Microwave-assisted Hydrothermal Reaction Research Articles

Temperature-Sensitive Template for Preparation of ZnO/CeO2 Composite Photocatalytic Materials and Its Catalytic Performance

In this work, a series of thermosensitive ionic liquid functionalized polymers, PNx(IL)y, with controllable morphology and particle size were prepared by free radical polymerization. Then, using the polymer PN64(IL)8 with uniform morphology as a templating agent, the ZnO composite photocatalytic materials doped with rare earth metal Ce were prepared in combination with a microwave-assisted and templated hydrothermal reaction method. Series different Ce-doping amount photocatalytic materials ZnO-Ce-x‰ were characterized by XRD, SEM, TEM, XPS, and other methods. The results demonstrated that the templated materials PN64(IL)8 can prepare ZnO-Ce-2‰ with uniform petaloid ambulacra shape, good distribution of elements, and excellent photocatalytic performance. Photocatalytic degradation experiments of methyl orange (MO) showed that when the Ce-doping amount is only 2‰, the degradation rate of organic dyes can reach 96.5% by reacting the photocatalytic materials in water for 1 h. In addition, this kind of photocatalyst can be used for the degradation of high-concentration MO, as well as being easily recovered and effectively reused by simple filtration. Therefore, the structure of this kind of photocatalyst is controllable in the preparation process with an extremely low Ce-doping amount compared with current reports, and it has a good application prospect in the field of wastewater treatment technology.

The role of cathode architecture and anion interactions on the performance of Al-substituted α-Ni(OH)2 in rechargeable Ni–Zn cells

Rechargeable alkaline Ni–Zn batteries configured with Zn sponge anodes provide an energy dense, safe alternative to Li-ion batteries for a wide range of risk-averse applications. Advanced cathodes that provide high rate and capacity performance are needed to match that of Zn sponge anodes. We show that aluminum-substituted nickel hydroxide, α-Ni0.9Al0.1(OH)2, expressed in a nanosheet morphology, can be directly deposited onto a flexible carbon nanofiber paper (CNP) using a rapid and scalable two-step microwave-assisted hydrothermal reaction. The architected electrode (α-Ni0.9Al0.1(OH)2@CNP) wires the energy-storing Ni to the carbon scaffold, resulting in high capacity and stable cycling in Ni–Zn cells, performance not obtained using conventional powder-composite cathodes. The growth reaction time and temperature influence mass loading, thickness, crystal structure, the ratio of interlayer ‘free’-to-lattice metal-coordinated ‘bound’ nitrates, and electrochemical performance. The architected α-Ni0.9Al0.1(OH)2@CNP||Zn sponge alkaline cell provides unprecedented performance, delivering high discharge capacity, storage of >1.4 electrons per Ni, good rate capability, excellent capacity retention, and high mass loading. Architected electrodes that combine 3D electronic wiring and structured active material provide a pathway to energy dense, safe, rechargeable Ni–Zn batteries and offer approaches to improve the electrochemical performance of a broad class of layered materials for multiple battery chemistries.

Performance comparison of 2D nickel phosphate nanoparticles prepared via sonochemical and microwave-assisted hydrothermal routes for supercapattery

Metal phosphates are broadly applied in electrochemical energy storage applications because of their abundance in nature, cost-effectiveness, and excellent electrochemical performance. Herein, we compare the performance of nickel phosphate (Ni3(PO4)2) prepared through sonochemical and microwave-assisted hydrothermal reaction (MW) synthesis routes for supercapattery. These methods are efficient, rapid, and facile, yielding a high quantity of nanoparticles. Field Emission Scanning Electron Microscopy reveals that Ni3(PO4)2 nanoparticles synthesized via the MW method are smaller than those produced via the sonochemical method. X-ray diffraction analysis confirmed that the MW method, followed by calcination at 200 °C for 3 h (NiPO4-MWB sample), produces amorphous nanoparticles, providing more exposure to redox-active sites. This work demonstrates that the NiPO4-MWB sample exhibits the highest specific capacity of 256.54C g−1 at a current density of 1 A g−1 compared to its counterpart electrode prepared via the sonochemical. A device fabricated using NiPO4-MWB//activated carbon (AC) delivered an energy density of 10.33 Wh kg−1 at a power density of 750 W kg−1, retaining 99.42 % of its capacity after 5000 cycles. The notable capacity retention makes it an attractive candidate for supercapattery electrodes. These findings suggest that MW synthesis can be used for the rapid production of tailored nanoparticles for electrochemical energy storage applications.

