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The electrosynthesis of valuable chemicals via carbon dioxide reduction reaction (CO2RR) has provided a promising way to address global energy and sustainability problems. However, the selectivity and activity of deep-reduction products (DRPs) still remain as big challenges. Here, a copper–carbon-based catalyst with a hydrophobic core–shell architecture has been constructed and was found to exhibit excellent DRPs of methane generation with a faradaic efficiency of 81 ± 3% in a neutral medium and a maximum partial current density of −434 mA cm−2 in a flow cell configuration, which is among the best of CO2-to-CH4 electrocatalysts. Density functional theory calculations suggest that the hydrophobic structure decreasing the water coverage on the catalyst surface can promote the protonation of the *CO intermediate and block CO production, further favoring the generation of methane. These results provide a new insight into the electrosynthesis of DRPs via constructing a hydrophobic core–shell architecture for tuning the surface water coverage.

The electrocatalytic reduction of CO2 presents a promising strategy in addressing environmental and energy crisis. Significant progress has been achieved via CO2 gas diffusion electrolysis, to react at high selectivity and high rate. However, the gas diffusion layer (GDL) of the gas diffusion electrode (GDE) still suffers from low tolerance and limited active sites. Here, the hydrophobic 1-octadecanethiol molecular was functionalized over the Cu catalyst layer of the GDE, which simultaneously stabilizes the GDL and exposes abundant active solid-liquid-gas three-phase interfaces. The resultant GDE exhibits multi-carbon (C2+) product selectivity over faradaic efficiency (FE) of 70.0% in the range of 100 to 800 mA·cm−2, with the peak FEC2+ of 85.2% at 800 mA·cm−2. Notably, the strengthened GDE could continuously drive high-current electrolysis for more than 100 h without flooding. This work opens a new way to improve CO2 gas diffusion electrolysis via surface molecular engineering. [Figure not available: see fulltext.]

Photoelectrochemical (PEC) water splitting for solar energy conversion into chemical fuels has attracted intense research attention. The semiconductor hematite (α-Fe2O3), with its earth abundance, chemical stability, and efficient light harvesting, stands out as a promising photoanode material. Unfortunately, its electron affinity is too deep for overall water splitting, requiring additional bias. Interface engineering has been used to reduce the onset potential of hematite photoelectrode. Here we focus instead on energy band engineering hematite by shrinking the crystal lattice, and the water-splitting onset potential can be decreased from 1.14 to 0.61 V vs. the reversible hydrogen electrode. It is the lowest record reported for a pristine hematite photoanode without surface modification. X-ray absorption spectroscopy and magnetic properties suggest the redistribution of 3d electrons in the as-synthesized grey hematite electrode. Density function theory studies herein show that the smaller-lattice-constant hematite benefits from raised energy bands, which accounts for the reduced onset potential.

A facile “plug-and-go” strategy for the fabrication of Janus membranes (JMs) is proposed that uses different combinational substrates with opposite wettability, and some suitable substrates are tightly integrated through a certain pressure. The excellent compactness and controllability of the optimal JMs using foam Ni and superhydrophilic Cu mesh are demonstrated in multifunctional applications, including unidirectional liquid transportation in air–water systems, on-demand immiscible oil–water separation, droplet collection in liquid–liquid systems, and on–off switch control. The dual function of the resulting JMs as water and oil diodes is attributed to the interpenetrating structure and similar thicknesses of the formed hydrophobic and hydrophilic layers, which minimize the penetration distance of the Janus membrane in both directions. This strategy provides a common route for the fabrication of novel composite materials with greater diversity and composability regarding membrane pore size and thickness.

The high-pressure structural, vibrational and electrical properties for realgar were investigated by in-situ Raman scattering and electrical conductivity experiments combined with first-principle calculations up to ~30.8 ​GPa. It was verified that realgar underwent an isostructural phase transition at ~6.3 ​GPa and a metallization at a higher pressure of ~23.5 ​GPa. The isostructural phase transition was well evidenced by the obvious variations of Raman peaks, electrical conductivity, crystal parameters and the As–S bond length. The phase transition of metallization was in closely associated with the closure of bandgap rather than caused by the structural phase transition. And furthermore, the metallic realgar exhibited a relatively low compressibility with the unit cell volume V0 ​= ​718.1.4 ​A3 and bulk modulus B0 ​= ​36.1 ​GPa.

Three thioantimonides charge compensated by Ln/S/Cl cationic layers, namely, La8S4Cl8La12S8Cl4[SbS3]8 and Ln12S8Cl8[SbS3]4 (Ln = La and Ce), have been discovered by conventional solid-state reactions. The former crystallizes in the centrosymmetric space group Pbcm (no. 57), while the latter adopts the polar non-centrosymmetric space group Cc (no. 9). Both of them contain isolated SbS3 trigonal-pyramidal units, which are connected either with the alternating centric [La8S4Cl8]8+ and mirror-symmetric [La12S8Cl4]16+ cationic layers perpendicular to the [001] direction in La8S4Cl8La12S8Cl4[SbS3]8 or with the acentric [Ln12S8Cl8]12+ cationic layers perpendicular to the [100] direction in Ln12S8Cl8[SbS3]4. Interestingly, the discrete SbS3 trigonal pyramids pack in a centrosymmetric and non-centrosymmetric fashion in La8S4Cl8La12S8Cl4[SbS3]8 and La12S8Cl8[SbS3]4, respectively, which can be ascribed to the different compositions and packing fashions in Ln/S/Cl cationic layers. In addition, optical gaps of 2.31 and 2.60 eV for La12S8Cl8[SbS3]4 and La8S4Cl8La12S8Cl4[SbS3]8, respectively, were determined by UV/vis reflectance spectroscopy, showing a blue shift with respect to La7Sb9S24, which can be attributed to the greater contributions of La to the bottom of the CB as confirmed by the DFT study.

