| Recently,the growing worsen of environmental and energy problems has stimulated intensive research on semiconductor photo-catalysts,which could absorb light and convert to chemical energy or degradation of organic pollutants.Especially,graphitic carbon nitride?g-C3N4?,a kind of conjugated polymer semiconductor,has drawn more interests owning to its suitable band gap?2.7 eV?,excellent stability,and non-toxicity.However,the pure g-C3N4 fabricated by the thermal polymerization method still have some shortcomings:low surface area,narrow visible-light response range,fast recombination of electron-hole pairs,which may lead to a lower solar energy utilization ratio.To increase the photocatalytic activity of g-C3N4,four methods have been developed in this thesis:increasing surface area which could provide enough interface to react,integrating with BiOBr,Ni/Fe co-doped and modification with Ag nanoparticles.The main aspects of this thesis are as follows:?1?A series of SiO2 and g-C3N4 composites?named as SiO2/C3N4?with high surface area were prepared by directly pyrolysis the mixture of SiO2 and melamine,XRD and SEM were used to confirm the morphology and structure of SiO2/C3N4.XPS was used to identify the chemical states of carbon and nitrogen.BET,DRS,and PL were used to further analysis the semiconducting properties of SiO2/C3N4.The changing of SiO2 proportion could modulate the surface area,C/N atomic ratio,and the band gap of g-C3N4.Specially,the as-prepared composite with an optimal SiO2/melamine mass ratio of 4:5?SiO2/C3N4-4:5?shows the best catalytic performance.?2?SiO2/C3N4/BiOBr photocatalyst was prepared by modifying SiO2/C3N4-4:5 with BiOBr.XRD and SEM were used to confirm the morphology and structure of SiO2/C3N4/BiOBr.BET,DRS,and PL were used to further analysis the semiconducting properties of SiO2/C3N4/BiOBr.The recombination rate of electrons and holes was reduced by forming g-C3N4/BiOBr heterojunction.Thus,compared with Si O2/C3N4 and BiOBr,SiO2/C3N4/BiOBr exhibited higher RhB photocatalytic activity.?3?A series of Ni and Fe co-doped graphitic carbon nitride?Ni/Fe-C3N4?photocatalysts were successfully prepared using Fe?NO3?3·9H2O,Ni?NO3?3·6H2O,and melamine as precursors.XRD and SEM were used to confirm the morphology and structure of Ni/Fe-C3N4.XPS was used to identify the chemical states of doping ion.BET,DRS,and PL were used to further analysis the semiconducting properties of Ni/Fe-C3N4.The results indicated that the co-doping of Ni and Fe increased the surface area of g-C3N4,decreased the semiconductor band gap,and reduced the recombination rate of electrons and holes effectively.Therefore,the Ni/Fe-C3N4 exhibited higher MO photocatalytic activity.Specially,the as-prepared photocatalyst with an optimal nitrates/melamine mass ratio of 10%?10%Ni/Fe-C3N4?shows the best catalytic performance.?4?A novel Ni/Fe-C3N4/Ag composite photocatalyst was successfully fabricated through modifying 10%Ni/Fe-C3N4 with Ag nanoparticles via a photodeposition method.XRD and SEM were used to confirm the morphology and structure of Ni/Fe-C3N4/Ag.XPS was used to identify the chemical states of Ag.BET,DRS,and PL were used to further analysis the semiconducting properties of Ni/Fe-C3N4.The results indicated that doping of Fe/Ni and deposition of Ag together decreased the semiconductor band gap,increased the photo generated electron-hole separation rate,and leading to a higher catalytic efficiency. |
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