g-C_3N_4-P25/光合细菌复合材料降解偶氮染料废水的机理

Degradation mechanism of azo dyes-contaminated wastewater by g-C_3N_4-P25/photosynthetic bacteria composite

采用海藻酸钙将g-C3N4-P25和光合细菌进行共固定,合成了光催化-微生物复合材料,并进行了降解模拟偶氮染料废水的研究.结果表明,光催化-微生物复合材料的染料(活性艳红X-3B)脱色率和COD去除率分别为94%和84.7%,远远大于固定光催化剂与固定光合细菌.利用UV-Vis、FT-IR及GC-MS对反应残留物进行表征,根据结果可推测:由光催化产生的自由基和光合细菌共同破坏X-3B的偶氮结构,生成的苯胺类化合物经过一系列的水解、氧化还原作用生成多种具有苯环结构的化合物,然后自由基破坏苯环结构产生长链烷烃,减少芳香烃化合物的累积对光合细菌活性的影响.光合细菌及时利用光催化生成的长链烷烃,产生分子量较小的物质,最后矿化为CO2和H2O.

Photocatalysts（ g-C3 N4-P25） and photosynthetic bacteria（ PSB） were encapsulated in calcium alginate beads by self-assembly,and its ability to treat simulated azo dyes-contaminated wastewater was studied. The removal efficiency by this photocatalysis-microorganism composite was 94% for the dye reactive brilliant red X-3 B and 84.7% for COD of synthetic wastewater samples,which were significantly higher than immobilized photocatalysis and PSB. Intermediates formed during the oxidation process were analyzed by UV-visible spectrophotometry,FT-IR and gas chromatography-mass spectrometry（GC-MS）. Based on the results,the degradation pathway was inferred as follows. First,the azo dye was converted into aniline and phenol derivatives,through combined photocatalytic and biocatalytic degradation of X-3 B by composites. Then,the aromatic rings of these products were attacked by free radicals generated by the photocatalyst,leading to the formation of linear alkyl compounds and preventing the inhibition of bacterial metabolism by aromatic hydrocarbon. Finally,the linear alkyl products could be degraded and mineralized to CO2 and H2 O by the photosynthetic bacteria.