scispace - formally typeset
Search or ask a question

Showing papers in "CrystEngComm in 2015"


Journal ArticleDOI
TL;DR: In this article, a novel growth concept based on colloidal stability is deduced, which is in contrast to nucleation models and allows a description of colloidal growth processes from a different perspective.
Abstract: In the past few decades, much effort was put into the development of synthetic strategies to produce nanoparticles of different sizes and morphologies and a large number of scientific contributions is dedicated to the characterization and application of metal nanoparticles. In contrast, only few studies deal with particle formation mechanisms. As a consequence, theoretical concepts that describe particle growth processes are very rare and the few existing models are hardly able to explain how synthesis parameters influence the final particle size distribution. This contribution discusses recent experimental results from which a novel growth concept based on colloidal stability is deduced. The growth concept is in contrast to nucleation models and allows a description of colloidal growth processes from a different perspective. It states that for most syntheses the minimal particle size is rather determined by colloidal than thermodynamic stability making a nucleation model irrelevant.

472 citations


Journal ArticleDOI
TL;DR: In this article, a single crystal of tetragonal CH3NH3PbI3 with dimensions of 10 mm × 10mm × 8 mm was grown by a temperature-lowering method in HI solution.
Abstract: Organic–inorganic hybrid perovskite materials have been receiving considerable attention due to their promising applications in many optoelectronic fields. However, some of the fundamental properties of perovskite materials are still disputed, because most of them are derived from a thin-film state. To comprehend the intrinsic characteristics in a single crystal, herein we report, for the first time, the bulk crystal growth of CH3NH3PbI3. Single crystals of tetragonal CH3NH3PbI3 with dimensions of 10 mm × 10 mm × 8 mm were grown by a temperature-lowering method in HI solution. Studies in to the refinement and orientations of the CH3NH3PbI3 single crystal structure were conducted based on a high quality crystal. The absorption edge of a CH3NH3PbI3 single crystal was located at about 836 nm, indicating that the band gap of CH3NH3PbI3 is approximately 1.48 eV, which is close to the theoretical results and smaller than those derived from polycrystalline and thin-films. CH3NH3PbI3 crystal exhibits a relatively wide absorption (from 250 nm to 800 nm) and a relatively good thermal stability.

456 citations


Journal ArticleDOI
TL;DR: In this paper, a computational study of 1061 experimentally determined crystal structures of 508 polymorphic organic molecules has been performed with state-of-the-art lattice energy minimisation methods, using a hybrid method that combines density functional theory intramolecular energies with an anisotropic atom-atom intermolecular model.
Abstract: A computational study of 1061 experimentally determined crystal structures of 508 polymorphic organic molecules has been performed with state-of-the-art lattice energy minimisation methods, using a hybrid method that combines density functional theory intramolecular energies with an anisotropic atom–atom intermolecular model. Rigid molecule lattice dynamical calculations have also been performed to estimate the vibrational contributions to lattice free energies. Distributions of the differences in lattice energy, free energy, zero point energy, entropy and heat capacity between polymorphs are presented. Polymorphic lattice energy differences are typically very small: over half of polymorph pairs are separated by less than 2 kJ mol−1 and lattice energy differences exceed 7.2 kJ mol−1 in only 5% of cases. Unsurprisingly, vibrational contributions to polymorph free energy differences at ambient conditions are dominated by entropy differences. The distribution of vibrational energy differences is narrower than lattice energy differences, rarely exceeding 2 kJ mol−1. However, these relatively small vibrational free energy contributions are large enough to cause a re-ranking of polymorph stability below, or at, room temperature in 9% of the polymorph pairs.

293 citations


Journal ArticleDOI
TL;DR: In this paper, a comprehensive review of the controllable growth of typical transition-metal oxide nanostructures (e.g., WOx, FeOx, ZnO, TiO2, VO2) is presented.
Abstract: Nanostructured transition-metal oxides exhibit excellent properties, such as ferromagnetic, ferroelectric, photoluminescence and semiconductive behaviors, etc. The band gap and electronic structure of these oxides can be controlled by size and dimensions; they can also be used in a wide range of applications including microelectronics, energy storage, sensors, and biomedicine due to their tunable chemical and physical properties. Here, we give a comprehensive review of the controllable growth of some typical transition-metal oxide nanostructures (e.g., WOx, FeOx, ZnO, TiO2, VO2, etc.), which can be used to effectively understand the fabrication methods as well as the growth mechanism and inspire their potential applications.

