Microwave Approach Research Articles

Testing Passive Microwave-Based Hail Retrievals Using GPM DPR Ku-Band Radar

AbstractSeveral studies in the literature have developed approaches to diagnose hail storms from satellite-borne passive microwave imagery and build nearly global climatologies of hail. This paper uses spaceborne Ku-band radar measurements from the Global Precipitation Measurement (GPM) mission Dual-Frequency Precipitation Radar (DPR) to validate several passive microwave approaches. We assess the retrievals on the basis of how tightly they constrain the radar reflectivity at −20°C and how this measured radar reflectivity aloft varies geographically. The algorithm that combines minimum 19-GHz polarization corrected temperature (PCT) with a 37-GHz PCT depression normalized by tropopause height constrains the radar reflectivity most tightly and gives the least appearance of regional biases. A retrieval that is based on a 19-GHz PCT threshold of 261K also produces tightly clustered profiles of radar reflectivity, with little regional bias. An approach using regionally adjusted minimum 37-GHz PCT performs relatively well, but our results indicate it may overestimate hail in some subtropical and midlatitude regions. A threshold applied to the minimum 37-GHz PCT (≤230 K), without any scaling by region or probability of hail, overestimates hail in the tropics and underestimates beyond the tropics. For all retrieval approaches, storms identified as having hail tended to have radar reflectivity profiles that are consistent with general expectations for hailstorms (reflectivity > 50 dBZ below the 0°C level, and > 40 dBZ extending far above 0°C). Profiles from oceanic regions tended to have more rapidly decreasing reflectivity with height than profiles from other regions. Subtropical, high-latitude, and high-terrain land profiles had the slowest decreases of reflectivity with height.

Microwave-assisted synthesis of superparamagnetic mesoporous Co-doped hydroxyapatite nanorods for various biomedical applications

Advanced methods to design biocompatible mesoporous superparamagnetic nanoparticles are required for various healthcare applications. This work was designated to synthesize superparamagnetic mesoporous hydroxyapatite (HAp) nanorods (NRs) with the intrinsic pure phase through the doping of cobalt ions inside it. This nanoparticle was synthesized using a black Scallop seashell as a low cost calcium source using oxalic acid as a strong chelating agent via microwave synthesis. The prepared magnetic HAp NRs are analyzed by diverse methods to understand the clarity of phase and its nanostructural features. XRD and EDX results prove that Co is distributed well in the HAp nanoparticles without affecting its structure. The BET surface areas of CoHAp-1, CoHAp-2, and pristine HAp NRs were found to be 69, 126, and 97 m2 g−1, correspondingly. Further, evaluated pore volume of CoHAp-1, CoHAp-2, and pristine HAp NRs are identified to be 0.0275, 0.0349, and 0.0368 cm3 g−1 and also pore diameters were found as 3.02, 4.67, and 4.71 nm. Hence, the HAp mesoporous NRs with higher surface area were achieved with the incorporation of Co in the HAp system. The superparamagnetic characteristics were identified only in the Co-doped HAp samples. The high saturation magnetization of 0.20 Am2 kg−1 was observed with the high doping of Co ions. Toxicity of the pristine and the Co-incorporated HAp samples were evaluated using zebrafish. The toxicity result reveals that Co incorporations in HAp do not affect significantly the biocompatible nature compared to the pristine HAp sample. Antibacterial test shows excellent antibacterial activities for Co-HAp samples among different pathogens. Hence, the approach of oxalic acid-associated microwave mediated synthesis of intrinsic mesoporous superparamagnetic HAp NRs from naturally occurring seashells as a precursor can be a superior method for obtaining nanomaterials towards various applications like magnetic resonance imaging, targeting of drug, hyperthermia, and cancer treatments.

