Self-propelled micromotors for cleaning polluted water

We describe the use of catalytically self-propelled microjets (dubbed micromotors) for degrading organic pollutants in water via the Fenton oxidation process. The tubular micromotors are composed of rolled-up functional nanomembranes consisting of Fe/Pt bilayers. The micromotors contain double functionality within their architecture, i.e., the inner Pt for the self-propulsion and the outer Fe for the in situ generation of ferrous ions boosting the remediation of contaminated water.The degradation of organic pollutants takes place in the presence of hydrogen peroxide, which acts as a reagent for the Fenton reaction and as main fuel to propel the micromotors. Factors influencing the efficiency of the Fenton oxidation process, including thickness of the Fe layer, pH, and concentration of hydrogen peroxide, are investigated. The ability of these catalytically self-propelled micromotors to improve intermixing in liquids results in the removal of organic pollutants ca. 12 times faster than when the Fenton oxidation process is carried out without catalytically active micromotors. The enhanced reaction-diffusion provided by micromotors has been theoretically modeled. The synergy between the internal and external functionalities of the micromotors, without the need of further functionalization, results into an enhanced degradation of nonbiodegradable and dangerous organic pollutants at small-scale environments and holds considerable promise for the remediation of contaminated water

Micromotors for Environmental Applications

[eng] Scarce supply of clean water and rising water pollution are key global challenges for water sustainability. Much of the wastewater generated by human agricultural and industrial activity is left untreated. Nanotechnological materials and systems have emerged as new tools for improving the efficiency of water treatment. Among those, self-propelled micromotors have shown several advantageous characteristics. Micromotors are autonomously propelled systems which either use chemical energy present in their environment or are propelled via external force fields. Diverse designs, materials composition and mechanisms of propulsion are reported for micromotors found in the literature. Among them, bubble-propelled micromotors, which move due to the generation and release of gas bubbles from their surface, are the main type of motors used for water remediation applications. In addition to the motion in fluids, the bubbles generated by the motors, also contribute with additional mixing of the fluid and enhance the mass transfer between active material and pollutant at the microscale. Additionally, the structure of micromotors can be modified to target a wide variety of pollutants, almost on demand. The micromotors that we synthesized during the research work for this thesis can remove organic and heavy metal pollutants, as well as exhibit bactericidal activity. We studied Iron/Platinum (Fe/Pt) micromotors for their reusability, effect of sizes, swimming behaviors and catalytic properties. These micromotors were fabricated by spontaneous roll-up of iron and platinum nanomembranes, deposited on the pre-fabricated patterns of a photoresist substrate. The iron layer present as the outer surface of these micromotors can degrade organic pollutants via Fenton-like reaction and the inner platinum layer acts as the engine decomposing hydrogen peroxide to oxygen for bubble propulsion. We observed that Fe/Pt micromotors can swim continuously for hours, and can be stored for weeks before reuse, without sacrificing much of their activity. The results suggested that Fe/Pt micromotors act as a heterogeneous catalyst due to in situ generated iron oxide species on the surface, without leaching high concentration of iron in the media. We developed graphene oxide-based micromotors (GOx-micromotors) for heavy metal removal, consisting of nanosized multilayers of graphene oxide, nickel, and platinum. These micromotors can capture, transfer, and remove heavy metals (i.e. lead) from contaminated water. GOx-micromotors are synthesized by electrodepositions of electro-reducible graphene oxide, nickel and platinum layers in the polycarbonate