BUSCADOR RECOLECTA

Pure magnetic metallic nickel was synthesized by a simple and fast microwave-assisted method using a monomode microwave reactor. Nickel chloride was employed as metal precursor, while an environmental-friendly mixture of ethylene glycol and ethanol was simultaneously used as solvent and reducing agent. The parameters combination, for the occurrence of the reaction, of the mixture molar fraction, and the metal precursor concentration was developed. The influence of the temperature and the time of the irradiation was investigated. The best performance (71% yield) was achieved at 250 °C in 5 min of microwave irradiation. The phase and the morphology of the metal were analyzed by X-ray diffraction, scanning emission microscopy, and transmission electron microscopy, while the surface area was determined by nitrogen physisorption. The material exhibited a strong magnetic behavior. The metallic nickel showed high catalytic activity for the hydrogenolysis of benzyl phenyl ether, a lignin model compound, in a microwave-assisted environmental-friendly reaction.

A microbial fuel cell (MFC) is a type of bio-electrochemical system with novel features, such as electricity generation, wastewater treatment, and biosensor applications. In recent years, progressive trends in MFC research on its chemical, electrochemical, and microbiological aspects has resulted in its noticeable applications in the field of sensing. This review was consequently aimed to provide an overview of the most interesting new applications of MFCs in sensors, such as providing the required electrical current and power for remote sensors (energy supply device for sensors) and detection of pollutants, biochemical oxygen demand (BOD), and specific DNA strands by MFCs without an external analytical device (self-powered biosensors). Moreover, in this review, procedures of MFC operation as a power supply for pH, temperature, and organic loading rate (OLR) sensors, and also self-powered biosensors of toxicity, pollutants, and BOD have been discussed.

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.

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.

Gold‐incorporated SBA‐15 catalyst was prepared by a solvent‐free ball milling approach. The catalyst showed high reactivity and selectivity in the reduction of a variety of nitroarenes to anilines operating in absolute EtOH using NaBH4 as reducing agent. The catalyst was reused in batch conditions over 5 consecutive runs without detecting any losses of activity and selectivity. Considering the high chemical stability and reusability of the catalytic system, a continuous flow protocol was also investigated and defined in order to minimize the production of waste associated to the process and optimize the continuous reuse of the catalyst. Benefits of flow conditions were proven by TON values that increased from 47.5 to 1902 and also by the minimization of both leaching (9.5 vs 1 ppm) and E‐factor values (8 vs 23 in batch).

The synthesis of imidazolones through the cycloisomerization of ureas, specifically propargylureas, has gained attention due to the large availability of starting materials. However, this type of synthesis normally requires the utilization of strong bases, such as NaOH, expensive homogeneous metal catalysts, such as Ag-, Au-, and Ru-based systems, or toxic and hazardous chemicals. Herein, a study of different synthetic routes for the preparation of imidazolones through the cycloisomerization of propargylic ureas under fast, mild, and environmentally friendly conditions with heterogeneous catalysis was undertaken. First, the synthesis were carried out under mild conditions using toluene and acetonitrile as solvents. Silver and gold nanoparticles supported on AlSBA-15 were used as heterogeneous catalysts. The catalysts were prepared by mechanochemical and microwave-assisted techniques. Sequentially, a range of solvents was replaced by the greener ethanol. Finally, all obtained results were combined in order to carry out the reaction using only water as solvent and promoter of the reaction. Aiming to expedite the procedure, the synthesis were carried out under conventional and microwave irradiation.

Silica-supported metallic species have emerged as valuable green-chemistry catalysts because their high efficiency enables a wide range of applications, even at industrial scales. As a consequence, the preparation of these systems needs to be finely controlled in order to achieve the desired activity. The present work presents a detailed investigation of an ultrasound-promoted synthetic protocol for the grafting of β-cyclodextrin (β-CD) onto silica. Truly, ultrasound irradiation has emerged as a fast technique for promoting efficient derivatization of a silica surface with organic moieties at low temperature. Three different β-CD silica-grafted derivatives have been obtained, and the ability of β-CD to direct and bind Cu when CD is bonded to silica has been studied. A detailed characterization has been performed using TGA, phenolphthalein titration, FT-IR, diffuse reflectance (DR), DR UV-Vis, as well as the inductively-coupled plasma (ICP) of the β-CD silica-grafted systems and the relative Cu-supported catalysts. Spectroscopic characterization monitored the different steps of the reaction, highlighting qualitative differences in the properties of amino-derivatized precursors and final products. In order to ensure that the Cu-β-CD silica catalyst is efficient and robust, its applicability in Cu(II)-catalyzed alkyne azide reactions in the absence of a reducing agent has been explored. The presence of β-CD and an amino spacer has been shown to be crucial for the reactivity of Cu(II), when supported.

