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The purpose of this work was to explore the application of low frequency ultrasound for the desorption of 4-chlorophenol (4-CP) from saturated granular activated carbon (GAC) in a continuous flow ultrasonic reactor. The effects of operating parameters such as the amount of adsorbent, intensity of ultrasound irradiation, temperature, flow rate of de...
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... adsorption kinetics of 4-CP onto virgin GAC and ultrasound regenerated activated carbon after three cycles of adsorption-regeneration are presented in Fig. 11. From this figure, it clearly appears that adsorption capacities of the activated carbon regener- ated by ultrasound and that of the virgin carbon remained the same. This indicates that recovery of the initial adsorption capacity of activated carbon was attained and regeneration of GAC was ...
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... scanning electron microscopy (SEM) technique was employed to observe the surface physical mor- phology of the activated carbon. Fig. 1(a) and (b) shows the SEM images of GAC surface at 400× and 4,000× magnification, respectively. These photographs clearly reveal the surface texture and different levels of poros- ity of the carbon. The carbon looks like a random pile of crystallized blocks of various sizes and ...
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... of 4-CP from GAC was investigated using a mixture of 10% (v/v) ethanol and 0.05 M NaOH as desorbing solution at different flow rates in the rage of 3-10 mL/min. Fig. 10 reported the desorption results obtained in a mixture of ethanol and sodium hydroxide. Desorption was improved when a mixture of ethanol and NaOH was employed as desorbing solution. This might be due to the lowering of cavitation threshold and the creation of repulsion forces between activated carbon surface and 4-chlorophenolate anions. Additionally, it was remarked that the desorption of 4-CP from GAC increased with increasing the volumetric flow rate of the desorbing solution, especially at a volumetric flow rate of 10 mL/min. ...
Citations
... [3] Regeneration of exhausted GAC can be done chemically by applying several processes such as regeneration with liquid water, [4] NaOH regeneration, [5] organic solvents regeneration [4] such as ethanol [6] and acidic ethanol, [7] regeneration with supercritical fluids, [4,8] electrochemical regeneration, [9] and oxidative regeneration. [10] Apart from the methods cited above, GAC can be regenerated also with microbiological, [11] ultrasonic, [10,12] microwaves, [1] and vacuum methods. [4] These regeneration methods suffer from several disadvantages, such us requirement of high energy, loss of carbon, high cost of regeneration, and low regeneration efficiency. ...
The use of d-limonene as a green solvent to regenerate granular-activated carbon exhausted with phenol in batch was investigated. The effect of experimental conditions was studied for both d-limonene and acetone. The obtained results using d-limonene show lower efficiency comparing to acetone. However, mixing d-limonene with acetone seemed to be more effective, the percent desorption reaches 85 using 100 ml of acetone/limonene mixture (80/20 vol%). The recovery of regenerated carbon adsorption capacity using solvents mixture was not complete, a part of surface is still occupied by d-limonene, then it would be important to improve a process to remove it.
The effluent of textile industries containing synthetic dyes contributed to substantial pollution to water bodies. The biosorption process of Congo Red dye was successfully performed by integrating ultrasonication in the adsorption step with spent brewery yeast as a novel and renewable biosorbent. The adsorption process was hindered when ultrasonication was employed together with the biosorbent, indicating that desorption process had occurred. The adsorption process showed that 4 g/L of biosorbent was the optimum dosage for adsorption of 50 mg/L of Congo Red dye, and that the adsorption equilibrium fitted to the Langmuir model, with kinetics best fitted with pseudo-second order model. The maximum capacity of the adsorption was 52.6 mg/g, showing the potential of spent brewery yeast to aid in removing wastewater pollutants. Maximal Congo Red dye recovery (100%) was achieved in the sonication-assisted desorption studies using 0.01M NaOH as the eluting agent. The ultrasonication effects contributed to the efficient recovery of dye and good conversion of spent brewery yeast to biosorbent can be beneficial for treating pollution from textile wastewater.
For the last two decades, application of ultrasound in materials synthesis has been a very promising topic especially for the fabrication or modification of various nanomaterials. Simplicity, high efficacy, short reaction tenure along with power saving features are responsible for the popularization of sonochemistry. The physical phenomenon essential for sonochemical process is largely accepted owing to acoustic cavitation, involving formation, growth, and implosive collapse of the micro-bubbles inside liquid. The resulting hot spots/microjets generate very high temperatures ~5000 K and high pressure ~150 MPa due to collapsing bubbles within a nanosecond, with high cooling rates exceeding 10¹¹ Ks⁻¹ at the local reaction centre, providing necessary activation for faster kinetics. These extreme reaction conditions are not typically attainable through conventional synthesis techniques, generating smarter systems with unique properties. Subsequently, ultrasound techniques have been massively employed in graphene preparation along with its dispersion in various solvents which otherwise requires several days with poor yield using conventional techniques. Graphene has been the material of the millennium owing to its unique large surface area, high charge transport features and mechanical properties and widely employed in nearly every aspects of modern technology. Ultrasonic irradiation offers tuning of graphene layer thickness also. Even oxidation to graphene oxide and subsequent reduction to reduced-graphene oxide at faster kinetics are possible without the use of any external redox agents. Besides, thin-layered functionalized graphenes has been achieved by sonochemistry. Ultrasonic treatment provides scope for direct exfoliation of graphite to graphene layers in presence of suitable intercalating/stabilizing agents with substantial dispersion stability. In addition, various geometries such as scrolled graphene, ribbon or foam graphenes can be purposefully designed. Even smooth and rough edged graphenes have displayed unique implications in energy storage, catalysis, biomedical and other technological fields. Ultrasonic-assisted synthesis of various graphene based composites lead to more homogeneous with diversified nanostructures formation like core-shell, nano-discs, nano-platelets, etc. along with specific deposition at the graphene edges have become feasible. This chapter provides comprehensive fundamental concepts of sonochemistry with first hand outline on the sonochemical/ultrasound assisted synthesis of graphene and its various derivatives. Moreover, the ultrasound assisted-dispersion, exfoliation of graphenes and formation of various graphene-based nanocomposites has been emphasized. Important tuneable sonochemical parameters including ultrasound frequency, input power, sonication time, type of sonication probes, etc. have been highlighted to provide an overview of the topic.
