Study On The Crystal-plane-effects Of Cu₂O-based Nanomatrials On Elimination Of Environmental Pollutants

It is well-known that the catalytic elimination of environmental pollutants (e.g. catalytic removal of vehicle exhaust pollution, photo-catalytic degradation of organic pollutants, catalytic oxidation of soot) are mainly belonged to heterogeneous catalysis, in which the surface structures of catalysts play an important role. In recent years, with the rapid development of the characterization techniques and controlled synthesis for different-shaped nanocrystals, the understanding of the relationship between the structures and catalytic properties of nanocrystals at the molecular level has become possible, which will provide an significant theoretical gudiance for the design of highly efficient and environmentally friendly catalysts. In this thesis, we focus on studying the issue about the crystal-plane-effects of cuprous oxide (Cu2O) on elimination of environmental pollutants. The details about our research are as follows:(I) The uniform Cu2O nanocrystals, including rhombic dodecahedrons{110}, octahedrons{111} and cubes{100} were prepared, and the samples before and after reaction were characterized by SEM, TEM, XRD, XPS, N2-physisorption, TPR and in-situ DRIFTS technologies. Moreover, NO reduction by CO was employed as a model reaction to determine the catalytic performance of the obtained catalysts, and the possible reaction mechanism was proposed. The activity results of NO+CO reaction showed that dodecahedral Ou2O{110} had the best NO conversion, octahedral Cu2O {111} was followed, and cubic Cu2O{100} was the poorest. Interestingly, the activity result was well consistent with the reducibility, and the metallic copper (Cu0) was observed on the used catalysts. The reasons might be that: (1) in-situ DRIFTS suggested that the Mars van Krevelen mechanism worked in our system and the rapid change in valence state of copper species was a crucial part. Thus, the reactivity was well correlated with their surface properties, especially the reducibility; (2) d-Cu2O{110} had the superior catalytic performance, because{110} surface was more sensitive to NO+CO reaction conditions and then Cu0 nanoparticles were generated, leading to the decomposition of NO and the migration of the dissociated oxygen atoms on the Cu0/Cu2O interface, which was considered as the key step for NO reduction by CO.(II) In the Part I, it was found that the surface structures of Cu2O nanocrystals with different crystal planes had a significant influence on the catalysis. As a result, in the present part, various interfacial structures between different-shaped Cu2O nanocrystals and reduced graphene oxide (rGO) were deeply investigated for visible light-degradation. Firstly, a facile method was developed to synthesize Cu2O-reduced graphene oxide (rGO) composites with different crystal facets. Cu2O nanocrystals ({111},{110},{100} facets) were in-situ anchored on rGO sheets. Secondly, the as-prepared catalysts were characterized in detail by means of SEM, TEM, XRD, XPS, N2-physisorption, Photoluminescence, Raman, FT-IR and in-situ ESR. Finally, the photo-degradation of methylene blue (MB) under visible light was carried on to evaluate the performance of three composites in comparison. The emphasis of the present work was that:exploring the influence of interfaces on the charge-transfer process and catalytic property. The characterization results suggested that the superior photo-activity of o-Cu2O-rGO composite came from the advantageous interface between o-Cu2O{111} and rGO sheets. Due to the highly-active coordinated unsaturated Cu on the interface, the interfacial interactions were intensified and photo-generated electrons rapidly transferred to rGO sheets, and the electrons were captured by adsorbed O2 to generate the superoxide radicals (O2·-), which oxidized the MB molecules.(Ⅲ) Based on the investigation of the Part Ⅱ, it was proposed that engineering the interfacial structures could enhance the catalytic performance. Therefore, in the present part, ceria (CeO2) nanocrystals were supported on Cu2O with different crystal planes exposed, and the catalytic performance of the obtained catalysts was studied by the CO+O2 model reaction. Firstly, the Cu2O supports (octahedron{111} and cube{100}) were synthesized, and then the CeO2/Cu2O catalysts were prepared by a novel photochemical technique. The above two-shaped CeO2/Cu2O catalysts were characterized by means of SEM, TEM, XRD, UV-Vis DRS, Raman, TPR and in-situ DRIFTS technologies. Moreover, CO+O2 reaction was employed as a model reaction to determine the catalytic performance of the obtained catalysts, and the possible relationship between the structures of catalysts and the catalytic performance was proposed. This work was mainly focused on the crystal-plane-effects of Cu2O on the catalytic CO oxidation for CeO2/Cu2O catalysts. The obtained results suggested that:(1) the introduction of CeO2 nanoparticles could promote the reducibility, oxygen vacancy concentration and the migration of lattice oxygen, leading to the enhancement of the catalytic performance; (2) the properties of catalysts were closely related to the interfacial structures of CeO2/Cu2O catalysts. The schematic showed that the coordinatively unsaturated copper on the interface of CeO2/o-Cu2O{111} was beneficial to enhance the interaction of CeO2 and Cu2O, which promoted the migration of lattice oxygen and the reducibility. Therefore, CeO2/o-Cu2O {111} had better catalytic performance of CO oxidation.