Showing papers in "CrystEngComm in 2019"

Stepwise and hysteretic sorption of CO2 in polycatenated metal–organic frameworks

Abstract: Two polycatenated metal–organic framework materials with different metal centers (Zn2+ for 1 and Cd2+ for 2) were synthesized, which underwent pronounced framework phase transition upon desolvation, and exhibited uncommon temperature-dependent stepwise adsorption and hysteretic desorption of CO2 around room temperature

Degradation of ZIF-8 in phosphate buffered saline media

Abstract: Understanding the stability of zeolitic imidazolate framework-8 (ZIF-8) under physiological conditions is critical in biotechnology and biomedicine for biosensing, biocatalysis, and drug delivery. The use of ZIF-8 has shown that this metal organic framework (MOF) and its derived bio-composites can degrade in presence of buffer solutions. Here we present an in-depth analysis of the structural and chemical changes of pure ZIF-8 particles exposed to phosphate buffered saline (PBS) media. Two different particle sizes (2 μm and 250 nm) were selected and the decomposition operated by 10 mM PBS (aka 1X) was studied using powder X-ray diffraction (PXRD), Fourier transformed infrared spectroscopy (FTIR), time resolved atomic force microscopy (AFM), in situ small angle X-ray scattering (SAXS), and 31P NMR.

A new Zn(II)-based 3D metal–organic framework with uncommon sev topology and its photocatalytic properties for the degradation of organic dyes

Abstract: A new d10-configuration based Zn(II) 3D metal–organic framework (MOF) with the formula {[Zn4(NDC)3.5(μ4-OH)(DMF)]·1.7DMF}n (1) has been synthesized using a 1,4-naphthalenedicarboxylic acid (H2NDC) ligand and characterized. The single crystal X-ray diffraction results indicate that in the newly synthesized MOF, 7-connected [Zn4(μ4-OH)(COO)7] clusters are formed which are extended by NDC2− ligands to generate an uncommon sev topology. The photocatalytic properties of 1 in the photodegradation of model organic dyes viz. methyl violet (MV) and rhodamine B (Rh B) have been systematically investigated. The photocatalysis results demonstrated that 1 shows promising photocatalytic degradation activity against these organic dyes. The possible photocatalytic mechanism through which 1 displayed photocatalytic properties to photodegrade organic dyes has also been proposed with the aid of density of states (DOS) calculations.

Phase and morphology evolution of CoAl LDH nanosheets towards advanced supercapacitor applications

Abstract: Al-Based LDH materials have been considered as promising active electrode materials for pseudocapacitors due to their structural tunability. In this work, we employed a hydrothermal method, alkali etching treatment, calcination and sulfofication to achieve crystalline phase transformation. According to this pathway, five materials, including CoAl LDH, Co2AlO4, Co(OH)2, Co3O4 and Co4S3, have been prepared. The structural and physical/chemical properties are characterized by XRD, XPS, BET, SEM, TEM and FTIR. The electrochemical behaviors in supercapacitor and asymmetric supercapacitor (ASC) devices are characterized, respectively. As the electrode materials in supercapacitors, the specific capacitances are in the order CoAl LDH > Co4S3 > Co2AlO4 > Co3O4 > Co(OH)2. The CoAl LDH exhibits the maximum specific capacitance due to the intercalation/deintercalation of electrolyte ions which is attributed to its unique layer structure. The CoAl LDH exhibits a high specific capacitance of 983.71 F g−1 at 1 A g−1, a superior rate capability of 79.00% at 20 A g−1 and excellent cycling stability with a capacitance retention of 89.10% after 15 000 cycles. After assembling the ASC device, a maximum energy density of 16.275 W h kg−1 and a high power density of 3500 W kg−1 are achieved in a potential window of 1.4 V. In a word, the study not only provides a dependable pathway for materials modification, but also promotes the development of cobalt-based electrode materials for energy storage.

Designs of continuous-flow pharmaceutical crystallizers: developments and practice

Abstract: Crystallization is an effective, low-cost purification & formulation process widely applied to pharmaceuticals and fine chemicals. This review describes recent advances in research on lab-scale solution-based continuous crystallization, including (1) a 5-step general design procedure; (2) key design/operational parameters; (3) process intensification strategies; and (4) a case study. The continuous crystallizers reviewed include mixed-suspension mixed-product removal, fluidized beds, oscillatory baffled flow, and tubular laminar/segmented/slug-flow crystallizers. Their corresponding design and operational considerations are summarized in terms of general parameters (e.g., residence time), and crystallizer-specific parameters and strategies (e.g., mixing strategies). In-line nucleation and crystal modification methods are categorized, including use of micromixers, wet milling, ultrasonication, temperature cycling, and recycling selection (filtration, sedimentation). Throughout the article, links are drawn with extensive existing knowledge of batch crystallizers, to facilitate the understanding and design of continuous crystallizers.

