Valorización de residuos y de biomasa mediante técnicas respetuosas con el medio ambiente

The scientific contributions described in this Doctoral Thesis were explored in the research group FQM-383, which main research topics include Nanochemistry, Heterogeneous Catalysis and Biomass/Waste Valorization (NANOVAL). More in detail, this Doctoral Thesis focused on the development of advanced materials for the catalytic transformation of biomass and waste into high value-added compounds through advanced methodologies. These methodologies were designed based on un-conventional and green procedures combined with technologies that offer environmentally friendly and low energy-impact characteristics. In particular, the potentiality of microwave, mechanochemistry and flow chemical processes were demonstrated in the production and in the application of novel waste/biomass derived materials. Most important results obtained during the Doctoral Thesis have been published in three research articles, which have been included in Chapter “Results and Discussion” and are summarized below. Moreover, the first section of the Chapter “Introduction” is constituted of a review titled “Advances in mechanochemical processes for biomass valorization”. The manuscript describes the potential of mechanochemistry and its new attractive possibilities in the area of biomass and waste valorization. In the first work, “Microwave-assisted preparation of Ag/Ag2S carbon hybrid structures from pig bristles as efficient HER catalysts”, a sequence of Ag/Ag2S heterostructures was successfully synthetized via a microwaveassisted procedure. The preparation was conducted employing silver nitrate in different amounts as silver precursor and a fixed quantity of pig bristles as carbon and sulphur source, resulting in a sequence on materials with different Ag(0)/Ag(I) ratios. The microwave method was proved to be simple, quick, and efficient, allowing the exploitation of wasted big bristles as a toxic-free source of carbon and sulphur in contrast to hazardous and toxic substances (e.g., thiols and H2S). The presence of metallic silver and silver sulphide was demonstrated by recording and analyzing X-ray diffraction (XRD) patterns. From the X-ray photoelectronic spectroscopy (XPS) analysis, an Ag(0)/Ag(I) ratio was also recognized, linearly correlated on pig bristles/silver nitrate ratio. The use of material has been promising in electrocatalytic processes, especially in the hydrogen evolution reaction (HER). The current density values were found linearly correlated to the Ag(0)/Ag(I) ratio, which could be controlled during the synthetic procedure. The most active sample allowed the production of 10 mA cm-2 of current density at -0.190 V applied potential. The manuscript “A sustainable approach for the synthesis of catalytically active peroxidase-mimic ZnS catalysts” discloses a simple methodology for the preparation of zinc sulphides using pig bristles, an economic and largely-available waste rich in carbon and sulphur. The catalysts were synthesized employing zinc acetate dihydrate and pig bristles, with different preparation times, i.e. 1 hour, 3 hours, 5 hours. The methodology included an easy, facile and low-cost refluxing procedure (pig bristles and zinc precursor in an aqueous solution of KOH). The so-synthetized materials were characterized using different techniques including X-ray diffraction (XRD), N2 adsorption/desorption, scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM-EDX) and X-ray photoelectronic spectroscopy (XPS). The presence of ZnS crystal structure was proved by XRD and by XPS analysis. The nanomaterials were demonstrated to possess high catalytic activity and high chemical stability in the selective microwave-assisted oxidations of toluene and benzyl alcohol to benzaldehyde (widely used compound in fragrances and perfumery industries). Finally, a reusability study was carried out in both reactions, demonstrating the stability