113 results on '"Tai-Chu Lau"'
Search Results
2. Visible Light-Induced Oxidation of Alcohols by a Luminescent Osmium(VI) Nitrido Complex: Evidence for the Generation of PhIO+ as a Highly Active Oxidant in the Presence of PhIO
- Author
-
Jing Xiang, Yi Pan, Lu-Lu Liu, Li-Xin Wang, Huan Yang, Shun-Cheung Cheng, Shek-Man Yiu, Chi-Fai Leung, Chi-Chiu Ko, Kai-Chung Lau, and Tai-Chu Lau
- Subjects
Colloid and Surface Chemistry ,General Chemistry ,Biochemistry ,Catalysis - Published
- 2023
3. Synergistic effects of CH3CO2H and Ca2+ on C–H bond activation by MnO4−
- Author
-
Huatian Shi, Lin Cheng, Yi Pan, Chi-Keung Mak, Kai-Chung Lau, and Tai-Chu Lau
- Subjects
General Chemistry - Abstract
The activation of metal-oxo species with Lewis acids is of current interest.
- Published
- 2022
4. Oxidative C–O bond cleavage of dihydroxybenzenes and conversion of coordinated cyanide to carbon monoxide using a luminescent Os(<scp>vi</scp>) cyanonitrido complex
- Author
-
Jing Xiang, Jiang Zhu, Miaomiao Zhou, Lu-Lu Liu, Li-Xin Wang, Min Peng, Bi-Shun Hou, Shek-Man Yiu, Wai-Pong To, Chi-Ming Che, Kai-Chung Lau, and Tai-Chu Lau
- Subjects
Materials Chemistry ,Metals and Alloys ,Ceramics and Composites ,General Chemistry ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
The photoreactions of OsN and dihydroxybenzenes lead to C–O bond cleavage of H2Q/H2Cat, accompanied by the conversion of the coordinated CN− into CO.
- Published
- 2022
5. Visible light-induced oxidative N-dealkylation of alkylamines by a luminescent osmium(vi) nitrido complex†
- Author
-
Yi Pan, Chi-Chiu Ko, Jing Xiang, Tai-Chu Lau, Li-Juan Luo, Shek-Man Yiu, Shun-Cheung Cheng, Min Peng, Xin-Xin Jin, Wai-Lun Man, and Kai-Chung Lau
- Subjects
N dealkylation ,DNA repair ,Chemistry ,medicine.medical_treatment ,Drug detoxification ,chemistry.chemical_element ,General Chemistry ,Oxidative phosphorylation ,Photochemistry ,Metal ,visual_art ,medicine ,visual_art.visual_art_medium ,Osmium ,Luminescence ,Visible spectrum - Abstract
N-Dealkylation of amines by metal oxo intermediates (M Created by potrace 1.16, written by Peter Selinger 2001-2019 O) is related to drug detoxification and DNA repair in biological systems. In this study, we report the first example of N-dealkylation of various alkylamines by a luminescent osmium(vi) nitrido complex induced by visible light., The visible light-induced N-dealkylation of various alkylamines by a luminescent osmium(vi) nitrido complex has been investigated. We provide definitive evidence that these reactions occur via an ET/PT mechanism.
- Published
- 2021
6. Hybridization of Molecular and Graphene Materials for CO2 Photocatalytic Reduction with Selectivity Control
- Author
-
Marc Robert, Gui Chen, Gaetano Granozzi, Lingjing Chen, Bing Ma, Julien Bonin, Matías Blanco, Tai-Chu Lau, Laura Calvillo, and Goran Dražić
- Subjects
Absorption spectroscopy ,Graphene ,General Chemistry ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,law ,Triethanolamine ,medicine ,Photocatalysis ,Formate ,Acetonitrile ,Selectivity ,medicine.drug - Abstract
In the quest for designing efficient and stable photocatalytic materials for CO2 reduction, hybridizing a selective noble-metal-free molecular catalyst and carbon-based light-absorbing materials has recently emerged as a fruitful approach. In this work, we report about Co quaterpyridine complexes covalently linked to graphene surfaces functionalized by carboxylic acid groups. The nanostructured materials were characterized by X-ray photoemission spectroscopy, X-ray absorption spectroscopy, IR and Raman spectroscopies, high-resolution transmission electron microscopy and proved to be highly active in the visible-light-driven CO2 catalytic conversion in acetonitrile solutions. Exceptional stabilities (over 200 h of irradiation) were obtained without compromising the selective conversion of CO2 to products (>97%). Most importantly, complete selectivity control could be obtained upon adjusting the experimental conditions: production of CO as the only product was achieved when using a weak acid (phenol or trifluoroethanol) as a co-substrate, while formate was exclusively obtained in solutions of mixed acetonitrile and triethanolamine.
- Published
- 2021
7. Slow magnetic relaxation in structurally similar mononuclear 8-coordinate Fe(<scp>ii</scp>) and Fe(<scp>iii</scp>) compounds
- Author
-
Song Gao, Bing-Wu Wang, Qiong Yuan, Tai-Chu Lau, Li-Xin Wang, Si-Huai Chen, Xiao-Fan Wu, Jing Xiang, Xin-Xin Jin, and Qian-Qian Su
- Subjects
Crystallography ,Materials science ,Magnet ,Materials Chemistry ,Metals and Alloys ,Ceramics and Composites ,Magnetic relaxation ,General Chemistry ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
A pair of structurally-similar and stable 8-coordinate high-spin Fe(ii) and Fe(iii) compounds have been obtained. Both compounds exhibit field-induced slow magnetic relaxation behaviour. The Fe(iii) compound represents the first example of 8-coordinate Fe(iii) single-molecule magnets (SMM).
- Published
- 2021
8. Cooperative activating effects of metal ion and Brønsted acid on a metal oxo species
- Author
-
Li Ma, Chi-Keung Mak, Po-Kam Lo, Tai-Chu Lau, Kai-Chung Lau, and Gui Chen
- Subjects
Cyclohexane ,Chemistry ,Metal ions in aqueous solution ,General Chemistry ,Ring (chemistry) ,Hydrogen atom abstraction ,Medicinal chemistry ,Metal ,chemistry.chemical_compound ,visual_art ,visual_art.visual_art_medium ,Chelation ,Lewis acids and bases ,Brønsted–Lowry acid–base theory - Abstract
Metal oxo (M Created by potrace 1.16, written by Peter Selinger 2001-2019 O) complexes are common oxidants in chemical and biological systems. The use of Lewis acids to activate metal oxo species has attracted great interest in recent years, especially after the discovery of the CaMn4O5 cluster in the oxygen-evolving centre of photosystem II. Strong Lewis acids such as Sc3+ and BF3, as well as strong Brønsted acids such as H2SO4 and CF3SO3H, are commonly used to activate metal oxo species. In this work, we demonstrate that relatively weak Lewis acids such as Ca2+ and other group 2 metal ions, as well as weak Brønsted acids such as CH3CO2H, can readily activate the stable RuO4− complex towards the oxidation of alkanes. Notably, the use of Ca2+ and CH3CO2H together produces a remarkable cooperative effect on RuO4−, resulting in a much more efficient oxidant. DFT calculations show that Ca2+ and CH3CO2H can bind to two oxo ligands to form a chelate ring. This results in substantial lowering of the barrier for hydrogen atom abstraction from cyclohexane., Combining a weak Lewis acid and weak Brønsted acid produces strong cooperative effects for activating metal oxo species towards alkane oxidation.
- Published
- 2021
9. Ru single atoms and nanoclusters on highly porous N-doped carbon as a hydrogen evolution catalyst in alkaline solutions with ultrahigh mass activity and turnover frequency
- Author
-
Tai-Chu Lau, Zhenguo Guo, Yijun Li, Huijing Liu, Zhenzhen Yang, Bing Li, Jian-Bo He, and Jianhui Xie
- Subjects
Tafel equation ,Materials science ,Renewable Energy, Sustainability and the Environment ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrocatalyst ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Nanoclusters ,Chemical engineering ,chemistry ,Water splitting ,General Materials Science ,0210 nano-technology ,Platinum ,Carbon - Abstract
Electrocatalytic water splitting is one of the most desirable ways to produce hydrogen, which is a clean and sustainable energy source. Improving the formation and the exposure of active sites is a key issue in the design of cost-effective and efficient metal-based electrocatalysts, especially for noble metals, in order to cut down the metal content and improve the mass activity of the metals, while maintaining high catalytic activity. Herein, we report a high-performance Ru-based electrocatalyst consisting of Ru single atoms and Ru nanoclusters encapsulated in highly porous N-doped carbon with abundant hierarchical pores (Ru/p-NC). Remarkably, Ru/p-NC shows excellent HER activity in 1.0 M KOH with a low overpotential of 10 mV at 10 mA cm−2, a small Tafel slope of 17 mV dec−1 as well as good durability for 24 h, outperforming commercial Pt/C and Ru/C catalysts. More importantly, the mass activity and turnover frequency (based on Ru loading) of Ru/p-NC are ultrahigh owing to the low loading of Ru, which are 17 A mgRu−1 and 8.9 H2 s−1, respectively, at a very low overpotential of 25 mV. Experimental results indicate that the porous N-doped carbon support not only leads to exposed active sites but also interacts strongly with the Ru moieties. In addition, it tunes the electronic structure of the catalyst, boosts the stability as well as facilitates mass transport and charge transfer kinetics. This work provides a new route for the synthesis of metal-based porous N-doped carbon hybrid electrocatalysts with abundant exposed active sites and strong metal-support interaction for energy conversion.
