Ultrasound-Assisted Adsorption of Perchlorate Using Calcined Hydrotalcites and the Thermal Stabilization Effect of Recycled Adsorbents on Poly(vinyl chloride).

Abstract

Due to their high anion exchange and memory effect, the layered double hydroxides (LHDs) have wide applications for some areas. In this work, an efficient and green recycling route for layered double hydroxide based adsorbents is proposed specifically for application as a poly(vinyl chloride) (PVC) heat stabilizer without requiring secondary calcination. Conventional magnesium-aluminum hydrotalcite was synthesized using the hydrothermal method followed by removal of carbonate anion (CO32-) between LDH layers by calcination. The adsorption of perchlorate anion (ClO4-) by the memory effect of calcined LDHs with and without ultrasound assistance was compared. Using ultrasound assistance, the maximum adsorption capacity of the adsorbents (291.89 mg/g) was increased, and the adsorption process was fitted using the kinetic Elovich rate equation (R2 = 0.992) and Langmuir adsorption model (R2 = 0.996). This material was characterized using XRD, FT-IR, EDS, and TGA which demonstrated that ClO4- was intercalated into the hydrotalcite layer successfully. The recycled adsorbents were used to augment a commercial calcium-zinc-based PVC stabilizer package applied in a epoxidized soybean oil plasticized cast sheet which is based on an emulsion type PVC homopolymer resin. Use of perchlorate intercalated LDH augmentation yielded significant improvement to static heat resistance as indicated by the degree of discoloration with a life extension of approximately 60 min. The improved stability was corroborated by evaluation of HCl gas evolved during thermal degradation using conductivity change curves and the Congo red test.