Given the toxic nature of many volatile organic compounds (VOCs) present within indoor settings, it behooves the building engineering community to develop control strategies for contaminant removal to mitigate health impacts and improve well-being within indoor building environments. Photocatalytic paints belong to a class of technologies potentially used to obtain self-cleaning wall surfaces for air decontamination within building environments. They offer a promising solution for the building engineering industry involved in paint manufacturing processes to produce paint formulations that limit indoor air pollution and consequently individual exposition of inhabitants. In this work, we report on the uptake efficiency of m-xylene on one reference paint and three mineral paints impregnated with a photocatalytic agent, namely, a conventional photocatalyst containing 3.5% of nano-TiO2 and two new nano-TiO2 photocatalysts coated with polyethylene glycol (PEG 3350) and a hybrid cellulose nanocrystals–nano-TiO2 (CNC) containing 3.5% and 0.5% of nanoparticles, respectively. The photocatalytic degradation of these paints under UV irradiation and the consequent VOC emissions were assessed to evaluate the photocatalytic stability of the nano-TiO2 photocatalytic paints. The experimental results shown neither photocatalytic activity nor VOC emissions for the reference paint containing exclusively micro-TiO2 (that is, no nano-TiO2 material) particles under given experimental conditions. On the other hand, the results showed that the paint containing CNC nanoparticles (NPs) had only a finite photocatalytic effect that was likely due to the low quantity of the nano-TiO2 photocatalyst present within the paint formulation matrix. Furthermore, it was observed that the paints containing nano-TiO2 and PEG 3350 NPs resulted in an important photocatalytic activity that, unfortunately, led to consequential VOC emissions resulting from the polymeric matrix photo-oxidation reactivity under the given experimental conditions employed. Overall, the experimental results indicate that the paint containing PEG 3350 NPs had a greater photocatalytic activity than the paint containing the nano-TiO2 particles. Further, it was observed that the VOC emissions of this PEG 3350 paint decreased with the aging time (28% and 10% for 500 hours and 1000 hours of aging, respectively). Based on these results, the PEG 3350 photocatalyst integrated in mineral paint is a promising indoor air decontamination engineering solution.