Method of full polarization control of microwave fields in a scalable transparent structure for spin manipulation

The application of transparent conducting oxides in electronic devices like solar cells or displays is common. By transferring this technology to quantum sensing and computing in the form of microwave conductors, it is possible to benefit from the advantages of these materials. By using indium tin oxide (ITO), it is demonstrated that at an arbitrary position below the conductor, an arbitrary elliptical microwave polarization can be produced by two independent sources. This is independent of the geometry and size of the ITO, whereby a non-resonant microwave approach can be chosen. Using single nitrogen vacancy (NV) centers in diamond in combination with a cross-like ITO structure, each NV center can be addressed with an ideal (clockwise or anticlockwise) microwave polarization. By optimizing the coupling of the microwave field to the NV centers and minimizing the conductor size, the creation of smaller devices compared to common approaches is possible.

Facile approach to synthesise zeolite X and its adsorption for Cu (II) and Zn(II)

Pure zeolite X was synthesised by a facile microwave-assisted two-step approach using high silicon fly ash, industrial-grade reagents and tap water. First, a microwave heating method was conducted to extract silicon and the extract process was completed in 20 min, which was more effective. Then, a microwave approach was used to synthesis zeolite X. The whole analysis process is <2 h. The composition, phase structure, morphology, particle size distribution, specific surface areas and adsorption of heavy metal ions were evaluated comprehensively. The results show that single phase zeolite X with octahedral structure and an average diameter of 1.10 μm is obtained, and the Brunauer–Emmett–Teller surface area is 583.22 m2/g. Especially, the adsorption of Cu2+ and Zn2+ are as high as 81.33 and 67.21 mg/g, respectively. It can be concluded that the Letter provides a facile and fast method utilising high silicon fly ash to synthetise zeolite X, which is an excellent adsorbent to remove heavy metal ions.

Devulcanization of ground tire rubber: microwave and thermomechanical approaches

We devulcanized ground tire rubber (GTR) in a laboratory microwave oven and an internal mixer, measured the soluble content and the cross-link density of the samples, and then used Horikx’s analysis. The results showed that microwave treatment caused severe degradation of the polymer chains, while in the case of thermomechanical devulcanization, the selective scission of covalent cross-links is more common. Four devulcanized ground tire rubber (dGTR) samples were chosen for further study and three groups of samples were produced: dGTR samples containing vulcanizing agents and different amounts of paraffin oil (dGTR-based mixtures), natural rubber-based rubber mixtures with different dGTR contents and reference rubber mixtures with dGTR-based mixtures (increased vulcanizing agent contents). Cure characteristics showed a plasticizer-like effect of dGTR. Tensile and tear strength decreased drastically with increasing dGTR content; however, elongation at break values did not follow such a trend. Mechanical properties improved with increased vulcanizing agent contents. The examined properties of the samples improved even further with the use of thermomechanically devulcanized samples. Horikx’s analysis showed that this is attributable to moderate polymer chain scission.

A holistic approach for microwave assisted solvent extraction of phenolic compounds from Ficus benghalensis fruits and its phytochemical profiling

AbstractFicus benghalensis is a fig species spread throughout Asia, especially India, which finds its place in the tradition Indian system of medicines for their renowned protective properties. This study explores the extraction and identification of phytochemicals from the fruits of Ficus benghalensis using a time‐saving nonconventional technique of microwave assisted solvent extraction (MASE). The influence of independent variables (viz., solid‐solvent ratio, microwave power and irradiation time) on the maximum total phenolic content (TPC) and total flavonoid content (TFC) values was analyzed and optimized using response surface methodology (RSM) with a Box–Behnken Design. The maximum values of TPC (340.14 ± 0.34 mg/g) and TFC (413.64 ± 0.19 mg/g) were found at a shorter extraction time of 5 min, solid‐solvent ratio of 1:17 g/ml and microwave power of 420 W. The GC chromatogram was used for the phenolic distribution analysis and screening of the secondary metabolites. The GC spectra showed the presence of 26 biologically active secondary metabolites. 7‐tetradecenal (Z) (42.14%) was the predominant compound followed by n‐hexadecanoic acid (20.61%) and octadecanoic acid (14.07%). These compounds, along with others reportedly exhibit anticancer, antioxidant, anti‐diabetic, and antibacterial activities, thereby validating the traditional uses of the Ficus benghalensis fruit as a pharmaceutical supplement.Practical applicationThe outcome of this work shows a time‐saving method of phytochemical extraction which can be used for extracting valuable metabolites from Ficus benghalensis fruits. Moreover, findings from this research work will aid as a baseline to facilitate future studies in the isolation and purification of the identified pharmaceutically active phytochemicals present in the Ficus benghalensis fruit extract. This can be further used to increase the fruits' bioprospecting.

