Polymers based on PLA from synthesis using D,L Lactic acid (or racemic lactide) and some biomedical applications : a short review

Poly(lactic acid) (PLA) is an important polymer that is based on renewable biomass resources. Because of environmental issues, more renewable sources for polymers synthesis have been sought for industrial purposes. In this sense, cheaper monomers should be used to facilitate better utilization of less valuable chemicals and therefore granting more sustainable processes. Some points are raised about the need to study the total degradability of any PLA, which may require specific composting conditions (e.g., temperature, type of microorganism, adequate humidity and aerobic environment). Polymerization processes to produce PLA are presented with an emphasis on D,L-lactic acid (or rac-lactide) as the reactant monomer. The syntheses involving homogeneous and heterogeneous catalytic processes to produce poly(D,L-Lactic acid) (PDLLA) are also addressed. Additionally, the production of blends, copolymers, and composites with PDLLA are also presented exemplifying different preparation methods. Some general applications of these materials mostly dedicated to the biomedical area over the last 10–15 years will be pointed out

Self-assembly and Mesocrystal Formation via Non-classical Crystallisation

New materials can be fabricated using small scaled building blocks as a repetition unit. Nanoparticles with their unique size-tuneable properties from quantum confinement can especially be utilised to form two- and three-dimensional ordered assemblies to introduce them into what would normally be considered to be incompatible matrices. Furthermore, new collective properties that derive from the ordered arrangement of the building blocks, are accomplished. Additionally, different materials can be combined by mixing different building blocks during self-assembly, so that size ranges and material combinations that are difficult to achieve by other means can be formed. The arrangement of small particles into highly ordered arrangements can be realised via self-assembly. To achieve such assemblies, highly monodisperse nanoparticular building blocks with a size distribution below 5 % have to be synthesised. The production and variation in the size of both lead chalcogenide and noble metal nanoparticles is presented in this work. Moreover, the syntheses of multicomponential nanoparticles (PbSe/PbS and Au/PbS) are investigated. Non-classical crystallisation methodologies with their varyious self-assembly mechanisms are used for the formation of highly symmetrical mesocrystals and supracrystals. Analogous to classical crystallisation methods and their formation processes the interparticle interactions, attractive as well as repulsive, determine the resulting crystalline structure. Variation of the environmental parameters consequently leads to structural variation due to the changing interparticle interactions. In contrast to classical crystallisation the length scale of the interparticle forces stays constant as the size dimension of the self-assembled building unit is changed. Two different non-classical crystallisation pathways are investigated in this work. One pathway focuses on the slow destabilisation of nanoparticles in organic media by the addition of a non-solvent. In this approach optimisation of parameters for the formation of highly symmetrical three-dimensional mesostructures are studied. Furthermore, to shine some light onto the mechanism of self-assembly, the intrinsic arrangement of the building units in a mesocrystal and the steps of non-solvent addition are analysed. The mechanistic investigations explain the differences observed in mesocrystal formation between metal and semiconductor nanoparticles. The lower homogeneity of the building units of the metal nanoparticles leads to smaller and less defined superstructures in comparison to semiconductor building blocks. Another pathway of non-classical crystallisation is the usage of electrostatic interactions as the driving force for self-assembly and supracrystal formation. Therefore, the building blocks are transferred into aqueous media and stabilised with oppositely charged ligands. The well-know procedure for metal nanoparticles was adapted for semiconductor materials. The lower stability of these nanoparticles in aqueous solution induces an agglomeration of the semiconductor nanoparticles without including oppositely charged metal nanoparticles. The destabilisation effect can be increased by the addition of equally charged metal nanoparticles in a salting out type process. In comparison to the slow formation of mesocrystals achieved via destabilisation in an organic media (up to 4 weeks), the salting out procedure takes place within two hours, but the faster agglomeration causes a less well defined assembly of the building units in the mesocrystals. Moreover, the arrangement of semiconductor nanoparticles with organic molecules such as polymers and proteins was investigated in order to use the nanoparticles as a light harvesting component. In combination with the directly bound polymer the charge carrier may be directly transferred to the conductive thiophene-based polymer, so that infrared light can be transformed into an electrical signal for use in further applications such as solar cells. The advantage of the nanoparticle-protein system is the self-assembly across a liquid-liquid interface and additionally a Förster resonance energy transfer can occur at this phase boundary. Hence, it is possible to transfer highly energetic photons directly to biological samples without destroying the biological material

