Efficient photocatalytic degradation of Safranin O by integrating solar-UV/TiO 2 /persulfate treatment: Implication of sulfate radical in the oxidation process and effect of various water matrix components

Non-radical activation of persulfate with Bi2O3/BiO1.3I0.4 for efficient degradation of propranolol under visible light

Non-radical activation of persulfate (PS) by photocatalysts is an effective approach for removing organic pollutants from aqueous environments. In this study, a novel Bi2O3/BiO1.3I0.4 heterojunction was synthesized using a facile solvothermal approach and used for the first time for non-radical activation of PS to degrade propranolol (PRO) in the presence of visible light. The findings found that the degradation rate of PRO in the Bi2O3/BiO1.3I0.4/PS system was significantly increased from 19% to more than 90% within 90 min compared to the Bi2O3/BiO1.3I0.4 system. This indicated that the composite system exerted an excellent synergistic effect between the photocatalyst and the persulfate-based oxygenation. Quenching tests and electron paramagnetic resonance demonstrated that the non-radical pathway with singlet oxygen as the active species played a major role in the photocatalytic process. The existence of photo-generated holes during the reaction could also be directly involved in the oxidation of pollutants. Meanwhile, a possible PRO degradation pathway was also proposed. Furthermore, the impacts of pH, humic acid and common anions on the PRO degradation by the Bi2O3/BiO1.3I0.4/PS were explored, and the system's stability and reusability were also studied. This study exhibits a highly productive catalyst for PS activation via a non-radical pathway and provides a new idea for the degradation of PRO.

Electro-oxidation of ammonia nitrogen using W, Ti-doped IrO2 DSA as a treatment method for mariculture and livestock wastewater

Animal farming wastewater is one of the most important sources of ammonia nitrogen (NH4+-N) emissions. Electro-oxidation can be a viable solution for removing NH4+-N in wastewater. Compared with other treatment methods, electro-oxidation has the advantages of i) high removal efficiency, ii) smaller size of treatment facilities, and iii) complete removal of contaminant. In this study, a previously prepared DSA (W, Ti-doped IrO2) was used for electro-oxidation of synthetic mariculture and livestock wastewater. The DSA was tested for chlorine evolution reaction (CER) activity, and the reaction kinetics was investigated. CER current efficiency reaches 60-80% in mariculture wastewater and less than 20% in livestock wastewater. In the absence of NH4+-N, the generation of active chlorine follows zero-order kinetics and its consumption follows first-order kinetics, with cathodic reduction being its main consumption pathway, rather than escape or conversion to ClO3-. Cyclic voltammetry experiments show that NH4+-N in the form of NH3 can be oxidized directly on the anode surface. In addition, the generated active chlorine combines with NH4+-N at a fast rate near the anode, rather than in the bulk solution. In electrolysis experiments, the NH4+-N removal rate in synthetic mariculture wastewater (30-40 mg/L NH4+-N) and livestock wastewater (~ 450 mg/L NH4+-N) is 112.9 g NH4+-N/(m2·d) and 186.5 g NH4+-N/(m2·d), respectively, which is much more efficient than biological treatment. The specific energy consumption (SEC) in synthetic mariculture wastewater is 31.5 kWh/kg NH4+-N, comparable to other modified electro-catalysts reported in the literature. However, in synthetic livestock wastewater, the SEC is as high as 260 kWh/kg NH4+-N, mainly due to the suppression of active chlorine generation by HCO3- and the generation of NO3- as a by-product. Therefore, we conclude that electro-oxidation is suitable for mariculture wastewater treatment, but is not recommended for livestock wastewater. Electrolysis prior to urea hydrolysis may enhance the treatment efficiency in livestock wastewater.

