Sunlight mediated enhanced photocatalytic activity of TiO2 nanoparticles functionalized CuO-Cu2O nanorods for removal of methylene blue and oxytetracycline hydrochloride.

Metal free heterojunctions have shown promising applicability as potential photocatalyst materials. Like the commonly explored metal-non metal heterojunctions, semiconductor-semiconductor junctions are also capable of facilitating charge separation and improved lifetimes, leading to augmented surface reaction efficacy. However, unlike the metal carrying heterojunctions, they are much economical and easier to fabricate and tune. Through this study, we present a facile one step hydrothermal route to synthesize CuO-Cu2O nanorods/TiO2 nanoparticles heterostructures (CTHS) with their potential application as a low cost photocatalytic alternative. The average size of the synthesized heterojunction components, as estimated from transmission electron microscopy (TEM) evaluation was 13 and 5 nm respectively for the nanorod length and width, while the functionalizing TiO2 nanoparticles were averaged around 10 nm. Heterojunction formation was confirmed using Raman spectroscopy, X-ray diffraction, high resolution TEM, and elemental mapping. X-ray photoelectron spectroscopy data marked with presence of Cu+ and Cu+2 state of CuO in CuXO-TiO2 also supported junction formation. Optical characteristics of the heterojunction were studied using UV-vis diffuse reflectance spectroscopy and photoluminescence spectroscopy. Compared to TiO2 nanoparticles, CTHS exhibited superior sunlight-induced photodegradation activity. CuXO/TiO2 heterojunction could also remediate toxic waste water containing model antibiotic residue (Oxytetracycline hydrochloride, 0.4 mg/mL) and organic pollutant (methylene blue, 10 µM) in 20 and 60 min respectively. Ultra-fast degradation using a nonmetal heterojunction nanohybrid, like ours, finds negligible mention in literature. Improved visible light absorption and reduction in recombination rate for CuXO-TiO2 nanohybrids were ascribed as major contributing factors towards their enhanced photocatalytic potential. The charge separation mechanism for nanohybrids has been studied and elaborated in detail.