Search Results (7)

The oxygen evolution reaction (OER), a key half-reaction in electrochemical water splitting, is limited by sluggish multi-electron transfer kinetics, starting extensive research into efficient, low-cost nanoscale electrocatalysts, particularly those based on nickel, cobalt, and iron, as well as mixed-metal, hybrid, and heteroatom-doped carbon-based metal-free systems, as presented here. Ni- and Co-based electrocatalysts show high efficiency for alkaline OER due to optimized nanostructures, surface modifications, heterostructure design, and multi-metal doping, which enhance activity, stability, and electronic properties. Their performance relies on precise atomic-level control of structure and synergistic interactions, enabling them to approach or rival noble-metal catalysts. Iron-based electrocatalysts are also promising due to their abundance, low cost, and flexible redox chemistry, forming active iron oxyhydroxide species during operation; however, their low conductivity requires structural and electronic optimization. Beyond Fe, Ni, and Co, copper-based compounds, zeolitic imidazolate framework-derived structures, and manganese phosphide–cerium oxide composites offer enhanced oxygen vacancies, tunable structures, and strong interfacial synergy. Furthermore, heteroatom-doped carbon materials incorporating nitrogen, phosphorus, or sulfur improve catalytic activity by modifying electronic structure, creating active sites, and enhancing charge transfer. Overall, careful control of composition, structure, and electronic properties enables the development of efficient, durable, and scalable noble-metal-free catalysts for OER. Full article

In this study, we assessed soil pollutants and surveyed the bacterial communities using 16S rRNA sequencing to better understand how to improve rehabilitation strategies for nickel-laterite mines in the Philippines. Representative soil samples and rhizospheres from Saccharum spontaneum L. in three post-mining sites rehabilitated in 2015, 2017, and 2019 were collected and analyzed. X-ray diffraction (XRD) identified iron oxyhydroxides, silicates, and clays as major soil components. Based on the pollution load index and contamination degree, the 2015A and 2015B sites were classified as “pristine” and had a “low degree of pollution”, while the remaining sites (2017A, 2017B, 2019A, and 2019B) were considered “moderately contaminated” with nickel, chromium, cobalt, lead, zinc, and copper. An analysis of the bacterial community composition revealed that the phyla Proteobacteria and Actinobacteria, along with the genus Ralstonia, were the most abundant groups across both control and rehabilitated sites. Our results showed that the soil pH and organic matter contents were strongly linked to specific bacterial community composition. These taxa have potential for inoculation in nickel-laterite soils to promote the growth of hyperaccumulator plants. Our results also showed a significant correlation between the structure of the bacterial communities and nickel, chromium, and manganese soil contents, but not with rehabilitation time. Furthermore, we identified the genera Diaphorobacter as potential bioindicators because they are sensitive to nickel and chromium. This study provides valuable baseline data on heavy metal pollution and microbial diversity in a rehabilitated Ni-laterite mine site. Full article

The conversion of carbon dioxide, a greenhouse gas, into valuable chemicals using sunlight is highly significant technologically and holds the promise of providing a more sustainable alternative to fossil fuels. To effectively utilize the abundant solar irradiation, it is essential to develop catalysts that can absorb a significant portion of the solar spectrum, particularly in the UV, visible, and infrared regions. Silicon nanowire arrays grown on silicon substrates meet this criterion, as they can absorb over 85% of solar irradiation and show minimal reflective losses across the UV, visible, and infrared portions of the solar spectrum. Herein, we report the deposition of various catalysts, including iron oxyhydroxides, copper, nickel, and ruthenium, on silicon nanowires using different catalyst deposition techniques. The photocatalytic reduction of carbon dioxide was evaluated using these catalysts. The results show that silicon nanowires coated with nickel and ruthenium oxide had the highest activity towards the photocatalytic reduction of carbon dioxide, with photomethanation rates reaching 546 μmolg_cat⁻¹h⁻¹ for RuO₂@SiNWs and 278 μmolg_cat⁻¹h⁻¹ for Ni/NiO@SiNWs. Continued improvement of photocatalysts using nanostructured silicon supports could enable the development of solar refineries for converting gas-phase CO₂ into value-added chemicals and fuels. Full article

