CDs-ICG@BSA nanoparticles for excellent phototherapy and in situ bioimaging.

For the diagnosis and treatment of cancer, a great challenge is the fabrication of straightforward, non-toxic, multifunctional green nanomaterials. In this study, carbon quantum dots self-assembled with indocyanine green dye at bovine serum albumin for phototherapy and in situ bioimaging are produced by a flexible hydrothermal method. We find that the synthesized nanoparticles have high tumor photothermal therapeutic activity when exposed to 808 nm light, with a photothermal conversion efficiency up to 61 %. The phototoxicity study revealed the excellent phototherapy of the nanoparticles mainly arises from photothermal therapeutic effect other than photodynamic therapy effect. Simultaneously, it allows biological imaging in the visible and near-infrared ranges because of the significant absorption at 365 nm and 840 nm. The current work offers a simple, environmentally friendly, and reasonable method for developing photothermal drugs with a high photothermal conversion efficiency in the near-infrared region, as well as good biosafety for multifunctional nanomaterials for bioimaging tumor diagnosis and direct phototherapy.

Construction of MoB@LDH heterojunction and its derivates through phase and interface engineering for advanced supercapacitor applications.

Layered double hydroxide (LDH) has been attracted widespread attention in supercapacitor due to their unique layered structure and associated advantages. However, the inherent limitations of low electrical conductivity and reaction kinetics rate of LDH restrict its widespread application. Various modification techniques, such as heterojunction formation, phosphorization and introduction of phosphorus vacancies, are employed to modify LDH with the goal of improving the electrochemical performance. Preparation of composite materials using MoB MBene as conductive template and phosphorization are the effective ways for enhancing the electrical conductivity of electrode materials. MoB MBene is prepared using a modified method that combines NaOH etching and a high-temperature hydrothermal process. The presence of phosphorus vacancy is beneficial for enhancing the kinetics rate during electrode reactions. Through the synergistic effect of various modification methods, MP2 demonstrates an optimal electrochemical performance with a superior specific capacitance of 1731.19F/g (238.28 mAh g-1) at 1 A/g. It also demonstrates an impressive rate capacity of 81.28 % at 10 A/g and maintains a satisfactory capacitance retention of 88.14 % after 5000 cycles. In addition, a fabricated MP2//AC ASC device achieves an impressive energy density of 39.91 Wh kg-1 at the power density of 948.25 W kg-1 and demonstrates satisfactory cycling stability of 78.76 % after 5000 cycles. This work presents a comprehensive framework for analyzing the impact of material structure, components, and crystal phases on energy storage performance. It also examines the regulatory impact of different modification methods on energy storage mechanisms.

C-Rich Carbon Nitride Conjugated Polymer Enabling Ion-Migration-Induced Precise Electrochromic Display.

The development of electrochromic (EC) displays has been in the challenge of displaying precise patterns, such as characters or high-resolution images of small size. High-performance EC materials as well as efficient, precise-display strategies are still urgent. To enable a microfactor-guided strategy for highly precise display, I3-/I- ion-migration-induced localized electrochromism is developed in an EC device based on the C-rich polymeric carbon nitride (CPCN). The CPCN material with an extended conjugated backbone of individual aromatic nuclei and heptazine rings has been reported possessing remarkable photorechargeable performance. Owing to the self-charging behavior, the CPCN exhibits color switching by the interfacial charge recombination with I3- ions in electrolyte and serves as the EC material with a coloration efficiency of 210.2 cm2 C-1 and an optical contrast of 48.6%. Material synthesis, electrode preparation, device design and fabrication, mechanism analysis, and performance evaluation of the CPCN-based EC display device are described.

Chirality dependent electromechanical properties of single-layer MoS2 under out-of-plane deformation: a DFT study.