- Published
- 2021
10. Structure and Reactivity of One- and Two-Electron Oxidized Manganese(V) Nitrido Complexes Bearing a Bulky Corrole Ligand
- Author
-
Huatian Shi, Runhui Liang, David Lee Phillips, Hung Kay Lee, Wai-Lun Man, Kai-Chung Lau, Shek-Man Yiu, and Tai-Chu Lau
- Subjects
Ions ,Manganese ,Colloid and Surface Chemistry ,Porphyrins ,Electrons ,General Chemistry ,Ligands ,Biochemistry ,Catalysis - Abstract
As a strategy to design stable but highly reactive metal nitrido species, we have synthesized a manganese(V) nitrido complex bearing a bulky corrole ligand, [Mn
- Published
- 2022
11. A highly active and robust iron quinquepyridine complex for photocatalytic CO2 reduction in aqueous acetonitrile solution
- Author
-
Lingjing Chen, Gui Chen, Yanfei Qin, Hongbo Fan, Zhenguo Guo, Lei Wang, Marc Robert, and Tai-Chu Lau
- Subjects
Aqueous solution ,Ligand ,Metals and Alloys ,General Chemistry ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Turnover number ,chemistry.chemical_compound ,chemistry ,Materials Chemistry ,Ceramics and Composites ,Photocatalysis ,Imidazole ,Acetonitrile ,Selectivity ,Nuclear chemistry - Abstract
The iron(II) complex bearing the 2,2′:6′,2′′:6′′,2′′′:6′′′,2′′′′-quinquepyridine (qnpy) ligand, [Fe(qnpy)(H2O)2]2+, is a highly efficient and robust catalyst for photocatalytic reduction of CO2 to CO in aqueous acetonitrile solution. A turnover number (TON) for CO of up to 14 095 with 98% selectivity can be achieved using Ru(phen)3Cl2 (phen = 1,10-phenanthroline) as the photosensitizer and BIH (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole) as the sacrificial reductant in a CO2-saturated MeCN/H2O (1 : 1, v/v) solution under visible light irradiation. This Fe complex is state-of-the-art for CO2 visible-light-driven catalysis.
- Published
- 2020
12. Molecular quaterpyridine-based metal complexes for small molecule activation: water splitting and CO2 reduction
- Author
-
Chi-Fai Leung, Marc Robert, Claudio Cometto, Lingjing Chen, Tai-Chu Lau, and Gui Chen
- Subjects
Reduction (complexity) ,Metal ,2019-20 coronavirus outbreak ,Coronavirus disease 2019 (COVID-19) ,Chemistry ,Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) ,visual_art ,visual_art.visual_art_medium ,Water splitting ,General Chemistry ,Photochemistry ,Small molecule ,Artificial photosynthesis - Abstract
Artificial photosynthesis is considered as one of the most promising strategies for solar-to-fuel conversion through sunlight-driven water splitting and CO2 reduction. This tutorial describes recent developments in the use of metal quaterpyridine complexes as electrocatalyts and photocatalysts for artificial photosynthesis.
- Published
- 2020
13. Highly Efficient Photocatalytic Reduction of CO 2 to CO by In Situ Formation of a Hybrid Catalytic System Based on Molecular Iron Quaterpyridine Covalently Linked to Carbon Nitride
- Author
-
Yue Wei, Lingjing Chen, Huan Chen, Lirong Cai, Guiping Tan, Yongfu Qiu, Quanjun Xiang, Gui Chen, Tai‐Chu Lau, and Marc Robert
- Subjects
General Chemistry ,General Medicine ,Catalysis - Published
- 2022
14. Structure and Reactivity of a Manganese(VI) Nitrido Complex Bearing a Tetraamido Macrocyclic Ligand
- Author
-
Huatian Shi, William W. Y. Lam, Yi Pan, Kai-Chung Lau, Hung Kay Lee, Tai-Chu Lau, Shek-Man Yiu, and Wai-Lun Man
- Subjects
Hydride ,Chemistry ,Ligand ,chemistry.chemical_element ,General Chemistry ,Manganese ,Biochemistry ,Medicinal chemistry ,Catalysis ,Colloid and Surface Chemistry ,Nucleophile ,Oxidation state ,Electrophile ,Reactivity (chemistry) ,Macrocyclic ligand - Abstract
Manganese complexes in +6 oxidation state are rare. Although a number of Mn(VI) nitrido complexes have been generated in solution via one-electron oxidation of the corresponding Mn(V) nitrido species, they are too unstable to isolate. Herein we report the isolation and the X-ray structure of a Mn(VI) nitrido complex, [MnVI(N)(TAML)]- (2), which was obtained by one-electron oxidation of [MnV(N)(TAML)]2- (1). 2 undergoes N atom transfer to PPh3 and styrenes to give Ph3P═NH and aziridines, respectively. A Hammett study for various p-substituted styrenes gives a V-shaped plot; this is rationalized by the ability of 2 to function as either an electrophile or a nucleophile. 2 also undergoes hydride transfer reactions with NADH analogues, such as 10-methyl-9,10-dihydroacridine (AcrH2) and 1-benzyl-1,4-dihydronicotinamide (BNAH). A kinetic isotope effect of 7.3 was obtained when kinetic studies were carried out with AcrH2 and AcrD2. The reaction of 2 with NADH analogues results in the formation of [MnV(N)(TAML-H+)]- (3), which was characterized by ESI/MS, IR spectroscopy, and X-ray crystallography. These results indicate that this reaction occurs via an initial "separated CPET" (separated concerted proton-electron transfer) mechanism; that is, there is a concerted transfer of 1 e- + 1 H+ from AcrH2 (or BNAH) to 2, in which the electron is transferred to the MnVI center, while the proton is transferred to a carbonyl oxygen of TAML rather than to the nitrido ligand.
- Published
- 2021
15. Room Temperature Aerobic Peroxidation of Organic Substrates Catalyzed by Cobalt(III) Alkylperoxo Complexes
- Author
-
Yunzhou Chen, Chi-Sing Lee, Huatian Shi, Wai-Lun Man, Shek-Man Yiu, and Tai-Chu Lau
- Subjects
chemistry.chemical_classification ,Chemistry ,Ligand ,chemistry.chemical_element ,General Chemistry ,Biochemistry ,Medicinal chemistry ,Catalysis ,Colloid and Surface Chemistry ,Electrophile ,Reactivity (chemistry) ,Cobalt ,Alkyl - Abstract
Room temperature aerobic oxidation of hydrocarbons is highly desirable and remains a great challenge. Here we report a series of highly electrophilic cobalt(III) alkylperoxo complexes, CoIII(qpy)OOR supported by a planar tetradentate quaterpyridine ligand that can directly abstract H atoms from hydrocarbons (R'H) at ambient conditions (CoIII(qpy)OOR + R'H → CoII(qpy) + R'• + ROOH). The resulting alkyl radical (R'•) reacts rapidly with O2 to form alkylperoxy radical (R'OO•), which is efficiently scavenged by CoII(qpy) to give CoIII(qpy)OOR' (CoII(qpy) + R'OO• → CoIII(qpy)OOR'). This unique reactivity enables CoIII(qpy)OOR to function as efficient catalysts for aerobic peroxidation of hydrocarbons (R'H + O2 → R'OOH) under 1 atm air and at room temperature.
- Published
- 2021
16. Generation and Reactivity of a One‐Electron‐Oxidized Manganese(V) Imido Complex with a Tetraamido Macrocyclic Ligand
- Author
-
Shek-Man Yiu, Chi-Keung Mak, Huatian Shi, Tai-Chu Lau, Jianhui Xie Xie, Wai-Lun Man, Hung Kay Lee, and William W. Y. Lam
- Subjects
chemistry.chemical_classification ,010405 organic chemistry ,Nitrene ,Organic Chemistry ,chemistry.chemical_element ,General Chemistry ,Manganese ,Electron ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Coordination complex ,chemistry ,Polymer chemistry ,Reactivity (chemistry) ,Macrocyclic ligand - Abstract
The synthesis and X-ray structure of a new manganese(V) mesitylimido complex with a tetraamido macrocyclic ligand (TAML), [MnV (TAML)(N-Mes)]- (1), are reported. Compound 1 is oxidized by [(p-BrC6 H4 )3 N]+. [SbCl6 ]- and the resulting MnVI species readily undergoes H-atom transfer and nitrene transfer reactions.
