On the interpretation of metastable zone width in anti‐solvent crystallization

Considering nonlinear dependence of solute concentration on anti‐solvent–solvent composition a modified Nývlt‐like equation based on traditional power‐law relation between nucleation rate and developing supersaturation and a new equation based on the classical theory of three‐dimension nucleation are proposed to explain the dependence of anti‐solvent addition rate on metastable zone width defined as excessive anti‐solvent composition in anti‐solvent crystallization. The experimental data on the metastable zone width in anti‐solvent crystallization of benzoic acid are analyzed and discussed from the standpoint of these equations. It is found that the new approach based on the classical nucleation theory provides better insight into the processes involved in anti‐solvent crystallization. Analysis of the experimental results on anti‐solvent crystallization of benzoic acid [D. O'Grady, M. Barret, E. Casey, and B. Glennon, Trans. IChemE A 85 , 945, (2007)] revealed that: (1) the value of metastable zone width for a solvent–anti‐solvent system is determined by the solute–solvent and solute–anti‐solvent interactions, (2) the dependence of the metastable zone width on stirring is associated with the enthalpy of mixing, and (3) the new approach predicts a threshold anti‐solvent addition rate associated with the setting up of an equilibrium between solvent and anti‐solvent and a maximum anti‐solvent addition rate connected with the induction period t_ind for the onset of crystallization. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Low temperature synthesis of spindle‐like ZnO nanostructures under microwave irradiation

A simple and general microwave route is developed to synthesize nanostructured ZnO using Zn(acac)₂·H₂O (acac = acetylacetonate) as a single source precursor. The reaction time has a great influence on the morphology of the ZnO nanostructures and an interesting spindle‐like nanostructure is obtained. The microstructure and morphology of the synthesized materials are investigated by X‐ray diffraction (XRD), scanning electron microscopy (SEM), field‐emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). It is found that all of them with hexagonal wurtzite phase are of single crystalline structure in nature. Ultraviolet–visible (UV‐vis) absorption spectra of these ZnO nanostructures are investigated and a possible formation mechanism for the spindle‐like ZnO nanostructures is also proposed.     

Synthesis of SrMoO4 microstructures by the microwave radiation‐assisted chelating agent method

SrMoO₄ rose‐like and persimmon‐like structures were synthesized via microwave radiation‐assisted chelating agent method. The microstructure and morphology of the as‐prepared samples were analyzed by X‐ray diffraction and field‐emission scanning electron microscope. According to the experimental results, ethylenediaminetetraacetic acid, as an outstanding chelating agent, plays an important role in inducing the morphology evolution. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of solvent and crystallization method on the crystal habit of metronidazole

In the present study, metronidazole was crystallized in several solvents, according to both the “cooling crystallization” and the “crystallization by non‐solvent addition”. Particle properties, such as crystal habit, elongation ratio, and mean particle size, were determined by SEM analysis. Structural changes and development of polymorphic forms were excluded by both Differential Scanning Calorimetry (DSC) and X‐Ray Powder Diffractometry (XRPD). Crystal habit (and thus elongation ratio) was typically influenced by both the solvent polarity index and the crystallization method: solvents with higher polarity index tended to promote acicular or stick‐shaped crystals with a high elongation ratio, while isodimensional crystals were promoted by decreasing the polarity index, as was particle aggregation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of multi‐linked ZnO rods by microwave heating

Synthesis of linked ZnO micro rods by microwave radiation and its characterization is presented in this report. In this simple microwave assisted solution phase route zinc nitrate and hexamethylenetetramine has been used as the starting materials for the synthesis of linked ZnO rods. Linked ZnO rods with various morphologies such as bipods, tripods, tetrapods and etc have been prepared. The influence of irradiation time of microwave on the formation of linked ZnO rods was investigated. X‐ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive spectroscopy (EDS) were used for the characterization of the product. The FESEM images showed ZnO rods of diameter in the range of 100‐200 nm and length around 5000 nm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spontaneous crystallization of potassium chloride from aqueous and aqueous‐ethanol solutions; Part 3: Model of the crystallization process

