Unique Ability of BiOBr To Decarboxylate D-Glu and D-MeAsp in the Photocatalytic Degradation of Microcystin-LR in Water
Unique Ability of BiOBr To Decarboxylate D-Glu and D-MeAsp in the Photocatalytic Degradation of Microcystin-LR in Water
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BiOBr 在光催化降解水中微囊藻毒素-LR 时使 D-Glu 和 D-MeAsp 脱羧的独特能力
DOI：
10.1021/es103422j
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发表时间：
2011-02-15
影响因子：
11.4
通讯作者：
Cheng Genwei
中科院分区：
文献类型：
--
作者：
Fang Yanfen;Huang Yingping;Cheng Genwei
用氧化溴化铋（BiOBr）在可见光下催化中性pH水中微囊藻毒素（MC-LR）的降解。在调查过程中，通过LC-MS鉴定了MC-LR分解过程中的12个中间体。除了攻击MC-LR的典型易感位点（即Adda链的共轭双键和Mdha链的末端不饱和键）外，BiOBr光催化剂还具有显著的脱羧d -谷氨酸（Glu）和甲基- d -天冬氨酸（MeAsp）上的游离酸基团的能力。这种反应性以前没有在TiO2光催化或其他MC-LR处理中观察到，在这些处理中，直到MC-LR环被切割或矿化成二氧化碳才发生脱羧。以(H2O)-O-18为溶剂，用氧-18标记法检测了一些预期的中间产物，证实了脱羧过程是由BiOBr介导的。中间体表征和氧18标记研究的结果表明，BiOBr光催化对MC-LR的氧化脱羧并不总是由羟基自由基攻击（和/或与空穴相互作用，然后水解）引发的，这是TiO2光催化中的一种机制。这种不寻常的脱羧行为似乎与BiOBr光催化剂的特定价带和导带状态有关。同样在BiOBr催化下，与TiO2光催化不反应的l -精氨酸（L-Arg）的一个非常稳定的胍基在MC-LR分解过程中转化为氨基，随后氧化为硝基。这个反应顺序也与脱羧有关，因为胍的转化需要一个完全或部分脱羧的前体。我们的研究结果表明，BiOBr是一种光催化剂，可以选择性地破坏对MC-LR毒性至关重要的位点，作为一种有效处理饮用水的手段，它显示出很大的前景。
Bismuth oxide bromide, BiOBr, was used to catalyze the degradation of microcystin-LR (MC-LR) in water at neutral pH under visible light. During the investigation, twelve intermediates from MC-LR decomposition were identified by LC-MS. In addition to attacking MC-LR at the typically susceptible sites (i.e., the conjugated double bond of the Adda chain and terminal unsaturated bond of the Mdha chain), the BiOBr photocatalyst has the remarkable ability to decarboxylate the free acid groups on D-glutamic acid (Glu) and methyl-D-aspartic acid (MeAsp). This reactivity has not been previously observed with TiO2 photocatalysis or with other MC-LR treatments in which decarboxylation does not occur until the MC-LR ring has been cleaved or mineralized to CO2. Some expected intermediate products were detected with oxygen-18 labeling by using (H2O)-O-18 as the solvent to confirm that the decarboxylation process is mediated by BiOBr. Results from characterizing the intermediates as well as oxygen-18 labeling studies indicates that oxidative decarboxylation of MC-LR by BiOBr photocatalysis is not always initiated by hydroxyl radical attack (and/or interaction with a hole followed by hydrolysis) proposed mechanism in TiO2 photocatalysis, whereas likely caused by a direct interaction between photoinduced hole of BiOBr and free carboxyl groups of MC-LR This unusual decarboxylation behavior seems to be associated with the particular valence band and conduction band state of BiOBr photocatalyst. Also under BiOBr catalysis, a very stable guanidine group of L-arginine (L-Arg) that is nonreactive with TiO2 photocatalysis is converted to an amino group and subsequently oxidized to a nitro group during the decomposition of MC-LR This reaction sequence is also related to decarboxylation because the guanidine conversion requires a completely or partially decarboxylated precursor. Our results indicate that BiOBr, a photocatalyst that selectively destroys sites crucial to MC-LR toxicity, shows great promise as a means of effectively treating drinking water.