You are invited to CHEM 591 – Graduate Student Seminars of Chemistry Department.
This week’s speakers are Arda Altan, Sena Nur Aykut and Hüseyin Orhun Tunçer.
Please see the seminar information and the abstracts below.
1.Solvent Effect on the Mesophase Self-Assembly and the Synthesis of Mesoporous LiMPO4 and LiMn1-xM’xPO4 (M = Mn, Co, Ni and M’ = Co, Ni) for Water Oxidation Electrocatalysis
Arda Altan
Advisor: Prof. Ömer Dağ
Time: May 13, 2025, 12:30, SBZ14
Abstract: Lithium metal phosphates and oxides are generally used in batteries and considered as a suitable electrocatalyst for oxygen evolution reaction (OER). This study presents the synthesis and characterization of mesoporous lithium transition metal phosphates (LMPs) of Mn (II), Co(II), and Ni(II) and lithium manganese metal phosphates (LMnM’P, M’=Co and Ni). Molten salt-assisted self-assembly (MASA) method was utilized during the synthesis of LMPs. Solutions of lithium nitrate (LiNO3), transition metal nitrate M(H2O)62, phosphoric acid (H3PO4, PA) and surfactant (Pluronic P123) in four different solvents (ethanol, methanol, 1-butanol, and trifluoroethanol) were spread on a microscope slide by drop-cast coating to form a lyotropic liquid crystalline (LLC) phase during gelation. Initial solutions undergo precipitations in all cases except LNiP and LiCoP in methanol. The precipitates were collected via centrifuge and both the precipitates and supernatants were characterized via ATR-FTIR, POM, SEM, EDX, XRD, XPS, and N2 adsorption-desorption techniques upon calcination at various temperatures.
Mesoporous olivine phase of LMPs were obtained by calcining the mesophases. The LCoP and LNiPs are generally amorphous up to 400 °C and crystallized above this temperature. The solutions, supernatants, and precipitates form mesoporous LMPs and LMnM’Ps, with surface areas around 10-50 m2/g. The porosity decreased drastically to a few m2/g after annealing to 500 °C. Precipitates of LMnM’P formed crystalline MnPO4.H2O, where the oxidation state of Mn is 3+ up to 400 °C. With further calcination MnPO4.H2O transforms to Mn2P2O7. The efficiency in OER was evaluated using cyclic voltammetry (CV), and stability of LMPs was monitored via multistep chronoamperometry (MCA) and chronopotentiometry (MCP). Both features improved in order of Mn<Co<Ni. The LMnM’Ps outperformed in OER.
2.Deciphering the Extreme Solubility Differences of Polyethers
Sena Nur Aykut
Advisor: Asst. Prof. Halil İ Okur
Co-Advisor: Asst. Prof. Fahri Alkan
Time: May 13, 2025, 12:30, SBZ14
Abstract: The solution behavior of polyethers exhibits substantial differences, especially their solubility in water. While polyethylene glycol (PEG) is readily soluble, polyoxymethylene (POM) is insoluble in aqueous medium. Yet, both molecules have very similar molecular structures. Although some experimental studies and numerous molecular simulations have provided insight into the thermodynamics and structural properties of aqueous polyether solutions, the macromolecule-solvent interaction information remains elusive [1]. In this study, the hydration shell structures of polyethylene glycol (PEG) and polyoxymethylene (POM) have been investigated by employing small molecule analogs to the structure of the monomers of these macromolecules. The vibrational spectra of the hydration shell around model small molecules were measured by employing the recently developed hydration shell spectroscopy (MCR) method [2]. Interestingly, the small molecules reveal a significant solubility difference. PEG-like monomers such as dioxane and dimethoxyethane are very soluble or miscible with water, whereas POM-like ones such as trioxane and dimethoxymethane have limited solubility. Their hydration structures are also quite distinct. PEG-like molecules contain more ordered water hydration molecules, evidenced by the dominant (3200 cm-1) water band. In contrast, POM-like ones have disordered water molecules (3500 cm-1) in the hydration shell. Such data serves a pivotal role, showing the hydration of the polyethers plays an important role in their solubility behaviors. It was also investigated by ATR-FTIR measurements and DFT calculations. It was demonstrated that the intramolecular delocalization of oxygen lone pair electrons is the main contribution on solubility behavior.
3.Creating Competing Charge-Transfer Pathways for Water Oxidation Photocatalysis
Hüseyin Orhun Tunçer
Advisor: Assoc. Prof. Ferdi Karadaş
Time: May 13, 2025, 12:30, SBZ14
Abstract: Earth-abundant photoactive complexes play a critical role in light-harvesting applications, including dye-sensitized solar cells, artificial photosynthesis, photocatalysis, and photodynamic therapy [1]. The main focus is centered on Fe(II) complexes owing to their isovalency with well-known precious Ru(II), Re(I), and Ir(III) based photosensitizers. However, the implementation of an iron chromophore to a photocatalytic application presents a three-fold problem: i) The metal-to-ligand charge transfer (MLCT) excited state lifetimes of iron complexes fall far short of the performance required for efficient charge separation, ii) they have relatively poor stabilities, and iii) the preparation of a bridging ligand that connects iron to a catalyst, is a synthetic challenge.
In this talk, I will present my research on Fe-Co photosensitizer-catalyst dyad assemblies, in which bipyridyl cyanoferrate complexes are utilized as visible light-absorbing photosensitizers and cobalt sites serve as catalytic sites. The compounds were characterized by Infrared, UV-vis, and Soft XAS. In Co-Fe dyad assemblies, Fe sites play a role in both metal-to-metal charge transfer (MMCT) and metal-to-ligand charge transfer (MLCT) processes. The interaction of the MLCT and MMCT processes was investigated using femtosecond transient absorption spectroscopy and photophysical trends were explained with the aforementioned characterization techniques.