The development of new materials for performing photocatalytic processes to remove contaminants is an interesting and important research line due to the ever-increasing number of contaminants on our planet. In this sense, we developed a layered double hydroxide material based on Zn and Cr, which was transformed into the corresponding oxide by heat treatment at 500 °C. Both materials were widely characterized for their elemental composition, and structural, morphological, optical and textural properties using several experimental techniques such as x-ray diffraction, x-ray photoelectron spectroscopy, scanning and transmission electron microscopy, Fourier transform infrared spectroscopy, UV-vis spectroscopy and physisorption techniques. In addition, the photocatalytic activity of both materials was analysed. The calcined one showed interesting photocatalytic activity in photodegradation tests using crystal violet dye. The operational parameters for the photocatalytic process using the calcined material were optimised, considering the pH, the initial concentration of the dye, the catalyst load, and the regeneration of the catalyst. The catalyst showed good photocatalytic activity, reaching a degradation of 100% in the optimised conditions and showing good performance after five photodegradation cycles.

The present study deals with the preparation and structural and adsorbent characterization of the ternary layered double hydroxides (LDHs; ZFA-HT) with molar ratio Zn2+/Al3+/Fe3+ = 2/0.5/0.5 and its product calcined (ZFA-350) at 350 °C, which is examined for the removal of phosphate P(V) and chromate Cr(VI) from aqueous media. The as-obtained materials are characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), thermogravimetric analysis-differential scanning calorimetry (TGA–DSC), scanning electron microscopy-X-ray energy dispersion (SEM-EDX) and Brunauer–Emmett–Teller (BET). Structural characterizations show that the LDHs is successfully synthesized and its calcined product is a mixed oxide. Batch sorption studies are conducted to investigate the effects of various experimental parameters such as contact time, solution pH, adsorbent amount, initial P(V) or Cr(VI) concentration and temperature. The isotherms, kinetics and thermodynamic parameters of adsorption of phosphate and chromium are studied. The adsorption processes are well described by the pseudo-second-order kinetic model than the other models examined. The adsorption isotherms data fit best to the Langmuir isotherm model instead of Freundlich and Dubinin–Radushkevich models. The maximum monolayer adsorption capacity of ZFA-350 was found to be 140.85 mg/g for P(V) and 52.63 mg/g for Cr(VI). The positive ΔH and ΔS and negative ΔG values reveal that the P(V) and Cr(VI) sorption onto ZFA-350 is endothermic, irreversible and spontaneous in nature.

The northwestern part of Algeria is characterized by a semi-arid climate which has created semi-permanent rivers and dams with low filling rates. It is important to preserve the water resource, which is becoming increasingly scarce. Additionally, it is worth indicating that the mobilized surface waters are continually under threat of significant organic pollution. Indeed, the dam of Cheurfas II, in the northwestern part of the country, is indicative of this situation. In order to establish a diagnosis of the state of the temporal evolution of water quality, time series of 11 variables indicating the presence of organic pollution in this dam were thus analyzed. The data collected were analyzed using the Mann-Kendall test to look for significant trends and the Webel-Ollech test to detect the presence of seasonality. The results obtained showed increasing trends in dry residues, organic matter, phosphates and dissolved oxygen. However, variables like BOD5, COD and NO-3 showed decreasing trends. As for the variables NH+4, NO-2 and pH, they presented no trend. Finally, the water volume of the dam exhibited a significant increase. In addition, no seasonality was detected in the variables studied, with the exception of the PO43- time series and water volume. These findings indicate that the watershed of the dam received pollutants from different origins, in particular industrial pollutants. This makes water biodegradability difficult to achieve.