The Effects on the Response of Metal Oxide and Fluorite Single Crystal Electrodes and the Equilibration Process in the Interfacial Region

Inner surface potential, one of the most important variables affecting the interfacial equilibrium of metal oxide aqueous systems, obtained by means of single crystal electrode gives valuable information about electrical charging of the metal oxide/aqueous electrolyte solu¬tion interfaces. The influence of the potential determining ions and ionic strength on the measured electrode potential as well as time of the equilibration, direction of the titration and the effect of the magnetic stirring enables the critical examination of the processes which take place during the interfacial equilibrium. For that purpose, the selected metal oxides (hematite, ceria, sapphire, and rutile) and fluorite single crystal electrodes were examined. This work is licensed under a Creative Commons Attribution 4.0 International License

27. hrvatski skup kemičara i kemijskih inženjera

U Velom Lošinju je od 5. do 8. listopada 2021. godine u organizaciji Hrvatskoga kemijskog društva i Hrvatskoga društva kemijskih inženjera i tehnologa održan 27. hrvatski skup kemičara i kemijskih inženjera s međunarodnim sudjelovanjem (27. HSKIKI) te mini-simpozij Vladimir Prelog. Skup je održan pod visokim pokroviteljstvom Predsjednika Republike Hrvatske g. Zorana Milanovića te Hrvatskog sabora kao i pod pokroviteljstvom Hrvatske akademije znanosti i umjetnosti, Ministarstva znanosti i obrazovanja, Ministarstva zaštite okoliša i energetike, Primorsko-goranske županije, grada Malog Lošinja, Sveučilišta u Zagrebu, Sveučilišta u Rijeci, Instituta Ruđer Bošković, Agencije za odgoj i obrazovanje, Hrvatskog inženjerskog saveza, Akademije tehničkih znanosti Hrvatske i Hrvatske gospodarske komore. Hrvatski skup kemičara i kemijskih inženjera ima više od 50 godina dugu tradiciju te se održava kontinuirano svake dvije godine. Prva konferencija organizirana je u Zagrebu 1969. godine. Unatoč teškom i izazovnom vremenu uzrokovanom pandemijom COVID-19 uspjeli smo organizirati konferenciju uživo i susreli smo se u respektabilnom broju. Tako je 27. HSKIKI bio izvrsno posjećen te je okupio oko 530 sudionika. Skup je privukao znanstvenike i stručnjake sa sveučilišta, istraživačkih instituta i industrije, kako iz Hrvatske tako i iz inozemstva, uz znatan udio mlađe populacije, studenata diplomskih i doktorskih studija te poslijedoktoranada. U nastavnoj sekciji je sudjelovalo i oko 30 nastavnika iz svih krajeva Hrvatske

Electrical characterization of metal oxide single crystal/electrolyte solution interfaces

Svojstva međupovršine čvrsto/tekuće ovise o stanjima i električnim svojstvima površine raspršenog materijala. Ta stanja povezana su s površinskim potencijalom. U ovoj disertaciji obrađen je nastanak zajedničkog potencijala izloženih različitih ploha čestice kristala u otopini elektrolita. Mjerena su električna svojstava (električni otpor, dielektričnost) odabranih monokristala metalnih oksida. Čistoća pojedinih kristala (CeO2, TiO2, Fe2O3) provjerena je elektronskom mikroskopijom (SEM i XPS). Površinski potencijal mjeren je korištenjem modificiranih monokristalnih elektroda. Nakon utvrđivanja stabilnosti i ponovljivosti mjerenja, metodom potenciometrijske titracije proučavan je utjecaj pH, ionske jakosti, sastava otopine i protoka otopine uz površinu monokristala na potencijal elektroda izrađenih od monokristala CeO2, TiO2, Fe2O3 i SiO2. Potenciometrijska mjerenja napravljena su i na parovima pojedinih monokristala različitih orijentacija, kako bi se odredio utjecaj pojedinih ploha na zajednički potencijal. Rezultati mjerenja površinskih potencijala na monokristalima obrađeni su numeričkim simulacijama upotrebom modela površinskog kompleksiranja. Utvrđen je doprinos pojedinih ploha zajedničkom površinskom potencijalu, a rezultati su uspoređeni s površinskim potencijalima nanočestica istog kemijskog sastava. Uveden je i opisan ekvivalentni električni krug temeljen na kapacitetima te pripadajući računalni model koji povezuju različite tehnike istraživanja površina i omogućavaju bolje razumijevanje i predviđanje svojstava čestica u ovisnosti o morfologiji.Properties of solid/liquid interfaces are relevant to many physicochemical phenomena in nature and technology. Interfacial properties are related to the state of the surface of dispersed material, which is extremely large in the case of colloidal and nano- dispersions. Surface properties such as reactivity and ability of adsorption depends on the surface electrical properties. One of important such properties is the surface potential, which occurs as a result of charged surface groups formation, surface reactions, and distribution of ions between the interface and bulk. As contrary to particles, surface potentials of crystals can be measured directly by single crystal electrodes. Measured surface potentials contribute to the understanding of thermodynamic and kinetic of surface reactions. The measurements of individual, and common potentials of different crystallographic planes of the same mineral were used to determine their contribution to common potential. Individual surface potentials and common surface potentials of the same crystal were calculated using surface complexation models, and compared to the measured values. An equivalent electrical circuit based on capacities has been introduced and described, as well as its associated computing model which links different techniques of surface investigation, thus enabling better understanding and prediction of particles’ properties in dependence on morphology

