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More specifically, N-doped CDs were prepared from citric acid via two main synthesis routes: Microwave-assisted hydrothermal treatment with addition of N-containing small organic molecules (urea and ethylenediamine (EDA)); and microwave-assisted solvothermal treatment in N-containing organic solvents (n,n-dimethylformamide (DMF), acetonitrile and pyridine). These syntheses produced CDs with similar blue emission. However, XPS analysis revealed that CDs synthesized via both hydrothermal routes presented a better N-doping efficiency (~15 at.%) than all three solvothermal-based strategies (0.6\u20137 at.%). However, from the former two hydrothermal strategies, only the one involving EDA as a nitrogen-source provided a non-negligible synthesis yield, which indicates that this should be the preferred strategy. This conclusion was supported by a subsequent life cycle assessment (LCA) study, which revealed that this strategy is clearly the most sustainable one from all five studied synthesis routes.<\/jats:p>","DOI":"10.3390\/ma13030504","type":"journal-article","created":{"date-parts":[[2020,1,21]],"date-time":"2020-01-21T11:25:59Z","timestamp":1579605959000},"page":"504","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":62,"title":["Evaluation of the Environmental Impact and Efficiency of N-Doping Strategies in the Synthesis of Carbon Dots"],"prefix":"10.3390","volume":"13","author":[{"given":"Suzanne","family":"Christ\u00e9","sequence":"first","affiliation":[{"name":"Chemistry Research Unit (CIQUP), Faculty of Sciences of University of Porto, R. Campo Alegre 697, 4169\u2013007 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8478-3441","authenticated-orcid":false,"given":"Joaquim C.G.","family":"Esteves da Silva","sequence":"additional","affiliation":[{"name":"Chemistry Research Unit (CIQUP), Faculty of Sciences of University of Porto, R. Campo Alegre 697, 4169\u2013007 Porto, Portugal"},{"name":"LACOMEPHI, GreenUPorto, Department of Geosciences, Environment and Territorial Planning, Faculty of Sciences of University of Porto, R. Campo Alegre 697, 4169\u2013007 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5647-8455","authenticated-orcid":false,"given":"Lu\u00eds","family":"Pinto da Silva","sequence":"additional","affiliation":[{"name":"Chemistry Research Unit (CIQUP), Faculty of Sciences of University of Porto, R. 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