxillofacial biomaterials in order to decrease the risk of implant failure due to bacterial infection. Silver nanoparticles and their compounds have been proven in eradicating oral bacteria responsible for peri-implant infections. Nevertheless, their evaluation as coating for implant abutments has not been extensively evaluated so far. This article describes a novel coating consisting of zinc oxide (ZnO) and silver (Ag) nanoparticles (NPs). This coating was used to modify healing abutments that could be used as drug delivery systems in oral implantology.Materials and MethodNanoparticles with a ZnO + 0.1% Ag composition were produced by microwave solvothermal synthesis and then incorporated into the surface of titanium healing abutments by high-power ultrasonic deposition. Surface morphology, roughness, wettability were evaluated. Ability of biofilm formation inhibition was tested against S. mutans, S. oralis, S. aureus and E. coli.ResultsZnO+0.1%Ag NPs were sufficiently deposed on the surface of the abutments creating nanostructured coating which increased surface roughness and decreased wettability. Modified abutments significantly decreased bacterial biofilm formation. Bacteria present in SEM studies were unlikely to settle and replicate on the experimental abutments as their cells were rounded, insufficiently spread on the surface and covered with released NPs.ConclusionExperimental nanostructured abutments were easily manufactured by high-power ultrasonic deposition and provided significant antibacterial properties. Such biomaterials could be used as temporary drug delivery abutments for prevention and treatment of intra- and extraoral peri-implant infections in the area of the head and neck.

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 solvothermal synthesis of cubic MnS@Ag2S core-shell photocatalysts with improved charge separation and photocatalytic activity

Cubic α-MnS and core-shell MnS@Ag2S photocatalysts were successfully synthesized with a microwave-assisted solvothermal and ion-exchange approach. The morphology, phase, crystal/optical properties, charge separation and photocatalytic H2 generation activity of these photocatalysts were studied. The morphology of these MnS nanomaterials can be tuned from microsphere to microcubes by altering the reaction temperature and duration. A HRTEM image of the MnS@Ag2S photocatalyst reveals that the surface of cubic MnS is decorated with uniformly distributed Ag2S nanoparticles. The formation of Ag2S shell can effectively increase the carrier separation and photocatalytic activity of MnS-based photocatalysts. The rate of hydrogen production of the MnS@Ag2S photocatalyst becomes 2548 μmol g−1h−1, which is 3.7 times that of the MnS photocatalyst. Mn L3-edge near-edge X-ray-absorption fine-structure (NEXAFS) spectra were monitored in situ before and after exposure to light to investigate the interfacial charge-transfer behaviors within the MnS@Ag2S photocatalysts. The results confirm that photogenerated electrons transfer from MnS to Ag2S.

Magnetic NiFe2O4 3D nanosphere photocatalyst: Glycerol-assisted microwave solvothermal synthesis and photocatalytic activity under microwave electrodeless discharge lamp

In this study, NiFe2O4 (NFO) nanocrystalline powder was synthesized using a glycerol-assisted microwave solvothermal process followed by annealing. In comparison with the traditional preparation method, this method does not require addition of any precipitate-controlling agents. The structural properties of NFO were characterized via different techniques, such as X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and ultraviolet–visible diffuse reflection spectra. The results suggested that the NFO crystal was a three-dimensional (3D) porous nanosphere with a diameter of approximately 400 nm, and the glycerol added during the preparation process played a crucial role in the formation of 3D nanospheres. The photocatalytic activity of NFO was evaluated by the degradation of methylene blue (MB) in a microwave electrodeless discharge lamp (MEDL) system. Additionally, the mechanism of MB photocatalytic degradation was studied. The results suggest that 88.6% of the MB degraded within 10 min under MEDL irradiation, and the mineralization rate reached 55%. The main active species of MB degradation were e-, h+, and •O2−. In addition, the cycle catalysis experiment confirmed the reusability of NFO 3D nanospheres. We believe that the NFO 3D nanospheres can serve as efficient photocatalysts suitable for MEDL systems.

