Synthesis and photocatalytic properties of new ternary Ni–Fe–Cr hydrotalcite-like compounds

Ternary Ni–Fe–Cr hydrotalcite-like compounds (NiFeCr-HTLcs) with different Fe³⁺/Cr³⁺ mole ratios were synthesized through coprecipitation method. The materials obtained from different synthesis conditions were characterized by powder X-ray diffraction (XRD). The results indicated that the Ni–Fe–Cr hydrotalcite-like compounds can be synthesized through metal coprecipitation when the pH value was in the range of 7.5–11.0 and the molar ratio of M²⁺/M³⁺ was in the range of 2–4. After calcining at 600 °C, the NiFeCr-HTLcs were converted to Ni–Fe–Cr complex metal oxides. The calcined samples showed higher photocatalytic activity than the NiFeCr-HTLcs precursors and their photocatalytic activity increased as the content of Cr rose in the Cr³⁺/Fe³⁺ molar ratio range of 0.05–2. The calcined materials which had a Cr³⁺/Fe³⁺ molar ratio of 2 possessed the best photocatalytic activity with 85% degradation of methylene blue (MB) dye under visible light irradiation. For the above composition, possible photocatalytic mechanisms are discussed. Moreover, this ternary complex metal oxide system exhibited satisfactory re-usability after four cycles. The facile synthesis process, higher photocatalytic activity under visible light irradiation and satisfactory re-usability enable this complex metal oxide material to be a promising candidate for environmental remediation using visible light.