Ammonia Diffusion Method Research Articles

Preparation of NiCo-LDHs@rGO composites with improved electrochemical performance by ammonia diffusion method under closed conditions

Layered double hydroxides (LDHs) have been considered to be favorable pseudocapacitance electrodes due to their adjustable composition and low cost. The NiCo-LDHs@rGO (reduced graphene oxide) compositeswere prepared by the ammonia diffusion method. The conductivity of NiCo-LDHs was improved by composite rGO. When 30 mg of rGO was added, the specific capacitance reached 1920.5F/g at 1 A/g. When being assembled into an asymmetric two-electrode supercapacitor, an energy density of 50.5 Wh/kg was achieved at a power density of 900 W/kg. The NiCo-LDHs@rGO composite has significantly improved the electrochemical properties.

Preparation and electrochemical properties of NiCo-layered double hydroxide supercapacitor

Layered double hydroxides (LDHs) are favorable pseudocapacitance electrodes due to their adjustable composition and low cost. Here, a series of NiCo-LDHs were prepared by a novel ammonia diffusion method at room temperature. Compared with other synthesis methods, this method is a simple, green, original and effective method. The morphology, structure, and elemental composition of NiCo-LDH electrode materials were characterized and their electrochemical properties were tested. The optimal honeycomb NiCo-LDH shows a specific capacitance (Cs) of 1463.2F·g−1 at 1 A·g−1, and the rate capacity is 75.2 % at 20 A·g−1. Particularly, the Cs is still 87.9 % after 2000 charge–discharge cycles at a high current density of 20 A·g−1. In addition, the hybrid supercapacitor with NiCo-LDH//activated carbon (AC) could show an energy density of 23.4 Wh·kg−1 at a power density of 900 W·kg−1, along with 73.4 % capacity retention after 5000 cycles.

Spherical Crystallization: A Tool to Improve the Physicochemical Properties of APIs

A greater challenge in solid dosage formulation is the development of spherical agglomerates which increases the solubility and bioavailability of the drug. Spherical crystallization is “An agglomeration process that transforms crystals directly into compact spherical forms during the crystallization process.” Spherical crystallization is the novel agglomeration technique that can transform directly the fine crystals produced in the crystallization process into a spherical shape. Direct Compression of powders is simple and easy way of making tablets. In direct compression of Good Compressibility and flowability plays a major role. Spherical crystallization methods are very useful methods in which the drug crystals are modified using different solvents to directly compressible agglomerates. which cost effective and time saving. The different Techniques discussed are Crystallization method, Solvent crystallization method, Quasi- emulsion diffusion method, Ammonia Diffusion method, neutralization method, and solvent agglomeration technique. This article gives a detailed and comprehensive review about different techniques, its advantages, mechanism and application of Spherical agglomeration Technique along with its Evaluation and Characterization methods.

Spherical Crystallization: An Overview

Introduction: In 1986, Kawashima developed the spherical crystallization technique for size enlargement of drugs in the field of pharmacy. Spherical crystallization is defined as “An agglomeration process that transforms crystalline drug directly into compact spherical forms for improving the flowability, solubility and compactability”. Methods: General methods for preparing spherical crystallization are spherical agglomeration, emulsion solvent diffusion method, ammonia diffusion method and neutralization method. Factors controlling the process of agglomeration include solubility profile, mode and intensity of agitation, temperature of the system and residence time. Results: Spherical crystals can be characterized by Optical microscopy, X-ray powder diffraction, Electron scanning microscopy, Fourier Transform Infrared spectrometer (FTIR) and differential scanning calorimeter (DSC).Spherical crystallization has wide applications in pharmaceuticals like improvement of flowability and compressibility of poorly compressible drugs, masking bitter taste of drugs and improving the solubility and dissolution rate of poorly soluble drugs. Conclusion: Spherically agglomerated crystals can be directly converted into a tablet thus saving time and reducing cost.

Bio-templated Fabrication of Highly Defective Carbon Anchored MnO Anode Materials with High Reversible Capacity

In this work, porous MnO/C composites were successfully synthesized via a new ammonia diffusion method, in which the MnO nanoparticles were tightly embedded into a porous carbon matrix. Kapok fibers (KFs) were used as both the bio-template and the renewable carbon source. The KFs-templated MnO/C electrodes exhibited a high reversible specific capacity of 1454mAhg−1 with a high coulombic efficiency, up to 98%, at a current density of 200mAg−1 over 150 cycles. The high reversible capacity of the MnO/C composites could be ascribed to the synergetic effects of several factors including the unique porous microstructure, the small MnO nanoparticle size and the high defective carbon matrix. Due to the small MnO nanoparticles size and a moderate amount of carbon (13.3wt%), the electrodes showed a small voltage polarization (about 0.89V).

