Elsevier

Applied Surface Science

Volume 434, 15 March 2018, Pages 1079-1085
Applied Surface Science

Full length article
Nitrogen-doped carbon quantum dots from biomass via simple one-pot method and exploration of their application

https://doi.org/10.1016/j.apsusc.2017.11.040Get rights and content

Highlights

  • Nitrogen-doped carbon quantum dots have been successfully prepared via one-pot method.

  • The optimized nitrogen-doped carbon quantum dots have outstanding optical properties.

  • The nitrogen-doped carbon quantum dots have been tentatively employed as light absorbers to fabricate solar cells.

  • The device yields a maximized solar-to-electrical conversion efficiency of 0.17% with a good fill factor of 67%.

Abstract

Pursuit of low-cost and large-scale method to prepare carbon quantum dots (CQDs) is a persistent objective in recent years. In this work, we have successfully synthesized a series of nitrogen-doped carbon quantum dots (N-CQDs) under different hydrothermal temperature employing Eichhornia crassipes (ECs) as precursors. Considering the pollution ability to water and low-cost, this study may direct the novel path to convert waste material to useful quantum dots. After measurements such as TEM, XRD, Raman, XPS, PL as well as the UV–vis absorbance ability, outstanding optical properties have been discovered. In this fashion, solar cells are tentative to be fabricated, yielding the maximized solar-to-electrical conversion efficiency of 0.17% with a good fill factor of 67%. Meanwhile, the above-mentioned quantum dots also show the up-conversion ability, suggesting the potential application in infrared detection or broadening light-absorbing devices.

Introduction

In 2006, scientists at Claremonton University discovered and named a new type of carbon nanomaterials during the single-walled carbon nanotubes purification process: Carbon quantum dots (CQDs) [1]. As a new member of the carbon family, the emerging of CQDs has aroused great attentions in recent decades. Comparing to conventional semiconductor quantum dots, the preparation method of CQDs is simple and environmental-friendly, and the source of precursor materials is distributed widely and low-cost. In addition to maintaining the optical property of the traditional semiconductor quantum dots, CQDs also have excellent biocompatibility, low toxicity, large two-photo absorption cross section and good photoinduced electron transfer ability [2], [3]. As a result, they have been widely applied in many fields such as bioimaging, sensors, photoelectrocatalysis, fluorescence sensing, and solar cells [4], [5], [6].

Arising from the photo-excitation characteristics of CQDs, they are expected to be applied in sensitized solar cells as light absorbers. Comparing to traditional light-harvesting absorbers such as N719, N3, PbS or CdSe ect in dye-sensitized solar cells (DSSCs), the CQDs are advantageous owing to their health and environmental-friendless. The concept of using carbon nanoparticles as sensitizers for mesoscopic TiO2 solar cells was first reported by Yan et al. in 2010, achieving a power conversion efficiency of 0.056% [7]. Following, Mirtchev et al. reported a nanocrystalline TiO2-based solar cell sensitized with CQDs prepared by means of a carbonization synthesis, realizing an efficiency of 0.13% [8]. Since then, this work has been further researched for practical application.

However, reducing the production cost is still a challenging to prepare large-scale carbon quantum dots with low-cost. Therefore, during this development progress, enormous efforts have been put into developing green methodologies for preparing CQDs using natural substances widely distributed in nature [9], [10], such as carbohydrates including glucose, sucrose, fructose [11] and biomass including orange juice, strawberry powders, watermelon peel and so on [12]. With the aim to accelerate the practical application of CQDs, how to utilize the useless material to prepare the precious CQDs is crucial. In the current work, we herein have prepared high-fluorescent water-soluble carbon quantum dots via one-pot method arising from the natural Eichhornia crassipes (ECs), which is a kind of discarded material for its pollution to pure water. There is a fact that the primary components of ECs include starch, cellulose and crude protein, which can be hydrolyzed into glucose and amino acid via hydrothermal treatment, therefore, playing a role of an excellent precursor for the preparation of CQDs. It should be noted that, according the elemental analysis, the as-prepared carbon quantum dots can be effectively doped by nitrogen atoms owing to no any further purification process for ECs before hydrothermal treatment, labeled as the N-CQDs, showing outstanding optical properties with unique up-conversion ability without any decoration. To further understand the application of this N-CQDs, we have experimentally fabricated the N-CQDs sensitized solar cells, yielding the lower power conversion efficiency from above-mentioned device in comparison to the state-of-art devices based on silicon, polymer, dye, CdS, CdSe, or perovskite. Till now, we can conclude that the strategy is proved an effective path to synthesize CQDs from biomass with expanded the precursors of CQDs.

Section snippets

Preparation of fluorescent N-CQDs

N-CQDs were synthesized by hydrothermal treatment of ECs as raw materials. In a representative synthesis, 0.3 g of ECs powder was added into 70 mL of deionized water. Then the mixture was transferred into a 100 mL Teflon-lined autoclave and heated at different temperatures (110, 140, 180 and 220 oC) for 6 h. The product was collected by filtration and centrifugation at 12,000 rpm for 10 min to remove large carbon product and finally freeze-dried under vacuum for 50 h. The obtained N-CQDs

Results and discussion

Using ECs as raw materials, N-CQDs can be facilely synthesized by a simple hydrothermal process under various temperature ranged from 110 to 220 oC, as illustrated in Fig. 1a. A potential mechanism behind this conversion is that the primary components for ECs are starch, cellulose and crude protein, which will be hydrolyzed into glucose and amino acid during the hydrothermal reaction process for starch and cellulose as well as crude protein, respectively [13]. Subsequently, the resultants can

Conclusions

In summary, we have employed a green and low-cost aquatic plants ECs to prepare cyan-fluorescence N-CQDs with uniform size about 1–2.5 nm via hydrothermal method. Enormous oxygenous functional groups, such as hydroxyl and carbonyl, endows the as-prepared N-CQDs water-soluble ability, facilitating the assemble process for many optoelectronic devices, such as the solar cells, which can yield the solar-to-electrical conversion efficiency of 0.17%. According to detailed characterizations, the

Acknowledgments

The authors gratefully acknowledge the financial supports from National Natural Science Foundation of China (51362031, 21503202 and 61604143). Yunnan Provincial Natural Science Foundation (Grant No. 2017FA024). Shandong Provincial Natural Science Foundation (ZR2015EM024) and Fundamental Research Funds for the Central Universities (201564002).

References (24)

  • P. Mirtchev et al.

    Solution phase synthesis of carbon quantum dots as sensitizers for nanocrystalline TiO2 solar cells

    J. Mater. Chem.

    (2012)
  • L.B. Tang et al.

    Deep ultraviolet to near-infrared emission and photoresponse in layered N-doped graphene quantum dots

    ACS Nano

    (2012)
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