Highly bright perovskite light-emitting diodes based on quasi-2D perovskite film through synergetic solvent engineering

Recently, quasi-two dimensional (2D) perovskites have attracted great interest as they can be facilely fabricated and yield high photoluminescence quantum yield. However, the luminance and the efficiency of perovskite light-emitting diodes (PeLEDs) based on quasi-2D perovskites are limited by the carrier transport and the crystallization properties of the quasi-2D perovskite films. Herein, a synergetic solvent engineering approach is proposed to improve the crystallinity and the carrier transport by optimizing the film morphology of the quasi-2D perovskite films. Consequently, the maximum luminance of green PeLEDs based on quasi-2D PEA₂ (MAPbBr₃)₂PbBr₄ perovskite is dramatically enhanced from 4000 cd m⁻² to 18 000 cd m⁻² and the current efficiency increases from 3.40 cd A⁻¹ to 8.74 cd A⁻¹. This work provides a promising way to control the morphology and the crystallinity properties of quasi-2D perovskite films for high-performance optoelectronic devices.

A synergetic solvent engineering approach to improve crystallinity and carrier transport, by optimizing film morphology of the quasi-2D perovskite films.     

Effect of Bi2O3 content on the microstructure and electrical properties of SrBi2Nb2O9 piezoelectric ceramics

Lead-free ceramics, SrBi₂Nb₂O₉–xBi₂O₃ (SBN–xBi), with different Bi contents of which the molar ratio, n(Sr) : n(Bi) : n(Nb), is 1 : 2(1 + x/2) : 2 (x = −0.05, 0.0, 0.05, 0.10), were prepared by conventional solid-state reaction method. The effect of excess bismuth on the crystal structure, microstructure and electrical properties of the ceramics were investigated. A layered perovskite structure without any detectable secondary phase and plate-like morphologies of the grains were clearly observed in all samples. The value of the activation energy suggested that the defects in samples could be related to oxygen vacancies. Excellent electrical properties (e.g., d₃₃ = 18 pC N⁻¹, 2P_r = 17.8 μC cm⁻², ρ_rd = 96.4% and T_c = 420 °C) were simultaneously obtained in the ceramic where x = 0.05. Thermal annealing studies indicated the SBN–xBi ceramics system possessed stable piezoelectric properties, demonstrating that the samples could be promising candidates for high-temperature applications.

Lead-free ceramics, SrBi₂Nb₂O₉–xBi₂O₃ (SBN–xBi), with different Bi contents of which the molar ratio, n(Sr) : n(Bi) : n(Nb), is 1 : 2(1 + x/2) : 2 (x = −0.05, 0.0, 0.05, 0.10), were prepared by conventional solid-state reaction method.     

Synthesis and anion recognition studies of new oligomethylene bis(nitrophenylureylbenzamide) receptors

A new series of oligomethylene bis(nitrophenylureylbenzamide) receptors were synthesized varying the relative position of the urea and amide groups (ortho4 and meta8) and the length of the oligomethylene chain (C₂ to C₈). An anion recognition study was performed with TBAX salts (X = AcO⁻, BzO⁻, F⁻, H₂PO₄⁻, and HP₂O₇³⁻) by UV-vis and ¹H NMR. The flexibility of these receptors allows a cooperative effect of both ureylbenzamide units in the receptors. Noteworthy, the ortho position favored the 1 : 1 stoichiometry in the complexes with the carboxylates. The formation of 2 : 1 receptor–anion complexes with both types of receptors 4 and 8 and with hydrogen pyrophosphate and high log K values obtained were very significant in this work. The NMR studies evidenced the formation of supramolecular complexes, even in a competitive solvent, such as DMSO.

Synthesis and supramolecular interaction of new oligomethylene bis(4-nitrophenylureylbenzamide) receptors with different anions.     

Preparation,characterization and application in cobalt ion adsorption using nanoparticle films of hybrid copper–nickel hexacyanoferrate

Different mole ratios (n_Cu : n_Ni = x : y) of hybrid copper–nickel metal hexacyanoferrates (Cu_xNi_yHCFs) were prepared to explore their morphologies, structure, electrochemical properties and the feasibility of electrochemical adsorption of cobalt ions. Cyclic voltammetry (CV), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) indicated that the x : y ratio of Cu_xNi_yHCF nanoparticles can be easily controlled as designed using a wet chemical coprecipitation method. The crystallite size and formal potential of Cu_xNi_yHCF films showed an insignificant change when 0 ≤ x : y < 0.3. Given the shape of the CV curves, this might be due to Cu²⁺ ions being inserted into the NiHCF framework as countercations to maintain the electrical neutrality of the structure. On the other hand, crystallite size depended linearly on the x : y ratio when x : y > 0.3. This is because Cu tended to replace Ni sites in the lattice structure at higher molar ratios of x : y. Cu_xNi_yHCF films inherited good electrochemical reversibility from the CuHCFs, in view of the cyclic voltammograms; in particular, Cu₁Ni₂HCF exhibited long-term cycling stability and high surface coverage. The adsorption of Co²⁺ fitted the Langmuir isotherm model well, and the kinetic data can be well described by a pseudo-second order model, which may imply that Co²⁺ adsorption is controlled by chemical adsorption. The diffusion process was dominated by both intraparticle diffusion and surface diffusion.

Cu_xNi_yHCF films with appropriate Cu/Ni ratios are expected to be prepared as designed for the recovery of Co²⁺ from spent LIBs.     