One-pot synthesis of reduced graphene oxide nanosheets anchored ZnO nanoparticles via microwave approach for electrochemical performance as supercapacitor electrode

One-pot synthesis of reduced graphene oxide nanosheets anchored ZnO nanoparticles via microwave approach for electrochemical performance as supercapacitor electrode

Design, Synthesis, DFT Studies and Anticancer Activity of Novel Metal Complexes Containing 1,3,5-triazino[1,2-a]benzimidazole Moiety Using Microwave as an Approach for Green Chemistry

2-(2-amino-4,10-dihydrobenzo[4,5]imidazo[1,2-a][1,3,5]triazin-4-yl)phenol (ligand) and its related metal complexes of Mn (II), Co (II), Ni (II), Cu (II) and Zn (II) were prepared under microwave irradiation. The structures of prepared compounds were elucidated in terms of elemental analysis, FT-IR, UV-Vis, 1HNMR, 13CNMR, EPR spectra and mass spectra in addition to magnetic studies at room temperature and thermal properties. Elemental analysis results determined mole ratios between the ligand and metal 1:1 or 1:2. The microwave approach provides clean, shorter reaction times and enhancements in yields. Coats Redfern and Horowitz Metzger equation were used to study Thermal kinetic parameters of dehydration and decomposition of the complexes. The geometries of the ligand and its Mn (II), Co (II), Cu (II) and Zn (II) complexes were optimized using Gaussian 09 W; density functional theory (DFT) B3LYP method. Also, the cytotoxic activity of the ligand and its metal complexes were evaluated against liver cancer cells (HepG-2) and the Cu (II) complex exhibited the highest cytotoxic activity with promising IC50 value = 3.5 µg/ml compared to standard reference cisplatin.

Solid-State Microwave Synthesis CuO/CNT: A High-Performance Electrode Material for Supercapacitors

CuO/CNT composites were synthesized via simple and rapid microwave approach. The nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Further, the electrochemical performances of CuO/CNT composites were evaluated. The prepared samples displayed high specific capacitances of 164.5[Formula: see text]F[Formula: see text]g[Formula: see text] at 1[Formula: see text]A[Formula: see text]g[Formula: see text], during the cycle process, the capacitance value aggrandized to 274.7[Formula: see text]F[Formula: see text]g[Formula: see text], and the capacitance remained at 166% of the primary value after 10 000 turns. Moreover, the CuO/CNT//AC asymmetric supercapacitor (ASC) exhibited an energy density of 17.08[Formula: see text]Wh[Formula: see text]kg[Formula: see text] at 775[Formula: see text]W[Formula: see text]kg[Formula: see text] and excellent electrochemical stability in 6M KOH aqueous electrolyte, showing its enormous potential in energy-storage devices.

