A carbon dot-based clay nanocomposite for efficient heavy metal removal

Carbon dots and their derivatives with fascinating photoluminescence properties have recently attracted tremendous scientific attention. This work describes the preparation of novel fluorescent bentonite clay (B), modified with carbon dot nanomaterials (CDs), and its usage as a lead removal platform. The CDs were prepared using a hydrothermal method from graphitic waste which served as the carbon source material. The as-obtained CDs were found to be fluorescent, being spherical in shape, positively charged, and smaller than 5 nm. Encouraged by their structure and photoluminescence features, they were used as surface modifiers to make fluorescent bentonite nanocomposites. Bentonite was used as a negatively charged model of aluminosilicate and reacted with the positively charged CDs. XRD, FTIR, XPS, and fluorescence analysis were used to characterize the prepared materials. The results indicate that the CDs intercalated inside the bentonite matrix were stable with excellent optical properties over time. They were finally used as an efficient hybrid platform for lead removal with a removal efficiency of 95% under light conditions, at room temperature, in an alkaline medium, and after only 10 min of reaction, compared to 70% under dark conditions. The pseudo-second-order kinetics and Langmuir isotherm models were better fitted to describe the adsorption process. The maximum adsorption capacity was equal to 400 mg g-1 toward Pb(ii) removal, at room temperature and pH = 8, under light conditions. To summarize, we have designed UV light stimuli responsive carbon dot-intercalated clay with high Pb(ii) adsorption capacity and long-term stability.

Unusual, hierarchically structured composite of sugarcane pulp bagasse biochar loaded with Cu/Ni bimetallic nanoparticles for dye removal

Biochar-supported nanocatalysts emerged as unique materials for environmental remediation. Herein, sugarcane pulp bagasse (SCPB) was wet-impregnated with Cu(NO₃)₂3H₂O and Ni(NO₃)₂6H₂O, then pyrolyzed at 500 °C, under N₂, for 1 h. We specifically focused on sugarcane pulp instead of SCB and biochar materials. The metal nitrate to biomass ratio was set at 0.5, 1, and 2 mmol/g, with Cu/Ni initial ratio = 1. The process provided hierarchically structured porous biochar, topped with evenly dispersed 40 nm-sized CuNi alloy nanoparticles (SCPBB@CuNi). The biochar exhibited an unusual fishing net-like structure induced by nickel, with slits having a length in the 3-12 μm range. Such a fishing net-like porous structure was obtained without any harsh acidic or basic treatment of the biomass. It was induced, during pyrolysis, by the nanocatalysts or their precursors. The CuNi nanoparticles form true alloy as proved by XRD, and are prone to agglomeration at high initial metal nitrate concentration (2 mmol/g). Stepwise metal loading was probed by XPS versus the initial metal nitrate concentration. This is also reflected in the thermal gravimetric analyses. The SCPBB@CuNi/H₂O₂ (catalyst dose: 0.25 g/L) system served for the catalyzed removal of Malachite Green (MG), Methylene Blue (MB), and Methyl Orange (MO) dyes (concentration = 0.01 mmol/L). Both single and mixed dye solutions were treated in this advanced oxidation process (AOP). The dyes were removed in less than 30 min for MG and 3 h for MB, respectively, but 8 h for MO, therefore showing selectivity for the degradation of MG, under optimized degradation conditions. The catalysts could be collected with a magnet and reused three times, without any significant loss of activity (∼85%). AOP conditions did not induce any nanocatalyst leaching. To sum up, we provide a simple wet impregnation route that permitted to design highly active Fenton-like biochar@CuNi composite catalyst for the degradation of organic pollutants, under daylight conditions.

Encapsulation of Ammoides pusila Essential Oil into Mesoporous Silica Particles for the Enhancement of Their Activity against Fusarium avenaceum and Its Enniatins Production

