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Progress in research on photoreduction mechanism of carbon dioxide on metal oxide surfaces
[ Instrument Network Instrument R & D ] Recently, Professor Zhao Jin's team at the School of Physics, University of Science and Technology of China and Hefei National Institute of Microscale Material Science International Research Center for Quantum Design of Functional Materials (ICQD) has made new progress in the research of CO2 photoreduction mechanism on oxide surfaces progress.
They used the first-principles excited state dynamics program developed by the team to reveal that the CO2 molecules on the oxide surface can excite the bending and asymmetric stretching vibration modes of the CO2 molecules by temporarily capturing electrons, reducing the energy of the CO2 LUMO orbit CO2 molecules can capture photoelectrons and reduce reactions.
Photoelectrons are the electrons generated by stimulated radiation in the photoelectric effect, which are essentially the electrons of a metal plate, corresponding to the concept of "photons". "Photons" are the nature of light that people currently think of: light is made up of photons, like balls. However, the essential difference from small balls is that photons have no mass, and have both wave and particle properties (wave-particle duality).
CO2 photoreduction on solid surfaces has always been a challenging scientific problem. The main bottleneck is that the LUMO orbital energy of CO2 molecules is too high, and it is difficult to capture light-excited hot electrons to generate a reduction reaction. Zhao Jin's team used the self-developed first-principles excited-state kinetics software Hefei-NAMD to study the CO2 photoreduction mechanism on the TiO2 surface. The study found that, because the LUMO energy of CO2 molecules is higher than the bottom energy of the conduction band of TiO2, it is difficult for CO2 molecules to capture electrons stably. Within a certain lifetime, the electrons on CO2 will decay back to the TiO2 conduction band.
The electrons in the semiconductor can be excited by absorbing certain energy (such as photons, external electric fields, etc.). The electrons in the excited state are called hot electrons. Electrons in the excited state can transition to lower energy levels and release energy in the form of optical radiation, which is the phenomenon of semiconductor light emission.
When the electric field strength in the channel of a MOS device exceeds 100 kV / cm, the energy obtained by the electron between two scatterings may exceed the energy it loses in the scattering, which will make some of the energy of the electrons significantly higher than the average kinetic energy at the time of thermal equilibrium. Hot electron. High-energy hot electrons can seriously affect the reliability of MOS devices and circuits.
However, if CO2 is adsorbed on the oxygen-deficient position of TiO2, and its lifetime of capturing electrons can exceed 12 femtoseconds to form a short-lived CO2.-, then the vibration modes of the bending and asymmetric stretching of CO2 molecules will be effective Excitation can reduce the LUMO orbital energy of CO2 below the bottom of the TiO2 conduction band and maintain it for about 150 fs. At this time, CO2 can effectively capture the electrons on the conduction band within 80 fs, and the following 30- 40 fs dissociates to form CO molecules. This work reveals the key role of CO2 vibration mode excitation in the photoreduction process, and gives a clear description of the excited state dynamics of the photoreduction of CO2 molecules on the surface of TiO2 from the perspective of first-principles calculations.
The invention relates to a method for preparing gold nanoparticles in an aqueous soft template by using ultrasonic to promote photoreduction, and belongs to the technical field of preparing nanoparticles in metallic materials. The present invention uses soft clusters formed by polyethylene glycol (PEG) and sodium lauryl sulfate (SDS) as soft templates, and uses chloroauric acid (HAUCL4) as a raw material. The next step is to induce the synthesis of spherical gold nanoparticles with adjustable particle size. During the reaction, the soft template composed of PEG and SDS plays a role in controlling the size of gold nanoparticles. After the reaction product was centrifuged at high speed, the precipitate was washed with water to obtain spherical gold nanoparticles with a particle size of about 20-80NM and a narrow particle size distribution. The invention is characterized in that the product is on a nanometer scale and has a narrow particle size distribution, little pollution during the preparation process, easy product separation, and simple operation.
Source: Encyclopedia, University of Science and Technology of China