Paper-based nanoplatforms for multifunctional applications

In this work, zinc oxide (ZnO) and titanium dioxide (TiO₂) nanostructures were grown on different cellulose paper substrates, namely, Whatman, office, and commercial hospital papers, using a hydrothermal method assisted by microwave irradiation. Pure ZnO and TiO₂ nanostructures were synthesized; however, the growth of TiO₂ above ZnO was also investigated to produce a uniform heterostructure. Continuous ZnO nanorod arrays were grown on Whatman and hospital papers; however, on office paper, the formation of nanoplates originating nanoflower structures could be observed. TiO₂ nanoparticles homogeneously covered all the substrates, in some conditions forming uniform TiO₂ films. Structural characterization was carried out by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Raman spectroscopy. The optical characterization of all the materials was carried out. The produced materials were investigated for multifunctional applications, like photocatalyst agents, bacterial inactivators, and ultraviolet (UV) sensors. To evaluate the photocatalytic activity under UV and solar radiations, rhodamine B was the model-test contaminant indicator and the best photocatalytic activity was achieved with Whatman paper. Hospital paper with TiO₂ nanoparticles showed significant antibacterial properties against Staphylococcus aureus. ZnO-based UV sensors demonstrated a responsivity of 0.61 μA W^-1.