Dyes adsorption

The dye adsorption experiment was adapted from the studies of Tumlos et al [54]. A stock solution, 500 mg/L, was prepared by mixing a methyl red dye with distilled water. Serial dilution process was used to 

For each adsorption experiment, Posidonia oceanica materials of varying size but of the same mass per set-up were placed inside a circular flat-bottomed flask and mixed with a 100 mL of dye stock solution of known concentration and pH. The flask was agitated at different contact times ranging from 20 min to 120 min. The adsorbent was separated and the remaining solution was centrifuged at 4000 rpm, the absorbance values were then measured. Methyl red concentration was determined from the absorbance values from a Perkin Elmer UV/Vis Spectrophotometer before and after treatment using the following equation  

The amount of dye adsorbed (Q ) on the sample was calculated from the following equation  

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An enlarged view of a crystal is shown in Fig. VII-11 assume for simplicity that the crystal is two-dimensional. Assuming equilibrium shape, calculate 711 if 710 is 275 dyn/cm. Crystal habit may be changed by selective adsorption. What percentage of reduction in the value of 710 must be effected (by, say, dye adsorption selective to the face) in order that the equilibrium crystal exhibit only (10) faces Show your calculation. 

Dye adsorption from solution may be used to estimate the surface area of a powdered solid. Suppose that if 3.0 g of a bone charcoal is equilibrated with 100 ml of initially 10 Af methylene blue, the final dye concentration is 0.3 x 10 Af, while if 6.0 g of bone charcoal had been used, the final concentration would have been 0.1 x Qr M. Assuming that the dye adsorption obeys the Langmuir equation, calculate the specific surface area of the bone charcoal in square meters per gram. Assume that the molecular area of methylene blue is 197 A. ... 

The crystalline mineral silicates have been well characterized and their diversity of stmcture thoroughly presented (2). The stmctures of siHcate glasses and solutions can be investigated through potentiometric and dye adsorption studies, chemical derivatization and gas chromatography, and laser Raman, infrared (ftir), and Si Fourier transform nuclear magnetic resonance ( Si ft-nmr) spectroscopy. References 3—6 contain reviews of the general chemical and physical properties of siHcate materials. 

Surface Area Determination The surface-to-volume ratio is an important powder property since it governs the rate at which a powder interacts with its surroundings. Surface area may be determined from size-distribution data or measured directly by flow through a powder bed or the adsorption of gas molecules on the powder surface. Other methods such as gas diffusion, dye adsorption from solution, and heats of adsorption have also been used. It is emphasized that a powder does not have a unique surface, unless the surface is considered to be absolutely smooth, and the magnitude of the measured surface depends upon the level of scrutiny (e.g., the smaller the gas molecules used for gas adsorption measurement the larger the measured surface). 

The surface grafting of a commercial sheet of poly(ethylene tere-phtalate) was analyzed by ESCA spectra and dye adsorption. The sheets were washed with acetone to remove impurities and then grafted by irradiation for 2 and 20 min. (Figure 9). The blank sample showed no Nls peak in the ESCA spectrum. After grafting the Nls peak increased with increasing grafting time. 

For the two methods, the resulting grafting of functional monomers, e.g. acrylic acid and acrylamide, has been measured by multiple reflection IR spectra, ESCA spectra, and dye adsorption from an aqueous solution of crystal violet. The measurements indicate that the inert surfaces of the polymer substrates are modified by a complete surface layer of the grafted monomers. 

The assessment of reaction kinetics by means of batch tests may be strongly affected by dye adsorption on the biophase and supports. The relevance of the adsorption phenomena of dyes on biophase has been addressed in studies regarding free cells [41], granular support biofilm [24], entrapped cells [11, 18], anaerobic sludge [10,24,31,34] and biological activated carbon (BAC) [42,45,47,48]. They have pointed out that the kinetics may be overestimated if the assessment of the adsorption contribution to the dye removal is not taken into account. Under batch conditions, the dye is fastly split between the liquid phase and the biophase, resulting in a sharp reduction of the dye concentration in the liquid phase until adsorption equilibrium is approached. The rate of dye adsorption must be estimated and ruled out in the kinetic assessment. 