of the novel nanosystem under the investigated reaction conditions, showing almost identical catalytic activities after 4 cycles. The last paper “Efficient Ru-based scrap waste automotive converter catalysts for the continuous-flow selective hydrogenation of cinnamaldehyde” proved the potentiality of an industrial waste, i.e the ceramic-cores of scrap automotive catalytic converters (CATs) as low-cost and high stable supporting materials. More in details, CATs were used as supporting material for the preparation of nanoruthenium-based catalysts. The materials were synthesized using a simple mechanochemical approach followed by a chemical reduction. The physico-chemical properties of the materials were studied by X-ray diffraction (XRD), X-ray photoelectronic spectroscopy (XPS), N2 physisorption, scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM-EDX), inductively coupled plasma mass spectrometry (ICP-MS) and transmission electron microscopy (TEM/HRTEM). The catalysts were tested in the selective flow hydrogenation of cinnamaldehyde to cinnamyl alcohol. Different reaction and synthesis parameters were optimized including H2 pressure, temperature, flow rate and ruthenium content. The catalytic activity of Ru/CATs was compared with Ru nanocatalysts supported on silica, alumina and activated alumina via the same mechanochemical procedure. The results indicated that Ru/CATs displayed outstanding catalytic performances and good stability with time-on-stream, proving also a synergism between ruthenium and the scrap catalytic converter. Finally, the E-factor of the entire protocol was calculated to validate the green credentials of the entire methodology.Los trabajos de investigación que componen la presente Memoria de Tesis Doctoral fueron desarrollados en el Grupo de Investigación FQM-383, cuyos principales temas de investigación incluyen nanoquímica, catálisis heterogénea y valorización de biomasa/residuos (NANOVAL). Más detalladamente, esta Tesis Doctoral se centró en el desarrollo de nuevos nanomateriales para la transformación catalítica de la biomasa y residuos a compuestos de alto valor añadido mediante técnicas avanzadas. Estas metodologías se diseñaron en base a procedimientos no convencionales y respetuosos con el medio ambiente combinados con tecnologías que ofrecen características ecológicas y de bajo impacto energético. En particular, el potencial que presentan los procesos asistidos mediante microondas, mecanoquímica y química de flujo quedo patente en el desarrollo y en la aplicación de nuevos materiales derivados de biomasa y residuos. Los principales resultados derivados de los trabajos de investigación llevados a cabo durante la presente Tesis Doctoral han sido incluido en el Capítulo “Results & Discussion" y se resumen a continuación. Además, la primera sección del Capítulo "Introduction" está constituida por una revisión bibliográfica titulada “Advances in mechanochemical processes for biomass valorization”. El manuscrito describe el potencial de la mecanoquímica y sus nuevas posibilidades aplicadas en el área de valorización de residuos y biomasa. En el primer trabajo, “Microwave-assisted preparation of Ag/Ag2S carbon hybrid structures from pig bristles as efficient HER catalysts ”, se sintetizó con éxito una serie de heteroestructuras de carbón Ag/Ag2S mediante un procedimiento asistido por microondas. Su preparación se realizó empleando nitrato de plata como precursor de plata en distintas cantidades y una cantidad fija de pelos de cerdo como fuente de carbono y azufre, dando como resultado una serie de materiales con diferentes relaciones Ag (0)/Ag (I). De esta forma, la síntesis asistida por microondas se reveló como una metodología simple, innovadora y eficiente, permitiendo la explotación de desechos de pelos de cerdo como fuente no tóxica de carbono y azufre en lugar de sustancias tóxicas y peligrosas. (por ejemplo, tioles y H2S). La presencia de plata metálica y sulfuro de plata se