Using photoactivated periodate to decompose TOC from hydrolysates of chemical warfare agents

Ozone- and Hydroxyl Radical-Induced Degradation of Micropollutants in a Novel UVA-LED-Activated Periodate Advanced Oxidation Process

In this study, novel light emitting diode (LED)-activated periodate (PI) advanced oxidation process (AOP) at an irradiation wavelength in the ultraviolet A range (UVA, UVA-LED/PI AOP) was developed and investigated using naproxen (NPX) as a model micropollutant. The UVA-LED/PI AOP remarkably enhanced the degradation of NPX and seven other selected micropollutants with the observed pseudo-first-order rate constants ranging from 0.069 ± 0.001 to 4.50 ± 0.145 min-1 at pH 7.0, demonstrating a broad-spectrum micropollutant degradation ability. Lines of evidence from experimental analysis and kinetic modeling confirmed that hydroxyl radical (•OH) and ozone (O3) were the dominant species generated in UVA-LED/PI AOP, and they contributed evenly to NPX degradation. Increasing the pH and irradiation wavelength negatively affected NPX degradation, and this could be well explained by the decreased quantum yield (ΦPI) of PI. The degradation kinetics of NPX by the UVA-LED/PI AOP in the presence of water matrices (i.e., chloride, bicarbonate, and humic acid) and in real waters were examined, and the underlying mechanisms were illustrated. A total of nine transformation products were identified from NPX oxidation by the UVA-LED/PI AOP, mainly via hydroxylation, dealkylation, and oxidation pathways. The UVA-LED/PI AOP proposed might be a promising technology for the treatment of micropollutants in aqueous solutions. The pivotal role of ΦPI during light photolysis of PI may guide the future design of light-assisted PI AOPs.

Emerging periodate-based oxidation technologies for water decontamination: A state-of-the-art mechanistic review and future perspectives

With the ever-increasing severity of the ongoing water crisis, it is of great significance to develop efficient, eco-friendly water treatment technologies. As an emerging oxidant in the advanced oxidation processes (AOPs), periodate (PI) has received worldwide attention owing to the advantages of superior stability, susceptible activation capability, and high efficiency for decontamination. This is the first review that conducts a comprehensive analysis of the mechanism, pollutant transformation pathway, toxicity evolution, barriers, and future directions of PI-based AOPs based on the scientific information and experimental data reported in recent years. The pollutant elimination in PI-based AOPs was mainly attributed to the in situ generate reactive oxygen species (e.g., ^•OH, O(³P), ¹O₂, and O₂^•-), reactive iodine species (e.g., IO₃^• and IO₄^•), and high-valent metal-oxo species with exceptionally high reactivity. These reactive species were derived from the PI activated by the external energy, metal activators, alkaline, freezing, hydroxylamine, H₂O_2, etc. It is noteworthy that direct electron transport could also dominate the decontamination in carbon-based catalyst/PI systems. Furthermore, PI was transformed to iodate (IO₃^-) stoichiometrically via an oxygen-atom transfer process in most PI-based AOPs systems. However, the production of I₂, I^-, and HOI was sometimes inevitable. Furthermore, the transformation pathway of typical micropollutants was clarified, and the in silico QSAR-based prediction results indicated that most transformation products retained biodegradation recalcitrance and multi-endpoint toxicity. The barriers faced by the PI-based AOPs were also clarified with potential solutions. Finally, future perspectives and research directions are highlighted based on the current state of PI-based AOPs. This review enhances our in-depth understanding of PI-based AOPs for pollutant elimination and identifies future research needs to focus on the reduction of toxic byproducts.

Modeling of Textile Dye Removal from Wastewater Using Innovative Oxidation Technologies (Fe(II)/Chlorine and H2O2/Periodate Processes): Artificial Neural Network-Particle Swarm Optimization Hybrid Model

An efficient optimization technique based on a metaheuristic and an artificial neural network (ANN) algorithm has been devised. Particle swarm optimization (PSO) and ANN were used to estimate the removal of two textile dyes from wastewater (reactive green 12, RG12, and toluidine blue, TB) using two unique oxidation processes: Fe(II)/chlorine and H₂O₂/periodate. A previous study has revealed that operating conditions substantially influence removal efficiency. Data points were gathered for the experimental studies that developed our ANN-PSO model. The PSO was used to determine the optimum ANN parameter values. Based on the two processes tested (Fe(II)/chlorine and H₂O₂/periodate), the proposed hybrid model (ANN-PSO) has been demonstrated to be the most successful in terms of establishing the optimal ANN parameters and brilliantly forecasting data for RG12 and TP elimination yield with the coefficient of determination (R2) topped 0.99 for three distinct ratio data sets.

Intensification of light green SF yellowish (LGSFY) photodegradion in water by iodate ions: Iodine radicals implication in the degradation process and impacts of water matrix components

The results of this work showed that UV/IO₃^- oxidation process supplies good performance in the degradation of light green SF yellowish (LGSFY) dye in deionized water. This process generated reactive iodine radicals that make the degradation much faster than the sole UV irradiation. The assistance of UV-irradiation by 10 mM of iodate increased the LGSFY removal after 10 min from 36% to 90% for C₀ = 10 mg/L and from 18% to 85% for C₀ = 20 mg/L. In parallel, a 2.5 and 4.72-fold increase in the LGSFY initial degradation rate, as compared with UV alone, were recorded for, respectively, 10 and 20 mg/L of LGSFY. IO₂ and IO played the most important role in the degradation of LGSFY by the UV/IO₃^- process. The degradation was not affected by the presence of chloride and nitrate ions even at high dosage levels (up to 0.1 M), whereas sulfate ions reduced the valuable effect of iodate to the half when they are present at 0.1 M. Correspondingly, humic acids, at usual concentrations as those measured in natural waters, did not affect significantly the LGSFY degradation upon photoactivated iodate process. These results revealed, in one part, that iodine radicals are selective oxidants and, in another part, that the process is likely to remove organic dyes from natural water which often contains mineral constitutes and humic substances.

