Hello everyone, I have gone through various journal papers of photochemical processes for arsenic and found that several authors talk of 30 min stirring before the UV/Visible lights are 'on'. It is also mentioned that adsorption-desorption equilibrium reaches by this time. My question is how this 'x' min is noted.
In some adsorption processes of arsenic, material 'M' has been tried & adsorption equilibrium was studied typically around 4 hrs.
There is the contradiction: if same material 'M' is stirred with arsenic solution for 30 min without light, how can equilibrium state be reached?
Equilibrium denotes that the rate of adsorption & desorption has become equal.
Hi Roy,
Sorption equilibrium time is a function of various factors such as temperature, initial concentration... etc. Constant concentration of adsorbate (equilibrium) is often attained in the range of 30 to 60 minutes for good adsorbents.
Photocatalysis does not necessarily require typical equilibrium to be attained, rather it requires reasonable mass tranfer rate. Remember, the photo-reaction is heterogeneous (takes place at the solid surface) so, for a start, reasonable amount of reactants should locate the active sites of the photocatalyst (the interest is more on photochemical reaction rather than mass transfer; so the adsorption only need to be enhanced in order not to slow down the reaction step). Based on several research results, 30 minutes is good enough to enhance sorption mass transfer (not necessarily to attain equilibrium). As for arsenic, I have not worked with it before but a good adsobent should not take that long.
I hope you find this helpful.
Regards
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