Departmental Seminar 2016

Table 2. Inhibition Efficiency of Leaf Extract of Cochlospermum tinctorium various Temperatures





Commonly Used Two-Parameter Isotherms





Table 1: Parameters of the AEI of some Plant Extracts at various Temperatures





Table 1 Cont'd





Applications cont'd





Thank you all
for the audience





THE ADEJO-EKWENCHI ADSORPTION ISOTHERM:
APPLICATION AND CHALLENGES





The Application of AEI




The Challenges
Applicable only to surface coverage data
----- should find equation applicable to solute
uptake, if possible!!!!!!!!
2) Applicable to all data we have worked with so far
……. to find surface coverage that do not fit into the model, if none…………….
3)

As C approaches zero the right hand should approach 1, and not zero !!


= + …….4
 
= + ……..
 
= + . ………6
 
Temkin -2aθ = lnKC …….7
Flory-Huggins log = log K + xlog (1 – θ) ……8
 
El-Awady log = log K' + ylog C ……9
 


Total Available surface for a given Quantity of Adsorbent = 1
Surface Coverage when adsorption occurs = Ө
Available Surface after every adsorption = 1- Ө
Therefore, 1- Ө decreases as concentration increases













Equation (3) is the linearised form of AEI
KAE and b - Isotherm Parameters
........1

.............2
.......3
Equation (2) is the Adejo-Ekwenchi Isotherm (AEI) Equation

The Adejo-Ekwenchi Isotherm (AEI)

Derivation of adsorption isotherm- largely empirical.
The importance and application of any isotherm model is dependent its parameters and mathematical simplicity
The Derivation of AEI
For an adsorption process, the total available surface for a given quantity of the adsorbent decreases with increase in adsorbate concentration.

The difference between the total available surface and the fractional surface coverage at a given temperature decreases with increase in adsorbate concentration (prior to the attainment of maximum surface coverage).

The more the surface coverage the less the available surface.
Therefore, there exist inverse relationship between available surface and adsorbate concentration.
Some Common Isotherms
Two – Parameter Isotherms
Langmuir, Freundlich, Temkin, Flory- Huggins, Frumkin, El-Awady, Dubini-Radushkevich, Hill, etc.

Three- Parameter isotherms
Sips, Toth, Redlich-Peterson, Koble-Corrigan, Khan, etc.

Multilayer
Brunaur-Emmett- Teller (BET)

Why another isotherm?
The world is large enough for all of us



Importance of Adsorption Isotherm
- Adsorption mechanism pathway, surface properties, capacity of adsorbent and effective design of the adsorption system.

for example- mechanism of corrosion inhibition is better understood through the use of isotherm .

Extract Temp R2 Slope Intercept Kads b - Gads
(K) (kJ/mol)
Portulaca oleracea leaves
303 0.9458 0.4991 0.5760 3.7670 0.4991 13.46
307 0.9784 0.3415 0.4174 2.6146 0.3415 12.71
311 0.9836 0.2682 0.3342 2.1587 0.2682 12.38
315 0.9545 0.1920 0.2456 1.7604 0.1902 12.00
Portulaca oleracea roots
303 0.9958 0.0578 0.2246 1.6773 0.0578 11.42
307 0.9697 0.0598 0.2422 1.7466 0.0598 11.68
311 0.9580 0.1048 0.2908 1.9534 0.1048 12.12
315 0.9264 0.1187 0.3154 2.0673 0.1187 12.42
Manihot esculentum leaves
303 0.9384 0.4035 0.5009 3.1688 0.4035 13.03
307 0.8906 0.2291 0.4001 2.5125 0.2291 12.61
311 0.7302 0.2530 0.3106 2.0446 0.2530 12.24
315 0.7729 0.1471 0.2042 1.6003 0.1471 11.75

Extract Temp R Slope Intercept K b - Gads
(K) (kJ/mol)

Manihot esculentum roots
303 0.9477 0.0805 0.1263 1.2375 0.0805 10.85
307 0.8519 0.0647 0.1094 1.2864 0.0647 10.90
311 0.9888 0.0525 0.0891 1.2277 0.0525 10.92
315 0.9827 0.0357 0.0703 1.1757 0.0357 10.94
Cochlospermum tinctorium leaves
303 0.8578 0.0706 0.6008 3.9884 0.0706 13.61
307 0.9664 0.1029 0.5650 3.6728 0.1029 13.57
311 0.9571 0.0433 0.3470 2.2233 0.0433 12.45
315 0.8484 0.1303 0.1916 1.5545 0.1303 11.68
Cochlospermum tinctorium roots
303 0.9844 0.0949 0.1214 1.3225 0.0949 10.82
307 0.9741 0.0988 0.1321 1.3555 0.0988 11.03
311 0.9229 0.1167 0.1598 1.4448 0.1167 11.34
315 0.8775 0.1031 0.1663 1.4666 0.1031 11.52