Effect of Sm-doping on microstructure and thermoelectric properties of textured n-type Bi2Te2.7Se0.3 compound due to change in ionic bonding fraction

Textured n-type Bi2-xSmxTe2.7Se0.3 compounds with x ​= ​0; 0.005; 0.02 and 0.05 have been prepared by microwave-solvothermal synthesis of starting powders and spark plasma sintering of bulk materials. Texturing [001] axis coincided with direction of spark plasma sintering pressuring. With increasing x, (i) an average lateral size of grains in the samples is decreasing; (ii) the Lotgering factor characterizing a degree of preferential orientation of the grains is increasing; (iii) anomalies of all the thermoelectric properties, related to onset of intrinsic conductivity, are shifted to higher temperatures. The Sm-doping effect on the grain structure and thermoelectric properties of samples is attributed to increasing in ionic bonding fraction, which can occur at increasing Sm content due to a difference in electronegativity of Bi and Sm atoms. Maxima in temperature dependences of the thermoelectric figure-of-merit, typical for Bi2Te3-based compounds and due to the intrinsic conductivity, were observed. The highest value of the thermoelectric figure-of-merit was found to be weakly dependent on x and falling into ~0.6 ÷ ~0.7 interval, whereas temperature position of the maxima is remarkably shifted to higher temperatures with increasing Sm content.

Size-dependent effects of ZnO nanoparticles on the photocatalytic degradation of phenol in a water solution

The effect of the ZnO nanoparticles (NPs) size on the photocatalytic degradation of phenol in a water solution under the influence of UV and Vis radiation was discussed. For the first time, research on photocatalytic degradation has used ZnO NPs produced by only one method (microwave solvothermal synthesis without heat treatment or other processes of reduction/oxidisation of the surface of NPs samples). ZnO NPs average size was determined using the Scherrer's formula, Nanopowder XRD Processor Demo web application, by converting the results of the specific surface area-density, and TEM tests. The ZnO NPs (average size between 23 nm and 71 nm) characterise by uniform morphology and narrow size distribution. The photocatalytic performance of ZnO NPs increases with the increase of the particle size and the decrease of the specific surface area. For both UV and Vis radiation, the highest reaction rate for phenol degradation was found for ZnO sample with the average particle size of 71 nm. Low concentrations of resorcine and hydroquinone (co-products of phenol degradation) were found for UV light photocatalytic test. However, high concentrations of hydro- and p-benzoquinone were observed for visible light photoactivity due to the slower decomposition of the main contamination associated with the utilized of other type of radiation. The photocatalytic activity was found to be attributable to the decrease in the charge carrier recombination rate.

Microwave Solvothermal Synthesis of Three-Dimensional Bi2MoO6 Microspheres with Enhanced Photocatalytic Activity.

In this study, three-dimensional (3D) Bi2MoO6 microspheres were successfully fabricated by a facile, rapid, and mild microwave solvothermal strategy for the first time. The resultant 3D Bi2MoO6 microspheres exhibited superior adsorption capacity and photocatalytic efficiency in the degradation of the representative antibiotic ciprofloxacin under visible light, for which the reaction kinetic rate constant is 7.5 times as high as that of the as-synthesized zero-dimensional Bi2MoO6 nanoparticles. The 3D hierarchical porous structure and the high Brunauer–Emmett–Teller surface area providing abundant reactive sites mainly contributed to the enhanced photocatalytic activity. The results highlight the feasibility of 3D Bi2MoO6 microspheres as an efficient visible-light-responsive photocatalyst for antibiotic removal in an aqueous system.

Microwave-Assisted Solvothermal Synthesis of Covalent Organic Frameworks (COFs) with Stable Superhydrophobicity for Oil/Water Separation.

COFs were synthesized by a microwave-assisted solvothermal route, with the building blocks containing 1,3,5-tris(4-aminophenyl) benzene and 2,3,5,6-tetra-fluoroterephthalaldehyde (or 1,4-phthalaldehyde). The -F groups introduced into the benzene ring promoted hydrophobicity and stability of the COFs. The universality and long effectiveness of oil adsorption can be realized when applying COFs as adsorbent. The powder also exhibited excellent water-in-oil emulsions separation performance, with the separation efficiency no lower than 99.5%. In this work, the use of microwave solvothermal synthesis of superhydrophobic COFs is potential to replace the conventional synthesis process and more suitable for industrial scale-up production. Furthermore, the findings provide a new strategy for solving the problem of oil spill treatment and industrial water-in-oil emulsions separation by using the emerging 2D COFs.