225 citations


Journal ArticleDOI
TL;DR: In this article, the basic elements of MOF assembly are discussed and a conceptual hierarchy of structural elements are presented to assist in understanding how unique properties in these materials can be achieved.
Abstract: Metal–Organic Frameworks (MOFs) are a rapidly expanding class of hybrid organic–inorganic materials that can be rationally designed and assembled through crystal engineering. The explosion of interest in this subclass of coordination polymers results from their outstanding properties and myriad possible applications, which include traditional uses of microporous materials, such as gas storage, separations, and catalysis, as well as new realms in biomedicine, electronic devices, and information storage. The objective of this Highlight article is to provide the reader with a sense of where the field stands after roughly fifteen years of research. Remarkable progress has been made, but the barriers to practical and commercial advances are also evident. We discuss the basic elements of MOF assembly and present a conceptual hierarchy of structural elements that assists in understanding how unique properties in these materials can be achieved. Structure–function relationships are then discussed; several are now well understood, as a result of the focused efforts of many research groups over the past decade. Prospects for the use of MOFs in membranes, catalysis, biomedicine, and as active components in electronic and photonic devices are also discussed. Finally, we identify the most pressing challenges in our view that must be addressed for these materials to realize their full potential in the marketplace.

224 citations


Journal ArticleDOI
TL;DR: The fabrication of metal nanoparticles (NP) in porous host matrices, especially metal-organic frameworks (MOFs), has become of great interest in recent years, due to the broad field of applications.
Abstract: The fabrication of metal nanoparticles (NP) in porous host matrices, especially metal–organic frameworks (MOFs) has become of great interest in recent years, due to the broad field of applications. In this article we summarize the progress in the field of NP@MOF materials and illustrate the different preparation methods as well as suitable characterisation techniques. Furthermore, practical applications in the fields of hydrogen storage and heterogeneous catalysis are briefly discussed.

190 citations


Journal ArticleDOI
TL;DR: In this paper, the function of the modulators under real synthesis conditions is rationalized by constructing free energy diagrams, and a mechanistic pathway is presented for the dehydroxylation process of the hexanuclear Zr cluster.
Abstract: The catalytic activity of the Zr-benzenedicarboxylate (Zr-BDC) UiO-66 can be drastically increased if some BDC linkers are missing, as this removes the full coordination of the framework metal ions. As a result, metal centers become more accessible and thus more active for Lewis acid catalysed reactions. Addition of modulators (MDL) to the synthesis mixture can create more linker deficiencies (Vermoortele et al., J. Am. Chem. Soc., 2013, 135, 11465) and leads to a significant increase in the catalytic activity due to the creation of a larger number of open sites. In this paper, we rationalize the function of the modulators under real synthesis conditions by the construction of free energy diagrams. The UiO-66 type materials form a very appropriate test case as the effect of addition of modulators hydrochloric acid (HCl) and trifluoroacetate (TFA) has been intensively investigated experimentally for the synthesis process and post-synthetic thermal activation. Under synthesis conditions, direct removal of BDC linkers requires a high free energy, but replacement of such linker by one or more TFA species might occur especially at high TFA : BDC ratios in the reaction mixture. Post-synthesis activation procedures at higher temperatures lead to substantial removal of the species coordinated to the Zr bricks, creating open metal sites. A mechanistic pathway is presented for the dehydroxylation process of the hexanuclear Zr cluster. For the citronellal cyclization, we show that the presence of some residual TFA in the structure may lead to faster reactions in complete agreement with the experiment. Hirshfeld-e partial charges for the Zr ions have been computed to investigate their sensitivity to substituent effects; a strong correlation with the experimental Hammett parameters and with the rates of the citronellal cyclization is found. The theoretical rationalization may serve as a basis for detailed active site engineering studies.

183 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of different aromatic polycarboxylates on the self-assembly and properties of d10 metal coordination frameworks was explored under hydrothermal conditions and characterized by physicochemical and spectroscopic methods as well as single-crystal X-ray diffraction analysis.
Abstract: To explore the influence of different aromatic polycarboxylates on the self-assembly and properties of d10 metal coordination frameworks, six coordination compounds containing a flexible bis(2-methylbenzimidazole) (pbmb) ligand, formulated as [Ag2(pbmb)(2,6-napdc)]n (1), {[Zn(pbmb)(tbta)]·H2O}n (2), {[Cd(pbmb)(tbta)]·H2O}n (3), [Zn2(pbmb)(btec)(H2O)]n (4), {[Zn2(OH)(pbmb)(bpdc)1.5]·H2O}n (5), and [Cd(pbmb)(3-npa)(H2O)]n (6), have been synthesized under hydrothermal conditions and characterized by physicochemical and spectroscopic methods as well as single-crystal X-ray diffraction analysis (2,6-H2napdc = 2,6-naphthalenedicarboxylic acid, H2tbta = tetrabromoterephthalic acid, H4btec = 1,2,4,5-benzenetetracarboxylic acid, H2bpdc = biphenyl-4,4′-dicarboxylic acid and H23-npa = 3-nitrophthalic acid). Complex 1 possesses an 8-connected 3D coordination framework with sqc3 topology based on rare tetranuclear Ag(I)-cluster secondary building units (SBUs). 2 and 3 possess 2D (4,4) grid structures. 4 shows a novel (3,4,5)-connected 2D network with the Schlafli symbol of {3·4·5}{3·42·52·6}{3·43·53·6·72}. 5 features a uninodal (4,4)-connected net containing binuclear {Zn2(OH)} SBUs and a 2-fold interpenetrating (3,6)-connected supramolecular framework with {42·6}{44·610·8}-3,6T24 topology that is formed via hydrogen bond interactions. Complex 6 is a 1D double-chain structure, which is finally extended to a 3D (4,5,5)-connected supramolecular network via hydrogen bonding interactions. Complexes 1–6 indicate high thermal stabilities and different photoluminescence behavior in the solid state. Moreover, all of these polymer materials manifest excellent photocatalytic activities for the degradation of methyl orange in the photo-Fenton-like process after 120 min (1: 99%, 2: 66%, 3: 91%, 4: 83%, 5: 91% and 6: 93%, respectively).

