Supersaturation Of Solution Research Articles

Microstructure development of hydrothermally grown TiO2 thin films with vertically aligned nanorods

AbstractTiO2 (rutile) thin films were deposited via a hydrothermal process by adjusting the amount of ethanol, deposition time, and temperature. Especially, various amounts of ethanol generated different degrees of supersaturation in precursor solution. It allowed us to systematically change the width, lengths, and crystallinity of a vertically aligned 1‐D nanorod structure of TiO2 films. The oriented attachment, confirmed by scanning electron microscopy and transmission electron microscopy, was shown to be responsible for their lateral growth of TiO2 nanorods bundled by numerous well‐oriented nanowires and their vertical growth. TiO2 nanorod thin films were also characterized via X‐ray diffraction and UV‐Vis‐NIR spectrophotometer to find a correlation between the process conditions and nanostructural evolution. Dye sensitized solar cells were assembled to relate the nanostructures of TiO2 films with the effectiveness of its role as a photoelectrode.

Influence of ammonia concentration on the microstructure, electrical and raman properties of low temperature chemical bath deposited ZnO nanorods

Nanostructured zinc oxide synthesized using an easy and low temperature chemical bath deposition method are among the most promising low cost semiconducting nanostructures investigated for a variety of applications. We successfully report the effects of ammonia solution in the growth of ZnO nanorods at a temperature of 60°C. Successive addition of ammonia altered the degree of supersaturation of the growth solution, causing a significant deviation in the morphology and crystal orientation of ZnO nanorods. Field emission scanning Electron Microscopy images revealed changes in surface morphology of ZnO nanorods with respect to addition of specific amounts of ammonia. X-ray diffraction analysis revealed wurtzite crystal structure of ZnO which was further supported by X-ray photoelectron studies, optical absorbance and Raman spectra that also revealed the existence of wurtzite ZnO. The current-voltage measurement showed the electrical properties of the synthesized ZnO nanorods. The vertically grown nanorods with flat tops, effect more rectifying Schottky contacts to be realized on comparison to needle like structures.

Growth of mixed K2(Ni,Co)(SO4)2·6H2O crystals under stationary conditions of supercooling and forced convection of the aqueous solution

The technique and the scheme of the system for growing single crystals, including complex mixed composition, under stationary conditions of supercooling and forced convection of aqueous solution were described. Solubility in water of various compositions of K2CoxNi1−x(SO4)2·6H2O (KCNSH) and the dependence of Co content in the KCNSH crystal of Co concentration in the saline part of aqueous solutions of KCNSH have been measured in the temperature range of 30–70°C. It was found that the growth sectors {001} and {110} differ in Ni and Co contents. The Ni/Co ratio is dependent on the value of solution supersaturation. The optical transmission spectra of crystals grown showed high transmittance in the UV region of the spectrum and the almost complete absorption of light in the visible spectrum. It is concluded that the crystals grown can be used as efficient UV filters.

Controlled nucleation assisted restricted volume solvent annealing for stable perovskite solar cells

Here we report, a controlled primary nucleation aided restricted volume solvent annealing method [NR method, NR stands for nucleation assisted restricted volume solvent annealing (RVSA)] along with mixed organic cation based perovskite film for highly efficient (highest PCE: 16.78%), thermally stable perovskite solar cells (PSCs) with full temperature compatibility for flexible substrates. To the best of our knowledge, this is the highest efficiency ever reported with PSCs incorporating low temperature processed ZnO as electron transport layer (ETL). Unlike the conventional RVSA method [CR method, CR refers to conventional restricted volume solvent annealing (RVSA)], the reported NR method raises the degree of supersaturation of the precursor solution due to high solvent evaporation rate during the crucial primary nucleation phase, that ensures smooth and uniform perovskite grain distribution during the rapid crystal growth phase. NR method also provides better perovskite crystallinity during the annealing induced secondary crystallization phase, as unlike CR, NR perovskite does not contain high amount of residual solvent at this stage of perovskite grain growth. The photovoltaic performance, hysteretic behaviour and device degradation phenomena of NR PSCs have been compared with CR PSCs. Enhanced power conversion efficiency (PCE) attained with NR method has been explained with elaborate surface morphology and topography study, along with charge transport analysis with electrochemical impedance spectroscopy and Mott-Schottky analysis. Substantially mitigated photo-current hysteresis phenomenon with NR method has been elucidated in terms of inherent electrode polarization process. Adding to the merits, NR PSCs also demonstrate over three times higher device stability compared to CR PSCs, which has been investigated with frequency-dependent capacitive spectra and Mott-Schottky characterization of the aged devices.

