One-step Crystallization Research Articles

Precipitating spinel into precursor glass and its assistance in crystallization

The crystallization phenomena of spinel in CaO-MgO-Al2O3-SiO2-Fe2O3 glass have received much attention due to the particular role in preparation of glass-ceramic materials, which represent an effective option to manage hazardous waste. In this study, both preliminary spinel and secondary spinel were precipitated in the precursor glass. The formation of these spinel was meticulously assessed by a combination of X-ray diffractometry and scanning electron microscopy. The structure of the microenvironment in the precursor glass was characterized by Raman spectrums. These advanced techniques highlight the potential for one-step crystallization of the glass. The investigation, which focused on one-step crystallization, demonstrated the growth of pyroxene on spinel accompanying a migration of chromium. The results also show the microstructure of the obtained glass-ceramic was very dependent on the heat-treat temperature. This study not only unambiguously reveals the precipitation mechanisms of spinel but also provides more documentation for one-step crystallization in the glass-ceramics field.

Self-Limited Growth of Nanocrystals in Structural Heterogeneous Phase-Change Materials during the Heating Process

Typical nanocomposite heterogeneous ZnSb-Al2O3 and ZnSb-ZnO phase-change materials were prepared. A direct comparison of the distinct structures in the amorphous, metastable, and stable states between two different materials was investigated systematically. Upon heating, ZnSb-Al2O3 films show a two-step crystallization process with the formation of the metastable orthorhombic ZnSb phase ahead of the stable trigonal ZnSb phase, while ZnSb-ZnO films could exhibit a one-step crystallization process with the formation of the stable trigonal ZnSb phase when the ZnO-doping concentration is more than 12.3 atom %. In the case of ZnSb-Al2O3, the structural transition to the metastable phase is accompanied by a pronounced increase in the grain size up to 100 nm. Such an increase in the crystal grain size is not found in ZnSb-ZnO films; i.e., the nanocrystals do not grow significantly when the crystallized film is precipitated with the metastable ZnSb phase. By the method of advanced scanning transmission electron m...

Performance enhancement of AgBi2I7 solar cells by modulating a solvent-mediated adduct and tuning remnant BiI3 in one-step crystallization.

We modulated a solvent-mediated adduct for one-step crystallization of lead-free AgBi2I7 at a lower temperature (90 °C) and to obtain remnant BiI3 by controlling the nature of the substrate and precursor concentration. This eventually resulted in remarkable enhancement in the power conversion efficiency, reaching 2.12%, and the long-term stability of AgBi2I7 solar cells towards light, heat and humidity.

Preparation, Characterization, and Formation Mechanism of Calcium Sulfate Hemihydrate Whiskers

Calcium sulfate hemihydrate whiskers were synthesized successfully via one-step hydrothermal crystallization method using phosphogypsum at 130 °C for 240 min with an initial slurry mass fraction of 2.5wt%. The phase compositions, microstructures, thermal properties and molecular structures of asprepared samples were analyzed by XRD, ESEM, EDS, TG-DTA, and FT-IR. The influence of raw materials’ ball-milling time on the morphologies of whiskers was investigated. The effects of impurities on crystallization morphologies and length to diameter ratio (L/D) of calcium sulfate hemihydrate whiskers were studied. The results indicated that the calcium sulfate dihydrate crystalline could be translated directly into fibrous calcium sulfate hemihydrate whiskers. It was beneficial to form fine fiber structure when the ball-milling time of the raw material was 15 min. Aspect ratio of calcium sulfate hemihydrate whiskers decreased with increasing content of impurities. Moreover, the relative growth mechanism of whisker crystals via one-step hydrothermal crystallization method was discussed in detail.

Synthesis of hierarchical titanium silicalite-1 in the presence of polyquaternium-7 and its application in the hydroxylation of phenol

Hierarchical titanium silicalite-1 (TS-1) without generated anatase TiO2 species was synthesized in the presence of polyquaternium-7 (M550) by one-step hydrothermal crystallization method and characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray fluorescence (XRF), Fourier transform infrared spectra, ultraviolet visible spectra, Raman spectroscopy and N2 adsorption–desorption measurements. The experimental results show that highly porous TS-1 crystals, with pores of ca. 2.6–4.9 nm diameter, are obtained under hydrothermal conditions by using polyquaternium-7 as the mesopore-directing agent. The polyquaternium-7 has a great influence on both the textural properties and the coordination of Ti species in the framework of TS-1. The catalytic properties and recyclability of the prepared mesoporous TS-1 for hydroxylation of phenol with H2O2 have been evaluated, and their activity has been compared with those of TS-1 with only micropores. The great catalytic activity, selectivity and stability of the hierarchical TS-1 as well as the cheap price and environmental-friendly nature of the used mesopore-directing agent allow to consider this hierarchical TS-1 as a promising catalyst for industry application.