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%.

The development of intensified processes for the preparation of novel catalytically active nanodimensional materials is a captivating challenge getting more attention day-by-day.1, 2 In fact, nanoparticle systems offer the possibility of combining the high activity of homogenous catalysts with the better recoverability of heterogeneous ones, opening to unlimited application in the chemical industry. The microwave-assisted technique – recognized as one of the most innovative methods for process intensification – makes it possible to both synthesize and test new nanocatalysts exploiting the unique characteristics of microwave heating. These characteristics include reduced reaction times, minimized (or suppressed) side reactions, highly reproducibility, enhanced yields and selectivity as well as selective heating and magnetic loss heating.3-5 The PhD thesis presented has been developed thanks to the experience of the research group FQM-383 (NanoVal) in nanoscale chemistry, heterogeneous catalysis and waste/biomass valorization. More in details, the research studies of the PhD thesis demonstrated the potentiality of microwave-assisted techniques for the development of efficient nanocatalytic systems specifically designed for photochemical applications, fine chemical synthesis and biofuel production.6-10 Most important results obtained during the PhD Thesis have been described in three research articles. In addition, a comprehensive minireview has been included in the introduction section in order to highlight the primary importance of nanocatalysts for the production of biofuels. The first research article, “Microwave-assisted valorization of pig bristles: towards visible light photocatalytic chalcocite composites”, discloses the preparation of nano-Cu2S carbon composites via a fast and low-toxicity microwave-assisted method.11 The synthesis was carried out employing ethylene glycol as solvent, copper chloride as metal precursor and waste pig bristles as sulfur and carbon source, avoiding the use of any toxic sulfur precursor (e.g. H2S, thiourea). The high microwave adsorption and high viscosity of ethylene glycol allowed for the preparation of homogeneous Cu2S carbon composites within a few minutes (4 minutes at 200°C operating in a multimode microwave oven). By contrast, conventional heating needed longer reaction times and formed inhomogeneous, low-active Cu2S carbon material. The so-produced composite has been characterized by X-ray diffraction (XRD), nitrogen physisorption (BET model), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX) and UV-Vis spectroscopy. Cu2S carbon composite has been successfully used for the photo degradation of methyl red, a common pollutant dye, under visible LED light irradiation, leading to ca. 40% of degradation within 3 hours. In the second research article, “Heterogeneously Catalyzed Synthesis of Imidazolones via Cycloisomerizations of Propargylic Ureas Using Ag and Au/Al SBA-15 Systems”, a study of environmentally friendly paths for the cycloisomerization of propargylic ureas has been explored.12 Specifically, different nanogold and nanosilver catalsyts have been prepared by supporting the metal nanoparticles over mesoporous silica (AlSBA-15) through mechanochemistry and microwave-assisted approaches. The catalysts have been used as heterogeneous systems in the microwave assisted synthesis of a library of imidazolones via a sequential study aimed to shift the reaction to greener operative conditions. The employed systems avoided the utilization of strong bases, such as NaOH, or expensive homogeneous metal catalysts. The best conditions have been combined in order to catalyse the cycloisomerization of propargyl ureas using only water as solvent and promoter of the reaction. The results demonstrated that the selected solvent highly influenced the reactions, where toluene promoted N-cyclization reactions, ethanol favoured the cyclization of propargylic