Fig. 1 Mechanism of anionic dye adsorption by chitosan under acidic conditions...

Robinson T, Chandran B, Nigam P (2002) Effect of pre-treatments of three waste residues, wheat straw, corncobs and barley husks on dye adsorption. Bioresour Technol 85 119-124... 

They found the percentage decolorization decrease with increasing bead diameter for all dyes. Adsorption was determined by Ca-ALG beads (without immobilization) and it showed an initial reduction of 20% of the color. The immobilized fungus in Ca-ALG beads showed a low K,lyl. value for the Congo Red, a high K,lyl. value for Acid Orange and almost a constant value for Acid Red 114. They reported that P. chrysosporium was not able to decolorize Acid Green at a concentration... 

The decolorization of diazo dye RB5 by T. pubescens immobilized on stainless steel sponges in a fixed-bed reactor was studied [66]. Laccase production in the presence of RB5 reached its maximum value of 1,025 U/L. They found that decolorization was due to dye adsorption onto the fungus mycelium and dye decolorization by laccase enzymes produced by the fungus. 

Xu et al. have reported a GO/DNA hydrogel with high mechanical strength, excellent environmental stability, high dye-adsorption capacity, and self-healing function... 

The reduction of silver chloride, precipitated in the presence of excess chloride ion, yielded the S-shaped curve typical of an autocatalyzed reaction (James, 25). The initial reaction rate, measured in terms of the reciprocal of the time required to complete 5 % of the total reaction, varied directly as the hydroxylamine concentration and inversely as the chloride ion concentration when the latter was relatively large. The specific surface of the freshly prepared precipitate, as measured by dye adsorption, decreased with aging, and the reaction rate decreased proportionately. 

The dependence of q0 on residence time has been noticed and modeled elsewhere, in the case of zinc and acid dyes adsorption by bone char and activated carbon, respectively (Ko et al., 2002). The following equations were successfully applied ... 

The quantum efficiencies shown in Fig. 27 have been determined with the 568.2 nm beam of a Krypton laser (compare Fig. 25) attenuated to 3 1014 photons/ cm2 s. The field dependence has been measured 4 minutes after contact formation between the dye solution and the virgin crystal surface when the dye adsorption has attained virtually its equilibrium value. The estimate for the dye coverage 6 = 0.4 indicated at the ordinate of Fig. 27 will be explained below. We have added 10-2 N Fe(CN)e to a solution of 10-6 M rhodamine at pH 7 for regeneration of the dye in a 1 electron step as has been formulated in Section 3 above. 

Rattee, I. D., Breuer, M. M. The physical chemistry of dye adsorption. London Academic Press 1974. 

Dye adsorption onto colloidal Sn02 is accompanied in most cases by essentially complete quenching of dye emission. The simplest interpretation is excited-state consumption via rapid electron injection—a suggestion supported by comparative studies with Si02 (an insulator incapable of accepting electrons) in place of Sn02 and confirmed, for several dyes, by measuring product spectra. 

It remains to be determined to what extent the dye adsorption technique is applicable to other substrates. No evidence was obtained for Pseudocyanine adsorption to Mn02, Fe2Os or to pure silver surfaces, although this dye can be bound to mica, lead halides, and mercury salts with formation of a /-band (61). Not only cyanines but other dye classes can yield surface spectra which may be similarly analyzed. This is specifically the case with the phthalein and azine dyes which were recommended by Fajans and by Kolthoff as adsorption indicators in potentio-metric titrations (15, 30). The techniques described are also convenient for determining rates and heats of adsorption and surface concentrations of dyes they have already found application in studies of luminescence (18) and electrophoresis (68) of silver halides as a function of dye coverage. 

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