A novel fluorescence phenomenon caused by amine induced ion-exchange between Cd2+ and Fe3+ ions

A 3D metal–organic framework {[Cd(5-Brp)(dpa)]·0.5DMF·H₂O}_n (1) was successfully synthesized and characterized, which markedly recognized iron ions under the induction of an amino group. With the concentration of Fe³⁺ increasing, the emission of 1 first declined, then enhanced with a red shift and was finally quenched, which was different from the reference compound [Cd(5-Brp)(bpp)(H₂O)]_n (2). This result drew our attention to amine induced ion-exchange. This peculiar phenomenon inspired us to construct an effective ion detector.

A 3D metal–organic framework {[Cd(5-Brp)(dpa)]·0.5DMF·H₂O}_n (1) was successfully synthesized and characterized, which markedly recognized iron ions under the induction of an amino group.     

NiII and CoII binary and ternary complexes of 3-formylchromone: spectroscopic characterization,antimicrobial activities,docking and modeling studies

Reactions of 3-formylchromone (L) with Ni(ii) and Co(ii) ions having different anions (acetate, perchlorate, nitrate, and chloride) yielded a series of binary and ternary octahedral complexes with the general formula [ML_nL′_mX_y(S)_a]Z_y·bS, where M = Ni or Co, n = 1–3, L′ = auxiliary ligand = 8-hydroxyquinoline or 1,10-phenanthroline, m = 1 or 2, X = acetate or chloride, y = 0 or 2, S = H₂O or MeOH, a = 0–2, Z = nitrate or perchlorate and b = 0–1.5. Elemental and thermal analyses and infra-red, electronic, mass, magnetic susceptibility and molar conductivity measurements were successfully utilized to characterize the structures of the chromone complexes. The chromone ligand acts as a neutral bidentate ligand through its formyl and γ-pyrone oxygen atoms. The obtained complexes were formed with molar ratios 1 : 2 and 1 : 3 M : L for the binary and 1 : 2 : 1 and 1 : 1 : 1 M : L : L′ for the ternary complexes. The kinetic parameters of the thermal degradation steps were estimated and explained using the Coats–Redfern equations. The synthesized complexes showed antimicrobial activity with higher activity toward Candida albicans and Bacillus subtilis. Docking studies showed good agreement with the antimicrobial activity. Molecular modeling of the synthesized complexes was performed using Hyperchem at the PM3 level and the calculated structures correlate with the experimental data.

Synthesis of 3-formylchromone and its chloro-Co(ii)- and -Ni(ii)-complexes.     

N-doped porous carbons derived from Zn-porphyrin-MOF

N-doped porous metal–organic framework (MOF)-derived carbons (MDCs) were directly synthesized from a new Zn-DpyDtolP-MOF (ZnDpyDtolP·1/2DMF, H₂DpyDtolP = 5,15-di(4-pyridyl)-10,20-di(4-methylphenyl)porphyrin) containing a 3D hexagonal network through a self-templated carbonization method. KOH-activated MDC derivatives denoted as MDC-700-nKOH were also prepared with different weight ratios of KOH activator to MDC (MDC : KOH = 1 : n, where n = 1, 2). Compared to bare MDC, MDC-700-nKOH showed effective improvements of both gas sorption and electrochemical capacitive properties. More developed microporosity by KOH activation might induce great enhancement of high operating capacitive performances. The N-doped MDC-700-2KOH had high maximum gravimetric specific capacitance (555.6 F g⁻¹) and specific energy (40.4 W h kg⁻¹) at 0.1 A g⁻¹ in 1 M H₂SO₄. Even at a high current density of 190 A g⁻¹ in 6 M KOH, it exhibited high capacitive performance with a large specific power of 80 423 W kg⁻¹. MDC-700-nKOH electrodes also showed good recycling properties of electrochemical capacitance up to 30 000 cycles.

The porphyrin-based Zn-MOF is directly carbonized and activated by KOH for the generation of N-doped porous carbons acting as high performance supercapacitor electrode materials.     

Molecular keypad controlled circuit for Ce(iii) and NO3− ions recognition by μw synthesized silicon-embedded organic luminescent sensor

This report demonstrates the mimicking of an electronic circuit diagram towards Ce(iii) ion sensing response supported by molecular keypads. The probe naphthyl based triazole linked silatrane (NTS) was efficiently synthesized using a series of microwave mediated reactions. The luminescent sensor NTS was explored for the ion sensing response towards Ce(iii) ions using DMSO and DMSO : H₂O 4 : 1 (v/v) as solvent media, respectively. The role of water in Ce(iii) ion sensing was detected as ‘turn-off’ response that contradicts the ‘turn-on’ with DMSO. Further, the sensing of NO₃⁻ ions by NTS–Ce(iii) ensemble was associated with blue shift on absorption maxima. These mimicking response studies were sketched as circuit diagrams assisted by molecular keypad behaviour as IMPLICATION output logic gate.

This report demonstrates the mimicking of an electronic circuit diagram towards Ce(iii) ion sensing response supported by molecular keypads.     

Direct synthesis of shaped MgAPO-11 molecular sieves and the catalytic performance in n-dodecane hydroisomerization

In industrial application, molecular sieves are usually used in a certain shape. This requires the addition of binder and causes the reduction of both the molecular sieve content and catalytic performance. Herein, pseudo-boemite was mixed with deionized water at room temperature, followed by the drop-wise addition of phosphoric acid, magnesium acetate solution, hydrofluoric acid, di-n-propylamine and 1-ethyl-3-methyl imidazolium bromide with vigorous stirring. The molar ratio of Al₂O₃ : P₂O₅ : MgO : HF : DPA : [EMIm]Br : H₂O in the gel was 1 : 1 : 0.03 : 0.18 : 0.4 : 1 : 45. Then the gel was dried, extruded and directly crystallized to form a shaped MgAPO-11 molecular sieve. X-ray diffraction, scanning electron microscopy, N₂ adsorption, ammonia temperature programmed desorption, pyridine adsorption infrared spectroscopy and nuclear magnetic resonance spectroscopy were used to investigate the physicochemical properties of the samples. X-ray diffraction, scanning electron microscopy and N₂ adsorption tests show that the shaped MgAPO-11 molecular sieve is fully crystallized and possesses hierarchical porosity. Mg is incorporated into the molecular sieve framework and the Pt catalyst supported by the obtained shaped MgAPO-11 exhibits excellent catalytic performance with n-dodecane conversion of 94% and isomer selectivity of 95% at 280 °C. Such a method for the direct synthesis of shaped molecular sieves shows potential for the green synthesis of molecular sieves in industry.