confirmó mediante la técnica de difracción de Rayos-X (DRX). Mediante el análisis de espectroscopía fotoelectrónica de rayos-X (XPS), ha sido posible establecer una relación Ag(0)/Ag(I), la cuál muestra una dependencia linear en función de la relación pelos de cerdo/nitrato de plata. La utilización de este material en procesos electrocatalíticos ha sido prometedora, en particular, para la reacción de producción de hidrogeno (HER). Los valores de densidad de corriente se encontraron linealmente correlacionados con la relación Ag(0)/Ag(I), la cual podría controlarse con esta metodología. La muestra con mejor actividad catalítica ha permitido la producción de 10 mA cm-2 de densidad de corriente a un potencial aplicado de -0,190 V. En el trabajo “A sustainable approach for the synthesis of catalytically active peroxidase-mimic ZnS catalysts ”, se ha presentado una metodología para la preparación de ZnS utilizando pelos de cerdo, un desecho económico y ampliamente disponible que contiene carbono y azufre. En concreto, los nanomateriales han sido sintetizados utilizando acetato de cinc dihidratado y cerdas de cerdo, llevando a cabo la síntesis a diferentes tiempos de reacción (1 hora, 3 horas, 5 horas). La metodología ha incluido un paso de ebullición, resultando en una preparación fácil, económica y rápida (pelos de cerdo y precursor de cinc en una solución acuosa de KOH). Los materiales sintetizados fueron caracterizados mediante diferentes técnicas que incluyeron la difracción de rayos-X (DRX), adsorción-desorción de N2, microscopía electrónica de barrido con detector de energía dispersiva rayos-X para el análisis elemental (SEM-EDX) y espectroscopía fotoelectrónica de rayos-X (XPS). La estructura cristalina de ZnS se confirmó mediante las técnicas de DRX y XPS. Los nanocatalizadores sintetizados mostraron una actividad catalítica elevada, así como estabilidad química en las reacciones de oxidación selectiva de tolueno y alcohol bencílico a benzaldehído (compuesto ampliamente utilizado en las industrias de fragancias y perfumería). Finalmente, se llevó a cabo el estudio de la reusabilidad de los nanocatalizadores en ambas reacciones demostrando la estabilidad de estos bajo las condiciones de reacción investigadas, así como una casi idéntica actividad catalítica tras cuatro ciclos de reacción. El último trabajo “Efficient Ru-based scrap waste automotive converter catalysts for the continuos-flow selective hydrogenation of cinnamaldehyde ” demostró el potencial de un residuo industrial, los núcleos cerámicos usados de los convertidores del coche (CATs) como materiales de soporte de bajo coste y alta estabilidad. Más en detalle, los CAT se usaron como material de soporte para la preparación directa de catalizadores basados en nano-rutenio. Los materiales fueron sintetizados mediante molienda mecanoquímica seguida de una reducción química. Las propiedades fisicoquímicas de los materiales fueron investigadas mediante las técnicas de DRX, fisisorción de N2, SEM-EDX, espectrometría de masas con plasma acoplado inductivamente (ICP-MS), microscopía electrónica de transmisión (TEM/HRTEM). Los catalizadores sintetizados fueron probados en la hidrogenación selectiva de cinemaldehído mediante flujo continuo. Se optimizaron distintos parámetros que incluyeron la presión de H2, temperatura, flujo y contenido en rutenio. La actividad catalítica de los materiales Ru/CATs fue comparada con otros catalizadores de rutenio soportados en distintos materiales, SiO2, Al2O3 y Al2O3 activado, sintetizados mediante la misma metodología mecanoquímica. Los resultados muestran que los catalizadores Ru/CATs poseen excelentes prestaciones catalíticas y buena estabilidad sin mostrar cambios en la conversión y selectividad con el tiempo en el flujo, demostrando una sinergia entre el rutenio y el convertidor catalítico usado de coche. Finalmente, las credenciales verdes de toda la metodología fueran evaluadas calculando el factor E del protocolo

