Imidazolium-based titanosilicate nanospheres as active catalysts in carbon dioxide conversion:Towards a cascade reaction from alkenes to cyclic carbonates

Porous silica-based nanospheres bearing titanium centres as single site were successfully synthesized employing a time- and energy-efficient procedure. The influence of the post-synthesis treatment on the insertion of Ti was investigated via DR UV-Vis and XPS spectroscopy and the titanium content was quantified through ICP-OES analysis. The textural and structural properties of the different solids were evaluated via XRD, TEM and N2 physisorption. The resulting materials were thereafter covalently functionalized with imidazolium chloride, followed by characterization via 29Si and 13C solid-state NMR, N2 physisorption and chemical combustion analysis. The bi-functional catalysts were tested in the challenging conversion of CO2 with cyclohexene oxide to the corresponding cyclic carbonate as well as with various other epoxides with excellent results. The insertion of Ti as single site played a key role substantially improving the activity of the solids. The most active bi-functional material was successfully recovered and reused through multiple cycle without loss of the catalytic activity. Moreover, the cyclohexene epoxidation reaction was tested as well employing the mono-functionalized Ti-based material. The catalytic mixture, composed by the mono-functional and bi-functional solids, was efficiently used to convert the cyclohexene into cyclohexene oxide and subsequently the cyclohexene oxide into the corresponding carbonate thus opening the prospect for a cascade reaction

Flexible and Conductive Bioelectrodes Based on Chitosan-Carbon Black Membranes: Towards the Development of Wearable Bioelectrodes

Wearable sensors for non-invasive monitoring constitute a growing technology in many industrial fields, such as clinical or sport monitoring. However, one of the main challenges in wearable sensing is the development of bioelectrodes via the use of flexible and stretchable materials capable of maintaining conductive and biocompatible properties simultaneously. In this study, chitosan-carbon black (CH-CB) membranes have been synthesized using a straightforward and versatile strategy and characterized in terms of their composition and their electrical and mechanical properties. In this sense, CH-CB membranes showed good conductivity and mechanical resistance thanks to the presence of carbon black, which decreases the insulating behavior of chitosan, while flexibility and biocompatibility are maintained due to the dual composition of the membrane. Thus, flexible and biocompatible conductive bioelectrodes have been developed by the combined use of CH and CB without the use of toxic reagents, extra energy input, or long reaction times. The membranes were modified using the enzymes Glucose Oxidase and Laccase in order to develop flexible and biocompatible bioelectrodes for enzymatic glucose biofuel cells (BFCs) and glucose detection. A BFC assembled using the flexible bioelectrodes developed was able to deliver 15 µW cm−2, using just 1 mM glucose as biofuel, and up to 21.3 µW·cm−2 with higher glucose concentration. Additionally, the suitability of the CH-CB membranes to be used as a glucose sensor in a linear range from 100 to 600 µM with a limit of detection (LOD) of 76 µM has been proven. Such demonstrations for energy harvesting and sensing capabilities of the developed membrane pave the way for their use in wearable sensing and energy harvesting technologies in the clinical field due to their good mechanical, electrical, and biocompatible properties

Low-Denaturazing Glucose Oxidase Immobilization onto Graphite Electrodes by Incubation in Chitosan Solutions