Highly porous silica synthesized by a microwave-assisted hydrothermal method derived from recycled silicon sludge for thermal insulation applications

In this study, we synthesize a porous silica nanoparticles (SiO2) derived from recycled semi-conducting silica sludge via a conventional hydrothermal and microwave-assisted hydrothermal methods for flame-resistant applications. The corresponding thermal properties of as-synthesized SiO2 nanoparticles are investigated. The effects of reaction temperature and urea concentration are investigated in terms of surface morphology and thermal conductivity. The results of thermal conductivity tests indicate that 180 °C reaction temperature for both conventional hydrothermal reaction and microwave-assisted hydrothermal reaction demonstrated the best thermal insulator performance. The thermal conductivities are determined to be 0.0193 W/m·K and 0.0192 W/m·K, respectively. For flame penetration and combustion tests, microwave-assisted one exhibits much better performance, maintaining a temperature of 34 °C after 600 s of combustion under a butane torch at nearly 800 °C. Furthermore, there is no deformation occurred when direct contact with the flame at a high temperature, proving that microwave-assisted hydrothermal reaction-synthesized silica is a potential candidate for thermal barrier applications.

Construction of BiVO4/Bi2WO6/WO3 heterojunctions with improved photocatalytic capability in elimination of dye and antibiotics and inactivation of E. coli

BackgroundRecently, semiconductor photocatalysts have been known as one of most promising strategies for environmental purification and remediation due to the rapid and nonselective oxidation of a broad range of organic pollutants. MethodsIn this article, BiVO4/Bi2WO6/WO3 ternary heterojunction with cascade energy band alignment has been proposed and prepared by microwave-assisted hydrothermal reaction. Significant findingsThe constructed ternary composite shows a broader absorption spectrum compared with the binary BiVO4/Bi2WO6 and pure BiVO4 samples. In addition, the ternary composite with gradient energy band alignment can accelerate the electron-hole separation and charge carrier transfer leading to decreased photoluminescence (PL) intensity and lifetime. As a result, the BiVO4/Bi2WO6/WO3 heterostructured composite can display higher photocurrent and possess an enhanced performance in the visible-light-driven degradation of methylene blue (MB). Our results indicate that the optimal molar ratio of BiVO4:Bi2WO6:WO3 is found to be 0.375:0.375:0.25, revealing the best photocatalytic activity. The ternary composite with optimal molar ratio exhibits a 50.9% greater degradation rate (rate constant (k) =0.0283 min−1) over the BiVO4 (k = 0.0139 min−1) for the photodegradation of MB. Besides, the resultant ternary system also shows excellent photocatalytic performance in the degradation of antibiotics and antibacterial capability with great biocompatibility.

Rapid synthesis of nickel‑copper phosphate electrode by microwave-assisted hydrothermal reaction for supercapattery

This study reports the fabrication of binder-free nickel‑copper phosphate (NCP) battery-type electrode via microwave-assisted hydrothermal method for the first time. This fabrication method involved microwave heating which significantly reduced the reaction time compared to the conventional hydrothermal method. The NCP electrodes with different precursor ratios (Ni:Cu of 4:0, 3:1, 1:1, 1:3, and 0:4) were fabricated at 90 °C for 12.5 min. Among all NCP binder-free electrodes, Ni3-Cu-P electrode (Ni:Cu of 3:1) exhibited superior electrochemical performance by showing the highest specific capacity of 1030.8 C/g and areal capacity of 0.72 C/cm2 at 3 A/g, and the lowest charge transfer (25.9 Ω) and ion diffusion resistances. These can be explained by the fact that Ni3-Cu-P electrode had a small-sized microsphere electrode material with an amorphous structure deposited on the nickel foam. The small-sized microsphere provided a larger surface area for faradaic reaction. Besides, the amorphous structure offered more electrochemical sites for faradaic reaction. Therefore, it was selected as the battery-type electrode for supercapattery. The Ni3-Cu-P//AC supercapattery delivered a higher energy density of 51.6 Wh/kg at 2.25 kW/kg power density, and outstanding stability with 91.3 % capacity retention after 3000 cycles.

