The CDs were homogeneous in size and exhibited a partially disordered graphite-like structure. Additionally, their satisfactory optical properties and low toxicity render them as suitable fluorescent probes for biological imaging.
This method has the advantages of cheap instrumentation, low energy consumption, and ease of manipulation of the synthesis parameters for the preparation of homogeneous and high-quality CDs [ 28 , 29 , 30 ].
For instance, Xu et al. By optimizing the ratio of precursors, temperature, and reaction time, CDs with homogeneous size distributions and good fluorescence properties were obtained. The CDs had an average size of 4. Fourier transform infrared spectroscopy revealed a large amount of hydroxyl moieties on the surface of the CDs, endowing them with good aqueous solubility.
Li et al. Such outstanding dual-mode PL provided them with the capability to detect morin in human urine samples with high sensitivity of 0. Many research groups have also developed hydrothermal syntheses using green precursors such as beverages [ 33 , 34 ], fruit extract [ 35 , 36 ], food products [ 37 , 38 , 39 ], and biomass [ 40 , 41 ]. Sahu et al. Wu et al. Despite the simple steps involved in the hydrothermal synthesis, this preparation route usually requires long synthesis times. This is a major impediment for the large-scale production of CDs.
Hence, microwave-assisted hydrothermal synthesis routes have been explored to prepare CDs, as they offer more rapid, uniform, and simple synthesis conditions. Purbia et al. The properties of the as-synthesized CDs could be manipulated by changing the synthesis temperature and duration. Generally, the CD precursor undergoes several processes, including dehydration, polymerization, carbonization, and subsequent formation of CDs. Niu et al. The precursors were liquefied and the color of the solution changed from clear to brown, indicating the formation of CDs.
Chandra et al. Green precursors, such as watermelon peel, have also been used to synthesize CDs in a similar manner. Besides pyrolysis of the precursors in the solid state, pyrolysis in liquid phase is another route to prepare fluorescent CDs. It is worth noting that the solvent where the precursors are dissolved in can play a significant role in the synthesis of CDs.
Mao et al. After naturally cooling down to room temperature, the obtained CDs were purified. This is due to the role of glycerol, which serves as the solvent as well as a carbonization promoter and surface passivation agent.
Wang et al. The CDs were prepared with anhydrous citric acid as the carbon precursor, octadecene as a noncoordinating solvent, and 1-hexadecylaine as the surface passivation agent. These results indicate that the solvents used in the synthesis of CDs influence the physical and optical properties of the as-synthesized CDs.
He et al. Microwave-assisted pyrolysis has also been widely reported as a facile synthesis route for CDs. This synthesis route has the added advantages of being rapid and providing uniform heating, with the possibility of being carried out using a conventional microwave oven.
The researchers produced these C-dots by breaking down the carbohydrate dextrin with microwaves. The resulting C-dots emitted different colours of light when excited by specific wavelengths, even without coating them.
Exactly how this multi-coloured luminescence arises is unclear, but it allows precise control of the light emission that can be tailored to specific needs. To ensure that the C-dots were not toxic, the team added different concentrations of the nanoparticles to cultured cells. After three days, they determined how many cells had survived. I'm an undergrad researcher, amateur carpenter, creator, and tinkerer. My main focus is material science and nanotechnology but I'm just a big nerd.
I like to make things and share my For years I've wanted a simple science experiment that a child could do with parental or adult supervision for nanoscience outreach. I'm tired of simple baking soda volcanoes. You are better than that
Additionally, their satisfactory optical properties and low toxicity render them as suitable fluorescent probes for biological imaging. Hence, microwave-assisted hydrothermal synthesis routes have been explored to prepare CDs, as they offer more rapid, uniform, and simple synthesis conditions. Tao et al. The CDs were released by etching the silica template with sodium hydroxide and purified through dialysis. Chang et al.
Chemical oxidation of green precursors has also been reported to produce homogeneous CDs. The CDs had an average size of 4. I like to make things and share my Also, a strong acid or alkali is required to etch away the template for the release of CDs and additional passivation steps are required to endow the CDs with fluorescence properties.
Original written by Ian Fyfe. The D band corresponds to the vibration of carbon atoms with incomplete bonds in the termination plane of disordered graphite, while the G band is associated with the E2g mode of graphite and the vibration of sp2-hybridized carbon atoms in a two-dimensional hexagonal lattice. Increasing concentrations of C-dots made little difference to cell survival, showing that the C-dots are not toxic and could therefore be used in live tissue. The surface of the CQDs was finally passivated through a platinum-catalyzed process.
They are less toxic than similar alternatives, making them more suitable for use in live biological systems, but the light-emitting properties of those currently made are not ideal.
Exactly how this multi-coloured luminescence arises is unclear, but it allows precise control of the light emission that can be tailored to specific needs. The micelles would reach a critical supersaturation point due to water evaporation, resulting in the simultaneous carbonization of the oligosaccharides and in situ passivation. I'm tired of simple baking soda volcanoes. It was found that higher synthesis temperatures favor the development of sulfur and nitrogen and sulfur co-doped CDs with smaller size, higher sulfur composition, and the occurrence of both down- and up-conversion PL. Also, a strong acid or alkali is required to etch away the template for the release of CDs and additional passivation steps are required to endow the CDs with fluorescence properties.
The composites were subjected to high-temperature treatment and etching to produce nanosized CDs. By optimizing the ratio of precursors, temperature, and reaction time, CDs with homogeneous size distributions and good fluorescence properties were obtained. Besides pyrolysis of the precursors in the solid state, pyrolysis in liquid phase is another route to prepare fluorescent CDs. As the interaction time is determined by the pulse width, bubbles containing different nuclei densities can be formed under the same laser energy but different pulse widths.