Adsorption of lindane (γ-hexachlorocyclohexane) on nickel modified graphitic carbon nitride: a theoretical study

Abstract

Adsorption of lindane (HCH) on nickel modified graphitic carbon nitride (Ni-gCN) was investigated using a novel, accurate and broadly parametrized self-consistent tight-binding quantum chemical (GFN2-xTB) method. Two graphitic carbon nitride (gCN) models were used: corrugated and planar, which represent the material with different thicknesses. Electronic properties of the adsorbates and adsorbent were estimated via vertical ionization potential, vertical electron affinity, global electrophilicity index and the HOMO and LUMO. Adsorption energy and population analyses were carried out to figure out the nature of the adsorption process. The results reveal that the introduction of the nickel atom significantly influences the electronic properties of gCN, and results in the improvement of adsorption ability of gCN for lindane. Lindane adsorption on Ni-gCN is considered as chemisorption, which is primarily supported by the interaction of the nickel atom and chlorine atoms of HCH. The effect of solvents (water, ethanol, acetonitrile) was investigated via the analytical linearized Poisson-Boltzmann model. Due to the strong chemisorption, Ni-gCN can collect lindane from different solvents. The adsorption configurations of HCH on Ni-gCN were also shown to be thermally stable at 298 K, 323 K, 373 K, 473 K, and 573 K via molecular simulation calculations. The obtained results are useful for a better understanding of lindane adsorption on Ni-gCN and for the design of materials with high efficiency for lindane treatment based on adsorption-photocatalytic technology.

Fig. 1. Optimized structures of Ni-cGN (a) and Ni-pGN (b) by the GFN2-xTB method; colours: grey: carbon, blue: nitrogen, white: hydrogen, violet: nickel; all key distances are in Å.

Fig. 2. HOMO and LUMO of Ni-gCN depicted at an isovalue of 0.03 e A⁻³: (a) – Ni-cGN, (b) – Ni-pGN.

Fig. 3. Optimized structure of HCH by GFN2-xTB method – (a); HOMO – (b) and LUMO – (c) of HCH depicted at isovalue of 0.03 e A⁻³, colours: grey: carbon, white: hydrogen, green: chlorine; all key distances are in Å.

Fig. 4. The favourable adsorption configurations of HCH on Ni-cGN: (a) HCH-ee/Ni-cGN; (b) HCH-ae/Ni-cGN; (c) HCH-aa/Ni-cGN colours: grey: carbon, blue: nitrogen, white: hydrogen, violet: nickel, green: chlorine; all key distances are in Å.

Fig. 5. The favourable adsorption configurations of HCH on Ni-pGN: (a) HCH-ee/Ni-pGN; (b) HCH-ae/Ni-pGN; (c) HCH-aa/Ni-pGN; colours: grey: carbon, blue: nitrogen, white: hydrogen, violet: nickel, green: chlorine; all key distances are in Å.

Fig. 6. (a) Energy diagram of HOMOs and LUMOs of Ni-cGN, Ni-pGN and HCH; the HOMO of the adsorption configurations: (b) HCH-aa/Ni-cGN and (c) HCH-aa/Ni-pGN depicted at isovalue of 0.03 e Å⁻³.

Fig. 7. Temperature profiles predicted for HCH-aa/Ni-pGN and HCH-aa/Ni-cGN: (a) at 298 K and; (b) at higher temperatures.