Shaped MgAPO-11 with hierarchical pores can be directly synthesized via a solid transformation route. Fewer synthesis steps and superior catalytic performance make the route possess great potential in practical applications.     

Systematic investigation of CO2 : NH3 ice mixtures using mid-IR and VUV spectroscopy – part 1: thermal processing

The adjustment of experimental parameters in interstellar ice analogues can have profound effects on molecular synthesis within an ice system. We demonstrated this by systematically investigating the stoichiometric mixing ratios of CO₂ : NH₃ ices as a function of thermal processing using mid-IR and VUV spectroscopy. We observed that the type of CO₂ bonding environment was dependent on the different stoichiometric mixing ratios and that this pre-determined the NH₃ crystallite structure after phase change. The thermal reactivity of the ices was linked to the different chemical and physical properties of the stoichiometric ratios. Our results provide new details into the chemical and physical properties of the different stoichiometric CO₂ : NH₃ ices enhancing our understanding of the thermally induced molecular synthesis within this ice system.

The stoichiometric mixing ratio of CO₂ : NH₃ ices determines both the initial chemical and physical properties of the ices and their evolution through thermal processing including CO₂ bonding environment, NH₃ crystallite size and amount of residue.     

An efficient method to obtain anti-inflammatory phenolic derivatives from Scindapsus officinalis (Roxb.) Schott. by a high speed counter-current chromatography coupled with a recycling mode

Herein, we provide an effective separation strategy based on liquid–liquid extraction and two different modes of high speed counter-current chromatography (HSCCC) for the rapid enrichment and separation of compounds from n-butanol-partitioned samples of S. officinalis. Liquid–liquid extraction of the crude sample was performed using a two-phase solvent system composed of ethyl acetate–n-butanol–water with volume ratios of 9 : 0 : 9, 5 : 4 : 9 and 3 : 6 : 9 (v/v), which allowed components with lower polarity and higher polarity to be enriched separately with the first ratio and the other two ratios, respectively. For separation, the conventional and recycling mode HSCCC were combined to develop a strategy for the acquisition of eight phenolic derivatives from the enriched samples, including one new compound, 7-O-[β-d-xylopyranosyl-(1–4)-β-d-glucopyranosyl-(1–4)-α-l-rhamnopyranosyl]-5-hydroxy-2-methyl-4H-1-benzopyran-4-one (5), three caffeoylquinic acid isomers, 3-O-caffeoylquinic acid butyl ester (6), 5-O-caffeoylquinic acid butyl ester (7), 4-O-caffeoylquinic acid butyl ester (8), salidroside (1), drynachromoside B (2), 3,4-dihydroxy-benzoic acid (3), and 5,7-dihydroxy-2-methyl chromone (4). Recycling HSCCC separation was successfully applied to separate the three isomers after six cycles. Furthermore, all the isolates were evaluated for their anti-inflammatory activity against nitric oxide (NO) production in vitro, with 6 and 7 showing significant inhibitory effects with IC₅₀ values of 13.8 μM and 17.6 μM, respectively.

Anti-inflammatory phenolic derivatives from S. officinalis by high speed counter-current chromatography.     

A novel resource utilization method using wet magnesia flue gas desulfurization residue for simultaneous removal of ammonium nitrogen and heavy metal pollutants from vanadium containing industrial wastewater

In the present study, a novel resource utilization method using wet magnesia flue gas desulfurization (FGD) residue for the simultaneous removal of ammonium nitrogen (NH₄–N) and heavy metal pollutants from vanadium (V) industrial wastewater was proven to be viable and effective. In this process, the wet magnesia FGD residue could not only act as a reductant of hexavalent chromium [Cr(vi)] and pentavalent vanadium [V(v)], but also offered plenty of low cost magnesium ions to remove NH₄–N using struvite crystallization. The optimum experimental conditions for Cr(vi) and V(v) reduction are as follows: the reduction pH = 2.5, the wet magnesia FGD residue dose is 42.5 g L⁻¹, t = 15.0 min. The optimum experimental conditions for NH₄–N and heavy metal pollutants removal are as follows: the precipitate pH = 9.5, the n(Mg²⁺) : n(NH₄⁺) : n(PO₄³⁻) = 0.3 : 1.0 : 1.0, t = 20.0 min. Finally the NH₄–N, V and Cr were separated from the vanadium containing industrial wastewater by forming the difficult to obtain, soluble coprecipitate containing struvite and heavy metal hydroxides. The residual pollutant concentrations in the wastewater were as follows: Cr(vi) was 0.047 mg L⁻¹, total Cr was 0.1 mg L⁻¹, V was 0.14 mg L⁻¹, NH₄–N was 176.2 mg L⁻¹ (removal efficiency was about 94.5%) and phosphorus was 14.7 mg L⁻¹.

A novel resource utilization method using wet magnesia flue gas desulfurization residue for the simultaneous removal of ammonium nitrogen and heavy metal pollutants from vanadium industrial wastewater was proven to be viable and effective.     

Purification,structure and anti-oxidation of polysaccharides from the fruit of Nitraria tangutorum Bobr.