Insight into the optical, color, photoluminescence properties, and photocatalytic activity of the N–O and C–O functional groups decorating spinel type magnesium aluminate

Abstract: MgAl2O4 with a spinel structure was successfully synthesized using a gamma-ray irradiation assisted polyacrylamide gel method. The samples were synthesized at different calcining temperatures to study the effects on the phase purity, optical, color and fluorescence properties and photocatalytic activity of the as-prepared samples. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis indicates that the calcining temperature has an obvious influence on the crystallinity and the formation of the MgAl2O4 spinel phase. Transmission electron microscopy (TEM) observation shows that the primary crystal of the MgAl2O4 nanoparticles is only 30 nm and exhibits a higher uniformity than those of MgAl2O4 nanoparticles fabricated using the conventional polyacrylamide gel method. Optical properties show that the optical energy gap (Eg) of the MgAl2O4 nanoparticles increases with the increasing calcining temperature, mainly due to the interaction between the N–O and C–O functional groups and the calcining temperature. An abnormal result for the color parameter of the MgAl2O4 xerogel powders calcined at 900 °C indicates the enhancement of the crystallinity and the phase purity of the MgAl2O4 nanoparticles. The fluorescence spectra indicates that the emission intensity of the emission peak at 395 nm decreases with the increasing calcining temperature. The photocatalytic activity of the MgAl2O4 nanoparticles prepared at different calcining temperature were then tested for photocatalytic degradation of the methylene blue (MB) dye. The result indicates that the MgAl2O4 xerogel powders calcined at 800 °C exhibit the highest photocatalytic activity, and that this is relevant to the light absorption ability, band edge position, separation and utilization efficiency of the photogenerated carriers of the as-prepared sample. The fluorescence and photocatalytic mechanisms show that a small number of N–O and C–O functional groups in the presence of the MgAl2O4 nanoparticles can help to improve the fluorescence properties and photocatalytic activity of the MgAl2O4 nanoparticles.

Symmetrical polyhedron-bowl Co/CoO with hexagonal plate to forward electromagnetic wave absorption ability

Abstract: Symmetrical polyhedron-bowl (twin-hexagonal frustum-pyramid) structured Co/CoO products were prepared via a simple polyol reduction approach. The effects of reaction conditions (solvent constituents and reaction times) on the morphologies of Co/CoO products were investigated in detail. The microwave absorption performances of Co/CoO polyhedron paraffin composites with various Co/CoO contents were also studied. The results showed that the Co/CoO polyhedron paraffin composites exhibit enhanced microwave absorption properties with an increased Co/CoO content in the certain amount range. This phenomenon is observed because the conductive networks are gradually formed to cause leakage current loss with increasing Co/CoO content. However, the large leakage current induces impedance mismatch to prohibit microwaves from entering absorbers with a relatively high Co/CoO content. Thus, the Co/CoO polyhedrons paraffin composite with 50 wt% Co/CoO displays excellent microwave absorption properties. The optimal reflection loss (RL) is −45.3 dB at 12.5 GHz with a thickness of 1.7 mm. The effective absorption (below −10 dB) bandwidth can be tuned to the frequency of 4.5–18.0 GHz with thickness of 1.0–4.0 mm. The abundant reflection and scattering were caused by the symmetrical polyhedron-bowl structure. The micro-capacitors formed between Co/CoO as electrodes, paraffin as a dielectric, and the interfacial polarization collectively contribute to microwave absorption abilities.

Fabrication of MoS2/TiO2 heterostructures with enhanced photocatalytic activity

Abstract: Two-dimensional nanophotocatalysts MoS2/TiO2 with a tunable decoration amount of MoS2 nanosheets were fabricated through a hydrothermal route. The microstructure and photocatalytic behaviors of the as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, electrochemical workstation, dye degradation and water splitting experiments. The result shows that these composites exhibited enhanced photocatalytic activity for RhB degradation and hydrogen generation. Nearly 95% photocatalytic degradation of RhB was obtained for 2 h and 1.93 mmol g−1 h−1 hydrogen production rate was achieved over MoS2/TiO2 at a MoS2 content of 10 wt%. And the corresponding photocurrent density of the composite photoelectrode was 5 times higher than that of pristine TiO2 architectures. It is believed that the boosted photocatalytic performance of the heterostructure could be ascribed to the synergetic effect between MoS2 and TiO2, which accelerated the separation and migration efficiency of charge carriers as well as enhancing the light-harvest efficiency.