Rational Design of Non-precious Metal Oxide Catalysts by Means of Advanced Synthetic and Promotional Routes

This reprinted edition of the Special Issue entitled “Rational Design of Non-Precious Metal Oxide Catalysts by Means of Advanced Synthetic and Promotional Routes” covers some of the recent advances in relation to the fabrication and fine-tuning of metal oxide catalysts by means of advanced synthetic and/or promotional routes. It consists of fourteen high-quality papers on various aspects of catalysis, related to the rational design and fine-tuning strategies during some of the most relevant applications in heterogeneous catalysis, such as N2O decomposition, the dry reforming of methane (DRM), methane combustion and partial oxidation, and selective catalytic reduction (SCR), among others

DESIGN AND SYNTHESIS OF POLYMER, CARBON AND COMPOSITE ELECTRODES FOR HIGH ENERGY AND HIGH POWER SUPERCAPACITORS

Supercapacitors (SCs) are promising energy storage devices because they deliver energy faster than Li-ion batteries and store larger amounts of charge compared to dielectric capacitors. SCs are classified in electrical double layer capacitors (EDLCs) and pseudocapacitors, based on their charge storage mechanism. EDLCs store charge electrostatically, i.e. by physical charge separation. This mechanism limits the storable amount of energy to the available surface area of the electrode, typically made of carbon materials, but grants good cycling stability of the SC device. Pseudocapacitor electrodes, commonly made of conducting polymers or metal oxides, store charge faradaically, i.e. through redox reactions throughout the bulk material, which allows them to store significantly larger amounts of energy than EDLCs, but their stability is compromised due to the partial irreversibility of the faradaic processes. To accomplish the commercialization of SCs, devices must show a combination of high charge storage capacities and long-term stability, besides being cost-effective. To tackle the current issues of SCs, this field of study has taken mainly two directions: 1) the development of new architectures and nanostructures of the active materials, which has shown to increase the surface area, enhance stability, and facilitate ion diffusion; and 2) fabrication of composites between non-faradaic (carbon), faradaic materials, and/or redox-active components to achieve a balance between the amount of energy stored and the stability. Following the first approach, a continuous process to grow vertically aligned carbon nanotubes (VACNTs) on cost-effective aluminum foil was developed. The resulting electrodes were analyzed as SC electrodes and in symmetric cells, and the influence of the arrangement of the nanotubes and the synthesis conditions was studied. The performance of the VACNTs produced continuously showed similar performance to the VACNTs produced stationarily and the ordered structure of the VACNTs showed superior performance compared to randomly oriented CNTs. To increase the energy density, the second approach was taken, by combining pre-synthesized conducting polymers (CPs) and carbon nanotubes (CNTs) using a facile scalable dispersion filtration method to produce free-standing electrodes. Composites with the three main CPs were prepared, analyzed in various electrolytes, and their performance was comparable with polymer/ CNT films prepared with more complex techniques such as in-situ polymerization and pellet pressing. Then, based on the idea that the quinone molecules present in lignin store charge by undergoing a 2 proton, 2 electron redox reaction, a composite between polypyrrole, a stable conducting polymer, and the prototypical molecule p-benzoquinone was fabricated by electropolymerization of pyrrole in the presence of the redox molecule. A significant increase in capacitance and capacity was obtained with respect to polypyrrole films. Furthermore, an important obstacle in the application of CPs in SCs is the lack of easily reduced (n-dopable) polymers. Poly(aminoanthraquinone) (PAQ) is a conjugated polymer that shows electroactivity in the negative potential range of 0 to -2 V, due to the redox moieties of the polymer. PAQ was electropolymerized on free-standing CNT films and its performance as anode for SCs was studied. The materials and processing techniques described in this dissertation are useful to further develop high power/high energy electrodes for SCs

Synthesis and gas sensing properties of inorganic semiconducting, p-n heterojunction nanomaterials

