Control of crystallite and particle size in the synthesis of layered double hydroxides: Macromolecular insights and a complementary modeling tool

Ageing influences the toxicity of two innovative nanofertilizers to the soil invertebrates Enchytraeus crypticus and Folsomia candida

The increasing global food demand is threatening the sustainability of agrifood production systems. The intensification of agricultural practices, with inadequate use of pesticides and fertilizers, poses major challenges to the good functioning of agroecosystems and drastically degrades the soil quality. Nanotechnology is expected to optimize the current farming practices and mitigate some associated impacts. Layered double hydroxides (LDHs) are a class of nanomaterials with high potential for use in agricultural productions, mostly due to their sustained release of nutrients. Considering its novelty and lack of studies on the terrestrial ecosystem, it is essential to assess potential long-term harmful consequences to non-target organisms. Our study aimed to evaluate the effect of Zn-Al-NO3 LDH and Mg-Al-NO3 LDH ageing on the survival and reproduction of two soil invertebrate species Enchytraeus crypticus and Folsomia candida. We postulated that the toxicity of nanomaterials to soil invertebrates would change with time, such that the ageing of soil amendments would mediate their impacts on both species. Our results showed that the toxicity of LDHs was species-dependent, with Zn-Al-NO3 LDH being more toxic to E. crypticus, while Mg-Al-NO3 LDH affected more F. candida, especially in the last ageing period, where reproduction was the most sensitive biological parameter. The toxicity of both nanomaterials increased with ageing time, as shown by the decrease of the EC50 values over time. The influence of LDH dissolution and availability of Zn and Mg in the soil pore water was the main factor related to the toxicity, although we cannot rule out the influence of other structural constituents of LDHs (e.g., nitrates and aluminium). This study supports the importance of incorporating ageing in the ecotoxicity testing of nanomaterials, considering their slow release, as effects on soil organisms can change and lead to more severe impacts on the ecosystem functioning.

Advanced High-Energy All-Solid-State Hybrid Supercapacitor with Nickel-Cobalt-Layered Double Hydroxide Nanoflowers Supported on Jute Stick-Derived Activated Carbon Nanosheets

Developing efficient, lightweight, and durable all-solid-state supercapacitors is crucial for future energy storage systems. The study focuses on optimizing electrode materials to achieve high capacitance and stability. This study introduces a novel two-step pyrolysis process to synthesize activated carbon nanosheets from jute sticks (JAC), resulting in an optimized JAC-2 material with a high yield (≈24%) and specific surface area (≈2600 m2 g-1). Furthermore, an innovative in situ synthesis approach is employed to synthesize hybrid nanocomposites (NiCoLDH-1@JAC-2) by integrating JAC nanosheets with nickel-cobalt-layered double hydroxide nanoflowers (NiCoLDH). These nanocomposites serve as positive electrode materials and JAC-2 as the negative electrode material in all-solid-state asymmetric hybrid supercapacitors (HSCs), exhibiting remarkable performance metrics. The HSCs achieve a specific capacitance of 750 F g-1, a specific capacity of 209 mAh g-1 (at 0.5 A g-1), and an energy density of 100 Wh kg-1 (at 250 W kg-1) using PVA/KOH solid electrolyte, while maintaining outstanding cyclic stability. Importantly, a density functional theory framework is utilized to validate the experimental findings, underscoring the potential of this novel approach for enhancing HSC performance and enabling the large-scale production of transition metal-based layered double hydroxides.

