DFT−D Study on Surface Structure and Water Adsorption of Molybdenite (001) and (100)
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摘要:
浮选法通过添加药剂改变矿物表面的亲疏水性来实现不同矿物间的分离,同时在浮选体系中水分子也会吸附在矿物表面上,从而对表面亲疏性产生影响。因此,研究辉钼矿表面的性质以及辉钼矿表面与水分子的相互作用对于揭示辉钼矿微观浮选机理和选择合适的浮选药剂有指导性意义。通过基于色散力校正的密度泛函理论(DFT−D)平面波赝势方法研究了辉钼矿(001)面和(100)面的结构和性质,对比了辉钼矿不同表面的表面能、表面弛豫以及态密度计算结果,并考察了不同表面的水分子吸附结构,计算了水分子在不同表面不同吸附位点的吸附能。结果表明,(001)面的表面能极低,约为0.012 J/m2,而(100)面的表面能是(001)面的10倍左右,说明(100)面具有更大的活性;也说明辉钼矿(001)面比(100)面更加稳定,辉钼矿会更倾向于平行(001)面解离。(100)面上的Mo和S原子在费米能级处具有较高的电子态密度,表面原子活性强于(001)面;(100)面第一层的Mo和第二层的S发生了一定程度的弛豫,而辉钼矿(001)面没有发生表面弛豫。水分子在(001)面上的吸附非常弱,主要由水分子中的H与矿物表面S发生弱作用,而在(100)面上的Mo位吸附能达到−94.16 kJ/mol。这说明(001)面疏水性非常好,而(100)面具有一定的亲水性,也说明非极性捕收剂更易作用于辉钼矿(001)面,而极性捕收剂更易作用于(100)面。
Abstract:The flotation process achieves separation between different minerals by altering the hydrophilic/hydrophobic properties of mineral surfaces through the addition of chemical reagents. Simultaneously, water molecules in the flotation system adsorb onto mineral surfaces, thereby influencing surface wettability and modifying the hydrophilic/hydrophobic characteristics. Therefore, studying the surface properties of molybdenite and the interaction between molybdenite surfaces and water molecules is of guiding significance for revealing the microscopic flotation mechanism of molybdenite and selecting suitable flotation reagents. The surface structures and properties of the (001) and (100) surface of molybdenite were studied by dispersion−correction density functional theory (DFT−D) plane−wave pseudopotential method. Comparative analyses were conducted on surface energy, surface relaxation, and density of states (DOS) between different crystal planes. The adsorption configurations of water molecules on surfaces were investigated, and the adsorption energies of water molecules at different sites were calculated. The results demonstrate that the (001) surface exhibits an extremely low surface energy (~0.012 J/m²), while the (100) surface shows approximately 10−fold higher surface energy, indicating greater surface reactivity. The results also indicates that the (001) plane of molybdenite is more stable than the (100) plane, leading to a preferential cleavage parallel to the (001) plane. The calculation of the density of states (DOS) of surface atoms also revealed that Mo and S atoms on the (100) surface have higher electron DOS at the Fermi level, suggesting that the surface atoms on the (100) surface are more active than those on the (001) surface. There is a certain degree of relaxation for the Mo atoms in the first layer and the S atoms in the second layer on the (100) surface, whereas no surface relaxation occurs on the (001) surface. The adsorption of water molecules on the (001) surface is very weak, mainly due to the weak interaction between H in water molecules and S on the surface. In contrast, the adsorption energy at molybdenum (Mo) sites on the (100) surface reaches −94.16 kJ/mol. These results demonstrate that the (001) surface exhibits excellent hydrophobicity, while the (100) surface displays moderate hydrophilicity. This distinction further implies that non−polar collectors preferentially interact with the molybdenite (001) surface, whereas polar collectors exhibit higher affinity towards the (100) surface.
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Key words:
- molybdenite /
- density functional theory /
- surface structure /
- water adsorption
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表 1 不同交换关联泛函测试结果
Table 1. Test results of different exchange correlation functionals
交换关联泛函 晶格常数/Å 禁带宽度
/eV相对实验值误差/% a b c a b c 禁带宽度 GGA−PW91 3.185 3.185 15.297 1.46 0.38 0.38 20.76 19.86 GGA−PW91−OBS 3.172 172172 3.172 12.669 1.03 0.03 0.03 0.01 11.97 GGA−PBE−Grimme 3.185 3.185 12.427 0.99 0.38 0.38 3.31 15.38 GGA−PBESOL 3.141 3.141 12.650 1.01 1.00 1.00 0.13 13.68 GGA−PBE−TS 3.154 3.154 12.049 0.77 0.60 0.60 4.82 34.19 实验值 3.173 3.173 12.667 1.17 0 0 0 0 表 2 辉钼矿(100)和(001)面的表面能
Table 2. Energy of molybdenite(100) and (001) surfaces
/(J·m−2) 原子层数 (100)面 (001)面 4 0.1179 0.0112 6 0.1186 0.0122 8 0.1200 0.0124 10 0.1212 0.0125 表 3 辉钼矿(001)表面原子的位移
Table 3. Displacement of atoms on the surface of molybdenite( 001 )
原子层 原子类型 原子位移/Å Δx Δy Δz 1 Mo1 0 0 −0.114 1 S1 0 0.032 0.025 1 S2 0 −0.028 0.025 2 Mo2 0 0 0.024 2 S3 0 −0.040 0.172 2 S4 0 0.039 0.172 3 Mo3 0 0 0.053 3 S5 0 −0.024 0.005 3 S6 0 −0.024 0.005 4 Mo4 0 0 −0.050 4 S7 0 −0.025 0.008 4 S8 0 −0.026 0.008 -
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