Fully recyclable gold-based nanocomposite catalysts with enhanced reusability for catalytic hydrogenation of p-nitrophenol

Abstract: A sustainable supply of pure water is a great challenge in most developing and third-world countries. Nanomaterial-based technology offers technological development for wastewater purification. Nanocatalysis hydrogenation of nitroarene and dye molecules is a hot model in many research fields. Herein, we report eco-friendly and facile technology to synthesize Ag-Au bimetallic nanocomposites. The synthesized nanocomposites are characterized by ultraviolet–visible spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and high-resolution transmission electron microscopy. The synthesized nanocomposite can efficiently degrade Congo red and 4-nitrophenol in water and in the presence of sodium borohydride. The results show that it degrades Congo red and 4-nitrophenol entirely within 6 and 7 min, respectively. These results could be useful for the green synthesis of Ag-Au bimetallic nanocomposites and help to remove organic dye molecules and nitroaromatics from wastewater.

Abstract: Apart from the fact that nitroaromatic compounds (NARs) have toxic and mutagenic characteristics, they are also essential substrates for the synthesis of aromatic amines (AAMs). In this context, the present study presents a new approach that enables NAR-contaminated wastewaters to be treated as a reagent for the synthesis of AAMs. It involves the fabrication of anion exchange membranes with Au nanoparticles (AuNPs) that simultaneously reduce 4-nitrophenol (4-NP) and separate the resultant 4-aminophenol (4-AP) via. the dialysis mechanism. The nanocomposite membranes were prepared by amino-modification of poly(vinyl chloride) films obtained in the presence of cyclohexanone (CH) or tetrahydrofuran (THF), followed by Au(III) reduction coupled-adsorption. The nanomaterials were analysed using scanning transmission electron microscopy (STEM) and Fourier-transformation infrared spectroscopy (FT-IR). The catalytic reaction was carried out in a dialysis unit, where the concentration of 4-NP in the wastewater, and the concentration of separated 4-AP were monitored using UV–Vis spectroscopy. The nanocomposite membranes formed using THF effectively reduced the 4-NP and separated the resultant 4-AP. The yield of the 4-NP conversion reached 80% with a rate constant of 11.30∙10–3 min−1. Based on the results, THF contributed to the formation of diffusion paths in which the 4-NP was simultaneously separated and reduced.

Abstract: In situ hydrogenation of unsaturated compounds by released hydrogen from various hydrogen sources is a good strategy to achieve highly selective hydrogenation. In this work, inexpensive CuO/TiO2 nanocomposites were systematically screened their performance for catalyzing dehydrogenation of ammonia borane (AB) and the tandem hydrogenation of some nitroaromatics. Those CuO/TiO2 binary nanocomposites were found to maximize the hydrogen production from the catalytic hydrolysis of AB. Owing to a positive in-situ hydrogen activation, under mild conditions these CuO/TiO2 nanocomposites exhibited highly excellent reactivities accompanying with better recyclability in the current one-pot hydrogenation. Notably, a selected CuO(0.5) /TiO2(0.5) nanocomposites displayed high activity and regioselectivity (up to100% yield of aim product) as well as increased ability of inhibiting the dehalogenation reaction, especially for 4-bromonitrobenzene or 4-iodonitrobenzene (up to 71.65% yield for 4-bromoaniline or 68.02% yield of 4-iodoaniline). Moreover, that CuO(0.5) /TiO2(0.5) nanocomposites from a co-precipitation method displayed relatively better recyclability against those two control samples obtained from a stepwise preparation process.

Abstract: In this work, novel silver nanoparticles supported on amino-functionalized peeled-watermelon-like silica-coated magnetic catalysts (Fe3O4@SiO2-NH2-Ag) were successfully synthesized for the catalytic reduction of 4-nitrophenol (4-NP) in wastewater. The Fe3O4 nanoparticles were further coated with silica forming a structure similar to peeled watermelon to improve the stability of magnetic Fe3O4 and inhibit their aggregation. Furthermore, surface modification of Fe3O4@SiO2 particles with amino groups was used for the immobilization of silver nanoparticles. As a result, the Fe3O4@SiO2-NH2-Ag (10%) exhibits excellent catalytic activity to reduce 4-NP, which obtained the first-best reaction rate constant of 0.026 s−1. Besides, the Fe3O4@SiO2-NH2-Ag could be easily recovered under an external magnetic field and was reused for 25 catalytic cycles without a significant decline in catalytic activity. The related catalytic mechanism of the reaction was discussed. Overall, the excellent magnetic recyclable nature and immortal catalytic activity make Fe3O4@SiO2-NH2-Ag a very promising material for practical use.

