## 3 Applications of Magnetically Recyclable Nanocatalysis (MRNCs) in Water
[PERSON] _et al._ reported magnetite-supported TEMPO nanocatalysts for metal-free and halogen-free oxidation of primary and secondary alcohols in aqueous medium [48]; the catalyst was synthesized by a multistep procedure starting from magnetite (Scheme 11). **Scheme 11. ** Synthesis of magnetite-supported TEMPO nanocatalyst. Magnetite-supported TEMPO nanocatalyst worked well for an array of alcohols (primary, secondary, air sensitive and sterically hindered alcohols), and all substrates are converted to the corresponding carbonyls in good to excellent yields (Scheme 12). **Scheme 12. ** Selective oxidation of alcohols catalyzed by magnetite-supported TEMPO. This highly efficient, metal- and halogen-free protocol could be used for the preparation of important pharmaceutical raw materials and drug intermediates. [PERSON] and [PERSON] have synthesized \(\beta\)-cyclodextrinrin-polyurethane polymer decorated Fe\({}_{3}\)O\({}_{4}\) magnetic nanoparticles (\(\beta\)-CDPU-MNPs) as a novel class of hybrid organic/inorganic molecular catalyst in two steps and evaluated their performance for solid-liquid phase-transfer catalyst in nucleophilic substitution reactions of benzyl halides in water [49]. First, superparamagnetic magnetite nanoparticles (MNPs) were prepared via chemical coprecipitation method [50] and then decorated by \(\beta\)-cyclodextrinrin-polyurethane (CDPU) polymer. The \(\beta\)-CDPU-MNPs (17-20 nm by TEM) was employed for the nucleophilic substitution reaction of benzyl halides with thiocyanate; acetate anions, azides, and cyanides; excellent yield of the corresponding products were obtained (Scheme 13). The desired products were obtained in pure form which does not require further purification and the formation of by-products such as isothioxane or alcohols was not discernible; nanomagnetic \(\beta\)-CDPU catalyst was easily separable from reaction mixture via application of a magnetic field, allowing straightforward recovery and reuse. **Scheme 13. ** Nucleophilic substitution reaction of benzyl halides with thiocyanate, azide, cyanide, and acetate anions in water. [PERSON] and co-workers have investigated a facile synthesis of magnetic-iron grafted polymer-palladium ternary nanocomposite microspheres [(Fe)-PPy-Pd] via the aqueous chemical oxidative polymerization of pyrrole, using PdCl\({}_{2}\) as the oxidant in the presence of Fe nanoparticles [51]. In typical synthesis of [(Fe)-PPy-Pd], carbon-coated magnetic Fe (Fe/C) nanoparticles were synthesized by an arc plasma method. The carbon shell was introduced to prevent oxidation of Fe and then oxidative polymerization of pyrrole was achieved by employing PdCl\({}_{2}\) as an oxidant (Scheme 14). The catalytic performance of (Fe)-PPy-Pd (\(14.6\pm 7.9\)\(\mu\)m) for the Suzuki-Miyaura cross-coupling reaction between p-methylphenylboronic acid and p-bromoacetophenone in aqueous media was investigated to generate 4-acetyl-4'-methylbiphenyl (98% yield). After the completion of this first reaction, (Fe)-PPy-Pd were recovered using a magnetic bar and reused for four successive cycles for the coupling reaction under the same conditions, affording the product in 99%, 99%, 94%, and 99% yields, respectively. In addition, ICP-AES results indicated little to no leaching of the Pd from the (Fe)-PPy-Pd after the fifth reaction. [PERSON] and [PERSON] have reported magnetically retrievable \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)/hydroxyapatite (HAP) nanoparticles for the cycloaddition reactions of alkyne, halide and azide in aqueous medium to 1,2,3-triazoleoles [52]. In general, these types of reactions are performed using Cu and Ru metal bearing catalysts [53,54]. Recently, magnetically recyclable copper-supported magnetic nanoparticles have been investigated for the synthesis of disubstituted 1,2,3-triazoleoles [55,56]. It is important to replace these non-recyclableand expensive metals by base metal such as iron. In typical synthesis of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)/HAP, the iron nanoparticle supported on HAP were prepared by simple co-precipitation method [52].