Nitretos de carbono: diferentes estratégias de modificação para melhores atividades fotocatalíticas

Abstract

In this work different strategies for structural and electronic modifications of materials based on carbon nitrides (CNs) are described, in order to investigate the influence of these modifications on their photocatalytic activities. In a first step, the synthesis of three polymeric carbon nitrides (PCNs) from different molar proportions of melamine and thiourea are described, aiming to control the number of defects in their structures. From the elemental analysis of CHNS, TEM and XRD it was possible to observe that, among the synthesized materials, the material obtained from thiourea (CN-T) is the one with the highest number of defects in its structure compared to the carbon nitride obtained from melamine (CN-M), which has the lowest number of defects. In addition, the CNT material presented 100% removal of AMX in the photocatalytic degradation tests, under solar simulation, after 24 hours of reaction. In a second step, the modification of Na-PHI is described, this material is a carbon nitride with a highly graphitic structure, and its functionalization consisted of the addition of - OR group (e.g. benzyl alcohol) to its structure. The photocatalytic activities of Na-PHI before and after functionalization were investigated, under different irradiations, using the Rhodamine B (RhB) degradation model reaction. In order to further optimize the photocatalytic degradation activities of CNs, taking into account the synergistic properties that gold can add to them, four new composites obtained from heterostructures formed by Na-PHI and Au nanorods (NRs) were synthesized by heat treated at different temperatures. It was observed that the hexadecyltrimethylammonium bromide (CTAB), a stabilizing agent used in the synthesis of Au NRs, acts as a spacer between the gold NRs and the PHI sheets, and the optimal distance between them favors their photocatalytic activities. Among the synthesized composites, the PHI-Au_250 oC, material that was heat treated at 250 oC, showed the best photocatalytic performance for RdB photodegradation, which may be associated with the optimal distance between the Au NRs and the PHI sheets in this material.