Harmonizing nanomaterial exposure methodologies in ecotoxicology: the effects of two innovative nanoclays in the freshwater microalgae Raphidocelis subcapitata

Layered double hydroxides (LDHs) are innovative nanomaterials (NMs) with a typical nanoclay structure (height <40 nm) consisting of layers of metallic cations and hydroxides stabilized by anions and water molecules. Upon specific triggers, anions can exchange by others in the surrounding environment. Due to this stimuli-responsive behavior, LDHs are used as carriers of active ingredients in the industrial or pharmaceutical sectors. Available technical guidelines to evaluate the ecotoxicity of conventional substances do not account for the specificities of NMs, leading to inaccuracies and uncertainty. The present study aimed to assess two different exposure methodologies (serial dilutions of the stock dispersion vs. direct addition of NM powder to each concentration) on the ecotoxicological profile of different powder grain sizes of Zn-Al LDH-NO3 and Cu-Al LDH-NO3 (bulk, <25, 25-63, 63-125, 125-250, and >250 µm) in the growth of the freshwater microalgae Raphidocelis subcapitata. Results revealed that the serial dilutions methodology was preferable for Zn-Al LDH-NO3, whereas for Cu-Al LDH-NO3 both methodologies were suitable. Thus, the serial dilutions methodology was selected to assess the ecotoxicity of different grain sizes for both LDHs. All Zn-Al LDH-NO3 grain sizes yielded similar toxicity, while Cu-Al LDH-NO3 powders with smaller grain sizes caused a higher effect on microalgae growth; thus, grain size separation might be advantageous for future applications of Cu-Al LDH-NO3s. Considering the differences between exposure methodologies for the Zn-Al LDH-NO3, further research involving other NMs and species must be carried out to achieve harmonization and validation for inter-laboratory comparison.

Zn-Al layered double hydroxides induce embryo malformations and impair locomotion behavior in Danio rerio

Layered double hydroxides (LDHs) are stimuli-responsive anionic nanoclays. The vast possibilities of using LDHs can lead to their existence in the ecosystem, raising a question of potential ecological concern. However, little is known about the effect of these nanomaterials on freshwater organisms. The present study aimed to assess the ecotoxicological effects of Zinc-Aluminium LDH-nitrate (ZnAl LDH-NO₃) in zebrafish (Danio rerio) early life stages. The endpoints measured were mortality, malformations and hatching rate after exposure of D. rerio embryos and larvae to ZnAl LDH-NO₃ following the OECD 236 guideline. The behavioral, biochemical (markers of oxidative stress and neurotoxicity), and molecular (at DNA level) alterations were also assessed using sub-lethal concentrations. No observable acute effects were detected up to 415.2 mg LDH/L while the 96 h-LC₅₀ was estimated as 559.9 mg/L. Tested LDH caused malformations in D. rerio embryos, such as pericardial edema, incomplete yolk sac absorption and tail deformities (96 h-EC₅₀ = 172.4 mg/L). During the dark periods, the locomotor behavior in zebrafish larvae was affected upon ZnAl LDH-NO₃ exposure. However, no significant biochemical and molecular changes were recorded. The present findings suggest that ZnAl LDH-NO₃ can be regarded as a non-toxic nanomaterial towards D. rerio (E/LC₅₀ > > 100 mg/L) although impairment of the locomotion behavior on zebrafish embryos can be expected at concentrations below 100 mg/L.

Layered double hydroxides for corrosion-related applications—Main developments from 20 years of research at CICECO

This work describes the main advances carried out in the field of corrosion protection using layered double hydroxides (LDH), both as additive/pigment-based systems in organic coatings and as conversion films/pre-treatments. In the context of the research topic “Celebrating 20 years of CICECO”, the main works reported herein are based on SECOP’s group (CICECO) main advances over the years. More specifically, this review describes structure and properties of LDH, delving into the corrosion field with description of pioneering works, use of LDH as additives to organic coatings, conversion layers, application in reinforced concrete and corrosion detection, and environmental impact of these materials. Moreover, the use of computational tools for the design of LDH materials and understanding of ion-exchange reactions is also presented. The review ends with a critical analysis of the field and future perspectives on the use of LDH for corrosion protection. From the work carried out LDH seem very tenable, versatile, and advantageous for corrosion protection applications, although several obstacles will have to be overcome before their use become commonplace.