Microwave-assisted growth of spherical core-shell NiFe LDH@CuxO nanostructures for electrocatalytic water oxidation reaction

The high energy demand for electrochemical water splitting arises from sluggish oxygen evolution reaction (OER) kinetics. In this regard, Layered double hydroxide (LDH) has been introduced as an outstanding catalyst for the OER due to its exceptional physiochemical and 2D infrastructure properties. Herein, we report the design and synthesiss of core-shell nanostructured electrocatalyst by rationally decorating vertically oriented NiFe LDH ultrathin nanosheets on CuxO support (NiFe LDH@CuxO) via microwave-assisted hydrothermal reaction. For OER, the NiFe LDH@CuxO core-shell nanostructured catalyst demonstrated promising electrocatalytic performance, requiring only 1.43 V onset potential and 270 mV overpotential at 10 mA cm−2. The NiFe LDH@CuxO also outperformed pristine NiFe LDH and iridium oxide (IrO2) in terms of electrocatalytic activity, durability, and Faradaic efficiency. The fabricated NiFe-LDH@CuxO electrocatalyst with outer shell NiFe-LDH ultrathin nanosheets provides numerous exposed active sites, benefits electrolyte diffusion and oxygen gas releasing and also reduces the interfacial charge transfer resistance to enhance OER activity. Furthermore, exclusive core-shell 3D infra-structure effectively prevents NiFe-LDH nanosheets agglomeration and restacking, enhancing electrochemical stability.

A new strategy to quickly synthetize true nanoparticles of the spinel LiMn2O4 by using a microwave-assisted hydrothermal route

Based on a microwave-assisted hydrothermal reaction, a new route is proposed to prepare highly pure true nanoparticles (≤15 nm) of the single-phase spinel LiMn2O4 (LMO) at a low temperature (140 °C) and short reaction time (5 min), using exclusively water-soluble reagents. The obtention of this material was confirmed by using different techniques such as X-ray diffractometry, Rietveld crystal structure refinement, inductively coupled plasma-atomic emission spectroscopy and high-resolution transmission electron microscopy. Electrochemical evaluations were performed by using cyclic voltammetry and galvanostatic charge and discharge tests. Only electrodes prepared from spinel LMO nanoparticles with an average size of ~15 nm showed electrochemical activity. From charge and discharge tests at a constant rate of C/5, the electrodes prepared from this active material exhibited an initial specific capacity of 128 mA h g–1 with a capacity retention of 95% after the 27th cycle. The hallmark of the synthesis route here described is the saving of energy while preparing truly nanoparticulate LMO with excellent chemical, structural and promising electrochemical properties.

Multifunctional MnCuInSe/ZnS quantum dots for bioimaging and photodynamic therapy.

In this work, manganese (Mn)-doped CuInSe quantum dots (QDs) with a ZnS passivation layer (MnCuInSe/ZnS) have been synthesized via a one-pot microwave-assisted hydrothermal reaction using glutathione (GSH) as a stabilizer. The MnCuInSe/ZnS core-shell QDs combine magnetic resonance imaging (MRI), excitation-dependent red emission, and reactive oxygen radical generation functions, in which regulation of Mn2+ incorporation leads to synergistic imaging and therapeutic modalities. The MnCuInSe/ZnS QDs exhibit high colloidal and photochemical stability in simulated media and at different pH values. An r2/r1 ratio of 9.99 was calculated from MRI studies suggesting their potential application as dual-modal imaging agents. Based on in vitro tests on Hela, B16, and HepG2 cell lines, it is apparent that MnCuInSe/ZnS QDs impose no significant cytotoxicity in the dark, while they can efficiently generate singlet oxygen radicals for photodynamic therapy of cancers, killing more than 80% of B16 cells within 5min of laser irradiation (671nm, 1W cm-2). Furthermore, in vitro fluorescence imaging and cellular internalization of QDs are examined to visualize cellular uptake and in situ ROS generation. Therefore, this research exemplifies a new set of multifunctional chalcogenide QDs for theranostic applications.