ureas characterized by more electron withdrawing groups and water favoured the cyclization of propargylic ureas containing electron donor compounds in the structure. The third research article, “Efficient and Environmentally Friendly Microwave-Assisted Synthesis of Catalytically Active Magnetic Metallic Ni Nanoparticles” describes the preparation of pure magnetic metallic nickel by a simple and fast microwave-assisted method using a monomode microwave reactor (CEM Discover, CEM Corp.).13 The synthesis has been carried out using nickel chloride as metal precursor and a mixture of ethylene glycol and ethanol (or isopropanol) as solvent and reducing agent. A fine study carried out varying the molar ratio of ethylene glycol and ethanol in function of the reaction temperature has highlighted the reaction conditions where the reduction of nickel occurred. The best performance (71% yield) has been achieved operating at 250°C for 5 minutes under microwave irradiation. The mechanism of reaction for oxidation of ethylene glycol and reduction of Ni2+ has been demonstrated by gas chromatography–mass spectrometry (GC-MS) analysis, while the behaviour of the mixture and its bubble point in function of the recorder pressure has been simulated by PRO/II software (Schneider Electric Group). The nanoparticles have been analysed by X-ray diffraction (XRD), scanning emission microscopy (SEM), transmission electron microscopy (TEM) and magnetic mass susceptibility. The surface area has been determined by nitrogen physisorption (BET model). The nanoparticles have showed good activity in the hydrogenolysis of benzyl phenyl ether (BPE), a lignin model compound, with a maximum conversion of 24%, and reusability up to 5 cycles without sensible loss of activity., El desarrollo de procesos destinado a la preparación de nuevos materiales con dimensiones nanométricas y, a su vez, catalíticamente activos, es un desafío fascinante que llama cada vez más la atención1, 2. De hecho, los sistemas compuestos de nanopartículas ofrecen la posibilidad de combinar la alta actividad de los catalizadores homogéneos con la mejor capacidad de recuperación de los heterogéneos, ofreciendo de esta manera un número ilimitado de aplicaciones en la industria química. La técnica asistida por microondas, reconocida como uno de los métodos más innovadores para la intensificación de procesos, permite sintetizar y probar nuevos nanocatalizadores que exploten las características únicas del calentamiento por microondas. Estas características incluyen tiempos de reacción reducidos, reacciones secundarias minimizadas (o suprimidas), alta reproducibilidad, rendimientos y selectividad mejorados, así como calentamiento selectivo y calentamiento por pérdida magnética.3-5 La presente tesis doctoral se ha desarrollado gracias a la experiencia del grupo de investigación FQM-383 (NanoVal) en química a nanoescala, catálisis heterogénea y valorización de residuos/biomasa. Más en detalle, los estudios de investigación de la tesis doctoral demostraron la potencialidad de las técnicas asistidas por microondas para el desarrollo de sistemas nanocatalíticos eficientes diseñados específicamente para aplicaciones fotoquímicas, síntesis química fina y producción de biocombustibles.6-10 Los resultados más importantes obtenidos durante la tesis doctoral se han descrito en tres artículos de investigación. Además, en la sección de introducción, un apartado va dedicado a resaltar la gran importancia de los nanocatalizadores en la producción de biocombustibles. El primer artículo de investigación, Microwave-assisted valorization of pig bristles: towards visible light photocatalytic chalcocite composites”, describe la preparación de compuestos nano-Cu2S de carbono mediante un método asistido por microondas rápido y de baja toxicidad.11 La síntesis se llevó a cabo empleando etilenglicol como disolvente, cloruro de cobre como precursor de metal y pelos de cerdo de desecho como fuente de azufre y carbono, evitando el uso de cualquier