2D transition metal dichalcogenides (TMDs) demonstrate significant promise in logic circuits and optoelectronic devices because of their unique structures and excellent semiconductor properties. However, they inevitably undergo out-of-plane deformation during practical applications due to their ultra-thin structures. Recent experiments have shown that out-of-plane deformation significantly affects the electronic structures of 2D TMDs. However, the underlying physical mechanism is largely unknown. Therefore, it is critical to have a deeper understanding of out-of-plane deformation in 2D TMDs to optimize their applications in different fields. Currently, one of the most pressing matters that requires clarification is the chirality dependence of out-of-plane deformation in tuning the electromechanical properties of 2D TMDs. In this work, using single-layer MoS2 as a probe, we systematically investigate the effects of out-of-plane deformation along different chirality directions on the bond length, bending stiffness, electric polarization, and band structure of 2D TMDs by employing first-principles calculations based on density functional theory. Our results indicate that the bond length, bending energy, polarization strength, and band gap size of single-layer MoS2 are isotropic under out-of-plane deformation, while the band gap type is closely related to the direction of deformation. Our study will provide an essential theoretical basis for further revealing the structure-performance relationship of 2D TMDs.

A and B sites dual substitution by Na+ and Cu2+ co-doping in CsPbBr3 quantum dots to achieve bright and stable blue light emitting diodes.

Light-emitting perovskite quantum dots (PeQDs) are extensively investigated owing to their evident merits. However, it is still a challenge to adjust their intrinsic emissions and enhance their thermal stability to achieve full-color highly emissive QD-based light-emitting diodes (QLEDs), especially blue QLEDs. Herein, we demonstrate an effective strategy to fundamentally stabilize the crystal structure of CsPbBr3 QDs by codoping Na+ and Cu2+ ions, which are designed to substitute Cs+ (A sites) and Pb2+ (B sites), respectively. It is found out that the codoping metal ions have significantly improved the thermal stability and the optical properties of the QDs. 40% of the emission intensity can be remained after 8 thermal cycles (20-120 °C) for CsPbBr3: Na+/Cu2+ QDs, whilst less than 10% is maintained for undoped CsPbBr3 QDs. Accordingly, stable blue QLEDs are packed by CsPbBr3: Na+/Cu2+ QDs. Strong electroluminescence with the maximum luminance of 7161 cd m-2 and low turn-on voltage of 2.4 V are realized. The CIE coordinates are tuned from green (0.10, 0.74) to blue (0.17, 0.25) via Na+ and Cu2+ codoping. The maximum external quantum efficiency (EQEmax) is obtained as 4.52% for PeLEDs based on codoped QDs. The proposed metal ions A and B sites dual substitution strategy guarantees PeQDs as an extremely promising prospect in potential applications as high-resolution displays and high-quality lightings.

Geometric, electronic and transport properties of bulged graphene: A theoretical study.

Out-of-plane deformation in graphene is unavoidable during both synthesis and transfer procedures due to its special flexibility, which distorts the lattice and eventually imposes crucial effects on the physical features of graphene. Nowadays, however, little is known about this phenomenon, especially for zero-dimensional bulges formed in graphene. In this work, employing first-principles-based theoretical calculations, we systematically studied the bulge effect on the geometric, electronic, and transport properties of graphene. We demonstrate that the bulge formation can introduce mechanical strains (lower than 2%) to the graphene's lattice, which leads to a significant charge redistribution throughout the structure. More interestingly, a visible energy band splitting was observed with the occurrence of zero-dimensional bulges in graphene, which can be attributed to the interlayer coupling that stems from the bulged structure. In addition, it finds that the formed bulges in graphene increase the electron states near the Fermi level, which may account for the enhanced carrier concentration. However, the lowered carrier mobility and growing phonon scattering caused by the formed bulges diminish the transport of both electrons and heat in graphene. Finally, we indicate that bulges arising in graphene increase the possibility of intrinsic defect formation. Our work will evoke attention to the out-of-plane deformation in 2D materials and provide new light to tune their physical properties in the future.

High-sensitivity and wide-temperature-range dual-mode optical thermometry under dual-wavelength excitation in a novel double perovskite tellurate oxide.

