Impact of Adsorption of Straight Chain Alcohol Molecules on the Optical Properties of Calcite (10.4) Surface

Abstract

Calcium carbonate plays a central role in controlling the chemistry of the oceans, biomineralization and oil production, to name a few. In this work, using density functional theory with semiempirical dispersion corrections and simplified TD-DFT using Tamm-Dancoff approximation, we investigated the impact of the adsorption of straight chain alcohol (ethanol and pentanol) molecules on the optical properties of a calcite (10.4) surface. Our results show that ethanol and/or pentanol molecules form a well-ordered monolayer (through their hydroxyl group with carbon chains sticking away in a standing-up position) on the calcite (10.4) surface. Additionally, we found intriguing modulations in the photoabsorption spectra and circular dichroism spectra. In particular, the latter was a unique optical fingerprint for a molecule-adsorbed calcite (10.4) surface. Our findings provide useful insights into the structural and optical features of calcite-based systems at the atomic level.

Keywords: DFT; TD-DFT; adsorption; calcite.

Figure 1

Pristine calcite (10.4) surface of 8 × 8 dimension consisting of 5 layers, namely L1, L2, L3, L4 and L5. Green, gray and red spheres depict Ca, C and O atoms, respectively.

Figure 2

The first four low-energy calcite(10.4)/ethanol configurations (a–d) obtained from our calculations. The most stable configuration is labeled S1 and the least stable configuration is labeled S4. The relative stability is given in the inset. Electron difference density plots of calcite(10.4)/ethanol configurations (e–h). The green/red region depicts accumulation/depletion in electron density. EDDs are plotted using a density isovalue of 0.0005 electrons/Bohr${}^3$.

Figure 3

The first four low-energy calcite(10.4)/pentanol configurations (a–d) emerged from our calculations. The most stable configuration is labeled by S1 and the least stable configuration is labeled by S4. The relative stability is given in the inset. Electron difference density plots of calcite(10.4)/pentanol configurations (e–h). The green/red region depicts an accumulation/depletion in electron density. EDDs are plotted using a density isovalue of 0.0005 electrons/Bohr${}^3$.

Figure 4

(a) Mass density profiles of the calcite(10.4)/ethanol S1 configuration; and (b) same as before, but for calcite(10.4)/pentanol S1 configuration.

Figure 5

(a) sTDA calculated the photoabsorption spectra of calcite(10.4)/ethanol configurations; and (b) the same as before but for calcite(10.4)/pentanol configurations. In each plot, we also provided the photoabsorption spectrum of the pristine calcite (10.4) surface. 2e+05 represents 2 × 10${}^5$, the same rule applies to other E notations.

Figure 6

(a) sTDA calculated circular dichroism spectra for calcite(10.4)/ethanol configurations; and (b) the same as before but for calcite(10.4)/pentanol configurations. In each figure, we also provided the circular dichroism spectrum of the pristine calcite (10.4) surface.