Graphene/Carbon Dot Hybrid Thin Films Prepared by a Modified Langmuir-Schaefer Method

The special electronic, optical, thermal, and mechanical properties of graphene resulting from its 2D nature, as well as the ease of functionalizing it through a simple acid treatment, make graphene an ideal building block for the development of new hybrid nanostructures with well-defined dimensions and behavior. Such hybrids have great potential as active materials in applications such as gas storage, gas/liquid separation, photocatalysis, bioimaging, optoelectronics, and nanosensing. In this study, luminescent carbon dots (C-dots) were sandwiched between oxidized graphene sheets to form novel hybrid multilayer films. Our thin-film preparation approach combines self-assembly with the Langmuir-Schaefer deposition and uses graphene oxide nanosheets as template for grafting C-dots in a bidimensional array. Repeating the cycle results in a facile and low-cost layer-by-layer procedure for the formation of highly ordered hybrid multilayers, which were characterized by photoluminescence, UV-visible, X-ray photoelectron, and Raman spectroscopies, as well as X-ray diffraction and atomic force microscopy.</p

Excitonic bands in the spectra of some organic-inorganic hybrid compounds based on metal halide units

Journal URL: http://www.sciencedirect.com/science/journal/0379677

Synthesis and characterization of calcium oxyboroapatite with bimodal porosity

Calcium oxyboroapatite with bimodal porosity and proposed general formula (CaO)x(PO2.5)y(BO1.5)z with 10 ≥ x ≥ 9, y ≥ 4 and z ≥ 1.6 have been prepared for the first time, by thermal processing of sol–gel-derived glass. F-127 triblock copolymer was incorporated in the sol–gel reactions as the structure directing agent under acidic conditions, whereas tributyl borate, triethyl phosphate and calcium nitrate were used as precursors for the glass structure. The prepared materials were chemically analyzed and characterized by X-ray diffraction (XRD), infrared absorption and Raman scattering spectroscopic techniques, where the related XRD patterns clearly revealed growth of rich in boron oxyboroapatite phase with increasing temperature. The oxyboroapatite phases treated at high temperatures exhibited bioactivity after soaking in simulated body fluid (SBF) solution within a few hours and these were observed by μ-Raman and scanning electron microscopy (SEM). Moreover, the external morphology of these materials has been directly observed with SEM microscopy before and after the immersion in SBF. Furthermore, mercury intrusion porosity measurements were taken in order to investigate the porosity, showing bimodal meso- and macro-porosity. Graphical Abstract: [Figure not available: see fulltext.

Efficient and Rapid Photocatalytic Reduction of Hexavalent Chromium Achieved by a Phloroglucinol-Derived Microporous Polymeric Organic Framework Solid

A microporous polymeric organic framework (POF) based on phloroglucinol (phlo-POF) was for the first time evaluated on photoreduction and removal processes of hexavalent chromium (Cr6+) from aqueous solutions. The phlo-POF synthesis was based on reaction of phloroglucinol and terephthalaldehyde under hydrothermal conditions. Structural and chemical characterization was performed using UV-vis-NIR diffuse reflectance spectroscopy (DRS), FT-infrared spectroscopy, and thermogravimetric methods, while surface area analysis was employed to determine other physical and surface properties. Batch experiments were conducted on contaminated water to determine the rate and extent of Cr6+ removal and its immobilization by the phlo-POF material. The kinetic studies showed a rapid removal of Cr6+ ions from the water in the presence of the phlo-POF, best described by the zero-order kinetic model. The efficiency of the material with UV-C irradiation on Cr6+ reduction was compared with a well-studied material, the Degussa P-25 TiO2 catalyst, and found to be ∼200% higher. Cycle experiments verify the successful reuse of the phlo-POF photocatalyst for at least ten times for Cr6+ reduction

Spectroscopic Studies of (C10h21nh3)2pbi4, (Ch3nh3)(C10h21nh3)2pb2i7, (Ch3nh3)Pbi3, and Similar Compounds

Journal URL: http://www.sciencedirect.com/science/journal/0379677

Synthesis, characterization and use of highly stable trimethyl sulfonium tin(IV) halide defect perovskites in dye sensitized solar cells

