Evaluation of the Environmental Impact and Efficiency of N-Doping Strategies in the Synthesis of Carbon Dots

Christé, Suzanne; Silva, Joaquim C. G. Esteves da; Silva, Luís Pinto da

doi:10.3390/ma13030504

Cited by 42 publications

(56 citation statements)

References 67 publications

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“…In this section, the three different synthesis routes were first evaluated individually to analyze their impact contributions in each category using a weight-based functional unit to produce 1 Kg of CDs. As in line with previous studies from our group [25,31], the use of CA accounts for most environmental impacts to all categories ( Figures S5-S7). Urea is clearly the second highest contributor to the different categories for hydrothermal synthesis, especially for the Resources category ( Figure S6).…”

Section: Comparative Lca Studysupporting

confidence: 90%

“…By their turn, bottom-up routes are arguably the most widely used synthesis methods [3,25,26]. They generally consist on the pyrolysis of smaller organic molecules either in powder form (calcination) [28] or in solution via hydrothermal [25,29] or microwave-based approaches [16,30,31]. Bottom-up strategies have the advantage of being suitable for mass production, being eco-friendly, and of low cost [26].…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of Different Bottom-up Routes for the Fabrication of Carbon Dots

Crista

Silva

2020

Nanomaterials

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Carbon dots (CDs) are carbon-based nanoparticles with very attractive luminescence features. Furthermore, their synthesis by bottom-up strategies is quite flexible, as tuning the reaction precursors and synthesis procedures can lead to an endless number of CDs with distinct properties and applications. However, this complex variability has made the characterization of the structural and optical properties of the nanomaterials difficult. Herein, we performed a systematic evaluation of the effect of three representative bottom-up strategies (hydrothermal, microwave-assisted, and calcination) on the properties of CDs prepared from the same precursors (citric acid and urea). Our results revealed that these synthesis routes led to nanoparticles with similar sizes, identical excitation-dependent blue-to-green emission, and similar surface-functionalization. However, we have also found that microwave and calcination strategies are more efficient towards nitrogen-doping than hydrothermal synthesis, and thus, the former routes are able to generate CDs with significantly higher fluorescence quantum yields than the latter. Furthermore, the different synthesis strategies appear to have a role in the origin of the photoluminescence of the CDs, as hydrothermal-based nanoparticles present an emission more dependent on surface states, while microwave- and calcination-based CDs present an emission with more contributions from core states. Furthermore, calcination and microwave routes are more suitable for high-yield synthesis (~27–29%), while hydrothermal synthesis present almost negligible synthesis yields (~2%). Finally, life cycle assessment (LCA) was performed to investigate the sustainability of these processes and indicated microwave synthesis as the best choice for future studies.

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Section: Comparative Lca Studysupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Evaluation of Different Bottom-up Routes for the Fabrication of Carbon Dots

Crista

Silva

2020

Nanomaterials

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“…To obtain comparative information regarding the sustainability of using SCG samples as CD precursors we have performed an LCA study, given that LCA aims to quantify the relevant environmental impacts of a given system during its life cycle [ 13 , 59 , 60 , 61 , 62 ]. To this end, the environmental impacts of synthesizing CDs with selected precursors (decaf-CDs, rossio-CDs and prestige-CDs) and typical reagents (CA@U-CDs) was analyzed and compared by using a mass-based functional unit of 1 kg of CDs.…”

Section: Resultsmentioning

confidence: 99%

Turning Spent Coffee Grounds into Sustainable Precursors for the Fabrication of Carbon Dots

et al. 2020

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Spent coffee grounds (SCGs) are known for containing many organic compounds of interest, including carbohydrates, lipids, phenolic compounds and proteins. Therefore, we investigated them as a potential source to obtain carbon dots (CDs) via a nanotechnology approach. Herein, a comparison was performed between CDs produced by SCGs and classic precursors (e.g., citric acid and urea). The SCG-based CDs were obtained via the one-pot and solvent-free carbonization of solid samples, generating nanosized particles (2.1–3.9 nm). These nanoparticles exhibited a blue fluorescence with moderate quantum yields (2.9–5.8%) and an excitation-dependent emission characteristic of carbon dots. SCG-based CDs showed potential as environmentally relevant fluorescent probes for Fe3+ in water. More importantly, life cycle assessment studies validated the production of CDs from SCG samples as a more environmentally sustainable route, as compared to those using classic reported precursors, when considering either a weight- or a function-based functional unit.

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“…LCA is the most suitable approach to address this issue, as it makes it possible to quantify the environmental impacts of a given system during its life cycle [24,25]. Also, LCA has already been used with success in the environmental evaluations of different nanomaterials, such as undoped TiO 2 [26], silver nanoparticles [20], copper nanoparticles [21], carbon nanotubes [22], magnetic nanoparticles [23], and carbon dots [27,28].…”

Section: Introductionmentioning

confidence: 99%

Life Cycle Assessment of the Sustainability of Enhancing the Photodegradation Activity of TiO2 with Metal-Doping

Fernandes

Silva

2020

Materials

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While TiO2 nanoparticles have shown potential as photocatalysts in the degradation of organic contaminants, their inability to absorb efficiently visible light has limited their industrial application. One strategy for solving this problem is monodoping TiO2 photocatalysts with transition metals, which has worked in the degradation of several pollutants. However, it is not clear if this improvement is enough to offset the potential environmental impacts of adding metal ions to the synthesis of TiO2. Herein, we have used Life Cycle Assessment (LCA) to determine the sustainability of monodoping TiO2 with transition metals (Fe, Co, Mn and Ni, with a 1% weight ratio) to enhance the photocatalytic properties of the photocatalyst toward the degradation of Carbamazepine and Methyl Orange, under UV-A and visible light irradiation. We found that the addition of transition-metals has no significant effect on the environmental impacts associated with the synthesis of TiO2, when a weight-based functional unit was considered. However, when photocatalytic activity was considered, major differences were found. Thus, our results demonstrate that the sustainability of monodoping with different transition metals is solely determined by their ability to enhance (or not) the photocatalytic activity of TiO2. Our data also demonstrated that isopropyl alcohol constitutes a critical point in the synthesis of TiO2 photocatalysts, with ethanol being a potential substitute.

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Evaluation of the Environmental Impact and Efficiency of N-Doping Strategies in the Synthesis of Carbon Dots

Cited by 42 publications

References 67 publications

Evaluation of Different Bottom-up Routes for the Fabrication of Carbon Dots

Evaluation of Different Bottom-up Routes for the Fabrication of Carbon Dots

Turning Spent Coffee Grounds into Sustainable Precursors for the Fabrication of Carbon Dots

Life Cycle Assessment of the Sustainability of Enhancing the Photodegradation Activity of TiO2 with Metal-Doping

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