Beatriz Escobar

Developing sustainable and low-cost electrocatalysts is important to reduce platinum dependence in alkaline fuel cells and support green hydrogen technologies. In this work, nickel nanoparticles (NiNPs) were synthesized through a green route using aqueous extracts of Sargassum spp. as reducing and stabilizing agents. The residual biomass was subsequently converted into activated biochar (BC) by KOH activation and pyrolysis at 700 °C, yielding a porous carbon support with a BET surface area of 1935 m² g⁻¹. Ni/BC electrocatalysts with nominal nickel loadings of 3, 5, 10, and 20 wt% were prepared and denoted BC–Ni3, BC–Ni5, BC–Ni10, and BC–Ni20. Physicochemical characterization confirmed the formation of Ni-based nanoparticles, graphitic carbon domains, and surface oxygen/nitrogen functionalities. Electrochemical evaluation in 0.1 M KOH showed that ORR performance depended on Ni loading. Among the Ni-based catalysts, BC–Ni20 delivered the highest current density (1.64 mA cm⁻² at 0.2 V vs. RHE), the most positive half-wave potential (0.67 V vs. RHE), and good durability after 5000 accelerated degradation cycles, with limited losses in onset and half-wave potentials. Although 10% Pt/Vulcan exhibited higher overall activity, the results demonstrate that Sargassum-derived Ni/biochar materials are promising platinum-group-metal-free electrocatalysts, offering a feasible route for biomass valorization and sustainable energy conversion.

Growing concern about the environmental impact associated with conventional chemical methods has driven the development of more sustainable synthesis routes in nanotechnology. In this context, the green synthesis of silver and copper-based materials was investigated using Rhodophyta biomass in an aqueous medium. The process involved the extraction of secondary metabolites, followed by reactions with silver nitrate and copper (II) chloride dihydrate under controlled conditions. The resulting materials were characterization by UV-Vis spectroscopy, FTIR, XRD, SEM and phytochemical screening. The results demonstrate that the aqueous extract of Rhodophyta represents a promising alternative for the green synthesis of silver- and copper-based materials by promoting the formation of metallic and oxidized phases through an environmentally benign route, with potential for future catalytic and technological applications.

The escalating atmospheric CO ₂ concentration has emerged as a critical environmental problem, significantly contributing to global warming and climate change. Addressing this issue, this study explores the electrochemical reduction reaction of CO ₂ (CO ₂ RR) utilizing green‐synthesized silver nanoparticles (AgNPs) supported onto biocarbon derived from Sargassum spp. AgNPs were synthesized via a green approach using AgNO ₃ at varying concentrations and characterized using UV–vis spectroscopy, FTIR, XRD, Raman spectroscopy, and TEM. The data validated the synthesis of AgNPs with a predominantly spherical morphology and an average size of approximately 20 nm, characterized by a surface plasmon resonance (SPR) band within the 390–450 nm range in the UV–vis spectrum. FTIR analysis revealed the presence of various functional groups in the Sargassum extract, which are likely involved in the reduction and stabilization processes during nanoparticle synthesis. Subsequently, electrocatalysts were prepared by integrating AgNPs into the biocarbon matrix and evaluated for CO ₂ RR activity via cyclic voltammetry (CV) in 0.1 M KHCO ₃ under both CO ₂ ‐saturated and CO ₂ ‐free conditions. The CV analysis established an electrochemical window between −1.8 and 0.05 V vs. saturated calomel electrode (SCE), within which CO ₂ reduction occurred. These findings demonstrate that the synthesized AgNP‐supported biocarbon exhibits promising characteristics for CO ₂ electroreduction applications.

