Simple Microwave Hydrothermal Method Research Articles

Enhancing Dy2O3/g-C3N4 visible photocatalytic hydrogen production performance by loading graphene-like carbon from Enteromorpha prolifera (EP-GL)

Using Enteromorpha prolifera (EP) as a raw material, biomass graphene-like carbon (EP-GL) can be prepared and used as a cocatalyst to modify semiconductor photocatalytic materials, which contributes to achieving a sustainable development strategy. In this study, graphene-like carbon was successfully obtained from EP biomass through high-temperature pyrolysis. It was then used to modify a Dy2O3/g-C3N4 semiconductor composite photocatalyst using a simple microwave hydrothermal method. The incorporation of EP-GL not only acted as a transfer channel for photogenerated electrons and enhanced the separation of photogenerated carriers, but also significantly increased the specific surface area of the catalyst, providing more active sites for photocatalytic reactions. Additionally, the heterojunction formed between Dy2O3/g-C3N4 aided in the separation of electron-hole pairs, further improving the efficiency of photocatalytic hydrogen production. The composite catalyst achieved a hydrogen generation rate of 683.16 μmol⋅g−1⋅h−1 in ethylene glycol solution and 723.57 μmol⋅g−1⋅h−1 in glucose solution. These rates were 3.84 and 3.56 times greater than those of Dy2O3 alone, respectively. This demonstrated the superior performance of the ternary composite photocatalyst in harnessing visible light for efficient hydrogen production.

Efficient Synthesis of Highly Photo‐stable N‐doped Carbon Quantum Dots and their Applications in Detection and Cellular Imaging of Mercury Ions

AbstractIn this work, the nitrogen doped carbon quantum dots (N‐CQDs) were synthesized by a simple microwave hydrothermal method using citric acid (carbon source) and urea (dopant) and optimized the preparation conditions by orthogonal tests. The synthesized N‐CQDs emitted a bright blue fluorescence with specific selectivity for Hg2+. The study revealed a static quenching mechanism of Hg2+ on the N‐CQDs. The N‐CQDs showed good linear correlation in the range of 0–120 μM for the detection of Hg2+ with a low detection limit of 22.50 nM. We also demonstrated the suitability of the N‐CQDs for the detection of Hg2+ in tap water and industrial wastewater with spiked recoveries of 97.56 %–103.58 %. In addition, the synthesized N‐CQDs with high fluorescence intensity, good optical stability and biocompatibility were successfully applied to fluorescent inks and imaging of Hela cells. This indicated that the synthesized N‐CQDs have promising applications in Hg2+ detection, bioimaging, and fluorescence anti‐counterfeiting.

CuO coatings on glass fibers: a hybrid material for CO2 adsorption and photocatalytic reduction to solar fuels

The CO2 capture and its photocatalytic conversion (CCPC) to solar fuels is one promising route to fighting global warming. The CCPC process implies the use of CO2, solar light, and materials to produce solar fuels of low carbon content. The materials must fulfill with the double function of capture and photocatalytic convert of the CO2 into solar fuels. For this purpose, copper oxide (CuO) is an excellent candidate to act as both: adsorbent and photocatalyst. Scaling-up the CCPC process requires the immobilization of CuO on commercially available substrates such as glass fibers, which offers a homogeneous surface exposure, efficient absorption of solar energy, and an easy application in reactors. In this work, the fabrication of CuO coatings on glass fibers by a simple microwave-hydrothermal method to produce solar fuels (CH3OH and HCOH) in CCPC process is proposed. Three glass fibers with different chemical compositions and slit (open area) were selected as supports. The best efficiency for CO2 capture (3080 mgCO2 g−1) was obtained with the CuO coating deposited in a substrate rich in Na2O and CaO. Once the CO2 was adsorbed, the coatings were exposed to visible LED light to carry out its conversion to solar fuels (CH3OH and HCOH). According to the results, both high CuO content and high slits in the fibers promoted an increase in the CO2 conversion to HCOH (2.7 nmol cm−2 h−1) and CH3OH (37.6 nmol h−1 cm−2). The presence of Na2O in the substrates played an essential role as a hole scavenger in the photocatalytic CO2 reduction, preventing the re-oxidation of the products. The use of glass fibers as support of CuO promoted efficiencies up to 11 times higher than other materials used in CCPC process.

