Intriguing electronic,optical and photocatalytic performance of BSe,M2CO2 monolayers and BSe–M2CO2 (M = Ti,Zr, Hf) van der Waals heterostructures

Using density functional (DFT) theory calculations, we have investigated the electronic band structure, optical and photocatalytic response of BSe, M₂CO₂ (M = Ti, Zr, Hf) monolayers and their corresponding BSe–M₂CO₂ (M = Ti, Zr, Hf) van der Waals (vdW) heterostructures. Optimized lattice constant, bond length, band structure and bandgap values, effective mass of electrons and holes, work function and conduction and valence band edge potentials of BSe and M₂CO₂ (M = Ti, Zr, Hf) monolayers are in agreement with previously available data. Binding energies, interlayer distance and Ab initio molecular dynamic simulations (AIMD) calculations show that BSe–M₂CO₂ (M = Ti, Zr, Hf) vdW heterostructures are stable with specific stacking and demonstrate that these heterostructures might be synthesized in the laboratory. The electronic band structure shows that all the studied vdW heterostructures have indirect bandgap nature – with the CBM and VBM at the Γ–K and Γ-point of BZ for BSe–Ti₂CO₂, respectively; while for BSe–Zr₂CO₂ and BSe–Hf₂CO₂ vdW heterostructures the CBM and VBM lie at the K-point and Γ-point of BZ, respectively. Type-II band alignment in BSe–M₂CO₂ (M = Ti, Zr, Hf) vdW heterostructures prevent the recombination of electron–hole pairs, and hence are crucial for light harvesting and detection. Absorption spectra are investigated to understand the optical behavior of BSe–M₂CO₂ (M = Ti, Zr, Hf) vdW heterostructures, where the lowest energy transitions are dominated by excitons. Furthermore, BSe–M₂CO₂ (M = Ti, Zr, Hf) vdW heterostructures are found to be potential photocatalysts for water splitting at pH = 0, and exhibit enhanced optical properties in the visible light zones.

Using density functional theory calculations, we have investigated the electronic band structure, optical and photocatalytic response of BSe, M₂CO₂ (M = Ti, Zr, Hf) monolayers and their corresponding BSe–M₂CO₂ (M = Ti, Zr, Hf) van der Waals heterostructures.     

Random anion distribution in MSxSe2−x (M = Mo,W) crystals and nanosheets

The group VIb dichalcogenides (MX₂, M = Mo, W; X= S, Se) have a layered molybdenite structure in which M atoms are coordinated by a trigonal prism of X atoms. Ternary solid solutions of MS_xSe_2−x were synthesized, microcrystals were grown by chemical vapor transport, and their morphologies and structures were characterized by using synchrotron X-ray diffraction, Rietveld refinement, DIFFaX simulation of structural disorder, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Double aberration corrected scanning transmission electron microscopy was used to determine the anion distributions in single-layer nanosheets exfoliated from the microcrystals. These experiments indicate that the size difference between S and Se atoms does not result in phase separation, consistent with earlier studies of MX₂ monolayer sheets grown by chemical vapor deposition. However, stacking faults occur in microcrystals along the layering axis, particularly in sulfur-rich compositions of MS_xSe_2−x solid solutions.

Nanosheets exfoliated from single crystals of the group VIb sulfoselenides (MS_xSe_2−x, M = Mo, W) are solid solutions at the atomic level.     

Two-dimensional MXO/MoX2 (M = Hf,Ti and X = S,Se) van der Waals heterostructure: a promising photovoltaic material

Nanoscale materials with multifunctional properties are necessary for the quick development of high-performance devices for a wide range of applications, hence theoretical research into new two-dimensional (2D) materials is encouraged. 2D materials have a distinct crystalline structure that leads to intriguing occurrences. Stacking diverse two-dimensional (2D) materials has shown to be an efficient way for producing high-performance semiconductor materials. We explored a 2D nanomaterial family, an MXO/MoX₂ heterostructure (M = Hf, Ti and X = S, Se), for their various applications using first-principles calculations. We discovered that all of the heterostructure materials utilized are direct band gap semiconductors with band gaps ranging from 1.0 to 2.0 eV, with the exception of hexagonal HfSeO/MoSe₂, which has a band gap of 0.525 eV. The influence of strain on the band gap of this HfSeO/MoSe₂ material was investigated. In the visible range, we obtained promising optical responses with a high-power conversion efficiency. With fill factors of 0.5, MXO/MoX₂ photovoltaic cells showed great PCE of up to 17.8%. The tunable electronic characteristics of these two-dimensional materials would aid in the development of energy conversion devices. According to our findings, the 2D Janus heterostructure of MXO/MoX₂ (M = Hf, Ti and X = S, Se) material is an excellent choice for photovoltaic solar cells.

