Study On α-Amylase Immobilized On Modified Carbon Nanotubes And Its Hydrolysis Performance For Kitchen Waste

With the development of economy and the continuous improvement of people’s living standards,the output of kitchen waste is also increasing.If it is not handled properly,it will cause environmental pollution and waste of resources.The largest proportion of kitchen waste is starch,which is difficult to be efficiently treated by traditional treatment methods.Therefore,it is very necessary to develop a safe,reliable and efficient treatment method.In this study,the immobilized carrier was prepared by modifying carbon nanotubes,and the conditions of preparation and immobilization ofα-amylase were optimized.The hydrolysis effects of freeα-amylase and immobilizedα-amylase on starch kitchen waste under different conditions were studied.The main research contents and results are as follows:（1）Carbon nanotubes were purified by modified nitric acid reflux,and magnetic carbon nanotubes were prepared by glycol reduction method.On this basis,magnetic carbon nanotubes were further prepared.Theα-amylase was fixed to two vectors by adsorption.The specific surface area and pore size,scanning electron microscopy and magnetic analysis of the two carriers showed that magnetic carbon nanotubes and calcium-carrying magnetic carbon nanotubes had larger specific surface area and pore size.They are 128.74 m²/g,0.91 cm³/g and108.03 m²/g,0.78 cm³/g,respectively.They have good adsorption capacity and can be observed between magnetic microspheres and carbon nanotubes.Both of the two carriers have good magnetic properties and can be recovered by magnets.The immobilized enzymes of two different materials were analyzed by Fourier infrared spectroscopy and X-ray photoelectron spectroscopy.The results showed thatα-amylase was successfully immobilized on the carrier.The effect of Ca²⁺concentration and Fe Cl₂·ethanol addition on the immobilization effect was investigated by single factor experiment.The results showed that the optimal concentration of Ca²⁺was 6 nmo L/L and the optimal concentration of Fe Cl₂·ethanol was 15 mg/m L,and the relative enzyme activity was the highest and the mass ratio of carrier recovery was as high as98%.（2）Based on the first part,the effects ofα-amylase concentration,immobilization temperature,time and p H on enzyme activity and enzyme load were investigated by single factor experiment.Based on the initial concentration of 1.5 mg/m L,α-amylase fixation conditions were optimized by response surface experiments.The optimal fixation conditions forα-amylase based on magnetic carbon nanotubes were as follows:immobilization temperature 40℃,immobilization time 2.3 h,and p H 6.0,and the measured relative enzyme activity was 96.9%.The optimal immobilization conditions forα-amylase were as follows:immobilization temperature 42℃,immobilization time 3.2 h,p H 5.0,and the relative enzyme activity was 95.3%.（3）By comparing the enzyme activities of free enzymes,the storage stability and thermal stability of magnetic carbon nanotubes immobilized enzymes and calcium-carrying magnetic carbon nanotubes were explored.The results showed that the storage stability and thermal stability of immobilized enzymes were better than that of free enzymes.After 30 days of storage,the immobilized enzymes of magnetic carbon nanotubes and calcium-carrying magnetic carbon nanotubes maintained 71.3%,respectively.The relative enzyme activity of 80.6%was much higher than that of 8.4%free enzyme.At the same time,this experiment also explored the treatment effect of free enzyme and immobilized enzyme on starch kitchen waste under different temperature,p H and treatment time,as well as the reusability of immobilized enzyme.The experimental results showed that immobilized enzyme broadened the catalytic range of enzyme,solved the defect of free enzyme easy inactivation,and could hydrolyze 40%of starch kitchen waste within 60 minutes.Compared with magnetic carbon nanotube immobilized enzyme,magnetic carbon nanotube immobilized enzyme has a higher hydrolysis rate under acidic conditions,which is due to the addition of Ca²⁺to maintain the optimal configuration ofα-amylase and higher enzyme activity.The two immobilized enzymes still had a hydrolysis rate of more than 20%for starch kitchen waste after 8 cycles.The results of this study show that immobilized enzyme has great advantages in the treatment of kitchen waste,broaden the practical application scenarios of immobilized enzyme,provide a technical reference for the resource utilization of kitchen waste,and also provide a part of the theoretical basis for the treatment of kitchen waste by immobilized enzyme,which has certain reference value.