Adsorption of Cu2+ using banana peels for pH 2,2.5,3,3.5,4

so basically I did my experiment which is the title. This is my procedure and results:

1. Make 0.05M CuSO4
2. pipette 50ml CuSO4
3. change to respective pH values using HCl
4. Add 2g of oven-dried banana peels
5. wait for half an hour
6. Filter the solution into 100ml volumetric flask
7. add 5ml of 2M HCl to change all replicates to approx. pH 1
8. top up to 100ml mark using deionized water
9. mix well
10. put solutions into cuvettes and place the into the UV-vis spectrometer to measure absorbance
11. compare it with the calibration curve to determine concentration

my 入max was 811.
For those wondering why I made all the replicate the same pH after filtration, it was so that the pH at the end would not affect the absorption value, because I found out that pH changes the colour of the solution.

results:

edit: so the first reading is a blank, the 2nd reading is the absorbance of the pH 2 solution after it has been made to pH 1, the 3rd reading is the absorbance of the pH 2.5 solution after it has been made to pH 1, the other readings are for pH 3,3.5 and 4 (in order). The K*abs value doesn’t matter.

calibration curve:

Does this look right? Cus I can’t find any research papers that do this. The ones that I found do pH 2,3,4,5,6 and use extremely small concentrations of CuSO4, something like 0.0002M. Even if u assume the trend will be the same, my results don’t follow the same trend, which is that the concentration of CuSO4 left in the solution after the experiment decreases as pH increases. Basically it means that at a higher pH, the banana peels can adsorb more Cu2+ ions.