[Reductive degradation of chlorophenols in aqueous solution by gamma irradiation]

Because chlorine is an electron withdrawing group, the highly chlorinated phenols may react quickly with hydrated electrons rather than with hydroxyl radicals. The process of reactions of four chlorophenols (4-CP, 2-CP, 2,4-DCP, 2,4,6-TCP) with e(aq)(-) was investigated in aqueous solutions by detecting the concentration of CPs, Cl- and intermediates. In the e(aq)(-) reductive system, the experimental results showed that the order of four kinds of chlorophenol degradation and dechlorination was 2,4,6-TCP > 2,4-DCP > 2-CP > 4-CP. The greater the chlorine content was the higher reactivity of hydrated electrons towards chlorophenols was. Furthermore, hydrated electrons may preferentially attack the ortho-position of chlorine atom rather than the para-position of chlorine atom. Phenol and Cl- were detected as the final product of the reductive reaction. Additionally, processes of degradation and dechlorination of CPs were observed as the pseudo-first-order kinetics. The reaction constant of degradation of 4-CP, 2-CP, 2,4-DCP and 2,4,6-TCP were 0.154, 0.253, 0.750 and 1.188 kGy(-1), respectively. Meanwhile, the dechlorination of 4-CP, 2-CP, 2,4-DCP and 2,4,6-TCP were 0.137, 0.219, 0.251 and 0.306 kGy(-1), respectively.

Biosorption of Methylene Blue onto spent corncob substrate: kinetics, equilibrium and thermodynamic studies

This study focuses on the possible use of the spent corncob substrate (SCS), an agricultural waste used after the cultivation of white rot fungus Pleurotus ostreatus, to adsorb Methylene Blue (MB) from aqueous solutions. A batch adsorption study was carried out with variable solution pH, adsorption time, temperature and initial MB concentration. It was found that MB uptake was favorable at pH ranging from 4.0 to 12.0 and the equilibrium adsorption capacity can be reached promptly within about 180 min. The biosorption data were also calculated by the pseudo-second-order kinetic model and Langmuir isotherm model. Thermodynamic parameters show that the adsorption is a spontaneous and endothermic process. The study highlighted a new pathway to develop potential low-cost biosorbent for the removal of dye pollutants from wastewater.

[FTIR study of adsorption of PCP on hematite surface]

The adsorption of pentachlorophenol on hematite was studied through adsorption experiments and FTIR analysis. The pH adsorption isotherms of pentachlorophenol onto hematite were obtained by the static state experiments. The largest adsorption quantity occurred at about pH 6. The adsorption quantity at pH 8.5 of the isoelectric point of hematite was about 31% of the largest adsorption quantity. Fourier transform infrared (FTIR) spectroscopy was used to analyse the change of hematite before and after PCP adsorption, and the species of PCP on hematite. It was discovered that: (1) the typical peak at 565 cm(-1) of the Fe-O bond in alpha-Fe2O3 did not change before and after adsorption, and the adsorption occurred on the surface of hematite. (2) At pH 6.0, the stretching vibration peak at 3 438 cm(-1) due to the hydrogen bond formed between O-H on the surface of alpha-Fe2O3 and water molecules shifted to 3 417 cm(-1). The bending vibration peak of H-O-H+ on the surface at 1 643 cm(-1) was weakened because of complex reaction. The peak owing to Fe-OH bond was displaced from 1 050-1 100 cm(-1) to 950 cm(-1) with increased intensity. The C-O bond stretching vibration peak of PCP was displaced from 1 215 to 1 122 cm(-1). The main interaction between PCP and hematite was static electric interaction. (3) At pH 8.5, the stretching vibration peak of the hydrogen bond formed between O-H on the surface of alpha-Fe2O3 and water molecules was displaced from 3 438 to 3 428 cm(-1). The bending vibration peak at 1 643 cm(-1) was obviously weakened because of the hydrogen bonding. The H-O-H+ bending vibration peak at 1 050-1 100 cm(-1) was displaced to 947 cm(-1) with obviously increased intensity, indicating that the interaction was mainly through hydrogen bond.

[FTIR study of nano-iron oxyhydroxides' decoloration on the azo dye]

IR spectra were used to analyse the azo dye solution decoloration action by two kinds of iron oxyhydroxides. It was discovered that: (1) Acid Red G and methyl orange are apt to form complex on the surface of iron oxyhydroxides > FeOH, especially Acid Red G. which possesses two -SO3Na structures has a relatively high decoloration efficiency as a result of complexation reaction; (2) after 2 hours adsorption, the IR spectra of iron oxyhydroxides show characteristic wave numbers at 1 033 and 1 030 cm(-1) which belong to -SO3Na, whereas the peaks at wave numbers between 1 450 and 1 400 cm(-1), which belong to azo dye, disappear. These phenomena indicate that azo dye molecules are adsorbed on the surface of iron oxyhydroxides due to the negative -SO3Na structure, and at the moment azo dye molecules are adsorbed on the surface of iron oxyhydroxides, the electron transfer occurs between the azo dye molecules and the iron oxyhydroxides surface's Fe3+ centre, which could lead to the rupture of azo bond. It can be infered that the decoloration of azo dye molecules is the co-effect of the selective chemical absorption and the oxidation-deoxidation effect on the surface of iron oxyhydroxides.