Zhuqi Chen

Functional IrIII Complexes and Their Applications

Iridium complexes are drawing great interest because they exhibit high phosphorescence quantum efficiency. Extensive efforts have been devoted to the molecular design of ligands to achieve phosphorescent emission over a wide range of wavelengths that is compatible with many applications. In this research news article, we focus on materials design to improve the performance of phosphorescent Ir(III) complexes for organic light-emitting diodes (OLEDs), luminescence sensitizers, and biological imaging.

Lewis-acid-promoted stoichiometric and catalytic oxidations by manganese complexes having cross-bridged cyclam ligand: a comprehensive study.

Redox-inactive metal ions have been recognized to be able to participate in redox metal-ion-mediated biological and chemical oxidative events; however, their roles are still elusive. This work presents how the redox-inactive metal ions affect the oxidative reactivity of a well-investigated manganese(II) with its corresponding manganese(IV) complexes having cross-bridged cyclam ligand. In dry acetone, the presence of these metal ions can greatly accelerate stoichiometric oxidations of triphenylphosphine and sulfides by the manganese(IV) complexes through electron transfer or catalytic sulfoxidations by the corresponding manganese(II) complexes with PhIO. Significantly, the rate enhancements are highly Lewis-acid strength dependent on added metal ions. These metal ions like Al(3+) can also promote the thermodynamic driving force of the Mn(IV)-OH moiety to facilitate its hydrogen abstraction from ethylbenzene having a BDE(CH) value of 85 kcal/mol, while it is experimentally limited to 80 kcal/mol for Mn(IV)-OH alone. Adding Al(3+) may also improve the manganese(II)-catalyzed olefin epoxidation with PhIO. However, compared with those in electron transfer, improvements in hydrogen abstraction and electron transfer are minor. The existence of the interaction between Lewis acid and the manganese(IV) species was evidenced by the blue shift of the characteristic absorbance of the manganese(IV) species from 554 to 537 nm and by converting its EPR signal at g = 2.01 into a hyperfine 6-line signal upon adding Al(3+) (I = 5/2). Cyclic voltammograms of the manganese(IV) complexes reveal that adding Lewis acid would substantially shift its potential to the positive direction, thus enhancing its oxidizing capability.

Degradation of Chlorophenols by Supported Co–Mg–Al Layered Double Hydrotalcite with Bicarbonate Activated Hydrogen Peroxide

Toxic and bioresistant compounds have attracted researchers to develop more efficient and cost-effective technologies for degradation of organic compounds in wastewater. This work demonstrates the degradation of 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, and phenol as model compounds using bicarbonate-activated H2O2 oxidation system in the presence of supported catalysts. The catalytic activity of the catalyst was investigated in term of degradation of target compounds, chemical oxygen demand (COD), and total organic carbon (TOC) removals both for batch mode and in fixed bed reactor using CoMgAl-HTs and CoMgAl-SHTs, respectively. The leaching of cobalt ion was efficiently prohibited because of the presence of a weakly basic medium provided by bicarbonate, and the CoMgAl-SHTs catalyst was found to retain its stability and good catalytic activity in fixed bed reactor for over 300 h. Extensive chemical probing, fluorescence, and electron paired resonance (EPR) studies were conducted to identify the actual reactive species in the degradation pathway, which revealed that the reaction proceeds through generation of superoxide, hydroxyl radical along with carbonate radical.

Multisignaling detection of cyanide anions based on an iridium(III) complex: remarkable enhancement of sensitivity by coordination effect

A new molecule, (Z)-4-(4-(dimethylamino)benzylidene)-3-methyl-1-(pyridin-2-yl)-1H-pyrazol-5(4H)-one (dmpp), and its novel heteroleptic iridium(III) complex, [(ppy)2Ir(dmpp)]PF6, were synthesized and characterized. Both dmpp and [(ppy)2Ir(dmpp)]PF6 could be used as highly selective and sensitive chemodosimeters for the cyanide anion by the naked eye, owing to the addition of the CN− to the vinyl group of dmpp. The addition of CN− to a solution of dmpp induced a change in the solution color from yellow to colorless, and to [(ppy)2Ir(dmpp)]PF6 induced a change in the solution color from pink to colorless. Moreover, [(ppy)2Ir(dmpp)]PF6 could also act as a phosphorescent and electrochemical probe of CN−. The green phosphorescence band at 520 nm and a new irreversible oxidation wave at 0.423 V showed up upon the addition of CN−, indicating that [(ppy)2Ir(dmpp)]PF6 was an excellent multisignaling chemodosimeter of CN−. Importantly, the Ir complex-based cyanide chemodosimeter [(ppy)2Ir(dmpp)]PF6 has much easier and faster detection of CN− than pure organic molecule dmpp.

