One-pot synthesis of high-index faceted AgCl nanocrystals with trapezohedral, concave hexoctahedral structures and their photocatalytic activity

Effect of non-additive mixing on entropic bonding strength and phase behavior of binary nanocrystal superlattices

Non-additive mixing plays a key role in the properties of molecular fluids and solids. In this work, the potential for athermal order-disorder phase transitions is explored in non-additive binary colloidal nanoparticles that form substitutionally ordered compounds, namely, for equimolar mixtures of octahedra + spheres, which form a CsCl lattice compound, and cubes + spheres, which form a NaCl crystal. Monte Carlo simulations that target phase coexistence conditions were used to examine the effect on compound formation of varying degrees of negative non-additivity created by component size asymmetry and by size-tunable indentations in the polyhedra's facets, intended to allow the nestling of neighboring spheres. Our results indicate that the stabilization of the compound crystal requires a relatively large degree of negative non-additivity, which depends on particle geometry and the packing of the relevant phases. It is found that negative non-additivity can be achieved in mixtures of large spheres and small cubes having no indentations and lead to the athermal crystallization of the NaCl lattice. For similarly sized components, athermal congruent transitions are attainable and non-additivity can be generated through indentations, especially for the cubes + spheres system. Increasing indentation leads to lower phase coexistence free energy and pressure in the cubes + spheres system but has the opposite effect in the octahedra + spheres system. These results indicate a stronger stabilizing effect on the athermal compound phase by the cubes' indentations, where a deeper nestling of the spheres leads to a denser compound phase and a larger reduction in the associated pressure-volume free-energy term.

Low-temperature synthesis of tetrapod CdSe/CdS quantum dots through a microfluidic reactor

Tetrapod CdSe/CdS quantum dots (QDs) have attracted extensive research interest in light-emitting applications due to their anisotropic optical properties and large absorption cross-section. Traditional synthesis methods for tetrapod CdSe/CdS QDs usually employ fatty phosphonic acid ligands to induce the growth of wurtzite CdS arms on cubic CdSe QDs at high temperatures (350-380 °C). Here, a low temperature (120 °C) route was developed for the synthesis of tetrapod CdSe/CdS QDs using mixed amine ligands instead of phosphonic acid ligands. A study of the growth mechanism reveals that the amine ligands induce the orientation growth of cubic CdS arms on wurtzite CdSe QDs through a pyramid-shaped intermediate structure. The low reaction temperature facilitates the growth control of the tetrapod CdSe/CdS QDs through a microfluidic reactor. This study substantially simplifies the synthetic chemistry for the anisotropic growth of CdS on CdSe QDs, paving the way for green and economic production of tetrapod CdSe/CdS QDs towards efficient light-emitting applications.

Cl−-Induced selective fabrication of 3D AgCl microcrystals by a one-pot synthesis method

Cl⁻ induces the shape evolution of AgCl crystals with different morphologies.

Spatial charge separation and high-index facet dependence in polyhedral Cu2O type-II surface heterojunctions for photocatalytic activity enhancement

Polyhedral 30-faceted Cu₂O microcrystal exposed with a {332}–{001} type-II surface heterojunction was synthesized, which displayed an efficient spatial charge separation and high-index facet dependence for photocatalytic activity enhancement.

Identification of the Miller indices of a crystallographic plane: a tutorial and a comprehensive review on fundamental theory, universal methods based on different case studies and matters needing attention

Micro-/nanostructures exposed with special crystallographic planes (surface or crystal facets) exhibit distinctive physicochemical properties because of their unique atomic arrangements, resulting in their widespread applications in the fields of catalysis, energy conversion, sensors, electrical devices and so on. Therefore, tremendous progress has been made in facet-dependent investigation of various micro-/nanocrystals over the past decades. However, a lot of beginners including undergraduate students as well as graduate students lack systematic knowledge and don't know how to identify the Miller indices of a crystallographic plane in the actual research process. So far, to the best of our knowledge, there is no specialized review article in this respect. Herein, we present a tutorial and a comprehensive review on the identification of the Miller indices of a crystallographic plane, including fundamental theory, universal methods based on different case studies, and matters needing attention. Hopefully, this tutorial review will be a beneficial theoretical and practical reference for beginners currently focusing on the controllable preparation and facet-dependent investigation of micro-/nanocrystals.

An Sc-based coordination polymer with concaved superstructures: preparation, formation mechanism, conversion, and their electrochemistry properties

Scandium-based coordination polymer octahedrons with concaved surfaces have been fabricated. The formation mechanism was also investigated. Sc₂O₃ octahedrons were obtained after simple calcination in a N₂ atmosphere.

One-pot sonochemical synthesis of 3D flower-like hierarchical AgCl microsphere with enhanced photocatalytic activity

A highly uniform 3D flower-like hierarchical AgCl microsphere was prepared by sonochemical method with the existence of β-dextrin. The 3D flower-like hierarchical structure can be ascribed to the existence of β-dextrin, which provides nucleation sites for the growth of nanosheets because of the strong interaction between β-dextrin and Ag⁺. The 3D flower-like hierarchical AgCl microspheres were assembled by numerous interleaving nanosheet petals with small thickness. Benefiting from the unique structural features, the as-prepared 3D flower-like hierarchical AgCl microsphere exhibited higher degradation efficiency with degrading 98.17% of methylene blue (MB) and 88.50% of tetracycline (TC) within 40 min, which were both remarkably higher than those of irregular AgCl under visible light irradiation. Besides, the photocatalytic degradation rate constant of 3D flower-like hierarchical AgCl microsphere (0.063 min^-1) for MB was 3.94 times higher than that of irregular AgCl (0.016 min^-1). Moreover, a possible mechanism for the formation and excellent photocatalytic performance of 3D flower-like hierarchical AgCl microsphere was also proposed.

