| To prepare Zn–Fe–NO3, the method of co-precipitation was used (Scheme 1). Zinc nitrate solution was mixed with an iron nitrate one
 (4:1 molar ratio). Under constant stirring, a solution of sodium hydroxide (3.7 mol/L) was added slowly till the precipitation was completed.
 The resulting precipitate was kept at 70±0.5 °C for 10 h. Then, it was
 filtered and washed with bi-distilled water a number of times. Then,
 the obtained precipitate was dried at 80±0.5 °C for 24 h
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