Due to the unique properties of the −NO2 group, nitroaromatic compounds (NARs) serve as key building blocks for the manufacturing of fine chemical products. This makes NARs the largest group of chemicals used on an industrial scale 1−4. Moreover, large quantities of NARs are detected on a daily basis in the exhaust of diesel engines. These significant waste sources render NARs as one of the major environmental and health hazards, as according to the International Agency for Research on Cancer (IARC), NARs significantly contribute to the risk of lung, bladder and pancreas cancers, and in case of children also urinary track and neurological-related cancers 5,6.
The most popular method for neutralizing NARs is the direct reduction of −NO2 to −NH2 groups. Such an approach is very convenient, as aromatic amines (AMMs) are crucial for the manufacturing of i.e. large-scale pharmaceuticals 7,8. However, for this to occur, the reduction requires a catalyst, and as such the application of metallic nanostructures (NSs) as catalysts is particularly important 9. NSs enable the carrying out of the effective reduction of NARs to AAMs under mild conditions. This has made the nanocatalysts (NCats) of NSs one of the most important scientific directions [9,10,49]. To date, the reduction of NARs was tested over various NCats, including AuNSs, AgNSs 10, PtNSs, and PdNSs 11,12. Based on this research, the PtNSs and PdNSs offer an extraordinary and unique activity, leading to the complete reduction of NARs - even at trace amounts of the NCats 11,12. Therefore, it is expected that the barely known nanomaterial (NM): rhenium NSs (ReNSs) would significantly boost the catalytic activity of NCats towards the reduction of NARs. Literature and practice provide numerous high-tech applications of Re in areas such as the aerospace, nuclear and petrochemical industries. Metallic Re is indispensable in the catalytical processes related to increasing the octane number of commercial gasolines, as well as Fisher-Tropsh and ammonia syntheses 13-16. The literature also proves that theNCats of ReNSs outperformed PGM catalysts in the decomposition of 4-nitroaniline 17, nitrobenzene, 4-nitrophenol, 2-nitroaniline, 2,4-dinitrophenol, and 2,4,6-trinitrophenol 18. However, ReNSs are difficult to be obtained. The worldwide scientific literature provides only a few reports on the production of ReNSs. This includes the hot-injection synthesis of Co-ReNSs 19, and also the production of ReNSs using pulsed-laser deposition 20, electrodeposition 21, gamma radiation 22, and chemical vapour deposition 23 approaches. Moreover, ReNSs, like any other NSs, suffer from a limited practical potential due to the fact they reveal a tendency to aggregate and to sediment 24.
Due to this, the following challenges related to the fabrication and application of ReNSs-based NCats for the reduction of NARs can be identified. First, it is possible to increase the rate and efficiency of the catalytic reduction of NARs by using ReNSs instead of other NSs. Second, ReNSs should be stable and possible to be re-used. Third, the synthesis of ReNSs could be facilitated. To address these challenges, a new approach is proposed in this work. This involves the synthesis and loading of ReNSs into polymeric anion exchange resins, in turn leading to the fabrication of new, heterogenous NCats with ReNSs. The proposed method exploits the amino functionalities present on a polymer’s surface to make them serve as reducing and capping agents towards Re(VII) and resultant ReNSs, respectively. The unique in-situ method facilitates the production and stabilization of ReNSs in the course of the reduction-coupled adsorption of the ReO4− anion. Moreover, the morphology of the so-prepared polymeric nanocomposites (pNCs) − polymeric beads, makes them easy to use and facilities the recycling of ReNS-based NCats.