Study On The Structure Of Ammonium Salt Aqueous Solutions

Ammonium sulfate is a commonly used nitrogen fertilizer and the main material of ammonium ferrous sulfate solution.Moreover,sulfate ion and ammonium ion are all ions in the famous Hofmeister sequence.However,there has not been a systematic study of the microstructure of?NH₄?₂SO₄ aqueous solution.The structure of?NH₄?₂SO₄ aqueous solution and the effects of K⁺and Cl^-on the solution structure are studied by X-ray diffraction,Raman spectroscopy and molecular simulation.The results show that with the destruction of hydrogen bond network,the proportion of DDAA and free hydroxyl hydrogen bond structure decreases with the increase of DDA,DAA and DA structrue.The contact ion pair appears in the solution when the mass fraction of salt solution is high.In the diffraction of X-ray,the peak at 13.5 degrees shifts to the higher angle and the peak intensity at 18.5 degrees reduces gradually.The peak at 0.225 nm increases while the peak at 0.300 nm decreases in the spectrum of structure function.The peak intensity of Raman spectrum at 3200 cm^-1 decreases meanwhile the peak at 3400 cm^-1 blue shifts,and the integral area of positive peak and negative peak increase at the same time,the mass fraction when the amount of contact ions increases is the turning point for the increase or descend tendency,the mass fraction of?NH₄?₂SO₄ solution is 12.00%and the mass fraction of NH₄Cl is 15.00%.The study of the radial distribution function and the diffusion coefficient by molecular simulation shows that with the mass fraction increases,the peak position of O-O and O-H shift to lower R value,the integral area decreases as well,and the peak position of the radial distribution function of H₂O and ions shift to the higher R value with a lower integral area.The study of mixed solutions showed that SO₄^2-has stronger influence on the structure of hydrogen bond network than Cl^-and K⁺has stronger influence on the structure than NH₄⁺,and NH₄⁺is easier to form ion pair with SO₄^2-.