Comparative Study of Adsorption Isotherms Steroidal Anti-Inflammatory Drug Dexamethasone on Carbon Nanotube and Activated Carbon

Abstract

In this research we have studied aimed to compare the adsorption of dexamethasone by two adsorbent; multi-wall carbon nanotube and activated carbon with the help of UV/VIS spectrophotometer Jenway 6505 model. Adsorption chart based on the wavelength of dexamethasone has been obtained and the relevant graph is plotted by considering factor of concentration. Four different concentrations necessary for adsorption of dexamethasone on multi wall carbon nanotube and activated carbon the maximum adsorption rate was determined. Study with on the results, the efficiency of that observation adsorption dexamethasone by multi wall carbon nanotube was more than activated carbon. The results can be useful in biological system and pharmacy.

Introduction

Carbon nanotubes (CNT) discovery by Iijima in 1991¹. Carbon nanotubes (CNTs) are hollow cylinders of graphite carbon atoms. These tubes are on the nano scale (10^-9 m), which is so small that 10,000 of them could fit within the diameter of one human hair. Carbon nanotubes are a new form of carbon with unique electrical and mechanical properties². They can be considered as the result of folding graphite layers into carbon cylinders. Multi walled nanotubes (MWNT) consist of multiple rolled layers (concentric tubes) of grapheme. There are two model, sheets of graphite are arranged in concentric cylinders, e.g., a (0.8) single walled nanotube (SWNT) within a larger (0.17) single-walled nanotube ³. Recent discoveries of various forms of CNTs have stimulated research on their applications in varied fields. The nature of bonding in carbon nanotubes (CNTs) is described by applied chemistry, specifically, orbital hybridization⁴. This chemical bonding is composed entirely of sp² bonds, similar to those of graphite. This bonding structure, which is stronger than the sp³ bonds found in diamond, provides the molecules with their particular strength⁵ . CNTs are the strongest and hard materials on earth, in terms of supple strength and elastic modulus respectively. This strength results from the covalent sp² bonds formed between the individual carbon atoms⁶. As for thermal conduction, the CNT surpasses even that of diamond, reaching almost double the value diamond. Carbon nanotubes (CNT) possess many particular characteristics that promise to revolutionize the world of structural materials resulting in significant impact on our capability to build lighter, higher performance structures for aerospace and many other industrial applications⁷. Dexamethasone is a type of steroid drug known as a glucocorticosteroid. It is a man-made version of a natural hormone produced by the adrenal glands.Glucocorticosteroids have a wide range of actions on many parts of the body⁸ .The ways in which they cause these many different effects aren’t exactly clear. The main effects of dexamethasone and steroids like it seem to be due to their anti-inflammatory properties and their ability to alter immune system responses. For example, dexamethasone helps prevent white blood cells from traveling to areas of the body where they might add to swelling problems (such as around tumors) ^9-10. It also seems to help with the treatment of certain blood cancers (such as leukemia’s) by causing some cancerous white blood cells to commit suicide .We studied adsorption of some drugs on carbon nanotubs ^11-27 The reasons for some of it’s other actions ( such as increasing appetite and reducing nausea ) aren’t as clear. Designated chemically as 9- Fluoro-11,17-dihydroxy-17-(2-hydroxyacetyl)-10,13,16-trimethyl6,7,8,9,10,11,12,13,14,15,16,17-dodecahydro-3H-cyclopenta [a]phenanthren-3-one. The molecular weight is 392.461 g/mol. Its molecular formula is C₂₂H₂₉FO₅. The structural formula is:

Experimental

Substances

Ethanol (purity %96) as solvent,activated carbon and multi-wall carbon nanotube with 95%pure degree, production of neutrino Company.Dexamethasonewith 99% pure degree production ofPharmaceuticalcompaniesdaro pakhsh.

Devices used

In this researcher spectrophotometer UV / VIS Jenway 6505 model England, magnetic stirrer (Heidolph, Mr3001 Model), Analytical balances (Sartorius Model), Filter paper (Albet), were used.

