Very thin nanogranular zinc oxide layers have been grown using sol-gel synthesis modified by incorporating ammonium acetate with varying content. Ammonium acetate has multiple correlated effects such as thickness reduction from 70 to 20 nm; grains size reduction from 50 nm to 25 nm; and morphology evolution from a dense stacking of grains to a single layer of grains. The potential application to photocatalytic degradation of pharmaceutical materials has been evaluated by carrying out the degradation of amoxicillin antibiotic under UV irradiation. The particular nanogranular morphology of the layers positively impacts the photodegradation efficiency.