En aquesta tesis utilitzant principalment Aerosol Assited Chemical Vapor Deposition, AACVD, com a metodologia de síntesis d'òxid de tungstè nanoestructurat s'han fabricat diferents sensors de gasos. Per tal d'estudiar la millora en la selectivitat i la sensibilitat dels sensors de gasos basats en òxid de tungstè aquest s'han decorat, via AACVD, amb nanopartícules d'altres òxids metàl·lics per a crear heterojuncions per tal d'obtenir un increment en la sensibilitat electrònica, les propietats químiques del material o bé ambdues. En particular, s'han treballat en diferents sensors de nanofils d'òxid de tungstè decorats amb nanopartícules d'òxid de níquel, òxid de cobalt i òxid d'iridi resultant en sensors amb un gran increment de resposta i selectivitat cap al sulfur d'hidrogen, per a l'amoníac i per a l'òxid de nitrogen respectivament a concentracions traça. A més a més, s'han estudiat els mecanismes de reacció que tenen lloc entre les espècies d'oxigen adsorbides a la superfície del sensor quan interactua amb un gas. I també s'ha treballat en intentar controlar el potencial de superfície de les capes nanoestructurades per tal de controlar la deriva en la senyal al llarg del temps, quan el sensor està operant, a través d'un control de temperatura.En esta tesis utilizando principalmente Aerosol Assited Chemical Vapor Deposition, AACVD, como metodología de síntesis de óxido de tungsteno nanoestructurado se han fabricado diferentes sensores de gases. Para estudiar la mejora en la selectividad y la sensibilidad de los sensores de gases basados en óxido de tungsteno estos se han decorado, vía AACVD, con nanopartículas de otros óxidos metálicos para crear heterouniones para obtener un incremento en la sensibilidad electrónica, las propiedades químicas del material o bien ambas. En particular, se han trabajado en diferentes sensores de nanohilos de óxido de tungsteno decorados con nanopartículas de óxido de níquel, óxido de cobalto y óxido de iridio resultante en sensores con un gran incremento de respuesta y selectividad hacia el sulfuro de hidrógeno, para el amoníaco y para el óxido de nitrógeno respectivamente a concentraciones traza. Además, se han estudiado los mecanismos de reacción que tienen lugar entre las especies de oxígeno adsorbidas en la superficie del sensor cuando interactúa con un gas. Y también se ha trabajado en intentar controlar el potencial de superficie de las capas nanoestructuradas para controlar la deriva en la señal a lo largo del tiempo, cuando el sensor está trabajando, a través de un control de temperatura.In this thesis, using mainly Aerosol Assited Chemical Vapor Deposition, AACVD, as a synthesis methodology for nanostructured tungsten oxide, different gas sensors have been manufactured. To study the improvement in the selectivity and sensitivity of gas sensors based on tungsten oxide, they have been decorated, via AACVD, with nanoparticles of other metal oxides to create heterojunctions to obtain an increase in electronic sensitivity, in the chemical properties of the material or at the same time in both. Particularly, we have worked on different tungsten oxide nanowire sensors decorated with nanoparticles of nickel oxide, cobalt oxide and iridium oxide resulting in sensors with a large increase in response and selectivity towards hydrogen sulfide, for ammonia. and for nitrogen oxide respectively at trace concentrations. In addition, the reaction mechanisms that take place between oxygen species adsorbed on the sensor surface when it interacts with a gas have been also studied. Furthermore, efforts have been put on trying to control the surface potential of the nanostructured layers to control the drift in the signal over time, when operating the sensors, through temperature control