Adsorption experiments

In order to provide dexamethasone solution, twice distilled water was use.multi walled carbon nanotube was used as an adsorbent. First 50ppm of dexamethasone was provided using this sample, some solutions with different concentrations of 4to 12 mg/lit of pure dexamethasone were prepared specific amount of carbon nanotube (0.005gr) was added to flasks containing dexamethasone , as an adsorbent .it was stirred , using a magnetic stirrer for 10 minutes. Then liquid and solid phase were separated by means of a filter paper. The concentration ofdexamethasone was measured by using on spectrophotometer tool adsorption rate, gained for dexamethasone. All tests have been performed at the lab with the temperature of (25 ± 2°C). In a two component system consisting ofabsorber solution, a graph of the concentration of dissolved solid phase qe (mg / g) was dissolved in the solution concentration Ce (mg/L) in an equilibrium adsorption isotherm is expressed. In a liquid-solid adsorption from solution on to the surface of the separation of dissolved solids remaining dissolvedin the solution until the solution reaches the dynamic equilibrium on a solid surface. The Freundlich, Langmuir and Temkin models are employed to analysis adsorption occurred in the experiment. Adsorption isotherms to describe the adsorption capacity to facilitate the process of evaluating the feasibility of the intended application and is useful for the analysis and design of adsorption systems.

Langmuir model

The Langmuir adsorption model is the most common model used to quantify the amount of adsorbs ate on an adsorbent as a function of partial pressure or concentration at a given temperature. This equation expressed by relation.

in this equation, (mg.) is the solution was adsorbed the surface andis equilibrium constant of adsorption and b is the capacity of adsorption in saturated single layer and (Mg.) Is solution in equilibrium state?

Freundlich model

The Freundlich equation or Freundlich adsorption isotherm is an adsorption isotherm,which a curve is relating the concentration of a solute on the surface of an adsorbent, to the concentration of the solute in the liquid with which it is in contact. In 1909, Freundlich gave an empirical expression representing the isothermal variation of adsorption of a quantity of gas adsorbed by unit mass of solid adsorbent with pressure. This equation is known as Freundlich adsorption Isotherm or Freundlich adsorption equation. This model is specified with equation.

In this equation, (mg.) is amount of absorbed material in absorbent surface, K; n in arrangement are adsorption capacity and adsorption intensification.

Temkin model

The Temkin model is linearly represented as equation (3) and generally applied in the form:

Where A and B are the Temkin isotherm constant (L/g) and heat of sorption (J/mol) respectively. R is the gas constant (J/mol/k), b is the Temkin isotherm constant linked to the energy parameter, B, as shown on equation:

T is the absolute temperature in Kelvin.

Results

Table 1 shown the absorbance of dexamethasonein the absent of activated carbon and carbonnanotube in 238 nm wavelength. As seen, table1 shown the amount of absorbance isincreased when concentrations are increased. Table2 shown the increasing absorbance of dexamethasone against the concentrations in the presence ofcarbon nanotube,Table3 also shown the increasing absorbance of dexamethasone against the concentrations in the presence ofactivated carbon.calculatedparameters of these models are shown in Table 4 and The Langmuir, Freundlich and Temkin isotherms of the adsorption process of dexamethasone on AC and CNT are shown in figures 3 to 5. It was observed that the experimental data were well represented by Langmuir Freundlich and Temkin models.

Table 4: Parameters of Langmuir, Freundlich and Temkin isotherms of theDexamethasone on Carbon nanotubes and Activated carbon

	Langmuir				Freundlich				Temkin
	b	q			n					B
Carbon nanotubes	0.36	1.25	0.994		1.59	7.48	0.92		188	0.66	0.896
Aactivated carbon	1.5	3.38	0.996		10.5	4.55	0.82		268	0.36	0.8264

Study of adsorption isotherm

Calculated parameters based on exothermic equations are shown in table 4, As seen, the values of correlation coefficient (R²) for the absorbance ofdexamethasonewith the use of carbonnanotube for Langmuir, Freundlich and Temkin models are 0.994, 0.92 and 0.896 and with the use of activated carbon are 0.996, 0.82 and 0.8264, respectively. The results showed

that the absorbance of dexamethasone on both absorbent is in conformance with Langmuir and Freundlich isotherm.

Conclusion

In this study we compare the adsorptionisotherms of dexamethasone by activated carbon and carbon nanotube. Base on obtained results we conclude that nanotube has moreefficiency in removal of dexamethasonerather than activated carbon.Results of isoth- ermic experiments showed that the correlation coefficient of Langmuir isothermic’s equation for carbon nanotube was more than activated carbon. The values of RL in carbon nanotube and activated carbon were less than 1, indicating that the absorbance is appropriate for both adsorbents. Therefore, in total, it is concludedthat correlation coefficient (RL) in Langmuir isotherm model for carbon nanotube were higher and it’s efficiency in the removal of dexamethasoneis better than activated carbon.