Chitosan-Cement Composite Mortars: Exploring Interactions, Structural Evolution, Environmental Footprint and Mechanical Performance.

The increasing environmental concerns about synthetic polymers as reinforcement in the construction industry have highlighted the need for eco-friendly, biodegradable fibers as potential alternative materials for cementitious composites. This study examines the influence of chitosan particle concentrations on the midterm compressive strength of mortars. Chitosan particles, derived from shrimp shells, were mixed with high early strength hydraulic cement at various percentages (0, 0.05, 0.25, 0.5, 1, and 2 wt %) and silica sand to prepare the mortar samples. The findings indicate that chitosan affects the hydration process through the distribution of chitosan particles within the mortar matrix and slightly improved midterm mechanical properties. A life cycle assessment (LCA) revealed a slight increase in greenhouse gas emissions and embodied energy for chitosan-modified mortars, likely due to the use of chemicals in the chitosan synthesis and purification process. In fact, the addition of 0.25 wt % of chitosan into the mortar only added 1.3% of the global warming potential of the sample when compared to the control sample. Incorporating chitosan into a mortar matrix does not significantly affect the resistance-mechanical properties of the composite. The hydration of the cement mortar appears to be slowed by the inclusion of chitosan particles in the cementitious matrix. This research lays the groundwork as one of the first studies for the development of high-performance, early strength cement using chitosan, contributing to a more sustainable construction industry.

Preparation, characterization, electrical conductivity, and life cycle assessment of carbon nanofibers-reinforced Ecuadorian natural zeolite-based geopolymer composites.

Geopolymers are inorganic crosslinked polymers with much less carbon footprint than ordinary Portland cement. Geopolymers and geopolymer-based materials have superior mechanical and durability properties with extreme thermal and chemical resistance. Carbon nano- or microfibers-reinforced geopolymers show potential properties such as electric conductivity, enhanced mechanical and thermal stability, and multi-functionality. This study evaluated the effect of incorporating carbon nanofibers in natural zeolite-based geopolymers and their impact on the mechanical, thermal, and electric conductivity of yielded geopolymer composites. Additionally, a life cycle assessment for 1 m3 geopolymer and its carbon fiber reinforced geopolymers' production has been conducted to evaluate the environmental impact of the processes.

Preparation, characterization, and life cycle assessment of banana rachis-recycled high-density polyethylene composites.

Agro-industrial wastes are sustainable resources that have advantages as a reinforcement for polymeric matrices. This study examined the use of banana rachis fiber (BRF) in reinforcing the recycled high-density polyethylene (rHDPE) matrix. For this purpose, polymer composites with 5-20 wt% of BRF were prepared by the extrusion process using a twin-screw extruder and followed a hot press method. The structure of rHDPE/BRF composites and their characteristic peaks of degradation were successfully identified by the Fourier-transformed infrared spectroscopy and thermogravimetric analysis techniques, respectively, revealing a good dispersion of BRF in rHDPE. Differential scanning calorimetry results of the composites demonstrated that melt enthalpy decreases as the amount of BRF increases. XRD diffractograms revealed a crystallinity reduction of rHDPE due to the increase of fiber within the polymer matrix, which is reflected in the characteristic peaks' intensity decrease of HDPE. Variation in thermal and chemical properties with the addition of BRF in rHDPE was successfully evaluated in this study. Life cycle assessment for 1 kg composite production has also been evaluated. The banana rachis-rHDPE composite materials reduce the overall environmental impacts when the filler concentration increases.

Dealumination and Characterization of Natural Mordenite-Rich Tuffs.

The present study evaluates the feasibility of partially dealuminated natural mordenite as a catalyst support by studying improvement in its textural properties. This is the first study that reports the dealumination of natural zeolite-based tuffs from Ecuador. For this purpose, mordenite-rich tuffs were obtained from deposits close to Guayaquil, Ecuador. The raw material was micronized in order to increase its surface, and treated with NH4Cl. NH4+ cation-exchanged samples were finally reacted with HCl(aq) to complete the dealumination process. The partially dealuminated samples were characterized using techniques such as XRD, FT-IR, SEM-EDS, and identification of their textural properties. Dealumination with HCl(aq) increased the Si/Al ratio up to 9 and kept the crystallographic structure of natural mordenite, as XRD results showed that the structure of mordenite was not altered after the dealumination process. On the other hand, textural properties such as surface area and microporosity were improved as compared to natural mordenite. In view of these results, the feasibility of using natural mordenite as a catalyst support is discussed in this study.

