A composite of TiO2 rutile with fly ash was prepared by a coupling method assisted with ultrasound irradiation in order to enhance the photocatalytic activity of the semiconductor oxide. The effect of the type of the acid added (acetic, oxalic, citric, and nitric) in the course of the coupling of TiO2 with the fly ash was investigated. The use of acids with carboxylic groups promoted a better integration of the fly ashes into the TiO2 surface, as was revealed from the photocatalytic experiments. Among the different acids tested, the acetic acid promoted the formation of the photocatalyst with the highest photocatalytic activity for the photo-oxidation reaction of nitric oxide (NO) in gaseous phase. For this reaction, the optimal load of fly ash on TiO2 rutile was determined in 1.0% of weight. The selectivity of the photo oxidation reaction of nitric oxide until the formation of nitrate ions (NO3-) was also investigated. The addition of fly ash over TiO2 ruffle had a positive effect in increasing the formation of nitrate ions in comparison with the bare TiO2 rutile. The composite made with affordable raw material represents a potential photocatalyst with low production cost.