Essential oils (EOs) that have antifungal activity and mycotoxin reduction ability are candidates to develop bioactive alternatives and environmentally friendly treatment against Fusarium species in cereals. However, their practical use is facing limitations such as high volatility, UV sensitivity, and fast oxidation. Encapsulation techniques are supposed to provide protection to the EOs and control their release into the environment. Ammoides pusilla essential oil (AP-EO) proved to be an efficient inhibitor of Fusarium avenaceum growth and its enniatins (ENNs) production. In the present work, AP-EO was encapsulated, using the impregnation method, into mesoporous silica particles (MSPs) with narrow slit pores (average diameter = 3.1 nm) and coated with chitosan. In contact assays using an agar medium, the antifungal activity of AP-EO at 0.1 µL mL^-1 improved by three times when encapsulated into MSPs without chitosan and the ENNs production was significantly inhibited both in coated and non-coated MSPs. Controls of MSPs also inhibited the ENNs production without affecting the mycelial growth. In fumigation experiments assessing the activity of the EO volatile compounds, encapsulation into MSPs improved significantly both the antifungal activity and ENNs inhibition. Moreover, coating with chitosan stopped the release of EO. Thus, encapsulation of an EO into MSPs improving its antifungal and antimycotoxin properties is a promising tool for the formulation of a natural fungicide that could be used in the agriculture or food industry to protect plant or food products from the contamination by toxigenic fungi such as Fusarium sp. and their potential mycotoxins.

Green, zero-waste pathway to fabricate supported nanocatalysts and anti-kinetoplastid agents from sugarcane bagasse

The conversion processes of sugarcane into direct-consumption sugar and juice are generating a tremendous amount of waste, the so-called sugarcane bagasse (SCB). Biochar preparation is among the practical solutions aiming to manage and valorize SCB into high added-value functional material (FM). Herein, we propose a novel zero-waste pathway to fabricate two FMs from one biomass. The SCB was first macerated and ultrasonicated to obtain the natural extract that served as bio-reducing medium. Then, the H₂O/EtOH-extracted SCB was in-situ impregnated with a bimetallic solution of copper and silver nitrates. The process produced an intermediate composite (FM₀), Ag/Cu-Ag⁺/Cu²⁺-loaded SCB which was carbonized to elaborate Ag/Cu-Biochar (FM₁), free Ag/Cu nanoparticles (FM₂) were obtained by microwaving the residual liquid waste. FM₁ exhibited high catalytic activity for the total Fenton-like degradation of methylene blue. The experimental data followed the pseudo-first and the pseudo-second order rate laws with apparent degradation rate constants K₁ 45 10^-3 min^-1 and K₂ 0.115 g.mg^-1.min^-1, respectively. FM₀, FM₁ and FM₂ were tested as new anti-kinetoplastid materials against two flagellated protozoans namely the Leishmania spp and the Trypanosoma cruzi. Notably, Ag/Cu (FM₂) showed exceptional leishmanicidal and trypanocidal effects with IC₅₀ values of 2.909 ± 0.051, 3.580 ± 0.016 and 3.020 ± 0.372 ppm for L.donovani, L. amazonensis and Trypanosoma cruzi, respectively. In this way, we combine green chemistry and agrowaste valorization in a full zero-waste process, to address the 3rd (indicator 3.3.5) and 6th (indicator 6.3.1) United Nations sustainable development goals, ″Good Health and Well-Being″ and ″Clean Water and Sanitation″.

Towards Clean and Safe Water: A Review on the Emerging Role of Imprinted Polymer-Based Electrochemical Sensors

This review critically summarizes the knowledge of imprinted polymer-based electrochemical sensors for the detection of pesticides, metal ions and waterborne pathogenic bacteria, focusing on the last five years. MIP-based electrochemical sensors exhibit low limits of detection (LOD), high selectivity, high sensitivity and low cost. We put the emphasis on the design of imprinted polymers and their composites and coatings by radical polymerization, oxidative polymerization of conjugated monomers or sol-gel chemistry. Whilst most imprinted polymers are used in conjunction with differential pulse or square wave voltammetry for sensing organics and metal ions, electrochemical impedance spectroscopy (EIS) appears as the chief technique for detecting bacteria or their corresponding proteins. Interestingly, bacteria could also be probed via their quorum sensing signaling molecules or flagella proteins. If much has been developed in the past decade with glassy carbon or gold electrodes, it is clear that carbon paste electrodes of imprinted polymers are more and more investigated due to their versatility. Shortlisted case studies were critically reviewed and discussed; clearly, a plethora of tricky strategies of designing selective electrochemical sensors are offered to "Imprinters". We anticipate that this review will be of interest to experts and newcomers in the field who are paying time and effort combining electrochemical sensors with MIP technology.