Nanoscale materials with multifunctional properties are necessary for the quick development of high-performance devices for a wide range of applications, hence theoretical research into new two-dimensional (2D) materials is encouraged.     

Preparation of boron nitride nanosheets via polyethyleneimine assisted sand milling: towards thermal conductivity and insulation applications

Hexagonal boron nitride (h-BN) is often used as a filler in polymer composites due to its good thermal conductivity and insulation properties. However, the compatibility between h-BN and the matrix limits its application areas. To overcome this issue, a combination of mechanical liquid phase exfoliation and chemical interfacial modification was adopted in this work. Polyethyleneimine (PEI) was used as the exfoliation reagent to prepare PEI-functionalized h-BN nanosheets, denoted as PEI@BNNS. Thermoplastic polyurethane (TPU) composites with different contents of h-BN and PEI@BNNS which were recorded as h-BN/TPU and PEI@BNNS/TPU were successfully prepared through a hot-pressing process, respectively. The results show that PEI@BNNS/TPU composites have better in-plane thermal conductivity while maintaining insulation, and with the content of 5 wt% PEI@BNNS, the in-plane thermal conductivity of the PEI@BNNS/TPU composite is up to 0.61 W m⁻¹ K⁻¹, which is three times that of pure TPU (0.22 W m⁻¹ K⁻¹).

The PEI-grafted boron nitride nanosheets were successfully prepared via sand-milling process, which were doped into thermoplastic polyurethane matrix for better in-plane thermal conductivity while maintaining insulation properties.     

High thermoelectric performance in metal phosphides MP2 (M = Co,Rh and Ir): a theoretical prediction from first-principles calculations

Although metal phosphides have good electronic properties and high stabilities, they have been overlooked in general as thermoelectrics based on expectation of high thermal conductivity. Here we propose the metal phosphides MP₂ (M = Co, Rh and Ir) as promising thermoelectrics through first-principles calculations of their thermoelectric properties. By using lattice dynamics calculations within unified theory of thermal transport in crystal and glass, we obtain the lattice thermal conductivities κ_l of MP₂ as 0.63, 1.21 and 1.81 W m⁻¹ K at 700 K for M = Co, Rh and Ir, respio ectively. Our calculations for crystalline structure, phonon dispersion, Grüneisen parameters and cumulative κ_l reveal that such low κ_l originates from strong rattling vibrations of M atoms and lattice anharmonicity, which significantly suppress heat-carrying acoustic phonon modes coupled with low-lying optical modes. Using mBJ exchange–correlation functional, we further calculate the electronic structures and transport properties, which are in good agreement with available experimental data, evaluating the relaxation time of charge carrier within deformation potential theory. We predict ultrahigh thermopower factors as 10.2, 7.1 and 6.4 mW m⁻¹ K² at 700 K for M = Co, Rh and Ir, being superior to the conventional thermoelectrics GeTe. Finally, we estimate their thermoelectric performance by computing figure of merit ZT, finding that upon n-type doping ZT can reach ∼1.7 at 700 K specially for CoP₂. We believe that our work offers a novel materials platform to search for high-performance thermoelectrics using metal phosphides.

We investigated the thermoelectric performance of metal phosphides MP₂ (M = Co, Rh and Ir), such as Seebeck coefficient, electrical conductivity, and lattice and electron thermal conductivity, using the density functional theory calculations.     