Metal–organic frameworks with 5,5′-(1,4-xylylenediamino) diisophthalic acid and various nitrogen-containing ligands for selectively sensing Fe(III)/Cr(VI) and nitroaromatic compounds

Abstract: Four novel Zn(II) metal–organic frameworks (MOFs) including {[Zn(L)0.5(bimb)]·2H2O·0.5(CH3)2NH}n (1), {[Zn(L)0.5(bimmb)]·2H2O}n (2), {[Zn(L)0.5(btdpe)]·H2O}n (3), and [Zn(L)0.5(bidpe)]n (4) (H4L = 5,5′-(1,4-xylylenediamino) diisophthalic acid, bimb = 1,4-bis(imidazol-1-yl)-butane, bimmb = 1,4-bis(imidazol-1-ylmethyl)benzene, btdpe = 4,4′-bis(4H-1,2,4-triazol-4-yl)diphenyl ether, and bidpe = 4,4′-bis(imidazolyl)diphenyl ether) were solvothermally prepared and further characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction, thermogravimetric (TG) analysis and powder X-ray diffraction (PXRD). Single-crystal X-ray diffraction analysis showed that complex 1 features a 3-fold interpenetrated bbf topological framework with the Schlafli symbol of (64·82)(66)2. Complex 2 displayed an unprecedented 2-nodal (4,4)-connected 3D framework with the Schlafli symbol of (86), while complexes 3 and 4 showed 3-nodal (2,4,4)-connected (4·8·104)2(4)2(84·10·12)-unprecedented frameworks. Luminescence studies revealed that complexes 1–4 can be used as high selectivity luminescence sensors for sensing Fe(III) cations, Cr(VI) anions (Cr2O72− and CrO42−) and nitroaromatic compounds. Furthermore, a possible sensing mechanism was investigated in this paper.

Crystal structure of nickel manganese-layered double hydroxide@cobaltosic oxides on nickel foam towards high-performance supercapacitors

Abstract: Rational design of the crystal structures of electrode materials is considered as an important strategy to construct high-performance supercapacitors. Herein, the three-dimensional crystal structure NiMn LDH@Co3O4 composites on Ni foam with different feeding Ni/Mn molar ratios were well-designed with hydrothermal, calcination and co-deposition methods, wherein urea hydrolysis supplied the alkali and carbonate ions. The electrochemical properties of the produced electrode materials were analyzed by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), electrochemical impedance spectroscopy (EIS) and cycling stability tests using 6 M KOH electrolyte. Indeed, the optimal feeding Ni/Mn molar ratio was determined to be 3 : 1. The resulting electrodes exhibited maximum specific capacitance (607.9 F g−1 at 0.5 A g−1), respectable rate capability and excellent cycling stability with less than 3% loss of capacitance after 1000 cycles, which could be ascribed to the well-designed core–shell architecture and ultrathin nanosheets structure of LDH. As for practical application, the asymmetric supercapacitor assembled using NiMn LDH@Co3O4 as the positive electrode and activated graphene (AG) as the negative electrode was also evaluated, which demonstrated a high energy density of 26.49 W h kg−1 at the power density of 350 W kg−1. The findings suggest that the three-dimensional crystal structure NiMn LDH@Co3O4 composites have potential application as promising electrode materials for energy storage devices or other applications.

Scalable, room temperature, and water-based synthesis of functionalized zirconium-based metal–organic frameworks for toxic chemical removal

Abstract: An inexpensive, environmentally benign, and scalable strategy was developed to synthesize UiO-66 derivatives in water at room temperature. Particularly, UiO-66-(COOH)2 with a significant amount of missing Zr6 clusters exhibited a higher surface area and higher pore volume than the same material synthesized at higher temperatures. The presence of both Lewis and Bronsted acidic active sites permits the high affinity for ammonia in both dry and humid environments. Additionally, we have applied our synthetic method to a hydrophobic analogue, UiO-66-F4, which hydrolyzed the hydrophobic VX agent at 50% relative humidity without a buffer and bulk water. The scalable synthesis of UiO-66 analogues in water at room temperature makes these materials practical and promising candidates for toxic chemical removal applications.

