Ying-Yue Chang

A mixed valence diiron(II/III) complex with the ligand 2,6-bis{bis[(2-pyridinylmethyl)amino]methyl}-phenol (bppH) has been covalently anchored onto graphene using a mild in situ microwave-assisted diazonium coupling through an aryl amino precursor and isoamyl nitrite. A dinuclear iron complex is then formed by complexation of the grafted bppH–graphene material with iron(II) in the presence of dioxygen. X-ray photoelectron spectroscopy (XPS), atomic force microscopy, cyclic voltammetry, scanning transmission electron microscopy, energy-dispersive X-ray spec-troscopy and electron paramagnetic resonance (EPR) spectroscopy confirms the formation of the anchored ligand and derivative diiron complexes. Semi-quantitative XPS analysis shows an average bppH ligand bulk loading of 0.33 mmol/g, corresponding to a significant 20.7 wt% of the functionalized material consisting of grafted moieties. EPR measurements reveal the existence of a strong isotropic S = 1/2 spin center associated with the graphene lattice, to-gether with a much weaker S = 5/2 signal, associated with the iron(III) center of the grafted complex. The grafted complex is redox-active with surface-confined FeIIFeII → FeIIFeIII (+0.56 V vs. NHE), FeIIFeIII → FeIIIFeIII (+0.73 V) and FeIIIFeIII → FeIIIFeIV (+0.95 V) redox processes accessible, with an estimated surface coverage of 58 pmol cm–2 estab-lished from the electrochemical measurements.

The nonheme iron(IV) oxo complex [Fe^IV(O)(tpenaH)]²⁺ and its conjugate base [Fe^IV(O)(tpena)]⁺ [tpena^– = N,N,N′-tris(2-pyridylmethyl)ethylenediamine-N′-acetate] have been prepared electrochemically in water by bulk electrolysis of solutions prepared from [Fe^III₂(μ-O)(tpenaH)₂](ClO₄)₄ at potentials over 1.3 V (vs NHE) using inexpensive and commercially available carbon-based electrodes. Once generated, these iron(IV) oxo complexes persist at room temperature for minutes to half an hour over a wide range of pH values. They are capable of rapidly decomposing aliphatic and aromatic alcohols, alkanes, formic acid, phenols, and the xanthene dye rhodamine B. The oxidation of formic acid to carbon dioxide demonstrates the capacity for total mineralization of organic compounds. A radical hydrogen-atom-abstraction mechanism is proposed with a reactivity profile for the series that is reminiscent of oxidations by the hydroxyl radical. Facile regeneration of [Fe^IV(O)(tpenaH)]²⁺/ [Fe^IV(O)(tpena)]⁺ and catalytic turnover in the oxidation of cyclohexanol under continuous electrolysis demonstrates the potential of the application of [Fe^III(tpena)]²⁺ as an electrocatalyst. The promiscuity of the electrochemically generated iron(IV) oxo complexes, in terms of the broad range of substrates examined, represents an important step toward the goal of cost-effective electrocatalytic water purification.

Covalently bound inorganic–organic hybrid coagulants are believed to be the goal of coagulant development for water treatment. In this study, covalently bound organic silicate aluminum hybrid coagulants were synthesized by employing γ-aminopropylmethyldiethoxysilane (APDES) as silicon source with different Si/Al molar ratios (Si/Al = 0.1, 0.2, 0.3, and 0.4) and basicity values (B = 0.5, 1.0, 1.5, and 2.0). The APDES–Al hybrid coagulants (HC-As) were characterized by the measurement and analysis of pH, zeta potential, Al species distribution, and morphology. The results indicated that Si/Al and B played important roles in aspects of the physical structure, the Al species distribution, and the electrochemistry characteristics. Specifically, the HC-A with Si/Al = 0.4 and B = 2.0 featured the highest content of Al₁₃, the reticulated aggregate and the largest pH range for high zeta potential. The coagulation performances of HC-As were also investigated by treating synthetic water. At a low dosage, the HC-A with Si/Al = 0.4 and B = 2.0 exhibited the best coagulation behavior in terms of humic acid removal and turbidity removal. Besides Si/Al and B, the effect of pH on the coagulation performance of HC-A was also studied using an additional hybrid coagulant with tetraethoxysilane as the Si source for comparison. The results showed that HC-A has a larger pH range for simultaneous humic acid and turbidity removal.

For the purpose of reducing the cost and improving the performance of cathodes in microbial fuel cells (MFCs), we prepared Pt/C and Pt-M/C (M = Ni, Co, Fe) electrodes, and characterized them by SEM, XRD and CV. The modified electrodes were used as the cathodes in double-chambered MFCs fed with synthetic medium and molasses sewage respectively. We have found that Pt-M/C catalysts had a better catalytic activity for oxygen reduction than Pt/C in the following order: Pt-Fe/C > Pt-Co/C > Pt-Ni/C > Pt/C. The maximum power density of the MFCs with Pt-M/C cathode was improved by 18–31% compared with the MFC with Pt/C cathode because of the decrease of activation loss in the cathode. This study shows that Pt-M/C catalysts can improve power generation of MFCs without affecting the COD removal and it is proposed that Pt-Fe functions best among the three Pt-M alloys as an efficient and cost-effective catalyst of MFCs.

Iron porphyrin and cobalt porphyrin were respectively modified on glassy carbon (GC) electrodes together with multiwalled carbon nanotubes (MWCNTs), and the modified electrodes were characterized by X-ray photoelectron spectroscopy (XPS). Their electrochemical performance for the reduction of oxygen (O₂) , proton (H⁺) and carbon dioxide (CO₂) were respectively investigated and compared by cyclic voltammetry (CV). The results showed that iron porphyrin-MWCNT modified electrode always had a better performance than cobalt porphyrin-MWCNT modified electrode. It is proposed that iron porphyrin-MWCNT modified electrode will have promising application in electrochemical architectures like microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) for its good biocompatibility, easy availability, as well as excellent electrochemical performance.