Treatment of nitrophenols by cathode reduction and electro-Fenton methods.
This study deals with the degradation of various nitrophenols by cathode reduction and electro-Fenton methods. Phenols (Poh), 2-nitrophenol (2-NP), 3-nitrophenol (3-NP), 4-nitrophenol (4-NP), and 2,4-dinitrophenol (2,4-DNP) are treated and different degradation sequences are obtained. The relationship between the structure and activities of nitrophenols is discussed. Using 4-NP as a model nitrophenol, the electrochemical behaviors on graphite cathode and Pt anode are analyzed by cyclic voltammetry. The contribution of different reactions to the degradation of 4-NP is investigated in divided cells. The degradation of 4-NP is much faster in the cathode cell than in the anodic cell. In the cathode cell, the degradation of 4-NP is significantly enhanced by the introduction of aeration and Fe(2+). Ultraviolet-visible (UV-vis) spectra reveal different reaction pathways for the degradation in the anodic cell and cathode cell. Treatment of high concentration of 4-NP in the undivided cell shows that more than 98% removal of 4-NP and about 13% removal of total organic carbon (TOC) are obtained for both processes, while the subsequent biodegradability test shows that electro-Fenton can eliminate the toxicity and improve the biodegradability of 4-NP. Negligible quantity of nitrate and nitrite ions detected in both processes indicates that there is no direct release of -NO(2) and -NO groups from 4-NP and its degradation intermediates. Intermediates such as hydroquinone and bezoquinone are detected by gas chromatography/mass spectrum (GC/MS). The degradation pathway of 4-NP in electro-Fenton process is proposed as the cathode reduction followed by hydroxyl oxidation.
Yuan
Songhu
S
Environmental Science Research Institute, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China. yuansonghu622@hotmail.com
Tian
Meng
M
Cui
Yanping
Y
Lin
Li
L
Lu
Xiaohua
X
D016227:Benzoquinones / Q000737:chemistry; D001673:Biodegradation, Environmental; D002244:Carbon / Q000737:chemistry; D004563:Electrochemistry / Q000379:methods*; D004566:Electrodes; D006873:Hydroquinones / Q000737:chemistry; D009566:Nitrates / Q000737:chemistry; D009573:Nitrites / Q000737:chemistry; D009596:Nitrophenols / Q000737:chemistry* / Q000378:metabolism*; D013053:Spectrophotometry / Q000379:methods; D013997:Time Factors; D014466:Ultraviolet Rays; D014865:Waste Disposal, Fluid; D018508:Water Purification / Q000379:methods*
D016227:Benzoquinones; D006873:Hydroquinones; D009566:Nitrates; D009573:Nitrites; D009596:Nitrophenols; C004532:quinone; D002244:Carbon; C031927:hydroquinone