For this study, we used cellulose nanocrystals (CNCs) as a water suspendable, and mildly reducing support. In this article, we present the novel synthetic method to access metal nanoparticles based on this principle, thus bypassing two industrial steps necessary to access such nanomaterials: (1) the need to form metal halide salts produced industrially via reacting pure metals with halohydric acids and (2) the reduction of the resulting halogenide salts, or other derivatives originating from these salts. In this interesting work, no external oxidizing, reducing agents or energy were needed to turn bulk into nanomaterials. 8 Bulk Cu and Ag materials were shown to generate nanoparticles in their surface vicinity, as the results of exposure to moisture, light and air. 4b A distinct and potentially milder approach relies on a result recently delineated by Hutchison and his group. 7 Bulk metal grinding is also a well-known approach, suffering from poor NP size and shape control. While metal (0) organometallic species have been developed, they often require some synthetic effort and careful handling. 6 An interesting avenue relies on by-passing the need to reduce metal salts and use a reduced metal form as starting material. 3 In recent years, efforts have been made to develop more sustainable synthetic methods to access these high-value materials, 3 including solvent-free methods, 4 biomass-based approaches 3d,5 and greener reducers development. The concept of atom economy, developed by Trost 1 and adopted within the 12 principles of green chemistry for organic synthesis, 2 remains to be systematically applied to nanosynthesis. However, because metal nanoparticles (NPs) are kinetically stabilized materials, their synthesis often relies on intensive use of solvents, reagents, reducing and capping agents. Many different synthetic methods have been developed to access metal nanomaterials with well controlled size, shape, aspect ratio and thus properties. These species were active for the hydrogenation of aldehydes, 4-nitrophenol, alkenes and alkynes. In 2 weeks, Ag nanoparticles of size 1.3 nm ± 0.3 nm were deposited onto the biopolymer. A water suspension of cellulose nanocrystals was exposed to an Ag wire, under air and light exposure. A highly atom-economical synthetic method to access nanocatalysts from bulk metal is described.
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