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Human activity and consequent technological advances caused a sharp increase in the demand for precious and rare metals. As a result, they are gradually dispersed on a scale unobserved in the past, passing in trace quantities to secondary raw materials, from which we are forced to recover them. Adsorbents possessing ion exchange and chelating properties may be a response for this scientific challenge. This article is a review that puts an emphasis on the most recent synthetic routes leading to resins possessing anion exchange and chelating properties, in particular as devoted to separation and recovery of the noble metals Au, Pt, and Pd. Selection of the presented materials is based on those techniques that allow researchers to (i) facilitate the synthesis process itself as well as (ii) acquire increased selectivity and adsorption capacity as compared to well-established materials – commercial as well as those reported in the past. [ABSTRACT FROM AUTHOR]

A series of new ion exchange resins was synthesized in a microwave radiation field by modification of chloromethylated styrene/divinylbenzene (S/DVB) and vinylbenzylchloride/divinylbenzene (VBC/DVB) copolymers using amines. The modification processes have been executed simultaneously using the microwave-assisted method and the most efficient, conventional one. The greatest total sorption capacities for noble metals were achieved for two resins conventionally modified using ETDA ion exchange resins based on S/DVB matrices. The microwave-modified resins reveal only slightly lower and in some circumstances even better sorption capacity for noble metals than their conventionally-modified equivalents. The differences are discussed by effect of the synthesis method as evaluated using FTIR spectrophotometry. [ABSTRACT FROM PUBLISHER]

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. [Display omitted] • The dialysis membranes were successfully loaded with Au nanoparticles. • The dialysis enabled the simultaneous reduction and separation of 4-nitrophenol. • The process is enhanced by catalysis-dialysis diffusion channels. [ABSTRACT FROM AUTHOR]

The present work presents a new nanocomposite catalyst with rhenium nanostructures (ReNSs) for the catalytic hydrogenation of 4-nitrophenol and 4-nitroaniline. The catalyst, based on an anion exchange resin with functionality derived from 1,1′-carboimidazole, was obtained in the process involving anion exchange of ReO4– ions followed by their reduction with NaBH4. The amino functionality present in the resin played a primary role in the stabilization of the resultant ReNSs, consisting of ≈1% (w/w) Re in the polymer mass. The synthesized and capped ReNSs were amorphous and had the average size of 3.45 ± 1.85 nm. Then, the obtained catalyst was used in a catalytic reduction of 4-nitrophenol (4-NP) and 4-nitroaniline (4-NA). Following the pseudo-first-order kinetics, 5 mg of the catalyst led to a 90% conversion of 4-NP with the mass-normalized rate constant (km1) of 6.94 × 10−3 min−1 mg−1, while the corresponding value acquired for 4-NA was 7.2 × 10−3 min−1 mg−1, despite the trace amount of Re in the heterogenous catalyst. The obtained material was also conveniently reused. [ABSTRACT FROM AUTHOR]

Nanocomposite (NC) materials, which demonstrate catalytic activity under mild conditions, have garnered considerable attention due to the environmental hazards associated with aromatic nitro compounds. Herein, a novel in-situ synthesis of NCs with zero-valent Au (Au°) is proposed. These materials are based on suspension copolymers with molecular reactors that enable the fabrication of Au° and the enhancement of both the catalytic activity and reusability. NCs were obtained using amino-based nanoreactors (3–14 mmol per gram of a polymer) derived from polyethyleneimine (PEI), 1-(2-hydroxyethyl)piperazine (HEP), 1,4-bis(3-aminopropyl)piperazine (APP). The resultant Au@PEI, Au@HEP, and Au@APP NCs were investigated using optical microscopy, SEM, and TEM. Additionally, the physiochemical structures of both the polymeric matrix and Au° were evaluated using, i.a., FT-IR and XRD. The so-obtained NCs were used as nanocatalysts (NCats) for the catalytic hydrogenation of 4-nitrophenol (4-NP) under mild conditions. The method developed for the synthesis of NCs produced gold-based NCats with 25–37 % Au° content. The synergism between the polymeric matrix and Au° enabled the hydrogenation of 4-NP within approx. 30―38 min with a rate constants of 0.071 min−1 (Au@HEP) and 0.028 min−1 (Au@APP) and, respectively. The spherical millimetric morphology of the polymeric support facilitated the facile recyclability of NCats that maintained their catalytic activity for more than 10 cycles of 4-NP reduction. [ABSTRACT FROM AUTHOR]

A unique in-situ approach for synthesis of polymeric nanocomposites (pNCs) with Au nanoparticles (AuNPs) resulted in producing highly efficient nanocatalysts for decomposition of 4-nitrophenol, which polymeric base guaranteed convenient, multiple re-use. In-situ synthesis involved preparation of the polymeric matrix, its modification by amines, and reduction-coupled adsorption of AuCl 4 −. The approach was successfully applied for production of pNCs. It resulted in obtaining facile, efficient, and extremely easy to use nanocatalysts. Based on the research, the polymeric matrix bearing functionalities derived from 1-amino-4-methylpiperazine (AMPp) allowed to effectively load AuNPs at a concentration of 15.5 %. These AuNPs were characterized by defined morphology and the average diameter of 4.51 ± 2.11 nm. This optimal catalyst, linking the relatively small size and the high concentration of AuNPs, exhibited excellent catalytic activity towards multiple reduction of 4-NP to 4-AP with the mass-normalized rate constant of 1.46 mg min-1. [ABSTRACT FROM AUTHOR]