High-Rota Synthesis of Single-/Double-/Multi-Unit-Cell Ti-HSZ Nanosheets To Catalyze Epoxidation of Large Cycloalkenes Efficiently.

This work first reports high-efficiency epoxidation of large cycloalkenes (carbon number ≥ 7) with tert-butyl hydroperoxide (TBHP) over single-/double-/multi-unit-cell nanosheet-constructed hierarchical zeolite, which is synthesized by one-step hydrothermal crystallization using piperidine as the structure-directing agent of the microporous structure. The excellent catalytic property of the material is ascribed to its unique structural characteristic. Plenty of surface titanols or silanols on the surface of MWW nanosheets are beneficial for the formation of transition-state intermediates; a large number of intercrystalline mesopores in the shell of the material not only facilitate the formation of the intermediate for TBHP but also have nearly no hindrance for the diffusion and mass transfer of bulky cycloalkene to the above intermediates; the 12-MR side cups penetrating into the crystals from the external surface are exposed as much as possible to the reaction system because of the single-/double-/multi-unit-cell MWW nanosheet, serving as the primary reaction space for the epoxidation of bulky cyclic alkene and oxidants and providing enough space for the transition state of Ti-OOtBu and bulky cycloalkane. Moreover, an efficient calcination-free catalytic reaction-regeneration method is developed to overcome the challenge for the recyclability of microporous Ti-zeolite in the catalytic epoxidation of bulky cycloalkenes.

One-step phase transition and thermal stability improvement of Ge2Sb2Te5 films by erbium-doping

The crystallization behavior of Er-doped Ge2Sb2Te5 phase-change materials is investigated systemically for phase change memory application. It is observed that Er dopants can serve as a center for suppression of face-centered-cubic to hexagonal phase transition of Ge2Sb2Te5 films, leading to a one-step crystallization process. The crystallization temperature, 10-year data retention ability and crystalline resistance of Ge2Sb2Te5 films can be significantly increased. Raman spectra suggest that GeTe component is mainly responsible for the phase transition in Er-doped Ge2Sb2Te5 films.

Facile preparation of hierarchically porous IM-5 zeolite with enhanced catalytic performance in methane aromatization

A novel hierarchically porous IM-5-H zeolite material was prepared through one-step crystallization route by means of adjusting the synthesis parameters without introducing any secondary template. The hierarchical IM-5-H zeolite is quite different from the conventional IM-5-C in morphology, textural and acidic properties. After loading Mo, the Mo-IM-5-H catalyst exhibits high activity and stability in non-oxidative aromatization of methane, with a methane conversion of 13.1% and aromatics yield of 7.5%, owing to the mesopores in the IM-5-H zeolite crystals. This work provides a simple way to synthesize hierarchical IM-5 zeolite and expands the application of micro-mesoporous composite material in methane dehydroaromatization.

Effects of Al thickness on one-step aluminium-assisted crystallization of Ge epitaxy on Si by magnetron sputtering

The effects of Al layer thickness on one-step aluminium-assisted crystallization of Ge on Si have been investigated and a better understanding of the Ge growth mechanism has been obtained. The thickness of the final Ge layer is larger than the initial Al layer. The Ge growth can be divided into two stages: (i) a predominantly-vertical growth until the Ge reaches the Al surface followed by (ii) a predominantly-lateral growth with a slow vertical growth rate in order to form a continuous film. The results suggest that surplus Ge is required to obtain continuous Ge layers in one-step aluminium-assisted crystallization.

Effects of precursor concentration and annealing temperature on CH3NH3PbI3 film crystallization and photovoltaic performance

The ability to prepare homogeneous and highly crystalline planar perovskite films via the precise manipulation of a one-step solution-based crystallization process is still a key issue that hinders improvements to the ultimate photoelectric conversion efficiency (PCE) of devices. In this study, we prepared a series of planar CH3NH3PbI3 films using a chlorobenzene-assisted fast perovskite crystallization process with various precursor concentrations ranging from 30 to 50wt% and subsequent annealing at 50–90°C in order to investigate the effects of the precursor concentration and annealing temperature on crystallization and the photovoltaic performance. By precisely controlling the precursor concentration and annealing temperature, we obtained a homogeneous and highly crystalline planar perovskite film with high coverage under the optimized conditions (ca. 40wt% and 70°C), which led to sufficient light absorption and inhibited charge recombination, thereby yielding an enhanced PCE of 16.21%. Furthermore, the unsealed cell still retained a PCE of 10.98% after ambient air exposure for a period of 408h.