porous templates. The outer layer of graphene oxide captures lead on their surface, and the inner layer of platinum provides self-propulsion in hydrogen peroxide, while the middle layer of nickel enables external magnetic control of the micromotors. We observed that the mobile GOx-micromotors can remove lead 10 times more efficiently than non-motile GOx-micromotors, cleaning water from 1000 ppb down to below 50 ppb. We have demonstrated control of their motion and directionality in a proof of concept microfluidic system. Silver nanoparticles (AgNPs) decorated Magnesium Janus micromotors were designed for disinfection and remove of Escherichia coli (E. coli) bacteria from contaminated water. Magnesium present in the micromotors functions as both, the template for the spherical shape and propulsion source by producing hydrogen bubbles while in contact with water. The inner layer of iron provides functionality for the magnetic remote guidance, and an outer AgNP coated gold layer facilitates adhesion of bacteria and gives bactericidal properties to the micromotors. We observed that the AgNPs-coated Au cap of the micromotors shows dual capabilities, capturing bacteria and killing them. In our efforts to develop multifunctional micromotors and scalable synthesis methods, we developed two types of micromotors. (i) Mesoporous silica-based micromotors with manganese dioxide (MnO2) layer on the inner surface and coated with γ-Fe2O3 nanoparticles (FeSiMnOx micromotors). These micromotors can remove both organic and heavy metal pollutants, and they are synthesized using only template-assisted chemical methods. (ii) Cobalt ferrite micromotors (CFO micromotors) synthesized by template-free chemical synthesis approach. They are made up of aggregated cobalt ferrite nanoparticles, which act as the catalyst for propulsion and for Fenton-like reactions. We qualitatively measured the generation of hydroxyl radicals by CFO micromotors and studied the effect of surfactants on the degradation efficiency of CFO micromotors. We hope that such approach of synthesizing micromotors via relatively facile methods will push the use of micromotors towards commercially practical solutions for water treatment. Overall, our results show that the multifunctional self-propelled micromotors have potential to become an effective tool for water remediation in the near future.[spa] El escaso suministro de agua limpia y el aumento de la contaminación del agua son desafíos globales clave para la sostenibilidad del agua, sobre todo teniendo en cuenta que gran parte del agua residual generada por la actividad agrícola e industrial humana no se trata. Los materiales y sistemas nanotecnológicos han surgido como nuevas herramientas para mejorar la eficiencia del tratamiento de aguas. Entre ellos, los micromotores autopropulsados han mostrado varias características ventajosas. Los micromotores son sistemas de propulsión autónoma que utilizan energía química presente en su entorno o pueden también ser propulsadas a través de campos de fuerzas aplicadas externamente. Varios diseños, composición de materiales y mecanismos de propulsión se han sido reportados en el campo de los micromotores. Entre ellos, principalmente los micromotores propulsados por burbujas, los cuales se mueven debido a la generación y liberación de burbujas de gas de su superficie, se utilizan como una herramienta para aplicaciones de remediación de aguas. Esto se debe a la eficacia añadida de la transferencia de masa a la microescala, que se origina a partir de su movimiento y el movimiento de las burbujas liberadas. Además, la estructura de los micromotores se puede modificar para dirigirse a una amplia variedad de contaminantes, según los requerimientos. Los micromotores que sintetizamos durante el trabajo de investigación para esta tesis pueden eliminar contaminantes orgánicos y metales pesados, así como exhibir actividad anti bactericida. Estudiamos micromotores de hierro / platino (Fe / Pt) por su reutilización, efecto de tamaños, su comportamiento durante su movimiento y propiedades catalíticas. Estos micromotores se fabricaron mediante enrollamiento espontáneo de nanomembranas de hierro y platino, depositadas en los patrones prefabricados definidos