A model of spontaneous crystallization process was proposed. The model describes kinetics of the crystallization process after the end of the induction period. To test the model the published earlier data on crystallization and aggregation kinetics of potassium chloride at its spontaneous crystallization from supersaturated aqueous and aqueous‐ethanol solutions were used. It was found excellent coincidence of the experimental and theoretical data on concentration of the salt and the total number of crystals in solution at crystallization. Somewhat change for the worse was at the theoretical calculations of crystal size distribution at the end of the crystallization process. It indicated that the ways of calculation of size of crystals and their weight fraction in deposit were very approximate. The model allows predicting with satisfactory accuracy kinetics of crystallization using such general parameters of potassium chloride as the specific surface energy and the height of the nucleus‐bridges between crystals at coalescence. It needs further test of the model for other salts. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spontaneous crystallization of sodium chloride from aqueous‐ethanol solutions; Part 3: Examination of a model of the crystallization process

In the present work the examination of the proposed earlier model of spontaneous crystallization process was done. The model describes kinetics of the crystallization process after the end of the induction period. To test the model the published data on crystallization and aggregation kinetics of sodium chloride at its spontaneous crystallization from supersaturated aqueous‐ethanol solutions were used. It was found an excellent coincidence of the experimental and theoretical data on concentration of the salt and the total number of crystals in solution at crystallization. The model allows predicting with satisfactory accuracy kinetics of crystallization using such general parameters of sodium chloride as the specific surface energy and the height of the nucleus‐bridges between crystals at coalescence. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal structure analysis of 5‐amino‐7‐(pyrrolidin‐1‐yl)‐2,4,4‐trimethyl‐1,4‐dihydro‐1,6‐naphthyridine‐8‐carbonitrile

The title compound [CCDC 199359], C₁₆H₂₀N₅ crystallized in Monoclinic system with the space group C2/c. The unit cell parameters are: a = 16.554(6), b = 12.145(4), c = 16.221(5)Å and β = 102.67(1)°. The molecular structure is stabilized by an intramolecular C‐H…N type hydrogen bond and the molecular packing by the intermolecular C‐H…N and N‐H…N type hydrogen bonds. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Evolution of hierarchical‐structured CaCO3 in binary mixed solvent

Calcium carbonate with hierarchical structure was synthesized in water/organic compound binary soluvent by a chemical solution process within CaCl₂/NaCO₃ reaction system. Acetone, isopropanol, glycol, tetrahydrofuran were selected as the organic compound. Evolution of the hierarchical structure of CaCO₃ was investigated. The as‐prepared products were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). CaCO₃ aggregations with spicate hierarchical structure were obtained with a high volume fraction of the organic solvent. Aspect ratio of the hierarchical structure increases to the highest when the volume fraction was 50%. Solvent with low dielectric constant was conducive to the oriented aggregation of the CaCO₃ grains.     

Multi‐factors on photocatalytic properties of Y‐doped Bi2WO6 crystallites prepared by microwave‐hydrothermal method

Different contents of Y‐doped Bi₂WO₆ crystallites were synthesized by a microwave‐hydrothermal method. The photocatalytic properties with different contents of Y‐doped Bi₂WO₆ crystallites were studied. The Y‐doped Bi₂WO₆ crystallites were also characterized by XRD, EDX, SEM and UV‐vis DRS and the multi‐factors on photocatalytic properties of Y‐Doped Bi₂WO₆ crystallites were discussed. The results indicate that Y³⁺ replacing Bi³⁺ enters into the Bi₂WO₆ lattice, producing a degree of Bi₂WO₆ lattice distortion. It also has an impact on the crystallinity of Bi₂WO₆ and the band gap is from 2.49 eV to 2.71 eV. The photocatalytic results show that when the content of Y doping becomes 10%, the degradation rate of rhodamine B is above 90% after 40 min irradiation, which shows that doping the proper rare earth ions is conducive to the photocatalytic properties of Bi₂WO₆ crystallites.     

