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Review

Efficiency of Graphene Quantum Dots in Water Contaminant Removal: Trends and Future Research Directions

by
Juliana P. Rodríguez-Caicedo
1,
Diego R. Joya-Cárdenas
1,2,
Miguel A. Corona-Rivera
3,
Noé Saldaña-Robles
1,4,
Cesar E. Damian-Ascencio
5,* and
Adriana Saldaña-Robles
1,4,*
1
Graduate Program in Biosciences, University of Guanajuato, Irapuato 36500, Guanajuato, Mexico
2
Facultad de Ingenierías y Tecnologías, Instituto Xerira, Universidad de Santander, Bucaramanga 680003, Santander, Colombia
3
Chemical Engineering, Unit Academic Multidisciplinary Region Altiplano UAMRA, Autonomous University of San Luis Potosí, Matehuala 78000, San Luis Potosí, Mexico
4
Department of Agricultural Engineering, University of Guanajuato, Irapuato 36500, Guanajuato, Mexico
5
Department of Mechanical Engineering, University of Guanajuato, Salamanca 36800, Guanajuato, Mexico
*
Authors to whom correspondence should be addressed.
Water 2025, 17(2), 166; https://doi.org/10.3390/w17020166
Submission received: 7 November 2024 / Revised: 8 December 2024 / Accepted: 27 December 2024 / Published: 10 January 2025
(This article belongs to the Special Issue The Control of Legacy and Emerging Pollutants in Soil and Water)
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Abstract

:
This review explores the efficiency and mechanisms of GQDs in removing contaminants from water, emphasizing their potential for environmental applications. GQDs possess unique physicochemical properties, such as a high surface area, tunable photoluminescence, and strong adsorption capacities, which enable the effective removal of diverse contaminants, including heavy metals, organic compounds, and dyes. Their electron-hole separation efficiency and functionalizability enhance their reactivity and selectivity. Notable findings include the integration of GQDs into advanced nanocomposites and supramolecular networks, significantly improving their adsorption and catalytic performance. However, challenges such as variability in synthesis methods, stability under environmental conditions, and the environmental impact of GQDs remain. Addressing these limitations and understanding the interaction mechanisms between GQDs and contaminants are critical. Future research should prioritize scalable green synthesis techniques, long-term environmental assessments, and optimized functionalization strategies to establish GQDs as a sustainable solution in water purification technologies.

1. Introduction

Water contamination by heavy metals, organic compounds, and other hazardous pollutants remains one of the greatest threats to human health and the environment worldwide. Conventional water treatment methods, while effective in some cases, have significant limitations in terms of cost, efficiency, and sustainability, especially when it comes to removing contaminants at trace concentrations or in the presence of multiple pollutants. Graphene Quantum Dots (GQDs), as emerging nanomaterials, have shown promising potential due to their unique optical, electronic, and adsorption properties [1,2]. However, significant gaps remain in the understanding of the efficiency and selectivity of GQDs in the removal of various contaminants, limiting their practical application in large-scale water treatment systems [3,4,5,6,7,8]. The structure and surface properties of GQDs allow for size modification and functionalization, making them attractive candidates for the removal of specific contaminants from water due to their ability to interact selectively with different pollutants [9,10,11,12,13].
Recent studies have shown that GQDs possess properties that enable the removal of contaminants such as lead (Pb), arsenic (As), and cadmium (Cd) [14,15,16]. Research has revealed that the efficiency of GQDs is influenced by factors such as their size, shape, and surface functionalization [17]. However, gaps remain in the understanding of the efficiency and selectivity of GQDs in the removal of specific contaminants in water. Therefore, it is necessary to conduct an evaluation of the efficiency of GQDs in removing various types of pollutants, including heavy metals, organic compounds, and other relevant contaminants present in water.
The challenge lies in the need to comprehensively understand the efficiency of GQDs in contaminant removal, given their growing relevance in environmental applications and wastewater treatment. The primary objective of this work is to carry out a review of the available scientific evidence on the efficacy and selectivity of GQDs in the removal of water pollutants, focusing on identifying current trends, knowledge gaps, and areas for improvement in research. This aims to provide a critical overview of the physicochemical properties of GQDs that influence their adsorption capacity and their potential to be applied in water treatment technologies. Through this review, clear guidelines will be offered on the necessary advancements to optimize the design and functionalization of GQDs, highlighting potential innovations that may enable their scale-up for industrial and environmental applications. This review article is justified by the need to synthesize and present the available scientific evidence on the use of GQDs for contaminant removal, identifying key trends, knowledge gaps, and opportunities for improvement in this field of research.