Graphene Quantum Dots Co-Doped with Nitrogen/Mn(II) or Nitrogen/Gd(III) for Bimodal Magnetic Resonance and Fluorescence Imaging

Graphene quantum dots (GQDs) are unique derivatives of graphene that show promise in multiple biomedical applications as biosensors, bioimaging agents, and drug/gene delivery vehicles. Their ease in functionalization, biocompatibility, and intrinsic fluorescence enable those modalities. However, GQDs lack deep tissue magnetic resonance imaging (MRI) capabilities desirable for diagnostics. Considering that the drawbacks of MRI contrast agent toxicity are still poorly addressed, we develop novel Mn2+ or Gd3+ doped nitrogen-containing graphene quantum dots (NGQDs) to equip the GQDs with MRI capabilities and at the same time render contrast agents biocompatible. Water-soluble biocompatible Mn-NGQDs and Gd-NGQDs synthesized via single-step microwave-assisted scalable hydrothermal reaction enable dual MRI and fluorescence modalities. These quasi-spherical 3.9–6.6 nm average-sized structures possess highly crystalline graphitic lattice structure with 0.24 and 0.53 atomic % for Mn2+ and Gd3+ doping. This structure ensures high in vitro biocompatibility of up to 1.3 mg ml−1 and 1.5 mg ml−1 for Mn-NGQDs and Gd-NGQDs, respectively, and effective internalization in HEK-293 cells traced by intrinsic NGQD fluorescence. As MRI contrast agents with considerably low Gd and Mn content, Mn-NGQDs exhibit substantial transverse/longitudinal relaxivity (r 2/r 1) ratios of 11.190, showing potential as dual-mode longitudinal or transverse relaxation time (T 1 or T 2) contrast agents, while Gd-NGQDs possess r 2/r 1 of 1.148 with high r 1 of 9.546 mM−1 s−1 compared to commercial contrast agents, suggesting their potential as T1 contrast agents. Compared to other nanoplatforms, these novel Mn2+ and Gd3+ doped NGQDs not only provide scalable biocompatible alternatives as T1/T2 and T1 contrast agents but also enable in vitro intrinsic fluorescence imaging.

Role of assisting reagents on the synthesis of α-Fe2O3 by microwave-assisted hydrothermal reaction

Currently, the controlled synthesis of well-defined metal oxide nanoparticles has received intense scientific attention to modulate the properties of materials through the size and shape. This paper focuses on providing a better understanding about the growth, morphology, size, and crystal structure of α-Fe2O3 nanoparticles synthesized by a microwave-assisted hydrothermal route, considering a detailed analysis of the influence of the reaction temperature, time, and ratio of assisting reagents (sodium citrate and urea) as well as the effects of calcination temperature. According to X-Ray Diffraction analysis, the α-Fe2O3 crystalline phase was directly prepared at 200 °C for 60 min using only urea, while materials with low crystallinity were obtained using only sodium citrate as well as sodium citrate:urea (in both ratio 1:1 and 2:2.5). Upon calcination at 600 °C, the crystallization of α-Fe2O3 started in the material prepared with a sodium citrate:urea ratio of 2:2.5. Scanning and Transmission Electron Microscopies results revealed that the materials synthesized using urea, sodium citrate, and sodium citrate:urea ratio of 1:1 are formed by nanoparticles less than 100 nm without a defined morphology, whereas the materials prepared using sodium citrate:urea ratio of 2:2.5 showed well-defined nanospheres with average sizes between 150 and 250 nm constituted by self-assembled crystals smaller than 10 nm. The shape and size of the nanospheres did not undergo significant changes even at high thermal treatments, such as 800 °C. Based on equilibrium diagrams, the role of each chemical agent was disclosed, indicating that the modulated precipitation through soluble complexes is a very important factor in controlling the hierarchical organization of the particles to form the nanospheres. This study demonstrates the versatility of sodium citrate and urea as assisting reagents to prepare a variety of α-Fe2O3 nanoparticles. Besides, these results could be useful in extending new ideas for the synthesis of other nanomaterials.

