Modelling adsorption interactions between vanadium incorporated on hydroxyapatite and the RR141 dye: Monte Carlo approach and DFT

Abstract

The substitution of vanadium in hydroxyapatite (HAP) presents promising possibilities for advanced adsorption and electronic applications. This study focused on two key aspects of this material. Firstly, Monte Carlo calculations were conducted to examine the adsorption processes of the dye Reactive Red 141 (RR141) on the (001) surface of vanadium-incorporated nanohydroxyapatite NPs-HAP/VAP (Ca 10 (PO 4 ) 6-x (VO 4 ) x (OH) 2 with × ranging from 0 to 6). These findings suggest that the adsorption is spontaneous, and the energy increases as the vanadium content increases. This implies that pure HAP needs more energy to desorb RR141 than is needed to desorb its vanadium-containing counterpart. Another notable advantage of the presence of vanadium is its impact on the stability of the molecular structure, which is important in the tune of adsorption properties. Moreover, the electronic properties of NPs-HAP/VAP were predicted using Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA) through the Density Functional Theory (DFT). The substitution related lattice changes were also studied. In the C-axis, GGA estimates an anisotropic expansion whereby the highest expansion is 13.27% at full phosphorus substitution, whereas LDA estimates an isotropic expansion whereby the highest expansion is 9.95%. The electronic property analysis reveals that the addition of vanadium into the NPs-HAP/VAP structure provides allowed states, mostly built on the d electrons of vanadium, interacting with the O-2p electrons in the band gap, which accounts for the narrowing of the gap.