Colloidal nanocrystals (NCs) of APbX3-type lead halide perovskites A = Cs+, CH3NH3 + (methylammonium or MA+) or CH(NH2)2 + (formamidinium or FA+); X = Cl–, Br–, I– have recently emerged as highly ...versatile photonic sources for applications ranging from simple photoluminescence down-conversion (e.g., for display backlighting) to light-emitting diodes. From the perspective of spectral coverage, a formidable challenge facing the use of these materials is how to obtain stable emissions in the red and infrared spectral regions covered by the iodide-based compositions. So far, red-emissive CsPbI3 NCs have been shown to suffer from a delayed phase transformation into a nonluminescent, wide-band-gap 1D polymorph, and MAPbI3 exhibits very limited chemical durability. In this work, we report a facile colloidal synthesis method for obtaining FAPbI3 and FA-doped CsPbI3 NCs that are uniform in size (10–15 nm) and nearly cubic in shape and exhibit drastically higher robustness than their MA- or Cs-only cousins with similar sizes and morphologies. Detailed structural analysis indicated that the FAPbI3 NCs had a cubic crystal structure, while the FA0.1Cs0.9PbI3 NCs had a 3D orthorhombic structure that was isostructural to the structure of CsPbBr3 NCs. Bright photoluminescence (PL) with high quantum yield (QY > 70%) spanning red (690 nm, FA0.1Cs0.9PbI3 NCs) and near-infrared (near-IR, ca. 780 nm, FAPbI3 NCs) regions was sustained for several months or more in both the colloidal state and in films. The peak PL wavelengths can be fine-tuned by using postsynthetic cation- and anion-exchange reactions. Amplified spontaneous emissions with low thresholds of 28 and 7.5 μJ cm–2 were obtained from the films deposited from FA0.1Cs0.9PbI3 and FAPbI3 NCs, respectively. Furthermore, light-emitting diodes with a high external quantum efficiency of 2.3% were obtained by using FAPbI3 NCs.
Crystal defects in highy luminescent colloidal nanocrystals (NCs) of CsPbX3 perovskites (X = Cl, Br, I) are investigated. Here, using X-ray total scattering techniques and the Debye scattering ...equation (DSE), we provide evidence that the local structure of these NCs always exhibits orthorhombic tilting of PbX6 octahedra within locally ordered subdomains. These subdomains are hinged through a two-/three-dimensional (2D/3D) network of twin boundaries through which the coherent arrangement of the Pb ions throughout the whole NC is preserved. The density of these twin boundaries determines the size of the subdomains and results in an apparent higher-symmetry structure on average in the high-temperature modification. Dynamic cooperative rotations of PbX6 octahedra are likely at work at the twin boundaries, causing the rearrangement of the 2D or 3D network, particularly effective in the pseudocubic phases. An orthorhombic, 3D γ-phase, isostructural to that of CsPbBr3 is found here in as-synthesized CsPbI3 NCs.
Highly anisotropic colloidal CsPbBr3 nanoplatelets (NPLs) represent an appealing class of colloidal quantum wells with enhanced light emissivity. Strong quantum confinement imposed by the small ...platelet thickness and atomic flatness gives rise to enhanced oscillator strength, higher exciton binding energy, and narrow emission linewidth. While discrete thicknesses manifest themselves in discrete bandgap energies, fine-tuning of the emission energy can be achieved by compositional modulations. Here we address one of the most debated aspects of perovskite nanoplatelets: their crystal structure. Starting with the direct imaging by high-resolution electron microscopy (providing a clue on the pseudocubic faceting of the NPLs), we focus the study on X-ray total scattering techniques, based on the Debye scattering equation (DSE) approach, to obtain better atomistic insight. The nanoplatelets are six-monolayers thick and exhibit an orthorhombic structure. A thorough structure–morphology characterization unveils a specific orientation of the axial and equatorial bromides of the PbBr6 octahedra versus the NPLs thickness; we found that {010} and {101} planes of the orthorhombic CsPbBr3 lattice (Pnma space group) correspond to the six facets of the NPL, with basal planes being of {101} type. The NPLs undergo a lattice relaxation in comparison to cuboidal CsPbBr3 NCs; the major deformation is observed in the axial direction, which suggests a structural origin of the higher compliance along the b axis. The DSE-based analysis also supports a CsBr surface termination model, with half Cs sites and a half (or slightly more) Br sites vacant.