Increasing topological diversity during computational “synthesis” of porous crystals: how and why

Abstract: Effectively tuning the properties of porous crystals could lead to breakthroughs in areas such as molecular separation, chemical sensing, and catalysis. The most tunable kind of porous crystals are metal–organic frameworks (MOFs). Their tunability has resulted in MOFs being the focus of intensive research. However, MOF tunability also gives rise to an overwhelmingly large “MOF-space” (the conceptual space of all MOFs) that cannot be comprehensively explored experimentally. Because of this, high throughput computational screening (HTCS) emerged as a tool to more rapidly explore MOF-space. However, the effectiveness of HTCS is tied to the ability of computational algorithms for automated crystal construction to access every point in MOF-space. To this end, here we introduce a crystallographic net rescaling algorithm to the topologically-based crystal constructor (ToBaCCo) code that allows for the automated construction of MOFs (or other porous crystals) of any topology by exploiting graph theory. We demonstrate the capabilities of the new version of the code (ToBaCCo 3.0) by computationally “synthesizing” seven sets of isomorphic MOFs, where chemical composition remains constant within each set, but crystal topology varies across 19 previously inaccessible topologies. Furthermore, we illustrate the importance of computationally synthesizing all possible isomorphs for a given MOF composition by showing how strongly crystal topology influences simulated adsorption and mechanical properties. Specifically, we show that among crystal isomorphs i) methane deliverable capacity can vary by values as large as 150 cc(STP)/cc ii) adsorption selectivity for ethene/ethane mixtures can switch from ethene- to ethane-selective between MOF isomorphs, and iii) mechanical stability can be lost, and bulk moduli can exhibit significant variations, all solely due to a change in crystal topology.

Two cadmium(II) coordination polymers as luminescent sensors for the detection of nitrofuran/nitroimidazole antibiotics

Abstract: Two Cd(II) coordination polymers (CPs) were assembled from the mixed ligand strategy of π-conjugated aromatic polycarboxylates and bis(imidazole) linkers, with the structures being a 2-fold interpenetrating 3D bbf net for 1 and a 2D hxl sheet for 2. The fluorescence measurements revealed that both Cd(II) CPs were promising luminescent sensors for the detection of nitrofuran/nitroimidazole antibiotics (ABXs) with low detection limits. Besides, the luminescence quenching of the two Cd(II) CPs toward ABXs was investigated by using DFT calculations and spectral overlap experiments.

A luminescent sensor based on a Zn(II) coordination polymer for selective and sensitive detection of NACs and Fe3+ ions

Abstract: To design an effective fluorescence probe for sensing nitroaromatic compounds (NACs) and metal ions, a novel two-dimensional (2D) coordination polymer, {Zn2(NO3)2(4,4′-bpy)2(TBA)} (1) {H2TBA = 4-(1H-tetrazol-5-yl)-benzoic acid, 4,4′-bpy = 4,4′-bipyridine} was synthesized via a hydrothermal method. As expected, 1 presented varying degrees of fluorescence intensity changes for detecting and recognizing trace NACs with high selectivity and sensitivity in water solution. Moreover, 1 not only exhibited a highly selective fluorescence quenching effect on Fe3+ ions in aqueous solution, but could also resist the interference of various other metal ions. In addition, it has been found that the fluorescence quenching mechanisms among NACs and Fe3+ ions are mainly related to the interactions between the host group and guest molecules by energy and electron transfer.

ReS2-Based electrode materials for alkali-metal ion batteries

Abstract: Alkali-metal (Li, Na, K) ion batteries have practically or potentially been widely used as power sources for portable electronic devices and electric vehicles. However, the lack of fast and high-capacity anodes is restricting their development. As a new member of two-dimensional transition metal dichalcogenides, rhenium disulfide (ReS2), with a large interlayer space and weak van der Waals interaction between layers, can enable a large number of intercalation ions to diffuse easily between the layers. In this review, we summarize the recent progress of ReS2 as an electrode for alkali-metal ion batteries, mainly focusing on the synthesis method, structures, the reaction mechanism, and the corresponding electrochemical performance. In addition, the perspective and challenges of ReS2 electrodes are also discussed. This review will provide comprehensive knowledge of ReS2 electrodes and guidelines for exploring more applications in batteries.

