Insight into the preparation of Fe3O4 nanoparticle pillared layered double hydroxides composite via thermal decomposition and reconstruction

As one of layered double hydroxides (LDH) based heterogeneous catalysts , transition metal oxide pillared LDH composite has attracted considerable research interests as its excellent catalytic efficiency and thermal stability. However, during the preparation especially by reconstruction techniques, abundant interlayer regions of LDH are contaminated by some unexpected anion such as LDH affinitive CO 3 2   − , which will result in inaccessible interlayer active site. In this paper, magnetic nanoparticle Fe 3 O 4 pillared LDH composite was synthesized with exchangeable NO 3 − as the main interlayer anion by decomposition and reconstruction route. The anion exchange, decomposition and reconstruction processes were comprehensively investigated. XRD , TG-DTA-MS, SEM and other methods have been employed to characterize materials. The results show that anion exchange between ferric citrate anion and LDH follows Langmuir isotherm model and pseudo-second-order model. The decomposition and oxidation of anion exchange product (LDH-Fe(C 6 H 4 O 7 ) − ) can be complete at 550   °C for 20   min and crystal Fe 3 O 4 with nanostructure is formed between 500 and 600   °C. When calcined product (LDO-Fe 3 O 4 ) is reconstructed by rehydration in 0.015   M HNO 3 -30   wt% NaNO 3 mixture aqueous solution, CO 3 2   − contamination derived from CO 2 in air can be averted and lamellar structure is successfully recovered with Fe 3 O 4 and NO 3 − remaining in the interlayer gallery of LDH.