- Published
- 2019
17. A Photocaged, Water-Oxidizing, and Nucleolus-Targeted Pt(IV) Complex with a Distinct Anticancer Mechanism
- Author
-
Zhiqin Deng, Guangyu Zhu, Yingying Liu, Zoufeng Xu, Zhigang Wang, Na Wang, and Tai-Chu Lau
- Subjects
Programmed cell death ,Nucleolus ,Chemistry ,Reducing agent ,Cell ,Rational design ,Water ,Antineoplastic Agents ,General Chemistry ,Prodrug ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Colloid and Surface Chemistry ,medicine.anatomical_structure ,Mechanism of action ,medicine ,Biophysics ,Immunogenic cell death ,Humans ,medicine.symptom ,Cell Nucleolus ,Platinum - Abstract
Targeted anticancer prodrugs that can be controllably activated are highly desired for personalized precision medicine in cancer therapy. Such prodrugs with unique action modes are also promising to overcome drug resistance. Herein, we report coumaplatin, an oxaliplatin-based and photocaged Pt(IV) prodrug, to realize nuclear accumulation along with "on-demand" activation. This prodrug is based on a Pt(IV) complex that can be efficiently photoactivated via water oxidation without the requirement of a reducing agent. Coumaplatin accumulates very efficiently in the nucleoli, and upon photoactivation, this prodrug exhibits a level of photocytotoxicity up to 2 orders of magnitude higher than that of oxaliplatin. Unexpectedly, this prodrug presents strikingly enhanced tumor penetration ability and utilizes a distinct action mode to overcome drug resistance; i.e., coumaplatin but not oxaliplatin induces cell senescence, p53-independent cell death, and immunogenic cell death along with T cell activation. Our findings not only provide a novel strategy for the rational design of controllably activated and nucleolus-targeted Pt(IV) anticancer prodrugs but also demonstrate that accumulating conventional platinum drugs to the nucleus is a practical way to change its canonical mechanism of action and to achieve reduced resistance.
- Published
- 2020
18. Efficient Visible-Light-Driven CO2 Reduction by a Cobalt Molecular Catalyst Covalently Linked to Mesoporous Carbon Nitride
- Author
-
Gui Chen, Marc Robert, Lingjing Chen, Julien Bonin, Ryo Kuriki, Osamu Ishitani, Claire Fave, Bing Ma, Tai-Chu Lau, Kazuhiko Maeda, Laboratoire d'Electrochimie Moléculaire (LEM (UMR_7591)), Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Dongguan University of Technology, Tokyo Institute of Technology [Tokyo] (TITECH), and City University of Hong Kong [Hong Kong] (CUHK)
- Subjects
Chemistry ,Graphitic carbon nitride ,chemistry.chemical_element ,[CHIM.CATA]Chemical Sciences/Catalysis ,General Chemistry ,[CHIM.INOR]Chemical Sciences/Inorganic chemistry ,Nitride ,010402 general chemistry ,7. Clean energy ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Chemical engineering ,X-ray photoelectron spectroscopy ,13. Climate action ,Selectivity ,Mesoporous material ,Cobalt ,Electrochemical reduction of carbon dioxide - Abstract
International audience; Achieving visible-light-driven carbon dioxide reduction with high selectivity control and durability while using only earth abundant elements requires new strategies. Hybrid catalytic material was prepared upon covalent grafting a Co–quaterpyridine molecular complex to semiconductive mesoporous graphitic carbon nitride (mpg-C3N4) through an amide linkage. The molecular material was characterized by various spectroscopic techniques, including XPS, IR, and impedance spectroscopy. It proved to be a selective catalyst for CO production in acetonitrile using a solar simulator with a high 98% selectivity, while being remarkably robust since no degradation was observed after 4 days of irradiation (ca. 500 catalytic cycles). This unique combination of a selective molecular catalyst with a simple and robust semiconductive material opens new pathways for CO2 catalytic light-driven reduction.
- Published
- 2020
19. A Carbon Nitride/Fe Quaterpyridine Catalytic System for Photostimulated CO2-to-CO Conversion with Visible Light
- Author
-
Osamu Ishitani, Marc Robert, Claudio Cometto, Kazuhiko Maeda, Tai-Chu Lau, Ryo Kuriki, and Lingjing Chen
- Subjects
Graphitic carbon nitride ,Quantum yield ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,Triethanolamine ,Photocatalysis ,medicine ,0210 nano-technology ,Mesoporous material ,Carbon nitride ,medicine.drug ,Visible spectrum - Abstract
Efficient and selective photostimulated CO2-to-CO reduction by a photocatalytic system consisting of an iron-complex catalyst and a mesoporous graphitic carbon nitride (mpg-C3N4) redox photosensitizer is reported for the first time. Irradiation in the visible region (λ ≥ 400 nm) of an CH3CN/triethanolamine (4:1, v/v) solution containing [Fe(qpy)(H2O)2]2+ (qpy = 2,2′:6′,2′′:6′′,2′′-quaterpyridine) and mpg-C3N4 resulted in CO evolution with 97% selectivity, a turnover number of 155, and an apparent quantum yield of ca. 4.2%. This hybrid catalytic system, comprising only earth abundant elements, opens new perspectives for solar fuels production using CO2 as a renewable feedstock.
- Published
- 2018
20. A Hybrid Co Quaterpyridine Complex/Carbon Nanotube Catalytic Material for CO2 Reduction in Water
- Author
-
Marc Robert, Min Wang, Lingjing Chen, and Tai-Chu Lau
- Subjects
Materials science ,010405 organic chemistry ,chemistry.chemical_element ,General Medicine ,02 engineering and technology ,General Chemistry ,Carbon nanotube ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Catalysis ,0104 chemical sciences ,law.invention ,chemistry ,Chemical engineering ,law ,0210 nano-technology ,Selectivity ,Hybrid material ,Carbon ,Faraday efficiency ,Electrochemical reduction of carbon dioxide - Abstract
Associating a metal-based catalyst to a carbon-based nanomaterial is a promising approach for the production of solar fuels from CO2 . Upon appending a CoII quaterpyridine complex [Co(qpy)]2+ at the surface of multi-walled carbon nanotubes, CO2 conversion into CO was realized in water at pH 7.3 with 100 % catalytic selectivity and 100 % Faradaic efficiency, at low catalyst loading and reduced overpotential. A current density of 0.94 mA cm-2 was reached at -0.35 V vs. RHE (240 mV overpotential), and 9.3 mA cm-2 could be sustained for hours at only 340 mV overpotential with excellent catalyst stability (89 095 catalytic cycles in 4.5 h), while 19.9 mA cm-2 was met at 440 mV overpotential. Such a hybrid material combines the high selectivity of a homogeneous molecular catalyst to the robustness of a heterogeneous material. Catalytic performances compare well with those of noble-metal-based nano-electrocatalysts and atomically dispersed metal atoms in carbon matrices.
- Published
- 2018
21. Highly Selective Molecular Catalysts for the CO2-to-CO Electrochemical Conversion at Very Low Overpotential. Contrasting Fe vs Co Quaterpyridine Complexes upon Mechanistic Studies
- Author
-
Marc Robert, Po-Kam Lo, Claire Fave, Zhenguo Guo, Tai-Chu Lau, Claudio Cometto, Kai-Chung Lau, Elodie Anxolabéhère-Mallart, and Lingjing Chen
- Subjects
Chemistry ,02 engineering and technology ,General Chemistry ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,Electrochemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Adduct ,chemistry.chemical_compound ,Cyclic voltammetry ,0210 nano-technology ,Brønsted–Lowry acid–base theory ,Selectivity ,Acetonitrile - Abstract
[MII(qpy)(H2O)2]2+ (M = Fe, Co; qpy: 2,2′:6′,2″:6″,2‴-quaterpyridine) complexes efficiently catalyze the electrochemical CO2-to-CO conversion in acetonitrile solution in the presence of weak Bronsted acids. Upon performing cyclic voltammetry studies, controlled-potential electrolysis, and spectroelectrochemistry (UV–visible and infrared) experiments together with DFT calculations, catalytic mechanisms were deciphered. Catalysis is characterized by high selectivity for CO production (selectivity >95%) in the presence of phenol as proton source. Overpotentials as low as 240 and 140 mV for the Fe and Co complexes, respectively, led to large CO production for several hours. In the former case, the one-electron-reduced species binds to CO2, and CO evolution is observed after further reduction of the intermediate adduct. A deactivation pathway has been identified, which is due to the formation of a Fe0qpyCO species. With the Co catalyst, no such deactivation occurs, and the doubly reduced complex activates CO2....