precursor de azufre tóxico (por ejemplo, H2S, tiourea). La alta adsorción por microondas y la alta viscosidad del etilenglicol permitieron la preparación de compuestos de carbono Cu2S homogéneos en pocos minutos (4 minutos a 200 ° C trabajando en un horno de microondas multimodo). Por el contrario, el calentamiento convencional necesitó tiempos de reacción más largos, dando como resultado un material de carbono Cu2S poco homogéneo y poco activo. El compuesto así producido se ha caracterizado por difracción de rayos X (XRD), fisisorción de nitrógeno (modelo BET), microscopía electrónica de barrido / espectroscopía de rayos X dispersiva de energía (SEM-EDX) y espectroscopía UV-Vis. El compuesto de carbono Cu2S se ha utilizado con éxito para la foto degradación del rojo de metilo, un colorante contaminante común, bajo irradiación de luz LED visible, que conduce a ca. 40% de degradación en 3 horas. En el segundo artículo de investigación, “Heterogeneously Catalyzed Synthesis of Imidazolones via Cycloisomerizations of Propargylic Ureas Using Ag and Au/Al SBA-15 Systems”, se han estudiado diversos caminos ecológicos para la cicloisomerización de ureas propargílicas12. Específicamente, diferentes nanocatalizadores de oro y plata se han preparado soportando las nanopartículas metálicas sobre sílice mesoporosa (AlSBA-15) utilizando mecanoquímica y radiación microondas. Los catalizadores se han utilizado como sistemas heterogéneos en la síntesis asistida por microondas de una biblioteca de imidazolonas a través de un estudio secuencial destinado a cambiar la reacción a condiciones operativas más ecológicas. Los sistemas empleados evitaron la utilización de bases fuertes, como NaOH, o catalizadores metálicos homogéneos y caros. Las mejores condiciones se han combinado para catalizar la cicloisomerización de las propargilureas utilizando solo agua como disolvente y promotor de la reacción. Los resultados demostraron que el disolvente seleccionado tiene una gran influencia en las reacciones, en concreto el tolueno promovió las reacciones de N-ciclación, el etanol favoreció la ciclación de las ureas propargílicas caracterizadas por más grupos de extracción de electrones y el agua favoreció la ciclación de la urea propargílica que contiene compuestos donadores de electrones en la estructura. El tercer artículo de investigación, “Efficient and Environmentally Friendly Microwave-Assisted Synthesis of Catalytically Active Magnetic Metallic Ni Nanoparticles” describe la preparación de níquel metálico y magnético mediante un método simple y rápido asistido por microondas utilizando un reactor monomodo (CEM Discover, CEM Corp .) 13 La síntesis se ha llevado a cabo utilizando cloruro de níquel como precursor metálico y una mezcla de etilenglicol y etanol (o isopropanol) como disolvente y agente reductor. Un buen estudio llevado a cabo variando la relación molar de etilenglicol y etanol en función de la temperatura de reacción ha llevado a las condiciones de reacción donde se produjo la reducción de níquel. El mejor rendimiento (71%) se ha logrado operando a 250 ° C durante 5 minutos bajo irradiación de microondas. El mecanismo de reacción para la oxidación de etilenglicol y la reducción de Ni2 + se ha demostrado mediante el análisis de cromatografía de gases-espectrometría de masas (GC-MS), mientras que el comportamiento de la mezcla y su punto de burbuja en función de la presión del registrador se ha simulado con PRO/II software (Grupo Schneider Electric). Las nanopartículas han sido analizadas por difracción de rayos X (XRD), microscopía de emisión de barrido (SEM), microscopía electrónica de transmisión (TEM) y susceptibilidad de masa magnética. El área superficial ha sido determinada por la fisisorción de nitrógeno (modelo BET). Las nanopartículas han mostrado una buena actividad en la hidrogenolisis del bencil fenil éter (BPE), un compuesto modelo de lignina, con una conversión máxima del 24%, y reutilización de hasta 5 ciclos sin aparente pérdida de actividad.