Electrical characterization of metal oxide single crystal/electrolyte solution interfaces

Svojstva međupovršine čvrsto/tekuće ovise o stanjima i električnim svojstvima površine raspršenog materijala. Ta stanja povezana su s površinskim potencijalom. U ovoj disertaciji obrađen je nastanak zajedničkog potencijala izloženih različitih ploha čestice kristala u otopini elektrolita. Mjerena su električna svojstava (električni otpor, dielektričnost) odabranih monokristala metalnih oksida. Čistoća pojedinih kristala (CeO2, TiO2, Fe2O3) provjerena je elektronskom mikroskopijom (SEM i XPS). Površinski potencijal mjeren je korištenjem modificiranih monokristalnih elektroda. Nakon utvrđivanja stabilnosti i ponovljivosti mjerenja, metodom potenciometrijske titracije proučavan je utjecaj pH, ionske jakosti, sastava otopine i protoka otopine uz površinu monokristala na potencijal elektroda izrađenih od monokristala CeO2, TiO2, Fe2O3 i SiO2. Potenciometrijska mjerenja napravljena su i na parovima pojedinih monokristala različitih orijentacija, kako bi se odredio utjecaj pojedinih ploha na zajednički potencijal. Rezultati mjerenja površinskih potencijala na monokristalima obrađeni su numeričkim simulacijama upotrebom modela površinskog kompleksiranja. Utvrđen je doprinos pojedinih ploha zajedničkom površinskom potencijalu, a rezultati su uspoređeni s površinskim potencijalima nanočestica istog kemijskog sastava. Uveden je i opisan ekvivalentni električni krug temeljen na kapacitetima te pripadajući računalni model koji povezuju različite tehnike istraživanja površina i omogućavaju bolje razumijevanje i predviđanje svojstava čestica u ovisnosti o morfologiji.Properties of solid/liquid interfaces are relevant to many physicochemical phenomena in nature and technology. Interfacial properties are related to the state of the surface of dispersed material, which is extremely large in the case of colloidal and nano- dispersions. Surface properties such as reactivity and ability of adsorption depends on the surface electrical properties. One of important such properties is the surface potential, which occurs as a result of charged surface groups formation, surface reactions, and distribution of ions between the interface and bulk. As contrary to particles, surface potentials of crystals can be measured directly by single crystal electrodes. Measured surface potentials contribute to the understanding of thermodynamic and kinetic of surface reactions. The measurements of individual, and common potentials of different crystallographic planes of the same mineral were used to determine their contribution to common potential. Individual surface potentials and common surface potentials of the same crystal were calculated using surface complexation models, and compared to the measured values. An equivalent electrical circuit based on capacities has been introduced and described, as well as its associated computing model which links different techniques of surface investigation, thus enabling better understanding and prediction of particles’ properties in dependence on morphology

Electrical characterization of metal oxide single crystal/electrolyte solution interfaces

Svojstva međupovršine čvrsto/tekuće ovise o stanjima i električnim svojstvima površine raspršenog materijala. Ta stanja povezana su s površinskim potencijalom. U ovoj disertaciji obrađen je nastanak zajedničkog potencijala izloženih različitih ploha čestice kristala u otopini elektrolita. Mjerena su električna svojstava (električni otpor, dielektričnost) odabranih monokristala metalnih oksida. Čistoća pojedinih kristala (CeO2, TiO2, Fe2O3) provjerena je elektronskom mikroskopijom (SEM i XPS). Površinski potencijal mjeren je korištenjem modificiranih monokristalnih elektroda. Nakon utvrđivanja stabilnosti i ponovljivosti mjerenja, metodom potenciometrijske titracije proučavan je utjecaj pH, ionske jakosti, sastava otopine i protoka otopine uz površinu monokristala na potencijal elektroda izrađenih od monokristala CeO2, TiO2, Fe2O3 i SiO2. Potenciometrijska mjerenja napravljena su i na parovima pojedinih monokristala različitih orijentacija, kako bi se odredio utjecaj pojedinih ploha na zajednički potencijal. Rezultati mjerenja površinskih potencijala na monokristalima obrađeni su numeričkim simulacijama upotrebom modela površinskog kompleksiranja. Utvrđen je doprinos pojedinih ploha zajedničkom površinskom potencijalu, a rezultati su uspoređeni s površinskim potencijalima nanočestica istog kemijskog sastava. Uveden je i opisan ekvivalentni električni krug temeljen na kapacitetima te pripadajući računalni model koji povezuju različite tehnike istraživanja površina i omogućavaju bolje razumijevanje i predviđanje svojstava čestica u ovisnosti o morfologiji.Properties of solid/liquid interfaces are relevant to many physicochemical phenomena in nature and technology. Interfacial properties are related to the state of the surface of dispersed material, which is extremely large in the case of colloidal and nano- dispersions. Surface properties such as reactivity and ability of adsorption depends on the surface electrical properties. One of important such properties is the surface potential, which occurs as a result of charged surface groups formation, surface reactions, and distribution of ions between the interface and bulk. As contrary to particles, surface potentials of crystals can be measured directly by single crystal electrodes. Measured surface potentials contribute to the understanding of thermodynamic and kinetic of surface reactions. The measurements of individual, and common potentials of different crystallographic planes of the same mineral were used to determine their contribution to common potential. Individual surface potentials and common surface potentials of the same crystal were calculated using surface complexation models, and compared to the measured values. An equivalent electrical circuit based on capacities has been introduced and described, as well as its associated computing model which links different techniques of surface investigation, thus enabling better understanding and prediction of particles’ properties in dependence on morphology

