Sorption properties of layered double hydroxides produced by ultrasonic exposure

Abstract

Layered double hydroxides (LDH) can be classified as promising materials due to the ease of synthesis, as well as their wide scope of application. However, the process of LDH synthesis, depending on the LDH chemical composition, can take from tens of hours to several days. It was previously identified that ultrasound exposure during the LDH production significantly reduces the synthesis time, and LDHs produced in this way are interesting in relation to the study of their physicochemical properties and sorption capacity. In this work, the authors produced Mg/Fe LDHs in nitrate form by the traditional method and by the combined action of ultrasound and increased hydrostatic pressure. The resulting samples are characterized by a complex of physicochemical methods of analysis, including scanning electron microscopy (SEM), infrared spectroscopy (IR), X-ray phase analysis (XRD), and thermal gravimetric analysis (TGA) with differential scanning calorimetry (DSC). Experiments were carried out to study the sorption capacity of the obtained Fe/Mg LDH samples in relation to chromate ions under normal conditions and under the influence of ultrasound, including in combination with increased hydrostatic pressure. A photoelectric photometer was used to obtain and analyze data with quantitative values of the sorption process. Data of comprehensive analysis of the finished product indicate that the synthesized material is a Mg/Fe layered double hydroxide. X-ray phase analysis identified that the LDH synthesis using ultrasound and pressure increases the crystallinity degree of the finished product. It has been found that the sorption properties of LDHs produced by the conventional method and LDHs produced under the influence of ultrasound and pressure are different. In Mg/Fe LDHs synthesized by the conventional method, chromate sorption proceeds better than in samples synthesized using ultrasonic treatment in combination with increased hydrostatic pressure. The study shows that the sorption process of the examined LDH samples is described by different mathematical models.