Adsorption effects of electron scavengers and inorganic ions on catalysts for catalytic oxidation of sulfamethoxazole in radiation treatment

This study aimed to investigate adsorption effects of electron scavengers (H2O2 and S2O82-) on oxidation performance for mineralization of sulfamethoxazole (SMX) in radiation treatment using catalysts (Al2O3, TiO2). Hydrogen peroxide (H2O2, 1 mM) as an electron scavenger showed weak adsorption onto catalysts (0.012 mmol g-1-Al2O3 and 0.004 mmol g-1-TiO2, respectively), leading to an increase in TOC removal efficiency of SMX within the absorbed dose of 30 kGy by 12.3% with Al2O3 and by 8.0% with TiO2. The weak adsorption of H2O2 onto the catalyst allowed it to act as an electron scavenger, promoting indirect decomposition reactions. However, high adsorption of S2O82- (1 mM) onto Al2O3 (0.266 mmol g-1-Al2O3) showed a decrease in TOC removal efficiency of SMX from 76.2% to 30.2% within the absorbed dose of 30 kGy. The high adsorption of S2O82- onto the catalyst inhibited direct decomposition reaction by reducing adsorption of SMX on catalysts. TOC removal efficiency for Al2O3 without electron scavengers in an acidic condition was higher than that in a neutral or alkaline condition. However, TOC removal efficiency for Al2O3 with S2O82- was higher in a neutral condition than in other pH conditions. This indicates that the pH of a solution plays a critical role in the catalytic oxidation performance by determining surface charges of catalysts and yield of reactive radicals produced from water radiolysis. In the radiocatalytic system, H2O2 enhances the oxidation performance of catalysts (Al2O3 and TiO2) over a wide pH range (3-11). Meanwhile, S2O82- is not suitable with Al2O3 in acidic conditions because of its strong adsorption onto Al2O3 in this study.

Sonochemistry dosimetries in seawater

Due to the complex physical and chemical interactions taking place in the sonicated medium, various methods have been proposed in the literature for a better understanding of the sonochemical system. In the present paper, the performance of calorimetry, iodometry, Fricke, 4-nitrophenol, H2O2, and ascorbic acid dosimetry techniques have been evaluated over the electric power range from 20 to 80 W (f = 300 kHz). These methods have been analyzed for distilled and seawater in light of the literature findings. It has been found that the lowest temperatures and calorimetric energies were obtained for seawater in comparison to distilled water. However, the discrepancy between both mediums disappears with the increase in the electric power up to 80 W. Compared to the calorimetry results, a similar trend was obtained for the KI dosimetry, where the discrepancy between both solutions (seawater and distilled water) increased with the reduction in the electric power down to 20 W. In contrast, over the whole range of the electric power (20-80 W), the H2O2 dosimetry was drastically influenced by the salt composition of seawater, where, I3- formation was clearly reduced in comparison to the case of the distilled water. On the other hand, a fluctuated behavior was observed for the Fricke and 4-nitrophenol dosimetry methods, especially at the low electric powers (20 and 40 W). It has been found that dosimetry techniques based on ascorbic acid or potassium iodide are the best means for accurate quantification of the sonochemical activity in the irradiated liquid. As a result, it has been concluded, in terms of the dosimetry process's performance, that the dosimetry methods are in the following order: Ascorbic acid ≈ KI > Fricke > 4-nitrophenol > H2O2.

Hydrodynamic cavitation coupled with zero-valent iron produces radical sulfate radicals by sulfite activation to degrade direct red 83

In the present research, hydrodynamic cavitation (HC) and zero-valent iron (ZVI) were used to generate sulfate radicals through sulfite activation as a new source of sulfate for the efficient degradation of Direct Red 83 (DR83). A systematic analysis was carried out to examine the effects of operational parameters, including the pH of the solution, the doses of ZVI and sulfite salts, and the composition of the mixed media. Based on the results, the degradation efficiency of HC/ZVI/sulfite is highly dependent upon the pH of the solution and the dosage of both ZVI and sulfite. Degradation efficiency decreased significantly with increasing solution pH due to a lower corrosion rate for ZVI at high pH. The corrosion rate of ZVI can be accelerated by releasing Fe2+ ions in an acid medium, reducing the concentration of radicals generated even though ZVI is solid/originally non-soluble in water. The degradation efficiency of the HC/ZVI/sulfite process (95.54 % + 2.87%) was found to be significantly higher under optimal conditions than either of the individual processes (<6% for ZVI and sulfite and 68.21±3.41% for HC). Based on the first-order kinetic model, the HC/ZVI/sulfite process has the highest degradation constant of 0.035±0.002 min-1. The contribution of radicals to the degradation of DR83 by the HC/ZVI/sulfite process was 78.92%, while the contribution of SO4•- and •OH radicals was 51.57% and 48.43%, respectively. In the presence of HCO3- and CO32- ions, DR83 degradation is retarded, whereas SO42- and Cl- ions promote degradation. To summarise, the HC/ZVI/sulfite treatment can be viewed as an innovative and promising method of treating recalcitrant textile wastewater.

