Preparation Of Platinum Quantum Dots Loaded Tungsten Disulfide Nanosheets Composites And Investigation Of Gas-sensing Properties?In Situ Raman For NH₃ At Room Temperature

The development of science and technology has brought about earth-shaking changes in people's lives.At the same time,the toxic,flammable and explosive gases such as industrial waste gases and automobile exhaust have threatened the health of residents.Ammonia is one of the most dangerous gases.The high concentration of ammonia in the air is unfavorable to human health.Even if the ammonia concentration in the chemical plant is too high,there is even the risk of explosion.In addition,the occurrence of some diseases is related to the amount of ammonia exhaled by the human body.Therefore,effective detection of ammonia is quite necessary.At present,the resistance type semiconductor gas sensors are widely concerned with advantages such as simple process,low cost and portability,and it mainly judges the gas-sensing performance through the change of electrical signal caused by the electrons transfer after gas interacting with the surface of sensitive materials.As a practical gas sensor,its main requirements are good response,stability and selectivity at room temperature.As a typical layered metal sulfide gas sensing material,WS₂ has an excellent structure,the narrow optical band gap,good electrons transport properties and so on.It has become an important research object in the field of gas sensing.However,the bulk WS₂ exhibits high response but hard recovery at room temperature.Therefore,how to ensure high response and improve recovery has become a research focus.In addition,due to the disadvantages of traditional gas-sensing detection methods in the processing of collection and treatment of electrical signals,this paper creatively uses the in-situ Raman technology under atmosphere to detect gas-sensing performance of sensitive materials,and this approach reflects the possibility of using light signals instead of traditional electrical signals to detect the gas-sensing performance.First,the bulk WS₂ was used as the raw material to synthesize ultra-thin WS₂nanosheets with the thickness of about 2 layers by lithium ion intercalation thinning method.On this basis,Pt QDs/WS₂ NSs composites with different molar ratios?Pt:WS₂?were synthesized by in-situ hydrothermal method.By comparing the gas-sensing properties of ammonia with pure WS₂ nanosheets and composites at room temperature,it was found that the recovery time of composites and pure WS₂ nanosheets were 912 s and1200 s respectively,indicating that the in-situ hydrothermal method guarantees that the composites have good recovery property.In addition,compared to pure WS₂ nanosheets,the response value of the composite to ammonia was greatly increased,and the response value increased nearly 10 times at the optimal molar ratio?0.1?.This is due to the adsorption and high catalytic activity of the Pt quantum dots to oxygen,and the generation of reactive O₂^-reacts with ammonia gas to produce a large amount of electrons to inject into WS₂ nanosheets,leading to a great change in the conductance of the host material.XPS results showed that there is Pt-S interface bonds between Pt and WS₂ interface,which is conducive to the electrons transfer between the two phases.Moreover,the response value of the composite material exhibits an approximately linear relationship with the ammonia concentration,and the composite materials hve good stability and selectivity to ammonia.The in situ Raman technology under atmosphere is adopted to measure the Raman spectra of pure WS₂ nanosheets and the composites of different molar ratios under the atmospheres of air and ammonia,and a characteristic peak(-NO₂:1328 cm^-1)was found in the Raman spectrum of composites under ammonia atmosphere compared with air.The peak intensity ratio of the characteristic peak to the strongest Raman peak of the pure WS₂nanosheet is taken to determine the relationship between the molar ratio in the atmosphere of air and 1000 ppm ammonia respectively and the optimum molar ratio of 0.4 was determined.In addition,the relationship between the peak intensity ratio and the ammonia concentration of the composites of the optimal molar ratio was studied.It was found that they presented an approximate linear relationship and exhibited good stability and selectivity to ammonia.What's more,by calculating the effective loading area percentage of the actual quantum dot loading on nanosheets,it is found that there is an approximate linear relationship between the theoretical molar ratio and the actual effective loading area percentage,indicating that the changing trend between the actual effective loading area percentage and the peak intensity ratio is consistent with it.The above research shows that in situ Raman technology has a huge application prospect in the field of gas detection in the future.