In this paper, polysaccharides were extracted from the fruits of Nitraria tangutorum Bobr. (NTWP) using a hot water extraction method and extraction conditions were optimized by RSM. The optimal conditions were determined as follows: extraction time 7 h, extraction temperature 60 °C, ratio of water to raw material 15 : 1, and with these conditions, the yield was 14.01 ± 0.11%. After purification using DEAE-cellulose column and Sephadex G-200 column, NTWP-II was successfully obtained. The results of GC-MS and SEC-LLS analysis suggested that monosaccharide composition of NTWP-II was composed of Rha, Ara, Man, Glc and Gal with the molar ratio of 1.14 : 2.5 : 3.00 : 2.69 : 5.28 and M_w, M_w/M_n and R_z 2.29 × 10⁵, 1.32, 15.22. The detailed structure of NTWP-II was characterized by FT-IR, NMR. Based on these analyses, the structure of the repeating unit of NTWP-II was established.

Antioxidant activity of NTWP-II, evaluated in vitro, indicates that NTWP-II has good potential as a natural antioxidant used in the food industry.     

Enhancement of CO2 capture performance of aqueous MEA by mixing with [NH2e-mim][BF4]

Alcohol amine solutions have a high absorption capacity and rate for CO₂ capture, however, there are some shortcomings such as high energy-consumption and low stability. To enhance CO₂ capture performance of aqueous MEA, a functional ionic liquid ([NH₂e-mim][BF₄]) was introduced based on the advantages for CO₂ capture. Absorbents were prepared with the molar concentration ratio of [NH₂e-mim][BF₄] to the 30 vol% aqueous MEA of 0 : 10, 1 : 9, 2 : 8, 3 : 7, 4 : 6 and 6 : 4. The density and the viscosity of the investigated absorbents were measured and the effects of the molar fraction of [NH₂e-mim][BF₄] (n_I) and temperature on CO₂ absorption performance were investigated. CO₂ desorption performance of the solvent at different temperatures was discussed. The stability performance of the absorbent with n_I of 2 : 8 (I/M_2:8) was examined by five consecutive cyclic tests. The results showed that for pure CO₂, the I/M_2:8 displayed the highest absorption performance at 303 K under 1 bar: a comparable CO₂ absorption capacity of the 30 vol% aqueous MEA and a higher CO₂ absorption rate at the later absorption stage. Moreover, with the increase of temperature, CO₂ absorption capacity and rate decreased, while CO₂ desorption efficiency and rate increased. 393 K was chosen as the optimum desorption temperature with the desorption efficiency of 99.31%. The introducing of IL contributed to CO₂ desorption performance of the absorbents significantly. The properties (CO₂ absorption capacity, mass loss, density and viscosity) of the I/M_2:8 during the cycles suggested that the IL-MEA mixture had an excellent stability performance.

Alcohol amine solutions have a high absorption capacity and rate for CO₂ capture, however, there are some shortcomings such as high energy-consumption and low stability.     

Protonation and anion-binding properties of aromatic sulfonylurea derivatives

In this work the anion-binding properties of three aromatic sulfonylurea derivatives in acetonitrile and dimethyl sulfoxide were explored by means of NMR titrations. It was found that the studied receptors effectively bind anions of low basicity (Cl⁻, Br⁻, I⁻, NO₃⁻ and HSO₄⁻). The stoichiometry of the complexes with receptors containing one binding site was 1 : 1 exclusively, whereas in the case of the receptor containing two sulfonylurea groups 1 : 2 (receptor : anion) complexes were also detected in some cases. The presence of strongly basic anions (acetate and dihydrogen phosphate) led to the deprotonation of the sulfonylurea moiety. This completely hindered its anion-binding properties in DMSO and only proton transfer occurred upon the addition of basic anions to the studied receptors. In MeCN, a complex system of equilibria including both ligand deprotonation and anion binding was established. Since ionisation of receptors was proven to be a decisive factor defining the behaviour of the sulfonylurea receptors, their pK_a values were determined using several deprotonation agents in both solvents. The results were interpreted in the context of receptor structures and solvent properties and applied for the identification of the interactions with basic anions.

Sulfonylurea derivatives were studied as receptors revealing that they effectively bind anions of low basicity, whereas basic anions cause receptor deprotonation.     

Self-assembly of the monohydroxy triterpenoid lupeol yielding nano-fibers,sheets and gel: environmental and drug delivery applications

Lupeol is a medicinally important naturally abundant triterpenoid having a 6–6–6–6–5 fused pentacyclic backbone and one polar secondary “–OH” group at the C3 position of the “A” ring. It was extracted from the dried outer bark of Bombax ceiba and its self-assembly properties were investigated in different neat organic as well as aquous-organic binary liquid mixtures. The triterpenoid having only one polar “–OH” group and a rigid lipophilic backbone self-assembled in neat organic non-polar liquids like n-hexane, n-heptane, n-octane and polar liquids like DMSO, DMF, DMSO–H₂O, DMF–H₂O, and EtOH–H₂O yielding supramolecular gels via formation of nano to micrometre long self-assembled fibrillar networks (SAFINs). Morphological investigation of the self-assemblies was carried out by field emission scanning electron microscopy, high resolution transmission electron microscopy, atomic force microscopy, optical microscopy, concentration dependent FTIR and wide angle X-ray diffraction studies. The mechanical properties of the gels were studied by concentration dependent rheological studies in different solvents. The gels were capable of removing toxic micro-pollutants like rhodamine-B and 5,6-carboxyfluorescein as well as the toxic heavy metal Cr(vi) from contaminated water. Moreover release of the chemotherapeutic drug doxorubicin from a drug loaded gel in PBS buffer at pH 7.2 has also been demonstrated by spectrophotometry.

