Gerson Márquez

In the present research, Zea mays stem (ZMS) agricultural waste and its corresponding activated carbon (AC-ZMS) were successfully utilized as alternative low-cost adsorbents for the removal of Acid Green 25 (AG25), a highly resilient and toxic contaminant textile dye. The evaluation was systematically conducted using synthetic wastewater precisely prepared in the laboratory by dissolving the commercial analytical-grade dye in distilled water to eliminate external chemical interference. The ZMS powder exhibited a fibrillar morphology characteristic of lignocellulosic materials, and AC-ZMS a porous morphology. The removal experiments showed that at an initial concentration of 50 mg/L, pH = 2, an adsorbent dose of 20 g/L, and 20 °C, both materials reached equilibrium in 30 min, achieving removal efficiencies of 87.57% (ZMS) and 91.43% (AC-ZMS). The equilibrium data were fitted to the Langmuir isotherm model, resulting in maximum adsorption capacities (q_mL) that increased with temperature, reaching maximum values of 12.61 mg/g for ZMS and 13.56 mg/g for AC-ZMS at 40 °C. Thermodynamic and mechanism analyses justified the process of preparing AC-ZMS from ZMS for the removal of AG25, since ZMS powder would exhibit predominantly weak and reversible physical adsorption (ΔH⁰ = 15.94 kJ/mol), driven by pH-sensitive electrostatic attraction; in contrast, the adsorption of AG25 onto AC-ZMS is consistent with a chemisorption regime (ΔH⁰ = 86.64 kJ/mol). This change would prevent the degradation of active sites, allowing AC-ZMS to retain a remarkable 80.66% of its initial capacity after 5 consecutive regeneration cycles, whereas untreated ZMS suffers a severe drop in performance to 49.25%. The theoretical study demonstrated that the defect and oxygenated sites present in AC-ZMS attract and immobilize AG25, which causes it to be efficiently removed from synthetic solutions. In conclusion, AC-ZMS is a promising adsorbent in synthetic solutions; further work needed for real wastewater and reuse.

A magnetite–eggshell nanocomposite (Fe₃O₄@eggshell NC) was synthesized by green coprecipitation and evaluated for Cr(VI) removal from water. Passiflora ligularis peel extract, evaluated using a 2³ factorial design, served as the biogenic medium, while eggshell waste acted as the support. Characterization included X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning and transmission electron microscopy (SEM and TEM), Brunauer–Emmett–Teller (BET) analysis, zeta potential measurements, thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), and Mössbauer spectroscopy. The NC preserved Fe₃O₄ and CaCO₃ crystalline phases, contained nanoparticles averaging 18 nm, and exhibited oxygenated surface functionalities, a BET surface area of 134.93 m²/g, amphoteric behavior, and a predominantly superparamagnetic response suitable for magnetic recovery. Under conditions of pH 4, 180 rpm, 60 min, 0.15 g NC, and 50 mg/L Cr(VI), removal reached 75.98%. Kinetic data followed the pseudo-first-order model, whereas equilibrium data were well described by the Sips isotherm, with an estimated capacity of 50.81 mg/g. At the investigated initial concentration of 50 mg/L, adsorption was exothermic and favored at temperatures up to 308 K, and the material retained moderate reusability during the first three alkaline-regeneration cycles. Overall, Fe₃O₄@eggshell NC is a waste-derived, magnetically recoverable adsorbent with favorable Cr(VI) uptake under moderately acidic conditions.

The use of organophosphate pesticides, such as profenofos, is a pressing environmental concern due to their persistence and toxicity to non-target organisms. For this reason, developing alternatives to remove them from the environment is crucial. The objective of this study was to biosynthesize ZnO nanoparticles (ZnO NPs) using an aqueous extract of Negra Criolla grape seeds for their application in the degradation of profenofos in synthetic solutions. The biosynthesized ZnO NPs had an average size of 52 ± 2 nm and a maximum absorption at 375 nm, characteristic of the surface plasmon resonance of ZnO NPs. The ATR-FTIR spectra showed peaks characteristic of ZnO NPs. The 2² × 3 factorial design showed that the optimal values for pH and ZnO NPs concentration are 5 and 3 g/L, respectively, achieving a primary degradation of profenofos (20 mg/L) of 59 ± 2% after 120 min of UV irradiation. In conclusion, it was demonstrated that ZnO NPs biosynthesized using an aqueous extract of Negra Criolla grape seeds exhibit photocatalytic activity for the degradation of profenofos; however, further studies are needed to evaluate their application in actual contaminated water.

