Homogeneous Photocatalytic Properties Of Water-Soluble Porphyrins

Human development is inseparable from chemistry,but the development of chemistry leads to environmental pollution and energy consumption.Since 1967,when Professor Fujijima discovered that titanium dioxide can split water into hydrogen and oxygen under light,photocatalysis came into people’s vision.The application of photocatalysis technology in the organic field has brought great development.Photocatalytic materials include transition metal complexes,semiconductor materials,conjugated organic molecules,etc.Conjugated organic molecules,such as organic dye molecules,with their unique conjugated structure and chromophobe group,have strong absorption of ultraviolet and visible light,can be used as photocatalysts,which are widely used in the field of photocatalysis.In this paper,water-soluble porphyrin as a photocatalyst,used in photocatalytic hydrogen production,azobenzene reduction and hydrazobenzene oxidation reaction.In order to realize the reuse of homogeneous photocatalyst,water-soluble porphyrins were combined with PCN to prepare composite materials,which were applied in azobenzene reduction and hydrazobenzene oxidation reaction,and its catalytic performance was investigated.The main work is as follows:（1）Preparation of water-soluble porphyrins and photocatalytic hydrogen production:5,10,15,20-tetracycline（4-carboxyphenyl）porphyrins（TCPP）and5,10,15,20-tetracycline（4-sulfonic acid phenyl）porphyrins（TPPS）were synthesized by Alder method with p-formylbenzoic acid,benzaldehyde and pyrrole as raw materials and propionic acid as solvent.Its structure and properties were characterized by infrared spectroscopy（FTIR）,hydrogen nuclear magnetic resonance spectroscopy（¹H NMR）,UV-visible absorption spectroscopy（UV-vis）and UV-visible diffuse reflection spectroscopy（DRS）.The results show that the prepared water-soluble porphyrin TCPP and TPPS have good absorption in the UV-visible region,and can be used as photocatalyst for photocatalytic hydrogen production reaction.The photocatalytic hydrogen production performance of porphyrin compounds is related to polarity groups outside the porphyrin ring,catalyst and triethanolamine concentration,hole sacrificant type and illumination conditions,etc.When the catalyst concentration is 40.0μM and triethanolamine concentration is 1.5 M under full spectrum irradiation,the maximum hydrogen production rate is 2761.7μmol·g^-1·h^-1.The possible mechanism of photocatalytic hydrogen production of water-soluble porphyrins was proposed.（2）Photocatalytic oxidation of hydrazobenzene and reduction of azobenzene by water-soluble porphyrins:azobenzene compounds are widely used in production and life,but the reaction conditions of traditional synthesis methods are harsh and complex.In this experiment,water-soluble porphyrins were applied to photocatalytic oxidation of hydrazobenzene and reduction of azobenzene.Using oxygen in the air as oxidant,the water-soluble porphyrin TCPP and TPPS can catalyze the oxidation of azobenzene at room temperature.Under the best reaction conditions,the highest yield can be reached within 6.0 h is 97%.The reduction reaction of azobenzene was catalyzed by water-soluble porphyrins.With hydrazine hydrate as reducing agent,the yield of azobenzene reached 95%in 45.0 min under light.The experimental process of photocatalysis is simple,the high yield is maintained,the selectivity is very high and the range of substrates is wide,which provides the idea for metal-free water-soluble porphyrins to catalyse organic reactions.（3）Heterogeneous of homogeneous TCPP catalyst:homogeneous catalyst has a large contact surface with the reaction substrate,and the catalyst reaction utilization rate is high.However,it may have certain limitations in some reactions or applications,and the heterogeneous of homogeneous catalyst has become a big trend,allowing the recovery and reuse of homogeneous catalyst.In this paper,TCPP was loaded on carbon nitride（PCN）by ultrasonic method,and TCPP/PCN composite was prepared.X-ray diffraction（XRD）,infrared spectrum,electron microscopy（SEM,TEM）,fluorescence spectrum（PL）,UV-visible diffuse reflection spectrum and electrochemical characterization were used to characterize the structure and properties of the composite.The interaction between TCPP and PCN is proved.It is applied to catalytic azobenzene reduction and hydrogenated azobenzene oxidation reaction.The results show that a small amount of TCPP loaded with carbon nitride can greatly improve the performance.The maximum yield of 1%TCPP/PCN catalytic reduction reaction can reach 97%within 15.0min,and the activity remains high after 5 cycles.The yield of the catalytic oxidation reaction was higher than that of TCPP and PCN within 6.0 h,and the possible reaction mechanism was proposed.