Recent Advances in Metal Nanoparticles Stabilization into Nanopores of Montmorillonite and Their Catalytic Applications for Fine Chemicals Synthesis

Applications of Metals and Metal Compounds in Improving the Sensitivity of Microfluidic Biosensors - A Review

The enhancement of detection sensitivity in microfluidic sensors has been a continuously explored field. Initially, many strategies for sensitivity improvement involved introducing enzyme cascade reactions, but enzyme-based reactions posed challenges in terms of cost, stability, and storage. Therefore, there is an urgent need to explore enzyme-free cascade amplification methods, which are crucial for expanding the application range and improving detection stability. Metal or metal compound nanomaterials have gained great attention in the exploitation of microfluidic sensors due to their ease of preparation, storage, and lower cost. The unique physical properties of metallic nanomaterials, including surface plasmon resonance, surface-enhanced Raman scattering, metal-enhanced fluorescence, and surface-enhanced infrared absorption, contribute significantly to enhancing detection capabilities. The metal-based catalytic nanomaterials, exemplified by Fe3O4 nanoparticles and metal-organic frameworks, are considered viable alternatives to biological enzymes due to their excellent performance. Herein, we provide a detailed overview of the applications of metals and metal compounds in improving the sensitivity of microfluidic biosensors. This review not only highlights the current developments but also critically analyzes the challenges encountered in this field. Furthermore, it outlines potential directions for future research, contributing to the ongoing development of microfluidic biosensors with improved detection sensitivity.

Aluminosilicates-based nanosorbents for heavy metal removal - A review

Contamination of water bodies with heavy metals poses a significant threat to human health and the environment, requiring the development of effective treatment techniques. In this context, aluminosilicates emerge as promising sorbents due to their cost-effectiveness and natural abundance. This review provides a clear, in-depth, and comprehensive description of the structure, properties, and characteristics of aluminosilicates, supporting their application as adsorbents and highlighting their diversity and adaptability to different matrices and analytes. Furthermore, the functionalization of these materials is thoroughly addressed, detailing the techniques currently used, exposing the advantages and disadvantages of each approach, and establishing comparisons and evaluations of the performances of various functionalized aluminosilicates in the extraction of heavy metals in aqueous matrices. This work aims not only to comprehensively review numerous studies from recent years but also to identify trends in the study of such materials and inspire future research and applications in the field of contaminant removal using aluminosilicates.

Modification of Pillared Intercalated Montmorillonite Clay as Heterogeneous Pd Catalyst Supports

Montmorillonite clay was modified by pillaring with AlMn oxides in different Al/Mn ratios and intercalation of two kinds of N-containing polymers (i.e., chitosan (CS) and polyvinyl pyrrolidinone (PVP)) chains. The modified pillared montmorillonite clay (PM) showed a rich two-dimensional layered porous structure with tunable parameters, such as large interlayer spacing, high specific area, and large porous volume. They were then used as supports for Pd nanoparticles. As applied in coupling reactions of aryl halides with terminal alkynes, Pd@CS/AlMn-PM showed better comprehensive catalytic performance than Pd@PVP/AlMn-PM. This was mainly attributed to its higher specific area, stronger chelation to Pd species, and better solvent resistance.

Application of Chitosan/Poly(vinyl alcohol) Stabilized Copper Film Materials for the Borylation of α, β-Unsaturated Ketones, Morita-Baylis-Hillman Alcohols and Esters in Aqueous Phase

A chitosan/poly(vinyl alcohol)-stabilized copper nanoparticle (CP@Cu NPs) was used as a heterogeneous catalyst for the borylation of α, β-unsaturated ketones, MBH alcohols, and MBH esters in mild conditions. This catalyst not only demonstrated remarkable efficiency in synthesizing organoboron compounds but also still maintained excellent reactivity and stability even after seven recycled uses of the catalyst. This methodology provides a gentle and efficient approach to synthesize the organoboron compounds by efficiently constructing carbon-boron bonds.

Green method of conversion of geraniol to value-added products in the presence of selected minerals

The study presents the results of research on the process of geraniol (GA) transformation in the presence of natural minerals: montmorillonite, mironekuton, halloysite and also in the presence of halloysite modified with 0.1 M water solution of H2SO4. To obtain information on the structure of the used catalysts, instrumental studies were performed (SEM, XRD, FT-IR, XRF, BET). The second part of the research consisted in examining the influence of individual parameters (temperature, catalyst content, and reaction time) on the course of GA transformation process. The syntheses were carried out without the application of solvent and under atmospheric pressure. To determine the most beneficial process conditions, two functions were selected: GA conversion and selectivity of GA. The proposed method of GA transformation on such minerals: montmorillonite, mironekuton, halloysite, has not been described in the literature so far.