Realizing white emission in Sc2(MoO4)3:Eu3+/Dy3+/Ce3+ phosphors through computation and experiment

Electronic structure was essential for the applications of materials. Modulating electronic structures can change the intrinsic properties to obtain the promising performances in materials. Herein, the electronic structures of Sc2(MoO4)3:Eu/Dy/Ce were chiefly studied through the first principles. An indirect band gap of ~3.56 ​eV was obtained turning into direct while rare earth ions were introduced into orthorhombic Sc2(MoO4)3. Theoretical calculations revealed that 4 f orbits of RE3+ pushed the conduction band (CB) towards low energy region, and the Ce 5 ​d hybrided with Sc 3 ​d around the fermi level, resulting in the CB shifted slightly towards high energy region. To complement and rationalize the calculations, a simple microwave hydrothermal method was used to synthesize Sc2(MoO4)3:Eu/Dy/Ce phosphors whose experimental bandgaps shared a same tendency with the DFT calculations. Additionally, the photoluminescence behaviors of as-prepared phosphors exhibited chiseled bands in the visible region. Especially, Eu/Dy/Ce tri-doped Sc2(MoO4)3 can obtain white emission. The decay curve and the correlated color temperature also identified that the RE-doped Sc2(MoO4)3 has a promising prospect for the warm white LEDs. Additionally, the PL properties enhanced at elevated temperature. These results not only promot an in-depth comprehension of the structure-property relationships in Sc2(MoO4)3-based phosphors, but also provide a way to design the electronic structures of materials with excellent performance, especially for the practical applications of a new phosphor in solid-state lighting.

Facile Synthesis of Antimony Tungstate Nanosheets as Anodes for Lithium-Ion Batteries.

Lithium-ion batteries (LIBs) have been widely used in the fields of smart phones, electric vehicles, and smart grids. With its opened Aurivillius structure, tungstate antimony oxide (Sb2WO6, SWO), constituted of {Sb2O2}2n+ and {WO4}2n−, is rarely investigated as an anode for lithium-ion batteries. In this work, Sb2WO6 with nanosheets morphology was successfully synthesized using a simple microwave hydrothermal method and systematically studied as an anode for lithium-ion batteries. The optimal SWO (SWO-60) exhibits a high specific discharge capacity and good rate capability. The good electrochemical performance could be ascribed to mesoporous nanosheets morphology, which is favorable for the penetration of the electrolyte and charge transportation. The results show that this nanostructured SWO is a promising anode material for LIBs.

A novel and simple microwave hydrothermal method for preparation of CoAl2O4/sepiolite nanofibers composite

A blue and bright CoAl2O4 nanocomposite is fabricated by the microwave hydrothermal synthesis at the optimum conditions (pH = 13, 240 °C, 4 h, 15:1 of the metal salt to sepiolite). More interestingly, a significant improvement in the distribution of the supported CoAl2O4 nanoparticles can be realized through the strategy of microwave hydrothermal coupled with surface modification by surfactants, which results in significantly improved suspension performance. The synthesis strategy is believed to provide a guide for the fabrication of supported nanocomposites with a uniform particle size for diverse applications such as heterogeneous catalytic reactions, ceramic materials, water-based coatings, and so on.

Inorganic-organic CdSe-diethylenetriamine nanobelts for enhanced visible photocatalytic hydrogen evolution

Inorganic-organic hybrid nanomaterials, with excellent chemical and physical properties and technology applications, have attracted much attention in many fields. In the photocatalytic field, it is still a problem to find a stable, adjustable morphology and band gap and effective photocatalyst in utilizing solar energy conversion to hydrogen (H2) to solve the energy crisis. Herein, with the assistance of diethylenetriamine (DETA), the novel inorganic-organic CdSe-DETA hybrids with different morphology and adjustable band gap have been synthesised via simple microwave hydrothermal method. The morphological transformation mechanism involves the consumption of organic components controlled by the mixed precursor and subsequent self-assembly of residual inorganic components (CdSe). Under the visible light irradiation (λ > 420 nm), CdSe-18DETA nanobelt, showed the best photocatalytic H2 production activity (5.75 mmol·g−1·h−1), which is 3.03 times greater than that of pure CdSe (1.90 mmol·g−1·h−1). Moreover, after four cycles, the photocatalytic H2 production activity can still remain 91.27% of initial value, which indicates its good photocatalytic stability. Our results provide a promising approach for designing visible-light photocatalysts with efficient electron-hole separation and adjustable morphology and band gap.