en una capa sacrificial fotorresistente. La capa de hierro presente como superficie externa de estos micromotores puede degradar los contaminantes orgánicos a través de la reacción tipo Fenton y la capa interna de platino actúa como el motor, siendo el catalizador que descompone el peróxido de hidrógeno en oxígeno para generar una propulsión por burbujas. Observamos que los micromotores Fe / Pt pueden nadar continuamente durante horas y pueden almacenarse durante semanas antes de volver a ser usados, sin que esto repercuta de manera significativa en su actividad. Los resultados de nuestros experimentos sobre el análisis de superficie de micromotores, estudio de nanoindentación y liberación de hierro sugirieron que los micromotores Fe / Pt actúan como un catalizador heterogéneo debido a las especies de óxido de hierro generadas in situ en la superficie, sin lixiviación de alta concentración de hierro en los medios. Desarrollamos micromotores basados en óxido de grafeno (micromotores GOx) para la eliminación de metales pesados que consisten en multicapas nanométricas de óxido de grafeno, níquel y platino. Estos micromotores pueden capturar, transferir y eliminar metales pesados (es decir, plomo) del agua contaminada. Los micromotores GOx se sintetizan mediante electrodeposiciones de capas de óxido de grafeno, níquel y platino, los cuales son electroreducidos en la parte interior de membranas de policarbonato porosas. La capa externa de óxido de grafeno captura el plomo en su superficie, y la capa interna de platino proporciona autopropulsión en presencia de peróxido de hidrógeno, mientras que la capa intermedia de níquel permite el control magnético externo de los micromotores. Observamos que los micromotores móviles GOx pueden eliminar el plomo hasta 10 veces más que los micromotores GOx no móviles (Figura 1B), limpiando el plomo en agua de 1000 ppb a menos de 50 ppb en menos de 60 min. Hemos demostrado el control de su movimiento y direccionalidad en un sistema microfluídico como prueba de concepto. Diseñamos también micromotores tipo Janus decorados con nanopartículas de plata (AgNP) para la desinfección y eliminación de la bacteria Escherichia coli (E. coli) en agua contaminada. Los micromotores Janus se sintetizaron recubriendo un lado de una micro-partícula de magnesio con capas de hierro y oro, las cuales posteriormente se funcionalizaron con AgNP. El magnesio presente en los micromotores funciona no sólo como estructura principal para conseguir una forma esférica, sino también como fuente de propulsión mediante la producción de burbujas de hidrógeno al entrar en contacto con el agua. La capa interna de hierro proporciona la funcionalidad requerida para el posterior control magnético externo, mientras que la capa de oro externa decorada con AgNPs promueve la adhesión de bacterias y dota de propiedades bactericidas a los micromotores. En nuestro esfuerzo por desarrollar micromotores multifuncionales y métodos de síntesis escalables, desarrollamos dos tipos de micromotores. (i) Micromotores mesoporosos basados en sílice con una capa de dióxido de manganeso (MnO2) en la superficie interna y recubiertos con nanopartículas γ-Fe2O3 (micromotores FeSiMnOx). Estos micromotores pueden eliminar contaminantes orgánicos y metales pesados, y se sintetizan utilizando solo métodos químicos asistidos por un molde (por ejemplo, una membrana porosa). (ii) Los micromotores de ferrita de cobalto (micromotores CFO) fueron sintetizados sin necesidad de utilizar ningún molde. Están formados por nanopartículas de ferrita de cobalto agregadas, que actúan como catalizadores para la propulsión y para reacciones tipo Fenton. Medimos cualitativamente la generación de radicales hidroxilos por micromotores CFO y estudiamos el efecto de los tensioactivos sobre la eficiencia de degradación de los micromotores CFO. Esperamos que la síntesis de micromotores a través de métodos relativamente fáciles empuje la implementación de micromotores en soluciones comercialmente prácticas para el tratamiento del agua. En general, nuestros resultados muestran que los micromotores autopropulsados multifuncionales tienen el potencial de convertirse en una herramienta efectiva para la limpieza de aguas en el futuro