The monohydroxy triterpenoid lupeol forms gels in organic and aqueous organic liquids via self-assembly. The resulting supramolecular gels could be utilized for pollutant capture, drug entrapment and release applications.     

Development of online-storage inner-recycling counter-current chromatography for the preparative separation of complex components of alkylphenols from sarcotesta of Ginkgo biloba L.

High-speed counter-current chromatography (HSCCC) is becoming an effective and non-absorptive separation method from natural products. Due to the insufficient separation efficiency, it is challenging to separate complex components, especially for compounds with similar K_D values. In this study, a novel and effective online-storage inner-recycling CCC method was used to separate alkylphenols from the sarcotesta of Ginkgo biloba L. A two-phase solvent system of n-heptane/ethyl acetate/methanol/acetic acid (5 : 4 : 1 : 1, v/v) was used for HSCCC separation of 500 mg crude extracts. After the inner-recycling of two fractions coupled with pre-HPLC, five main ginkgolic acids (C13:0, C15:1, C17:2, C15:1, C17:1) coupled with bilobol (C15:1) and a mixture were obtained from a non-stop separation using a storage loop and two six-way valves. This novel method was also evaluated and predicted by formula derivation. This method could be an effective, rapid, and simple approach to separate alkylphenols from the sarcotesta of G. biloba.

High-speed counter-current chromatography (HSCCC) is becoming an effective and non-absorptive separation method from natural products.     

Self-assembly of pyrene-appended glucono gelators: spacer regulated morphological change and inversion of circularly polarized luminescence

Pyrene-appended glucono gelators with different spacer lengths (two and four methylene units) were designed and found to form supramolecular gels in organic aqueous solvents. The shorter spacer gelator 1 was prone to self-assemble into nanotubes due to well stacking multi-bilayer unit, while gelator 2 with the longer spacer formed nanofibers due to the relatively disordered packing structure. Both of the gels showed supramolecular chirality as well as circularly polarized luminescence (CPL) due to the chirality transfer from the glucose moiety to the assembly. Interestingly, the CD and CPL signals were opposite for the two gels. It was suggested that the packing of the pyrene unit in the gels were different due to the spacer and resulted in the inversed chiroptical properties. The work provided a deeper understanding of the origin of the supramolecular chirality and furthers the design of the CPL materials.

Pyrene-appended glucono gelators with different spacer lengths (two and four methylene units) were designed and found to form supramolecular gels in organic aqueous solvents.

