Green synthesis and multifaceted applications: challenges and innovations in carbon dot nanocomposites

Discover Nano Review Green synthesis and multifaceted applications: challenges and innovations in carbon dot nanocomposites S. Varadharajan1,2 · Kirthanashri S. Vasanthan1,3 · Vidhi Mathur1,3 · N. Hariperumal1,2 · Nirmal Mazumder1,4 Received: 10 July 2024 / Accepted: 14 October 2024 © The Author(s) 2024  OPEN Abstract This paper describes the potential of carbon dot nanocomposites (CDs) synthesized from waste materials by top-down and bottom-up state-of-the-art approaches. Through sustainable practices, wastes are converted into valuable nanomaterials, solving environmental problems and pioneering advances in nanotechnology. In this paper, an overview of the synthesis aspects of CDs is presented with the formation of their versatile nanocomposites and metal/metal oxide elements. The phase of this paper has been devoted to elaborate study of the multifaceted applications of CDs in various sectors, ranging from electronics and biomedicine to environmental remediation. Although having huge potential, CDs application is presently hampered due to limitations on scalability, stability, and reproducibility. In this review paper, most profound insights have been drawn into overcoming these barriers for clear routes toward future innovations. The present research being undertaken in this area has, therefore, underscored sustainable nanotechnology to resolve global problems and achieving technological development through green synthesis. Necessitating the efficient sewage disposal systems ensuring minimum toxin generation. 1 Introduction An enormous increase in industrialization and population has put considerable pressure on natural resources, ecosystems, and infrastructures in addition to comprehensive increase in the environmental pollution due to generation of waste material and toxins. These toxins have catastrophic impacts on environment, ecosystem and human health. Likewise, heavy metals, organic dyes, pesticides, and pharmaceuticals are well-known pollutants which have hazardous impact on living beings even causing death. Therefore, the research initiative and the regulatory measures are essential in handling and controlling hazardous impacts from such toxic chemicals [1, 2]. These issues can be effectively addressed by use of nanomaterials and zeolites. Thus, a great attention has been paid to nanomaterials due to their unique physical and chemical properties which makes it suitable for widespread application in industry, agriculture, and environmental remediation. Common nano-environmental remediation materials include metallic nanomaterials, metal oxide nanomaterials, nanomaterials based on polymers, core–shell nanomaterials, and carbon dots (CDs). CDs are commonly utilized as they exhibit nontoxicity, excellent fluorescence, optical behaviour, solubility, biocompatibility, and excellent photostability. CDs have a small diameter starting from 1 to 10 nm range [3, 4] and quasi-spherical structure of CDs show carbon atoms embedded into sp2 and sp3, with hydrophilic functional groups on their surface. Moreover, CDs * S. Varadharajan, ; * Kirthanashri S. Vasanthan, | 1Manipal Academy of Higher Education, Manipal, Karnataka, India. 2Department of Civil Engineering, Manipal Institute of Technology, Manipal Institute of Technology, Manipal, Karnataka, India. 3Manipal Center for Biotherepeutics Reserach, Manipal, Karnataka, India. 4Manipal School of Life sciences, Manipal, Karnataka, India. Discover Nano (2024) 19:205 | https://doi.org/10.1186/s11671-024-04124-3 Vol.:(0123456789) Review Discover Nano (2024) 19:205 | https://doi.org/10.1186/s11671-024-04124-3 have spheroidal geometry and consist of amorphous carbon with nanocrystalline regions of sp2- hybridized graphitic carbon [5, 6]. CDs can be synthesized from a wide range of carbon sources like carbon-containing organic molecules, precursors of carbon, and even from wastes. These surfaces could be functionalized with various chemical groups to provide increased functionality and stability. CDs properties can be modified by combining it with materials like polymers, metals, metal oxides, and nanoparticles to make them suitable for diverse applications. CD synthesis using toxic traditional chemical reagents is quite expensive and time consuming in addition to potential environmental hazards. Thus, there is a need to reduce dependence on toxic materials and petrochemicals. To avert this issue, CDs can be synthesised using greener approach from waste materials [7–9] like plant extracts, peanut shells, rice husk, kitchen waste, fruit or vegetable peels and microbes thereby addressing the key issues of waste management and pollution control leading to sustainable development [7–9]. Following this CDs has been synthesized with waste ionic liquid for effective sensing and detoxification of Cr(VI). Gedda et al. (2023) synthesized CDs from Azadirachta indica leaves using a one-step, onepot sand-bath method and observed excellent antimicrobial and antioxidant properties in generated CDs [10]. Qasim et al. (2023) synthesized CDs from renewable precursors for biomedicine and environmental applications [11]. Rocco et al. (2023) conducted electrochemical synthesis of CDs from biomass waste highly preferable in sustainable applications [12]. Differing from previous approach, Bressi et al. (2022) performed large-scale synthesis of CDs using waste biomass through top down and bottom up approach , thus balancing waste management with circular economy goals [13]. Likewise, Tohamy et al. (2022) synthesized carbon quantum dots (CQDs) derived from bagasse and cellulose using microwave irradiation. The authors observed CQDs to posses excellent absorption capacity of Pb(II) ions from aqueous solution [14]. Wang et al. (2022) synthesized nanocarrier carbon dots (nCDs) using hyaluronic acid and carboxymethyl chitosan and observed nCds to exhibit good luminescence with excellent water solubility [15]. Chen et al. (2022) used forsythia-derived CDs to prepare Nylon-11 nanofibers with enhanced mechanical properties and biocompatibility [16]. Likewise, Aumber Abbas et al. (2022) prepared graphene quantum dots from biomass waste and reported suitability of generated CDs in photocatalytic, bioimaging, and sensing applications [17]. The details of synthesis of CDs from waste materials has been presented in the next section. 2 Synthesis of CDs using waste materials The preparation of CDs from waste resources has gained wide attention and significance due to enormous environmental benefits and economy. Majority of the research works have adopted Top down & bottom up strategy for synthesis of CDs from waste materials [18, 19]. The detailed methodology and tabular comparison between different top to bottom down methods has been presented in Fig. 1 and Table 1. Using these methods, multicolour CDs with tuneable emission wavelengths were synthesized (hydrothermal/solvothermal approach) from waste leather scrap [20]. Also, materials like Rice husk (...truncated)