Jong-Nan Chen

Catalytic decomposition of hydrogen peroxide and 2-chlorophenol with iron oxides.

The aim of this study was to examine the catalyzed decomposition of hydrogen peroxide and 2-chlorophenol (2-CP) in the presence of iron oxides. Granular ferrihydrite, goethite, and hematite were selected as catalysts in this study. 2-CP was used as the model compound because it is a typical toxic compound and has not been investigated in the catalytic decomposition by iron oxides. The catalytic activity for hydrogen peroxide decomposition followed the sequence: granular ferrihydrite > goethite > hematite. However, hematite exhibited the highest activity in catalyzing 2-CP oxidation. The oxidation efficiency of 2-CP corresponded with the inverse sequence of specific area and pHpzc of the iron oxides. The catalytic activity of granular ferrihydrite was affected significantly by the mixing speed and particle size for its large value of Thiele modulus (phi) and Damkohler number (Da). The strong diffusion resistance for granular ferrihydrite was attributed either to its microporous structure or to the formation of oxygen in the pores of the iron oxide leading to the unexpected catalytic activity of granular ferrihydrite to hydrogen peroxide and 2-CP.

Catalytic decomposition of hydrogen peroxide and 4-chlorophenol in the presence of modified activated carbons

The objective of this research was to examine the heterogeneous catalytic decomposition of H(2)O(2) and 4-chlorophenol (4-CP) in the presence of activated carbons modified with chemical pretreatments. The decomposition of H(2)O(2) was suppressed significantly by the change of surface properties including the decreased pH(pzc) modified with oxidizing agent and the reduced active sites occupied by the adsorption of 4-CP. The apparent reaction rate of H(2)O(2) decomposition was dominated by the intrinsic reaction rates on the surface of activated carbon rather than the mass transfer rate of H(2)O(2) to the solid surface. By the detection of chloride ion in suspension, the reduction of 4-CP was not only attributed to the advanced adsorption but also the degradation of 4-CP. The catalytic activity toward 4-CP for the activated carbon followed the inverse sequence of the activity toward H(2)O(2), suggesting that acidic surface functional group could retard the H(2)O(2) loss and reduce the effect of surface scavenging resulting in the increase of the 4-CP degradation efficiency. Few effective radicals were expected to react with 4-CP for the strong effect of surface scavenging, which could explain why the degradation rate of 4-CP observed in this study was so slow and the dechlorination efficiency was independent of the 4-CP concentration in aqueous phase. Results show that the combination of H(2)O(2) and granular activated carbon (GAC) did increase the total removal of 4-CP than that by single GAC adsorption.

Role of goethite dissolution in the oxidation of 2-chlorophenol with hydrogen peroxide.

It is well known that the dissolution of goethite plays an important role in catalyzing the oxidation of organic chemicals. Therefore, this study investigates how surface dissolution of goethite affects 2-chlorophenol oxidation in the goethite/H2O2 process. Experimental results indicate that ligand and reductant can enhance the dissolution rate of goethite, which is surface-controlled. Our results further indicate 2-chlorophenol degradation depends on goethite concentration. In addition, the oxidation rate of 2-CP is correlated with reductive dissolution rate at various dosages of goethite. Moreover, the oxidation mechanism of 2-CP is also a surface-controlled reaction. A mechanism proposed herein indicates that, in addition to the contaminant, its intermediate species affect the oxidation rate as well.

Oxidation of explosives by Fenton and photo-Fenton processes

In this study, the Fenton process was used to explore the possibility of treating explosives, namely 2,4,6-trinitrophenol (PA), ammonium picronitrate (AP), 2,4-dinitrotoluene (DNT), methyl-2,4,6-trinitrophenylnitramine (Tetryl) and 2,4,6-Trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The photo-Fenton process was also conducted to compare its oxidation efficiency with the Fenton process. The inhibition of hydroxyl radical and theory of crystal field stabilization energy were introduced in this study. Results show that oxidation efficiencies in Fenton system are in the following sequence: DNT > PA > AP > TNT > Tetryl > RDX > HMX. The degradation of the explosives obeys a pseudo-first-order behavior, and possible decomposing mechanisms are also discussed. For all explosives, the oxidation rates significantly increased with increasing the concentration of Fe(II), as well as illumination with UV light.

Oxidation of dichlorvos with hydrogen peroxide using ferrous ion as catalyst

This study examines how Fentons reagent (Fe2+ and H2O2) decomposed dichlorvos insecticide. Results showed that dichlorvos decomposed in a two-stage reaction. The first stage is a Fe2+/H2O2 reaction in which dichlorvos swiftly decomposed. In the second stage, dichlorvos decomposed somewhat less rapidly, and it is a Fe3+/H2O2 reaction. The detection of ferrous ions also supports the theory of the two-stage reaction for the dichlorvos oxidation with Fentons reagent. The dissolved oxygen of the solution decreased rapidly in the first stage reaction, but it slowly increased in the second stage with a zero-order kinetics. The Fenton system decomposed dichlorvos most rapidly when the initial pH in the solution is 3-4. In addition, increasing the concentration of hydrogen peroxide or ferrous ions can enhance the decomposition of dichlorvos. Consequently, the relationship of rate constant (kobs), [H2O2] and [Fe2+] at initial pH 3 is determined as kobs = 2.67 x 10(4)[H2O2]0.7[Fe2+]1.2.

