| The continuous burning of fossil fuels and excessive emissions of greenhouse gases(e.g.,CO2)have caused serious environmental pollution problems that need to be addressed urgently.In recent years,photocatalytic CO2reduction reaction(CO2RR)has been developed as a valuable and sustainable CO2conversion strategy owing to its ability to selectively reduce CO2to carbon-based energy products using renewable solar energy.However,due to the inherent inertness of the CO2molecule,the photocatalytic CO2RR is difficult to perform.Therefore,the development of superior photocatalysts is the key factor in reducing the activation energy of CO2and realizing the photocatalytic CO2reduction reaction.TiO2has been widely applied in many photocatalytic applications,such as photocatalytic dye and pollutant degradation,photocatalytic hydrogen production and photocatalytic CO2reduction reaction,due to its high photostability,simple composition,low cost,easy operation,non-pollution and many other excellent properties.To further exploit the photocatalytic advantages of Ti-based materials,titanium oxide clusters(TOCs),whose structural composition is very similar to that of TiO2,have received extensive attention and research in recent years.TOCs not only inherit the similar catalytic activity,low cost and less pollution of titanium dioxide,but also are easy to grow as single crystals.Importantly,the well-defined structural information allows understand the relationship between structure and performance at the molecular level.With the continuous improvement of structure synthesis methods and the continuous development of performance of TOCs,many research groups have made important progress in the synthesis and photocatalytic performance(photocatalytic hydrogen production,dye degradation and CO2RR)of TOCs modified by ligands.However,the application of functionalized TOCs in the photocatalysis of CO2RR is still rare.Therefore,the main purpose of this paper is to select ferrocene carboxylic acids(1,1-ferrocene dicarboxylic acid and ferrocene carboxylic acid)and9-anthracenecarboxylic acid as functionalized ligands,to synthesize novel structures of ligand-functionalized TOCs by a solvothermal method,and to investigate their crystal structures and the properties of photoreduction CO2reactions.The main work of this paper includes the following three aspects:(1)We have successfully synthesized two TOCs(PTi16and PTi12),[Ti16(OH)4O20(PO4)(OiPr)16](PTi16,HOiPr=isopropanol)and[Ti12O15(PO4)(iPr PO4)3(OiPr)12](CHA)3(H2O)(PTi12,CHA=cyclohexylamine)by solvothermal method.Crystal structure analysis showed that PTi16and PTi12are typical?-Keggin structures,and this was the first time to find?-Keggin structure in the titanium oxide clusters.Then the photocatalytic CO2RR under UV light driving was tested on PTi16and PTi12.The results of the photocatalytic CO2RR exhibited that PTi16and PTi12could be used as effective photocatalysts for CO2reduction,and PTi16exhibited high selectivity(93.4%)and activity(268.12?mol h-1g-1)for the conversion of CO2-to-HCOOH.(2)We have successfully synthesized three TOCs by a solvothermal method using 1,1-ferrocene dicarboxylic acid as an organic functionalized ligand,[Ti6(?3-O)2(?2-O)2(PPO)2(O2CCF3)2(?2-OiPr)4(OiPr)6](CF3COOH=trifluoroacetic acid,HOiPr=isopropanol,Ti6)and 1,1-ferrocene dicarboxylic acid(Fcdc)functionalized[Ti8(?3-O)4(tea)2((Fcdc)2)4(OiPr)10]·2HOiPr(tea H3=triethanolamine,Ti8-Fcdc)and[Ti6(?3-O)2(Fcdc)2(?2-SO4)2(?2-OiPr)2(OiPr)10]·2HOiPr(Ti6-Fcdc),and their photoreduction performance of CO2have been investigated.Among them,Ti6has been reported in previous work.In this work,the light absorption range of Ti8-Fcdc and Ti6-Fcdc modified with Fcdc ligands extends from the traditional ultraviolet region to the visible region,and their photocurrent response(effective photogenerated charge transfer rate)was significantly improved comparing with Ti6.The results of photocatalytic CO2RR performance showed that the three TOCs could accomplish the conversion of CO2-to-HCOOH with high selectivity.Compared with Ti6,Ti8-Fcdc and Ti6-Fcdc functionalized with Fcdc ligand exhibited higher photocatalytic activity and selectivity.(3)We have successfully synthesized three polyoxotitanium cluster structures modified by 9-Ac and Fc ligands by a solvothermal method,respectively.9-Ac-functionalized[Ti10(?3-O)12(9-Ac)6(OiPr)8(C3H6NO)2](OiPr=isopropoxy.C3H6NO=N,N-dimethylformamide,Ti10Ac6),9-Ac and Fc-functionalized[Ti12(?3-O)10(?4-O)2(Fc2(9-Ac)4(?2-OC2H5)4(C2H5O)14](C2H5O=ethoxyl,Ti12Fc2Ac4)and Fc-functionalized[Ti10(?3-O)12(Fc)8(C3HF6O)8](C3HF6O=hexafluoroisopropoxy,Ti10Fc8),and their photocatalytic CO2RR performance have been investigated.Single crystal X-ray diffraction results showed that the three TOCs have similar nuclear structures.The results of photocurrent response and its performance of photocatalytic CO2RR show that the photocurrent response of functionalized Ti12Fc2Ac4was obviously enhanced by the introduction of mixed ligands,and the performance of photocatalytic CO2RR was significantly improved compared with Ti10Ac6and Ti10Fc8. |
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