Adsorption characteristics of metal–organic framework MIL-101(Cr) towards sulfamethoxazole and its persulfate oxidation regeneration

A metal–organic framework, MIL-101(Cr), was used to adsorb sulfamethoxazole (SMZ) in water and activated persulfate (PS) oxidation was investigated to regenerate SMZ-saturated MIL-101(Cr). Adsorption and oxidation were combined in this study. MIL-101(Cr) was characterized by SEM, BET, XPS and FT-IR analyses. Effects of various operating parameters on adsorption efficiency were studied. The dosages of persulfate for SMZ desorption and oxidation were investigated. The results showed that the recommended pH was 6–8 for SMZ adsorption and optimum MIL-101(Cr) dosage was 0.1 g L⁻¹. SMZ adsorption by MIL-101(Cr) was a spontaneous process and nearly exothermic. Saturation adsorption capacity was achieved in 180 s and the adsorption followed the pseudo-second-order model. The maximum adsorption amount of MIL-101(Cr) to SMZ was 181.82 mg g⁻¹ (Langmuir). MIL-101(Cr) also showed good adsorption capacities for sulfachloropyridazine (SCP), sulfamonomethoxine (SMM), and sulfadimethoxine (SDM). Persulfate was helpful for SMZ desorption from the surface of saturated MIL-101(Cr) and sufficient persulfate could simultaneously oxidize the SMZ. XPS analysis showed that the structure of MIL-101(Cr) was stable after the persulfate oxidation process. Regenerated MIL-101(Cr) had the same level of adsorption capacity as fresh MIL-101(Cr). An adsorption–oxidation combined process may be set up based on the results. This study provides basic data for the deep treatment of organic micropollutants in urban water bodies.

A metal–organic framework, MIL-101(Cr), was used to adsorb sulfamethoxazole (SMZ) in water and activated persulfate (PS) oxidation was investigated to regenerate SMZ-saturated MIL-101(Cr).     

Electrical and electrochemical properties of Li2M(WO4)2 (M = Ni,Co and Cu) compounds

Li₂M(WO₄)₂ (M = Co, Cu or Ni) materials have been synthesized using the solid-state reaction method. X-ray diffraction measurements confirmed the single phase of the synthesized compounds in the triclinic crystal system (space group P$\bar{1}$). The SEM analyses revealed nearly spherical morphology with the particle size in the range of 1–10 μm. The IR spectra confirm the presence of all modes of WO₄²⁻. The impedance spectroscopy measurements showed the presence of grain boundaries and allow determination of the conductivity of the synthesized materials at room temperature. As positive electrode materials for lithium ion batteries, Li₂M(WO₄)₂ (M = Co, Cu or Ni) cathode materials deliver initial discharge capacities of 31, 33 and 30 mA h g⁻¹ for cobalt, nickel, and copper, respectively.

Li₂M(WO₄)₂ (M = Co, Cu or Ni) materials have been synthesized using the solid-state reaction method.     

First principles study of optoelectronic and photocatalytic performance of novel transition metal dipnictide XP2 (X = Ti,Zr, Hf) monolayers

Low cost and highly efficient two dimensional materials as photocatalysts are gaining much attention to utilize solar energy for water splitting and produce hydrogen fuel as an alternative to deal with the energy crisis and reduce environmental hazards. First principles calculations are performed to investigate the electronic, optical and photocatalytic properties of novel two dimensional transition metal dipnictide XP₂ (X = Ti, Zr, Hf) monolayers. The studied single layer XP₂ is found to be dynamically and thermally stable. TiP₂, ZrP₂ and HfP₂ systems exhibit semiconducting nature with moderate indirect band gap values of 1.72 eV, 1.43 eV and 2.02 eV, respectively. The solar light absorption is found to be in energy range of 1.65–3.3 eV. All three XP₂ systems (at pH = 7) and the HfP₂ monolayer (at pH = 0) that straddle the redox potentials, are promising candidates for the water splitting reaction. These findings enrich the two dimensional family and provide a platform to design novel devices for emerging optoelectronic and photovoltaic applications.

Low cost and highly efficient two dimensional materials as photocatalysts are gaining much attention to utilize solar energy for water splitting and produce hydrogen fuel as an alternative to deal with the energy crisis and reduce environmental hazards.     