Flash microwave-assisted solvothermal (FMS) synthesis of photoactive anatase sub-microspheres with hierarchical porosity.

The synthesis of nanostructured sub-microspheres of TiO2 anatase with hierarchical nano- and mesoporosity was successfully achieved by using an innovative approach that applies the principles of acidic digestion to microwave (MW) solvothermal synthesis. This process, termed flash microwave-assisted solvothermal (FMS) synthesis, facilitates the formation of spherical particles without surfactants or templating agents, exploiting the rapid reaction kinetics engendered by MW heating. Unlike many other MW-assisted solvothermal methods, the application of constant MW power leads to a rapid increase of the autogenous pressure, inducing burst-nucleation of small primary crystallites and subsequent rapid agglomeration into secondary particles, with reaction times reduced to minute-timescales. The use of non-aqueous polar solvents such as ethanol is key to the production of regular spheres with a narrow size distribution, composed of nanocrystallites. Morphology, porosity, specific surface area, phase composition, crystallite size and optical properties of the particles can be controlled via a judicious selection of physical and chemical synthesis parameters, especially precursor choice and acid concentration. The complex structure of the particles leads to surface areas of up to ca. 500 m2 g−1 with intergranular mesoporosity. The as-synthesised FMS particles show increased adsorption under dark conditions and selective de-ethylation of rhodamine B under visible light compared to a commercial photocatalyst (Degussa P25). The photodegradation mechanism hinges on the capacity of the spheres to accept electrons from the photoexcited state of molecules at the particle surface, with the large sphere surface area maximising adsorption capacity and improving the efficiency of the photocatalytic processes. The singular characteristics and properties of the particles could pave the way for further applications in water purification and optoelectronic devices.

Nanoparticles And Human Saliva: A Step Towards Drug Delivery Systems For Dental And Craniofacial Biomaterials.

AimThe aims of this study were to investigate new nano-formulations based on ZnO and Ag nanoparticle (NP) compounds when used against clinical strains of oral gram-positive and gram-negative bacteria, and to examine the stability and behaviour of nano-formulation mixtures in saliva based on different compositions of Ag NPs, ZnO NPs and ZnO+x·Ag NPs. Methods: ZnO NPs with and without nanosilver were obtained by microwave solvothermal synthesis. Then, antibacterial activity was evaluated against bacteria isolated from human saliva. Behavior and nanoparticle solutions were evaluated in human saliva and control (artificial saliva and deionized water). Results were statistically compared.ResultsThe NP mixtures had an average size of 30±3 nm, while the commercial Ag NPs had an average size of 55±5 nm. The suspensions displayed differing antibacterial activities and kinetics of destabilisation processes, depending on NPs composition and fluid types.ConclusionThe present study showed that all NPs suspensions displayed significant destabilisation and high destabilisation over the 24 h of the analyses. The agglomeration processes of NPs in human saliva can be reversible.

Prominent Visible Light Photocatalytic and Water Purification Activity of PbS/CdS/CdO Nanocomposite Synthesized via Simple Co-Precipitation Method

