High-temperature Thermal Treatment Research Articles

Enhanced visible-light induced photocatalytic activity in core-shell structured graphene/titanium dioxide nanofiber mats

Semiconductor photocatalysts suffer from low photocatalytic quantum efficiency, diminished solar energy utilization, and inadequate photostability, thereby impeding their widespread adoption. Meanwhile, graphene emerges as an ideal substrate material for fabricating high-performance composite photocatalysts owing to its distinctive single-layer sp2-hybridized carbon atom arrangement, substantial specific surface area, exceptional electron conductivity, and pronounced transparency. In this study, a graphene-anatase-rutile core-shell structured nanofiber mat architecture is successfully synthesized by sol-gel-assisted coaxial electrospinning with high-temperature thermal treatment. This innovative architecture effectively narrows the bandgap of TiO2 and synergizes adsorption and catalysis processes to achieve heightened catalytic efficiency and prolonged stability. Photocatalytic assays conducted under visible light irradiation demonstrate the excellent photocatalytic activity and stability of the graphene-titanium dioxide hybrid material during the degradation of phenol. The kinetics and mechanism of the phenol degradation of the nanofiber mat have been explored. Furthermore, the unique mesh-like configuration intrinsic to the nanofiber assembly confers sedimentation and recyclability upon the composite material.

Formation of volatile chlorinated and brominated products during low temperature thermal decomposition of the representative PFAS perfluorohexane sulfonate (PFHxS) in the presence of NaCl and NaBr

Per- and polyfluoroalkyl substances (PFAS) are synthetic organofluorine compounds known for their chemical and physical stability as well as their wide range of uses. Some PFAS are widely distributed in the environment, leading to concerns related to both environmental and human health. High temperature thermal treatment (i.e., incineration) has been utilized for PFAS treatment, but this requires significant infrastructure and energy, prompting interest in lower temperature approaches that may still lead to efficient destruction. Lower treatment temperatures, however, increase the potential for incomplete PFAS mineralization and formation of volatile organofluorine (VOF) products. Herein, we report the formation of novel VOF products that include chlorinated and brominated compounds during the thermal treatment of potassium perfluorohexane sulfonate (PFHxS), a representative perfluoroalkyl acid (PFAA). By comparing the gas chromatography-mass spectrometry (GC-MS) results of known VOF stocks to evolved VOF during thermal treatment of PFAS, the formation of perfluorohexyl chloride and perfluorohexyl bromide was observed when PFHxS was heated at temperatures between 275 and 475 °C in the presence of NaCl and NaBr, respectively. To our knowledge, this is the first report of chlorinated or brominated VOF products during thermal treatment of a PFAA. These findings suggest that a range of mixed halogenated VOF may form during thermal treatment of PFAS at relatively low temperature (e.g., 500 °C) and that these can be a function of salts present in the matrix.

Debundling and reorganization of CNT networks under high temperature treatment

Highly purified and uniformly distributed carbon nanotube (CNT) network is one of the key issues for developing advanced nanocomposites. However, the challenge for mitigation of the aggregation of CNT bundles during the CNT film fabrication still remained. In this work, debundling and reorganization of CNT bundles have been realized simultaneously by using a high-temperature thermal treatment. The debundling of large CNT bundles into small ones started after they were heat treated under 1400 °C and uniformly distributed CNT networks with small bundles were obtained after heat treated under 1800 °C. The tensile strength of the CNT film significantly increased by about 64% compared to the pristine film. Microstructural observations showed that the iron nanoparticles started to evaporate at 1400 °C and were completely removed at 1800 °C. Hollow amorphous carbon shells wrapped on the nanoparticles were left inside the CNT networks after the removal of the iron nanoparticles. Interestingly, these amorphous carbon shells act as carbon source for the deposition of a carbon layer on the CNT surface when the heat treatment temperature was up to 2000 °C, and they were completely consumed after being treated at 2800 °C. The microstructural evolution process of CNT bundles during heat treatment suggests the simple high-temperature treatment strategy could be applied for fabrication of highly purified CNT networks with well-distributed small bundles, enabling the development of advanced multifunctional nanocomposites in the near future.

