Interfacial chemical method

Nanoparticles of Mn and Pr-doped ZnS and CdS-ZnS were synthesized by wrt chemical method and inverse micelle method. Physical and fluorescent properties wra cbaractmzed by X-ray diffraction (XRD) and photoluminescence (PL). ZnS nanopatlicles aniKaled optically in air shows higher PL intensity than in vacuum. PL intensity of Mn and Pr-doped ZnS nanoparticles was enhanced by the photo-oxidation and the diffusion of luminescent ion. The prepared CdS nanoparticles show cubic or hexagonal phase, depending on synthesis conditions. Core-shell nanoparticles rahanced PL intensity by passivation. The interfacial state between CdS core and shell material was unchan d by different surface treatment. 

The sulfite reaction is used for the above-mentioned purpose and hence is an analytical tool for judging micro-reactor performance [5,9,10]. The sulfite oxidation as a chemical method provides complementary information to optical analysis of the specific interfacial area. 

The chemical method used to estimate the interfacial area is based on the theory of the enhancement factor for gas absorption accompanied with a chemical reaction. It is clear from Equations 6.22-6.24 that, in the range where y > 5, the gas absorption rate per unit area of gas-liquid interface becomes independent of the liquid phase mass transfer coefficient /cp, and is given by Equation 6.24. Such criteria can be met in the case of absorption with... 

In order to determine rate constants rigorously in interfacial reactions, methods are required which allow determination of reactant concentrations and chemical rates actually at the reactive surface. This requires a degree of control of the hydrodynamics which is not available in stirred vessels, and more sophisticated methods are used in these cases. Minimal criteria for the unambiguous determination of interfacial chemical kinetics have been enumerated elsewhere and are as follows [13]. 

In many practical applications, gas-liquid mass transfer plays a significant role in the overall chemical reaction rate. It is, therefore, necessary to know the values of effective interfacial area (aL) and the volumetric or intrinsic gas-liquid mass transfer coefficients such as kLah, kL, ktaL, kg, etc. As shown in Section IX, the effective interfacial area is measured by either physical e.g., photography, light reflection, or light scattering) or chemical methods. The liquid-side or gas-side mass-transfer coefficients are also measured by either physical (e.g., absorption or desorption of gas under unsteady-state conditions) or chemical methods. A summary of some of the experimental details and the correlations for aL and kLaL reported in the literature are given by Joshi et al. (1982). In most practical situations, kgaL does not play an important role. 

Joshi and Sharma (1976) also evaluated interfacial area and liquid-side mass-transfer coefficients using chemical methods in columns of 0.38, 0.57, and 1.0 m diameters. The optimum liquid submergence ratio (H/dT) and impeller spacing ratio (L,/dT) were found to be in the range of 0.6-0.7 and 1.4-1.6, respectively. The following correlations were proposed ... 

The overall interfacial area for the whole reactor can be determined by chemical techniques. These techniques, however, must be used with restrictions. For example, chemical methods are difficult to use for fast-coalescing systems, since the presence of a chemical compound may reduce coalescence rates. Furthermore, in fast-coalescing systems, the specific area may depend strongly on the position in the reactor, which complicates the interpretation of an average value obtained with chemical methods. Indeed, both physical and chemical techniques should be used together to describe the phenomena that occur within gas-liquid reactors. While chemical methods allow the determination of the much-needed average interfacial area, information on the variations of the interfacial parameters, such as aL and dsv, within the reactor, which is important for scale-up, cannot be obtained by this method. 

Many physical and chemical methods were used to functionalize CNTs for enhancing interactions between CNTs and polymer (11-12). Three general approaches have been adopted to modify the surface of CNTs to promote the interfacial interactions chemical,... 

The gas-liquid interfacial area has been measured by both physical and chemical methods. The accuracy of these measurements is generally very poor (15). The interfacial area has been related to the energy input per unit volume and the gas holdup by the expression (6-19)... 

Various physical and chemical methods can be applied to determine interfacial areas. Unfortunately, the different methods yield largely differing results. The methods used most often are photography and sulfite oxidation. Schumpe and Deckwer recently showed... 

Different chemical methods do not lead to equal interfacial areas either. This is demonstrated in Fig. 

The interfacial area is known accurately only in some systems used in laboratory studies falling laminar films, laminar cylindrical jets, undisturbed gas-liquid and liquid-liquid interfaces, and solid castings of known dimensions immersed in liquids. In all reactor systems used industrially such as packed towers, spray towers, and bubble trays, the interfacial area is relatively difficult to determine. Photographic, gamma-ray, light scattering and chemical methods have been used to determine a in bubble dispersions (5, 6, 7, 8, iO, 42). For an average bubble diameter dn, a superficial gas velocity Usa and a bubble rise velocity Un,... 

In this section we consider the rate of absorption of gases into liquids that are agitated so that dissolved gas is transported from the interfacial surface to the interior by convective motion. The next section, based on this one, treats chemical methods for determining interfacial areas and mass-transfer coefficients in agitated gas-liquid reactors. 

This corresponds to absorption with fast pseudo-first-order kinetics. Thus the film thickness, or the value of /cl, is irrelevant and does not appear in the expression for the average rate of absorption

unit volume of reactor 4 . This important case will be the basis of a chemical method for measuring the interfacial area directly from the rate of absorption when C% Df is known. 

