Synthesis, characterization and environmental applications of Zn-Al and Co-Al mixed oxides derived from layered-like precursors

Development of cost-effective nanomaterials with tailored surfaces and bulk properties play a fundamental role in enhancing efficiency in environmental and energy-related applications. Layered double hydroxides (LDHs) belong to a family of two-dimensional materials, defined by the general formula [M²⁺_1-xM³⁺_x(OH)₂]^x+ (A^n-)_x/n•mH₂O, where M²⁺ and M³⁺ represent divalent and trivalent cations and A^n- is an anion. These compounds exhibit outstanding characteristics such as friendly preparation, tunable composition and anion exchange capacity, being widely used in various fields like drug delivery, energy storage, catalysis, etc. An interesting way to obtain oxide catalysts is through the controlled thermal decomposition of the corresponding LDHs precursors. In this way, mixed-metal oxides with desirable properties including high specific surface area, thermal stability and homogeneous metal dispersion are obtained.

This study investigates the synthesis, characterization and environment-related applications of Zn-Al and Co-Al mixed oxides derived from LDH materials. Both Zn-Al and Co-Al LDH precursors were prepared by a coprecipitation method at a constant pH, starting from the corresponding metal nitrates with a molar ratio of M²⁺/M³⁺ being kept at 3. The precipitating solution was a mixture of NaOH (1 M) and Na₂CO₃ (0.2 M). The slurry was kept under stirring and aged at 75 °C for 12 h. The suspension was then washed with deionized water and dried at 110 °C for 12 h prior to the calcination at 650 °C for 6 h, in air atmosphere. The obtained Zn-Al and Co-Al mixed oxides were characterized by several techniques (e.g., powder X-ray diffraction (XRD), UV-Vis spectra, DRIFT-ATR spectroscopy, specific surface area measurements, etc.), revealing their physicochemical properties. The photocatalytic activity of these catalysts was evaluated for the photodegradation of persistent organic pollutants (e.g., phenol) under simulated solar irradiation, showing good performance.