Nanomaterial Based on Metal-Doped Carbon Dots for Textile Applications

Different green syntheses of fluorescent carbon dots (Cdots) are being developed using several raw materials such as food, fruits, roots, seeds, leaves, oils and animal wastes [1- 6]. Cdots are reported to be spherical or semi-spherical, with average sizes typically below 10nm. They exhibit fluorescent properties, enabling various applications across different fields, including textiles [7,8]. The sustainable synthesis of carbon dots continues to attract considerable attention and interest due to their relatively simple production and low toxicity [9,10]. Thus, considering environmental sustainability and availability of natural resources, carbon-based nanomaterials stand out as alternatives to metals, metal oxide materials, and inorganic quantum dots for various applications such as catalysts, sensors, lighting sources, and biomedical purposes [11-21]. Several studies have used green carbon dots as metal ion sensors such as Fe3+, Fe2+, Hg2+, Cu2+, Cd2+, Cr6+, Co2+, Al3+, Au3+ and Ag+ [15,16,18,20,21]. However, functional (nano)materials such as metal nanoparticles, and metal oxides, have been inserted or linked in carbon dots to develop the composite probes [21]. Metal-based carbon dots composites have been developed for several technological applications, such as optoelectronics, sensors, fuel cells, photocatalysts, light-emitting diodes [21-23]. The Agdoped C-dots and Au-doped Cdots synthesized using the low melting point metals route, were reported for the first time in 2019 for possible neural tissue engineering applications [24]. The iron-doped Cdots were synthesized for the first time using ultrasound-assisted methodology, for possible bioimaging and diagnostic devices applications [25]. However, nanomaterials based on copper, silver or iron metal-doped Cdots have been proposed using different carbon sources such as Iles paraguariensis, L-cysteine, sodium alginate, and citric acid [26-29]. This work presents an overview of metal-doped carbon dots and their applications in the textile industry, including effective industrialization of textiles, degradation of textile wastewater, applications of self-cleaning and antibacterial cotton fibers [26-29]. The synthesis method used, the average sizes of Cdots, and relevant information about fluorescence of the metal-doped Cdots, such as the fluorescence quantum yield (η) parameter, along with the emphasis on their applications in textiles, are presented. In addition, studies developed are reported using other synthesis of metal-doped nanoparticles (NPs) such as cellulose-copper nanoparticles by using green synthesis [30], composite materials of cotton fabric coated with metal oxide NPs for antibacterial properties [31], oxide NPs for degradation of dye from wastewater [32,33], fibers functionalized with silver NPs [34], silver-graphene coated textile composites [35], aiming applications in textile development and smart textiles [30-35].

Table 1 presents several nanomaterials based on metal-doped Cdots or metal-based carbon dots composites, synthesized by the hydrothermal method, and developed for textile engineering applications [26-29]. Nanosilver doped-Cdots (AgNPs-Cdots) have been investigated for textile applications, in production of antimicrobial and UV-resistant cotton fabrics [26]. Several carbon antioxidant precursors such as (L-cysteine, citrate, and ascorbic acid) and transition metal ions (copper (II), zinc (II) and titanium (IV)) have been reported for optimization of the best performance of copper (II)-doped carbon-based nanomaterials (Cu- doped Cdots) [27]. The Cu-doped Cdots have been developed for a catalytic ozonation oxidation process for textile wastewater treatment [27]. On the other hand, silver nanoparticles (AgNPs) synthesis was carried out on Cdots-coated onto the activated cotton fibers for self-cleaning and antibacterial textiles [28]. In addition, hydrothermal synthesis process was used for the surface functionalization of magnetite (Fe₃O₄) with the Cdots (HT-Cdots), using Ilex paraguariensis (yerba mate YM) as carbon source, for possible photocatalytic degradation of textile wastewater through the photo-Fenton reaction [29]. Figure 1 presents an overview of the metal-doped Cdots and metal-carbon dots nanocomposites synthetized for textile applications [26-29].

Table 1:Several carbon sources have been presented for metal-doped Cdots or metal-carbon dots nanocomposites, by hydrothermal synthesis and textile applications. The average sizes of the Cdots, doping material, and the  parameter are presented.

^aSilver nanoparticle was synthesized on the surface of the Cdots coated cotton fabric [28] ^bHydrothermal routes for CdotsN synthesis using HNO3 [29]
^cHydrothermal routes for CdotsS synthesis using H2SO4 [29]
^dCdots coated magnetic nanoparticles (HT-Cdots) using hydrothermal synthesis [29]

Figure 1:Overview of metal-doped Cdots and metal-carbon dots nanocomposites synthetized for textile applications [26-29].

Table 2 presents metal-doped nanoparticles [30-35] synthesized for textile interest. The green synthesis using cotton textile fibers (commercial cellulose) for metallic copper nanoparticles development is present as reducing agent and stabilizer [30]. Antimicrobial action of fabrics coated with metal oxide ZnO and/ or TiO2 nanoparticles in a tropical climate was reported [31]. Zinc oxide nanoparticles and ZnO/NiFe2O4 nanocomposite have been proposed for methylene blue dye degradation from textile wastewater [32,33]. On the other side, jute fibers functionalized with silver NPs have been proposed for improved conductivity values and potential for application in smart textile composites [34], and silver-graphene nanocomposites have been synthesized for possible antimicrobial medical textile [35]. Figure 2 presents the overview of several metal NPs composites developed for textile improvement [30-35].

Table 2:The different metal nanoparticles (NPs) composites, NPs size average, and the applications in the textile area.

Figure 2:Overview of several metal nanoparticles (NPs) composites synthetized for textile applications [30-35].

Several metal-doped nanocomposites are being developed for applications of interest in textile engineering, however, the fluorescence characterizations of these nanomaterials are still strictly investigated for possible photoelectronic devices, as well as the possibility of developing novel metal-doped carbon dots using green synthesis for environmentally friendly applications. Finally, other chemical elements, such as boron and nitrogen, have been used to dope or co-dope carbon dots through hydrothermal green synthesis for the multifunctional cotton fabrics [36-38]. This highlights nanomaterials-based carbon dots as valuable tools for various textile applications.

Novel nanomaterials based on copper, silver or iron metaldoped Cdots have been proposed using different carbon sources such as sodium alginate, L-cysteine, Iles paraguariensis, and other chemical sources. This work presented an overview of metal-doped Cdots using green synthesis for environmentally friendly applications, as tools for several textile applications such as effective industrialization of textiles, degradation of textile wastewater, applications of self-cleaning and antibacterial cotton fibers. In addition, studies developed are presented using other synthesis of metal-doped nanoparticles, such as cellulose-copper nanoparticle by using green synthesis, silver-graphene coated textile composites, aiming applications in textile development. Over the years, new synthesis of metal and carbon dot composites have been proposed targeting different research areas, enabling 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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