At the outset, we recognize that a technique that measures overall values cannot be used without the restrictions that arise from the results observed with physical methods. For example, the chemical method can hardly be used with fast-coalescing systems, since the presence of a chemical compound may well reduce the coalescence rates. In fast-coalescing systems, as observed with physical methods, the wide variation of specific contact area at different locations in the reactor negates the meaning of an average value. In fact, physical and chemical techniques should be used simultaneously to identify more fully the phenomena that occur in gas-liquid reactors. While chemical methods provide overall values of interfacial area that are immediately usable for design, we must also know the variations in the local interfacial parameters (a, dgM) within the reactor in order to deal competently with scale-up. These complementary data, measured by physical methods, should be obtained from local simultaneous measurements of two of the three interfacial parameters as discussed above. 

Chemical methods for determining gas-liquid interfacial areas and mass-transfer coefficients have been intensively developed for the last 10 years. The principles of these methods are deduced from the results presented in Section III,B,2 A gas A is absorbed into a liquid where it undergoes a reaction with a dissolved reactant B ... 

Our objective here is to try to answer the following questions For a proposed type of gas-liquid contactor compatible with the properties and flow rates of the phases and with the reaction type, what are the likely values of the specific interfacial area and the gas and liquid mass-transfer coefficients by which the contact performance can be predicted And what is the expected accuracy of these values Table XVIII gives typical values of these parameters in typical contactors shown in Fig. 12 for fluids with properties not very different from those of air and water (especially, liquid viscosity under 5 cP where the liquid is nonfoaming). Because this review is especially concerned with the chemical method of determining these parameters, experimental data obtained by this method will be given in subsequent tables and figures. 

Sharma (S35), including the use of organic solvents (such as toluene, xylene, diethylene glycol, and polyethylene glycol) for the measurement of a and by the chemical method. In each case, the reaction between CO2 and selected amines is employed to determine a. For example, values of interfacial areas obtained in a reaction of CO2 with cyclohexylamine in xylene plus 10% isopropanol, in a 10-cm-i.d. column packed with 0.5 in. ceramic Raschig rings, are reported in Fig. 15. A comparison with the values for aqueous systems shows a 50% improvement attributable to the lower surface tension of xylene ([Pg.74]

The chemical method for the measurement of interfacial area in liquid-liquid dispersions was first suggested by Nanda and Sharma (S19). They calculated the effective interfacial area a by sparingly extracting soluble esters of formic acid such as butyl formate, amyl formate, etc., into aqueous solutions of sodium hydroxide. This method has been employed by a number of workers, using esters of formic acid, chloroacetic acid, and oxalic acid, which are sparingly soluble in water (D9, DIO, FI, F2, F3, 04, P8, SI5, S20). Sankholkar and Sharma (S5) employed the extraction of diisobutylene into aqueous sulphuric acid. Sankholkar and Sharma (S6, S7) have also found that the extraction of isoamylene into aqueous solutions of sulphuric acid, and desorption of the same from the loaded acid solutions into inert hydrocarbons such as n-heptane and toluene, can be used for determining the effective interfacial area. Recently, Laddha and Sharma (L2) employed the extraction of pinenes into aqueous sulphuric acid. 

The chemical methods for the preparation of nanomaterial could be categorized as either template-directed or template-free. The template synthesis methods commonly used for the production of one-dimensional nanostructured PANI are further subdivided into hard template (physical template) synthesis and soft template (chemical template) synthesis approach according to the solubility of the templates in the reaction media. Non-template routes for the synthesis of one-dimensional nanostructured PANI such as rapid-mixing reaction method, radiolytic synthesis, interfacial polymerization, and sonochemical synthesis have also been reported [56], Other approaches like combined soft and hard template synthesis are also known. An overview of hard-template, soft-template, and template-free procedures are presented in the following paragraphs. 

This finding suggested, that the deviation between the chemical and the photographic (or other) determination of the interfacial area in plate columns (the chemical method generally provides lower values ) was not due to the material system. One possibility could be the depletion of the reaction component in the gas, which was dependent of the bubble size. Hofer and Mersmann [212] overcome this discrepancy with a relationship, which was related to the gas bubble and pressupposed knowledge of the bubble size distribution (d, was the characteristic diameter of the distribution) and the superficial velocity u ... 

Many researches have synthesized calcium phosphate / organic molecule composites in general, as experimental evaluation on organic-inorganic interfaces is so difficult and complicated, the detailed interfacial interactions have not been elucidated yet. In this study, we adopted a HAp / poly-L-lactide (PLLA) composite and a HAp / glycine composite as model materials to elucidate the interfacial chemical interactions using ab initio calculation method, i.e. discrete variational (DV)-Xo method. 

Hydrophilic coatings have also been popular because of their low interfacial tension in biological environments [Hoffman, 1981]. Hydrogels as well as various combinations of hydrophilic and hydrophobic monomers have been studied on the premise that there will be an optimum polar-dispersion force ratio which could be matched on the surfaces of the most passivating proteins. The passive surface may induce less clot formation. Polyethylene oxide coated surfaces have been found to resist protein adsorption and cell adhesion and have therefore been proposed as potential blood compatible coatings [Lee et al., 1990a]. General physical and chemical methods to modify the surfaces of polymeric biomaterials are listed in Table 40.7 [Ratner et al., 1996]. 

Solid-State Mechanochemical Synthesis Facile template-free solid-state mechano-chemical synthesis of highly branched PANI-NFs with coralloid tree-like superstrueture, via the oxidative polymerization of aniline hydrochloride with FeCl3 6H2O, has been demonstrated [194]. The synthetic yield ( 8%) was comparable to that of the solution interfacial polymerization method. Solid-phase mechanochemical synthesis of branched PANI-NFs was also achieved by using anhydrous FeCl3 as the oxidant [195]. 

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