Molecular sieve

A method of preparation of a molecular sieve having high selectivity to ammonia nitrogen in wastewater, the method comprising the following steps:

• a) dissolving a magnesium salt into water to obtain 1-5 mol/L of a magnesium salt solution;
• b) dissolving phosphoric acid into water to obtain 1-4 mol/L of a phosphoric acid solution;
• c) adding a molecular sieve into the magnesium salt solution prepared in the step a), stirring for 10-30 minutes, standing for 1-6 hours, drying for dehydration, and baking for 2-6 hours under a temperature of 300-600° C.;
• wherein the molecular sieve has a pore diameter of between 1.5 and 10 nm, a BET specific surface area of greater than 600 m2/g, a degree of crystallinity of more than 90%, and a silica to alumina ratio of greater than 1;
• and
• d) adding a molecular sieve with supported magnesium compounds obtained from the step c) into the phosphoric acid solution prepared in the step b), stirring for 10-30 minutes, standing for 1-6 hours, drying for dehydration, and baking for 2-6 hours under a temperature of 300-600° C. to obtain the molecular sieve having high selectivity to ammonia nitrogen in wastewater.