Strategies for Modulating Photogenerated Charges of g-C3N4 to Improve Its Photocatalytic Performance and the Mechanism Insight

Author:Zhang Xu Liang

Supervisor:jing li qiang


Degree Year:2019





Recently,the global environmental pollution and energy crisis are becoming more and more serious as the global energy consumption and environmental burden have gradually increased with the growth of population,the development of urbanization and the rapid improvement of people’s living standards.Photocatalysis technology has been widely studied for it can effectively use solar energy to solve the environment and energy problems which human beings are facing today,and the key of photocatalysis technology is the development of photocatalysts.Graphite phase carbonitride(g-C3N4),as a kind of novel polymer semiconductor photocatalyst material with the advantages such as non-metal,cheap and easy to prepare,has been extensively studied in recent years.However,its photocatalytic activity is still not satisfactory as its photogenerated charge carriers are difficulate to separate.Modulation about the photogenerated carriers of g-C3N4 is an effective strategy to promote the separation of photocharges and it is usually divided into two sides:modulation of photogenerated holes and modulation of photogenerated electrons.Therefore,to enhance the charge separation of g-C3N4,works from three aspects are carried out in this thesis,including modulation of holes,modulation of electrons and co-modulation of holes and electrons.(1)The effects of the modified chlorine on the surface of g-C3N4 to the modulation of holes and the photocatalytic properties were explored.Firstly,g-C3N4 nanosheets were obtained by a calcination method using urea as the raw material.Then chlorine is modified on the surface of the g-C3N4 by a wet chemical method using hydrochloric acid.The results show that the modification of chlorine with a proper amount on the surface of g-C3N4 is beneficial to improve the performance of CO2 reduction and degradation of 2,4-DCP,phenol and RhB.The improvement of photoactivities are mainly due to the fact that the introduced chlorine has a trapping effect on the photogenerated holes of g-C3N4,and the trapping effect can suppress the recombination of electrons and holes,thereby promote the charge separation.(2)The effects of simultaneous modification of silver and titanium dioxide nanoparticles on the electrons modulation of g-C3N4 and their synergistic effects on the photocatalytic properties were investigated.Firstly,the anatase phase TiO2 nanoparticles are combined with carbon nitride by a simple wet chemical method.Subsequently,silver nanoparticles are deposited onto the composite by photodeposition method to achieve co-modification of silver and TiO2.The results show that the introduction of silver and TiO2can enhance the photocatalytic hydrogen evolution activity of g-C3N4,and the co-modification is more obvious.The increase in activity is mainly attributed to the fact that TiO2 is a proper energy level platform which can of accept electrons of g-C3N4 and promote the separation of the electron-hole pairs.While silver can provide catalytic functions,thereby promoting electron participation in the reduction reaction.Finally,the photocatalytic performance of g-C3N4 is better improved by the synergistic effect of them.(3)The effects of the introduced highly-dispersed cobalt and nickel species to the co-modulation of the holes and electrons on g-C3N4 and to the photocatalytic properties were explored.Firstly,g-C3N4 was synthesized by the cyanuric acid-mixed melamine-calcination method.The Co species are introduced into the precursor of g-C3N4 by adding cobalt nitrate to the cyanuric acid solution,thereby synthesizing cobalt-modified carbon nitride.Finally,the Ni species were modified on the obtained sample by a simple impregnation method to obtain cobalt-nickel co-modified g-C3N4.The results show that the modification of Co and Ni can improve the photocatalytic CO2 reduction activity of g-C3N4,and the co-modification can better improve the performance.The improvement of performance is mainly attributed to the fact that the modified Co species can capture photogenerated holes and promote water oxidation reaction,while nickel can capture photogenerated electrons and catalyze CO2 reduction reaction.The synergistic effect of them can better improve the photocatalytic performance of g-C3N4.