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Heterostructured photoactive nanomaterials represent innovative construction to absorb UV and UV-vis light. This feature makes heterostructures exciting candidates for environmental photocatalytic applications such as organic pollutants degradation and removal of heavy metals, among others. Therefore, the efficient design of heterostructures based on thin films of oxide semiconductors will allow obtaining a novel material with outstanding properties. This work presents a review of the current heterostructures based on α-Fe2O3 and CuO thin films, which were deposited onto different substrates using physics and chemistry routes. Moreover, we will discuss the key factors to promote structural and morphology control and the drawbacks such as low absorption of the solar spectra, low active surface area, and charge carrier recombination. Finally, the relevance of the results and future directions of the heterostructures as materials for the purification of aqueous systems were discussed.

In this study, novel zinc oxide-reduced graphene oxide (ZnO-RGO) nanorods have been fabricated on fluorine-doped tin oxide (FTO) glass substrate by the electrospinning process followed by a hydrothermal technique to grow supported nanorods. The ZnO-RGO precursor seed nanostructured layers were made by calcination of electrospinned nanofibers containing polyvinyl pyrrolidone, zinc acetate and different amounts of RGO at 400 °C for 1 h. Then they were used for hydrothermally growth (ZnO-RGO) Nanorods. The effect of amounts of RGO on the properties of ZnO-RGO NRs was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and Photoluminescence (PL). The obtained results evidenced that the coupling of RGO with ZnO improved the photocatalytic activity of ZnO. The ZnO-RGO nanostructure with 1.0 mL of RGO showed the highest photocatalytic activity through degradation of methyl orange (MO) under UV irradiation.

ZnO has been well-known as a significant photocatalyst material due to its high surface area, efficient charge transport, and superior photosensitivity. Even though photocatalysis using bare ZnO NRs is useful in pollutant remediation, two main drawbacks scale down their performance as photocatalysts. First, ZnO NRs absorb mainly the UV light, which compromises a small portion of the solar spectrum, and second, the high recombination rate in the ZnO NRs prevents the path of electron-hole outward and then reduces the photocatalysis efficiency. In this work, ZnO-NRs, ZnO-NRs/Graphene Oxide (GO), and ZnO-NRs/Reduced Graphene Oxide (rGO) array composites were vertically grown on conductive glass substrates of SnO2:F (FTO). The films were synthesized by hydrothermal method using ZnO seed layers deposited by spray pyrolysis technique. The nanosheets of GO and rGO were anchored onto the surface of the as-prepared ZnO-NRs by using the spray deposition technique (SDT). The photocatalytic activity of these materials was studied by analyzing the degradation of methylene orange (MO) in an aqueous solution under ultraviolet light, and we found that the decoration of ZnO-NRs with nanosheets of GO and rGO resulted in a significant enhancement of the photocatalytic degradation efficiency, where ZnO-NRs/rGO are more efficient than ZnO-NRs/GO and the latter better than pure ZnO-NRs.

The light absorption of wide bandgap semiconductors in contaminated water, allows them to promote redox chemical reactions. The foremost condition that ensures success is related to the spontaneous jump in the energy of the photogenerated charge carriers. The jump is from their conduction/valence band energy positions to the oxidizing/reducing levels of those contaminants, which produces the so-called heterogeneous photocatalytic water purification. In this work, ZnO thin films composed by nanostructured nanofibers and nanorods (NRs) were compared to address the drawbacks such as low absorption of the solar spectra, low active surface area, charge carrier’s recombination. These films were fabricated with various coupling and doped materials by electrospinning and hydrothermal techniques on fluorine-doped tin oxide (FTO) glass substrate. First, ZnO/TiO2 films were fabricated using different zinc acetate-to-PVA ratios by an electrostatically modified electrospinning technique and then sintered at 600°C. Second, ZnO doped with nitrogen and silver (ZnO:N-Ag) nanorods films were vertically supported on undoped and N doped ZnO seed layers fabricated with different N:Zn ratio in the solution precursor by a wet chemical method.

In this work, ZnO/TiO2 nanostructures were fabricated by an electrostatically modified electrospinning technique using zinc acetate and commercially available TiO2-P25, polyvinyl alcohol, and a solvent. The ZnO/TiO2 nanostructures were fabricated on fluorine-doped tin oxide (FTO) glass substrate by electrospinning of aqueous solution containing different amounts of zinc acetate. The TiO2-P25 nanoparticles were immobilized within zinc acetate/PVA nanofibers. The precursor nanofibers obtained were converted into polycrystalline ZnO and ZnO/TiO2 by calcination at 600 °C. The structure and morphology of the obtained nanostructures were characterized by X-ray diffraction and field emission scanning electron microscopy, respectively. It was found that the TiO2-P25 nanoparticles were attached to the ZnO nanostructures, and the mean diameter of the nanoparticles forming the nanostructures ranged from 31 to 52 nm with increasing the amount of zinc acetate. The incident photon-to-current efficiency (IPCE) spectra of the fabricated nanostructures were measured in a three-electrode cell. The photocatalytic activities of ZnO and ZnO/TiO2 nanostructures were evaluated toward the decomposition of methyl orange. The obtained results evidenced that the coupling of TiO2 with ZnO enhanced the IPCE and improved the photocatalytic activity of ZnO. Particularly, the ZnO/TiO2 nanostructures fabricated with a zinc acetate-to-PVA ratio of 2:3 exhibited the highest IPCE and photocatalytic activity. Fil: Ramos, Pierre G.. Universidad Nacional de Ingeniería; Perú Fil: Flores, Edson. Universidad Nacional de Ingeniería; Perú Fil: Sánchez, Luis Ángel. Universidad Nacional de Ingeniería; Perú Fil: Candal, Roberto Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín; Argentina Fil: Hojamberdiev, Mirabbos. Turin Polytechnic University in Tashkent; Uzbekistán Fil: Estrada, Walter. Universidad Nacional de Ingeniería; Perú Fil: Rodriguez, Juan. Universidad Nacional de Ingeniería; Perú