Microwave-assisted Hydrothermal Technique Research Articles

Magnetic fibrous silica mesoporous as a selective and efficient system for removal of Cd(II) ions with a focus on optimization by response surface methodology

ABSTRACT In this study, the removal efficiency of Cd (II) ions from aqueous solutions by Fe3O4@SiO2@KCC-1 as a simple and efficient adsorbent was studied. The prepared adsorbent was synthesised by using the microwave-assisted hydrothermal technique in a short period of time and characterised by SEM, FTIR, XRD, VSM, TEM, and BET analyses. The effect of various parameters on the removal percentage of the Cd (II) ions was studied by central composite design and the optimal condition of factors for maximum Cd (II) removal percentage was as follows: pH = 5.97, adsorbent dosage: 1.49 g L−1, Cd (II) concentration: 59.29 mg L−1, and contact time: 54.79 min, respectively. The results illustrated that the Central Composite Designs) CCD(model has an ideal ability in predicting the removal percentage of Cd (II) ions from the aqueous solutions.

Microwave-assisted hydrothermal synthesis of CuWO4-palygorskite nanocomposite for enhanced visible photocatalytic response

CuWO4-Pal nanocomposite formed by copper (II) tungstate nanoparticles with palygorskite clay mineral (Pal) was synthesized via coprecipitation method followed by microwave-assisted hydrothermal technique and applied in the photodegradation of the antibiotic ciprofloxacin (CIP) using visible-light irradiation. The formation of CuWO4-Pal nanocomposite was confirmed by XRD, Raman spectroscopy and DRIFT studies. X-ray photoelectron spectroscopy (XPS) and photoelectrochemical studies of the nanocomposite showed structural changes, which induced the formation of oxygen vacancies and better charge carrier mobility. Field emission scanning electron microscopy (FE–SEM) and transmission electron microscopy (TEM) images revealed the fibrous morphology of Pal as well as the control of CuWO4 crystal growth with the formation of the nanocomposite. The CIP photodegradation was influenced by the adsorption power and the pH solution. CuWO4-Pal exhibited 92% of CIP photodegradation and 50% of total organic carbon (TOC) removal using an initial concentration of 8 mg L−1 at pH 10 after 90 min. Together with the photoelectrochemical study, the scavengers used indicated that the hole (h+) is the main oxidative species in CIP photodegradation.

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.

Rapid deposition of (K,Na)NbO3 thick films using microwave-assisted hydrothermal technique

Rapid processing for hydrothermal deposition of (K,Na)NbO3 (KNN) thick films was proposed with the assistance of microwave (MW) heating, for short-time fabrication of ferroelectric/piezoelectric films with thicknesses of several micrometers within 1 h. MW irradiation raised the temperature of water medium up to 240 °C within 10 min, whereas conventional heating using hot-air convection required more than 2 h. Epitaxial KNN films were successfully deposited on single-crystal substrates of (100)SrTiO3:Nb and (100)SrRuO3//(100)SrTiO3 at reaction temperature of 180 °C–240 °C within 1 h; especially, the films with thicknesses over 10 μm could be obtained on at 220 °C for 40 min. The resulting film exhibited domain structure and dielectric/ferroelectric properties comparable with the KNN films derived from conventional hydrothermal deposition.

Effects of Desilication in NaOH/Piperidine Medium and Phosphorus Modification on the Catalytic Activity of HZSM-5 Catalyst in Methanol to Propylene Conversion.