Facile fabrication of mesoporous biochar/ZnFe2O4 composite with enhanced visible-light photocatalytic hydrogen evolution

A promising biochar/ZnFe2O4 (BZF) composite has been synthesized to improve the efficiency of visible-light-driven H2 evolution via a simple microwave hydrothermal method. The materials were investigated through diverse characterization means including XRD, FTIR, SEM, BET, XPS, VSM, UV–vis/DRS, PL, EIS. Different ratios of BZF composites expressed enhanced photocatalytic H2 evolution performance over pure ZnFe2O4. Especially, biochar/ZnFe2O4 catalysts with 5:1 mass ratio (BZF-5) attained the optimal H2 evolution rate, which is around 6 times higher than that of pure ZnFe2O4. Biochar acts as an electron mediator can effectively promote the separation of electron-hole pairs to enhance the rate of photocatalytic hydrogen evolution. Moreover, Eosin Y, photocatalyst and TEOA have synergistic effects accounted for enhanced photocatalytic performance in reaction system. Three cyclic runs for the photocatalytic H2 evolution on BZF-5 sample illustrated its good stability and sustainable reusability.

High-throughput technologies for gathering data

Electronic structure was essential for the applications of materials. Modulating electronic structures can change the intrinsic properties to obtain the promising performances in materials. Herein, the electronic structures of Sc2(MoO4)3:Eu/Dy/Ce were chiefly studied through the first principles. An indirect band gap of ~3.56 ​eV was obtained turning into direct while rare earth ions were introduced into orthorhombic Sc2(MoO4)3. Theoretical calculations revealed that 4 f orbits of RE3+ pushed the conduction band (CB) towards low energy region, and the Ce 5 ​d hybrided with Sc 3 ​d around the fermi level, resulting in the CB shifted slightly towards high energy region. To complement and rationalize the calculations, a simple microwave hydrothermal method was used to synthesize Sc2(MoO4)3:Eu/Dy/Ce phosphors whose experimental bandgaps shared a same tendency with the DFT calculations. Additionally, the photoluminescence behaviors of as-prepared phosphors exhibited chiseled bands in the visible region. Especially, Eu/Dy/Ce tri-doped Sc2(MoO4)3 can obtain white emission. The decay curve and the correlated color temperature also identified that the RE-doped Sc2(MoO4)3 has a promising prospect for the warm white LEDs. Additionally, the PL properties enhanced at elevated temperature. These results not only promot an in-depth comprehension of the structure-property relationships in Sc2(MoO4)3-based phosphors, but also provide a way to design the electronic structures of materials with excellent performance, especially for the practical applications of a new phosphor in solid-state lighting.

Constructing a MoS₂ QDs/CdS Core/Shell Flowerlike Nanosphere Hierarchical Heterostructure for the Enhanced Stability and Photocatalytic Activity.

MoS2 quantum dots (QDs)/CdS core/shell nanospheres with a hierarchical heterostructure have been prepared by a simple microwave hydrothermal method. The as-prepared samples are characterized by XRD, TEM, SEM, UV-VIS diffuse reflectance spectra (DRS) and N2-sorption in detail. The photocatalytic activities of the samples are evaluated by water splitting into hydrogen. Results show that the as-prepared MoS2 QDs/CdS core/shell nanospheres with a diameter of about 300 nm are composed of the shell of CdS nanorods and the core of MoS2 QDs. For the photocatalytic reaction, the samples exhibit a high stability of the photocatalytic activity and a much higher hydrogen evolution rate than the pure CdS, the composite prepared by a physical mixture, and the Pt-loaded CdS sample. In addition, the stability of CdS has also been greatly enhanced. The effect of the reaction time on the formations of nanospheres, the photoelectric properties and the photocatalytic activities of the samples has been investigated. Finally, a possible photocatalytic reaction process has also been proposed.

Preparation of Self-Assembled Spherical g-C3N4/tz-Bi(0.92)Gd(0.08)VO4 Heterojunctions and Their Mineralization Properties.