Enhancement of NH3-SCR performance of LDH-based MMnAl (M = Cu,Ni, Co) oxide catalyst: influence of dopant M

Transition metal (Cu, Ni, Co) doped MnAl mixed oxide catalysts were prepared through a novel method involving the calcination of hydrotalcite precursors for the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR). The effects of transition metal modification were confirmed by means of XRD, BET, TEM, XPS, NH₃-TPD, and H₂-TPR measurements. Experimental results evidenced that CoMnAl-LDO presented the highest NO_x removal efficiency of over 80% and a relatively high N₂ selectivity of over 88% in a broad working temperature range (150–300 °C) among all the samples studied. Moreover, the CoMnAl-LDO sample possessed better stability and excellent resistance to H₂O and SO₂. The reasons for such results could be associated with the good dispersion of Co₃O₄ and MnO_x, which could consequently provide optimum redox behavior, plentiful acid sites, and strong NO_x adsorption ability. Furthermore, dynamics calculations verified the meaningful reduction in apparent activation energy (E_a) for the CoMnAl-LDO sample, which is in agreement with the DeNO_x activity.

In situ doping of M (M = Cu, Ni, Co) into MnAl-LDH laminate to promote the NH₃-SCR performance of the MnAl-LDO catalyst.     

Adsorption of lindane (γ-hexachlorocyclohexane) on nickel modified graphitic carbon nitride: a theoretical study

Adsorption of lindane (HCH) on nickel modified graphitic carbon nitride (Ni-gCN) was investigated using a novel, accurate and broadly parametrized self-consistent tight-binding quantum chemical (GFN2-xTB) method. Two graphitic carbon nitride (gCN) models were used: corrugated and planar, which represent the material with different thicknesses. Electronic properties of the adsorbates and adsorbent were estimated via vertical ionization potential, vertical electron affinity, global electrophilicity index and the HOMO and LUMO. Adsorption energy and population analyses were carried out to figure out the nature of the adsorption process. The results reveal that the introduction of the nickel atom significantly influences the electronic properties of gCN, and results in the improvement of adsorption ability of gCN for lindane. Lindane adsorption on Ni-gCN is considered as chemisorption, which is primarily supported by the interaction of the nickel atom and chlorine atoms of HCH. The effect of solvents (water, ethanol, acetonitrile) was investigated via the analytical linearized Poisson–Boltzmann model. Due to the strong chemisorption, Ni-gCN can collect lindane from different solvents. The adsorption configurations of HCH on Ni-gCN were also shown to be thermally stable at 298 K, 323 K, 373 K, 473 K, and 573 K via molecular simulation calculations. The obtained results are useful for a better understanding of lindane adsorption on Ni-gCN and for the design of materials with high efficiency for lindane treatment based on adsorption-photocatalytic technology.

A comprehensive theoretical study on the adsorption of lindane on nickel modified g-C₃N₄ was performed. The influence of material thickness, different solvents and temperature on the adsorption process was discussed and analyzed in detail.     

Heterostructured Bi2S3@NH2-MIL-125(Ti) nanocomposite as a bifunctional photocatalyst for Cr(vi) reduction and rhodamine B degradation under visible light

A series of bismuth sulfide (Bi₂S₃) nanorods and amine-functionalized Ti-based metal–organic framework heterojunctions [denoted by Bi₂S₃@NH₂-MIL-125(Ti)] were constructed and explored as bifunctional photocatalysts for Cr(vi) reduction and rhodamine B (RhB) degradation under visible light illumination. Compared with the individual NH₂-MIL-125(Ti) and Bi₂S₃, the as-synthesized Bi₂S₃@NH₂-MIL-125(Ti) photocatalyst exhibited an enhanced photocatalytic activity toward Cr(vi) and RhB owning to the synergetic effect between Bi₂S₃ and NH₂-MIL-125(Ti). Moreover, the Bi₂S₃@NH₂-MIL-125(Ti) heterojunctions showed increased Cr(vi) removal efficiency by adding RhB in the system. The photocatalytic mechanism was proposed based on the analysis of different scavenger for active species and electron spin resonance spectrometry. The introduction of Bi₂S₃ into NH₂-MIL-125(Ti) can extend the light adsorption and improve the transfer and separation of photogenerated charge carriers through the Bi₂S₃@NH₂-MIL-125(Ti) heterojunction with unique band gap structure. The synthesized Bi₂S₃@NH₂-MIL-125(Ti) photocatalyst also exhibited good reusability and stability.

Bi₂S₃@NH₂-MIL-125(Ti) heterojunction exhibited enhanced photocatalytic activity for Cr(vi) reduction and RhB degradation under visible light irradiation.     

