Juan David Giraldo

Chitosan bioactivity has been widely evaluated in seed germination; however, its effects remain inconsistent. Some studies report biostimulant effects, while others manifest inhibitory effects, and some show no effect on germination. A major factor contributing to this poor reproducibility appears to be the variation in the degree of polymerization (X), the molar fraction of acetylation (f_A), and the chitosan concentration. However, it remains unclear whether controlling these parameters alone is sufficient to ensure consistent bioactivity in conventional polymeric chitosan samples. To elucidate this, maize seeds (Zea mays L. var. Jubilee) were soaked in chitosan solutions (pH 5) at concentrations ranging from 0.25 to 1.00% w/w for 4 h, as per the literature, to evaluate their effect on germination compared to a control (water). Nine chitosan samples were tested, differing in X (5558 to 17,161) and f_A (0.07 to 0.33). After germination, several response factors were measured, including fresh and dry biomass, root number, and root and epicotyl length. The results showed that chitosans with higher X values (9134 to 17,161) inhibit germination, decreasing it by up to a value of 3% ± 6 at 1.00% w/w. Chitosans with a lower X (5694 ± 131) exhibited a reduced inhibitory effect (63% ± 6 to 100%) across all evaluated concentrations. None of the treatments showed biostimulation; instead, chitosan consistently delayed the germination rate compared to the control, confirming an inhibitory effect regardless of the final percentage. Nevertheless, while X and concentration establish the general inhibitory trends, considerable residual variability suggests that these factors alone are insufficient to ensure consistent bioactivity. A Gauge Repeatability and Reproducibility (R&R) analysis provides preliminary evidence suggesting that molecular heterogeneity, specifically dispersity (Ð_X), is a key factor driving the observed inconsistencies and significantly affecting the reproducibility of the results within the scope of this study.

Plant growth-promoting rhizobacteria (PGPR) have significant potential for enhancing soil quality and plant growth; however, their agricultural application is limited by challenges such as immobilization and desiccation vulnerability. Background: This study addressed PGPR solid formulation by applying JetCutter-assisted immobilization technology to PGPR strains isolated from the rhizosphere of hazelnut (Corylus avellana). Methods: Four immobilized PGPR strains were evaluated under controlled greenhouse conditions: Serratia proteamaculans, Pseudomonas mohnii, Pseudomonas baetica, and Bacillus safensis. Their effects on root development, gas exchange parameters, dissolved organic carbon (DOC), and soil enzymatic activities (phosphatase, urease, protease, and β-glucosidase) were assessed. Principal component analysis (PCA) was used to identify the top-performing strain. Results: Treatment with encapsulated bacteria resulted in a 27% increase in DOC compared to controls (p < 0.05), while phosphatase and urease activities increased by 35% and 28%, respectively. Root length and volume improved by 18% and 22%, respectively, with PCA identifying P. baetica as the most effective strain. Conclusions: Immobilized Gram-negative PGPR strains enhanced root development and soil biochemical activity in hazelnuts, whereas B. safensis enhanced photosynthesis but had minimal impact on soil properties. These results highlight functional differences and support the use of PGPR immobilization to promote early plant establishment.

The selective separation of molybdenite from copper sulfide concentrate in flotation process is realized using sodium hydrosulfide (NaHS) to depress the chalcopyrite and permit only the flotation of the molybdenite. However, this reagent is a highly toxic and flammable gas. The objective of this research was to study the feasible application of commercial lignosulfonates (LSs) in the separation by froth flotation process of molybdenite and chalcopyrite in seawater to present a novel application for LSs, as well as an alternative reagent to sodium hydrosulfide (NaHS). To achieve this, microflotation, absorbance tests and zeta potential measures were performed at pH 8 in seawater and 0.01 M NaCl. The results obtained in this study showed that it is possible to achieve selective separation of copper and molybdenum in both aqueous media due to high depressant effect of molybdenite and low depression of chalcopyrite in microflotation tests at 10 ppm of LSs, when the collector, PAX, is added prior to the addition of LSs. Absorbance study and zeta potential measurements showed that LSs adhere more to the molybdenite surface in seawater than in freshwater. This is related to the high ionic charge of the media that influences a greater interaction of LSs with the mineral surface.

Ceramic foams were fabricated without using melting pots through the direct foaming of compacted powder mixtures of commercial quartz (SiO₂) with fluxing agents (Na₂CO₃ and CaO) and a foaming agent (Na₂SiO₃·5H₂O) at a relatively low temperature range (850−870 °C). The effects of the pressing pressure of the powders, the foaming time, foaming temperature, and mixture content were evaluated. The obtained cellular solid materials presented an acceptable volumetric expansion at a pressing pressure of 4 t. The materials only presented porosity at a minimum temperature of 850 °C and at a minimum time of 30 min. All the foamed samples showed an acceptable symmetric expansion and non-appreciable fissures. The study of the mixture content through the statistical software MODDE® shows that the porosity of the samples was principally affected by the Na₂SiO₃ content and the foaming temperature. The samples obtained at the optimum controlling factors proposed by this statistical software presented an apparent density, porosity, and mechanical strength of 1.09 ± 0.03 g/cm³, 56.01% ± 1.12%, and 3.90 ± 0.16 MPa, respectively. Glass and ceramics foams such as those obtained in this work become attractive as insulation materials in applications where high temperatures occur due to their higher melting points.