ZnO is an exciting material for photocatalysis applications due to its high activity, easy accessibility of raw materials, low production costs, and nontoxic. Several ZnO nano and microstructures can be obtained, such as nanoparticles, nanorods, micro flowers, microspheres, among others, depending on the preparation method and conditions. ZnO is a wide bandgap semiconductor presenting massive recombination of the generated charge carriers, limiting its photocatalytic efficiency and stability. It is common to mix it with metal, metal oxide, sulfides, polymers, and nanocarbon-based materials to improve its photocatalytic behavior. Therefore, ZnO–nanocarbon composites formation has been a viable alternative that leads to new, more active, and stable photocatalytic systems. Mainly, graphene is a well-known two-dimensional material, which could be an excellent candidate to hybridize with ZnO due to its excellent physical and chemical properties (e.g., high specific surface area, optical transmittance, and thermal conductivity, among others). This review analyses ZnO–graphene nanocomposites’ recent advances, addressing the synthesis methods and the resulting structural, morphological, optical, and electronic properties. Moreover, we examine the ZnO–graphene composites’ role in the photocatalytic degradation of organic/inorganic pollutants.

This work focuses on the synthesis of composite materials based on reduced graphene oxide reinforced with zinc oxide. The zinc precursor concentration was varied, and the effect on the structural, morphological, chemical and photocatalytic properties of the resultant composites was studied. The results show that possible variations in the kinetics of the crystal growth due to the Zn precursor concentration can change the final sizes and morphologies of the ZnO structures anchored in the composite. Two different morphologies, ZnO flowers (rGO/ZnO-flowers) and ZnO rods (rGO/ZnO-rods), were obtained and analyzed. Both composites were synthesized using a microwave-assisted hydrothermal route under the same experimental conditions. They were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and UV-VIS DRS. Both composites presented high adsorption (60–70%) and photocatalytic degradation (ca. 100%) of aqueous methylene blue, which was explained in terms of the excellent coupling between the rGO sheets and the different ZnO morphologies.

A chemical synthesis route for facile, fast and economical production of reduced graphene oxide/zinc oxide composites (rGO/ZnO) via a microwave-assisted hydrothermal method is presented. For a particular concentration (124 mM) of zinc acetate di-hydrate (Zn(CH3COO)2.2H2O) acting as precursor of Zn, different microwave irradiation times of the order of seconds were tested in order to select the more adequate time. Furthermore, with the selected irradiation time (40 s), different concentrations (31, 62 and 124 mM) were then considered and chemical and morphological properties of the obtained composites were evaluated. For their characterizations SEM, EDS, FTIR, Raman spectroscopy and XRD were employed. Experimental results confirm that the proposed synthesis route for the fabrication of rGO/ZnO is efficient, environmentally friendly and cost-effective.

PCBs were used for several decades as coolants, lubricants in transformers, plasticizers, and dielectric fluids, being highly carcinogenic and representing a severe environmental problem in soil and water. Pure and modified TiO₂ has been the most studied photocatalyst looking to degrade PCBs into less toxic products. Lately, ZnO-graphene composites have played an essential role in the photocatalytic degradation of various toxic organic compounds. In this work, ZnO nanostructures were coupled with reduced graphene oxide (ZnO-rGO) via a one-pot microwave-assisted hydrothermal route. As a result, the composites exhibited improved photocatalytic performance for PCBs degradation compared to ZnO nanoparticles. Thus, this research provides an in-situ method to grow different morphologies of ZnO on rGO. Graphical Abstract

In this work the effect of doping with aluminum (Al) and boron (B) an armchair (6,6) carbon nanotube on its sensibility to carbon dioxide (CO₂) for possible application in sensors of this gas was studied. Using first-principles calculations within the framework of the density functional theory (DFT), adsorption energies were obtained in the cases when the molecule is initially perpendicular to the surface of the nanotube, near the dopant atom, and located above a carbon atom of the nanotube, above a C-C bond, or directly above the center of a hexagon. It was found that doping with Al does not improve the adsorption of the molecule compared to the pristine nanotube. However, doping with B slightly favors the adsorption for some of the considered positions. The results suggest that B doping might be an acceptable option in the design and construction of nano devices for CO₂ detection.