The vibrational, electrical and structural properties of gallium sulfide (Ga2S3) were explored by Raman spectroscopy, electrical conductivity measurements, high-resolution transmission electron microscopy and first-principles theoretical calculations under different pressure environments up to 36.4 GPa. Upon compression, Ga2S3 underwent a first-order structural phase transition accompanied by a semiconductor-to-metal transformation at 17.2 GPa under non-hydrostatic conditions, whereas, the transition occurred at a much lower pressure of 11.3 GPa under hydrostatic conditions because of the influence of the pressure medium. Upon decompression, two possible new high-pressure polymorphs were observed at 8.0 and 3.0 GPa under non-hydrostatic conditions, and similar transition points were obtained under hydrostatic conditions. The structural and electrical transport evolution for Ga2S3 upon compression and decompression can help us to deeply understand the high-pressure behaviors of other similar A2B3-type structural compounds.

Mesoporous single crystals have attracted considerable attention owing to their wide applications in (photo)catalysis, photovoltaics, and numerous other electrical energy conversion and storage technologies. Here, by using low-valent Ti3+ precursors, we have successfully synthesized well-defined mesoporous single-crystal strontium titanate (MSC SrTiO3) without a template via a facile hydrothermal method. The BET surface area and average pore diameter of MSC SrTiO3 are 18.6 m2 g−1 and 22 nm, respectively. Moreover, the as-synthesized MSC SrTiO3 features abundant oxygen vacancies. By using time-dependent structural and morphological characterizations, a hypothetical crystal growth mechanism was proposed.

Co-catalysts have been widely studied to improve photocatalytic water oxidation efficiency, and the precise control of their oxidation states and minimizing particle sizes can optimize the practical performance. In this work, ultrafine cobalt oxide (CoOx) co-catalysts with specific Co valence states have been successfully synthesized, which are anchored on a tantalum oxynitride (TaON) host photocatalyst via a photochemical metal–organic deposition method. Photoelectrochemical and photoluminescence analyses prove that the Co2+ dominant CoOx co-catalyst is favorable for charge separation and transportation because of its excellent hole-capturing properties, consequently enhancing the photocatalytic water oxidation performance. The resultant TaON with the Co2+ dominant CoOx co-catalyst exhibits an outstanding O2 production rate up to 6.10 ± 0.17 mmol h−1 g−1 and possesses an excellent apparent quantum efficiency of 21.2% at 420 nm, which are among the best values of water-oxidation photocatalysts.

Mn4+-activated oxide-fluoride phosphors are attractive for application in a wide range of solid-state lighting devices because of their distinct red emission at about 630 nm and the abundant storage of Mn ions. However, the zero-phonon line (ZPL) of Mn4+ ions is too weak to be detected in most host materials due to the magnetic dipole nature. In this article, we introduce a co-precipitation method for synthesizing a Mn4+-doped oxyfluoride perovskite KNaMoO2F4 phosphor containing [MoO2F4]2− building units. The electron paramagnetic resonance (EPR) spectra are consistent with the presence of a MnF62− species at g = 1.991. The KNaMoO2F4:0.01Mn4+ phosphor exhibits strong absorption under blue light and an internal quantum yield (IQE) of 65.8%. Attributed to the distorted octahedral environment of the Mn4+ ions, visible ZPL emission was detected at 625 nm. Based on theoretical calculations, the Mn4+ ions in the KNaMoO2F4 host exist in a strong crystal field with a high Dq/B value of ∼3.86. A series of photoluminescence-dependent low-temperature spectra indicates that the Mn4+ emissive state experiences weak electron–phonon interactions upon calculating the Huang–Rhys factor. Benefiting from the ZPL, a warm white-light-emitting diode is achieved using YAG:Ce3+ and KNaMoO2F4:Mn4+ as color converters, in which the color rendering index was Ra = 83.5 and CCT = 4490 K.

Exploring the vibrational properties of experimental or theoretical finding of new phase two-dimensional (2D) materials is one key to expand their promising application. The GaGeTe monolayer with high carrier mobility, tunable band structure, and low cleavage energy attracts rapidly growing interests in electronics. However, their vibrational modes and phonon properties are not explored. Based on first-principles calculations within the framework of density functional perturbation theory, we systematically study the lattice vibrational modes as well as phonon thermal conductivity of single-layer GaGeTe, which could be exfoliated from the experimentally synthesized GaGeTe crystal. We find that the frequencies and intensities of A1g and Eg Raman modes, contributing to the main peaks in Raman spectra of monolayer GaGeTe, show distinct responses to different external strains. The calculated lattice thermal conductivity of GaGeTe is about 58 Wm-1 K−1, which is comparable to that of MoS2 (around 52 Wm−1K−1) and two orders of magnitude lower than that of graphene (2000 Wm−1K−1) at room temperature. This is mainly due to the partial couple for acoustic branches and low frequency optic phonon branches, moderate group velocity, strong anharmonic ZA phonon branch. Moreover, atom substitution at tellurium could be as an effective strategy to further decrease lattice thermal conductivity. Our findings fill in the gap about the thermal transport properties of GaGeTe monolayer and trigger for further experimental verification of the predicted properties.

Summary Photocatalytic water splitting holds a key to realizing the hydrogen economy but faces a grand challenge, namely, the severe charge recombination causes low solar-to-hydrogen (STH) efficiency. This work reports a new form of MAPbI3 microcrystal (MAPbI3-MC)/monolayer MoS2 nanosheets (ML-MoS2) composite photocatalyst with type II heterojunction to effectively suppress the charge recombination for efficient photocatalytic hydrogen generation via HI splitting. The ML-MoS2/MAPbI3-MC is made of a large-sized MAPbI3-MC light harvester anchored with electrocatalytically active ML-MoS2 nanosheets to form a type II heterojunction that possesses a strong built-in electric field aligned between the spatially well-defined MAPbI3-MC and ML-MoS2 nanosheets to empower the photocatalyst with superior capability to effectively promote the charge separation. The ML-MoS2/MAPbI3-MC brings the hydrogen generation performance of the perovskite-based photocatalysts to a new horizon with a champion STH efficiency of 1.09% and a record hydrogen generation activity of 13.6 mmol g−1 h−1 under visible light.