Maintaining Supersaturation of Active Pharmaceutical Ingredient Solutions with Biologically Relevant Bile Salts

Currently, it is of interest to improve the oral absorption of poorly water-soluble therapeutic agents using supersaturating formulations. Understanding crystallization kinetics of supersaturated drug solutions is central to the design and evaluation of such formulations. Bile salts have drawn increasing attention in this context as they serve important roles in biorelevant dissolution media, in vivo, and have been shown to slow down the crystallization of active pharmaceutical ingredients. The goal of this study was to evaluate the impact of bile salt monomers and micelles on the crystallization of telaprevir, a poorly water-soluble drug, from aqueous solution. To better describe the crystallization driving force in the presence of the bile salts, a side-by-side diffusion cell was used to evaluate telaprevir mass flow rate, and hence solute activity, in the absence and presence of different bile salts. The effectiveness of monomeric and miceller bile salts as crystallization inhibitors was then evaluated...

Insight into bubble nucleation at high-pressure drop rate

This paper presents insight in bubble nucleation in polymer foaming with physical blowing agent using a batch foaming technique. In our experiments the bubble nucleation is triggered by a sudden pressure drop that causes the supersaturation in the polymer gas solution. In fact, the pressure drop rate is an important process variable since it plays a role in both bubble nucleation and growth. Herein, we investigated very high pressure drop rates, and confirmed the great importance of the pressure drop rate as foaming process variable. The results show that the number of nucleated bubbles increases of one order of magnitude and the foam density is reduced if the pressure drop rate is increased from 50 to 500 MPa/s. Interestingly, the number of nucleated bubble increases linearly in a bi-logarithmic scale as function of pressure drop rate at all the investigated temperatures. Moreover, in the current paper, it is discussed how talc used as nucleating agent plays a role in cooperation with pressure drop rate on bubble nucleation at different foaming temperatures.

Phosphorus recovery from simulated municipal wastewater (SMW) through the crystallization of magnesium ammonium phosphate hexahydrate (MAP)

AbstractBACKGROUNDPhosphorus and nitrogen recovery from municipal and/or industrial wastewater treatment plants in the form of magnesium ammonium phosphate hexahydrate (MgNH4PO4·6H2O, MAP, Struvite) is an attractive alternative for the valorization of wastes. Although efforts have been focused on the recovery of nitrogen and phosphorus nutrients from wastewater at alkaline pH, removal of these nutrients in weakly acid pH is still challenging. The advantage of acid pH is that the precipitation of heavy metals in the form of insoluble hydroxides is avoided provided that their concentrations are relatively low.RESULTSThe metastable zone width of solutions, supersaturated with respect to MAP at pH 6.50 was investigated. The kinetics of MAP formation both in unseeded and in seeded solutions was investigated in batch reactors at constant supersaturation. The rates of crystal growth of MAP on seed crystals showed a parabolic dependence on the relative supersaturation. The concentration of the inoculating seed crystals affected the rates of crystal growth.CONCLUSIONSIt is possible to crystallize MAP at pH values of 6.50 provided that the supersaturation is sufficient. From the rate dependence on relative supersaturation (parabolic) it was concluded that the crystal growth mechanism was surface diffusion controlled for the integration of the growth units at the active crystal growth sites. Secondary nucleation, depending on the solution supersaturation, was observed within the stable domain of the metastable zone. The morphology of MAP seed crystals remained unchanged, while the mean particle size increased reaching comparable sizes irrespective of the degree of supersaturation. © 2017 Society of Chemical Industry

Effects of supersaturation control strategies on hydroxyapatite (HAP) crystallization for phosphorus recovery from wastewater.