Redox Inactive Metal Ion Promoted CH Activation of Benzene to Phenol with PdII(bpym): Demonstrating New Strategies in Catalyst Designs

Al in: A new strategy was introduced to modify the electronics and steric hindrance of the Pd(II) ion in order to change its reactivity towards benzene hydroxylation. In trifluoroacetic acid, free Pd(II) ions provide dominantly biphenyl, with phenol as minor product. Ligation of bpym to the Pd(II) ion results in its deactivation with regard to benzene functionalization. The addition of the redox inactive Al(III) ion to the Pd(II)(bpym) complex recovers its catalytic activity, and alters the reactivity of Pd(II) ion from benzene coupling to hydroxylation.

Energy transfer pathways in the carbazole functionalized β-diketonate europium complexes

Two novel Eu3+ complexes Eu(CDBM)3·2H2O and Eu(CCDBM)3·2H2O have been synthesized (CDBM = 1-(4-(9-carbazol)phenyl)-3-phenyl-1,3-propanedione, CCDBM = 1-((4-(9-carbazol)methyl)phenyl)-3-phenyl-1,3-propanedione). Eu(CDBM)3·2H2O showed strong internal ligand charge transfer (ILCT) fluorescence and sensitized emission of Eu3+. Due to the charge transfer character, the fluorescence band of CDBM shifted from 403 nm in cyclohexane to 559 nm in acetonitrile. Photophysical studies demonstrated that no energy was migrated from the ILCT excited state of the ligands to Eu3+, and that Eu3+ was sensitized by the triplet state which was localized in the 1,3-diphenyl-1,3-propanedione (DBM) part. The quantum efficiencies of Eu3+ in the three complexes are in the order Eu(DBM)3·2H2O > Eu(CCDBM)3·2H2O > Eu(CDBM)3·2H2O in both solution and the solid state. The energy transfer pathways in the three Eu3+ complexes were discussed in detail. Based on the systematic photophysical studies, a new guideline for the organo-lanthanide light emitting materials has been proposed: ILCT should be avoided during molecular modification.

Synthesis and electroluminescent property of novel europium complexes with oxadiazole substituted 1,10-phenanthroline and 2,2′-bipyridine ligands

Several 1,10-phenanthroline derivatives (PhoR), 2,2′-bipyridine derivatives (BpoR) and related europium complexes Eu(TTA)3PhoR and Eu(TTA)3BpoR were synthesized (HTTA = 2-thenoyltrifluoroacetone). Single crystal X-ray diffraction of Eu(TTA)3Php (Php = 2-(pyridyl)-1,10-phenanthroline) shows that Php acts as a tridentate N⁁N⁁N ligand, leading to a high stability of the complex for vacuum evaporation. When an oxadiazole moiety is incorporated into the ligand, the corresponding europium complexes show improved carrier-transporting abilities as well as thermal stabilities under vapor deposition for electroluminescence (EL) applications. Experiments revealed that these complexes have high photoluminescence (PL) quantum yields due to suitable triplet energy levels (ET) of the ligands, between 19 724 and 22 472 cm−1, for the sensitization of Eu(III) (5D0: 17 500 cm−1). Utilizing Eu(TTA)3PhoB (PhoB = 2-(5-phenyl-1,3,4-oxadiazol-2-yl)-1,10-phenanthroline) as the dopant emitter in CBP (4,4′-N,N′-dicarbazolebiphenyl), EL devices with a structure of TPD (4,4′-bis[N-(p-tolyl)-N-phenylamino] biphenyl, 30 nm)/Eu(TTA)3PhoB:CBP (7.5%, 20nm)/BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, 20 nm)/Alq3 (tris(8-hydroxyquinoline), 30 nm) exhibited a pure emission from europium ions. The highest efficiency obtained was 5.5 lm W−1, 8.7 cd A−1 and the maximum brightness achieved was 1086 cd m−2. At a practical brightness of 100 cd m−2, the efficiency remains above 2.0 cd A−1.