Degradation of Safranin O in Water by UV/TiO2/IO4− Process: Effect of Operating Conditions and Mineralization

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.

Facile synthesis of magnetic ZnFe2O4/AC composite to activate peroxydisulfate for dye degradation under visible light irradiation

Heterogeneous photocatalysis/persulfate oxidation process has been considered as a promising technology for dye contaminants removal. The magnetic ZnFe₂O₄/active carbon (AC) composites were hydrothermally synthesized and firstly used to activate peroxydisulfate (PDS) for rhodamine B (RhB) degradation under visible LED light irradiation. The optimized Vis-ZnFe₂O₄/AC(4/1)-PDS system can enhance the RhB degradation efficiency by 32.01% and 13.87% compared with Vis-ZnFe₂O₄-PDS and Vis-AC-PDS systems, respectively. The influence of operational parameters such as catalyst dosage (0.2 - 0.4 g L^-1), PDS concentration (1.0 - 2.0 g L^-1), temperature (25 - 45 °C), solution pH (2.7 - 10.9), and coexisting inorganic ions (Cl^-, NO₃^-, HCO₃^-, PO₄^3-, Cu²⁺, Fe³⁺, and Ca²⁺) on RhB degradation was studied, and 100% of RhB (20 mg L^-1) was degraded after 80 min at operational condition: 0.30 g L^-1 of ZnFe₂O₄/AC(4/1) and 1.5 g L^-1 of PDS, solution pH of 2.74, reaction temperature of 25 °C. The quenching experiments, EPR test, and XPS analysis were employed to reveal the proposed mechanism, which demonstrated that ¹O₂ played a more important role than other reactive species (SO₄^•-, •OH, O₂^•-, and h⁺) in RhB degradation. The generation of ¹O₂ via the two routes was as follows: (i) the in situ formed active oxygen (O^*) reacted with HSO₅^- to produce ¹O₂; (ii) O₂^•- was oxidized by h⁺ to form ¹O₂. After five consecutive cycles, the photodegradation efficiency of RhB by ZnFe₂O₄/AC(4/1) catalyst slightly decreased from 88.52 to 83.92%, indicating the excellent reusability of ZnFe₂O₄/AC(4/1) photocatalyst. As designed, Vis-ZnFe₂O₄/AC-PDS oxidation system can effectively remove RhB from the different real water matrices, and the degradation efficiency of RhB in tap water, river water, and secondary effluent was 78.24%, 79.55%, and 74.53% after 80 min of reaction, respectively.

UV/solar photo-degradation of furaltadone in homogeneous and heterogeneous phases: Intensification with persulfate

Previous studies on removal of the pharmaceutical drug Furaltadone (FTD) in water have not shown to be totally efficient or are very expensive. In this study, sulfate radicals derived from persulfate anions activated with different irradiation sources (UVA, UVC and solar light) and combined with H₂O₂ and/or TiO₂ have been tested in homogeneous and heterogeneous phases under different operation modes and reaction systems. In homogeneous phase, UV produces a slow mineralization (k = 0.0013 min^-1). The combined processes are faster (k_UV/H2O2 = 0.0185 min^-1, k_UV/PS = 0.0206 min^-1) with the best performance for the UV/PS system yielding nearly 80% of mineralization in half an hour. The overall process (UV/H₂O₂/PS) does not show synergy and mineralization is even slower (k_UV/H2O2/PS = 0.015 min^-1) due to the production of a high amount of radicals favouring unproductive reactions (scavenger effect). A mineralization mechanism is proposed involving formation of 5hydroxymethylene-2(5H)-furanone and NO as the main intermediates. In heterogeneous phase (UVA/TiO₂/PS), the holes play an important role changing the mineralization mechanism. The main intermediates formed were C₁₂H₁₇N₄O₄ and C₁₁H₁₄N₃O₄, which rapidly were degraded to form C₈H₁₅O₃N₃, C₄H₁₀NO and C₅H₁₀NO. An economic study of operation costs has been made for selected processes: UVC/PS, UVA/TiO₂/PS and Solar/TiO₂/PS. The Solar/TiO₂/PS process has the lowest operation costs due to the use of solar energy. However, it would need an additional stage to recover the catalyst. Finally, a loss of 27% in efficiency during mineralization was found after 5 cycles, but the catalyst recovers its initial performance after regeneration at 500 °C.

