Antisolvent Crystallization Method Research Articles

Embedding PbS Quantum Dots (QDs) in Pb-Halide Perovskite Matrices: QD Surface Chemistry and Antisolvent Effects on QD Dispersion and Confinement Properties

Hybrid materials of metal chalcogenide colloidal quantum dots (QDs) embedded in metal halide perovskites (MHPs) have led to composites with synergistic properties. Here, we investigate how QD size, surface chemistry, and MHP film formation methods affect the resulting optoelectronic properties of QD/MHP “dot-in-matrix” systems. We monitor the QD absorption and photoluminescence throughout synthesis, ligand exchange, and transfer into the MHP ink, and we characterize the final QD/MHP films via electron microscopy and transient absorption. In addition, we are the first to globally map how PbS QDs are distributed on the micrometer scale within these dot-in-matrix systems, using three-dimensional (3D) tomography time-of-flight secondary ion mass spectrometry. The surface chemistry imparted during synthesis directly affects the optical properties of the dot-in-matrix composites. Pb-halide passivation leads to QD/MHP dot-in-matrix samples with optical properties that are well-described by a theoretical model, based on a Type I finite-barrier heterostructure between the PbS QD and the MHP matrix. Samples without Pb-halide passivation show complicated size-dependent behavior, indicating a transition from a Type I heterostructure between the PbS QD wells and MHP barriers for small-sized QDs to PbS QDs that are electronically decoupled from the MHP matrix for larger QDs. Furthermore, the choice in perovskite antisolvent crystallization method leads to a difference in the spatial QD distribution within the perovskite matrix, differences in carrier lifetime, and photoluminescence shifts of up to 180 meV for PbS in methylammonium lead iodide. This work establishes an understanding of such emerging synergistic systems relevant for technologies such as photovoltaics, infrared emitters and detectors, and other unexplored technological applications.

One-step synthesis at room temperature of low dimensional perovskite single crystals with high optical quality

Hybrid organic-inorganic perovskites have emerged among the most promising materials for optoelectronic applications thanks to the great synthetic versatility that allows tailoring their structural and photophysical properties. In the two-dimensional (2D) crystalline form, these semiconductors have multiple-quantum-well structure with stable excitonic resonances at room temperature. In this work we present an easy and effective anti-solvent crystallization method to synthesize n = 1 and n = 2 dodecylammonium (DA) lead iodide perovskite single crystals. Different synthetic conditions have been explored and general guidelines for single crystals preparation are provided revealing that γ-butyrolactone is the best solvent for its ability to weakly coordinate Pb2+ centers and that diethyl ether is the best anti-solvent because fast diffuses into the precursors solution.We exploit the high optical quality of the synthesized perovskites to observe strong exciton−photon coupling in single-crystal waveguides, avoiding the need to embed them within mirror microcavities.

Self-Assembly of Monodispersed Carnosine Spherical Crystals in a Reverse Antisolvent Crystallization Process

Spherical crystallization is an effective way to increase particle size, raise bulk density, and improve flowability and compressibility of crystals with small sizes, especially needle-like and flake-like microcrystals. In this work, a reverse antisolvent crystallization method was used to obtain the spherical crystals of carnosine instead of commercially available needle-like carnosine material. Besides, the solubility of carnosine in a binary solvent mixture of water + ethanol was measured at temperatures ranging from 288.05 to 323.15 K by using a gravimetric method under atmospheric pressure to optimize this crystallization process and increase the yield of carnosine. On the basis of these thermodynamic data, single factor analysis in a reverse antisolvent crystallization process was performed, including carnosine aqueous solution concentration, feeding rate, volume ratio of solution to antisolvent, temperature, and stirring speed. Polarizing microscopy, particle size distributions, and in situ particl...

