Photo-fenton Effect On The Conversion Of Para-chlorophenol In Ice

At present the organic pollutants in the polar regions is an indisputable fact. Compared with the flow of air and water, the physical transmission, microbial and conventional chemical reactions of the organic pollutants in snow and ice are relatively weak, and the photochemical reaction plays an important role in the particular environment of snow and ice due to its less influence by the temperature. The photochemical reaction can leads to the transform of some organic pollutants into more toxic substances in snow and ice, which are then released when melt, and become a potential secondary pollution sources. Therefore, it is of great significance to research on the photochemical reaction of the pollutants in snow and ice. Though some basic research on the photochemical reaction has been carried out domestic and overseas, the present research focuses on the direct photolysis of the organic pollutants and the indirect photolysis with the effect of H₂O₂,NO₂^- and NO₃^-. While in fact, there are some other components which might take part in the photochemical reactions, such as Fe²⁺ and Fe³⁺, humic acid, acetic acid, oxalic acid, citric acid and some other organic acids of small molecules. The influence of there components on the photochemical reaction in snow and ice has not been concerned.The iron is an rich element on the earth, which is widely present in the air, water, soil, plants and animals, and it is also a common component in ice, which acts in lots of chemical and biological processes. The Fenton effect, that is the catalytic decomposition of H₂O₂ by Fe²⁺ with the generation of·OH,has been widely used in the cleanup of the refractory organic pollutants in the water. So the action mechanism of the Fenton effect in the water is always an important research topic in the environmental science. But so far,there is no report of the research on the photocatalytic effect in ice. It can be anticipated that the reaction and mechanism of the Fenton-like effect composed of Fenton reagent, humic acid, oxalic acid, citric acid and Fe²⁺, Fe³⁺ will be special in the photochemical process in ice, due to the characteristics distinction between ice and water. Therefore, the paper took the 4-CP as the research object, and carried out the research on the photoconversion of 4-CP in both ice and aqueous solution by the simulated sunlight-H₂O₂-Fe²⁺ effect. The paper discussed the influence of some factors on the photoconversion of 4-CP, such as the initial concentration of 4-CP, H₂O₂ and Fe²⁺, the light intensity, the initial pH of the system, the coexist negative ions, the dissolved oxygen content, and gave out the kinetic discipline of the photoconversion of 4-CP by the photo-Fenton effect, the intermediate production was also analyzed and the reaction mechanism was also deduced. The paper captured the·OH in ice and the aqueous solution by chemical probe technique for further understanding the microscope mechanism of the photo-Fenton in ice. Moreover, the paper researched on the photoconversion of 4-CP by the simulated sunlight–Fe(â…¢) -oxalic acid effect in ice with the same light source, discussed the influence of the initial concentration of Fe³⁺ and oxalic acid, the concentration ratio of Fe³⁺/oxalic acid, the initial pH of the system, built up the rule of the photoconversion of 4-CP, with the intermediate production analyzed and the reaction mechanism deduced. The paper also paid attention to the concentration alteration of·OH by the simulated sunlight-Fe(â…¢)-oxalic acid effect in the system for further understanding of the microscope mechanism of the Fenton-like effect.In ice, the photoconversion of 4-CP in simulated sunlight-H₂O₂-Fe²⁺ system obeyed the first order kinetics equation. When the concentration of 4-CP, H₂O₂ and Fe²⁺ was 0.4 mmol/L, 0.8 mmol/L and 0.004 mmol/L respectively, pH value was 5.50, and light intensity was 32000 Lx, the conversion rate constant of 4-CP was 0.1177h-1, the half-life was 5.8879 h. The conversion rate of 4-CP increased with the increase of the initial concentration of H₂O₂, and Fe²⁺ and light intensity, and decreased with the increase of the initial concentration of 4-CP. The photoconversion of 4-CP was accelerated under strong acidic conditions, and was inhibited in alkaline conditions. Cl^- obviously promoted the photoconversion of 4-CP, HCO₃^- suppressed the photoconversion of 4-CP, the effects of SO₄^2- and NO₃^- on the photoconversion of 4-CP were different with different concentrations. The photoconversion of 4-CP