- Published
- 2018
22. Electronic modulation of NiS-PBA/CNT with boosted water oxidation performance realized by a rapid microwave-assisted in-situ partial sulfidation
- Author
-
Tai-Chu Lau, Zegao Wang, Wanli Zhang, Xiaojuan Zhang, Katam Srinivas, Bin Wang, Xinqiang Wang, Dongxu Yang, Yuanfu Chen, and Bo Yu
- Subjects
Tafel equation ,Materials science ,Hydrogen ,General Chemical Engineering ,Doping ,Sulfidation ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Industrial and Manufacturing Engineering ,0104 chemical sciences ,Catalysis ,Electron transfer ,Chemical engineering ,chemistry ,Environmental Chemistry ,Density functional theory ,0210 nano-technology - Abstract
Hydrogen is considered as the promising renewable resources in future C-free systems, but more efficient and scalable synthesis is required to enable its widespread deployment. Here, in-situ generated hierarchical NiS-PBA/CNT hybrid has been fabricated which combined the high conductivity and electrocatalytic activity together. Through study the electronic structure, it was found that the electron transfer among metal atom enable higher activity. The optimized NiS-PBA/CNT delivers an ultralow overpotential of 253 mV @ 20 mA cm−2, a small Tafel slope of 49.8 mV dec-1, and can work steadily for more than 40 h with a Faradic efficiency of 95.5%. Density functional theory calculations based on the NiS-PBA, NiS and PBA model reveal that the enhanced catalytic activities of NiS-PBA is mainly manifested in its lower free energy of rate-determining step (the oxidation of *OH to *O) and higher electrical conductivity. This work provides a novel partial sulfidation strategy for PBA to significantly boost catalytic performance. And the microwave-assisted solvothermal reaction offers a novel mild implementation toward in situ heterogeneous doping for carbon matrix.
- Published
- 2021
23. Highly Selective and Efficient Ring Hydroxylation of Alkylbenzenes with Hydrogen Peroxide and an Osmium(VI) Nitrido Catalyst
- Author
-
Hajime Hirao, Kai-Chung Lau, Po-Kam Lo, Tai-Chu Lau, Hoi-Ki Kwong, and Shek-Man Yiu
- Subjects
010405 organic chemistry ,chemistry.chemical_element ,General Medicine ,General Chemistry ,010402 general chemistry ,Ring (chemistry) ,Photochemistry ,01 natural sciences ,Ethylbenzene ,Medicinal chemistry ,Catalysis ,0104 chemical sciences ,Hydroxylation ,chemistry.chemical_compound ,chemistry ,Osmium ,Alkylbenzenes ,Hydrogen peroxide ,Mesitylene - Abstract
The OsVI nitrido complex, OsVI(N)(quin)2(OTs) (1, quin=2-quinaldinate, OTs=tosylate), is a highly selective and efficient catalyst for the ring hydroxylation of alkylbenzenes with H2O2 at room temperature. Oxidation of various alkylbenzenes occurs with ring/chain oxidation ratios ranging from 96.7/3.3 to 99.9/0.1, and total product yields from 93 % to 98 %. Moreover, turnover numbers up to 6360, 5670, and 3880 can be achieved for the oxidation of p-xylene, ethylbenzene, and mesitylene, respectively. Density functional theory calculations suggest that the active intermediate is an OsVIII nitrido oxo species.
- Published
- 2017
24. Monitoring of metal pollution in waterways across Bangladesh and ecological and public health implications of pollution
- Author
-
Debbrota Mallick, Rudolf S.S. Wu, Golam Kibria, Maruf Hossain, and Tai-Chu Lau
- Subjects
Pollution ,Irrigation ,Environmental Engineering ,010504 meteorology & atmospheric sciences ,Health, Toxicology and Mutagenesis ,media_common.quotation_subject ,Wetland ,010501 environmental sciences ,01 natural sciences ,Rivers ,Aquaculture ,Environmental protection ,Metals, Heavy ,Water Quality ,Humans ,Environmental Chemistry ,Effluent ,0105 earth and related environmental sciences ,media_common ,Bangladesh ,geography ,geography.geographical_feature_category ,Ecology ,business.industry ,Public Health, Environmental and Occupational Health ,Environmental engineering ,Agriculture ,General Medicine ,General Chemistry ,Wetlands ,Bioaccumulation ,Environmental science ,Public Health ,Water quality ,business ,Water Pollutants, Chemical ,Environmental Monitoring - Abstract
Using innovative artificial mussels technology for the first time, this study detected eight heavy metals (Cd, Cu, Fe, Mn, Ni, Pb, U, Zn) on a regular basis in waterways across Bangladesh (Chittagong, Dhaka and Khulna). Three heavy metals, viz. Co, Cr and Hg were always below the instrumental detection levels in all the sites during the study period. Through this study, seven metal pollution "hot spots" have been identified, of which, five "hot spots" (Cu, Fe, Mn, Ni, Pb) were located in the Buriganga River, close to the capital Dhaka. Based on this study, the Buriganga River can be classified as the most polluted waterway in Bangladesh compared to waterways monitored in Khulna and Chittagong. Direct effluents discharged from tanneries, textiles are, most likely, reasons for elevated concentrations of heavy metals in the Buriganga River. In other areas (Khulna), agriculture and fish farming effluents may have caused higher Cu, U and Zn in the Bhairab and Rupsa Rivers, whereas untreated industrial discharge and ship breaking activities can be linked to elevated Cd in the coastal sites (Chittagong). Metal pollution may cause significant impacts on water quality (irrigation, drinking), aquatic biodiversity (lethal and sub-lethal effects), food contamination/food security (bioaccumulation of metals in crops and seafood), human health (diseases) and livelihoods of people associated with wetlands.
- Published
- 2016
25. Photochemical nitrogenation of alkanes and arenes by a strongly luminescent osmium(VI) nitrido complex
- Author
-
Jing Xiang, Chi-Chiu Ko, Chi-Ming Che, Liangliang Wu, Minying Xue, Tai-Chu Lau, Shun Cheung Cheng, Wai-Lun Man, Qian Qian Su, and Xin Xin Jin
- Subjects
Ligand ,Photodissociation ,Quantum yield ,chemistry.chemical_element ,General Chemistry ,Photochemistry ,Biochemistry ,lcsh:Chemistry ,lcsh:QD1-999 ,chemistry ,Excited state ,Electrophile ,Materials Chemistry ,Environmental Chemistry ,Reactivity (chemistry) ,Osmium ,Amination - Abstract
The search for a highly active nitrido complex that can transfer its nitrogen atom to inert organic molecules remains a challenge to chemists. In this regard, the use of solar energy to generate a reactive nitrido species is an appealing strategy to solve this problem. Here we report the design of a strongly luminescent osmium(VI) nitrido compound, [OsVI(N)(NO2-L)(CN)3]− (NO2-OsN) with emission quantum yield (Φ) and life time (τ) of 3.0% and 0.48 μs, respectively in dichloromethane solution. Upon irradiation with visible light, this complex readily activates the aliphatic C-H bonds of various hydrocarbons, including alkanes. The excited state of NO2-OsN can undergo ring-nitrogenation of arenes, including benzene. Photophysical and computational studies suggest that the excited state of NO2-OsN arises from O^N ligand to Os ≡ N charge transfer transitions, and as a result it possesses [Os = N•] nitridyl character and is highly electrophilic.
- Published
- 2019
26. Activation of Metal Oxo and Nitrido Complexes by Lewis Acids
- Author
-
Yingying Liu and Tai-Chu Lau
- Subjects
Photosystem II ,biology ,Chemistry ,Metal ions in aqueous solution ,Active site ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Medicinal chemistry ,Catalysis ,0104 chemical sciences ,Metal ,Colloid and Surface Chemistry ,visual_art ,Oxidizing agent ,biology.protein ,visual_art.visual_art_medium ,Lewis acids and bases ,Brønsted–Lowry acid–base theory - Abstract
Metal oxo species (M═O) play key roles as oxidants in chemical and biological systems. Although Bronsted acids have long been known to enhance the oxidizing power of metal oxo complexes, the use of Lewis acids (LAs), such as metal ions, to activate these complexes has received much less attention until recently. The report of the presence of a Mn4CaO5 cluster active site in the oxygen-evolving center of photosystem II in 2004 has stimulated intense interest in understanding the interaction of LAs with metal oxo species. This Perspective analyzes the various modes of activation of metal oxos by LAs and the pathways for the oxidation of various substrates by LA/M═O systems. The interaction of LAs with metal nitrides will also be discussed, although it is much less studied than that with metal oxo complexes.