Expanding production regions of α-form and β-form glycine using an antisolvent crystallization method assisted by N2 fine bubbles

To develop a crystallization technique that can enhance the production of metastable α-form and unstable β-form glycine, we studied the antisolvent crystallization of glycine using the gas–liquid interfaces around N2 fine bubbles as novel crystallization fields. In the regions near the gas–liquid interfaces, local supersaturation is generated because of the accumulation of glycine and alcohol as an antisolvent as a result of the negative electric charge on the fine bubble surface. Hence, the produced glycine polymorphs change from the stable γ-form to a α-form or β-form glycine. Additionally, local supersaturation at the gas–liquid interfaces can be expected to change via modification of the accumulation of the glycine and alcohol molecules and the interaction of glycine-water-alcohol with the different alcohol additives. At a solution temperature of 303 K, methanol (MeOH), ethanol (EtOH), or isopropanol (IPA) as an antisolvent were rapidly mixed into the saturated glycine solution. While mixing MeOH, EtOH, or IPA with the saturated glycine solution, N2 fine bubbles with an average size of 10 µm were continuously supplied to the mixed solution using a self-supporting bubble generator and a glycine polymorph was crystallized within 5 min. For comparison, an antisolvent crystallization free of N2 fine bubbles was conducted using a propeller type mixer. During antisolvent crystallization with/without fine bubble injection, the additional alcohol volume was varied to control the generation rate of the supersaturation in the bulk solution (rC/CS). Consequently, the production regions of the α-form and β-form glycine were broadened to lower rC/CS via N2 fine bubble injection. The expansion behavior for α-form or β-form glycine significantly increased because of the enhancement of local supersaturation at the regions near the gas–liquid interfaces of the N2 fine bubbles owing to the decreasing carbon number in the alcohol.

Effect of high pressure homogenization on physicochemical properties of curcumin nanoparticles prepared by antisolvent crystallization using HPMC or PVP

Dissolution enhancement of poorly water soluble drugs is a major challenge in pharmaceutical industry. The aim of this study is to fabricate curcumin nanoparticles by antisolvent crystallization in the presence of PVP-K30 or HPMC with various concentrations as a stabilizer. The effect of high pressure homogenization on properties of curcumin particles is also investigated in this study. The antisolvent crystallization method followed by freeze drying (CRS-FD) and also antisolvent crystallization and high pressure homogenization followed by freeze drying (HPH-FD) were employed to modify curcumin particles. Physical mixtures of the drug and additives were also prepared for comparison purposes. The solid state analysis (DSC, XRPD and FT-IR studies), particle size measurement, morphological analysis, saturation solubility and dissolution behavior of the samples were investigated. The curcumin crystallized without using stabilizer produced polymorph 2 curcumin with lower crystallinity and higher solubility. The samples obtained in the presence of stabilizers showed higher solubility compared to its physical mixtures counterpart. It was found that the stabilizers used in the current study were capable of inhibiting the crystal growth of particles during crystallization. High pressure homogenizer method generated smaller particles compared to those samples that were not subjected to high pressure homogenizer (for example, 2748 nm for 5% PVP CRS-FD sample and 706 nm for 5% PVP HPH-FD sample). Particles obtained via HPH showed better solubility and dissolution rate compared to those samples that HPH was not employed (for example, the saturated solubility of 25% PVP CRS-FD sample was near 2 μg/ml while this amount was approximately 4.3 μg/ml for 25% HPH-FD sample. The effect of high pressure homogenization on dissolution rate is more pronounced for samples with lower stabilizer ratio. The samples prepared with high pressure homogenizer using 50% PVP showed 25-fold higher solubility compared to untreated curcumin. Generally, it can be concluded that the method of preparation, selection of suitable stabilizer and concentration of stabilizer play a critical role on particle size and dissolution rate of curcumin.

Thermodynamic properties in ternary system of NH4HCO3–H2O–ethanol based on antisolvent method to strengthen crystallization of carbonized ammonia

One of the main challenges of the ammonia-based CO2 capture process is how to further reduce the regeneration energy consumption. An antisolvent crystallization method was proposed to strengthen the crystallization process of carbonized ammonia, and heating the crystal products instead of rich solution can greatly reduce renewable energy consumption. The main component of the crystal product was NH4HCO3 analyzed by X-ray diffraction. Therefore, it is very important to study the thermodynamic properties of ammonium bicarbonate in the ternary system of NH3–H2O–ethanol. In this paper, the solubility curves under different temperature and solvent compositions were determined by static method and the mathematical model of solubility was established. The effects of the addition of ammonium carbamate which was produced in the initial stage of the CO2 absorption process and the addition of ammonia on the solubility in ternary system of NH4HCO3–H2O–ethanol were studied. The dissolution heat was also calculated in the end. The research of this article has a guiding significance for the antisolvent method to strengthen the crystallization of carbonized ammonia of ammonia-based carbon capture technology. It is helpful to further strengthen the crystallization process of low carbonized ammonia and improve the crystallization yield.

