I am currently degrading ethylbenzene with some nanoparticles/photocatalyst and I am using Shimadzu 1800 UV-Vis spec to analyze the degradation. After blank scanning with ethanol and also scanning the ethylbenzene mixed with my photocatalyst in the dark for 45 minutes, I am observing increased absorbance when the light is turned on for the photodegradation of the ethylbenzene mixed with photocatalyst. I need some inputs to guide me on my errors with respect to this experiment. After scanning the ethanol mixed with photocatalyst in the dark and getting its absorbance, do I need to do another auto zero before scanning ethylbenzene mixed with photocatalyst in the presence of light?