Synthesis and growth mechanism of ZnO rod‐like nanostructures by a microwave‐assisted low‐temperature aqueous solution route

A zinc oxide (ZnO) nanoarray (rod‐like nanostructure) was successfully synthesized through a low‐temperature aqueous solution and microwave‐assisted synthesis using zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and hexamethylenetetramine (HMTA) as raw materials, and using FTO glass as substrate. The effects of parameters in the preparation process, such as solution concentration, reaction temperature and microwave power, on the morphology and microstructure of ZnO nanoarray were studied. Phase structure and morphology of the products were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results indicated that hexagonal wurtzite structure ZnO nanoarray with good crystallization could be prepared through a low‐temperature solution method. When the concentration of the mixed solution was 0.05 M, the reaction temperature was 95 °C, and the reaction time was 4 h, high‐density ZnO regular nanorods of 200 nm diameter were obtained. A possible mechanism with different synthesis methods and the influence of microwave processing are also proposed in this paper.     

Growth of TGS crystals using uniaxially solution‐crystallization method of Sankaranarayanan‐Ramasamy

The recently discovered crystal growth method called uniaxially solution‐crystallization method of Sankaranarayanan–Ramasamy (SR) is modified in some aspects and used for growth of triglycine sulphate (TGS) crystals. The modification leads to the simplicity, reduction of cost and avoided the temperature fluctuations. The 〈010〉 direction of TGS is very important and used for fabrication of infrared detectors. Using this method, the 〈001〉, 〈010〉 directional crystals of TGS were successfully grown in a glass crystallizer. The grown crystal was characterized by HRXRD, UV‐Visible and dielectric studies. The results prove the suitability of the modified SR method for oriented TGS crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polyelectrolytes inhibition effect on crystallization of gypsum

The spontaneous precipitation of calcium sulfate dihydrate (gypsum) at 30 °C was investigated in the presence of polyelectrolytes. The degree of inhibition is measured as the reduction in initial crystallization rate, determined by conductivity of the crystallizing solution. The inhibition increases with acid content of the copolymer. Changing the butyl ester to a hydrophilic ethylene oxide resulted in higher inhibition efficiency. The inhibition efficiency is believed to arise from the closer chain packing on the crystal surface. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Facile synthesis of silver‐nanobeadwire transparent conductive film by organic‐precursor paint reduction

A new facile process has been developed to synthesize silver nanowire transparent conductive films by reducing high‐aspect‐ratio, needle‐shaped silver carboxylates, prepared as the precursor, while retaining their morphology. Nanowire precursors are simply obtained by ultrasound irradiation when silver (I) oxide and carboxylic acids are used as starting materials. The aspect ratio of the precursors is increased when the ultrasound irradiation is followed by microwave irradiation. Silver nanowires can be easily obtained by reducing these precursors with hydrazine gas or irradiating them with Ar plasma for a short time. The morphology of the resulting nanowires is different from that of typical nanowires that have been reported. The nanowires have porous morphology, where small nanoparticles are connected to form nanobeadwire. The nanobeadwire is considered to increase the transparency of the film because of its rough morphology. This new method can synthesize silver nanobeadwires and fabricate the transparent conductive film simultaneously, in one‐step, so that it can significantly simplify manufacturing processes.     

Phase‐manipulable synthesis of Cu‐based nanomaterials using ionic liquid 1‐butyl‐3‐methyl‐imidazole tetrafluoroborate

Using the ionic liquid (IL), 1‐butyl‐3‐methyl‐imidazole tetrafluoroborate, and the precursor Cu₇Cl₄(OH)₁₀·H₂O, series of phase‐manipulable Cu‐based nanomaterials were synthesized by hydrothermal and microwave assisted routes, respectively. The structural characters of the as‐prepared CuO, CuO/Cu₂O composites and pure Cu nanoparticles were investigated by XRD, SEM, TEM and HRTEM, and their surface photovoltaic properties were studied by surface photovoltage spectra. Via hydrothermal route Cu²⁺ ions were found to be reduced gradually into Cu⁺ and subsequently Cu⁰ with increasing the IL, and various phase ratio of CuO, Cu₂O and Cu composite nanosheets and pure Cu nanoparticles were obtained. This implies that the IL could function as both a reductant in the oxygen‐starved condition and a template for the nanosheet products. The ¹H‐NMR result of the IL supports it being a reductant. In microwave assisted route, however, only monoclinic single crystalline CuO nanosheets were obtained, which indicates the IL being a template only in oxygen‐rich condition. Therefore, the crystal phase, composition and morphology of the Cu‐based products could be controlled by simply adjusting the quantity of the IL and oxygen in solution routes. The molecular structure of the IL after oxidation reactions was investigated by ¹H‐NMR and a possible reaction mechanism was proposed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