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.

The design of sustainable procedures for the preparation of cobalt/carbon-based materials as an anode for hydrogen fuel production through electrocatalytic water splitting has attracted much interest in the last few years. Herein, a novel environmentally friendly approach for the development of stable and active catalysts for the oxygen evolution reaction (OER) is reported. In detail, the methodology aimed at developing a sequence of composites having a low cobalt loading (<4%wt) using polyphenols extracted from green tea as metal stabilizers and activated carbon derived from pinecones as a metal-support as well as a coactive material. The approach exploited ultrasound (US), microwave (MW) and combined US/MWassisted techniques with the purpose of enhancing the final electrocatalytic activity of these new composites, replacing conventional high-temperature approaches. The results indicated that the soproduced electrocatalytic materials followed the order of activity US > MW/US > MW > conventional heating, with the best sample requiring an overpotential of 365 mV to deliver a current density of 10 mA cm_2 and a Tafel slope of 58 mV dec_1.

The synthesis of silver nanoparticles with small average size and narrow size distribution is a requirement for applications in different fields such as antibacterial or catalysis. Previous studies of nanoparticles synthesis confirm the advantages of combining continuous flow and microwave dielectric heating, given the possibilities that arise regarding the control of residence time and localized volumetric heating. In this paper, we present two experimental set-ups to perform the continuous synthesis of silver nanoparticles using microwave heating (MWH) and conventional heating (CH). Experimental and simulated data confirm a different temperature profile along the reactor, with the case of MWH being more favorable. As a result, the nanoparticles synthesized under MWH presented a synthesis yield of 54% and a narrow particle size distribution (19 ± 4.3 nm). Furthermore, MWH led to reduced wall fouling by deposition of product material and allowed fast cooling of the product stream, preventing further growth of the nanoparticles.

Despite the continuous developments in the synthesis of noble metal nanoparticles, the uniformity of particle size distribution still represents a critical aspect. A fast and homogeneous nucleation is a key requirement to achieve a monodisperse particle size distribution and in this scenario, the application of alternative energy sources may constitute a winning strategy for the development of highly active nanocatalysts with unique properties. Here we present several approaches to control the synthesis of Ag nanoparticles stabilized by an anionic template, and the results evidence the advantages of adopting unconventional heating techniques such as microwave heating. The fast and selective electromagnetic heating strongly reduced the nucleation and growth times, impacting on the homogeneity of the resulting particle size distribution. In this work, we have carried out the microwave-assisted synthesis of Ag nanoparticles and the resulting nanoparticles were compared to those synthesized under conventional heating using an oil bath, showing that the differences in temperature profile and heating rates between the two synthesis pathways had a clear effect on the size distribution of the resulting nanoparticles as well as on their stability under long term storage. Finally, the synthesized ultra-small Ag nanoparticles were deposited on a mesoporous substrate, reducing undesired Ostwald ripening and facilitating their reusability. This nanocatalyst was adopted for the abatement of 4-nitrophenol, a well-known carcinogenic pollutant with adverse effects on human beings and aquatic life. The catalytic results confirm the high activity of the catalyst thanks to the high dispersion achieved afforded by ultra-small Ag nanoparticles and the accessibility provided by the wide SBA-15 mesoporous channels.

One of the hallmarks of microwave irradiation is its selective heating mechanism. In the past 30 years, alternative designs of chemical reactors have been introduced, where the microwave (MW) absorber occupies a limited reactor volume but the surrounding environment is MW transparent. This advantage results in a different heating profile or even the possibility to quickly cool down the system. Simultaneous cooling-microwave heating has been largely adopted for organic chemical transformations. However, to the best of our knowledge there are no reports of its application in the field of nanocluster synthesis. In this work, we propose an innovative one-pot procedure for the synthesis of Cu nanoclusters. The cluster nucleation was selectively MW-activated inside the pores of a highly ordered mesoporous substrate. Once the nucleation event occurred, the crystallization reaction was instantaneously quenched, precluding the growth events and favoring the production of Cu clusters with a homogenous size distribution. Herein, we demonstrated that Cu nanoclusters could be successfully adopted for radical cascade annulations ofN-alkoxybenzamides, resulting in various tricyclic and tetracyclic isoquinolones, which are widely present in lots of natural products and bioactive compounds. Compared to reported homogeneous methods, supported Cu nanoclusters provide a better platform for a green, sustainable and efficient heterogeneous approach for the synthesis of tricyclic and tetracyclic isoquinolones, avoiding a variety of toxic waste/byproducts and metal contamination in the final products.

The activity and selectivity of Mo/ZSM-5, benchmarking catalyst for the non-oxidative dehydroaromatization of methane, strongly depend on the cluster size, spatial distribution, and chemical environment of the Mo-based active sites. This study discloses the use of an ultrasound-assisted ion-exchange (US-IE) technique as an alternative Mo/ZSM-5 synthesis procedure in order to promote metal dispersion along the zeolite framework. For this purpose, a plate transducer (91.8 kHz) is employed to transmit the ultrasonic irradiation (US) into the ion-exchange reactor. The physico-chemical properties and catalytic activity of samples prepared under the said irradiation procedure and traditional impregnation (IWI) method are critically evaluated. Characterization results suggest that US neither affects the crystalline structure nor the particle size of the parent zeolite. However, US-IE promotes molybdenum species dispersion, avoids clustering at the external fresh zeolite surface and enhances molybdate species anchoring to the zeolite framework with respect to IWI. Despite the improved metal dispersion, the catalytic activity between catalysts synthesized by US-IE and IWI is comparable. This suggests that the sole initial dispersion enhancement does not suffice to boost the catalyst productivity and further actions such ZSM-5 support and catalyst pre-conditioning are required. Nevertheless, the successful implementation of US-IE and the resulting metal dispersion enhancement pave the way toward the application of this technique to the synthesis of other dispersed catalysts and materials of interest.

