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.
Ju
Yongming
Y
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, PR China.
Yang
Shaogui
S
Ding
Youchao
Y
Sun
Cheng
C
Zhang
Aiqian
A
Wang
Lianhong
L
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