Three Colors Emission from S,N Co‐doped Graphene Quantum Dots for Visible Light H₂ Production and Bioimaging

Abstract

A facile solvothermal route to synthesize S,N co‐doped graphene quantum dots (S,N‐GQDs) with unique optical properties is demonstrated. Three absorption bands are observed at 338, 467, and 557 nm, which is different from any previous reports. The photoluminescent spectra display emissions in three primary colors that are independent of the excitation wavelength, within the excitation wavelength ranges of 340–420 nm, 460–540 nm, and 560–620 nm. The PL excitation spectra indicate that each emission is related to a single excitation band. It is proposed that three independent luminescent centers coexist in S,N‐GQDs because the doping with S and N may change the chemical environment of the GQDs. However, energy‐transfer processes usually do not occur among the independent luminescent centers under different wavelength light excitation. Heteroatom‐doping of GQDs provides an attractive means of effectively tuning their optical properties for the purpose of exploiting new applications in visible‐light photocatalytic and bioimaging. S,N‐GQDs/TiO2 composites exhibit better hydrogen production activities under visible light (λ > 420 nm) than commercial TiO2 (P25), owing to the presence of characteristic absorption bands in the visible region. Furthermore, the S,N‐GQDs have a pronounced biocompatibility and bioimaging ability under long‐wavelengths excitation for live A549 cells.

Carbon Dots: Bottom‐Up Syntheses, Properties, and Light‐Harvesting Applications

“…[58] To enhance the catalytic efficiency of H 2 evolution, CDs play ac ritical role as electron acceptor/donors and photosensitizers. [59] For example, Bhattacharyya et al developed N-doped CDs to confirm the Ne ffecti np hotocatalytic efficiency.T hey prepared the different Nc ontentsa nd configuration of CDs (from citric acid) by controlling the amounts of polyethyleneimine (PEI). [60] At ah igh PEI content,Natoms were distributed at the edge sites of the aromatic domains, thus enablinge fficient charge separation and production of H 2 at ar ate of 18.7 mmol g À1 h À1 .X ue tal.…”

Graphene Quantum Dots Decorated Titania Nanosheets Heterojunction: Efficient Charge Separation and Enhanced Visible‐Light Photocatalytic Performance

“…However,c ompared to the extensive investigation of GQDs in solar cells, [36][37][38] biosensing [39,40] and bioimaging, [41][42][43] the photocatalytic applications have attracted little attention of GQDs althought his is increasing. It is wellk nown that graphene is az ero band gap conductor that cannotb ed irectly used as ap hotocatalyst.…”

Recent Advances in Graphene Quantum Dots as Bioimaging Probes

“…Because of their low cost and easy availability, natural resources such as coffee grounds [100], cow milk [101,102] and neem leaf extract [103] are used to fabricate fluorescent GQDs by hydrothermal or microwave irradiation strategies. Low-cost organic compounds, such as citric acid [104][105][106][107][108][109][110][111][112], acetylacetone [113], glucose [114][115][116][117], fructose [118], ethylene diamine tetraacetic acid (EDTA) [119], adenosine 5′-triphosphate disodium salt (ATP) [119,120], glutamic acid [121] and humic acid [122], are also the most commonly used starting materials for the synthesis of GQDs either via pyrolysis or microwave irradiation or hydrothermal/solvothermal treatment. Moreover, due to their similarity in structure, polycyclic aromatic hydrocarbons are generally regarded as nanoscaled fragments of graphene, which gives them great promise for preparing monodispersed GQDs with precisely tailored structure, morphology and size.…”

“…So, dicyandiamide (DCD) [105,106,112], ammonium hydroxide [77,89,91,93,114,115,[129][130][131][132], diethylenetriamine (DETA) [133], urea [107], ethylenediamine (EDA) [111], dimethylformamide (DMF) [38,134] and hydrazine hydrate [123] are chosen as the nitrogen source for doping or modifying GQDs to synthesize nitrogen-functionalized GQDs, while 1,4-phenylene bis(boronic acid) [65], boron oxide (B 2 O 3 ) [76] and Na 2 B 4 O 7 [135] are employed as boron sources to prepare boron-functionalized GQDs. Also, nitrogen and sulfur co-functionalized GQDs are successfully obtained using nitrogen and sulfur containing compounds of 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl) imide [68], polythiophene [136] and thiourea [110]. Moreover, o-dichlorobenzene [128], ATP [119,120] and 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide [68] are utilized as sources to prepare chloride-, phosphorus-and fluoride-functionalized GQDs, respectively.…”

“…With the increase of effective π-conjugation length and N content, the emission band of N-GQDs redshifts to green and yellow. In the other case, by using citric acid as the carbon source, thiourea as the N and S source and DMF as a solvent, the three colors of blue-, green-and redemitting N,S-doped GQDs (N,S-GQDs) were synthesized [110]. Being different from other reported GQDs, this N, S-GQDs exhibited three excitation wavelength-independent photoluminescence regions with emission peaks at 440 nm (blue), 550 nm (green) and 640 nm (red) at excitation wavelength intervals ranging from 340 to 420 nm, 460 to 540 nm, and 560 to 620 nm, respectively, suggesting each emission is related to a unified chromophore on the N, S-GQDs.…”