Spherical Crystallization: A Novel Drug Delivery Approach

Spherical crystallization is a fast developing technique of particle design in which crystallization and agglomeration can be achieved simultaneously in one step. It has been successfully utilized for improvement of flow ability and compactability of crystalline drugs. The principle steps involved in the process of spherical crystallization are flocculation zone, zero growth zone, fast growth zone and constant size zone. General methods of spherical crystallization are emulsion solvent diffusion, spherical agglomeration, ammonia diffusion method and neutralization method. Factors controlling the process of agglomeration are solubility profile, mode and intensity of agitation, temperature of the system and residence time. Characterization of spherical crystals can be carried out using Optical Microscopy, Scanning Electron Microscopy, X-ray Powder Diffraction, Fourier Transform Infrared spectroscopy, Differential Scanning Calorimetry and Thin layer Chromatography.

Elucidating Mechanisms of Diffusion‐Based Calcium Carbonate Synthesis Leads to Controlled Mesocrystal Formation

AbstractAggregation‐based crystal growth often gives rise to crystals with complex morphologies which cannot be generated via classical growth processes. Despite this, understanding of the mechanism is rather poor, particularly when organic additives or amorphous precursor phases are present. In this work, advantage is taken of the observation that aggregation‐based growth of calcium carbonate, and indeed many other minerals, is most often observed using diffusion‐based synthetic methods. By fully characterizing the widely used ammonia diffusion method (ADM)–which is currently used as a “black box”–the solution and supersaturation conditions which accompany CaCO3 precipitation using this method are identified and insight is gained into the nucleation and growth processes which generate calcite mesocrystals. This reveals that the distinguishing feature of the ADM is that the initial nucleation burst consumes only a small quantity of the available ions, and the supersaturation then remains relatively constant, and well above the solubility of amorphous calcium carbonate (ACC), until the reaction is almost complete. New material is thus generated over the entire course of the precipitation, a feature which appears to be fundamental to the formation of complex, aggregation‐based morphologies. Finally, the importance of this understanding is demonstrated using the identified carbonate and supersaturation profiles to perfectly replicate CaCO3 mesocrystals through slow addition of reagents to a bulk solution. This approach overcomes many of the inherent problems of the ADM by offering excellent reproducibility, enabling the synthesis of such CaCO3 structures in large‐scale and continuous‐flow systems, and ultimately facilitating in situ studies of assembly‐based crystallization mechanisms.

Growth process and crystallographic properties of ammonia-induced vaterite

Metastable vaterite crystals were synthesized by increasing the pH and consequently the saturation states of Ca2+- and CO2-3-containing solutions using an ammonia diffusion method. SEM and TEM analyses indicate that vaterite grains produced by this method are polycrystalline aggregates with a final morphology that has a sixfold-symmetry. The primary structure develops within an hour and is almost a spherical assemblage of nanoparticles (5-10 nm) with random orientation, followed by the formation of hexagonal platelets (1-2 μm), which are first composed of nanoparticles and that develop further into single crystals. As determined using transmission electron microscopy, these hexagonal crystallites are terminated by (001) surfaces and are bounded by {110} edges. The hexagonal crystals subsequently stack to form the “petals” (20 μm wide, 1 μm thick) of the final “flower-like” vaterite morphology. The large flakes gradually tilt toward the center as growth progresses so that their positions become more and more vertical, which eventually leads to a depression in the center. Since this sequence encompasses several morphologies observed in previous studies (spheres, hexagons, flowers etc.), they may actually represent different stages of growth rather than equilibrium morphologies for specific growth conditions.