Self-assembly offers an efficient method to construct supramolecular gels, where small gelator molecules self-assembled into nanostructures and immobilized solvents via non-covalent interactions including hydrophobic interaction, hydrogen bonding, π–π stacking, electrostatic interaction, van der Waals forces and charge–transfer interactions.^1–5 Interestingly, many of the chiral molecules easily form supramolecular gels meaning that the gels can be applied in chiral recognition, chiral separation, asymmetric catalysis and chiroptical functional materials.^6–16Circularly polarized luminescence (CPL) is a unique function that pertains to chiral systems, which emit different left- and right-handed circularly polarized light and have attracted great interest in recent years.^16–22 By combining the chiral units and fluorophores, many of the chiral molecular self-assembly systems have been developed and efficient chiroptical CPL have been realized.^18–22In general, molecular systems show only one direction of CPL, this is determined by the molecular chirality of the chiral moiety. However, at a supramolecular level, supramolecular chirality can be controllably changed via regulating the self-assembly process or slightly modifying the molecules while maintaining the molecular chirality. For example, DNA could have right-handed B-DNA and left-handed Z-DNA was formed while originating from the same molecular chirality of d-sugar.²³ In an artificial system, supramolecular chirality was also observed to be reversed by external stimulus. For example, the opposite CD spectra can be achieved through changing solvent, temperature, light irradiation, and addition of metal ions or achiral dopants.^24–28 However, there were only limited cases that realize the inversion of CPL in supramolecular gels by tuning the self-assembly process.^29–32 It still remains unknown why such chirality inversion could happen in supramolecular systems.Here we designed two pyrene based derivatives (1–2, Fig. 1), in which a pyrene core served as an emission moiety, and a glucono group served as chiral source. The two parts were covalently connected via two amide bonds with different lengths of alkyl spacers. These molecules (1–2) can form supramolecular gels in the organic aqueous media. The self-assembled behaviour and luminescent property of the gel could be tuned dependent on the solvents and length of alkyl spacer chains, the nanotubes and nanofibers together with opposite CD and CPL signals were observed based on the different length of space alkyl chain in the gelator, as illustrated in Fig. 1.Open in a separate windowFig. 1Molecular structure of gelator 1–2 and photographs of formed gel in EtOH–H₂O mixture solution (EtOH : H₂O = 1 : 2) under natural light and UV light (365 nm). The gelator 1 self-assembled into nanotube with left-handed CPL, while gelator 2 self-assembled into nanofibers with right-handed CPL.4-(1-Pyrenyl)butyric acid methyl ester was employed as staring material, which was first reacted with ethylenediamine and 1,4-butanediamine respectively, the intermediate was separated and purified by gel column chromatography, and the desired gelator 1–2 was obtained after the intermediates were further reacted with glucono δ-lactone (ESI^†).The gelation behaviour of molecule 1–2 was tested in various solvents at a standard concentration with 1% (w/v). The results were summarized in Table S1,^† both gelator 1 and gelator 2 were insoluble in a series of polar and nonpolar organic solvents including petroleum ether, dichloromethane, n-hexane, cyclohexane, acetone, ethyl acetate, THF, acetonitrile, methanol and ethanol (Table S1,^† entry 1–10), and complex 1–2 were soluble in DMF and DMSO (Table S1,^† entry 11 and 12). To our delicious, the compound 1–2 can form gel in the organic-water mixture solutions, including THF–H₂O, DMSO–H₂O and EtOH–H₂O. In the case of ethanol water mixture solvent, the molecule 1 and 2 was first dissolved in ethanol–H₂O (1 : 1) mixture solution (Table S1,^† entry 13). Further improving the content of water, the gel was formed (Table S1,^† entry 14–16). Especially, when the volume ratio of EtOH : H₂O equal to 1 : 2, gelator 1 formed nearly transparent gel with critical gelation concentration (CGC) about 3 mg mL⁻¹, while gelator 2 formed translucent gel with the CGC about 5 mg mL⁻¹ (Fig. 1, photographs). In addition, the white gels were observed in the pure water (Table S1,^† entry 17). Furthermore, the complex 1–2 exhibited similar gel behaviour in THF and DMSO aqueous solution as in ethanol–water solution (Table S1,^† entry 18–22).The morphology of 1 and 2 based gel in ethanol aqueous solution was first investigated (the gels were named as gel₁ and gel₂ corresponding to gelator 1 and gelator 2). It was found that the morphology of gel₁ have obvious solvent dependent behaviour, scanning electron microscope (SEM) images shown that gel₁ underwent change from nanofibers to nanorods and further to amorphous nanosheets in ethanol aqueous solution when gradually increasing the water content (Fig. S1^†). It should be noted that uniform nanofibers were observed when gel₁ formed in 1 : 2 of ethanol : H₂O mixture solvent, the diameter distribution of nanofibers is extremely narrow (15 nm ± 1 nm), the length of nanofibers reached tens to hundred micrometers (Fig. 2a and S2^†). TEM image indicated that these nanofibers were actually nanotubes, in which the diameter of nanotube was about 15 nm and the wall thickness of nanotube was around 2.5–2.7 nm (Fig. 2b and S2^†). AFM image further verified that the height of the nanotube was around 15 nm (Fig. 2c and S3^†). In the case of gel₂, the nanofibers with the diameter around a few nanometers to tens of nanometers were observed in ethanol aqueous solution (Fig. S4^†). Also, the size distribution of nanofibers was relatively uniform at 1 : 2 of ethanol water solution (Fig. 2d). TEM and AFM images further proved that gel₂ was nanofiber structure with the diameter of nanofiber around 5–10 nm (Fig. 2e, f and S5^†). These results indicated that assembly behaviour of gelator 1 and 2 formed well defined nanostructures under 1 : 2 ethanol water mixed solvent.Open in a separate windowFig. 2SEM images of (a) gel₁ and (d) gel₂, TEM images of (b) gel₁, (e) gel₂ and AFM of images of (c) gel₁ and (f) gel₂. The gels were formed in mixed solvent of ethanol and water (EtOH : H₂O = 1 : 2).UV-vis spectra showed four main peaks at 266 nm, 277 nm, 328 and 345 nm of gelator 1 in DMSO dilute solution (Fig. 3a, black line, 1 × 10⁻⁵M), which can be assigned to the un-aggregated form of pyrene units (Fig. S6,^† SEM and TEM of gelator 1 and 2 in DMSO indicated no assembly happened). The absorption peaks are blue shifted to 265 nm, 275 nm, 326 nm and 343 nm for gelator 1 in gel state (Fig. 3a, red line, gel in 1 : 2 of ethanol : water). The blue-shifted bands were also observed in gel₂ in comparison with 2 in DMSO diluted solution (Fig. 3b), these results suggested that in both cases, the gelator 1–2 prone to form H-aggregates in the gel state. Furthermore, it was found that the UV-vis spectra of gel₁ and gel₂ in different volume ratio of ethanol and water were nearly same as in 1 : 2 of ethanol : water solution (Fig. S7^†).Open in a separate windowFig. 3(a) UV-vis spectra of gelator 1 in DMSO (black line) and gel₁ in 1 : 2 of ethanol : water mixed solvent (red line). (b) UV-vis spectra of gelator 2 in DMSO (black line) and gel₂ in 1 : 2 of ethanol : water mixed solvent (red line).For exploring the emission properties of 1–2 gels, the fluorescence spectra were measured. In the diluted DMSO solution, two emission peaks at 380 nm and 396 nm ascribed to the monomer emission together with a very weak peak at 480 nm belong to excimer emission were observed for gelator 1 (Fig. 4a, purple line). In the gel₁, the monomer emission peak decreased and excimer peak increased significantly, and the strong excimer emission peak at 442 nm was observed for the gel in 1 : 2 of ethanol : water mixture solution (Fig. 4a, black line). This phenomenon was also observed in the case of gel₂, and found that the strong excimer peak at and 470 nm was observed (Fig. 4b, black line, gel in 1 : 2 of ethanol : water). The fluorescence quantum yields of gel₁ and gel₂ was about 28.2% and 9.4% respectively. Obviously, these results indicated that both gel₁ and gel₂ have strong π–π interaction between pyrene moieties.Open in a separate windowFig. 