Preparation of nano-TiO_2/diatomite-based porous ceramics and their photocatalytic kinetics for formaldehyde degradation

Diatomite-based porous ceramics were adopted as carriers to immobilize nano-TiO_2 via a hydrolysis-deposition technique. The thermal degradation of as-prepared composites was investigated using thermogravimetric–differential thermal analysis, and the phase and microstructure were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy. The results indicated that the carriers were encapsulated by nano-TiO_2 with a thickness of 300–450 nm. The main crystalline phase of TiO_2 calcined at 650℃ was anatase, and the average grain size was 8.3 nm. The FT-IR absorption bands at 955.38 cm^(-1) suggested that new chemical bonds among Ti, O, and Si had formed in the composites. The photocatalytic(PC) activity of the composites was investigated under UV irradiation. Furthermore, the photodegradation kinetics of formaldehyde was investigated using the composites as the cores of an air cleaner. A kinetics study showed that the reaction rate constants of the gas-phase PC reaction of formaldehyde were κ = 0.576 mg·m^(–3)·min^(–1) and K = 0.048 m^3/mg.

Preparation and photo-catalytic activity of TiO_2-coated medical stone-based porous ceramics

Medical stone-based porous ceramics as a carrier were prepared by ultra-fine grinding and low-temperature sintering method. Nano-TiO2 thin films were loaded on the carrier by chemical liquid deposition method using titanium tetrachloride as a precursor. The micro-morphology and microstructure of the synthesized samples were characterized using X-ray diffraction, scanning electron microscopy with energy dispersive spectrometry, and mercury injection method. The photo-catalytic activity of the TiO2 thin films was investigated by degrading formaldehyde. The main crystalline phase in the TiO2 thin films calcined at 550 C is anatase with the average particle size about 10nm. The specific surface area of the carrier-coated nano-TiO2 increases from 3.68 to 5.32 m2/g. The formaldehyde removal rate of the TiO2/medical stone-based porous ceramics irradiated under an ultraviolet lamp for 120min reaches 85.6%.

Morphology characterization of periclase–hercynite refractories by reaction sintering

A periclase?hercynite brick was prepared via reaction sintering at 1600°C for 6 h in air using magnesia and reaction-sintered hercynite as raw materials. The microstructure development of the periclase?hercynite brick during sintering was investigated using X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy. The results show that during sintering, Fe2+, Fe3+ and Al3+ ions in hercynite crystals migrate and react with periclase to form(Mg1-xFex)(Fe2-yAly)O4 spinel with a high Fe/Al ratio. Meanwhile, Mg2+ in periclase crystals migrates into hercynite crystals and occupies the oxygen tetrahedron vacancies. This Mg2+ migration leads to the formation of(Mg1-uFeu)(Fe2-vAlv)O4 spinel with a lower Fe/Al ratio and results in Al3+ remaining in hercynite crystals. Cation diffusion between periclase and hercynite crystals promotes the sintering process and results in the formation of a microporous structure.

Tunable fabrication of single-crystalline CsPbI_(3) nanobelts and their application as photodetectors

Lead halide perovskites have received increasing attention recently as a candidate material in various optoelectronic areas because of their high performance as light absorbers.Herein,we report the growth of CsPbI_(3) nanobelts via a solution process.A single-crystalline CsPbI_(3) nanobelt with uniform morphology can be achieved by controlling the amount of PbI_(2).A single-crystalline CsPbI_(3) nanobelt possesses a mean width,length,and thickness of 100 nm,5μm,and 20 nm,respectively.In this work,photodetectors(PDs)based on individual CsPbI_(3) nanobelts are constructed and found to perform well with an external quantum efficiency and responsivity of 2.39×10^(5)% and 770 A/W,respectively.The PDs also show a high detectivity of up to 3.12×10^(12) Jones,which is at par with that of Si PDs.The PDs developed in this work exhibit great promise in various optoelectronic nanodevices.

Microwave absorption properties of SiC@SiO2@Fe3O4 hybrids in the 2–18 GHz range

To enhance the microwave absorption performance of silicon carbide nanowires(SiCNWs), SiO_2 nanoshells with a thickness of approximately 2 nm and Fe_3O_4 nanoparticles were grown on the surface of SiCNWs to form SiC@SiO_2@Fe_3O_4 hybrids. The microwave absorption performance of the SiC@SiO_2@Fe_3O_4 hybrids with different thicknesses was investigated in the frequency range from 2 to 18 GHz using a free-space antenna-based system. The results indicate that SiC@SiO_2@Fe_3O_4 hybrids exhibit improved microwave absorption. In particular, in the case of an SiC@SiO_2 to iron(III) acetylacetonate mass ratio of 1:3, the microwave absorption with an absorber of 2-mm thickness exhibited a minimum reflection loss of-39.58 d B at 12.24 GHz. With respect to the enhanced microwave absorption mechanism, the Fe_3O_4 nanoparticles coated on SiC@SiO_2 nanowires are proposed to balance the permeability and permittivity of the materials, contributing to the microwave attenuation.