Co1−xBaxFe2O4 (x = 0, 0.25, 0.5, 0.75 and 1) nanoferrites as gas sensor towards NO2 and NH3 gases

Co_1−xBa_xFe₂O₄ (x = 0, 0.25, 0.5, 0.75 and 1) nanoferrites were synthesized using a controlled chemical co-precipitation technique. Their structural, optical, dielectric and gas sensing properties were characterized by X-ray diffractometry, UV-Vis spectroscopy and an LCR meter with a gas sensing unit. The crystalline sizes were estimated using the Scherrer formula and were found to be 7.8 nm, 14.4 nm, 21.8 nm, 16.5 nm and 30.3 nm for x = 0, 0.25, 0.5, 0.75 and 1, respectively. The fundamental optical band gaps were calculated by extrapolating the linear part of (αhυ)²vs. hυ of the synthesized nanoferrites. The SEM and EDX spectra also confirmed the formation of nanoferrites. Dramatic behavior was observed in the dielectric constant and dissipation factor with varying temperature, which provides a substantial amount of information about electric polarization. The synthesized nanoferrites were tested towards NO₂ and NH₃ gases. The order of sensitivity (%) towards NH₃ was analyzed as x = 0.75 > x = 0.5 > x = 0.25 > x = 0 > x = 1, while the order was x = 0 > 0.75 > 1 > 0.5 > 0.25 for NO₂ gas.

XRD pattern and sensitivity (%) as a function of flow rate (ppm) of Co_1−xBa_xFe₂O₄ (x = 0, 0.25, 0.5, 0.75 and 1.0) nanoferrites towards NO₂ and NH₃ gases.     

Improvement of low-temperature NH3-SCR catalytic performance over nitrogen-doped MOx–Cr2O3–La2O3/TiO2–N (M = Cu,Fe, Ce) catalysts

A series of MO_x–Cr₂O₃–La₂O₃/TiO₂–N (M = Cu, Fe, Ce) catalysts with nitrogen doping were prepared via the impregnation method. Comparing the low-temperature NH₃-SCR activity of the catalysts, CeCrLa/Ti–N (xCeO₂–yCr₂O₃–zLa₂O₃/TiO₂–N) exhibited the best catalytic performance (NO conversion approaching 100% at 220–460 °C). The physico-chemical properties of the catalysts were characterized by XRD, BET, SEM, XPS, H₂-TPR, NH₃-TPD and in situ DRIFTS. From the XRD and SEM results, N doping affects the crystalline growth of anatase TiO₂ and MO_x (M = Cu, Fe, Ce, Cr, La) which were well dispersed over the support. Moreover, the doping of N promotes the increase of the Cr⁶⁺/Cr ratio and Ce³⁺/Ce ratio, and the surface chemical adsorption oxygen content, which suggested the improvement of the redox properties of the catalyst. And the surface acid content of the catalyst increased with the doping of N, which is related to CeCrLa/TiO₂–N having the best catalytic activity at high temperature. Therefore, the CeCrLa/TiO₂–N catalyst exhibited the best NH₃-SCR performance and the redox performance of the catalysts is the main factor affecting their activity. Furthermore, in situ DRIFTS analysis indicates that Lewis-acid sites are the main adsorption sites for ammonia onto CeCrLa/TiO₂–N and the catalyst mainly follows the L–H mechanism.

A series of MO_x–Cr₂O₃–La₂O₃/TiO₂–N (M = Cu, Fe, Ce) catalysts with nitrogen doping were prepared via the impregnation method.     

Metallic boro-carbides of A2BC (A = Ti,Zr, Hf and W): a comprehensive theoretical study for thermo-mechanical and optoelectronic applications

