One-Step Simultaneous Crystallization of Hydrocalumite and Hydrotalcite-like Materials: Evaluation of Their Uncalcined and Calcined Products on the Photocatalytic Degradation of Toxic Phenolic Compounds

Simultaneous crystallization of hydrotalcite and hydrocalumite-like compounds was carried out by a one-step coprecipitation method. A nominal molar ratio M2+/M3+ = 2 was established, while the zinc amount varied in the 5–50% mol range. Thermal treatments at 500, 600, and 700 °C were performed. Samples were characterized by X-ray powder diffraction (XRD), diffuse reflectance spectroscopy (DRS), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and N2 physisorption. Likewise, the uncalcined and calcined samples were evaluated in the UV photodegradation of 2,4-dichlorophenol, 4-chlorophenol, and phenol. ZnO and P25-TiO2 were also evaluated for comparison. The simultaneous crystallization of hydrotalcite, hydrocalumite, and ZnO occurred in uncalcined samples, while the coexistence of structurally expanded CaO and Al-doped ZnO was observed in the calcined ones. Also, the band gap values decreased progressively with the annealing temperature and the zinc amount. The best photoactivity was achieved with the calcined solids at 700 °C, specifically the sample with nominal 50% zinc mol percent whose percentages of photodegradation in a lapse time of 3 h were 85% for 2,4-dichlorophenol, 99% for 4-chlorophenol, and 35% for phenol, being higher than ZnO (15% for 2,4-dichlorophenol, 0% for 4-chlorophenol, and 8% for phenol) and TiO2 (52% for 2,4-dichlorophenol, 85% for 4-chlorophenol, and 52% for phenol). Mineralization percentages were also higher than ZnO and TiO2. The reutilization study revealed that samples maintained their activity up to the third cycle, and catalyst deactivation was caused by calcium leaching. It was verified that by controlling the zinc content and the annealing temperature, the structural, textural, optical, and catalytic performance can be adjusted, yielding high photoactive materials.