Sulfur Pigments Synthesized from Zeolite LTA under Vacuum and in Air. XRD and Spectroscopic (UV-vis, FTIR, Raman, ESR, ESE) Characterization

X-ray, UV-vis, FT-infrared, Raman, continuous wave, and pulsed ESR spectroscopy were applied to characterize pigments prepared at 500 C under vacuum or in air from mixtures of zeolite A (LTA) with sulfur (40 wt %) and anhydrous sodium sulfide (Na-2/S = 0.1-0.4). The samples maintained the LTA structure. Sample color results from an S-3(-) absorption band and the shoulder of a UV band. The fingerprint and asymmetric stretch region of the IR spectra show that the pigments synthesized in air have more disordered structures. The S-2(-)/S-3(-) ratio was estimated from Raman spectra. The ESR spectra of S-3(-) radicals show the existence of several phases visible as five different ESR components. Two components dominate: ideal [Na4S3-](3+) clusters and clusters existing in a disordered environment. The samples synthesized in air show a substantial distortion of local structure. Synthesis in vacuum leads to products containing about 20% of the ordered crystalline phase.