Short communication
Table sugar derived carbon dot—A promising green reducing agent

https://doi.org/10.1016/j.materresbull.2021.111284Get rights and content

Highlights

  • Green synthesis of carbon dots.

  • Excellent reducing efficiency of the system, as illustrated through Au(III) reduction.

  • Facile synthesis of nanogold within seconds.

  • Demonstration of catalytic activity of nanogold.

Abstract

In the present work, carbon dots derived from Table sugar are used as a green reducing agent. Microwave assisted green synthesis is adopted for achieving bright cyan luminescent carbon dots from commercially available table sugar (sucrose). The particles are characterised by TEM analysis, XRD analysis, FTIR, XPS, Raman as well as photoluminescence spectral analyses. The system served as an environmentally benign reducing agent for Au(III) reduction. Gold nanoparticles of size ∼ 8.3 nm are achieved within seconds in presence of starch under mild heating. The system showed excellent stability for more than one month, and exhibited superior catalytic activity as evidenced by the hydrogenation of 4-nitro phenol.

Introduction

Implementation of green practices in chemical reactions, eliminating or least reducing the hazardous chemicals, has become a pressing necessity of high priority. Usage of safer alternative chemicals and more benign reaction pathways are always recommended for maintaining the green protocol [1]. There have been numerous efforts in this direction, by the substitution of every chemical reagent with an alternative, less hazardous one. Herein, we propose carbon dots as a green alternative for conventional reducing agents. Reduction is one of the most industrially significant chemical processes that paves way to an array of fine chemicals, which obviously demands large quantities of highly reactive reducing agents. Most of the reducing agents in the series often involve the use of expensive metals such as Pt and Pd, as well as toxic functional moieties, which initiated ceaseless efforts to green up the reduction process, including more effective and benign reducing agents which are also cost-effective.

Carbon dots, particles with size below 10 nm, are marked by a carbon core, crystalline or a bit amorphous, anchored with surface functional groups. It has been established that these nanoparticles have fascinating electronic properties, as evidenced by their spectroscopic attributes such as fluorescence, which bestow the system with fine applications in numerous fields, including sensing, biomedical field and catalysis [[2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16]]. Presence of surface oxygen functionalities tunes the system as an electron donor with potential applications as reducing agents. It will indeed be worthwhile to examine the use of these carbon dots as a novel class of environmentally friendly and economically viable reducing agents, which can at least replace some reagents in reduction processes, even if such applications are of limited scope. In this work, we demonstrate that table sugar (sucrose) derived carbon dots (TSCDs) can be used as an environmentally benign reducing agent in the synthesis of metal nanoparticles, and can be an effective substituent for traditional chemicals like NaBH4 and hydrazine. Significant attention has been there in recent years towards greening-up the metal nanoparticle synthesis, by replacing the above-mentioned reagents. Several alternatives like plant/animal origin extracts, living body cells, algae, fungi, natural polymers etc., have been examined to this effect [[17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34]].

The present work involves microwave assisted green synthesis of carbon dots, and the successful application in Au (III) reduction. Gold nanoparticles of average size 8.3 nm are yielded within a few seconds in presence of carbon dots and soluble starch under mild conditions. At this context, it is worthy to note that the precedented works available on the reaction of our interest using carbon dots involve harsh chemicals as well as significantly long reaction duration in the synthesis of carbon dots as well as the reduction process. Wang et al. have suggested a reaction path which involved large amount of sodium citrate, and took almost 4–8 hrs for the successful formation of gold nanoparticles with desirable size and features [35]. Though another group offered a reaction path devoid of capping agents, it strictly demanded the addition of concentrated NaOH solution and proceeds through stringent experimental procedures including overnight stirring and tedious post-chemical treatments for ensuring the purity of the prepared Au-NPs [36]. When compared to the previous efforts, the present approach for Au(III) reduction using table sugar derived carbon dots is of course greener in several aspects.

Section snippets

Synthesis of Table sugar derived carbon dots

Cyan emitting carbon nano dots were synthesised from commercially available table sugar (sucrose). Table sugar was subjected to caramelization followed by the addition of small amounts of diluted ammonia (90 % pure, Merck). The above solution was placed inside a micro wave reactor and was heated for 3 min at 120 ⁰C. The collected solution was further subjected to ultra-centrifugation for about 20 min at 15,000 rpm. The purity of the carbon dots thus obtained was ensured by conducting dialysis

Characterization of carbon nanodots

Formation of quasi spherical particles with average size 3−4 nm was confirmed from the HR-TEM analysis (Fig. 1a), which was supported by the average size distribution profile of the system (Fig. 1b). Fig. 1 (c) shows the XRD pattern of carbon dots with characteristic peaks at 2θ values 24 and 44.5° corresponding respectively to (002) and (101) planes of graphitic carbon. The system was observed to be considerably amorphous in nature. The surface groups anchored on the carbon core were

Conclusion

The reducing nature of table sugar derived carbon dots was illustrated in the study. Bright cyan luminescent carbon dots were synthesised from commercially available table sugar (sucrose) via Microwave assisted green synthesis. A facile synthesis strategy to gold nano particles via an environmentally benign route was presented, using table sugar derived carbon dots as the reducing agent, in presence of green capping agent, starch. Compared to the previous reports in this direction, the current

CRediT authorship contribution statement

Ansi V.A: Investigation, Writing - original draft. Sreelakshmi P: Resources. Raveendran Poovathinthodiyil: Resources. Renuka N.K: Conceptualization, Supervision, Writing - review & editing.

Declaration of Competing Interest

The authors declare no competing financial interest

Acknowledgements

Ansi V.A gratefully acknowledges the financial support received from the Government of Kerala. Authors also thank Department of Chemistry, University of Calicut for providing the research facilities and STIC, CUSAT for providing the HR-TEM images.

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