Molecular Dynamics Model to Explore the Initial Stages of Anion Exchange involving Layered Double Hydroxide Particles

A classical molecular dynamics (MD) model of fully unconstrained layered double hydroxide (LDH) particles in aqueous NaCl solution was developed to explore the initial stages of the anion exchange process, a key feature of LDHs for their application in different fields. In particular, this study focuses on the active corrosion protection mechanism, where LDHs are able to entrap aggressive species from the solution while releasing fewer corrosive species or even corrosion inhibitors. With this purpose in mind, it was explored the release kinetics of the delivery of nitrate and 2-mercaptobenzothiazole (MBT, a typical corrosion inhibitor) from layered double hydroxide particles triggered by the presence of aggressive chloride anions in solution. It was shown that the delamination of the cationic layers occurs during the anion exchange process, which is especially evident in the case of MBT^-.

Activated layered double hydroxides: assessing the surface anion basicity and its connection with the catalytic activity in the cyanoethylation of alcohols

Layered double hydroxides (LDHs) act as catalysts in several reactions like in the cyanoethylation of alcohols with acrylonitrile to produce alkoxypropionitriles. Here we report an experimental and theoretical study in which it is shown that the experimental catalytic activity of LDHs in the cyanoethylation of 2-propanol and methanol correlates with the predicted strength of the basicity of the adsorbed surface species. First, it is shown that using activated LDHs containing Mg²⁺ and Al³⁺ (MgAl-LDH), Mg²⁺ and Ga³⁺ (MgGa-LDH), and Mg²⁺, Al³⁺ and Ga³⁺ (MgAlGa-LDH) great conversions to alkoxypropionitriles in high yields are obtained. Next, the basicity of these LDHs is estimated by means of the local softness, a local reactivity index calculated using density functional theory and appropriate surface models. For that, the adsorption of hydroxide and methoxide anions at the (001) surface of MgAl and MgGa-LDHs is investigated. We include LDHs containing Zn²⁺ and Al³⁺ (ZnAl-LDH) and Zn²⁺ and Ga³⁺ (ZnGa-LDH) in this part of the study to account for the effect of changing the divalent and trivalent metal composition on the basicity. It is found that hydroxide anions adsorbed on the MgGa-LDH surface and methoxide anions adsorbed on the MgAl-LDH surface are the most basic ones. This basicity trend correlates with our experimental findings about the catalytic activity of the activated LDHs. Further analyzing the connection between the LDH composition and the anion basicity, it is argued that the key steps dictating the LDH catalytic activity are the alcohol deprotonation in the cyanoethylation of 2-propanol, as it has been previously suggested, and the methoxide anion attack to the acrylonitrile double bond in the methanol cyanoethylation reaction.

Use of Ethylamine, Diethylamine and Triethylamine in the Synthesis of Zn,Al Layered Double Hydroxides

Amines with two carbon atoms in the organic chain [ethylamine (EA), diethylamine (DEA), triethylamine (TEA)] have been used as precipitant agents to obtain a hydrotalcite-like compound with Zn (II) and Al (III) as layered cations and with nitrate anions in the interlayered region to balance the charge. This Layered Double Hydroxide was prepared following the coprecipitation method, and the effect on the crystal and particle sizes was studied. Also, the effect of submitting the obtained solids to hydrothermal post-synthesis treatment by conventional heating and microwave assisted heating were studied. The obtained solids were exhaustively characterized using several instrumental techniques, such as X-ray diffraction, Thermal Analysis (DTA and TG), Chemical Analysis, Infrared Spectroscopy (FT-IR), determination of Particle Size Distribution and BET-Surface area. Well crystallized solids were obtained showing two possible LDH phases, depending on the orientation of the interlayer anion with respect to the brucite-like layers. The results indicated that there is a certain influence of the amine, when used as a precipitating agent, and as a consequence of the degree of substitution, on the crystallinity and particle size of the final solid obtained. The LDHs obtained using TEA exhibited higher crystallinity, which was improved after a long hydrothermal treatment by conventional heating. Regarding the shape of the particles, the formation of aggregates in the former solid was detected, which could be easily disintegrated using ultrasound treatments, producing solid powder with high crystallinity and small particle size, with homogeneous size distribution.

