Nanomaterials with very specific features (purity, colloidal stability, composition, size, shape, location…) are commonly requested by cutting-edge technologic applications, and hence a sustainable process for the mass-production of tunable/engineered nanomaterials would be desirable. Despite this, tuning nano-scale features when scaling-up the production of nanoparticles/nanomaterials has been considered the main technological barrier for the development of nanotechnology. Aimed at overcoming these challenging frontier, a new gas-phase reactor design providing a shorter residence time, and thus a faster quenching of nanoclusters growth, is proposed for the green, sustainable, versatile, cost-effective, and scalable manufacture of ultrapure engineered nanomaterials (ranging from nanoclusters and nanoalloys to engineered nanostructures) with a tunable degree of agglomeration, composition, size, shape, and location. This method enables: (1) more homogeneous, non-agglomerated ultrapure Au-Ag nanoalloys under 10 nm; (2) 3-nm non-agglomerated ultrapure Au nanoclusters with lower gas flow rates; (3) shape-controlled Ag NPs; and (4) stable Au and Ag engineered nanostructures: nanodisks, nanocrosses, and 3D nanopillars. In conclusion, this new approach paves the way for the green and sustainable mass-production of ultrapure engineered nanomaterials.

This work is aimed at investigating the influence of the inter-electrode spacing on the production rate and size of nanoparticles generated by evaporating a cathode on an atmospheric pressure dc glow discharge. Experiments are conducted in the configuration of two vertically aligned cylindrical electrodes in upward coaxial flow with copper as a consumable cathode and nitrogen as a carrier gas. A constant current of 0.5 A is delivered to the electrodes and the inter-electrode distance spanned from 0.5 to 10 mm. Continuous stable nanoparticle production is attained by optimal coaxial flow convection cooling of the cathode. Both the particle production rate and the primary particle size increase with the inter-electrode spacing up to nearly 5 mm and strongly decrease with an increasing inter-electrode distance beyond 5 mm. Production rates in the range of 1 mg h⁻¹ of very small nanoparticles (<10 nm) are attained by a micro glow discharge (<1 mm); while glow discharges of intermediate sizes (<5 mm) result in production rates of up to 10 mg h⁻¹ and primary particles of sizes between 10 and 20 nm. No correlation is found between the measured spatially averaged plasma parameters and nanoparticle production. Since the latter is largely determined by the properties of the cathode surface, spatially resolved spectrometric measurements are needed to discern between the positive column and the cathode region of the glow discharge plasma.

This work describes the technical features and the performance of two different types of metal-oxide semiconductor sensors, based on ZnO:Ga thin films and SnO₂-G nanofibrous layers, for tropospheric ozone monitoring in ambient air. These nanostructures were tested and compared with commercial metal-oxide semiconductor sensors under controlled laboratory conditions and in a field campaign during summer 2021 in Monfragüe National Park (western Spain). The paper also details the design of the electronic device developed for this purpose. A machine learning algorithm based on Support Vector Regression (SVR) allowed the conversion of the resistive values into ozone concentration, which was evaluated afterward. The results showed that the manufactured sensors performed similarly to the commercial sensors in terms of R² (0.94 and 0.95) and RMSE (5.21 and 4.83 μg∙m⁻³). Moreover, a novel uncertainty calculation based on European guides for air quality sensor testing was conducted, in which the manufactured sensors outperformed the commercial ones.

Chemical nanodevices based on tin dioxide, graphene and a mixture of both materials were developed and characterized for NO₂ detection at low concentrations. The chemiresistors were prepared by both electrospinning and drop casting. The films morphologies were investigated by scanning electron microscopy (SEM). The devices response to sub-ppm NO₂ concentrations was measured from room temperature up to 300 °C. An improvement in the performance in terms of sensitivity and response time, as well as higher responses at room temperature, was obtained when a mixture of these materials is used.

In this work, we investigate the electrospray technique for the preparation of graphene layers for use in chemiresistive gas sensors. A dispersion of reduced graphene oxide (rGO) in isopropyl alcohol (0.1 mg/mL) is electrosprayed and the rGO flakes are deposited onto a polymeric substrate with printed interdigitated electrodes. The surface area of the substrate covered with rGO is mainly determined by the distance between the needle and the substrate, while the rGO deposition pattern strongly depends on the flowrate and the applied voltage. Homogeneous layers of rGO are obtained in a stable cone-jet regime, and the room temperature detection behavior of the sensors towards NO₂, O₃ and CO is assessed. The sensors were not capable of detecting CO (up to 5 ppm), but they detected 0.2 ppm NO₂ and 0.05 ppm O₃. The results are encouraging regarding the use of electrospray for the production of low-cost and low-power gas sensors based on graphene for air quality applications.