176 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of the crystal phases or crystal plane figure on the catalytic properties of MnO2 for the total oxidation of propane was evaluated, and the results showed that α-, β-, γ-, and δ-MnO2 exhibited a 2D layered-structure material.
Abstract: Nanosized MnO2 particles with α-, β-, γ-, and δ-crystal phases were synthesized hydrothermally, and characterized by XRD, SEM, HR-TEM, low temperature N2 adsorption, TPR, TPD, FT-IR and Raman spectroscopy. The density functional theory (DFT) method was used to calculate the adsorption of propane and O2 on MnO2 catalysts. The effect of the crystal phases or crystal plane figure on the catalytic properties of MnO2 for the total oxidation of propane was evaluated. The results showed that α-, β- and γ-MnO2 exhibited a 1D structure, and δ-MnO2 was a 2D layered-structure material. For deep oxidation of propane, the catalytic activities of the MnO2 samples decreased in the order of α- ≈ γ- > β- > δ-MnO2. Compared with the other three MnO2 samples, α-MnO2 exhibited the highest catalytic activity and stability for propane oxidation, its T10 and T90 were 204 °C and 290 °C, respectively. For the different crystal phases of MnO2, there are distinct differences in the chemical bonds (Mn–O–Mn and Mn–O) and linking modes of [MnO6] octahedra, the adsorption energies of propane on the surface of MnO2 are varied in the order of (310) facet of α- > (120) of γ- > (110) of β- > (001) of δ-MnO2, and the presence of translational motion in α-MnO2 along with its stronger deformation and stretching modes may lead to its better catalytic activity for propane oxidation.

166 citations


Journal ArticleDOI
TL;DR: In this paper, UiO-66 with crystal size ranging from hundreds of nanometers to a few micrometers and with cubic and cuboctahedral morphologies were synthesized.
Abstract: UiO-66 with crystal size ranging from hundreds of nanometers to a few micrometers and with cubic and cuboctahedral morphologies were synthesized. Crystal size and morphology varied with the additive amount of hydrofluoric acid and the concentration of reactants (ZrCl4 and H2BDC) during solvothermal synthesis. According to energy dispersive spectrometry (EDS) and 19F MAS NMR measurements, the fluorine ions directly bonded to Zr in the SBUs (secondary building units) in the MOF framework due to their strongest electronegativity. The bonding of the fluorine ions and Zr not only compensated for the charge imbalance of the framework caused by missing linkers but also competed with the linkers to coordinate with the Zr metal centers, thereby controlling the processes of nucleation and growth of the UiO-66 crystals. The samples were further characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and Ar sorption isotherms, showing that the introduction of fluorine enhanced the thermostability and porosity of UiO-66.

164 citations


Journal ArticleDOI
TL;DR: In this paper, the authors show that hydrated calcite nanoparticles form after spinodal liquid-liquid phase separation and transform via dissolution/(re)precipitation into poorly hydrated and anhydrous ACC nanoparticles that aggregate, forming a range of 1D, 2D and 3D structures.
Abstract: Amorphous calcium carbonate (ACC) is a key precursor of crystalline CaCO3 biominerals and biomimetic materials. Despite recent extensive research, its formation and amorphous-to-crystalline transformation are not, however, fully understood. Here we show that hydrated ACC nanoparticles form after spinodal liquid–liquid phase separation and transform via dissolution/(re)precipitation into poorly hydrated and anhydrous ACC nanoparticles that aggregate, forming a range of 1D, 2D and 3D structures. The formation of these structures appears to be achieved by oriented attachment (OA), facilitated by the calcite medium-range order of ACC nanoparticles. Both electron irradiation processes in the TEM and under humid air exposure at room temperature of the latter ACC structures result in pseudomorphs of single crystalline mesostructured calcite. While the high-vacuum/e-beam heating leads to solid-state transformation, the transformation in air occurs via an interface-coupled dissolution/precipitation mechanism. Our results differ significantly from the currently accepted model, which considers that the low T ACC-to-calcite transformation in air and during biomineralization is a solid-state process. These results may help to better understand how calcite biominerals form after ACC and offer the possibility of biomimetically preparing single crystalline calcite structures after ACC by tuning pH2O at room temperature.

