Ultrasonic assisted preparation of ultrafine Pd supported on NiFe-layered double hydroxides for p-nitrophenol degradation

NiFe-layered double hydroxide (NiFe-LDH)–loaded ultrafine Pd nanocatalysts (Pd/NiFe-LDHs) were prepared by a facile ultrasonic-assisted in situ reduction technology without any stabilizing agents or reducing agents. Pd/NiFe-LDHs were characterized by FT-IR, XRD, XPS, and TEM. PdNPs are uniformly dispersed on NiFe-LDHs with a particle size distribution of 0.77–2.06 nm and an average particle size of 1.43 nm. Hydroxyl groups in Fe–OH and Ni–OH were dissociated into hydrogen radicals (·H) excited by ultrasound, and ·H reduced Pd2+ to ultrafine PdNPs. Then, Pd was coordinated with O in Ni–O and Fe–O, which improved the stability of the catalysts. Pd/NiFe-LDHs completely degraded 4-NP in 5 min, and the TOF value was 597.66 h−1, which was 16.7 times that of commercial Pd/C. The 4-NP conversion rate remained at 98.75% over Pd/NiFe-LDHs after 10 consecutive catalytic cycles. In addition, the catalyst also has high catalytic activity for the reduction of Congo red, methylene blue, and methyl orange by NaBH4.