The HAP crystallization for phosphorus removal from wastewater contributes to an environmental friendly production due to the fact that it helps reduce or eliminate the water eutrophication as well as increases the recovery of mineral resources. However, the generated microcrystalline with poor settleability in high levels of supersaturation solution has a negative effect on the phosphorus recovery efficiency. To overcome the drawback, multiple reagent feed ports (four feed ports) and different recirculation ratio (1.0, 1.5, 2.0, 2.5, 3.0) were investigated to control the levels of supersaturation in an air-agitated reactor with calcite as seeds. Results showed that the approach of multiple reagent feed ports could improve the conversion ratio of orthophosphate, but it had a limited effect (∼3% improvement) on phosphorus recovery efficiency (deposition on the seeds). With the increase of the recirculation ratio, the recovery efficiency was increased gradually and reached an optimal value of 85.63% under the recirculation ratio of 2.5 and four feed ports. This is because the adopted strategies could reduce the level of supersaturation by diluting the concentration of the reagents and inhibit large numbers of microcrystalline coinstantaneous occurrence. Meanwhile, the crystallized products were detected and analyzed by scanning electron micrograph (SEM) with energy-dispersive spectrometry (EDS) and X-ray diffraction (XRD), which were proved to be HAP with a high purity. Collectively, these results demonstrated that supersaturation control using conventional approaches had a limited improvement on the phosphorus recovery efficiency in the form of HAP, and the new control strategies for supersaturation dispersion should be developed in the further study.

Effect of the supersaturation on the precipitation kinetics of the Guinier-Preston zones in Al-rich Ag alloys

The precipitation kinetics of the GP zones in a supersaturated solid solution depends on the level of its supersaturation which induces a driving force. The magnitude of this driving force increases with the increasing of the undercooling and the increasing of the solute supersaturation. At a given temperature, the increasing of the supersaturation accelerates the precipitation of the GP zones. In an Alxat.%Ag alloy, the transformation kinetics depends on the contribution of the driving force and on that of the thermal activation which is preponderant.

Kinetics of the Formation of Nanosize Niobium Carbonitride Precipitates in Low-Alloy Structural Steels

A detailed study is made using original methods of kinetic features of nanosize niobium carbonitride precipitate formation in relation to metal temperature and deformation regimes on the example of an industrial melt of low-alloy structural steel. It is established that in the absence of deformation there are considerable kinetic difficulties for niobium carbonitride precipitation, and for its occurrence to some significant extent a time interval of not less than 20–40 min at 900°C is necessary, even in the presence of considerable supersaturation and solid solution supercooling. With equivalent conditions, preliminary deformation considerably accelerates formation of nanosize niobium carbonitride precipitates that commences approximately after 10 sec and ceases after isothermal soaking at 900°C in 200–300 sec. A fundamental dependence is demonstrated for the amount and mechanism of nanosize niobium carbonitride precipitate formation on thermal prehistory. In addition, prior cooling to room temperature and subsequent heating to an exposure temperature of 700°C leads to a marked increase in number of nanosize carbonitride precipitates formed.

Heterogeneous crystallization of calcium hydrogen phosphate anhydrous (monetite)

The crystal growth of monetite (CaHPO4, DCPA), the least stable calcium phosphate has been investigated by the seeded growth method from solutions supersaturated exclusively with respect to this phase alone. The kinetics of crystal growth was measured at constant supersaturation at 37°C, pH 6.0. The measurements of the rates of crystal growth of DCPA showed a second order dependence on the relative supersaturation of the solutions with respect to DCPA, suggesting that the rate determining step is surface diffusion of the growth units to the active growth sites of the crystals. The heterogeneous crystallization of brushite (CaHPO4·2H2O, DCPD) on DCPA seed crystals in solutions supersaturated with respect to both DCPD and DCPA showed that DCPD nucleation and growth took place selectively by heterogeneous nucleation on the DCPA seed crystals. The same parabolic dependence of the rates on the relative supersaturation of the solutions with respect to DCPD was found, showing that the mechanism was the same as in the case of growth of DCPA on DCPA seed crystals. Seeding of solutions supersaturated with respect to both DCPA and DCPD at pH 6.0, 37°C with collagen type II in powdered form, resulted to the formation of an apatitic solid. The morphology of the crystals formed on the collagenous matrix suggested that the identified mineral was probably the result of rapid hydrolysis of metastable calcium phosphatephases. The formation of the mineral phase on collagen took place past long induction time periods inversely proportional to the relative supersaturation with respect to DCPD and showed that the collagen substrate did not stabilize calcium phosphate at the same conditions at which DCPA did.