This study reports the design of N- and S-doped ordered mesoporous carbon hollow spheres (OMCHS) as metal-free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media. Three electrocatalysts were synthesized using molecular precursors: (i) 2-thiophenemethanol (S-OMCHS), (ii) 2-pyridinecarboxaldehyde/2-thiophenemethanol (N1-S-OMCHS), and (iii) pyrrole/2-thiophenemethanol (N2-S-OMCHS). Among them, S-OMCHS exhibited the best activity (E_onset = 0.88 V, E_½ = 0.81 V, n ≈ 3.95), surpassing both co-doped analogs. After conducting an accelerated degradation test (ADT), S-OMCHS and N1-S-OMCHS showed improved catalytic behavior and outstanding long-term stability. Surface analysis confirmed that performance evolution correlates with heteroatom reorganization: S-OMCHS retained and regenerated thiophene-S and C=O/quinone species, while N1-S-OMCHS converted N-quaternary into N-pyridinic/pyrrolic, both enhancing O₂ adsorption and *OOH reduction through synergistic spin–charge coupling. Conversely, oxidation of N and loss of thiophene-S in N2-S-OMCHS led to partial deactivation. These results establish a direct link between surface chemistry evolution and electrocatalytic durability, demonstrating that controlled heteroatom doping stabilizes active sites and sustains the four-electron ORR pathway. The approach provides a rational design framework for next-generation, metal-free carbon electrocatalysts in alkaline fuel cells and energy conversion technologies.

Extraction processes of alginates from Sargassum spp. generate a substantial number of solid residues that are commonly discarded. This study explores the sustainable transformation of these residues into nitrogen-doped biocarbon through chemical activation with KOH and nitrogen doping using urea. XRD, FTIR, SEM-EDX, Raman spectroscopy, BET surface area analysis, XPS, and CHNS elemental analysis were used to characterize the materials. The doped and activated biocarbon (BDA) demonstrated excellent physicochemical properties, including a specific surface area of 1790 m² g⁻¹ and a mesoporous structure. Electrochemical evaluation in alkaline media revealed a current density of −4.37 mA cm⁻², an onset potential of 0.922 E vs. RHE, and a half-wave potential of 0.775 E vs. RHE. Koutecky–Levich analysis indicated a two-electron reduction pathway. The superior performance was attributed to the synergistic effects of high surface area, nitrogen functionalities (pyridinic-N and pyrrolic-N), and enhanced accessibility of active sites. These results highlight the potential of waste-derived, nitrogen-doped biocarbon as a sustainable and low-cost alternative for ORR electrocatalysis in alkaline fuel cells.

This experiment aims to study the potential use of biochar derived from Sargassum spp. as an innovative ingredient in homemade soap, focusing on its antibacterial activity. The pyrolysis process was conducted at 700 °C with a heating rate of 10 °C min^-1 for 2 h under a nitrogen atmosphere with KOH chemical activation. The physicochemical properties of the biochar were investigated using XRD, FTIR, Raman, BET surface analysis, and SEM. Highly porous biochar was successfully synthesised, achieving a large specific surface area of 1600 m² g^-1 and a well-developed microporous structure distributed across the surface of the biochar. Klebsiella pneumoniae, Staphylococcus aureus, and Salmonella choleraesuis were used as model pathogens to evaluate the antibacterial activity of biochar-enriched homemade soap using Müeller-Hinton Agar and the Kirby-Bauer test. The antibacterial evaluations demonstrated that the incorporation of biochar into homemade soap partially inhibited the growth of these model pathogens bacteria.

A sewage sludge-derived biocarbon (SSB) was produced using biomass from a water treatment plant in Saltillo, Mexico. Its specific surface area was 412.0 m² g⁻¹, with an average pore diameter of 4.4 nm. Evaluation in an SSB||SSB symmetrical supercapacitor showed a high performance in several electrolytes (6 M KOH, 0.5 M Na₂SO₄, and 1 M NaClO₄). The supercapacitor in KOH exhibited the highest specific capacitance (C_sp) of 144.80 F g⁻¹ at 1 mV s⁻¹. Nevertheless, the widest operating voltage window of 2.5 V was attained in NaClO₄. This enhanced behavior led to achieving energy density (E_D) and power density (P_D) values of 22.52 Wh kg⁻¹ and 508.0 W kg⁻¹, respectively, in the organic electrolyte. Moreover, rotating ring-disc electrode tests in 0.1 M KOH showed that SSB catalyzes the oxygen reduction reaction, with a low percentage of perhydroxyl ion produced ( % H O 2 − ) of 7.41% and a high electron transfer number (n) of 3.85 before an accelerated degradation test of 3000 cycles, sustaining a high stability after the cycling. This study provided evidence that high-performance active catalytic materials for symmetric supercapacitors and cathodes for anion exchange membrane fuel cells can be produced from Earth-abundant sewage sludge biomass.