Abstract
An increasingly important issue in nanoscience and nanotechnology is the accurate determination of nanoparticle sizing. Wide angle X-ray total scattering (WAXTS) data are frequently used to ...retrieve the Particle Size Distributions (PSDs) of nanocrystals of highly technological relevance; however, the PSD shape typically relies on an a-priori assumption. Here, we propose a modified version of the classical iterative Lucy-Richardson (LR) algorithm, which is simple, fast and highly reliable against noise, and demonstrate that the inversion of WAXTS data can be profitably used for recovering accurate PSD regardless of its shape. Computer simulations based on the use of the Debye Scattering Equation (DSE) modelling WAXTS data show that the algorithm is capable of recovering accurate PSDs even when the sample is made of a mixture of different polymorphs and/or exhibits microstrain effects. When applied to the inversion of WAXTS data taken on real samples, the method requires accurate modelling of the nanoparticle crystal structure, which includes structural defects, microstrain and surface induced distortions. Provided that this information is correctly fed to the program, the inversion algorithm reconstructs the WAXTS data with high accuracy and recovers highly robust (against noise) PSDs. Two examples reporting the characterization of Magnetite-Maghemite and commercial P25-Titania nanopowders, are discussed. We demonstrate that pre-assumption of wrong PSD shape leads to inaccurate number-based average sizes in highly polydisperse samples.
Nanosized fertilizers are the new frontier of nanotechnology towards a sustainable agriculture. Here, an efficient N-nanofertilizer is obtained by post-synthetic modification (PSM) of nitrate-doped ...amorphous calcium phosphate (ACP) nanoparticles (NPs) with urea. The unwasteful PSM protocol leads to N-payloads as large as 8.1 w/w%, is well replicated by using inexpensive technical-grade reagents for cost-effective up-scaling and moderately favours urea release slowdown. Using the PSM approach, the N amount is ca. 3 times larger than that obtained in an equivalent one-pot synthesis where urea and nitrate are jointly added during the NPs preparation. In vivo tests on cucumber plants in hydroponic conditions show that N-doped ACP NPs, with half absolute N-content than in conventional urea treatment, promote the formation of an equivalent amount of root and shoot biomass, without nitrogen depletion. The high nitrogen use efficiency (up to 69%) and a cost-effective preparation method support the sustainable real usage of N-doped ACP as a nanofertilizer.
Hybrid organic–inorganic and fully inorganic lead halide perovskite nanocrystals (NCs) have recently emerged as versatile solution-processable light-emitting and light-harvesting optoelectronic ...materials. A particularly difficult challenge lies in warranting the practical utility of such semiconductor NCs in the red and infrared spectral regions. In this context, all three archetypal A-site monocationic perovskitesCH3NH3PbI3, CH(NH2)2PbI3, and CsPbI3suffer from either chemical or thermodynamic instabilities in their bulk form. A promising approach toward the mitigation of these challenges lies in the formation of multinary compositions (mixed cation and mixed anion). In the case of multinary colloidal NCs, such as quinary Cs x FA1–x Pb(Br1–y I y )3 NCs, the outcome of the synthesis is defined by a complex interplay between the bulk thermodynamics of the solid solutions, crystal surface energies, energetics, dynamics of capping ligands, and the multiple effects of the reagents in solution. Accordingly, the rational synthesis of such NCs is a formidable challenge. Herein, we show that droplet-based microfluidics can successfully tackle this problem and synthesize Cs x FA1–x PbI3 and Cs x FA1–x Pb(Br1–y I y )3 NCs in both a time- and cost-efficient manner. Rapid in situ photoluminescence and absorption measurements allow for thorough parametric screening, thereby permitting precise optical engineering of these NCs. In this showcase study, we fine-tune the photoluminescence maxima of such multinary NCs between 700 and 800 nm, minimize their emission line widths (to below 40 nm), and maximize their photoluminescence quantum efficiencies (up to 89%) and phase/chemical stabilities. Detailed structural analysis revealed that the Cs x FA1–x Pb(Br1–y I y )3 NCs adopt a cubic perovskite structure of FAPbI3, with iodide anions partially substituted by bromide ions. Most importantly, we demonstrate the excellent transference of reaction parameters from microfluidics to a conventional flask-based environment, thereby enabling up-scaling and further implementation in optoelectronic devices. As an example, Cs x FA1–x Pb(Br1–y I y )3 NCs with an emission maximum at 735 nm were integrated into light-emitting diodes, exhibiting a high external quantum efficiency of 5.9% and a very narrow electroluminescence spectral bandwidth of 27 nm.