Journal ArticleDOI
TL;DR: A family of six new homo-lanthanide coordination polymers incorporating a conjugated ligand of 2,5-di(2′,4′-dicarboxylpheny)pyridine, namely, {[Ce(μ3−ddpp)]·4H2O}n (1), {[Nd(μ 3 −ddpp]·2H 2O})n (2), {Sm(μ6−dd pp)]·H 2 O )n (3), {Eu(μ 6 −dd pp
Abstract: A family of six new homo-lanthanide coordination polymers incorporating a conjugated ligand of 2,5-di(2′,4′-dicarboxylpheny)pyridine, namely, {[Ce(μ3−ddpp)]·4H2O}n (1), {[Nd(μ3−ddpp)]·2H2O}n (2), {[Sm(μ6−ddpp)]·H2O}·H2O}n (3), {[Eu(μ6−ddpp)]·H2O}n (4), {[Tb(μ6−ddpp)]·H2O}n (5), and {[Er(μ6−ddpp)]·H2O}n (6) (H3ddpp = 2,5-di(2′,4′-dicarboxylpheny)pyridine acid), has been prepared successfully through solvothermal reactions. Polymers 1–6 exhibit various coordination environments and different multi-dimensions, but they are all assembled in a one dimensional (1-D) Ln–carboxylate chain. Polymer 1 only shows a 1-D ribbon chain, while polymer 2 exhibits a binodal (3, 8)-connected topology net. Heavy lanthanide polymers 4–6 possess 3D frameworks based on a rare (4, 8)-connected msw framework. Thermogravimetric and different thermal analysis measurements indicate that they all display high thermal stability. The luminescence emission spectra display characteristic f–f transition emissions of Ln(III) polymers in visible or near infrared (NIR) regions. The fluorescent ligand H2ddpp provides efficient energy transfer for the sensitization of Eu(III) and Tb(III) ions in the visible region, among which a Tb(III) polymer may be employed as a fluorescence ratiometric probe for the pollutant CrO42− anion.

Journal ArticleDOI
TL;DR: In this article, three gas sensing hybrid nanostructures based on noble metal (Au, Pd and Pt) decorated octahedral SnO2 nanocrystals were specifically constructed.
Abstract: Surface modification with noble metals is considered as an effective strategy to enhance sensitivity and selectivity of metal oxide-based gas sensors. This enhancement with noble metal decoration is generally attributed to the formation of a heterogeneous interface between the noble metal and metal oxide. However, the sensitization mechanism of noble metals on the specific facets of the metal oxide support lacks a unified understanding. In this work, three gas sensing hybrid nanostructures based on noble metal (Au, Pd and Pt) decorated {221} faceted octahedral SnO2 nanocrystals were specifically constructed. Our results showed that, on these {221} specific facets of SnO2, Au exhibited a positive effect for enhancing the sensitivity and selectivity of SnO2 sensors, while Pd and Pt played the opposite roles. It is considered that the sensitization effects of noble metals are related to their surface chemical states and interaction with the metal oxide support. The methodology demonstrated in this work is beneficial to probing into the sensitization mechanisms of noble metals in semiconductor/metal hybrid sensors.

Journal ArticleDOI
TL;DR: In this article, a Co-containing zeolitic imidazolate framework with a leaf-like morphology was synthesized in aqueous media and proved to be the transient phase in the formation of ZIF-67.
Abstract: A novel Co-containing zeolitic imidazolate framework with a leaf-like morphology (ZIF-L-Co) was synthesized in aqueous media and proved to be the transient phase in the formation of ZIF-67. The phase and morphology of the products could be tailored by changing the concentration and molar ratio of the reagents. Our study herein provides a new insight into the crystal growth of ZIFs.

