Theoretical Study On Doping Modification And Molecular Adsorption Of Titanium Dioxide

Finding sustainable and renewable energy is an urgent task due to the energy and environmental crisis.Titanium dioxide is a common semiconducting metal oxide and is receiving increasing attention due to its chemical stability,strong oxidizing power,non-toxicity and low cost.Doping is an effective means to improve the photocatalytic performance of rutile titanium dioxide.In addition to the common rutile titanium dioxide,TiO₂-B has also attracted more and more attentions due to its potential applications in lithium ion batteries and dye-sensitized solar cells.People pay more attention to the surface stability and activity of TiO₂-B.By using first-principles calculations based on density functional theory,Nb atom doped rutile titanium dioxide and acetic acid adsorption on different TiO₂-B surfaces was studied.The main findings in our thesis are as follows:1.The structural and electronic properties of Nb doped rutile TiO₂ with several doping configurations were investigated by first-principles calculations based on density functional theory.Firstly,our calculations show that although the band gap in Nb_Ti,2(Nb_Ti),and Nb_Ti+O_i systems is small,the intragap states would be the electron-hole recombination center,leading to low photocatalytic efficiency.Secondly,for 2(Nb_Ti)+O_i configuration,the impurities states are mainly located at the top of the valence band and the electron-hole recombination would be inhibited,indicating relatively higher photocatalytic efficiency.Based on charge compensated theory,two electrons on the transition metal Nb atoms compensate the same amount of holes on the acceptor level of nonmetal interstitial oxygen,in the model of2(Nb_Ti)+O_i.Such donor-acceptor codoping may not only suppress the electron-hole recombination but also maintain a reduced band gap,suggesting that the doping models would exhibit higher photocatalytic activity than pure TiO₂.Finally,our calculation results show that the interstitial oxygen atoms play an essential role in manipulating the valence state of impurity Nb.The role of interstitial oxygen in Nb-doped rutile TiO₂ suggests that it can give rise to beneficial charge compensation effects.2.Interaction between acetic acid and different TiO₂-B surfaces（i.e.,（001）,（110）,（010）,（100）facets）are investigated by density functional calculations.Several configurations are considered to construct adsorption structures,including non-dissociative and dissociative mode.The main findings are:1).The dissociative mode is energetic favorable with a noticeable adsorption energy.2).The adsorption configuration is not only correlated with the matched interface structures,but also correlated with the electrostatic potential distribution on Lewis acid（Ti*）and basic（O*）sites.3).TiO₂-B（010）and TiO₂-B（100）surfaces provide a considerable oscillation of electrostatic potential between Lewis acid and basic sites.Such oscillatory electrostatic potential provides an extra driving force to promote acetic acid dissociation.4).Adsorption energy of acetic acid on TiO2-B（010）and TiO2-B（100）are very similar,therefore the adsorption process does not show selectivity toward these two specific surface.