Dissolution and diffusion of TiO_2 in the CaO-Al_2O_3-SiO_2 slag

The dissolution of TiO2 in the CaO-Al2O3-SiO2 slag under static conditions was studied in the temperature range from 1643 K to 1703 K. After TiO2 dissolved, the microstructure of the interface between TiO2 and the slag was observed by scanning electron microscopy, and the concentration profiles of Ti4+ and other ions across the TiO2/slag interfaces were analyzed by energy-dispersive X-ray spectroscopy. On the basis of these results, the dissolution behavior of TiO2 was evaluated, and the diffusivity of Ti4+ in the bulk slag was estimated. According to the Stokes–Einstein relation, the viscosity calculated by a previously reported model gave a diffusivity of Ti4+ ions greater than that estimated by the concentration profiles of Ti4+ ions. The mechanism of TiO2 dissolution in the CaO-Al2O3-SiO2 slag is discussed in detail.

Reaction mechanisms for 0.5Li_2MnO_3 ·0.5LiMn_(0.5)Ni_(0.5)O_2 precursor prepared by low-heating solid state reaction

Lithium-excess manganese layered oxides, which are commonly described in chemical formula 0.5Li2MnO3 ·0.5LiMn0.5Ni0.5O2 , were prepared by low-heating solid state reaction. The reaction mechanisms of synthesizing precursors, the decomposition mechanism, and intermediate materials in calcination were investigated by means of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The major diffraction patterns of 0.5Li2MnO3 ·0.5LiMn0.5Ni0.5O2 powder calcinated at 720°C for 15 h are indexed to the hexagonal structure with a space group of R 3m , and the clear splits of doublets at (006)/(102) and (108)/(110) indicate that the sample adopts a well-layered structure. FESEM images show that the size of the agglomerated particles of the sample ranges from 100 to 300 nm.

Molten salt synthesis of mullite nanowhiskers using different silica sources

Mullite nanowhiskers with Al-rich structure were prepared by molten salt synthesis at 1000°C for 3 h in air using silica, amorphous silica, and ultrafine silica as the silica sources. The phase and morphology of the synthesized products were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy. A thermogravimetric and differential thermal analysis was carried out to determine the reaction mechanism. The results reveal that the silica sources play an important role in determining the morphology of the obtained mullite nanowhiskers. Clusters and disordered arrangements are obtained using common silica and amorphous silica, respectively, whereas the use of ultrafine silica leads to highly ordered mullite nanowhiskers that are 80-120 nm in diameter and 20-30 μm in length. Considering the growth mechanisms, mullite nanowhiskers in the forms of clusters and highly ordered arrangements can be attributed to heterogeneous nucleation, whereas disordered mullite nanowhiskers are obtained by homogenous nucleation.

Supercapacitor electrode based on few-layer h-BNNSs/rGO composite for wide-temperature-range operation with robust stable cycling performance

Currently,developing supercapacitors with robust cycle stability and suitability for wide-temperature-range operations is still a huge challenge.In the present work,few-layer hexagonal boron nitride nanosheets(h-BNNSs)with a thickness of 2−4 atomic layers were fabricated via vacuum freeze-drying and nitridation.Then,the h-BNNSs/reduced graphene oxide(rGO)composite were further prepared using a hydrothermal method.Due to the combination of two two-dimensional(2D)van der Waals-bonded materials,the as-prepared h-BNNSs/rGO electrode exhibited robustness to wide-temperature-range operations from−10 to 50℃.When the electrodes worked in a neutral aqueous electrolyte(1 M Na2SO4),they showed a great stable cycling performance with almost 107%reservation of the initial capacitance at 0℃ and 111% at 50℃ for 5000 charge−discharge cycles.

Review of electrochemical degradation of phenolic compounds

Phenolic compounds are widely present in domestic and industrial sewage and have serious environmental hazards.Electrochemical oxidation(EO)is one of the most promising methods for sewage degradation because of its high efficiency,environmental compatibility,and safety.In this work,we present an in-depth overview of the mechanism and factors affecting the degradation of phenolic compounds by EO.In particular,the effects of treatment of phenolic compounds with different anode materials are discussed in detail.The non-active anode shows higher degradation efficiency,less intermediate accumulation,and lower energy consumption than the active anode.EO combined with other treatment methods(biological,photo,and Fenton)presents advantages,such as low energy consumption and high degradation rate.Mean-while,the remaining drawbacks of the EO process in the phenolic compound treatment system have been discussed.Furthermore,future re-search directions are put forward to improve the feasibility of the practical application of EO technology.

