Solvothermal Crystallization Research Articles

In Situ Observation of Topotactic Linker Reorganization in the Aperiodic Metal-Organic Framework TRUMOF-1.

We use in situ synchrotron X-ray diffraction measurements to monitor the solvothermal crystallization mechanism of the aperiodic metal-organic framework TRUMOF-1. Following an initial incubation period, TRUMOF-1 forms as a metastable intermediate that subsequently transforms into an ordered product with triclinic crystal symmetry. We determine the structure of this ordered phase, which we call msw-TRUMOF-1, and show that it is related to TRUMOF-1 through topotactic reorganization of linker occupancies. Our results imply that the connectivity of TRUMOF-1 can be reorganized, as required for data storage and manipulation applications.

Freeze-Drying-Assisted Preparation of High-Compaction-Density LiMn0.69Co0.01Fe0.3PO4 Cathode Materials with High-Capacity and Long Life-Cycle for Lithium Ion Batteries

As a successor to LiFePO4, the research interest in LiMn1−yFeyPO4 has been sustained due to its higher working voltage and safety features. However, its further application is limited by the low compaction density caused by uncontrolled particle size. In this study, the high-quality LiMn0.69Co0.01Fe0.3PO4 (LMFP) materials were prepared using the freeze-drying method to process the LMFP precursor synthesized through a solvothermal crystallization method followed by a calcination process at different temperatures (400–550 °C). The results demonstrate that the obtained particles exhibit a spheroidal shape with a low specific surface area after secondary crystallization calcination at 700 °C. The compaction density increased from 1.96 g/cm3 for LMFP precursor (LMFP-M1) to 2.18, 2.27, 2.34, and 2.43 g/cm3 for samples calcined at 400, 450, 500 and 550 °C, respectively, achieving a maximum increase of 24%. The full cell constructed with the high-compaction-density material calcined at 500 °C displayed discharge capacities of 144.1, 143.8, and 142.6 mAh/g at 0.5, 1, and 3 C rates, respectively, with a retention rate of 99% at 3 C rate. After undergoing charging and discharging cycles at a rate of 1 C for up to 800 cycles, the capacity retention rate was found to be 90%, indicating an expected full cell life span exceeding 2500 cycles.

ZIF-8 membranes on ZIF-8-PVDF/PVDF dual-layer polymeric hollow fiber supports for gas separation

ZIF-8 membranes have attracted extensive research attention due to their ease of synthesis, stable properties, and wide applicability. Compared to expensive inorganic supports, organic polymer supports are more flexible and inexpensive. However, addressing the issue of weak adhesion between the surface of the organic support and the ZIF-8 membrane layer poses a significant challenge. In this study, we present a strategy for preparation of ZIF-8 membrane by the fabrication of an asymmetric dual-layer polymeric hollow fiber support using polyvinylidene fluoride (PVDF) as the material. The outer layer of the support is composed of PVDF embedded with ZIF-8 seeds, while the inner layer consists of pure PVDF. This approach addresses the weak adhesion between the support and the ZIF-8 membrane layer formed through a one-step solvothermal crystallization process. The effects of ZIF-8 seed size, content, and crystallization conditions on the membrane structure and performance are investigated. Under the synergistic molecular sieving effects of ZIF-8 continuous membrane layer and ZIF-8 crystals within the outer layer of the support, larger gas molecules are difficult to penetrate the membrane layer, making the resulting membrane highly selective for the gas separation. Under the optimal fabrication conditions, the H2 permeability of the ZIF-8 membrane is determined to be 1.52 ± 0.1 × 10−7 mol·Pa−1·s−1·m−2, with a H2/N2 ideal separation selectivity of 69.5 ± 4. This method demonstrates simplicity and high reproducibility for preparation of ZIF-8 membranes on dual-layer hollow fibers, and it is expected to be extended to the growth and fabrication of other MOF membranes.

Scale-up approach for the preparation of magnetic ferrite nanocubes and other shapes with benchmark performance for magnetic hyperthermia applications.