High-hardness materials with ductile deformation behavior have recently piqued interest due to their prospective applications, particularly as hard and protective coatings. The crack formation, especially in metal and ceramic materials, is one of the biggest problems of the surface hard coatings on heavy-duty tools. In this regard, mechanical properties (Vickers hardness, fracture toughness, machinability index, index of brittleness, as well as Pugh''s ratio) have been studied for the metallic boro-carbides of A₂BC (A = Ti, Zr, Hf, and W) compounds using the state-of-the-art density functional theory in detail. The compounds under investigation are both thermodynamically and mechanically stable. The value of Vickers hardness (in GPa) for A₂BC (A = Ti, Zr, Hf, and W) compounds are 28.20, 23.12, 12.44, and 35.70, respectively, which indicates the W₂BC could be a member of the hard family (H_v > 30 GPa). Pugh''s ratio suggests ductile deformation for the W₂BC compound, whereas the other three (Ti₂BC, Zr₂BC, and Hf₂BC) compounds exhibit brittle deformation behavior. The W₂BC compounds have the highest ductility among the other metallic boro-carbides (M₂BC; M = V, Nb, Mo and Ta) and some other benchmark coating materials (TiN, TiAlN, C-BN, and Cr_0.5Al_0.5N). The fracture toughness (K_IC) values are in the following sequence: Zr₂BC < Ti₂BC < Hf₂BC < W₂BC, which indicates that, the highest resistance (K_IC = 4.96 MPam^1/2) found for W₂BC is suitable to prevent the crack propagation within the solid. In addition, the structural, electronic, optical, and thermal properties are also investigated for the A₂BC (A = Ti, Zr, Hf, and W) compounds. The Ti₂BC (W₂BC) reflectivity spectra never fall below 53 (45)% in the 0 to 10.3 eV (0 to 16.70 eV) photon energy range, suggesting that these compounds have promise for usage as coating materials to reduce solar heating. Hf₂BC and W₂BC compounds could also be exploited as promising thermal barrier coating materials, while Ti₂BC could be used as heat sink material based on the results of Debye temperature, melting temperature, thermal conductivity, and thermal expansion coefficient. The electronic properties reveal the metallic behavior of these compounds. The results obtained here are compared with those of some commercially known compounds, where available.

The Ti₂BC reflectivity spectra never fall below 53% in the 0 to 10.3 eV photon range, showing as a coating material to reduce solar heating. The W₂BC has a Vickers hardness of ∼36 GPa with ductility, showing potential for hard coating application.     

Seawater splitting for hydrogen evolution by robust electrocatalysts from secondary M (M = Cr,Fe, Co,Ni, Mo) incorporated Pt

Water splitting is a promising technique for clean hydrogen energy harvesting. The creation of cost-effective electrocatalysts with improved hydrogen evolution reaction (HER) activity and stability is crucial in realizing persistent hydrogen evolution by reducing the reaction overpotential and minimizing energy consumption. Herein, we present the preparation of alloyed PtM (M = Cr, Fe, Co, Ni, Mo) modified titanium (Ti) mesh by a simple electrodeposition method, aiming at hydrogen generation from seawater splitting. The preliminary results indicate that the Ti/PtM electrodes feature markedly reduced onset overpotentials and Tafel slopes as well as significantly increased exchange current densities compared with pristine Pt electrodes, arising from the incorporation of secondary M atoms into the Pt lattice for alloying effects. Moreover, the competitive dissolution reaction between guest M species to Pt with Cl₂ in seawater is beneficial for enhancing the long-term stability of resultant PtM alloy electrodes. The optimized PtMo alloy electrode maintains 91.13% of the initial current density upon 172 h operation in real seawater, making it promising in practical applications.

Water splitting is a promising technique for clean hydrogen energy harvesting.     

Supercapacitive performance of TiO2 boosted by a unique porous TiO2/Ti network and activated Ti3+

TiO₂ has been reported to have considerable capacity through appropriate surface modification. Previous studies of TiO₂-based supercapacitors mainly focused on anodized TiO₂ nanotubes and TiO₂ powder, even though the capacitance still lags behind that of carbon-base materials. In this work, a three-dimensional porous TiO₂/Ti (PTT) network was constructed by anodic oxidation and its capacitance was boosted by subsequent aluminum-reduction process. Activated Ti³⁺ was proved to be being successfully introduced into the surface of pristine PTT, resulting in the prominent enhancement of supercapacitive performance. An areal capacitance of 81.75 mF cm⁻² was achieved from Al-reduced PTT (Al-PTT) at 500 °C in 1 M H₂SO₄ electrolyte, which was among the highest value of pure TiO₂-based electrodes. Good electrochemical stability was also confirmed by the 3.12% loss of the highest capacity after 5000 CV cycles. More importantly, the activated Ti³⁺/Ti⁴⁺ redox couple in modified TiO₂ is solidly confirmed by being directly observed in CV curves. The capacitive mechanism of the redox reaction is also studied by electrochemical tests. The construction of a 3D porous network structure and efficient Ti³⁺ introduction provide an effective method to boost the supercapacitive performance of TiO₂-based materials for energy storage applications.