In situ determination of metastable zone width by a simple optical probe

The metastable zone width (MSZW), which denotes the region between the solubility curve and the onset of nucleation, is an important control parameter for successful operation of a solution crystallization process as it defines an operating boundary for the crystallization process. The MSZW can be approximated as the gap between the loci of cloud points that correspond to onset of nucleation and clear points that closely represent solubility. This work presents the design and application of a simple optical probe consisting of a line laser source, a light‐dependent resistor, and a simple processing circuit for in situ determination of onset of nucleation of a crystallization process. Three different crystallization processes, namely, cooling crystallization of glycine, cooling crystallization of L‐asparagine monohydrate, and anti‐solvent crystallization of glycine, are investigated to assess the performance of the in situ probe. In all the cases, the cloud points and clear points are conveniently detected by sharp changes in output voltage of the probe with reasonable accuracy. The presented optical probe can be used as a simple and inexpensive alternative tool in the area of crystallization process monitoring.     

Ultrasound assisted crystallization for the recovery of lactose in an anti‐solvent acetone

Continuous worldwide increase in high‐scale production of dairy products leads to the constant generation of vast amounts of liquid by‐product, whey. Disposal of liquid whey is costly due to its high biological oxygen demand (BOD) and water content. More than 90% of whey BOD is due to lactose. Recovery of lactose from whey solves both the problems of improving economics of whey utilization and pollution reduction as lactose recovery itself can reduce BOD of whey by more then 80%. Commercial effluent treatment techniques focus on degradation rather than recovery of useful by‐products like lactose. Also, these techniques are time consuming and hence not effective enough. Sonocrystallization is the use of power ultrasound to control the crystallization process during the nucleation phase. In the present study, the process of lactose crystallization has been studied for the recovery of lactose from reconstituted lactose solutions with the aid of ultrasound, in the presence of ‘acetone’, as an anti‐solvent. The crystallization is found to be completed with excellent yields in the range of 80 – 92% within 4 minutes of sonication. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of the phase diagram for the crystallization of L‐asparaginase II by a turbidity technique ‐ part II. ‐MPD and crystallography studies‐

The phase diagram for the crystallization of L‐asparaginase II including the metastable zone width (MZW), in the presence of PEG₆₀₀₀ and ethanol, respectively, has been studied by an online turbidity technique out of the crystallization in solution (see part I of this work 1 ). Here this paper describes a further investigation on constructing a phase diagram including MZW for the crystallization of L‐asparaginase II with a different precipitant agent of 2‐methyl‐2, 4‐pentandiol (MPD). Along with the phase diagram, the single crystal X‐ray data were successfully collected at 100K from a crystal formed in the presence of 26% (v/v) MPD. The crystals indicate an orthorhombic form and belong to the space group of P2₁2₁2₁ with the unit cell parameters a = 93.9, b = 125.77, c = 151.75Å. The crystal diffracted up to a resolution of 2.88 Å.     

Growth and characterization of superconductive Nd2‐xCexCuO4‐y single crystals

Nd_2‐xCe_xCuO_4‐y single crystals with different x values have been successfully grown by Traveling Solvent Floating Zone method (TSFZ). Electronic properties of Nd_2‐xCe_xCuO_4‐y single crystals with various x have been studied in detail. The results show that superconductivity can be found in crystals with x > 0.1 (0.13‐0.18) directly grown at oxygen‐reduced atmosphere without post‐annealed, while no superconductivity appears in crystals with x < 0.1 at the same atmosphere. It is also found that, the segregation coefficient of Ce is determined to be 0.946 and transition temperature Tc (onset) reaches maximum value of 23.5 K at nominal composition x = 0.165. With further increase of Ce concentration, transition temperature of single crystals declines due to the precipitation of secondary Phases. In addition, the variation of lattice constants of Nd_2‐xCe_xCuO_4‐y single crystals with different x is also given. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)