Calculation values of probability sticking(S*) and apparent

activation energy (AAE) from adsorption of some aromatic

carboxylic acids on the surface of a new adsorbed substance

Khaleel – Ibrahim -A- Alniemi

Department of chemistry, University of Mosul, College of education for a pure science, Iraq

dr.alnime@gmail.com

Abstract—The research including the calculation of a potential sticking probability (S*) and apparent activation energy by

adsorption of some aromatic carboxylic acids using the clay collected from sand winds which arrived to Mosul city as a new

adsorbed substance, the results give indicates that the physical adsorption was happened which favorite by applying a modified

arrhinuss equation through values of (S*) and (AAE) with low value and negative charge, the adsorption process happened by

mechanism with two steps, the effect of concentration and temperature was studied as well as the substituted groups (OH, NO2,

NH2) on the nature of binding between the acidic organic anions and inorganic metal oxides to formation surface complex model.

The additional new original study by using the acidity function in different temperatures to modify the arrhinuss equation.

Keywords: probability sticking , apparent activation energy , adsorption , clay

Introduction The society facing a large problem to obtain an active method to remove pollution, the adsorption is an important

method and suitable to remove the pollution (Langmuir, 2007) because of the simplicity of doing and low of cost

(Choy.K.K.H,et al 1999)

The benzoic acid is used in food industrial (Xin.X,et al 2011) and harmful for the human health (Andreozzi-R, et al

2003) (Memcorthy.J.J.et al 1997). The clay as adsorbed substance from rocks origin have poly metals (Durrant.P.J

1986) (Copper.T.W,1987)and different inorganic materials containing a polarity negative charges (Tamura.H et al

2003)as active sites attractive positive ions by physical forces called physical adsorption as well as the clay mixed

easily with water, the chemical adsorption happens when the surface containing A non-saturated electrons material, studying the mechanism of adsorption is an important point to introducing ideal

adsorption systems with a low cost. Using values of the probability of sticking (S*) and apparent activation energy

(AAE) gives important information about the adsorption system, the limited values of (S*) refers to the type of

adsorption while the (AAE) refers to favorites temperature needs to achievement the adsorption process instead of

studying thermodynamic functions. This research describes briefly mechanism of adsorption by means transition of

ions from solution to the surface forming surface complex model between these ions and metal oxides.

Experimental 1-Chemical: The chemical used without additional purification from (fluke) and (BDH). Chemicals and there Symbols

A-Benzoic acid (BA). B -Para hydroxy Benzoic acid (PHBH). C -Orthe nitro Benzoic acid (ONBA). D -Orthe amino Benzoic acid (OABA). E-Sodium hydroxide. F -Potassium hydrogen phthalate. G -Distilled water.

H -Ethanol. 2- The new absorbent (clay) which collected from sand winds which arrived to Mosul city by using a cleaned and

dried plastic containers with (60) cm diameter which conducted on it process of sieve using a sieve with (75)

micrometer. The clay was dried and measurement the surface area which amounted to (3434)cm2/gm by using

device (plaine) in a technical institute department of chemical industries as well as study the component of clay by

using x-ray appearance type (PAN analytical 7602 EA, Almelo) in Badush cement factory which listed in table [1].

Table 1. The components of clay

3-Preparation of solutions:- The prepared of a standard solutions for (BA, PHBA, ONBA, OABA) by using mixture solvent of 95% distilled

water and 5% ethanol for a required concentration and (0.1, 0.01) molar solutions for sodium hydroxide which

adjust their molarity before using it by titrated with solution of potassium hydrogen phthalate and ph.ph as indicator

to determination the concentration of a residual acid.

4-Used the one-batch method to introduce adsorption process with different concentration of acids and adds equal

amount of clay and shaking the solution continuously by rate (100 cycle/min) in shaking water bath.

5-The optimum conditions for adsorption process was founded as followed: A-The weight of clay used =0.06 gm. B-Concentration of acids =5x10-3 molar C-The favorite pH = natural pH for each acid D-contact time for each acid with percentage of adsorption tabulated in table 2.

Table (2).Contact time and percentage of adsorption for acids on clay surface at 25 C°

The increasing of temperature increases the values of adsorption percentage by (3-6%) only when the temperature

arrived to 60 C°.

E- To obtain the values of (S*), the adsorption process was studied at different temperatures (20-60) C°. F- To find the concentration of acids after adsorption process by difference between the initial and residual

concentration by using spectrophotometric and titrimetric methods.

G- Calculation the coverage on the surface, (S*) and AAE.

The values of coverage calculated as following at different temperature:-

θ = (1- 𝑪𝒆

𝑪∘ ) ------------ (1)

𝑪 ∘ = The initial concentration (mole/ liter)

𝑪𝒆 = The residual concentration (mole/ liter)

S* = (1 - θ) 𝒆− 𝑬𝒂

𝑹𝑻

Ln (1 – θ) = ln S* - 𝑬𝒂

𝑹𝑻

When draw Ln (1-θ) at (x) axis and 𝟏

𝑻 at (y) axis gives intercept (Ln S*) while slope equal

−𝑬𝒂

𝑹 which gives (AAE).

