【作者】 高佳；

【导师】 杨绍贵；

【作者基本信息】 南京大学 ， 环境科学， 2016， 硕士

【摘要】 近年来,由于印染行业的迅猛发展,大量的废水随之产生,从而导致环境水体质量下降,同时也对人体健康造成潜在危害。作为一种高级氧化技术,微波诱导催化氧化技术由于反应快速、催化效率高、不产生二次污染等特点,在染料废水的处理中受到广泛关注。其中,催化剂对反应的进行有重要影响,因而选取对微波有强烈吸收的催化剂至关重要。本论文制备了新型、高效的微波催化剂-碳化硅负载的铁酸镁,以直接黑BN为目标物进行微波诱导催化降解研究,主要的工作如下:(1)采用溶胶凝胶法成功制备了材料MgFe2O4和MgFe2O4-SiC,通过对MgFe2O4-SiC的制备条件进行优化制得活性最好的复合材料。XRD分析表明MgFe2O4和MgFe2O4-SiC中都出现了相对应的特征衍射峰,其粒径大小分别为25.39 nm和19.58 nm。SEM和TEM中MgFe2O4粒子类似链状球形,其均匀负载在SiC的表面上,且内部存在大量的微孔。MgFe2O4和MgFe2O4-SiC的BET比表面积分别为26.23和105.3 m2/g,孔径属于介孔范围,其等电点分别在pH4.5和3.6附近。XPS中MgFe2O4-SiC中两相很好地复合在一起,元素价态没有发生改变。此外,MgFe2O4-SiC的介电常数的值远高于MgFe2O4,复合材料的介电损耗显著增强,而它们均存在一定的磁损耗。(2)通过对偶氮染料直接黑BN进行降解研究,反应5 min后,单独微波作用、单独催化剂MgFe2O4-SiC,微波-MgFe2O4体系和微波-MgFe2O4-SiC体系对直接黑BN的去除率分别为6%,17.7%,42.3%和96.5%。通过MnFe2O4-SiC和MgFe2O4-SiC分别对直接黑BN和活性艳红X-3B的微波催化降解比较可知MgFe2O4-SiC的微波催化活性更高。通过对反应的影响因素分析表明MgFe2O4-SiC在很宽的pH范围内都有良好的微波催化性能,最佳的反应条件为MgFe2O4-SiC的加入量1.5 g/L,微波功率800 W。在微波-MgFe2O4-SiC体系中TOC的去除率为65%,大部分的直接黑BN分子被矿化分解。由生物毒性变化可知反应液对发光菌的抑制率从32%减小到11%,毒性明显降低。MgFe2O4-SiC经过10次使用后对直接黑BN的去除率仍高达80.2%,且其晶体结构没有发生改变。MgFe2O4-SiC对无论对偶氮染料还是其他染料都有很高的去除率,因而MgFe2O4-SiC有良好的的微波催化能力。(3)通过对材料的微波吸收性能研究的结果表明,MgFe2O4的反射损失(RL)在整个频段均大于-5 dB,而MgFe2O4-SiC的最大RL小于-10 dB,且在5.0 mm厚度时其值最大为13.32 dB,对应的频率为2.57 GHz,与微波装置的2.45 GHz相近,因而其对微波的吸收能力显著增强。MgFe2O4-SiC对微波的吸收能力主要源于材料的介电损耗,材料吸收了超过90%的微波能量用于直接黑BN的降解,使其降解率和矿化率提高。MgFe2O4-SiC的最大反射损失和有效带宽均高于MnFe204-SiC,因而与MnFe204-SiC相比,MgFe2O4-SiC有更好的微波吸收性能,这与微波催化降解的结果相对应。(4)为了测定反应中产生的活性物种,分别向反应体系中加入羟基自由基·OH的抑制剂叔丁醇和空穴h+的抑制剂草酸钠。结果表明·OH和h+是此体系所产生的活性物种。且与h+相比,·OH对降解反应起到更为关键的作用。它们可与直接黑BN发生反应,从而促使其快速、有效降解成为小分子物质和无机离子。并通过离子色谱、GC-MS和LC-MS分析测定直接黑BN的降解产物,推导出直接黑在此微波诱导催化体系中的降解路径。(5)基于上述研究结果,本论文提出了微波诱导MgFe2O4-SiC催化降解直接黑BN的作用机制:即在微波条件下,SiC作为典型的介电材料,能强烈地吸收微波能量,这些能量随后迅速转移到MgFe2O4粒子上,使其表面迅速升温,随之产生大量的热点,且热点随着微波吸收能力的增强而增多,使得材料内部形成的电子空穴对和体系及空气中的O2、H2O发生反应,产生·OH等活性物种参与直接黑BN的降解反应中,促使其快速降解去除。更多还原