Electrochemical oxidation of ammonia is an attractive process for wastewater treatment, hydrogen production, and ammonia fuel cells. However, the sluggish kinetics of the anode reaction has limited its applications, leading to a high demand for novel electrocatalysts. Herein, the electrode with the in situ growth of NiCu(OH)₂ was partially transformed into the NiCuOOH phase by a pre-treatment using highly oxidative solutions. As revealed by SEM, XPS, and electrochemical analysis, such a strategy maintained the 3D structure, while inducing more active sites before the in situ generation of oxyhydroxide sites during the electrochemical reaction. The optimized NiCuOOH-1 sample exhibited the current density of 6.06 mA cm⁻² at 0.5 V, which is 1.67 times higher than that of NiCu(OH)₂ (3.63 mA cm⁻²). Moreover, the sample with a higher crystalline degree of the NiCuOOH phase exhibited lower performance, demonstrating the importance of a moderate treatment condition. In addition, the NiCuOOH-1 sample presented low selectivity (<20%) towards NO₂⁻ and stable activity during the long-term operation. The findings of this study would provide valuable insights into the development of transition metal electrocatalysts for ammonia oxidation. Full article

Children spend most of their time in playgrounds and, in parallel, constitute the social group most sensitive to contaminants. Here, we present the results of a comparative study of heavy-metal contents between soils and sand from sandboxes obtained from playgrounds of Çanakkale city. Average contents of soils followed the order of iron (Fe) (12,901 mg kg⁻¹) > manganese (Mn) (475 mg kg⁻¹) > zinc (Zn) (58 mg kg⁻¹) > copper (Cu) (28 mg kg⁻¹) > nickel (Ni), chromium (Cr) (21 mg kg⁻¹) > lead (Pb) (18 mg kg⁻¹). Sand had lower contents, however, due to the reduction of particles size through prolonged use, and accumulation of Fe/Mn (oxyhydr)oxides on sand grains tended to diminish the differences between soils and sand. Through chemometric analysis, Cr and Ni were found to have a lithogenic origin, while the rest of metals were related to anthropogenic activities. Spatially, heavy-metal contents followed the pattern of the city’s sprawl. Risk estimates on children’s health showed that ingestion was the most important exposure route, followed by dermal contact and inhalation. Exposure of children to sand was of similar importance to that of soils. These findings are significant, as the contamination of sand has not yet received much attention compared to the soil of playgrounds. Full article

The main objectives of the present study were to (i) investigate the effects of mineralogy and solid-phase distribution on element bioaccessibility and (ii) perform a risk assessment to calculate the risks to human health via the ingestion pathway. Multiple discriminant analysis showed that the dust chemistry discriminates between indoor and outdoor samples. The solid-phase distribution of the elements in indoor dust indicated that a large proportion of zinc, nickel, lead, copper, and cobalt is associated with an aluminum oxy-hydroxides component, formed by the weathering of aluminum silicates. This component, which seems to influence the mobility of many trace elements, was identified for a group of indoor dust samples that probably had a considerable contribution from outdoor dust. An iron oxide component consisted of the highest percentage of chromium, arsenic, antimony, and tin, indicating low mobility for these elements. The bioaccessible fraction in the stomach phase from the unified BARGE method was generally high in zinc, cadmium, and lead and low in nickel, cobalt, copper, chromium, and antimony. Unlike other potentially toxic elements, copper and nickel associated with aluminum oxy-hydroxides and calcium carbonates were not extracted by the stomach solutions. These trace elements possibly form stable complexes with gastric fluid constituents such as pepsin and amino acid. Lead had a hazard quotient >1, which indicates the risk of non-carcinogenic health effects, especially for children. Full article

Coastal restoration through diversion of suspended sediments from the Lower Mississippi River (LMR) into hydrologically isolated marshlands of Mid-Barataria Bay and Mid-Breton Sounds in southern Louisiana has the potential to mobilize lead (Pb), and other trace elements. We investigate the potential impact(s) of the diversion on marsh porewater through analysis of modern riverbank and suspended sediments, compared to sediments from pre-industrial deltaic deposits of LMR. Sequential extraction methods were used to evaluate Pb, cobalt (Co), copper (Cu), nickel (Ni), and zinc (Zn) in the sediments. Our results show that metal contents are higher (e.g., 8- to 10-fold for Pb) in the modern sediments relative to pre-industrial deposits. Also, the reducible fraction, presumably iron/manganese (Fe/Mn) oxides/oxyhydroxides, is the chief reservoir of environmentally available metals. The substantially higher trace metal contents of the modern relative to pre-industrial sediments suggest that the modern sediments contain a sizeable amount of anthropogenic contributions. Furthermore, the concentration of the trace metals in the reducible fraction suggests bioavailability to marsh organisms upon reductive dissolution within the planned, constructed coastal marshes. Still, additional sediment samples from the marshlands during the diversion implementation phase will be necessary to support the preliminary findings in this contribution as it affects coastal marshes and vital local fisheries. Full article