Thermal decomposition of metatitanic acid and its application as a heavy metal adsorbent

摘要

Thermal decomposition of metatitanic acid and its application as a heavy metal adsorbent One-dimensional (1D) nanostructured inorganic materials (nanowires, nanorods, or nanotubes) are interesting from various aspects. Such structures can be considered as building blocks for sensors, electronics, photonics, and bioelectronics applications. Their potential relies on the subtle control of their physical properties, which are based on their atomic scale structures, and their 1D morphology, i.e., their length and diameter dimensions at the nano- and microscale. By controlling these parameters, a variety of chemical and physical properties can be tailoredl. A unique way of synthesis of advanced materials via extraction of sulfate ions from the crystals of titanyl sulfate and their replacement with hydroxyl groups leaving the Ti-O framework untouched has been proposed2,3. The particle size and morphology of the starting hydrated titanyl sulfate is well preserved in the pseudomorphs of amorphous metatitanic acid including such details like the layered structure of the original hydrated titanyl sulfate crystals. The thermal transformations of metatitanic acid with rod-shaped structure were followed by simultaneous TG/DTA measurements at different heating rates with simultaneous analysis of evolved gases. The first step is characterized as the water and carbon dioxide loss. The second step is represented by the evolution of residual water. In the third step, a sharp exothermic peak representing the crystallization of anatase can be seen (as evidenced by XRD). This phase transition is also accompanied with a small mass loss that can be explained by the opening of cavities and evolution of captured gases at the temperature of crystallization. Then, the potential of adsorptive removal of Pb(II) ions from aqueous environment was investigated. It was observed that with the increasing initial lead(II) ion concentration from 1-10 mM, the maximum adsorption capacities increased gradually. The kinetic experiments showed that the time necessary to reach equilibrium is less than 60 minutes. The maximum adsorbed amount for Pb(II) as calculated from the Langmuir adsorption model was 3.4 mmol g-1. The influence of annealing temperature of prepared material on sorption of Pb(II) was tested with a result that prepared sample seems to be high efficient sorbent. However, the higher the annealing temperature the lower the adsorbed amount of heavy metal ions. Combining the results of adsorption experiments with material characteristics leads to conclusion that the heavy metal ions adsorption efficiency increase with decreasing degree of crystallinity.