First-principles study of the temperature-induced band renormalization in thermoelectric filled skutterudites.

Band structure characteristics, such as band gap and band dispersion, are fundamental properties of materials. Temperature can affect them because of lattice expansion and phonon-induced atomic vibrations. Here, we apply the recently developed electron-phonon renormalization method to study the temperature effect on the band structures of thermoelectric (TE) filled skutterudites BaCo4Sb12, BaFe4Sb12, and YbFe4Sb12 from first-principles. The results reveal that the band gap in BaCo4Sb12 drops slower with temperature compared with our previous study on CoSb3, where it considerably reduces from 0 K to 800 K for BaFe4Sb12 (∼0.222 eV) and YbFe4Sb12 (∼0.201 eV). Furthermore, the band dispersions near the band edges at the Γ-point in the three systems at high temperatures are similar to those at 0 K, and the electron energies have small linewidths, whereas the linewidths for energies near the Fermi level are large. The different phenomena are due to the different phonon vibration-induced electronic structure disorders, reflecting the strength of electron-phonon coupling. Band renormalization would further affect the TE properties of these filled skutterudites. Our work provides a deeper understanding of the temperature-dependent band structure in skutterudites.

Modulating the Graphitic Domains of Hard Carbons Derived from Mixed Pitch and Resin to Achieve High Rate and Stable Sodium Storage.

Resin derived hard carbons (HCs) generally demonstrate remarkable electrochemical performance for both sodium ion batteries (SIBs) and potassium-ion batteries (KIBs), but their practical applications are hindered by their high price and high temperature pyrolysis (≈1500 °C). Herein, low-cost pitch is coated on the resin surface to compromise the cost, and meanwhile manipulate the microstructure at a relatively low pyrolysis temperature (1000 °C). HC-0.2P-1000 has a large number of short graphitic layer structures and a relatively large interlayer spacing of 0.3743 nm, as well as ≈1 nm sized nanopores suitable for sodium storage. Consequently, the as produced material demonstrates a superior reversible capacity (349.9 mAh g-1 for SIBs and 321.9 mAh g-1 for KIBs) and excellent rate performance (145.1 mAh g-1 at 20 A g-1 for SIBs, 48.5 mAh g-1 at 20 A g-1 for KIBs). Furthermore, when coupled with Na3 V2 (PO4 )3 as cathode, the full cell exhibits a high energy density of 251.1 Wh kg-1 and excellent stability with a capacity retention of 73.3% after 450 cycles at 1 A g-1 .

Temperature-dependence of the band gap in the all-inorganic perovskite CsPbI3 from room to high temperatures.

Understanding the micro-mechanism of the temperature dependence of the band gap in all-inorganic perovskites is of great significance for their optoelectronic and photovoltaic applications in various temperature environments. Herein, based on the recently developed electron-phonon renormalization method, the temperature-dependent band gaps of the optoelectronic perovskite CsPbI3 are studied from 300 K to 750 K (including orthorhombic, tetragonal, and cubic phases). It is found that the temperature-induced structural fluctuation makes the structure of perovskites deviate from the 0 K one, and the corresponding renormalized band gap differs from that at 0 K, especially for the high-temperature cubic phase (e.g., ΔEg is ∼177 meV at 600 K). However, within the temperature range of each CsPbI3 phase, the band gap Eg is enlarged slightly with the increase of temperature (e.g., ΔEg is ∼26 meV from 600 K to 750 K for the cubic phase), showing the insensitivity of the structural fluctuation effect to the temperature change. The reason is that the chemical characters of band edges are determined by PbI3-, and due to the strong correlation between Pb and I, the Pb-I bond lengths and Pb-I-Pb bond angles are almost unchanged as the temperature increases. Our work provides a fundamental understanding of the temperature-dependent band gaps in all-inorganic perovskites and shed light on the commercialization of perovskites.

