Wei Chu

Degradation of iopromide by combined UV irradiation and peroxydisulfate.

Abstract The aqueous degradation of iopromide, an iodinated X-ray contrast media (ICM) compound, by the combination of UV254 irradiation and potassium peroxydisulfate (K2S2O8) has been studied in laboratory scale experiments. The influence of various parameters on the performance of the treatment process has been considered, namely the UV irradiation light intensity, the initial concentrations of iopromide and peroxydisulfate, and the initial solution pH. Iopromide degradation increased with UV light intensity and peroxydisulfate concentration, but decreased with initial pH. Under specific conditions complete removal of iopromide was achieved within 30min, and near-complete mineralisation (loss of solution TOC) within 80min. Degradation was believed to be caused by a combination of direct photolysis, sulphate radical attack, and, to a minor degree, direct oxidation by peroxydisulfate. Approximate values for the reaction rate constants have been determined and found to be equal to 1–2×104 M−1 s−1 for sulfate radicals, and 1–2M−2 s−1 for S2O8 2−. Overall compound degradation was observed to follow first-order kinetics where the rate constant decreased with initial solution pH. During the reaction, the solution pH decreased as a consequence of sulfate radical scavenging.

Determination and toxicity evaluation of the generated products in sulfamethoxazole degradation by UV/CoFe2O4/TiO2.

The photodegradation of sulfamethoxazole (SMX) under UV radiation with a recyclable catalyst CoFe2O4/TiO2 was examined. The reaction mechanism during the treatment was determined. The toxicity of the degradation intermediates to aquatic organisms, including the green alga Chlorella vulgaris and the brine shrimp Artemia salina was investigated. SMX was completely removed and about 50% TOC was degraded in 5h. Sixteen intermediates were detected, from which four of them were reported for the first time in this study. Four main decay pathways, i.e., hydroxylation, cleavage of SN bond, nitration of amino group, and isomerization were proposed. About 45% of the total mass sulfur source transformed to sulfate ion, and around 25%, 1%, and 0.25% of the total nitrogen transformed to ammonium, nitrogen, and nitrite ions. The toxicity of the treated solution was significantly reduced compared to that of the parent compound SMX. A variation of the algae growth was observed, which was due to the combination of generation of toxic intermediates (i.e., sulfanilamide) and the release of inorganic substances and carbon source as additional nutrients. The adverse effect on the clearance rate of the brine shrimp was also observed, but it can be eliminated if longer degradation time is used.

Photodegradation of 4-chlorophenoxyacetic acid under visible LED activated N-doped TiO2 and the mechanism of stepwise rate increment of the reused catalyst

Photodegradation of 4-chlorophenoxyacetic acid (4-CPA) was systematically investigated using N-doped TiO2 (N-TiO2) under commercially available visible light emitting diode (Vis LED) as a novel Vis LED illumination in photocatalysis applications. The synergetic effect of Vis LED/N-TiO2 process was studied in detail by varying reaction conditions including the initial concentration of 4-CPA, catalyst dosage, light intensity, and initial pH. Additionally, the influence of inorganic anions and radical scavengers on the performance of the Vis LED/N-TiO2 process was also evaluated. The Vis LED/N-TiO2 was found to be a promising process in terms of mineralization of 4-CPA. It is interesting to note that the performance of this process was not reduced after successive usage of the recycled catalyst; instead, the reaction rate of 4-CPA decay actually increased by using the spent catalyst. The mechanism behind rate enhancement after/during reuse was explored by XPS and FT-IR analyses and it was proven that hydroxyl groups can be incorporated into the catalyst surface by the repeated wetting of N-TiO2 after each reuse. This facilitates the formation of hydrogen bonds between the 4-CPA molecules and N-TiO2, thereby allowing more collisions between the trapped 4-CPA and radicals at the interface of bulk solution and catalyst, respectively.

Heterogeneous Catalytic Ozonation of Sulfamethoxazole in Aqueous Solution over Composite Iron–Manganese Silicate Oxide

ABSTRACT Composite iron–manganese silicate oxide (FMSO) was synthesized and used as a heterogeneous catalyst for the ozonation of sulfamethoxazole. Results showed that FMSO/O3 process significantly increased the TOC removal efficiency from 27% (sole ozonation) to 79.8%. Generated intermediates exhibited much higher adsorption affinity on FMSO than sulfamethoxazole. Presence of FMSO could accelerate the mass transfer of ozone, adsorb a certain amount of ozone on its surface, and subsequently decompose ozone into hydroxyl radical. Neutral charge surface of FMSO was more favorable to interact with the ozone molecules. FMSO maintained a good catalytic activity after several repeated use and revealed low metal ion leaching during ozonation.

Investigation on the Kinetics of Heterogeneous Catalytic Ozone Decomposition in Aqueous Solution over Composite Iron-Manganese Silicate Oxide

ABSTRACT The kinetics of heterogeneous catalytic ozone decomposition in aqueous solution over composite iron-manganese silicate oxide (FMSO) was investigated. Results showed that the presence of FMSO significantly accelerated the ozone decomposition rate from 0.022 (without FMSO) to 0.101 min−1. The effects of inorganic anions and solution pH indicated that surface hydroxyl groups on FMSO were the active sites for catalyzing ozone decomposition and neutral charge surface seemed to show the highest catalytic performance. Tert-butanol inhibition experiments demonstrated that FMSO effectively accelerated the transformation rate of ozone into hydroxyl radicals. The contribution of hydroxyl radicals on ozone decomposition with and without FMSO was subsequently determined.

Hybrid porous magnetic bentonite-chitosan beads for selective removal of radioactive cesium in water

Easy-to-obtain magnetic bentonite-chitosan hybrid beads (Bn-CTS) were prepared by immobilizing bentonite within a porous structure of chitosan beads to achieve a hybrid adsorption effect for the removal of cesium ion (Cs+) from water. The hybrid adsorbent, which had a porous structure and abundant binding sites contributed by both chitosan and bentonite, ensured superb adsorption characteristics. The paramagnetic character of the beads enabled their facile separation for recycling. The chitosan/bentonite ratio, pH and contact time were optimized to achieve the optimal Cs+ efficiency, and the adsorption kinetics and isotherms were thoroughly discussed. The adsorption kinetics obeyed the pseudo-second-order model, and the best fitted equation for equilibrium data was the Langmuir isotherm model. The maximum adsorption capacity of the bentonite-chitosan beads was 57.1 mg g-1. The adsorbent had excellent selectivity towards Cs+ adsorption in the presence of abundant cations (Li+, Na+, K+ and Mg2+). The adsorbent was able to be recycled by treating the beads with 0.1 mol L-1 of MgCl2 to quantitatively desorb Cs+ from the beads. Overall, the magnetic bentonite-chitosan beads can be used as a highly efficient adsorbent for radioactive waste disposal and management.