Adsorption of azole molecules on oxidized copper surface and their inhibition of copper corrosion

Gustinčič, Dunja (author), Kokalj, Anton (mentor), Kogej, Ksenija (comentor)

Azoles and their derivatives are known for their corrosion inhibition of copper. For this reason the bonding of imidazole, triazole, and tetrazole|used as archetypal models of azole corrosion inhibitors|on various Cu2O(111)- and Cu2O(110)-type surfaces was characterized using density functional theory (DFT) calculations. Both non-dissociative and dissociative adsorption modes were considered. We nd that molecules bind much stronger to unsaturated Cu sites compared to saturated ones. Dissociated molecules bind considerably stronger to the surface compared to non-dissociative molecules, although even the latter can bind rather strongly to specic unsaturated (CUS) Cu sites. All three azole molecules display similar non-dissociative adsorption energies, but signicant dierence between them appears for dissociative adsorption mode. It was found that N{H dissociative adsorption is favorable only for triazole and tetrazole, but only at oxygen vacancy sites, where it proceeds barrierlessly (or almost so). This observation may suggest that, for imidazole, only the neutral form, but, for triazole and tetrazole, also their deprotonated forms are the active species for inhibiting corrosion under near neutral pH conditions, where copper surfaces are expected to be oxidized. In addition, we also addressed the bonding of Cl, which can be seen as a corrosion activator. The calculations indicate that only dissociated triazole and tetrazole bind strong enough to rival the Cl{surface bonds. An ab initio thermodynamics approach was used to construct two-dimensional phase diagrams for all three molecules. Although dissociated molecules bind to surfaces more strongly, none of the considered structures that involve dissociated molecules appear on the phase diagrams. According to the calculated phase diagrams for Cu2O(111)-type surfaces, the three azole molecules adsorb to specic CUS sites and stabilize them, under all conditions at which molecular adsorption is stable. This tentatively suggests that their corrosion inhibition capability may stem, at least in part, from their ability to passivate reactive surface sites. We also addressed the adsorption of non-dissociated and dissociated water molecules on three (111)-type surface models. Non-dissociative water molecules form O{Cu bond only with unsaturated Cu surface sites. If the surface model lacks these sites, water forms hydrogen bonds with surface oxygen ions. Dissociation of water molecules was found to be exothermic only at oxygen vacancy sites.

• Language: English
• Keywords: DFT calculations, azoles, adsorption, copper-oxide, corrosion.
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2019
• PID: 20.500.12556/RUL-111799
• COBISS.SI-ID: 300738816
• Publication date in RUL: 14.10.2019

Secondary language

• Language: Slovenian
• Title: Adsorpcija azolnih molekul na oksidirano površino bakra in njihova inhibicija korozije bakra

Abstract

Azoli in njihovi derivati spadajo med ucinkovite organske inhibitorje korozije bakra. Z molekulskim modeliranjem na osnovi teorije gostotnega funkcionala (angl. density functional theory, DFT) smo obravnavali interakcijo modelnih azolov (imidazola, triazola in tetrazola) z oksidirano povrsino bakra. V raziskavo smo vkljucili Cu2O(111) in Cu2O(110) modela oksidirane povrsine bakra. Proucevali smo nevtralne (nedisociirane) in disociirane oblike omenjenih azolov. Ugotovili smo, da se molekule bistveno mocneje vezejo na koordinacijsko nenasicena (angl. coordinatively unsaturated, CUS) mesta bakra kot na nasicena (angl. coordinatively saturated, CSA). Disociirane molekule se na obravnavane povrsine vezejo bistveno mocneje kot nevtralne, ceprav se lahko tudi slednje mocno vezejo na specicna mesta CUS. Vse tri obravnavane azolne molekule se v nevtralni obliki vezejo s podobnimi adsorpcijskimi energijami, medtem ko pride do razlik pri vezavi disociiranih oblik azolov. Opazili smo, da je pri cepitvi N{H vezi disociativna adsorpcija ugodna le za triazol in tetrazol, vendar le na kisikovih prazninah, kjer poteka brez bariere (ali z minimalno bariero). Na podlagi tega smo sklepali, da sta triazol in tetrazol|pod nevtralnimi pogoji, kjer je baker pogosto oksidiran|lahko aktivna kot inhibitorja korozije v disociirani obliki, medtem ko je imidazol bolj relevanten v nedisociirani obliki. Nadalje smo proucili vezavo Cl, ki ga lahko obravnavamo kot aktivatorja korozije. Izracuni so pokazali, da se lahko samo disociirana triazol in tetrazol vezeta tako mocno, da izpodrineta Cl, ki je vezan na povrsino. Na osnovi termodinamskega pristopa smo opisali dvo-dimenzionalne fazne diagrame za vse tri molekule. Kljub temu, da se disociirane molekule na povrsine vezejo mocneje, se nobena od obravnavanih struktur disociiranih molekul ne pojavi na faznih diagramih. Rezultati faznih diagramov za Cu2O(111) model so pokazali, da se vse tri molekule (imidazol, triazol in tetrazol) vezejo na specicna mesta CUS in jih tudi stabilizirajo pod pogoji, kjer je molekularna adsorpcija se stabilna. Rezultati nakazujejo na to, da je inhibicijska ucinkovitost azolov morda lahko povezana z njihovo sposobnostjo pasivacije reaktivnih mest na povrsini. Nadalje smo proucili adsorpcijo nedisociirane in disociirane oblike molekule vode na tri modele Cu2O(111) povrsine. Nedisociirana molekula vode se veze na povrsino preko O{Cu vezi le z nenasicenimi mesti bakra. V primeru, da teh mest na povrsini ni, voda tvori vodikove vezi s kisikom na povrsini. Ugotovili smo, da je adsorpcija disociiranih molekul vode eksotermna le v primeru vezave na kisikove praznine.

• Keywords: DFT izracuni, azoli, adsorpcija, bakrov oksid, korozijski procesi.