Rutile nanoparticles decorated onto permanently polarized hydroxyapatite for polypropylene solar photodegradation

The accumulation of microplastics (μPls) in ecosystems has become a serious environmental concern. Despite increasing awareness, the development of efficient technologies for their removal and remediation remains a major challenge. Herein, we investigate the photocatalytic degradation of polypropylene (PP) μPls using nanocomposite catalysts composed of permanently polarized hydroxyapatite microparticles (pp-HAp) and rutile TiO 2 nanoparticles (TiO 2 NPs). pp-HAp, a macroporous bioceramic, is known for its ability to convert gases (CO 2 or/and N 2 ) into small value-added chemical products. While pp-HAp serves both as the substrate and thermocatalytic part of the composite, TiO 2 NPs are incorporated as the photocatalytic component. A series of XTiO 2 /pp-HAp photocatalyts, where X represents the weight percentage of TiO 2 (X = 2.5, 5, 10 and 20), were prepared applying a thermal stimulated polarization treatment. The resulting materials show no formation of undesirable calcium titanate. After thorough chemical and physical characterization, the photocatalytic performance of the XTiO 2 /pp-HAp in the degradation of PP-μPls was evaluated. Under 1 sun irradiation, the process is selective toward ethanol, which indicates the cleavage of consecutive C C bonds along the PP chains, with the highest yield obtained for 2.5TiO 2 /pp-HAp. When the irradiation intensity decreases (0.5 sun), ethanol and isopropanol are produced, suggesting a reduction in the efficiency of the C C cleavage. In all cases, the nanocomposite catalysts exhibit significantly higher yields than TiO 2 NPs or pp-HAp individually, which indicates cooperative electronic effects between both components. Regarding selectivity, in addition to the solar irradiation, the TiO2:pp-HAp ratio also determines which product is obtained. Within the framework of circular economy, our strategy yields added-value chemical products from PP waste using only sunlight and an environmentally friendly catalyst.