Protein-Coated Aryl Modified Gold Nanoparticles for Cellular Uptake Study by Osteosarcoma Cancer Cells

Gold nanoparticles coated with proteins have shown extraordinary biocompatibility which advanced to several nanomedicine engineering applications. We synthesized protein-coated gold nanoparticles using green and chemical reduction routes for cellular uptake study. In the current work, we coated gold-aryl nanoparticles of the type AuNPs-C₆H₄-4-COOH with bovine serum albumin (BSA), collagen, zein, and lysozyme proteins. Both routes were carried out without phase-transfer catalysts or extraneous stabilizing agents. High crystallinity of the AuNPs synthesized by the green route can be seen in transmission electron microscopy images. Osteosarcoma cancer cells are malignant bone tumors with abnormal cellular functions. Studies using MG-63 cells will provide mechanistic suggestions on the details of the amplification in tumors. We studied the cellular uptake of the bioconjugates by MG-63 osteosarcoma cells using laser confocal fluorescence microscopy (LCFM) and flow cytometry. In the LCFM study, BSA-AuNPs were uptaken most efficiently of all protein-coated gold nanoparticles synthesized by the green route. Lysozyme-AuNPs synthesized by the chemical reduction method were mostly efficiently internalized by MG-63 cells among all AuNPs. Zein- and lysozyme-coated AuNPs, though of relatively small size, prepared by the green method were not efficiently uptaken by MG-63. The two nanoparticles are negatively charged, and zein is also a hydrophobic coat. The difference in hydrophobicity and charge might have affected the internalization. All of those coated nanoparticles that were efficiently uptaken can potentially be used as diagnostic and therapeutic agents for osteosarcoma.

Different Electrochemical Sensor Designs Based on Diazonium Salts and Gold Nanoparticles for Pico Molar Detection of Metals

We report a comparison of sensors’ performance of different hybrid nanomaterial architectures modifying an indium tin oxide (ITO) electrode surface. Diazonium salts and gold nanoparticles (AuNPs) were used as building units to design hybrid thin films of successive layers on the ITO electrode surface. Different architectures of hybrid thin films were prepared and characterized with different techniques, such as TEM, FEG-SEM, XPS, and EIS. The prepared electrodes were used to fabricate sensors for heavy metal detection and their performances were investigated using the square wave voltammetry (SWV) method. The comparison of the obtained results shows that the deposition of AuNPs on the ITO surface, and their subsequent functionalization by diazonium salt, is the best performing architecture achieving a high sensitivity in terms of the lower detection limit of pico molar.

Can Plasmon Change Reaction Path? Decomposition of Unsymmetrical Iodonium Salts as an Organic Probe

Plasmon-assisted transformations of organic compounds represent a novel opportunity for conversion of light to chemical energy at room temperature. However, the mechanistic insights of interaction between plasmon energy and organic molecules is still under debate. Herein, we proposed a comprehensive study of the plasmon-assisted reaction mechanism using unsymmetric iodonium salts (ISs) as an organic probe. The experimental and theoretical analysis allow us to exclude the possible thermal effect or hot electron transfer. We found that plasmon interaction with unsymmetrical ISs led to the intramolecular excitation of electron followed by the regioselective cleavage of C-I bond with the formation of electron-rich radical species, which cannot be explained by the hot electron excitation or thermal effects. The high regioselectivity is explained by the direct excitation of electron to LUMO with the formation of a dissociative excited state according to quantum-chemical modeling, which provides novel opportunities for the fine control of reactivity using plasmon energy.

Development of Latent Fingerprints via Aryldiazonium Tetrachloroaurate Salts on Copper Surfaces: An XPS Study

Surface studies of developed fingerprints have aided in the elimination of criminal cases before moving to the court. The combination of X-ray photoelectron spectroscopy (XPS) with the aryldiazonium gold(III), 4-O₂NC₆H₄N₂⁺AuCl₄^-, surface modifier has been shown to be a novel approach in latent fingerprint detection and development for the quantification of film elements. The robust gold-aryl film was developed on the reducing chemicals excreted in the sebaceous fingerprints without the need for external stimuli and at a lesser extent after contacting the free metal surface. The concurrent reduction of the diazonium functional group and gold(III) from [AuCl₄]^- developed a robust gold-aryl film, which showed increasing gold(0) quantity in the time range of 30-120 min over copper coins and model flat sheets. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) support the presence of reduced gold on the top of the latent fingerprints and the presence of CuO resulting from the reaction of the diazonium salt with copper metal. This research combines the quantification of deposits using XPS, a surface-sensitive technique for chemical analysis, in addition to surface imaging.

