Spinel ZnCo₂O₄ nanoparticles were synthesized by means of the microwave-assisted colloidal method. A solution containing ethanol, Co-nitrate, Zn-nitrate, and dodecylamine was stirred for 24 h and evaporated by a microwave oven. The resulting solid material was dried at 200 °C and subsequently calcined at 500 °C for 5 h. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy, confirming the formation of spinel ZnCo₂O₄ nanoparticles with average sizes between 49 and 75 nm. It was found that the average particle size decreased when the dodecylamine concentration increased. Pellets containing ZnCo₂O₄ nanoparticles were fabricated and tested as sensors in carbon monoxide (CO) and propane (C₃H₈) gases at different concentrations and temperatures. Sensor performance tests revealed an extremely high response to 300 ppm of CO at an operating temperature of 200 °C.

Three pilot-scale two-stage hybrid constructed wetlands were evaluated in order to compare their efficiency for total coliforms (TCol) and Escherichia coli removal and to analyze their performances in two 1-year periods of experimentation. System I consisted of a horizontal flow (HF) constructed wetland (CW) followed by a stabilization pond. System II was also configured with a HF CW as a first stage which was then followed by a vertical flow (VF) CW as a second stage. System III was configured with a VF CW followed by a HF CW. In the first year of evaluation, the HF–VF system was the most effective for TCol removal (p < 0.05) and achieved a reduction of 2.2 log units. With regard to E. coli removal, the HF–VF and VF–HF systems were the most effective (p < 0.05) with average reductions of 3.2 and 3.8 log units, respectively. In the second year, the most effective were those with a VF component for both TCol and E. coli which underwent average reductions of 2.34–2.44 and 3.44–3.74 log units, respectively. The reduction achieved in E. coli densities, in both years, satisfy the World Health Organization guidelines that require a 3–4 log unit pathogen reduction in wastewater treatment systems.

The fundamental aspects of the manufacturing of gold nanoparticles (AuNPs) are discussed in this review. In particular, attention is devoted to the development of a simple and versatile method for the preparation of these nanoparticles. Eco-friendly synthetic routes, such as wet chemistry and biosynthesis with the aid of polymers, are of particular interest. Polymers can act as reducing and/or capping agents, or as soft templates leading to hybrid nanomaterials. This methodology allows control of the synthesis and stability of nanomaterials with novel properties. Thus, this review focus on a fundamental study of AuNPs properties and different techniques to characterize them, e.g., Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), UV-Visible spectroscopy, Dynamic Light Scattering (DLS), X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy, Small-angle X-Ray Scattering (SAXS), and rheology. Recently, AuNPs obtained by “green” synthesis have been applied in catalysis, in medicine, and as antibacterials, sensors, among others.

In this research, we are reporting the treatment of tequila vinasse by a coagulation–flocculation process coupled with heterogeneous photocatalysis using two types of titanium dioxide nanoparticles, i.e. (1) commercial nanoparticles, and (2) nanoparticles synthesized by sol–gel. The efficiency in the elimination of phenol, which is one of the most harmful contaminants in tequila vinasse, was also included in the evaluation of the treatment process. The synthesized titanium dioxide nanoparticles were annealed in air at 400°C for 1 h and were characterized by X-ray diffraction, transmission electron microscopy, ultraviolet-visible and Raman spectroscopy. Anatase phase was observed in both samples, with a crystallite size of 22.5 and 9.8 nm for commercial and synthesized nanoparticles respectively. Tequila vinasse was characterized before and after the treatments by measuring physicochemical parameters such as pH, chemical oxygen demand (COD), colour, total suspended solids (TSS), as well as using ultraviolet-visible spectroscopy and Raman spectroscopy to identify the presence of organic compounds, and gas chromatography (GC) for phenol quantification. Raw vinasse was treated initially by coagulation–flocculation producing clarified vinasse, which in turn was treated by photocatalysis for 3 h using hydrogen peroxide as oxidizing agent. The use of synthesized titanium dioxide nanoparticles allowed the highest efficiencies, reaching reductions of 99.4%, 86.0%, and 70.0% for TSS, colour, and COD respectively. GC results showed the reduction of phenol concentrations in 89.7% with our synthesized nanoparticles in contrast to 82.7% reduction, with commercial titanium dioxide nanoparticles. GRAPHICAL ABSTRACT