Effect of high temperature thermal treatment on the electrochemical performance of natural flake graphite

Natural graphite is currently considered as a critical raw material in EU. The demand for graphite is still increasing as it is commonly used in the anodes of the Li-ion batteries (LIBs). The total graphite content for energy storage applications such as LIBs should be more than 99.95%. Several purification processes for natural graphite exist but the requirement of high purity is challenging. Here we present the high temperature thermal treatment for natural graphite ores. Thermal treatment at 2400 °C for 15 min can produce battery-grade graphite with high purity and crystallinity needed for the optimum performance of the battery cells. In addition, the crystallinity and crystalline structure of graphite was improved during the treatment. The electrochemical studies of thermally treated graphite powders showed increased electrochemical performance compared to the untreated graphite samples. The improved performance was attributed to the increased purity and crystallinity of the thermally treated powders.Graphical Effect of thermal purification on the electrochemical performance of natural flake graphite

Thermal decomposition mechanism and characterization of phosphogypsum in suspension under multifactor coupling effect

Phosphogypsum (PG) is solid waste generated by the phosphate fertilizer industry. However, by high-temperature thermal treatment, it can be effectively decomposed into byproducts like SO2 and CaO, which are valuable raw materials for the production of sulfuric acid and construction materials, respectively. In this study, we investigated the thermal decomposition properties of suspended PG, as well as the factors governing the PG decomposition procedure. The results show that the PG decomposition rate was influenced by several parameters, with temperature being the most significant, followed by time, atmosphere, and charcoal powder dosing. Similarly, the desulfurization rate was primarily influenced by time, followed by temperature, atmosphere, and charcoal powder dosing. The PG exhibited maximum decomposition and desulfurization rates of 97.73% and 97.2%, respectively, at a calcination temperature of 1180 °C, a calcination period of 15 min, a carbon powder dosage of 4%, and a CO concentration of 6%. Kinetic studies revealed that the activation energy of the PG decomposition reaction decreased from 303.45 to 254.28 kJ/mol as the CO concentration increased from 4% to 6% upon addition of charcoal powder as a reducing agent. Furthermore, higher CO concentrations had a more pronounced effect on lowering the activation energy of PG pyrolysis. When the contents of SiO2 and Al2O3 impurities in the PG content were higher, they reacted with CaO in the decomposition products to produce silicate and aluminate minerals, respectively, decreasing both the CaO content in the product and the PG decomposition rate.

Perovskite evolution on La modified Mn1.5Co1.5O4 spinel through thermal ageing with enhanced oxidation activity: Is sintering always an issue?

Non-precious metal oxides have great potential in catalytic deep oxidation of emitted hydrocarbons to help address various environmental pollution concerns. However, sintering issue is a stumbling block in practical application upon long-term high-temperature operation or thermal shock experience. Herein, La was applied to modify Mn1.5Co1.5O4 spinel to get a highly active oxidation catalyst with exceptional stability against high-temperature thermal ageing treatment. With thermal ageing at 750 °C for 100 h, the La modified Mn–Co composite reached 90 % conversion in toluene oxidation at 265 °C under the high WHSV of 120,000 mL g−1 h−1, while this value increased to 312 °C over blank Mn–Co spinel. The addition of La not only inhibited the growth of spinel nanocrystals, but also brought about perovskite formation through sintering, generating perovskite-spinel interfaces, thus enhancing both activity and stability. Meanwhile, the La modified Mn–Co spinel exhibited superior performance in presence of water or sulfur dioxide after thermal ageing treatment. This work offers a versatile strategy to design anti-sintering and active oxidation nanocatalysts based on non-precious metal oxides for industrial applications.

