Yanlin Wu

Sulfate Radical Photogeneration Using Fe-EDDS: Influence of Critical Parameters and Naturally Occurring Scavengers.

In this study, the activation of persulfate induced by Fe(III)-ethylenediamine-N,N′-disuccinic acid (EDDS) under dark and irradiation conditions and the reactivity of the generated sulfate radical (SO4•–) under a wide range of experimental conditions were investigated by means of experimental kinetic analyses and modeling. The Fe(III)-EDDS induced activation of persulfate was found to be efficient across a wide range of pH value (3–7), whereas the second order rate constant of SO4•– with 4-tert-butylphenol (4tBP) kSO4•–,4tBP = (4.21 ± 0.22) × 109 M–1 s–1 was found to be unchanged between pH 2.5 and 8.5. Experimental and theoretical investigations showed clearly that the 4tBP degradation was enhanced in the presence of chloride (10 mM), whereas an almost complete inhibition was observed in the presence of carbonates (10 mM). For the first time, second order rate constants evaluated by laser flash photolysis experiments revealed that SO4•– has a similar reactivity with EDDS (6.21 × 109 M–1 s–1) and 4tBP (4....

Activation of persulfate by Fe(III) species: Implications for 4-tert-butylphenol degradation

In this study, the activation of persulfate induced by Fe(III) species, including 5 kinds of iron oxhydroxides (IOs) and dissolved Fe3+ under dark condition were investigated. Ferrihydrite (FH) and akaganeite (AK) showed the highest activity in 4-tert-butylphenol (4tBP) removal. The 4tBP degradation rate constant decreased as the solution pH increased from pH 3.2 to 7.8 in FH/S2O82- system. However, the pH value had no significant effect on the 4tBP degradation in AK/S2O82- system. The degradation of 4tBP in Fe3+/S2O82- system was also performed to investigate the role of ferric species in persulfate activation. The pH dependency of 4tBP degradation rate was closely related to the speciation of FeIII, whereas the Fe(H2O)63+ was found to be the most active soluble iron complex form in the activation of S2O82-. 4tBP degradation was mainly due to the SO4- in IOs/S2O82- system, while SO4- and HO2 both had great contribution on 4tBP degradation in Fe3+/S2O82- system. Further investigations showed clearly that 4tBP degradation efficiency was decreased significantly due to the trapping of SO4- by chloride. This finding may have promising implications in developing a new technology for the treatment of contaminated waters and soils, especially where Fe3+ species are naturally occurring.

Toward a Better Understanding of Fe(III)−EDDS Photochemistry: Theoretical Stability Calculation and Experimental Investigation of 4-tert-Butylphenol Degradation

The present work describes in detail the chemical structure of the complex Fe(III)–EDDS and the predominance of different species with respect to pH. These results were obtained with ab initio calculations. From the photoredox process, the formation of hydroxyl radical was confirmed, and HO(•) is the main species responsible for the degradation of the organic compound present in aqueous solution. The degradation of 4-tert-butylphenol (4-t-BP), used as a model pollutant, was investigated in different conditions. For the first time, the second-order rate constant of the reaction between HO(•) and 4-t-BP and the formation rate of HO(•) (R(HO(•))(f)) from the photochemical process were evaluated. Through the degradation of 4-t-BP, the effect of Fe(III)–EDDS concentration, oxygen, and pH was also investigated. The pH, which plays a role in the iron cycle and in the Fe(III)–EDDS speciation, was noticed as an important parameter for the efficiency of 4-t-BP degradation. Such a result could be explained by taking into account the complex speciation and presence of a predominant form (FeL–) up to pH 8. These results are very useful for the use and optimization of such iron complexes in water treatment processes.

Photocatalytic degradation of 4-tert-octylphenol in a spiral photoreactor system

A spiral photoreactor system (SPS) was developed for the degradation of 4-tert-octylphenol (4-t-OP) in aqueous phase. 4-t-OP was previously considered as a endocrine disrupting compound frequently present in water. The direct photodegradation reaction caused by the SPS was found to accord with the characteristic of apparent first-order reaction with reaction rate constant k = 4.8 x 10(-2) min(-1). However, the direct photodegradation reaction could not make the 4-t-OP mineralized. The photodegradation efficiency increased from 88% to 91.2% in 45 min irradiation period after the internal surface of SPS was sintered with TiO2 thin film as catalyst. Catalyst concentration, number of catalyst coating layers and initial concentration of 4-t-OP were proven to be the factors affecting the photocatalytic degradation performance of the SPS on aqueous 4-t-OP. The degradation mechanism was investigated and the byproducts were analyzed using total organic carbon analyzer (TOC) and LC-MS. The possible chemical structures of the products were suggested. SPS with single layer of TiO2 prepared by sintering 13.6% of TiO2 precursor was proven to be more efficient than most of previous systems for removal of 4-t-OP from aqueous phase. 28.3% of the 4-t-OP was mineralized in 45 min according to the decreased amount of TOC value.

Activation of peroxymonosulfate by BiOCl@Fe3O4 catalyst for the degradation of atenolol: Kinetics, parameters, products and mechanism

BiOCl@Fe3O4 photocatalyst was synthesized to activate peroxymonosulfate (PMS) for atenolol (ATL) degradation under simulated sunlight irradiation in present study. XRD, SEM, adsorbability and pore size distribution of BiOCl@Fe3O4 were analyzed. Magnetic BiOCl performed high activity in PMS activation and could be easily solid-liquid separation by applying an external magnetic field. Many parameters were inspected, including scavengers, PMS concentration, catalyst dosage, pH, anions (Cl- and CO3-). h+, SO4-, HO, O2-, SO5- were involved in ATL degradation in BiOCl@Fe3O4/PMS/sunlight system. The second-order rate constant of the reaction between ATL and SO4- (kATL, SO4-) was estimated via laser flash photolysis experiments. Moreover, ATL mineralization was followed by TOC analyzer. Twelve possible intermediate products were identified through LC-QTOF-MS analysis, and six ATL degradation pathways were concluded. This type of magnetic photocatalyst is characterized by ease of separation, high activation and good reusability. It may have application potential in refractory organic pollutants degradation.