Hydrothermal modification of calcined diatomite with CaO: Effect of NaOH pretreatment

The development and application of high-adsorptive calcined diatomite (C-D) can provide a cost-effective solution for the filter aid industry, which remains a challenge in this field. Herein, an alkali (NaOH) pretreatment was introduced before the calcium oxide (CaO)-mediated hydrothermal activation of C-D. The adsorption performance of the alkali-modified samples (modified calcined diatomite: M-D) was significantly improved. The methylene blue trihydrate (MB) adsorption capacity of the optimal M-D sample reached 45.76 mg/g, which was 2.73 times higher than that of the sample prepared without the alkali treatment. The substantial enhancement in adsorption performance of M-D was mainly attributed to the abundant SiO32- species which was primarily generated during the NaOH pretreatment. SiO32- species are helpful for generating silicate substances with a larger specific surface area. By regulating the amount of NaOH, it was feasible to control the morphology/nanostructure and composition of the final materials. Well-developed flower-like nanoclusters was synthesized on the surface of C-D, resulting in higher specific surface area and adsorption capacity. This work paves the way to the value-added application of natural diatomite resources via providing an efficient modification method to optimize the properties of C-D.