Tungsten oxide nanostructures and their electrochromic performance

The electrochromic behaviour of tungsten oxide (WOx) bulk forms has attracted huge research interest for decades owing to advantages of fast response time, good reversibility and high colouration efficiency compared with other electrochromic materials. Nanomaterials have certainly brought in new opportunities and opened the door for better, higher and smarter devices fabrication. This thesis will first investigate, explore, and understand the electrochromic performance of WOx in the nanoscale, and identify ways to enhance its performance via effective doping electrolyte selection and heat treatment. Moreover, the thesis will evaluate the prototype device performance based on our new understandings obtained in this project. The main findings are as follows: • Successfully synthesised crystalline WOx-based nanomaterials using a simple solvothermal technique, and achieved a series of La-, Ce- and Na-doped nanomaterials. The results show that the dopants caused distortion of the parental WOx¬ frameworks and increased the oxygen vacancy inside the structure, which is beneficial for the chromic properties. • The best electrochromic performance was obtained from Ce/W = 1 : 15 samples which presented 44.3% for optical contrast colouration efficiency of 67.3 cm2 C−1. • Conducted in-situ phase transition investigations using both WO3 nanoparticles and W18O49 nanowires, and found out that temperature was affecting the relaxation of W-O framework and phase transition. Based on the investigation, the 187.6 cm-1 band has identified as a fingerprint band for the phase transition from γ- to β- of the WO3 nanoparticle at 275 °C. W18O49 nanowires exhibit better thermal stability than the WO3 nanoparticles. • Intensive electrochemical investigations of La- and Ce-doped WOx structures were exhibit better diffusion kinetics, stability and colouration efficiency compare with plain WOx. These improvements are contributed to the improved oxygen vacancy (Vo). DLi+ of the Ce-doped samples were much higher than that of the plain W18¬O49 nanowires, by 177%, 102% and 84% for the 1:15, 1:10 and 1:5 samples respectively. DLi+ values of all La-doped samples were over 100% higher than those of the plain W18O49. The La-doped thin films increased the stability by 9%, 4% for intercalation, and 25% and 23% for de-intercalation, for La/W = 1:15 and 1:10 samples respectively, against the plain W18O49. • Provided experimental evidence to explain the degradation of chromic thin films, which is related to the Li+ trapping and loss of Vo in the WOx the structures. • The 350 °C annealed W18O49 thin film sample showed better diffusion kinetics by 25% for intercalation and 30% for de-intercalation compared with the un-annealed W18O49 samples. Stabilities also showed 31% improvement for the de-intercalation, against the un-annealed W18O49 sample. • Fabricated electrochromic device prototypes, and investigated the influence of various electrolytes, an optimal combination of LiClO4/PPC/PC polymer electrolyte has been developed, to improve the performance in ion kinetics and switching time of W18O49. These results have shown that WOx nanomaterials via further effective modification including doping with rare-earth elements or proper heat treatment are promising and practical candidate for the creation of fast, reliable and highly efficient electrochromic devices/smart windows for various applications

Immobilized Non-Precious Electrocatalysts for Advanced Energy Devices

The successful commercialization of advanced energy devices, including fuel cells and solar cells (e.g., dye-sensitized solar cells) is somewhat dependent on the cost, activity and durability of the electrocatalysts. Nowadays, precious metal electrodes are the most widely used. Accordingly, the manufacturing costs are relatively high, which constrains wide application. Recently, some reports have introduced some promising non-precious electrocatalysts to be exploited in both oxidation and reduction reactions. It was concluded that immobilization of the functional material on a proper support can distinctly improve catalytic activity. Moreover, due to the synergetic effect, metallic alloy nanoparticles show very good electrocatalytic activity in this regard. This Special Issue aims to cover the most recent progress and the advances in the field of the immobilized non-precious electrocatalysts. This includes, but is not limited to, non-precious electrocatalysts for alcohol (methanol, ethanol, etc.) oxidation, oxygen reduction reaction and electrolyte reduction in dye-sensitized solar cells

Nanoestructuras de TiO2 de baja dimensionalidad para la obtención fotocatalítica de hidrógeno