Efficient broadband yellow-emitting Mg2.5Lu1.5Al1.5Si2.5O12:Ce3+ garnet phosphors for blue-light-pumped white light-emitting diodes

The discovery of yellow-emitting phosphors with higher luminescence intensity and wider bandwidth than the commercial Y3Al5O12:Ce3+ (YAG:Ce3+) phosphor upon blue light excitation remains one of the significant challenges for establishing human-centered warm white light-emitting diode towards high-performance illumination. Herein, we innovatively synthesized a novel Ce3+-activated broadband yellow-emitting garnet phosphor of Mg2.5Lu1.5Al1.5Si2.5O12:Ce3+ (MLASO:Ce3+) via conventional high-temperature solid-state reaction method. The as-prepared MLASO:10%Ce3+ garnet sample possesses a cubic structure with Ia3‾d space group and lattice parameters of a = b = c = 11.85098 Å and V = 1664.421(0.044) Å3. Luminescence spectroscopy tests indicates that the optimal MLASO:10%Ce3+ yellow-emitting phosphor features 1.2 times higher relative integral luminescence intensity and an impressive full width at half maximum (FWHM) of up to 145 nm with respect to the most extensively available commercial YAG:Ce3+ phosphor (FWHM = 122 nm) under the identical blue light irradiation, which can provide more red-components for improving color rendering index. Additionally, the CIE color coordinates and a satisfactory internal quantum efficiency are determined to be (0.4751,0.5028) and 74%, respectively. More importantly, the representative optimal sample can preserve 77% luminescence emission intensity at a 423 K high temperature thermal treatment environment compared to the ambient temperature. As a result, this study sheds light on newly discovered broadband yellow-emitting MLASO:10%Ce3+ garnet phosphor containing more of the red chromatic spectrum can sever as one of the promising color-conversion-materials in high-performance white LEDs with high color rendering index for healthy solid-state lighting.

Investigation of Fracture Evolution and Failure Characteristics of Rocks under High-Temperature Liquid Nitrogen Interaction

The utilization of liquid nitrogen as a sustainable and water-free fracturing medium exhibits immense promise in engineering applications. In this investigation, Brazilian split tests and acoustic emission tests were conducted to explore the impact of liquid nitrogen cooling on the internal structure and mechanical properties of rock specimens. To examine the influence of liquid nitrogen cooling on the tensile strength of rocks, displacement-load curves were obtained from samples subjected to varying cycles of high-temperature liquid nitrogen cooling using Brazilian split tests. Acoustic emission experiments were conducted to investigate the characteristics of granite samples exposed to various cycles of high-temperature liquid nitrogen cooling. Based on these findings, the impact of liquid nitrogen cooling on the internal structure of rock masses was analyzed. The findings of this study demonstrate that high-temperature liquid nitrogen thermal treatment significantly modifies the microscopic structure and mechanical properties of rocks, with potential implications for overall stability and reliability. Notably, an observable decline in tensile strength was observed as the number of cycles of high-temperature liquid nitrogen treatment increased. These findings underscore the substantial impact of liquid nitrogen cooling on the behavior of rocks. High-temperature liquid nitrogen treatment effectively promotes the generation of microcracks within rocks, thereby increasing their permeability. During the experiment, granite specimens primarily exhibited shear-type fractures when subjected to high-temperature freeze-thaw cycles induced by liquid nitrogen.

The effects of high temperature thermal treatments on β-Ga2O3 films grown on c-sapphire by low-pressure CVD

As a simple and effective method for improving the crystalline quality of epitaxial Ga2O3 film, post-thermal treatment has been identified as a competitive process involving crystal reconstruction accompanied by defect formation. In this study, β-Ga2O3 films grown on a c-sapphire substrate using low-pressure chemical vapor deposition were subjected to thermal treatment at 1000 °C in air for various duration to investigate the effects of treatment time on the films. The full width at half maximum (FWHM) of x-ray rocking curves initially decreased from 1.62° to 0.98° with increasing treatment time up to 5 h, indicating improved crystallinity. This improvement is likely a result of the reduced angle between Ga2O3 grains and the reconstructed Ga2O3 lattice, oriented towards the (−201) plane due to the thermal treatment, as observed in the transmission electron microscope and electron back-scattering diffraction results. However, under 7 h of treatment, the crystallinity of Ga2O3 degraded, as evidenced by an increased FWHM, as well as by x-ray photoelectron spectroscopy, photoluminescence, and time-of-flight secondary ion mass spectrometry results. This degradation can be attributed to the presence of massive oxygen vacancies and the substitutional incorporation of nitrogen into oxygen sites (NO), resulting in defects.

