Research On The Photocatalysis And SERS Performance Of Modified TiO₂ Nanorod Arrays

Highly ordered Titanium dioxide nanorod arrays has attracted considerable attention because of its safety,low cost,chemical stability,nontoxicity,and biocompatibility.However,there are still two major challenges.The first one is inefficient utilization of visible energy due to its large band gap（3.0–3.2 e V）and the other one is fast recombination of e^--h⁺pairs,which leads to low photoreactive performance and photocatalytic activity.To overcome these two major disadvantages,many attempts have been made.For example,using plasma metal nanoparticles to sensitize TiO₂ can not only enhance the separation of charge carriers,but also provide effective excitation sites for photocatalytic reactions,resulting in the flow of high-energy hot electrons to semiconductors,and broaden the range of light absorption.Au,Ag and Pt have been used to enhance the photoelectric response ability of TiO₂,which has been applied in the fields of photodegradation removal of organic pollutants and surface-enhanced Raman scattering（SERS）.In addition,black phosphorus nanosheets（BPNS）are highly promising two-dimensional materials due to their honeycombed structure,excellent electronic properties,excellent carrier mobility,adjustable direct bandgap ranging from 0.3 e V（bulk）to 2.0 e V（monolayer）,anisotropy,and inherent in-plane ferroelectric properties.It has attracted much attention in the field of electronics and optoelectronics.At the same time,zero-dimensional（0D）black phosphorus quantum dots（BPQDs）derived from two-dimensional BP nanosheets have the advantages of smaller size,higher specific surface area,and more active cell edge positions,which are considered to have good photoelectric and catalytic properties.The construction of TiO₂-based ternary heterojunction co-modified by quantum dots（nanosheets）and plasma metal nanoparticles has been proved to be a very effective method to improve catalyst and SERS base activity,but there are still many challenges.The main contents are as follows:1.Ternary heterojunction BPQDs/Au/TiO₂ with efficient degradation of levofloxacin were prepared.The results indicated that the decomposition efficiency of levofloxacin reached93.7%,and the reaction rate constant（Kα）was as high as 32.66×10^-3 min^-1.Based on the results obtained from both density functional theory（DFT）calculations and experiments,three possible decomposition pathways of levofloxacin were suggested.Moreover,photocatalysis can effectively decrease the toxicity of the intermediates.The outstanding activity of BPQDs/Au/TiO₂ is due to the cooperative effect of all the components.First,Au,as an LSPR motivator,can offer many high-energy electrons during the catalytic process.Second,the indirect interfacial electron transport mode from BPQDs to Au and then to TiO₂promotes the separation of photoinduced carriers,which prolongs the lifetime of e^--h⁺pairs and significantly improves the performance.Third,the good light-capture ability of BPQDs is an important feature.In summary,this study suggests a new direction for the construction of heterojunction catalysts with excellent performance in advanced oxidation processes.2.Herein,a high-performance ternary heterostructure fabrication of BPQDs and Ag nanoparticles co-modified TiO₂ nanorod（BPQDs/Ag/TiO₂）was successfully developed.The highest efficiency for tetracycline hydrochloride（TC）photodegradation could reach 92.4%.Meanwhile,the corresponding degradation constant Kαwas up to 27.84×10^-3 min^-1.In the TC removal reaction,two possible degradation pathways were revealed.BPQDs/Ag/TiO₂could also reduce the toxicity of TC via photocatalytic reaction.Synergistic action of TiO₂,Ag,and BPQDs were responsible for excellent photocatalytic performance.First,TiO₂nanorods served as good support and transfer channels.Second,Ag nanoparticles acted as LSPR photosensitizer,which provided high-density hot electrons injection into TiO₂.Third,efficient charge separation in BPQDs was achieved by the charge delivery from BPQDs to TiO₂via Ag as an electron relay,leading to a prolonged lifetime of carriers.In addition,both BPQDs and Ag could expand the light harvest ability.3.BPQDs and Ag nanoparticles co-sensitized TiO₂ nanorod arrays were successfully fabricated as powerful SERS substrate.For BPQDs/Ag/TiO₂,its detection limit of 4-mercaptobenzoic acid（4-MBA）molecules could achieve even at as low as 1.0×10^-12 M,and the enhancement factor（EF）is up to 2.5×10⁵,exhibiting an excellent SERS sensitivity.Furthermore,a good uniformity is also observed during the detection process,the relative standard deviation of 4-MBA Raman fingerprint peak intensity at 1587 cm^-1 is only 7.3%.Furthermore,BPQDs/Ag/TiO₂ substrate is demonstrated to have good repeatability and stability.The synergistic effect of BPQDs,Ag nanoparticles and TiO₂ nanorod array is mainly responsible for improved SERS activity,namely,high-density hot spot,optical capture expansion and enhanced charge transfer.4.High-performance surface-enhanced Raman scattering（SERS）substrates and photocatalysts based on TiO₂ nanorod arrays co-sensitized with black phosphorus nanosheets（BPNS）and Ag nanoparticles（BPNS/Ag/TiO₂）were successfully synthesized.The detection limit of the rhodamine 6G（R6G）on this novel SERS substrate was as low as 1.0×10^-14 M.The calculated enhancement factor（EF）was as high as 3.81×10⁵.These results prove the excellent SERS sensitivity of the BPNS/Ag/TiO₂substrate.Furthermore,a good uniformity of the signals was observed during the detection process.The relative standard deviation of the intensity of the Raman fingerprint peak of R6G at 1650 cm^-1 was only 8.41%.Moreover,the BPNS/Ag/TiO₂ substrate exhibited self-cleaning abilities through the photocatalytic degradation of the adsorbed R6G molecules.The BPNS/Ag/TiO₂ substrate exhibited a maximum rate of 93.5%for the photocatalytic degradation of R6G.The corresponding photodegradation rate constant was 34.2×10^-3 min^-1,which was approximately 3.98 and 2.01times higher than those of the TiO₂ and Ag/TiO₂arrays.The improved SERS performance and excellent photocatalytic activity of the BPNS/Ag/TiO₂ substrate was due to the formation of high-density hot spots,expansion of the optical capture abilities,and enhancement of the charge transfer properties.