Synthesis of chitosan-functionalized MCM-41-A and its performance in Pb(II) removal from synthetic water

Abstract The aim of the work is to develop a novel chitosan modified MCM-41-A, for Pb(II) removal from aqueous solution. This novel material was synthesized by one-step crystallization method and modified by chitosan. The adsorbent was characterized via scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, N2-BET analysis and thermo-gravimetric analysis. Batch experiments were carried out to investigate the effect of contact time, initial pH, adsorbent dose and initial concentration on Pb(II) adsorption. Kinetic and thermodynamic modelings were carried out and sorption data interpreted in terms of the Langmuir and Freundlich equations. Results showed that, the optimal dosage, initial pH and reaction time in the initial Pb(II) concentration of 100 mg L−1 solution are 3 g L−1, pH = 6, and 60 min, respectively, at which the removal efficiency of Pb(II) was 99.83%. The equilibrium data fitted Langmuir isotherm better than Freundlich isotherm, and they were well explained by pseudo-second-order kinetic model. This study demonstrates the newly developed adsorbent is a promising efficient material for Pb(II) adsorption from aqueous solution.

Glass-ceramics one-step crystallization accomplished by building Ca2+ and Mg2+ fast diffusion layer around diopside crystal

CaOMgOSiO2 (CMS) glass-ceramics preparation normally needs two-step heat treatment (nucleation and crystal growth). In this work, CMS glass-ceramics are successfully produced by one-step heat treatment by building Ca2+ and Mg2+ fast diffusion layer between the residual glass and diopside crystal. High-temperature X-ray diffraction (HTXRD) shows that diopside crystals formed during the crystallization of CMS glass. At the glass layer between diopside crystal and residual glass, an enrichment of Na+ is observed by energy dispersive spectroscopy line scanning (EDSLS), which increases the SiONa bonds that promote Ca2+ and Mg2+ ions diffusion. This layer eventually promotes further growth or ripening of the diopside crystals. Thus, nucleation and crystal growth of the CMS glass proceed continuously at the crystallization peak temperature (Tnc), detected by differential scanning calorimetry. Thereby, one-step crystallization of the CMS glass-ceramics becomes possible and practical.

Synthesis of Micro-Mesoporous Composites MCM-41/13X and Their Application on CO2 Adsorption: Experiment and Modeling

Two micromesoporous composites of MCM-41/13X are synthesized through a two-step crystallization process and a one-step crystallization process, respectively. The results of X-ray diffraction, nitrogen adsorption–desorption isotherms, Fourier transform infrared spectroscopy, and transmission electron microscopy results show that the as-prepared samples possessed both micropores and mesopores. The materials take advantage of not only the large adsorption capacity and thermal stability of the microporous material, but also the rapid diffusion and mass transfer of mesoporous materials, which lead to improve CO2 adsorption capacities compared to the pure microporous or mesoporous materials.

One-step Crystallization Kinetic Parameters of the Glass-ceramics Prepared from Stainless Steel Slag and Pickling Sludge

AbstractOne-step crystallization is one of the most energy conserving methods for glass-ceramics preparation. However, only a few kinetics studies focused on the glass-ceramics prepared by the one-step crystallization. The one-step crystallization kinetic parameters were studied using differential scanning calorimetry. The activation energy (Ea) and the Avrami parameter (n) were calculated as 152. 79 kJ · mol−1 and 4. 39, respectively. These parameters indicate that continuous nucleation and three-dimensional crystal growth are the dominating mechanisms in the one-step crystallization process of the parent glass. The properties of the obtained glass-ceramics can be compared to the glass-ceramics prepared by the two-stage heat treatment and sintering method. This crystallization kinetics research can be used to evaluate the one-step crystallization potential of a parent glass.

Phase separation and crystallization in double crystalline symmetric binary polymer blends

Blending of two or more pure polymers is an effective way to produce composites with tunable properties. In this paper, we report dynamic Monte Carlo simulation results on the crystallization of crystalline/crystalline (A/B) symmetric binary polymer blend, wherein the melting temperature of A-polymer is higher than B-polymer. We study the effect of segregation strength (arises from the immiscibility between A- and B-polymers) on crystallization and morphological development. Crystallization of A-polymer precedes the crystallization of B-polymer upon cooling from a homogeneous melt. Simulation results reveal that the morphological development is controlled by the interplay between crystallization driving force (viz., attractive interaction) and de-mixing energy (viz., repulsive interaction between two polymers). With increasing segregation strength, the interface becomes more rigid and restricts the development of crystalline structures. Mean square radius of gyration shows a decreasing trend with increasing segregation strength, reflecting the increased repulsive interaction between A- and B-polymers. As a consequence, a large number of smaller size crystals form with lesser crystallinity. Isothermal crystallization reveals that the transition pathways strongly depend on segregation strength. We also observe a path-dependent crystallization behavior in isothermal crystallization: two-step (sequential) isothermal crystallization yields superior crystalline structure in both A- and B-polymers than one-step (coincident) crystallization.