Novel double perovskite SrLaLiTeO6 (abbreviated as SLLT):Mn4+,Dy3+ phosphors synthesized using a solid-state reaction strategy exhibit distinct dual-emission of Mn4+ and Dy3+. High-sensitivity and wide-temperature-range dual-mode optical thermometry was exploited taking advantage of the diverse thermal quenching between Mn4+ and Dy3+ and the decay lifetime of Mn4+. The thermometric properties in the range of 298-673 K were investigated by utilizing the fluorescence intensity ratio (FIR) of Dy3+ (4F9/2→6H13/2)/Mn4+ (2Eg→4A2g) and the Mn4+ (2Eg→4A2g) lifetime under 351 nm and 453 nm excitation, respectively. The maximum relative sensitivities (SR) of the resultant SLLT:1.2%Mn4+,7%Dy3+ phosphor under 351 nm and 453 nm excitation employing the FIR technology were determined to be 1.60% K-1 at 673 K and 1.44% K-1 at 673 K, respectively. Additionally, the maximum SR values based on the lifetime-mode were 1.59% K-1 at 673 K and 2.18% K-1 at 673 K, respectively. It is noteworthy that the SR values can be manipulated by different excitation wavelengths and multi-modal optical thermometry. These results suggest that the SLLT:Mn4+,Dy3+ phosphor has prospective potential in optical thermometry and provide conducive guidance for designing high-sensitivity multi-modal optical thermometers.

Single Transition Metal Atom Bound to the Unconventional Phase of the MoS2 Monolayer for Catalytic Oxygen Reduction Reaction: A First-Principles Study.

Supported single-atom catalysts (SACs) have received a lot of attention due to their super-high atom utilization and outstanding catalytic performance. However, the instability of the supported transition-metal (TM) atoms hampers their widespread applications. Exploration of an appropriate substrate to stabilize the supported single atom is crucial for the future implementation of SACs. In recent years, two-dimensional materials have been proposed as possible substrates due to their large specific surface areas, but their chemically inert surfaces are difficult to stabilize TM atoms without defecting or doping. Herein, by means of systematic first-principles calculations, we demonstrate that the defect-free MoS2 monolayer in the unconventional phase (1T') can effectively immobilize single TM atoms owing to its unique electrophilic property as compared to the conventional 2H phase. As a prototype probe, we investigated oxygen reduction reaction (ORR) catalyzed by a total of 21 single TM atoms stabilized on 1T'-MoS2 and successfully screened out two candidates, Cu and Pd@1T'-MoS2, which have a low overpotential of 0.41 and 0.32 V respectively, outperforming most of the previously reported ORR catalysts. Furthermore, we reveal that the adsorption energy of the ORR intermediate, *OH, provides an excellent descriptor to assess the ORR activity, which is further determined by the d-band center of the supported TM adatoms, thus being a great advantage for future design of stable and high-performance SACs.

Constructing ultra-sensitive dual-mode optical thermometers: Utilizing FIR of Mn4+/Eu3+ and lifetime of Mn4+ based on double perovskite tellurite phosphor.

A strategy of optical temperature sensing was developed by using various thermal quenching of Mn4+ and Eu3+ for double perovskite tellurite phosphor in optical thermometers. Herein, SrGdLiTeO6 (SGLT): Mn4+,Eu3+ phosphors were synthesized by a high-temperature solid-state reaction method. The temperature-dependent emission spectra indicated that two distinguishable emission peaks originated from Eu3+ and Mn4+ exhibited significantly diverse temperature responses. Therefore, optical thermometers with a dual-mode mechanism were designed by employing a fluorescence intensity ratio (FIR) of Mn4+ (2Eg→4A2g) and Eu3+ (5D0→7F1,2) and the decay lifetime of Mn4+ as the temperature readouts. The temperature sensing of the phosphors ranging from 300 to 550 K were studied. The maximum relative sensitivities (Sr) are obtained as 4.9% K-1 at 550 K. Meanwhile, the 695 nm emission of Mn4+ possessed a temperature-dependent decay lifetime with Sr of 0.229% K-1 at 573 K. Relevant results demonstrate the SrGdLiTeO6:Mn4+, Eu3+ phosphor as an optical thermometer candidate and also provide constructive suggestions and guidance for constructing high-sensitivity dual-mode optical thermometers.