Multi-Photonic behavior of Nb2O5 and its correlation with synthetic methods

The performance of niobium pentoxide (Nb2O5) as photoanodes in dye-sensitized solar cells (DSSCs) and as catalysts in the photocatalytic degradation of Rhodamine B (RhB) was investigated. Four samples of Nb2O5 (Nb2O5_SG, Nb2O5_CR, Nb2O5_PP, and Nb2O5_MA) were synthesized by four different methods, respectively, entailing the sol-gel, combustion, polymeric precursors, and a microwave-assisted hydrothermal reaction. In all these samples, the orthorhombic phase of Nb2O5 was obtained, which resulted in different shapes and assemblies, which is very relevant because the surface area, shape, and size distribution of the nanoparticles significantly contribute to the optical process. The bandgap remained constant at 3.0 eV for all the samples, even for the sample prepared by the combustion method. An additional phase, which is related to local distortions, was revealed by Raman spectroscopy within the vibration range of 688–260 cm−1. DSSCs using photoanodes with smaller and more dispersed Nb2O5 particles showed better results than those with inhomogeneities. For comparison, DSSCs were assembled using two different counter electrodes, platinum and graphite. The DSSC with platinum showed better photovoltaic results, mainly with photocurrents from 1.17 mA.cm−2 for Nb2O5_CR to 1.64 mA.cm−2 for Nb2O5_SG. The same trend was observed for the photocatalytic degradation of RhB, where the smaller and dispersed particles of Nb2O5_CR and Nb2O5_SG exhibited the best performance and, respectively, degraded approximately 75% and 61% of the RhB dye over 180 min. Therefore, the results of this study established a correlation between the synthesis methods and photonic behavior.

A flexible fibrous membrane based on copper(II) metal-organic framework/poly(lactic acid) composites with superior antibacterial performance.

A flexible antibacterial fibrous membrane employing high antibacterial efficiency has great potential in healthcare applications. Herein, a three-dimensional copper(ii) metal-organic framework [Cu2(CA)(H2O)2, Cu-MOF-1] and poly(lactic acid) (PLA) composite fibrous membrane was prepared through a facile electrospinning method. The sphere-like Cu-MOF-1 was rapidly synthesized by a microwave-assisted hydrothermal reaction of Cu(ii) salts with citric acid (H4CA) in the presence of polyvinyl pyrrolidone (PVP). The surface morphology, thermal stability, mechanical properties and hydrophilicity test of the as-prepared Cu-MOF-1/PLA fibrous membrane were studied systematically. Compared with commercial copper nanoparticles (Cu-NPs), citric acid and copper citrate, Cu-MOF-1 showed higher antibacterial properties with the bacteriostatic rates of 97.9% and 99.3% against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), respectively, when the used dose was 250 μg mL-1. The Cu-MOF-1/PLA fibrous membrane also exhibited outstanding bactericidal activities against E. coli and S. aureus with the antibacterial rates up to 99.3% and 99.8%, respectively. Mechanism investigation indicated that the slowly released Cu2+ ions could destroy the microenvironment of bacteria cells and destroy the integrity and permeability of the cell membrane, leading to enzyme inactivation. Therefore, the as-prepared flexible fibrous membrane will advance progress toward developing a broad spectrum antibacterial textile for healthcare protection related applications.

Manganese–nitrogen and gadolinium–nitrogen Co-doped graphene quantum dots as bimodal magnetic resonance and fluorescence imaging nanoprobes

Graphene quantum dots (GQDs) are unique derivatives of graphene that show promise in multiple biomedical applications as biosensors, bioimaging agents, and drug/gene delivery vehicles. Their ease in functionalization, biocompatibility, and intrinsic fluorescence enable those modalities. However, GQDs lack deep tissue magnetic resonance imaging (MRI) capabilities desirable for diagnostics. Considering that the drawbacks of MRI contrast agent toxicity are still poorly addressed, we develop novel Mn2+ or Gd3+ doped nitrogen-containing graphene quantum dots (NGQDs) to equip the GQDs with MRI capabilities and at the same time render contrast agents biocompatible. Water-soluble biocompatible Mn-NGQDs and Gd-NGQDs synthesized via single-step microwave-assisted scalable hydrothermal reaction enable dual MRI and fluorescence modalities. These quasi-spherical 3.9–6.6 nm average-sized structures possess highly crystalline graphitic lattice structure with 0.24 and 0.53 atomic % for Mn2+ and Gd3+ doping. This structure ensures high in vitro biocompatibility of up to 1.3 mg ml−1 and 1.5 mg ml−1 for Mn-NGQDs and Gd-NGQDs, respectively, and effective internalization in HEK-293 cells traced by intrinsic NGQD fluorescence. As MRI contrast agents with considerably low Gd and Mn content, Mn-NGQDs exhibit substantial transverse/longitudinal relaxivity (r 2/r 1) ratios of 11.190, showing potential as dual-mode longitudinal or transverse relaxation time (T 1 or T 2) contrast agents, while Gd-NGQDs possess r 2/r 1 of 1.148 with high r 1 of 9.546 mM−1 s−1 compared to commercial contrast agents, suggesting their potential as T1 contrast agents. Compared to other nanoplatforms, these novel Mn2+ and Gd3+ doped NGQDs not only provide scalable biocompatible alternatives as T1/T2 and T1 contrast agents but also enable in vitro intrinsic fluorescence imaging.