An efficient micromixer combining oscillatory flow and divergent circular chambers

Oscillatory/pulsatile flow is an important approach for mixing enhancement at micro scales. Here we report a micromixer that consists of a microfluidic oscillator and divergent chambers. The oscillator autonomously produces an oscillatory flow, which further causes efficient stretching and folding of the fluids to improve the mixing. Testing results show that the design works well at relatively high flow rates and high viscosities. At around 40 ml/min, the mixing index can reach 0.97 at 8 mPa s, and 0.89 at 12 mPa s, respectively. Efficient mixing can also be achieved at viscosity ratios of up to 10 (20 mPa s:2 mPa s). Application of the micromixer for preparation of nano sized RDX (cyclotrimethylenetrinitramine) is investigated. Using the anti-solvent crystallization method, nano-RDX particles with the size ranging from 150 to 900 nm are obtained. Its thermal decomposition characteristics are tested and compared with the raw RDX.

A Low‐Sensitivity Nanocomposite of CL‐20 and TATB

AbstractIn order to improve the safety of 2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane (CL‐20) while preserving its high energy yield, a nanocomposite containing CL‐20 and 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) with a particular structure is prepared using an facile and fast antisolvent crystallization method. Using this approach, which takes advantage of strong antisolvent and temperature effects, a lamellar arrangement structure is created consisting of nanosheets containing CL‐20 and TATB, and further coated with dendritic nanometer‐scale TATB. XRD and Raman spectra indicate that CL‐20 in the resulting nanocomposite takes the form of α polymorph owing to the presence of ultrapure water. The HPLC results show that the TATB content of the nanocomposite is 20.2 wt%. When the surface coating of TATB is removed, 8 wt% TATB remains between the internal nanosheets. Due to the multiple desensitization effects of this structure, the nanocomposite has much lower sensitivity, roughly comparable to that of the insensitive explosive LLM‐105. Thermal analysis by thermogravimetry (TG) and differential scanning calorimeter indicates that the thermal decomposition activity of the nanocomposite is higher than those of raw materials, and in addition, its thermal stability is greater.

Effective Separation of N‐benzyl‐2‐methyl‐4‐nitroaniline (BNA) Polymorphs through Antisolvent Crystallization Method

AbstractThe Influence of antisolvent water on the polymorphic nucleation of N‐benzyl‐2‐methyl‐4‐nitroaniline (BNA) during its crystallization from methanol solution is revealed. The solubility of BNA in methanol‐water solvent mixtures is determined by gravimetric method and the variation in the level of supersaturation generated with respect to antisolvent concentration is assessed at different volume combinations of saturated methanol BNA solution and water. The supersaturation dependent polymorphic nucleation of orthorhombic and monoclinic forms and their growth morphologies such as platy‐like orthorhombic and needle‐like monoclinic are examined through in‐situ optical microscopy. Single crystals of the grown polymorphs are successfully separated and their structural, thermal, spectroscopic and optical transmittance properties are confirmed through PXRD, DSC, FTIR and UV‐Vis‐near IR analyses respectively.

Reverse Anti-solvent Crystallization Process for the Facile Synthesis of Zinc Tetra(4-pyridyl)porphyrin Single Crystalline Cubes

Synthesis of morphologically well-defined crystals of metalloporphyrin by direct crystallization based on conventional anti-solvent crystallization method without using any additives has been rarely reported. Herein, we demonstrate an unconventional and additive-free synthetic method named reverse anti-solvent crystallization method to achieve well-defined zinc-porphyrin cube crystals by reversing the order of the addition of solvents. The extended first solvation shell effect mechanism is therefore suggested to support the synthetic process by providing a novel kinetic route for reaching the local supersaturation environment depending on the order of addition of solvents, which turned out to be critical to achieve clean cube morphology of the crystal. We believe that our work not only extends fundamental knowledge about the kinetic process in binary solvent systems, but also enables great opportunities for shape-directing crystallization of various organic and organometallic compounds.