Corrosion Resistance of Li-Al LDHs Film Modified by Methionine for 6063 Al Alloy in 3.5 wt.% NaCl Solution

Methionine (Met) was introduced to modify the Li-Al layered double hydroxides (LDHs) film prepared on 6063 aluminum alloy by in situ method for the first time. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Scanning electron microscopy, and X-ray diffraction confirmed the successful insertion of Met into LDHs film and revealed that the introduction of Met could make the LDHs film much denser. Electrochemical tests illustrated that the corrosion rate of the Met modified LDHs film was reduced by more than an order of magnitude compared with the bare Al alloy. Moreover, the corrosion rate of the modified LDHs film after immersion in 3.5 wt.% NaCl solution for 21 days was almost the same as that without immersion, which indicates that the modified film has good corrosion durability. The corrosion resistance of the scratched modified film could recover to the level without a scratch on the 14th day based on the scratch test results, meaning the modified film has a good self-healing property. Finally, the anti-corrosion mechanism of the Met was proved by molecular dynamic simulations and found that the enhanced corrosion resistance may be attributed to the addition of Met that slowed the diffusion of the corrosive medium Cl− and water molecules.

Can the toxicity of polyethylene microplastics and engineered nanoclays on flatfish (Solea senegalensis) be influenced by the presence of each other?

Microplastics and nanomaterials are applied in a myriad of commercial and industrial applications. When leaked to natural environments, such small particles might threaten living organisms' health, particularly when considering their potential combination that remains poorly investigated. This study investigated the physiological and biochemical effects of polyethylene (PE; 64-125 μm in size, 0.1, 1.0, and 10.0 mg·L^-1) single and combined with an engineered nanomaterial applied in antifouling coatings, the copper-aluminium layered double hydroxides (Cu-Al LDH; 0.33, 1.0, and 3.33 mg·L^-1) in the flatfish Solea senegalensis larvae (8 dph) after 3 h exposure, in a full factorial design. Particles ingestion, histopathology, and biochemical biomarkers were assessed. Fish larvae presented <1 PE particles in their gut, independently of their concentration in the medium. The histological health index showed minimal pathological alterations at PE combined exposure, with a higher value observed at 1 mg LDH·L^-1 × 0.1 mg PE·L^-1. Gut deformity and increased antioxidant defences (catalase), neurotransmission (acetylcholinesterase), and aerobic energy production (electron transport system) were observed at PE ≥ 1.0 mg·L^-1. No oxidative damage (lipid peroxidation) or alterations in the detoxification capacity (glutathione-S-transferase) was observed on single and combined exposures. PE, combined or not with Cu-Al LDH, does not seem to compromise larvae's homeostasis considering levels reported so far in the marine and aquaculture environments. However, harsh effects are expected with MP contamination rise, as projections suggest.

Ciprofloxacin in Layered Double Hydroxides: Looking for the Best Synthesis Method

It is important to develop new methods of release to improve pharmacokinetic parameters of drugs, especially antibiotics, whose plasmatic concentration is determinant to ensure an effective treatment. Layered double hydroxides (LDH) are inorganic and biocompatible materials with high drug intercalation capacity and release properties that can be tuned by controlling the pH value. These materials can be an excellent choice to achieve a sustained release and an optimal drug concentration in plasm. In this work, LDH were synthesized with intercalated ciprofloxacin (CIP) by three different methods: coprecipitation, reconstruction and ion exchange. LDH-CIP complexes were characterized by XRD, TG-DSC, TEM, SEM, FTIR, electrophoretic mobilities, and drug release and dissolution kinetics in NaCl solutions and under physiological conditions. The coprecipitation and reconstruction methods lead to the formation of ill-defined products, whereas the ion exchange method rendered the best intercalation results. CIP release was controlled by dissolution at pH<3 and by desorption and ion exchange at intermediate and high pH. In comparison with a commercial formulation, the LDH-CIP complex prepared by ion exchange presented a slower release profile. The fast dissolution at gastric pH raises the need of developing some type of coating for protecting LDH materials.