4a) Fluorescence spectra of gelator 1 in DMSO (purple line) and gel₁ in EtOH/H₂O mixture solution. (b) Fluorescence spectra of gelator 2 in DMSO (purple line) and gel₂ in EtOH/H₂O mixture solution.Since the glucono group is chiral, the chiroptical properties of gels were further explored. There revealed several interesting features. First, when the gelator molecules 1–2 were dissolved into DMSO solution as a molecular state, no CD spectra can be detected in the absorption band of pyrene (Fig. S8^†). However, obvious CD signals were observed when compounds 1–2 formed gels in mixed ethanol and water (1 : 2) solvent. The negative CD signal of gel₁ with the peaks at 294 nm, 366 nm and 382 nm were observed (Fig. 5a), which were consistency of corresponding to the UV-vis spectra of gel₁, indicated that pyrene segments oriented in the chiral manner in the gel state. In the case of gel₂, to our surprise, the positive CD signal with the peak at 290 nm, 344 nm and 367 nm were observed. It should be noted that gel₂ presented opposite CD signal in comparison with gel₁ in the longer wavelength regions. These results indicated that chiral packing manners of chromophore pyrene units in the gel state could be different, where the gelator spacer may regulate the supramolecular chirality of resulted gel assemblies. For quantitatively discuss comparison the supramolecular chirality, the dissymmetry factor of ECD, g_CD value were found to be 9 × 10⁻⁴ and 1.4 × 10⁻⁴ for gel₁ and gel₂ respectively, indicated that gel₁ with more uniform nanotube structure gave a stronger g_CD. The CD signal based on the pyrene moiety was due to the chirality transfer from the glucose. Since in gel₁, the distance between the pyrene and chiral unit is shorter, it is more efficient to transfer the chirality, thus leading to a larger g_CD In addition, the CD spectra of gel₁ and gel₂ under different volume ratio of ethanol and water were also measured, and found that all of gel₁ samples under different ethanol aqueous solution present negative CD, all of gel₂ samples under different ethanol aqueous solution present positive CD (Fig. S9^†), proved that the supramolecular chirality of both gel₁ and gel₂ was stable toward ethanol aqueous solvents.Open in a separate windowFig. 5(a) CD spectra of gel₁ (black line) and gel₂ (red line); (b) CPL of gel₁ (black line) and gel₂ (red line) (gelled in EtOH/H₂O mixture solution, EtOH : H₂O = 1 : 2), excited at 320 nm.Since the gel is fluorescent, the CPL spectra of gels were further investigated. It was found that both of gels exhibited CPL signals. The gel₁ exhibited CPL signal with a maximum emission peak at 445 nm, which was coincided with the fluorescent excimer emission peaks (Fig. 5b). However, no obvious CPL can be detected when gelator 1 dissolved in DMSO (Fig. S10^†), confirmed that CPL was originated from the supramolecular chiral aggregation of fluorescent pyrene units in the gel. The luminescence dissymmetry factor, g_lum = 2 × (I_L − I_R)/(I_L + I_R) was used to characterize CPL performance, where I_L and I_R are the luminescence intensities of right and left circularly polarized light respectively. The g_lum of gel₁ is about 2.5 × 10⁻³. As expected, gel₂ exhibited a nearly completely opposite CPL signal in comparison to gel₁, the g_lum of which is about −3.3 × 10⁻³. Therefore, it was confirmed that supramolecular chiral alignment of pyrene fragments in the gel is able to emit the CPL, while changing the length of space in the gelator can inverse CPL. In addition, the CPL of gel₁ and gel₂ under different volume ratio of ethanol and water were also investigated, and found that the highest g_lum was found at 1 : 2 ethanol and water solvent both for gel₁ and gel₂ (Fig. S11^†), indicated that ordered assembly architectures gave a higher CPL intensity.X-ray diffraction (XRD) was employed for exploring the molecular pacing in xerogels. As shown in Fig. 6a, gel₁ showed the peaks with d-spacing of 2.7, 1.4 and 0.90 nm based on the Braggs eqn, indicating a lamellar packing structure according to the ratio of 1, 1/2 and 1/3. The d space of lamellar structure is about 2.7 nm, which is close to the wall thickness of nanotube observed by TEM. In the case of the gel₂, the gelators also self-assembled into the lamellar structure with d spacing of 2.6 nm according to the diffraction peaks, suggesting that nanofibers consist of gel₂ was about two to multi lamellar thickness.Open in a separate windowFig. 6a) X-ray diffraction patterns of the xerogels of gel₁ and gel₂. (b) FTIR spectra of xerogels of gel₁ and gel₂. (c) The probable packing manner of gel₁ and gel₂. The pyrene segments in gel₁ were parallel packing, gave left-handed CPL; while the pyrene segments in gel₂ were overlapped packing, gave right-handed CPL.FT-IR spectrum was employed to provide the interaction modes in the gels. Two strong vibrations were observed at 3410 and 3300 cm⁻¹, which could be assigned to O–H and N–H vibrations, respectively. These two bands were from the glucone unit and the amide band, respectively. From the wavenumbers of the vibrations, it is clear that these gelators molecules formed H-bond between the glucone and amide groups. In addition, in both of gel state, the band at 1640 cm⁻¹ were observed, which was assigned to the vibration of amide I. However, the different in the position and hydrogen bonding interaction showed characteristic peaks for a hydrogen bonded amide II, the stretching bonds at 1550 cm⁻¹ was belonged to gel₁, and gel₂ shown the vibration band at 1540 cm⁻¹ (Fig. 6b), indicated the hydrogen-bonding interaction between gelators in gel₂ was weaker than that in gel₁.Based on these data, a possible packing model of gel₁ and gel₂ was proposed. In both of the gel systems, the molecules packed in a basic bilayer mode, like many of the amphiphiles. Here, the glucone group are in the outside while the pyrene packed inside the bilayer. Such bilayers were stabilized by the intermolecular H-bond between amide and the glucono unit, as shown in the FT-IT spectra. Furthermore, the strong excimer peak was observed, indicating that π–π interactions existed in both gel systems. It should be noted the π–π conjugated degree between pyrene units of gel₂ may be different, which is regulated by the spacers. It should be noted that gelator 2 has a longer spacer length with four methylene units, while gelator 1 has only two methylene units. However, the d spacer from the XRD is longer for gel₁ (2.7 nm), while shorter for gel₂. This indicated that in gel₂, the molecules are more tilted oriented. A possible orientation could be illustrated as in Fig. 6c. In the case of gel₁, pyrene packed parallel to each other and the bilayer showed ordered structures. Due to the ordered packing, the bilayer rolled into nanotube and showed a stronger excimer emission. Due to the well-packing in an H-aggregate, the excimer appeared in a relatively shorter wavelength. In the gel₂, due to the longer spacer and flexibility, the pyrene packed relatively disordered. It seems that the pyrene can interpenetrate between each layers and caused partial overlap stacking of the pyrene unit, which can be seen from the Cotton effect in the case of gel₂, where a split existed around 250–300 nm, belonging to the shorter axis of the pyrene. Thus, in gel₁, the dipole moment of the pyrene is parallel, while in gel₂, those of the dipole moments constituted a larger angle, as indicated in Fig. 4c. According the exciton theory, these two alignments would cause the opposite CD signals. Thus, we observed the opposited CD signals in gel₁ and gel₂. In the excited state, it seemed that there is no big change of the conformation, thus, we observed also the opposite CPL. Thus, through the spacer regulation, we can realized the inversion of CD and CPL signals, which provided a deep insight into the origin of the supramolecular chirality and regulating method.In conclusion, two pyrene based gelators were designed and found to form gels in the mixed solvents of water and ethanol. Due to the hydrogen bond between amide and glucone and the π–π stacking of the pyrene, lamellar structures were formed as a basic unit. The shorted spacer of gel₁ caused the well-defined π–π stacking of the pyrene and rolled into nanotube. In gel₂, a well-packed bilayer unit and relatively disordered packing of pyrene lead to the nanofiber formation. The molecular chirality of the glucone unit can transfer to the assemblies that lead to the CD and CPL of the nanotube and nanofiber. Interestingly, the nanotube and the nanofiber showed the opposite CD and CPL signals, which was suggested to be due to the different packing of the pyrene units in the lamellar structures. Thus, the work provided a new understanding of the origin of the supramolecular chirality and a way to regulate the chiral self-assembly and the chiroptical via spacer length.     