Paving the Way for a Green Transition in the Design of Sensors and Biosensors for the Detection of Volatile Organic Compounds (VOCs)

The efficient and selective detection of volatile organic compounds (VOCs) provides key information for various purposes ranging from the toxicological analysis of indoor/outdoor environments to the diagnosis of diseases or to the investigation of biological processes. In the last decade, different sensors and biosensors providing reliable, rapid, and economic responses in the detection of VOCs have been successfully conceived and applied in numerous practical cases; however, the global necessity of a sustainable development, has driven the design of devices for the detection of VOCs to greener methods. In this review, the most recent and innovative VOC sensors and biosensors with sustainable features are presented. The sensors are grouped into three of the main industrial sectors of daily life, including environmental analysis, highly important for toxicity issues, food packaging tools, especially aimed at avoiding the spoilage of meat and fish, and the diagnosis of diseases, crucial for the early detection of relevant pathological conditions such as cancer and diabetes. The research outcomes presented in the review underly the necessity of preparing sensors with higher efficiency, lower detection limits, improved selectivity, and enhanced sustainable characteristics to fully address the sustainable manufacturing of VOC sensors and biosensors

Scrap waste automotive converters as efficient catalysts for the continuous-flow hydrogenations of biomass derived chemicals

The catalytic activity of the scrap ceramic-core of automotive catalytic converters (SCATs) was investigated in the continuous-flow hydrogenation of different biomass derived chemicals. The waste SCATs powders were deeply characterized by ICP-MS, TGA, MP-AES, XRD, N2 physisorption, HRTEM and EDS before and after the utilization as catalyst. The hydrogenation reactions of isopulegol to menthol; cinnamyl alcohol to hydrocinnamyl alcohol; isoeugenol to dihydroeugenol; vanillin to vanillyl alcohol and benzaldehyde to benzyl alcohol were performed studying the influence on of various reaction parameters (temperature, pressure, flow rate and concentration of the starting material) on final yields. The outstanding performance and stability obtained for the low metal content of waste-derived catalysts can be attributed to the co-presence of different noble metals as well as to the composite structure itself

A Sustainable Approach for the Synthesis of Catalytically Active Peroxidase-Mimic ZnS Catalysts

Zinc sulfides are emerging as promising catalysts in different fields such as photochemistry or organic synthesis. Nevertheless, the synthesis of ZnS compounds normally requires the utilization of toxic sulfur precursors, e.g., thiourea which is a contaminant and carcinogenic agent. As a result, new green and sustainable synthetic methodologies are needed. Herein, an innovative, simple, and cheap approach for the synthesis of ZnS carbon composites is reported. Zinc acetate dihydrate was employed as metal precursor while wasted pig bristles were employed as carbon and sulfur source. The phase and the morphology of the compounds were analyzed by XRD, XPS, SEM, and EDX and the surface area was determined by nitrogen physisorption. ZnS carbon materials showed remarkable peroxidase-like catalytic activity for two different model reactions: the liquid-phase selective oxidation of benzyl alcohol and toluene to benzaldehyde (conversions up to 63% and 29% and selectivities up to 86% and 87%, respectively) using hydrogen peroxide as oxidant under microwave irradiation

Technology and Process Design for Phenols Recovery from Industrial Chicory (Chicorium intybus) Leftovers

Vegetal leftovers from the agro–food industry represent a huge source of primary and secondary metabolites, vitamin, mineral salts and soluble as well as insoluble fibers. Economic reports on the growth in the polyphenol market have driven us to focus our investigation on chicory (Chicorium intybus L.), which is one of the most popular horticultural plants in the world and a rich source of phenolic compounds. Ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE) and their simultaneous combination, using either ethanol/water or water alone (also sub-critical), have been investigated with the aim of designing a green and efficient extraction process. Higher total-polyphenol yields as well as dramatic reductions in extraction times and solvent consumption have been obtained under these conditions. ANOVA test for analyses of variance followed by the Tukey honestly significant difference (HSD) post-hoc test of multiple comparisons was used in the statistical analysis. MAE experiments performed with sub-critical water, and MW/US experiments with an ethanol solution have shown polyphenol recovery values of up to ~3 g of gallic acid equivalents (GAE) per kg of fresh material in only 15 min, while conventional extraction required 240 min to obtain the same result

Boosting the Ni-Catalyzed Hydrodeoxygenation (HDO) of Anisole Using Scrap Catalytic Converters

The large availability and renewable nature of lignin makes its upgrading to bioproducts of particular interest for sustainable development. The hydrodeoxygenation (HDO) of anisole specifically represents a model reaction for the conversion of lignin to biofuels through the removal of the aromatic carbon-oxygen bonds. To date, a range of Ni-based catalysts have been reported as highly active systems for the HDO of anisole. However, there has been a substantial lack of consideration given to the environmental characteristics of these catalytic systems, in contrast with the scope of the sustainable production of biofuels. Herein, Ni-based SiO2 catalysts are prepared by a solventless and highly efficient mechanochemistry approach, having a considerably lower environmental impact as compared to standard impregnation methods. Importantly, scrap catalytic converters (SCATs) are employed as co-catalysts, proving the possibility of enhancing the catalytic HDO of anisole, with a scarcely exploited waste material. The results demonstrate that the combined use of Ni/SiO2 as catalysts and Ni/SCATs as co-catalysts remarkably boosts the rate of the conversion of anisole up to more than 50% by achieving an almost complete conversion of anisole in only 40 min instead of at 200 °C and 4 MPa H2