Journal ArticleDOI
TL;DR: In this paper, the authors focused on water adsorption in two representative MOFs: M(bdc)(ted)0.5 and MOF-74 with unsaturated metal centers and showed that the reactivity and initial decomposition pathway of MOFs in water vapor critically depend on their structure and the specific metal cation in the building units.
Abstract: Metal organic frameworks (MOFs) have a strong potential for gas adsorption and separation such as H2 and CH4 storage, and CO2 capture. However, their instability in the presence of water vapor (many MOFs are hygroscopic) is one of the key issues that limit their large-scale application. Previous studies of water adsorption in MOFs have mainly relied on isotherm measurements that provide useful parameters such as adsorption uptake and isosteric heat of adsorption. The structural stability of MOFs in water vapor was also evaluated by powder X-ray diffraction measurements (PXRD). However, more studies are required to unravel the water interaction or reaction mechanisms within MOFs, which would be beneficial for the development of more robust frameworks. This review highlight focuses on water adsorption in two representative MOFs: M(bdc)(ted)0.5 [M = Cu2+, Zn2+, Ni2+, Co2+; bdc = 1,4-benzenedicarboxylate; ted = triethylenediamine] with saturated metal centers and MOF-74 [M2(dobdc), M = Mg2+, Zn2+, Ni2+, Co2+ and dobdc = 2,5-dihydroxybenzenedicarboxylic acid] with unsaturated metal centers. It shows how vibrational spectroscopy combined with van der Waals density functional (vdW-DF) calculations makes it possible to elucidate the details of water reaction in MOFs. The results presented in this highlight suggest that the reactivity and initial decomposition pathway of MOFs in water vapor critically depend on their structure and the specific metal cation in the building units. Water interaction with a hydrophobic MOF, in this case FMOF-1, is also reviewed. This information provides a framework for understanding water interactions or reactions within different types of MOFs.

Journal ArticleDOI
TL;DR: In this article, the authors presented an achiral hybrid bent-core liquid crystal trimer that at temperatures below the conventional N phase exhibits the Ntb phase from approximately 80 °C down through room temperature.
Abstract: The nanostructured heliconical twist-bend nematic (Ntb) phase is a new condensed phase of matter with unique properties. Here we present the first example of an achiral hybrid bent-core liquid crystal trimer that at temperatures below the conventional N phase exhibits the Ntb phase from approximately 80 °C down through room temperature. The Ntb phase has a helical structure with a period of ~19 nm.

Journal ArticleDOI
TL;DR: In this paper, a review article is focused on the compositions, phases and crystal structures, and different synthetic methodologies involved in the fabrication of 0D, 1D and 2D nanostructured copper sulfides.
Abstract: Among different metal chalcogenides, copper sulfides have been extensively studied in the past few years due to their semiconducting and non-toxic nature, making them useful in a wide range of applications from the energy to the biomedical fields. A series of stoichiometric compositions of copper sulfides from Cu-rich, Cu2S to Cu-deficient, CuS2 exist with different crystal structures as well as phases, resulting in different unique properties. The suitable band gap values in the range of 1.2–1.5 eV and unique optoelectronic properties indicate that the material is photocatalytically active and exhibits excellent plasmonic behavior. The material is also known for promising thermoelectric properties, converting waste heat into electricity through the Seebeck effect. The nanodimensional form of copper sulfides promotes their use to a more advanced level, tuning their properties with the size of the materials. In view of this, the present review article is focused on the compositions, phases and crystal structures, and different synthetic methodologies involved in the fabrication of 0D, 1D and 2D nanostructured copper sulfides. Moreover, recent advancements on their use in various applications will also be briefly discussed.

Journal ArticleDOI
TL;DR: The high stability of this material and the maintenance of its antibacterial properties make BioMIL-5 a good candidate for future bioapplications, for skin care and in cosmetics.
Abstract: A novel biocompatible and bioactive Metal–Organic Framework (BioMOF), named BioMIL-5 (Bioactive Materials from Institut Lavoisier), was hydrothermally synthesized from a Zn2+ salt and azelaic acid, both with interesting antibacterial and dermatological properties. Its structure was determined by high resolution X-ray powder diffraction, and further characterized by infrared spectroscopy, thermogravimetric analysis and elemental analysis. The determination of the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values of BioMIL-5 in Staphylococcus aureus and Staphylococcus epidermidis demonstrated that the antimicrobial activity of the individual components of BioMIL-5 were maintained after its synthesis. Moreover, BioMIL-5 was found to be stable in water and in bacterial culture medium, especially in water, leading to the subsequent progressive release of its active constituents, AzA and Zn2+ ions. Interestingly, this slow active delivery allowed control of the growth of a S. epidermidis suspension over 7 days. The high stability of this material and the maintenance of its antibacterial properties make BioMIL-5 a good candidate for future bioapplications, for skin care and in cosmetics.

Journal ArticleDOI
TL;DR: In this paper, the authors focus on oxyanion/cation removal from aqueous solutions using metal-organic frameworks (MOFs) as contaminant-selective sponges.
Abstract: Water pollution is an issue that should be carefully monitored and addressed. A major source of water pollution originates from high temperature industrial processes such as fossil fuel combustion and solid waste incineration. This waste typically contains high levels of oxyanion/cation forming elements which are particularly hazardous due to their inherent solubility in water and their resulting bioavailability. One approach for oxyanion/cation removal from water involves using an adsorbing medium to soak up and remove pollutants. Metal–organic frameworks (MOFs) offer an interesting platform for water remediation. MOFs are structurally diverse, porous materials that are constructed from metal nodes bridged by organic ligands. This highlight will focus on oxyanion/cation (PO43−, AsO43−, SeO32−, SeO42−, UO22+) removal from aqueous solutions using MOFs as contaminant-selective sponges. The mechanism of adsorption in different frameworks will be explored to gain insight into some design features that are important for MOFs to be used in applications to help alleviate water pollution.

