Green Synthesis of Carbon Dots from Lemon Juice with Precursor Ratio–Dependent Emissions
Main Article Content
Abstract
Carbon dots (CDs) are fluorescent nanomaterials with great potential for applications in sensing and imaging. This study explores the synthesis of CDs using a simple, low-cost, and rapid household microwave-assisted approach, utilizing lemon juice and urea as precursors. By modulating the precursor ratio, we obtained two types of CDs with different optical properties: green-emitting fluorescent CDs (g-CDs) and blue-emitting CD (b-CDs). Both particles showed quantum yields of approximately 10%. The synthesis process, conducted under solvent-free and ambient- pressure conditions, demonstrates an environmentally benign and sustainable route compared to conventional hydrothermal methods. Structural and optical characterizations confirmed that precursor ratio control directly influenced the emission behavior of the CDs. Preliminary investigations further revealed that the g-CDs exhibited selective and sensitive fluorescence quenching toward Hg2+ ions indicating their promise as sustainable and cost-effective probes for heavy metal detection. This study highlights the potential of green-synthesized carbon dots for environmental sensing applications, contributing to developing simple early-warning tools for pollution monitoring
Keywords
Carbon dots, fluorescence, metal ion sensor, nanomaterial.
Article Details
This work is licensed under a Creative Commons Attribution 4.0 International License.
References
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[2] A. Sharma and J. Das, Small molecules derived carbon dots: Synthesis and applications in sensing, catalysis, imaging, and biomedicine, Journal of Nanobiotechnology, vol. 17, Aug. 2019, Art. no. 92. https://doi.org/10.1186/s12951-019-0525-8
[3] X. Guan, Z. Li, X. Geng, Z. Lei, A. Karakoti, T. Wu, P. Kumar, J. Yi, and A. Vinu, Emerging trends of carbon-based quantum dots: Nanoarchitectonics and applications, Small, vol. 19, iss. 17, Art. no. 2207181, Apr. 2023. https://doi.org/10.1002/smll.202207181
[4] R. Lamba, Y. Yukta, J. Mondal, R. Kumar, B. Pani, and B. Singh, Carbon dots: Synthesis, characterizations, and recent advancements in biomedical, optoelectronics, sensing, and catalysis applications, ACS Applied Bio Materials, vol. 7, iss. 4, pp. 2086–2127, Mar. 2024. https://doi.org/10.1021/acsabm.4c00004
[5] S. Y. Lim, W. Shen, and Z. Gao, Carbon quantum dots and their applications, Chemical Society Reviews, vol. 44, iss. 1, pp. 362–381, Oct. 2015. https://doi.org/10.1039/C4CS00269E
[6] C. Cheng, M. Xing, and Q. Wu, A universal facile synthesis of nitrogen and sulfur co-doped carbon dots from cellulose-based biowaste for fluorescent detection of Fe3+ ions and intracellular bioimaging, Materials Science and Engineering: C, vol. 99, pp. 611–619, Jun. 2019. https://doi.org/10.1016/j.msec.2019.02.070
[7] H. Ding, S.-B. Yu, J.-S. Wei, and H.-M. Xiong, Full-color light-emitting carbon dots with a surface-state-controlled luminescence mechanism, ACS Nano, vol. 10, iss. 1, pp. 484–491, Jan. 2016. https://doi.org/10.1021/acsnano.5b05406
[8] Y. Song, S. Zhu, S. Zhang, Y. Fu, L. Wang, X. Zhao, and B. Yang, Investigation from chemical structure to photoluminescent mechanism: a type of carbon dots from the pyrolysis of citric acid and an amine, Journal of Materials Chemistry C, vol. 3, iss. 23, pp. 5976–5984, May 2015. https://doi.org/10.1039/C5TC00813A
[9] S. Zhu, Y. Song, X. Zhao, J. Shao, J. Zhang, and B. Yang, The photoluminescence mechanism in carbon dots (graphene quantum dots, carbon nanodots, and polymer dots): Current state and future perspective, Nano Research, vol. 8, pp. 355–381, Feb. 2015.
