Theoretical Invesitgation On Adsorption Mechanisms And Degradation Feasibility Of Typical Carbonyl-Containing VOCs Onto Anatase TiO₂ Based Photocatalysts

Carbonyl-containing Volatile Organic Compounds?CVOCs?is a kind of atmospheric pollutants with high chemical reactivity.CVOCs mainly come from vehicle emission,industrial production emission and plants release,etc.It widely consists in the atmospheric environment,including indoor and outdoor environment and inside car environment.CVOCs would stimulate people's eyes,throat,skin and nose mucous membrane system,causing headache,nausea,fatigue and other symptoms,even more cancer.Thus,it attracted widespread attention to the adsorption and degradadtion of CVOCs.In particular,photocatalytic degradation process is a kind of low energy consumption methods of air purification,without pollution.Anatase titanium dioxide is one of the most common types of photocatalyst.Based on density function theory,this work was carried out by Vienna Ab-initio Simulation Package.We have investigated the adsorption mechanisms of acetaldehyde,acetone and methyl acetate adsorbing onto the active?001?surface of anatase titanium.Through the modification of precious metal gold?Au?,the electron configurations of anatase can be changed,then leading to the change of its catalytic activity.Thus,this thesis further consider the effect of modification by different Au_n?n=1-8?clusters size on anatase?001?surface to seek a certain Au_n clusters size which can make the anatase?001?surface with the highest catalytic activity,then achieve the goal of energy saving.The main results of this study were showed as follows:1.Anatase TiO₂?001?surface is more likely to interact with the carbonyl group C atom(O_C=O)of three CVOCs via the Ti_5c sites.There are four O_C=O-Ti_5c adsorption modes for acetaldehyde,three for acetone,and two for methyl acetate,respectively.Especially,acetaldehyde is easily adsorbed onto anatase TiO₂?001?surface via the interaction of C_C=O=O with O_2c,and O_C=O with Ti_5c to form a saddle-like adsorption structure,while acetone and methyl acetate have not this adsorption characteristics.2.Anatase TiO₂?001?surface adsorbs the bare carbonyl group of acetaldehyde with the adsorption energy of 2.30 eV.It is obvious greater than the adsorption energy 0.86 V and0.82 V of acetone and methyl acetate whose carbonyl group are surrounded by methyl and methoxy group,respectively.It is thus clear that the bare carbonyl group is more easily adsorbed onto the anatase TiO₂?001?surface.3.Several small Au_n clusters were optimized,with the range of Au atoms number?n?from 1 to 8,getting the growth structures of the gold particles.Then all Au_n clusters were simulated to load onto anatase TiO₂?001?surface to obtain the geometric structures of load materials.The binding energies and local density of states?LDOS?of the most stable configurations for Au_n/TiO₂?n=1-8?were also calculated.It indicates that all Au-induced states in the anatase?001?surface band gap are predominantly distributed nearby in fermi level,resulting that the overall gap is reduced around 1.00 eV.In particularly,the binding energy?2.74 eV?of Au₃/TiO₂ is the highest.Moreover,when n>1,its band gap of 0.86 eV is the most narrow one.It shows that Au₃/TiO₂ maybe is the most stable Au_n/TiO₂ modified photocatalyst in this study with the highest catalytic activity.4.Acetaldehyde adsorbed onto each stable Au_n/TiO₂ catalysts has been simulated further.The results show that Au₃/TiO₂ has ability to capture acetaldehyde more than the other studied small Au_n/TiO₂ with the adsorption energy of 2.83 eV,even stronger than pure anatase TiO₂?001?surface whose adsorption energy is 2.83 eV.It indicates that the promotion of adsorption capacity of Au_n/TiO₂ catalysts depends on the size and the structure of Au clusters.Especially,Au₃/TiO₂ is lucky to be the most favorable catalyst to adsorb acetaldehyde in all studied Au_n/TiO₂ catalysts with the highest degradation property.Thus,through controlling the size of Au clusters,the researchers may synthesize higher proportional Au₃/TiO₂ catalyst to adsorb and degrade acetaldehyde to realize idea of energy conservation and environmental protection.