Journal ArticleDOI
TL;DR: In this paper, two new three-dimensional porous Cd(II)-based metal-organic frameworks, [Cd2(oba)2(4-bpdb)2]n·(DMF)x (TMU-8) and [cd(oba)(4,4′-bipy)]n· (DMFy)y (TM U-9), have been synthesized via mechanosynthesis by using nonlinear dicarboxylate and linear N-donor ligands and then characterized by single-crystal X
Abstract: Two new three-dimensional porous Cd(II)-based metal–organic frameworks, [Cd2(oba)2(4-bpdb)2]n·(DMF)x (TMU-8) and [Cd(oba)(4,4′-bipy)]n·(DMF)y (TMU-9), have been synthesized via mechanosynthesis by using nonlinear dicarboxylate and linear N-donor ligands and then characterized by single-crystal X-ray crystallography. The effect of using different N-donor ligands 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene (4-bpdb) and 4,4′-bipyridine (4,4′-bipy) as pillars on the final structure has been studied. Also, the removal efficiency and order reaction kinetics of these MOFs in the presence of Congo red were investigated.

Journal ArticleDOI
TL;DR: In this paper, the authors describe the synthesis of 2D WO3 crystals with the {002} facet primarily exposed, octahedral wO3 or WO 3·nH2O with exposed {111} facets, and WO-3 films with dominant orientations, such as orientation along the ''002'' facet.
Abstract: The photocatalysis, chromism, and sensing capabilities of nanostructured tungsten oxides, such as tungsten trioxide (WO3), its suboxides (WOx, 0 < x < 3) and hydrates (WO3·nH2O, n = 1/3 (0.33), 0.5, 0.75, 1, 2, etc.), tungsten bronzes MxWO3 (M = Li, Na, K, Rb, Cs and NH4), and metal tungstates (such as Bi2WO6 and CuWO4) have attracted much attention. To improve these properties, many strategies have been pursued, such as morphology control, doping, and heterostructuring. Crystal facet engineering has recently become a very important method of fine-tuning the physicochemical properties of semiconductors. The photocatalytic reactivity of a photocatalyst is significantly affected by its surface environment, including its surface electronic and atomic structures, which strongly depend on the crystal facets. It is believed that crystals with different exposed facets will have different properties, with the exposure of highly activated facets enhancing the photocatalytic and sensing properties. This article describes the syntheses of 2D WO3 crystals with the {002} facet primarily exposed, octahedral WO3 or WO3·nH2O with exposed {111} facets, and WO3 films with dominant orientations, such as orientation along the {002} facet. WO3 doping, WO3-based heterostructuring and their applications are also presented in this paper.

Journal ArticleDOI
TL;DR: In this paper, an oxide based nanostructure hybrid has been realized by integrating low bandgap copper oxide nanosheet with high bandgap one dimensional zinc oxide nanowires on a flexible carbon cloth as well as on a flat substrate.
Abstract: The possibility of integrating manifold functionalities, coupled with various associated noble interface phenomena in the hierarchical nanoforms, either comprised of geometrical intricacies or achieved via the rational coupling of several components, has made them immensely pertinent from both research and technological aspects. Here, an oxide based nanostructure hybrid has been realized by integrating low bandgap copper oxide nanosheet with high bandgap one dimensional zinc oxide nanowires on a flexible carbon cloth as well as on a flat substrate. These bandgap modulated hybrid nanostructures are generated for the efficient absorption of visible light, targeting their possible use in waste water management. Our work presents a novel ambient condition protocol for morphological tuning in the nanoscale or their organization in a hierarchical structure. Environmental remediation through catalytic activity under the visible light irradiation of the synthesized samples was inspected using both anionic and cationic dyes (methyl orange and Rhodamine B, respectively) as the model contaminants, where the optimized heterostructure exhibits significantly better performance than the mono component oxides. Such enhanced performance could be explained by the formation of favorable staggered gap multiple p–n junctions at ZnO/CuO interface, which in turn retards the photogenerated electron–hole pair recombination within the heterostructure. The signature of successful p–n junction formation at ZnO nanorod/CuO nanosheet interface has been identified via current–voltage measurements with a conducting tip AFM in contact mode. The creative designing of novel heterojunctions adopting this protocol will pave the way for the utilization of the entire visible light range: thus, offering potential in solar energy conversion devices.

