Insights into the role of common sulfur precursors in hydrothermally synthesized N,S-doped carbon dots: fluorescence modulation via surface oxidation rather than sulfur doping

While heteroatom doping is widely used to enhance the fluorescence of carbon dots, the actual mechanism underlying this claimed enhancement remains unclear. Herein, we report a systematic comparison between nitrogen-doped carbon dots (N-CDs) and nitrogen/sulfur co-doped carbon dots (N,S-CDs) synthes...

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Autores: Fernandes, Sónia, Algarra González, Manuel, Brandão, Ana T.S.C., Gil Bravo, Antonio, Pereira, Carlos, Esteves da Silva, Joaquim C.G., Pinto da Silva, Luís
Tipo de recurso: artículo
Estado:Versión publicada
Fecha de publicación:2026
País:España
Institución:Universidad Pública de Navarra
Repositorio:Academica-e. Repositorio Institucional de la Universidad Pública de Navarra
OAI Identifier:oai:dnet:academicae__::1591e88e4f27b663b0d409248ea18a61
Acceso en línea:https://hdl.handle.net/2454/56962
Access Level:acceso abierto
Palabra clave:Nitrogen-doped carbon dots (N-CDs)
Nitrogen/sulfur co-doped carbon dots (N,S-CDs)
Sulfur precursors
Surface oxidation
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spelling Insights into the role of common sulfur precursors in hydrothermally synthesized N,S-doped carbon dots: fluorescence modulation via surface oxidation rather than sulfur dopingFernandes, SóniaAlgarra González, ManuelBrandão, Ana T.S.C.Gil Bravo, AntonioPereira, CarlosEsteves da Silva, Joaquim C.G.Pinto da Silva, LuísNitrogen-doped carbon dots (N-CDs)Nitrogen/sulfur co-doped carbon dots (N,S-CDs)Sulfur precursorsSurface oxidationWhile heteroatom doping is widely used to enhance the fluorescence of carbon dots, the actual mechanism underlying this claimed enhancement remains unclear. Herein, we report a systematic comparison between nitrogen-doped carbon dots (N-CDs) and nitrogen/sulfur co-doped carbon dots (N,S-CDs) synthesized hydrothermally, with ethylenediamine and sodium thiosulfate as the N- and S-dopants, respectively. Contrary to expectations, the inclusion of the S-precursor significantly reduced the quantum yield by 63%, from 35.9% to 13.2%, while leaving the emission profile and response largely unchanged. Characterization assays revealed that S-doping in N,S-CDs was residual, whereas the surface oxygen content increased markedly, indicating surface oxidation. The data suggest that sodium thiosulfate acted not as a dopant but overall as an oxidant, generating oxygen-based surface defects that introduced nonradiative recombination pathways. Thus, our findings show that co-doping with this S-precursor can decrease the quantum yield by promoting surface oxidation and the effective formation of more oxidized N-CDs, rather than heteroatom incorporation and production of co-doped CDs. This decreasing effect on the quantum yield was also observed when using thiourea as the S-precursor. Future work should include the study of other common S-precursors. In conclusion, our research shows that specific heteroatom-based precursors can alter the optical characteristics of CDs through redox/surface-modification effects instead of actual compositional doping, and thus, claims based on heteroatom doping may need closer examination.Fundação para a Ciência e a Tecnologia (FCT, Portugal, https://ror.org/00snfqn58) is acknowledged for funding the R&D Unit CIQUP (UID/00081/2025), project 2023.13127.PEX and the Associated Laboratory IMS (LA/P/0056/2020). The NORTE2030 program is also acknowledged for funding the project NORTE2030-FEDER-02706400 (iChem4M). Luís Pinto da Silva acknowledges funding from the FCT under the Scientific Employment Stimulus (CEECINST/00069/2021). Sónia Fernandes also acknowledges the FCT for funding her Ph.D. grant (2021.05479.BD).Royal Society of ChemistryCienciasZientziakInstitute for Advanced Materials and Mathematics (INAMAT2)2026info:eu-repo/semantics/articleinfo:eu-repo/semantics/publishedVersionapplication/pdfhttps://hdl.handle.net/2454/56962reponame:Academica-e. Repositorio Institucional de la Universidad Pública de Navarrainstname:Universidad Pública de NavarraInglésinfo:eu-repo/grantAgreement/AEI/Plan Estatal de Investigación Científica y Técnica y de Innovación 2021-2023/PID2021-122613OB-I00© The Royal Society of Chemistry 2026. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.https://creativecommons.org/licenses/by/3.0/info:eu-repo/semantics/openAccessoai:dnet:academicae__::1591e88e4f27b663b0d409248ea18a612026-06-17T12:41:47Z
dc.title.none.fl_str_mv Insights into the role of common sulfur precursors in hydrothermally synthesized N,S-doped carbon dots: fluorescence modulation via surface oxidation rather than sulfur doping
title Insights into the role of common sulfur precursors in hydrothermally synthesized N,S-doped carbon dots: fluorescence modulation via surface oxidation rather than sulfur doping
spellingShingle Insights into the role of common sulfur precursors in hydrothermally synthesized N,S-doped carbon dots: fluorescence modulation via surface oxidation rather than sulfur doping
Fernandes, Sónia
Nitrogen-doped carbon dots (N-CDs)
Nitrogen/sulfur co-doped carbon dots (N,S-CDs)
Sulfur precursors
Surface oxidation
title_short Insights into the role of common sulfur precursors in hydrothermally synthesized N,S-doped carbon dots: fluorescence modulation via surface oxidation rather than sulfur doping
title_full Insights into the role of common sulfur precursors in hydrothermally synthesized N,S-doped carbon dots: fluorescence modulation via surface oxidation rather than sulfur doping
title_fullStr Insights into the role of common sulfur precursors in hydrothermally synthesized N,S-doped carbon dots: fluorescence modulation via surface oxidation rather than sulfur doping
title_full_unstemmed Insights into the role of common sulfur precursors in hydrothermally synthesized N,S-doped carbon dots: fluorescence modulation via surface oxidation rather than sulfur doping
title_sort Insights into the role of common sulfur precursors in hydrothermally synthesized N,S-doped carbon dots: fluorescence modulation via surface oxidation rather than sulfur doping
dc.creator.none.fl_str_mv Fernandes, Sónia
Algarra González, Manuel
Brandão, Ana T.S.C.
