Hybrid advanced oxidation processes employed to degrade recalcitrant organic pollutants in water have been widely examined in recent years. In the present work, the potential of TiO₂-mediated photocatalysis in the presence of the periodate anion (IO₄⁻) toward Safranin O (SO) removal from aqueous solutions was investigated. The findings revealed a high efficiency of the UV/TiO₂/IO₄⁻ system due to the production of more reactive radicals (^•OH, IO₃^• and IO₄^•) and non-radical species (O₃, IO₃⁻ and IO₄⁻). Additionally, the presence of IO₄⁻ as an effective electron acceptor avoids electron-hole recombination, which induces more oxidative reactions at the hole level, increasing the degradation rate of SO. Kinetically, the involvement of IO₄⁻ anions in the UV/TiO₂ system enhanced substantially the initial rate of degradation; from 0.295 to 12.07 mg L⁻¹ min⁻¹. The performance of both systems, i.e., UV/TiO₂ and UV/TiO₂/IO₄⁻, was examined under different conditions such as initial dye concentration, photocatalyst loading, periodate dosage, initial solution pH, temperature and dissolved gases. The SO degradation was found to be maximized at low concentration of pollutant at the optimum loading of catalyst (0.4 g L⁻¹). The continuous increasing in periodate concentration over the range of 0.01–3 mM improved the system reactivity with no overdose effect. Both systems seemed to be insensitive to minor variations in temperature in the range of 15–45 °C, and showed a strong dependence on initial solution pH where the degradation rates increased proportionally with pH values up to pH 10 and decreased afterwards. A slight negative effect on the photocatalytic removal yield was noted under either aeration, nitrogen or argon atmospheres in the presence of periodate (UV/TiO₂/IO₄⁻), with minor enhancement under aeration for the classical system (UV/TiO₂). The mineralization of the organic substrate was also monitored. The depletion of organic matter with time was measured using total organic carbon (TOC) analysis. Despite the rapid decolorization of the dye solution in the UV/TiO₂/IO₄⁻ system, a TOC removal efficiency of ~62% was obtained with both systems after 180 min of treatment.

This study investigates the impacts of the gas environment, water matrix, and reactive species on the TiO₂-mediated photocatalytic degradation of safranin O (SO), a dye commonly found in wastewater. A slurry reactor (UVA, 365 nm) was used to quantify SO oxidation while systematically varying the SO concentration (5–40 mg/L), the TiO₂ loading (0–3 g/L), the temperature (15–45 °C), and the pH (2–12). The dissolved gases (air, nitrogen, and argon) and matrices (deionized water, mineral water, and seawater) were also examined. Eight mechanistic probes (ascorbic acid, methanol, azide, nitrite, benzoquinone, oxalate, sucrose, and phenol) were used to identify active oxidants. UVA/TiO₂ achieved rapid decolorization in approximately 90 min at 10 mg/L of SO and 0.4 g/L of TiO₂. Decolorization rates decreased with increasing SO concentration due to active-site competition and inner-filter effects. Rates also exhibited a bell-shaped dependence on TiO₂ loading due to light scattering and aggregation at high solids concentrations. Temperature exhibited a non-monotonic profile with an optimum around 25 °C, and the pH displayed an optimum range with maximal removal occurring around pH 10 and declining at pH 12. Air saturation outperformed N₂ and Ar, indicating that O₂ is the terminal electron acceptor. Photocatalytic performance decreased in the order deionized water > mineral water > seawater, owing to bicarbonate/chloride scavenging and ionic-strength effects. Scavenger tests converged on ^•OH dominance, with measurable contributions from superoxide/hydrogen peroxide (O₂^•−/H₂O₂) and valence-band holes (h⁺); singlet oxygen (¹O₂) played a minor role. These findings underscore the critical interplay between operational and environmental factors and offer a practical framework for scaling TiO₂-based SO abatement in real waters.

In the present paper, the influence of iodate (IO₃⁻) ions on the photocatalytic process using titanium dioxide (UV/TiO₂) was systematically examined. The innovative studied system (UV/TiO₂/IO₃⁻) demonstrated high performance in the elimination of safranin O (SO), a model dye, from water due to the implication of iodine radicals (IO₃^•, IO₂^•, IO^•, etc.). The degradation was assessed by monitoring the change in initial substrate concentration (5–30 mg∙L⁻¹), TiO₂ loading (0.01–3 g∙L⁻¹), IO₃⁻ concentration, liquid temperature, and initial pH. Further enhancement of oxyanion amount was beneficial for the initial rate of degradation (r₀) over the range 0.1–50 mM, such that r₀ rose from 0.724 to 1.12 mg∙L⁻¹∙min⁻¹. However, a concentration of 100 mM IO₃⁻ slowed the removal kinetics. Low pH values were found to be favorable for pollutant removal. Furthermore, a variety of inorganic and organic substances was employed to clarify the effect of the UV/TiO₂/IO₃⁻ process in natural waters. The findings revealed a negative impact of chloride excess in seawater and a decline in SO degradation in mineral water as a result of HCO₃⁻ presence at more than 1 mM. At high concentrations of natural organic matter, the heterogeneity and the strong adsorption of humic acid on the TiO₂ surface were found to be harmful for SO decay.

The effectiveness of periodate-assisted photocatalysis in removing the cationic dye Safranin O (SO) was evaluated using a UV/TiO₂/IO₄⁻ process operated at room temperature under near-neutral pH conditions. Under base conditions ([IO₄⁻] = 0.15 mM, [TiO₂] = 0.4 g/L, [SO] = 10 mg/L), the ternary system achieved a pseudo-first-order rate constant of 0.6212 min⁻¹, outperforming the UV/TiO₂ and UV/IO₄⁻ processes by approximately 21- and 29-fold, respectively. This yielded a synergy ratio of about 12 compared to the sum of the binary processes. Targeted quenching experiments revealed the operative pathways. Strong inhibition by ascorbic acid and phenol indicates that interfacial holes and ^•OH are key oxidants. Methanol caused a moderate slowdown, consistent with ^•OH and hole scavenging. Benzoquinone and oxalate suppressed removal by intercepting the electron and O₂^•− pathways, respectively. Dichromate markedly inhibited the process via optical screening and competition for electrons. Azide had little effect, suggesting a minor role for singlet oxygen. Matrix studies showed progressively slower kinetics from deionized water to mineral water to seawater. This was due to halides, sulfate, alkalinity, and TiO₂ aggregation driven by ionic strength. Additional tests confirmed that the dominant modulators of performance were humic acid (site fouling and light screening), chloride and sulfate (radical speciation and surface effects), nitrite (near-diffusion radical quenching), and bicarbonate at pH 8.3 (conversion of ^•OH to CO₃^•−). Nonionic surfactants (Tween 80, Triton X-100) also depressed SO removal through micellar sequestration and competitive adsorption on TiO₂. The study confirms the potential of UV/TiO₂/IO₄⁻ as a tunable AOP capable of delivering rapid and reliable dye degradation under a wide range of water quality conditions. The mechanistic mapping unifies two roles for IO₄⁻, an electron acceptor that inhibits recombination and a photochemical precursor of iodine centered and ^•OH radicals and connect these roles to the observed synergy and to the trend across deionized water, mineral water, and seawater. The scavenger outcomes assign the main oxidant flux to holes and ^•OH radicals with a contributory electron or O₂^•− branch from IO₄⁻ reduction.