Phenyl‐Modified Carbon Nitride Quantum Dots with Distinct Photoluminescence Behavior

Abstract

An ovel type of quantum dot (Ph-CN) is manufactured from graphitic carbon nitride by "lining" the carbon nitride structure with phenyl groups through supramolecular preorganization. This approach requires no chemical etching or hydrothermal treatments like other competing nanoparticle syntheses and is easy and safe to use.The Ph-CN nanoparticles exhibit bright, tunable fluorescence,with ahigh quantum yield of 48.4 %i na queous colloidal suspensions.I nterestingly,t he observed Stokes shift of approximately 200 nm is higher than the maximum values reported for carbon nitride based fluorophores.T he high quantum yield and the large Stokes shift are related to the structural surface organization of the phenyl groups,w hich affects the p-electron delocalization in the conjugated carbon nitride networks and induces colloidal stability.T he remarkable performance of the Ph-CN nanoparticles in imaging is demonstrated by as imple incubation study with HeLa cells.Inthe last years,m etal-free graphene-based materials with high biocompatibility,a pparently low toxicity,a nd unique optical properties have been considered to be promising candidates to replace traditional metal-containing quantum dots in bioimaging and biomedical applications.[1] However, the large-scale chemical preparation of graphene-based nanomaterials is far from being simple and usually involves the use of corrosive and toxic agents,w hile the resulting materials exhibit relatively low photoresponse.Furthermore, the origins (quantum confinement, surface states,size effects) of the optical properties are still under debate.[2] Therefore,it is still rewarding to search for new metal-free materials with high fluorescence efficiency.Ametal-free analogue is graphitic carbon nitride with an ideal stoichiometry of C 3 N 4 ,which is set up from layered (tris-)triazine units.Graphitic carbon nitride (referred to as CN) has attracted enormous attention as ap olymeric semiconductor in photocatalysis and electrocatalysis in the last decade.[3] Nevertheless,m ost of these applications focus on the use of macroscopic materials with micrometer-sized particles,a nd the usage of nanosized CN quantum dots in bioimaging and biomedicine,for example,has been limited by their low photoluminescence (PL) quantum efficiency.[4] In the last years,several methods were successfully introduced to enhance the fluorescence efficiency. However,these methods rely on the use of concentrated acid/base processes,e tching, and/or hydro/solvothermal cutting,a nd in some cases,t he emission even fell back into the ultraviolet region.[5] Therefore,afacile,m ild, and more environmentally friendly preparation method for highly fluorescent CN is still required. Ideally,t his method should enable us to tune the PL properties (such as the Stokes shift) of the CN nanoparticles and achieve emission in the visible range.Large Stokes shifts can improve the fluorescence efficiencyowing to the drop in reabsorption events that lead to non-radiative recombination. Thus far, the maximum reported S...

Tuning the Functional Groups on Carbon Nanodots and Antioxidant Studies

“…The unmodified CNDs were characterized with a few spectroscopic techniques. XRD of the CNDs (Figure 1b) shows a diffraction peak at 21.4° with a full width at half maximum (FWHM) of 18.75°, indicating an interlayer distance between the planar carbon-based sheets for disordered graphite structure is about 0.41 nm [35]. Figure 1c shows the Raman spectrum with D bands at 1340 cm −1 (sp 3 -hybridized) and G bands at 1562 cm −1 (sp 2 -hybridized), which presents an intensity ratio I D /I G of 0.91 [36].…”

Controllable Synthesis of Carbon Nitride Films with Type-II Heterojunction for Efficient Photoelectrochemical Cells

“…2,34,35 One general obstacle for the growth and PEC performance of the CN layer lies in the difficulty in preparing a CN/fluorine-doped tin oxide coated glass (FTO) substrate interface with intimate contact. Though great efforts have been made on the modification of these CN precursors to give a better intrinsic photoresponse via heteroatom doping, [36][37][38][39][40][41][42] the introduction of foreign functional groups, 43,44 acid pretreatment 40,45 and precursor design strategy, 21,[46][47][48] the weak CN/substrate interface dramatically impedes the charge collection and thus leads to decreased photoresponse. 1 Moreover, the choice of monomers and growth conditions will determine the quality of CN films for PEC application, i.e., defect states can strongly affect charge separation and overall performance.…”

Synthesis of barbituric acid doped carbon nitride for efficient solar-driven photocatalytic degradation of aniline

“…However, the photocatalytic activity of CN versus the degradation organic pollutants is quite low because of its relatively fast charge recombination and insufficient absorption in the visible-light spectral range. To improve the photocatalytic performance of CN, various modification methods have been applied through structure regulation [10][11][12][13][14][15][16][17][18][19], doping [20][21][22][23][24][25][26][27], surface hetero-junction and copolymerization [28][29][30][31][32][33][34][35][36][37]. Among those methods, copolymerization of CN has been regarded as an efficient route, not only for obtaining an enhance light-absorption, but also for creating surface hetero-structures which could reduce the recombination of photogenerated electron-holes.…”