Searching for coexistence of wide energy gap (Eg > 3.5 eV) and large second-harmonic generation efficiency (dij > 0.6  AgGaS2) for the non-centrosymmetric (NCS) materials in the IR nonlinear optic...

A nickel nitrocarburizing strategy is proposed to prepare efficient electrocatalysts for carbon dioxide (CO2) reduction. In the nitrocarburizing process, Ni,N-codoped carbon nanotubes could be grown from nickel substrates and provide catalytic sites and a fast electron transmission route for reducing CO2. A high performance of syngas [carbon monoxide (CO) and hydrogen (H2)] production has been realized with an industrial total current density (230 mA cm-2) and a tunable CO/H2 ratio (0.2-4.5). This shows the feasibility of the nitrocarburizing method to prepare electrocatalysts.

To boost the practical applications of rechargeable Zn–air batteries (ZABs), there is a need to design and synthesize bifunctional air electrodes with high catalytic activity and low cost used in s...

CuFe2O4 ferrite is considered to be a promising material to improve the radiation heat transfer of industrial furnaces due to its high infrared emissivity in middle and short wavebands. CuFe2O4 ferrites were prepared by sintering at different temperatures (800, 900, 1000, 1100 and 1200 °C). The thermal behaviour and phase composition were measured by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results validate that the I41/amd structure of CuFe2O4 ferrite transforms to the Fd-3m structure at temperatures above 1000 °C. The cation valence states of CuFe2O4 ferrite with I41/amd and Fd-3m structures were determined by X-ray photoelectron spectroscopy. Through the analysis of the results, it is found that there are differences for the ratio of Cu+/Cu2+ and Fe2+/Fe3+ between the two structures of I41/amd and Fd-3m, which can be attributed to the existence of oxygen vacancy. The different vibrations of metal oxides were measured by Raman spectroscopy, which confirmed the formation of oxygen vacancy. With first principle calculations, the electron transition properties and optical absorption coefficients of the I41/amd and Fd-3m structures were calculated and compared. The calculation results show that the band gap of Fd-3m structure is 0.798eV, which is higher than that of I41/amd structure (0.573eV). This indicates that compared with I41/amd structure, Fd-3m structure has no advantage in improving the emissivity of 3–5 μm waveband. However, VO can introduce donor level into the band gap, which plays a key role in reducing the band gap and increasing the emissivity of 3–5 μm waveband. In the first principle calculations, VO was introduced to calculate the absorption coefficient of Fd-3m structure. It is found that the absorption coefficient of CuFe2O4 ferrite with Fd-3m structure in 3–5 μm waveband is higher than that of I41/amd structure, which indicates that VO can improve the optical absorption of 3–5 μm waveband, so as to improve the emissivity of corresponding waveband. By measuring the emissivity of 3–5 μm waveband, it is verified that the emissivity of Fd-3m structure (0.88) is higher than that of I41/amd structure (0.71).

Conical morphologies with sharp tips exhibit excellent optical absorption and electric field enhancement features. We have synthesized conical structured BiVO4 crystals with a smooth curved surface and sharp tips by a simple two-phase route. The samples possess the ability to expand the visible light absorption region and are suitable for photocatalytic water oxidation.

Recently, two-dimensional (2D) rect-AlB6 [B. Song, Y. Zhou, H.-M. Yang, J.-H. Liao, L.-M. Yang, X.-B. Yang and E. Ganz, J. Am. Chem. Soc., 2019, 141, 3630–3640] has been reported to be an excellent system, exhibiting intrinsic superconductivity. Here, on the basis of the CALYPSO structure prediction method and first-principles calculations, we predict two novel systems of 2D XB6 (rect- and hex-XB6) (X = Ga, In), verify their thermal stability and calculate their mechanical properties. Then, we study their bonding nature, electron and phonon properties, and electron–phonon coupling (EPC). The results show that rect-, hex-GaB6, rect- and hex-InB6 are intrinsic phonon-mediated superconductors with a superconducting transition temperature (Tc) of 1.67, 14.02, 7.77 and 4.83 K, respectively. Furthermore, we study the influence of strain on these intrinsic superconductors. Their Tc can be modulated to some extent, especially for hex-InB6, the Tc of which can be enhanced to 19.23 K under the compressive strain of 2%. According to our calculations, they may be prepared by growing on suitable substrates, such as Cu(100) and Pt(111). Our findings may broaden the configurations of 2D superconducting materials and will stimulate more efforts in this field.

Commercial nickel nanoparticles (Ni NPs) were directly converted to efficient electrocatalysts for CO2 reduction by urea-Ni solid powder pyrolysis, in which a Ni, N-co-doped graphite carbon shell wraps the Ni NPs in situ. 98.3% CO selectivity was realized with a current density of -20.2 mA cm-2 and an overpotential of 0.69 V.

Compositional tailoring externally enables the fine tuning of thermal transport parameters of materials using the dual modulation of electronic or thermal transport properties. Theoretically, we examined the lattice dynamics of three particularly ternary representatives with different stoichiometry, BaMgSi, Ba2Mg3Si4, and BaMg2Si2, and identified the inherent bonding hierarchy and rattling Ba atoms, which were responsible for reducing the lattice thermal conductivity. BaMgSi and Ba2Mg3Si4 exhibited inherently ultra-low lattice thermal conductivity of 1.27-0.37 W m-1 K-1 in the range of 300-1000 K due to the bonding hierarchy and rattling Ba atoms. The low-energy optical phonons are overlapping with the acoustic phonons. This is associated with the intrinsic rattler-like vibration of Ba cations and leads to the characteristic in the localization of the propagative phonons and large anharmonicity. Although BaMg2Si2 had a dumbbell-shaped Si-Si covalent and Ba-Si/Mg ionic bonding environment and intrinsic rattler-like vibration of Ba cations, the middle frequency optic phonon branches contribute considerably to the thermal conductivity of the lattice. At the same temperature, compared with BaMgSi and Ba2Mg3Si4, the lattice thermal conductivity of BaMg2Si2 almost doubles owing to the higher phonon lifetime and group velocities. Our findings highlight considerable potential for thermoelectric applications with a different stoichiometric ratio of Ba/Mg/Si systems due to their low lattice thermal conductivities via intrinsic modulating stoichiometry.