Journal ArticleDOI
TL;DR: Systematic refinements of the obtained powder patterns demonstrate that these materials expand along a specific direction while undergoing total volume reduction under an increase in hydrostatic pressure, confirming for the first time the Negative Linear Compressibility behaviour of this family of materials.
Abstract: We report a series of powder X-ray diffraction experiments performed on the soft porous crystals MIL-53(Al) and NH2-MIL-53(Al) in a diamond anvil cell under different pressurization media. Systematic refinements of the obtained powder patterns demonstrate that these materials expand along a specific direction while undergoing total volume reduction under an increasing hydrostatic pressure. The results confirm for the first time the negative linear compressibility behaviour of this family of materials, recently predicted from quantum chemical calculations.

Journal ArticleDOI
TL;DR: In this paper, the authors summarize various standard protocols and recent advances for the shape-controlled synthesis of such nanocrystals, which is a key process in advancing the applications of nanomaterials including biosensing, catalysis, photonics, electronics and photovoltaics.
Abstract: The term “Nanocrystal Engineering” can be defined as the design and synthesis of nanocrystals with desired morphologies and compositions based on understanding and exploitation of the nucleation and growth process. It is a key process in advancing the applications of nanomaterials including biosensing, catalysis, photonics, electronics and photovoltaics. As compared to the accomplishments of organic synthesis, we are still far from the complete understanding and experimental control over the synthesis of nanocrystals with well-defined morphology. However, the last two decades of research have resulted in excellent control over the morphology and composition of noble metal and metal chalcogenide nanocrystals. In this Highlight article, we summarize various standard protocols and recent advances for the shape-controlled synthesis of such nanocrystals. From the discussion in this article, it is clear that significant progress has been made toward the design and synthesis of nanocrystals with desired shape, crystallinity and composition by controlling the nucleation and growth process using specific synthetic protocols. We hope that this Highlight article will help researchers to follow some general rules to engineer the morphology and composition of noble metal and metal chalcogenide nanocrystals to maximise their efficiency for various applications.

Journal ArticleDOI
TL;DR: In this article, the optimal working temperature of the sensor based on porous rhombohedral In2O3 nanoflowers was proved to be 280 °C, corresponding to chemisorbed oxygen analysis based on a temperature changeable XPS.
Abstract: Porous rhombohedral In2O3 (corundum-type In2O3, rh-In2O3) with a morphology of uniform nanoflowers was fabricated by using a mild, facile solvent-thermal method. The formation mechanism and transformation of phase were studied. The results revealed that the precursors were transformed from In(OH)3 to InOOH with an increase in reaction time. The phase transformation was attributed to the stability of the InOOH phase at small crystal volume, less water molecules and small pH value, which in turn led to the formation of metastable rh-In2O3. The optimal working temperature of the sensor based on porous rh-In2O3 nanoflowers was proved to be 280 °C, corresponding to chemisorbed oxygen analysis based on a temperature changeable XPS, further demonstrating the surface resistance controlled gas sensing mechanism of In2O3. The sensor exhibited an enhanced response and rapid response/recovery toward ethanol vapour, which was ascribed to hierarchical porous structures and more active defects.

Journal ArticleDOI
TL;DR: In this paper, a simple solvothermal approach for phase controlled synthesis of SnSe and SnSe2 hierarchical nanostructures (HNs) was presented for the first time SnSe HNs have been prepared by reacting SnCl4 and SeO2 under solvatorial conditions using oleylamine as solvent by adding a calculated amount of 1-dodecanethiol (1-DDT) to the reaction mixture.
Abstract: The electronic and optoelectronic properties of tin selenide nanostructures are of great interest for application in energy conversion and storage devices Despite the great progress achieved in nanoparticle synthesis, controlling the crystal phase in tin selenide nanostructures remains a challenge In this article, we present a simple solvothermal approach for the phase controlled synthesis of SnSe and SnSe2 hierarchical nanostructures (HNs) for the first time SnSe HNs have been prepared by reacting SnCl4 and SeO2 under solvothermal conditions using oleylamine as solvent By adding a calculated amount of 1-dodecanethiol (1-DDT) to the reaction mixture the crystal phase can be tuned from SnSe to SnSe2 The obtained HNs were composed of single crystalline thin nanosheets with thickness in the range of 7–12 nm A possible mechanism has been proposed for the phase controlled synthesis of tin selenides The obtained SnSe and SnSe2 HNs showed good electrocatalytic activity in the redox reaction of the I−/I3− shuttle Dye sensitized solar cells (DSSC) employing SnSe and SnSe2 HNs as counter electrodes showed photovoltaic performances similar to the device made with a conventional platinum (Pt) counter electrode

