Investigation Of Adsorption Mechanisms Of Aromatic Carboxyl Groups On TiO₂Nanoparticles By Raman Spectroscopy

Surface-enhanced Raman Scattering （SERS） spectroscopy has become a widelyused tool for explorations of interfacial properties and molecular interaction and forcharacterizations of adsorption behaviors and molecular structure. At present,Various SERS active substrates have been reported： such as some noble metals,transitional metals, silver halides, semiconductor and grapheme. Semiconductorsubstrates are used as study chemistry enhanced mechanism, Very few studies ofsemiconductor about SERS in field of application have been reported, the mainreasons that the nature of the enhancement mechanism of semiconductors-basedSERS substrate is still ambiguous, the majority work about semiconductor SERS ison enhance mechanism. In this work, The major contributions of this work are asfollows:1. Surface-enhanced Raman spectroscopy （SERS） has long been considered as anexcellent technique to investigate what happened on surface of nanoparticles. In orderto explore how the aromatic carboxyl groups, which is an kind of traditional group ofSERS probe molecule, absorbed on TiO₂nanoparticles surface, Surface-enhancedRaman scattering of4-cyanobenzoic acid （4-CBA） and4-mercaptobenzoic acid（4-MBA） adsorbed on TiO₂substrate were studied. We designed a TiO₂nanoparticlesseparately absorbed by4-CBA and4-MBA system. By comparison of the Ramanresults obtained by changing the experimental parameters, such as Raman spectrum ofsolid probe molecules, their aqueous solution, and SERS spectra of them afterabsorbed on TiO₂nanoparticles with different sizes, we demonstrated that carboxylgroups would serve as binding group to lead4-CBA absorb on TiO₂. And also, whenput4-MBA on TiO₂nanoparticles surface, both thiol group and carboxyl groupswould bond with TiO₂simultaneously.2.That4-CBA is adsorbed onto TiO₂substrates a wide range of solution pH conditions（pH1.8-10.9） were used to examine the effects of pH on sorption mechanisms. Raman spectroscopy was employed to obtain vibrational frequencies of the organicligands on the TiO₂surfaces and in solution. UV/visible spectroscopy on supernatantsolutions was also employed to confirm that adsorption from solution had taken placefor4-CBA.The SERS of4-CBA on TiO₂surface have been examined over a widerange of solution pH conditions （pH2-12）, Raman spectral features of adsorbed4-CBA are very similar to those measured for4-CBA in solution at basic pH. Theseobservations confirm that4-CBA are predominantly adsorbed at the TiO₂surface inan outer-sphere fashion, with minor inner-sphere adsorption complexes being formedonly under quite acidic conditions. And desorption occur until the ambient solution isalkaline.3. In this part, Pd-decorated TiO₂complex, with surface-enhanced Raman scattering（SERS） enhancement and photocatalytic property, were prepared. The structure andoptical properties of the Pd-decorated TiO₂complex have been characterized.UV/visible spectroscopy on supernatant solutions was also employed to confirm thatadsorption from solution had taken place for PATP and that it does not photooxidationoccur in adsorption progress. Compared with the pure TiO₂. The Pd-decorated TiO₂complex substrates display significant fluorescence quenching ability and SERSresponses. The photochemical characteristics of Pd-decorated TiO₂complex4-aminobenzenethiolate （Pd-decorated TiO₂complex4-ABT） have been investigatedby means of Raman spectroscopy. These surface-induced photooxidationcharacteristics were investigated by monitoring the appearance of Raman peaks of4-NBT. The experimental results showed that When Pd-decorated TiO₂complex4-ABT is irradiated with an argon ion laser at514.5nm, its Raman spectrum changes,resulting in the production of4-NBT capped Pd-decorated TiO₂complex, whichexhibit good performance due to TiO₂-assisted enhanced charge-transfer from TiO₂toPd. The surface-enhanced Raman scattering （SERS） spectrum of4-ABT adsorbed onthose Pd-decorated TiO₂complex is subsequently converted to that of4-NBT.