Stepwise Evolution of AgCl Microcrystals from Octahedron into Hexapod with Mace Pods and their Visible Light Photocatalytic Activity

In this work, we have synthesized hexapods AgCl crystals with mace pods for the first time. Diallyldimethylammonium chloride (DDA)-controlled stepwise evolution of AgCl crystals from octahedron to hexapods with mace pods are achieved by one-pot method. The intermediates have been captured which show the basic process of crystal growth. In this process, octahedra AgCl crystals firstly grow along the <100> direction and then change to grow in the <110> direction. At the same time, the size of AgCl grow from 2 μm to 20 μm. Due to the poor absorption of visible light by AgCl, sodium borohydride(NaBH4) is used to reduce AgCl hexapods with mace pods crystals. By changing the mole ratio(R) of NaBH4 to AgCl, the new structure was reduced to obtain a series of Ag@AgCl microstructures. Visible light catalysis effects of the Ag@AgCl microstructures on degradation of methyl orange (MO) were investigated. The Ag@AgCl microstructures with R = 0.02 have a high photocatalytic performance, which completely degrades MO in 40 minutes.

Revisiting the Polyol Synthesis of Silver Nanostructures: Role of Chloride in Nanocube Formation

Chloride (Cl^-) is often used together with polyvinylpyrrolidone (PVP) in the polyol synthesis of Ag nanocubes. In the literature, shape control is attributed predominantly to the preferential binding of PVP to Ag(100) facets compared to Ag(111) facets, whereas the role of Cl^- has not been well studied. Several hypotheses have been proposed regarding the role of Cl^-; however, there is still no consensus regarding the exact influence of Cl^- in the shape-controlled synthesis of Ag nanocubes. To examine the influence of Cl^-, we undertook a joint theoretical-experimental study. Experimentally, we examined the influence of Cl^- concentration on the shape of Ag nanoparticles (NPs) at constant H⁺ concentration. In the presence of H⁺, in situ formed HNO₃ etches the initially formed Ag seeds and slows down the overall reduction of Ag⁺, which promotes the formation of monodisperse Ag NPs. Ex situ experiments probed the evolution of Cl^- during the growth of Ag nanocubes, which involves the initial formation of AgCl nanocubes, and their subsequent dissolution to release Cl^-, which adsorbs onto the surfaces of single crystal seeds to impact shape evolution through apparent thermodynamic control. The formation of cubes is independent of the source of AgCl, indicating temporal control of the Cl^- chemical potential in solution leads to high-yield synthesis of Ag nanocubes. Increasing the concentration of Cl^- alone leads to a progression in shape from truncated octahedra, to cuboctahedra, truncated cubes, and ultimately cubes, directly demonstrating the importance of Cl^- in Ag NP shape control. We used ab initio thermodynamics calculations based on density functional theory to probe the role of Cl^- in directing shape control. With increasing Cl chemical potential (surface coverage), calculated surface energies γ of Ag facets transition from γ₁₁₁ < γ₁₀₀ to γ₁₀₀ < γ₁₁₁ and predict Wulff shapes terminated with an increasing (100) contribution, consistent with experimental observations. The combination of theory and experiment is beneficial for advancing the understanding of nanocrystal formation.

Controllable synthesis of Au nanocrystals with systematic shape evolution from an octahedron to a truncated ditetragonal prism and rhombic dodecahedron

Stepwise evolution of Au nanocrystals from an octahedron to a truncated ditetragonal prism and rhombic dodecahedron was achieved by the polyol synthesis method.

Large-scale synthesis of Au–WO3 porous hollow spheres and their photocatalytic properties

Uniform Au–WO₃ porous hollow spheres have been synthesized on a large-scale by a general in situ reaction. The hybrid materials exhibit excellent activity for visible-light photocatalytic degradation of organic pollutants.

Facet-Engineered Surface and Interface Design of Photocatalytic Materials

The facet-engineered surface and interface design for photocatalytic materials has been proven as a versatile approach to enhance their photocatalytic performance. This review article encompasses some recent advances in the facet engineering that has been performed to control the surface of mono-component semiconductor systems and to design the surface and interface structures of multi-component heterostructures toward photocatalytic applications. The review begins with some key points which should receive attention in the facet engineering on photocatalytic materials. We then discuss the synthetic approaches to achieve the facet control associated with the surface and interface design. In the following section, the facet-engineered surface design on mono-component photocatalytic materials is introduced, which forms a basis for the discussion on more complex systems. Subsequently, we elucidate the facet-engineered surface and interface design of multi-component photocatalytic materials. Finally, the existing challenges and future prospects are discussed.

Sheet-like and truncated-dodecahedron-like AgI structures via a surfactant-assisted protocol and their morphology-dependent photocatalytic performance

Sheet-like and truncated-dodecahedron-like AgI structures are synthesized via a surfactant-assisted method, the latter display boosted photocatalytic performances and excellent recyclability.

Size-tunable uniform gold octahedra: fast synthesis, characterization, and plasmonic properties

Well-defined octahedral Au nanocrystals were facilely and precisely prepared in high yield by modified polyol process.

A template-free solvent-mediated synthesis of high surface area boron nitride nanosheets for aerobic oxidative desulfurization

Hexagonal BN nanosheets with high surface area are developed via methanol-mediated synthesis, presenting outstanding catalytic performance in aerobic oxidative desulfurization.