| Graphite carbon nitride(g-C3N4),as a unique of organic two-dimensional(2D)semiconductor materials,due to its excellent visible-light response and suitable band edge position,has the very good application prospect in the field of photocatalysis.In this work,a suitable catalyst is built for photocatalytic CO2 reduction by combining theoretical simulation and experimental method.In this paper,the calculation software of Material Studio was used to reveal the adsorption behavior of small molecule gas H2S,H2O and CO2 on the pure g-C3N4(001)surface and VIB doped g-C3N4(001)surface,and explore their trends of adsorption under an additional electric field.On the above basis,the mechanism of Co2 reduction on the pure g-C3N4(001)surface and the transition state metal Cu and Mo doped g-C3N4(001)was studied.There is concluded that Mo doped g-C3N4(001)can effectively reduce the activation energy of reducing Co2 and improve the selectivity of the targeted product.In order to apply the above theoretical prediction to the experiment,two evaluation systems for photocatalytic reduction of Co2 are first constructed.Then,the most simple thermal condensation method was used to synthesize Mo doped g-C3N4(Mo-C3N4)with the different Mo concentration.The evaluation systems were was performed to test Mo-C3N4 performance for the reduction of CO2 under the visible light(?>420 nm).The results of the experiment showed that the 4%Mo-C3N4 was the optimal performance which the main product were syngas(CO/H2),and converted CO2 to produce the maximum CO of 106 mol g-1 after the 6 h visiable light irradiation,which was about 10.6 times higher than that of g-C3N4.Meanwhile,the amount of H2 is also detected to be 220 mol g-1,which is about 4 times higher than g-C3N4.A series of characterization methods were used to study the causes of performance difference of Mo-C3N4.Finally,it was concluded that the amorphous material enhances the ability of light absorption,and the formation of new Mo-C/N bonds in the Mo-C3N4 promoted the transfer of the photo-induced carriers,which are the essential reasons for the difference in the photocatalytic activity of Mo-C3N4.At the same time,the results show that the theoretical prediction is consistent with experimental research.Meanwhile,many defects in semiconductor materials greatly influence the photocatalytic performance.Therefore,the 2D photocatalysts,BiOCl materials with oxygen vacancies(BOC-OV),was chosen as object of study.Under visible light irradiation,BOC-OV converted C02 to CO with the rate at 4.15 umolg-1h-1,while the rate of CO at BOC is 0.36 umolg-1h-1.Through the study,it was found that oxygen vacancies can enhanc exciton dissociation,which is attributed to the photocatalytic efficiency.However,BOC-OV had some shortcomings such as the limitation of light response range,a high degree of crystallization and low photocatalytic activity.In the terms of these disadvantages,g-C3N4 and BOC-OV was successfully composited using the new solvothermal method.It is proved by experiment that both crystallinity and catalytic activity of BOC-OV prepared by the new method was superior to the preparation method in the early stage.Meanwhile,it can be seen that the composite method can broaden the response range of light and enhance the photocatalytic activity in visible light by means of materials characterization and photocatalytic evaluation of CO2 reduction.As a result,best optimization ratio of g-C3N4/BOC-OV(1:1)composites in visible light have enchaned the photocatalytic performance of CO2 reduction compared to previous preparation of BOC-OV and g-C3N4,which showed 1.5 and 6.3 times higher activity than that of BOC-OV and even g-C3N4. |
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