Dynamic optical behaviour and selective adsorptive properties of MOF-199: insights from the DFT, Monte Carlo and molecular dynamics simulations

Nathanael Damilare Ojo^1,2,3*, Margaret Damilola Olawale^4*, Blessing Bukola Olalere¹, Olayinka Azeez Ladigbolu¹, Oluwatoba Emmanuel Oyeneyin^5,6, Oluwatobi Samuel Oluwafemi^2,3

1. Department of Chemistry, University of Ibadan, Oyo State, Nigeria
2. Department of Chemical Sciences, University of Johannesburg, Doornfontein 2028, South Africa
3. Centre for Nanomaterials Science Research, University of Johannesburg, South Africa
4. Department of Physical and Chemical Sciences, Elizade University, Ilara-Mokin, Ondo State, Nigeria
5. Theoretical and Computational Chemistry Unit, Department of Chemical Sciences, Adekunle Ajasin University, Akungba-Akoko, Ondo State, Nigeria.
6. School of Chemistry and Physics, College of Agriculture and Engineering, University of KwaZulu Natal, Westville, Private Bag X54001, Durban, 4000, South Africa

Abstract

Materials that modulate and interconvert light energy are potential replacements for fossil-fuel-based energy sources. Fossil fuels contribute to the recent surge in greenhouse gases and air pollution, posing a global threat as they promote climate change. Investigating the optical and molecular properties of metal-organic frameworks (MOFs) gives insight into their energy-related and climate-friendly applications. Here, we investigated the dual role of MOF-199 as both a nonlinear optical material and an adsorbent for greenhouse gases using computational techniques. The dynamic nonlinear optical (NLO) behaviour (electrooptic Pockels effect: EOPE [β(-ω;ω,0)]; dynamic second harmonic generation: SHG [β(-2ω; ω, ω)]; electrooptic Kerr effect: EOKE [γ(-ω;ω,0,0)]; and the electric field induced second harmonic generation: EFISHG [γ(-2ω;ω,ω,0)]), the molecular reactivity, and adsorption properties of MOF-199 were studied using density functional theory (DFT), Monte Carlo (MC) and molecular dynamics (MD). The dynamic NLO properties were studied at two laser frequencies (ħω = 0.085645 au; ħω = 0.042823 au). Apart from β(-2ω; ω, ω), other dynamic NLO properties (EOKE, EOPE, EFISHG) of the MOF were enhanced under high-energy laser frequency (ħω = 0.085645 au) by approximately two, five, and twenty-two times, respectively. The dynamic NLO properties of MOF-199 were comparable to those of a similar copper-based MOF in the literature. The molecular reactivity of the MOF was revealed by its low energy gap (E_g = 0.45 eV), depicting its semiconducting potential. Molecular electrostatic potential revealed good charge separation, and the carboxylic acid oxygen atoms as the nucleophilic sites. The MC and MD showed that MOF-199 displayed good adsorption properties towards CH₄, CO₂, NH₃ and H₂S molecules. Strong adsorption capacity was confirmed to be an interplay of physical and chemical interactions as revealed by the close contact and pair distribution function analyses. Interestingly, MOF-199 portrayed selective binding affinity for H₂S (dE_ad/dN_i = -2.64 kcal/mol; r = 2.7 – 5.0 Å) and CO₂ (dE_ad/dN_i = -0.99 kcal/mol; r = 3.2 – 4.6 Å) gases. This implies that MOF-199 is a dual-purpose dynamic NLO material for optical switching, optical communication and optical storage, with greenhouse gas adsorbing ability.

  

Keywords: dynamic nonlinear optical material; EFISHG; MOF-199; adsorption; DFT; Molecular Dynamics

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