Acid-base properties of aluminosilicates from rice husk and straw

Abstract

We obtained aluminosilicates of sodium and potassium from alkaline hydrolysate of rice straw and husk. Chemical, phase composition of the samples was determined, and nature of the functional groups was studied. We presented results of studying acid-base properties of aluminosilicates’ surface by pH-metry and Hammett methods. We built distribution curves of a number of acid-base centers of the samples from pКa indicators. It was found that the surface of the as-prepared aluminosilicates is characterized by a wider spectrum of Bronsted acid centers (pKa + 2.5; + 3.46; + 6.4), presence of Lewis acid centers (pKa + 16.8) and main Bronsted centers (pKa + 9.45). The largest number of Lewis acid centers was recorded on the surface of sodium aluminosilicates with a narrow ratio of Al2O3:SiO2 = 1:2, the smallest—on the surface of potassium aluminosilicate with a wide ratio of Al2O3:SiO2 = 1:5. The maximum number of Bronsted acid centers was present on the surface of sodium aluminosilicates from rice straw, the minimum—on the surface of potassium aluminosilicate with the amount of SiO2 equal to 41%.