Preparation And Multifunctional Applications Of Carbon Dots Assembled Into Mesoporous Aluminas Composites

Carbon dots（CDs）are a new class of carbon nanomaterials smaller than 10 nm.Due to excellent water solubility,environmentally friendly,low toxicity and excellent biocompatibility,CDs have great potential applications in the fields of chemistry sensing,biological imaging,nanomedicine and optoelectronic devices.Because of self-absorption effect of CDs in condensed state,resulting in the quenching of solid-state CDs fluorescence.It is seriously hampered the application of CDs in optoelectronic devices.Compared with traditional matrix,such as starch and inorganic salts,organic starch matrix is thermally instable and NaCl-embedded CNDs do not possess resistance to water,acids or alkali.Mesoporous alumina（MAs）with high surface areas,narrow and order pore distribution in range from 2 to 50 nm,high thermal stability and nonfluorescence have great potential as a matrix.In this work,we carry out the research on the preparation and application of CDs and CD-based fluorescent materials.At the same time,we further explore the properties,mechanism and applications.The summaries of the related studies are as follows:1)A simple method of carbon dot（CD）-based fluorescent materials with good luminescence properties were reported.Polyvinyl alcohol is as carbon source,The blue-light emitting carbon dots（BCDs）enriching in hydrophilic functional groups were prepared by hydrothermal reaction.The quantum yields（QYs）were 34%.Aluminum isopropoxide is as aluminum source,MAs were synthesized by the sol-gel method.Due to the hydrogen bonding between the functional groups of BCDs and the hydroxyls of MAs on the surfaces,BCDs can be successfully assembled into the pores of MAs,the BCD-based fluorescent materials（BCDs/MAs）emitting blue light were synthesized,the QYs were 38%.Because of the ordered pore structure and high surface-to-volume ratios of MAs,BCDs/MAs fluorescent materials have good selectivity and sensitivity to oxygen.2)The CD-based fluorescent materials with dual-emissive peaks were reported.First,Eu³⁺doped mesoporous aluminas(MAs:Eu³⁺)were prepared,then,polyvinyl alcohol is as carbon source,the blue-light-emitting carbon dots（BCDs）were synthesized.Then,by a simple washing,filtration and drying process,the CD-based fluorescent materials(CDs/MAs:Eu³⁺)were synthesized with blue-light and red-light regions.More importantly,the dual-emissive colors can be regularly adjusted through regulating their excitation wavelength or relative mass ratio.The emission intensity of red-light region of the CDs/MAs:Eu³⁺co-doped materials gradually decreased with increasing temperature showing the clear temperature dependence,but that of blue-light region remains almost unchanged,this dual-emissive thermometer was fabricated,owning a great fitted curve in the range from 100 to 360 K under a single wavelength excitation.3)We first reported the blue-and red-light-emitting CDs-based multifunctional fluorescent materials assembled into MAs（BCDs/RCDs/MAs）.Under the excitation of 365nm wavelength,the double CDs-based fluorescent materials（BCDs/RCDs/MAs）are with dual characteristic peaks at 420 nm and 635 nm.The MAs non-fluorescence matrix neither competes for absorbing excitation light nor absorbs the emissions of CDs,lending to excellent PL emitting of the sample.the dual-emissive colors can be regularly adjusted through regulating their excitation wavelength or relative mass ratio.The emissive colors are tunable to white-light region,showing great potential in phosphor-based WLEDs.Then,due to their small particles and the absorption of red and blue lights in the photosynthesis of plants,sunlight conversion films can be prepare with transparent,tensile resistant and high sunlight conversion efficiency.The fluorescent materials can also build a ratiometric fluorescent determination of oxygen.It has a great potential in the field of optical devices,sensing and agricultural conversion film.4)The“off-on”RCDs-based fluorescent probe was fabricated.The fluorescence intensity of the synthesized RCDs solution can be effectively quenched by H⁺,p-phenylenediamine is used as carbon source.After adding OH^-to the CDs/H⁺system,the fluorescence intensity of the CDs/H⁺system will be gradually restored.So we can effectively detect OH^-using CDs/H⁺as a fluorescent probe.The RCDs system can detect H⁺with the linear range of 0-45mM,the LOD is 0.201mM.The CDs/H⁺system can detect OH^-with the linear range of 0-30mM,the detection limit is 0.241mM.Naturally,the pH sensor is fabricated with the linear detection range of 4-13.The nanoprobe can be successfully applied in lake water and urine to detect of H⁺and OH^-.The"off-on"probe shows highly selectivity,repeatability and stability.The CD-based probe provides a good platform for environmental and biosensing applications.