was not only influenced by the concentration of ? OH, but also influenced by the existence of QLL in ice. The influence of different factors on the concentration of·OH generated in the system was not entirely consistent with that on the photoconversion of 4-CP. enerated in the system was not entirely consistent with the amount of 4-CP photoconversion. the concentration of·OH generated in the system was accelerated under acidic conditions, but was inhibited in strong acid and alkaline conditions. Cl^- and SO₄^2- had little effect on the generation of·OH, NO₃^- promoted the generation of·OH, and HCO₃^- suppressed the generation of·OH.In aqueous solution, the photoconversion of 4-CP in simulated sunlight- H₂O₂-Fe²⁺ system obeyed the first order kinetics equation, but the conversion of 4-CP in aqueous solution was faster than that in ice. Similar with the photoconversion of 4-CP in ice, the conversion rate of 4-CP in aqueous solution increased with the increase of the initial concentration of H₂O₂, Fe²⁺ and light intensity, and decreased with the increase of the initial concentration of 4-CP. The photoconversion of 4-CP was accelerated under acidic conditions, and was inhibited in strong acid and alkaline conditions. Cl^- and HCO₃^- inhibited the photoconversion of 4-CP; SO₄^2- had no obvious effect on the photoconversion of 4-CP; the effects of NO₃^- on the photoconversion of 4-CP were different with different concentrations. The photoconversion of 4-CP was mainly influenced by·OH generated in the system. The influence of different factors on the concentration of·OH generated in the system was not entirely consistent with that on the photoconversion of 4-CP. the concentration of·OH generated in the system was accelerated under acidic conditions, but was inhibited in strong acid and alkaline conditions. SO₄^2- had little effect on the generation of·OH, NO₃^- promoted the generation of·OH, Cl^- and HCO₃^- suppressed the generation of·OH.The influence of the simulated sunlight- H₂O₂-Fe²⁺ in ice and water on the photoconversion of 4-CP is not completely same. The distinction are: (1) the concentration of the generated·OH in aqueous solution is 7.30μmol/L, which is higher than the concentration in ice; (2) the photoconversion of 4-CP is inhibit by strong acidic conditions in aqueous solution, but promoted in ice; (3) Cl^- inhibits the photoconversion of 4-CP in aqueous solution, but promots the photoconversion in ice; (4) SO₄^2- has no effect on the photoconversion of 4-CP in aqueous solution, while in ice, the photoconversion of 4-CP alters with the alternation of the SO₄^2- concentration.The photoconversion of 4-CP in ice by the simulated sunlight-Fe(â…¢)-oxalic acid effect follows the first-order kinetic reaction mode. When the initial concentration of oxalic acid is 0.80mmol/L, the ratio of the initial concentration of Fe³⁺ and oxalic acid is 1/5, the initial pH of the solution is 6.50, the photoconversion ratio of 4-CP after 7.5h will reach 39.1%. The captured·OH in the system suggests that the simulat sunlight- Fe(â…¢)-oxalic acid accelerated the photoconversion of 4-CP through the generation of·OH.The photoconversion intermediate products of 4-CP in three different systems were enriched by direct extraction and derivatization, and were analyzed by GC-MS. Thus the reaction mechanisms of 4-CP were proposed. The main intermediate production of the photoconversion of 4-CP in ice by the simulated sunlight-H₂O₂-Fe²⁺ effect are 1,4-Benzoquinone, 4-chlorobenzene-1,2-diol, 5-chlorobiphenyl-2,4'-diol, 4-(4-chlorophenoxy) phenol, 2-(4-chlorophenoxy) benzene-1,4-diol, 4-chloro-2- (4-chlorophenoxy) phenol and a dichlorobiphenyldiols. The main intermediate production of the photoconversion of 4-CP in aqueous solution by the simulated sunlight-H₂O₂-Fe²⁺ effect are 1,4-Benzoquinone, 2-hydroxycyclohexa- 2,5-diene-1,4 -dione and 4-chlorocatechol. The main intermediate production of the photoconversion of 4-CP in ice by the simulated sunlight-Fe(â…¢)-oxalic acid effect are 1,4- benzoquinone,4-chorocatechol, biphenyl-4,4'-diol, biphenyl-2,4'-diol, 5-chloro- biphenyl-2,4'-diol,4-(4-chlorophenoxy)-phenol and 2-(4-chlorophenoxy) -phenol. Hydroxylation occurred in the three systems both in ice and in aqueous solution. Meanwhile, coupling products (i.e. dimmer) were identified in the two systems in ice.The laboratory simulation experiments revealed the micromechanism of photo-Fenton effect in ice, which will supply the theoretic accordace for the prevent and evaluation of the potential environmental risks by the pollution of the ice and snow.