A series of four novel alkaline earth metal–organic frameworks constructed of Ca(ii), Sr(ii), Ba(ii) ions and tetrahedral MTB linker: structural diversity,stability study and low/high-pressure gas adsorption properties

A series of four novel microporous alkaline earth metal–organic frameworks (AE-MOFs) containing methanetetrabenzoate linker (MTB) with composition {[Ca₄(μ₈-MTB)₂]·2DMF·4H₂O}_n (UPJS-6), {[Ca₄(μ₄-O)(μ₈-MTB)_3/2(H₂O)₄]·4DMF·4H₂O}_n (UPJS-7), {[Sr₃(μ₇-MTB)_3/2]·4DMF·7H₂O}_n (UPJS-8) and {[Ba₃(μ₇-MTB)_3/2(H₂O)₆]·2DMF·4H₂O}_n (UPJS-9) (UPJS = University of Pavol Jozef Safarik) have been successfully prepared and characterized. The framework stability and thermal robustness of prepared materials were investigated using thermogravimetric analysis (TGA) and high-energy powder X-ray diffraction (HE-PXRD). MOFs were tested as adsorbents for different gases at various pressures and temperatures. Nitrogen and argon adsorption showed that the activated samples have moderate BET surface areas: 103 m² g⁻¹ (N₂)/126 m² g⁻¹ (Ar) for UPJS-7′′, 320 m² g⁻¹ (N₂)/358 m² g⁻¹ (Ar) for UPJS-9′′ and UPJS-8′′ adsorbs only a limited amount of N₂ and Ar. It should be noted that all prepared compounds adsorb carbon dioxide with storage capacities ranging from 3.9 to 2.4 wt% at 20 °C and 1 atm, and 16.4–13.5 wt% at 30 °C and 20 bar. Methane adsorption isotherms show no adsorption at low pressures and with increasing pressure the storage capacity increases to 4.0–2.9 wt% of CH₄ at 30 °C and 20 bar. Compounds displayed the highest hydrogen uptake of 3.7–1.8 wt% at −196 °C and 800 Torr among MTB containing MOFs.

Four novel microporous alkaline earth metal–organic frameworks (AE-MOFs) containing methanetetrabenzoate linker (MTB): UPJS-6, UPJS-7, UPJS-8 and UPJS-9 have been successfully prepared, characterized and tested as adsorbents for different gases.     

Co3O4 composite nano-fibers doped with Mn4+ prepared by the electro-spinning method and their electrochemical properties

In this work, based on the electrospinning method, pure Co₃O₄, pure MnO₂, and Co₃O₄ composite nano-fiber materials doped with different ratios of Mn⁴⁺ were prepared. XRD, XPS, BET and SEM tests were used to characterize the composition, structure and morphology of the materials. An electrochemical workstation was used to test the electrochemical performance of the materials. The results showed that the material properties had greatly improved on doping Mn⁴⁺ in Co₃O₄ nano-fibers. The relationship between the amount of Mn⁴⁺ doped in the Co₃O₄ composite nano-fiber material and its electrochemical performance was also tested and is discussed in this report. The results show that when n_Co : n_Mn = 20 : 2, the Co₃O₄ composite nano-fiber material had a specific surface area of 68 m² g⁻¹. Under the current density of 1 A g⁻¹, the 20 : 2 sample had the maximum capacitance of 585 F g⁻¹, which was obviously larger than that of pure Co₃O₄ nano-fibers (416 F g⁻¹). After 2000 cycles of charging/discharging, the specific capacitance of the 20 : 2 sample was 85.9%, while that of the pure Co₃O₄ nano-fiber material was only 76.4%. The mechanism of performance improvement in the composite fibers was analyzed, which demonstrated concrete results.

In this work, based on the electrospinning method, pure Co₃O₄, pure MnO₂, and Co₃O₄ composite nano-fiber materials doped with different ratios of Mn⁴⁺ were prepared.