A novel kind of spherical g-C3N4/tz-Bi0.92Gd0.08VO4 heterojuctions are prepared via a simple microwave hydrothermal method. The sphere self-assembled mechanism and the heterojunction photocatalytic mechanism are mainly studied in this article. The results show that the added g-C3N4 sheets first anchor on ms-BiVO4 surfaces and then polymerize to form the coating layers, generating steric effect which is competing with Gd(3+) induction effect to affect the crystal transformation (from ms-BiVO4 to tz-BiVO4) and its growth during those processes. Afterward, independent coated structures are further polymerized and assembled into g-C3N4/tz-Bi0.92Gd0.08VO4 spheres. Because ECB (-0.95 V) of g-C3N4 is more negative than ECB (-0.05 V) of tz-BiVO4, the photoelectrons of g-C3N4 can be transferred into tz-BiVO4 surfaces through the heterojunction structure, so as to promote the separation rate of electron-hole pairs. In general, the adding of g-C3N4 can introduce hydroxyl groups to catch the photoholes and can inject electrons to react with dissolved oxygen to boost the production of active groups. Depending on such an orderly cooperation, g-C3N4/tz-Bi0.92Gd0.08VO4 heterojunction catalysts exhibit high and stable mineralization properties.

Microwave-hydrothermal method for the synthesis of composite materials for removal of arsenic from water.

Composite material Zr-doped TiO2, suitable for the removal of arsenic from water, was synthetized with fast and simple microwave-hydrothermal method. Obtained material, Zr-TiO2, had uniform size and composition with zirconium ions incorporated into crystal structure of titanium dioxide. Synthetized composite material had large specific surface area and well-developed micropore and mesopore structure that was responsible for fast adsorption of As(III) and As(V) from water. The influence of pH on the adsorption capacity of arsenic was studied. The kinetics and isotherm experiments were also performed. The treatment of natural water sample containing high concentration of arsenic with composite material Zr-TiO2 was efficient. The concentration of arsenic was reduced to the value recommended by WHO.

Characteristics of Nitrogen and Boron Co-Doped Graphene Nanosheets Synthesized By Simple Microwave-Hydrothermal Method

Graphene nanosheets have received much attention in electrochemical energy research areas because of its remarkable properties such as high specific surface area and electrical conductivity. The properties satisfy various requirements for electrochemical device’s electrode. In that application, the enhancement of the oxygen reduction reaction (ORR) activity has been considered as one of the important issues. For enhancing ORR activity, various precious metal catalysts have been investigated in spite of their high prices. In recent years, research efforts have been focused on developing various non-metal catalysts for overcoming the disadvantage of metal catalysts. Most of carbon-based non-metal catalysts were synthesized via expensive method such as chemical vapor deposition (CVD) method. The method is not suitable for mass production method. In this study, we synthesized nitrogen and boron co-doped graphene nanosheets (BNG) from graphene oxide (GO) by simple microwave-hydrothermal method. The synthesis time can be significantly reduced result from assistance of microwave heating. The synthesis process includes doping and reduction process. The samples were prepared under different reduction temperature conditions. For observing the morphology of samples, we carried out scanning electron microscopy (SEM). From Raman spectra analysis, we confirmed that intensity ratio (ID/IG) increased with reduction temperature. And we investigated chemical composition and bonding configuration of the BNG samples by X-ray photoelectron spectroscopy (XPS). The results of XPS analysis demonstrated that co-doping and reduction process are successfully achieved. Catalytic activities were characterized by three-electrode system. Linear sweep voltammetry (LSV) was measured in 0.1M KOH electrolyte purged oxygen gas over 1 h, with a 1500 rpm electrode rotation speed and a 10 mVs-1 scan rate. The LSV results revealed that co-doped samples show higher ORR activity compared to that of non-doped sample and the activity is enhanced with reduction temperature. Acknowledgement This research was supported by the MSIP(Ministry of Science, ICT and Future Planning), Korea, under the “IT Consilience Creative Program” (NIPA-2014-H0201-14-1002) supervised by the NIPA(National IT Industry Promotion Agency)

Enhanced photocatalytic activity of tetragonal BiVO4: Influenced by rare earth ion Yb3+

BiVO4 products doped with different contents of rare earth Yb3+ were prepared by a simple microwave-hydrothermal method. X-ray diffraction and Raman spectra reveal the structural transition from monoclinic (space group I2/a) to tetragonal structure (space group I41/amd) with Yb3+ doping. The morphology of Yb-doped BiVO4 has also changed from irregular plarelike structure to dispersive particles with rodlike structure, resulting in the increase of specific surface area (from 3.31m2/g to 11.02m2/g). The photocatalytic results demonstrate that tetragonal BiVO4 with the rodlike morphology and high surface area has an enhanced photocatalytic activity, which is quite different from the previous reports.

