The Effects Of Surface Modifications With Organic Function Group And Noble Metals On The Performance Of Photocatalytic Reduction Of CO₂ For The TiO₂

With the rapid development of social economy,the greenhouse effect and energy shortage become increasingly serious.At present,most of the energy still comes from the burning of fossil fuels.On one hand,fossil fuel is the non-renewable resources.On the other hand,the burning of fossil fuels produces a large amount of CO₂,which is the main cause of the greenhouse effect.Photocatalytic reduction of CO₂ producing CO and hydrocarbons such as CH₄,is a new way to solve both the energy shortage and the environmental problems at the same time.The key to the technology of photocatalytic reduction of CO₂ is to explore effective and low-cost photocatalyst.In this thesis,different methods are tried to prepare surface modified TiO₂ photocatalyst in order to improve the photocatalytic activity of TiO₂ semiconductor.The main contents and conclusions of this thesis are as follows:The design,preparation and CO₂ photocatalytic reduction activity of tetramethylguanidine surface-modified titanium dioxide photocatalyst.The tetramethylguanidine precursor was prepared,and used to modify the TiO₂.Compared with the reference sample,the photocatalytic activity of tetramethylguanidine surface-modified titanium dioxide is promoted significantly,and the selectivity of CH₄is increased.The C=N bond in tetramethylguanidine organic group can help to absorp and activate CO₂ molecule,forming large?bond.At the same time,the motion of the organic groups has advantages to help actived CO₂ contact with the active site of catalyst,which is conductive to the subsequently catalytic conversion process.The preparation and CO₂ photocatalytic reduction activity of noble metal modified TiO2 photocatalyst prepared by different methods.Based on the TiO2 with specific crystal structure,Ru/TiO₂ was prepared by the methods of NaBH₄,H₂ reduction and organic thermal reduction respectively.It was find that most of the ruthenium on the surface of TiO₂ is the oxide before reduction.While after reducing by H₂,most of ruthenium exist as Ru⁰,which enhances the adsorption for CO₂,resulting in the significant improvement of it's photocatalytic activity.Thus,Ru⁰ is thought to be the main active species.When prepare Ru/TiO₂ by organic thermal reduction,the photocatalytic activity is influenced by the dosage of PVP?k30?.And the activity can reach the maximum when the mole ratio of PVP to Ru is 1:5.The preparation and CO₂ photocatalytic reduction activity of Pt and Ru bimetals modified TiO₂ photocatalyst.Pt/TiO₂,Ru/TiO₂ and Pt-Ru/TiO₂ were prepared,it was found that the photocatalytic activity of Pt-Ru/TiO₂ is improved compared with that of Pt/TiO₂ or Ru/TiO₂.Especially the selectivity of CH₄ increases from 70%to 87%.What's more,the reasons why the selectivity of CH₄ over Pt/TiO₂and Ru/TiO₂ catalysts are different is proposed.It seems that the decomposition of water is not only a competing reaction,but also plays a key role in the generating of CH₄ from CO₂.