Study On Adsorption And Activation Of Molecules On Low-dimensional Tio₂ Nanomaterials

Due to its unique physical and chemical properties,low-dimensional TiO₂ has broad application prospects in fields such as dye-sensitized solar cell,photocatalysts and sensors.Considering the complexity of low-dimensional TiO₂ structures and the related processes,it is of much necessity to employ both theoretical and experimental methods to examine it.In this study,several typical molecules and different low-dimensional TiO₂ structures?for example TiO₂ surfaces and nanotubes?are chosen as model systems.By the combination of multiscale simulation and experiments,the adsorption,activation and reaction of these molecules on different TiO₂ structures are systematically investigated.These studies have important scientific significance and certain guiding value for the applications of low-dimensional TiO₂.Firstly,formic acid photodegradation is one of the most important reactions in organic pollution control,and also one major pathway for the hydrogen production on titanium dioxide photocatalysis.Based on density functional theory and ReaxFF molecular dynamics,the adsorption,diffusion and activation of formic acid on the different anatase TiO₂?101?,?001?,?010?surfaces are investigated.The following conclusions can be drawn:The highly active anatase TiO₂?001?surface can intensely adsorb formic acid and its dissociated intermediates,but a bad reconstruction of the anatase TiO₂?001?surface occurs simultaneously.Consequently,anatase TiO₂?001?surface does not adsorb and activate formic acid.The stable anatase TiO₂?101?surface can adsorb formic acid and hardly cause surface reconstruction.The stability of its total energy is beneficial for the adsorption and activation of formic acid.The adsorption of dissociated intermediate COOH on different anatase TiO₂ surface is stronger than that of HCOO,which also leads to a drastic surface reconstruction.With the synergistic effect of acid of hydroxy and acid of O on TiO₂?101?surface,the hydroxyl H is first removed during the dehydrogenation reaction of formic acid on anatase TiO₂?101?surface.The high active intermediate HCOO radical makes the subsequent removal of a-H much easier.The removal of a-H determines the rate of the dehydrogenation reaction.The conclusions from ReaxFF molecular dynamics study on the adsorption,diffusion and activation of formic acid are consistent with those from DFT calcualtions.Secondly,the adsorption and reaction of molecules in confined space show unique properties.The CO adsorption and oxidation on titania nanotube arrays are investigated.Density functional theory?DFT?calculations are adopted to investigate the structural andelectronic properties of V-,Cr-,Pd-,Pt-,and Au-doped titania nanotube arrays?TNTAs?where Ti is replaced by dopants.The adsorption of CO and the formation of CO₂ on these various nanotube arrays are also studied in detail.It is found that CO physisorbes weakly inside the TNTAs and CO is oxidized by lattice oxygen to form CO₂ by the redox mechanism.This may thus be attributed to the unique confinement effect and to different metal doping.All the metal doped systems except theCr-TNTAs show a lower activation energy barrier than the undoped TNTAs,indicating that proper metal dopants can promote CO oxidation.The reaction on the Pd-or Au-doped TNTAs has the lowes barrier.Therefore,it is found that Pd-or Au-doped TNTAs leads to enhanced catalytic activity for CO oxidation at low temperatures.Thirdly,the properties of glyoxal on Pd clusters with or without TiO₂ surfaces are investigated.It is found that TiO₂ enhances the adsorption of glyoxal on Pd clusters.While on bare Pd clusters,the study also shows that the C-H bond in glyoxal is easily to be broken to form HCOOC groups,which react with 0 or OH respectively to form glyoxylic acid.The reaction barriers of these process are smaller than 11.53 Kcal/mol.Finally,the photodecomposition of methyl orange on TiO₂-based composite photocatalyst under different conditions is investigated.Optimal experimental conditions are obtained:1.7 mL TBT,0.6 mL HF,15 mg GO and 10 mL ethanol.This catalyst exhibits higher activity than P25,and after repeated cycles,a methyl orange degradation rate of up to 90%can still be achieved.