Crystal growth of aragonite in the presence of phosphate

The crystal growth of aragonite was investigated at pH 7.8, 37°C and constant solution supersaturation from aragonite-seeded supersaturated solutions. The effect of the presence of orthophosphate ions in the supersaturated solution on the kinetics of crystallization of aragonite was investigated over the range of orthophosphate concentrations of 0.25µM–1mM. In the presence of orthophosphate in the range of 0.25µM–8µM, the crystal growth rate of aragonite decreased with increasing phosphate concentration. At orthophosphate concentration levels exceeding 2µM, induction times were measured and were found to increase with orthophosphate concentration. At orthophosphate concentration levels >8µM, the crystal growth of aragonite was inhibited, suggesting the blockage of the active growth sites by the adsorption of orthophosphate ions. Adsorption was confirmed by the investigation of orthophosphate uptake on aragonite, which was: i) found to depend on the equilibrium concentration of orthophosphate in aqueous solutions saturated with respect to aragonite; ii) not influenced by the ionic strength of the electrolyte up to 0.15M NaCl, showing that electrostatic interactions between orthophosphate and CaCO3 did not play a significant role in this concentration range. Adsorption data of orthophosphate on the aragonite crystals gave satisfactory fit to the Langmuir adsorption model and was confirmed by XPS analysis.

Post‐crystallization cooling behavior of aqueous supersaturated ammonium dihydrogen phosphate solutions containing acetone and methanol antisolvents added at different rates

Experimental results of post‐crystallization cooling behavior of aqueous supersaturated ammonium dihydrogen phosphate (ADP) solutions containing acetone and methanol antisolvents fed at different rate RA are described and discussed. The supersaturated solutions were contained in a double‐walled crystallizer connected to a thermostating arrangement maintaining the temperature at 30 °C. It was found that: (1) there is a steady decrease in temperature Ts of aqueous ADP solutions with increasing time t, which follows Newton's law of cooling, with constant K as characteristic of solution composition and its value for a system increases with an increase in RA, and (2) at a particular acetone and methanol feeding rate RA, the value of constant K for aqueous ADP solutions is much higher than that obtained from the data of decrease in the temperature Tm of pure water. The experimental results are discussed from consideration of a steady decrease in solution supersaturation with increasing t as a result of diffusion of ions/molecules involved in transporting heat from aqueous ADP solutions contained in the crystallizer to the thermostating system.

ChemInform Abstract: Bioinspired Synthesis of Magnetite Nanoparticles

AbstractReview: 230 refs.

Investigation of Growth Mechanisms of Sodium Chlorate Crystals from Aqueous Solutions

Difficulties in determining the crystal growth mechanism from growth rate versus solution supersaturation dependence are discussed. Obtained results indicate that in the supersaturation range of 0.66–1.56%, sodium chlorate crystals grow in accordance with the spiral growth model. It is shown that in the supersaturation range of 0.44–1.32%, the growth mechanism depends on crystal growth history. Namely, the exponent n in the power law R = Kσn depends on the manner of supersaturation changes (varied from 1.3 to 1.9%). This indicates that the overlapping of diffusion fields of neighboring steps depends on growth history.

An efficient approach for phosphorus recovery from wastewater using series-coupled air-agitated crystallization reactors

Homogeneous nucleation of hydroxyapatite (HAP) crystallization in high levels of supersaturation solution has a negative effect on phosphorus recovery efficiency because of the poor settleability of the generated HAP microcrystalline. In this study, a new high-performance approach for phosphorus recovery from anaerobic supernatant using three series-coupled air-agitated crystallization reactors was developed and characterized. During 30-day operation, the proposed process showed a high recovery efficiency (∼95.82%) and low microcrystalline ratio (∼3.11%). Particle size analysis showed that the microcrystalline size was successively increased (from 5.81 to 26.32 μm) with the sequence of series-coupled reactors, confirming the conjectural mechanism that a multistage-induced crystallization system provided an appropriate condition for the growth, aggregation, and precipitation of crystallized products. Furthermore, the new process showed a broad spectrum of handling ability for different concentrations of phosphorus-containing solution in the range of 5–350 mg L−1, and the obtained results of phosphorus conversion ratio and recovery efficiency were more than 92% and 80%, respectively. Overall, these results showed that the new process exhibited an excellent ability of efficient phosphorus recovery as well as wide application scope, and might be used as an effective approach for phosphorus removal and recovery from wastewater.

