Effect of ultrasound on the structural and textural properties of copper-impregnated cerium-modified zirconium-pillared bentonite

In this study, the synthesis of zirconium-pillared bentonite modified with cerium was performed via two different methods by the application of conventional and ultrasonic treatments during the intercalation stage. To synthesise copper-impregnated pillared clays by wet impregnation, cerium-modified zirconium-pillared clays were used as supportive materials after being calcined at 300 °C. Ultrasonic treatment significantly decreased the required processing time compared with the conventional treatment of the synthesised pillared bentonites. Chemical analysis confirmed the incorporation of Zr4+, Ce4+ and Cu2+ species into the pillared bentonites. X-ray diffraction (XRD) patterns of zirconium- and cerium/zirconium-pillared bentonites prepared by conventional treatment show that one large d-spacing above 3.5 nm corresponds to the mesoporous delaminated part, and another small d-spacing above 1.7 nm is indicative of the microporous pillared part. Zirconium- and cerium/zirconium-pillared bentonites prepared via ultrasonic treatment exhibited similar results, with the same high d-spacing but with a second low-intensity d-spacing above 1.9 nm. The delaminated structures of the pillared bentonites synthesised by both methods were conserved after copper impregnation. Nitrogen-adsorption isotherm analysis showed that the textural characteristics of products synthesised by ultrasonic treatment were comparable to those of products synthesised by conventional treatment. Fourier-transform infrared spectroscopy (FTIR) analyses showed the presence of Brønsted- and Lewis-acid sites, and zirconium-pillared clays synthesised by conventional treatment exhibited increased numbers of Brønsted- and Lewis-acid sites after cerium addition and copper impregnation. However, the products synthesised by ultrasonic treatment exhibited an increased number of Brønsted- and Lewis-acid sites after cerium addition, but a decreased number of acid sites after copper impregnation.

The figure shows HK micropore and BJH mesopore size distributions of Zr-, Ce/Zr- and Cu@Ce/Zr-pillared-bentonite samples synthesized by applying conventional and ultrasonic treatment during the intercalation stage. The micro- and mesopore distributions for all samples are not uniform across samples prepared by both methods, and it can be observed that they include micro- and mesopores with diameters of 0.3-2.0 and 2.0-30.0 nm.Highlights► Zr-, Ce/Zr- and Cu@Ce/Zr-pillared bentonite were prepared via conventional and ultrasonic treatment during the intercalation stage. ► It was found that using ultrasonic treatment at the intercalation stage caused a considerable decrease in the required synthesis time. ► The ultrasonically processed samples possessed characteristics that were comparable to those of conventionally treated samples.