This study is aimed at developing a simple and low-cost method to fabricate ZnO-loaded porous activated carbon (AC-ZnO) prepared from the Algerian olive-waste cakes and utilize it as a photocatalyst for the degradation of Ethyl Violet dye. The synthesized AC-ZnO material was characterized using powder X-ray diffraction, BET surface area measurements, Raman microscopy, thermogravimetric analysis, UV-visible diffuse reflectance spectroscopy, and zeta potential measurements. The degradation efficiency was evaluated with Ethyl Violet (EV) dye in aqueous solution under UV irradiation supplied by a Xenon arc lamp through a Pyrex glass filter (cutoff 280 nm), and the degraded products were identified by using electrospray ionization mass spectroscopy. Additional experiments were carried out under N₂ flow and with isopropyl alcohol to examine the role of superoxide and hydroxyl radicals, respectively. The amount of ^●OH radical formed on irradiated AC-ZnO was tested with terephthalic acid which can act as a chemical trap for the ^●OH radicals. The results from this study indicate that the AC-ZnO is a potential catalyst for the pollutant removal and the ^●OH radicals are the key species for the degradation of EV. Further, this study opens up an opportunity to produce cheaper activated carbon support from olive wastes for environmental remediation applications.

This study examines the use of a1 mm-diameter tubular microreactor submerged in a temperature-controlled water bath to activate potassium persulfate (KPS) via thermal, Fe²⁺-catalyzed, and combined thermo-catalytic processes for degrading the persistent textile dye Safranin O (SO). The efficiency of these methods was evaluated under varying conditions, including KPS, dye, and Fe^2⁺ flow rates, solution pH, reactor length, and water matrix quality (deionized water, tap water, seawater, and secondary effluent from a wastewater treatment plant (SEWWTP)) across bath temperatures of 30–80 °C. Total organic carbon (TOC) analysis validated the results. Maximum dye conversion (up to 89%) occurred at 70 °C, with no improvement beyond this temperature, mainly due to radical-radical recombination. Longer reactors (2–6 m) enhanced conversion, though this effect diminished at higher temperatures due to efficient thermal activation. Increasing dye flow rates reduced removal efficiency, particularly above 50 °C, highlighting kinetic and mass transfer limitations. Persulfate flow rate increases improved conversion, but a plateau emerged at 80 °C. At lower temperatures (30–40 °C), Fe²⁺ addition significantly boosted SO conversion in deionized water. Between 40 and 50 °C, conversion rose from 30.27% (0 mM Fe²⁺) to 85.91% (0.2 mM Fe²⁺) at 50 °C. At higher temperatures (60–80 °C), conversion peaked at 70 °C for lower Fe²⁺ concentrations (100% for 0.01–0.05 mM Fe²⁺), but higher Fe²⁺ levels (0.1–0.2 mM) caused a decline above 60 °C, dropping to 68.44% for 0.2 mM Fe²⁺ at 80 °C. Deionized, tap, and mineral water showed similar performance, while river water, secondary effluent, and seawater inhibited SO conversion at lower temperatures (30–60 °C). At 70–80 °C, all matrices achieved efficiencies comparable to deionized water for both thermal and thermo-catalytic activation. The thermo-catalytic system achieved >50% TOC reduction, indicating significant organic matter mineralization. The results were comprehensively analyzed in relation to thermal and kinetic factors influencing the performance of continuous-flow reactors.

The aim of this study is to test the ability of photochemical processes (photolysis, Acetone/UV and H₂O₂/UV at 254 nm) to eliminate the Methyl Green (MG, cationic structure) and Bromocresol Purple (BCP, anionic structure) in aqueous solution in mono and binary systems. The obtained results show that the rate of decolorization by UV photolysis at 254 nm in single system is weak for BCP (25%) and acceptable for MG (66%). In dark conditions, preliminary experiments show no decolorization of the two dyes in the presence of acetone and in the presence of H₂O₂ for BCP. However, classical oxidation has been observed for MG in H₂O₂ for concentrations superior to 5 × 10⁻⁴ M. In the presence of light, a real improvement in the decolorization rate of both dyes is obtained using H₂O₂/UV (acting via issued from photolysis of H₂O₂ at 254 nm) and Acetone/UV (acting via energy transfer from the sensitizer which is Acetone to the dye). In the mixture systems, the Acetone/UV process is more effective than direct UV photolysis and H₂O₂/UV. In the three photochemical processes used, each dye decreases the removal efficiency of the other. The dyes removal kinetics follows the pseudo-first-order model in Acetone/UV and H₂O₂/UV systems for both dyes in single and binary systems.

The objective of this study is to investigate the use of photochemical systems (photolysis, H ₂ O ₂ /UV _MP and NaOCl/UV _MP ) to deplete monochloramine compound with a medium pressure lamp as an irradiation source (200–600 nm). First, it was found that the direct photolysis treatment was a suitable method to degrade the given compound and that this degradation was greatly enhanced by H ₂ O ₂ /UV _MP . This could be attributed to radical ^• OH produced in great amount by the photolysis of H ₂ O ₂ . However, no big advantages were observed when we used NaOCl/UV _MP system. Indeed, this process generated radical ^• OH (but in feeble amount) and also radical Cl ^• (to form chloramins) and leading consequently to a less degradation rate comparatively to that obtained with H ₂ O ₂ /UV _MP . This could be explained by a competition between the two species: ^• OH and Cl ^• for the compound. In addition, kinetics data for the three systems were best represented by a pseudo-first-order model and the photodecomposition of NH ₂ Cl has led to the formation of nitrite, nitrate without forming ammonia. It is essential to mention that ^• OH radicals produced from H ₂ O ₂ /UV _MP and NaOCl/UV _MP was detected by a photoluminescence (PL) technic using terephthalic acid (TA) as a probe molecule.