Ultrasound/chlorine sono-hybrid-advanced oxidation process: Impact of dissolved organic matter and mineral constituents

In this work, after exploring the first report on the synergism of combining ultrasound (US: 600 kHz) and chlorine toward the degradation of Allura Red AC (ARAC) textile dye, as a contaminant model, the impact of various mineral water constituents (Cl-, SO42-, NO3-, HCO3- and NO2-) and natural organic matter, i.e., humic acid (HA), on the performance of the US/chlorine sono-hybrid process was assessed for the first time. Additionally, the process effectiveness was evaluated in a real natural mineral water (NMW) of a known composition. Firstly, it was found that the combination of ultrasound and chlorine (0.25 mM) at pH 5.5 in cylindrical standing wave ultrasonic reactor (f = 600 kHz and Pe = 120 W, equivalent to PA ∼ 2.3 atm) enhanced in a drastic manner the degradation rate of ARAC; the removal rate being 320% much higher than the arithmetic sum of the two separated processes. The source of the synergistic effect was attributed to the effective implication of reactive chlorine species (RCS: Cl, ClO and Cl2-) in the degradation process. Radical probe technique using nitrobenzene (NB) as a specific quencher of the acoustically generated hydroxyl radical confirmed the dominant implication of RCS in the overall degradation rate of ARAC by US/chlorine system. Overall, the presence of humic acid and mineral anions decreased the efficiency of the sono-hybrid process; however, the inhibition degrees depend on the type and the concentration of the selected additives. The reaction of these additives with the generated RCS is presumably the reason for the finding results. The inhibiting effect of Cl-, SO42-, NO3- and NO2- was more pronounced in US/chlorine process as compared to US alone, whereas the inverse scenario was remarked for the effect of HA. These outcomes were associated to the difference in the reactivity of HA and mineral anions toward RCS and OH oxidizing species, in addition to the more selective character of RCS than hydroxyl radical. The displacement of the reaction zone with increasing the additive concentration may also be another influencing factor that favors competition reactions, which subsequently reduce the available reactive species in the reacting medium. The NMW exerted reductions of 43% and 10% in the process efficiency at pH 5.5 and 8, respectively, thereby confirming the RCS-quenching mechanism by the water matrix constituents. Hence, this work provided a precise understanding of the overall mechanism of chlorine activation by ultrasound to promote organic compounds degradation in water.

The multiple role of inorganic and organic additives in the degradation of reactive green 12 by UV/chlorine advanced oxidation process

The impact of various mineral anions, diverse organic substrates and different environmental matrices on the removal of C.I. reactive green 12 (RG12), a refractory textile dye, by UV/chlorine emerging advanced oxidation process (AOP) was performed. The co-exposure of RG12 (20 mg L^-1) to UV and chlorine (0.5 mM) at pH 5 produced a strong synergism on the degradation rate. Radical probe technique showed that ^●OH and Cl₂^●- were the main source of the synergistic effect. Bromide, bicarbonate and chloride at small dosage, i.e. 1 mM, enhanced the rate of RG12 degradation, but higher concentrations of these anions quenched the degradation process. Sulphate anions did not alter the degradation rate of the dye, but nitrite quenched it at ∼ 90%. The inhibiting effect of nitrate appeared only at advanced reaction time (>1 min).On the other hand, natural organic matter (NOM) reduced effectively the degradation rate. Besides, SDS surfactant at only 1 µM accelerated the degradation efficiency by ∼12%. However, Tween 80 has shown an insignificant effect, whereas reductions of 10% and 30% were recorded by Triton X100 and Tween 20, respectively. The RG12-degradation rate was not affected in the mineral water, but it was drastically improved in seawater. Conversely, a huge drop in the RG12-degradation efficiency was obtained in the wastewater effluent. UV/chlorine process is highly viable for degrading pollutant in matrices free of NOM. However, the process losses its potential application in matrices riche of NOM.