Evolution of Chemical Bonding and Crystalline Swelling-Shrinkage of Montmorillonite upon Temperature Changes Probed by in Situ Fourier Transform Infrared Spectroscopy and X-ray Diffraction

Clay minerals are distributed in Earth's crust and troposphere and in Martian crust where temperature varies. Understanding the changes of chemical bonding and crystalline swelling-shrinkage of montmorillonite (Mnt) upon temperature changes is fundamental for studying its surface reactivity and interaction in specific surroundings. However, such an issue remains poorly understood. Here, in situ high- and low-temperature Fourier transform infrared (HT- and LT-FTIR) spectroscopy and X-ray diffraction (HT- and LT-XRD) were performed to study the evolution of chemical bonding and crystalline swelling-shrinkage of sodium-montmorillonite (NaMnt) upon temperature changes. The FTIR results show that the hydroxyl content in NaMnt decreased when the temperature increased from 20 to 700 °C, while it is independent of temperature from 0 to -150 °C. The formation of hydroxyls at the "broken" layer edges of NaMnt is related to adsorbed water molecules on the surfaces, and its content increased when the particle size of the NaMnt decreased. The water molecules in the interlayer space of NaMnt could bond to the tetrahedral sheet of NaMnt through Si₂O-H₂O bonds. HT- and LT-XRD results reveal that all of those water molecules in NaMnt were removed after heating to 100 °C in the heating chamber. The NaMnt was transformed from a state of monolayer interlayer water molecules at 20 °C to a dehydrated state at 100 °C, and then to a dehydroxylated state at 700 °C. Accordingly, the basal spacings of NaMnt were changed from 1.27 to 0.97 nm and then to 0.96 nm, respectively. When NaMnt was cooled from 20 to -268 °C, a crystalline swelling of NaMnt occurred with an increase of 0.03 nm of basal spacing. This work demonstrates that high/low temperature has a remarkable effect on the hydroxyls and the water molecules in NaMnt, which in turn affects its swelling-shrinkage performance. These findings provide some in-depth understanding of the changes of chemical bonding and crystalline swelling-shrinkage of montmorillonite upon temperature changes and the reasons behind these, which might be helpful for the design of engineering Mnt in high-/low-temperature applications.

Colloidal nanomaterials for water quality improvement and monitoring

Water is the most important resource for all kind forms of live. It is a vital resource distributed unequally across different regions of the globe, with populations already living with water scarcity, a situation that is spreading due to the impact of climate change. The reversal of this tendency and the mitigation of its disastrous consequences is a global challenge posed to Humanity, with the scientific community assuming a major obligation for providing solutions based on scientific knowledge. This article reviews literature concerning the development of nanomaterials for water purification technologies, including collaborative scientific research carried out in our laboratory (nanoLAB@UA) framed by the general activities carried out at the CICECO-Aveiro Institute of Materials. Our research carried out in this specific context has been mainly focused on the synthesis and surface chemical modification of nanomaterials, typically of a colloidal nature, as well as on the evaluation of the relevant properties that arise from the envisaged applications of the materials. As such, the research reviewed here has been guided along three thematic lines: 1) magnetic nanosorbents for water treatment technologies, namely by using biocomposites and graphite-like nanoplatelets; 2) nanocomposites for photocatalysis (e.g., TiO2/Fe3O4 and POM supported graphene oxide photocatalysts; photoactive membranes) and 3) nanostructured substrates for contaminant detection using surface enhanced Raman scattering (SERS), namely polymers loaded with Ag/Au colloids and magneto-plasmonic nanostructures. This research is motivated by the firm believe that these nanomaterials have potential for contributing to the solution of environmental problems and, conversely, will not be part of the problem. Therefore, assessment of the impact of nanoengineered materials on eco-systems is important and research in this area has also been developed by collaborative projects involving experts in nanotoxicity. The above topics are reviewed here by presenting a brief conceptual framework together with illustrative case studies, in some cases with original research results, mainly focusing on the chemistry of the nanomaterials investigated for target applications. Finally, near-future developments in this research area are put in perspective, forecasting realistic solutions for the application of colloidal nanoparticles in water cleaning technologies.

Montmorillonite-based Heterogeneous Catalysts for Efficient Organic Reactions

In this review, we give a brief overview of recently developed montmorillonite-based heterogeneous catalysts used for efficient organic reactions. Cation-exchanged montmorillonite catalysts, metal catalysts supported on montmorillonite, and an interlayer design used for selective catalysis are introduced and discussed. In traditional syntheses, homogeneous acids and metal salts were used as catalysts, but the difficulty in separation of catalysts from products was a bottleneck when considering industrialization. The use of solid heterogeneous catalysts is one of the major solutions to overcome this problem. Montmorillonite can be used as a heterogeneous catalyst and/or catalyst support. This clay material exhibits strong acidity and a stabilizing effect on active species, such as metal nanoparticles, due to its unique layered structure. These advantages have led to the development of montmorillonite-based heterogeneous catalysts. Acidic montmorillonite, such as proton-exchanged montmorillonite, exhibits a high catalytic activity for the activation of electrophiles, such as alcohols, alkenes, and even alkanes. The montmorillonite interlayer/surface also functions as a good support for various metal species used for oxidation and carbon-carbon bond forming reactions. The use of an interlayer structure enables selective reactions and the stabilization of catalytically active species.