2. Materials and Methods

2.1. Research Questions for the Review

To guide the review, the following research questions will be formulated: What are the synthesis methods used for the production of GQDs? What are the potential advantages of using GQDs as adsorbents for heavy metals in water? What are the knowledge gaps and potential areas for improvement in the application of GQDs for water contaminant removal?

2.2. Search Strategies

Relevant studies will be identified through searches in scientific databases such as Scopus and Web of Science. Search terms like “graphene quantum dots”, “water treatment”, “contaminant removal”, “selectivity”, and “efficiency” will be used, combined with Boolean operators, to retrieve articles that address the efficiency of GQDs in contaminant removal. Articles published within the last 10 years will be considered to ensure the inclusion of the most up-to-date scientific evidence.

3. Results

3.1. Synthesis Methods of GQDs

The synthesis of GQDs has been one of the most active research areas in recent years, with a wide variety of methods and approaches employed for their production. The two main synthesis pathways for GQDs are known as top-down and bottom-up, as illustrated in Figure 1. The top-down approach involves the reduction of carbon structures to nanoscale dimensions, using materials like graphene or carbon. Common techniques include physical, chemical, or electrochemical methods [18], such as chemical exfoliation and acid treatments.
Top-down methods offer significant advantages in the production of GQDs, especially in terms of controlling size and morphology. For example, GQDs derived from oxidized graphene can achieve sizes of approximately 2.5 nm and exhibit good dispersion in water, a crucial characteristic for contaminant removal applications [19,20]. Additionally, these methods allow for the surface functionalization of GQDs, enhancing their adsorption capacity and, consequently, their efficiency in contaminant removal [21].
However, these methods also have disadvantages. Chief among them are the complexity of the process, the need for multiple steps, which reduces yield, and the generation of unwanted by-products [22]. Chemical oxidation, often used in these methods, can alter the crystalline structure of graphene, compromising its electronic properties [23]. Furthermore, variability in the quality of GQDs produced remains a challenge, as synthesis conditions affect the uniformity and reproducibility of their properties [24,25,26]. While top-down methods offer a promising approach for producing GQDs aimed at contaminant removal, overcoming these limitations is crucial to improving their efficiency and commercial viability in environmental applications.
On the other hand, the bottom-up synthesis approach has emerged as a promising alternative, particularly for applications in water contaminant removal. This approach, based on constructing GQDs from molecular precursors, allows for precise control over their structural and functional properties. Among its advantages is the production of GQDs with high purity and homogeneity, as well as precise control over their optical and electronic properties, key aspects for their efficacy in contaminant removal [27]. Additionally, the functionalization of GQDs can enhance their water solubility and adsorption capacity, further improving their effectiveness in such processes.
Another advantage is the production of GQDs with tunable photoluminescent properties, expanding their applications in contaminant detection [28]. Furthermore, this approach is scalable, making it viable for large-scale production, as demonstrated by the microwave-assisted method developed by Hoang et al. [19], which enables the rapid and efficient synthesis of GQDs—an essential factor for industrial use in water purification.