Propylene is one of the main petrochemical building blocks applied as a feedstock for various chemical and polymer intermediates. The methanol-to-propylene (MTP) processes are reliable options for propylene production from non-petroleum resources. The highsilica ZSM-5 zeolite is found to be a reliable candidate for the methanol to propylene catalysis. In this study, the mesoporosity was first introduced into a high silica ZSM-5 zeolite via an alkaline treatment by NaOH solution with piperidine to decrease the diffusion limitation, and then the structure of zeolite was stabilized by phosphorus modification to improve the acidic properties and to enhance the catalyst stability. High-silica H-ZSM-5 catalysts (Si/Al = 200) were successfully prepared through microwave-assisted hydrothermal technique in the presence of tetrapropyl ammonium hydroxide (TPAOH) structure-directing agent. The mesoporosity was efficiently introduced into the ZSM-5 crystals via desilication derived from alkaline NaOH/piperidine solution. Then, the acidity of the desilicated ZSM-5 samples was improved using phosphorus modification. The catalysts were subjected to XRD, ICP-OES, FE-SEM, BET, TGA, FT-IR and NH3-TPD analysis. The catalytic performance of the prepared catalysts in the methanol to propylene (MTP) reaction was examined in a fixed-bed reactor at 475 °C, atmospheric pressure and methanol WHSV of 0.9 h-1. The results showed that the alkaline treatment in NaOH/piperidine solution created uniform mesoporosity with no severe damage in the crystal structure. Similarly, phosphorus modification developed the acidic features and led to the optimal catalytic efficiency in terms of the maximum propylene selectivity (49.16%) and P/E ratio (5.97) as well as the catalyst lifetime. The results showed an excellent catalytic activity in terms of 99.21% methanol conversion, good propylene selectivity up to 49.16%, a high ratio of P/E of 5.97 and a low selectivity to C5 + hydrocarbons of 11.57% for ZS-D-PI-P sample.

Structural, Morphological and Photoluminescence Studies of Pure ZrO2 and ZrO2: Eu+3 Nanophosphors Synthesised by Microwave-Assisted Hydrothermal Technique

The luminescence properties of pure and ZrO2: Eu+3 nanophosphors with different concentration of the Eu+3 is synthesised and studied. A novel and environment benign microwave-induced hydrothermal process is used to synthesise the nanoparticles. As-formed pure ZrO2 nanoparticles were X-ray amorphous, and upon calcination at higher temperatures, they crystallise to a combination of both cubic and tetragonal phases. However, the ZrO2: Eu+3 nanophosphors prepared through the same technique under similar conditions yield exclusively cubic ZrO2, and it entirely depends on the concentration of Eu+3 as revealed by XRD studies. The nanoparticles are found to be spherical, non-porous and agglomerated as observed by SEM. The surface area of the nanoparticles of pure ZrO2 is found to be 30 m2/g for as-formed samples and 130 m2/g for calcined samples by BET studies. The increase in the surface area for calcined sample is due to the escaping of the adsorbed hydroxyl groups from the surface of the nanoparticles. The photoluminescence properties of the pure and Eu+3-doped ZrO2 nanoparticles were measured under 251 nm excitation wavelength. Under this excitation, pure ZrO2 gives the emissions at 394 nm, whereas Eu+3-doped nanoparticles gives the emissions at 613 nm, which corresponds to inter-f-f transition from 5D0 ➔7F2 (613 nm) and is arising due to electronic dipole in the Eu+3 activator ion. CIE colour space (x, y) coordinates corresponding to 613 nm in the CIE chromaticity diagram is 0.680, 0.319.

Photoluminescent Investigation of the Doping Site of Eu3+-Doped [Zn3(BTC)2∙12H2O] Metal-Organic Framework Prepared by Microwave-Assisted Hydrothermal Synthesis

The [Zn3(BTC)2·12H2O] (BTC = 1,3,5-tricarboxylate) metal-organic framework (MOF) was successfully synthesized using a microwave-assisted hydrothermal synthesis technique, which allowed for significantly decreased reaction time compared to the production of the same compound via conventional heating. In situ doping with Eu3+ ions at concentrations ranging from 1.0 to 5.0 mol% produced doped materials whose emission ranged from blue to red color. The Eu3+ spectroscopic properties were used to study the incorporation of the dopant into the structure of [Zn3(BTC)2·12H2O], even at very low concentrations. These experiments confirmed the usefulness of this ion as a luminescent probe, as it permitted the identification of small variations in structure not perceptible by X-ray diffraction. The variation in the coordination environment induced by increases in doping percentage was analyzed by evaluating changes in the characteristic Eu3+ excitation and emission profiles, using them to calculate luminescence lifetimes, experimental intensity parameters Ωλ (λ: 2 and 4) as well as the intrinsic quantum yield (QEu+3Eu+3) of the 5D0 emitting level of each doped MOF. The excitation and luminescence spectra show that intramolecular energy transfer from the BTC linker to Eu3+ ion, and we could observe the emission color tuning originated from the emissions of the BTC ligand and Eu3+ ion.