- Published
- 2019
27. Efficient pollutant degradation via non-radical dominated pathway by self-regenerative Ru(bpy)32+/peroxydisulfate under visible light
- Author
-
Chen-Xuan Li, Wen-Wei Li, Zhenguo Guo, Yingying Liu, Zhi-Yan Guo, Yun-Jie Wang, and Tai-Chu Lau
- Subjects
Chemistry ,General Chemical Engineering ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Industrial and Manufacturing Engineering ,0104 chemical sciences ,Catalysis ,Chemical kinetics ,Metal ,chemistry.chemical_compound ,visual_art ,Peroxydisulfate ,Rhodamine B ,visual_art.visual_art_medium ,Ultraviolet light ,Environmental Chemistry ,Degradation (geology) ,0210 nano-technology ,Visible spectrum - Abstract
Advanced oxidation processes based on activation of peroxydisulfate (PDS) typically require energy or chemical input, for which ultraviolet light and metal catalyst are commonly adopted. However, the sluggish reaction kinetics due to insufficient catalyst redox cycling and limited solar energy utilization remain a key challenge to be addressed. Here, we report a visible light-driven Ru(bpy)32+/PDS system that allows for highly-efficient and sustained pollutant degradation, at efficiencies far exceeding the existing PDS-based reaction systems. The degradation rate of Rhodamine B (RhB) was 40-fold higher than that achievable by the state-of-the-art Fe2+/PDS system. The Ru(bpy)33+ reduction was closely coupled with the pollutant oxidation, enabling an efficient Ru(bpy)32+/Ru(bpy)33+ cycling and RhB degradation via non-radical dominated pathway in the Ru(bpy)32+/PDS/vis system. The high activity of the catalyst towards multiple antibiotics and its high stability and robustness over a wide pH range and in the presence of various environmental anions were also demonstrated. This work provides solid evidence to support a direct oxidation of pollutant by high-valent metal complex, and may inspire new development of solar-responsive catalysts for efficient, sustainable advanced oxidation processes.
- Published
- 2020
28. Highly Efficient and Selective Photocatalytic CO2 Reduction by Iron and Cobalt Quaterpyridine Complexes
- Author
-
Zhenguo Guo, Claudio Cometto, Siwei Cheng, Guijian Liu, Siu-Mui Ng, Tai-Chu Lau, Marc Robert, Elodie Anxolabéhère-Mallart, Lingjing Chen, and Chi-Chiu Ko
- Subjects
010405 organic chemistry ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Turnover number ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,Triethanolamine ,Photocatalysis ,medicine ,Imidazole ,Photosensitizer ,Selectivity ,Cobalt ,medicine.drug - Abstract
The design of highly efficient and selective photocatalytic systems for CO2 reduction that are based on nonexpensive materials is a great challenge for chemists. The photocatalytic reduction of CO2 by [Co(qpy)(OH2)2](2+) (1) (qpy = 2,2':6',2″:6″,2‴-quaterpyridine) and [Fe(qpy)(OH2)2](2+) (2) have been investigated. With Ru(bpy)3(2+) as the photosensitizer and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole as the sacrificial reductant in CH3CN/triethanolamine solution under visible-light excitation (blue light-emitting diode), a turnover number (TON) for CO as high as 2660 with 98% selectivity can be achieved for the cobalt catalyst. In the case of the iron catalyst, the TON was3000 with up to 95% selectivity. More significantly, when Ru(bpy)3(2+) was replaced by the organic dye sensitizer purpurin, TONs of 790 and 1365 were achieved in N,N-dimethylformamide for the cobalt and iron catalysts, respectively.
- Published
- 2016
29. Kinetics and Mechanism of the Reaction of a Ruthenium(VI) Nitrido Complex with HSO3 − and SO3 2− in Aqueous Solution
- Author
-
Kai-Chung Lau, Tai-Chu Lau, Wai-Lun Man, Hong Yan Zhao, William W. Y. Lam, and Qian Wang
- Subjects
Reaction mechanism ,Aqueous solution ,010405 organic chemistry ,Chemistry ,Organic Chemistry ,Inorganic chemistry ,Kinetics ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,Redox ,Catalysis ,0104 chemical sciences ,Ruthenium ,Deuterium ,Kinetic isotope effect ,Molecule - Abstract
The kinetics and mechanism of the reaction of S(IV) (SO3 (2-) +HSO3 (-) ) with a ruthenium(VI) nitrido complex, [(L)Ru(VI) (N)(OH2 )](+) (Ru(VI) N, L=N,N'-bis(salicylidene)-o-cyclohexyldiamine dianion), in aqueous acidic solutions are reported. The kinetic results are consistent with parallel pathways involving oxidation of HSO3 (-) and SO3 (2-) by Ru(VI) N. A deuterium isotope effect of 4.7 is observed in the HSO3 (-) pathway. Based on experimental results and DFT calculations the proposed mechanism involves concerted N-S bond formation (partial N-atom transfer) between Ru(VI) N and HSO3 (-) and H(+) transfer from HSO3 (-) to a H2 O molecule.
- Published
- 2016
30. Photocatalytic oxidation of alkenes and alcohols in water by a manganese(<scp>v</scp>) nitrido complex
- Author
-
Gui Chen, Li Ma, Tai-Chu Lau, Hoi-Ki Kwong, and Lingjing Chen
- Subjects
inorganic chemicals ,010405 organic chemistry ,Metals and Alloys ,chemistry.chemical_element ,General Chemistry ,Manganese ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry ,Materials Chemistry ,Ceramics and Composites ,Photocatalysis ,Photosensitizer ,Efficient catalyst - Abstract
Mn(v) nitrido complex [Mn(N)(CN)4](2-) is an efficient catalyst for visible-light induced oxidation of alkenes and alcohols in water using [Ru(bpy)3](2+) as a photosensitizer and [Co(NH3)5Cl](2+) as a sacrificial oxidant. Alkenes are oxidized to epoxides and alcohols to carbonyl compounds.
- Published
- 2016
31. A Highly Reactive Seven-Coordinate Osmium(V) Oxo Complex: [OsV (O)(qpy)(pic)Cl]2+
- Author
-
Shek-Man Yiu, Yingying Liu, William W. Y. Lam, Tai-Chu Lau, and Siu-Mui Ng
- Subjects
010405 organic chemistry ,chemistry.chemical_element ,General Medicine ,General Chemistry ,Crystal structure ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Medicinal chemistry ,Bond-dissociation energy ,Catalysis ,0104 chemical sciences ,Ruthenium ,Metal ,Pentagonal bipyramidal molecular geometry ,chemistry ,visual_art ,X-ray crystallography ,visual_art.visual_art_medium ,Osmium - Abstract
Seven-coordinate ruthenium oxo species have been proposed as active intermediates in catalytic water oxidation by a number of highly active ruthenium catalysts, however such species have yet to be isolated. Reported herein is the first example of a seven-coordinate group 8 metal-oxo species, [Os(V)(O)(qpy)(pic)Cl](2+) (qpy = 2,2':6',2'':6'',2'''-quaterpyridine, pic = 4-picoline). The X-ray crystal structure of this complex shows that it has a distorted pentagonal bipyramidal geometry with an Os=O distance of 1.7375 Å. This oxo species undergoes facile O-atom and H-atom-transfer reactions with various organic substrates. Notably it can abstract H atoms from alkylaromatics with C-H bond dissociation energy as high as 90 kcal mol(-1). This work suggests that highly active oxidants may be designed based on group 8 seven-coordinate metal oxo species.
- Published
- 2015
32. Mechanism of Water Oxidation by Ferrate(VI) at pH 7-9
- Author
-
Po Kam Lo, Wai-Lun Man, Gui Chen, Kai-Chung Lau, William W. Y. Lam, Lingjing Chen, and Tai-Chu Lau
- Subjects
medicine.diagnostic_test ,010405 organic chemistry ,Chemistry ,Organic Chemistry ,Phosphate buffered saline ,Kinetics ,Inorganic chemistry ,Protonation ,General Chemistry ,Bond formation ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Reaction rate ,chemistry.chemical_compound ,Intramolecular force ,Spectrophotometry ,medicine ,Ferrate(VI) - Abstract
The kinetics of water oxidation by K2 FeO4 has been reinvestigated by UV/Vis spectrophotometry from pH 7-9 in 0.2 m phosphate buffer. The rate of reaction was found to be second-order in both [FeO4 2- ] and [H+ ]. These results are consistent with a proposed mechanism in which the first step involves the initial equilibrium protonation of FeO4 2- to give FeO3 (OH)- , which then undergoes rate-limiting O-O bond formation. Analysis of the O2 isotopic composition for the reaction in H2 18 O suggests that the predominant pathway for water oxidation by ferrate is intramolecular O-O coupling. DFT calculations have also been performed, which support the proposed mechanism.