Magnetic nanoparticles are increasingly used in medical applications, including cancer treatment by magnetic hyperthermia. This protocol describes a solvothermal-based process to prepare, at the gram scale, ferrite nanoparticles with well-defined shape, i.e., nanocubes, nanostars and other faceted nanoparticles, and with fine control of structural/magnetic properties to achieve point-of-reference magnetic hyperthermia performance. This straightforward method comprises simple steps: (i) making a homogeneous alcoholic solution of a surfactant and an alkyl amine; (ii) adding an organometallic metal precursor together with an aldehyde molecule, which acts as the key shape directing agent; and (iii) reacting the mixture in an autoclave for solvothermal crystallization. The shape of the ferrite nanoparticles can be controlled by the structure of the aldehyde ligand. Benzaldehyde and its aromatic derivatives favor the formation of cubic ferrite nanoparticles while aliphatic aldehydes result in spherical nanoparticles. The replacement of the primary amine, used in the nanocubes synthesis, with a secondary/tertiary amine results in nanoparticles with star-like shape. The well-defined control in terms of shape, narrow size distribution (below 5%), compositional tuning and crystallinity guarantees the preparation, at the gram scale, of nanocubes/star-like nanoparticles that possess, under magnetic field conditions of clinical use, specific adsorption rates comparable to or even superior to those obtained through thermal decomposition methods, which are typically prepared at the milligram scale. Here, gram-scale nanoparticle products with benchmark features for magnetic hyperthermia applications can be prepared in ~10 h with an average level of expertise in chemistry.

Solvothermal Crystallization Kinetics and Control of Crystal Size Distribution of MOF-808 in a Continuous Flow Reactor

Solvothermal Crystallization Kinetics and Control of Crystal Size Distribution of MOF-808 in a Continuous Flow Reactor

Solvothermal Crystallization of Ag/AgxO-AgCl Composites: Effect of Different Chloride Sources/Shape-Tailoring Agents

In the present work, AgCl microcrystals were obtained by solvothermal crystallization to investigate the effect of H+, Na+, K+, and different shape-tailoring agents (non-ionic: polyvinylpyrrolidone vs. anionic: sodium dodecyl sulfate) on the textural and photocatalytic properties of the samples. The crystallization process resulted in secondary products, such as AgxO or Ag, AgClO3, AgClO4, which were further transformed during the photocatalytic tests. The most efficient photocatalyst (assessed for methyl orange degradation) was synthesized using HCl, as a chloride source and polyvinylpyrrolidone, as a shape-tailoring agent. Therefore, the ability of polyvinylpyrrolidone to enhance the photocatalytic activity was also investigated, and it was found that the addition of 0.6 g polyvinylpyrrolidone resulted in the most efficient photocatalyst. Moreover, AgxO, being a charge separator, could play a critical role in the photocatalytic process, while reversibly transforming to Ag back and forth.

The impact of Au nanoparticles and lanthanide-doped NaYF4 on the photocatalytic activity of titania photocatalyst

Composite systems were prepared by doping NaYF4 (NYF) with lanthanide cations (Yb3+, Er3+, Tm3+), TiO2, and gold nanoparticles to exploit the light conversion properties of NYF and its possible impact on the photocatalytic activity of the composites. The composites were synthesized via solvothermal crystallization and the obtained structures were anatase TiO2, hexagonal NYF, and gold nanoparticles of 5–7 nm. The presence of NYF enhanced the photoactivity of TiO2 towards Rhodamine B degradation under UV irradiation, while it decreased its performance under visible light. The presence of Au was beneficial when visible light was applied for the degradation experiments. The reason behind the enhanced activity was the fluorescence of NYF at 400 nm that was the most intense for the composites that did not contain gold. The NYF-based samples also showed signs of up-conversion when 900 nm was the excitation light source, highlighting the potential of this material for photocatalytic applications that utilize the full (UV–IR) light spectrum.

Significance of the surface and bulk features of hierarchical TiO2 in their photocatalytic properties

Solvothermal crystallization is an adequate approach for preparing differently shaped TiO2 crystalline materials because it is highly sensitive to the synthesis parameters change. This study presents two sample series, one prepared from tetraisopropyl orthotitanate TTIP and one from tetrabutyl orthotitanate TBU. The influence of the applied temperature, different capping agents' amount, and the precursor volume ratio affected the measured characteristics (crystal phase composition, primary crystallity size, morphology, surface chemistry and optical properties). Although the samples revealed strong differences in crystal phase and size distribution, mostly spherical hierarchical morphology was achieved. The as-prepared samples were applied in photocatalytic processes to assess their efficiency under UV light and examine the influence of the structural features on the photocatalytic process. Not only the chosen precursor but the subtle changes in the listed parameters resulted in catalytical performance differences. Besides the crystal phase composition and the Ti3+ and Ti4+ species, it was found that organic surface particularities influenced the semiconductors’ photocatalytic performance.

