No abstract

Photocatalytic materials can perform oxidative and reductive reactions over their surfaces when excited with light. Intrinsic characteristics of the material such as superficial area, morphological structure, and crystalline phase exposition play a fundamental role in the corresponding reaction paths. However, especially in doped semiconductors, as ZnO:N, less is known about how the synthesis parameters affect the morphologies and the photocatalytic activity simultaneously. To solve this issue, ZnO and ZnO:N samples were obtained using microwave-assisted hydrothermal and modified polymeric precursor methods of synthesis. Samples morphologies were characterized by TEM and FE-SEM. Crystallographic phases were observed by XRD and optical characteristics by DRS. XPS results confirmed the doping process. Degradation of Rhodamine-B and Cr(VI) reduction were employed as probe reactions to investigate their photocatalytic activity. Although the crystallographic structure of these powders maintains the ZnO hexagonal wurtzite structure, the optical properties and morphologies, and photocatalytic activities present different behaviors. Also, density functional theory calculations were employed to determine the specific features related to electronic structure, morphology, and photocatalytic activity.Different synthesis methods produce a singular behavior in the physicochemical properties of materials, and the doping effect produces various modifications in RhB degradation and Cr(VI) reduction for each synthesis method. Crystal face exposition and morphologies are related to the improvement in the photocatalytic activity of the materials.

Zinc oxide (ZnO) presents vast applicability in different areas. Diverse chemical elements are used in doping ZnO in order to modify desired properties-as proposed for enhanced visible photocatalytic activity through anion doping. Thus, the goal of this work is to develop a simple, fast and easy method for ZnO:N synthesis by a modified citrate precursor method. The as-prepared ZnO:N nanoparticles were utilized for dye photodegradation, in particular to study modifications in radical generation during photoactivation. The characterization of the nanoparticles confirms that the doping process affects neither particle morphology and crystalline structure, nor the bandgap of the samples. However, it largely affects photocatalytic activity for Rhodamine-B (Rhod-B) degradation, with an optimum N content for UV activity at 4% N and visible activity at 2% N. Under UV illumination, the photodegradation mechanism observed confirms that the ZnO:N nanoparticles presents clusters of p type ZnO:N embedded in n type ZnO particles endorsing the doping method as effective. These results enhance the essential comprehension of the photocatalytic activity of n type semiconductor doping processes and the modification of dye degradation mechanism related specially after doping.

In N-doping on TiO2 nanomaterial occurs a big decrease of band-gap (1 eV); however, its photocatalysis is low. We clarify such fact from effective mass, i.e., the electron–hole recombination is more than creation of electron–hole pair.