Photocatalytic Co₂ Reduction Over Defective NH₂-UiO-66 Under Visible Light

The capture and efficient utilization of CO₂ are an important issue since CO₂ released by burning of fossil fuels is a primary cause of global warming.One of the best solutions is to convert CO₂ into valuable organic products by means of solar energy.The key to the efficient utilization of CO₂ is the development of high efficient photocatalysts for CO₂ reduction.The emerging of the metal-organic frameworks?MOFs?has provided a new dimension to develop new photocatalysts.Defect engineering in MOFs is an exciting concept for tailoring material properties,which opens up novel opportunities not only in adsorption and catalysis,but also in controlling more challenging physical characteristics such as band gap as well as magnetic and electrical/conductive properties.In this thesis,either hydrochloric acid or trifluoroacetic acid was used as modulator molecule to induce defects in the frameworks of NH₂-UiO-66?Zr?and NH₂-UiO-66?Hf?.The prepared samples were characterized by several techniques,such as XRD,TGA,photoluminescence,N2 adsorption-desorption and so on,to investigate the effects of defects on their physicochemical properties.Then the synthesized MOFs were used as catalysts in the reduction of CO₂ upon visible light irradiation.Additionally,the mechanism of the photocatalytic reduction of CO₂ over defective NH₂-UiO-66 was proposed.The main results and conclusions are summarized as follows:1.The crystal defects can be induced into the frameworks of NH₂-UiO-66 when HCl is used as modulator molecule.With increasing the crystallization temperature,the amount of defects caused by the linker vacancies increases,enhancing the surface area of the resultant MOF.2.The lack of the organic linkers can create several extra unsaturated metal centers that can enhance the efficiency of photo-charge transfer during CO₂ reduction,leading to a higher photocatalytic activity.3.Trifluoroacetic acid as modulator molecule can also induce the defects in the frameworks of NH₂-UiO-66?Zr?.Meanwhile,the amino groups in the organic linkers will interact with trifluoroacetic acid to form peptide bonds.Significantly,the formation of the peptide bonds would reduce the electron donating ability of the amino groups despite of the existence of crystal defects,leading to a lower photocatalytic activity of CO₂ reduction.Novelty of the thesis research:The photocatalytic activity of CO₂ reduction over NH₂-UiO-66 could be significantly enhanced by the introduction of crystal defects caused by the linker vacancies,providing a new avenue to develop efficient visible-light-driven photocatalysts for CO₂ fixation.