Nonetheless, bottom-up synthesis also faces challenges. The process often requires specific conditions and expensive precursors, which can limit its economic viability for large-scale production [29]. Additionally, variability in the properties of the produced GQDs can be problematic, as the quality depends on the synthesis conditions, which may affect their performance in practical applications. For instance, Zeng et al. [11] pointed out that the functionalization of GQDs can impact their stability and effectiveness in photonic applications, highlighting the need for rigorous control during synthesis.
The influence of quantum dot size on their properties has been widely studied. Research has shown that the formation of quantum dots with conical and pyramidal shapes can affect the reduction of transition energies between subbands and increase the overlap of states by enlarging the system’s dimensions [30]. Additionally, the effect of magnetic fields on the optical rectification of cylindrical quantum dots has been explored, revealing that these systems exhibit a higher optical rectification coefficient compared to spherical quantum dots [31]. Scientific literature has also investigated optical effects in conical and pyramidal quantum dots, where changes in the system’s optical properties, such as red or blue shifts in light emission, were observed depending on factors like the intensity of the applied electric field [30]. These findings suggest that the size and shape of GQDs can influence their luminescent behavior and the optical properties they exhibit. The size of GQDs is closely related to the type of luminescence they can present. Variations in the size and shape of quantum dots can affect their optical properties, such as the emitted light wavelength and changes in luminescence in response to different external stimuli, as shown in Figure 2.
The synthesis of graphene quantum dots (GQDs) has progressed toward more sustainable methods, such as green production approaches with applications in biomedicine and biotechnology [32,33,34]. These methods include fullerene opening and the use of plant extracts [35,36], highlighting the importance of sustainability. For instance, the mild oxidation of coal tar with hydrogen peroxide enables the production of fluorescent GQDs with high yields [20], while the exfoliation of carbon nanotubes allows for the efficient production of water-soluble GQDs [37].
Contaminant removal through sustainable methods is a critical challenge, particularly given the growing concerns about pollution and water scarcity. Green synthesis methods, which use natural resources such as fruits and vegetables, reduce the reliance on hazardous chemical reagents, offering advantages in terms of cost and toxicity. For example, GQDs synthesized from tomato extracts have been shown to be non-toxic and environmentally friendly. This approach not only minimizes environmental impact but also facilitates low-cost GQD production, which is crucial for large-scale applications in water contaminant removal [38].
Moreover, GQDs have demonstrated a remarkable ability to adsorb and remove water contaminants, such as heavy metals and organic compounds. Their high surface area and fluorescent properties allow for efficient contaminant detection, making them ideal candidates for water treatment systems [39]. The functionalization of GQDs has further enhanced their adsorption capacity, increasing their effectiveness in removing specific contaminants [40]. Current research focuses on optimizing green synthesis methods and exploring new biomass sources for GQD production. For instance, agricultural waste and food industry by-products are being investigated as precursors for GQDs, contributing to sustainability and promoting a circular economy [41,42]. Additionally, integrating GQDs into water treatment systems, such as photocatalytic reactors, has shown significant potential for improving contaminant removal efficiency, positioning these nanomaterials as a viable and eco-friendly solution for wastewater treatment [43].