Electrochemical Exfoliation and Thermal Deoxygenation of Pristine Graphene for Various Industrial Applications

The transition of graphene from the lab to consumer goods is still a challenging job that necessitates efficient and cost-effective large-scale graphene production. This study combines electrochemical exfoliation in an aqueous solution of sulfuric acid (1M H2SO[Formula: see text] and hydrogen peroxide (3% H2O[Formula: see text] followed by thermal deoxygenation at a temperature of 800[Formula: see text]C within the ambient environment. This method allows the inexpensive synthesis of pristine graphene for various industrial applications. X-Ray diffraction (XRD) results for pristine graphene showed a distinct peak at 2[Formula: see text] with a corresponding interplanar distance ([Formula: see text] of 3.3754 Å and a crystallite size of 18 nm. XRD statistics indicated that the crystal structure of the original graphene was preserved. The crystalline structure was recovered and the interplaner distance was decreased following the high temperature thermal reduction. According to Raman spectroscopy, the impurity degree (I[Formula: see text]/I[Formula: see text] region fraction of pristine graphene was 0.211. This indicates that the original graph produced by the current method has little distortion. Raman analysis shows that there is a linear red shift in peaks D-band (D), G-band (G), and second order of the D-band (2D) due to the increase in phonon–phonon nonlinear interactions with increasing temperature, so that peaks (D), (G) and (2D) shifts are shown. The majority of the functional groups were discovered to be eliminated after high temperature thermal treatment. The three-dimensional graphene sheet is highly defined and intricately coupled in the microstructure analysis, resulting in a laxer and porous structure. When treated at a temperature below 800[Formula: see text]C, there was only minor damage to the reduced graphene oxide (RGO) microstructure. The results of the Atom Force Microscope (AFM) demonstrated that the flaws spread over time from the layer boundaries and pores to the edges and eventually resulted in a separate RGO archipelago. According to TGA analysis, at temperatures up to 800[Formula: see text]C, the RGO sheet loses up to 45% of its weight.

Effect of low sintering temperature on the structural and magnetic properties of M-type strontium hexaferrite

A pure M-type strontium hexaferrite with nominal composition SrFe12O19 has been prepared via the modified conventional citrate precursor method.The entirework emphasizes on improvingthe standardof hexagonal ferrite without undergoing high-temperature thermal treatments. By incorporating some adjustments in processing conditions, the prepared sampleis sintered at 800 °C and 910 °C, identified through thermalgravimetric analysis(TGA/DTA). The impact of the low-temperature sintering process on structural, spectroscopic, and magnetic properties are investigated via using different characterization techniques like XRD, FESEM, FTIR, Raman spectroscopy (RS), and VSM respectively. The XRD confirmed the formation of the M-phasealong withsome impurities of Fe2O3 and these results are strongly supported via both FTIR and RS. Similarly, FESEM analysis confirmed the formation of densely packed grains some hexagonal platelets. The magnetic properties of SrM hexaferrites show the increment of saturation magnetization Ms from 81 emu/g to 92 emu/g as the sintering temperature increases from 800 °C to 910 °C. Apart from the higher Ms for SrM hexaferrite, the Hc values 107 Oe and 262 Oe respectively are the vital findings of this research. This rare nature of SrM hexaferrite signifies the erection of soft character in hard SrM hexaferrites. Moreover the abrupt increase in the squarenes ratio (SQR) from 0.26 to 0.54 represents the transformation from multidomains to single domain. Material with such properties can be utilized in switching devices, recording media, high frequency applications.

