Yao-Hui Huang

Heterogeneous Degradation of Organic Pollutants by Persulfate Activated by CuO-Fe3O4: Mechanism, Stability, and Effects of pH and Bicarbonate Ions

Magnetic CuO-Fe3O4 composite was fabricated by a simple hydrothermal method and characterized as a heterogeneous catalyst for phenol degradation. The effects of pH and bicarbonate ions on catalytic activity were extensively evaluated in view of the practical applications. The results indicated that an increase of solution pH and the presence of bicarbonate ions were beneficial for the removal of phenol in the CuO-Fe3O4 coupled with persulfate (PS) process. Almost 100% mineralization of 0.1 mM phenol can be achieved in 120 min by using 0.3 g/L CuO-Fe3O4 and 5.0 mM PS at pH 11.0 or in the presence of 3.0 mM bicarbonate. The positive effect of bicarbonate ion is probably due to the suppression of copper leaching as well as the formation of Cu(III). The reuse of catalyst at pH0 11.0 and 5.6 showed that the catalyst remains a high level of stability at alkaline condition (e.g., pH0 11.0). On the basis of the characterization of catalyst, the results of metal leaching and EPR studies, it is suggested that phenol is mainly destroyed by the surface-adsorbed radicals and Cu(III) resulting from the reaction between PS and Cu(II) on the catalyst. Taking into account the widespread presence of bicarbonate ions in waste streams, the CuO-Fe3O4/PS system may provide some new insights for contaminant removal from wastewater.

Identification of produced powerful radicals involved in the mineralization of bisphenol A using a novel UV-Na2S2O8/H2O2-Fe(II,III) two-stage oxidation process

A two-stage oxidation (UV-Na(2)S(2)O(8)/H(2)O(2)-Fe(II,III)) process was applied to mineralize bisphenol A (BPA) at pH(i) (initial pH) 7. We take advantage of the high oxidation potential of sulfate radicals and use persulfate as the 1st-stage oxidant to oxidize BPA to less complex compounds (stoichiometric ratio: [S(2)O(8)(2-)](0)/[BPA](0)=1). Afterwards, the traditional photo-Fenton process was used to mineralize those compounds to CO(2). To the best of our knowledge, this is the first attempt to utilize the two processes in conjunction for the complete degradation of BPA. During the 2nd-stage reaction, other oxidants (H(2)O(2) and Iron alone) were also employed to observe the extent of enhancement of photo-Fenton. Further, qualitative identification of both hydroxyl and sulfate radicals was performed to evaluate their dominance under different conditions. The BPA degradation in this UV/persulfate process formulated a pseudo-first-order kinetic model well, with a rate constant of approximately 0.038 min(-1) (25 degrees C), 0.057 min(-1) (35 degrees C), and 0.087 min(-1) (50 degrees C), respectively. The much lower activation energy (DeltaE = 26 kJ mol(-1)) was further calculated to clarify that the thermal-effect of an illuminated system differs from single heat-assisted systems described in other research. Final total organic carbon (TOC) removal levels of BPA by the use of such two-stage oxidation processes were 25-34%, 25%, and 87-91% for additional Fe(II,III) activation, H(2)O(2) promotion, and Fe(II,III)/H(2)O(2) promotions, respectively.

Kinetics of 2,6-dimethylaniline degradation by electro-Fenton process.

A new approach for promoting ferric reduction efficiency using a different electrochemical cell and the photoelectro-Fenton process has been developed to degrade organic toxic contaminants. The use of UVA light and electric current as electron donors can efficiently initiate the Fenton reaction. 2,6-Dimethylaniline (2,6-DMA) was the target compound in this study. Effects of initial pH (pH(i)), Fe(2+) loading, H(2)O(2) concentration and current density were determined to test and to validate a kinetic model for the oxidation of organic compound by the electro-Fenton process. Kinetic results show evidence of pseudo-first-order degradation. When reaction pH was higher than 2, amorphous Fe(OH)(3(s)) was generated. Increasing ferrous ion concentration from 1.0 to 1.5 mM increased the hydroxyl radicals and then promote the degradation efficiency of 2,6-DMA. The optimal H(2)O(2) concentration for 2,6-DMA degradation in this study was 25 mM. The degradation of 2,6-DMA was increased with the increase of current density from 3.5 to 10.6 A/m(2). Oxalic acid was the major detected intermediate of 2,6-DMA degradation. The final TOC removal efficiencies were 10%, 15%, 60% and 84% using the electrolysis, Fenton, electro-Fenton and photoelectro-Fenton processes, respectively.

