The synthesis, characterization and photoreduction ability of a new class of carbon dots made from fish scales is here described. Fish scales are a waste material that contains mainly chitin, one of the most abundant natural biopolymers, and collagen. These components make the scales rich, not only in carbon, hydrogen and oxygen, but also in nitrogen. These self-nitrogen-doped carbonaceous nanostructured photocatalyst were synthesized from fish scales by a hydrothermal method in the absence of any other reagents. The morphology, structure and optical properties of these materials were investigated. Their photocatalytic activity was compared with the one of conventional nitrogen-doped carbon dots made from citric acid and diethylenetriamine in the photoreduction reaction of methyl viologen.

The brewery industry annually produces huge amounts of byproducts that represent an underutilized, yet valuable, source of biobased compounds. In this contribution, the two major beer wastes, that is, spent grains and spent yeasts, have been transformed into carbon dots (CDs) by a simple, scalable, and ecofriendly hydrothermal approach. The prepared CDs have been characterized from the chemical, morphological, and optical points of view, highlighting a high level of N-doping, because of the chemical composition of the starting material rich in proteins, photoluminescence emission centered at 420 nm, and lifetime in the range of 5.5−7.5 ns. With the aim of producing a reusable catalytic system for wastewater treatment, CDs have been entrapped into a polyvinyl alcohol matrix and tested for their dye removal ability. The results demonstrate that methylene blue can be efficiently adsorbed from water solutions into the composite hydrogel and subsequently fully degraded by UV irradiation.

This work systematically compares both structural features and photocatalytic performance of a series of graphitic and amorphous carbon dots (CDs) prepared in a bottom-up manner from fructose, glucose, and citric acid. We demonstrate that the carbon source and synthetic procedures diversely affect the structural and optical properties of the CDs, which in turn unpredictably influence their photo electron transfer ability. The latter was evaluated by studying the photo-reduction of methyl viologen. Overall, citric acid-CDs were found to provide the best photocatalytic performance followed by fructose- and glucose-CDs. However, while the graphitization of glucose- and citric acid-CDs favored the photo-reaction, a reverse structure–activity dependence was observed for fructose-CDs due to the formation of a large graphitic-like supramolecular assembly. This study highlights the complexity to design in advance photo-active bio-based carbon nanomaterials.

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The fish industry produces every year huge amounts of waste that represent an underutilized source of chemical richness. In this contribution, type I collagen was extracted from the scales of Mugil cephalus and carbon dots (CDs) were synthesized from the scales of Dicentrarchus labrax. These materials were combined to make hybrid films with UV-blocking ability, by casting a mixture of gelatin, glycerol (15%), and CDs (0, 1, 3, and 5%). The films were fully characterized from the mechanical, morphological, and optical point of view. Here, 40 μm thick films were obtained, characterized by a high water solubility (70%); moreover, the presence of CDs improved the film mechanical properties, in particular increasing the tensile strength (TS) up to 17 MPa and elongation at break (EAB) up to 40%. The CDs also modulated water vapor permeability and the thermal stability of the films. From the optical point of view, with just 5% loading of CDs the films blocked almost 70% of the UV radiation with negligible change in transparency (88.6% for the nonloaded vs 84.4% for 5% CDs) and opacity (1.32 for nonloaded vs 1.61 for 5% CDs). These types of hybrid biobased films hold promise for the production of sustainable UV-shields both for human health and for prolonging the shelf life of food.

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The Front Cover image illustrates the degradation of water contaminants using carbon dots in continuous flow. The filament inside the light bulb represents the coiled continuous flow photoreactor used for the photooxidative degradation of azo dyes using as catalysts carbon dots derived from the hydrothermal treatment of fish waste in the presence of oxygen (represented by the luminescent dots and trail on the left). The system allowed complete mineralization of azo dyes in only 2 minutes under UV light irradiation. Cover design by Davide Brunelli and Carlotta Campalani. More information can be found in the Research Article by Jean‐Christophe M. Monbaliu, Alvise Perosa and co‐workers.