| Recently,photocatalytic nitrogen fixation technology based on semiconductor has gradually developed into a promising ammonia synthesis technology,which is green and environmentally friendly,driven by solar energy and can be carried out under normal temperature and pressure.Traditional photocatalysts for nitrogen fixation are usually metal oxides or metal sulfides.However,the pure metal oxide/sulfide photocatalyst can not take into account the light energy utilization and strong redox ability,moreover,the carriers are easy to be combined.Therefore,it is important to find a cocatalyst that can improve the performance of nitrogen fixation catalysts.Ti3C2 MXene is a twodimensional material,which shows metal like conductivity and hydrophilic groups,making it easy to form heterojunction composites with semiconductor materials.The excellent light absorption properties of MXene can improve the utilization of light energy in the composites.In addition,the good conductivity can effectively promote the separation of carriers.Therefore,MXene is a potential cocatalyst.In this paper,CeO2/MXene composites and SnS2/MXene composites with high photocatalytic activity for nitrogen fixation were prepared by hydrothermal method and mechanical mixing method.In addition,APTES was used as a surface modifier to modify the CdS nanosheets with ammonium ions,and then the 2D/2D CdS/MXene composites were prepared by electrostatic self-assembly.(1)CeO2/MXene composites were prepared through in-situ growth of CeO2 nanoparticles on MXene nanosheets.MXene could reduce the size of CeO2 and shorten the transport path of carriers(e-/h+ pairs)in the process of photocatalytic reaction,which was beneficial to the photocatalytic reaction.UVVis DRS showed that the response range of the composites to light was broadened to the visible light region(400-800 nm).The excellent conductivity of MXene promoted the separation and transfer of photogenerated electron hole pairs,which significantly improved the photocatalytic nitrogen fixation activity of the composites.In 2.5 hours,the nitrogen fixatio1 of CeO2-1%MXene composite photocatalyst under visible light reached 58.40 ?mol/gcat,which was about 4 times higher than that of pure CeO2.(2)2D/2D SnS2/MXene composites were prepared by loading twodimensional SnS2 nanosheets on MXene nanosheets by mechanical mixing method.MXene could effectively alleviate the stacking phenomenon of SnS2 nanosheets and the large contacted area between MXene and SnS2 nanosheets was conducive to the charge migration.XPS showed that the surface electron density of SnS2 in the composite decreased,indicating that electrons migrate from SnS2 to MXene,which improved the separation efficiency of electron hole pairs and make more electrons participate in N2 reduction reaction.In addition,MXene as a cocatalyst can effectively broaden the visible light absorption range of SnS2/MXene composites.For the above reasons,the nitrogen fixation capacity increased from 37.06 ?mol/gcat to 74.3 1 ?mol/gcat within 2.5 hours,and the SnS2/MXene composite showed excellent light stability.(3)The 2D/2D CdS/MXene composites were fabricated by electrostatic self-assembly,and the effect of MXene content on photocatalytic nitrogen fixation was investigated.A small amount of MXene could broaden the response of the composite to light.However,when the loading of MXene was more than 1%,this characteristic was not obvious.Meanwhile,due to the strong interaction between MXene and Cd2+,the Cd2+generated by CdS photoetching was confined between MXene layers,which prevented the leaching of Cd2+,and further improved the photo corrosion resistance of CdS.Under visible light,the nitrogen fixation amount of the CdS-1%MXene was 133.28 ?mol/gcat after 9 hours,which showed outstanding performance for nitrogen fixation. |
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