Enhanced production of α-form indomethacin using the antisolvent crystallization method assisted by N2 fine bubbles

In this study, using the gas-liquid interfaces near fine bubbles as new crystallization fields where nucleation proceeds dominantly, a crystallization technique to enhance the production of α-form Indomethacin (IMC) at a constant temperature was developed. IMC is reported to show a complicated polymorphism that consists of five true polymorphs and a wide range of solvate forms, which are collectively named the β-form. IMC was crystallized using the antisolvent method assisted by nitrogen (N2) fine bubbles. In the regions around the minute gas-liquid interfaces, local supersaturation increases because of the accumulation of IMC, which is caused by the negative electric charge on the fine-bubble surface. Hence, the rate of crystal nucleation increases, and the crystallization of metastable polymorph is enhanced. At a solution temperature of 298K, a saturated IMC-EtOH solution and water as an antisolvent were mixed by two different addition orders, as follows: the IMC-EtOH/H2O system: water was quickly added into a saturated IMC-EtOH solution; the H2O/IMC-EtOH system: a saturated IMC-EtOH solution was rapidly added into water. While water was mixed with the saturated IMC-EtOH solution, N2 fine bubbles with an average diameter of 25µm were continuously supplied to the mixed solution using a self-supporting bubble generator and IMC was crystallized within a crystallization time of 5min. In both systems, the supersaturation ratio in the bulk solution (lnC0/CS) was varied in the range of 1.5–5.7 by controlling the addition volume of water or saturated IMC-EtOH solution. For comparison, antisolvent crystallization free of fine bubbles was performed. The results show that in both systems, N2 fine-bubble injection enhanced the production of metastable α-form at ln(C0/CS) below 3.5, and decreased the required ln(C0/CS) for the high-yield crystallization of α-form.

Antisolvent precipitation technique: A very promising approach to crystallize curcumin in presence of polyvinyl pyrrolidon for solubility and dissolution enhancement

Curcumin with a vast number of pharmacological activities is a poorly water soluble drug which its oral bioavailability is profoundly limited by its dissolution or solubility in GI tract. Curcumin could be a good anticancer drug if its solubility could be increased. Therefore, the aim of the present study was to increase the dissolution rate of curcumin by employing antisolvent crystallization technique and to investigate the effect of polyvinyl pyrrolidone K30 (PVP) as colloidal particles in crystallization medium on resultant particles. Curcumin was crystalized in the presence of different amounts of PVP by antisolvent crystallization method and their physical mixtures were prepared for comparison purposes. The samples were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD) and Fourier transform infrared spectroscopy (FT-IR). The solubility and dissolution of the treated and untreated curcumin were also determined. Antisolvent crystallization of curcumin led to the formation of particles with no definite geometric shape. It was interesting to note that the DSC and XRPD studies indicated the formation of a new polymorph and less crystallinity for particles crystallized in the absence of PVP. However, the crystallized curcumin in the presence of PVP was completely amorphous. All crystalized curcumin samples showed much higher dissolution rate compared to untreated curcumin. The amount of curcumin dissolved within 10 for treated curcumin in the presence of PVP (1:1 curcumin:PVP) was 7 times higher than untreated curcumin and this enhancement in the dissolution for curcumin samples crystallized in the absence of PVP was around 5 times. Overall‚ the results of this study showed that antisolvent crystallization method in the absence or presence of small amounts of PVP is very efficient in increasing the dissolution rate of curcumin to achieve better efficiency for curcumin.

Encapsulation of Agents inside Crystals as Liquid Inclusions

AbstractThere are many approaches to the issue of agent encapsulation as a method to protect sensitive substances against outer influences. The possibility of the use of inclusion‐containing crystals as encapsulation material was investigated. Since many products are water‐based media, the low‐water‐soluble substance salicylic acid (SA) was chosen to investigate its qualities as a container substance. Therefore, the solubility of SA was investigated in dependence on the proportions of the antisolvent water and the solvent ethanol by means of a ternary phase diagram. Moreover, SA container crystals were generated and filled by means of an antisolvent crystallization method. In two case studies, copper sulfate and ascorbic acid could successfully be encapsulated.

Importance of the Direct Contact of Amorphous Solid Particles with the Surface of Monolayers for the Transepithelial Permeation of Curcumin.