- Published
- 2018
33. Molecular Catalysis of the Electrochemical and Photochemical Reduction of CO2 with Earth-Abundant Metal Complexes. Selective Production of CO vs HCOOH by Switching of the Metal Center
- Author
-
Xi-Guang Wei, Marc Robert, Tai-Chu Lau, Zhenguo Guo, Charlotte Gallenkamp, Kai-Chung Lau, Julien Bonin, Elodie Anxolabéhère-Mallart, and Lingjing Chen
- Subjects
Formic acid ,Ligand ,chemistry.chemical_element ,General Chemistry ,Photochemistry ,Biochemistry ,Catalysis ,Metal ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,visual_art ,visual_art.visual_art_medium ,Acetonitrile ,Cobalt ,Carbon monoxide ,Electrochemical reduction of carbon dioxide - Abstract
Molecular catalysis of carbon dioxide reduction using earth-abundant metal complexes as catalysts is a key challenge related to the production of useful products--the "solar fuels"--in which solar energy would be stored. A direct approach using sunlight energy as well as an indirect approach where sunlight is first converted into electricity could be used. A Co(II) complex and a Fe(III) complex, both bearing the same pentadentate N5 ligand (2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene), were synthesized, and their catalytic activity toward CO2 reduction was investigated. Carbon monoxide was formed with the cobalt complex, while formic acid was obtained with the iron-based catalyst, thus showing that the catalysis product can be switched by changing the metal center. Selective CO2 reduction occurs under electrochemical conditions as well as photochemical conditions when using a photosensitizer under visible light excitation (λ460 nm, solvent acetonitrile) with the Co catalyst. In the case of the Fe catalyst, selective HCOOH production occurs at low overpotential. Sustained catalytic activity over long periods of time and high turnover numbers were observed in both cases. A catalytic mechanism is suggested on the basis of experimental results and preliminary quantum chemistry calculations.
- Published
- 2015
34. Cerium(IV)-Driven Water Oxidation Catalyzed by a Manganese(V)-Nitrido Complex
- Author
-
Tai-Chu Lau, Li Ma, Qian Wang, Wai-Lun Man, Chi-Chiu Ko, and Hoi-Ki Kwong
- Subjects
Cerium ,Chemistry ,Homogeneous ,Inorganic chemistry ,chemistry.chemical_element ,Homogeneous catalysis ,General Chemistry ,Manganese ,General Medicine ,Medicinal chemistry ,Catalysis ,Turnover number - Abstract
The study of manganese complexes as water-oxidation catalysts (WOCs) is of great interest because they can serve as models for the oxygen-evolving complex of photosystem II. In most of the reported Mn-based WOCs, manganese exists in the oxidation states III or IV, and the catalysts generally give low turnovers, especially with one-electron oxidants such as Ce(IV) . Now, a different class of Mn-based catalysts, namely manganese(V)-nitrido complexes, were explored. The complex [Mn(V) (N)(CN)4 ](2-) turned out to be an active homogeneous WOC using (NH4 )2 [Ce(NO3 )6 ] as the terminal oxidant, with a turnover number of higher than 180 and a maximum turnover frequency of 6 min(-1) . The study suggests that active WOCs may be constructed based on the Mn(V) (N) platform.
- Published
- 2015
35. Catalytic oxidation of water and alcohols by a robust iron(<scp>iii</scp>) complex bearing a cross-bridged cyclam ligand
- Author
-
Peng Tan, Tai-Chu Lau, and Hoi-Ki Kwong
- Subjects
Inorganic chemistry ,Hexadecane ,Ligands ,Ferric Compounds ,Catalysis ,chemistry.chemical_compound ,Cyclam ,Polymer chemistry ,Materials Chemistry ,Molecular Structure ,Ligand ,Sodium periodate ,Metals and Alloys ,Water ,General Chemistry ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Turnover number ,chemistry ,Catalytic oxidation ,Alcohols ,Alcohol oxidation ,Ceramics and Composites ,Azabicyclo Compounds ,Oxidation-Reduction - Abstract
An iron(iii) complex bearing a cross-bridged cyclam ligand (4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane) is an efficient catalyst for the oxidation of both water and alcohols using sodium periodate as the oxidant. In catalytic water oxidation a maximum turnover number (TON) of 1030 is achieved, while in catalytic alcohol oxidation >95% conversions and yields can be obtained.
- Published
- 2015
36. Zero-valent iron nanoparticles with sustained high reductive activity for carbon tetrachloride dechlorination
- Author
-
Houqi Liu, Ying-Chao Huo, Raymond J. Zeng, Dan-Dan Wang, Tai-Chu Lau, Qin Kong, Di Min, and Wen-Wei Li
- Subjects
chemistry.chemical_compound ,Zerovalent iron ,Reaction rate constant ,chemistry ,Environmental remediation ,General Chemical Engineering ,Inorganic chemistry ,Carbon tetrachloride ,Nanoparticle ,Particle ,Sewage treatment ,Reactivity (chemistry) ,General Chemistry - Abstract
Zero-Valent Iron nanoparticles (nZVI) have been extensively applied for the reduction of various recalcitrant organic contaminants, but their reactivity usually declines over time due to the formation of passive iron oxides. In this study we observed a sustained reactivity of nZVI for the dechlorination of carbon tetrachloride (CT) in water during several consecutive reaction cycles. The dechlorination rate constants increased substantially in Cycle 2, then remained at a high level over several consecutive cycles, and ultimately declined in Cycle 7. In the entire process, the solution pH increased only slightly from 7.0 to 7.8, which was different from other unbuffered nZVI reduction systems reported before. Characterization of the particle surface morphology and composition revealed an important role of Fe oxyhydroxide formation in self-buffering the solution pH and sustaining a high nZVI reactivity. Our study provides new knowledge on the nZVI dechlorination process and may offer implications for extending the lifetime of nZVI in wastewater treatment and environmental remediation applications.
- Published
- 2015
37. Effects of morphology and exposed facets of α-Fe2O3 nanocrystals on photocatalytic water oxidation
- Author
-
Quanjun Xiang, Gui Chen, and Tai-Chu Lau
- Subjects
Materials science ,Morphology (linguistics) ,Fabrication ,Nanocrystal ,Chemical engineering ,General Chemical Engineering ,Inorganic chemistry ,Photocatalysis ,Reactivity (chemistry) ,General Chemistry ,Facet ,Heterogeneous catalysis ,Catalysis - Abstract
Shape and facet engineering of crystals at the nanoscale level has become an important strategy for optimizing the reactivity of catalysts in heterogeneous catalysis. We report here the fabrication of four morphology-controlled α-Fe2O3 catalysts with exposed specific facets by a solvothermal method. The effects of morphology and exposed facets of these α-Fe2O3 nanocrystals towards visible light-driven water oxidation have been investigated. Water oxidation was carried out using two catalytic systems, Fe2O3/[Ru(bpy)3]2+/S2O82− and Fe2O3/AgNO3, at λ > 420 nm. The α-Fe2O3 nanocubes with exposed {012} facets exhibit much higher catalytic activity than α-Fe2O3 nanoflakes with {001} facets. This work demonstrates that the catalytic activity of α-Fe2O3 nanocrystals in photocatalytic water oxidation is morphology-dependent and the reactivity trend can be rationalized in terms of exposed facets in the order of {012} > {001}. This study provides a new approach to the design of highly effective water oxidation catalysts by engineering the morphology and the exposed facets of crystals.
- Published
- 2015
38. Dual Homogeneous and Heterogeneous Pathways in Photo- and Electrocatalytic Hydrogen Evolution with Nickel(II) Catalysts Bearing Tetradentate Macrocyclic Ligands
- Author
-
Chi-Fai Leung, Elodie Anxolabéhère-Mallart, Chi-Chiu Ko, Gui Chen, Shek-Man Yiu, Marc Robert, Tai-Chu Lau, and Lingjing Chen
- Subjects
Proton ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,Catalysis ,chemistry.chemical_compound ,Nickel ,chemistry ,Polymer chemistry ,Atom ,Photocatalysis ,Photosensitizer ,Absorption (chemistry) ,Triethylamine - Abstract
A series of nickel(II) complexes bearing tetradentate macrocyclic N4, N3S, and N3P ligands were synthesized, and their photocatalytic activity toward proton reduction has been investigated by using [Ir(dF(CF3)ppy)2(dmbpy)]PF6 (dF(CF3)ppy = 2-(2,4-difluorophenyl)-5-trifluoromethylpyridine and dmbpy = 4,4′-dimethyl-2,2′-dipyridyl) as the photosensitizer and triethylamine (TEA) as the sacrificial reductant. The complex [Ni(L4)]2+ (L4 = 2,12-dimethyl-7-phenyl-3,11,17-triaza-7-phospha-bicyclo[11,3,1]heptadeca-1(17),13,15-triene), which bears a phosphorus donor atom, shows the highest efficiency with TON up to 5000 under optimized conditions, while the tetraaza macrocyclic nickel complexes [Ni(L1)]2+ and [Ni(L2)]2+ (L1 = 2,12-dimethyl-3,7,11,17-tetra-azabicyclo[11.3.l]heptadeca-1(17),2,11,13,15-pentaene; L2 = 2,12-dimethyl-3,7,11,17-tetra-azabicyclo[11.3.l]heptadeca-1(17),13,15-triene) show lower photocatalytic activities. Transient UV–vis absorption and spectroelectrochemical experiments show that Ni(II) is re...