Adsorption of Polyions on Flat TiO2 Surface

In this study, the surface properties of Ti/TiO2 substrate before and after the adsorption of polyelectrolytes were investigated. As model polyelectrolytes, strongly charged polycation poly(diallyldimethylammonium) (PDADMA) and strongly charged polyanion poly(4-styrenesulfonate) (PSS) were used. Initially, the bare titanium substrate was characterized by means of ellipsometry, atomic force microscopy (AFM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and measurements of inner surface potential using crystal electrode (CrE). It was shown that the substrate surface is very smooth with the roughness of 3.5 nm and oxide layer thickness of 3.8 nm. After the adsorption of PDADMA and PSS, polyelectrolyte-coated titanium surface was examined using the above-mentioned methods under the same conditions. It was found that both PDADMA cations and PSS anions form a stable polymeric nanofilm on Ti/TiO2 surface that partially covers the surface, without significant impact on the surface roughness. The corrosion protection effectiveness values indicate that the corrosion properties were greatly enhanced upon polyion adsorption and polyelectrolyte coating formation on the flat TiO2 surface. The obtained results were additionally confirmed by inner surface potential measurements. According to the methods employed, PDADMA nanofilm modification offers enhanced corrosion protection to the underlying titanium material in sodium chloride electrolyte solution

Adsorption of Polyions on Flat TiO₂ Surface

In this study, the surface properties of Ti/TiO2 substrate before and after the adsorption of polyelectrolytes were investigated. As model polyelectrolytes, strongly charged polycation poly(diallyldimethylammonium) (PDADMA) and strongly charged polyanion poly(4-styrenesulfonate) (PSS) were used. Initially, the bare titanium substrate was characterized by means of ellipsometry, atomic force microscopy (AFM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and measurements of inner surface potential using crystal electrode (CrE). It was shown that the substrate surface is very smooth with the roughness of 3.5 nm and oxide layer thickness of 3.8 nm. After the adsorption of PDADMA and PSS, polyelectrolyte-coated titanium surface was examined using the above-mentioned methods under the same conditions. It was found that both PDADMA cations and PSS anions form a stable polymeric nanofilm on Ti/TiO2 surface that partially covers the surface, without significant impact on the surface roughness. The corrosion protection effectiveness values indicate that the corrosion properties were greatly enhanced upon polyion adsorption and polyelectrolyte coating formation on the flat TiO2 surface. The obtained results were additionally confirmed by inner surface potential measurements. According to the methods employed, PDADMA nanofilm modification offers enhanced corrosion protection to the underlying titanium material in sodium chloride electrolyte solution

Electrochemical Perspective on Hematite–Malonate Interactions

Organic matter (OM) interactions with minerals are essential in OM preservation against decomposition in the environment. Here, by combining potentiometric and electrophoretic measurements, we probed the mode of coordination and the role of pH-dependent electrostatic interactions between organic acids and an iron oxide surface. Specifically, we show that malonate ions adsorbed to a hematite surface in a wide pH window between 3 and 8.7 (point of zero charge). The mode of interactions varied with this pH range and depended on the acid and surface acidity constants. In the acidic environment, hematite surface potential was highly positive (+47 mV, pH 3). At pH < 4 malonate adsorption reduced the surface potential (+30 mV at pH 3) but had a negligible effect on the diffuse layer potential, consistent with the inner-sphere malonate complexation. Here, the specific and electrostatic interactions were responsible for the malonate partial dehydration and surface accumulation. These interactions weakened with an increasing pH and near PZC, the hematite surface charge was neutral on average. Adsorbed malonates started to desorb from the surface with less pronounced accumulation in the diffuse layer, which was reflected in zeta potential values. The transition between specific and non-specific sorption regimes was smooth, suggesting the coexistence of the inner- and outer-sphere complexes with a relative ratio that varied with pH