MOF衍化TiO_2修饰石墨相氮化碳的光催化性能研究
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摘要
石墨相氮化碳(g-C_3N_4)材料是一种极具潜力的有机光催化材料,尤其是在可见光驱动的光催化分解水制氢方面的应用.然而,较差的光生载流子分离效率严重制约了其光催化活性.选择TiO_2作为修饰材料,在g-C_3N_4表面构建合理的异质结构可以有效解决该问题,但需要进行合理的设计.本文通过较为简单的工艺过程,以金属有机框架材料(MOFs)为牺牲模板,制备MOF衍化TiO_2修饰的g-C_3N_4复合光催化剂.制得的MOF衍化TiO_2的比表面积大,约为124.5 m2/g,并由锐钛矿相/金红石相两相混合组成,这会有效增加光催化剂的光生电子分离效率,并提供更多的催化反应活性位点.通过XRD、SEM、TEM、UV-Vis、PL等表征手段,对材料的物相及相关的光谱学、电化学性质进行了详细的表征,并通过成分调控确定了优化工艺参数.通过相关表征结果可以看出,MOF衍化TiO_2修饰的g-C_3N_4复合光催化剂随着TiO_2的负载量提高而表现更好的载流子分离效率,但其可见光响应会随之降低.因此,存在一个最优的负载量可以均衡二者的影响,从而表现出最高的光催化活性.实验发现,TiO_2的质量分数为6%的光催化剂,其光催化制氢活性在可见光(l≥420 nm)驱动下体现了最高的制氢速率,达836μmol/(g·h).实验结果表明:由MOF衍化TiO_2与g-C_3N_4构建的异质结构可以有效地抑制光生载流子的复合,从而显著提高光催化分解水制氢的性能.
Graphitic carbon nitride(g-C_3N_4)is a promising organic photocatalytic material,especially in visible-lightdriven photocatalytic water-splitting hydrogen production. However,poor photogenerated carrier separation efficiency severely restricts the photocatalytic activity of g-C_3N_4. Using titanium dioxide(TiO_2)as modifier and constructing a reasonable heterostructure on the surface of g-C_3N_4 can effectively solve the aforementioned problem,but it needs a reasonable design. In this study,MOF-derived TiO_2-modified g-C_3N_4 composites were prepared through a facile preparation process using metal-organic frameworks(MOFs)as sacrificial template. The prepared MOF-derived TiO_2 has a large specific surface area of 124.5 m~2/g and is a mixture of anatase and rutile phases,which can effectively increase the photoelectron separation efficiency of the photocatalyst and provide more active sites for the photocatalytic reaction. XRD,SEM,TEM,UV-Vis,PL,and other characterization methods were used to characterize thephase and related spectroscopic and electrochemical properties of the materials in detail,and the optimized process parameters were determined by composition control. Results show that the MOF-derived TiO_2-modified g-C_3N_4 composite photocatalyst exhibits good carrier separation efficiency with the increase in the loading of TiO_2,but its visible light response decreases accordingly. Therefore,the optimum load to balance the effects of MOF and TiO_2 exists,resulting in the highest photocatalytic activity. Notably,the photocatalytic activity of the photocatalyst with 6% TiO_2 exhibited the highest hydrogen production rate of 836 μmol/(g·h) under visible light(l≥ 420 nm). The experimental results show that the heterojunction structure constructed using MOF-derived TiO_2-modified g-C_3N_4 can effectively inhibit the recombination of photogenerated carriers,thus significantly improving the photocatalytic decomposition of water for hydrogen production.
Graphitic carbon nitride(g-C_3N_4)is a promising organic photocatalytic material,especially in visible-lightdriven photocatalytic water-splitting hydrogen production. However,poor photogenerated carrier separation efficiency severely restricts the photocatalytic activity of g-C_3N_4. Using titanium dioxide(TiO_2)as modifier and constructing a reasonable heterostructure on the surface of g-C_3N_4 can effectively solve the aforementioned problem,but it needs a reasonable design. In this study,MOF-derived TiO_2-modified g-C_3N_4 composites were prepared through a facile preparation process using metal-organic frameworks(MOFs)as sacrificial template. The prepared MOF-derived TiO_2 has a large specific surface area of 124.5 m~2/g and is a mixture of anatase and rutile phases,which can effectively increase the photoelectron separation efficiency of the photocatalyst and provide more active sites for the photocatalytic reaction. XRD,SEM,TEM,UV-Vis,PL,and other characterization methods were used to characterize thephase and related spectroscopic and electrochemical properties of the materials in detail,and the optimized process parameters were determined by composition control. Results show that the MOF-derived TiO_2-modified g-C_3N_4 composite photocatalyst exhibits good carrier separation efficiency with the increase in the loading of TiO_2,but its visible light response decreases accordingly. Therefore,the optimum load to balance the effects of MOF and TiO_2 exists,resulting in the highest photocatalytic activity. Notably,the photocatalytic activity of the photocatalyst with 6% TiO_2 exhibited the highest hydrogen production rate of 836 μmol/(g·h) under visible light(l≥ 420 nm). The experimental results show that the heterojunction structure constructed using MOF-derived TiO_2-modified g-C_3N_4 can effectively inhibit the recombination of photogenerated carriers,thus significantly improving the photocatalytic decomposition of water for hydrogen production.