Measuring nitrification in sediments – comparison of two techniques and three 15NO measurement methods

Nitrification is a crucial process in sediment nitrogen cycling. We compared two 15N tracer-based nitrification measurement techniques (isotope pairing technique (IPT) combined with 15N nitrate pool dilution and 15N ammonium oxidation) and three different 15N analyses from bottom water nitrate (ammonia diffusion, denitrifier and SPINMAS) in a sediment mesocosm. The 15N nitrate pool dilution technique combined with IPT can be used to quantify the in situ nitrification, but the minimum detection limit for the total nitrification is higher than that in the 15N ammonium oxidation technique. The 15N ammonium oxidation technique, however, is not applicable for sediments that have high ammonium content. If nitrate concentration and the amount of 15N label in the sample are low, the 15N nitrate analysis should be done with the denitrifier method. In higher 15N concentrations, the less sensitive SPINMAS method can also be applied. The ammonia diffusion method is not suitable for bottom water 15N nitrate analyses.

PHARMACEUTICAL OVERVIEW OF SPHERICAL CRYSTALLIZATION

Spherical crystallization is a particle design technique, by which crystallization and agglomeration can be carried out simultaneously in one step and which has been successfully utilized for improvement of flowability, compactability and bioavailability of crystalline drugs. General methods of spherical crystallization are spherical agglomeration, emulsion solvent diffusion and ammonia diffusion method. The principle steps involved in the process of spherical crystallization are flocculation zone, zero growth zone, fast growth zone and constant size zone. Spherical crystallization is having wide applications in pharmaceuticals like improvement of flowability and compressibility of poorly compressible drugs, masking bitter taste of drugs and improving the solubility and dissolution rate of poorly soluble drug.

Measuring –NH4+ in marine, estuarine and fresh waters: An adaptation of the ammonia diffusion method for samples with low ammonium concentrations

Abstract We present a method for measuring 15 N –NH4+ in marine, estuarine and fresh waters. The advantage of this method is that it is broadly applicable to all types of water and it allows measurements in samples with lower ammonium concentrations than has previously been possible. The procedure is a modification of the ammonia diffusion method and uses large sample volumes (often 4 l) to obtain sufficient N for isotope ratio mass spectrometric analysis. Large volume samples have not previously been used with the diffusion procedure because isotopic fractionation occurs due to incomplete recovery of ammonium. However, the method we present accounts for this fractionation and allows precise correction of measured δ 15 N values.

Natural abundance-level measurement of the nitrogen isotopic composition of oceanic nitrate: an adaptation of the ammonia diffusion method

Abstract We have adapted the “ammonia diffusion” method of nitrate extraction for natural-abundance level nitrogen isotopic measurement of oceanic nitrate. The method involves: (1) sample concentration (by boiling or evaporation); (2) conversion of nitrate to ammonia using Devarda's alloy; and (3) the gas-phase diffusion of ammonia onto an acidified glass fiber disk which is sandwiched between two porous Teflon membranes. We have investigated the conditions necessary to effect complete ammonia recovery from natural seawater samples and the use of Devarda's alloy under these conditions. In addition, we have characterized the blanks in this method and designed a protocol to minimize them. Here, we report our protocol for nitrate extraction from seawater and provide an explanation of the protocol based on our method development work. To demonstrate the performance of the method, we present nitrate nitrogen isotopic data from nitrate standard additions to Sargasso Sea surface water and from several Southern Ocean depth profiles. The nitrate extraction method gives highly reproducible, complete recovery of nitrate and a standard deviation for isotopic analysis of The blanks inherent in the extraction procedure are from Devarda's alloy and seawater dissolved organic nitrogen (“DON”). The N blank of the Devarda's alloy reagent depends on brand and lot number. The Devarda's alloy which we are currently using results in a blank of ~ 0.4 nmol N per 100 ml of seawater (effectively 0.4 μM). An isotopic correction is made for this blank. For standard incubation conditions, stored Woods Hole seawater (with ~ 10 μM DON) gives a ~ 0.6 μM DON blank, while stored Sargasso Sea (with ~ 6 μm DON) surface water gives a DON blank of 0.3–0.5 μM. The DON blank appears to cause the ≤ 0.3%. difference between the measured and actual isotopic composition of nitrate added to Sargasso Sea surface water at the 5 μM nitrate level. We discuss several ways to lower the DON blank for samples in which the DON concentration is high relative to the nitrate concentration. The nitrogen isotopic data from several Southern Ocean profiles, in conjunction with the other results presented in this paper, demonstrate the consistency of the data produced by the ammonia diffusion method. The ammonia diffusion-based protocol is more reliable and allows for better precision than the nitrate reduction/ammonia distillation method ( Cline and Kaplan, 1975 ) in our hands. While the samples have an incubation time of 4 days or longer, we find that the diffusion method allows for higher throughput than the distillation method because samples can be run conveniently in large batches.