Presented- PREP 2013 (USA) and Published -www.iosrjournals.org
The two (2) basic applications:-
1 - Determination of isotherm best fit.
2- Determination of adsorption mechanism.
Isotherm Best fit-
- The fitness of adsorption data - commonly based coefficient of determination, R2
- Gads value determine whether the process is physisorption or chemisorption.
- Resolved isotherm best fit for plant extracts
Isotherm model best fit for methanol leaf extract of Securinega virosa as corrosion inhibitor for corrosion of mild steel. Journal of Advances in Chemistry (2014) www.cirjac.com
- Resolution of Adsorption characteristic ambiguity of leaf extract of Hyptis suaveolen as inhibitor of corrosion mild steel. Presented @ SCIR 2014 in Accra, Ghana and published in Jeteas.scholarlinkresearch.com (2015).
Modeling of adsorption isotherm for methanol leaf extract of
Manihot esculentum as green corrosion inhibitor of corrosion
of mild steel in HCl medium. Journal of Corrosion Science and engineering, UK. (In Print)
The use of Adejo-Ekwenchi Adsorption Isotherm Model for the
determination of Isotherm Best fit for Corrosion Inhibition of Mild Steel by Leaf and Stem-Back Extracts of Swientia macrophylla. Accepted for presentation @ FOA 2016 International Conference in Germany ( May, 2016)


Table 4. R2 Fitting for Adsorption of Leaf Extract of Portulaca oleracea


Isotherm Temp R2 Slope Intercept Kads - Gads
(K) (kJ/mol)
Langmuir 303 0.9918 0.5712 0.4384 2.2805 12.20
307 0.9568 0.7464 0.4953 2.0190 12.05
311 0.9794 0.8726 0.5738 1.7400 11.82
315 0.9756 1.3724 0.6481 1.5430 11.66
Freundlich n
303 0.9936 0.7798 0.0925 1.2374 0.7798 10.66
307 0.9919 0.7413 0.0031 1.0072 0.7413 10.27
311 0.9967 0.7310 -0.0739 0.8435 0.7310 9.58
315 0.9981 0.6567 -0.2178 0.6056 0.6567 9.21
El-Awady K' y
303 0.9950 1.3437 0.7194 3.4307 5.2408 1.3437 13.23
307 0.9913 1.1470 0.4657 2.5469 2.9221 1.1471 12.64
311 0.9959 1.0529 0.3026 1.9382 2.0072 1.0529 12.10
315 0.9963 0.8630 0.0407 1.1147 1.0982 0.8630 10.80
Flory-Huggins x
303 0.9895 0.4005 0.3383 2.1792 0.4005 12.08
307 0.9070 0.6093 0.2891 1.9458 0.6093 11.92
311 0.9389 0.8124 0.2348 1.7171 0.8124 11.60
315 0.9515 1.5991 0.2034 1.5973 1.5991 11.94
Temkin a
303 0.9872 1.4185 -1.2501 17.7869 -1.6334 17.37
307 0.9788 1.7146 -1.2645 18.3865 -1.9744 17.69
311 0.9794 2.0084 -1.2672 18.5012 -2.3127 17.93
315 0.9769 2.7702 -1.3236 21.0669 -3.2002 18.50
 
 
Table 3. Values of Activation Energy and Thermodynamic Parameters for Leaf Extract of Cochlospermum tinctorium


Conc.
(g/dm3)
Ea (kJ/mol)
 
-ΔQads
(kJ/mol)
 
+ΔH*ads,
(kJ/mol)
ΔS*ads
(J/mol)
 
-ΔGads
(kJ/mol)
303K 307K 311K 315K
Blank
 
0.1
 
0.2
 
0.3
 
0.4
 
0.5
 
43.76
 
129.86
 
129.83
 
127.18
 
126.83
 
124.49
 
 
173.92
 
170.47
 
153.43
 
138.90
 
128.92
 
41.20
 
126.88
 
126.95
 
124.20
 
123.85
 
122.16
-1.33
 
+2.58
 
+2.58
 
+2.54
 
+2.42
 
+2.34
 
 
18.15 17.79 16.39 13.08
 
16.50 16.24 14.70 11.72
 
15.57 15.43 13.76 11.45
 
15.03 14.65 13.11 11.18
 
14.56 14.36 12.64 11.05
Conc. Inhibition Efficiency
(g/dm3) (%)
303K 307K 311K 315K

0.1 70.79 65.71 50.49 21.03
 
0.2 71.53 67.62 51.48 24.00

0.3 72.27 69.52 52.46 30.00
 
0.4 73.76 70.47 53.46 34.01
 
0.5 74.44 71.42 54.45 38.30

R2 and other error functions- are obtained from linearised forms of the isotherms.

Value of