Urease-driven Preparation Of Calcium Carbonate Micro-nanoparticles With Different Polymorphs

Sporosarcina pasteurii is a high urease producing microorganism in nature.It can decompose urea to produce carbonate and react with calcium ions in the environment to produce CaCO₃ precipitation.This technology is widely used in the field of geotechnical engineering,such as biological cement,restoration of buildings and cultural relics,solidification of sand and so on.Although there are many studies on this method,there are few reports on the preparation of micro nano CaCO₃ by urease hydrolysis of urea.By studying the growth characteristics of S.pasteurii and the properties of urease,and urease was used to prepare calcium carbonate micro and nano particles with different crystal shapes,which provided a new idea for the preparation of calcium carbonate micro and nano particles.Firstly,the effects of fermentation methods and fermentation conditions on S.pasteurii were studied in a 5 L fermentor.Fermentation for 24 h,the concentration of fed-batch fermentation reached 2.2 times of that of batch fermentation and the activity of urease reached1.7 times.It was found that the optimum temperature of S.pasteurii was 30?,and the growth of S.pasteurii was promoted by increasing the ventilation rate.Using cheap raw materials corn steep dry powder and molasses,the orthogonal experiment was used to optimize the culture medium of S.pasteurii.The optimal combination was as follows: corn steep dry powder 5 g/L,molasses 5 g/L,urea 5 g/L,ammonium sulfate 10 g/L.The urease activity of S.pasteurii was 1.67 ± 02 mmol/L/min,which was verified by experiments.The cost of the optimized medium is only 898 yuan/ton,which is conducive to the large-scale application of S.pasteurii in the engineering field.Secondly,the enzymatic properties of urease were studied,and the effects of temperature,p H and metal ions on its production were investigated.The optimum temperature and p H of urease were 50? and 7,respectively.The study of thermal stability showed that the activity of urease kept at 20? was consistent with that kept at 4?.The stability of urease was poor at 50?.The stability of urease under alkaline conditions was studied.It was found that the stability of urease was better when p H was 8 and 9,and worse when p H was 10.Ca²⁺,Fe²⁺,Ni²⁺,Mg²⁺ and Cu²⁺ all showed inhibitory effect on urease activity.Ca²⁺ had weak inhibitory effect on urease activity,while Cu²⁺ had the strongest inhibitory effect on urease activity.Finally,urease produced by S.pasteurii was used to hydrolyze urea and react with calcium chloride to obtain calcium carbonate crystal.Different forms of urease solution had significant effect on the crystal form of calcium carbonate.Using urease in the supernatant of fermentation broth as catalyst,the mesoporous hollow micron pure vaterite can be obtained by self-assembly of nanometer vaterite;100% calcite can be obtained by urease catalysis.Infrared spectrum analysis showed that oval calcium carbonate obtained from crude urease solution was affected by hydroxyl rich substances.Furthermore,the effects of reactant addition sequence,temperature,urease activity and reactant concentration on the formation of vaterite were investigated.Compared with CaCO₃ obtained by chemical method(reaction of sodium carbonate and calcium chloride),the pure vaterite obtained by urease catalysis can be preserved for a longer time(7 days)in aqueous solution.OH-and CO₃^2- were obtained by urease decomposition of urea,and then reacted with FeCl₂ and CaCl₂ to obtain magnetic composite vaterite,which is of great significance for the study of calcium carbonate as drug carrier to reach specific sites through in vitro magnetic field manipulation.