Journal ArticleDOI
TL;DR: In this article, n-type homoepitaxial semiconducting β-Ga2O3 layers were attained by MOVPE. The interplay between deposition conditions and structural and electrical properties of the layers was studied.
Abstract: Layers of β-Ga2O3in situ doped with Sn were grown on Al2O3 (0001) and native β-Ga2O3 (100) substrates by metal organic vapor phase epitaxy. Homoepitaxial growth of good-quality Sn-doped β-Ga2O3 layers with rocking curve values comparable to that of Czochralski-grown β-Ga2O3 substrates was attained. Sn incorporation in a wide range of concentrations (from 1017 to 1019 cm−3) was achieved without disturbing the crystallinity of the material grown. The interplay between deposition conditions and structural and electrical properties of the layers was studied. The Ga vacancy-related defects and the residual carbon from Ga-containing organic precursor carbon-related complexes have been revealed as acceptors compensating for intentionally introduced Sn donors. The advantage of employment of the melt-grown β-Ga2O3 crystals as homo-substrates for deposition of good-quality β-Ga2O3 layers is demonstrated. For the first time, n-type homoepitaxial semiconducting β-Ga2O3 layers were attained by MOVPE. The good quality of the epilayers was elucidated through HR-XRD measurements and a FWHM of the rocking curve of the (100) peak of 43 arcsec was obtained, which was comparable to those of the Czochralski-grown β-Ga2O3 substrates, demonstrating similar dislocation densities for epilayers and substrates.

Journal ArticleDOI
TL;DR: WO3-Bi2WO6 heterostructures were synthesized by a facile hydrothermal method using WO3 nanorods and Bi(NO3)3 solution as raw materials as mentioned in this paper.
Abstract: WO3–Bi2WO6 heterostructures were synthesized by a facile hydrothermal method using WO3 nanorods and Bi(NO3)3 solution as raw materials. The Bi2WO6 nanosheets uniformly anchored onto the surface of the WO3 nanorods. The photocatalytic activity of the samples was assessed for degradation of rhodamine B (RhB) and phenol under solar light irradiation. The WO3–Bi2WO6 heterostructures showed higher photocatalytic activities than pure WO3 and Bi2WO6. As the content of Bi2WO6 increased, the photocatalytic activity of the WO3–Bi2WO6 heterojunction was enhanced and the optimal sample was WO3–Bi2WO6 with a nWO3 : nBi3+ mole ratio of 5 : 3. The efficient separation of electron–hole pairs because of the staggered band potentials between WO3 and Bi2WO6 may account for the higher photoactivity of WO3–Bi2WO6 hybrid structures. Radical scavenger experiments indicate that holes (h+) and superoxide radicals (˙O2−) were the main active species for RhB degradation during the photocatalytic process.

Journal ArticleDOI
TL;DR: In this article, single-phase nickel sulfide nanoparticles were synthesized from elemental sulfur and nickel nitrate hexahydrate, using a temperature-controlled precursor injection method, and the results showed that the catalytic activity of the NiS nanoparticles in the reduction of 4-nitrophenol to 4-aminophenol was higher than those of the other NiS phases.
Abstract: Nanoparticle single-phase nickel sulfides such as NiS, NiS2, Ni3S4, and Ni7S6 were prepared from elemental sulfur and nickel nitrate hexahydrate, using a temperature-controlled precursor injection method. The initial ratio of the concentrations of the sources was used to control the size and phase of the final product. Phase control was confirmed using X-ray diffraction and transmission electron microscopy. The synthesized nickel sulfide phases, which had metallic characteristics, were used to study the catalytic reduction of 4-nitrophenol. The results showed that the catalytic activity of the NiS nanoparticles in the reduction of 4-nitrophenol to 4-aminophenol was higher than those of the other nickel sulfide phases. In addition, the nanocrystals showed good separation ability and reusability for reduction of 4-nitrophenol.

Journal ArticleDOI
TL;DR: In this paper, flux preparations of metal-oxide photocatalysts assist in the growth and optimization of their particles in order to understand and tune their reaction rates at their surfaces, such as for the reduction of water to hydrogen in aqueous solutions.
Abstract: Molten-salt reactions can be used to prepare single-crystal metal-oxide particles with morphologies and sizes that can be varied from the nanoscale to the microscale, subsequently enabling a growing number of novel investigations into their photocatalytic activities. Crystal growth using flux-mediated methods facilitates finer synthetic manipulation over particle characteristics. The synthetic flexibility that flux synthesis affords for the growth of metal-oxides has led to the stabilization of phases with limited stability, the discovery of new compositions, and access to alternate crystal morphologies and sizes that exhibit significant changes in photocatalytic activities at their surfaces, such as for the reduction of water to hydrogen in aqueous solutions. This approach has significantly impacted the current understanding of the optical and photocatalytic properties of metal-oxides, such as the dependence of band gap energies on the structure and chemical composition (i.e., obtained from flux-mediated ion-exchange reactions). Thus, flux preparations of metal-oxide photocatalysts assist in the growth and optimization of their particles in order to understand and tune the photocatalytic reaction rates at their surfaces.