不同氧化锰矿物对光催化降解苯酚的影响

Photocatalytic Degradation of Phenol with Manganese Oxides:The Effects of Crystal Structure and Reaction Mechanisms

合成层状结构的酸性和碱性水钠锰矿以及隧道结构的锰钾矿和钙锰矿,将其用于苯酚的光催化降解研究。分别采用X射线衍射(XRD)、原子吸收光谱(AAS)、扫描电镜(SEM)、BET氮气吸附法和紫外可见漫反射光谱(UV-Vis DRS)对供试锰氧化物的晶体结构、化学组成、微观形貌、比表面积以及光吸收性能等进行了表征。研究表明,暗反应条件锰氧化物对苯酚的降解作用较弱,而UV-Vis光照能显著促进锰氧化物对苯酚的降解。光照反应12 h后,锰钾矿、酸性水钠锰矿、钙锰矿以及碱性水钠锰矿的苯酚降解率分别为92.1%、77.3%、57.4%和45.8%;对应的TOC去除率分别由暗反应时的6.3%、11.2%、2.0%和4.6%提高至62.1%、43.1%、25.4%和22.5%。4种供试锰氧化物均具有光催化活性,其大小顺序为:锰钾矿>酸性水钠锰矿>钙锰矿>碱性水钠锰矿。UV-Vis光照下氧化锰矿物光化学降解苯酚主要存在3种降解机制———苯酚的直接光解,锰氧化物的化学氧化和锰氧化物的光化学催化,其中光催化降解起主导作用。

Acidic and alkaline birnessites,and tunnel-structured cryptomelane and todorokite have been synthesized,characterized,and applied in photocatalytic degradation of phenol.In order to elucidate phenol degradation mechanisms,structure,composition,morphology,surface area and optical absorption properties were studied in detail by using XRD（X-ray diffraction）,ICP-AES（inductively coupled plasma-atomic emission spectroscopy）,SEM（scanning electronic microscope）,TEM（transmission electronic microscope）,N2 physisorption at 77 K and UV-Visible diffuse reflectance spectroscopy（UV-vis DRS）.The results revealed a weak ability of manganese oxides to degrade phenol in the dark condition,while UV-Vis light irradiation could significantly enhance phenol degradation.All these manganese minerals exhibited photocatalytic activities in the order of cryptomelane acidic birnessite todorokite alkaline birnessite.There were three possible mechanisms of photochemical degradation of phenol on manganese oxides assisted by light irradiation：（1） direct oxidation of phenol by UV-Vis light,（2） oxidation of phenol by manganese oxides,and（3） photocatalytic oxidation by manganese oxides.Among them,photocatalytic oxidation appeared to be the dominant mechanism.