Fast, low-pressure, low-temperature microwave synthesis of ABW cesium aluminosilicate zeolite nanocatalyst in organotemplate-free hydrogel system

Cs-ABW zeolite nanocrystals were synthesized using a microwave-assisted hydrothermal technique without an organic template. Using powder X-ray diffraction Rietveld refinement and spectroscopy, we found that pure ABW-type CsAlSiO4 zeolite nanocrystals (Si/Al ratio = 1.08) with an orthorhombic structure (space group Pc21n, a = 9.4425(21) Å; b = 5.4437(11) Å; c = 8.9152(19) Å) can be crystallized from a clear precursor solution of 4SiO2:1Al2O3:16Cs2O:160H2O (180 °C, 6 min). The Cs-ABW nanoparticles had a mean particle size of 68 nm and were thermally and colloidally stable. The nanocrystals—which had high accessible basic sites, (Si–O–Al)−Cs+, located at their external surface—were active in catalyzing the cyanoethylation of aliphatic alcohols under non-microwave instant heating, with 100 % selectivity to the desired product and high catalyst reusability. Furthermore, the cyanoethylation of methanol catalyzed by nanocrystalline Cs-ABW under instant heating had equal or better reactivity than those catalyzed by other solid base catalysts.

Microwave-assisted hydrothermal synthesis, structure and electrochemical properties of the Na3V2-yFeyО2x(PO4)2F3-2x electrode materials for Na-ion batteries

The Na3V2-yFeyО2x(PO4)2F3-2x (x = 1–0.8, y = 0–0.8) solid solutions have been prepared using a microwave-assisted hydrothermal technique. The materials crystallize in the disordered I4/mmm crystal structure as evidenced with electron diffraction and Rietveld refinement from powder X-ray diffraction data (Na3V1.2Fe0.8O1.6(PO4)2F1.4: a = 6.38666(9)Å, c = 10.6562(2)Å, RF = 0.023, RP = 0.013). A combination of electron energy loss spectroscopy and 57Fe Mössbauer spectroscopy revealed that vanadium is in the mixed 4+/5 ​+ ​oxidation state, whereas iron is exclusively in the 3 ​+ ​state, thus pointing to the V4+ → Fe3+/V5+ co-substitution. The solid solutions demonstrate reversible Na+ (de)intercalation in the electrochemical cells with Na metal counter-electrode through two sloping potential plateaus at near 3.5 and 4.0 V vs Na+/Na. The electrochemical capacity decays from 105 mAh/g for y = 0 to ~50 mAh/g for y = 0.8 because of decreasing amount of electrochemically active V4+ upon increasing the Fe content.

Physical and chemical characteristics of hematite nanoparticles prepared using microwave-assisted synthesis and its application as adsorbent for Cu, Ni, Co, Cd and Pb from aqueous solution

Hematite nanoparticles were synthesized using the microwave-assisted hydrothermal technique and from aqueous solution. The structure of the prepared material was characterized using x-ray fluorescence (XRF), X-ray diffraction (XRD), electron spin resonance (ESR), transmission electron microscopy (TEM), and electron diffraction (ED). The average particle size was found to be 18 nm while the XRD and ESR results confirmed the formation of hydrogenated hematite phase. XRD matched the hexagonal phase of Fe1.9H0.06O3 in which two ESR absorptions at Landé g-factor of 2.022 and 2.424 are attributed electron splitting at Fe3＋ and H+ sites, respectively. Radial distribution function (RDF) showed that the lattice parameters equal to a=5.82 Å and c=13.7 Å. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to determine the ability of the material to adsorb Cu, Ni, Co, Cd and Pb ions from their aqueous solution. The effect of hydrogen concentration (pH)and the kinetic analysis showed that pseudo-second-order model of adsorption is suitable for rate-limiting processes around the particles surface that may involve chemisorption and physicochemical interactions between ionic species. Sorption isotherm study showed that the Langmuir isotherm model for single mono-layer sorption was more suitable and the maximum sorption capacity attained by the prepared hematite nanoparticle was around 100 mg/g and independent on the ion.

Nanocrystalline Hydroxyapatite Loaded with Resveratrol in Colloidal Suspension Improves Viability, Metabolic Activity and Mitochondrial Potential in Human Adipose-Derived Mesenchymal Stromal Stem Cells (hASCs).

