水分子在铵伊利石表面吸附的密度泛函研究

Mechanism of H_2O adsorption on ammonium-illite surface based on density functional theory

为实现黏土矿物颗粒界面疏水调控进而提高难沉降煤泥水处理效果,研究了水分子在铵伊利石表面的吸附机理.采用密度泛函理论方法对水分子在铵伊利石有晶格取代的(001)面和不存在晶格取代的(001)面上的吸附进行模拟计算.结果表明:水分子在(001)面吸附的最强活性点位于晶格取代原子Al成键的氧原子处,吸附最稳定的水分子垂直于有NH_4^+的硅氧环,并与NH_4^+和活性原子形成共2个氢键作用,吸附能为-0.67eV,且水分子有将NH_4^+拉离(001)面的趋势;水分子在(001)面的最稳定吸附主要是位于硅氧环空穴上方,水分子与表面氧原子形成3个氢键,吸附能为-0.41eV.2种最稳定吸附均存在微弱的静电吸附.选择合适的阳离子型疏水药剂与NH+4发生交换吸附,覆盖(001)面活性点,破坏水分子的稳定吸附,理论上可实现铵伊利石等黏土类矿物颗粒界面的疏水调控.

To control the hydrophobicity of clay mineral interface and improve the treatment effect of coal slurry which is difficult to sediment,the mechanism of H_2O adsorption on the ammonium-illite surfaces was investigated.The adsorption of water on two lattice planes of ammonium-illite,namely the（001）lattice plane in the presence of crystalline substitution and the（001）lattice plane in the absence of crystalline substitution,was simulated using the method of density functional theory.The results show that on the（001）lattice plane,the strongest active site is the position of oxygen atom which interacts with substituted Al.The most stable adsorption is vertically on the Si-O atoms ring in the presence of NH_4~＋.There are two hydrogen bonds between the water molecule and the active atom,with the adsorption energy of-0.67 eV.The NH_4~＋ tends to be pulled away from（001）lattice plane by adsorbed water molecules.By contrast,the most stable adsorption on（001）lattice plane is located above the hollow of Si-O atoms ring,with adsorption energy of-0.41 eV.There are three hydrogen bonds between the water molecule and the surface oxygen atoms.The two most stable adsorptionsmentioned are weak electrostatic interactions.In conclusion,choosing the appropriate cationic hydrophobic agent to exchange with NH_4~＋ can cover active sites on（001）lattice plane,and destroy the stable adsorption of H_2O,then the hydrophobic regulation of ammonium-illite and its similar clay mineral interface can be achieved in theory.