Through first-principles calculations and using the Boltzmann transport equation, we explore the thermoelectric (TE) properties of CaP3 from the three-dimensional (3D) bulk form to a two-dimensional (2D) monolayer. Herein, our results prove that reducing the dimensionality not only can avoid the poor TE performance along certain crystal orientations, but also can effectively reduce the thermal conductivity. More remarkably, the Seebeck coefficients of the monolayer exhibit a dramatic enhancement compared to its bulk form. Some inherent phonon properties, such as the low acoustic phonon group velocity of ∼1.41 km s−1, large Gruneisen parameters of ∼30, and short phonon relaxation time, can greatly hinder its heat transport ability, leading to an ultralow lattice thermal conductivity of ∼0.65 W m−1 K−1 for the monolayer at room temperature. The size effect is much less sensitive due to the short intrinsic phonon mean free path (MFP). The maximum figure of merit (ZT) for n-type doping at 700 K can reach 6.39 in the nanosheet along the a direction, which is enhanced nearly two times compared to its bulk form (2.83), due to the quantum confinement effect. Collectively, this work shows that low-dimensional nanostructure technology can effectively improve the thermoelectric conversion of this class of materials.

Electrocatalysts featuring high activity, selectivity and stability are urgently needed in solar-electricity powered energy-conversion technologies. In the past decade, various electrocatalysts have been demonstrated to be electrocatalytically active toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Despite the significant progress, catalyst discovery is still dominated by “trial-and-error” practice due to the lack of understanding of the origin of electrocatalytic activity, active site structures and key factors determining the operando electrocatalytic performance. Therefore, this critical review focuses on summarizing effective catalyst activation strategies to enable efficient catalyst discovery, on the basis of understanding real active sites for the HER and OER. Meanwhile, theory prediction and operando characterization techniques have also been introduced to identify the origin of electrocatalytic activity and active site structures. Moreover, catalyst atomic structure reconstruction/rearrangement under working conditions and the accompanying catalyst activation strategies have been discussed to address the negative impacts of reaction media. Finally, a brief perspective on the challenges and future directions for predicting, characterizing and understanding operando active sites to discover efficient activation strategies will also be presented.

Based on first-principles calculations, we explore the electronic and phonon transport properties of a new-type two-dimensional (2D) hexagonal material XSe (X = Ge, Sn, and Pb), which can be prepar...

Single-atom catalysts have found considerable applications in the field of electrochemical CO2 reduction reaction (CO2RR) due to their unique coordination environments. However, during the preparat...

Generating clean and sustainable hydrogen from water splitting processes represent a practical alternative to solve the energy crisis. Ultrathin two-dimensional materials exhibit attractive properties as catalysts for hydrogen production owing to their large surface-to-volume ratios and effective chemisorption sites. However, the catalytically inactive surfaces of the transition metal dichalcogenides (TMD) possess merely small areas of active chemical sites on the edge, thus decreasing their possibilities for practical applications. Here, we propose a new class of out-of-plane deformed TMD (cTMD) monolayer to anchor transition metal atoms for the activation of the inert surface. The calculated adsorption energy of metals (e.g., Pt) on curved MoS2 (cMoS2) can be greatly decreased by 72% via adding external compressions, compared to the basal plane. The enlarged diffusion barrier energy indicates that cMoS2 with an enhanced fixation of metals could be a potential candidate as a single atom catalyst (SAC). We made a well-rounded assessment of the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), which are two key processes in water splitting. The optimized Gibbs free energy of 0.02 for HER and low overpotential of 0.40 V for OER can be achieved when the proper compression and supported metals are selected. Our computational results provide inspiration and guidance towards the experimental design of TMD-based SACs.

Aiming to find an excellent anode material for Li-ion batteries, we report the two-dimensional Zr2B2 monolayer combining the density functional theory and crystal structure prediction techniques. We find that the monolayer Zr2B2 has initial metallicity and good stability, and keeps excellent electrical conductivity during the whole process of lithiation. The adsorption energy of lithium is −0.628 eV, which is enough to make sure the stability of the processing of lithiation. Furthermore, the ultralow diffusion energy barrier of Li ion on the surface of the monolayer Zr2B2 (17 meV) indicates an excellent charge-discharge rate. The theoretical specific capacity of 526 mA h g−1 is larger than that of the commercial graphite electrode. All these results propose the hexagonal monolayer Zr2B2 as an excellent anode material for Li-ion batteries.

In this study, durable superhydrophobic sponge with magnetic-responsive and fire-retarding was prepared. In the preparation process, polydopamine (PDA), layered double hydroxide (LDH), Fe3O4 nanoparticles and n-Octadecyl mercaptan (OM) acted as the “bio-glue”, fire retardant, magnetic materials and hydrophobic reagent, respectively. LDH and Fe3O4 nanoparticles were adhered on the skeleton surface of PU sponge via PDA to build micro/nano structure, and then the -NH2 of PDA could react with the -SH of OM (Michael addition reaction), which made the sponge repellent to water. The prepared sponge exhibited remarkable hydrophobicity (water contact angle = 163°)and highly oleophilic (oil contact angle = 0°). When used for absorbing oil and organics, the prepared sponge floated on the surface of oily wastewater, and it could be moved towards oil droplet under magnetic actuation. The as-prepared sponge could absorb various kinds of oils and organics up to 53.6 times of its own weight, and the absorbed oils could be collected through a simple squeezing process. The prepared sponge could be withstood at least 50 cycles of laundering without losing its magnetic properties and superhydrophobicity due to the viscidity of PDA and strong interaction between PDA and OM. In addition, it was difficult to ignite the prepared sponge in air after anchored LDH and Fe3O4 on the sponge skeleton surface. This might offer an environmentally friendly way to prepare “smart and safe” oil-recovery materials.

