Preparation Of High-efficient Silver/Semiconductor SERS Substrates And Their Applications

Surface enhanced Raman scattering(SERS)has been widely used in biology,environment,and chemistry as one of the most powerful analytical techniques.As the heart of SERS performance,SERS substrate plays a key role in the detection of analytes.Until now,the substrates have been extended from noble metals and transition metal to semiconductor materials,graphene and organic molecular films.Compared with noble metals,semiconductors show some more superior properties,e.g.,adjustable band gaps,better chemical stability,lower cost,and higher uniformity.Therefore,SERS substrates based on semiconductor have attracted increasing interest in recent years.However,the SERS activities of semiconductors are much lower than those of noble metals,which imped their practical application in various chemical and biological sensing.Studies demonstrate that combination of noble metal with semiconductor could effectively improve properties due to the synergistic effect of electromagnetic enhancement and chemical enhsancement Overall,to date,most of reports on semiconductor substrates in SERS performance are mainly focused on oxide semiconductor-based materials including ZnO-based,TiO2-based,WO3-based substrate and so on.Therefore,it is also important to explore other potential semiconductor-based substrates in their SERS use beyond their traditional applications.Cadmium sulfide(CdS)is an n-type ?-? semiconductor with a direct energy band gap of 2.42 eV,which makes it many possible applications in light-emitting diodes,low-cost photovoltaic devices,lasers,and fluorescent labels.However,there are few works on the SERS performance of CdS-based substrates.As a non-toxic and environmentally friendly semiconductor,cuprous oxide(Cu2O)has a narrow band gap(?2.0 eV).And it is also an ideal SERS substrate.Based on the above research background,Ag/CdS nanocomposites and Ag/Cu2O nanocomposites have been chosed as a substrate,and their preparation and SERS performance have been explored deeply.The main research contents of this thesis are as follows:In charpter 2,a simple,economical and environmentally friendly method for hollow sphere-like Ag/CdS nanocomposites with multi-hot spots has been innovatively established.The entire reaction was carried out at room-temperature without the addition of any surfactant.It is worth noting that cadmium ions in aqueous solutions from self-template core dissolved with acid are retrieved and recycled via a simple approach,avoiding waste of resources and environmental problems.Moreover,the strong electromagnetic enhancement located between two neighboring silver nanoparticles on CdS sphere-like surface can be achieved by conveniently adjusting the amount of AgNO3 reagent.Notably,the as-prepared substrate with low loading of silver presents superior SERS performance with the ultralow limit of detection of 10-12 Mol/L for R6G and CV,much lower than many recently reported composite substrates.The significantly enhanced SERS effect is attributed to combinations of several contribution including plasmonic coupling between the Ag nanoparticles and synergistic charge-transfer resonances in the Ag/CdS/dye molecules system,as well as the cadmium defect induced electrostatic forces.As a consequence,the present study not only develops a convenient,environmentally friendly approach toward fabrication of noble/CdS metal composites but also indicates their promising potential application as an ideal SERS substrate in detection of organic pollutants.In chapter 3,a novel,simple and universal method is proposed to synthesize porous sponge-like Ag/Cu2O nanocomposites with oxygen-deficient defects.The method uses urea as a carbon source to synthesize a sponge-like Ag/Cu2O nanocomposite with a porous structure by doping a magnesium source at room temperature.This work found that Ag/Cu2O nanocomposites have a high sensitivity for SERS detection of organic dyes with a minimum detection limit of 10-12 M and an enhancement factor of 107.Therefore,the Ag/Cu2O substrates synthesized in this work have important practical application value for detecting pollutants.In addition,we also explored its enhancement mechanism in detail.The excellent SERS properties of Ag/Cu2O nanosponge can be attributed to the adsorption of cuprous oxide nano-sponge spheres,charge transfer associated with oxygen defects,and electromagnetic interactions between silver particles.This work provides a new idea for preparing an efficient semiconductor-based SERS substrate.