New Strategies For Synthesis And Applications Of Carbon Dots

Carbon nano dots are well known and relatively new among carbon nanostructures. Thesecarbon dots offer certain advatntages such as highly photoluminiscent and waterdispersible. Moreover these carbon dots are inexpenmsive and biocompatible so they arepotentially a replacement of semiconductor quantum dots for application especially cellimaging and other bio uses.mostly carbon dots are applied in cell imaging with otherapplications are sensors and catalysts. But mostly the synthesis of carbon nanodots is along and tedious process and requires surface passivating agents to introduceluminescence. So here we purposefully prepared carbon dots through simple and greenroutes. Then these carbon dots have been applied for different applications.In Chapter1we designed and synthesized carbon dots through a green synthesis route.Highly luminescent carbon dots were prepared from a vitamin (Ascorbic acid) and anAmino acid (L-lysine). No surface passivation was required and as synthesized carbondots showed good luminescent properties. Synthesis of carbon dots was done at140°Cwhich is lower than the decomposition temperature of both Lysine and Ascorbic acid. Theprepared carbon dots were highly water dispersible. It was concluded fromcharacterization that in these carbon dots surface carboxylate groups are present whichmake these materials highly dispersible in water and a very good candidate forapplication in bioimaging. From photoluminescence spectroscopy it was observed that when excitation is done at360nm then maximum in emission spectra is440nm whichlies in blue region. By changing excitation wavelength emission spectra also shifts and at480nm excitation it lies in the greenish yellow region.In chapter3we designed and synthesized carbon dots on mesoporous silica. Noimpregnation was done. Ordered mesoporous silica (MCM41) was synthesized.Uncalcined ordered mesoporous silica was subjected to hydrothermal conditions withAscorbic Acid. It was observed from different experiments that Ascorbic acid acts ascarbonizing agent and reduces suitable carbon source to luminescent carbon nanodots. Asa result of hydrothermal treatment surface directing agent inside the pores of non calcinedmesoporous silica was converted into carbon dots. Filterate after the hydrothermaltreatment showed considerable luminescence when was observed under ultra violet lamp.While TEM picture indicated presence of carbon dots on silica surface. Mesoporous silicawith carbon dots can be obtained with different surface areas. Surface area of mesoporoussilica in this case can be controlled by varying conditions like amount of ascorbic acidand time of the treatment. These carbon dots synthesized on the mesoporous silica wereused as catalysts for the photodegradation of methylene blue.equlibrium was establishedunder dark and then under ultra violet lamp photocatalytic reaction were done. Thesecarbon dots as metal free photocatalysts showed good catalytic activity. Ultra violetvisible spectra showed that with the passage of time methylene blue was degraded. Totalorganic carbon (TOC) was measured in comparison with the methylene blue and catalystat equilibrium to ensure that dye was properly degraded. More than50%of TOC resultsshowed that carbon dots catalysts showed good activity and organic carbon wereconverted into carbon dioxide. In chapter4we designed and synthesized carbon dots with high amount of nitrogen andtheir application as sensors. Carbon dots were synthesized from melamine and ascorbicacid. These carbon dots were luminescent but the difference was that the carbon dotssolution was not dark brown as normally it is. The reason was high amount of nitrogenpresent and relatively low carbon contents. These luminescent materials were used assensors for Zinc ions. When zinc ions are added the luminescence of carbon dots isincreased and it tends to continue until a certain amount of zinc. When zinc ions incarbon dots solution were captured by EDTA then luminescence was restored to originalone. These carbon dots have been applied as luminescent bio sensor for zinc ions.