Efficient degradation method of emerging organic pollutants in marine environment using UV/periodate process: Case of chlorazol black

Sea has historically been subject to high anthropogenic pressures of direct and indirect loads of emerging organic pollutants (EOPs) from intensive industrial and agricultural activities. Photoactivated periodate (UV/IO₄^-) is an innovative oxidation technique that was never tested in seawater as pollutants matrix. In this work, we attempted to investigate the treatment of seawater contaminated with chlorazol black (CB) dye, as a model of EOPs, using photoactivated periodate process. It was found that periodate (0.5mM) assisted-UV treatment of CB (20mgL^-1) in seawater resulted in 13.16-fold increase in the initial degradation rate, compared to UV alone, and 82% of CB was removed after 40min face to 38% under UV alone. The beneficial effect of UV/IO₄^- treatment is strongly dependent on operational parameters. More interestingly, SDS surfactant, as an organic matter, did not affect the degradation process, making UV/IO₄^- a promising technique for treating seawater contaminated with EOPs.

Clarifying the Equilibrium Speciation of Periodate Ions in Aqueous Medium

Equilibria of periodate ion were reinvestigated in aqueous solution by using potentiometric titration, UV and Raman spectroscopies, and gravimetry simultaneously at 0.5 M ionic strength and at 25.0 ± 0.2 °C. Stepwise acid dissociation constants of orthoperiodic acid were found to be pK₁ = 0.98 ± 0.18, pK₂ = 7.42 ± 0.03, and pK₃ = 10.99 ± 0.02, as well as pK₂ = 7.55 ± 0.04 and pK₃ = 11.25 ± 0.03 in the presence of sodium nitrate and sodium perchlorate as background salts, respectively. pK₁ cannot be determined unambiguously from our experiments in the presence of sodium perchlorate. The molar absorptivity spectrum of H₄IO₆^- and H₃IO₆^2- was determined in the range of 215-335 nm, as major species of periodate present from slightly acidic to slightly alkaline conditions. The solubility of periodate decreases significantly under alkaline conditions, and it was determined to be (2.8 ± 0.4) mM by gravimetry, under our experimental conditions. None of these studies gave any clear evidence for an ortho-meta equilibrium and the frequently invoked dimerization of periodate. All measurements can quantitatively be described by the presence of orthoperiodic acid and its three successive deprotonation steps.

Improvement of sonochemical degradation of Brilliant blue R in water using periodate ions: Implication of iodine radicals in the oxidation process

In this paper, the effect of periodate (IO₄^-) on the ultrasonic degradation at 300kHz of Brilliant Blue R (BBR), an organic dye pollutant, was investigated. The experiments were realized in the absence and presence of periodate for various operating conditions including initial solution pH (2-8) and delivered ultrasonic power (20-80W). It was found that periodate greatly enhanced the sonochemical degradation of BBR. The degradation rate increased significantly with increasing IO₄^- concentration up to 10mM and decreased afterward. With 10mM of periodate, the degradation rate was 2.4-fold higher than that with ultrasound alone. The chemical probes experiments showed that periodate activation into free radicals (IO₃, IO₄ and OH) takes place by sonolysis and iodine radicals contribute significantly in the oxidation process. It was found that the periodate-enhanced effect was strongly experimental parameters dependent. The advantageous effect of periodate increased significantly with decreasing power and the best enhancing effect was obtained for the lowest power. Correspondingly, the periodate-enhanced effect increased with pH increase in the range 2-8 and it was more remarkable at near alkaline condition (pH 8). A reaction scheme for periodate sonolysis was proposed, for the first time, discussed and then used for interpreting the obtained results.

Oxidizing capacity of periodate activated with iron-based bimetallic nanoparticles

Nanosized zerovalent iron (nFe0) loaded with a secondary metal such as Ni or Cu on its surface was demonstrated to effectively activate periodate (IO4-) and degrade selected organic compounds at neutral pH. The degradation was accompanied by a stoichiometric conversion of IO4- to iodate (IO3-). nFe0 without bimetallic loading led to similar IO4- reduction but no organic degradation, suggesting the production of reactive iodine intermediate only when IO4- is activated by bimetallic nFe0 (e.g., nFe0-Ni and nFe0-Cu). The organic degradation kinetics in the nFe0-Ni(or Cu)/IO4- system was substrate dependent: 4-chlorophenol, phenol, and bisphenol A were effectively degraded, whereas little or no degradation was observed with benzoic acid, carbamazepine, and 2,4,6-trichlorophenol. The substrate specificity, further confirmed by little kinetic inhibition with background organic matter, implies the selective nature of oxidant in the nFe0-Ni(or Cu)/IO4- system. The comparison with the photoactivated IO4- system, in which iodyl radical (IO3•) is a predominant oxidant in the presence of methanol, suggests IO3• also as primary oxidant in the nFe0-Ni(or Cu)/IO4- system.