Formation of Scrolled Silver Vanadate Nanopeapods by Both Capture and Insertion Strategies

Ag-containing vanadate nanopeapods (NPPs) have been prepared by two distinct approaches. In the first, solvothermal methods utilizing 12-nm Ag nanoparticles (NPs) and vanadate nanosheets (NSs) lead to the formation of Ag NPPs where NPs are captured during the scrolling of NSs. High NP loadings are obtained with ∼40% of the NPPs ≥80% full. In the second approach, NPs and preformed nanoscrolls (NScs) are combined in toluene, and on slow evaporation of the solvent, NPs are drawn into the scrolls. This insertion approach produces much lower loadings with larger NP–NP interparticle distances. Surface plasmon resonance measurements on the series show a red shift in the NPPs relative to free Ag NPs with the solvothermally prepared NPPs exhibiting the greatest effect. Also of significance is that some vanadate NScs and NPPs demonstrate unusual asymmetric scrolling behavior; eccentric convolution occurs such that small and large interlayer spacings are realized on opposite sides of a scroll

Fabrication of Nanopeapods: Scrolling of Niobate Nanosheets for Magnetic Nanoparticle Chain Encapsulation

Scrolling of niobate nanosheets (NSs) in the presence of magnetic nanoparticle (NP) chains can lead to peapodlike structures. Surface functional groups on both the NSs and NPs are important in directing the assembly and subsequent NS convolution. The dimensions of the peapods are typically dictated by the diameters of the NPs and the length of the NP chains

Particle Placement and Sheet Topological Control in the Fabrication of Ag–Hexaniobate Nanocomposites

Synthetic methods are demonstrated that allow for the fabrication of Ag–hexaniobate nanocomposites with directed nanoparticle (NP) placement and nanosheet morphological control. The solvothermal treatment of exfoliated nanosheets (NSs) in the presence of Ag NPs leads to a high yield of Ag nanocomposites. This approach is quite flexible and, with control of time and temperature, can be used to produce nanocomposites with specific architectures; Ag NPs can be attached to nanosheets, attached to the surfaces of nanoscrolls, or at higher temperatures, captured within nanoscrolls to form nanopeapod (NPP) structures. The decorated nanosheets and nanoscrolls show surface plasmon resonance (SPR) maxima similar to that of free Ag NPs, while the Ag NPPs exhibit a red shift of about 10 nm

Rapid Topochemical Modification of Layered Perovskites via Microwave Reactions

An effective microwave approach to the topochemical modification of different layered oxide perovskite hosts is presented where cation exchange, grafting, and intercalation reactions with acid, <i>n</i>-alkyl alcohols, and <i>n</i>-alkylamines, respectively, are successfully carried out. Microwave-assisted proton exchange reactions involving double- and triple-layered Dion–Jacobson and Ruddlesden–Popper perovskite family members, RbLnNb₂O₇ (Ln = La, Pr), KCa₂Nb₃O₁₀, Li₂CaTa₂O₇, and Na₂La₂Ti₃O₁₀, were found to be quite efficient, decreasing reaction times from several days to ≤3 h. Grafting and intercalation reactions involving double-layered perovskites were also quite rapid with full conversions occurring in as fast as an hour. Interestingly, triple-layered hosts were found to show different behavior; when complete intercalations were possible, grafting reactions were limited at best. Utilization of this rapid synthetic approach could help facilitate the fabrication of new organic–inorganic hybrids

Topochemical Synthesis of Alkali-Metal Hydroxide Layers within Double- and Triple-Layered Perovskites

The formation of alkali-metal hydroxide layers within lamellar perovskites has been accomplished by a two-step topochemical reaction strategy. Reductive intercalation of ALaNb₂O₇ with alkali metal (A = K, Rb) and RbCa₂Nb₃O₁₀ with Rb leads to A₂LaNb₂O₇ and Rb₂Ca₂Nb₃O₁₀, respectively. Oxidative intercalation with stoichiometric amounts of water vapor, produced by the decomposition of calcium oxalate monohydrate in a sealed ampule, allows the insertion hydroxide species. Compounds of the form (A₂OH)­LaNb₂O₇ (A = K, Rb) and (Rb₂OH)­Ca₂Nb₃O₁₀ are accessible. X-ray diffraction data indicates a clear layer expansion of almost 3 Å on the insertion of hydroxide relative to that of the parent. Rietveld refinement of neutron diffraction data collected on deuterated samples of (Rb₂OD)­LaNb₂O₇ (<i>P</i>4/<i>mmm</i> space group, <i>a</i> = 3.9348(1) Å, <i>c</i> = 14.7950(7) Å) finds that both rubidium and oxygen species reside in cubic sites forming a CsCl-like interlayer structure between niobate perovskite blocks. Hydrogens, attached to the interlayer oxygens, are disordered over a 4-fold site in the <i>x</i>–<i>y</i> plane and have O–H bond distances (0.98 Å) consistent with known hydroxide species. This synthetic approach expands the library of available topochemical reactions, providing a facile method for the construction of alkali-metal hydroxide layers within receptive perovskite hosts

High-Yield Solvothermal Synthesis of Magnetic Peapod Nanocomposites via the Capture of Preformed Nanoparticles in Scrolled Nanosheets

A versatile method has been developed for the fabrication of magnetic peapod nanocomposites with preformed nanoparticles (NPs). With use of a solvothermal treatment, NPs combined with acid-exchanged hexaniobate crystallites readily produce nanopeapods (NPPs). This approach is effectively demonstrated on a series of ferrite NPs (≤14 nm) where Fe₃O₄@hexaniobate NPPs are rapidly (∼6 h) generated in high yield. When NP samples with different sizes are reacted, clear evidence for size selectivity is seen. Magnetic dipolar interactions between ferrite NPs within the Fe₃O₄@hexaniobate samples lead to significant rise in coercivity, increasing almost fourfold relative to free particles. Other magnetic ferrites NPPs, MFe₂O₄@hexaniobate (M = Mn, Co, Ni), can also be prepared. This synthetic approach to nanopeapods is quite versatile and should be readily extendable to other, nonferrite NPs or NP combinations so that cooperative properties can be exploited while the integrity of the NP assemblies is maintained

From Tetrahedral to Octahedral Iron Coordination: Layer Compression in Topochemically Prepared FeLa₂Ti₃O₁₀

Synthesis, characterization, and thermal modification of the new layered perovskite FeLa₂Ti₃O₁₀ have been studied. FeLa₂Ti₃O₁₀ was prepared by ion exchange of the triple-layered Ruddlesden–Popper phase Li₂La₂Ti₃O₁₀ with FeCl₂ at 350 °C under static vacuum. Rietveld refinement on synchrotron X-ray diffraction data indicates that the new phase is isostructural with CoLa₂Ti₃O₁₀, where Fe^II cations occupy slightly compressed/flattened interlayer tetrahedral sites. Magnetic measurements on FeLa₂Ti₃O₁₀ display Curie–Weiss behavior at high temperatures and a spin-glass transition at lower temperatures (<30 K). Thermal treatment in oxygen shows that FeLa₂Ti₃O₁₀ undergoes a significant cell contraction (Δ<i>c</i> ≈ −2.7 Å) with a change in the oxidation state of iron (Fe²⁺ to Fe³⁺); structural analysis and Mössbauer studies indicate that upon oxidation the local iron environment goes from tetrahedral to octahedral coordination with some deintercalation of iron as Fe₂O₃ to produce Fe_0.67La₂Ti₃O₁₀