Synthèse de nanoparticules à base de cuivre sur une kaolinite anionique fonctionnalisée par des groupes sulfonates : Application à la réduction catalytique de quelques composés nitroaromatiques

Abstract

In this work, kaolinite clay mineral was modified by grafting an organic compound (1,3 propanesultone) into the interlayer space. The aim was to obtain a cations exchanger material that could be used as a support for copper-based nanoparticles. Physico-chemical characterizations (XRD, FTIR, 13C NMR, 29Si NMR, SEM, TEM and ATG) performed on the clay mineral at different stages of the modification process revealed for the first time to the best of our knowledge, the synthesis of an anionic kaolinite (named K-S). This nanohybrid material was characterized by a larger interlayer space compared to native kaolinite (1.22 nm instead of 0.71 nm). Scanning electron microscopy also revealed partial delamination, which reduced the thickness of the clay mineral aggregates. Quantification of the grafted organic compound by thermogravimetric analysis allowed the determination of the chemical formula of the nanohybrid kaolinite: Al2Si2O5(OH)3.77(O(CH2)3SO3H)0.23. Cations exchanger property of K-S was demonstrated by the quantitative adsorption of methylene blue, a model cationic dye. K-S was subsequently used as a support for the in-situ synthesis of copper-based nanoparticles, using a bottom-up approach. The cations exchanger property was exploited to accumulate the nanoparticle precursor (Cu2+ cations) on the surface of the support prior to its reduction by sodium borohydride. The resulting material (K-S/Cu) was structured as thin functionalized kaolinite platelets on which agglomerated copper-based nanoparticles (with diameter in the range 6 nm to 8 nm) were deposited. Based on XRD characterization, these nanoparticles were mainly copper(I) oxides (Cu2O), with few amounts of copper nanoparticles. This composite material displays excellent catalytic properties for the reduction of 4-nitrophenol, 4-chloro-2-nitroaniline and 4-nitrocatechol. These catalytic reactions were characterized by fast kinetics and induction times of varying magnitude, depending on the nitroaromatic compound considered. The reaction was generally more favorable for 4-chloro 2-nitroaniline, the most hydrophobic compound of the series studied. These results once again demonstrate the potential of kaolinite for the synthesis of new and high-value-added materials.