Bimetallic Cu-Rh Nanoparticles on Diazonium-Modified Carbon Powders for the Electrocatalytic Reduction of Nitrates

4-Benzenethiol-functionalized high-surface-area graphite powder was prepared and decorated with bimetallic Cu_100-xRh_x nanoparticles (NPs) to serve as electrocatalysts for the reduction of nitrates. In the first step, the HSAG powder was grafted with in-situ-generated diazonium compounds from 4-aminothiophenol (ATP) in an acidic medium using NaNO₂ for the diazotization process. The surface composition was tuned using different initial quantities of ATP. The surface XPS-determined S/C atomic ratio was found to increase stepwise with the initial quantity of amine. In a second step, the grafted and untreated HSAG powders were decorated with Cu_100-xRh_x NPs by a wet chemical method and the elemental composition of the end composites was assessed by EDS-SEM and ICP, whereas TEM and EDS-TEM served to characterize the NP morphology and their composition on the nanometer scale. In all cases, the NP size was invariably found to be ∼1.7 nm but with a size distribution becoming narrower under an increasing grafting rate and the global composition enriched in copper. Voltammetry was performed with a cavity microelectrode to evaluate the electrocatalytic performance of the composites for nitrate reduction. Increasing diazonium grafting led to a progressive reduction of the peak current intensity and a shift of the peak potentials toward cathodic values. The maximum intensity was obtained for 0.005 μmol of diazonium salt per mg of HSAG, with a gain of 40% in comparison to the best untreated sample. This improvement and a change in the voltammogram characteristics after grafting seem to result from modifications of the local composition at the level of NPs that differ from the global composition. This work conclusively shows that diazonium surface modification is important not only in attaching electrocatalytic NPs to carbon supports but also in providing a narrower size distribution of the electrocatalysts together with finely tuned catalytic properties.

Novel Enzyme-Free Multifunctional Bentonite/Polypyrrole/Silver Nanocomposite Sensor for Hydrogen Peroxide Detection over a Wide pH Range

Precise designs of low-cost and efficient catalysts for the detection of hydrogen peroxide (H₂O₂) over wide ranges of pH are important in various environmental applications. Herein, a versatile and ecofriendly approach is presented for the rational design of ternary bentonite-silylpropyl-polypyrrole/silver nanoarchitectures (denoted as BP-PS-PPy/Ag) via the in-situ photo polymerization of pyrrole with salinized bentonite (BP-PS) in the presence of silver nitrate. The Pyrrolyl-functionalized silane (PS) is used as a coupling agent for tailoring the formation of highly exfoliated BP-PS-PPy sheet-like nanostructures ornamented with monodispersed Ag nanoparticles (NPs). Taking advantage of the combination between the unique physicochemical properties of BP-PS-PPy and the outstanding catalytic merits of Ag nanoparticles (NPs), the as-synthesized BP-PS-PPy/Ag shows a superior electrocatalytic reduction and high-detection activity towards H₂O₂ under different pH conditions (from 3 to 10). Intriguingly, the UV-light irradiation significantly enhances the electroreduction activity of H₂O₂ substantially, compared with the dark conditions, due to the high photoelectric response properties of Ag NPs. Moreover, BP-PS-PPy/Ag achived a quick current response with a detection limit at 1 μM within only 1 s. Our present approach is green, facile, scalable and renewable.

A novel fluorescent sensor based on electrosynthesized benzene sulfonic acid-doped polypyrrole for determination of Pb(II) and Cu(II)

To develop conducting organic polymers (COPs) as luminescent sensors for determination of toxic heavy metals, a new benzene sulfonic acid-doped polypyrrole (PPy-BSA) thin film was electrochemically prepared by cyclic voltammetry (CV) on flexible indium tin oxide (ITO) electrode in aqueous solution. PPy-BSA film was characterized by FTIR spectrometry, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The optical properties of PPy-BSA were investigated by ultraviolet (UV)-visible absorption and fluorescence spectrometry in dimethylsulfoxide (DMSO) diluted solutions. PPy-BSA fluorescence spectra were strongly quenched upon increasing copper(II) ion (Cu²⁺ ) and lead(II) ion (Pb²⁺ ) concentrations in aqueous medium, and linear Stern-Volmer relationships were obtained, which indicated the existence of a main dynamic fluorescence quenching mechanism. BSA-PPy sensor showed a high sensitivity for detection of both metallic ions, Cu²⁺ and Pb²⁺ , with very low limit of detection values of 3.1 and 18.0 nM, respectively. The proposed quenching-fluorimetric sensor might be applied to the determination of traces of toxic heavy metallic ions in water samples.