Recent innovations in functionalized layered double hydroxides: Fabrication, characterization, and industrial applications

Layered Double Hydroxides (LDHs) are a group of hydrotalcite-like nano-sized materials with cationic layers and exchangeable interlayer anions. The wide range of divalent and trivalent cationic metals and anionic compounds are employed in the synthesis of LDH materials, which have improved their importance among the researchers. Because of their high anion exchange property, memory effect, tunable behavior, bio-friendly, simple preparation, and their affordability, these nano-materials are essentially interested today. Modification of LDHs improves their behaviours to make them appropriate in industrial fields, including biological, adsorbent, mechanical, optical, thermal, electrical fields, etc. This review has critically discussed the structural features, main properties, and also clarified the most important methods of modification and intercalation of LDH nano-materials. Moreover, some novel reported researches related to the successful modification of LDH materials have been characterized and briefly the advantages, disadvantages, and applications are presented in the industrial fields.

Experimental Investigation of Chloride Uptake Performances of Hydrocalumite-Like Ca-Al LDHs with Different Microstructures

In this study, hydrocalumite-like Ca2Al-NO3− layered double hydroxides (Ca-Al LDHs) with different microstructures were synthesized. The crystalline properties, structure composition, morphology and particle size distribution of the Ca-Al LDH (CAL) samples were illustrated. To obtain the chloride uptake performances of CAL, the influences of contact time, initial concentration of Cl−, pH of reaction solution and coexistence anions on the chloride uptake were examined systematically. Compared to the CAL samples obtained at a higher aging temperature, CAL synthesized at 60 °C demonstrated the minimum average particle size (6.148 μm) and the best Cl− adsorption capacity (211.324 mg/g). Based on the test results, the main adsorption mechanism of chloride ion on CAL was recognized as an interlayer anion exchanging reaction other than the dissolution-precipitate mode. With the increase in the pH value of reaction solution from 7 to 13, it was found that the amount of chloride ion adsorbed by CAL increased slightly, and the solution could remain at relatively high pH value even after the adsorption. The presence of CO32− and SO42− reduced the adsorption capacity of CAL dramatically as compared with OH− due to the destruction of layered structure and the formation of precipitates (CaCO3 or CaSO4). The interference sequence of the investigated anions on the chloride uptake of CAL was SO42−, CO32− and OH−, and the order of interlayer anionic affinity was Cl− > OH− > NO3−. The results illustrated that the synthesized CAL could be used as a promising chloride ion adsorbent for the corrosion inhibition of reinforcement embedded cement-based materials.

Layered Double Hydroxide Protective Films Developed on Aluminum and Aluminum Alloys: Synthetic Methods and Anti-Corrosion Mechanisms

This work reviews the characteristics of layered double hydroxides (LDHs) in the context of protective thin films to enhance the corrosion resistance properties of aluminum alloys. A discussion is made in detail about the LDH protection mechanism and the effect of synthesis approaches on LDH structural variations and the corresponding anti-corrosion behavior. LDHs anion-exchange behavior to host inorganic/organic anions makes them a potential material to investigate for anti-corrosion film. This unique advantage and the availability of a wide range of metal oxide-based layers, interlayer anions, and self-healing properties make LDH family an attractive choice for the development of compact LDHs based smart coating systems.

