Synthesis,Characterization And Catalytic Properties Of Series Of Porphyrins And Nanotube-immobilized Porphyrin Catalysts

Porphyrins are active centers of many natural proteins and enzymes,which play great roles in the fields of chromogenic agents,semiconductor materials,photosensitive solar cells and so on.Nowadays energy and environmental issues affect human health and economic development.Porphyrins have been paid more attentions for their unique structural properties and wide applications.It is a topic of growing interest to synthesize the water soluble porphyrin derivatives whose water-solubility is of vital importance in medicinal purposes such as being DNA cleavage catalysts and wastewater treatments.However,the tedious preparation and purification,self-aggregation oxidative degradation,and difficult catalyst recovery and recycling are the critical problems associated with these water soluble porphyrin catalysts.Hence,immobilization of these porphyrins to insoluble supports such as carbon nanotubes has great advantages.Series of tetraphenylporphyrins with different substituents were synthesized.Series of water-soluble sulfonated porphyrins with different substituents and substituted positions have been successfully synthesized by modifying the traditional sulfonation route,sulfonating agent,phase,temperature and sulfonation time,and then been characterized by 1H NMR,IR,UV-Vis and MS methods.This process not only increased productivity,but also reacted more environmentally-friendly.Then these porphyrins have been used as photocatalysts for the oxidation of 1,5-dihydroxynaphthalene using H2O2 as oxidant.The kinetics data showed that the reaction was firstorder reaction and the product was 5-hydroxy-1,4-naphthoquinone,an important intermediate for many drugs.The short cut multiwalled carbon nanotubes(MWCNT)have been grafted with polyethylenimine(PEI)for further non-covalent conjugation to water-soluble 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrins(TPPS).These novel MWCNT-PEI-TPPS composites can be easily and efficiently prepared and characterized by methods of TEM,SEM,IR,UV-Vis and TGA.They have been firstly used as heterogeneous photocatalysts for the oxidation of 1,5-dihydroxynaphthalene using H2O2 as oxidant.A waterdichloromethane biphasic system has been established to maintain the heterogeneous catalyst in homogenous form in the catalytic process and rapidly remove the main product 5-hydroxy-1,4-naphthoquinone from aqueous phase to organic phase.The catalytic results show that the conversion rate of 1,5-dihydroxynaphthalene could be up to 88% within 120 minutes.The catalyst could be easily separated and reused several times without significant loss of the catalytic activity.Findings from this study suggest that these MWCNT-PEI-TPPS composites have been proved to be efficient,robust and recyclable catalysts for photooxidation and are expected to be used in industrial wastewater treatments.