Luminescence phenomena of carbon dots derived from citric acid and urea – a molecular insight

Kasprzyk, Wiktor; Świergosz, Tomasz; Bednarz, Szczepan; Walas, Karolina; Башмакова, Н. В.; Bogdał, Dariusz

doi:10.1039/c8nr03602k

Cited by 200 publications

(204 citation statements)

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“…Citric acid (CA) is a weak organic acid, which is largely employed as a non‐toxic and low‐cost precursor, alone or in combination with other compounds, to synthesise fluorescent carbon dots (C‐dots). C‐dots synthesised from CA exhibit, in general, a blue luminescence of lower intensity in comparison to C‐dots prepared from other precursors .…”

Section: Introductionmentioning

confidence: 99%

Carbon Dots from Citric Acid and its Intermediates Formed by Thermal Decomposition

Ludmerczki

Mura

Carbonaro

et al. 2019

Chemistry A European J

104

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Thermal decomposition of citric acid is one of the most common synthesis methods for fluorescent carbon dots; the reaction pathway is, however, quite complex and the details are still far from being understood. For instance, several intermediates form during the process and they also give rise to fluorescent species. In the present work, the formation of fluorescent C‐dots from citric acid has been studied as a function of reaction time by coupling infrared analysis, X‐ray photoelectron spectroscopy, liquid chromatography/mass spectroscopy (LC/MS) with the change of the optical properties, absorption and emission. The reaction intermediates, which have been identified at different stages, produce two main emissive species, in the green and blue, as also indicated by the decay time analysis. C‐dots formed from the intermediates have also been synthesised by thermal decomposition, which gave an emission maximum around 450 nm. The citric acid C‐dots in water show short temporal stability, but their functionalisation with 3‐aminopropyltriethoxysilane reduces the quenching. The understanding of the citric acid thermal decomposition reaction is expected to improve the control and reproducibility of C‐dots synthesis.

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Section: Introductionmentioning

confidence: 99%

Carbon Dots from Citric Acid and its Intermediates Formed by Thermal Decomposition

Ludmerczki

Mura

Carbonaro

et al. 2019

Chemistry A European J

104

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“…Hydrothermal treatment in an autoclave and microwave exposure are simple synthesis for producing luminescent C-dots from citric acid and urea. Low QY (16%) 1 have been obtained by processing the dots via oven treatments, with even lower QY values observed in microwave processed samples (10-15%) 11,13,14 . An exception has been reported 15 for a synthesis carried out in microwave.…”

mentioning

confidence: 98%

“…The UV-Vis spectra of the CU2 sample dispersed in water ( Fig. 1a) (black line) show two UV absorption bands attributed to the π-π* transition of aromatic sp 2 domains (234 nm) and to the n -π* transition of C=O bond (345 nm) 13 . Another absorption band, peaking at 425 nm, is assigned to n-π* transitions of the functional groups on the C-dots surfaces.…”

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confidence: 99%

“…1d). Because the UV-Vis absorption of citrazinic acid is characterised by a main band peaking around 340 nm, this molecule and its derivates should be the primary source of the fluorescence at around 450 nm 1,7,13 ( Supplementary Information, Fig. S1).…”

mentioning

confidence: 99%

“…2a) show the presence of different absorption bands around 213, 248, 272 and 410 nm. In a recent article, Kasprzyk et al 13 have discussed the origin of the green emission of CA-urea C-dots formed at high molar ratios. They have identified 4-hydroxy-1H-pyrrolo [3,4-c]pyridine-1,3,6(2 H,5 H)-trione (HPPT), which forms from the citrazinic acid, as the main source of fluorescence.…”

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confidence: 99%

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Integrating sol-gel and carbon dots chemistry for the fabrication of fluorescent hybrid organic-inorganic films