Excess oxygen in delafossite CuFeO2+δ: Synthesis, characterization, and applications in solar energy conversion

As an alternative to high-temperature oxidation, the present study demonstrates a new approach to the intercalation of excess O into 3R-delafossite CuFeO2, based on a non-equilibrium hydrothermal synthesis. At lower temperatures, or during the initial stage of this hydrothermal reaction, a large amount of excess O remains between the self-assembled block layers, owing to the incomplete reduction of propionaldehyde in the hydrothermal process. This work not only confirmed the presence of this excess O and quantified the excess O concentrations, but also established the mechanism by which non-stoichiometric CuFeO2+δ is generated, on the basis of experimental observations and theoretical calculations. Normally, highly crystalline CuFeO2+δ prepared using the conventional hydrothermal process only contains low levels of excess O, but the present work shows that this problem can be mitigated by employing a microwave-assisted hydrothermal reaction. This technique can rapidly synthesize high quality 3R-delafossite CuFeO2+δ containing elevated concentrations of excess O. Electronic structures calculated based on density functional theory showed that CuFeO2+δ should exhibit half-metallic ferromagnetism and multiple band gaps. Systematic experimental characterization and theoretical calculations were used to elucidate the manner in which excess O significantly affects the microstructure of this material, while enhancing the electrical, optical and electrochemical properties of CuFeO2. As a result of these enhancements, this material is suitable for the improvement of solar energy conversion. Photoelectrochemical trials and data from the photocatalytic performances confirm these properties, suggesting that non-stoichiometric 3R-delafossite CuFeO2+δ compounds have potential applications in solar energy conversion.

A High-Temperature Na-Ion Battery: Boosting the Rate Capability and Cycle Life by Structure Engineering.

High-temperature sodium ion batteries (SIBs) have drawn significant heed recently for large-scale energy storage. Yet, conventional SIBs are in the depths of inferior charge/discharge efficiency and cyclability at elevated temperatures. Rational structure design is highly desirable. Hence, a 3D hierarchical flower architecture self-assembled by carbon-coated Na3 V2 (PO4 )3 (NVP) nanosheets (NVP@C-NS-FL) is fabricated via a microwave-assisted glycerol-mediated hydrothermal reaction combined with a post heat-treatment. The growth mechanism of NVP@C-NS-FL is systematically investigated, by forming a microspherical glycerol/polyglycerol-NVP complex initially and then converting into flower-like architecture during the subsequent annealing at a low temperature ramping rate. Benefiting from the integrated structure, fast Na+ transportation, and highly effective heat transfer, the as-obtained NVP@C-NS-FL exhibits an excellent high-temperature SIB performance, e.g., 65 mAh g-1 (100 C) after 1000 cycles under 60 °C. When coupled with NaTi2 (PO4 )3 anode, the full cell can still display superior power capability of 1.4 kW kg-1 and long-term cyclability (2000 cycles) under 60 °C.

High-efficiency As(III) oxidation and electrocoagulation removal using hematite with a charge−discharge technique

Arsenite (As(III)) is generally removed by adsorption or coprecipitation after being oxidized to arsenate (As(V)). Electrocoagulation is regarded as an effective and environment-friendly method for arsenic (As) removal from wastewater. However, some disadvantages including the passivation of electrode and high energy consumption limit its wide application. Herein, a multi-cycle galvanostatic charge−discharge technique was employed to remove aqueous As(III) using hematite prepared through a microwave-assisted hydrothermal reaction. When charge−discharge experiments were conducted at the potential window of −0.8–0 V (vs. SCE) in As(III) solution with NaCl as the background electrolyte, ClO− intermediates and the counter electrode at high potential contributed much to As(III) oxidation. As(V) was adsorbed on ferrihydrite generated from the re-oxidation of released Fe2+, forming FeAsO4 precipitate. A higher removal ratio of As(T) was achieved at initial pH 7.0 compared with that at initial pH 5.0 and 9.0. When the hematite mass was 4, 10 and 15 mg, the removal ratio of As(T) reached 55.2%, 79.6% and 98.6% after 600 cycles of charge−discharge. The periodic redox reactions of hematite electrodes occurred in each charge−discharge process, effectively avoiding the passivation of electrode. Additionally, the electrochemical system can be used as a supercapacitor for power output. The present work provides a novel strategy for high-efficiency As(III) immobilization and removal from aqueous solution.