Cemented paste backfill (CPB) plays a vital role in mineral engineering and understanding the cement hydration is crucial for its successful application. As an important constituent in ordinary Portland cement (5–15 wt%), ferrite is heavily used in CPB without being fully demonstrated due to its composition complexity. In this paper, the structural and electronic properties of Ca2Fe2O5 (C2F), Ca2AlFeO5 (C4AF) and Ca2Al2O5 (C2A) were investigated using first-principles calculations. The results indicated that lattice parameters and bond length decreased with increasing substitution of the smaller Al3+ for the larger Fe3+. The chemical reactivity of the unit cell was derived mainly from O 2p, Fe 3p, Fe 3d, and Al 3p orbitals. The O atoms were prone to electrophilic attack with cations such as H+. In contrast, the Fe/Al atoms were prone to nucleophilic attack with anions such as OH– and the Fe atoms were more reactive than the Al atoms. This study provides new insight into the structural and electronic properties of ferrite at the atomic level, which will provide a better understanding of cement hydration and promote the application of CPB.

Superamphiphobic surfaces generally need a specific combination of low surface energy and re-entrant surface structure. Herein, we have created a hexane suspension of trichloro(1H,1H,2H,2H-tridecafluoro-n-octyl) silane, tetraethyl orthosilicate, silicon dioxide and titanium dioxide nanoparticles and modify a series of filter papers by one-step immersion in 10 min. Superhydrophobic and quasi-superoleophobic properties are obtained for the optimal filter papers, which repel both of polar and non-polar liquids such as water, glycerol, 1,4-butanediol, soybean oil and 1-octadecene with the contact angles of 168°, 158°, 154°, 145° and 121°, respectively. More importantly, the respective contribution of each component to the superhydrophobic and oleophobical property is explicated through a series of comparative experiments based on the optimal suspension prescription. The wettability transformation from quasi-superamphiphobicity to superhydrophilicity after UV irradiation is evaluated and illustrated. What’s more, the patterned paper is successfully used for the colorimetric detection of glucose using a simple paper-based analytical device. A linear correlation between gray intensity (GI) and glucose concentration (C), GI = − 10.7C + 161.8 is achieved with a correlation coefficient of 0.991, indicating the potential for semi-quantitative analysis of real sample in the field.

A single-phase white light emitting NaBi(WO4)2:Dy3+, Tm3+ phosphor has been successfully prepared by conventional high-temperature solid-state method. First-principles calculations were used to investigate the electronic structures of NaBi(WO4)2. The calculation results show that NaBi(WO4)2 has an indirect band gap with 3.02 eV. The crystal structure and PL properties of the obtained phosphor are characterized by SEM, powder X-ray and photoluminescence spectra, respectively. The results demonstrate that all as-prepared crystalline in a tetragonal crystal system with a space group of I 4 ¯ . PL results confirmed that the obtained phosphors can be efficiently excited by 365 nm and generated white light emission. Then the energy transfer between Dy3+ and Tm3+ in the host NaBi(WO4)2 was investigated. Finally, the chromaticity coordinates of preferred NaBi0.91-x(WO4)2:0.09Dy3+, 0.11 Tm3+ (0.3319, 0.3395) were close to the standard white light point (0.333, 0.333). All these results reveal that NaBi(WO4)2:Dy3+/Tm3+ was a potential single phase white light-emitting phosphor candidate for NUV-based w-LEDs.

In this study, the vibrational and electrical transport properties of molybdenum diselenide were investigated under both non-hydrostatic and hydrostatic conditions up to ∼40.2 GPa using the diamond anvil cell in conjunction with Raman spectroscopy, electrical conductivity, high-resolution transmission electron microscopy, atomic force microscopy, and first-principles theoretical calculations. The results obtained indicated that the semiconductor-to-metal electronic phase transition of MoSe2 can be extrapolated by some characteristic parameters including abrupt changes in the full width at half maximum of Raman modes, electrical conductivity and calculated bandgap. Under the non-hydrostatic condition, metallization occurred at ∼26.1 GPa and it was irreversible. However, reversible metallization occurred at ∼29.4 GPa under the hydrostatic condition. In addition, the pressure-induced metallization reversibility of MoSe2 can be revealed by high-resolution transmission electron and atomic force microscopy of the recovered samples under different hydrostatic conditions. This discrepancy in the metallization phenomenon of MoSe2 in different hydrostatic environments was attributed to the mitigated interlayer van der Waals coupling and shear stress caused by the insertion of pressure medium into the layers.

It is of paramount importance to design and develop highly active and selective electrocatalysts for the CO2 reduction reaction. Herein, we obtained bismuth-based catalysts consisting of oxidized Bi2O2CO3 and metallic Bi featuring local shortened inter-layer Bi–Bi bonds from in situ reduction of bismuth oxyiodide (BiOI) microflowers, which showed over 90% formate faradaic efficiency in a wide negative potential region.

The rational design and synthesis of low-dimensional chalcogenides with desired properties is vital but still an enormous challenge. Herein, a novel quaternary sulphide, Ba8Zn4Ga2S15 (FJ-2), has been designed by a cation regulation strategy and successfully prepared. It comprises a one-dimensional (1D) {[Zn4Ga2S15]16-}∞ anion chain constructed from supertetrahedron [Zn4S10] clusters. The structure of FJ-2 is unique, as in the literature there are no other 1D structures of the type X/Zn/Ga/Q (X = cations; Q = chalcogen). Moreover, FJ-2 exhibits strong yellow photoluminescence emission at room temperature. DFT calculations using the VASP software package have aided the understanding of the relationship between the optical properties and electronic structure.

