Microwave-assisted rapid photocatalytic degradation of malachite green in TiO2 suspensions: mechanism and pathways.
Microwave-assisted photocatalytic (MPC) degradation of malachite green (MG) in aqueous TiO2 suspensions was investigated. A 20 mg/L sample of MG was rapidly and completely decomposed in 3 min with the corresponding TOC removal efficiency of about 85%. To gain insight into the degradation mechanism, both GC-MS and LC-ESI-MS/MS techniques were employed to identify the major intermediates of MG degradation, including N-demethylation intermediates [(p-dimethylaminophenyl)(p-methylaminophenyl)phenylmethylium (DM-PM), (p-methylaminophenyl)(p-methylaminophenyl)phenylmethylium (MM-PM), (p-methylaminophenyl)(p-aminophenyl)phenylmethylium (M-PM)]; a decomposition compound of the conjugated structure (4-dimethylaminobenzophenone (DLBP)); products resulting from the adduct reaction of hydroxyl radical; products of benzene removal; and other open-ring intermediates such as phenol, terephthalic acid, adipic acid, benzoic acid, etc. The possible degradation mechanism of MG included five processes: the N-demethylation process, adduct products of the hydroxyl radical, the breakdown of chromophores such as destruction of the conjugated structure intermediate, removal of benzene, and an open-ring reaction. To the best of our knowledge, it is the first time the whole MG photodegradation processes have been reported.
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, PR China.
Yongming
Y
Ju
Shaogui
S
Yang
Youchao
Y
Ding
Cheng
C
Sun
Aiqian
A
Zhang
Lianhong
L
Wang
D001555:Benzene Derivatives / Q000737:chemistry; D002384:Catalysis; D004396:Coloring Agents / Q000737:chemistry / Q000378:metabolism; D008401:Gas Chromatography-Mass Spectrometry; D017665:Hydroxyl Radical / Q000737:chemistry; D008027:Light; D008872:Microwaves; D015394:Molecular Structure; D010777:Photochemistry; D012394:Rosaniline Dyes / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects*; D021241:Spectrometry, Mass, Electrospray Ionization; D013997:Time Factors; D014025:Titanium / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D001555:Benzene Derivatives; D004396:Coloring Agents; D012394:Rosaniline Dyes; D014867:Water; C005095:malachite green; C009495:titanium dioxide; D017665:Hydroxyl Radical; D014025:Titanium