Comparative Study of the Synthesis of a Red Ceramic Pigment Using Microwave Heat Treatment

In this study, a new red ceramic pigment has been developed within a perovskite structure, and microwave heat treatments have been applied. Those red ceramic pigments within the YAlO3 system doped with chromium with the nominal composition Y0.98Al0.98Cr0.04O3 were synthesized by traditional routes and alternative methods like coprecipitation. Also, heat treatment has been studied comparing a traditional electric and microwave kiln. Different flux agents have been incorporated to improve the synthesis reaction. Prepared pigments have been characterized by X-ray diffraction (XRD) as having a predominant phase of perovskite structure, which is responsible for the red shade, and a minority garnet phase that causes more brown colorations. Studies by Ultraviolet-Visible spectroscopy gave rise to a series of absorption bands that indicate the presence of Cr(III) in the octahedral position corresponding to perovskite and Cr(IV) corresponding to garnet in both the octahedral and tetrahedral positions. The perovskite phase is favored with the use of flux mix, corroborating the UV-visible results and being more pronounced in traditional high temperature thermal treatments. The coprecipitation route has been studied to increase the reactivity of the particles given their nanometric size; however, this reactivity favors a greater appearance of undesirable garnet phases with both types of flux. Scanning Electron Microscopy (SEM) micrographs offer information obtained from the secondary electrons of predominantly cubic crystalline phases with sizes between 1 µm and 2 µm in pigments synthesized via the traditional method and sizes less than 1µm together with the glassy phase in pigments synthesized via coprecipitation. Microwave thermal treatments have been studied, obtaining pigments with a majority structure of perovskite and garnet at lower temperatures and relatively short synthesis times. The feasibility of use in porous single-fired ceramic glazes has been studied, whose chromatic coordinates have been collected using an Ultraviolet-Visible Spectrophotometer based on the CIEL*a*b* system.

Study on the effect of high temperature heat treatment of H2 on the pore structure of activated carbon

As a high-quality adsorbent, activated carbon is widely used in air purification, natural gas storage, sewage treatment, gas enrichment, and separation, etc. The pore microstructure of activated carbon directly affects the adsorption capacity. In this paper, the altered in the microstructure of activated charcoal before and after high-temperature treatment were investigated by high-temperature thermal treatment of activated charcoal at 600°C and 700°C under an H2 atmosphere. The results of low-temperature (77 K) nitrogen adsorption showed that after high-temperature H2 heat treatment, the pores of activated carbon would be ablated and the pore structure would be significantly changed. The specific surface area, micropore specific surface area, total pore volume, and micropore pore volume all increased, and the degree of enhancement was proportional to the temperature of the heat treatment. The pore size distribution of activated charcoal before and after heat treatment was analyzed by density functional theory, and it was concluded that the pore volume of activated carbon mesopores (2-4 nm) increased significantly after high-temperature heat treatment, which could effectively improve the adsorption and separation capacity of activated carbon in larger molecular systems.

Effects of Annealing on Surface Residual Impurities and Intrinsic Defects of β-Ga2O3

In this study, the effects of annealing on the surface residual impurities and intrinsic defects of unintentionally doped (UID) β-Ga2O3 are investigated by adopting high-temperature thermal treatments at 1000 °C for 1 h under vacuum and O2 ambience. It is found that the recovery between the divacancies VGa+VO and interstitials (Oi) occurs during annealing, and the residual impurities are identified as Si and Cr, which are repelled toward the surface during annealing. Interestingly, these impurities occupy the formation of Ga vacancies (VGa) near the surface formed by oxygen annealing, consequently weakening the relevant impurity scattering and improving carrier mobility. Moreover, the carrier density of the samples is explored using temperature-dependent Hall measurements, which show a slight reduction in both vacuum and oxygen annealing. This reduction might be a result of the VGa pushing the Fermi level away from the conduction band. In addition, the activation energy of Si ions occupying VGa(I) is lower than that of the interstitial Si ions.