Abstract: There is a world demand for biobased materials in many areas of (nano)science and (nano)technology. In particular, one can benefit from the abundant agricultural waste residues to design high performance materials provided this is achieved through smart surface chemical processes. In this context, olive pit particles were modified with in situ generated aryl diazonium salts in organic medium to provide new functional materials. Various chemical functionalities were successfully anchored onto the olive pit surfaces, namely thiol (SH), amine (NH2) and carboxylic acid (COOH) moities. The as-modified olive pits served for the immobilization of gold and silver metal nanoparticles (Au and Ag NPs) and selected olive pit/NP hybrids were evaluated as catalysts. Surface composition and morphology of the pristine, grafted and nanoparticle-decorated olive pit particles were characterized by X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The hybrid materials were found to catalyse remarkably well the reduction of 4-nitrophenol to 4-aminophenol, taken as an example.

Abstract: The third edition of this highly successful manual is not only a revised text but has been extended to meet the interpretive needs of Raman users as well as those working in the IR region. The result is a uniquely practical, comprehensive and detailed source for spectral interpretation. Combining in one volume, the correlation charts and tables for spectral interpretation for these two complementary techniques, this book will be of great benefit to those using or considering either technique.In addition to the new Raman coverage the new edition offers:* new section on macromolecules including synthetic polymers and biomolecules;* expansion of the section on NIR (near infrared region) to reflect recent growth in this area;* extended chapter on inorganic compounds including minerals and glasses;* redrawn and updated charts plus a number of new charts covering data new to this edition.This new edition will be invaluable in every industrial, university, government and hospital laboratory where infrared (FT-IR) and Raman spectral data need to be analysed.

Abstract: Monodisperse samples of silver nanocubes were synthesized in large quantities by reducing silver nitrate with ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP). These cubes were single crystals and were characterized by a slightly truncated shape bounded by {100}, {110}, and {111} facets. The presence of PVP and its molar ratio (in terms of repeating unit) relative to silver nitrate both played important roles in determining the geometric shape and size of the product. The silver cubes could serve as sacrificial templates to generate single-crystalline nanoboxes of gold: hollow polyhedra bounded by six {100} and eight {111} facets. Controlling the size, shape, and structure of metal nanoparticles is technologically important because of the strong correlation between these parameters and optical, electrical, and catalytic properties.

Abstract: Manmade nanoparticles range from the well-established multi-ton production of carbon black and fumed silica for applications in plastic fillers and car tyres to microgram quantities of fluorescent quantum dots used as markers in biological imaging. As nano-sciences are experiencing massive investment worldwide, there will be a further rise in consumer products relying on nanotechnology. While benefits of nanotechnology are widely publicised, the discussion of the potential effects of their widespread use in the consumer and industrial products are just beginning to emerge. This review provides comprehensive analysis of data available on health effects of nanomaterials.

Abstract: Metal nanoparticles have properties that are significantly different from the bulk properties of the metals. Moreover, their high surface-to-volume ratio renders them ideal candidates for application as catalysts. However, the pronounced tendency of nanoparticles to aggregate must be overcome by using suitable carrier systems. Recently, a number of systems have been discussed that are suitable for applications in aqueous environments. These include polymers, dendrimers, microgels, 18] and other colloidal systems. 20] In all the cases studied so far, these carrier systems only provide a suitable support for the nanoparticles and prevent them from aggregating. In this way the carrier system of, for example, dendrimers or microgels acts much in the same way as a “nanoreactor” that immobilizes the particles and leads to their more convenient handling. Here we report on the first system that allows us to modulate the activity of nanoparticles through a thermodynamic transition that takes place within the carrier system. Figure 1 displays the principle. Metallic nanoparticles are embedded in a polymeric network attached to a colloidal core particle. In all the cases discussed here the core consists of poly(styrene) (PS) while the network consists of poly(Nisopropylacrylamide) (PNIPA) cross-linked with N,N’-methylenebisacrylamide (BIS). The particles are suspended in water, which swells the PNIPA at room temperature. The PNIPA network, however, undergoes a phase transition around 30 8C, during which most of the water is expelled. Previous experiments have demonstrated that this transition is perfectly reversible and the process of shrinking and reswelling can be repeated without degradation or coagulation of the particles. Metallic nanoparticles embedded in such a network are fully accessible to reactants at low temperature. Above the phase transition, however, the marked shrinkage of the network should be followed by a concomitant slowing down of the diffusion of the reactants within the network. The rate of reactions catalyzed by the nanoparticles should thus be slowed down considerably. In this way, the network could act as a “nanoreactor” that can be opened or closed to a certain extent. Herein we demonstrate that thermosensitive core–shell networks may indeed be used as such a nanoreactor. The activity of the catalyst can be modulated by temperature over a wide range. As the model reaction we chose the reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride. The reaction was repeatedly performed to check the catalytic activity of the metal nanoparticles, and the results obtained in the present study can be directly compared to literature data. The carrier particles having a PS core and a PNIPA shell were prepared as described recently. 24] Figure 2 shows a schematic representation of the silver nanoparticles being