Metal-oxide-based microjets for the simultaneous removal of organic pollutants and heavy metals

Water contamination from industrial and anthropogenic activities is nowadays a major issue in many countries worldwide. To address this problem, efficient water treatment technologies are required. Recent efforts have focused on the development of self-propelled micromotors that provide enhanced micromixing and mass transfer by the transportation of reactive species, resulting in higher decontamination rates. However, a real application of these micromotors is still limited due to the high cost associated to their fabrication process. Here, we present Fe2O3-decorated SiO2/MnO2 microjets for the simultaneous removal of industrial organic pollutants and heavy metals present in wastewater. These microjets were synthesized by low-cost and scalable methods. They exhibit an average speed of 485 ± 32 μm s–1 (∼28 body length per s) at 7% H2O2, which is the highest reported for MnO2-based tubular micromotors. Furthermore, the photocatalytic and adsorbent properties of the microjets enable the efficient degradation of organic pollutants, such as tetracycline and rhodamine B under visible light irradiation, as well as the removal of heavy metal ions, such as Cd2+ and Pb2+

Innovative designs and applications of Janus micromotors with (photo)-catalytic and magnetic motion

El objetivo principal de esta Tesis Doctoral es el diseño y desarrollo de micromotores Janus biocompatibles y su aplicación en ámbitos relevantes de la salud y de la protección medioambiental. Los micromotores Janus son dispositivos en la microescala autopropulsados que tienen al menos dos regiones en su superficie con diferentes propiedades físicas y químicas, lo que les convierte en una clase distintiva de materiales que pueden combinar características ópticas, magnéticas y eléctricas en una sola entidad. Como la naturaleza del micromotor Janus -el dios romano de las dos caras- los objetivos de esta Tesis Doctoral presentan naturaleza dual y comprenden desarrollos de química fundamental y de química aplicada. En efecto, por una parte, el objetivo central aborda el diseño, síntesis y ensamblaje, así como la caracterización de micromotores Janus poliméricos propulsados por mecanismos (foto)-catalíticos y/o accionados por campos magnéticos. Por otra parte, el objetivo central implica la aplicación de los micromotores desarrollados para resolver desafíos sociales relevantes en los ámbitos químico-analítico, biomédico y ambiental. Partiendo de estas premisas, en la primera parte de la Tesis Doctoral, se sintetizaron micromotores Janus de policaprolactona propulsados químicamente integrando nanomateriales para el diseño de sensores móviles para la detección selectiva de endotoxinas bacterianas. De esta forma, el movimiento autónomo del micromotor mejora la mezcla de fluidos y la eficacia de las reacciones implicadas permitiendo detectar el analito en pocos minutos, incluso en muestras viscosas y medios donde la agitación no es posible. Además, esta autopropulsión es altamente compatible con su empleo en formatos ultra-miniaturizados para el desarrollo de futuros dispositivos portátiles en el marco de la tecnología point of care para aplicaciones clínicas y agroalimentarias. Con el fin de incrementar su biocompatibilidad para aplicaciones in vivo, en una segunda etapa de la Tesis Doctoral, se diseñaron micromotores Janus con propulsión autónoma utilizando luz visible para la eliminación de toxinas relevantes en procesos inflamatorios. El fenómeno autopropulsivo del micromotor y su capacidad de interacción con agentes tóxicos condujo a metodologías más rápidas y eficaces infiriéndose un futuro prometedor de estos micromotores para el tratamiento del shock séptico o intoxicación. En una tercera etapa, se sintetizaron micromotores propulsados por campos magnéticos. Estos micromotores utilizan una aproximación elegante de propulsión, exenta del empleo de combustibles químicos tóxicos como sucede en la propulsión catalítica y, en consecuencia, biocompatible. Asimismo, este mecanismo propulsivo permite controlar e incluso programar su trayectoria para aplicaciones que requieran de un guiado y de un control preciso de esta. De manera específica, estos micromotores han sido aplicados en esta Tesis Doctoral para la liberación controlada de fármacos en el tratamiento de cáncer pancreático y como elementos de remediación ambiental en la eliminación de agentes nerviosos en aguas contaminadas

From Fenton and ORR 2e−-Type Catalysts to Bifunctional Electrodes for Environmental Remediation Using the Electro-Fenton Process

Currently, the presence of emerging contaminants in water sources has raised concerns worldwide due to low rates of mineralization, and in some cases, zero levels of degradation through conventional treatment methods. For these reasons, researchers in the field are focused on the use of advanced oxidation processes (AOPs) as a powerful tool for the degradation of persistent pollutants. These AOPs are based mainly on the in-situ production of hydroxyl radicals (OH center dot) generated from an oxidizing agent (H2O2 or O-2) in the presence of a catalyst. Among the most studied AOPs, the Fenton reaction stands out due to its operational simplicity and good levels of degradation for a wide range of emerging contaminants. However, it has some limitations such as the storage and handling of H2O2. Therefore, the use of the electro-Fenton (EF) process has been proposed in which H2O2 is generated in situ by the action of the oxygen reduction reaction (ORR). However, it is important to mention that the ORR is given by two routes, by two or four electrons, which results in the products of H2O2 and H2O, respectively. For this reason, current efforts seek to increase the selectivity of ORR catalysts toward the 2e(-) route and thus improve the performance of the EF process. This work reviews catalysts for the Fenton reaction, ORR 2e(-) catalysts, and presents a short review of some proposed catalysts with bifunctional activity for ORR 2e(-) and Fenton processes. Finally, the most important factors for electro-Fenton dual catalysts to obtain high catalytic activity in both Fenton and ORR 2e(-) processes are summarized.Ministry of Science and Innovation, Spain (MICINN) Spanish Government PID2021-127803OB-I00Junta de Andalucia B.RNM.566.UGR2