8.5 PH

37.36% CaO

19.71% SiO2

5.91% AL2O3

3.47% MgO

1.89% Fe2O3

0.48% SO3

% Adsorption Contact time

(min)

Acid

82 30 BA

76 50 PHBA

92 30 ONBA

74 40 OABA

6- The Instruments:- A- Vibrator water path programming type (Julabo sw 23) for the purpose of adjust the temperature through

adsorption process. B-Electrical oven type (Memmert) to dry the clay at 100 C°. C-Double-beam spectrophotometer (schimaduz) model UV-1800.

Result and discussion The modified Arrhenius equation(Michael.H.J et al 2003) that relate to surface coverage (θ) very important in order

to get an additional support to confirm a physical or chemical adsorption happened or both and which one was

predominate in adsorption process as follows:

S* = (1 - θ) 𝒆− 𝑬𝒂

𝑹𝑻 S*= potential sticking probability. E= Apparent Activation Energy (AEE).

θ = Amount of coverage.

The (S*) calculated from experimental results to obtained the coverage for each concentration using different

temperatures. The possibility of sticking as a function to system (adsorbed/adsorbent) it look in consideration

where it should be this value in range (0<S*<1) and it depend on the temperature of adsorption system. The value of (S*) describe measured potential of adsorbent substance to stay on clay as followed: S*>1 the adsorbent substance non-sticking on the adsorbed. S*=1 the liner relationship of sticking between the adsorbed and adsorbent. Substance for a mixture of physical and

chemical adsorption is predominate. S*=0 sticking happened on adsorbed substance and the chemical adsorption is predominate. 0 < S <1 the favorite sticking for adsorbent substance on the clay and the physical adsorption is predominate. The (AAE) is values with negative or positive sign these values aren't the real activation energy. In this study the (AAE) values give only description that only the adsorption process favorite at lower temperature

to remove the aromatic acidic molecules and exothermic, the lower negative value for (AAE) gives suggestion that

the adsorption is a controlled diffusion process controlled, by this study no needs to obtain thermodynamic

functions. The best value for (S*) when gives value less than one, this refer gives a high physical adsorption for ions on surface

and we can recover the adsorbed substance.

Table (3, 4, 5, 6) values of (S*) and (AAE) FOR BA, PHBA, ONBA, OABA at different concentration on the

surface of clay.

Table3. (BA) Table 4 (PHBA)

Table 5 (ONBA) Table 6 (OABA)

R2 AAE(Kj/mole) S* Conc(M)

0.99 -6.575 0.0175 0.005

0.89 - 1.247 0.2577 0.007

0.97 - 0.916 0.3664 0.009

0.96 - 0.734 0.3942 0.011

0.97 - 0.664 0.5094 0.013

R2 AAE(Kj/mole) S* Conc(M)

0.98 - 4.548 0.028 0.005

0.96 - 2.367 0.1396 0.007

0.92 - 2.202 0.1925 0.009

0.88 - 1.747 0.2795 0.011

0.90 - 1.136 0.2559 0.013

R2

AAE(Kj/mole) S* Conc(M)

0.97 -29.488 611×10-9 0.005

0.93 -4.568 0.0480 0.007

0.98 -2.547 0.1590 0.009

0.99 -1.397 0.3078 0.011

0.99 -0.961 0.4043 0.013

R2 AAE(Kj/mole) S* Conc(M)

0.99 -7.423 0.0125 0.005

0.99 -2.749 0.1460 0.007

0.99 -1.654 0.2878 0.009

0.99 -1.192 0.3905 0.011

0.99 -0.835 0.4885 0.013

The results tabulated in table (3, 4, 5, 6) for acids (BA, PHBA, ONBA, OABA) at different

concentration for each acid used different temperatures upon each concentration between (20-60) C°.

The results from tables give the following conclusion:

1- The values of (S*) for most acids more than zero and less than one this indicates that the physical adsorption was

predominate and favorite for adsorbent substance on adsorbed (Michael.H.J et al 2003) (Mekhemer .G.A.H, etal

2005).

2-Increasing the concentration of acids solutions leads to increase (S*) values in which the physical adsorption

converted to a mixture of physical and chemical adsorption when the values of (S*) near to unite one while at the

dilute concentration the ions easily arrived to surface of clay continuously, because of availability of active site on

clay and no competition between the ions, at this point the mechanism of chemical adsorption predominates.

3-The values of (AAE) are negative with low values these indicate that the acidic solution favorite the lower

temperature in adsorption process, these values decrease with increasing of concentration and the large decrease in

values give indicates that the adsorption process was a controlled diffusion process and exothermic (Michael.H.J et

al 2003) (Mekhemer .G.A.H, etal 2005) (Karamen.M.E,et al .2001).

4-The important attention notice in results are when the increasing of concentration the values of (AAE) converted

from high negative values to lower negative values, this means that the value arrived to

zero, because the increasing in concentration leads to increasing a molecular association (Pimental,G.C,1960).

