Decoration {001} TiO₂ With Bi₂S₃ QDs And CQDs For Photocatalytically Reducing CO₂ To Methanol

Photocatalytic reduction of CO₂ has become a hot spot in recent years.It has a very important application both in energy development and environmental protection.The CO₂ in the air can be used as raw materials and be photocatalyticaly reduced to methanol.Both CO₂ and clean,abundant solar energy can be stored by converting into organic chemicals,and at the same time,the main content of the "greenhouse effect" CO₂ can be decreased.So photoreduction of CO₂ is a good way to protect the environment as well as to achieve the green and sustainable development of energy,which is of great economic and social significance.In our paper,we synthesized two kind of composite catalysts: Bi₂S₃ QDs/TiO₂ and CQDs/Ag-TiO₂.The {001} TiO₂ is modified by controlling the crystal growth of {001} TiO₂ and depositing the noble metal and quantum dots at the same time to enhance the separation of photogenerated carriers and improve the photocatalytic activity of the composite catalysts.The specific research contents are as follows:1)F ions were chosen as the only surface capping agent to synthesis anatase TiO₂ nanosheets exposed with {001} high energy facets.When 3m L HF（40wt%）was added,the thickness of the nanosheet is about 5nm and the size of truncated nanosheet is between 50 nm and 70 nm.The photoreduction activity of different facet is different.Part of the photogenerated electrons will transfer to {001} facets of TiO₂ nanosheets and take part in the reduction reaction immediately;the other part will transfer to {101} facets,which can effectively prevent the recombination of photogenerated carriers on the surface of catalyst.So the synergistic effect played a key role in the photocatalytic reaction system.2)Bi₂S₃ QDs/TiO₂ composite photocatalyst was successfully synthesized through solvothermal method.In the experiment,isopropanol was chosen as sacrificial agent.Under the irradiation of ultraviolet lamp,CO₂ was reduced into methanol and isopropanol was oxidized into acetone.Using on-line ATR-FTIR spectroscopy to testing the change of the content of CO₂ in the reaction system,we further confirmed that CO₂ was indeed reduced during the reaction.The methanol yield was increased as the increase of the deposition amount of Bi₂S₃ QDs and the highest yield was 1169.15μmol/g/h when the mole ratio of TiO₂ and Bi₂S₃ was 20（x=20）.The little volume of sample Bi₂S₃ QDs/TiO₂ offered a sufficient surface for optical absorption.The deposition of Bi₂S₃ QDs makes the photogenerated carriers transfer smoothly between the semiconductor and the quantum dots,which making sure the successful separation of photogenerated carriers,and thus improving the photocatalytic activity.3)Using sucrose as raw material,CQDs was prepared by a simple hydrothermal method.By depositing Ag and CQDs on {001} TiO₂ simultaneously,the CQDs/Ag-TiO₂ composite catalyst was well prepared.The photocatalytic activity showed obvious improvement with the deposition of Ag and CQDs.The up-conversion fluorescence effect of CQDs and the role of electron trap and plasmon resonance effect of Ag play a great role in expansion the absorption edge of composite catalyst and effective separation of photogenerated carriers.At the same time,we compared the photocatalytic efficiency with different ratio of {001} and {101} facets,experiment proved that when the volume of HF was 3ml,the photocatalytic activity reached the highest at 699.5μmol/g/h,which is 3.8 times of that {001} TiO₂,which further confirmed the synergistic effect between {001} and {101} facets of {001}TiO₂.