引文
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[16]Yang C,Qin J,Xue Z,et al.Rational design of carbon-doped TiO2 modified g-C3N4 via in-situ heat treatment for drastically improved photocatalytic hydrogen with excellent photostability[J].Nano Energy,2017,41:1-9.
[17]Mohamed M A,Salleh W N W,Jaafar J,et al.Carbon as amorphous shell and interstitial dopant in mesoporous rutile TiO2:Bio-template assisted sol-gel synthesis and photocatalytic activity[J].Appl Surf Sci,2017,393:46-59.
[2]Fujishima A.Electrochemical photolysis of water at a semiconductor electrode[J].Nature,1972,238:37-38.
[3]Lin F,Boettcher S.W.Adaptive semiconductor/electrocatalyst junctions in water-splitting photoanodes[J].Nat Mater,2014,13(1):81-86.
[4]Zhu Y P,Ren T Z,Yuana Z Y.Mesoporous phosphorus-doped g-C3N4 nanostructured flowers with superior photocatalytic hydrogen evolution performance[J].ACSAppl Mater Interfaces,2015,7:16850-16856.
[5]Zhou Y,Zhang L,Liu J,et al.Brand new P-doped gC3N4:Enhanced photocatalytic activity for H2 evolution and Rhodamine B degradation under visible light[J].JMater Chem A,2015,3:3862-3867.
[6]Ge L,Han C,Xiao X,et al.Enhanced visible light photocatalytic hydrogen evolution of sulfur-doped polymeric g-C3N4 photocatalysts[J].Mater Res Bull,2013,48:3919-3925.
[7]Wei X,Shao C,Li X,et al.Facile in situ synthesis of plasmonic nanoparticles-decorated g-C3N4/TiO2 heterojunction nanofibers and comparison study of their photosynergistic effects for efficient photocatalytic H2 evolution[J].Nanoscale,2016,8:11034-11043.
[8]Li J,Zhang M,Li X,et al.Synergistic effect of surface and bulk single-electron-trapped oxygen vacancy of TiO2 in the photocatalytic reduction of CO2[J].Appl Catal B:Environ,2017,212:106-114.
[9]Wang Z,Li X,Xu H,et al.Porous anatase TiO2constructed from a metal-organic framework for advanced lithium-ion battery anodes[J].J Mater Chem A,2014,2(31):12571-12575.
[10]Wang X,Maeda K,Thomas A,et al.A metal-free polymeric photocatalyst for hydrogen production from water under visible light[J].Nat Mater,2009,8:76-80.
[11]Li J,Xu X,Liu X,et al.Novel cake-like N-doped anatase/rutile mixed phase TiO2 derived from metalorganic frameworks for visible light photocatalysis[J].Ceram Int,2017,43:835-840.
[12]Zhang J,Guo F,Wang X.An optimized and general synthetic strategy for fabrication of polymeric carbon nitride nanoarchitectures[J].Adv Funct Mater,2013,23:3008-3014.
[13]Jiang Z,Zhu C,Wan W,et al.Constructing graphitelike carbon nitride modified hierarchical yolk-shell TiO2spheres for water pollution treatment and hydrogen production[J].J Mater Chem A,2015,4(5):1806-1818.
[14]Hu Z,Yuan L,Liu Z,et al.An elemental phosphorus photocatalyst with a record high hydrogen evolution efficiency[J].Angew Chem-Int Ed,2016,55(33):9580-9585
[15]Ma J,Wang C,He H.Enhanced photocatalytic oxidation of NO over g-C3N4-TiO2 under UV and visible light[J].Appl Catal B:Environ,2016,184:28-34.
[16]Yang C,Qin J,Xue Z,et al.Rational design of carbon-doped TiO2 modified g-C3N4 via in-situ heat treatment for drastically improved photocatalytic hydrogen with excellent photostability[J].Nano Energy,2017,41:1-9.
[17]Mohamed M A,Salleh W N W,Jaafar J,et al.Carbon as amorphous shell and interstitial dopant in mesoporous rutile TiO2:Bio-template assisted sol-gel synthesis and photocatalytic activity[J].Appl Surf Sci,2017,393:46-59.