Efficient and Recyclable Heterogeneous Catalyst Based on PdNPs Stabilized on a Green-Synthesized Graphene-like Nanomaterial: Effect of Surface Functionalization

Abstract

This work reports for the first time a straightforward and efficient approach to covalent surface functionalization of a sustainable graphene-like nanomaterial with abundant carboxylic acid groups. This approach results in an efficient and robust chelatant platform for anchoring highly dispersed ultrasmall palladium particles with excellent catalytic activity in the reduction of both cationic (methylene blue, MB) and anionic (eosin-Y, Eo-Y) toxic organic dyes. The large-specific-surface-area (S BET = 266.94 m 2 /g) graphene-like nanomaterial (GHN) was prepared through a green and cost-effective pyrolysis process from saccharose using layered bentonite clay as a template. To introduce a high density of carboxylic acid functions, GHN was first doubly functionalized by successive grafting reaction using two different strategies: (i) in the first case, GHN was first grafted by (3-glycidyloxypropyl) trimethoxysilane (GPTMS) and then bifunctionalized by chemical grafting of tris(4-hydroxyphenyl)methane triglycidyl ether (TGE). In the second case, the grafting order of the two molecules has been reversed. GHN-GPTMS-TGE provided the highest number of grafted reactive epoxy groups, and it was selected for further functionalization with carboxylic acid functions via a ringopening reaction through a two-step hydrolysis (H 2 SO 4 )/oxidation (KMnO 4 ) approach. The GHN nanomaterial bearing carboxylic acid groups was then treated with sodium hydroxide to produce a deprotonated carboxylic acid-rich platform. Finally, due to a high density of accessible chelatant carboxylic acid groups, GHN−COO − binds strongly a great amount of Pd 2+ ions to form stable complexes which after reduction by NaBH 4 leads to highly dispersed, densely anchored, and uniformly distributed nanoscale Pd particles (d ∼ 4.5 nm) on the surface of the functionalized GHN. The GHN−COO − @PdNPs nanohybrid proved to be highly efficient for dye reduction by NaBH 4 in aqueous solution at room temperature. Moreover, because of the high stability of the asprepared graphene-like supported PdNPs, it exhibited very good reusability and could be recycled up to eight times without any significant loss in activity.

Metal–Organic Framework Accelerated One-Step Capture and Reduction of Palladium to Catalytically Active Nanoparticles

“…To prepare Pd NPs, further dissociation, elution, and reduction are required, which span hours to days. Moreover, harsh physical and chemical treatments involving extremely high temperature are used during processing, having problems including high-energy consumption and generation of pollution. ,, To address these, advanced absorbents such as silica, organic polymers, and biomass have been investigated for efficient and selective isolation. ,− Novel supports and methodology have also emerged for loading and reducing Pd to the metallic form. − However, it is rarely explored to capture Pd ions from complicated systems and directly reduce them to functional Pd NPs, which not only requires extraordinary selectivity and affinity but also has to address issues during reduction. The coexistence of various metal ions can interfere with both the adsorption and reduction of Pd. − Furthermore, the high tendency of Pd NPs to aggregate due to the high surface energy can dramatically decrease their activity. ,, Therefore, it is challenging to meet all the requirements for selective capture, reduction, and stabilization of Pd(0) in one step, which however holds great promise in resource recovery for creating advanced materials in an environment-friendly manner.…”