Structure and solvents effects on the optical properties of sugar-derived carbon nanodots.

Carbon nanodots are a new and intriguing class of fluorescent carbon nanomaterials and are considered a promising low cost, nontoxic alternative to traditional inorganic quantum dots in applications such as bioimaging, solar cells, photocatalysis, sensors and others. Despite the abundant available literature, a clear formation mechanism for carbon nanodots prepared hydrothermally from biomass precursors along with the origins of the light emission are still under debate. In this paper, we investigate the relationships between the chemical structure and optical properties of carbon nanodots prepared by the hydrothermal treatment of glucose. Our major finding is that the widely reported excitation-dependent emission originates from solvents used to suspend the as-prepared carbon nanodots, while emission from dry samples shows no excitation-dependence. Another important highlight is that the hydrothermal conversion of biomass-derivatives under subcritical conditions leads to a heterogeneous mixture of amorphous-like nanoparticles, carbon onion-type and crystalline carbons composed of at least three different phases. The potential chemical reaction pathways involved in the formation of these hydrothermal carbon products along with a comprehensive structural and optical characterization of these systems is also provided.

Carbon-Nanodot Solar Cells from Renewable Precursors.

It has recently been shown that waste biomass can be converted into a wide range of functional materials, including those with desirable optical and electronic properties, offering the opportunity to find new uses for these renewable resources. Photovoltaics is one area in which finding the combination of abundant, low-cost and non-toxic materials with the necessary functionality can be challenging. In this paper the performance of carbon nanodots derived from a wide range of biomaterials obtained from different biomass sources as sensitisers for TiO2 -based nanostructured solar cells was compared; polysaccharides (chitosan and chitin), monosaccharide (d-glucose), amino acids (l-arginine and l-cysteine) and raw lobster shells were used to produce carbon nanodots through hydrothermal carbonisation. The highest solar power conversion efficiency (PCE) of 0.36 % was obtained by using l-arginine carbon nanodots as sensitisers, whereas lobster shells, as a model source of chitin from actual food waste, showed a PCE of 0.22 %. By comparing this wide range of materials, the performance of the solar cells was correlated with the materials characteristics by carefully investigating the structural and optical properties of each family of carbon nanodots, and it was shown that the combination of amine and carboxylic acid functionalisation is particularly beneficial for the solar-cell performance.

Fe-N-Doped Carbon Capsules with Outstanding Electrochemical Performance and Stability for the Oxygen Reduction Reaction in Both Acid and Alkaline Conditions.

High surface area N-doped mesoporous carbon capsules with iron traces exhibit outstanding electrocatalytic activity for the oxygen reduction reaction in both alkaline and acidic media. In alkaline conditions, they exhibit more positive onset (0.94 V vs RHE) and half-wave potentials (0.83 V vs RHE) than commercial Pt/C, while in acidic media the onset potential is comparable to that of commercial Pt/C with a peroxide yield lower than 10%. The Fe-N-doped carbon catalyst combines high catalytic activity with remarkable performance stability (3500 cycles between 0.6 and 1.0 V vs RHE), which stems from the fact that iron is coordinated to nitrogen. Additionally, the newly developed electrocatalyst is unaffected by the methanol crossover effect in both acid and basic media, contrary to commercial Pt/C. The excellent catalytic behavior of the Fe-N-doped carbon, even in the more relevant acid medium, is attributable to the combination of chemical functions (N-pyridinic, N-quaternary, and Fe-N coordination sites) and structural properties (large surface area, open mesoporous structure, and short diffusion paths), which guarantees a large number of highly active and fully accessible catalytic sites and rapid mass-transfer kinetics. Thus, this catalyst represents an important step forward toward replacing Pt catalysts with cheaper alternatives. In this regard, an alkaline anion exchange membrane fuel cell was assembled with Fe-N-doped mesoporous carbon capsules as the cathode catalyst to provide current and power densities matching those of a commercial Pt/C, which indicates the practical applicability of the Fe-N-carbon catalyst.

Biomass-derived carbon quantum dot sensitizers for solid-state nanostructured solar cells.

New hybrid materials consisting of ZnO nanorods sensitized with three different biomass-derived carbon quantum dots (CQDs) were synthesized, characterized, and used for the first time to build solid-state nanostructured solar cells. The performance of the devices was dependent on the functional groups found on the CQDs. The highest efficiency was obtained using a layer-by-layer coating of two different types of CQDs.