A silver nanoparticle-anchored UiO-66(Zr) metal–organic framework (MOF)-based capacitive H2S gas sensor

Abstract: Hydrogen sulfide (H2S) is a highly poisonous gas; if present in a workplace, it must be identified immediately at concentrations greater than 10 ppm. Although there are numerous reports on sensing H2S gas using various techniques and approaches, there still exists a gap in terms of the limit of detection (LOD) and feasibility. In this work, we demonstrated capacitive H2S sensing for the first time using metal–organic frameworks (MOFs) decorated with silver oxide (Ag2O) nanoparticles as the sensing materials. The nanoparticles were deposited on three MOFs (UiO-66(Zr) BDC, UiO-66(Zr) BDC-NO2, and UiO-66(Zr) BDC-N3) using the impregnation technique. The sensing materials were characterized for morphology using X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy techniques. The synthesized MOFs were coated on interdigitated electrode capacitors as the dielectric materials and a comparison of their sensing properties was presented; among them, UiO-66(Zr) BDC-NO2 loaded with Ag2O showed the highest sensitivity towards H2S. The optimized MOF–Ag2O composite demonstrated experimental LOD of 1 ppm of H2S at room temperature, showing high chemical absorption affinity towards H2S. The work presented here is promising for developing sensitive H2S sensors and in addition paves the way to explore and develop other possible MOF-based composite materials for gas sensing applications.

Topology, magnetism and dye adsorption properties of metal organic frameworks (MOFs) synthesized from bench chemicals

Abstract: Herein, two metal organic frameworks (MOFs), namely, [{Cu2(μ-OH)(μ-OAc)(H2O)(OAc)(bpy)2}NO3·4H2O]n (CuMOF-1) and [{Co(bpy)(ClO4)2(H2O)2}·bpy]n (CoMOF-2), where bpy = 4,4′-bipyridine, were synthesized, characterized and explored for their material importance in magnetism and dye adsorption. Under solvothermal conditions, two different metal salts (nitrate and perchlorate) were reacted with a simple bench chemical, i.e., a dipyridine derivative, namely, bpy to afford two MOFs having different yet interesting topologies and adsorption properties. The structure of CuMOF-1 was built from the repeating building blocks of the dinuclear cationic Cu(II) units composed of two Cu(II) ions, two bpy ligands, two acetate ions (OAc), one hydroxide ion (OH−) and a water molecule. Interestingly, two different Cu atoms existed in the structure with two different coordination geometries, i.e., octahedral and trigonal bipyramidal. The sql topology of the resulting 4-c uninodal net with point symbol {44·62} was obtained for CuMOF-1. The cluster representation of CuMOF-1 further gave hxl topology with 6-c uninodal nets (point symbol: {36·46·53}). CoMOF-2 was built from repeating mononuclear Co(II) units, where each Co atom coordinated with two bpy ligands, two perchlorate ions and two water molecules, resulting in octahedral geometry around the Co(II) ions. The surprising nature of the structure of CoMOF-2 was that one bpy ligand was coordinated with cobalt, while the second bpy ligand was present in the lattice in between layers, thus consolidating the structure by strong hydrogen bonding with the coordinated water molecules of the neighboring units. The resulting underlying net in CoMOF-2 was 2C1 with sql topology. The magnetic data indicated the presence of strong antiferromagnetic interactions in MOFs (J = −98.21 cm−1 in CuMOF-1 and θ = −8.8 K in CoMOF-2). The present MOFs were exploited for the adsorption of two dyes, namely, methylene blue (MB) and methyl orange (MO), which are organic pollutants. The adsorption studies confirmed that CoMOF-2 is a more selective adsorbent for MB. The kinetic data disclosed the pseudo-second-order mechanism of adsorption in both cases. The cation/anion–π interaction between the dyes and π-electron-rich bpy was responsible for the adsorption behaviour of MOFs. Moreover, the presence of free bpy in the lattice of CoMOF-2 gave rise to the strongest interactions, making CoMOF-2 the best adsorbent.

