Degradation Of Water-Soluble Dyes Using Mimetic Peroxidase Of PCN-222(Fe)

Natural enzymes are highly specific to biological substrates and have high catalytic efficiency under mild reaction conditions.They are widely used in biosensors,environmental science and food industry.However,natural enzymes have many inherent defects and are prone to inactivation under the influence of external environment.In addition,enzymes are time-consuming and expensive in preparation,purification and storage.In order to overcome the shortcomings of known natural enzymes,people have shifted their research direction to mimic enzymes.MOFs are widely used in biosensor,medical diagnosis,cancer treatment,food processing,chemical industry and environmental monitoring due to its advantages of large specific surface area,convenient preparation,low cost,good recovery,high stability under harsh conditions,easy storage,adjustable composition and mimetic enzyme activity in various temperature and pH ranges.Therefore,MOFs-based mimetic enzymes are considered as promising candidates for mimetic natural enzymes.Dyes with high color intensity,high toxicity,synthetic sources and complex molecular mechanisms,make them stable and difficult to be biodegraded by the environment.Effective degradation and removal of these pollutants has become a major concern of biotechnologists and environmental scientists.At present,physical,chemical and biological methods are often used to treat dyes in industrial wastewater.The physical method is simple to operate,but only centralized collection of dyes can not degrade the treated dyes.Chemical methods can degrade dyes,but other products harmful to the environment will be produced during the reaction.Biological method,using enzymatic properties to catalyze the degradation of dye molecules,has the advantages of environmental protection,high cost performance,low sludge yield,no toxic and harmful substances and complete mineralization.Mimetic enzymes are non-protein compounds with enzymatic properties synthesized by organic methods.Compared with natural enzymes,mimetic enzymes are limited by many physical and chemical factors.Their chemical properties are stable and their catalytic ability is limited.They can be widely used in industrial production.In this paper,PCN-222?Fe?was synthesized and its structure was analyzed by light microscopy,XRD and nitrogen adsorption.The enzymatic properties of PCN-222?Fe?were studied by using the classical peroxidase substrate 3,3,5,5-tetra-methyl-benzidine?TMB?.When pH=4.0 and ambient temperature is 20°C,the mimetic enzyme has the maximum catalytic activity.The steady-state kinetic parameters were calculated.The Km value of PCN-222?Fe?with TMB as the substrate is 2.063 mM.The Km values of H₂O₂ as substrates are 0.58mM,which are smaller than those of HRP for H₂O₂.The affinity of PCN-222?Fe?for H₂O₂ is higher than that of HRP for H₂O₂.After confirming that PCN-222?Fe?has the function of mimicking peroxidase,water-soluble dyes were degraded by its catalytic properties.Two representative cationic and anionic dyes,methylene blue?MB?and methyl orange?MO?,were used as the research objects.The results showed that MB and MO degraded by PCN-222?Fe?were completely decolorized at about 48h.When MB and MO were used as substrates,the maximum enzyme activity was obtained at pH=4.0.It was found that the degradation efficiency of MB and MO increased gradually with the increase of temperature.The optimum degradation temperature of MB and MO was 80°C and70°C,which accorded with the discharge temperature of industrial dyestuff wastewater and was beneficial to the degradation of industrial dyestuff wastewater.PCN-222?Fe?exhibits adsorption capacity in the absence of H₂O₂.Two representative cationic and anionic dyes,methylene blue?MB?and methyl orange?MO?,are studied.The results showed that the maximum adsorption capacity of MO was 803.664 mg/g at pH=5.0 and382.35 mg/g at pH=9.0.The reusability of PCN-222?Fe?was measured by adsorption column.The adsorption efficiency of MB and MO was 93.4%and 87.6%after 8 times of reuse.XRD and optical microscopy showed that the structure of PCN-222?Fe?was determined after 8 times of reuse.It is stable without any change and can be used repeatedly as adsorbent.Finally,the method of dye treatment by combined application of adsorption and degradation was designed to provide theoretical basis for the practical application of PCN-222?Fe?.