- Published
- 2014
39. Oxidation of Alkanes by Periodate Using a MnVNitrido Complex as Catalyst
- Author
-
Li Ma, Tai-Chu Lau, and Lingjing Chen
- Subjects
010405 organic chemistry ,Organic Chemistry ,chemistry.chemical_element ,Periodate ,Homogeneous catalysis ,General Chemistry ,Manganese ,010402 general chemistry ,01 natural sciences ,Biochemistry ,0104 chemical sciences ,Catalysis ,Turnover number ,chemistry.chemical_compound ,chemistry ,Organic chemistry ,Ton ,Efficient catalyst - Abstract
The design of catalytic systems that can selectively oxidize unactivated C-H bonds under mild conditions is a challenge to chemists. We report here that the manganese(V) nitrido complex [MnV (N)(CN)4 ]2- is a highly efficient catalyst for the oxidation of alkanes by periodate (IO4- ) at ambient conditions. Excellent yields of alcohols and ketones (>95 %) are obtained with a maximum turnover number (TON) of 3000.
- Published
- 2016
40. Cytotoxic (salen)ruthenium(iii) anticancer complexes exhibit different modes of cell death directed by axial ligands
- Author
-
Ming-Liang He, Cai Li, Dan Song, Guangyu Zhu, Wai-Lun Man, Kwok-Wa Ip, Tai-Chu Lau, and Shek-Man Yiu
- Subjects
Programmed cell death ,010405 organic chemistry ,DNA damage ,Chemistry ,Stereochemistry ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Ruthenium ,Amidine ,chemistry.chemical_compound ,Mechanism of action ,Cancer cell ,medicine ,medicine.symptom ,Cytotoxicity ,Guanidine - Abstract
A cancer-cell selective bis(guanidine)-ruthenium(iii) complex induces apoptosis, whereas its amidine analogue effectively kills cancer cells through paraptosis pathways., Two novel series of (salen)ruthenium(iii) complexes bearing guanidine and amidine axial ligands were synthesized, characterized, and evaluated for anticancer activity. In vitro cytotoxicity tests demonstrate that these complexes are cytotoxic against various cancer cell lines and the leading complexes have remarkable cancer-cell selectivity. A detailed study of the guanidine complex 7 and the amidine complex 13 reveals two distinguished modes of action. Complex 7 weakly binds to DNA and induces DNA damage, cell cycle arrest, and typical apoptosis pathways in MCF-7 cells. In contrast, complex 13 induces paraptosis-like cell death hallmarked by massive vacuole formation, mitochondrial swelling, and ER stress, resulting in significant cytotoxicity against human breast cancer cells. Our results provide an extraordinary example of tuning the mechanism of action of (salen)ruthenium(iii) anticancer complexes by modifying the structure of the axial ligands.
- Published
- 2017
41. Enhancing Extracellular Electron Transfer of Shewanella oneidensis MR-1 through Coupling Improved Flavin Synthesis and Metal-Reducing Conduit for Pollutant Degradation
- Author
-
Yang Mu, Han-Qing Yu, Dao-Bo Li, Di Min, Dong-Feng Liu, Lei Cheng, Feng Zhang, Xue-Na Huang, and Tai-Chu Lau
- Subjects
0301 basic medicine ,Shewanella ,Microbial fuel cell ,Anaerobic respiration ,030106 microbiology ,Electrons ,Flavin group ,Electron Transport ,03 medical and health sciences ,Electron transfer ,Flavins ,Environmental Chemistry ,Shewanella oneidensis ,chemistry.chemical_classification ,biology ,Chemistry ,General Chemistry ,Biodegradation ,Electron acceptor ,biology.organism_classification ,Electron transport chain ,030104 developmental biology ,Biochemistry ,Metals ,cardiovascular system ,Biophysics ,lipids (amino acids, peptides, and proteins) - Abstract
Dissimilatory metal reducing bacteria (DMRB) are capable of extracellular electron transfer (EET) to insoluble metal oxides, which are used as external electron acceptors by DMRB for their anaerobic respiration. The EET process has important contribution to environmental remediation mineral cycling, and bioelectrochemical systems. However, the low EET efficiency remains to be one of the major bottlenecks for its practical applications for pollutant degradation. In this work, Shewanella oneidensis MR-1, a model DMRB, was used to examine the feasibility of enhancing the EET and its biodegradation capacity through genetic engineering. A flavin biosynthesis gene cluster ribD-ribC-ribBA-ribE and metal-reducing conduit biosynthesis gene cluster mtrC-mtrA-mtrB were coexpressed in S. oneidensis MR-1. Compared to the control strain, the engineered strain was found to exhibit an improved EET capacity in microbial fuel cells and potentiostat-controlled electrochemical cells, with an increase in maximum current density by approximate 110% and 87%, respectively. The electrochemical impedance spectroscopy (EIS) analysis showed that the current increase correlated with the lower interfacial charge-transfer resistance of the engineered strain. Meanwhile, a three times more rapid removal rate of methyl orange by the engineered strain confirmed the improvement of its EET and biodegradation ability. Our results demonstrate that coupling of improved synthesis of mediators and metal-reducing conduits could be an efficient strategy to enhance EET in S. oneidensis MR-1, which is essential to the applications of DMRB for environmental remediation, wastewater treatment, and bioenergy recovery from wastes.
- Published
- 2017
42. Catalytic Water Oxidation by Ruthenium(II) Quaterpyridine (qpy) Complexes: Evidence for Ruthenium(III) qpy-N,N′′′-dioxide as the Real Catalysts
- Author
-
Yingying Liu, Kai-Chung Lau, William W. Y. Lam, Shek-Man Yiu, Tai-Chu Lau, Siu-Mui Ng, and Xi-Guang Wei
- Subjects
Pyridines ,Chemistry ,Molecular Conformation ,Water ,chemistry.chemical_element ,Homogeneous catalysis ,General Medicine ,General Chemistry ,Crystallography, X-Ray ,Photochemistry ,Medicinal chemistry ,Ruthenium ,Catalysis ,chemistry.chemical_compound ,Coordination Complexes ,Pyridine ,Oxidation-Reduction - Abstract
Polypyridyl and related ligands have been widely used for the development of water oxidation catalysts. Supposedly these ligands are oxidation-resistant and can stabilize high-oxidation-state intermediates. In this work a series of ruthenium(II) complexes [Ru(qpy)(L)2 ](2+) (qpy=2,2':6',2'':6'',2'''-quaterpyridine; L=substituted pyridine) have been synthesized and found to catalyze Ce(IV) -driven water oxidation, with turnover numbers of up to 2100. However, these ruthenium complexes are found to function only as precatalysts; first, they have to be oxidized to the qpy-N,N'''-dioxide (ONNO) complexes [Ru(ONNO)(L)2 ](3+) which are the real catalysts for water oxidation.
- Published
- 2014
43. Highly Efficient Alkane Oxidation Catalyzed by [MnV(N)(CN)4]2–. Evidence for [MnVII(N)(O)(CN)4]2– as an Active Intermediate
- Author
-
Gui Chen, Li Ma, Yi Pan, Wai-Lun Man, Tai-Chu Lau, Kai-Chung Lau, Hoi-Ki Kwong, and William W. Y. Lam
- Subjects
Alkane ,chemistry.chemical_classification ,Cyclohexane ,Chemistry ,Inorganic chemistry ,chemistry.chemical_element ,Substrate (chemistry) ,General Chemistry ,Manganese ,Biochemistry ,Heterolysis ,Medicinal chemistry ,Catalysis ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Reaction rate constant ,Kinetic isotope effect - Abstract
The oxidation of various alkanes catalyzed by [Mn(V)(N)(CN)4](2-) using various terminal oxidants at room temperature has been investigated. Excellent yields of alcohols and ketones (>95%) are obtained using H2O2 as oxidant and CF3CH2OH as solvent. Good yields (>80%) are also obtained using (NH4)2[Ce(NO3)6] in CF3CH2OH/H2O. Kinetic isotope effects (KIEs) are determined by using an equimolar mixture of cyclohexane (c-C6H12) and cyclohexane-d12 (c-C6D12) as substrate. The KIEs are 3.1 ± 0.3 and 3.6 ± 0.2 for oxidation by H2O2 and Ce(IV), respectively. On the other hand, the rate constants for the formation of products using c-C6H12 or c-C6D12 as single substrate are the same. These results are consistent with initial rate-limiting formation of an active intermediate between [Mn(N)(CN)4](2-) and H2O2 or Ce(IV), followed by H-atom abstraction from cyclohexane by the active intermediate. When PhCH2C(CH3)2OOH (MPPH) is used as oxidant for the oxidation of c-C6H12, the major products are c-C6H11OH, c-C6H10O, and PhCH2C(CH3)2OH (MPPOH), suggesting heterolytic cleavage of MPPH to generate a Mn═O intermediate. In the reaction of H2O2 with [Mn(N)(CN)4](2-) in CF3CH2OH, a peak at m/z 628.1 was observed in the electrospray ionization mass spectrometry, which is assigned to the solvated manganese nitrido oxo species, (PPh4)[Mn(N)(O)(CN)4](-)·CF3CH2OH. On the basis of the experimental results the proposed mechanism for catalytic alkane oxidation by [Mn(V)(N)(CN)4](2-)/ROOH involves initial rate-limiting O-atom transfer from ROOH to [Mn(N)(CN)4](2-) to generate a manganese(VII) nitrido oxo active species, [Mn(VII)(N)(O)(CN)4](2-), which then oxidizes alkanes (R'H) via a H-atom abstraction/O-rebound mechanism. The proposed mechanism is also supported by density functional theory calculations.