Ferrous Tartrate recognition of sodium chloride {111} and its effect on crystal growth

The surface morphology and growth pattern of some molecules could be altered by the recognition of ferrous tartrate (FeC4H4O6, FeTA). We have explored this phenomenon in the aspect of growth rate and morphology alteration of sodium chloride crystals where few researches have been done. In this paper, the crystallization behavior of NaCl with added FeTA was studied by supersaturation test, conductivity, scanning electron microscopy (SEM), and X‐ray diffraction (XRD). The results showed that the supersaturation of NaCl solution could be increased to about 5.5 % in presence of FeTA prior to the onset of crystallization. Furthermore, SEM images and XRD results indicated that the addition of FeTA could change the morphology of NaCl crystal from cubic to octahedron by impeding the growth of {111} and {110} faces. Besides, the interaction between NaCl {111} face and FeTA was discussed and the possible spatial structure of FeTA was speculated through the lattice parameters of NaCl.

A simple method to model the reduced environment of lake bottom sapropel formation

The Kambala and Barchin brackish lakes (Baraba steppe, southern West Siberia) contain an organic-rich sapropel layer that was formed in oxygen-depleted waters. We measured the bulk sediment elemental composition, the water chemistry and determined the mineralogical composition and predominant biota species (Diatoms and Cyanobacteria in phytoplankton community respectively) in the lakes. The result indicates that the first lake has a siliceous type of sapropel and the second a carbonaceous one. A computer thermodynamic model was developed for chemical interaction in water-bottom sediment systems of the Kambala and Barchin Lakes. The surface sodium bicarbonate waters are supersaturated with respect to calcite, magnesite (or low Mg-calcite), quartz and chlorite with minor strontianite, apatite and goethite (pH 8.9–9.3, Eh 0.3 V). Nevertheless, it is shown that during sapropel deposition, deep silt waters should be anoxic (Eh<0 V). The virtual component CH2O has been used to create an anoxic environment suitable for pyrite formation due to the biotic community impact and abiotic reduction. Thermodynamic calculation has shown that silt water is not necessarily euxinic (anoxic and sulfidic). Depending on Eh, sulfate sulfur can dominate in solution, causing the formation of gypsum together with pyrite. An attempt was made to find a reason for solution supersaturation with respect to Ca and Mg ions due to their complexation with humic acids.

Measurement of Crystal Face Specific Growth Kinetics

An instrument for measurement of face specific growth kinetics of crystals growing in a solution is developed and applied to crystallization of sodium nitrate (NaNO3) and potassium dihydrogen phosphate (KH2PO4, KDP). The device consists of three major components, a stereovision imaging system that captures in real time the size change in each face direction of the crystal, an ATR-FTIR probe measuring solution concentration and supersaturation, and a small purpose-designed crystallizer that allows a crystal to be fixed in the solution and adequate solution mixing so the concentration measured can reflect the solution concentration near the surfaces of the crystal. The growth rates of all independent faces of NaNO3 and KDP crystals were derived at each time interval. For the NaNO3 crystal, growth rates in the temperature range 298.15–318.15 K and the supersaturation range 0.01–0.11 were measured, enabling a systematic kinetic study. For the KDP crystal, the growth rates were measured just to show the capabi...

Surfactant free, simple, morphological and defect engineered ZnO nanocatalyst: Effective study on sunlight driven and reusable photocatalytic properties

Abstract We demonstrate the facile synthesis of solution grown ZnO structures (rods, buds, brooms, spindles, stars, flowers, multipods) without using any surfactant and capping agents. Morphology of the nanostructures was simply controlled by varying the Zn supersaturation in the growth solution which transforms the growth mode from anisotropic to isotropic and then to hierarchical nature. All photocatalysts were characterized by X-ray diffraction, UV–vis absorption, photoluminescence, scanning electron microscopy, high resolution transmission electron microscopy analysis. ZnO nanoflowers show excellent photocatalytic (PC) degradation efficiency above 95% against Methyl orange, Rodamine B and Methylene blue dyes in 120 min under natural solar irradiation compared to the other nanostructures. It is noteworthy that the PC performance of the ZnO nanostructures correlates well with the defect states and the production of photo induced reactive oxide species (ROS). Investigations show that the enhanced PC performance of ZnO nanoflowers was due to the synergy of larger surface area and oxygen related defects assisted ROS production. The photocatalytic recycling ability of ZnO nanoflowers was investigated. ZnO flowers showed excellent recyclability with a slight decrease in photocatalytic efficiency after being subjected to ten consecutive cycles.