In response to the demand for new multifunctional materials characterized by high biocompatibility, hydrogel (HG) nanocomposites as a platform for bioactive compound delivery have been developed and fabricated. A specific crosslinking/copolymerization chemistry was used to construct hydrogels with a controlled network organization. The hydrogels were prepared using 3,6-anhydro-α-l-galacto-β-d-galactan (galactose hydrogel) together with resveratrol (trans-3,5,4′-trihydroxystilbene) and calcium hydroxyapatite nanoparticles. The resveratrol was introduced in three different concentrations of 0.1, 0.5, and 1 mM. Nanosized calcium hydroxyapatite was synthesized by a microwave-assisted hydrothermal technique, annealed at 500 °C for 3 h, and introduced at a concentration 10% (m/v). The morphology and structural properties of Ca10(PO4)6(OH)2 and its composite were determined by using XRPD (X-ray powder diffraction) techniques, as well as the absorption and IR (infrared) spectroscopy. The average nanoparticle size was 35 nm. The water affinity, morphology, organic compound release profile, and cytocompatibility of the obtained materials were studied in detail. The designed hydrogels were shown to be materials of biological relevance and of great pharmacological potential as carriers for bioactive compound delivery. Their cytocompatibility was tested using a model of human multipotent stromal cells isolated from adipose tissue (hASCs). The biomaterials increased the proliferative activity and viability of hASCs, as well as reduced markers of oxidative stress. In light of the obtained results, it has been thought that the designed materials meet the requirements of the tissue engineering triad, and may find application in regenerative medicine, especially for personalized therapies.

The rapid microwave-assisted hydrothermal synthesis of NASICON-structured Na3V2O2x (PO4)2F3-2x (0 < x ≤ 1) cathode materials for Na-ion batteries.

NASICON-structured Na3V2O2x(PO4)2F3−2x (0 < x ≤ 1) solid solutions have been prepared using a microwave-assisted hydrothermal (MW-HT) technique. Well-crystallized phases were obtained for x = 1 and 0.4 by reacting V2O5, NH4H2PO4, and NaF precursors at temperatures as low as 180–200 °C for less than 15 min. Various available and inexpensive reducing agents were used to control the vanadium oxidation state and final product morphology. The vanadium oxidation state and O/F ratios were assessed using electron energy loss spectroscopy and infrared spectroscopy. According to electron diffraction and powder X-ray diffraction, the Na3V2O2x(PO4)2F3−2x solid solutions crystallized in a metastable disordered I4/mmm structure (a = 6.38643(4) Å, c = 10.62375(8) Å for Na3V2O2(PO4)2F and a = 6.39455(5) Å, c = 10.6988(2) Å for Na3V2O0.8(PO4)2F2.2). With respect to electrochemical Na+ (de)insertion as positive electrodes (cathodes) for Na-ion batteries, the as-synthesized materials displayed two sloping plateaus upon charge and discharge, centered near 3.5–3.6 V and 4.0–4.1 V vs. Na+/Na, respectively, with a reversible capacity of ∼110 mA h g−1. The application of a conducting carbon coating through the surface polymerization of dopamine with subsequent annealing at 500 °C improved both the rate capability (∼55 mA h g−1 at a discharge rate of 10C) and capacity retention (∼93% after 50 cycles at a discharge rate of C/2).

Synthesis of Single Phase Tin(II) Oxide Nanoparticles by Microwave-Assisted Hydrothermal Technique

This paper presents a novel microwave-assisted hydrothermal technique for synthesizing tin(II) oxide nanoparticles. This technique can be used for producing large quantities of homogeneous nanoparticles in a short time. The effect of the solution molarity, final pH, hydrothermal processing time and microwave power were studied. The tin(II) oxide structure verified from XRD and the mean crystallite size was evaluated to be about 5 nm using the Debye-Scherrer formula on the most intense peak. The particle size was measured from STM pictures in the range between 4-5 nm. For different samples, UV-Vis spectroscopy showed the absorption peak due to tin(II) oxide at about 240 nm and an exitonian peak at about 280 nm that shifted with respect to solution molarity, final pH, hydrothermal processing time and microwave power. The photoluminescence spectroscopy (PL) results showed the emission peaks in the visible spectrum range. The results showed that synthesized SnO nanoparticles have a direct bandgap equal to about 2.5 eV, an Urbach energy of about 2.7 eV and activation energy of 47.75kJ/mol.