Following the prediction given by first-principles simulations [J. Am. Chem. Soc.137, 2757 (2015)], a Dirac nodal-line Cu2Si monolayer has been successfully synthesized on a Cu(111) surface [Nat. Commun.8, 1007 (2017)] or on a Si(111) substrate [Phys. Rev. Mater.3, 044004 (2019)]. However, its superconducting properties have never been reported in experiments or theory. Here, through first-principles calculations, we study its electron and phonon properties and electron–phonon coupling to investigate the possibility of superconductivity for a metallic Cu2Si monolayer. The results show that it is an intrinsic BCS-type superconductor, with the estimated superconducting temperature Tc being ∼4.1 K. We further find that the Fermi surface nesting is partially responsible for its superconducting character. Carrier doping as well as biaxial strains will suppress the Tc. Our results help to explain the challenges to experimentally probe superconductivity in substrate-supported Cu2Si monolayers and provide clues for further experiments.

Two-dimensional (2D) superconductors, which can be widely applied in optoelectronic and microelectronic devices, have gained renewed attention in recent years. Based on the crystal structure prediction method and first-principles calculations, we obtain four novel 2D tungsten boride structures of tetr-, hex-, and tri-W2B2 and hex-WB4 and investigate their bonding types, electronic properties, phonon dispersions and electron-phonon coupling (EPC). The results show that both tetr- and hex-W2B2 are intrinsic phonon-mediated superconductors with a superconducting transition temperature (Tc) of 7.8 and 1.5 K, respectively, while tri-W2B2 and hex-WB4 are normal metals. We demonstrate that carrier doping as well as biaxial strain can soften the low-frequency phonon modes and enhance the strength of the EPC. While the Tc of tetr-W2B2 can be increased to 15.4 K under a compressive strain of -2%, the Tc of hex-W2B2 can be enhanced to 5.9 K by a tensile strain of +4%. With the inclusion of spin-orbit couping (SOC), the value of Tc decreases by 38.5% in our systems. Furthermore, we explore the stabilities and mechanical properties of tetr- and hex-W2B2 and indicate that they may be prepared by growing on ZnS(100) and ZnS(111), respectively. Our findings provide novel 2D superconducting materials and will stimulate more efforts in this filed.

In this study, we report two new Mo2B2 monolayers and investigate their stabilities, electronic structures, lattice dynamics, and properties as anode materials for energy storage by using the crystal structure prediction technique and first-principles method. The calculated phonon spectra and electrical structures indicate that our predicted tetragonal and trigonal Mo2B2 (tetr- and tri-Mo2B2) monolayers possess excellent electronic conductivity and great stability. The adsorption energies of Li/Na on them are negative enough to ensure stability and safety under operating conditions. Besides, tetr-Mo2B2 possesses a theoretical specific capacity of ∼251 mA h g−1 for both Li- and Na-ion batteries (LIBs and NIBs), while tri-Mo2B2 possesses ∼251 and ∼188 mA h g−1 for LIBs and NIBs, respectively. The diffusion energy barriers of Li/Na over tetr- (0.029/0.010 eV) and tri- (0.023/0.013 eV) Mo2B2 are very small, indicating their excellent charge/discharge capability. In addition, the low electrode potential of Li/Na-intercalated tetr- and tri-Mo2B2 is beneficial to their performance as anode materials. This work is of great importance for widening the families of both anode materials for LIBs/NIBs and two-dimensional transition metal borides.

Superconductivity has attracted much interest in two-dimensional (2D) compounds because of their application in constructing nano-superconducting devices. Based on the crystal structure prediction method and first-principles calculations, we obtain two new 2D molybdenum boride structures of tetr- and tri-Mo2B2. Then, we calculate their electronic structures, phonon spectra, electron–phonon coupling (EPC), and superconducting properties. The results show that both tetr- and tri-Mo2B2 are intrinsic phonon-mediated superconductors with superconducting transition temperatures (Tc) of 3.9 and 0.2 K, respectively. We demonstrate that the EPC is mainly from the low-frequency phonon vibrations of Mo atoms. Our findings will enrich 2D superconducting materials and stimulate more efforts in this field.

Recently, an air-stable layered semiconductor Bi2O2Se has been synthesized [Nat. Nanotechnol., 2017, 12, 530; Nano Lett. 2017, 17, 3021]. It possesses ultrahigh mobility, semiconductor properties, excellent environmental stability and easy accessibility. Here, we report on the thermal transport properties in monolayer (ML), bilayer (BL), and bulk forms of Bi2O2Se using density-functional theory and the Boltzmann transport approach. The results show that the ML exhibits better thermal transport properties than the BL and bulk. The intralayer opposite phonon vibrations greatly suppress the thermal transport and lead to an ultralow lattice thermal conductivity of ∼0.74 W m−1 K−1 in the ML, which has a large band gap of ∼2.12 eV, a low value of average acoustic group velocity of ∼0.76 km s−1, low-lying optical modes of ∼0.54 THz, strong optical-acoustic phonon coupling, and large Gruneisen parameters of ∼5.69. The size effect for all three forms is much less sensitive due to their short intrinsic phonon mean free path (MFP).

Monolayer SnP3 is a novel two-dimensional (2D) semiconductor material with high carrier mobility and large optical absorption coefficient, implying its potential applications in the photovoltaic and thermoelectric (TE) fields. Herein, we report on the TE properties of monolayer SnP3 utilizing first principles density functional theory (DFT) together with semiclassical Boltzmann transport theory. Results indicate that it exhibits a low lattice thermal conductivity of ∼4.97 W m-1 K-1 at room temperature, mainly originating from its small average acoustic group velocity (∼1.18 km s-1), large Gruneisen parameters (∼7.09), strong dipole-dipole interactions, and strong phonon-phonon scattering. A large in-plane charge transfer is observed, which results in a non-ignorable bipolar effect on the lattice thermal conductivity. The exhibited mixed mode between in-plane and out-of-plane vibrations enhances the complexity of the phonon phase space, which enhances the possibility of phonon scattering processes and results in suppression of thermal conductivity. A highly twofold degeneracy appearing at the K point gives a high Seebeck coefficient. Our calculated figure of merit (ZT) for optimal p-type doping at 500 K can approach 3.46 along the armchair direction, which is better than the theoretical value of 1.94 reported in the well-known TE material SnSe. Our studies here shed light on monolayer SnP3 in use as a TE material and supply insights to further optimize the TE properties in similar systems.

