Synthesis of Fluorescent Carbon Dots from Raw Materials: An Overview of Textile Applications

Fluorescent carbon nanoparticles or carbon dots (C-dots) were discovered in 2004 during the process of carbon nanotube fragment purification [1-3]. These nanomaterials are widely reported to have average sizes typically smaller than 10nm, are spherical or semispherical in shape, are water soluble, and have fluorescent properties, enabling a wide range of bio applications [4-6]. Carbon dot synthesis has recently attracted increasing attention and interest due to its sustainable synthesis, low toxicity, low cost, and easy implementation [4- 7]. These carbon-based nanoparticles have been widely explored, but green syntheses stand out because the raw materials used as carbon sources are components of plants and fruits (such as roots, seeds, leaves, flours, fruit peels, and extracts) and other foods [2,4,8-10]. The first reported green synthesis using coffee grounds as a carbon source occurred in 2012, with C-dots of approximately 5±2nm in size [8]. Several novel C-dots have been proposed using different carbon sources [8,11-22], and this work presents an overview of these carbon dots, the values of their average sizes, fluorescence quantum yield (η), fluorescence lifetime (τ) values, and high potential for reported textile applications [23-27].

Figure 1 presents the timeline of the main raw carbon sources and methods used in green synthesis from 2012-2024 [8,11-22]. The synthesis C-dots involves hydrothermal, pyrolysis, and microwave methods [11,16,17]. Several carbon sources, such as coffee grounds, sweet pepper, corn flour, Jinhua Bergamot, Lotus roots, Acacia Concinna seeds, Carica papaya waste, cherry tomatoes, microalgae Spirulina, grapefruit juice, Naregamia alata leaves and Pumpkin seeds used for C-dot green synthesis are presented in Figure 1. The fluorescence quantum efficiency (η) and fluorescence lifetime (τ) are given for some C-dots reported in Table 1. A hydrothermal method or heating reaction was used for all the synthesized C-dots, as shown in Table 1. These photophysical characteristics are crucial for fluorescence applications of C-dots.

Figure 1:Some raw carbon sources and methods used in C-dot green synthesis from 2012-2024 [8,11-22].

Table 1:Several carbon sources have been presented for C-dot green hydrothermal or heating reaction synthesis and textile applications. The average sizes of the C-dots and the  and  parameters are presented.
^aAverage lifetime.

Table 1 presents different C-dots synthesized by the green method and used in textile engineering applications [23-28]. Rice straw was used as a carbon source in nitrogen-doped C-dot synthesis and applied as a fluorescent sensor for acetone detection in cotton in textile masks [23]. The natural dyes extracted from Curcuma longa and Sophora japonica L. were used in C-dot synthesis and tested as possible textiles for anti-counterfeiting [24]. Other textile applications using C-dots are presented in Table 1. The values obtained for η and τ for rice straw as raw materials highlight the fluorescent sensor textile applications of C-dots.

Equipment

The equipment used for this work included a sample dyeing machine, dryer, pipette, scissor, electric balance, washing machine, beaker, color matching cabinet, gray scale, and crock meter.

Table 2 presents different green processes for C-dot synthesis [29-38], such as hydrothermal, pyrolyzed, and calcination processes. These nanodots are potential candidates for detecting and degrading dyes typically used in textile fabrics [29,31,32,35- 38]. C-dots and N-doped C-dots were synthesized using carbon sources such as peels, seeds, fruits, and leaves. Table 2 presents the average C-dot sizes and fluorescence quantum yield parameters η. For doped C-dots, L-aspartic acid or aqueous ammonia was used for nitrogen doping [36,37], and green synthesis was achieved via hydrothermal processes. N-doped C-dots have been reported to have potential in wastewater analysis for Congo Red dye detection and Safranin-O dye degradation [36,37]. Table 2 presents other C-dot applications for the detection and degradation of dyes.

Table 2:The different carbon sources used in green synthesis and the average of the C-dots used in dye removal ^applications in textiles are presented.
^aCarica papaya juice was used as a carbon source [30].
^bC-dots were doped with nitrogen (pyrolysis for 3h) [32].
^cA hydrothermal method was used, and C-dots with a size of 1nm were obtained [33].
^dThe excitation wavelength was 380nm [34].

Furthermore, other carbon dots or nanoparticles have been reported in textile applications [39-45]. The carbon quantum dots synthesized by the hydrothermal method can be highlighted by using banana leaves as a carbon source. These nanomaterials are applied for superhydrophobic coating on fabrics for oil and water separation [39]. On the other hand, graphene films integrated with Prussian blue and quantum dots have been reported for textile devices [40]. These proposed advanced films show potential for wearable biosensors and photoelectronic devices, such as glucose and H2O2 monitoring sensors [40]. Red-emissive carbon dots (R-Cdots) are used to construct smart fabrics. The hydrothermal synthesis of these R-Cdots uses o-phenylenediamine and catechol in ethanol as carbon sources. R-Cdots exhibit fluorescent patterns on cotton fabrics, are pH sensitive, and can be used for MnO4 detection in aqueous solutions [41]. Finally, fabric scraps can also be reused as a carbon source for new carbon dot synthesis, ranging from leather scraps to hospital masks [42-44].

Since the first green synthesis of carbon dots (C-dots), different carbon sources obtained from seeds, leaves, peels, and other parts of plants have been used in novel synthesis processes. The fluorescence properties, water solubility, and low toxicity are characteristics of carbon dots that stand out for their wide range of applications. C-dots have been used in different applications, such as in printing on textiles to combat counterfeiting and in textiles, highlighting their antioxidant and antimicrobial properties. Another important carbon nanoparticle approach is evaluated for the detection and degradation of dyes commonly used in textile fabrics. Over the years, important new applications of carbon dots have emerged in different research areas of investigation, increasing opportunities for the development of relevant applications in textile engineering.

The authors would like to thank the Brazilian funding agencies Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG), CAPES and Instituto Nacional de Ciência e Tecnologia de Fotônica INCT/CNPq for their financial support.

The authors declare that there are no conflicts of interest.

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