This research focuses on the synthesis and characterization of advanced materials for hydrogen storage. Two biocarbon samples were synthesized from Sargassum spp. The first was activated with KOH (SKPT) and the second was doped with sulfur (SSKTP); both were obtained through pyrolysis at 900 °C. The sulfur-doped biocarbon (SSKTP), with its high specific surface area (2377 m² g^ࢤ1), exhibited enhanced electrocatalytic properties, making it an efficient candidate for hydrogen storage applications. Various characterization techniques were employed to study the relationship between physicochemical properties and hydrogen uptake. The presence of micropores and sulfur doping significantly improved hydrogen uptake at 45 °C and 50 bar, where SSKTP achieved 0.40 wt%. In comparison, the non-doped biocarbon (SKPT) showed a lower hydrogen storage capacity of 0.33 wt%, with a specific surface area of 1620 m² g^ࢤ1. The results highlight the potential of sulfur-doped activated biocarbon as a functional material in energy conversion systems, specifically for electrocatalytic hydrogen storage processes. This study demonstrates a sustainable approach to utilizing biomass waste for advanced electrocatalysts, contributing to renewable energy solutions.

Las actividades agrícolas generan grandes cantidades de residuos y dependiendo de su composición química es el nivel de impacto que pueden provocar, por ejemplo, los residuos orgánicos contribuyen a la generación de gases contaminante. Hablando específicamente de la cascarilla de arroz, presenta una limitante la cual es su elevado contenido de sílice, sin embargo, a su vez es un área de oportunidad para ser aprovechada. El objetivo del presente trabajo es demostrar las distintas aplicaciones que tiene la cascarilla de arroz para su aprovechamiento. Debido a su composición química, la cascarilla de arroz puede someterse a diferentes procesos, uno de ellos es la carbonización hidrotérmica. Mediante este proceso se produce hidrochar, agua de proceso y gas de síntesis, estos productos tienen distintas aplicaciones, de las cuales, una de ellas es su uso como bioenergéticos. Un parámetro que evaluar entre los productos de la carbonización es el poder calorífico. El poder calorífico que contiene el hidrochar es superior al del agua de proceso. De esta manera, un residuo puede tener una aplicación sostenible y adquiere un valor agregado junto con un beneficio ambiental, debido a que se aprovecha un residuo y a su vez, se sustituyen combustibles provenientes de productos fósiles.

This study presents a green method of producing copper nanoparticles (CuNPs) using aqueous extracts from Sargassum spp. as reducing, stabilizing, and capping agents. The CuNPs created using this algae‐based method are not hazardous, they are eco‐friendly, and less toxic than their chemically synthesized counterparts. The XRD characterization of the CuNPs revealed the presence of Cu and CuO, with a crystallite size ranging from 13 to 17 nm. Following this, the CuNPs were supported onto a carbon substrate, also derived from Sargassum spp. (biochar CSKPH). The CuNPs in biochar (CuNPs‐CSKPH) did not appear in the XRD diffractograms, but the SEM‐EDS results showed that they accounted for 36 % of the copper weight. The voltamperometric study of CuNps‐CSKPH in acid media validated the presence of Cu and the amount was determined to be 2.58 μg. The catalytic activity of CuNPs‐CSKPH was analyzed for the electrochemical reduction of CO₂. The use of Sargassum spp. has great potential to tackle two environmental problems simultaneously, by using it as raw material for the synthesis of activated biochar as support, as well as the synthesis of CuNPs, and secondly, by using it as a sustainable material for the electrochemical conversion of CO₂.