Recognition of the π-hole donor ability of iodopentafluorobenzene – a conventional σ-hole donor for crystal engineering involving halogen bonding

Abstract: Iodopentafluorobenzene (IPFB or PhFI) was co-crystallized with tetra(n-butyl)ammonium tetraiodo-μ,μ′-diiododiplatinate(II), [n-Bu4N]2[Pt2(μ-I2)I4] (1), to give the adduct 1·2IPFB. The XRD experiment revealed that 1·2IPFB displays previously unreported C⋯I–Pt anion–π interactions formed along with the expected PhF–I⋯I–PtII halogen bond (XB); these two interactions join two complexes and two IPFBs in a heterotetrameric cluster. Processing of the available CSD data revealed only one structure (CSD code: IKIYAE) with a heterotetrameric cluster bearing simultaneous two PhF–I⋯X (X = I–PtIV, N) XBs and C⋯I lp(I)–π contacts between the two IPFBs. Results of the DFT calculations (M06/DZP-DKH level of theory) followed by the topological analysis of the electron density distribution within the framework of Bader's approach (QTAIM) for both 1·2IPFB and IKIYAE confirmed the availability of these (anion/lp)–π weak interactions. The estimated energies of the observed (anion/lp)–π and XBs contacts are in the 0.9–1.3 kcal mol−1 and 1.3–5.3 kcal mol−1 ranges, respectively. π-Hole donor ability of IPFB was additionally confirmed by theoretical calculations of the molecular surface electrostatic potential for the optimized equilibrium structure of IPFB.

Two triphenylamine-based luminescent metal–organic frameworks as a dual-functional sensor for the detection of nitroaromatic compounds and ofloxacin antibiotic

Abstract: Two Zn2+-based luminescent metal–organic frameworks containing the same components, {[Zn(TIPA)pim0.5]2H2O·NO3}n (1) and {[Zn(TIPA)(pim)]3H2O}n (2) have been synthesized based on a π-electron rich semi-rigid triangular ligand TIPA (TIPA = tris(4-(1H-imidazol-1-yl)-phenyl)amine and H2pim = pimelic acid). 1 is a two-fold interpenetrating 3D framework containing four chiral (10,3)-a subnets, and 2 is merely a 2D + 2D → 2D entangled network, although they were synthesized from the same starting materials. A photoluminescence investigation revealed that the emissions of 1 and 2 entirely originate from the intraligands charge transfer transitions (π → π*). Metal–organic framework 1 can be applied as a dual functional chemical sensor for nitroaromatic (NAC) compounds and antibiotics detection with a high sensitivity and quick response. In addition, the effective detection of nitroaromatic compounds and antibiotics was rationalized by the density functional theory (DFT) calculation of the energy bands of the NAC compounds and antibiotics, which revealed that a photoinduced electron transfer mechanism is largely responsible for the sensing of nitroaromatic compounds, and the resonance energy transfer is largely responsible for the exclusive sensing of ofloxacin (OFX).

Construction of novel hybrid PdO–ZnO p–n heterojunction nanostructures as a high-response sensor for acetaldehyde gas

Abstract: P–n heterojunction nanostructures (NSs) are emerging as a promising class of hybrid materials for gas-sensing applications. In this work, we report a facile, cost-effective synthesis technique to fabricate unique, hybrid PdO@ZnO p–n heterojunction NSs as high response and selective acetaldehyde gas sensors. Initially, Pd@ZnO core–shell NSs (CSNSs) were synthesized, and subsequently transformed into hybrid PdO@ZnO p–n heterojunction NSs by a simple high-temperature calcination method. The morphological study of the prepared hybrid NSs was carried out by transmission electron microscopy (TEM), which revealed that 10 ± 5 nm sized Pd nanoparticles (Pd NPs) were encapsulated in the center of the ZnO shell of 40–50 nm to form approximately 75–135 nm sized Pd@ZnO CSNSs. The more crystalline, flower-shaped PdO@ZnO p–n heterojunction NSs were formed after the Pd@ZnO CSNSs were calcined at 500 °C for 2 h. When employed as a gas sensor, the hybrid PdO@ZnO p–n heterojunction NSs demonstrated high sensitivity and selectivity to acetaldehyde gas amongst other gases (ethanol, CO, H2, and CH4). The PdO@ZnO p–n heterojunction NSs-based sensor delivered the highest response (Ra/Rg = 76) to 100 ppm acetaldehyde at 350 °C, as compared to the pristine ZnO NSs sensor (Ra/Rg = 18). The improved sensing performance of the hybrid PdO@ZnO p–n heterojunction NSs-based sensor over the pristine ZnO NSs-based sensor was attributed to the combination of the resulting synergistic effect due to the formation of the p–n heterojunction between PdO and ZnO NPs, the catalytic dissociation effect of PdO, and the high surface area of the PdO@ZnO p–n heterojunction NSs.

