Natural clay attapulgite as the raw material for synthesis of Al/Ti/Mg-containing mesoporous silicates with cubic, 3D hexagonal, and lamellar mesostructures

Abstract

A series of Al/Ti/Mg-containing ordered mesostructured silicates were synthesized using the natural attapulgite clay as the raw material, which was first pretreated by 4 M hydrochloric acid without other special treatment such as grinding. By varying the pH value in the synthetic gel, different mesophases with cubic, 3D hexagonal, and lamellar mesostructures were obtained. Their mesostructures were confirmed by low-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM). Their morphology and textural properties were analyzed by scanning electron microscopy (SEM) and N2 adsorption. It was found that the hetero-atoms including Al, Ti, and Mg in the clay could be effectively transformed into these ordered mesostructured silicate frameworks in sufficient content, as revealed by inductively coupled plasma (ICP) emission spectroscopy and fourier transform infrared (FT-IR) spectrum. NH3-TPD showed the accessibility of Al species as Bronsted and Lewis acid sites in the mesostructured framework located on the pore surface. All above suggests the potential of attapulgite as a low-cost precursor for the industrial scale production of high quality heteroatom-doped mesophases for various applications. Low-angle powder X-ray diffraction patterns of mesostructured silicates with cubic, 3D hexagonal, and lamellar mesophases, synthesized by using natural clay attapulgite as raw material: uncalcined (left) and calcined (right).