Hi,
I am doing experiments with biochar for Cr(VI) and at 10 and 20 ppm concentration i am getting negative reading or zero reading with UV vis spectrometer. Also, i am using DPC method and no color development was there which means 100% removal. Then in such case how could I calculate the Ce and Qe (adsorption capacity (mg/g)) as there was no final reading i obtained. I need these two reading to calculate the Langmuir and Freundlich model. Please guide me.
You can either reduce the amount of adsorbent or increase the concentration of adsorbate.
You can either reduce the amount of adsorbent or increase the concentration of adsorbate.
I think you can increase the concentration of adsorbate and applied the same experiment condition. I agree with Mohamed Hasnain Isa.
This means that you got 100% removal, the negative value technically arises because of a problem in the instrument baseline. To capacity in these cases = (Ci-Ct)*V/Weight of the adsorbent. To avoid the negative value (Experimentally) you may increase the Cr concentration or decrease the weight of the adsorbent.
Dear Hany Fathy Heiba Patrick Fotsing Mohamed Hasnain Isa
Thank you for your answers. but my question is how do i calculate the value of qe and ce. Since I am getting 100% removal so shall I avoid these reading from my data? I am working with the range of 10-50 ppm which was pre-decided and so the dose. Now, kindly let me know how do I include 100% values i.e. 10 and 20 ppm to my data and apply it to adsorption isotherm analysis.
Thank you for putting out your query Amita Shakya . I sincerely suggest you to change the initial loading concentration. If you are doing a preliminary experiment to see the effect of Cr(VI) removal with the biochar, I would not suggest you to increase the dosage of the biochar. Rather if I would like to find the trend and be able to model them with the right isotherm fits, I would go for a higher concentration of Cr(VI); again depends on your objective as to what you are studying.
I have faced similar scenarios, where I could not get any absorbance in UV/visible and have repeated the experiments (pH edge or isotherm or kinetics) from scratch. For hexavalent chromium removal, I would recommend the below papers:
Ahmad, M., Rajapaksha, A. U., Lim, J. E., Zhang, M., Bolan, N., Mohan, D., … Ok, Y. S. (2014). Biochar as a sorbent for contaminant management in soil and water: A review. Chemosphere. https://doi.org/10.1016/j.chemosphere.2013.10.071
Kumarathilaka, P., Jayaweera, V., Wijesekara, H., Kottegoda, I. R. M., Rosa, S. R. D., & Vithanage, M. (2016). Insights into Starch Coated Nanozero Valent Iron-Graphene Composite for Cr(VI) Removal from Aqueous Medium. Journal of Nanomaterials, 2016. https://doi.org/10.1155/2016/2813289
Thanks for your query Amita Shakya , I suggested you to increase the initial strength of Cr or decrease the dosage of biochar and do the experiments again.
Dear Amita Shakya ,
I am not sure if I answered your query but after reading your question again, if the data points for 10-20 ppm showed complete removal of Cr(VI) then we include in the isotherm analysis. While modeling for a particular fit, we need to decide then, if we need to include those data points or not.
There are instances where we need to nullify/eliminate the data points to rightly fit an isotherm/kinetic model, making the assumption that particular data point arises from experimental/instrument error.
I am sure you must have published by now. Hope this helped!
Cheers!
Thank you @asif ayub!
Good reference for those starting out on adosrption modeling.
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