https://doi.org/10.1007/s12274-014-0644-3
[10] W. Kasprzyk, T. Świergosz, S. Bednarz, K. Walas, N. V. Bashmakova, and D. Bogdał, Luminescence phenomena of carbon dots derived from citric acid and urea - a molecular insight, Nanoscale, iss. 29, pp. 13889–13894, Jun. 2018. https://doi.org/10.1039/C8NR03602K
[11] D. Qu, M. Zheng, L. Zhang, H. Zhao, Z. Xie, X. Jing, R. E. Haddad, H. Fan and Z. Sun, Formation mechanism and optimization of highly luminescent N-doped graphene quantum dots, Scientific Reports, vol. 4, Art. no. 5294, Jun. 2014. https://doi.org/10.1038/srep05294
[12] R. Wang, K.-Q. Lu, Z.-R. Tang, and Y.-J. Xu, Recent progress in carbon quantum dots: synthesis, properties and applications in photocatalysis, Journal of Materials Chemistry A, vol. 5, iss. 8, pp. 3717–3734, Jan. 2017. https://doi.org/10.1039/C6TA08660H
[13] A. Sciortino, A. Cannizzo, and F. Messina, Carbon nanodots: A review-from the current understanding of the fundamental photophysics to the full control of the optical response, C-Journal of carbon research, vol. 4, no. 4, Oct. 2018, Art. no. 67.
https://doi.org/10.3390/c4040067
[14] J. Shen, S. Shang, X. Chen, D. Wang, and Y. Cai, Facile synthesis of fluorescence carbon dots from sweet potato for Fe3+ sensing and cell imaging, Materials Science and Engineering: C, vol. 76, pp. 856–864, Jul. 2017. https://doi.org/10.1016/j.msec.2017.03.178
[15] H. Li, Z. Kang, Y. Liu, and S.-T. Lee, Carbon nanodots: Synthesis, properties and applications, Journal of Materials Chemistry, vol. 22, iss. 46, pp. 24230–24253, Aug. 2012. https://doi.org/10.1039/c2jm34690g
[16] Y. Dong, R. Wang, G. Li, C. Chen, Y. Chi, and G. Chen, Polyamine-functionalized carbon quantum dots as fluorescent probes for selective and sensitive detection of copper ions, Analytical Chemistry, vol. 84, iss. 14, pp. 6220–6224, Jun. 2012. https://doi.org/10.1021/ac3012126
[17] S. Zhu, J. Zhang, S. Tang, C. Qiao, L. Wang, H. Wang, X. Liu, B. Li, Y. Li, W. Yu, X. Wang, H. Sun, and B. Yang, Surface chemistry routes to modulate the photoluminescence of graphene quantum dots: From fluorescence mechanism to up-conversion bioimaging applications, Advanced Functional Materials, vol. 22, iss. 22, pp. 4732–4740, Nov. 2012. https://doi.org/10.1002/adfm.201201499
[18] Y. Huang, X. Hu, W. Zhang, J. Zheng, J. Shao, Y. Chen, and Y. Chi, Multiwalled carbon nanorings found in raw single-walled carbon nanotubes and applied for electrochemiluminescent immunoassay, ACS Sensors, vol. 10, iss. 6, pp. 4589–4599, May 2025.
https://doi.org/10.1021/acssensors.5c00949
[19] U. Abd Rani, L. Y. Ng, C. Y. Ng, and E. Mahmoudi, A review of carbon quantum dots and their applications in wastewater treatment, Advances in Colloid and Interface Science, vol. 278, Apr. 2020, Art. no. 102124. https://doi.org/10.1016/j.cis.2020.102124
[20] H. Li, X. He, Y. Liu, H. Huang, S. Lian, S.-T. Lee, and Z. Kang, One-step ultrasonic synthesis of water-soluble carbon nanoparticles with excellent photoluminescent properties, Carbon, vol. 49, no. 2, pp. 605–609, Feb. 2011. https://doi.org/10.1016/j.carbon.2010.10.004
[21] M. L. Liu, B. B. Chen, C. M. Li, and C. Z. Huang, Carbon dots: Synthesis, formation mechanism, fluorescence origin and sensing applications, Green Chemistry, vol. 21, iss. 3, pp. 449–471, Jan. 2019. https://doi.org/10.1039/C8GC02736F
[22] M. Hamed, S. Chinnam, A. Bedair, S. Emara, and F. R. Mansour, Carbon quantum dots from natural sources as sustainable probes for metal ion sensing: Preparation, characterizations and applications, Talanta Open, vol. 10, Dec. 2024, Art. no. 100348.
https://doi.org/10.1016/j.talo.2024.100348
[23] K. L. Penniston, S. Y. Nakada, R. P. Holmes, and D. G. Assimos, Quantitative assessment of citric acid in lemon juice, lime juice, and commercially available fruit juice products, Journal of Endourology, vol. 22, iss. 3, pp. 567–570, Mar. 2008.