Use of ZnAl-Layered Double Hydroxide (LDH) to Extend the Service Life of Reinforced Concrete

This work investigated the use of ZnAl-layered double hydroxide (LDH) intercalated with nitrate or nitrite ions for controlling the corrosion of steel in reinforced concrete. The work started by analyzing the stability of the powder in the 1–14 pH range and the capacity for capturing chloride ions in aqueous solutions of different pH. The effect of the ZnAl-LDH on the corrosion of steel was studied in aqueous 0.05 M NaCl solution and in mortars immersed in 3.5% NaCl. It was found that the LDH powders dissolved partially at pH > 12. The LDH was able to capture chloride ions from the external solution, but the process was pH-dependent and stopped at high pH due to the partial dissolution of LDH and the preferential exchange of OH^– ions. These results seemed to imply that ZnAl-LDH would not work in the alkaline environment inside the concrete. Nonetheless, preliminary results with mortars containing ZnAl-LDH showed lower penetration of chloride ions and higher corrosion resistance of the steel rebars.

Effects of Cu2+ incorporation on ZnAl-layered double hydroxide

The incorporation of copper affects the particle size of LDHs and the coordination number of aluminum.

Sonication accelerated formation of Mg-Al-phosphate layered double hydroxide via sol-gel prepared mixed metal oxides

Single-phase magnesium-aluminium layered double hydroxide (LDH) intercalated with dihydrogen phosphate was successfully produced by hydration of nanopowder of the respective mixed metal oxide (MMO) obtained using sol-gel based method followed by a two-step anion exchange hydroxide-to-chloride and chloride-to-phosphate. The MMO with the metal cation ratio of Mg/Al = 2:1 was prepared using the aqueous sol-gel method. Processes of the parent Mg₂Al-OH LDH formation and the successive anion-exchanges, ОН^- → Cl^- and Cl^- → H₂PO₄^-, were considerably accelerated via the application of high-power (1.5 kW) ultrasound. The crystalline phases formed at all stages of the Mg₂Al-H₂PO₄ LDH production were characterized using X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy, inductive coupled plasma optical emission spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Based on the data of chemical analysis and the XRD data, the type of the intercalated phosphate anion was determined and the arrangement of this anion in the interlayer was modelled.

LDH Post-Treatment of Flash PEO Coatings

This work investigates environmentally friendly alternatives to toxic and carcinogenic Cr (VI)-based surface treatments for aluminium alloys. It is focused on multifunctional thin or flash plasma electrolytic oxidation (PEO)-layered double hydroxides (LDH) coatings. Three PEO coatings developed under a current-controlled mode based on aluminate, silicate and phosphate were selected from 31 processes (with different combinations of electrolytes, electrical conditions and time) according to corrosive behavior and energy consumption. In situ Zn-Al LDH was optimized in terms of chemical composition and exposure time on the bulk material, then applied to the selected PEO coatings. The structure, morphology and composition of PEO coatings with and without Zn-Al-LDH were characterized using XRD, SEM and EDS. Thicker and more porous PEO coatings revealed higher amounts of LDH flakes on their surfaces. The corrosive behavior of the coatings was studied by electrochemical impedance spectroscopy (EIS). The corrosion resistance was enhanced considerably after the PEO coatings formation in comparison with bulk material. Corrosion resistance was not affected after the LDH treatment, which can be considered as a first step in achieving active protection systems by posterior incorporation of green corrosion inhibitors.

Nanocontainer-based self-healing coatings: current progress and future perspectives

Nanocontainers add more functionalities to the standard coating formulations.

Comparison of transition metal (Fe, Co, Ni, Cu, and Zn) containing tri-metal layered double hydroxides (LDHs) prepared by urea hydrolysis