Applications of GQDs

The applications of GQDs have been the subject of numerous studies across various fields. Among the applications receiving significant attention are optoelectronics [44], photodetection [45], luminescence [46], spin qubit formation [2], long-term cell tracking in three-dimensional tissue engineering [47], automated reconstruction of bound states in GQDs [48], and their potential for single-photon emission at room temperature [49].
Studies have revealed a range of intriguing properties of GQDs, including their light sensitivity, spectral selectivity, fluorescence, and potential for applications in bioengineering and nanotechnology. Their light sensitivity has enabled their use as long-term tracers in tissue engineering, highlighting their versatility in biomedical applications [47]. Additionally, the formation of spin qubits in GQDs has opened new possibilities in quantum computing [2,50]. The ability to manipulate the photoluminescent properties of GQDs allows tuning of light emission through charge transfer effects [17]. These materials have also been shown to possess intrinsic magnetic properties [51], paving the way for applications in magnetism and nanostructured magnetic devices.
In the field of nanotechnology, an approach has been proposed for the automated reconstruction of bound states in bilayer GQDs [48], demonstrating the potential of these materials for advanced applications in nanostructures. Regarding the synthesis and functionalization of GQDs, the creation of zinc oxide nanocomposites with GQDs for the photocatalytic degradation of organic dyes and commercial herbicides has been explored [52], showing a promising path for environmental purification. These approaches highlight the diversity of available strategies for synthesizing these nanostructured materials, such as water–oil interface-driven self-assembly used to uniformly immobilize CdTe quantum dots in reduced graphene nanocomposites [53]. Furthermore, the construction of gold nanoparticles stabilized with GQDs has been achieved by mixing chloroauric acid in varying amounts without the need for reducing agents [54]. Given the physical and chemical properties that GQDs exhibit in various applications, their potential for the removal of various compounds from water has been explored, opening the door to environmental applications.
GQDs have demonstrated significant potential in removing water contaminants, including heavy metals, organic compounds, and dyes, due to their high surface area and adsorption capacity. However, large-scale implementation of GQDs in water purification systems faces considerable challenges. The synthesis of GQDs on an industrial scale can be costly and complex, limiting their widespread application. Some production methods require strong acids and high temperatures, increasing expenses and complicating scalability. Nonetheless, low-cost methodologies have been developed, showing promise for biomedical and environmental applications [55]. Producing high-quality GQDs at scale remains challenging, necessitating further efforts to develop economically viable and scalable synthesis methods [55,56]. Additionally, the production of graphene and its derivatives, such as GQDs, often involves substantial use of sulfuric acid, water, and energy, generating hazardous by-products. These processes may have ecotoxic effects and health risks that are not yet fully understood. It is crucial to assess and mitigate the potential environmental impacts associated with the production and use of GQDs in water purification applications. To establish GQDs as a sustainable solution in water purification, advancing green and scalable synthesis techniques and conducting long-term environmental assessments are essential. Future research should focus on developing production methods that minimize the use of hazardous substances and reduce waste generation, ensuring that the application of GQDs does not compromise human health or the environment [57,58].