https://doi.org/10.1089/end.2007.0304
[24] D. M. Crista, A. El Mragui, M. Algarra, J. C. Esteves da Silva, R. Luque, and L. Pinto da Silva, Turning spent coffee grounds into sustainable precursors for the fabrication of carbon dots, Nanomaterials, vol. 10, no. 6, Jun. 2020, Art. no. 1209. https://doi.org/10.3390/nano10061209
[25] B. De and N. Karak, A green and facile approach for the synthesis of water soluble fluorescent carbon dots from banana juice, RSC Advances, vol. 3, iss. 22, pp. 8286–8290, Mar. 2013. https://doi.org/10.1039/c3ra00088e
[26] J. Schneider, C. J. Reckmeier, Y. Xiong, M. von Seckendorff, N. Susha, P. Kasák, and A. L. Rogach, Molecular fluorescence in citric acid-based carbon dots, The Journal of Physical Chemistry C, vol. 121, iss. 3, pp. 2014–2022, Dec. 2016. https://doi.org/10.1021/acs.jpcc.6b12519
[27] S. Zhu, X. Zhao, Y. Song, S. Lu, and B. Yang, Beyond bottom-up carbon nanodots: Citric-acid derived organic molecules, Nano Today, vol. 11, no. 2, pp. 128–132, Apr. 2016. https://doi.org/10.1016/j.nantod.2016.04.001
[28] D. Qu and Z. Sun, The formation mechanism and fluorophores of carbon dots synthesized via a bottom-up route, Materials Chemistry Frontiers, vol. 4, is. 2, pp. 400–420, 2020. https://doi.org/10.1039/C9QM00552H
[29] V. Strauss, H. Wang, S. Delacroix, M. Ledendecker, and P. Wessig, Carbon nanodots revised: The thermal citric acid/urea reaction, Chemical Science, vol. 11, iss. 31, pp. 8256–8266, Jul. 2020. https://doi.org/10.1039/D0SC01605E
[30] F. Zu, F. Yan, Z. Bai, J. Xu, Y. Wang, Y. Huang, and X. Zhou, The quenching of the fluorescence of carbon dots: A review on mechanisms and applications, Microchimica Acta, vol. 184, no. 7, pp. 1899–1914, May 2017. https://doi.org/10.1007/s00604-017-2318-9
[31] D. Dai, C. Zhang, N. T. D. Thuy, G. Zhao, W. Lu, and J. Fan, Strong fluorescence quenching of carbon dots by mercury(II) ions: Ground-state electron transfer and diminished oscillator strength, Diamond and Related Materials, vol. 126, Jun. 2022, Art. no. 109076. https://doi.org/10.1016/j.diamond.2022.109076
[32] K. Laptinskiy, S. Burikov, G. Chugreeva, and T. A. Dolenko, The mechanisms of fluorescence quenching of carbon dots upon interaction with heavy metal cations, Fullerenes, Nanotubes and Carbon Nanostructures, vol. 30, iss. 1, pp. 46–52, Jan. 2022.
https://doi.org/10.1080/1536383X.2021.1995365
[33] H. Shabbir, E. Csapó, and M. Wojnicki, Carbon quantum dots: The role of surface functional groups and proposed mechanisms for metal ion sensing, Inorganics, vol. 11, no. 6, Art. no. 262, Jun. 2023. https://doi.org/10.3390/inorganics11060262
[34] F. Yan, Y. Zou, M. Wang, X. Mu, N. Yang, and L. Chen, Highly photoluminescent carbon dots-based fluorescent chemosensors for sensitive and selective detection of mercury ions and application of imaging in living cells, Sensors and Actuators B: Chemical, vol. 192, pp. 488–495, Mar. 2014. https://doi.org/10.1016/j.snb.2013.11.041
[35] D. Sun, T. Liu, C. Wang, L. Yang, S. Yang, and K. Zhuo, Hydrothermal synthesis of fluorescent carbon dots from gardenia fruit for sensitive on-off-on detection of Hg2+ and cysteine, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, vol. 240, Oct. 2020, Art. no. 118598. https://doi.org/10.1016/j.saa.2020.118598
[36] Y. Xie, D. Cheng, X. Liu, and A. Han, Green hydrothermal synthesis of N-doped carbon dots from biomass highland barley for the detection of Hg(II), Sensors, vol. 19, no. 14, Art. no. 3169, Jul. 2019. https://doi.org/10.3390/s19143169
[37] L. Li, B. Yu, and T. You, Nitrogen and sulfur co-doped carbon dots for highly selective and sensitive detection of Hg(II) ions, Biosensors and Bioelectronics, vol. 74, pp. 263–269, Dec. 2015. https://doi.org/10.1016/j.bios.2015.06.050