The degradation of organic pollutants in wastewaters assisted by oxide semiconductor nanostructures has been the focus of many research groups over the last decades, along with the synthesis of these nanomaterials by simple, eco-friendly, fast, and cost-effective processes. In this work, porous zinc oxide (ZnO) nanostructures were successfully synthesized via a microwave hydrothermal process. A layered zinc hydroxide carbonate (LZHC) precursor was obtained after 15 min of synthesis and submitted to different calcination temperatures to convert it into porous ZnO nanostructures. The influence of the calcination temperature (300, 500, and 700 °C) on the morphological, structural, and optical properties of the ZnO nanostructureswas investigated. All ZnO samples were tested as photocatalysts in the degradation of rhodamine B (RhB) under UV irradiation and natural sunlight. All samples showed enhanced photocatalytic activity under both light sources, with RhB being practically degraded within 60 min in both situations. The porous ZnO obtained at 700 °C showed the greatest photocatalytic activity due to its high crystallinity, with a degradation rate of 0.091 and 0.084 min−1 for UV light and sunlight, respectively. These results are a very important step towards the use of oxide semiconductors in the degradation of water pollutants mediated by natural sunlight.

Laser-induced graphene (LIG) has gained preponderance in recent years, as a very attractive material for the fabrication and patterning of graphitic structures and electrodes, for multiple applications in electronics. Typically, polymeric substrates, such as polyimide, have been used as precursor materials, but other organic, more sustainable, and accessible precursor materials have emerged as viable alternatives, including cellulose substrates. However, these substrates have lacked the conductive and chemical properties achieved by conventional LIG precursor substrates and have not been translated into fully flexible, wearable scenarios. In this work, we expand the conductive properties of paper-based LIG, by boosting the graphitization potential of paper, through the introduction of external aromatic moieties and meticulous control of laser fluence. Colored wax printing over the paper substrates introduces aromatic chemical structures, allowing for the synthesis of LIG chemical structures with sheet resistances as low as 5 Ω·sq–1, translating to an apparent conductivity as high as 28.2 S·cm–1. Regarding chemical properties, I D/I G ratios of 0.28 showcase low defect densities of LIG chemical structures and improve on previous reports on paper-based LIG, where sheet resistance has been limited to values around 30 Ω·sq–1, with more defect dense and less crystalline chemical structures. With these improved properties, a simple transfer methodology was developed, based on a water-induced peel-off process that efficiently separates patterned LIG structures from the native paper substrates to conformable, flexible substrates, harnessing the multifunctional capabilities of LIG toward multiple applications in wearable electronics. Proof-of concept electrodes for electrochemical sensors, strain sensors, and in-plane microsupercapacitors were patterned, transferred, and characterized, using paper as a high-value LIG precursor for multiples scenarios in wearable technologies, for improved sustainability and accessibility of such applications.

Bottom-up microwave-assisted seed-mediated synthesis of gold nanoparticles onto nanocellulose to boost stability and high performance for SERS applications,

In the present study, titanium dioxide (TiO2) nano-photocatalysts were synthesized through microwave irradiation. In a typical microwave synthesis, TiO2 nanomaterials were simultaneously produced in powder form and also directly covering cork substrates. The TiO2 nanopowder was analyzed by X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM), revealing that the solvothermal microwave synthesis resulted only in the TiO2 anatase phase. From Fourier-transform infrared spectroscopy (FTIR), cork’s organic species, along with bands of TiO2, were detected. UV–VIS absorption spectrum revealed an absorption extension to the visible region, since a brown powdered TiO2 product was obtained. Very fine nanoparticles were observed displaying a nearly spherical shape that agglomerates in larger particles. These larger particles fully covered the surface of the honeycomb cork cells, originating TiO2 functionalized cork platforms. The TiO2 functionalized substrates were further tested as floating photocatalysts and their photocatalytic activity was assessed from rhodamine B degradation under solar simulating light and natural sunlight. Reusability tests were also performed under natural sunlight. The strategy applied in this research work allowed the production of green and low-cost cork platforms based on TiO2 photoactive materials with the ability to purify polluted water under natural sunlight.

Diabetes mellitus affects a significant percentage of the world’s population, and the incidence of this disease is expected to increase exponentially in the coming years. The development of practical and low-cost glucose sensors is of utmost importance to monitor and manage diabetes and diabetes associated complications. In this scope, a nonenzymatic glucose sensor was produced by growing zinc oxide (ZnO) nanorods on a cellulose-based substrate by microwave-assisted hydrothermal synthesis. The developed sensor relies on ZnO nanorods’ photocatalytic ability to photo-oxidize glucose, eliminating the need to use an oxidase enzyme. The quantification of glucose is based on the quenching of the ZnO’s photoluminescence signal by the hydrogen peroxide produced during the nonenzymatic oxidation of this monosaccharide. The developed sensor possesses a sensitivity of 1.46%/mM, a linear range between 0.5 and 30 mM, and a limit of detection of 0.103 mM. The sensor showed good selectivity for glucose, and it was also demonstrated that there was a high correlation between the glucose concentration values obtained using the sensor’s calibration curve and the clinical data of human plasma samples, therefore validating the use of ZnO nanorods to monitor the glucose concentration in human plasma samples. This work reports for the first time a ZnO-based eco-friendly, stable, and highly selective alternative for glucose monitoring, pointing to a promising future for metal oxide nanostructures for biomedical sensors.