【Abstract】 In recent years,with the rapid development of printing and dyeing industry,a large number of dyestuff wastewater is discharged into environmental water,not only leading to the decline in environmental water quality,but also posing a potential hazard to human health.As one of advanced oxidation technology,microwave-induced catalytic oxidation technology has received more and more attention.Due to its rapid reaction,high catalytic efficiency and no secondary pollution,it is widely used in the treatment of dye wastewater.And the catalyst has an important influence on the reaction.Thus,it is very important to select the catalyst with the capability to absorb microwave energy strongly in the microwave induced catalytic reaction.A novel and efficient microwave catalyst—magnesium ferrite supported on silicon carbide,is prepared in this study.And azo dye Direct Black BN is chosen as the target to investigate microwave-induced catalytic degradation property of the material.The main research contents are as follows:(1)MgFe2O4and MgFe2O4-SiC were successfully synthesized by sol-gel method.MgFe2O4-SiC for the best catalytic activity was prepared by optimizing the preparation conditions.XRD analysis showed that the corresponding characteristic diffraction peaks of MgFe2O4 and MgFe2O4-SiC appeared,and the particle sizes of MgFe2O4 and MgFe2O4-SiC were 25.39 nm and 19.58 nm,respectively.As can be seen from SEM and TEM images,MgFe2O4 was chain-like spherical particles.MgFe2O4was uniformly supported on the surface of SiC and a large number of pores existed in MgFe2O4-SiC.Moreover,the specific surface areas calculated by BET equation for MgFe2O4 and MgFe2O4-SiC were found to be 26.2 and 105.3 m2/g,respectively,and their pore size belonged to the mesoporous range.Zeta potential measurements indicated that the isoelectric points of MgFe2O4 and MgFe2O4-SiC were in the vicinity of pH 4.5 and 3.6,respectively.XPS analysis showed that the two phases of MgFe2O4-SiC were well combined together,and the valence state of the elements were not changed.In addition,the dielectric constant(real and imaginary)of MgFe2O4-SiC were much higher than that of MgFe2O4.The dielectric loss of the composite was greatly enhanced when MgFe2O4 was loaded on SiC.The permeability(real and imaginary)of MgFe2O4 and MgFe2O4-SiC were high in the low frequency band and the values decreased with the frequency increased.The materials exhibited certain magnetic loss.(2)Degradation experiments of azo dye Direct Black BN showed that after 5 minutes of reaction the removal of DB BN in four systems(separate microwave radiation,MgFe2O4-SiC,microwave-MgFe2O4 system and microwave-MgFe2O4-SiC system)were 6%,17.7%,42.3%and 96.5%,respectively.MgFe2O4-SiC presented higher degradation efficiency of DB BN and RBR X-3B(Brilliant Red X-3B)than that of MnFe2O4-SiC.The effects of initial pH,MgFe2O4-SiC dosage and MW power on DB BN degradation were investigated,respectively.It can be viewed that MgFe2O4-SiC presented a broad pH range;the optimal conditions for dosage of MgFe2O4-SiC and microwave power were 1.5 g L-1 and 800 W,respectively.The removal of TOC was 65%in this system,and most of DB BN molecules were degraded.The change of the biological toxicity of the reaction solution showed that the toxicity of this system obviously decreased,and the inhibiting effect to Photobacteriumphosphoreum T3 reached 11%far below the initial inhibition of 32%.Moreover,DB BN degradation efficiency after 10 runs still reached 80.2%,and the crystal structure of MgFe2O4-SiC after 10 runs hardly changed.MgFe2O4-SiC presented high removal for five different kinds of dyes under microwave radiation,Therefore,MgFe2O4-SiC possessed excellent microwave catalytic ability.(3)Based on the results of microwave absorbing properties of the materials,the reflection loss of MgFe2O4 were greater than 5 dB in the whole frequency range,while the maximum reflection loss of MgFe2O4-SiC was less than-10 dB.The maximum absorption value was 13.32 dB with 5.0 mm thickness and the corresponding frequency was 2.57 GHz,which was close to microwave frequency of 2.45 GHz.Hence,the microwave absorbing capacity of MgFe2O4-SiC was significantly enhanced.The microwave absorbing ability of MgFe2O4-SiC was mainly due to the dielectric loss of the material and MgFe2O4-SiC absorbed more than 90%of the microwave energy for the degradation of DB BN,so that the degradation and mineralization efficiency increased.The maximum reflection loss and efective bandwidth of MgFe2O4-SiC were higher than MnFe2O4-SiC.Thus MgFe2O4-SiC had better microwave absorbing performance compared with MnFe2O4-SiC,which was in accord with the result of microwave catalytic degradation.(4)To determine the main active oxygen species during the degradation,tert-butyl alcohol and sodium oxalate as·OH scavenger and h+scavenger were added in the reaction solutions,respectively.The results showed that ·OH and h+were the main active species in the reaction system,playing an important role in the degradation of DB BN.Moreover,·OH played a more critical role compared with h+ in this system.They can react with DB BN,thus promoting its rapid and efficient degradation to be small molecular substances and inorganic ions.By means of ion chromatography,GC-MS and LC-MS analysis,the degradation products of DB BN were determined,and the degradation pathway of DB BN in the microwave-induced catalytic system was analyzed.(5)Based on the above research results,the degradation mechanism of DB BN in the microwave-induced catalytic system was proposed.With microwave radiation,SiC,which is known as the typical dielectric,can strongly absorb microwave energies.Then,these energies could be quickly transferred to the MgFe2O4 particles on the surface of SiC.In consequence,lots of hot spots were generated on its surface simultaneously with the surface temperature of MgFe2O4-SiC increasing,causing numerous activated sites and holes.Hence,the electron hole pairs can be generated to react with O2 and H2O in this system to form active species(e.g.·OH),which participated in the degradation of DB BN.Therefore,the microwave-induced catalytic degradation of DB BN could be enhanced significantly.更多还原