Efficient Ru-based scrap waste automotive converter catalysts for the continuous-flow selective hydrogenation of cinnamaldehyde

The selective, efficient and sustainable continuous flow hydrogenation of a α,β-unsaturated aldehyde, i.e. cinnamaldehyde, to the corresponding unsaturated alcohol, i.e. cinnamyl alcohol, using a novel catalyst based on Ru-containing scrap waste automotive converters is reported. The catalyst was prepared by recycling and upgrading waste ceramic-cores of scrap automotive catalytic converters as supporting materials. Ruthenium was incorporated into the ceramic structures using a simple, fast and solventless mechanochemically assisted procedure followed by a chemical reduction step. Different catalysts were prepared with varying Ru contents. The materials were characterized by XRD, N2 physisorption, XPS, TEM, HRTEM and SEM/mapping analyses. Compared to Ru supported over most studied silica and alumina supports, the new system displayed an outstanding catalytic performance under continuous-flow conditions in terms of conversion and selectivity and a remarkable stability with time-on-stream, demonstrating a synergistic action between Ru and the waste catalytic converter support. A Ru loading of 10 wt% provided the optimum results, including a cinnamaldehyde conversion of up to 95% with a selectivity to cinnamyl alcohol of 80%

Continuous flow synthesis of menthol via tandem cyclisation–hydrogenation of citronellal catalysed by scrap catalytic converters

A continuous flow synthesis of menthol starting from citronellal catalysed by scrap catalytic converters is reported. The reaction was conducted in a tandem system connecting in series two catalytic systems, with the first having Lewis acid properties (favouring the cyclisation of citronellal to isopulegols) and the second having hydrogenation catalytic activity (catalysing the hydrogenation of isopulegols to menthols). A Lewis acid catalyst was prepared by supporting iron oxide nanoparticles over a waste material, i.e. the ceramic core of scrap catalytic converters (SCATs) via a microwave assisted method. Most importantly, SCATs, containing a low residual noble metal content, could be directly employed in the second step as hydrogenation catalysts. The reaction was performed studying the influence on the yield and selectivity to (−)-menthol of various reaction parameters (T, p and flow rate). Under the best reaction conditions (at a flow rate of 0.1 mL min−1 and at 373 K and 413 K for cyclisation and hydrogenation steps respectively) a conversion of >99% of (+)-citronellal to (−)-menthol with 77% final yield was achieved

Microwave-assisted preparation of Ag/Ag2S carbon hybrid structures from pig bristles as efficient HER electrocatalysts

Ag/Ag2S hybrid structures have recently attracted significant interest due to their high chemical and thermal stability, in addition to their unique optical and electrical properties. However, their standard synthetic protocols have important drawbacks including long term and harsh reaction conditions and the utilization of highly toxic sulfur precursors. Herein, an innovative, simple one-pot green approach for the synthesis of Ag/Ag2S carbon hybrid structures is reported. The procedure involved a one-step microwave-assisted step using ethylene glycol as solvent and reducing agent, pig bristles as sulphur and carbon source and silver nitrate as metal precursor. Different amounts of silver nitrate were employed in order to investigate the synthetic mechanism for the formation of zerovalent silver over silver sulphide nanoparticles, producing three different samples. Materials were characterized by XRD, SEM, EDX, N2 physisorption and XPS spectroscopy. Aiming to prove the efficiency of the as-synthesized compounds, their electrocatalytic activities were explored in the hydrogen evolution reaction (HER) performing linear sweep voltammetries

Characterisation of microbial attack on archaeological bone

As part of an EU funded project to investigate the factors influencing bone preservation in the archaeological record, more than 250 bones from 41 archaeological sites in five countries spanning four climatic regions were studied for diagenetic alteration. Sites were selected to cover a range of environmental conditions and archaeological contexts. Microscopic and physical (mercury intrusion porosimetry) analyses of these bones revealed that the majority (68%) had suffered microbial attack. Furthermore, significant differences were found between animal and human bone in both the state of preservation and the type of microbial attack present. These differences in preservation might result from differences in early taphonomy of the bones. © 2003 Elsevier Science Ltd. All rights reserved