Passiflora ligularis (granadilla) is widely cultivated in tropical regions across the Americas. Its consumption generates waste, such as peels, that are typically discarded. In line with the principles of the circular economy, this study explores the green synthesis of metal oxide nanoparticles using granadilla shell extract, with potential applications in antimicrobial treatments and in the remediation of water contaminated with heavy metals or textile dyes. ZnO, CuO, and mixed Zn-Cu oxide nanoparticles were synthesized via an eco-friendly coprecipitation method, using the peel extract as a natural complexing and capping agent. The nanoparticles were characterized by electron diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and infrared spectroscopy to determine their crystalline structure, morphology, size, aggregation state, and elemental composition. The nanoparticles obtained were ultrasmall (3-5 nm), with low crystallinity. ZnO exhibited a hexagonal wurtzite structure, while CuO showed a monoclinic phase. The mixed Zn-Cu oxide displayed a Zn:Cu atomic ratio of approximately 1:3, corresponding to the formula Zn0.25Cu0.75O. The results suggest that granadilla shells are a viable green resource for synthesizing metal oxide nanoparticles with high specific surface areas, making them promising candidates for environmental and antimicrobial applications.

Concrete is an essential material in construction worldwide; however, its production entails a significant carbon footprint. A viable strategy to mitigate this environmental impact is the development of sustainable concretes through the partial replacement of cement or aggregates with natural waste or industrial by-products. This Systematic Literature Review analyzes the effect of steel slag and seashells on the mechanical properties of concrete incorporating these residues. The literature search, based on the PICO methodology, was conducted in the Scopus, EBSCOhost, and Scilit databases, identifying 2,384 sources. After applying the eligibility criteria in accordance with the PRISMA statement, 62 relevant articles were selected. The results indicate that steel slag is mainly used in ultra-high performance concretes, while seashells are more frequently applied in cellular concretes. Both residues proved effective in improving mechanical properties. Compressive strength ranged from 24.8 MPa to 206.9 MPa, with the highest value achieved by replacing 100% of the fine aggregate with steel slag. A tensile strength of up to 10.5 MPa was also reported in mixtures with slag as fine aggregate. Seashells significantly contributed to improving concrete strength and durability, in addition to reducing cracking. In conclusion, although the benefits of steel slag in eco-friendly concretes are well documented, further research is needed to explore the potential of seashells and the development of combined formulations that harness possible synergistic effects in sustainable concrete production.

The objective of this study was to compare the effect of three fertilizers (fish fertilizer, humic acid, and urea) on the yield of radish (Raphanus sativus) crops. Five experimental groups were established, each consisting of five plants. The treatments included: control (no fertilizer), 100% fish fertilizer, 100% humic acid, a mixture (50% fish fertilizer and 50% humic acid), and 100% urea. Yield was assessed by periodic measurements of leaf and stem growth, as well as the size and mass of the harvested radishes. The results showed that fish fertilizer produced the highest yield, with superior values across all evaluated variables: stem diameter (7.52 mm), plant height (101 mm), number of leaves (7), leaf width (55.8 mm), germination time (3.6 days), polar diameter (60.42 mm), and equatorial diameter (45.44 mm) of the radish, as well as average radish mass per plant (62 g), totaling 310 g for the five treated plants. The estimated yield projection was approximately 24.72 tons per hectare. Furthermore, both humic acid and its combination with fish fertilizer outperformed urea in terms of yield. In conclusion, fish fertilizer proved to be the most effective and sustainable alternative for enhancing radish crop productivity.

Clay bricks modified with leather chips were developed to evaluate their acoustic absorption capacity in comparison with conventional bricks. The leather chips were ground and mixed with clay in a proportion of 4 wt.%. Two types of bricks were manufactured: one conventional and the other with the addition of leather chips, both with an approximate mass of 2 kg and dimensions of 14 cm x 22 cm x 7 cm. The bricks were made following the traditional brick manufacturing procedure. To evaluate the acoustic absorption of the bricks, acoustic tests were carried out on structures built with both types of bricks, using a sound level meter for the measurements. Sound intensities ranging between 58 and 75 dB were recorded, with no significant decrease in noise level when leather chips were incorporated into the bricks. The results indicate that there is no difference in the sound absorption capacity of the two types of bricks evaluated. Nevertheless, the use of leather chips in the manufacture of bricks represents an ecologically and economically viable alternative for use in construction.