Insight into the liquid adsorption of tobacco specific nitrosamines on ZIF-8

Liquid adsorption of TSNA by ZIF-8 was studied in this paper for the first time, applying the deformable molecular sieve to adsorb and separate TSNA. ZIF-8 can adsorb the bulky NNK molecules whose size exceeds its pore size, whereas NaA and KA zeolites cannot though they have similar pore sizes. Moreover, ZIF-8 selectively adsorbed NNK in solution and reached adsorption equilibrium within 5 min. In contrast, NNN was hard to be adsorbed and easy to be eluted by water, which is useful for the separation of TSNA. The influence of solid-liquid (S/L) ratio and other factors on TSNA liquid adsorption was investigated in detail. When S/L was 0.2, ZIF-8 exerted the highest efficiency and the adsorption capacity per unit surface area reached 12–15 nmol. Through the comparison of adsorption of NNK, NNN and NPYR, it is found that the adsorption of TSNA by ZIF-8 depended on π-π electron interaction mainly, rather than geometric confinement effect. The liquid adsorption curve of NNK conforms to Langmuir isothermal adsorption model, and its saturated adsorption capacity Qm was estimated to be 4.34 mg g−1, but actually it could reach 3.19 mg g−1 only. In addition, ZIF-8 had a mixing effect in liquid adsorption of TSNA: the presence of NNK promoted the adsorption of NNN slightly. ZIF-8 has the characteristics of fast adsorption and easy elution of TSNA in solution, which is beneficial for removal of TSNA to protect the environment and public health.