Low-Coordinate Step Atoms via Plasma-Assisted Calcinations to Enhance Electrochemical Reduction of Nitrogen to Ammonia.

The electrochemical N2 reduction reaction (NRR) is emerging as a promising alternative to the industrial Haber-Bosch process for distributed and modular production of NH3 . Nevertheless, developing high-efficiency catalysts to simultaneously realize both high activity and selectivity for the development of a sustainable NRR is very critical but extremely challenging. Here, a unique plasma-assisted strategy is developed to synthesize iridium diphosphide nanocrystals with abundant surface step atoms anchored in P,N-codoped porous carbon nanofilms (IrP2 @PNPC-NF), where the edges of the IrP2 nanocrystals are extremely irregular, and the ultrathin PNPC-NF possesses a honeycomb-like macroporous structure. These characteristics ensure that IrP2 @PNPC-NF delivers superior NRR performance with an NH3 yield rate of 94.0 µg h-1 mg-1 cat. and a faradaic efficiency (FE) of 17.8%. Density functional theory calculations reveal that the unique NRR performance originates from the low-coordinate step atoms on the edges of IrP2 nanocrystals, which can lower the reaction barrier to improve the NRR activity and simultaneously inhibit hydrogen evolution to achieve a high FE for NH3 formation. More importantly, such a plasma-assisted strategy is general and can be extended to the synthesis of other high-melting-point noble-metal phosphides (OsP2 @PNPC-NF, Re3 P4 @PNPC-NF, etc.) with abundant step atoms at lower temperatures.

Optimizing edges and defects of supported MoS2 catalysts for hydrogen evolution via an external electric field.

As a fascinating non-precious catalyst for hydrogen evolution reaction (HER), two-dimensional (2D) molybdenum disulphide (MoS2) has attracted ever-growing interest. While the pristine basal plane of MoS2 is chemically inactive, certain edges and defects have been recognized to be catalytically active for HER. Nevertheless, the per-site activity of MoS2 is still much lower than that of Pt. Therefore, further optimization of active sites becomes highly desirable to enhance the overall catalytic activity of MoS2. In this work, we propose to use an electric field to engineer the electronic structure of edges and defects of MoS2, aiming to optimize its catalytic performance. Via systematic density functional theory based first-principles calculations, we investigated the adsorption of H atoms on different edges of free-standing and supported MoS2, revealing the critical role of S p-resonance states near the Fermi level in determining H adsorption, which offers an excellent descriptor for the catalytic activity associated with the electronic structure. Remarkably, by introducing an external electric field, we demonstrate the ability to fine tune the position of S p-resonance states, which can give an optimal H adsorption strength on MoS2 for HER. We also explored field effects on S vacancies in the basal plane, which show a different behavior for H adsorption due to the presence of Mo d states that are insensitive to the electric field. We expect these findings to shed new light on the design and control of MoS2-based catalysts for industrial applications.

Two-dimensional Au-1,3,5 triethynylbenzene organometallic lattice: Structure, half-metallicity, and gas sensing.

On the basis of first-principles calculations, we investigated the structural and electronic properties of the two-dimensional (2D) Au-1,3,5 triethynylbenzene (Au-TEB) framework, which has been recently synthesized by homocoupling reactions in experiments. Featured by the C-Au-C linkage, the 2D Au-TEB network has a kagome lattice by Au atoms and a hexagonal lattice by organic molecules within the same metal-organic framework (MOF), which exhibits intrinsic half-metallicity with one spin channel metallic and the other spin channel fully insulating with a large energy gap of 2.8 eV. Two branches of kagome bands are located near the Fermi level, with each branch including one flat band and two Dirac bands, which originates from the out-of-plane dxz and dyz orbitals of Au and may lead to many exotic topological quantum phases. We further studied the adsorption of F atoms, Cl atoms, and small gas molecules including O2, CO, NO2, and NH3 on the Au-TEB network, aiming to exploit its potential applications in gas sensors. Detailed analyses on adsorption geometry, energy, molecular orbital interaction, and electronic structure modification suggest the great potential of Au-TEP as a promising alternative for gas sensing. We expect these results to expand the universe of low-dimensional half-metallic MOF structures and shed new light on their practical applications in nanoelectronics/spintronics.

