Active Solvent Hydrogen-Enhanced p-Nitrophenol Reduction Using Heterogeneous Silver Nanocatalysts@Surface-Functionalized Multiwalled Carbon Nanotubes

Cellulose Membranes Embedded with Gold-Silver Bimetallic Nanoparticles for the Efficient Reduction of 4-Nitrophenol

Bimetallic nanoparticles (BNPs) have attracted much attention recently due to their improved properties compared to monometallic ones. Gold and silver nanoparticles (AuAgNPs) are among the most studied BNPs. Using these particles as powder or dispersion has drawbacks such as ease of aggregation and difficulty separating and recovering from the reaction medium. Therefore, immobilizing these nanoparticles in polymeric matrices, such as cellulose, is appealing. In this context, the present work focused on preparing unmodified cellulose membranes containing AuAgNPs for use as heterogeneous catalysts in reducing the pollutant 4-nitrophenol. Incorporating these nanoparticles into cellulose membranes represents a significant advancement in heterogeneous catalysis. In addition to being eco-friendly, cellulose membranes offer ease of handling and the potential for reusability, which are crucial factors in catalysis. The nanoparticles were prepared in an aqueous medium from the seeded growth of a silver shell around AuNP seeds. Images recorded by transmission electron microscopy showed that the particles have diameters smaller than 100 nm and are core-shell type. The cellulose membrane was prepared by dissolving microcrystalline cellulose in an ionic liquid, followed by a regeneration process using water. Next, the bimetallic nanoparticles were incorporated into the cellulose membrane. The analyses revealed that the membranes contain bimetallic nanoparticles homogeneously distributed in the matrix, and the inductively coupled plasma-optical emission spectroscopy (ICP-OES) showed that the membrane has 0.339 wt % in silver and 0.069% in gold. The membranes produced were efficient heterogeneous catalysts in reducing 4-nitrophenol, used for at least four cycles without loss of efficiency. This material can be easily isolated from the reaction medium, avoiding centrifugation or filtration processes for reuse. This study represents the first use of AuAgNPs supported on nonmodified cellulose membranes as heterogeneous catalysts, marking an advancement in catalysis and material science.

Facile Synthesis of Natural Kaolin-Based CuO Catalyst: An Efficient Heterogeneous Catalyst for the Catalytic Reduction of 4-Nitrophenol

Water contamination by nitro compounds from various industrial processes has significantly contributed to environmental pollution and severely threatened aquatic ecosystems. Inexpensive, efficient, and environmentally benign catalysts are required for the catalytic reduction of such nitro compounds. This study reports the fabrication of various nanocomposites (NCs) of copper oxide nanoparticles (CuO NPs) supported on a kaolin sheet using straightforward and simple one-pot synthesis procedures that control the metal precursor to kaolin ratios. The selected as-synthesized CuO/kaolin NC was characterized using a range of advanced spectroscopic and microscopic methods, such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV-vis) spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), high-angle annular dark-field scanning TEM (HAADF-STEM), and N2 adsorption/desorption analysis. The characterization results confirmed the successful incorporation of CuO NPs into the kaolin sheets, which had an average size of about 18.7 nm. The fabricated CuO/kaolin NC was used as a heterogeneous catalyst for the efficient reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of sodium borohydride (NaBH4) in an aqueous system at room temperature. The catalyst demonstrated superior catalytic performance with high 4-NP conversion into 4-AP (>99%) in the aqueous phase (50 mL, 20 mg L-1) within 6 min. In addition, the reaction kinetics of 4-NP reduction was also investigated, and the reaction followed the pseudo-first-order kinetics equation with the apparent rate constant of 1.76 min-1. Furthermore, the Arrhenius and Eyring parameters for the catalytic hydrogenation reaction of 4-NP were calculated in order to investigate the catalytic reaction process in more detail. Moreover, the catalyst exhibited excellent reusability and stability over seven repeated catalytic test cycles without any noticeable decline in catalytic activity. Therefore, this paper could provide a novel, efficient, and environmentally promising clay-based non-noble metal oxide nanocatalyst to reduce nitro compounds in the aqueous system.

Formation Features of Polymer-Metal-Carbon Ternary Electromagnetic Nanocomposites Based on Polyphenoxazine

Novel ternary hybrid polyphenoxazine (PPOA)-derived nanocomposites involving Co-Fe particles and single-walled (SWCNTs) or multi-walled (MWCNTs) carbon nanotubes were prepared and investigated. An efficient one-pot method employing infrared (IR) heating enabled the formation of Co-Fe/CNT/PPOA nanocomposites. During this, the dehydrogenation of phenoxazine (POA) units led to the simultaneous reduction of metals by released hydrogen, yielding bimetallic Co-Fe particles with a size range from the nanoscale (5-30 nm) to the microscale (400-1400 nm). The synthesized Co-Fe/CNT/PPOA nanomaterials exhibited impressive thermal stability, demonstrating a half-weight loss at 640 °C and 563 °C in air for Co-Fe/SWCNT/PPOA and Co-Fe/MWCNT/PPOA, respectively. Although a slightly broader range of saturation magnetization values was obtained using MWCNTs, it was found that the type of carbon nanotube, whether an SWCNT (22.14-41.82 emu/g) or an MWCNT (20.93-44.33 emu/g), did not considerably affect the magnetic characteristics of the resulting nanomaterial. By contrast, saturation magnetization escalated with an increasing concentration of both cobalt and iron. These nanocomposites demonstrated a weak dependence of electrical conductivity on frequency. It is shown that the conductivity value for hybrid nanocomposites is higher compared to single-polymer materials and becomes higher with increasing CNT content.

Phosphorus-Doped Activated Coconut Shell Carbon-Anchored Highly Dispersed Pt for the Chemoselective Hydrogenation of Nitrobenzene to p-Aminophenol

Highly dispersed Pt nanoparticles (∼2.5 nm) on phosphorus-doped activated coconut shell carbon (Pt/P-ACC) were synthesized by a two-step impregnation route. Pt/P-ACC showed a high activity, chemoselectivity, and reusability toward the hydrogenation of nitrobenzene to p-aminophenol, with hydrogen as the reducing agent in sulfuric acid. The effects of P species on the catalyst structure, surface properties, and catalytic performance were investigated. It was found that the Pt/P-ACC catalyst had an excellent catalytic activity due to its smaller Pt nanoparticles and higher content of surface-active metal compared with Pt/ACC. Besides, the experimental results and in situ infrared studies demonstrated that the interaction effect between the Pt and P species imbued the surface of Pt with an electron-rich feature, which decreased the adsorption of electron-rich substrates (that is, phenylhydroxylamine) and prevented their full hydrogenation, leading to enhanced selectivity during the hydrogenation of nitrobenzene to p-aminophenol.