Very small superparamagnetic iron oxide nanoparticles were characterized by innovative synchrotron X-ray total scattering methods and Debye function analysis. Using the information from both Bragg ...and diffuse scattering, size-dependent core–shell magnetite–maghemite compositions and full size (number- and mass-based) distributions were derived within a coherent approach. The magnetite core radii in 10 nm sized NPs well match the magnetic domain sizes and show a clear correlation to the saturation magnetization values, while the oxidized shells seem to be magnetically silent. Very broad superstructure peaks likely produced by the polycrystalline nature of the surface layers were experimentally detected in room temperature oxidized samples. Effective magnetic anisotropy constants, derived by taking the knowledge of the full size-distributions into account, show an inverse dependence on the NPs size, witnessing a major surface contribution. Finally, an additional amorphous component was uncovered within the diffuse scattering of the “ordered” magnetite–maghemite NPs. Under the hypothesis that this material may form an external dead layer, an additional thickness varying between 0.3 and 1.0 nm should be added to the overall core–shell NPs size.
Tafamidis, chemical formula C14H7Cl2NO3, is a drug used to delay disease progression in adults suffering from transthyretin amyloidosis, and is marketed worldwide under different tradenames as a free ...acid or in the form of its meglumine salt. The free acid (CAS no. 594839-88-0) is reported to crystallize as distinct (polymorphic) crystal forms, the thermal stability and structural features of which remained thus far undisclosed. In this paper, we present—by selectively isolating highly pure batches of Tafamidis Form 1 and Tafamidis Form 4—the full characterization of these solids, in terms of crystal structures (determined using state-of-the-art structural powder diffraction methods) and spectroscopic and thermal properties. Beyond conventional thermogravimetric and calorimetric analyses, variable-temperature X-ray diffraction was employed to measure the highly anisotropic response of these (poly)crystalline materials to thermal stimuli and enabled the determination of the linear and volumetric thermal expansion coefficients and of the related indicatrix. Both crystal phases are monoclinic and contain substantially flat and π-π stacked Tafamidis molecules, arranged as centrosymmetric dimers by strong O-H···O bonds; weaker C-H···N contacts give rise, in both polymorphs, to infinite ribbons, which guarantee the substantial stiffness of the crystals in the direction of their elongation. Complete knowledge of the structural models will foster the usage of full-pattern quantitative phase analyses of Tafamidis in drug and polymorphic mixtures, an important aspect in both the forensic and the industrial sectors.
Two isoreticular series of pyrazolate-based 3D open metal–organic frameworks, MBDP_X, adopting the NiBDP and ZnBDP structure types H2BDP = 1,4-bis(1H-pyrazol-4-yl)benzene, were synthesized with the ...new tagged organic linkers H 2 BDP_X (X = −NO2, −NH2, −OH). All of the MBDP_X materials have been characterized through a combination of techniques. IR spectroscopy proved the effective presence of tags, while X-ray powder diffraction (XRPD) witnessed their isoreticular nature. Simultaneous TG/DSC analyses (STA) demonstrated their remarkable thermal stability, while variable-temperature XRPD experiments highlighted their high degree of flexibility related to guest-induced fit processes of the solvent molecules included in the channels. A structural isomer of the parent NiBDP was obtained with a sulfonate tagged ligand, H 2 BDP_SO 3 H. Structure solution from powder diffraction data collected at three different temperatures (room temperature, 90, and 250 °C) allowed the determination of its structure and the comprehension of its solvent-related flexible behavior. Finally, the potential application of the tagged MOFs in selective adsorption processes for gas separation and purification purposes was investigated by conventional single component adsorption isotherms, as well as by advanced experiments of pulse gas chromatography and breakthrough curve measurements. Noteworthy, the results show that functionalization does not improve the adsorption selectivity (partition coefficients) for the resolution of gas mixtures characterized by similar high quadrupole moments (e.g., CO2/C2H2); however, the resolution of gas mixtures containing molecules with highly differentiated polarities (i.e., N2/CO2 or CH4/CO2) is highly improved.
Tunable hydrophobicity: Efficient air filters for the protection against chemical warfare agents might be achieved by surface functionalization of the pores in robust metal–organic frameworks (MOFs) ...with fluoroalkyl residues and the precise control of their pore size (see picture). These MOFs capture harmful volatile organic compounds even under extremely moist conditions (80 % relative humidity).
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