Excellent supercapacitive performance is achieved by constructing a 3D porous TiO₂/Ti network structure and introducing an activated Ti³⁺/Ti⁴⁺ redox couple.     

A first-principles study of electronic structure and photocatalytic performance of GaN–MX2 (M = Mo,W; X= S,Se) van der Waals heterostructures

Modeling novel van der Waals (vdW) heterostructures is an emerging field to achieve materials with exciting properties for various devices. In this paper, we report a theoretical investigation of GaN–MX₂ (M = Mo, W; X= S, Se) van der Waals heterostructures by hybrid density functional theory calculations. Our results predicted that GaN–MoS₂, GaN–MoSe₂, GaN–WS₂ and GaN–WSe₂ van der Waals heterostructures are energetically stable. Furthermore, we find that GaN–MoS₂, GaN–MoSe₂ and GaN–WSe₂ are direct semiconductors, whereas GaN–WS₂ is an indirect band gap semiconductor. Type-II band alignment is observed through PBE, PBE + SOC and HSE calculations in all heterostructures, except GaN–WSe₂ having type-I. The photocatalytic behavior of these systems, based on Bader charge analysis, work function and valence and conduction band edge potentials, shows that these heterostructures are energetically favorable for water splitting.

Modeling novel van der Waals (vdW) heterostructures is an emerging field to achieve materials with exciting properties for various devices.     

Anion order in perovskite oxynitrides AMO2N (A = Ba,Sr, Ca; M = Ta,Nb): a first-principles based investigation

Perovskite-type oxynitrides have attracted a lot of research interest as emerging functional materials with promising wide applications. The ordering of O/N anions in perovskite oxynitrides plays an important role in determining their physical properties, while it is still challenging to characterize the actual anion order in a particular material and understand the underlying physics. In this work, we have investigated anion order in a series of perovskite oxynitrides AMO₂N (A = Ba, Sr, Ca; M = Ta, Nb) through first-principles calculations and the cluster-expansion-model-based Monte Carlo simulations. In terms of cluster correlation functions, it can be explicitly demonstrated that short-range anion order is present in all these perovskite oxynitrides. In addition, the anion order varies with the temperature of thermal equilibrium and depends on the cation type. Special quasi-ordered structures are then constructed as representative structures by taking the calculated anion order at finite temperature into consideration and their band gaps and dielectric tensors are predicted by first-principles calculations and compared to experimental values.

Anion order in perovskite oxynitrides is investigated by a combination of first-principles calculations, cluster expansion method and Monte Carlo simulations.     

Vacancy impacts on electronic and mechanical properties of MX2 (M = Mo,W and X = S,Se) monolayers

Monolayers of transition metal dichalcogenides (TMD) exhibit excellent mechanical and electrical characteristics. Previous studies have shown that vacancies are frequently created during the synthesis, which can alter the physicochemical characteristics of TMDs. Even though the properties of pristine TMD structures are well studied, the effects of vacancies on the electrical and mechanical properties have received far less attention. In this paper, we applied first-principles density functional theory (DFT) to comparatively investigate the properties of defective TMD monolayers including molybdenum disulfide (MoS₂), molybdenum diselenide (MoSe₂), tungsten disulfide (WS₂), and tungsten diselenide (WSe₂). The impacts of six types of anion or metal complex vacancies were studied. According to our findings, the electronic and mechanical properties are slightly impacted by anion vacancy defects. In contrast, vacancies in metal complexes considerably affect their electronic and mechanical properties. Additionally, the mechanical properties of TMDs are significantly influenced by both their structural phases and anions. Specifically, defective diselenides become more mechanically unstable due to the comparatively poor bonding strength between Se and metal based on the analysis of the crystal orbital Hamilton population (COHP). The outcomes of this study may provide the theoretical knowledge base to boost more applications of the TMD systems through defect engineering.

The impacts of six different types of vacancies on the electronic and mechanical properties of MX2 (M = Mo, W and X = S, Se) monolayers have been theoretically revealed.