Azure A embedded in carbon dots as NADH electrocatalyst: Development of a glutamate electrochemical biosensor

Carbon nanodots modified with azure A (AA-CDs) have been synthesized and applied as redox mediator of bioelectrocatalytic reactions. A deep characterization of AA-CDs nanomaterial has been carried out, proving the covalent attachment of azure A molecules into the carbon dots nanostructure. Disposable screen-printed carbon electrodes (SPCE) have been modified with AA-CDs, through the action of chitosan polymer (Chit-AA-CDs/SPCE). The Chit-AA-CDs/SPCE electrocatalytic activity towards the oxidation of NADH has been proved, obtaining excellent results regarding the low oxidation potential achieved (−0.15 V vs. Ag) and low detection and quantification limits (LOD and LOQ) for NADH, 16 and 53 µM, respectively. The developed electrochemical platform has been applied for the construction of a glutamate biosensor by immobilizing L-glutamic dehydrogenase (GLDH/Chit-AA-CDs/SPCE). The morphology of GLDH/Chit-AA-CDs/SPCE platform was analysed by AFM at each different step of the electrode modification process. The resulting biosensing platform is capable of detect NADH enzymatically generated by GLDH in the presence of glutamate and NAD+. Good analytical parameters were obtained for glutamate analysis using GLDH/Chit-AA-CDs/SPCE, as LOD and LOQ of 3.3 and 11 µM, respectively. The biosensor has been successfully applied to the analysis of food and biological samplesThis work has been supported by the Spanish Ministerio de Ciencia e Innovacion (PID2020–116728RB-I00) and Comunidad Autonoma de Madrid (SI3/PJI/2021–00341, P2018/NMT-4349 TRANSNANOAVANSENS Program

Microwave-Driven Exsolution of Ni Nanoparticles in A-Site Deficient Perovskites

[EN] Exsolution has emerged as a promising method for generating metallic nanoparticles, whose robustness and stability outperform those of more conventional deposition methods, such as impregnation. In general, exsolution involves the migration of transition metal cations, typically perovskites, under reducing conditions, leading to the nucleation of well-anchored metallic nanoparticles on the oxide surface with particular properties. There is growing interest in exploring alternative methods for exsolution that do not rely on high-temperature reduction via hydrogen. For example, utilizing electrochemical potentials or plasma technologies has shown promising results in terms of faster exsolution, leading to better dispersion of nanoparticles under milder conditions. To avoid limitations in scaling up exhibited by electrochemical cells and plasma-generation devices, we proposed a method based on pulsed microwave (MW) radiation to drive the exsolution of metallic nanoparticles. Here, we demonstrate the H-2-free MW-driven exsolution of Ni nanoparticles from lanthanum strontium titanates, characterizing the mechanism that provides control over nanoparticle size and dispersion and enhanced catalytic activity and stability for CO2 hydrogenation. The presented method will enable the production of metallic nanoparticles with a high potential for scalability, requiring short exposure times and low temperatures.The project that gave rise to these results received the supportof a fellowship from the La Caixa Foundation (Grant100010434). The fellowship code is LCF/BQ/PI20/11760015. This study forms part of the MFA program andwas supported by MCIN with funding from European UnionNextGenerationEU (Grant PRTR-C17.I1) and by GeneralitatValenciana. Financial support by the Spanish Ministry ofScience and Innovation (Grants PID2022-139663OB-100 andCEX2021-001230-S funded by MCIN/AEI/10.13039/501100011033). Also, we acknowledge the support of theServicio de Microscopía Electrónica of the UniversitatPolitècnica de Valè ncia (UPV).López-García, A.; Domínguez-Saldaña, A.; Carrillo-Del Teso, AJ.; Navarrete Algaba, L.; Valls-Esteve, MI.; García-Baños, B.; Plaza González, PJ.... (2023). Microwave-Driven Exsolution of Ni Nanoparticles in A-Site Deficient Perovskites. ACS Nano. 17(23):23955-23964. https://doi.org/10.1021/acsnano.3c085342395523964172

Modulating redox properties of solid-state ion-conducting materials using microwave irradiation

[EN] The industrial adoption of low-carbon technologies and renewable electricity requires novel tools for electrifying unitary steps and efficient energy storage, such as the catalytic synthesis of valuable chemical carriers. The recently-discovered use of microwaves as an effective reducing agent of solid materials provides a novel framework to improve this chemical-conversion route, thanks to promoting oxygen-vacancy formation and O-2-surface exchange at low temperatures. However, many efforts are still required to boost the redox properties and process efficiency. Here, we scrutinise the dynamics and the physicochemical dependencies governing microwave-induced redox transformations on solid-state ion-conducting materials. The reduction is triggered upon a material-dependent induction temperature, leading to a characteristically abrupt rise in electric conductivity. This work reveals that the released O-2 yield strongly depends on the material's composition and can be tuned by controlling the gas-environment composition and the intensity of the microwave power. The reduction effect prevails at the grain surface level and, thus, amplifies for fine-grained materials, and this is ascribed to limitations in oxygen-vacancy diffusion across the grain compared to a microwave-enhanced surface evacuation. The precise cyclability and stability of the redox process will enable multiple applications like gas depuration, energy storage, or hydrogen generation in several industrial applications.This study forms part of the MFA programme and was supported by MCIN with funding from European Union NextGenerationEU (PRTR-C17.I1) and by Generalitat Valenciana. Financial support by the Spanish Ministry of Science and Innovation (PID2022-139663OB-100 and CEX2021-001230-S grants funded by MCIN/AEI/10.13039/501100011033, and "Ramon y Cajal" Fellowship RYC2021-033889-I), and the Universitat Politecnica de Valencia (UPV) are gratefully acknowledged. Also, we acknowledge the support of the Servicio de Microscopia Electronica of the UPV.Serra Alfaro, JM.; Balaguer Ramirez, M.; Santos-Blasco, J.; Borrás-Morell, JF.; García-Baños, B.; Plaza González, PJ.; Catalán-Martínez, D.... (2023). Modulating redox properties of solid-state ion-conducting materials using microwave irradiation. Materials Horizons. 10(12):5796-5804. https://doi.org/10.1039/d3mh01339a57965804101