Biobased Carbon Dots: From Fish Scales to Photocatalysis

he 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 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

Biobased Carbon Dots: From Fish Scales to Photocatalysis

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

N-Doped Carbon Dot Hydrogels from Brewing Waste for Photocatalytic Wastewater Treatment

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, photo-luminescence 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

Chemical biowaste upgrading: carbon dots, biopolymers and actives

The herein reported thesis finds its roots in the concepts of sustainability and circular economy and has as purpose the valorisation of agro- and fishery-waste for the production of added-value products. In particular, different types of waste biomass were used as starting material for the synthesis of carbon dots (CDs) used as photocatalysts, for the obtainment of biopolymers, namely collagen and chitin, and for the extraction of valuable compounds using supercritical CO2. The investigation started studying the dependence of structure and photocatalytic behaviour of CDs on the carbon source. Six different types of carbon nanoparticles were synthesized and compared from the morphological and optical point of view revealing a strong correlation of their properties with the starting material and the synthetic method. The citric acid-derived CDs were then employed to photoactivate the atom transfer radical polymerization of a methacrylate leading to the obtainment of the polymer in high conversions (89%) and narrow dispersity (1.4). The study on CDs proceeded then with the employment of more complex starting material, namely fish scales. Naturally nitrogen doped carbon dots were successfully synthesized starting from bass scales, fully characterized and employed as photocatalyst for the reduction of methyl viologen. The bass-CDs were compared with classic citric acid-derived CDs resulting in higher initial photoreduction rate (7.5·10−8 M·s−1 vs 4.9·10−8 M·s−1). The fish-derived nanoparticles were then applied as photocatalyst for the continuous flow degradation of azo dyes highlighting a quantitative degradation of five model dyes in only 2 min. This study was conducted during a research period abroad (September 2021-April 2022) in the laboratories of the Université de Liège under the supervision of Prof. Jean-Christophe Monbaliu. The upgrading of fishery waste was then developed more during the second part of this thesis where the possibility to extract biopolymers from fish scales or crab carapaces was explored. After a review study on the production of UV-shields using biopolymers, an investigation on the preparation of UV-blocking films from mullet scales-derived gelatin and bass-CDs was conducted. The obtained materials were fully characterized from the morphological, mechanical and optical point of view; by adding just 5% of CDs the films blocked almost 70% of the UV radiation with negligible change in opacity and in transparency. A further study on the possibility to obtain chitin from crab shells using a one-step protocol using ionic liquids was then conducted. All characterization data confirmed that in the conditions tested, ammonium formate prepared in situ seems to be a promising candidate for one-pot chitin pulping process, allowing quantitative isolation, high purity and a high degree of acetylation (DA > 90%). To have a complete overview on the possibility to exploit waste biomass for the production of added-value products, an investigation on the valorisation of agro-waste was then conducted. In this frame, a supercritical CO2 extraction method was developed to obtain natural preservatives from hops and jimsonweed. scCO2 extracts were compared to ethanolic ones: the supercritical fluid led to the selective extraction of volatile compounds resulting in a better recovery for preservatives. The scCO2 technique was then applied to obtain fatty acids for cosmetic formulations from fruit pomace, resulting again more selective when compared to classical organic solvents.The herein reported thesis finds its roots in the concepts of sustainability and circular economy and has as purpose the valorisation of agro- and fishery-waste for the production of added-value products. In particular, different types of waste biomass were used as starting material for the synthesis of carbon dots (CDs) used as photocatalysts, for the obtainment of biopolymers, namely collagen and chitin, and for the extraction of valuable compounds using supercritical CO2. The investigation started studying the dependence of structure and photocatalytic behaviour of CDs on the carbon source. Six different types of carbon nanoparticles were synthesized and compared from the morphological and optical point of view revealing a strong correlation of their properties with the starting material and the synthetic method. The citric acid-derived CDs were then employed to photoactivate the atom transfer radical polymerization of a methacrylate leading to the obtainment of the polymer in high conversions (89%) and narrow dispersity (1.4). The study on CDs proceeded then with the employment of more complex starting material, namely fish scales. Naturally nitrogen doped carbon dots were successfully synthesized starting from bass scales, fully characterized and employed as photocatalyst for the reduction of methyl viologen. The bass-CDs were compared with classic citric acid-derived CDs resulting in higher initial photoreduction rate (7.5·10−8 M·s−1 vs 4.9·10−8 M·s−1). The fish-derived nanoparticles were then applied as photocatalyst for the continuous flow degradation of azo dyes highlighting a quantitative degradation of five model dyes in only 2 min. This study was conducted during a research period abroad (September 2021-April 2022) in the laboratories of the Université de Liège under the supervision of Prof. Jean-Christophe Monbaliu. The upgrading of fishery waste was then developed more during the second part of this thesis where the possibility to extract biopolymers from fish scales or crab carapaces was explored. After a review study on the production of UV-shields using biopolymers, an investigation on the preparation of UV-blocking films from mullet scales-derived gelatin and bass-CDs was conducted. The obtained materials were fully characterized from the morphological, mechanical and optical point of view; by adding just 5% of CDs the films blocked almost 70% of the UV radiation with negligible change in opacity and in transparency. A further study on the possibility to obtain chitin from crab shells using a one-step protocol using ionic liquids was then conducted. All characterization data confirmed that in the conditions tested, ammonium formate prepared in situ seems to be a promising candidate for one-pot chitin pulping process, allowing quantitative isolation, high purity and a high degree of acetylation (DA > 90%). To have a complete overview on the possibility to exploit waste biomass for the production of added-value products, an investigation on the valorisation of agro-waste was then conducted. In this frame, a supercritical CO2 extraction method was developed to obtain natural preservatives from hops and jimsonweed. scCO2 extracts were compared to ethanolic ones: the supercritical fluid led to the selective extraction of volatile compounds resulting in a better recovery for preservatives. The scCO2 technique was then applied to obtain fatty acids for cosmetic formulations from fruit pomace, resulting again more selective when compared to classical organic solvents