Gum Acacia‐cl‐poly(acrylamide)@carbon nitride Nanocomposite Hydrogel for Adsorption of Ciprofloxacin and its Sustained Release in Artificial Ocular Solution

AbstractIn the present work, a nanocomposite hydrogel is designed consisting of gum acacia, poly(acrylamide) and carbon nitride by facile microwave approach. This nanocomposite hydrogel is sensitive to environmental stimuli which is essential for its application in environmental remediation and as a drug delivery system. The effects of carbon nitride percentage and microwave Watt variation on swelling capacity of gum acacia‐cl‐poly(acrylamide)@carbon nitride (Ga‐cl‐PAM@C3N4) nanocomposite hydrogel are analyzed. The structural characterizations are considered by numerous techniques such as FTIR (Fourier transform infra‐red spectroscopy), X‐ray diffraction, transmission electron microscopy, scanning electron microscopy, and elemental mapping. Batch experiment is performed for remediation of ciprofloxacin (CIP) drug from water. Various parameters such as effect of ciprofloxacin doses, Ga‐cl‐PAM@C3N4 nanocomposite hydrogel dosage, pH, time and temperature for adsorption of CIP on gum acacia‐cl‐poly(acrylamide)@carbon nitride nanocomposite hydrogel is examined. Maximum adsorption capacity of Ga‐cl‐PAM@C3N4 nanocomposite hydrogel observed is 169.49 mg g−1 at pH 6.4. The drug loading and drug release capacity of Ga‐cl‐PAM@C3N4 nanocomposite hydrogel is investigated for ciprofloxacin. Drug release is monitored in artificial ocular solution (pH 8), saline (pH 5.5), acetate buffer (pH 2.2), and distilled water. Maximum drug release is observed in artificial ocular solution.

Application of Variable Frequency Microwaves in Microwave-Assisted Chemistry: Relevance and Suppression of Arc Discharges on Conductive Catalysts

The application and advantages of variable frequency microwaves (VFM; range, 5.85–6.65 GHz) are reported for the first time in microwave chemistry, particularly when carrying out reactions catalyzed by metallic conductive catalysts so as to avoid the formation of arc discharges, and especially when using a strong microwave absorber such as activated carbon (AC) particulates as supports of metal-based catalysts. Two model reactions performed in low boiling point nonpolar solvents are described wherein arc discharges easily occur under the more conventional fixed frequency microwave (FFM) approach: (i) the synthesis of 4-methylbiphenyl (4MBP) by the Suzuki-Miyaura cross-coupling process catalyzed by Pd particles supported on AC particulates (Pd/AC), and (ii) the synthesis of toluene via the dehydrogenation of methylcyclohexane (MCH) catalyzed by Pt particles dispersed on AC particulates (Pt/AC). Contrary to the usage of fixed frequency microwaves (5.85 GHz and 6.65 GHz), the use of VFM microwaves increased the chemical yields of 4MBP {49% versus 5–8% after 60 min} and toluene {89% versus 24% after 10 min} by suppressing the formation of discharges that otherwise occur on the catalyst/AC surface with FFM microwaves. Consequently, relative to the latter approach, the VFM technology is significantly advantageous, especially in reactions with solid conductive catalysts, not least of which are the reduction in power consumption, thus energy savings, and the prevention of potential mishaps.

A new microwave approach for the synthesis of green emitting Mn2+-doped ZnAl2O4: A detailed study on its structural and optical properties