This paper details a successful synthesis and comparison of a range of tri-metal hydrotalcite-like layered double hydroxides (LDHs) using urea hydrolysis. Transition-metal-substituted MgMAl-LDHs were synthesized with M = Fe, Co, Ni, Cu or Zn. 5 mol% and 10 mol% substitutions were performed, where Mg was substituted with Co, Ni, Cu and Zn, and Al with Fe. The successful synthesis of crystalline MgMAl-LDHs was confirmed using X-ray powder diffraction (XRD) analysis. Energy-dispersive X-ray (EDX) spectroscopy was used to identify substituted metals and determine changes in composition. Changes in morphology were studied using scanning electron microscopy (SEM). Thermogravimetric analysis was used to determine the effect of Fe-, Co-, Ni-, Cu- or Zn-substitution on the thermal degradation of the MgMAl-LDH phase. The structure, morphology and thermal behavior of the LDHs were shown to be influenced by the substituted transition metals. The observed thermal stability took the order MgNiAl- > MgFeAl- = MgAl- ≥ MgCoAl- > MgCuAl- > MgZnAl-LDH. The urea hydrolysis method was shown to be a simple preparation method for well-defined crystallite structures with large hexagonal platelets and good distribution of transition metal atoms in the substituted LDHs.

This paper details a successful synthesis and comparison of a range of tri-metal hydrotalcite-like layered double hydroxides (LDHs) using urea hydrolysis.

Hydrodynamic assembly of two-dimensional layered double hydroxide nanostructures

Formation mechanisms of two-dimensional nanostructures in wet syntheses are poorly understood. Even more enigmatic is the influence of hydrodynamic forces. Here we use liquid flow cell transmission electron microscopy to show that layered double hydroxide, as a model material, may form via the oriented attachment of hexagonal nanoparticles; under hydrodynamic shear, oriented attachment is accelerated. To hydrodynamically manipulate the kinetics of particle growth and oriented attachment, we develop a microreactor with high and tunable shear rates, enabling control over particle size, crystallinity and aspect ratio. This work offers new insights in the formation of two-dimensional materials, provides a scalable yet precise synthesis method, and proposes new avenues for the rational engineering and scalable production of highly anisotropic nanostructures.

While liquid-phase synthesis of 2D materials presents opportunities for large-scale production, achieving precise control over product quality, size and morphology remains challenging. Here, the authors show that hydrodynamic manipulation of nanoparticle assembly enables control over crystallinity, size and aspect ratio.

Efficacy and Ecotoxicity of Novel Anti-Fouling Nanomaterials in Target and Non-Target Marine Species

Biofouling is a global problem that affects virtually all the immersed structures. Currently, several novel environmentally friendly approaches are being tested worldwide to decrease the toxicity of biocides in non-fouling species, such as the encapsulation/immobilization of commercially available biocides, in order to achieve control over the leaching rate. The present study addresses the toxicity of two widely used booster biocides, zinc pyrithione (ZnPT) and copper pyrithione (CuPT), in its free and incorporated forms in order to assess their toxicity and anti-fouling efficacy in target and non-target species. To achieve this goal, the following marine organisms were tested; the green microalgae Tetraselmis chuii (non-target species) and both target species, the diatom Phaeodactylum tricornutum and the mussel Mytilus edulis. Organisms were exposed to both biocides, two unloaded nanostructured materials and nanomaterials loaded with biocides, from 10 μg/L to 100 mg/L total weight, following standard protocols. The most eco-friendly and simultaneously efficient anti-fouling solution against the two photosynthetic species (nanoclays loaded with ZnPT) was then tested on mussels to assess its lethal efficacy (LC₅₀ = 123 μg/L) and compared with free biocide (LC₅₀ = 211 μg/L) and unloaded material (LC₅₀ > 1000 μg/L). A second exposure test with sub-lethal concentrations (lower than 100 μg/L), using mussels, was carried out to assess biochemical changes caused by the tested compounds. Oxidative stress, detoxification and neurotransmission markers were not responsive; however, different antioxidant patterns were found with free ZnPT and loaded nanoclay exposures. Thus, the immobilization of the biocide ZnPT into nanoclays proved to be a promising efficient and eco-friendly anti-fouling strategy.

Catalytic performance of layered double hydroxide nanosheets toward phenol hydroxylation

CuMgAl-LDH@mSiO₂ nanosheets are prepared by delaminating the CuMgAl(NO₃)-LDH microcrystals followed by coating a porous layer of SiO₂, which show excellent catalytic performance toward phenol hydroxylation.