Synthesis & Characterization of Caron Nanomaterials from Natural Sorbents

The enclosing and burying of hazardous waste is becoming increasingly unacceptable due to growing concern about the effect of pollutants on the environment and more restrictive environmental regulations. Efficient regeneration systems are required to permit a wider application of carbon adsorption processes and to ensure their economic feasibility. This has motivated companies to develop methods for regenerating and reusing saturated activated carbon. Over the years, a wide variety of regeneration techniques have been suggested and applied. These are based either on desorption induced by increasing the temperature or by displacement with solvents, or on decomposition induced by thermal, chemical, catalytic or microbiological processes. By far the most extensively used technique is thermal regeneration under steam or an inert atmosphere. Unfortunately, the regeneration process is time consuming and after successive heating and cooling cycles, the carbon becomes damaged. The application of microwave heating technology for regenerating industrial waste activated carbon has been investigated, with very promising results. The main difference between microwave devices and conventional heating systems is in the way the heat is generated. Thermal regeneration is conventionally performed in rotary kilns or vertical furnaces, where the carbon bed is indirectly heated by conduction and convection. In the microwave device, the microwaves supply energy directly to the carbon bed. Energy transfer is not by conduction or convection as in conventional heating, but is readily transformed into heat inside the particles by dipole rotation and ionic conduction. When high frequency voltages are applied to a material, the response of the molecules with a permanent dipole moment or induced dipole to the applied potential field is to change their orientation in the direction opposite to that of the applied field. The synchronized agitation of molecules then generates heat. Microwave regeneration offers possible advantages over conventional treatment. These include the rapid and precise control of the carbon bed temperature, a more compact furnace, and energy savings. Some authors have also found that microwave regeneration gives rise to a better performance of the activated carbons in terms of ulterior adsorption capacity and rate of adsorption compared to conventional heating. Consequently, processes based on microwave energy are gaining importance in several fields of application on an industrial scale, and microwave technology is now considered a promising available technology for the regeneration of carbon materials. The aim of this work was to acquire a deeper insight into the thermal regeneration of activated carbons. To this end a comparative study of the regeneration of activated carbons by conventional thermal methods and single mode microwave energy was performed. Changes in the porous texture of the regenerated carbons resulting from the thermal treatment in both devices were studied in relation to

Methylene blue method was used for surface area calculation, which involves following accounting to accomplish surface area measurement, five Standard solutions of Methylene blue were made in concentration range 10 to 100 ppm having same volume. All solutions were made in distilled water. Methylene blue spectrum was obtained with spectrophotometer to find out its λmax, found to be 670 nm; hence a standard calibration graph was plotted between optical density and concentration of Methylene blue. Henceforth, 100 ml variable range (10 to 100ppm) Methylene blue solution + 15 milligrams of

Where, S is the specific surface area (m2/g) of carbon material, Ng is the number of molecules of Methylene blue adsorbed by CNM, A is the surface area of one molecule of Methylene blue (197.2 ˚A2)1, N is Avogadro number (6.02 × 10−23 mol−1) and M is the molecular weight of Methylene blue (373.9 g) 1

In case of sunflower the value of total concentration of Methylene blue left in the solution was 103.597ppm. The initial concentration of Methylene blue was 2000ppm. The difference attributes to the quantity of Methylene blue adsorbed by 15 mg of sunflower seeds based carbon nanomaterial. Using the given formula;

Ng = (2000 – 103.597) X 10 – 6 gram = 1.896 X 10– 3

gram The molecular weight of Methylene blue is 373.9 gram, Moles of Methylene blue = 1.896 X 10– 3/373.9 = 5.071 X 10 – 6 moles 1 mole of a pure compound corresponds to 6.023 X 10 23 molecules, Thus 5.071 X 10 – 6 moles correspond to, 5.071 X 10 – 6 X 6.023 X 10 23 = 3.05 X 10 18 molecules Hence, for calculating surface area we revert to the equation given back,

S = 3.05 X 10 18 X 197.2 X 6.023 X 10 23 / 373.9 X 10 20

S = 96.9 m2/gram

(Initial quantity of precursor- finally obtained quantity of pyrolysed precursor) Hence, the comparative results of microwave and furnace materials which clearly give better performance of microwave irradiated material which is shown in figure 3

The SEM images of the microwave material shown in Fig. 4,5 clearly demonstrate that the material exhibits uniform particle morphologies as well as a highly ordered mesostructure, even though it is obtained using microwave irradiation for only 10 min at 400 0C. The SEM image shows the overall particle morphology

(a)

(c) (d)

(a) (b) (c) (d)

The experimental findings reveal that the sunflower seeds gave the highest surface area per unit weight of adsorbent (96.9m2/gm), while the highest yield (90.10%) obtained by instant carbonization within 10 min using the energy efficient microwave assisted carbonization process as determined by the Methylene Blue method. Thus as far as capacity for hydrogen storage is concerned, sunflower seeds are the best available option due to high specific surface

the above analysis was a great simplification of what may be actual conditions encountered, but to an extent lay the footstone for the further research on usage of plant fibers and oilseeds as potent precursors for nanomaterial preparation and their usage in hydrogen storage, should have great potential for use in applications such as selective adsorbents, catalyst supports and so on.

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Dept. of Chemical Engineering, Bharati Vidyapeeth College of Engineering, Navi Mumbai, (MS) India