Influence of calcium(II) and chloride on the oxidative reactivity of a manganese(II) complex of a cross-bridged cyclen ligand

Available data from different laboratories have confirmed that both Ca(2+) and Cl(-) are crucial for water oxidation in Photosystem II. However, their roles are still elusive. Using a manganese(II) complex having a cross-bridged cyclen ligand as a model, the influence of Ca(2+) on the oxidative reactivity of the manganese(II) complex and its corresponding manganese(IV) analogue were investigated. It has been found that adding Ca(2+) can significantly improve the oxygenation efficiency of the manganese(II) complex in sulfide oxidation and further accelerate the oxidation of sulfoxide to sulfone. Similar improvements have also been observed for Mg(2+), Sr(2+), and Ba(2+). A new monomeric manganese(IV) complex having two cis-hydroxide ligands has also been isolated through oxidation of the corresponding manganese(II) complex with H2O2 in the presence of NH4PF6. This rare cis-dihydroxomanganese(IV) species has been well characterized by X-ray crystallography, electrochemistry, electron paramagnetic resonance, and UV-vis spectroscopy. Notably, using the manganese(IV) complex as a catalyst demonstrates higher activity than the corresponding manganese(II) complex, and adding Ca(2+) further improves its catalytic efficiency. However, adding Cl(-) decreases its catalytic activity. In electrochemical studies of manganese(IV) complexes with no chloride ligand present, adding Ca(2+) positively shifted the redox potential of the Mn(IV)/Mn(III) couple but negatively shifted its Mn(V)/Mn(IV) couple. In the manganese(II) complex having a chloride ligand, adding Ca(2+) shifted both the Mn(IV)/Mn(III) and Mn(V)/Mn(IV) couples in the negative direction. The revealed oxidative reactivity and redox properties of the manganese species affected by Ca(2+) and Cl(-) may provide new clues to understanding their roles in the water oxidation process of Photosystem II.

Synergistic degradation of phenols using peroxymonosulfate activated by CuO-Co3O4@MnO2 nanocatalyst

The development of transition metal based heterogeneous catalysts with efficient reactivity and intensive stability is of great demand in peroxymonosulfate based AOPs in water treatment. Herein, we present a novel approach of creating stable and effective nano-rod catalyst of CuCo@MnO2 with tetragonal structure. A remarkable synergetic effect was found between bi-metallic oxides of Cu and Co: 0.5%Cu-2%Co-MnO2 can efficiently degrade 100% of 30ppm phenol, while 0.5%Cu@MnO2 or 2%Co@MnO2 alone is apparently sluggish for the degradation of organic contaminants. The nanocatalyst retained good stability in recycling tests, during which little leaching of Co and Cu ions can be detected and crystallinity of support α-MnO2 remained unchanged. Mechanism study indicated that SO4- and OH are accounted to participate the degradation, and the generation of radicals is originated from the interaction of CuCo@MnO2 and PMS through metal site with peroxo species bond. The redox cycle among the active metals (M2+↔M3+↔M2+) and Cu enhanced generation of Co(II)-OH complex are critical for the remarkable performance in CuCo@MnO2/PMS system. Both the synergetic acceleration of catalyst activity and instinct mechanism are highly suggestive to the design of heterogeneous catalysts for the degradation of organic contaminants in PMS based advanced oxidation processes.

Highly Efficient Lead Distribution by Magnetic Sewage Sludge Biochar: Sorption Mechanisms and Bench Applications

Highly efficient magnetic sewage sludge biochar (MSSBC) discloses feasible fabrication process with lower production cost, superior adsorption capacity, usage of waste sewage sludge as resource, selected by external magnetic field and exceptional regeneration property. 2gL-1 MSSBC exhibited a high adsorption capacity of 249.00mgg-1 in 200ppmPb(II) and the lead-MSSBC equilibrium was achieved within one hour, owing to the existence of the copious active sites. The adsorption kinetics was well described by the pseudo-second-order model while the adsorption isotherm could be fitted by Langmuir model. Mechanism study demonstrated the adsorption involved electrostatic attraction, ion exchange, inner-sphere complexation and formation of co-precipitates at the surface of MSSBC. Additionally, adsorption performance maintained remarkable in a broad pH window. These outcomes demonstrated the promising waste resource utilization by a feasible approach that turns the solid waste of sewage sludge into biochar adsorbent with auspicious applications in elimination of Pb(II) from wastewater.