We report here on the crystal structure and physical properties of ((CH3)3S)2SnX6 (X = Cl, Br, I) compounds as well as the application of ((CH3)3S)2SnI6 in dye-sensitized solar cells. Powder X-ray diffraction and Rietveld analysis show that the materials form a cubic structure with a 0D network of [SnX6] octahedra, which can be considered as a defect variant (AB0.5X3) of the perovskite archetype (ABX3). The electronic band gaps of ((CH3)3S)2SnX6 were determined by UV–Vis reflectance spectroscopy at 4.1, 2.9 and 1.4 eV for X = Cl, Br, and I, respectively. The direct bandgap and its relative decrease in the order of light to heavy halide was independently verified by density-of-states calculations. According to Raman spectroscopy, the lattice vibrations also depend largely on the halogen atom. The air-stable and non-toxic ((CH3)3S)2SnI6 compound was incorporated in electrolyte-free, dye-sensitized solar cells based on the Z907 chromophore chemisorbed onto mesoporous titania electrodes. A power conversion efficiency of 5% is achieved for these photovoltaic devices, confirming efficient charge transport in the bulk ((CH3)3S)2SnI6 and hole extraction at the perovskite-Pt interface. © 2018 Elsevier Lt

Synthesis and Characterization of Lead-Free (CH3)3SSnI3 1-D Perovskite

We report on the preparation, crystal structure and spectral properties of the trimethylsulfonium tin triiodide perovskite, (CH3)3SSnI3. The air-sensitive lead-free perovskite compound is prepared by reacting the (CH3)3SI and SnI2 solid precursors in evacuated silica tubes at 100°C. According to powder x-ray diffraction and Rietveld analysis, (CH3)3SSnI3 crystallizes at room temperature in hexagonal symmetry and forms a 1D network of face-sharing [SnI6] octahedra along the c axis. UV–Vis reflectance and photoluminescence spectroscopies reveal a direct energy band gap of 2.85 eV accompanied by a weak luminescence signal. Multi-temperature Raman spectroscopy reveals a fully reversible structural phase transition just below 0°C related to the reduction of the unit cell symmetry. Comparison with the widely studied Cs-, CH3NH3- and (NH2)2CH-based 3D-perovskites that are commonly used in third generation solar cells confirms the higher stability of (CH3)3SSnI3. This is attributed to the beneficial role of the bulky trimethylsulfonium group in the ASnI3 structure. © 2019, The Minerals, Metals &amp; Materials Society

New configuration of metallic photocathodes prepared by pulsed laser deposition

We propose a new photocathode configuration which presents the quantum efficiency and work function of yttrium (Y) and at the same time preserves all of the advantages of copper (Cu) when inserted into a radio-frequency gun. The configuration consists of a disk of Y covered by a coating of Cu deposited using the pulsed laser ablation technique, while masking the central part of the Y disk by a shield making the photoemission directly from the Y bulk possible. The new device was characterised by scanning electron microscopy to deduce the morphology and by X-ray diffraction to obtain structure information on both Cu film and Y substrate. The electrical resistivity of the Cu film was also measured obtaining a value slightly greater than that of bulk high purit

Synthesis and characterization of PbI<inf>2</inf> semiconductor quantum wires within layered solids

PbI2 semiconductor quantum wires have been synthesized in the interlayer space of montmorillonite organic modified clays by simple intercalation reactions. The experimental results showed that the quantum wires have been retained within the lamellar space of layer silicates exhibiting a well-defined diameter and narrow length distribution. The synthetic procedure involves chemical reactions within the clay interlayer, which are achieved through a slow mass transport between the clay platelets via a low solubility path between two different lead iodide phases. The structure and properties of the hybrid composites have been studied by means of X-ray diffraction, energy dispersive spectroscopy, Transmission electron microscopy, optical absorption and photoluminescence experiments. The experimental techniques have verified that the resultant organo-clay-semiconductor composite contains within the clay platelets nano sized low dimensional semiconductor species in the form of wires that exhibit well defined energy gap absorption peaks, which are blue shifted due to quantum confinement phenomena

Optical and related properties of natural one-dimensional semiconductors based on PbI and SnI units

Journal URL: http://www.sciencedirect.com/science/journal/0379677