Porous Membranes with Special Wettabilities: Designed Fabrication and Emerging Application

Porous materials have become a burgeoning research interest in materials science because of their intrinsic porous characteristics, versatile chemical compositions, and abundant functionalities. Re...

Self-assembly of defect-free polymer-based zeolite imidazolate framework composite membranes with metal-phenolic networks for high efficient H2/CH4 separation

In this study, defect-free metal organic framework membrane was first constructed on metal-phenolic networks (MPN) modified hollow fibers by competitive coordination based in-situ solvothermal crystallization. The activated MPN offered massive heterogeneous nucleation sites, facilitating the rapid synthesis of continuous and defect-free MOF membrane. Since different electrostatic environments of MPN may influence the growth rate of ZIF-8 nuclei on MPN, the thickness of MOF layer can be controlled by simply adjusting the preparation process of MPN. The coordination-driven cross-linking rather than tedious oxidative coupling reaction by tannin displayed higher kinetic rate, thereby effectively cut down the operation time of coating procedure to as fast as 10 s. Various techniques such as SEM, FTIR, XPS, XRD and EDS were applied to analyze the structure and morphology of MPN and MOF membranes, and gases separation experiments were applied to investigate the behavior of polymer-based MOF composite membranes. High performance continuous and dense ZIF-8/polyethersulfone hollow fiber membranes were successfully synthesized, which exhibited H2 permeance as large as 3.3 × 10−7 mol m−2 s−1 Pa−1 with very competitive ideal selectivity of 35.1 for H2/CH4.

Mild-temperature hydrogenation of carbonyls over Co-ZIF-9 derived Co-ZIF-x nanoparticle catalyst

Benzimidazole and metal cobalt salts were employed in the synthesis of Co-ZIF-9 by solvothermal crystallization. Highly active catalysts for selective hydrogenation of carbonyl compounds were developed. The optimal nanocatalyst Co-ZIF-350 manifested remarkable activity and selectivity for the hydrogenation of cyclohexanone under mild conditions. Catalytic conversion of cyclohexanone reached the highest over the catalyst of Co-ZIF-9-pyrolyzed at 350 °C for 2 h, in which the conversion of cyclohexanone was 100 % and the selectivity of cyclohexanol was ＞99 % at 50 °C. A wide scope of ketones/aromatic aldehydes could be selectively reduced to the corresponding alcohols with high yields. Importantly, the nanocatalyst Co-ZIF-350 presented good tolerance of substrates with various functional groups under mild conditions.

Composites based on silicate bioactive glasses and silver iodide microcrystals for tissue engineering applications

AgI microcrystals are used as Ag nanoparticles’ source to avoid the transformation of silver into AgCl, whose presence can affect the materials’ biocompatibility. The AgI microcrystals are obtain by using solvothermal crystallization and then they are embedded into bioactive glass matrices using a sol-gel method. The influence of AgI concentration on the structural, morphological, bioactive and biocompatible properties of the composites is carefully analyzed. By using the above-mentioned approach, all the obtained samples are AgCl free. Furthermore, the sample with 0.1 mol% AgI shows the signature of mobile I− and Ag° metallic species that negatively affect the in vitro bioactivity. It is also demonstrated that the presence of Ag° metallic species restrained the keratinocytes cells viability. The composites with AgNPs and Ag2O species exhibited excellent bioactivity and good cell proliferation rate. A moderate antibacterial effect against Pseudomonas aeruginosa was also evidenced in the case of the composites with AgNPs content.

Hydrothermal crystallization of bismuth oxybromide (BiOBr) in the presence of different shape controlling agents

Bismuth oxybromide samples were synthesized using solvothermal crystallization and different additives (CTAB-cetyltrimethylammonium bromide, PVP–polyvinylpyrrolidone, SDS–sodium dodecyl sulfate, U–urea and TU–thiourea). The effect of the mentioned compounds was investigated through structural (crystallite size, crystal phase composition, etc.), morphological (crystal shape), optical (band gap energy) parameters, surface properties (surface oxidation states), and the resulting photocatalytic activity. It was found that the ratio of the (1 0 2)/(1 1 0) crystallographic planes, the presence of oxidized Bi4+ and Bi5+ species were responsible for the obtained photocatalytic activity. Moreover, a strong dependency was revealed between the surface tension of the shape tailoring agents and the overall morpho-structural parameters, pointing out the fact that the properties of the semiconductor can be more easily tuned using the surface tension modification as a tool.