3.2. Efficiency of GQDs in Water Contaminant Removal

Recent studies have highlighted the efficiency of GQDs in removing water contaminants, including heavy metals and organic compounds, emphasizing the close relationship between their structure, functionalization, and interaction mechanisms, as illustrated in Figure 3 [59,60].
Recent research has emphasized the capability of GQDs in contaminant removal. Studies conducted by Liao et al. [61], Mohammad-Rezaei and Jaymand [62], and Saleem et al. [33] have demonstrated their effectiveness in eliminating various pollutants. The efficiency of GQDs in contaminant removal has been shown to be enhanced by their ability to separate electron–hole pairs, making them highly effective in dye degradation and hydrogen production [29,63].
For instance, Yuan et al. [64] developed a photocatalyst composed of GQDs decorated with graphitic carbon nitride nanorods (g-CNNR), achieving approximately 80% removal of antibiotics. In other studies, Choi et al. [65,66] explored various GQD-based materials for the removal of harmful vapors. In Choi et al. [65], they demonstrated that incorporating GQDs into gCN/ODBOC nanocomposites enhanced their photocatalytic activity, achieving up to 95% hexanal removal. Additionally, in Choi et al. [66], they developed NGQDs and applied them to FeWO4/g-C3N4 heterostructures, resulting in average removal efficiencies of 97.3% for vaporized 2-butoxy ethanol and 55.1% for ethylbenzene.
Sarkar et al. [67] investigated GQDs integrated into magnetic graphene oxide (GO/Fe3O4/GQD). The high surface area of GQDs, with a layered graphene-like structure, makes them more sensitive to environmental changes, and they are considered eco-friendly candidates with a cell viability of approximately 86.7% for dye removal applications. Additionally, Mahmoud et al. [68] developed an innovative supramolecular network, GQDs@FA@Fe-TA, which demonstrated high efficacy in removing inorganic contaminants, such as Cr(VI), and organic dyes like malachite green (MG). Furthermore, Mahmoud et al. [69] synthesized ZnO/C-Foam/GQDs/Alginate, which exhibited high efficiency in removing inorganic pollutants such as Pb(II), and organic dyes like Methylene Blue (MB).
Considering the above, the most commonly employed modifications to GQDs to enhance their efficiency in water contaminant removal include decoration with nanomaterials such as graphitic carbon nitride, integration into nanocomposites like magnetic graphene oxide and ferrous compounds, and the formation of innovative supramolecular networks like GQDs@FA@Fe-TA. These modifications not only increase the removal and degradation efficiency of GQDs but also impart specific properties for the removal of various types of contaminants, as shown in Table 1.
Ongoing research has led to significant advancements in the desirable properties of GQDs for heavy metal removal applications. For example, their utility as sensors for detecting residual chlorine in drinking water has been demonstrated, highlighting their potential for practical applications in monitoring and remediating contaminated water [70,71]. Additionally, various studies have emphasized the effectiveness of GQDs in water contaminant removal through diverse technologies. For instance, Gen et al. [72] employed a ternary photoelectrode composed of Bi2S3/GQDs/TNWs, achieving a 97% removal of Cr(VI).
In another study, Mohamed et al. [73] used rice husk as a sustainable source to synthesize GQDs with a 2D morphology. They optimized the adsorption parameters for Pb(II) and La(III) on GQDOs using a microwave sorption method, achieving excellent removal rates for different water samples containing lead (98.5%–99.8%) and lanthanum (94.6%–96.2%). In a different context, Shafai et al. [74] investigated the electrochemical properties of ferric ferrous oxide quantum dots obtained from graphene oxide nanocomposites (GO@Fe3O4). The synthesis of GO@Fe3O4 resulted in a low band gap, which enhanced its activity compared to oxidized graphene (GO), and provided new optical properties. Photoinduced charge transfer was observed, with efficient degradation of the dye Rose Bengal in a short period. Additionally, GO@Fe3O4 proved to be an effective adsorbent for the removal of the insecticide Lambda and heavy metal ions such as Cr(III) from an aqueous solution.
GQDs have demonstrated significant potential in the removal of nitrophenols from contaminated water due to their unique properties. Their high surface area and tunable photoluminescence enable effective adsorption and degradation of organic pollutants, including nitrophenols [55,58,75]. For instance, sulfur-doped GQDs have been developed as sensitive and selective fluorescence probes for detecting 4-nitrophenol in water, achieving detection limits as low as 0.7 nM in deionized water and 3.5 nM in wastewater [76]. Additionally, GQD-based membranes have been fabricated to enhance wastewater treatment processes, demonstrating improved removal efficiencies for various contaminants [75]. Furthermore, GQDs have been integrated into photocatalytic systems, exhibiting superior performance in the degradation of pollutants under light irradiation [77].
GQDs have demonstrated remarkable efficiency in removing a wide range of compounds from water, including dyes, antibiotics, and heavy metals, with removal efficiencies reaching up to 97%, as shown in Table 2.
This finding underscores the significant potential of GQDs for environmental treatment. Ongoing research and development in this field could drive the broader application of GQDs in water treatment technologies, promoting substantial improvements in water quality and environmental protection. Specifically, their capacity as adsorbents for heavy metals stands out as a promising approach to effectively and sustainably address water pollution.