Mura

Ludmerczki

Stagi

et al. 2020

Sci Rep

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Highly fluorescent blue and green-emitting carbon dots have been designed to be integrated into solgel processing of hybrid organic-inorganic materials through surface modification with an organosilane, 3-(aminopropyl)triethoxysilane (APTES). The carbon dots have been synthesised using citric acid and urea as precursors; the intense fluorescence exhibited by the nanoparticles, among the highest reported in the scientific literature, has been stabilised against quenching by APTES. When the modification is carried out in an aqueous solution, it leads to the formation of silica around the C-dots and an increase of luminescence, but also to the formation of large clusters which do not allow the deposition of optically transparent films. On the contrary, when the C-dots are modified in ethanol, the APTES improves the stability in the precursor sol even if any passivating thin silica shell does not form. Hybrid films containing APTES-functionalized C-dots are transparent with no traces of C-dots aggregation and show an intense luminescence in the blue and green range.Carbon dots (C-dots) are fluorescent nanomaterials with optical properties comparable to semiconductor quantum dots. C-dots, however, have a much lower cost and environmental impact, which make them a hot topic of research 1,2 . A major advantage is the possibility to produce C-dots from an almost endless variety of precursors and methods. On the other hand, strict control of the properties through the process is still challenging to achieve, and the main efforts are now dedicated to obtaining reliable and reproducible synthesis.The citric acid (CA) alone or in combination with other compounds is one of the most popular precursors for C-dots 3 . CA-based C-dots have on their surface different carboxy-groups, which increase the solubility and allow surface passivation or functionalization with organic molecules 4-6 or polymers 7 . In general, pure CA C-dots, without any modification, show a weak emission, and doping 1 with B, N, S, Si and P atoms is a possible solution to improve their quantum yield. Most of the CA C-dots are doped with nitrogen that enhances the luminescence by producing azo-compounds through the reaction between the carboxylic and amino groups; after carbonisation, they form water-dispersible and highly emitting C-dots 8 . Different amines have been used for this purpose, such as ethylenediamine (EDA) 2,5,9 , hexamethylenetetramine 6 , o-phenylenediamine (o-PD) 10 , triethylenetetramine 11 , hexadecylamine (HDA) 8 , and triethanolamine 6 . Quantum yields (QY) under 8% for most of the amines, with the exception of EDA 6 which gives a QY of 86%, have been obtained. Urea, because of the high nitrogen content, can be used for doping CA C-dots 1,5,12-17 and different methods have been developed so far. Hydrothermal treatment in an autoclave and microwave exposure are simple synthesis for producing luminescent C-dots from citric acid and urea. Low QY (16%) 1 have been obtained by processing the dots via oven treatments, with even lower QY value...

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A Supraparticle‐Based Five‐Level‐Identification Tag That Switches Information Upon Readout

Miller

Wintzheimer

Prieschl

et al. 2020

Advanced Optical Materials

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Product identification tags are of great importance in a globalized world with increasingly complex trading routes and networks. Beyond currently used coding strategies, such as QR codes, higher data density, flexible application as well as miniaturization and readout indication are longed for in the next generation of security tags. In this work, micron‐sized supraparticles (SPs) with encoded information (ID) are produced that not only exhibit multiple initially covert identification levels but are also irreversibly marked as “read” upon readout. To achieve this, lanthanide doped CaF2 nanoparticles are assembled in various quantity‐weighted ratios via spray‐drying in presence of a broad‐spectrum stealth fluorophore (StFl), yielding covert spectrally encoded ID‐SPs. Using these as pigments, QR codes, initially dominated by the green fluorescence of the StFl, could be generated. Upon thermal energy input, these particle‐based tags irreversibly switch to an activated state revealing not only multiple luminescent colors but also spectral IDs. This strategy provides the next generation of material‐based security tags with a high data density and security level that switch information upon readout and can be, therefore, used as seal of quality.

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Luminescence phenomena of carbon dots derived from citric acid and urea – a molecular insight

Cited by 200 publications

References 53 publications

Carbon Dots from Citric Acid and its Intermediates Formed by Thermal Decomposition

Carbon Dots from Citric Acid and its Intermediates Formed by Thermal Decomposition

Integrating sol-gel and carbon dots chemistry for the fabrication of fluorescent hybrid organic-inorganic films

A Supraparticle‐Based Five‐Level‐Identification Tag That Switches Information Upon Readout

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