Self-Assembly of CsPbBr₃ Nanocubes into 2D Nanosheets

All-inorganic metal halide perovskites have attracted considerable attention due to their high application potentials in optoelectronics, photonics, and energy conversion. Herein, two-dimensional (2D) CsPbBr3 nanosheets with a thickness of about 3 nm have been synthesized through a simple chemical process based on a hot-injection technique. The lateral dimension of CsPbBr3 nanosheets ranges from 11 to 110 nm, which can be tuned by adjusting the ratio of short ligands (octanoic acid and octylamine) over long ligands (oleic acid and oleylamine). The nanosheets result from the self-assembly of CsPbBr3 nanocubes with an edge length of about 3 nm, which possess the same crystal orientation. In addition, an amorphous region of about 1 nm in width is found between adjacent nanocubes. To investigate both the structure and the growth mechanism of these nanosheets, microstructural characterizations at the atomic scale are conducted, combined with X-ray diffraction analysis, 1H nuclear magnetic resonance (1H NMR) measurement, and density functional theory (DFT) calculation, aiming to determine the configuration of different ligands adsorbed onto CsPbBr3. Our results suggest that the adjacent nanocubes are mainly connected together by short ligands and inclined long ligands. On the basis of the DFT calculation results, a relationship is derived for the volume ratio of short ligands over long ligands and the lateral dimensions of CsPbBr3 nanosheets. Moreover, a physicochemical mechanism is proposed to explain the 2D growth of CsPbBr3 nanosheets. Such a finding provides new insights regarding the well-ordered self-arrangement of CsPbBr3 nanomaterials, as well as new routes to synthesize 2D CsPbX3 (X = Cl and I) nanosheets of suitable dimensions for specific and large-scale applications

Reactable Polyelectrolyte-Assisted Synthesis of BiOCl with Enhanced Photocatalytic Activity

The reactable polyelectrolyte, poly­(allylamine hydrochloride), was used for the first time to fabricate BiOCl materials via an assisted solvothermal method. The influence of polyelectrolyte concentrations on the formation of BiOCl was systematically investigated. The samples were characterized by energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), N₂ gas sorption, infrared spectroscopy (FT-IR), as well as ultraviolet–visible diffuse reflectance spectroscopy (DRS). The results showed that the polyelectrolyte, which acted as reactant, template, or structure-directing agent, had a great effect on the structure of as-fabricated BiOCl materials during the reactive process. The possible formation mechanism of the BiOCl materials has been studied. Moreover, the photocatalytic activity of the as-fabricated BiOCl was evaluated by the degradation of rhodamine B (RhB) under visible light irradiation. Furthermore, the relationship between the structure of the BiOCl materials and the photocatalyic activity was studied in detail. The holes rather than ^•OH were the predominant active species in the photocatalytic process. Also, it can be supposed that the improved light harvesting, high surface area, O-vacancies, enhanced adsorption capability of dye, faster interfacial charge separation, and the special structure of BiOCl had contributed to the good photocatalytic activity and high photostability of BiOCl microspheres. This route preparing the BiOCl materials with special structure can be expected to be applicable to the preparation of other materials with novel morphologies and advanced properties in all kinds of fields, including photocatalysis and electrochemistry

Self-Assembly Hierarchical Silica Nanotubes with Vertically Aligned Silica Nanorods and Embedded Platinum Nanoparticles

We report a simple method for the fabrication of hierarchical silica-Pt nanotubes. In the system, initial Pt NPs can be obtained via the reduction of H₂PtCl₆ with trisodium citrate as reductant. The self-assembled SiO₂@Pt@SiO₂ spheres were stuck together and etched through the “surface-protected etching” strategy. Many vertically aligned silica branches <i>in situ</i> grew from the inlaid SiO₂@Pt@SiO₂ spheres, fabricating the hierarchical silica-Pt nanotubes automatically. TEM and SEM were conducted to monitor the morphological evolution. The effects of the PVP concentration and molar ratios of NH₄OH to TEOS have also been investigated with a series of contrast experiments. Furthermore, in this work, several potential applications of HSNs have been investigated, such as the synthesis of Pt-CeO₂ nanotubes and other single or double metal nanotubes. Besides, the hierarchical silica-Pt nanotubes exhibited a high thermal stability and excellent catalytic performance in the reaction of propane dehydrogenation, suggesting their potential application in various high-temperature reactions