3.3. Adsorption of Heavy Metals with GQDs

Research in the field of heavy metal adsorbents using GQDs has gained significant relevance, driven by the need to address water contamination effectively and sustainably. These adsorbents are characterized by their nanometric structure, which provides a high surface area and numerous active sites for the adsorption of metallic contaminants.
Recent advancements reveal significant progress in the synthesis and functionalization of these adsorbents, as well as in understanding their adsorption mechanisms. For example, studies by Chen et al. [54] and Lei et al. [29] have demonstrated the efficacy of GQDs in adsorbing heavy metals such as lead, cadmium, and mercury, underscoring their potential for water decontamination.
Moreover, the functionalization of GQDs with specific groups to enhance their adsorption capacity has been explored, as evidenced by research conducted by Tachi et al. [78]. Additionally, the combination of GQDs with other materials, such as gold nanoparticles, has revealed synergies in heavy metal adsorption, highlighting the versatility and potential of these hybrid materials [54].
Among the most significant advancements, studies such as Alvand [79] have demonstrated the effectiveness of multifunctional fluorescent probes based on Fe3O4@SiO2@GQDs nanospheres for the simultaneous detection and removal of Hg(II). This research emphasizes the ability of these materials to adsorb mercury due to their high specific surface area and numerous binding sites in the GQDs. Moreover, thanks to their superparamagnetism, the material can be separated with a magnet and recycled using EDTA, reducing environmental contamination. Furthermore, research led by Nagaraj et al. [80] has highlighted the potential of coating GQDs with functional ionic liquid (IL-GQD) for Cr(VI) removal from water. This study emphasizes the high adsorption capacity of IL-GQD and its efficiency in chromium removal through electrostatic attraction, complexation, ion exchange, and hydrogen bonding mechanisms, offering a promising solution for the decontamination of water affected by this heavy metal.
The potential utility of GQDs for the adsorption of other heavy metals from water is undeniable. These materials offer several advantages, including high selectivity, regeneration capacity, and potential for industrial-scale application. Research by Mohammad [62] highlighted the feasibility of GQD-based adsorbents coated on quartz sand (GQDs|QS) for the removal of Hg(II) and Pb(II) from aqueous solutions. This study underscores the stability, efficiency, and low cost of these materials, suggesting their application on an industrial scale for the treatment of water contaminated with heavy metals. Additionally, studies such as those by Pirhaji et al. [14] and Nuengmatcha [81] have explored the covalent immobilization of GQDs on other materials to enhance the adsorption of heavy metals such as lead and cadmium. These studies have demonstrated significant adsorption capacities and regeneration properties.
The reviewed research highlights the effectiveness and versatility of functionalized GQDs in the adsorption of heavy metals from water. The combination of the high surface area of GQDs with various functionalization strategies has proven effective for the removal of metals such as lead, cadmium, mercury, and chromium, among others. The mentioned studies underscore the importance of considering both the intrinsic properties of GQDs and specific modifications to optimize their adsorption capacity. For an overview of the adsorption capacities of functionalized GQDs for heavy metals, Table 3 summarizes the materials, contaminants, and adsorption capacities.
GQD-based materials not only offer an efficient and selective alternative for water decontamination but also contribute significantly to environmental protection and the improvement of quality of life. Their potential application extends beyond the heavy metals mentioned, opening new possibilities for the adsorption of other metallic contaminants present in water.

