First-principles Study Of Non-metal Co-doping, Metal And Non-metal Co-doping Rutile Titanium Dioxide

Rutile TiO2 is a new semiconductor photocatalytic material.It has many advantages such as good stability,innocuity,corrosion resistance,high efficiency,no pollution and low price.It has become the most widely used material nowadays.Because rutile TiO2 has a wide band gap(3 eV).it only has catalytic activity in the range of ultraviolet light(wavelength less than 400 nm),which makes low utilization of visible light.These limit the practical application of TiO2 in the field of photocatalysis technology.Therefore,most scholars use ion-doping to expand the response to visible light.For this reason,the first principles study is carried out on the influence of non-metal single doping,non-metal co-doping,and metal-nonmetal co-doping on the geometric structures,defect formation energies,density of states,charge distribution and optical properties of TiO2.Based on the density functional theory,we use the CASTEP module in the Materials Studio program to optimize the geometric structure,using the plane-wave ultrasoft pseudopotentials method.After optimizing the structures,we use HSE06 hybrid functional with modified 6-31G basis sets under the framework of the Gaussiantype orbital to calculate electronic performance.The calculated bandgaps are very close to the experimental values,thus they could be deemed as real experimental values.The results show that the lattice distortion will occur after substituting B/C/N/F/S for O,and the lattice distortion will be more obvious after C/N/S interstitial doping.Non-metal substitution single-doping systems have better stability under Ti-rich condition,and the N substitution doped system is the most stable one.However,Non-metal interstitial single-doping systems have better stability under O-rich condition.After C interstitial doping,a shallow impurity energy level near the top of the valence band is introduced,which can capture photo-generated holes and improve the photocatalytic activity in the visible light region.The non-metal substitution co-doping rutile TiO2 are also more stable under the Ti-rich condition.After(C,N)substitution co-doping,a shallow impurity energy level is introduced into the forbidden band,and the spin up/down band gaps decrease obviously.The band gap of(N,S)substitution co-doping decreases obviously,without any impurity energy levels in band gap.The synthesis of non-metal interstitial co-doping systems is more stable under O-rich condition.The B-N interstitial co-doping system is most stable when they are mixed in the symmetrical interstitial position.After(N,S)interstitial co-doping,the shallow impurity energy levels are introduced into the spin up/down band gaps.Moreover,the band gap decreases most obviously.Therefore,this doping scheme can greatly improve the photocatalytic activity of rutile TiO2 in the visible light region.Metal and non-metal substitution co-doped systems have relatively high stability under O-rich condition.The formation energy of(Nb,N)co-doping is the lowest,which is the most easily synthesized in the experiment.After(Cr,C)substitution co-doping,the shallow impurity energy level is coupled with the top of valence band and the bottom of conduction band,respectively,which results in band gap narrowing and decreasing the energy for the electron transition to the conduction band.This greatly improves the conversion efficiency of photon-quantum.Metal and non-metal interstitial co-doping systems are also relatively stable under O-rich condition.After doping,the deep impurity energy levels are introduced in the band gap.Although these systems expand the range of response to visible light,the recombination probability of the photo-generated carrier is increased,which is not beneficial to improve the photocatalytic activity of the rutile TiO2.