Highly fluorescent N,S,P tri-doped carbon dots for Cl detection and their assistance of TiO2 as the catalyst in the degradation of methylene blue

https://doi.org/10.1016/j.jphotochem.2020.112772Get rights and content

Highlights

  • High quantum yield N,S,P tri-doped carbon dots (NSP-CDs) were prepared.

  • The fluorescence of NSP-CDs was sensitive to pH irrelevant to the buffer type.

  • NSP-CDs were successfully applied in detection of Cl in simulated sweat.

  • NSP-CDs modified TiO2 had higher degradation efficiency of methylene blue.

Abstract

The preparation and application exploration of multi-heteroatom doped carbon dots (CDs) have drawn tremendous attention. In this study, the N, S, P tri-doped carbon dots (NSP-CDs) were prepared by one-pot hydrothermal method with sulfonamide and phosphoric acid as precursors, possessing a fluorescence quantum yield up to 33 %. The fluorescence intensity of NSP-CDs exhibited a good linear relationship with the surrounding pH in the range of 3–7, showing the great promising pH sensing potential of NSP-CDs. Moreover, the fluorescence of NSP-CDs could be selectively quenched by Cl; based on it, a Cl fluorescence sensor was constructed and successfully applied to detecting Cl in sweat samples with the recoveries of 94 %–110 %. Furthermore, TiO2 was modified with the NSP-CDs by simple immersion method, and the as-prepared composite demonstrated higher photocatalytic activity for the degradation of methylene blue under UV irradiation than pristine TiO2. The prepared NSP-CDs had potential for multiple applications.

Introduction

Carbon dots (CDs), emerging carbon-based fluorescent nanomaterials, are extensively applied in wide fields, owing to their diversified attractive properties, like small size, high water solubility, low toxicity, benign biocompatibility, photostability and ease of surface functionalization [[1], [2], [3], [4], [5], [6], [7], [8]]. Much effort has been devoted to developing the highly fluorescent CDs with desirable properties for multiple applications. Doping is an efficient approach to enhance the fluorescence performance of CDs, as different elements can adjust the surface states of CDs and provide diverse emissive sites [1,[9], [10], [11]]. Especially, the multi-heteroatom doping is in some cases more effective to tune the physical and chemical properties of CDs [12,13], extending the applicability of CDs. For examples, the fluorescence of S and N co-doped CDs prepared with water chestnut and onion was quenched by Cu(II) and then restored by coenzyme A, based on which an off-on fluorescence probe for high sensitivity determination of coenzyme A was constructed [14]. Wang et al. fabricated the N and Cl co-doped CDs using a choline chloride-glycerine deep eutectic solvent, showing pH-sensitive fluorescent emission and obvious fluorescence response to cytochrome c [15]. The fluorescent probes for manganese(VII) and l-ascorbic acid were established based on the N, S, P co-doped CDs fabricated with Saccharomyces cerevisiae [13].

Cl is an essential electrolyte that maintains body fluid and ion homeostasis. The change of Cl concentration levels in biological fluids may indicate various abnormal conditions and the occurrence of diseases [16]. Cystic fibrosis (CF) is a genetic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator gene presented in a variety of organs. Elevated Cl concentration in swear (>60 mM) is the gold standard for diagnosis of CF [17,18]. However, most of the existing Cl detection methods, like ion exchange chromatography, ion-selective electrodes and colorimetry, cannot meet the high-performance and low-cost clinical needs. Hence, it is of great importance to develop a selective, sensitive, rapid and low-cost method for Cl determination. To the best of our knowledge, few studies about the fluorescence sensor for the determination of Cl in sweat were reported.

Photocatalytic degradation is a commonly-adopted method for wastewater treatment [[19], [20], [21]]. Thanks to the advantages of low toxicity, chemical inertness, high catalytic efficiency and low cost, TiO2 nanoparticles were the most popular catalyst for photocatalytic degradation [22]. However, TiO2 had some disadvantages, such as electron-hole recombination, wide band gap energy, high concentration aggregation, low specific surface area, etc., which limited the degradation efficiency. Carbonaceous substance modification on the surface of TiO2 was documented as a solution to these issues [[23], [24], [25], [26]]. Since the introduced carbonaceous substance could act as the binding center of electron-hole pairs, the photoexcited electrons in TiO2 may be transferred to carbonaceous substance thus hindering the recombination of electrons and holes and enhancing the photocatalytic efficiency of TiO2 [[23], [24], [25], [26]]. As far as CDs are concerned, they are less than 10 nm, and more edges and defects are present on the surface. Additionally, different functional groups or chemical structures is beneficial to the adsorption and reduction of oxygen. Therefore, CDs is expected to enhance the catalytic ability of TiO2.