Ionic-liquid-based dispersive liquid-liquid microextraction combined with magnetic solid-phase extraction for the determination of aflatoxins B1 , B2 , G1 , and G2 in animal feeds by high-performance liquid chromatography with fluorescence detection.

A novel two-step extraction technique combining ionic-liquid-based dispersive liquid-liquid microextraction with magnetic solid-phase extraction was developed for the preconcentration and separation of aflatoxins in animal feedstuffs before high-performance liquid chromatography coupled with fluorescence detection. In this work, ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate was used as the extractant in dispersive liquid-liquid microextraction, and hydrophobic pelargonic acid modified Fe3 O4 magnetic nanoparticles as an efficient adsorbent were applied to retrieve the aflatoxins-containing ionic liquid. Notably, the target of magnetic nanoparticles was the ionic liquid rather than the aflatoxins. Because of the rapid mass transfer associated with the dispersive liquid-liquid microextraction and magnetic solid phase steps, fast extraction could be achieved. The main parameters affecting the extraction recoveries of aflatoxins were investigated and optimized. Under the optimum conditions, vortexing at 2500 rpm for 1 min in the dispersive liquid-liquid microextraction and magnetic solid-phase extraction and then desorption by sonication for 2 min with acetonitrile as eluent. The recoveries were 90.3-103.7% with relative standard deviations of 3.2-6.4%. Good linearity was observed with correlation coefficients ranged from 0.9986 to 0.9995. The detection limits were 0.632, 0.087, 0.422 and 0.146 ng/mL for aflatoxins B1 , B2, G1, and G2, respectively. The results were also compared with the pretreatment method carried out by conventional immunoaffinity columns.

Simultaneous preconcentration of cadmium and chromium(III) in water samples by cloud point extraction and their determination by flame atomic absorption spectrometry.

A sensitive and simple method for flame atomic absorption spectrometry determination of traces of cadmium and chromium(III) species in water samples after preconcentration by cloud point extraction has been developed. A novel complex agent of alizarin complexone with cadmium (Cd) and chromium (Cr(III)) was quantitatively extracted in surface primary alcohol ethoxylate-rich phase at 33 °C. The effects of experimental conditions including pH of sample solution, concentration of chelating agent and salt, equilibration temperature and time, and foreign ions were evaluated in order to enhance sensitivity of the method. Under optimal conditions, the low limit detections were 6.7 and 3.2 µg/L, and the enrichment factors were 24 and 20 for Cd and Cr(III), respectively. The relative standard deviations were 3.8 and 2.5% for Cd and Cr(II), respectively (n = 11). The high recoveries of the spiked Cd and Cr(III) ions were obtained in the range of 90-116%. The proposed method has been successfully applied for the determination of Cd and Cr(III) in water samples.

Cloud point extraction-flame atomic absorption spectrometry method for preconcentration and determination of trace cadmium in water samples.

A method based on cloud point extraction (CPE) separation/preconcentration of trace cadmium (Cd) as a prior step to its determination by flame atomic absorption spectrometry has been developed. Cadmium reacted with 8-hydroxyquinoline to form hydrophobic chelates, which were extracted into the micelles of nonionic surfactant oligoethylene glycol monoalkyl ether (Genapol X-080) in an alkaline medium. Octanol was used to depress the cloud point of Genapol X-080 in the extraction process. The chemical variables that affect the CPE, such as pH of complexation reaction, amount of chelating agent, Genapol X-080 and octanol were evaluated and optimized. Under optimized conditions, linearity was obeyed in the range of 10-500 µg/L, with the correlation coefficient of 0.9993. For 5 mL of sample solution, the enhancement factor was about 20. The limit of detection and limit of quantification of the method were 0.21 and 0.63 µg/L, respectively. The relative standard deviations (n = 6) was 3.2% for a solution containing 100 µg/L of Cd. The accuracy of the preconcentration system was evaluated by recovery measurements on spiked water samples. Recoveries of spiked samples varied in the range of 94.1-103.8%.

A Critical Review of Machine Learning Techniques on Thermoelectric Materials.