Research Trends on Pillared Interlayered Clays (PILCs) Used as Catalysts in Environmental and Chemical Processes: Bibliometric Analysis

Over the last four decades, a large number of studies have been published on pillared interlayered clays (PILCs) used as adsorbent materials and catalysts or supports for transition metals in heterogeneous catalysis. Particularly, PILCs have been used for water treatment through advanced oxidation processes (AOPs) to remove organic pollutants. They have also been studied in various chemical and environmental processes. Because of the growing interest in PILCs, this article is focused on analyzing scientific publications such as research/review articles and book chapters from the last four decades (from 1980 to 2019) through a bibliometric analysis (BA) to visualize and describe research trends on PILCs. By narrowing the bibliographic search to titles, keywords, and abstracts of publications related to PILCs, using Scopus and Web of Science (WoS) (the two scientific databases), a total of 3425 documents have been retrieved. The bibliometric dataset was analyzed by VantagePoint®. The main research trends identified in the last four decades were the use of PILCs in environmental processes (34.4% of total publications) along with chemical processes (petrochemical reactions 17.5%, SCR NOx 10.8%, and decomposition 8.2%). In environmental processes, PILCs have been used in photo-oxidation (32%), CWPO (21.1%), and heterogeneous catalysis (19.4%). Phenols, dyes, and VOCs have been the main pollutants studied using PILCs as catalysts. Fe, Ti, Zr, Cu, and Co are the most supported active phases in PILCs. Other research trends grouped by characterization techniques, countries, research areas, institutes, scientific journals that have published the most on this topic, number of publications per 5-year period, and most frequently used keywords through the last four decades have been identified. It was determined that the number of publications on PILCs has increased since 1980 and the countries with the highest number of publications are China, Spain, and The United States of America.

Direct Alkylation of Benzene at Lower Temperatures in the Liquid Phase: Catalysis by Montmorillonites as Noble-Metal-Free Solid Acids

Alkylated benzenes are widely used as raw materials for the production of a variety of chemical compounds. Conventionally, they are obtained by the Friedel-Crafts reaction between alkyl halides and benzene. In this study, the synthesis of halogen-free alkylated benzenes was made possible by the direct alkylation of benzene with alkanes using montmorillonites as noble-metal-free solid acid catalysts. The direct alkylation of benzene with n-heptane was performed at 150 °C. Aluminum-exchanged montmorillonite showed the highest yield of the target C-7 alkylated products (Ph-C7) compared with other homogeneous and heterogeneous acid catalysts: 1.8 % conversion of benzene with 58 % selectivity in 16 h. The montmorillonite catalyst system was applied to other linear and cyclic alkanes to give the corresponding alkylated products with good selectivities.

Synthesis, photophysical and electrochemical properties of donor–acceptor type hydrazinyl thiazolyl coumarins

A practical green MCR strategy has been developed for the synthesis of D–A type hydrazinyl thiazolyl coumarins catalyzed by an environmentally compatible MMT K10 clay in water at RT.

Formation of C–C, C–S and C–N bonds catalysed by supported copper nanoparticles

Copper nanoparticles on different supports are effective reusable catalysts for the palladium- and ligand-free coupling of aryl halides with alkynes, thiols and azoles.

In situ generated and stabilized Pd nanoparticles by N2,N4,N6-tridodecyl-1,3,5-triazine-2,4,6-triamine (TDTAT) as a reactive and efficient catalyst for the Suzuki–Miyaura reaction in water

The Suzuki–Miyaura coupling reaction was efficiently catalyzed by the in situ generated and stabilized Pd nanoparticles employing TDTAT in water.

Aromatic ring hydrogenation catalysed by nanoporous montmorillonite supported Ir(0)-nanoparticle composites under solvent free conditions

Ir nanoparticles supported on nanoporous montmorillonite clay showing efficient catalytic activity for hydrogenation of aromatic compounds.

Novel Metal Nanomaterials and Their Catalytic Applications

In the rapidly developing areas of nanotechnology, nano-scale materials as heterogeneous catalysts in the synthesis of organic molecules have gotten more and more attention. In this review, we will summarize the synthesis of several new types of noble metal nanostructures (FePt@Cu nanowires, Pt@Fe₂O₃ nanowires and bimetallic Pt@Ir nanocomplexes; Pt-Au heterostructures, Au-Pt bimetallic nanocomplexes and Pt/Pd bimetallic nanodendrites; Au nanowires, CuO@Ag nanowires and a series of Pd nanocatalysts) and their new catalytic applications in our group, to establish heterogeneous catalytic system in "green" environments. Further study shows that these materials have a higher catalytic activity and selectivity than previously reported nanocrystal catalysts in organic reactions, or show a superior electro-catalytic activity for the oxidation of methanol. The whole process might have a great impact to resolve the energy crisis and the environmental crisis that were caused by traditional chemical engineering. Furthermore, we hope that this article will provide a reference point for the noble metal nanomaterials' development that leads to new opportunities in nanocatalysis.