Research On Different Meso-porphyrins In The Photoegradation Of 4-NP And The Detection Of Hg²⁺in Water

As one of the organic pollutants in water,4-nitrophenol?4-NP?is harmful to people and the environment.Photodegradation of 4-NP is regarded as a environmental-friendly technology,with renewable light energy as energy source and complete degradation.However,the commonly used photocatalyst TiO₂ only responds to ultraviolet light.Sensitizer porphyrins not only can expand the response spectrum of TiO₂ to visible light,but also can inhibit the recombition of photogenerated electrons and holes during the photocatalytical process,which can significantly improve the photodegradation efficiency of organic pollutants by TiO₂.Second,Hg²⁺heavy metal ion in water are harmful to human and the environment.Recognition and trace detection of heavy metal ions have always been a hot topic.The central nitrogen atoms and peripheral substituents of porphyrin easily coordinate with heavy metal ions.The changes of fluorescence spectrum in system before and after combined with metal ions can be used to detect the heavy metal ions in water.Therefore,in this paper different meso-porphyrins were synthesized to degrade the organic pollutant and to detect the heavy metal.On one hand,three different copper-porphyrins 1a,1b and 1c were prepared.The CuPp-TiO₂ catalysts was obtained by impregnation of 1a,1b,1c respectively onto the surface of two different TiO₂,commercial?cTiO₂?and home-prepared?pTiO₂?.The CuPp-TiO₂ composites were characterized by XRD,BET,UV-vis,FTIR and SEM-EDS.To study the effcct of CuPp and TiO₂ on the composites,the photocatalytic activity of 4-NP in aqueous solution under metal halide lamp irradiation by six CuPp-TiO₂ composites was studied.The results showed that the highest photocatalytic efficiency in the degradation of 4-NP was catalysts sensized by CuP_-COOH?1c?because of the strong interaction between 1c and the surface of TiO₂.The partial hydroxyl group on the surface of TiO₂ was substitued by 1c,which contributes to the transfer of photogenerated electrons electron.The interaction of CuPp with TiO₂ was the main factor affecting the photocatalytic efficiency.When porphyrin was substitued by polar groups,the photodegradation efficiency of composites is dependent on CuPp.The higher the polarity of substituents is,the stronger interaction with the surface of TiO₂ becomes.When porphyrin was substitued by nonpolar group,the main factor is TiO₂.On the other hand,four different number of hydroxyl prophyrins H₂P_1-OH,H₂P_2-OH,H₂P_3-OH-OH and H₂P_4-OH-OH were synthesized to detect the Hg²⁺.To study the fluorescent response of hydroxyl substituent and Hg²⁺,the selectivity and sensitivity of four hydroxyl porphyrins to the detection of Hg²⁺and the stability of time and pH were compared.Combined with the Job's method,UV visible spectrum and orbital composition calculation,the detection mechanism of four fluorescent probes was speculated.The trace amount of Hg²⁺can be detected by different numbers of free hydroxyporphyrins and the lowest detection limit of porphyrin can be up to 10^-8mol/L.The results showed that the mercury ion preferred to combine with—OH,not coordinate with the central N,along with the increasing numbers of hydroxyl groups.With the increase of hydroxyl number,the binding probability of peripheral hydroxyl as a metal ion binding site increases,while the coordination probability of central N atoms decreases.The aggregation of hydroxylporphyrins affects the sensitivity and binding with mercury during fluorescence detection process.Finally,hydroxyl porphyrin was loaded on the filter paper to immobilize the Hg²⁺in the water,the high sensitive and visual Hg²⁺test paper with rapid response was obtained.