Synthesis of newly wings like structure non-crystalline Ni++-1,3,5-tribenzyl-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione coordinated MOFs for CO2-Capture

The newly Ni++-1,3,5-tribenzyl-1,3,5-triazine-2,4,6-(1H,3H, 5H)-trione coordinated polymeric MOFs were carefully synthesized via microwave-assisted hydrothermal technique. Theoretical investigations were predicted by two different stereo-orientations which can be present inside unite cell of Ni(II)-MOFs, one of them (wings like structure) is strongly recommend to form 3D-Ni(II)-1,3,5-tribenzyl-1,3,5-triazine-2,4,6-(1H,3H, 5H)-trione coordinated polymeric MOFs. The synthesized amorphous Ni-MOFs were characterized by mass spectroscopy, Uv/Vis spectra, scanning electron microscope (SEM) and three dimensional atomic force microscope (3D-AFM). Furthermore BET specific surface area was measured and found 3181 m2/g. Ni(II)-MOFs exhibit high adsorption capacity for carbon dioxide uptake recording a maximum adsorption capacity of 118.2 mg CO2/g of Ni(II)-aMOFs at 30 °C, 27 bar.

Chemical free synthesis of graphene oxide in the preparation of reduced graphene oxide-zinc oxide nanocomposite with improved photocatalytic properties

In the present investigation, the reduced graphene oxide – zinc oxide (rGO-ZnO) was prepared by rapid microwave-assisted hydrothermal technique. The chemical free graphene oxide (GO), synthesized by Tang Lau technique, was used in the preparation of rGO-ZnO nanocomposite. The GO gets reduced to rGO during microwave irradiation and provides the necessary nucleation site for the ZnO nanorods to grow in [0 0 0 1] direction. These ZnO nanorods were completely wrapped with rGO sheets, confirmed by the synchrotron XRD and TEM techniques. The phases and cell parameters were calculated by Rietveld method. The prepared composite was used for the photodegradation of methyl orange (MO) dye from water under UV light. Investigation revealed that the incorporation of rGO into the ZnO increased the photodegradation ability of the bare ZnO. The performance of the composite is also compared with the rGO-ZnO nanocomposite, where rGO was prepared by Hummer’s method. rGO obtained from Tang Lau method formed stable and efficient composite with ZnO and exhibited higher activity compared to the composite, wherein rGO was prepared from conventional Hummer's method. Under UV light, the ZnO liberates photoelectrons which reacts with surface oxygen to form superoxide radicals (O−2) and (OH−) in the water medium. The rGO nanosheets could reduce the charge recombination during the reaction. The active species adsorbs the MO molecules and degrades into CO2, H2O and other byproducts. More than 3.5 times increase in the rate constant was observed for rGO-ZnO compared to the bare ZnO.

Synergistic effect of graphene nanosheets and zinc oxide nanoparticles for effective adsorption of Ni (II) ions from aqueous solutions

The threat of toxic substances such as heavy metals to public health and wildlife has led to an increasing public awareness. Different techniques for neutralizing the toxic effects of heavy metals in wastewater have been used. Here, we prepared a new and efficient type of adsorbent, zinc oxide–graphene nanocomposite (ZnO–Gr), via a green method to remove Ni (II) ions from aqueous solutions. A facile microwave-assisted hydrothermal technique in the presence of an ionic liquid, 1-hexyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide [C6mim] [NTf2], was used to prepare ZnO–Gr. The synergistic effect between graphene nanosheets and ZnO nanoparticles in this new adsorbent for Ni (II) ions caused a maximum adsorption capacity of 66.7 mg g−1 at room temperature which is much higher than that of graphene nanosheets (3.8 mg g−1) and other carbonaceous nanomaterials used as an adsorbent in the literature. The maximum desorption percentage (90.32%) was achieved at pH 3.6. By thermodynamic study, we found that the adsorption of this heavy metal ion on ZnO–Gr was spontaneous (ΔG° = −6.14 kJ mol−1) and endothermic (ΔH° = 53.31 kJ mol−1) with entropy change of ΔS° = 199.45 J K−1 mol− 1.

