Immobilization Of Metal Phthalocyanines And Their Sensitization Activities For Chlorophenol Degradation Under Visible Light Irradiation

Environmental contamination is a crucial issue that will affect both the existence of human being and the development of national economy in 21th century. The advanced oxidation technology (AOT), which could produce various reactive oxygen species through activation of molecular oxygen by solar light irradiation at ambient conditions, has made some progress for degradation or complete mineralization of toxic organic pollutants. Hence, AOT has attracted great attention in recent years. Photosensitization of metal phthalocyanine is a typical AOT that can directly utilize visible light to produce singlet oxygen for fast elimination of phenol derivatives from water, and thus it would be a promising technology for practical application.In this thesis, emphasis is on the immobilization of metal phthalocyanines, and a systemstic investigation has made into various factors, including the structural effect of organobentonite and layered double hydroxide, and the effect of sensitizer loading method and loading amount, on the efficiency of photosensitized chlorophenol degradation and the related mechanism.The photosentization efficiency is greatly improved, whereas the practical issue on organoclay regeneration and recycle after use is solved. A composite system of metal phthalocyanine with polyoxometalate is also addressed first time, which leads to great improvement in the ultilization of excited metal phthalocyanine. This thesis has gained some valuable results both in academic discipline and practical application.(1) Bentonite modified with cationic surfactant was an effective sorbent for organic pollutants in water. After further inserting AlPc into the clay interlayer, it was successfully recycled by the photosensitized production of singlet oxygen. Under visible light irradiation, the composite catalyst exhibited remarkable activity for the adsorption and degradation of the recalcitrant pollutants nitro- and chlorophenols in water. The initial rate of the photoreaction was found to increase with the initial amount of the substrate sorption, and well fitted the Langmuir-Hinshelwood model. Loading AlPc into organoclay led to slight expansion of the clay basal spacings from 1.82 to 2.15 nm, but notably decreased the TCP adsorption. The optimal loading of AlPc was about 0.25 wt%. The result demonstrates that surfactant-modified bentonite not only offers a hydrophobic zone for enrichment of organic contaminants but also provides a flexible environment for the photosensitization reaction. It was noted, however, that during four repeated experiments, both the sorption and the photosenstization gradually decreased, due to some intermediates formed and sorbed onto the catalyst surface.(2) Water-soluble palladium complex of sulfonated phthalocyanine (PdPcS) was successfully intercalated into organobentonite. The composite was applied in the removal of 2,4,6-trichlorophenol from water under visible light irradiation which attained complete dechlorination. The initial rate of TCP degradation was observed to increase with the initial amount of TCP sorption, the kinetics following well the Langmuir-Hinshelwood equation. The resulting rate constant fo TCP oxidation was found to increase with the alkyl chain length of the intercalated surfactant. Such the trend in photoactivity was in agreement with catalyst capacity for TCP sorption. The result showed that enrichment of TCP on the catalyst was indeed an efficient way for enhancement of the photosensitized degradation. However, PdPcS loading led to a notable decrease in TCP sorption, and its optimal loading was about 1.0 wt%. The incorporated PdPcS, coexisted with the intercalated surfactant in the clay interlayers, greatly restrained its aggregation. Seven repeated experiments showd that the composite clay was relatively stable in both sorption and photosensitization activity.(3) The anionic PdPcS was immobilized onto anionic surfactant-pillared LDH (layered double hydroxide). The composite clays were synthesized by two different routes: PdPcS intercalation into the clay interlayer via direct coprecipitation and PdPcS adsorption on the clay external surface via ion exchange. Under visible light irradiation, all the PdPcS containing solid were effective for the sensitized oxidation of 2,4,6-trichlorophenol in aerated aqueous solution. But the reaction efficiency was notably different from one catalyst to another, because of different location and arrangement of the immobilized PdPcS. Among the samples studied, the highest activity was observed with the immobilized PdPcS in the SDS-LDH interlayers which also increased with the initial amount of TCP adsorption and with the amount of PdPcS present in the clay. Recycling experiments demonstrated that the composite was relatively stable.(4) Cationic aluminium phthalocyanine (AlTNPc) was firstly combined with Keggin-type polyoxometalate (POM) for the elimination of phenol derivatives from water. The generation of singlet oxygen upon visible light irradiation remained, but the electron transfer from excited AlTNPc to POM also occurred efficiently. With the addition of H₂O₂, the production of oxidative AlTNPc^·+ was greatly improved, which enhanced the removal of phenol derivatives from water.