Adsorption of Cationic Contaminants by Cyclodextrin Nanosponges Cross-Linked with 1,2,3,4-Butanetetracarboxylic Acid and Poly(vinyl alcohol)

Cationic organic pollutants (dyes and pesticides) are mainly hydrosoluble and easily contaminate water and create a serious problem for biotic and abiotic species. The elimination of these dangerous contaminants from water was accomplished by adsorption using cyclodextrin nanosponges. These nanosponges were elaborated by the cross-linking between 1,2,3,4-butanetetracarboxylic acid and β-cyclodextrin in the presence of poly(vinyl alcohol). Their physicochemical characteristics were characterized by gravimetry, acid-base titration, TGA, 13C NMR, ATR-FTIR, Raman, X-ray diffraction, and Stereomicroscopy. The BP5 nanosponges displayed 68.4% yield, 3.31 mmol/g COOH groups, 0.16 mmol/g β-CD content, 54.2% swelling, 97.0% PQ removal, 96.7% SO removal, and 98.3% MG removal for 25 mg/L of initial concentration. The pseudo-second-order model was suitable for kinetics using 180 min of contact time. Langmuir isotherm was suitable for isotherm with the maximum adsorption of 120.5, 92.6, and 64.9 mg/g for paraquat (PQ), safranin (SO), and malachite green (MG) adsorption, respectively. Finally, the reusability performance after five regeneration times reached 94.1%, 91.6%, and 94.6% for PQ, SO, and MG adsorption, respectively.

Ti2O3/TiO2-Assisted Solar Photocatalytic Degradation of 4-tert-Butylphenol in Water

Colored Ti2O3 and Ti2O3/TiO2 (mTiO) catalysts were prepared by the thermal treatment method. The effects of treatment temperature on the structure, surface area, morphology and optical properties of the as-prepared samples were investigated by XRD, BET, SEM, TEM, Raman and UV–VIS spectroscopies. Phase transformation from Ti2O3 to TiO2 rutile and TiO2 anatase to TiO2 rutile increased with increasing treatment temperatures. The photocatalytic activities of thermally treated Ti2O3 and mTiO were evaluated in the photodegradation of 4-tert-butylphenol (4-t-BP) under solar light irradiation. mTiO heated at 650 °C exhibited the highest photocatalytic activity for the degradation and mineralization of 4-t-BP, being approximately 89.8% and 52.4%, respectively, after 150 min of irradiation. The effects of various water constituents, including anions (CO32−, NO3, Cl and HCO3−) and humic acid (HA), on the photocatalytic activity of mTiO-650 were evaluated. The results showed that the presence of carbonate and nitrate ions inhibited 4-t-BP photodegradation, while chloride and bicarbonate ions enhanced the photodegradation of 4-t-BP. As for HA, its effect on the degradation of 4-t-BP was dependent on the concentration. A low concentration of HA (1 mg/L) promoted the degradation of 4-t-BP from 89.8% to 92.4% by mTiO-650, but higher concentrations of HA (5 mg/L and 10 mg/L) had a negative effect.

Removal of Toluidine Blue and Safranin O from Single and Binary Solutions Using Zeolite

The studies on dye removal from solutions attracted great attention due to the increased use of color dyes in different fields. However, most of the studies were focused on dye removal from a single solution. In reality, wastewater from the fabric industry could contain mixed dyes. As such, evaluating different dye removal from mixed solutions may have more practical importance. In terms of sorbents evaluated for dye removal, most of them were an organic type generated from agricultural wastes. Clay minerals and zeolites were also studied extensively, because of the vast reserves, inexpensive material cost, larger specific surface area (SSA) and high cation exchange capacity (CEC). However, evaluating the factors controlling the dye removal from mixed dye solutions was limited. In this study, the removal of cationic dyes safranin O (SO) and toluidine blue (TB) by clinoptilolite zeolite (ZEO) was evaluated under single and binary systems. The results showed that removal of TB was preferred over SO by approximately a 2:1 ratio. The counterion Cl− sorption from mixed dye solution helped the formation of mixed dye aggregates on mineral surfaces. Molecular dynamic simulation confirmed the multilayer mixed dye formation on ZEO under high loading levels.