Synthesis and Characterization of ZSM-5/EU-1 Composite Zeolite with Core-shell Structure by One Step

ZSM-5/EU-1 core-shell intergrowth composite zeolite was synthesized by one-step crystallization method based on dual-template and appropriate citric acid addition. The properties of core-shell zeolite were characterized by XRD, TEM, FT-IR, NH3-TPD, etc. The results showed that there were ZSM-5 and EU-1 zeolite crystalline phases formed in the core-shell zeolite, as EU-1 overgrowing around ZSM-5 surface defects. The synthetic sample composed of microporous and mesoporous multiple porous composite zeolite, with micropore diameter of 0.94 nm. The core-shell structure increased strong acid content and improved its acidity as compared with the single zeolite. Based on the investigation of citric acid addition and crystallization time influence on the structure and Zeta potential of core-shell zeolite, the optimum condition of core-shell intergrowth was as follows, i.e. n(citrate)/n(Al2O3)=0.8–1.2 and crystallization time of 72–96 h. And the possible growth process of core-shell zeolite was proposed.

Structure and optical band gap study of transparent oxyfluoride glass-ceramics containing CaF2 nanocrystals

Oxyfluoride glass-ceramics containing CaF2 nanocrystals were prepared by one-step crystallization of SiO2–Al2O3–CaO–CaF2 glasses at different temperatures. X-ray diffraction (XRD) results have revealed that CaF2 was the only precipitated crystalline phase in glass-ceramic samples. Fourier transform infrared spectroscopy (FT-IR) study of the samples showed the effect of crystallization temperature on the structure. According to DTA and XRD results, suitable glass and its associated glass-ceramics were selected as the best sample in order to study the effect of crystallization on the optical properties. UV–Vis spectra of samples were recorded to determine optical properties. Fermi energy level decreased for glass-ceramics due to the increment of semiconducting behavior. Urbach energy, optical band of the specimens have been reduced by increasing of nanocrystals in glassy matrix which could be attributed to increasing of the order of the structural and formation of crystals and dangling bonds, respectively.

Separation and purification of epigallocatechin-3-gallate (EGCG) from green tea using combined macroporous resin and polyamide column chromatography.

Epigallocatechin-3-gallate (EGCG) is a major bioactive ingredient of green tea that produces beneficial neuroprotective effects. In this paper, to optimize the EGCG enrichment, thirteen macroporous resins with different chemical and physical properties were systemically evaluated. Among the thirteen tested resins, the H-bond resin HPD826 exhibited best adsorption/desorption capabilities and desorption ratio, as well as weakest affinity for caffeine. The absorption of EGCG on the HPD826 resin followed the pseudo-second-order kinetics and Langmuir isotherm model. The separation parameters of EGCG were optimized by dynamic adsorption/desorption experiments with the HPD826 resin column. Under the optimal condition, the content of EGCG in the 30% ethanol eluent increased by 5.8-fold from 7.7% to 44.6%, with the recovery yield of 72.1%. After further purification on a polyamide column, EGCG with 74.8% purity was obtained in the 40-50% ethanol fraction with a recovery rate of 88.4%. In addition, EGCG with 95.1% purity could be easily obtained after one-step crystallization in distilled water. Our study suggests that the combined macroporous resin and polyamide column chromatography is a simple method for large-scale separation and purification of EGCG from natural plants for food and pharmaceutical applications.

Beyond the H2/CO2upper bound: one-step crystallization and separation of nano-sized ZIF-11 by centrifugation and its application in mixed matrix membranes

Nano-sized ZIF-11 with similar features to ZIF-11 has been used for the adsorption of H2and CO2and in the preparation of mixed matrix membranes for H2/CO2separation.

Rare earth-modified kaolin/NaY-supported Pd-Pt bimetallic catalyst for the catalytic combustion of benzene.

A new type of porous kaolin/NaY composite (KL-NY) with a large specific surface area and large pore sizes was synthesized through a one-step crystallization process, and rare earth-modified KL-NY-supported Pd-Pt catalysts were studied for benzene combustion. The results indicated that the pore volume and specific surface area of KL-NY after calcination and crystallization were 0.298 cm(3)/g and 365 m(2)/g, respectively, exhibiting appropriate pore structure and good thermal stability. Catalysts with rare earth metals greatly enhanced the activity of Pd/KL-NY, and the addition of Pt and Ce into the Pd catalyst improved the catalytic activity as well as the stability. The catalyst with an optimal Ce content and Pt/Pd molar ratio (0.2%Pd-Pt (6:1)/6%Ce/KL-NY) demonstrated the best activity for the complete oxidation of benzene at 230 °C, and the catalyst above maintained the 100% benzene conversion for 960 h.