Gil Bravo, Antonio
Pereira, Carlos
Esteves da Silva, Joaquim C.G.
Pinto da Silva, Luís
author Fernandes, Sónia
author_facet Fernandes, Sónia
Algarra González, Manuel
Brandão, Ana T.S.C.
Gil Bravo, Antonio
Pereira, Carlos
Esteves da Silva, Joaquim C.G.
Pinto da Silva, Luís
author_role author
author2 Algarra González, Manuel
Brandão, Ana T.S.C.
Gil Bravo, Antonio
Pereira, Carlos
Esteves da Silva, Joaquim C.G.
Pinto da Silva, Luís
author2_role author
author
author
author
author
author
dc.contributor.none.fl_str_mv Ciencias
Zientziak
Institute for Advanced Materials and Mathematics (INAMAT2)
dc.subject.none.fl_str_mv Nitrogen-doped carbon dots (N-CDs)
Nitrogen/sulfur co-doped carbon dots (N,S-CDs)
Sulfur precursors
Surface oxidation
topic Nitrogen-doped carbon dots (N-CDs)
Nitrogen/sulfur co-doped carbon dots (N,S-CDs)
Sulfur precursors
Surface oxidation
description While heteroatom doping is widely used to enhance the fluorescence of carbon dots, the actual mechanism underlying this claimed enhancement remains unclear. Herein, we report a systematic comparison between nitrogen-doped carbon dots (N-CDs) and nitrogen/sulfur co-doped carbon dots (N,S-CDs) synthesized hydrothermally, with ethylenediamine and sodium thiosulfate as the N- and S-dopants, respectively. Contrary to expectations, the inclusion of the S-precursor significantly reduced the quantum yield by 63%, from 35.9% to 13.2%, while leaving the emission profile and response largely unchanged. Characterization assays revealed that S-doping in N,S-CDs was residual, whereas the surface oxygen content increased markedly, indicating surface oxidation. The data suggest that sodium thiosulfate acted not as a dopant but overall as an oxidant, generating oxygen-based surface defects that introduced nonradiative recombination pathways. Thus, our findings show that co-doping with this S-precursor can decrease the quantum yield by promoting surface oxidation and the effective formation of more oxidized N-CDs, rather than heteroatom incorporation and production of co-doped CDs. This decreasing effect on the quantum yield was also observed when using thiourea as the S-precursor. Future work should include the study of other common S-precursors. In conclusion, our research shows that specific heteroatom-based precursors can alter the optical characteristics of CDs through redox/surface-modification effects instead of actual compositional doping, and thus, claims based on heteroatom doping may need closer examination.
publishDate 2026
dc.date.none.fl_str_mv 2026
dc.type.none.fl_str_mv info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
format article
status_str publishedVersion
dc.identifier.none.fl_str_mv https://hdl.handle.net/2454/56962
url https://hdl.handle.net/2454/56962
dc.language.none.fl_str_mv Inglés
language_invalid_str_mv Inglés
dc.relation.none.fl_str_mv info:eu-repo/grantAgreement/AEI/Plan Estatal de Investigación Científica y Técnica y de Innovación 2021-2023/PID2021-122613OB-I00
dc.rights.none.fl_str_mv https://creativecommons.org/licenses/by/3.0/
info:eu-repo/semantics/openAccess
rights_invalid_str_mv https://creativecommons.org/licenses/by/3.0/
eu_rights_str_mv openAccess
dc.format.none.fl_str_mv application/pdf
dc.publisher.none.fl_str_mv Royal Society of Chemistry
publisher.none.fl_str_mv Royal Society of Chemistry
dc.source.none.fl_str_mv reponame:Academica-e. Repositorio Institucional de la Universidad Pública de Navarra
instname:Universidad Pública de Navarra
instname_str Universidad Pública de Navarra
reponame_str Academica-e. Repositorio Institucional de la Universidad Pública de Navarra
collection Academica-e. Repositorio Institucional de la Universidad Pública de Navarra
repository.name.fl_str_mv
repository.mail.fl_str_mv
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