The reactor design and comparison of Fenton, electro-Fenton and photoelectro-Fenton processes for mineralization of benzene sulfonic acid (BSA)

A new approach for promoting ferric reduction efficiency using a different electrochemical cell and the photoelectro-Fenton process has been developed. The use of UVA light and electric current as electron donors can efficiently initiate the Fenton reaction. Benzene sulfonic acid (BSA) was the target compound in this study. The parameters investigated to evaluate the reactor design include the electrode working area, electrode distance, energy consumption. Furthermore, the study also contains the intermediates and the mineralization efficiency of electrolysis, Fenton, electro-Fenton and photoelectro-Fenton process. Oxalic acid, the major intermediate of aromatic compound degradation, can complex with ferric ions. Meanwhile, a double cathode reactor could increase the current efficiency by 7%, which would translate to greater ferrous production and a higher degradation rate. Although the current efficiency of an electrode distance 5.5 cm device is 19% higher than 3.0 cm, results show that after 2 h of electrolysis the electronic expense using an electrode gap of 5.5 cm is much higher than 3.0 cm. The final TOC removal efficiency was 46, 64 and 72% using the Fenton, electro-Fenton and photoelectron-Fenton processes, respectively.

Behavioral evidence of the dominant radicals and intermediates involved in Bisphenol A degradation using an efficient Co2+/PMS oxidation process

This study investigated the degradation and mineralization of Bisphenol A (BPA) at pH 7, taken as a model compound in the presence of the trace metal-ions, Co(2+), and peroxymonosulfate (Oxone: PMS). We took advantage of the high oxidation-reduction potential of hydroxyl and sulfite radicals transformed from PMS as the oxidants to oxidize BPA to less complex compounds (stoichiometric ratio: [PMS](0)/[BPA](0)=2). Afterwards, the expected radicals were used to mineralize those compounds more efficiently (TOC removal approximately 40%) as compared to the 1% removal demonstrated in the UV/persulfate system in our previous study. To the best of our knowledge, this is the first attempt to evidence that the dominant behavior of radicals in a (bi)sulfite process is very different from that in a persulfate process. Additionally, the utilization of extremely small amounts of activator and oxidant for the complete degradation of BPA was achieved. The BPA degradation in this Co(2+)/PMS process formulated a pseudo-first-order kinetic model well over a practicable range of 25-45 degrees C. The activation energy (DeltaE=57.6 kJ mol(-1)) was calculated under different conditions, and the detailed discussion indicates that the activity of BPA degradation is not obviously dependent on the PMS concentration, but rather is related to Co(2+) dosage. Possible BPA side-chain oxidative metabolic pathways are suggested based on experimental results incorporating the evidence from EPR (electron paramagnetic resonance) and analysis from GC-MS (gas chromatography-mass spectrometry).

Efficient decolorization of azo dye Reactive Black B involving aromatic fragment degradation in buffered Co2+/PMS oxidative processes with a ppb level dosage of Co2+-catalyst

In order to generate powerful radicals as oxidizing species for the complete decolorization and degradation of azo dye Reactive Black B (RBB) at near neutral pH (pH 6), homogeneous activation of peroxymonosulfate (Oxone: PMS) by the trace Co2+-catalysts was explored. We not only took advantage of the high oxidation-reduction potential of produced hydroxyl and sulfite radicals but also an opportunity to oxidize RBB to less complex compounds with extremely low dosages, especially the ppb level of the Co2+-catalyst (stoichiometric ratio: [Co2+](0)/[RBB](0)=1.7 x 10(-6)-1.7 x 10(-5); [PMS](0)/[RBB](0)=8-32). Anion effects and pH effects were also carried out and discussed to simulate an actual application such as that of a textile waste stream. Both the degradations of RBB and its derivative aromatic fragments were illustrated successfully at UV-visable absorptions of 591 and 310 nm, respectively, and the possible relationships between them were also proposed and discussed, based on the experimental results. The RBB degradation in this Co2+/PMS oxidative process successfully formulated a pseudo-first-order kinetic model at an isothermal condition of 25 degrees C with or without different anions present. The initial rate and rate constant were calculated under different comparative conditions, and the results indicate that the activity of both RBB decolorization and its degradation are not obviously dependent on the PMS concentration, but rather are related to the Co2+ dosage.

