Bonding of Aqueous Citrate with Zn²⁺ and ZnO Nanoclusters: A Theoretical Study

Abstract

To gain insight into how citrate bonds to ZnO, we have studied how aqueous citrate bonds to zinc cations (Zn2+) as well as zinc oxide nanoclusters [(ZnO)n, n=8 to 12] through density functional theory modelling. The infrared (IR) spectra of each complex in water has been calculated at the M05‐2X/cc‐pVTZ level of theory with the SMD solvent model and is presented over the region of 1700 cm−1 to 1250 cm−1; this region corresponds to the stretching modes of the carboxylate group, which change when bonding occurs. Citrate forms bidentate chelating and monodentate bonds with Zn2+; bidentate bonds result in antisymmetric stretching modes of lower wavenumber, while monodentate bonds result in higher wavenumber modes. The most stable structures involve bonds between multiple carboxylate groups and the Zn2+ and sometimes involve the hydroxyl group. Carboxylate groups not involved in bonding generally do not exhibit shifts in their infrared spectra. Similar trends are also observed in complexes of (Zn)2‐citrate, (Zn)3‐citrate and (Zn)‐citrate2. Citrate bonds weakly with the nanoclusters, forming one or two monodentate bonds to different zinc atoms; the IR spectra are not as strongly affected as when bonding occurs with Zn2+.

Non-seed chemical bath deposition of ZnO films in a rotating continuous flow reactor with various carboxylic acids and their application to transparent conductive films

“…Considering the suggested bonding structure of citrate to the ZnO surface, i.e. , one is “two terminal carboxylate groups” 41 and the other is “one terminal carboxylate group and one central carboxylate group as well as a hydroxyl group”, 42 both malic acid and tartaric acid, which have two carboxylate groups with one hydroxyl group, should have a growth-suppression effect on the ZnO crystals. However, the effect of both acids was significantly limited, as shown in Fig.…”

“…The effect of both acids on the growth of the ZnO crystal explains the effect of the hydroxyl group in citric acid. Since malic acid has two carboxylate groups and one hydroxyl group, which are requirements for carboxylic acids coordinating on ZnO suggested by the above research, 41,42 it is expected to affect the growth of the ZnO crystal. Tartaric acid has two carboxylate groups and two hydroxyl groups and will show a similar effect to malic acid.…”

“…41 In contrast, Sutton et al have investigated the adsorption of citrates on Zn 2+ and ZnO clusters by a computational method, suggesting that citrates are bound on {0001} via one terminal carboxylate group, one central carboxylate group, and a hydroxyl group. 42 Therefore, to clarify the roles of the carboxylate and hydroxyl groups in citrate, we investigate the effect of various carboxylic acids on the growth of the ZnO crystal. The carboxylic acids we investigated in this study are shown in Fig.…”

One Pot Synthesis of Au_ZnO Core‐Shell Nanoparticles Using a Zn Complex Acting as ZnO Precursor, Capping and Reducing Agent During the Formation of Au NPs

“…Our results are in agreement with previous studies, which, on the basis of IR, XPS, scanning tunneling microscopy (STM) and TEM analyses, indicated that the citrate anions form self‐assembled layers on Au NPs surfaces through central carboxylate groups thus stabilizing the (111) surface of the Au NPs . Moreover, density functional theory calculations also indicated that the citrate anion forms one or two monodentate bonds to different zinc ions within the ZnO nanoclusters and, in particular, attenuated total reflectance spectroscopy showed that the citrate anion strongly and selectively adsorbs to the (0001) ZnO face …”

Overcoming the Inhibition Effects of Citrate: Precipitation of Ferromagnetic Magnetite Nanoparticles with Tunable Morphology, Magnetic Properties, and Surface Charge via Ferrous Citrate Oxidation

“…[ 5,20,21,24,29,43–48 ] Usually, the adsorption proceeds in such a way that not all carboxyl groups coordinate to the surface. [ 29,43,44,46–50 ] On the one hand, this causes the stabilizing effect, but on the other hand, it also allows the free carboxyl groups to be used as basis for further modifications, which might otherwise not be possible on bare particle surfaces. Thus, citrate can be considered as a small but highly adhesive molecule that is capable to act as an anchor in order to modify different particles in the same way.…”