Hydrogen is one of the most promising solutions for the energy future, since its combustion only produces water vapour, so it does not pollute. In addition, it can be obtained from abundant and renewable substances. Fuel cells in vehicles can use hydrogen directly and it has multiple applications in the industry. Today, hydrogen is primarily produced by steam reforming of natural gas. However, this process of production does not reduce emissions of greenhouse gases and requires high temperatures and pressures, which implies a high-energy supply. In addition, it does not use a non-renewable energy source to produce it. In contrast, photocatalytic production of H2 can be carried out at environmental conditions and using directly the Sun and renewable substances such as ethanol. In this research work, different catalysts have been prepared using different synthetic methods for the photocatalytic production of hydrogen from ethanol-water mixtures. Chapter 1 presents the most relevant aspects related to the experimental work carried out in this doctoral thesis. In addition, the background and objectives are included. Chapter 2 describes the preparation of TiO2 lyogels decorated with preformed gold nanoparticles and their photocatalytic behaviour in the production of hydrogen. Two different series were prepared. Initially, TiO2 lyogels were calcined at different temperatures before depositing the preformed gold nanoparticles and then a different group of lyogels was calcined after depositing the nanoparticles. The characterization results showed differences in the composition of crystalline phases present in the materials. After performing the photocatalytic tests, they revealed a strong dependence on the crystalline phase of the catalyst with its photocatalytic activity. In Chapter 3, the influence of the morphology of catalysts decorated with pre-formed Au-Cu nanoparticles on the photocatalytic production of hydrogen is studied. The synthetic methods used to produce nanostructures with defined morphology are often very complicated or difficult to reproduce. Here, a microstructure prepared by a simple synthetic method is explored and compared to other materials with morphology that have already been clearly established in the literature, in addition to the commercial catalyst TiO2-P25. The photocatalytic results showed that this microstructure achieved the highest photocatalytic activity of all the morphologies tested and was equivalent to that of the commercial catalyst TiO2-P25. In Chapter 4, the effect of depositing isolated platinum atoms on the surface of TiO2 with defined morphology in the photocatalytic production of hydrogen is studied. They have been compared with the commercial catalysts TiO2-P90 and P25 and with the catalysts decorated with AuCu nanoparticles. The effect of two types of thermal treatments, calcination and reduction, is studied. Besides, the effect of the reduction temperature and the stability of the reduced catalyst was also studied. The results showed a high photocatalytic activity compared to the samples with Au. The reduced catalysts showed a higher photocatalytic activity than the calcined ones but they were less stable.El hidrógeno se presenta como una de las fuentes de energía más prometedoras para el futuro puesto que su combustión tiene como único producto vapor de agua, por lo que no resulta contaminante. Además, es una sustancia abundante y renovable, se puede utilizar como combustible para vehículos y tiene múltiples aplicaciones en la industria. Actualmente, el hidrógeno que se produce es en gran parte a partir del reformado catalítico del gas natural con vapor. Sin embargo, este método de producción no reduce las emisiones de gases de efecto invernadero y aparte requiere de altas temperaturas y altas presiones, lo que implica un alto suministro energético. Además, no ayuda a resolver el tema de la energía puesto que utiliza una fuente de energía no renovable para producirlo. En cambio, la producción fotocatalítica de H2 puede realizarse a condiciones ambientales y hacer uso de sustancias renovables como etanol. Sin embargo, uno de los desafíos es el desarrollo de catalizadores más eficientes que permitan una transición hacia energías limpias. En este trabajo de investigación, se han fabricado diferentes catalizadores a través de diferentes métodos sintéticos para la producción fotocatalítica de hidrógeno a partir de mezclas etanol-agua. El capítulo 1 se aborda de una manera general y concisa los aspectos más relevantes en los que se basa el trabajo experimental realizado en esta tesis doctoral. Además, se incluyen los antecedentes y los objetivos. En el capítulo 2 se describe la preparación de liogeles de titania de alta área superficial decoradas con nanopartículas de oro preformadas y su comportamiento fotocatalítico en la producción de hidrógeno. Se prepararon dos diferentes series, en la primera serie los liogeles fueron previamente calcinados a diferentes temperaturas antes de depositar las nanopartículas de oro preformadas y en la segunda serie los liogeles fueron calcinados después de depositarles las nanopartículas. Los resultados de caracterización mostraron diferencias en la composición de fases cristalinas presentes en los materiales. Después de realizar las