Microwave-assisted hydrothermal synthesis of carbon materials with tunable microstructure

A facile microwave-assisted hydrothermal route has been developed for a synthesis of versatile carbon materials. The monosaccharide fructose aqueous solution was adopted as the starting material, and the pH of the solution was adjusted to be in acidic (pH 4), neutral (pH 7) and basic (pH 10.5) conditions. The pH buffered fructose solutions were treated at different temperatures by a microwave-assisted hydrothermal technique. As-prepared carbon materials displayed pH and temperature dependent multi-morphologies (porous, spherical or core-shell), which were determined by transmission and scanning electron microscopic analyses (TEM and SEM). And the hypothesis of dehydration mechanism of hydrothermal synthesis was analyzed by ultraviolet extinction and Fourier transform infrared spectroscopy. It was found that as compared with normal hydrothermal synthesis, microwave assistance could efficiently increase the production yield and improve the spherical geometry of the carbon particles in neutral condition. By changing the pH of the system, acidic pH induces aggregation of the spheres, while basic pH produces more trends toward core-shell or sponge-like porous structure. The study opens a novel route to the production of polytropic carbon materials and suggests a potential niche market established from the green synthesis.

Synergetic effect of MoS2 and graphene as cocatalysts for enhanced photocatalytic activity of BiPO4 nanoparticles

The photodegradation of organic pollutants is an attractive green chemistry technology for water pollution control. Here we prepared a new composite material consisting of BiPO4 nanocrystals grown on layered graphene and MoS2 as a high-performance photocatalyst for the photodegradation of organic pollutants. This composite material was synthesized by a facile one-pot microwave-assisted hydrothermal technique in the presence of layered graphene and MoS2. Through optimizing the loading content of each component, the BiPO4-MoS2/graphene nanocomposite exhibited the highest photocatalytic activity for the degradation of Rhodamine (RhB) when the content of MoS2 and graphene was 2wt% and 7wt%, respectively. The enhanced photocatalytic activity of the new composite photocatalyst was attributed to the positive synergetic effect of the layered graphene and MoS2 as cocatalyst, which acted as electron collector and transporter for the interfacial electron transfer from BiPO4 to electron acceptor in the aqueous solution and thus suppressed the charge recombination and made the photogenerated holes more available to participated in the oxidation process. Moreover, the presence of layered MoS2/graphene hybrid could offer more reactive sites and activated the O2 molecular in water to form superoxide radical, thereby resulting in the enhanced photocatalytic activity.

Fabrication of NiCo2-Anchored Graphene Nanosheets by Liquid-Phase Exfoliation for Excellent Microwave Absorbers.

Graphene nanosheets (GNSs) were prepared by an efficient liquid-phase exfoliation method, and then the NiCo2/GNS nanohybrids were fabricated using the single-mode microwave-assisted hydrothermal technique. The NiCo2/GNS composites with different GNS proportions were investigated as microwave absorbers. Morphology investigation suggested that NiCo2 nanocrystals were uniformly anchored on the GNS without aggregation. The electromagnetic parameters of NiCo2/GNS nanohybrids could be artificially adjusted by changing the GNS proportion, which led to an exceptional microwave-absorbing performance. A reflection loss (RL) exceeding -20 dB was obtained in the frequency range of 5.3-16.4 GHz for the absorber thicknesses of 1.2-3.2 mm, while an optimal RL of -30 dB was achieved at 11.7 GHz for a thickness of 1.6 mm. The enhanced microwave-absorbing performance indicated that the NiCo2/10 wt % GNS composite has great potential for use as an excellent microwave absorber.

Microwave—assisted hydrothermal synthesis of monoclinic bismuth trioxide nanorods: optical and photocatalytic properties

Herein, the successful synthesis of bismuth trioxide (Bi2O3) nanorods via a new microwave-assisted hydrothermal technique is reported. Detailed characterizations for the prepared nanorods employing various analytical techniques were considered for their structural, compositional, morphological, optical and photocatalytic properties. The detailed results confirmed that the prepared nanorods have a well-crystalline structure, growing with a high density and having pure monoclinic crystal structure. The prepared nanorods exhibited good optical properties were confirmedly the room-temperature photoluminescence (PL) spectroscopy. The as-prepared Bi2O3 nanorod structures showed efficient photocatalytic activity for the degradation of methyl orange (MO) dyes under the application of UV light irradiation (365 nm). The pseudo-first order reaction rate constant is 0.007 min− 1. The fabricated Bi2O3 nanorods are very useful as ultraviolet light activated photocatalyst nanorod materials for decomposing methyl orange and various types of organic dyes.