3.4. Trends and Knowledge Gaps in GQDs

Some potential areas for improving the application of GQDs in water contaminant removal lie in the need to explore innovative approaches, such as functionalizing these materials to enhance their adsorption capacity and selectivity [82]. Additionally, investigating new characterization techniques and monitoring the effectiveness of GQDs in contaminant removal could open up new opportunities for their use in water purification [83]. Recent studies have shown growing interest in functionalizing GQDs with specific compounds to improve their heavy metal adsorption capacity [84]. The incorporation of ions into GQDs has been explored as a strategy to enhance selectivity in heavy metal removal from water [85]. Moreover, combining GQDs with materials like tin dioxide has shown promise in heavy metal adsorption in aqueous solutions [86].
Despite these advancements, there are knowledge gaps in current research that need attention. Most studies have focused on the preparation and characterization of GQDs, with less emphasis on their analytical application [70]. Additionally, the interaction between GQDs and heavy metals remains an area that requires further understanding to optimize the efficiency of metallic contaminant removal from water [87]. The sensitivity and selectivity of GQDs in heavy metal detection are aspects that must be addressed to enhance their applicability in water purification [88].
To advance in this field, it is crucial to explore new strategies for modifying GQDs and improving their adsorption capacity and selectivity toward heavy metals. The integration of GQDs with other nanostructured materials, such as carbon nanotubes, could offer synergies in removing metal contaminants from water [89]. Furthermore, research on the functionalization of GQDs with specific compounds for the detection and adsorption of heavy metals could open new pathways for more effective environmental applications [90].
For future research, experimental studies are strongly recommended to directly assess the efficiency and selectivity of GQDs in water contaminant removal. Standardizing the synthesis and characterization methods of GQDs is also crucial to ensure consistency and facilitate comparability between studies. Additionally, investigating the long-term environmental and human health impacts of GQDs, alongside exploring their specific applications under diverse contexts and conditions, is imperative to advance their practical use.
While GQDs exhibit significant potential across various applications, their environmental and practical implications require careful consideration. Studies suggest that GQDs may induce cytotoxic effects, such as the generation of reactive oxygen species and DNA damage, particularly at high concentrations or during prolonged exposure [91,92,93,94,95,96,97,98]. The risk of bioaccumulation and their long-term environmental persistence remains uncertain, highlighting the need for comprehensive ecological impact assessments [93,99,100]. Furthermore, the production of graphene-based materials often involves the use of hazardous chemicals and energy-intensive processes, raising additional environmental concerns. Addressing these challenges is vital to ensure the safe and sustainable development of GQD applications. Consequently, adopting environmentally friendly synthesis methods and conducting thorough evaluations of the life cycle and disposal of GQDs are essential steps toward their responsible use.
In the future, two critical trends are expected to influence the development of GQDs. First, there is a growing emphasis on the exploration of sustainable and scalable production methods. Advances in green synthesis techniques, including the use of renewable or recycled raw materials, promise to minimize the environmental footprint of GQD production without compromising their essential properties. Second, the application of GQDs for water contaminant removal is gaining prominence as a highly relevant field for environmental protection. GQDs have demonstrated the ability to adsorb and degrade organic and inorganic pollutants in wastewater and contaminated water, offering innovative and efficient solutions to address global water quality challenges. These applications span a range of contexts, from industrial wastewater treatment to the purification of drinking water sources. By integrating these two research directions, the environmental viability of GQD production can be enhanced while maximizing their positive impact on pressing global environmental issues.

4. Conclusions

This review has provided a comprehensive overview of the efficiency and selectivity of GQDs in water contaminant removal. The review highlights that GQDs possess unique properties, such as high adsorption capacity and selectivity in removing various types of contaminants, making them promising candidates for contaminant removal applications. The synthesis and systematic presentation of the available scientific evidence have helped identify trends, knowledge gaps, and potential areas for improvement in this field, contributing to the advancement and development of effective strategies for water contaminant removal. The importance of systematically synthesizing and presenting the available scientific evidence lies in the need to thoroughly understand the efficiency and selectivity of GQDs in water contaminant removal. This review emphasized the need to standardize the synthesis and characterization methods of GQDs and the importance of conducting direct experimental studies to evaluate their efficiency and selectivity in contaminant removal. Additionally, it has underscored the significance of investigating the long-term impact of GQDs on the environment and human health, as well as exploring specific applications in various contexts and conditions. For future research, it is recommended to conduct experimental studies that directly assess the efficiency and selectivity of GQDs in water contaminant removal.

Author Contributions

Conceptualization, J.P.R.-C. and D.R.J.-C.; methodology, J.P.R.-C. and D.R.J.-C.; formal analysis, J.P.R.-C., D.R.J.-C., C.E.D.-A. and A.S.-R.; investigation, J.P.R.-C., C.E.D.-A. and A.S.-R.; resources, N.S.-R., M.A.C.-R. and A.S.-R.; writing—original draft preparation, J.P.R.-C. and D.R.J.-C.; writing—review, J.P.R.-C., D.R.J.-C., C.E.D.-A. and A.S.-R.; editing, all the authors; visualization, J.P.R.-C. and D.R.J.-C.; supervision, N.S.-R., M.A.C.-R., C.E.D.-A. and A.S.-R.; project administration, C.E.D.-A. and A.S.-R. All authors have read and agreed to the published version of the manuscript.