Biobased Carbon Dots: From Fish Scales to Photocatalysis

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

Fish-Waste-Derived Gelatin and Carbon Dots for Biobased UV-Blocking Films

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 mu m 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

Continuous Flow Photooxidative Degradation of Azo Dyes with Biomass-Derived Carbon Dots

peer reviewedThe presence of persistent organic pollutants in industrial wastewaters is becoming a problem of major concern. In the present study we explored the degradation of azo dyes, well-known common hazardous contaminants, by a green and efficient procedure using continuous flow photooxidative degradation. In particular, carbon dots synthesized from fishery waste (bass-CDs) were used as a cheap and readily available photocatalyst in combination with oxygen and UV light. Methyl orange, acid red 18, amaranth, sunset yellow and chromotrope were chosen as model substrates and their degradation was studied both in batch and in continuous flow conditions. All the azo dyes were fully degraded with both techniques highlighting the suitability of bass-CDs for the decontamination of wastewater. The main advantages are of using a “disposable” photocatalyst, in aqueous solvent and in continuous flow. In particular, continuous flow operation allowed faster decompositions: circa 2 min versus 1–3 hours needed in batch

Carbon Dots as Green Photocatalysts for Atom Transfer Radical Polymerization of Methacrylates

We herein report the use of carbon dots (CDs) in photoinduced atom transfer radical polymerizations (ATRP) as green metal-free sensitizers. In particular, the production of a polymethacrylate (poly-METAC, METAC = 2-(methacryloyloxy)ethyl]trimethylammonium chloride) by using cheap and easily affordable CDs made from citric acid and diethylenetriamine, under both ultraviolet (UV, λ = 365 nm) and visible light was studied. Different solvent systems have been tested and a CuII complex was used as catalyst. Under the best conditions a polymer in 89% conversion and with a narrow dispersity (1.4) was obtained. The first order kinetics and the “on-off” experiments gave further evidence of the constant concentration of radicals and of the controlled mechanism of the polymerization

Supercritical CO2 as a green solvent for the circular economy: extraction of fatty acids from fruit pomace

One of the empowering actions for the circular economy is deriving value from waste. In this context, recycling waste agro-food streams to make more sustainable chemical products through greener technologies promises to move away from the linear development model based on continuous growth and increasing resource throughput. We describe here the use of supercritical fluid extraction with carbon dioxide to extract fatty acids from waste pomace deriving from the preserves industry along with a comparison using hexane as solvent. The fatty acids extracted from the seeds and peels of raspberry, blueberry, wild strawberry, pomegranate, blackberry and blackcurrant using supercritical CO2 as a greener solvent were purer and richer in essential fatty acids than the hexane ones. The wild strawberry pomace extraction with supercritical CO2 is a representative example: selectivity towards fatty acids was 26 wt% (vs. 1.4 % with hexane) and the extracts contained, 145.8 mg mL−1 polyunsaturated, 64.0 mg mL−1 monounsaturated and 46.8 mg mL−1 saturated fatty acids (vs. 14.3 mg mL−1 total fatty acids with hexane)

Supercritical CO2as a green solvent for the circular economy: Extraction offatty acids from fruit pomace

One of the empowering actions for the circular economy is deriving value from waste. In this context, recycling waste agro-food streams to make more sustainable chemical products through greener technologies promises to move away from the linear development model based on continuous growth and increasing resource throughput. We describe here the use of supercritical fluid extraction with carbon dioxide to extract fatty acids from waste pomace deriving from the preserves industry along with a comparison using hexane as solvent. The fatty acids extracted from the seeds and peels of raspberry, blueberry, wild strawberry, pomegranate, blackberry and blackcurrant using supercritical CO2 as a greener solvent were purer and richer in essential fatty acids than the hexane ones. The wild strawberry pomace extraction with supercritical CO2 is a representative example: selectivity towards fatty acids was 26\u202fwt% (vs. 1.4 % with hexane) and the extracts contained, 145.8\u202fmg\u202fmL 121 polyunsaturated, 64.0\u202fmg\u202fmL 121 monounsaturated and 46.8\u202fmg\u202fmL 121 saturated fatty acids (vs. 14.3\u202fmg\u202fmL 121 total fatty acids with hexane)