Adsorption of fluoride by waste iron oxide: The effects of solution pH, major coexisting anions, and adsorbent calcination temperature

In this study, a waste iron oxide material (BT3), which is a by-product of the fluidized-bed Fenton reaction (FBR-Fenton), was thermally treated between 200 and 900°C and was used as an efficient adsorbent for the removal of fluoride ions in an aqueous system. The highest fluoride adsorption capacity occurred at the termination of the BT3 goethite dehydroxylation phase at about 300°C calcination where both the volume of nanopores formed by dehydroxylation and the specific surface area reached their maximum values. Above 300°C, BT3 transformed to the hematite phase in which fluoride adsorption capacity decreased as calcination temperature increased. On the other hand, the effect of pH on the fluoride adsorption capacity of BT3 for various initial fluoride concentrations was examined. The optimum pH value was found to be about 4. After that efficiency decreased as pH became more alkaline. Finally, coexisting anions affected the fluoride adsorption capacity of BT3 at pH 3.9±0.2 in this order: PO(4)(3-)>SO(4)(2-)>Cl(-)>NO(3)(-).

Mineralization and deflourization of 2,2,3,3-tetrafluoro-1-propanol (TFP) by UV/persulfate oxidation and sequential adsorption

This work demonstrates the combination of UV/persulfate and adsorption processes for treating 2,2,3,3-tetrafluoro-1-propanol (TFP) wastewater. Under the optimum conditions, 20mM persulfate (S(2)O(8)(2-)), 254 nm UV-C, and pH 3, 99.7% of TOC removal from an initial TFP solution of 1.39 mM was achieved. The photolysis of persulfate (S(2)O(8)(2-)) by UV irradiation yielded the sulfate radical (SO(4)(-)) with high activity, which mineralized most of the TFP in 2h. The released fluoride ions were then removed by using a waste iron oxide, BT-4 adsorbent. 20 g L(-1) BT-4 adsorbed 95% of the fluoride that was produced by mineralization of 1.39 mM TFP. The kinetics and isotherms of adsorption were examined to determine the fluoride removal efficiency of BT-4 which co-existed with the sulfate ions from the consumed sulfate radicals. Accordingly, the kinetics of adsorption was described by a pseudo-second-order rate model, while the adsorption isotherms were well fitted with the Langmuir model. BT-4 had a high adsorption capacity of 26.4 mg g(-1) (25°C) in removing the fluoride from TFP mineralization, suggesting that the co-existing sulfate ions never significantly affected the fluoride removal efficiency.

Removal of citrate and hypophosphite binary components using Fenton, photo-Fenton and electro-Fenton processes

Both citrate and hypophosphite in aqueous solution were degraded by advanced oxidation processes (Fe2+/H2O2, UV/Fe2+/H2O2, and electrolysis/ Fe2+/H2O2) in this study. Comparison of these techniques in oxidation efficiency was undertaken. It was found that Fenton process could not completely degrade citrate in the presence of hypophosphite since it caused a series inhibition. Therefore, UV light (photo-Fenton) or electron current (electro-Fenton) was applied to improve the degradation efficiency of the Fenton process. Results showed that both photo-Fenton and electro-Fenton processes could overcome the inhibition of hypophosphite, especially the electro-Fenton.

Degradation of the azo dye Orange G in a fluidized bed reactor using iron oxide as a heterogeneous photo-Fenton catalyst

The heterogeneous Fenton process was employed to degrade Orange G (OG) using waste iron oxide as the catalyst in a three-phase fluidized bed reactor (3P-FBR). The morphology and the FTIR spectra of the used BT4 were compared with the fresh catalyst to illustrate the catalyst stability. The catalyst reusability was evaluated by measuring the colour removal in four successive cycles. The effects of major parameters, including pH, H2O2 concentration and catalyst addition on the decolourization of OG were investigated. A satisfactory decolourization efficiency (>92%) could be obtained under the conditions tested, and 78.9% of TOC removal was achieved at a 50 mg L−1 initial OG concentration, 25 mg L−1 H2O2 concentration, pH = 3 and 6 g L−1 BT4 addition. The decolourization of OG was mainly attributed to the homogeneous photo-Fenton reaction, while the heterogeneous catalytic process played an important role in TOC removal. The main intermediates were identified by the GC/MS technique and the degradation pathway of OG was proposed.