Bilayer transition metal dichalcogenide heterostructures obtained by vertical stacking have attracted considerable attention because of their potential applications in thermoelectric and optoelectronics devices. The thermal transport behavior plays a pivotal role in assessing their functional performance. Here, we systematically investigate the thermal transport properties of the MoS2/MoSe2 bilayer heterostructure (MoS2/MoSe2-BH) by combining first-principles calculations and Boltzmann transport theory (BTE). The results show that the thermal conductivity of MoS2/MoSe2-BH at room temperature is 25.39 W m−1 K−1, which is in-between those of monolayer MoSe2 and MoS2. According to our calculated orbital-resolved phonon dispersion curves, Gruneisen parameters, phonon group velocity and relaxation time, we find that the acoustic and low-frequency optical branches below 172.65 cm−1 have strong coupling and contribute mainly to the lattice thermal conductivity. Compared with free standing monolayer MoS2 and MoSe2, the lattice thermal conductivity of MoS2/MoSe2-BH is influenced by the weak van der Waals interlayer interactions.

Two new mid-infrared (MIR) nonlinear optical (NLO) chalcogenide crystals, Ba10Zn7In6S26 (1) and Ba10Zn7Ga6Se26 (2) were discovered by traditional solid state reactions. Compounds 1 and 2 are isostructural, and they represent a novel three-dimensional (3D) framework made by apex-sharing T2 supertetrahedron 2D layers that are stacked alternately by another kind of T2 supertetrahedra though sharing apexes along the c direction, with T1 tetrahedra inserting in the tunnels and Ba2+ cations locating both in the voids and in the tunnels. Among them, 1 shows attractive MIR NLO properties with a wide band gap of 3.0 eV, a strong second harmonic generation (SHG) signal about 4.1 times that of the commercial AgGaS2 at particle sizes of 30–46 μm under a 2.05 μm laser radiation, and a high laser damage threshold (LDT) of 37.2 times that of benchmark AgGaS2 at particle sizes of 150–210 μm under a 1.064 μm laser radiation. This distinguishes 1 as a new promising MIR NLO material. In addition, the density functional theo...

The perovskite structure of manganate yields a series of intriguing physical properties. Based on the results of first-principles calculations, strontium manganate appears to undergo a magnetic phase transition and a metal-insulator transition-from antiferromagnetic insulator to ferromagnetic metal and then to ferromagnetic insulator-under isotropic volume expansion combined with oxygen octahedral distortions. Interestingly, the results show that increasing the Mn-O bond length and adding rotation of the oxygen octahedra can soften the breathing distortion and account for the insulator phase. We further build a simple model to explain such transitions. Due to electron transfer and the favoring of a hole state of ligandporbitals, the electron state transfer from2(t2g3)to2(eg1+t2g2)and then tot2g3eg1+(t2g3L1). Such rearrangement of charges is responsible for the transitions of its magnetic order and electronic structure. Furthermore, we calculate spin susceptibility under the bare conditions and random phase approximation. The magnetic order of the intermediate metal state of itinerant electrons behaves as a ferromagnetic.

Through first-principles calculations, we report the thermoelectric properties of two-dimensional (2D) hexagonal group-IV tellurides XTe (X = Ge, Sn and Pb), with quadruple layers (QL) in the Te-X-X-Te stacking sequence, as promising candidates for mid-temperature thermoelectric (TE) materials. The results show that 2D PbTe exhibits a high Seebeck coefficient (∼1996 μV K-1) and a high power factor (6.10 × 1011 W K-2 m-1 s-1) at 700 K. The lattice thermal conductivities of QL GeTe, SnTe and PbTe are calculated to be 2.29, 0.29 and 0.15 W m-1 K-1 at 700 K, respectively. Using our calculated transport parameters, large values of the thermoelectric figure of merit (ZT) of 0.67, 1.90, and 2.44 can be obtained at 700 K under n-type doping for 2D GeTe, SnTe, and PbTe, respectively. Among the three compounds, 2D PbTe exhibits low average values of sound velocity (0.42 km s-1), large Gruneisen parameters (∼2.03), and strong phonon scattering. Thus, 2D PbTe shows remarkable mid-temperature TE performance with a high ZT value under both p-type (2.39) and n-type (2.44) doping. The present results may motivate further experimental efforts to verify our predictions.

Given a desired property, locating relevant materials is always highly desired but very challenging in a range of areas, including heterogeneous catalysis. Obviously, object-oriented design/screening is an ideal solution to this problem. Herein, we develop an inverse catalyst design workflow in Python (CATIDPy) that utilizes a genetic-algorithm-based global optimization method to guide on-the-fly density functional theory calculations, successfully realizing the highly accelerated location of active single-atom alloy (SAA) catalysts for the hydrogen evolution reaction (HER). 70 binary and 752 ternary SAA candidate catalysts are identified for the HER. Furthermore, via considering the segregation stability and cost of materials, we extracted 6 binary and 142 ternary SAA candidate catalysts that are recommended for experimental synthesis. Remarkably, guided by these theoretical identifications, homogeneously dispersed Ni-based bimetallic catalysts (e.g., NiMo, NiAl, Ni3Al, NiGa, and NiIn) were synthesized experimentally to test the reliability of the CATIDPy workflow, and they showed superior HER performance to bare Ni foam, indicating huge potential for use in real-world water electrolysis techniques. Perhaps more importantly, these results demonstrate the capacity of such a proposed approach for investigating unexplored chemical spaces to efficiently design promising catalysts without knowledge from the expert domain, which has far-reaching implications., An inverse catalyst design workflow in Python (CATIDPy) for discovering unexplored chemical spaces successfully realized the highly accelerated location of active single-atom alloy (SAA) catalysts for the hydrogen evolution reaction (HER).