Funding

J.P.R.-C. and D.R.J.-C. thank the National Council of Humanities, Science and Technology (CONAHCyT), Mexico for Grant 1252574 and 825526. D.R.J.-C. thanks the University of Santander (UDES) for its support. M.A.C-R., N.S.-R., C.E.D.-A. and A.S.-R. gratefully acknowledge the financial support of CONAHCyT through S.N.I.I program. The authors thank the University of Guanajuato for its support.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

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Water 17 00166 g001
Figure 1. Synthesis Methods of Graphene Quantum Dots.
Figure 1. Synthesis Methods of Graphene Quantum Dots.
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Water 17 00166 g002
Figure 2. Size-dependent absorption and emission.
Figure 2. Size-dependent absorption and emission.
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Figure 3. Application of GQDs in Water Contaminants.
Figure 3. Application of GQDs in Water Contaminants.
Water 17 00166 g003
Table 1. Functionalized GQDs for Contaminant Removal.
Table 1. Functionalized GQDs for Contaminant Removal.
MaterialContaminantpHEfficiency
%		Reference
GQDs/g-CNNRAntibiotic
OTC		-80[64]
GQDs/gCN/ODBOCVapores orgánicos-95[65]
FeWO4/g-C3N4 (NGQD/FWO/CN)Vapores
2-butoxietanol etilbenceno		-97.3[66]
55.1
PVA/CMC-B@GO/Fe3O4/GQDDye pollutants886.7[67]
GQDs@FA@Fe-TACr(VI)
MG		399.5[68]
94.8
ZnO/C-Foam/GQDs/AlginatePb (II)
Azul metileno MB		6
7		100[69]
92.2
Table 2. Functionalized GQDs for Heavy Metal Removal.
Table 2. Functionalized GQDs for Heavy Metal Removal.
MaterialContaminantpHEfficiency
%		Reference
Bi2S3/GQDs/TNWsCr(VI)-97 [72]
GQDOs-BaPb(II)
La(III)		798.5–99.8
94.6–96.2		[73]
GO@Fe3O4Cr(III)6
4		17
31		[74]
Table 3. Functionalized GQDs for Heavy Metal Adsorption.
Table 3. Functionalized GQDs for Heavy Metal Adsorption.
MaterialContaminantAdsorption CapacityReference
Fe3O4@SiO2@GQDsHg(II)68 [79]
IL-GQDCr(VI)934.62[80]
GQDs|QSHg(II)24.65
Pb(II)24.92[63]
NiFe2O4/HNTs/GQDsPb(II)42.02[14]
Fe2O3-GQDs-SHCd(II)128.21[81]
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Rodríguez-Caicedo, J.P.; Joya-Cárdenas, D.R.; Corona-Rivera, M.A.; Saldaña-Robles, N.; Damian-Ascencio, C.E.; Saldaña-Robles, A. Efficiency of Graphene Quantum Dots in Water Contaminant Removal: Trends and Future Research Directions. Water 2025, 17, 166. https://doi.org/10.3390/w17020166

AMA Style

Rodríguez-Caicedo JP, Joya-Cárdenas DR, Corona-Rivera MA, Saldaña-Robles N, Damian-Ascencio CE, Saldaña-Robles A. Efficiency of Graphene Quantum Dots in Water Contaminant Removal: Trends and Future Research Directions. Water. 2025; 17(2):166. https://doi.org/10.3390/w17020166

Chicago/Turabian Style

Rodríguez-Caicedo, Juliana P., Diego R. Joya-Cárdenas, Miguel A. Corona-Rivera, Noé Saldaña-Robles, Cesar E. Damian-Ascencio, and Adriana Saldaña-Robles. 2025. "Efficiency of Graphene Quantum Dots in Water Contaminant Removal: Trends and Future Research Directions" Water 17, no. 2: 166. https://doi.org/10.3390/w17020166

APA Style

Rodríguez-Caicedo, J. P., Joya-Cárdenas, D. R., Corona-Rivera, M. A., Saldaña-Robles, N., Damian-Ascencio, C. E., & Saldaña-Robles, A. (2025). Efficiency of Graphene Quantum Dots in Water Contaminant Removal: Trends and Future Research Directions. Water, 17(2), 166. https://doi.org/10.3390/w17020166

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