5-When considering the effect of substituted groups on the values of both (S*) and (AAE) for acids at optimum

concentration reaches to a general conclusion that the values of (S*) less by the effect of substituted groups

according to the following sequence:

We notice that (NO2) as electron with drawing group, published the negative charge increase the stability of anions

(Bray.L.G,ET AL 1957) and ionization of acid while the amino and hydroxyl groups localize the negative charge

decrease the stability of anions and ionization, the both acids have a physical adsorption while (ONBA) closed to a

chemical adsorption compared with (BA) which have (ka) more than (PHBA) and (OABA) and have a physical

adsorption.

And for clarification the effect structure formula of acid on the adsorption mechanism, it means how the acidic ions

and solvent binding with the surface of clay, and for more details study of adsorption so we can show that this

system consists of three components, first, the ions and molecular of acid, second, the surface of clay which contains

several metal oxides as showed in table (1) which make the surface more polarity by contains negative charge,

which regarded of an important factor to describe the mechanism of adsorption, the aluminum oxide have more

polarity than other metal oxides (Bray.L.G,ET AL 1957) (Felmin.H.L,1986) and acidic position more response for a

polarity compounds (Felmin.H.L,1986).

The third component is solvent (water) which affected on both (acid and clay) (Kovacevic.D,et al 1998)

(Luiz.N,2004) (Joan.T,et al 2010), when the clay mixed with acid solution the first step of mechanism is changing

charges of surface from a polarity negative to a polarity positive by water molecules (Luiz.N,2004) (Joan.T,et al

2010)and (H+) ions from the ionized molecules of acid as followed:

Surface of metal oxides = M-O¯

≡ M-O¯ + H2O → ≡ M-OH --------1

≡ M-OH + H+ → ≡ M-OH2 + -------2

This step is a first step for adsorption process The presence of acids anions (RL¯) for carboxylic group after ionization gives, the second step of adsorption:

≡ M-OH2+ + HL¯ → ≡ M-OH2

+ ------ ¯ LR -----3

Where RL¯ = anione

BA > PHBA > OABA > ONBA Acids

0.028>0.0175> 0.0125>611×10- S* -4.548 >-6.575 >-7.423 >-29.48 AAE 6.3×10-5>2.6×10-5>1.6×10-5>670×10-5 Ka

The anions of carboxylic acid transition from solution to adsorbed with a new polarity positive charges on the

surface of clay. The second effect of water in solution itself when associated with acid molecules and anions by

hydrogen bonding (Pimental,G.C,1960) producing ionic atmosphere which decrease the transition of anions. To confirmation the sharing of (H+) in the mechanism of adsorption the acidic function (pH) measured for a solution

before and after adsorption for all acids and tabulated in table (7)

Table (7). Acidity functions before and after adsorption for acids

We notice from table (7) increasing of (pH) after adsorption, this confirms the transmitted of (H+) from solution to

surface of clay. The three steps of mechanism are an important key for the association between the organic

molecular and inorganic surface (Joan.T,et al 2010).

The values of AAE in this equation equal the amount of required energy to produce the adsorption process the

negative charge of AAE gives indicates that the adsorption process favorite the low temperature for solution and

exothermic and spontaneity .This study try to arrivals to a simple method for transition of positive and negative ions

from acid solution to surface we noted that the AAE for BA , PHBA closed to them different than ONBA ,OABA

the modified of arrhinuss equation to obtains Kn* and AAE represent a simple addition to literatures. The shapes of surface complex models (scm) formation for acids and clay.

1 – BA PHBA: The main shape of (scm) produced from a physical adsorption as following.

2- ONBA: This acid have a (scm) with two-polarity position.

Δ pH pH after

adsorption pH before

adsorption Acid

1.18 5.12 3.94 BA

1.21 5.20 3.99 PHBA

0.81 3.61 2.80 ONBA

1.57 5.17 3.60 OABA

3- ONBA: this acid contains two groups after ionization in solution (acidic) and (basic) (Dipole) with follows

mechanism:

The presence dipole in molecules gives several mechanisms, and hydrogen bonding between NH3+ from one

molecule and (COO - ) from another molecule(Pimental,G.C,1960).

The adsorbed ions arrangement from the surface by two static layers (no moving) the first ( OH2+ --- OH2

+ ---

OH2+)(3 molecular thicknesses and the second layer (organic anions) as will as the third moving layer consist of

solvent and non-ionized molecules of acid or positive and negative ions non adsorbed, the results agreement with

literature (Karamen.M.E,et al .2001) (Richard.T.A,et al 1939) (Khaleel.I.A,et al 2004).

Conclusion Most acids favorite the physical adsorption and the increasing of concentration caused increasing of (S) values this

leads to convert the physical adsorption to chemical adsorption, the values of AAE and its sign are important to

describe the thermodynamically functions directly and this type of adsorption system favorites a low temperature in

adsorption or happened spontaneously, we noticed effect of substituent on the adsorption of acid on clay and the

natural acidity function for each gives high percentage of adsorption as well as the presence of water as solvent

effect on the charges of clay surface.

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