Surface Plasmon-Polariton: A Novel Way To Initiate Azide-Alkyne Cycloaddition

Plasmon catalysis has recently generated tremendous interest in the field of modern chemistry. Application of plasmon introduces the principally new stimulus for the activation of organic reactions, keeping the optical energy concentrated in the vicinity of plasmonic structure, creating an optical near-field enhancement as well as hot electron injection. In this work, for the first time, we presented a new way for the initiation of the azide-alkyne cycloaddition (AAC) using the surface plasmon-polariton wave, supported by the gold grating. With this concept in hand, the plasmon-active gold grating was functionalized with 4-ethynylbenzenediazonium compound. Then, surface-grafted 4-ethynylphenyl groups were plasmon activated and clicked with 4-azidobenzoic acid. Additional experiments allowed to exclude the potential effect of photon, heating, and metal impurities confirmed the key role of surface plasmon-polariton AAC activation. For the investigation of plasmon-induced AAC mechanism, 4-azidophenyl groups (instead of 4-ethynylphenyl groups) were also grafted to the grating surface. Further careful evaluation of reaction kinetics demonstrates that the AAC reaction rate is significantly higher in the case of acetylene activation than in the case of azide activation.

Highly Selective Copper Ion Imprinted Clay/Polymer Nanocomposites Prepared by Visible Light Initiated Radical Photopolymerization

There is an urgent demand worldwide for the development of highly selective adsorbents and sensors of heavy metal ions and other organic pollutants. Within these environmental and public health frameworks, we are combining the salient features of clays and chelatant polymers to design selective metal ion adsorbents. Towards this end, the ion imprinting approach has been used to develop a novel nanohybrid material for the selective separation of Cu2+ ions in an aqueous solution. The Cu2+-imprinted polymer/montmorillonite (IIP/Mt) and non-imprinted polymer/montmorillonite (NIP/Mt) nanocomposites were prepared by a radical photopolymerization process in visible light. The ion imprinting step was indeed important as the recognition of copper ions by IIP/Mt was significantly superior to that of NIP/Mt, i.e., the reference nanocomposite synthesized in the same way but in the absence of Cu2+ ions. The adsorption process as batch study was investigated under the experimental condition affecting same parameters such as contact time, concentration of metal ions, and pH. The adsorption capacity of Cu2+ ions is maximized at pH 5. Removal of Cu2+ ion achieved equilibrium within 15 min; the results obtained were found to be fitted by the pseudo-second-order kinetics model. The equilibrium process was well described by the Langmuir isothermal model and the maximum adsorption capacity was found to be 23.6 mg/g. This is the first report on the design of imprinted polymer nanocomposites using Type II radical initiators under visible light in the presence of clay intercalated with hydrogen donor diazonium. The method is original, simple and efficient; it opens up new horizons in the general domain of clay/polymer nanocomposites.

Synthesis of water-soluble gold–aryl nanoparticles with distinct catalytic performance in the reduction of the environmental pollutant 4-nitrophenol

In-depth kinetic insight into the catalytic reduction of nitrophenol pollutant using gold–carbon nanoparticles is described.