Response surface modeling of Carbamazepine (CBZ) removal by Graphene-P25 nanocomposites/UVA process using central composite design

Graphene-P25 (Gr-P25) nanocomposites were synthesized by a simple microwave hydrothermal method. The nanocomposites with different graphene loading were evaluated for the degradation of an important pharmaceutical water pollutant, Carbamazepine (CBZ) under UVA irradiation in a batch reactor. Response surface methodology (RSM) was used to optimize three key independent operating parameters, namely Gr-P25 nanocomposites dose (X1), CBZ initial concentration (X2) and UV light intensity (X3), for photocatalytic degradation of CBZ. The central composite design (CCD) consisting of 20 experiments determined by 23 full factorial designs with six axial points and six center points was used to conduct experiments. The results showed that CBZ removal was significantly affected by the synergistic effect of linear term of Gr-P25 dose (X1) and UV intensity (X3). However, the quadratic terms of Gr-P25 (X12) and UV intensity (X32) had an antagonistic effect on CBZ removal. The obtained RSM model (R2 = 0.9206) showed a satisfactory correlation between experimental and predicted values of CBZ removal. The optimized conditions for achieving 100% CBZ removal with 5 min UVA irradiation were 25.14 mg/L, 167.68 ppb and 1.35 mW/cm2 for Gr-P25 dose, initial concentration of CBZ and UV intensity, respectively.

Comparison of photoprotection efficiency and antiproliferative activity of ZnO commercial sunscreens and CeO2

Cerium oxide (CeO2) nanopowders were successfully synthesized by a simple microwave-hydrothermal method. The UVB protection of an emulsion containing CeO2 was evaluated in vitro and compared to the one provided by the same emulsion, zinc oxide (ZnO) instead of CeO2. CeO2 offered better protection against UVB radiation. Finally, in vitro cytotoxicity of CeO2 and various ZnO commercial sunscreens was carried out using NCTC2544 cell line. Assessment of cell viability demonstrated that all tested ZnO commercial sunscreens reduce cell viability in a dose- and time-dependent manner whereas CeO2 particles did not produce any effects on NCTC2544 growth at the highest concentration tested (80µg/ml).

Microwave-hydrothermal preparation of a graphene/hierarchy structure MnO2 composite for a supercapacitor

Graphene/hierarchy structure manganese dioxide (GN/MnO2) composites were synthesized using a simple microwave-hydrothermal method. The properties of the prepared composites were analyzed using field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) measurements. The electrochemical performances of the composites were analyzed using cyclic voltammetry, electrochemical impedance spectrometry (EIS), and chronopotentiometry. The results showed that GN/MnO2 (10wt% graphene) displayed a specific capacitance of 244F/g at a current density of 100mA/g. An excellent cyclic stability was obtained with a capacity retention of approximately 94.3% after 500 cycles in a 1mol/L Li2SO4 solution. The improved electrochemical performance is attributed to the hierarchy structure of the manganese dioxide, which can enlarge the interface between the active materials and the electrolyte. The preparation route provides a new approach for hierarchy structure graphene composites; this work could be readily extended to the preparation of other graphene-based composites with different structures for use in energy storage devices.

Synthesis of large-scale uniform mulberry-like ZnO particles with microwave hydrothermal method and its antibacterial property

Large-scale uniform mulberry-like ZnO particles were successfully synthesized via a fast and simple microwave hydrothermal method. The formation mechanism of mulberry-like ZnO particles was investigated by adding different types of alkalis and different amounts of triethanolamine (TEA). Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to observe the morphology and crystal structure of the obtained ZnO. The results revealed that the as-prepared ZnO products had an average diameter of about 150nm and polycrystalline wurtzite structure. The existence of TEA was vital for the formation of nanoparticle-assembled mulberry-like ZnO particles. These mulberry-like ZnO particles exhibited stronger antibacterial effects on Candida albicans than did sheet-like and flower-like ZnO.

Preparation of CeO 2 by a simple microwave–hydrothermal method

Cerium carbonate hydroxide (orthorhombic Ce(OH)CO 3) hexagonal-shaped microplates were synthesized by a simple and fast microwave–hydrothermal method at 150 °C for 30 min. Cerium nitrate, urea and cetyltrimethylammonium bromide were used as precursors. Ceria (cubic CeO 2) rhombus-shape was obtained by a thermal decomposition oxidation process at 500 °C for 1 h using as- synthesized Ce(OH)CO 3. The products were characterized by X-ray powder diffraction, field-emission scanning electron microscopy, thermogravimetric analysis and Fourier transformed infrared spectroscopy. The use of microwave–hydrothermal method allowed to obtain cerium compounds at low temperature and shorter time compared to other synthesis methods.