Strain-engineered two-dimensional MoS2 as anode material for performance enhancement of Li/Na-ion batteries.

Recent years have witnessed a surge of research in two-dimensional (2D) nanostructures for development of new rechargeable Li/Na-ion battery systems. Herein, via first-principles calculations we demonstrate strain-engineered Li/Na adsorption and storage in 2D MoS2 as anode material, aiming to enhance the operating performance of Li/Na-ion batteries. Our results show that tensile strain greatly increases the adsorption of Li/Na atoms on MoS2, and a modest strain of 6% increases Li (Na) adsorption energy by over 70%, which originates from the strain-induced upshift of Mo d states towards Fermi level that interact strongly with Li/Na s states, in analogy with the d-band model in metal catalyst. Significant narrowing of the n-doped semiconducting gap of MoS2 suggests the improved electric conductivity that may benefit charge carrier transport. By mapping out the potential energy surfaces, we show shallow energy barriers of ion diffusion with ~0.2 eV for Li and 0.1 eV for Na. Furthermore, the strain-steered competition between chemical bonding and coulomb repulsion results in high Li/Na storage capability and relatively low average operating voltage. We believe that the fundamental principle underlying the use of strain to enhance performance of renewable ion battery is applicable to other stretchable low-dimensional nanomaterials.

Halogen-Adatom Mediated Phase Transition of Two-Dimensional Molecular Self-Assembly on a Metal Surface.

Construction of tunable and robust two-dimensional (2D) molecular arrays with desirable lattices and functionalities over a macroscopic scale relies on spontaneous and reversible noncovalent interactions between suitable molecules as building blocks. Halogen bonding, with active tunability of direction, strength, and length, is ideal for tailoring supramolecular structures. Herein, by combining low-temperature scanning tunneling microscopy and systematic first-principles calculations, we demonstrate novel halogen bonding involving single halogen atoms and phase engineering in 2D molecular self-assembly. On the Au(111) surface, we observed catalyzed dehalogenation of hexabromobenzene (HBB) molecules, during which negatively charged bromine adatoms (Brδ-) were generated and participated in assembly via unique C-Brδ+···Brδ- interaction, drastically different from HBB assembly on a chemically inert graphene substrate. We successfully mapped out different phases of the assembled superstructure, including densely packed hexagonal, tetragonal, dimer chain, and expanded hexagonal lattices at room temperature, 60 °C, 90 °C, and 110 °C, respectively, and the critical role of Brδ- in regulating lattice characteristics was highlighted. Our results show promise for manipulating the interplay between noncovalent interactions and catalytic reactions for future development of molecular nanoelectronics and 2D crystal engineering.

High performance NiFe layered double hydroxide for methyl orange dye and Cr(VI) adsorption.

The NiFe layered double hydroxides (LDHs) with different mole ratio of Ni/Fe (4:1, 3:1, 7:3 and 1:1) were prepared by a simple coprecipitation method. The adsorption performance were evaluated by the removal of methyl orange (MO) dye and hexavalent chromium(VI) heavy metal ion. It is found that Ni4Fe1-LDH can remove more than 92% of MO in 10 min at the 10 mg/L MO initial concentration, and 97% of Cr(VI) in 1 h at 4 mg/L Cr2O7(2-) initial concentration. The saturated adsorption capacity of Ni4Fe1-LDH is found to be as large as 205.76 mg/g for MO and 26.78 mg/g for Cr(VI). The adsorption behavior of this new adsorbent is fitted well with Langmuir isotherm and the pseudo-second-order kinetic model, indicative of a monolayer and chemical adsorption that synergistically originates from exchangeable anions mechanism and layer charge density. Due to the excellent removal capacity of MO and Cr(VI), the NiFe-LDHs could be a promising adsorbent for wastewater treatment.