I analyzed adsorption of NO3- ions by using a surfactant treated biochar as an adsorbent.
650 ml of NO3- soln with initial NO3- conc 50mg/L was taken and 1.625g of adsorbent was added (based on optimum dosage 2.5 g/L) and shaken for 03 hours and sample soln was taken out at intervals and filtered and samples were analysed on IonChromatograph. The data and graph obtained are attached. Does this graph seem acceptable as an adsorption capacity vs. contact time study?
In Adsorption studies, q basically represents efficiency of adsorption which is expressed as q=(amount of adsorbate adsorbed in mg)/(amount of adsorbent used for adsorption expressed in gm). In the above question we have initial concentration Ci as 1 ppm or 1 mg/L and final concentration (Cf) as 0.01 ppm or 0.01 mg/L of copper solution. The volume is 25 ml and amount of adsorbent used(in this case magnetic nano particles) is 0.01 gm.
Now we use the formula q=[(Ci-Cf)*V] / W. ( also with courtesy to one of the responses above from Mr Obeagili Omeugochukwu :)
Here Ci=10 mg/L, Cf=0.01 mg/L, V=25 ml or 0.025 L, W=0.01 gm.
Putting these values in the equation we get,
q=[(10-0.01)mg/L * 0.025 L]/0.01 gm or
q=[9.99 mg *0.025]/0.01 gm {Note that the L gets cancelled} or
q=[0.24975 mg/0.01 gm] or
q=24.975 mg / gm
Thus 24.975 mg of Cu ions are adsorbed by 1 gm of Magnetic nano particles. This q value you have got for the contact time of 30 minutes.
You must do a contact time study for 5, 10, 15, 20, 30, 45, 60, 120, 180,.... and so on minutes. Find the q values for all the contact time.Plot q vs time. You will find that a particular time your q value saturates. That is your qe or q at equilibrium. [Note that the initial concentration should be same for all the sets]
The qt will correspond to q values for the respective time t.
For determination of equilibrium time:
you have to prepare set of suspensions,(Cu2+ solution with magnetic nanoparticles). after that you have to agitate the system. while agitating the system you have to remove, set of suspension. Then filter or centrifuge it and analyse for residual metal concentration. likewise remove another set of suspension at desired time intervals (I recommend you to use 5 min intervals). after that plot a graph "q" vs "t". from that graph find the time that "q" value become constant.
this time is the equilibrium time. amount adsorbed at that time is the experimental "qe"
For kinetic model interpretation:
use "q" value until it reach equilibrium. then plot a graph according to the equations mentioned in my 1st comment.
Pseudo first order plot you graph
ln(qe-qt ) vs t
Pseudo second order
1⁄(qt) vs 1/t
by analyzing kinetic data we cannot say any thing about isotherm. for Isotherm study u have to use different initial Cu2+ confrontations.
At equilibrium time remove suspensions and analyse for residual metal concentration.
Then plot your data according to these equations.
Langmuir isotherm model
1⁄qe= 1⁄(bq0 Ce )+1⁄q0 : (1/qe Vs 1/Ce)
Freundlich isotherm
lnqe= lnk+ 1⁄(n lnCe) : (lnqe Vs lnCe)
use these linearized equations when the R^2 is higher that 0.95 usually we say tha adsorption process follows relevant model. if not we have to accept the model which has the higher R^2 value
Tariq Mehmood The wavy line at the end is likely due to outliers. try measuring triplicates. If the data points are "averaged" or are mean result, I suspect two points from the last point are outliers. you can remove one of them using the outlier GraphPad online calculator that uses Grubs's test
https://www.graphpad.com/quickcalcs/Grubbs1.cfm
But for two points, try the ROUT method available in the GraphPad software
Another thing, the "climbing stage" of adsorption kinetics is very important (see attached pic) to assess the best model (either PFO, PSO or others). Try to get at least two points, say 2 and 4 minutes, if possible.
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