Thermal oxidation of SiAlON powders synthesized from coal gangue

The oxidation behavior of different SiAlON phases(β-SiAlON,X-phase SiAlON and 12H powders) synthesized from coal gangue in air atmosphere was investigated using isothermal thermogravimetry(TG) and field-emission scanning electron microscopy(FE-SEM).The effect of ferric oxide impurities in coal gangue was studied.The results show that ferric oxide contributes to the growth of SiAlON crystalline during the synthesis process.In the oxidation experiment,the existence of ferric oxide decreases the oxidation resistance of SiAlON.The reason is that the impurity causes the formation of a liquid phase at a higher temperature.At 1423-1623 K,the oxidation of SiAlON powders is diffusion controlled and it can be described by Chou's model.A fair agreement is found between theoretical calculations and the experimental data.

Effect of w(MgO)/w(Al_(2)O_(3)) ratio and basicity on microstructure and metallurgical properties of blast furnace slag

The CaO–SiO_(2)–Al_(2)O_(3)–MgO system is the main component unit in the slag formation process in blast furnace smelting.Its structural changes directly affect the high-temperature metallurgical properties of slag.Molecular dynamics simulations were thus conducted to analyze the microstructure changes of the quaternary slag system under different basicities and w(MgO)/w(Al_(2)O_(3))ratios.The changes in w(MgO)/w(Al_(2)O_(3))ratio and basicity could affect the stability of each ion-oxygen.Increasing the basicity and w(MgO)/w(Al_(2)O_(3))ratio,the average coordination number of O surrounding Si atom only changed a little and remained approximately 4,indicating that Si exists as a stable structure of the[SiO4]4−tetrahedron in the slag structure,while the average coordination number of O surrounding Al atom changed greatly from 4 to 6,which indicated that the Al existence form could be transformed from[AlO_(4)]^(5−) tetrahedron to[AlO_(5)]^(7−) pentahedron and[AlO_(6)]^(9−) octahedron.Also,the diffusion rate of ions was accelerated with the increase in w(MgO)/w(Al_(2)O_(3))ratio and basicity.Moreover,the self-diffusion coefficients of each ion were obtained,and the magnitudes were observed to be in the following order:Mg^(2+)>Ca^(2+)>Al^(3+)>Si^(4+).The calculation and analysis of the slag viscosity and activation energy of viscous flow under different basicities and w(MgO)/w(Al_(2)O_(3))ratios revealed that the metallurgical properties of slag at high temperature depend on the flow-unit diffusivity and the microstructure stability,simultaneously,the basicity should be controlled between 1.0 and 1.2,and the w(MgO)/w(Al_(2)O_(3))ratio could be controlled between 0.45 and 0.55.

High-performance chromite by structure stabilization treatment

Chromite is an important raw material applied in refractories.Efforts have been made to obtain high-performance chromite by adding MgO and Al203 from the viewpoint of structure optimization.In order to explore the effect of Al203 and MgO on the structure,two formulas,i.e.,Mg-rich and Al-rich ones,were selected.The phase and microstructure development of samples heated in the temperature range of 1200-1600℃ were studied by X-ray diffraction and scanning electron microscopy with energy-dispersive spectrometry.MgO and Al203 added have diffused into chromite successfully by heat treatment.MgO diffuses into chromite,occupying the tetrahedral vacancies caused by the diffusion and oxidation of Fe2+ions to stabilize the structure.Al203 diffuses into the surface layer of chromite,forming spinel-sesquioxide structure.Al-rich sample which has spinel-sesquioxide structure shows better corrosion resistance toward fayalite slag than Mg-rich sample which has single spinel structure by blocking the interdiffusion between Fe^2+ions in fayalite slag and Mg^2+ions in chromite.

Effect and mechanism of nano-Ca_(10)(PO_(4))_(6)(OH)_(2)additive on compressive strength of calcium aluminate cement at high temperature

Calcium aluminate cement(CAC)is widely used as a binder for refractory materials,and thus the improvement in compressive strength is of vital importance for CAC applied at high temperature.For this purpose,nano-Ca_(10)(PO_(4))_(6)(OH)_(2)additive with a ratio of 0.5–1.5 mass%was added with the water-cement ratio to be 0.4.X-ray diffraction and isothermal calorimetry analysis demonstrate that nano-Ca_(10)(PO_(4))_(6)(OH)_(2)additive can shorten the hydration process and promote the formation of main hydrates of CaAl2O4·10H2O(CAH10)and Ca2Al2O5·8H2O(C2AH8).In addition,scanning electron microscopy results suggest that nano-Ca_(10)(PO_(4))_(6)(OH)_(2)can protect CAH10 and C2AH8 from being destroyed during the calcination,guaranteeing that these thin lamellar crystals are intertwined to form the denser microstructure.Benefited from above effects,nano-Ca_(10)(PO_(4))_(6)(OH)_(2)can obviously improve the compressive strength of the CAC mortar samples cured for 7 d after calcination at 1100°C,while the improving effect is dependent upon its contents.Especially,compared with the one without the additive,the compressive strength of the sample with 1.0%nano-Ca_(10)(PO_(4))_(6)(OH)_(2)is increased by 14%.