High surface area, high catalytic activity titanium dioxide aerogels prepared by solvothermal crystallization

Titanium dioxide has been considered to be one of the most effective and environmental friendly photocatalytic material. It has been widely used in photocatalytic degradation of various pollutants. As we known, an anatase crystal form typically obtained by high temperature heat treatment (>600℃), usually shows higher catalytic activity. In order to further improve the catalytic efficiency, we prepared TiO2 with a non-supercritical drying method to form a high specific surface area aerogel structure, along with an increased active contact site. However, with the inevitable of internal pores collapse in the process of high temperature crystallization, a large amount of porous structure and specific surface area is reduced. Here, to enhance the photocatalytic activity of titania, we propose a synergistic strategy to fabricate a porous titania structure with a high specific surface area. It was crystallized at a lower temperature (120℃) in a low-boiling solvent (ethanol, acetone, etc.). The lattice structure was identified by X-ray diffractometry; specific surface area (over 300 m2/g) of our sample was also measured through BET test; in the subsequent photocatalytic degradation test, the photocatalytic degradation efficiency of fabricated TiO2 is proved to be more excellent than P25 powder. By a freeze-drying/mild crystallization method, a high-specific surface area and high catalytic activity TiO2 aerogel was synthetized. This study provides some insights in the combining of crystallization and high specific surface area of titanium dioxide photocatalysis.

Guiding solvothermal synthesis

Machine Learning Machine learning is rapidly revolutionizing computer-aided synthesis design, occasionally producing vivid use cases when the reaction parameters important for the synthesis are hidden in a complex chemical space. Xie et al. report a machine learning–assisted framework for the synthesis of metal-organic nanocapsules (MONCs), giant molecular building units potentially useful in different fields, based on predicting the crystallization propensity using experimental attempts as a training dataset. Machine-learning algorithms achieve prediction accuracies of more than 90%, considerably outperforming trained chemists, and the generated synthesis parameters direct solvothermal crystallization to new structures of MONCs. The proposed strategy for the discovery of new materials can be applied more broadly beyond MONCs. J. Am. Chem. Soc. 10.1021/jacs.9b11569 (2019).

Influences of solvothermal-assisted crystallization process on the microstructure and properties of SiO2-W0.02TiO2.06 composite aerogels synthesized via ambient pressure drying

In this work, the influence of solvothermal crystallization processes on the microstructure, pore characteristic, and adsorption/photocatalysis of SiO2-W0.02TiO2.06 composite aerogels synthesized via ambient pressure drying have been investigated. It has been clarified that the composite aerogels prepared via solvothermal crystallization at 120 °C for 0.5 h and 180 °C for 3 h exhibited high-specific surface area (416–729 m2/g) and pore volume (2.26–2.70 cm3/g). With the increase of solvothermal crystallization temperature and time, the crystallinity of composite aerogels increased gradually, but excessive solvothermal crystallization time at higher temperature decreased the pore volume greatly. Furthermore, it is found that bacterial cellulose (BC) in the composite gel plays an important role in enhancing the pore volume and crystallization of the SiO2-W0.02TiO2.06 composite aerogels as a pore-expanding agent and structure-directing agent. The as-synthesized SiO2-W0.02TiO2.06 composite aerogels exhibited higher adsorption and removal efficiency for RhB than the commercial P25-TiO2, which can be ascribed to its high pore volume and specific surface area, as well as the synergistic action of adsorption and photocatalysis.

The effect of the synthesis temperature and duration on the morphology and photocatalytic activity of BiOX (X = Cl, Br, I) materials

Bismuthoxyhalides photocatalysts (BiOX, X = Cl, Br, I) were prepared using solvothermal crystallization method. The influence of the synthesis temperature (120 °C, 140 °C, 160 °C) and duration (3 h, 24 h, 48 h) on the structural (crystal size, phase composition etc.), morphological (crystal shape), optical (bandgap values) parameters and on the resulting photocatalytic activity were investigated. The samples were characterized by the means of X-ray diffractometry (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the synthesized materials was evaluated under visible- (≥ 400 nm) and UV light (≈ 365 nm) by degrading methyl orange and Rhodamine B (RhB). The results pointed out the importance of the crystallization temperature and duration in achieving the highest photocatalytic activity, showing that the lowest temperature and the shortest duration time resulted the highest removal yields. Furthermore, a possible degradation mechanism was elaborated based on a direct hole oxidation approach and the detected degradation intermediates.