Anti-corrosive and oil sensitive coatings based on epoxy/polyaniline/magnetite-clay composites through diazonium interfacial chemistry

Epoxy polymer nanocomposites filled with magnetite (Fe3O4) clay (B), named (B-DPA-PANI@Fe3O4) have been prepared at different filler loading (0.1, 0.5, 1, 3, 5 wt. %). The surface modification of clay by polyaniline (PANI) is achieved in the presence of 4-diphenylamine diazonium salt (DPA). The effects of the nanofiller loading on Tensile, mechanical and dielectric properties were systematically studied. Improved properties was highlighted for all reinforced samples. The addition of only 3 wt. % of the filler enhanced the tensile strength of the composites by 256%, and the glass transition temperature Tg by 37%. The dielectric spectra over a broad frequency showed a robust interface between the hybrid (B-DPA-PANI@Fe3O4) fillers and epoxy matrix. The results showed most significant improvement in corrosion inhibition using electrochemical impedance spectroscopy (EIS) in 3.5 wt % NaCl, as well as a significant response in oil sensing test. High charge transfer resistance of 110 × 106 Ω.cm2 using 3-wt % of filler was noted compared to 0.35 × 106 Ω.cm2 for the pure epoxy. The results obtained herein will open new routes for the preparation of efficient anticorrosion sensor coatings.

Tracking metal ions with polypyrrole thin films adhesively bonded to diazonium-modified flexible ITO electrodes

Adhesively bonded polypyrrole thin films doped with benzene sulfonic acid (BSA) were electrodeposited on aminobenzenediazonium-modified flexible ITO electrodes and further employed for the detection of Pb²⁺, Cu²⁺, and Cd²⁺ metal ions in aqueous medium. The aminophenyl (AP) adhesive layer was grafted to ITO by electroreduction of the in situ generated parent diazonium compound. Polypyrrole (PPy) thin films exhibited remarkable adhesion to aminophenyl (ITO-AP). The strongly adherent polypyrrole films exhibited excellent electroactivity in the doped state with BSA which itself served to chelate the metal ions in aqueous medium. The surface of the resulting, modified flexible electrode was characterized by XPS, SEM, and electrochemical methods. The ITO-AP-PPy electrodes were then used for the simultaneous detection of Cu²⁺, Cd²⁺, and Pb²⁺ by differential pulse voltammetry (DPV). The detection limits were 11.1, 8.95, and 0.99 nM for Cu²⁺, Cd²⁺, and Pb²⁺, respectively. In addition, the modified electrodes displayed a good reproducibility, making them suitable for the determination of heavy metals in real wastewater samples.

Sonochemical synthesis of Fe3O4@NH2-mesoporous silica@Polypyrrole/Pd: A core/double shell nanocomposite for catalytic applications

There is a growing interest in sonochemistry for either the controlled design of nanostructured materials or for the synthesis of polymers and polymer composites. It is fast and highly efficient method that provides materials with exceptional and enhanced structural and chemical properties. Herein, we take advantage of the versatile sonochemical process in order to design core/double layered shell nanocomposite denoted by Fe₃O₄@NH₂-mesoporous silica@ PPy/Pd. This magnetic, multicomponent material was designed in a three-step sono-process: (i) synthesis of magnetic core, (ii) cure of mesoporous silica, and (iii) sonochemical deposition of PPy/Pd. This last step was achieved within 1 h, a much shorter duration compared to conventional routes which usually take several hours to few days. The final nanocomposite can be recovered with a simple magnetic stick. X-ray diffraction patterns highlighted the presence of zerovalent palladium on the surface of the magnetic nanocomposite. The catalytic activity of the solid support was investigated by the study of the p-nitrophenol (p-NP) reduction and the Methyl Orange (MO) degradation in aqueous media. Results showed a very high catalytic efficiency, a high conversion yield of p-NP into 4-aminophenol (more than 94%) and an almost entire degradation of MO (99%) with a fast kinetics fitting to the first order model. This work demonstrates conclusively the benefits of sonochemistry in the design of metal nanoparticle-decorated inorganic/polymer hybrid system with outstanding performances.

Size-Controlled 3D Colloidal Crystals Formed in an Aqueous Suspension of Polystyrene/Polyglycidol Microspheres with Covalently Bound l-DOPA

Stable three-dimensional colloidal crystals were fabricated in an aqueous suspension of Tris buffer at pH > 8. The basic building blocks of the crystals were submicron-sized polystyrene-polyglycidol core-shell particles (D_n(SEM) = 270 ± 18 nm) with covalently bound 3,4-dihydroxyphenylalanine (l-DOPA). The growth of the crystals was triggered by a thermodynamically favorable arrangement of particles leading to their close packing and by the formation of covalent cross-links between the individual particles. Under alkaline conditions, molecules of l-DOPA are oxidized, which allows their participation in cross-linking, necessary for the stabilization of the formed colloidal crystals. The average size of the fabricated colloidal crystals is determined by their weight, density of the suspending medium, and the energy of their Brownian motion. Crystals generated during the suspension of particles fall down after reaching the critical weight. Therefore, crystals of similar dimensions are deposited at the bottom of the vessel. The described system is the first example of the formation of stable colloidal crystals in a suspension.