A simple recipe for synthesizing green emitting Mn2+-doped ZnAl2O4 phosphor has been developed. Metal-organic complexes, with their unique properties, were employed as precursors to obtain phase-pure, nanocrystalline material in the as-prepared form within just 5 min of microwave irradiation. The Mn2+ doping concentration that showed the highest photoluminescence (PL) intensity was optimized and a comprehensive investigation of the structural and optical properties were made for various annealing temperatures. Rietveld refinement of the samples annealed at 1200 °C and 1400 °C, showed that the cationic inversion in the spinel decreased from 3.4 to 2.1% and this change was validated by the X-ray photoelectron spectroscopy results. XPS confirmed that the inversion for Zn2+, Al3+, and Mn2+ cations decreased with annealing temperature, despite of which, inversion remained at 20%, 10%, and 15%, respectively for the sample annealed at 1400 °C, emphasizing the fact that synthesis plays an important role in controlling the amount of inversion in an otherwise normal spinel. Electron paramagnetic resonance spectra of the as-prepared and the samples annealed at high temperatures confirmed that the Mn2+ hyperfine spectrum was not just a function of the crystal field environment but also strongly depends on the doping concentration. The PL spectrum taken at different annealing temperatures, comprised of the characteristic 4T1 (G) → 6A1 (S) spin-forbidden Mn2+ transitions, showed that the emission intensity depends on the material crystallinity. The sample annealed at 1400 °C displayed a significantly higher PL intensity compared to those annealed at lower temperatures. The variation of PL spectrum of this sample was investigated between 9 K and 300 K to determine the origins of the asymmetry at room temperature and the vibrational sidebands at lower temperatures. The energy levels of the Mn2+ dopant, calculated theoretically and verified experimentally, were used to determine the spectroscopic parameters such as the Racah B and C values and the crystal field energy, Dq. These values showed that the Mn2+ was in a weak tetrahedral field. This work demonstrates a technologically important, green, and swift technique in synthesizing phosphors for various applications in displays, bioimaging, solid state lighting, etc.

Structure, Raman and luminescence characteristics of Zn1-xHfxO (0≤x≤0.1) nanocrystals prepared via N-(methyl)mercaptoacetamide assisted microwave approach

A series of Zn1-xHfxO (0 ≤ x ≤ 0.1) nanocrystals was synthesized via the N-(methyl)mercaptoacetamide assisted microwave approach. The influence of the Hf dopant on the crystal structure, Raman lattice vibrations, and luminescent emission spectra was studied. XRD measurements revealed that the inclusion of the Hf dopant in the Zn cites instigated the expansion of the ZnO lattice while preserving its hexagonal structure. The XRD, SEM and DLS measurements demonstrated that the Hf dopant increased the size of ZnO nanocrystals from 2.5 ± 0.1 nm to 11.5 ± 0.1 nm. The EDS spectra confirmed the stoichiometry of the prepared samples. The zeta potential measurement revealed that the Hf dopant is incorporated within the ZnO nanostructure. The Raman spectra showed that the Hf dopant was efficiently incorporated into the ZnO crystals without altering its internal structure. The UV–vis. spectroscopy indicated that the partial substitution of Zn atoms by Hf atoms leads to modulation of the optical bandgap. Luminescence measurements revealed that the inclusion of the Hf dopant in the Zn cites resulted in suppression of the ZnO crystal defects. The XPS measurements confirmed that the inclusion of Hf dopant in the Zn cites resulted in a reduction of the amount of oxygen vacancy which actes as a trap centers for the photogenerated electrons. Therefore, a modulation of the visible spectra occurred, while the Hf dopant did not affect the intensity of UV-emission band of ZnO nanocrystals. Therefore, the Zn1-xHfxO (0 ≤ x ≤ 0.1) nanocrystals are favorable as potential candidates for both catalytic and luminescent device applications.

Fluorescent sensor array for selective recognition of biothiols

Biological thiols play essential roles in life activities. Detection and differentiation of different biothiols is of crucial need in biomedical research and diagnostics. Herein, a novel fluorescent sensor array was constructed to discriminate six kinds of biothiols including Cysteine (Cys), N-acetylcystein (NAC), 2-mercaptoethanol (MCE), Homocysteine (Hcy), Glutathione (GSH), and Glutathione disulfide (GSSG) simultaneously. This sensor array was fabricated by using three kinds of metal ions (i.e., Fe3+, Ni2+, and Cu2+)–N-CDs pairs. The N-CDs were synthesized with urea as nitrogen sources and folic acid as carbon sources via a simple microwave approach. Based on the competitive interactions of N-CDs with metal ions and thiols, the sensor array exhibits diverse fluorescence intensity response patterns, six thiols could be effectively and simultaneously differentiated in a wide concentration range (≧50 μM) by principal component analysis (PCA). Morover, double-blind samples of biothiols were recognized with 97.2% accuracy through linear discrimination analysis (LDA). More importantly, the sensor array showed good practicability in complex media such as fetal bovine serum, demonstrating this proposed sensor array held a great potential for the identification of biological thiols in real samples.