The use of zeolite-based geopolymers as adsorbent for copper removal from aqueous media.

Copper has been proven to have hazardous effects on human beings depending on its concentration levels. Recently, there has been a growing interest in developing geopolymers using local industrial minerals and by-products. However, research on the adsorption of heavy metals by geopolymer based on mordenite-rich tuffs is still limited. The geopolymer adsorbents have been synthesized using natural Ecuadorian zeolite-rich tuffs containing quartz, mordenite calcite and amorphous content with 20.8%, 28.5%, 4.2% and 46.4%, respectively. The geopolymers showed a maximum compressive strength of 26.86 MPa for 28 d of curing time. In the present study, an Ecuadorian zeolite-based geopolymer's removal capacity on copper ions in aqueous solutions, varying concentration and contact time were tested. Kinetic models were developed using pseudo first-order, pseudo second-order and the Elovich model. The adsorption data, using Cu2+ concentrations from 20 to 160 ppm, at 25°C were described by the Langmuir and Freundlich isotherms. Linear coefficient of determination (R 2) results show that the Langmuir model fits the best. The attained adsorption capacity of 52.63 mg g-1 demonstrates the low-cost geopolymer's effectiveness for this study and its competitiveness compared with other studies. Adsorption kinetics follows the pseudo second-order kinetics model at the lower initial concentration of Cu2+.

Effects of Recycled Rubber Particles Incorporated as Partial Sand Replacement on Fresh and Hardened Properties of Cement-Based Concrete: Mechanical, Microstructural and Life Cycle Analyses.

Cement is one of the most valuable materials in today's society, as it is used in most construction developments known to mankind. However, the energy intensive process and significant environmental impacts related to the production of Ordinary Portland Cement have shown the importance of searching for more sustainable materials. Concrete uses different aggregates added to the cement binder to lower, not only cost, but other factors like environmental burden, while maintaining good mechanical properties. This study analyzes the properties of fresh and hardened concrete incorporating recycled rubber to replace fine aggregate. Locally sourced 2 mm diameter rubber was incorporated in a regular strength concrete matrix into three different replacement levels, i.e., 3%, 5%, and 10%. Compression, tensile, flexural, and modulus of elasticity of hardened concrete were carried out in specimens aged 7, 14, and 28 days. In addition, non-destructive ultrasonic pulse velocity and rebound number tests were only performed on specimens aged 28 days. Once the tests were carried out, the fresh and hardened concrete properties were obtained. Similarly, the compressive and flexural strengths had the exact relationship between the values obtained. On the other hand, the modulus of elasticity tends to decrease due to the presence of the rubber. Consequently, it is recommended not to develop mix designs with more than 5% rubber because it is not meaningfully affected. The fine aggregate can be partially replaced by the rubber, keeping almost the same performance compared with sand-only counterparts. In addition, the life cycle assessment showed a reduction of up to 40% in the global warming potential. In fact, the 15% recycled rubber concrete mix has a climate change indicator of approximately 245 kg of CO2 eq.

Preparation, characterization, and evaluation of compressive strength of polypropylene fiber reinforced geopolymer mortars.

The study of the fiber-matrix interface represents a crucial topic to determine the mechanical performance of geopolymer-based materials reinforced with polypropylene fibers (PPF). This research proposes the use of natural zeolite in the preparation geopolymers mortars through alkaline activation with NaOH, Ca(OH)2 and Na2SiO3, and with river sand as a fine aggregate. PPF were incorporated into the geopolymer-based mortar matrix in different proportions like 0, 0.5, and 1 wt.%. The mortars were cured for 24 h at 60 °C and then aged for six days more at room temperature. All samples analyzed through compressive strength were also characterized by X-ray diffraction, thermal analysis, Infrared Spectroscopy, and scanning electron microscopy techniques. The results indicated that the best mix design among the ones used: NaOH (10 M), Na2SiO3/NaOH = 3, Ca(OH)2 = 1.5 wt.% and PPF = 0.5 wt.%. The optimum mix design showed a compressive strength of 4.63 MPa on average. Besides, the fibers enhanced the compressive strength of those samples which the PP fibers probably have better dispersion inside the matrix of the geopolymer mortar.

γ-Tubulin small complex formation is essential for early zebrafish embryogenesis.