Reactive Diazonium-Modified Silica Fillers for High-Performance Polymers

We describe a simple way of modification of three silica-based fillers with in situ generated 4-hydroxymethylbenzenediazonium salt (⁺N₂-C₆H₄-CH₂OH). The rationale for using a hydroxyl-functionalized diazonium salt is that it provides surface-functionalized fillers that can react with phenolic resins. The modification of silica by diazonium salts was assessed using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). FTIR spectroscopy permitted the tracking of benzene ring breathing and C-C. The absence of the characteristic N≡N stretching vibration in the 2200-2300 cm^-1 range indicates the loss of the diazonium group. XPS results indicate a higher C/Si atomic ratio after the diazonium modification of fillers and the presence of π-π* C1s satellite peaks characteristic of the surface-tethered aromatic species. Adhesion of aryl layers to the silicas is excellent because they withstand harsh thermal and organic solvent treatments. Phenolic resins (used, for example, as binders in abrasive products) were filled with diazonium-modified silicas at 10-25 wt %. The reactivity of the fillers toward phenolic resins was evaluated by the determination of the flow distance. After annealing at 180 °C, the diazonium-modified silica/phenolic resin composites were mechanically tested using the three-point flexural method. The flexural strength was found to be up to 35% higher than that of the composites prepared without any diazonium salts. Diazonium-modified silica with surface-bound -CH₂-OH groups is thus ideal reactive filler for phenolic resins. Such filler ensures interfacial chemical reactions with the matrix and imparts robust mechanical properties to the final composites. This specialty diazonium-modified silica will find potential application as fillers in the composites for the abrasive industry. More generally, aryl diazonium salts are a unique new series of compounds for tailoring the surface properties of fillers and tuning the physicochemical and mechanical properties of polymer composites.

Clay/Polyaniline Hybrid through Diazonium Chemistry: Conductive Nanofiller with Unusual Effects on Interfacial Properties of Epoxy Nanocomposites

The concept of conductive network structure in thermoset matrix without sacrificing the inherent mechanical properties of thermoset polymer (e.g., epoxy) is investigated here using "hairy" bentonite fillers. The latter were prepared through the in situ polymerization of aniline in the presence of 4-diphenylamine diazonium (DPA)-modified bentonite (B-DPA) resulting in a highly exfoliated bentonite-DPA/polyaniline (B-DPA/PANI). The nanocomposite filler was mixed with diglycidyl ether of bisphenol A (DGEBA), and the curing agent (4,4'-diaminodiphenylsulfone) (DDS) at high temperature in order to obtain nanocomposites through the conventional melt mixing technique. The role of B-DPA in the modification of the interface between epoxy and B-DPA/polyaniline (B-DPA/PANI) is investigated and compared with the filler B/PANI prepared without any diazonium modification of the bentonite. Synergistic improvement in dielectric properties and mechanical properties points to the fact that the DPA aryl groups from the diazonium precursor significantly modify the interface by acting as an efficient stress transfer medium. In DPA-containing nanocomposites, unique fibril formation was observed on the fracture surface. Moreover, dramatic improvement (210-220%) in fracture toughness of epoxy composite was obtained with B-DPA/PANI filler as compared to the weak improvement of 20-30% noted in the case of the B/PANI filler. This work shows that the DPA diazonium salt has an important effect on the improvement of the interfacial properties and adhesion of DGEBA and clay/PANI nanofillers.

Diazonium salt-based photoiniferter as a new efficient pathway to clay–polymer nanocomposites

Diazonium salts were used to prepare clay–polymer nanocomposites by living free radical photopolymerization of glycidyl methacrylate. The resulting intercalated nanocomposites have an organic mass loading of ∼41 wt% and a polymer-rich surface.

Ligand-modified mesoporous silica SBA-15/silver hybrids for the catalyzed reduction of methylene blue

Mesoporous silica SBA-15 was prepared and functionalized by (3-glycidyloxypropyl)trimethoxysilane in order to bind 2-aminothiazole and aminopropyl-triazole ligands.