Heterogeneous and homogeneous photoassisted wastewater treatment

Abstract

Photochemical degradation of 4-chlorophenol (4-CP) as a model wastewater contaminant with three methods: UVfriO2, UV/H20, and UVfFiO2/H202 (2 > 310nm) has been investigated and compared to the dark Fenton reaction and to direct photolysis. A UV-irradiated combination of TiO2 and H202 was found to be the most effective degradation method for TOC (total organic carbon). 4-CP was degraded most rapidly by the dark Fenton reaction. In the heterogeneous process on illuminated TiO2 without H 202, only small amounts of by-products were formed during irradiation in contrast to homogeneous processes where H,O2 was involved. During UV/H202 and Fenton experiments, coloured by-products appeared during irradiation and degradation rates of 4-CP and TOC showed strong differences between homogeneous and heterogeneous processes.

Catalytic Fe3+ Clusters and Complexes in Nafion Active in Photo-Fenton Processes. High-Resolution Electron Microscopy and Femtosecond Studies

“…During the past decade, the abatement of contaminants in aqueous solution activated by UV−vis light and in the presence of the Fenton reagent Fe 2+ /Fe 3+ /H 2 O 2 has gained in importance and application. − Heterogeneous photoassisted Fenton systems have been reported to proceed with a slower kinetics when compared with the homogeneous systems during the degradation of the organic pollutants. − The activity of the Fenton catalytic system strongly depends on the nature of the iron complexes…”

VUV/UV light inducing accelerated phenol degradation with a low electric input

“…Both Fe(OH) 2+ reduction and H 2 O 2 hydrolysis under UVC light (see eqn (5) and (6)), generated additional HO˙ compared to the dark Fenton system. 31 , 34 , 46 The Fe( iii )–aqua complexes present different molar absorption coefficients and optical absorption wavelength ranges as a function of the solution pH. 35 , 36 This in turn induced a different rate of phenol degradation and quantum yield as a function of pH.…”

“…31 – 33 The fully hydrated Fe(H 2 O) 6 3+ complex was reported as a catalytic species in the Fenton system at pH < 3. 34 At pH ≤ 3.5, the complexes Fe(OH)(H 2 O) 5 2+ and Fe(OH) 2 (H 2 O) 4 + interact with H 2 O 2 in the Fenton system, which has been comprehensively described. 35 , 36 These Fe–aqua complexes have optical absorption up to 390 nm.…”

“…This accelerates the degradation of organic compounds compared to the dark Fenton system. 34 The HO˙ generated led in the first reaction step to an aromatic ring addition to the phenol, leading to the hydroxyl-cyclohexadienyl radical. 37 , 38 …”