Help!! Organic contaminant absorbancy via charcoal, cotton

[trying to understand]

Hi, I am hoping someone could offer some assistance with a chemistry lab I am doing. It is comparing the absorbance of organic contaminants of cotton/cellulose to that of charcoal. We started with two cottonballs that were treated with NaOH for 15 minutes, then rinsed, and then treated it with cyanuric chloride for one hour. We washed them with acetone and then water and dried via vacuum filtration. Then we treated the cotton balls with 100 mL piperazine for thirty minutes in a flask, rinsed, and then dried in vacuum filtration. We also had to dilute a atrazine analog solution(red dye), and determine its wavelength maximum using a digital spectrophotometer. The red dye was 1ppm which we diluted to 1 part dye to 10 parts water. I think we need to determine the wavelength maximum for the charcoal that comes in a few different sizes. How would I go about testing charcoal and cotton balls in a spectrophotometer? Or is that not possible? I just really don't know how to conduct this experiment at all. I am so lost! Any help you can offer would be more appreciated than you know.
Thanks so much,
A Mom who decided to go back to school.