The amorphization has been generally known to improve the absorption and permeation of poorly water-soluble drugs through the enhancement of the solubility. The present study focused on the direct contact of amorphous solid particles with the surface of the membrane using curcumin as a model for water-insoluble drugs. Amorphous nanoparticles of curcumin (ANC) were prepared with antisolvent crystallization method using a microreactor. The solubility of curcumin from ANC was two orders of magnitude higher than that of crystalline curcumin (CC). However, the permeation of curcumin from the saturated solution of ANC was negligible. The transepithelial permeation of curcumin from ANC suspension was significantly increased as compared to CC suspension, while the permeation was unlikely correlated with the solubility, and the increase in the permeation was dependent on the total concentration of curcumin in ANC suspension. The absorptive transport of curcumin (from apical to basal, A to B) from ANC suspension was much higher than the secretory transport (from basal to apical, B to A). In vitro transport of curcumin through air-interface monolayers is large from ANC but negligible from CC particles. These findings suggest that the direct contact of ANC with the absorptive membrane can play an important role in the transport of curcumin from ANC suspension. The results of the study suggest that amorphous particles may be directly involved in the transepithlial permeation of curcumin.

Application of Artificial Neural Networks for Prediction of Ibuprofen Yield from Ultrasound-Assisted Anti-Solvent Crystallization

The aim of the study was to develop neural network model to predict the yield obtained from ultrasound-assisted anti-solvent crystallization of ibuprofen in terms of formulation and processing factors. The different factors of anti-solvent crystallization method, such as type of additive, concentration of additive, sonication time and harvesting time, were used as independent variables. The ibuprofen yield was used as response variable. The correlation between independent and response variables was investigated using feed forward-back propagation neural networks. The goodness of fit test and predictability were used for optimization of in silico models. The results revealed that the type of polyethylene glycol (PEG) was a critical factor that affected the response variable in different patterns. The best artificial neural networks (ANNs) model with a configuration of 3-4-1 for input, hidden, and output layers gave the r2 of 0.7067 and 0.8729 and the root mean square error of 0.3693 and 0.2667 for the model using PEG 400 and PEG 4000, respectively. The predictive ability of these models was validated by a set of 4 formulations that were not included in the training set. The predicted and experimental of ibuprofen yields were correlated.

Solubility measurement of a metastable achiral crystal of sodium chlorate in solution growth

The solubility of the metastable achiral monoclinic phase in NaClO3 crystallization from an aqueous solution, which appears prior to the nucleation of chiral crystals, was successfully measured in the range from 10°C to 23°C. Antisolvent crystallization method was used to obtain metastable crystals for the measurement. The solubility was determined to be about 1.6 times higher than that of the chiral stable cubic phase by observing growth or dissolution of the crystal in aqueous solution at the temperature and concentration of which is predetermined.

Self-Assembled Organic Nanowires for High Power Density Lithium Ion Batteries

The electroactive organic materials are promising alternatives to inorganic electrode materials for the new generation of green Li-ion batteries due to their sustainability, environmental benignity, and low cost. Croconic acid disodium salt (CADS) was used as Li-ion battery electrode, and CADS organic wires with different diameters were fabricated through a facile synthetic route using antisolvent crystallization method to overcome the challenges of low electronic conductivity of CADS and lithiation induced strain. The CADS nanowire exhibits much better electrochemical performance than its crystal bulk material and microwire counterpart. CADS nanowire with a diameter of 150 nm delivers a reversible capability of 177 mAh g(-1) at a current density of 0.2 C and retains capacity of 170 mAh g(-1) after 110 charge/discharge cycles. The nanowire structure also remarkably enhances the kinetics of croconic acid disodium salt. The CADS nanowire retains 50% of the 0.1 C capacity even when the current density increases to 6 C. In contrast, the crystal bulk and microwire material completely lose their capacities when the current density merely increases to 2 C. Such a high rate performance of CADS nanowire is attributed to its short ion diffusion pathway and large surface area, which enable fast ion and electron transport in the electrode. The theoretical calculation suggests that lithiation of CADS experiences an ion exchange process. The sodium ions in CADS will be gradually replaced by lithium ions during the lithiation and delithiation of CADS electrode, which is confirmed by inductively coupled plasma test.