Facile synthesis of graphitic carbon nitride from acetic acid pretreatment to activate persulfate in presence of blue light for photocatalytic removal of metronidazole

Activation of persulfate (PS) in presence of blue LED light (λ_max ∼454 nm) using acetic acid modified graphitic carbon nitride (ACN) was investigated. Usage of acetic acid had improved the specific surface area (SSA, 21.89 m² g^-1) of ACN compared with pristine graphitic carbon nitride (GCN) and it also reduced interfacial charge transfer resistance in ACN. Subsequently, photocatalytic removal of metronidazole (MET) was investigated using ACN. It was observed that upward shift in the conduction band (CB) in ACN produced the reduction of PS to form sulfate radicals (SO₄^.-) (CB of ACN (-1.25 V vs normal hydrogen electrode (NHE); Bandgap = 2.77 eV) and GCN (-1.23 V vs NHE; Bandgap = 2.73 eV)), which enhanced the MET removal. Moreover, batch experiments were conducted to quantify the effects of PS dosage (0.08-0.40 g L^-1), ACN dosage (0.20-2 g L^-1), light intensity (15-45 W), and pH (2-13.50). ACN (1 g L^-1) and GCN (1 g L^-1) with 0.16 g L^-1 of PS have shown 100% and 76.1% MET (C_o-10 mg L^-1) removal within 300 min, respectively, and the removal followed zero-order kinetics (k ∼2.39 mg L^-1 h^-1). However, MET mineralization was approximately 30% with ACN. MET removal had decreased with increase in pH and almost complete inhibition was observed at pH ∼12. Overall, it was identified that SO₄^.- was the major reactive species whereas holes (h⁺) in the valence band (VB) of ACN (1.52 V vs NHE) played a minor role in MET removal.

Enhancement of LED based photocatalytic degradation of sulfolane by integration with oxidants and nanomaterials

In this study, oxidants and nanomaterials were used to improve titanium dioxide based photocatalytic degradation of sulfolane. Hydrogen peroxide (H₂O₂), sodium persulfate (SPS) and ozone (O₃) were the oxidants studied and carbon nanotubes (CNT) and nanosized zero valent iron (nZVI) were used as the nanomaterials. The impact of these oxidants and nanomaterials was evaluated at various dosages in both Milli-Q water and groundwater. The results indicate that with a suitable dose of oxidants or nanomaterials, photocatalytic degradation of sulfolane in Milli-Q water can be enhanced. The addition of ozone contributed to a significant increase in sulfolane degradation rate in Milli-Q water. The experiments conducted in groundwater showed that oxidants (H₂O₂, SPS and O₃) increased the degradation of sulfolane while the nanomaterials (CNT and nZVI) impeded sulfolane degradation in groundwater.

Influence of processing conditions on the synergism between UV irradiation and chlorine toward the degradation of refractory organic pollutants in UV/chlorine advanced oxidation system

The synergy of applying UV/chlorine advanced oxidation process (AOP) for the degradation of organic pollutants was usually reported. However, very limited information is available on the influence of processing conditions on the resulted synergism. In this work, C.I. reactive green 12 (RG12), a refractory textile dye, has been selected as a pollutant model to examine the synergism dependence of operational conditions in UV/chlorine AOP. Initial tests conducted with 500 μM of chlorine and 20 mg L^-1 of RG12 have resulted in a high synergy index (SI) of 3. Operating conditions sensitively affect the value of SI. This latter increased with increasing initial chlorine and RG12 concentrations up to certain optimums at 500 μM of chlorine and 20 mg L^-1 of RG12 and decreased afterward. The best SI value, i.e. 3, was obtained at pH 5, followed by pH 7 (SI = 2.2) and then pH 9-10.5 (SI ~ 2). On the other hand, the synergistic index decreased importantly from 3 at 25 °C to only 1.2 at 55 °C. Finally, by using different radical scavengers, it was found that among various suspected oxidants, only ^●OH and Cl₂^●- play a key role in the synergistic effect between UV and chlorine toward RG12 degradation.