High pressure: a complementary tool for probing solid-state processes

Abstract: Since the early days of X-ray diffraction, researchers have tried to follow the evolution of crystal structures under extremes of pressure. Recently, interest in this area has exploded, attracting scientists from backgrounds across the physical and life sciences. Much of this rapid expansion has been due to the enhancement of diffraction equipment, including detectors, goniometers, and high-pressure cells, and the development of synchrotron radiation and neutron sources. The high-pressure research generally focuses on the direct effects of pressure on the structural evolution of a system. The present contribution describes examples of a less common application: hydrostatic compression of crystals of organic and coordination compounds can be used as a complementary tool in order to rationalise the mechanisms of the transformations in these solids that take place at atmospheric pressure. The data on the compressibility, equations of state, phase changes, or the effects of pressure on intermolecular distances, molecular conformations and chemical bonds can shed light on the factors that are important for thermal and photochemical reactions in the same crystals without an external load as well as on their solid-state or solvent-assisted polymorphic transformations. The manuscript also discusses how structural studies under extreme conditions can help to rationalise the thermo- and photosalient effects that accompany some solid-state transformations. This knowledge is currently of great importance for materials science since mechanically responsive materials have the potential to be used for the design and manufacture of new supramolecular devices.

Conductive Ti3C2 and MOF-derived CoSx boosting the photocatalytic hydrogen production activity of TiO2

Abstract: Design and synthesis of high-efficiency and low-cost photocatalysts is essential for converting solar energy into clean hydrogen energy. Herein, we report a novel TiO2 nanocrystal photocatalyst confined by ZIF-67-templated porous CoSx, with conductive Ti3C2 boosting the transport efficiency of the charge carriers. TiO2–CoSx and TiO2–Ti3C2–CoSx exhibit a photocatalytic H2-production activity 2.8 and 5.8 times larger than that of pristine TiO2, respectively, because of the existence of the highly porous MOF-templated CoSx hydrogen evolution reaction cocatalyst and highly conductive Ti3C2. This study will provide a practical reference for the design and preparation of efficient photocatalysts with high transport and utilization efficiency of charge carriers.

Hierarchical NiSe2 spheres composed of tiny nanoparticles for high performance asymmetric supercapacitors

Abstract: To achieve superior performance of electrode materials, the design of rational and advantageous hierarchical structures has been confirmed as an effective and feasible approach. Herein, we report an effective strategy for the synthesis of hierarchical NiSe2 spheres composed of nanoparticles: Ni(OH)2 flowers were firstly prepared as the precursor via a solvothermal method followed by a solvothermal selenylation reaction to prepare hierarchical NiSe2 spheres. Investigated as electrode materials for asymmetric supercapacitors, the NiSe2 spheres//AC device exhibits enhanced electrochemical performance with a high specific capacitance of 99.7 F g−1 at a current density of 2 A g−1. In addition, high energy/power density and long-term cycling stability over 10 000 cycles have been shown, which derive from the nanosized building-blocks and secondary micro-architecture.

Ball size or ball mass – what matters in organic mechanochemical synthesis?

Abstract: Ball mass is an important parameter that is known to have an influence on the outcome of a mechanochemical reaction induced by ball-milling. A standard way of modifying the ball mass is to change the size of the ball made of the same material. In this case, however, a change in mass is accompanied by a simulatneous change in the ball size. It is therefore not possible to disentangle the effects of mass and surface area in these cases. In the present work we report the results of experiments with specially designed and manufactured balls in which (1) milling ball mass is held constant, but their size differs, and (2) the ball mass is altered, with the diameter of the milling ball being held constant. Using the cocrystallisation of theophylline + nicotinamide as a case study it was found that both diameter and ball mass play crucial roles in determining the rate of a mechanochemical reaction. For comparison, we have also used milling balls with the same size (different mass), and others with the same mass (different size) made of different materials, as would be “traditional”. It was found that, despite having the same size, the lightest milling ball (nylon) was the most efficient in initiating the co-crystallisation, presumably due to the sorption of EtOH. Hence, the results of this manuscript also demonstrate how milling ball material can in fact be the most influential parameter, and potentially counterintuitive to classical mechanics.

Application of electric fields for controlling crystallization

Abstract: This highlight investigates the different aspects of electric fields controlling crystallization, focusing on strong electric fields. Application of both internal and external electric fields, as well as utilizing both alternating and direct currents (AC and DC) are discussed, with an emphasis on protein crystallization. Attention is drawn to the similarities and opposing findings within the papers published in the field to date. It has been demonstrated that the crystallization process can be significantly enhanced by the application of electric fields. Namely, electric fields can reduce the nucleation time, control the location of nucleation, increase the product yield, control the product crystal size, enhance overall crystal quality, control the crystal orientation and control the polymorphism. In addition, recent advances including the use of an electric field for separation of multicomponent mixtures, electric field-assisted crystallization in a continuous flow, and transformation of amorphous material into crystalline are discussed.