Sn²⁺-Doped Double-Shelled TiO₂ Hollow Nanospheres with Minimal Pt Content for Significantly Enhanced Solar H₂ Production

H2 evolution by photocatalytic water splitting has attracted a lot of attention due to the global depletion of oil resources. Therefore, much effort is devoted to develop low-cost, highly active photocatalysts. Here, a facile strategy is proposed for the synthesis of low Pt content Sn2+-doped double-shelled Pt/TiO2 hollow nanocatalyst (DHS–PtSn2+) with excellent solar H2 production properties. After calcination in N2, DHS–PtSn2+ showed highest photocatalytic H2 production rate of 28 502 μmol h–1 g–1, nearly threefold higher than the Sn4+-doped counterpart, thereby demonstrating better synergistic effect of Sn2+ than Sn4+ in H2 evolution. The influences of calcination atmosphere, Sn2+ content, and Sn/Pt atomic ratio on H2 production have been investigated with a series of contrast experiments. Besides, the proposed Sn2+-doping strategy could also be applied in other light-sensitive materials (e.g., homemade TiO2 nanoparticles, commercial P25, and g-C3N4), suggesting its extensive applications in H2 production. Finally, based on the excellent synergistic effect of Sn2+ in H2 production, a possible photocatalytic mechanism was tentatively proposed

Hierarchical Honeycomb Br-, N‑Codoped TiO₂ with Enhanced Visible-Light Photocatalytic H₂ Production

The halogen elements modification strategy of TiO2 encounters a bottleneck in visible-light H2 production. Herein, we have for the first time reported a hierarchical honeycomb Br-, N-codoped anatase TiO2 catalyst (HM-Br,N/TiO2) with enhanced visible-light photocatalytic H2 production. During the synthesizing process, large amounts of meso–macroporous channels and TiO2 nanosheets were fabricated in massive TiO2 automatically, constructing the hierarchical honeycomb structure with large specific surface area (464 m2 g–1). cetyl trimethylammonium bromide and melamine played a key role in constructing the meso–macroporous channels. Additionally, HM-Br,N/TiO2 showed a high visible-light H2 production rate of 2247 μmol h–1 g–1, which is far more higher than single Br- or N-doped TiO2 (0 or 63 μmol h–1 g–1, respectively), thereby demonstrating the excellent synergistic effects of Br and N elements in H2 evolution. In HM-Br,N/TiO2 catalytic system, the codoped Br–N atoms could reduce the band gap of TiO2 to 2.88 eV and the holes on acceptor levels (N acceptor) can passivate the electrons on donor levels (Br donor), thereby preventing charge carriers recombination significantly. Furthermore, the proposed HM-Br,N/TiO2 fabrication strategy had a wide range of choices for N source (e.g., melamine, urea, and dicyandiamide) and it can be applied to other TiO2 materials (e.g., P25) as well, thereby implying its great potential application in visible-light H2 production. Finally, on the basis of experimental results, a possible photocatalytic H2 production mechanism for HM-Br,N/TiO2 was proposed

Fabrication of Ellipsoidal Silica Yolk–Shell Magnetic Structures with Extremely Stable Au Nanoparticles as Highly Reactive and Recoverable Catalysts

