Lately, the development of green chemistry methods with high efficiency for metal nanoparticle synthesis has become a primary focus among researchers. The main goal is to find an eco-friendly technique for the production of nanoparticles. Ferro- and ferrimagnetic materials such as magnetite (Fe₃O₄) exhibit superparamagnetic behavior at a nanometric scale. Magnetic nanoparticles have been gaining increasing interest in nanoscience and nanotechnology. This interest is attributed to their physicochemical properties, particle size, and low toxicity. The present work aims to synthesize magnetite nanoparticles in a single step using extracts of green lemon Citrus Aurantifolia residues. The results produced nanoparticles of smaller size using a method that is friendlier to health and the environment, is more profitable, and can be applied in anticorrosive coatings. The green synthesis was carried out by a co-precipitation method under variable temperature conditions. The X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) characterization showed that magnetite nanoparticles were successfully obtained with a very narrow particle size distribution between 3 and 10 nm. A composite was produced with the nanoparticles and graphene to be used as a surface coating on steel. In addition, the coating’s anticorrosive behavior was evaluated through electrochemical techniques. The surface coating obtained showed good anticorrosive properties and resistance to abrasion.

By way of the sol–gel chemical synthesis method, it is possible to synthesize SiO₂ nanoparticles with a defined specific particle size, a surface area, and a defined crystal structure that can be effectively used as a nanoadsorbent to remove various organic dyes. SiO₂ nanoparticles were synthesized by the sol–gel method using sodium silicate (Na₂SiO₃) by a green method without using a tetraethyl orthosilicate (TEOS) precursor, which is very expensive and highly toxic. This sol–gel process involves the formation of a colloidal suspension (sol) and solid gelation to form a network in a continuous liquid phase (gel). In addition, it requires controlled atmospheres. XRD indicates the presence of an amorphous phase with a diffraction angle of 2θ = 23°, associated with SiO₂. UV-Vis spectroscopy reveals an absorbance value in the region of 200 nm to 300 nm, associated with SiO₂ nanoparticles. The application as a nanoadsorbent to remove dyes was measured, and it was found that the nanoparticles with the best performance were those that were synthesized with pH 7, showing a 97% removal with 20 mg of SiO₂ nanoparticles in 60 min. Therefore, SiO₂ nanoparticles can be used as a nanoadsorbent, using a low-cost and scalable method for application to remove methylene blue in an aqueous medium.

Concrete is the most used construction material, needing large quantities of Portland cement. Unfortunately, Ordinary Portland Cement production is one of the main generators of CO₂, which pollutes the atmosphere. Today, geopolymers are an emerging building material generated by the chemical activity of inorganic molecules without the Portland Cement addition. The most common alternative cementitious agents used in the cement industry are blast-furnace slag and fly ash. In the present work, the effect of 5 wt.% µ-limestone in mixtures of granulated blast-furnace slag and fly ash activated with sodium hydroxide (NaOH) at different concentrations was studied to evaluate the physical properties in the fresh and hardened states. The effect of µ-limestone was explored through XRD, SEM-EDS, atomic absorption, etc. The addition of µ-limestone increased the compressive strength reported values from 20 to 45 MPa at 28 days. It was found by atomic absorption that the CaCO₃ of the μ-limestone dissolved in NaOH, precipitating Ca(OH)₂ as the reaction product. SEM-EDS analysis showed a chemical interaction between C-A-S-H- and N-A-S-H-type gels with Ca(OH)₂, forming (N, C)A-S-H- and C-(N)-A-S-H-type gels, improving mechanical performance and microstructural properties. The addition of μ-limestone appeared like a promising and cheap alternative for enhancing the properties of low-molarity alkaline cement since it helped exceed the 20 MPa strength recommended by current regulations for conventional cement.

In the present work, the effect of mineral aggregates (pumice stone and expanded clay aggregates) and chemical admixtures (superplasticizers and shrinkage reducing additives) as an alternative internal curing technique was investigated, to improve the properties of high-performance concrete. In the fresh and hardened state, concretes with partial replacements of Portland cement (CPC30R and OPC40C) by pulverized fly ash in combination with the addition of mineral aggregates and chemical admixtures were studied. The physical, mechanical, and durability properties in terms of slump, density, porosity, compressive strength, and permeability to chloride ions were respectively determined. The microstructural analysis was carried out by scanning electronic microscopy. The results highlight the effect of the addition of expanded clay aggregate on the internal curing of the concrete, which allowed developing the maximum compressive strength at 28 days (61 MPa). Meanwhile, the replacement of fine aggregate by 20% of pumice stone allowed developing the maximum compressive strength (52 MPa) in an OPC-based concrete at 180 days. The effectiveness of internal curing to develop higher strength is attributed to control in the porosity and a high water release at a later age. Finally, the lowest permeability value at 90 days (945 C) was found by the substitutions of fine aggregate by 20% of pumice stone saturated with shrinkage reducing admixture into pores and OPC40C by 15% of pulverized fly ash. It might be due to impeded diffusion of chloride ions into cement paste in the vicinity of pulverized fly ash, where the pozzolanic reaction has occurred. The proposed internal curing technology can be considered a real alternative to achieve the expected performance of a high-performance concrete since a concrete with a compressive strength range from 45 to 67 MPa, density range from 2130 to 2310 kg/m³, and exceptional durability (< 2000 C) was effectively developed.

In the present work, reduced graphene oxide was obtained by green synthesis, using extracts of Larrea tridentata (gobernadora) and Capsicum Chinense (habanero). Graphene oxide was synthesized by the modified Hummers’ method and subsequently reduced using natural extracts to obtain a stable and environmentally friendly graphene precursor. Consequently, the gobernadora aqueous extract was found to have a better reducing power than the habanero aqueous extract. This opportunity for green synthesis allows the application of RGO in photocatalysis for the degradation of the methylene blue dye. Degradation efficiencies of 60% and 90% were obtained with these materials.