Synthesis of SiO2–W x TiO2 composite aerogels via solvothermal crystallization under the guidance of bacterial cellulose followed by freeze drying method

In order to obtain aerogel-based photocatalytic materials with higher adsorptivity and photocatalytic activity, SiO2–W x TiO2 composite aerogels were synthesized by the method of combining freeze drying with solvothermal crystallization under the guidance of bacterial cellulose using BC–SiO2 composite gel as skeleton. The influences of W/Ti mol ratio, solvothermal process parameters on the microstructure and properties of the SiO2–W x TiO2 composite aerogels were investigated. The results indicate that the obtained composite aerogels have higher specific surface area with 297–377 m2 g−1 and pore volume with 0.46–0.66 cm3 g−1. The adsorption/photocatalysis test indicates that the obtained aerogels showed prominent adsorption/photocatalytic activity, and the adsorption/photocatalytic degradation rate for Rhodamine B in aqueous solution could attain to 95 % within 120 min, which is obviously better than that of P25. With the increase of solvothermal crystallization time, the adsorption/photocatalysis tends to increase and the SiO2–W x TiO2 composite aerogel sample exhibited better removing efficiency for Rhodamine B. Doping of 2–3% W is favorable for improving the adsorption/photocatalytic properties of the SiO2–W x TiO2 composite aerogels. The SiO2–W x TiO2 composite aerogels were synthesized by the method of combining freeze drying with solvothermal crystallization under the guidance of bacterial cellulose (BC). The presence and hydrolysis of BC as a template and inducer during the solvothermal process played an important role in enhancing the porous network structure of the composite aerogels and inducing the deposition/crystallization of W x TiO2 nanoparticles. The SiO2–W x TiO2 composite aerogels exhibited higher adsorptivity and photocatalytic activity simultaneously.

Time-Resolved Powder X-ray Diffraction of the Solvothermal Crystallization of Cobalt Gallate Spinel Photocatalyst Reveals Transient Layered Double Hydroxides

High energy X-ray diffraction is used to follow in situ the crystallization of a cobalt gallate from metallic gallium under solvothermal conditions in an aminoalcohol, revealing the formation and decay of transient metastable layered double hydroxides. Photocatalytic studies show the spinel product has activity as a water oxidation catalyst for oxygen evolution.

Structural variety in ytterbium dicarboxylate frameworks and in situ study diffraction of their solvothermal crystallisation

The ytterbium 1,4-benzenedicarboxylate (BDC) framework [Yb2(BDC)3(DMF)2]·H2O (1) crystallises from a N,N-dimethylformamide (DMF)-rich solution at 80–120 °C. (1) is constructed from infinite chains of dicarboxylate-bridged seven-coordinate Yb atoms, cross-linked in two directions by BDC to yield diamond-shaped channels (sra topology) lined by coordinated DMF molecules and occluded water. Increasing the water content in the synthesis solution yields a material with more crystal water Yb2(BDC)3(DMF)2(H2O)2 (2), in which the Yb centres are eight-coordinate and form dimers bridged by BDC to give two interpenetrating networks of pcu (α-Po) topology. Upon extended reaction in this water-rich solvent mixture, an alternative phase is formed: an anhydrous mixed BDC-formate, Yb(BDC)(HCO2), (3), which has a pillared, layered structure, with formate produced by hydrolysis of the DMF. An isoreticular version of (2) can also be formed under similar conditions using 2,6-naphthalene-dicarboxylate (NDC) as linker: [Yb2(NDC)3(H2O)4]·2DMF (4). Despite their different structures, (1) and (2) are calcined to a common porous, desolvated phase Yb2(BDC)3 at 300 °C. Using high energy X-rays at Diamond Light Source we are able to penetrate the solvothermal reaction vessels and to follow the formation of (1) and (2) in real time. This allows accurate crystallisation curves to be obtained from which qualitative kinetic information is extracted. Importantly, the high angular resolution of the in situ powder XRD patterns allows refinement of crystal structure: this permits the temporal evolution of unit cell parameters to be followed, which are ascribed to changes in coordinated solvent composition within the materials during their formation, while analysis of phase fraction allows kinetic parameters to be quantified using the nucleation-growth model of Gualtieri.