Thermoelectric (TE) materials can directly convert heat to electricity and vice versa and have broad application potential for solid-state power generation and refrigeration. Over the past few decades, efforts have been made to develop new TE materials with high performance. However, traditional experiments and simulations are expensive and time-consuming, limiting the development of new materials. Machine learning (ML) has been increasingly applied to study TE materials in recent years. This paper reviews the recent progress in ML-based TE material research. The application of ML in predicting and optimizing the properties of TE materials, including electrical and thermal transport properties and optimization of functional materials with targeted TE properties, is reviewed. Finally, future research directions are discussed.

Preparation of Modified Fluorographene Oxide with Interlayer Supporting Structure.

Fluorinated graphene (FGi) is easy to agglomerate, after which it turns into a curly and wavy shape, which results in a great decrease in the properties of the resultant composite materials and coatings. In this study, fluorinated graphene oxide (FGO) modified with p-phenylenediamine (PPD) was prepared, but with a view to avoid its agglomeration and retain a sheet-like structure. Through the reaction between PPD and the epoxy groups of FGO, the modified FGO with an amino group (N-PGO) had a larger interlayer d-spacing than FGO. The stability of N-PGO was also improved, and nitrogen, fluorine, oxygen, and carbon were evenly distributed in the N-PGO sheets. All the results indicate that PPD can act as an effective spacer to separate graphene sheets for good anti-agglomeration properties. This method produced modified graphene with fluorine, amino, and carbonyl groups. It shows potential in introducing N-PGO as a reactive modifier in composite materials and coatings for a variety of industrial applications including waterborne epoxy materials.

Preparation and Application of Fluorine-Free Finishing Agent with Excellent Water Repellency for Cotton Fabric.

Water repellent is an important functional finish for cotton fabric. However, cotton fabrics often have poor washing resistance and other performances after actual finishing. In this study, based on the structural characteristics of cotton fiber and durability of water repellent, a cross-linked amino long-chain alkyl polysiloxane (CAHPS) was first prepared, and then reacted with modified silica. Finally, a chemically bonded organic-inorganic nanohybrid cross-linked polysiloxane (rSiO2-CAHPS) was fabricated. Furthermore, the rSiO2-CAHPS was emulsified to obtain a durable fluorine-free water repellent. The water repellent finishing for cotton fabric was carried out by the pad-dry-cure process. After finishing, the cotton fabric had good resistance to conventional liquids and excellent washing resistance, and still maintained good water repellency after 30 rounds of soaping. Moreover, properties including air permeability, mechanical property and whiteness are hardly affected after finishing. SEM and XPS characterization show that a layer of dense silicon film is formed on the surface of cotton fabric by rSiO2-CAHPS water repellent. The existence of nanosilica can improve the surface roughness of cotton fibers. The synergistic effect of fiber matrix, nanoparticles and CAHPS endows the fabric with a micro/nano-multi-scale micro-rough structure, which improves the water repellency of cotton fabric after water repellent finishing.

Fabrication of Iron Pyrite Thin Films and Photovoltaic Devices by Sulfurization in Electrodeposition Method.

Iron pyrite is a cheap, stable, non-toxic, and earth-abundant material that has great potential in the field of photovoltaics. Electrochemical deposition is a low-cost method, which is also suitable for large-scale preparation of iron pyrite solar cells. In this work, we prepared iron pyrite films by electrochemical deposition with thiourea and explored the effect of sulfurization on the synthesis of high-quality iron pyrite films. Upon sulfurization, the amorphous precursor film becomes crystallized iron pyrite film. Optical and electrical characterization show that its band gap is 0.89 eV, and it is an n type semiconductor with a carrier concentration of 3.01 × 1019 cm-3. The corresponding photovoltaic device shows light response. This work suggests that sulfurization is essential in the electrochemical preparation for fabricating pure iron pyrite films, and therefore for low-cost and large-scale production of iron pyrite solar cells.