Development of Sn^(2+)-based oxyfluoride photocatalyst with visible light response of ca.650 nm via strengthened hybridization of Sn 5s and O 2p orbitals

The hybridization between the outmost s orbitals of metal(Bi^(3+),Sn^(2+),Pb^(2+),Ag^(+))and O 2 p orbitals has been widely employed to develop innovative semiconductors with upshift valence band as well as extended visible light response,but it is still challenging to obtain photocatalyst with absorption edge of above 550 nm.Here we report a novel Sn^(2+)-based oxyfluoride Sn_(2)TiNbO_6 F(STNOF)photocatalyst with a pyrochlore structure to exhibit an extended absorption edge to 650 nm and dual functionalities of both water reduction and oxidation.Density functional theory calculations suggest that the unprecedented broad-spectrum response of STNOF is mainly ascribed to the strengthened hybridization between O 2 p and Sn 5 s orbitals remarkably upshifting the valence band,which is caused by the distortion and compressive strain in the Sn06 F2 dodecahedron with second-order Jahn-Teller effect due to partial fluorine substitution.The structural distortion and compressive strain are experimentally confirmed by the Fourier-transformed extended X-ray absorption fine spectra.As probe tests of the photocatalytic functionalities,water reduction and oxidation half reactions were examined to see obvious H_(2)and O_(2)evolution under visible light irradiation.This work may provide an alternative strategy of developing extended visible light responsive semiconductors for promising solar energy conversion.

Heterostructure of Ta_(3)N_(5) nanorods and CaTaO_(2)N nanosheets fabricated using a precursor template to boost water splitting under visible light

Fabrication of heterostructure composed of one-dimensional(1D)and 2D semiconductors has inspired extensive interest in promoting photogenerated charge separation as well as performances of solar fuel production,but it is still challenging for(oxy)nitride photocatalysts due to their uncontrollable ammonia thermal preparative process.In this work,we report a synthesis on heterostructure of Ta_(3)N_(5)nanorods and CaTaO_(2)N(CTON)nanosheets(denoted as Ta_(3)N_(5)/CTON)by directly nitriding a 2D Dion-Jacobson(DJ)type of perovskite KCa_(2)Ta_(3)O_(10)(KCTO)precursor under the assistance of K_(2)CO_(3)flux.It is demonstrated that the 2D morphology of KCTO can be well inherited to get 2D CTON,and the Ta-rich(nonstoichiometric ratio of Ca:Ta compared to CTON)feature of the KCTO as well as the easy evaporation of K species results in the formation of 1D Ta_(3)N_(5)nanorods.Meanwhile,the formation of intermediate species K_(2)Ca_(2)Ta_(3)O_(9)N owning similar crystal lattice as Ta_(3)N_(5)was detected and deduced to be responsible for the generation of Ta_(3)N_(5)nanorods and observation of intimate interface between CTON and Ta_(3)N_(5).Benefitting from the formation of special 1D/2D type-II heterostructure,obviously promoted charge separation as well as photocatalytic water splitting performance can be obtained.Extended discussion demonstrates the generality of the hard-template preparative strategy developed here.To our knowledge,this should be the first fabrication of 1D/2D heterostructure for the(oxy)nitride semiconductors,and the developed hard-template strategy may provide an alternative way of fabricating heterostructures of other semiconductors prepared at high temperature.