Multipurpose chemical liquid sensing applications by microwave approach.

In this work, a novel sensor based on printed circuit board (PCB) microstrip rectangular patch antenna is proposed to detect different ratios of ethanol alcohol in wines and isopropyl alcohol in disinfectants. The proposed sensor was designed by finite integration technique (FIT) based high-frequency electromagnetic solver (CST) and was fabricated by Proto Mat E33 machine. To implement the numerical investigations, dielectric properties of the samples were first measured by a dielectric probe kit then uploaded into the simulation program. Results showed a linear shifting in the resonant frequency of the sensor when the dielectric constant of the samples were changed due to different concentrations of ethanol alcohol and isopropyl alcohol. A good agreement was observed between the calculated and measured results, emphasizing the usability of dielectric behavior as an input sensing agent. It was concluded that the proposed sensor is viable for multipurpose chemical sensing applications.

The optical performance of Cd1 − xTmxTe (0 ≤ x≤ 0.07) QDs synthesized via s,s′-phenylenebis-ethynediyl-phenylene-bisthioacetate assisted microwave approach for laser devices

Here, we have developed a new series of quantum dots based on the incorporation of thulium, Tm, atoms as efficient dopant in the cubic CdTe crystal structure for laser diode application potential. Therefore, Cd1 − xTmxTe (0 ≤ x ≤ 0.07) quantum dots were synthesized using s,s′-phenylenebis-ethynediyl-phenylene-bisthioacetate assisted microwave approach. The measurements of X-ray diffractions implied the preservation of the cubic phase of the CdTe crystals at all Tm dopant contents. The transmission electron microscopy inspected the formation of monodisperse and self-assemble nanoparticles with mean diameter from 1.8 ± 0.2 nm to 5.7 ± 0.3 nm, depending on the amount of Tm incorporated in the CdTe nanocrystals. A modulation of the optical bandgap was observed because of the doping of CdTe with Tm atoms. Highly luminescent emission spectra with tunable colors were obtained. The emission spectra showed sharp intense emitted light with an enhancement of its intensity reached to seven folds compared with the un-doped CdTe crystals. An increasing of quantum yields from 31% to 94% was realized. A decrease of the Stokes shift was observed which implies the synthesis of Cd1 − x TmxTe QDs free of defects for the first time. This unique performance renders the prepared Cd1 − x TmxTe to be potential candidate for the manufacturing of laser diodes.

The luminescence behavior of Zn1-xTaxO nanophotonic crystals prepared via Di-N-(2-hydroxyethyl)oleylamin assisted microwave approach

Semiconducting Zn1-xTaxO nanophotonic crystals were synthesized via Di-N-(2-hydroxyethyl)oleylamin assisted microwave approach using tantalum acetylacetonate, zinc acetylacetonate and 8-ethylquinoline N-oxide. The developed Zn1-xTaxO nanophotonic crystals exhibited a hexagonal crystalline structures and their lattice constant increased with increasing Ta atoms. The Zn1-xTaxO nanostructures demonstrated emission spectrum in the visible region from 354 to 430 nm. The inclusion of Ta atoms in the ZnO QDs enhanced the luminescent light and the quantum yields for ZnO nanocrystals by five orders at concentration of 5 wt%. The change of the power and time of microwave irradiation for the Zn0.95Ta0.05O nanocrystals instigated shift of the luminescence peak positions toward blue light and a modulation of the optical band gap. The increase of the microwave power to 850 W for 35 min for Ta-doped ZnO at concentration of 5 wt% comprised a remarkable increase of the luminescence intensity 7 times, decreased the emission band width by 5 times and enlarged the quantum yield to 92 %. These outstanding features may render the Zn0.95Ta0.05O nanocrystals to be used as laser material for the laser diode applications.

