Focus on Defect Chemistry and Physics in Functional Nanomaterials

Grain boundaries and pores commonly manifest in graphene sheets during experimental preparation. Additionally, pores have been intentionally incorporated into graphene to fulfill specific functions for various applications. However, how does the simultaneous presence of pores and grain boundaries impact the mechanical properties of graphene? This paper establishes uniaxial tension models of single-layer graphene-containing pores and three types of experimentally observed. The effect of interaction between pores and grain boundaries on the fracture strength of graphene was studied respectively for three types of grain boundaries by employing molecular dynamics simulations and considering factors such as pore size, the distance between pores and grain boundaries, and loading angle. A competitive mechanism between the intrinsic strength of pristine graphene with grain boundaries (referred to as pristine GGBs), which varies with the loading angle and the fracture strength of graphene sheets with pores that changes with the size of the pores, governs the fracture strength and failure modes of GGBs with pores. When the former exceeds the latter, the fracture strength of GGBs with pores primarily depends on the size of the pores, and fractures occur at the edges of the pores. Conversely, when the former is lower, the fracture strength of GGBs with pores relies on the loading angle and the distance between pores and grain boundaries, leading to grain boundary rupture. If the two strengths are comparable, the failure modes are influenced by the distance between pores and grain boundaries as well as the loading angle. The findings further elucidate the impact of coexisting grain boundaries and pores on the fracture behavior of graphene, providing valuable guidance for the precise design of graphene-based devices in the future.

Niobium-tungsten bimetal oxides have received wide attention due to their excellent lattice properties. In this work, Nb₁₈W₁₆O₉₃ (NbWO) with a tetragonal tungsten bronze structure was synthesized by simple hydrothermal method. NbWO was modified to provide high specific surface area via combining with hollow carbon nanotubes. Meanwhile, NbWO grows along the tube wall of carbon nanotubes, thus buffering the volume effect of NbWO particles. Also, the migration distance of Li-ion is effectively shortened, as well as the improved ion transfer efficiency and the reaction kinetics. In addition, carbon tube can enhance conductivity of NbWO, contributing to outstanding charge storage capacity and rate energy. Precisely, NbWO@C as electrode possesses large specific capacity (249.6 F g⁻¹ at 0.5 A g⁻¹) and good rate performance (55.9% capacity retention from 0.5 to 2 A g⁻¹). The aqueous Li-ion capacitor presents the advantages of high safety, low cost and good environmental friendliness. An asymmetric aqueous capacitor AC//NbWO@C, based on 'water-in-salt' electrolyte with high concentration lithium acetate, exhibits a large energy density of 43.2 Wh kg⁻¹ and a power density of 9 kW kg⁻¹. Generally, NbWO@C as anode materials shows superior application perspective.

Nano-silver has the characteristics of low-temperature sintering and high-temperature service, which can reduce the thermal stress in the packaging process. Because of the high melting point and good high-temperature mechanical properties, silver is widely used in high-temperature packaging and connection fields. Sintered nano-silver has a porous structure on the microscopic level, it is necessary to study the mechanical properties of nano-silver with porosity. In this paper, we proposed a method for finite element modeling of porous nano-silver. Finite element analysis and nanoindentation test were used to investigate the Young's modulus of nano-silver. At the same time, and the quadratic equation of porosity and Young's modulus was fitted, and it was verified by Ramakrishnan model and nanoindentation results. These results show that the Young's modulus of nano-silver decreases with the increase of internal porosity, and the Young's modulus and porosity show a quadratic function correlation. As the porosity increases, the Young's modulus of nano-silver decreases at a slower rate. The modeling method presented in this paper can well predict the Young's modulus of nano-silver.

The low light absorption and rapid recombination of photogenerated charge carriers are primary contributors to the low activity of various photocatalysts. Fabrication of oxygen vacancy defect-rich materials for improved photocatalytic activities has been attracting tremendous attention from researchers all over the world. In this work, we have compared the photocatalytic activities of oxygen vacancy-rich Bi₂MoO₆ (BMO-O_V) and Bi₂WO₆ (BWO-O_V) for the degradation of a model pharmaceutical pollutant, ciprofloxacin under visible light irradiation. The photocatalytic activity was increased from 47% to 77% and 40% to–67% for BMO-O_V and BWO-O_V, respectively in comparison to pristine oxides. This enhancement can be ascribed to suppressed charge carrier recombination and increased surface active sites. In addition, scavenger studies have been done to explain the role of photoinduced charge carriers in the degradation mechanism. Moreover, oxygen vacancy-rich photocatalysts have remained stable even after three consecutive cycles, making them promising materials for practical applications. Overall, this work provides deeper insight into the design and development of oxygen vacancy-rich materials.

The structures of the disordered 1D (pseudo-)perovskites of general TMSO(Pb_xBi_y)I₃ formulation [TMSO = (CH₃)₃SO⁺], obtained by doping the TMSOPbI₃ species with Bi³⁺ ions, are investigated through the formulation of a statistical model of correlated disorder, which addresses the sequences of differently occupied BI₆ face-sharing octahedra (B = Pb, Bi or vacant site) within ideally infinite [(BI₃)⁻]_n chains. The x-ray diffraction patterns simulated on the basis of the model are matched to the experimental traces, which show many broad peaks with awkward (nearly trapezoidal) shapes, under the assumption that the charge balance is fully accomplished within each chain. The analysis allowed to establish a definite tendency of the metal species to cluster as pure Pb and Bi sequences. The application of the model is discussed critically, in particular as what concerns the possibility that further B-site neighbors beyond the second may influence the overall B-site occupancies.

The γ-phase cuprous iodide (CuI) emerges as a promising transparent p-type semiconductor for next-generation display technology because of its wide direct band gap, intrinsic p-type conductivity, and high carrier mobility. Two main peaks are observed in its photoluminescence (PL). One is short wavelength (410–430 nm) emission, which is well attributed to the electronic transitions at Cu vacancy, whereas the other long wavelength emission (680–720 nm) has not been fully understood. In this paper, through first-principles simulations, we investigate the formation energies and emission line shapes for various defects, and discover that the intrinsic point defect cluster ${{\rm{V}}}_{{\rm{I}}}+{{{\rm{Cu}}}_{{\rm{i}}}}^{2+}$ is the source of the long wavelength emission. Our finding is further supported by the prediction that the defect concentration decreases dramatically as the chemical condition changes from Cu-rich to I-rich, explaining the significant reduction in the red light emission if CuI is annealed in abundant I environment.