Numerical analysis of plasma gasification of hazardous waste using Aspen Plus

The COVID-19 pandemic raised the problem of dealing with the hazardous wastes generated. The World Health Organization (OMS) recommends the treatment of these wastes at high temperatures in order to neutralize their negative impact. For this reason, the main objective of this work is the development and analysis of a sustainable way to treat hazardous wastes generated by the COVID-19 pandemic. Thus, to achieve that goal, this paper presents an improved computational model that replicates a high-temperature thermal treatment system for COVID-19 wastes using plasma gasification in Aspen Plus V12.2. The distinctive aspect of the present plasma gasification model is the inclusion of an extra Gibbs reactor in order to enhance the calorific value of the syngas. The model validation results show an increase in the CO and CH4 molar fractions and a decrease of the H2 and CO2 molar fractions, which allows to increase the calorific value of the syngas from 4.97 to 5.19 MJ/m3. The most common types of hazardous waste generated during the pandemic were determined to be masks and syringes. COVID-19 waste from Turkey, discarded masks from Indonesia, Korea, and Lithuania, and Chinese syringes were used as feedstock into the computational model. The results suggest that the hazardous waste that allows for higher hydrogen molar fractions is Korean masks. On the other hand, the highest carbon monoxide molar fractions are obtained with medical waste from Turkey, while the highest molar fractions of methane are obtained with medical waste from Lithuania. A conclusion could be drawn that the lowest syngas calorific value is obtained with medical wastes from Turkey, while the highest syngas calorific value is obtained with medical wastes from Korea.

Three-dimensional porous nitrogen-doped carbon nanosheets with ultra-high surface area for high-performance oxygen reduction reaction electrocatalysts

A series of three-dimensional (3D) porous nitrogen-doped carbon nanosheets (PNCNs) have been successfully fabricated via a high-pressure carbonization followed by high-temperature thermal treatment. With the prolonging of thermal treatment time, the 3D PNCNs demonstrate several remarkable advantages for oxygen reduction reaction (ORR) electrocatalysts, including ultra-high specific surface area (more than 2100 m2/g−1), unique 3D porous structure, abundant defects, and suitable configuration of nitrogen. With these merits, the N-C-2 h based electrocatalyst exhibits outstanding ORR activities with a comparable onset potential of −40 mV (vs. Ag/AgCl), half-wave potential of −120 mV (vs. Ag/AgCl), satisfactory electron transfer number (4) and superior stability to those of commercial 20% Pt/C. The excellent electrochemical behaviors of 3D PNCNs are confirmed to be dominated by structural characteristics, which can be optimized by varying thermal treatment time. Our work offers a promising way for controllably constructing carbon-based materials with optimized ORR performance.

Facile synthesis and excellent electromagnetic wave absorption properties of Air@RGO/CoNi hollow microspheres

The rational synergy of chemical composition and spatial nanostructures plays an important role in high-performance electromagnetic wave (EMW) absorption materials. Here, reduced graphene oxide (RGO) hollow microspheres loaded with CoNi alloy nanoparticles (Air@RGO/CoNi) were constructed by a facile water-in-oil emulsification route followed by high-temperature thermal treatment. The crystal structure, composition, microstructure, and magnetic properties of Air@RGO/CoNi were characterized by XRD, XPS, TEM, and VSM, respectively. The results demonstrated that the as-obtained Air@RGO/CoNi composites showed a uniform spherical morphology with a remarkably hollow structure. Impressively, nano-CoNi particles were compactly and uniformly distributed on the surface of RGO. Benefiting from the unique structure and compositional merits, the optimized Air@RGO/CoNi hollow microspheres exhibit superior (EMW) absorption performance. The minimum reflection loss (RLmin) value reached up to −56.16 dB at 13.67 GHz with a thin thickness of 2.55 mm and the widest effective absorption bandwidth (RL values are below −10 dB) covered 8.65 GHz (9.15–17.8 GHz) with a thinner thickness of 2.4 mm. Furthermore, possible EMW attenuation mechanisms had been proposed. Given these outstanding findings, we believe the as-fabricated Air@RGO/CoNi hollow microspheres can be promising candidates as highly microwave absorption materials with thin thickness, wide absorption bandwidth, and high absorption capacity.