pruebas fotocatalíticas, estas revelaron una fuerte dependencia de la fase cristalina del catalizador con su actividad fotocatalítica. En el capítulo 3 se estudia la influencia que tiene la morfología de catalizadores decorados con nanopartículas preformadas de Au-Cu en la producción fotocatalítica de hidrógeno. Los métodos de síntesis utilizados para producir nanoestructuras con morfología definida suelen ser muy complicados o difíciles de reproducir. Aquí, se explora una microestructura fabricada mediante un método sintético simple y se compara contra otros materiales con morfología que ya han sido claramente establecidos en la literatura, además del catalizador comercial TiO2-P25. Los resultados fotocatalíticos mostraron que esta microestrutura obtuvo la actividad fotocatalítica más alta de todas las morfologías ensayadas y fue equivalente a la del catalizador comercial TiO2-P25. En el capítulo 4 se estudia el efecto de depositar átomos aislados de platino sobre la superficie de TiO2 con morfología definida en la producción fotocatalitica de hidrógeno. Se han comparado con los catalizadores comerciales TiO2-P90 y P25 y con los catalizadores decorados con nanopartículas de AuCu. Se estudia el efecto de dos tipos de tratamientos térmicos: calcinación y reducción. Además del efecto de la temperatura de reducción y la estabilidad del catalizador reducido. Los resultados mostraron una alta actividad fotocatalítica en comparación con las muestras con AuCu. Los catalizadores reducidos mostraron una actividad fotocatalítica superior que las calcinadas, pero resultaron ser menos estables.L'hidrogen es presenta com una de les fonts d'energia més prometedores per al futur ja que la seva combustió té com a únic producte vapor d'aigua, pel que no resulta contaminant. A més, és una substància abundant i renovable, es pot utilitzar com a combustible per a vehicles i té múltiples aplicacions en la indústria. Actualment, l'hidrogen que es produeix és en gran part a partir del reformat catalític del gas natural amb vapor. No obstant això, aquest mètode de producció no redueix les emissions de gasos d'efecte hivernacle ia part requereix d'altes temperatures i altes pressions, el que implica un alt subministrament energètic. A més, no ajuda a resoldre el tema de l'energia ja que utilitza una font d'energia no renovable per produir-lo. En canvi, la producció fotocatalítica d'H2 pot realitzar-se a condicions ambientals i fer ús de substàncies renovables com etanol. No obstant això, un dels reptes és el desenvolupament de catalitzadors més eficients que permetin una transició cap a energies netes. En aquest treball d'investigació, s'han fabricat diferents catalitzadors a través de diferents mètodes sintètics per a la producció fotocatalítica d'hidrogen a partir de mescles etanol-aigua. El capítol 1 s'aborda d'una manera general i concisa els aspectes més rellevants en què es basa el treball experimental realitzat en aquesta tesi doctoral. A més, s'inclouen els antecedents i els objectius. En el capítol 2 es descriu la preparació de liogeles de titania d'alta àrea superficial decorades amb nanopartícules d'or preformades i el seu comportament fotocatalític en la producció d'hidrogen. Es van preparar dos diferents sèries, en la primera sèrie dels liogeles van ser prèviament calcinats a diferents temperatures abans de dipositar les nanopartícules d'or preformades i en la segona sèrie dels liogeles van ser calcinats després de dipositar les nanopartícules. Els resultats de caracterització van mostrar diferències en la composició de fases cristal·lines presents en els materials per a una mateixa temperatura, excepte per a 400 ⁰C. Després de realitzar les proves fotocatalítiques, aquestes van revelar una forta dependència de la fase cristal·lina del catalitzador amb la seva activitat fotocatalítica. En el capítol 3 s'estudia la influència que té la morfologia de catalitzadors decorats amb nanopartícules preformades d'Au-Cu en la producció fotocatalítica d'hidrogen. Els mètodes de síntesi utilitzats per produir nanoestructures amb morfologia definida solen ser molt complicats o difícils de reproduir. Aquí, s'explora una microestructura fabricada mitjançant un mètode sintètic simple i es compara contra altres materials amb morfologia que ja han estat clarament establerts en la literatura, a més del catalitzador comercial TiO2-P25. Els resultats fotocatalíticos van mostrar que aquesta microestrutura va obtenir l'activitat fotocatalítica més alta de totes les morfologies assajades i va ser equivalent a la del catalitzador comercial TiO2-P25. En el capítol 4 s'estudia l'efecte de dipositar àtoms aïllats de platí sobre la superfície de TiO2 amb morfologia definida en la producció fotocatalítica d'hidrogen. S'han comparat amb els catalitzadors comercials TiO2-P90 i P25 i amb els catalitzadors decorats amb nanopartícules de AuCu. S'estudia l'efecte de dos tipus de tractaments tèrmics: calcinació i reducció. A més de l'efecte de la temperatura de reducció i l'estabilitat del catalitzador reduït. Els resultats van mostrar una alta activitat fotocatalítica en comparació amb les mostres amb Au. Els catalitzadors reduïts van mostrar una activitat fotocatalítica superior que les calcinades però van resultar ser menys establesPostprint (published version