Background: Due to unique chemical and physical properties and potential application in many fields, nanostructured materials have attracted many attentions. Cadmium sulfide (CdS) is a semiconductor that has a wide band gap of 2.42 eV at room temperature and can be served in solar cells and photoluminescence devices. Cadmium sulfide (CdS) is a kind of attractive semiconductor material, and it is now widely used for optoelectronic applications. CdS nano and microstructures can be synthesized via different chemical methods such as microwave-solvothermal synthesis, surfactant-ligand coassisting solvothermal method and hydrothermal route. Also different morphologies of this semiconductor such as dendrites, nanorods, sphere-like, flakes, nanowires, flower-like shape triangular and hexagonal plates, were synthesized. Methods: To synthesis of the nanocomposite, a simple co-precipitation method was served. In briefly, 0.1 g of Pb(NO3)2 was dissolved in the distilled water (Solution 1). Also different aqueous solutions were made from dissolving different mole ratio of Cd(NO3)2.6H2O respect to the lead source in the water (Solution 2). Two solutions were mixed together under vigorous stirring and then S2- solution (0.02 g thiourea in the water) was added to the Pb2+/Cd2+ solution. After that 0.1 g of CTAB as surfactant was added to the final solution. Finally to the synthesis of both sulfide and oxide nanostructures, NaOH solution was added to the prepared solution to obtain pH= 10. Distilled water and absolute ethanol were used to wash the obtained precipitate and then it dried at 80 °C for 8 h. Results: From the XRD pattern it was found that the peaks placed at 24.9°, 27°, 44.1°, 48°, 52°, 54°, 57.8°, 66.8°, 71.2° are associated to CdS compound with hexagonal phase (JCPDS=00-001-0780) that belong to (100), (002), (110), (103), (112), (201), (202), (203), (211) Miller indices respectively. The Other peaks belong to PbS with hexagonal phase (JCPDS=01-078-1897), and CdO with cubic phase (JCPDS=00-001-1049). From SEM images, it was found by choosing the mole ratio to 1:1, very small and uniform particles were achieved. By increasing Pb2+/Cd2+ mole ratio to 1:2, very tiny particles aggregated together were achieved. Conclusion: The results showed that the product can adsorb extra 80% of heavy metal ions from the water. So it can be said that the nanocomposite can be used in the water treatment due to its high photocatalytic and surface adsorption activities. In other words, it can remove heavy metals from the water and also decompose organic pollutions.

Photocatalytic defluorination of perfluorooctanoic acid by surface defective BiOCl: Fast microwave solvothermal synthesis and photocatalytic mechanisms

There is an urgent need for developing cost-effective methods for the treatment of perfluorooctanoic acid (PFOA) due to its global emergence and potential risks. In this study, taking surface-defective BiOCl as an example, a strategy of surface oxygen vacancy modulation was used to promote the photocatalytic defluorination efficiency of PFOA under simulated sunlight irradiation. The defective BiOCl was fabricated by a fast microwave solvothermal method, which was found to induce more surface oxygen vacancies than conventional solvothermal and precipitation methods. As a result, the as-prepared BiOCl showed significantly enhanced defluorination efficiency, which was 2.7 and 33.8 times higher than that of BiOCl fabricated by conventional solvothermal and precipitation methods, respectively. Mechanistic studies indicated that the defluorination of PFOA follows a direct hole (h+) oxidation pathway with the aid of •OH, while the oxygen vacancies not only promote charge separation but also facilitate the intimate contact between the photocatalyst surface and PFOA by coordinating with its terminal carboxylate group in a bidentate or bridging mode. This work will provide a general strategy of oxygen vacancy modulation by microwave-assisted methods for efficient photocatalytic defluorination of PFOA in the environment using sunlight as the energy source.

Noble-metal-free Ni2P as cocatalyst decorated rapid microwave solvothermal synthesis of inorganic-organic CdS-DETA hybrids for enhanced photocatalytic hydrogen evolution

Inorganic-organic hybrid materials, a class of probable candidates for combining two counterparts into one structure could be beneficial for improving or combing the excellent electronic, magnetic, rigidity and thermal stability, and optical feathers of inorganic frameworks with diverse structure, processability, flexibility and good geometric controllability of organic molecules. Anchoring inorganic-organic hybrid materials with cocatalysts is a usually used strategy for enhancing their catalytic performance. However, noble metal cocatalysts always limit their practical application. Herein, we report that noble metal free cocatalyst of Ni2P decorated CdS-diethylenetriamine (CdS-DETA) can effectively overcome this limitation to achieve highly photocatalytic hydrogen production. The rapid microwave solvothermal synthesis of CdS-DETA (MCdS-DETA) process shortens reaction time, saves energy and lead to achieve highly photocatalytic activity due to its low crystallinity. When Ni2P decorated MCdS-DETA, The 0.4%Ni2P/MCdS-DETA exhibited the highest photocatalytic hydrogen evolution activity (6836 μmmol h−1 g−1), which is 4.14 times, 2.06 times and 1.34 times higher than traditional solvothermal CdS-DETA(TCdS-DETA), MCdS-DETA and Pt cocatalysted MCdS-DETA, respectively. The method reported here can be extended to other inorganic-organic hybrid materials, and develops new strategies for exploring inorganic-organic hybrid-based photocatalysts.