Microwave-Assisted Synthesis of High-Energy Faceted TiO2 Nanocrystals Derived from Exfoliated Porous Metatitanic Acid Nanosheets with Improved Photocatalytic and Photovoltaic Performance.

A facile one-pot microwave-assisted hydrothermal synthesis of rutile TiO2 quadrangular prisms with dominant {110} facets, anatase TiO2 nanorods and square nanoprisms with co-exposed {101}/[111] facets, anatase TiO2 nanorhombuses with co-exposed {101}/{010} facets, and anatase TiO2 nanospindles with dominant {010} facets were reported through the use of exfoliated porous metatitanic acid nanosheets as a precursor. The nanostructures and the formation reaction mechanism of the obtained rutile and anatase TiO2 nanocrystals from the delaminated nanosheets were investigated. The transformation from the exfoliated metatitanic nanosheets with distorted hexagonal cavities to TiO2 nanocrystals involved a dissolution reaction of the nanosheets, nucleation of the primary [TiO6]8− monomers, and the growth of rutile-type and anatase-type TiO2 nuclei during the microwave-assisted hydrothermal reaction. In addition, the photocatalytic activities of the as-prepared anatase nanocrystals were evaluated through the photocatalytic degradation of typical carcinogenic and mutagenic methyl orange (MO) under UV-light irradiation at a normal temperature and pressure. Furthermore, the dye-sensitized solar cell (DSSC) performance of the synthesized anatase TiO2 nanocrystals with various morphologies and crystal facets was also characterized. The {101}/[111]-faceted pH2.5-T175 nanocrystal showed the highest photocatalytic and photovoltaic performance compared to the other TiO2 samples, which could be attributed mainly to its minimum particle size and maximum specific surface area.

Zinc ions pillared vanadate cathodes by chemical pre-intercalation towards long cycling life and low-temperature zinc ion batteries

Recently, aqueous zinc ion batteries have emerged as attracting alternatives to conventional lithium ion batteries with the merits of low cost and operation safety. However, the Zn host material with fast Zn kinetic and could sustain reversible Zn2+ insertion and extraction is still a big challenge. Here, a nanowire morphology (NH4)2V6O16·1.5H2O nanostructures fabricated via a facile microwave-assisted hydrothermal reaction are presented as a prospective zinc ion battery cathode. The trapped Zn(H2O)62+ ions in the initial discharge process not only help make the vanadium oxide layer stable but also provide enough interlayer distance for fast ion kinetics during the preceding intercalation/deintercalation process. Owing to the large interplane distance pillared by cations, crystal water molecular and the high diffusion coefficient of (NH4)2V6O16·1.5H2O cathode, it presents an excellent low temperature performance (120 mAh g−1 at a current density of 0.1 A g−1) and highly reversible cycling performance (75% after 10000 cycles at 8 A g−1). The outstanding performance, the easy fabrication along with the low-cost feature make (NH4)2V6O16·1.5H2O cathode reliable in aqueous zinc ion battery application.

One-Pot Synthesis of Titanate Nanotubes Decorated with Anatase Nanoparticles Using a Microwave-Assisted Hydrothermal Reaction

A nanoheterostructure of titanate nanotubes decorated with anatase nanoparticles (TiNT@AnNP) was synthesized for the first time by a microwave-assisted hydrothermal one-pot reaction. Characterization by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, selected-area electron diffraction, and X-ray photoelectron spectroscopy showed highly crystalline and nanometer-sized TiNT@AnNP. The synthesized TiNT@AnNP degraded an anionic dye (Remazol blue) more efficiently under UV-visible light (380–780 nm) than a commercial anatase-TiO2 precursor. We correlated this increased efficiency of photodegradation to the large surface area and the efficient separation of photoinduced electron-hole pairs. Finally, we propose a mechanism to highlight the influence of a microwave-assisted hydrothermal synthesis in the production of TiNT@AnNP for environmental applications.