In the present study, the N, S, and P tri-doped CDs (NSP-CDs) were prepared by one-pot hydrothermal method with sulfonamide and phosphoric acid as precursors. The fluorescence of NSP-CDs was sensitive to the concentration of Cl, which was adopted to determine Cl in sweat. Meanwhile, NSP-CDs can also enhance the photocatalytic activity of TiO2 for the degradation of methylene blue under UV irradiation.

Section snippets

Reagents and instruments

Sulfanilamide, H3PO4, NaOH, H2SO4, H3BO3, K2SO4, Na2SO4, CaSO4, MgSO4, (NH4)2SO4, HAcO, NaAcO, NaH2PO4, Na2HPO4, Na3PO4, NaCl, KBr, KI, glucose, citric acid and methylene blue (MB) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Ultrapure water was produced by a Heal Fore NW system (Shanghai, China). Aeroxide TiO2 P25 was received from Evonik Degussa Corporation (Frankfurt, Germany).

Transmission electron microscopic (TEM) images were captured by a JEM-2100 microscope

Preparation and characterization of NSP-CDs

In this study, sulfanilamide with both abundant nitrogen and sulfur was for the first time chosen as the carbon source to prepare carbon dots, in addition to use phosphoric acid as the phosphorus source. After the hydrothermal reaction, the pale brown solution was obtained, giving out bright blue fluorescence under UV irradiation. In order to achieve the high fluorescence quantum yield, the amount of sulfonamide, the hydrothermal temperature and the reaction time were optimized successively

Conclusion

The N,S,P tri-doped carbon dots (NSP-CDs) were prepared by one-pot hydrothermal method with sulfonamide and phosphoric acid as precursors. Under optimal conditions (0.10 g sulfanilamide dissolved in 5 mL phosphoric acid was heated at 220 °C for 10 h), the NSP-CDs achieved a high fluorescence quantum yield up to 33 %. The particularly multi-heteroatom-doping made the fluorescence intensity of NSP-CDs sensitive to pH and Cl. The Cl probe based on NSP-CDs was successively applied in sweat

CRediT authorship contribution statement

Lu-Shuang Li: Methodology, Writing - review & editing. Li Xu: Supervision, Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

The authors gratefully acknowledge the financial support of this research by the Fundamental Research Funds for the Central Universities (No. 2172019KFYRCPY112) and Starting Research Fund from the Hainan University (No. KYQD(ZR)19106).

References (41)

  • H. Safardoust-Hojaghan et al.

    Degradation of methylene blue as a pollutant with N-doped graphene quantum dot/titanium dioxide nanocomposite

    J. Clean. Prod.

    (2017)
  • P. Nuengmatcha et al.

    Sonocatalytic performance of ZnO/graphene/TiO2 nanocomposite for degradation of dye pollutants (methylene blue, texbrite BAC-L, texbrite BBU-L and texbrite NFW-L) under ultrasonic irradiation

    Dye. Pigment.

    (2016)
  • R. Atchudan et al.

    In-situ green synthesis of nitrogen-doped carbon dots for bioimaging and TiO2 nanoparticles@nitrogen-doped carbon composite for photocatalytic degradation of organic pollutants

    J. Alloys. Compd.

    (2018)
  • D. Zhao et al.

    Enhanced photocatalytic degradation of methylene blue under visible irradiation on graphene@TiO2 dyade structure

    Appl. Catal. B-Environ.

    (2012)
  • F. Wu et al.

    Highly enhanced photocatalytic degradation of methylene blue over the indirect all-solid-state Z-scheme g-C3N4-RGO-TiO2 nanoheterojunctions

    Appl. Surf. Sci.

    (2017)
  • F. Gao et al.

    Rational design of high quality citric acid-derived carbon dots by selecting efficient chemical structure motifs

    Carbon

    (2017)
  • F. Yang et al.

    Controllable and eco-friendly synthesis of P-riched carbon quantum dots and its application for copper (II) ion sensing

    Appl. Surf. Sci.

    (2018)
  • M. Zan et al.

    A strong green fluorescent nanoprobe for highly sensitive and selective detection of nitrite ions based on phosphorus and nitrogen co-doped carbon quantum dots

    Sens. Actuator B-Chem.

    (2018)
  • M. Amjadi et al.

    Sulfur and nitrogen co-doped carbon quantum dots as the chemiluminescence probe for detection of Cu2+ ions

    J. Lumin.

    (2017)
  • J. Zhang et al.

    Rapid synthesis of N, S co-doped carbon dots and their application for Fe3+ ion detection

    J. Nanopart. Res.

    (2018)
  • Cited by (0)

    View full text