The centrosomal protein γ-tubulin is part of the cytoplasmic γ-tubulin small (γ-TuSCs) and large complexes (γ-TuRCs). Both, molecular and cellular evidence indicate that γ-tubulin plays a central role in microtubule nucleation and mitotic spindle formation. However, the molecular mechanisms of complex formation and subsequent biological roles in animal development remain unclear. Here, we used γ-tubulin gene knockdown in the zebrafish early embryo model to gain insights into its activity and cellular contribution during vertebrate embryogenesis. γ-Tubulin loss-of-function impaired γ-TuSC formation, impacting the microtubule nucleation rate in vitro. Moreover, decreased γ-tubulin synthesis caused dramatic defects in nuclear dynamics and cell cycle progression, leading to developmental arrest at the mid-gastrula stage. At the subcellular level, microtubule organization and function were altered, affecting chromosome segregation and triggering cell proliferation arrest and apoptosis. Our results suggest that de novo translated γ-tubulin participates in γ-TuSC formation required for early animal development. Importantly, formation of this complex is essential for both centrosome assembly and function, and cell proliferation. Thus, γ-TuSC integrity appears to be critical for cell cycle progression, and concomitantly, for coordinating the many distinct activities carried out by the early embryo. Our findings identify a novel role for γ-TuSC in the regulation of early vertebrate embryogenesis, providing molecular and biochemical starting points for future in depth studies of γ-tubulin functionality and its specific role in development.

Citrate-Coated Silver Nanoparticles Interactions with Effluent Organic Matter: Influence of Capping Agent and Solution Conditions.

Fate and transport studies of silver nanoparticles (AgNPs) discharged from urban wastewaters containing effluent organic matter (EfOM) into natural waters represent a key knowledge gap. In this study, EfOM interfacial interactions with AgNPs, and their aggregation kinetics were investigated by atomic force microscopy (AFM) and time-resolved dynamic light scattering (TR-DLS), respectively. Two well-characterized EfOM isolates, i.e., wastewater humic (WW humic) and wastewater colloids (WW colloids, a complex mixture of polysaccharides-proteins-lipids), and a River humic isolate of different characteristics were selected. Citrate-coated AgNPs were selected as representative capped-AgNPs. Citrate-coated AgNPs showed a considerable stability in Na(+) solutions. However, Ca(2+) ions induced aggregation by cation bridging between carboxyl groups on citrate. Although the presence of River humic increased the stability of citrate-coated AgNPs in Na(+) solutions due to electrosteric effects, they aggregated in WW humic-containing solutions, indicating the importance of humics characteristics during interactions. Ca(2+) ions increased citrate-coated AgNPs aggregation rates in both humic solutions, suggesting cation bridging between carboxyl groups on their structures as a dominant interacting mechanism. Aggregation of citrate-coated AgNPs in WW colloids solutions was significantly faster than those in both humic solutions. Control experiments in urea solution indicated hydrogen bonding as the main interacting mechanism. During AFM experiments, citrate-coated AgNPs showed higher adhesion to WW humic than to River humic, evidencing a consistency between TR-DLS and AFM results. Ca(2+) ions increased citrate-coated AgNPs adhesion to both humic isolates. Interestingly, strong WW colloids interactions with citrate caused AFM probe contamination (nanoparticles adsorption) even at low Na(+) concentrations, indicating the impact of hydrogen bonding on adhesion. These results suggest the importance of solution conditions and capping agents on the stability of AgNPs in solution. However, the characteristics of organics would play a crucial role in the fate and transport of these nano contaminants in urban wastewaters and natural water systems.

Synthesis, characterization and experimental, theoretical, electrochemical, antioxidant and antibacterial study of a new Schiff base and its complexes.

A new Schiff base ligand was synthesized by reaction of salicylaldehyde with 1,6-bis(4-chloro-2-aminophenoxy)hexane. Then the Schiff base complexes were synthesized by metal salts and the Schiff base. The metal to ligand ratio of metal complexes was found to be 1:1. The Cu(II) complex is proposed to be square planar and the Co(II), Ni(II), Mn(II) and Zn(II) complexes are proposed to be tetrahedral geometry. The Ti(III) and V(III) complexes are proposed to be a capped octahedron in which a seventh ligand has been added to triangular face. The complexes are non-electrolytes as shown by their molar conductivities (ΛM). The structure of metal complexes is proposed from elemental analysis, FT-IR, UV-vis, magnetic susceptibility measurements, molar conductivity measurements, Mass Spectra and thermal gravimetric analysis. In addition antimicrobial and antioxidant studies, cyclic voltammetry of the complexes, theoretical 1H NMR and HOMO-LUMO energy calculations of the new di-functional ligand were done.