Liquid-liquid Interfacial Synthesis Of Ag₂S Quantum Dots With Near-infrared Fluorescence

In recent years,rapid development of nanoscience has promoted the interdisciplinary studies of physics,chemistry,and biomedicine.Nanomaterials,which are the indispensable foundation of nanoscience,have attracted intensive research interests.Quantum dots?QDs?,as an important branch of semiconductor nanomaterials,possess excellent fluorescence characteristics.Fluorescence in second near-infrared window?NIR-II,1000-1400 nm?has obvious superiority on bioimaging in vivo owing to its deep penetration depth of the tissues and organs.Therefore,it is of great significance to synthesize near-infrared fluorescent QDs with high qualities.Nowadays,many researchers have been focusing on the synthesis and application of Ag₂S QDs,which have emerged as the typical low-toxicity near-infrared fluorescent QDs.However,the controllable synthesis of Ag₂S QDs still remains to be challenging.Aimed at aforementioned difficulties,our group has prepared high-quality QDs based on droplet microreactors which have the advantages of delicate reaction operations,and fast heat and mass transfer.In this thesis,we have dedicated to prepare Ag₂S QDs at the liquid-liquid interface.The primary progress has been summarized as follow:?1?The liquid-liquid interfacial reaction was utilized to prepare Ag₂S QDs with the emission in the near-infrared window.The main work were illusrtrated in details:?Tween 20 was employed to promote the fast emulsification of biphase to form droplets with fine size distribution.In addition,the systems was classified as positive?oil-in-water?emulsion on the basis of fluorescence labelling.?The oil phase dissolved Ag+ capped by oleic acid and oleylamine together,was injected into the water phase dissolved Na2S and Tween 20 while stirring.The precursors distributed in biphase will touch and react at the liquid-liquid interface as a result of emulsification.Hence,Ag₂S QDs with emission-tunable spectra?1001-1279 nm?can be obtained at room temperature?25??.?To control the nucleation and growth of Ag₂S QDs,the constant-flow pump was employed to ensure the aqueous solution containing S2-dropwise into oil solution containing Ag+.Hence,Ag₂S QDs with fine size distributions can be prepared.? Due to the effect of post-synthesis ripening of nanocrystals,the fluorescence intensity of as-prepared Ag₂S QDs can be enhanced greatly with the treatment at 120?.?2?Based on the study of liquid-liquid interfacial reaction,a further developed method involved droplet microdluidic technique was employed in the controllable preparation of Ag₂S QDs.PDMS-glass device was used to achieve interfacial reaction in microchannels.In order to generate uniform O/W droplets,a technique based on repeated processes of adsorption,drying and heat immobilization of poly?vinyl alcohol??PVA?onto PDMS was utilized to make the device hydrophilic.The experiments of water drop contact angles?WCA?indicated that PVA-modified PDMS can be wetted better than native PDMS by water.Consequently,O/W droplets with different patterns and sizes can be obtained by regulating and controlling the flow rates in hydrophilic device.With the fixed flow rates and concentrations of precursors,Ag₂S QDs with the emission peak wavelength at 1056 nm can be prepared based on this simple routine.