Experimental study on the nonlinear flow characteristics of fractured granite after high-temperature cycling

To understand the influence of temperature on the flow characteristics of fractured granite, high-temperature cyclic thermal treatment and flow tests on the fractured rock sample with different joint roughness coefficients and intact rock samples were conducted. The larger confining pressure and larger joint roughness coefficient will increase the resistance of fluid flow and affect the flow characteristics of the fluid. With the temperature increasing, the aperture of the fractures, the number of micro-fractures, and micropores increase which forms a large number of new connected hydraulic channels in the matrix. Forchheimer's law and Izbash equation can well describe the nonlinear flow characteristics, and the fitting coefficients are greater than 0.99. As the increasing temperature, the slope of the curve between the volumetric flow rate and pressure gradient gradually decreases, and the coefficients in Forchheimer's law and the Izbash equation decrease. The transmissivity decrease with the increasing Reynolds number and the change range of that increase with the increasing temperature. When the temperature is at the lower level (T = 200 ~ 600 °C), the contribution of split fracture to the permeability is greater than that of the matrix. When the temperature continuously increases to 800 °C, the contribution of the matrix to the permeability gradually rises and then exceeds that of split fracture. The results indicate that 400 °C is the critical temperature, after which the flow characteristics of fractured granite after high-temperature cycling change more obviously.

Electrospinning synthesis and characterization of zirconia nanofibers annealed at different temperatures

The main goal of this study was to produce, in a two-step process, ceramic nanofibers, which were obtained by electrospinning of composite fibrous mats and high-temperature thermal treatment at temperatures of 500 and 600 °C. The next step was to determine the effect of the nanofibers calcination temperature on the morphology and surface, structural and optical properties and photocatalytic activity of zirconia nanostructures. For this purpose, ZrO2 500 and ZrO2 600 were analyzed using scanning electron microscopy with an energy dispersive X-ray spectroscopy, high-resolution transmission electron microscopy and nitrogen adsorption isotherms specific surface tests. The structure of zirconium oxide nanofibers was investigated using X-ray diffraction, which confirmed highly crystalline nature of the materials and the presence of two crystalline phases - monoclinic and tetragonal. Analysis of optical properties, carried out on the basis of graphs of absorbance as a function of wavelength, revealed width of the optical band gap equal to 4.9 and 5.6 eV for nanostructures calcined at 500 and 600 °C, respectively. The nanofibers with a lower energy gap and a higher specific surface area degraded 38.47 % of methylene blue in an aqueous solution under ultraviolet radiation within 210 min.

Improved U(VI) electrosorption performance of hierarchical porous heteroatom-doped electrode based on double-template method

As an indispensable element in the field of nuclear energy, uranium (U(VI)) is widely concerned because it is abundant and easy to obtain from seawater. Herein, we report a promising dual-template strategy to prepare heteroatom-doped carbon materials with hierarchical micro−/meso−/macroporous from low-cost biomass precursors. The carbon materials with hierarchical porosity nitrogen/oxygen are synthesized through freeze-drying, high-temperature thermal treatment and subsequent HF etching treatment by in-situ growth of SiO2 on the precursor with ethyl silicate as silicon source and introduction of ZnCl2 as hard template and starch/ammonia as carbon and nitrogen source. Based on the advantages of three-dimensional interconnected hierarchical porous heteroatom doping, the electrosorption capacity reaches 67.25 mg/g, and the removal efficiency is as high as 98.45%, when the initial UO2(NO3)2 concentration is 80 mg/L in capacitive deionization. The isothermal adsorption of nitrogen doped hierarchical porous carbon (NHPC) is consistent with the Langmuir model, with a maximum electrosorption capacity of 152.43 mg/g, good cycle stability and high charge efficiency (energy consumption is only 0.77 kg-U kWh−1). Fascinatingly, the initial UO2(NO3)2 concentration is 80 mg/L and it also has a high adsorption capacity in 3.5 wt% NaCl solution, and the U(VI) removal efficiency could reach 42.5% after 8 h of continuous adsorption, with high selectivity. The prepared adsorbent NHPC shows good selectivity for U(VI) in the solution of 11 metal ions co-existing, and the effective selectivity Kd value of U(VI) is 1620.84 mL/g. Finally, X-ray photoelectron spectroscopy analysis reveals that in addition to Coulomb interaction and chelation during the adsorption process, there is also a synergistic effect of the conversion of U(VI) to UO2 under electric drive to improve the adsorption capacity of U(VI).