Understanding the lattice dynamics and low thermal conductivities of oxychalcogenide materials is critical to the development of a new generation of better thermoelectric oxide materials. Here we systematically investigate the lattice vibrational modes as well as phonon thermal conductivity of experimentally synthesized layered oxychalcogenides BiAgOCh (Ch = S, Se, and Te). First-principles calculations indicate that BiAgOSe and BiAgOTe are dynamically stable and low-thermal-conductivity materials. The room-temperature lattice thermal conductivity for BiAgOTe is calculated to be 0.53 W m−1 K−1, which is smaller than that (0.88 W m−1 K−1) of the promising thermoelectric material BiCuOSe. The strong anharmonicity in BiAgOTe causes short lifetime and low group velocity, which accordingly gives rise to ultralow thermal conductivity in BiAgOTe compounds. Our work of the insights into the lattice dynamics and low thermal conductivity will help the development of high-performance thermoelectric oxide materials.

Combining crystal structure search and first-principles calculations, we report a series of two-dimensional (2D) metal borides including orthorhombic (ort-)$M{\mathrm{B}}_{6}$ $(M=\mathrm{Mg},\mathrm{Ca},\mathrm{Ti},\mathrm{Y})$ and hexagonal (hex-)$M{\mathrm{B}}_{6}$ $(M=\mathrm{Mg},\mathrm{Ca},\mathrm{Sc},\mathrm{Ti})$. Then, we investigate their geometrical structures, bonding properties, electronic structures, mechanical properties, phonon dispersions, thermal stability, dynamic stability, charge density wave (CDW) phase transition, electron-phonon coupling (EPC), superconducting properties, and so on. Our ab initio molecular dynamics simulation results show that these $M{\mathrm{B}}_{6}$ can maintain their original configurations up to about 1000 or 700 K (only for hex-${\mathrm{MgB}}_{6}$), indicating their excellent thermal stability. All their elastic constants satisfy the Born mechanically stable criteria and no imaginary frequencies are observed in their phonon dispersions. Interestingly, there may exist a CDW phase transition for ort-${\mathrm{TiB}}_{6}$ from type-I to type-II $2\ifmmode\times\else\texttimes\fi{}1$ supercell structure and for ort-${\mathrm{YB}}_{6}$ from type-I to type-III $2\ifmmode\times\else\texttimes\fi{}1$ supercell structure. Besides, these 2D $M{\mathrm{B}}_{6}$ are all predicted to be intrinsic phonon-mediated superconductors. By analytically solving the McMillan-Allen-Dynes formula derived from the microscopic theory of Bardeen, Cooper, and Schrieffer, we obtain the superconducting transition temperature (${T}_{\mathrm{c}}$) for these materials, which are in the range of 1.4--22.6 K. Among our studied $M{\mathrm{B}}_{6}$, the highest ${T}_{\mathrm{c}}$ (22.6 K) appears in hex-${\mathrm{CaB}}_{6}$, whose EPC constant $(\ensuremath{\lambda})$ is 0.87. By applying tensile/compressive strains on ort-/hex-${\mathrm{CaB}}_{6}$, we find that the compressive strain can obviously soften the acoustic-phonon branch and enhance the EPC as well as ${T}_{\mathrm{c}}$. The ${T}_{\mathrm{c}}$ of the hex-${\mathrm{CaB}}_{6}$ can be increased from 22.6 to 28.4 K under compressive strain of 3%. These findings enrich the database of 2D superconductors and should stimulate experimental synthesizing and characterizing of 2D superconducting metal borides.

Defect formation energies, electronic structures and optical properties of non-metal S, lanthanide metal Sc-doped and Sc–S co-doped anatase TiO2 were systematically investigated via a GGA + U method based on density functional theory (DFT). The on-site Coulomb corrections were applied to both 3d orbitals of Ti atom (UTi_3d) and 2p orbitals of O atom (UO_2p). The results show all doped TiO2 systems exhibit a certain degree of red-shift due to the presence of impurity levels in the bandgap; in particular, the S-doped and Sc–S co-doped TiO2 exhibit better light absorption properties in the visible light range than either pure or Sc-doped TiO2. In addition, the positive synergistic effect between the Sc and S atoms not only expands the absorption edge, but also increases the light absorption coefficient in the visible region. As a result, the Sc–S co-doped anatase TiO2 shows the best optical absorption spectrum in all doping systems.

The Heusler alloys CoFeRGa (R = Ti, V, Cr, Mn, Cu, and Nb) have similar chemical compositions, but exhibit remarkably distinct electronic structures, magnetism and transport properties. These structures cover an extensive range of spin gapless semiconductors, half-metals, semiconductors and metals with either ferromagnetic, ferrimagnetic, antiferromagnetic, or nonmagnetic states. The Heusler alloys have three types of structures, namely, type-I, type-II, and type-III. By means of first-principles calculation combined with the Boltzmann equation within the consideration of spin-freedom, we explore the transport feature of the most stable structure (type-I). In addition, we provide evidence that all the considered materials are mechanically and dynamically stable, possessing high strength and toughness to resist compression and tensile strain. Moreover, the distinct electronic (metallic, insulating, and half-metallic) properties and magnetic behaviors originate mainly from a cooperative electron transfer and electronic structures have been verified by our calculation. Finally, we found that the tunable electronic structure with varied atomic numbers has significant influence on the spin-Seebeck effect. Correspondingly, the calculated spin-Seebeck coefficient of CoFeCrGa is -60.29 μV K-1 at 300 K, which is larger than that of other quaternary Heusler compounds. Our results provide a band-engineering platform to design Heusler structures with different electronic behaviors in isomorphic compounds, which provide the way for accelerating the pre-screening of materials to advance and for using the quaternary Heusler compounds for potential applications in spin caloritronic devices.