Responsive and structured silica-polypeptide composite particles and their components

Nature can produce multifunctional particles by seamlessly combining a variety of molecules and components into a single system. No synthetic particle or collection of particles has approached this elegant combination of function. This dissertation discusses the beginning of building functional and structured particles. It describes a system that combines colloidal silica, known for its ability to assume different and stable shapes, and polypeptides, known for their chirality and ability to change shape. Throughout, the goal is to produce silica-polypeptide composite particles (PCPs) that can illuminate a path to multiple function. The focus is on creating these multi-functional particles and understanding their physical properties and behaviors. This work has presented detailed studies for increased understanding of the degradation and conformational transition of poly(carbobenzyloxy-L-lysine) (PCBL) both free in solution and attached to a core particle. It has also presented composite materials synthesized with varying responsive and physical properties. These findings provide understanding to continue expanding work with polypeptides and biomaterials for use in a variety of applications such as polycolloids, vesicles, and other responsive materials.Ph.D

Layered Double Hydroxides

Very few materials have attracted so much attention in recent years, both from researchers and industry, as layered double hydroxides (LDHs) have. LDHs, which are also referred to as anionic clays or hydrotalcites, are a wide class of inorganic ionic lamellar clay materials consisting of alternately stacked positively charged metal hydroxide layers with intercalated charge-balancing anions in hydrated interlayer regions. Their unique properties, such as their extremely high versatility in chemical composition and intercalation ability, extraordinary tuneability in composition as well as morphology, good biocompatibility and high anion exchangeability, have triggered immense interdisciplinary interest for their use in many different fields of chemistry, biology, medicine, and physics. Indeed, the applications of LDHs are constantly growing: LDHs, in the form of aggregated lamellar clusters, exfoliated single-layer nanosheets, or hierarchical films of interconnected nanoplatelets, can be effectively used as nanoscale vehicles in drug delivery, heterogeneous catalysts and supports for molecular catalysts, ion exchangers and adsorbents, solid electrolytes or fillers in electrochemistry, for the fabrication of superhydrophobic surfaces, water treatment and purification, and the synthesis of functional thin films. This book gathers the contributions to the Special Issue “Layered Double Hydroxides” of Crystals, which includes two review articles and seven research papers

Applications and immobilization strategies of the copper-centred laccase enzyme : a review

DATA AVAILABILITY STATEMENT: No data was used for the research described in the article.Laccase is a multi-copper enzyme widely expressed in fungi, higher plants, and bacteria which facilitates the direct reduction of molecular oxygen to water (without hydrogen peroxide production) accompanied by the oxidation of an electron donor. Laccase has attracted attention in biotechnological applications due to its non-specificity and use of molecular oxygen as secondary substrate. This review discusses different applications of laccase in various sectors of food, paper and pulp, waste water treatment, pharmaceuticals, sensors, and fuel cells. Despite the many advantages of laccase, challenges such as high cost due to its non-reusability, instability in harsh environmental conditions, and proteolysis are often encountered in its application. One of the approaches used to minimize these challenges is immobilization. The various methods used to immobilize laccase and the different supports used are further extensively discussed in this review.The National Research Foundation (NRF) of South Africa.https://www.cell.com/heliyonChemical Engineerin

Inmovilización de enzimas en MOFs: diseño y aplicaciones

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Física Aplicada. Fecha de Lectura: 24-02-202