Enhanced proton conductivity of a MOF-808 framework through anchoring organic acids to the zirconium clusters by post-synthetic modification

Abstract: The modified MOF-808 frameworks MOF-808-EDTA/OX show better proton conduction behaviours than the original framework. A high proton conductivity (1.94 × 10−4 S cm−1) of MOF-808-OX can be obtained at 30 °C and 98% relative humidity. This is the first example where proton conductivity is tuned by modifying the metal cluster-based nodes via a post-synthetic modification method.

A stable anionic metal–organic framework with open coordinated sites: selective separation toward cationic dyes and sensing properties

Abstract: A novel metal–organic framework, [H2bpy]0.5[Cd3(OH)(L)2(bpy)(H2O)2]·(bpy)0.5·2H2O (1) (H3L = 3-(3,5-dicarboxylphenyl)-4-carboxylpyridine, bpy = 4,4′-bipyridine), with blue luminescence, was successfully synthesized under solvothermal conditions. Structure analysis indicates that this compound is composed of triangle [Cd3(μ3-OH)] clusters linked by L ligands, forming a novel 3D framework with a (3,3,8)-connected (42·6)(42·6)(44·55·64·78·87) topology. Cd-MOF-1 contains microporous channels with accessible Lewis-base sites (N), uncoordinated carboxylate groups and coordinated H2O molecules, which are easy to recognize various small molecules. Meanwhile, this compound exhibits a microporous structure with [H2bpy]2+ cations being located in the channels, which can be easily replaced by some cationic dyes. Particularly, Cd-MOF-1 displays high water and pH stability. Based on the aforementioned considerations, when Cd-MOF-1 was immersed in the different metal ion aqueous solutions and different nitro explosive EtOH solutions, it performed as a highly selective and sensitive sensor for Fe3+ ions and TNP (2,4,6-trinitrophenol). Moreover, the probable sensing mechanism was also investigated in detail. More interestingly, dye adsorption studies revealed that Cd-MOF-1 can adsorb cationic dyes in aqueous solution while the anionic and neutral dyes cannot be absorbed and the cationic dye adsorption amounts decrease with the increase in dye size. Therefore, Cd-MOF-1 can potentially act as a column-chromatographic filter for the separation of dye molecules.

Engineering PPy decorated MnCo2O4 urchins for quasi-solid-state hybrid capacitors

Abstract: In this work, three dimensional PPy decorated MnCo2O4 urchins on Ni foam are fabricated via a hydrothermal strategy and an electro-polymerization process. The as-synthesized products are utilized as the electrode materials for hybrid capacitors. Due to the synergistic effect of PPy and MnCo2O4, the hybrid electrode exhibits excellent charge transport ability and cycling stability. The as-assembled device presents remarkable electrochemical performance with a high energy density of 0.785 mW h cm−3 at a power density of 7.49 W cm−3 and a maximum power density of 37.49 W cm−3 at an energy density of 0.488 mW h cm−3. The electrode materials reported here might present potential applications in next generation energy storage devices.

The PO13 crystal structure of ROY

Abstract: A novel polymorph of ROY was found by thermal methods. The crystal structure was solved by matching calculated powder X-ray diffraction patterns from a previously published crystal structure prediction to the experimental data. The structure was further refined by the Rietveld method. The new polymorph is pumpkin-orange in color and was therefore designated as PO13. At room temperature PO13 is less stable than form Y. After 5 years, a sample of 99% pure form PO13 converted to a mixture of 45% PO13/55% form Y.

Room temperature growth of CH3NH3PbCl3 single crystals by solvent evaporation method

Abstract: We report a new route to synthesize high-quality, large-size crystals of CH3NH3PbCl3 through proper selection of DSMO–GBL solution via solvent evaporation method at room temperature. A detailed evaluation of the structural, electronic, optical and electrical properties of these crystals was carried out. Our XPS studies suggested that organic–inorganic halide perovskites are sensitive to X-ray-induced damage, and hence, their properties may get altered. Also, photoluminescence studies displayed two peak spectra, indicating coexistence of order–disorder domains of CH3NH3 in the sample. Further observation of low defect concentration and longer diffusion length indicates that crystals grown by the presented method can offer promising solutions for optoelectronic devices.