Fluorescent chemosensor for pyridine based on N-doped carbon dots

doi:10.1016/j.jcis.2015.07.053

Journal of Colloid and Interface Science

Volume 458, 15 November 2015, Pages 209-216

https://doi.org/10.1016/j.jcis.2015.07.053 Get rights and content

Abstract

Fluorescent carbon dots (CDs) and its nitrogen doped (N-CDs) nanoparticles have been synthesized from lactose as precursor using a bottom-up hydrothermal methodology. The synthesized nanoparticles have been characterized by elemental analysis, FTIR, Raman, TEM, DLS, XPS, and steady-state and life-time fluorescence. The synthesized carbon nanoparticles, CDs and N-CDs, have a size at about 7.7 ± 2.4 and 50 ± 15 nm, respectively, and quantum yields of 8% (CDs) and 11% (N-CDs). These techniques demonstrated the effectiveness of the synthesis procedure and the functionalization of the CDs surface with amine and amide groups in the presence of NH₃ in aqueous media. The effect of excitation wavelength and pH on the luminescent properties was studied. Under the optimal conditions, the nitrogen doped nanoparticles can be used as pyridine sensor in aqueous media because they show an enhancement of its fluorescence with a good linear relationship. The analytical method is simple, reproducible and very sensitive for pyridine determination.

Graphical abstract

Introduction

Among the recent advances of novel materials, carbon quantum dots nanoparticles (in short carbon dots, CDs), are a new class of carbonaceous nanomaterials with potential advantages to the toxic metal based quantum dots (QDs). Both nanoparticles share traditional nanosized semiconductors properties, namely: size and wavelength luminescence emission dependence, resistance to photobleaching, biocompatibility associated with their nanoscale structures in conjunction with chemical functionality, among others. CDs are easily functionalized and they present some advantageous properties when they are compared to QDs [1], [2], [3], [4], [5].

CDs can be obtained either by chemical bottom up and/or top down synthesis methods, using different procedures. Thus, electrochemical, combustion, thermal, hydrothermal, acidic oxidation, microwave and ultrasonic, laser ablation, have been reported as techniques used for these purposes [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. Although fluorescent CDs have easily been obtained by these strategies, emission features (in terms of sensitivity, meanly) and quantum yield (QY) of CDs are still scarce and highly desirable to be improved.

Doping heteroatoms into CDs has been demonstrated an effective approach to improve QY and for incorporating a surface passivation, which has showed good results [14], [20]. Different strategies have been used to obtain doped CDs with nitrogen, such as those obtained by heating carbon tetrachloride and 1,2-ethylendiamine [21], by pyrolyzing ethanolamine [22], from citric acid and l-cysteine [23], glutamic [24], and folic acid [25]. The effect of different doping atoms such as N, P or B was deeply studied, as well as their influence on the photo-physical properties [26], showing that N-CDs are the most efficient [27], [28], [29], [30].

Pyridine is an organic liquid very soluble in water [31]. It is released to the environment from industrial sources, as fugitive emissions from facilities such as coal gasification and oil shale processing [32], [33]. It is used for synthesis of drugs, insecticides and herbicides [34], [35], [36]. In this way, inhalation, ingestion or skin absorption induced in humans many symptoms like headaches, infertility, respiratory distress or puke [37]. This is the reason why the determination of pyridine is very important in environmental, food and clinic fields. Some methods have been reported in the literature for the detection and quantification of pyridine, including electrostatic precipitation [38], GC [39], [40], liquid chromatography–mass spectrometry (LC–MS) [41], and GC–MS [42], [43].

In this article, lactose was used as precursor to develop a new method of preparing fluorescent nitrogen doped carbon dots (N-CDs) via a facile hydrothermal (solvothermal) methodology [44]. By this method, the surface of the CDs is populated by C single bond N organic functionalities, such as amine and amide. After exploring its chemical and physical properties, the detection capabilities of prepared N-CDs for pyridine was further exploited, revealing an enhancement of their luminescent signal, this can be used for analytical purposes.

Section snippets

Chemicals

d-Lactose monohydrate (99%), aqueous ammonia (37%) and hydrochloric acid (37%) were purchased from Panreac SAU (Barcelona, Spain). Pyridine, anhydrous (98.8%) was purchased from Sigma–Aldrich (St. Louis, USA). Ultrapure water, used throughout all experiments, was purified through a Millipore system. All reagents were used as received without further purification.

Synthesis of doped CD nanoparticles

Raw CDs were obtained by addition of 50 mL of concentrated HCl (37%) to 50 mL of a lactose solution (1 M), followed by hydrothermally

Synthesis and analysis of CDs and N-CDs nanoparticles

The raw material (lactose) was selected due to its low cost and, as previously reported, because it is a source of CDs showing an excellent fluorescence signal, and presenting good surface functionalization capabilities [14], [46]. Solvothermal process was chosen because allowed us to obtain a precise control over the size and shape distribution of nanoparticles [47]. Fig. 1A shows the TEM image of raw CDs, which revealed that these spherical nanoparticles were well dispersed from each other,

Conclusions

In conclusion, we have presented a facile and rapid method to obtain N-CDs by using lactose as the precursor under a solvothermal process, under the treatment with NH₃ at 100 °C. The as-prepared N-CDs, with spherical morphology and a distribution of nanoparticles with an 3 × 10⁻⁵ average diameter of 50 ± 15 nm (lager than the un-treated with NH₃, 7.7 ± 2.4 nm). N-CDs showed a moderate quantum yield (10.75%) and bright green fluorescence. By XPS and Raman spectroscopy it was elucidated the presence of

Acknowledgments

M. Algarra is gratefully to the PLASMON program from ESF for the Exchange Grant. B.B Campos is gratefully to Grant SFRH/BD/84318/2012 to FCT (Lisbon, Portugal) Financial support from the Spanish Ministry of Economy and Competitiveness (CTQ2013-48411-P) and Junta Comunidades Castilla-La Mancha (Project PEIC-2014-001-P) are gratefully acknowledged. The support given through an “INCRECYT” research contract to M. Zougagh is also acknowledged.

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Fluorescent chemosensor for pyridine based on N-doped carbon dots

Abstract

Graphical abstract

Introduction

Section snippets

Chemicals

Synthesis of doped CD nanoparticles

Synthesis and analysis of CDs and N-CDs nanoparticles

Conclusions

Acknowledgments

Carbon

Nano-Micro Lett.

Carbon

Sens. Act. B Chem.

J. Luminescence

Nano Energy

J. Chromatogr. A

J. Chromatogr. A

Talanta

Mat. Lett.

Prog. Cryst. Growth Charact. Mater.

Carbon

Carbon

Anal. Chim. Acta

Appl. Surf. Sci.

Microchem. J.

J. Alloys Comp.

J. Am. Chem. Soc.

Angew. Chem. Int. Ed.

Angew. Chem. Int. Ed.

J. Mater. Chem. C

Angew. Chem. Int. Ed.

Dalton Trans.

J. Am. Chem. Soc.

J. Mater. Chem. B

Chem. Commun.

Catal. Sci. Technol.

Chem. Commun.

J. Mater. Chem. A

Nanoscale

Chem. Commun.

J. Appl. Phys.

RSC Adv.

J. Mat. Chem.