Factors affecting the photocatalytic degradation of dichlorvos over titanium dioxide supported on glass

Abstract The photocatalytic degradation of organophosphorus insecticide, dichlorvos, on glass-supported titanium dioxide was investigated. The photoreactor coated with titanium dioxide was illuminated with a 20 W black-light UV fluorescent tube. The aqueous solution containing dichlorvos was continuously pumped through the photoreactor. Several factors, such as the initial dichlorvos concentration, dissolved oxygen, electrolytes, flow rate and temperature, affecting the oxidation rate of dichlorvos were studied. The results indicate that photocatalysis can be an effective process for the degradation of dichlorvos. The activated energy for the photocatalytic degradation of dichlorvos is 28.4 kJ mol−1. The initial quantum yield for the destruction of dichlorvos is 2.67%. Increasing the flow rate and initial dichlorvos concentration increases the dichlorvos degradation rate. Total mineralization requires a much longer illumination time than the disappearance of dichlorvos. Phosphate-containing intermediates are more stable than chloride-containing intermediates. It is shown that the photocatalytic oxidation of dichlorvos follows the Langmuir—Hinshelwood-type behavior, and reaction byproducts display an inhibiting effect on degradation rate.

Effect of inorganic ions on the oxidation of dichlorvos insecticide with Fenton's reagent

This study analyzes the oxidation of dichlorvos with Fenton‘s reagent in solutions containing various ions. Results show that the larger the added amount of ferrous ions, the higher the elimination rate of dichlorvos and the oxidization rate after the addition of ferric ions is far smaller than that of adding ferrous ions. Anions suppress the decomposition of dichlorvos in the following sequence: HzPO4‘ > > Cl- > NO,- - ClO4. . It can be seen that the Fenton reaction is extremely sensitive to anions, and phosphate ions in particular will seriously suppress the Fenton system’s ability to oxidize dichlorvos. The main reason for the suppression of phosphate ions is that phosphate ions will produce a complex reaction together with ferrous ions and ferric ions, which then lowers its ability to catalyze hydrogen peroxide. 81997 Flsevier Science Ltd

Effect of adsorbents coated with titanium dioxide on the photocatalytic degradation of propoxur

Photocatalytic oxidation of pesticides in aqueous media irradiated by UV light is a rapidly growing field of research. Therefore, the treatment technology for degradation of propoxur (an insecticide) using titanium dioxide coated on the supports such as activated carbon, zeolite, brick, quartz and glass beads, was performed in this research. Results show that GAC/TiO2 is the best complexing agent for oxidizing propoxur because of its adsorption properities. The others follow the sequence: plain TiO2 > glass beads > zeolite > brick > quartz. The degradation rate of propoxur with plain TiO2 is higher than that with TiO2/GAC complexing agent. But the mineralization rate of propoxur with plain TiO2 is lower than that with TiO2/GAC complexing agent. However, it can be concluded that using GAC as the support can improve the photocatalytic efficiency.

Adsorption characteristics of dichlorvos onto hydrous titanium dioxide surface

Abstract Adsorption of dichlorvos (2,2-dichlorovinyl-o,o-dimethl phosphate) onto hydrous TiO2 from water was evaluated in the laboratory using a batch reactor. The presence of organic solvents resulted in a decreasing dichlorvos adsorption on TiO2 surface. These data were used to assess a cosolvent model. Decreased adsorption of dichlorvos was observed at an initial pH of 4 with increasing ionic strength. The inhibitory adsorption is attributed to the blockade of surface sites by electrolytes. In addition, electrolytes play an important role on the pH-dependent dichlorvos adsorption. It is suggested that at pH pHpzc, the adsorption density of dichlorvos decreases with increasing solution pH due to the decrease of surface group, Ti OH, on the TiO2 surface. The variation of adsorption density with temperature over the range 10°–40°C has been investigated. Results show that the reaction is controlled by enthalpy. The adsorption of dichlorvos onto the TiO2 surface is primarily brought about by hydrogen bonding.

Decomposition of 2-naphthalenesulfonate in aqueous solution by ozonation with UV radiation

This study investigates the ozonation of 2-naphthalenesulfonate (2-NS) combined with ultraviolet (UV) radiation. Naphthalenesulfonic acids are of importance as dye intermediates for the dye and textile auxiliary industries. Its derivatives, such as 2-NS, have been found in rivers and tannery effluents causing pollution problems. Thus, the 2-NS is of concern for the aquatic pollution control especially in the surface and waste waters. Ozonation combined with UV radiation is employed for the removal of 2-NS in the aqueous solution. Semibatch ozonation experiments were proceeded under different reaction conditions to study the effects of ozone dosage and UV radiation on the oxidation of 2-NS. The concentrations of 2-NS and sulfate are analyzed at specified time intervals to elucidate the decomposition of 2-NS. In addition, values of pH and oxidation reduction potential are continuously measured in the course of experiments. Total organic carbon is chosen as a mineralization index of the ozonation of 2-NS. The mineralization of 2-NS via the ozonation is remarkably enhanced by the UV radiation. These results can provide useful information for the proper removal of 2-NS in the aqueous solution by the ozonation with UV radiation.