Photo-Fenton removal of tetracycline hydrochloride using LaFeO3 as a persulfate activator under visible light

In this work, LaFeO₃ nanoparticles were fabricated by a facile sol-gel method and applied to degrade tetracycline hydrochloride (TC-HCl) through heterogeneous activation of persulfate under visible-light illumination. The structure, compositions, photocatalytic properties, and morphological features of the as-obtained sample were investigated by XRD, XPS, DRS, and FESEM techniques. Optimizations of dosage of LaFeO₃ (0-0.4 g/L), dosage of PS (0-4 g/L), concentration of TC-HCl (10 ppm-80 ppm), and pH of initial solution (2.09-9.59) were conducted. Radical trapping experiments indicated that SO₄^- was the dominant radical for TC-HCl removal while OH was also involved. In addition, LaFeO₃ was proved with excellent stability and reusability in degrading TC-HCl molecules in the Vis/LaFeO₃/PS system. The findings of this work revealed the potential application of the Vis/LaFeO₃/PS system toward degrading organic pollutants in wastewater.

Solar photo-degradation of aniline with rGO/TiO2 composites and persulfate

The solar photodegradation of aniline using reduced graphene oxide-based composites (rGO/TiO₂) and different electron acceptors such as H₂O₂ and persulfate (PS) has been studied. To this end, an innovative self-sufficient drum reactor (operating with solar irradiation and artificial UV light) has been employed. The role of radicals and the new graphene morphology is evaluated. Finally, changes in the degradation/mineralization mechanism are explained according to intermediates evolution (obtained from mass spectroscopy). In the Solar/rGO/TiO₂/H₂O₂ system, hydroxyl radicals react with the reduced graphene oxide (rGO) producing oxidized rGO (OrGO). The process creates new pores increasing surface area favouring adsorption. Also, other radicals such as superoxide or singlet oxygen are also formed, affecting the degradation mechanism. The hole reacts with adsorbed aniline to form the aniline-radical-cation. Nitrosobenzene is then formed with the active participation of superoxide radical anion, finally yielding azobenzene. It was found that the addition of 2.5% wt of rGO increases mineralization from 0 to 14% during the solar stage after 120 min, reaching 82.5% when lamps are switched on after 240 min. On the other hand, activation of PS with UV-C light is a very efficient process, since aniline is wholly degraded in 10-20 min depending on PS initial concentration, reaching a high mineralization degree close to 90% in 120 min. During this process, degradation occurs in a very different route, via the formation of phenol. In the first stage (t < 25 min), sulfate radical is the primary oxidant involved to yield benzoquinone. In a second step (t > 25 min), hydroxyl radicals play the leading role to reach C₂-C₆ organic acids.

Exhaustive Photocatalytic Lindane Degradation by Combined Simulated Solar Light-Activated Nanocrystalline TiO2 and Inorganic Oxidants

Organochlorine compounds (OCs) are very toxic, highly persistent, and ubiquitous contaminants in the environment. Degradation of lindane, a selected OC, by simulated solar light-activated TiO2 (SSLA-TiO2) photocatalysis was investigated. The film types of the TiO2 photocatalyst were prepared using a dip-coating method. The physical properties of the films were investigated using X-ray diffraction, transmission electron microscopy, and environmental scanning electron microscopy. The SSLA-TiO2 photocatalysis led to a lindane removal of 23% in 6 h, with 0.042 h−1 of an observed pseudo first-order rate constant (kobs). The SSLA-TiO2 photocatalysis efficiency was greatly enhanced by adding hydrogen peroxide (H2O2), persulfate (S2O82−), or both combined, corresponding to a 64%, 89%, and 99% lindane removal in the presence of 200 µM of H2O2, S2O82−, or equimolar H2O2-S2O82−, respectively. The hydroxyl and sulfate radicals mainly participated in lindane degradation, proven by the results of a radical scavenger study. The degradation kinetics were hindered in the presence of the water constituents, indicated by a 61%, 35%, 50%, 70%, 88%, and 91% degradation of lindane in 6 h, using a SSLA-TiO2/S2O82−/H2O2 photocatalysis system containing 1.0 mg L−1 humic acid (HA), or 1 mM of CO32−, HCO3−, NO3−, SO42−, and Cl−, respectively. The TiO2 film demonstrated high reusability during four runs of lindane decomposition experiments. The SSLA-TiO2/S2O82−/H2O2 photocatalysis is very effective for the elimination of a persistent OC, lindane, from a water environment.

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.