Preparation Of MIL-100(Fe)-based Photocatalyst And Its Degradation Performance For Nitroaromatic Compounds

Nitroaromatic compounds have been released into wastewater during industrial production.And they are difficult to redox because of a stable benzene ring,resulting from contaminating even and destroying the ecological environment including biology,soil,and water.Photo-Fenton technology emerges as a promising wastewater treatment by virtue of environment,no secondary pollution,and high efficiency.The central of Photo-Fenton technology is photo-Fenton catalysts.However,traditional photo-Fenton catalysts are metal oxides,which generally are few active sites and small specific surface areas,resulting in poor catalytic efficiency.To address the situation,more efficient photo-Fenton catalysts are urgent to further improve the efficiency of photo-Fenton.The natural characteristic of MIL-100（Fe）determines its more reaction sites,high specific surface area,permanent pores,and good stability.The transfer of photoelectrons to metal clusters can effectively promote the separation of electron-hole pairs.So,MIL-100（Fe）is a promising photo-Fenton catalyst.Herein,photocatalysis-self-Fenton systems were constructed based on MIL-100（Fe）.Their degradation behaviors were studied while their mechanisms were revealed for wastewater with nitroaromatic compounds.The specific research work is as follows:（1）A new morphology of MIL-100（Fe）photo-Fenton catalyst was prepared by hydrothermal method using Fe（NO₃）₃·9H₂O and trimesic acid（H₃BTC）as raw materials.The composition and structure of MIL-100（Fe）were confirmed by modern testing methods,such as infrared spectroscopy,powder X-ray,transmission electron microscopy,and X-ray photoelectron spectroscopy.The results show that MIL-100（Fe）is a nanoplatelet with a diameter of<100nm.The optical properties were studied by UV-visible diffuse reflection with a band gap 2.34e V.Under ultraviolet irradiation,the effects of catalyst dosage,p H value,wastewater concentration,and H₂O₂ addition on the degradation efficiency of aromatic nitro compounds wastewater including 4-nitrophenol（PNP）,2,4,6-trinitrophenol（2,4,6-TNP）,nitrobenzene（NB）and 2,4-dinitrotoluene（2,4-DNT）were deeply investigated.The degradation efficiency was 93.5%-97.6%at 2 min after optimization of conditions,with MIL-100（Fe）0.3 g/L,p H=7,wastewater concentration 40 mg/L,and H₂O₂ concentration 0.84 mmol/L.The degradation mechanism was studied by free radical capture experiments.The results showed that·OH was the main active carrier and played a decisive role in the degradation of aromatic nitro compounds,followed by superoxide radicals（·O₂^-）and holes（h⁺）.（2）g-C₃N₄ quantum dots（CQDs）were prepared by hydrothermal method using ammonium citrate as raw material.And CQDs were loaded on melamine and cyanuric acid by ultrasonic deposition to precursors.Then,g-C₃N₄ quantum dots/g-C₃N₄（CQDs/CN）nanocomposites were obtained by calcining precursors.The composition and structure of CQDs/CN nanocomposites were characterized by powder X-ray diffraction,scanning electron microscopy,X-ray photoelectron spectroscopy,and elemental analysis.The results show that CQDs have been successfully doped,and CQDs/CN composites are micron flower balls stacked by nanosheets with a large number of pore structures.Doping CQDs will not affect the crystal structures of the composite because the material matches exactly the characteristic peak of g-C₃N₄.A novel photocatalytic-self-Fenton system was constructed by combining the composite material with MIL-100（Fe）and O₂.Then,under visible light irradiation,the effects of the catalytic system on PNP,2,4-DNT,2,4,6-TNP,and 2,4-DNP aromatic nitro compounds were studied.The effects of different doping amounts of CQDs,p H,and catalyst addition on the degradation efficiency of wastewater were investigated.When the doping amount of CQDs with a concentration of 4 mg/m L was 1.5 wt%,the CQDs/CN1.5 composite is the best.The degradation efficiency of PNP can reach 98.2%after 6 h with p H=7,the mass ratio of CQDs/CN and MIL-100（Fe）is 3:1.The degradation mechanism was studied by free radical trapping experiments combined with electron paramagnetic resonance technology.The results showed that·OH was still the main active carrier,followed by h⁺and·O₂^-.