Structural and Magnetic Properties of Co‒Mn Codoped ZnO Nanoparticles Obtained by Microwave Solvothermal Synthesis

Zinc oxide nanoparticles codoped with Co2+ and Mn2+ ions (Zn(1−x−y)MnxCoyO NPs) were obtained for the first time by microwave solvothermal synthesis. The nominal content of Co2+ and Mn2+ in Zn(1−x−y)MnxCoyO NPs was x = y = 0, 1, 5, 10 and 15 mol % (the amount of both ions was equal). The precursors were obtained by dissolving zinc acetate dihydrate, manganese (II) acetate tetrahydrate and cobalt (II) acetate tetrahydrate in ethylene glycol. The morphology, phase purity, lattice parameters, dopants content, skeleton density, specific surface area, average particle size, average crystallite size, crystallite size distribution and magnetic properties of NPs were determined. The real content of dopants was up to 25.0% for Mn2+ and 80.5% for Co2+ of the nominal content. The colour of the samples changed from white to dark olive green in line with the increasing doping level. Uniform spherical NPs with wurtzite structure were obtained. The average size of NPs decreased from 29 nm to 21 nm in line with the increase in the dopant content. Brillouin type paramagnetism and an antiferromagnetic interaction between the magnetic ions was found for all samples, except for that with 15 mol % doping level, where a small ferromagnetic contribution was found. A review of the preparation methods of Co2+ and Mn2+ codoped ZnO is presented.

Effect of Microwave Radiation Power on the Size of Aggregates of ZnO NPs Prepared Using Microwave Solvothermal Synthesis.

This paper reports the possibility of changing the size of zinc oxide nanoparticles (ZnO NPs) aggregates through a change of synthesis parameters. The effect of the changed power of microwave heating on the properties of ZnO NPs obtained by the microwave solvothermal synthesis from zinc acetate dissolved in ethylene glycol was tested for the first time. It was found that the size of ZnO aggregates ranged from 60 to 120 nm depending on the power of microwave radiation used in the synthesis of ZnO NPs. The increase in the microwave radiation power resulted in the reduction of the total synthesis time with simultaneous preservation of the constant size and shape of single ZnO NPs, which were synthesized at a pressure of 4 bar. All the obtained ZnO NPs samples were composed of homogeneous spherical particles that were single crystals with an average size of 27 ± 3 nm with a developed specific surface area of 40 m2/g and the skeleton density of 5.18 ± 0.03 g/cm3. A model of a mechanism explaining the correlation between the size of aggregates and the power of microwaves was proposed. This method of controlling the average size of ZnO NPs aggregates is presented for the first time and similar investigations are not found in the literature.

Size Control of Cobalt-Doped ZnO Nanoparticles Obtained in Microwave Solvothermal Synthesis

This article presents the method of size control of cobalt-doped zinc oxide nanoparticles (Zn1−xCoxO NPs) obtained by means of the microwave solvothermal synthesis. Zinc acetate dihydrate and cobalt(II) acetate tetrahydrate dissolved in ethylene glycol were used as the precursor. It has been proved by the example of Zn0.9Co0.1O NPs (x = 10 mol %) that by controlling the water quantity in the precursor it is possible to precisely control the size of the obtained Zn1−xCoxO NPs. The following properties of the obtained Zn0.9Co0.1O NPs were tested: skeleton density (helium pycnometry), specific surface area (BET), dopant content (ICP-OES), morphology (SEM), phase purity (XRD), lattice parameter (Rietveld method), average crystallite size (FW1/5/4/5M method and Scherrer’s formula), crystallite size distribution (FW1/5/4/5M method), and average particle size (from TEM and SSA). An increase in the water content in the precursor between 1.5% and 5% resulted in the increase in Zn0.9Co0.1O NPs size between 28 nm and 53 nm. The X-ray diffraction revealed the presence of only one hexagonal phase of ZnO in all samples. Scanning electron microscope images indicated an impact of the increase in water content in the precursor on the change of size and shape of the obtained Zn0.9Co0.1O NPs. The developed method of NPs size control in the microwave solvothermal synthesis was used for the first time for controlling the size of Zn1−xCoxO NPs.