In this work, glucose oxidase (GOx) has been immobilized onto graphite rod electrodes through an assisted-chitosan adsorption reaching an enzyme coverage of 4 nmol/cm2. The direct and irreversible single adsorption of the Flavine Adenine Dinucleotide (FAD) cofactor has been minimized by electrode incubation in a chitosan (CH) solution containing the enzyme GOx. Chitosan keeps the enzyme structure and conformation due to electrostatic interactions preventing FAD dissociation from the protein envelope. Using chitosan, both the redox cofactor FAD and the protein envelope remain in the active form as demonstrated by the electrochemistry studies and the enzymatic activity in the electrochemical oxidation of glucose up to a concentration of 20 mM. The application of the modified electrodes for energy harvesting delivered a power density of 119 µW/cm2 with a cell voltage of 0.3 V. Thus, chitosan presents a stabilizing effect for the enzyme conformation promoted by the confinement effect in the chitosan solution by electrostatic interactions. Additionally, it facilitated the electron transfer from the enzyme to the electrode due to the presence of embedded chitosan in the enzyme structure acting as an electrical wiring between the electrode and the enzyme (electron transfer rate constant 2.2 s−1). This method involves advantages compared with previously reported chitosan immobilization methods, not only due to good stability of the enzyme, but also to the simplicity of the procedure that can be carried out even for not qualified technicians which enable their easy implementation in industry

Low-Denaturazing Glucose Oxidase Immobilization onto Graphite Electrodes by Incubation in Chitosan Solutions

In this work, glucose oxidase (GOx) has been immobilized onto graphite rod electrodes through an assisted-chitosan adsorption reaching an enzyme coverage of 4 nmol/cm2. The direct and irreversible single adsorption of the Flavine Adenine Dinucleotide (FAD) cofactor has been minimized by electrode incubation in a chitosan (CH) solution containing the enzyme GOx. Chitosan keeps the enzyme structure and conformation due to electrostatic interactions preventing FAD dissociation from the protein envelope. Using chitosan, both the redox cofactor FAD and the protein envelope remain in the active form as demonstrated by the electrochemistry studies and the enzymatic activity in the electrochemical oxidation of glucose up to a concentration of 20 mM. The application of the modified electrodes for energy harvesting delivered a power density of 119 µW/cm2 with a cell voltage of 0.3 V. Thus, chitosan presents a stabilizing effect for the enzyme conformation promoted by the confinement effect in the chitosan solution by electrostatic interactions. Additionally, it facilitated the electron transfer from the enzyme to the electrode due to the presence of embedded chitosan in the enzyme structure acting as an electrical wiring between the electrode and the enzyme (electron transfer rate constant 2.2 s−1). This method involves advantages compared with previously reported chitosan immobilization methods, not only due to good stability of the enzyme, but also to the simplicity of the procedure that can be carried out even for not qualified technicians which enable their easy implementation in industry

Development of Flexible, Conductive and Biocompatible Chitosan-Based Miniaturized Bioelectrodes for Enzymatic Glucose Biofuel Cells

The need for new clean energy sources for portable devices in biomedical, agro-food industry and environmental related sectors boosts scientists towards the development of new strategies for energy harvesting for their application in biodevices development. In this sense, enzymatic biofuel cells (BFCs) have gained much attention in the last years. This work faces the challenge of develop new generation of BFCs able to be adapted to remote and personal monitoring devices within the framework of wearable technologies. To this aim, one of the main challenges consists of the development of conductive and biocompatible electrodes, which constitute a challenge itself due to the non-conductive capabilities of most of the biocompatible supports. Additionally, bioelectrodes may achieve good mechanical properties and resilience in order to be suitable for the envisioned application, which involves exposure to deformation during long-term use. Furthermore, it is desirable that the systems developed are versatile enough to be adapted to miniaturized supports for new personal wearable devices development. In the present work, self-standing chitosan-carbon black membranes have been synthesized and modified with suitable enzymes for the assembly of an enzymatic glucose BFC. The membranes have been adapted to be integrated in miniaturized interdigitated gold electrodes as the step forward to miniaturized systems, modified with enzymes and metallic particles clusters and tested for energy harvesting from glucose solutions. The miniaturized system produces a power density of 0.64 µW/cm2 that is enhanced to 2.75 µW/cm2 in the presence of the metallic clusters, which constitute a 76% incensement. Such preliminary demonstrations highlight the good response of metals in bioelectrode configuration. However, energy harvesting real application of the developed miniaturized electrodes need still improvements but pave the way for the use of BFC as an energy source in wearable technologies due to their good mechanical, electrical and biocompatible properties