Synthesis Of High Efficiency Photocatalyst And Its Application In Visible Light Catalytic Lignin Depolymerization

The depletion of the Earth’s fossil fuel reserves and the rapid increase in the emission of greenhouse gases and other environmental pollutants are driving the development of renewable energy technologies. As a result of its rich content of aromatic carbon, lignin has the potential to be decomposed to yield valuable chemicals and alternatives to fossil fuels. However, the complex and stable chemical bonds of lignin make the depolymerization of lignin a difficult challenge with regard to its valorization. Specifically, these normal catalytic lignin degradation approaches typically always requires elevated temperatures(>80℃) and functional groups such as free phenols and γ-alcohols are not well tolerated. Solar energy is an ideal renewable energy source as an alternative to fossil fuels. With its renewable, non-toxic and sustainable characteristics, the utilization of solar radiation has been attracting increasing attention. As a result of the potential future energy crisis and environment pollution, there is increasing interest in clean, renewable sources of energy. The concept of utilizing solar energy at room temperature and atmospheric pressure to selectively convert lignin to important aromatic chemicals and value-added products via photocatalysis and for the treatment of waste water polluted with lignin is a highly innovative approach. Therefore, we sought to address these above issues by developing the room temperature lignin degradation methods that could be performed efficiently in photocatalysis condition, in order to achieve the goal of sustainable development.This paper combined with the conception about promoting energy conservation and environmental protection, and sustainable development of green chemistry, introduced visible light into the lignin depolymerization reaction, by building new heterogeneous and the homogeneous catalysts, and achieved the goal about effectively depolymerization of lignin model compounds under the atmospheric temperature and pressure in photocatalysis condition, and their successful application in the natural lignin monomer depolymerization. The thesis also studied the structure-activity relationship and the catalytic mechanism through a series of characterization and experimental design.The main jobs, introduced in this thesis, are divided into the following two parts:1. In order to overcome the heavy metal ions pollution to the environment caused by the homogeneous metal catalyst and reduce the cost of the reaction, we successfully loaded the homogeneous iridium pyridine catalyst on the sulfhydryl group functionalized silica mesoporous cellular foam by clicking reaction, the prepared heterogeneous catalyst(Ir-MCF) has high stability, big specific surface area(355 m2/g), and good dispersion in organic solvent. Also the heterogeneous catalyst(Ir-MCF) could be successfully applied in visible light depolymerization reaction of lignin model compounds, obtained more than 85% of the conversion rate and yield. Ir-MCF catalyst could be reused five times, and the reaction activity did not significantly reduced, remained more than 80% of the yield. Several common lignin monomer derivatives also have good depolymerizing activity, and the yields could be reached about 90%, illustrating that the Ir-MCF has a certain application prospect in natural lignin depolymerization reaction.2. For the purpose of effectively alleviate the excessive dependence on transition metal catalysts in the natural lignin depolymerization progress, we find a kind of non-metallic small-molecule organocatalyst perylene bisimide(PDI), which could be applied in depolymerization of lignin model compounds under the visible light condition, and obtained more than 95% of the conversion rate and yield. This cheap and available perylene bisimide catalyst PDI has good catalytic effect, strong visible-light responseand, mild reaction conditions, and greatly reduces the cost of the depolymerization reaction. For several kinds of common lignin monomer derivatives, PDI also showed good depolymerization activity, and the yields could be reached about 90%, which highlights the potential of PDI catalyst for natural lignin depolymerization progress.