Short communication
Green synthesis of biomass-derived carbon quantum dots as fluorescent probe for Fe3+ detection

https://doi.org/10.1016/j.inoche.2021.108636Get rights and content

Highlights

  • The conversion of whole biomass wastes to CQDs using one-pot strategy.

  • Polar groups brought from the biomass make the CQDs with good water compatibility.

  • The CQDs have strong fluorescence and selective quenching effect for Fe3+.

  • The detection of Fe3+ is desired in environmental remediation and medical diagnosis.

Abstract

Eco-friendly synthesis of Carbon quantum dots (CQDs) in water is reported, exploiting various typical crop biomasses as carbon sources. The resultant CQDs exhibit strong fluorescence, good dispersion in common solvents and uniformly dispersed particle size. The synthesized CQDs are highly dispersible in water, due to the presence of surface hydroxyl and carboxyl groups. The CQDs suspension exhibits strong blue fluorescence under UV irradiation, with an optimal excitation wavelength in the range from 350 to 390 nm, which varies with the change of CQD concentration. The emission corresponds to two band transitions, which are originated from π → π* of Csingle bondC bonds and n → π* of Csingle bondO bonds, respectively. Due to its strong fluorescence and energy transfer, the synthesized CQDs materials can be used as a fluorescent probe for the detection of Fe3+ ions with good selectivity and sensitivity, within the Fe3+ concentration range of 0–500 μM. The research is of significance for converting crop waste to high added-value products, and the obtained CQDs with selective Fe3+ ions determination ability are attractive for the environmental monitoring and medical diagnosis.

Graphical abstract

The most abundant agricultural biomass in the Northeast of China can be directly converted into the carbon quantum dots. The obtained carbon quantum dots is able to detect iron(III) with high selectivity and good efficiency.

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Introduction

Carbon quantum dots (CQDs) are advanced carbon-based nanomaterials with their particle sizes below 10 nm. Since the pioneer research reported by Xu et al. [1] in 2004, CQDs have attracted extensive attention due to their unique advantages, such as high photoluminescence, good photo-induced charge transfer property, light resistance, high chemical stability, hydrophilicity and low toxicity. For their excellent performance, CQDs have been widely applied in chemical sensing [2], [3], [4], [5], [6], [7], bio-sensing [8], [9], [10], bio-imaging [11], [12], nanomedicine [13], [14], [15], photo-catalysis [16], [17], [18] and electro-catalysis [19], [20], just to name a few [21], [22], [23]. The preparation of CQDs has become a hot research topic at the moment. Over the past years, the synthesis of CQDs has experienced explosive development. Various synthetic methods have been reported. According to the starting materials, these methods can be classified into two synthetic strategies, namely “top-down” and “bottom-up” synthesis. “Top-down” synthesis [24], [25] refers to those CQDs obtained by stripping bulky carbon materials by physical or chemical treatments. The carbon sources for “top-down” synthesis of CQDs mainly include carbon nanotubes, carbon fibers, graphite rods, carbon ash and activated carbon. These carbon-rich materials were decomposed by arc discharge, laser ablation or electrochemical processing, leading to the formation of CQDs. In contrast to the “top-down” method, in “bottom-up” route [26], [27], CQDs were synthesized from carbon-containing compounds such as small organic molecules or oligomers. The common carbon sources include citric acid, glucose, polyethylene glycol, urea, ionic liquids, and they can be treated by chemical oxidation, combustion, hydrothermal/solvothermal synthesis, microwave synthesis, or templating method to afford CQDs. Among these treatments, the hydrothermal method is the most common one due to its low cost, environmentally-friendly and non-toxic features, which comply with the desires for green chemistry.

Biomass is renewable, naturally produced with large output, and considered as feedstocks for many organic compounds. However, the chemical conversion of biomass to high value-added product is relatively inadequate. Many biomass materials such as crop straws are usually burned directly, which is not only a waste of bio resources but also aggravates environmental pollution. Therefore, the efficient utilization of biomass has attracted significant attention. Considering their broad applications, direct synthesis of CQDs from biomass via the bottom up strategy has been reported recently [28], [29], [30], [31]. For example, Mohapatra et al. successfully synthesized the CQDs with a size of 1.5–4.5 nm from orange juice and applied them in bioimaging [30]. Liu et al. reported a hydrothermal method synthesis of amino-functionalized fluorescent CQDs using chitosan as precursor treated at 180 °C for 12 h [28]. As one of the most common agricultural wastes, crop straws from corn, wheat and rice are highly output annually. Exploiting these raw materials as the feedstock of useful chemicals or materials would provide a new gateway for chemical and farming industry. As far as we know, there are few reports about the preparation of CQDs from typical crop wastes. Herein, a new type of CQDs material was prepared by hydrothermal method from typical crop wastes such as corn straw, wheat straw and rice straw. This is a combination of top-down and bottom strategies in one-pot, which brings the ease of operation and high synthetic efficiency to the preparation. Comprehensive characterizations were carried out to obtain their structural and fluorescent properties. Specifically, the fluorescence of CQDs is selectively quenched by the addition of Fe3+ ion in aqueous solution. Detecting of Fe3+ by CQDs holds the potential for the applications such as environmental remediation [32] and medical diagnosis [33].

Section snippets

Results and discussion

The main components in typical crop biomass are biopolymers,such as cellulose, hemicellulose and lignin.They are rich in carbon, so they are very suitable as carbon sources to prepare CQDs. Meanwhile, there are abundant hydroxyl and ether groups in biomass molecules, rendering their water compatibility. Therefore, the biomasses are readily reacted in water. The synthetic procedure is demonstrated in Fig. 1. Firstly, those biopolymers including cellulose, hemicellulose and lignin were hydrolyzed

Conclusions

In summary, we have reported a simple and environmental friendly method in producing CQDs materials from typical crop wastes. The biomass derived CQDs exhibited significant photoluminescence, good homogeneity and water compatibility. The PL spectra showed that the optimum excitation wavelength of the synthesized CQDs materials is between 350 and 390 nm. The XRD and TEM results proved that the synthesized CQDs materials possess a narrow size distribution at 2–5 nm. The UV–Vis spectrum clearly

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.

Acknowledgements

The authors gratefully acknowledge the financial supports from National Natural Science Foundation of China (No. 51875249), Jilin Engineering Normal University PhD startup foundation (No. BSKJ201829) and Jilin Engineering Normal University general intramural foundation (No. XYB201822).

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