Coprecipitation is by far the most common synthesis method for iron oxide nanoparticles (IONPs). However, reproducibility and scalability represent a major challenge. Therefore, innovative processes for scalable production of IONPs are highly sought after. Here, we explored the combination of microwave heating with a flow reactor producing IONPs through coprecipitation. The synthesis was initially studied in a well-characterised microwave-heated flow system, enabling the synthesis of multicore IONPs, with control over both the single core size and the multicore hydrodynamic diameter. The effect of residence time and microwave power was investigated, enabling the synthesis of multicore nanostructures with hydrodynamic diameter between ∼35 and 70 nm, with single core size of 3–5 nm. Compared to particles produced under conventional heating, similar single core sizes were observed, though with smaller hydrodynamic diameters. The process comprised of the initial IONP coprecipitation followed by the addition of the stabiliser (citric acid and dextran). The ability of precisely controlling the stabiliser addition time (distinctive of flow reactors), contributed to the synthesis reproducibility. Finally, scale-up by increasing the reactor length and using a different microwave cavity was demonstrated, producing particles of similar structure as those from the small scale system, with a throughput of 3.3 g/h.

Given the exciting potential of metallic clusters in a variety of fields, the development of novel preparation methods to accurately controlling the cluster size has become a research priority. Specifically, for catalytic applications, the synthesis and deployment of metallic nanoclusters on a proper substrate is perhaps the main bottleneck. Here, we have adopted an alternative reactor that uses simultaneous ice cooling and microwave heating (unlike water ice is a low microwave absorber) for the synthesis of Ag nanoclusters directly over a support with ordered mesopores (SBA-15). The reactor design exploits the selectivity of microwave heating, assuring a rapid localized nucleation followed by a nearly instantaneous quenching that largely avoids the aggregation of nascent clusters as well as Ostwald ripening mechanisms. We have compared this new synthesis approach with some previously reported methods for the production of supported silver nanoclusters: conventional batch reactor and also a continuous flow microreactor. The resulting Ag clusters were initially analyzed in terms of size distribution, textural properties and catalytic activity in the reduction of 4-nitrophenol. Finally, encouraged by the good results obtained, these nanoclusters were also employed in the production of different cyclic organic compounds, building blocks for pharmaceutical and photochemical applications. The nanoclusters displayed a high catalytic activity, lowering the metal loading required to achieve high yield and selectivity. Furthermore, the stabilization of the clusters over the mesoporous substrate allowed their reuse in several reaction cycles. In fact, the method produced exceptionally stable Ag clusters, whose catalytic properties were preserved even after one year of storage.

In the pharma and fine chemical industries, the development of continuous flow technologies is a process intensification step of primary importance towards the manufacturing of high-quality products, while reducing the environmental impact and cost of production. The sustainability and profitability of a process can be measured through life cycle Assessment and cost evaluation. However, when applied to emerging technologies, these need to be performed at different stages of the process development in order to limit the uncertainties arising from the scale-up, and hence providing high-fidelity projections of environmental impacts and costs at larger scales. The output of the assessment can in fact vary significantly depending on the maturity of the technology and this translates into having different results at commercial scale compared to early estimations. Therefore, in this article, we perform an assessment at two different scales of production, lab and mini-pilot scale, with the aim of quantifying the uncertainties of the assessment related to the scale-up, identifying the hotspots of the system, and hence providing guidelines for the further steps of process development. The subject of the assessment is the continuous flow synthesis of Rufinamide. It is the first time that this synthesis is evaluated at pilot-scale. The results show that low yields in the cycloaddition drastically affect the waste management and the production of precursors, and hence increases environmental impacts and cost of production. This calls for the need of prioritizing the optimization of this synthesis step in order to deploy a green and economically competitive production technology., European Union's Horizon 2020 research and innovation, Grant/Award Number: Marie Sklodowska-Curie grant agreement no.721290