A novel strategy was reported for the fabrication of yolk–shell magnetic MFSVmS-Au nanocomposites (NCs) consisting of double-layered ellipsoidal mesoporous silica shells, numerous sub-4 nm Au nanoparticles (NPs), and magnetic Fe central cores. The hierarchical FSVmS NCs with ellipsoidal α-Fe₂O₃@mSiO₂/mSiO₂ as yolks/shells were first prepared through the facile sol–gel template-assisted method, and plenty of extremely stable ultrafine Au NPs were postencapsulated within interlayer cavities through the unique deposition–precipitation method mediated with Au­(en)₂Cl₃ compounds. Notably, ethylenediamine ligands were used to synthesize the stable cationic complexes, [Au­(en)₂]³⁺, that readily underwent the deprotonation reaction to chemically modify negatively charged mesoporous silica under alkaline conditions. The subsequent two-stage programmed hydrogen annealing initiated the in situ formation of Au NPs and the reduction of α-Fe₂O₃ to magnetic Fe, where the synthesized Au NPs were highly resistant to harsh thermal sintering even at 700 °C. Given its structural superiority and magnetic nature, the MFSVmS-Au was demonstrated to be a highly efficient and recoverable nanocatalyst with superior activity and reusability toward the reduction of 4-nitrophenol to 4-aminophenol, and the pristine morphology was retained after six recycling tests

Sn²⁺-Doped Double-Shelled TiO₂ Hollow Nanospheres with Minimal Pt Content for Significantly Enhanced Solar H₂ Production

H₂ evolution by photocatalytic water splitting has attracted a lot of attention due to the global depletion of oil resources. Therefore, much effort is devoted to develop low-cost, highly active photocatalysts. Here, a facile strategy is proposed for the synthesis of low Pt content Sn²⁺-doped double-shelled Pt/TiO₂ hollow nanocatalyst (DHS–PtSn²⁺) with excellent solar H₂ production properties. After calcination in N₂, DHS–PtSn²⁺ showed highest photocatalytic H₂ production rate of 28 502 μmol h^–1 g^–1, nearly threefold higher than the Sn⁴⁺-doped counterpart, thereby demonstrating better synergistic effect of Sn²⁺ than Sn⁴⁺ in H₂ evolution. The influences of calcination atmosphere, Sn²⁺ content, and Sn/Pt atomic ratio on H₂ production have been investigated with a series of contrast experiments. Besides, the proposed Sn²⁺-doping strategy could also be applied in other light-sensitive materials (e.g., homemade TiO₂ nanoparticles, commercial P25, and g-C₃N₄), suggesting its extensive applications in H₂ production. Finally, based on the excellent synergistic effect of Sn²⁺ in H₂ production, a possible photocatalytic mechanism was tentatively proposed

Monodisperse PdBi Nanoparticles with a Face-Centered Cubic Structure for Highly Efficient Ethanol Oxidation

Alloyed Pd-based nanocatalysts are considered as highly active fuel cell anodes toward the ethanol oxidation reaction (EOR). However, challenges remain in synthesizing free-standing monodisperse nanoparticles (NPs) with outstanding mass activity and long-term stability. In this work, PdBi NPs are synthesized by a one-step oil bath method with controllable sizes and compositions. The doping of Bi displays a positive effect on the oxidation of ethanol. The Pd8Bi NPs with an average size of 9.0 nm are found to possess an exceptional electrocatalytic mass activity with superior antitoxic ability and outstanding long-term stability toward EOR. These are mainly attributed to the change in the electronic structure and the d-band center of Pd, increase of the interatomic distance within a unit cell, and large electrochemically active surface area values, with lots of reaction sites provided by the morphology-optimized NPs. Higher electrocatalytic temperatures, higher pH values, and higher concentrations of C2H5OH accelerate each step of electro-oxidation on EOR. The density functional theory calculations demonstrate that the energy barrier of PdBi NPs can be reduced by adjusting the Bi content, resulting in excellent electrocatalytic activity toward EOR. This work provides a promising strategy to prepare monodisperse PdM alloys as efficient catalysts for fuel electro-oxidation