Entanglement of Microwave and Optical Fields Using Electrical Capacitor Loaded With Plasmonic Graphene Waveguide

We propose a novel approach for microwave and optical fields entanglement using an electrical capacitor loaded with graphene plasmonic waveguide. In the proposed scheme, a quantum microwave signal of frequency f_m drives the electrical capacitor, while an intensive optical field (optical pump) of frequency f_1 is launched to the graphene waveguide as surface plasmon polariton (i.e., SPP) mode. The two fields interact by the means of electrically modulating the graphene optical conductivity. It then follows that an upper and lower SPP sideband modes (of f_2 = f_1 + f_m and f_3 = f_1 -f_m frequencies, respectively) are generated. We have shown that the microwave signal and the lower sideband SPP mode are entangled, given a proper optical pump intensity is provided. A quantum mechanics model is developed to describe the fields evolution. The entanglement of the two fields is evaluated versus many parameters including the waveguide length, the pump intensity, and the microwave frequency. We found that the two fields are entangled over a vast microwave frequency range. Furthermore, our calculations show that a significant number of entangled photons are generated at the lower SPP sideband. The proposed scheme attains tunable mechanism for microwave-optical entanglement which paves the way for efficient quantum systems.

One‐Step Microwave Approach to Generate Carbon Dots/Gelatin Composite with Both Thermoresponsive Sol–Gel Transition and Fluorescence Properties

AbstractCarbon dots (CDs) have drawn considerable research interest for their attractive applications in sensors, bioimaging, and photonic devices. Here, an aqueous gelatin solution is employed as the only reactant to directly generate a CDs/gelatin composite through a green and simple one‐step microwave approach. The resulting CDs/gelatin composite owns a typical excitation‐dependent photoluminescence property that comes from CDs, which can be potentially applied for multicolor fluorescence bioimaging. More importantly, the CDs/gelatin composite possesses a thermoresponsive sol–gel transition property that is associated with gelatin, which can be exquisitely enlisted to fabricate CDs/gelatin gel beads and fluorescent gel patterns. Also the release of CDs from the gel beads can be triggered by the thermoresponsive sol–gel transition. Thus, for the first time this study creates the CDs/gelatin composite with both thermoresponsive sol–gel transition and fluorescence properties, which is promising for applications in stimuli‐responsive materials, nanocomposites, controlled release, and fluorescence imaging.

A facile microwave-assisted synthesis of highly crystalline red carbon dots by adjusting the reaction solvent for white light-emitting diodes

Microwave approach has been widely used for the synthesis of fluorescent carbon dots (CDs) due to its advantages of short reaction time and homogeneous heating. Currently, it is still difficult to synthesize red light-emitting CDs (R-CDs) via the microwave-assisted method at atmospheric pressure. Herein, we report a solvent-controlled synthesis of R-CDs using domestic microwave. As a result, for an ammonium citrate tribasic, formamide and glycerol blend reaction solvent, the R-CDs with emission peak of 622 nm were achieved and exhibited a photoluminescence (PL) quantum yield of 37.4% and excitation-independent PL emission spectrum. During the formation process of R-CDs, glycerol and formamide not only promote the carbonization of ammonium citrate tribasic, but can also enhance the crystalline nature of CDs. Finally, the warm white light-emitting diode (WLED) with a high colour rendering index (CRI) of 90.9 and Commission Internationale de L’Eclairage (CIE) coordinates of (0.344, 0.333) was realized by combining conventional yellow YAG:Ce phosphor and R-CDs/mesoporous silica (MPS) composites with a blue chip. This result demonstrates a low-cost R-CD synthetic method for potential substitution for red phosphor materials in solid-state lighting applications.