- Published
- 2014
44. Photoinduced water oxidation catalyzed by a double-helical dicobalt(<scp>ii</scp>) sexipyridine complex
- Author
-
Siu-Mui Ng, Raymond J. Zeng, Man Chen, Shek-Man Yiu, Tai-Chu Lau, and Kai-Chung Lau
- Subjects
Chemistry ,Stereochemistry ,Materials Chemistry ,Metals and Alloys ,Ceramics and Composites ,General Chemistry ,Medicinal chemistry ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Turnover number - Abstract
A double-helical dicobalt(II) complex [Co2(spy)2](ClO4)4 (spy = 2,2':6',2″:6″,2‴:6‴,2'''':6'''',2'''''-sexipyridine) (1) is found to catalyze visible light-induced water oxidation by [Ru(bpy)3](2+)/Na2S2O8, with a maximum turnover number of 442. Several lines of evidence suggest that functions as a molecular catalyst and does not produce any CoOx in water oxidation.
- Published
- 2014
45. Synthesis of nitrogen-doped KNbO3 nanocubes with high photocatalytic activity for water splitting and degradation of organic pollutants under visible light
- Author
-
Yufeng Zhu, Jun He, Yongfu Qiu, Tai-Chu Lau, Chi-Fai Leung, Guijian Liu, and Ruwei Wang
- Subjects
Materials science ,General Chemical Engineering ,Doping ,General Chemistry ,Photochemistry ,Industrial and Manufacturing Engineering ,chemistry.chemical_compound ,chemistry ,Rhodamine B ,Photocatalysis ,Environmental Chemistry ,Water splitting ,Hydrothermal synthesis ,Orange G ,Photodegradation ,Visible spectrum - Abstract
The effects of KOH concentration (10–30 M) on the morphology of KNbO 3 produced from Nb 2 O 5 by hydrothermal synthesis have been investigated. High purity KNbO 3 nanocubes have been obtained using 30 M KOH at 200 °C. The KNbO 3 nanocubes can be readily doped with nitrogen by heating with urea at 425 °C without significant change in morphology. The band gap of KNbO 3 decreases from 3.13 to 2.76 eV as a result of N-doping, the surface area also increases substantially. The photocatalytic activity of the N-doped KNbO 3 nanocubes has been evaluated by photodegradation of four organic contaminants (rhodamine B, orange G, bisphenol A and pentachlorophenol) as well as water splitting under visible light irradiation. The results show that the photocatalytic activity of N-doped KNbO 3 is significantly higher than that of pure KNbO 3 nanocubes and Degussa TiO 2 P25 under visible light irradiation.
- Published
- 2013
46. A Robust Palladium(II)-Porphyrin Complex as Catalyst for Visible Light Induced Oxidative CH Functionalization
- Author
-
Wai-Pong To, Chi-Ming Che, Yungen Liu, and Tai-Chu Lau
- Subjects
Tertiary amine ,Nitromethane ,Cyanide ,Organic Chemistry ,chemistry.chemical_element ,General Chemistry ,Photochemistry ,Dimethyl malonate ,Catalysis ,chemistry.chemical_compound ,chemistry ,Nucleophile ,Photocatalysis ,Palladium - Abstract
A series of palladium(II)-porphyrin complexes that display dual emissions with lifetimes up to 437 μs have been synthesized. Among the four complexes, PdF20TPP is an efficient and robust catalyst for photoinduced oxidative C-H functionalization by using oxygen as terminal oxidant. α-Functionalized tertiary amines were obtained in good to excellent yields by light irradiation (λ>400 nm) of a mixture of PdF20TPP, tertiary amine, and nucleophile (cyanide, nitromethane, dimethyl malonate, diethyl phosphite, and acetone) under aerobic conditions. Four examples of intramolecular cyclized amine compounds could be similarly prepared. Comparison of the UV-visible absorption spectra before and after the photochemical reaction revealed that PdF20TPP was highly robust (>95 % recovery). The practical application of PdF20TPP has been revealed by the photochemical reactions performed by using a low catalyst loading (0.01 mol %) and on a 10 mmol scale. The PdF20TPP catalyst could sensitize photoinduced oxidation of sulfides to sulfoxides in excellent yields. Mechanistic studies revealed that the photocatalysis proceeded by singlet-oxygen oxidation.
- Published
- 2013
47. Oxidation of hydroquinones by a (salen)ruthenium(vi) nitrido complex
- Author
-
Li Ma, Po-Kam Lo, Tai-Chu Lau, William W. Y. Lam, Shek-Man Yiu, Jianhui Xie, Kai-Chung Lau, and Wai-Lun Man
- Subjects
Hydroquinone ,010405 organic chemistry ,Ligand ,Chemistry ,Metals and Alloys ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,Ring (chemistry) ,Photochemistry ,01 natural sciences ,Benzoquinone ,Catalysis ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Ruthenium ,chemistry.chemical_compound ,Electrophile ,Polymer chemistry ,Pyridine ,Materials Chemistry ,Ceramics and Composites - Abstract
In the presence of pyridine, [RuVI(N)(L)(MeOH)]+ (L = N,N′-bis(salicylidene)-o-cyclohexyldiamine dianion) readily oxidizes hydroquinone to p-benzoquinone under ambient conditions. Experimental and computational studies suggest a mechanism that involves an initial electrophilic attack at the aromatic ring of hydroquinone by the nitrido ligand.
- Published
- 2016
48. Four-Electron Oxidation of Phenols to p-Benzoquinone Imines by a (Salen)ruthenium(VI) Nitrido Complex
- Author
-
Xiaoyong Chang, Wai-Lun Man, Jianhui Xie, Chi-Ming Che, Tai-Chu Lau, and Chun-Yuen Wong
- Subjects
010405 organic chemistry ,Imine ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Medicinal chemistry ,Benzoquinone ,Catalysis ,0104 chemical sciences ,Ruthenium ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Deprotonation ,chemistry ,Intramolecular force ,Pyridine ,Electrophile ,Organic chemistry ,Phenols - Abstract
Proton-coupled electron-transfer reactions of phenols have received considerable attention because of their fundamental interest and their relevance to many biological processes. Here we describe a remarkable four-electron oxidation of phenols by a (salen)ruthenium(VI) complex in the presence of pyridine in CH3OH to afford (salen)ruthenium(II) p-benzoquinone imine complexes. Mechanistic studies indicate that this reaction occurs in two phases. The first phase is proposed to be a two-electron transfer process that involves electrophilic attack by Ru≡N at the phenol aromatic ring, followed by proton shift to generate a Ru(IV) p-hydroxyanilido intermediate. In the second phase the intermediate undergoes intramolecular two-electron transfer, followed by rapid deprotonation to give the Ru(II) p-benzoquinone imine product.
- Published
- 2016
49. Frontispiece: Ca2+ -Induced Oxygen Generation by FeO4 2− at pH 9- 10
- Author
-
Li Ma, Po-Kam Lo, William W. Y. Lam, Tai-Chu Lau, and Kai-Chung Lau
- Subjects
chemistry ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,Lewis acids and bases ,Calcium ,Oxygen ,Catalysis - Published
- 2016
50. Ligand-Accelerated Activation of Strong CH Bonds of Alkanes by a (Salen)ruthenium(VI)-Nitrido Complex
- Author
-
Shek-Man Yiu, Hoi Ki Kwong, Tai-Chu Lau, Wai-Lun Man, and Wai Yan William Lam
- Subjects
Alkane ,chemistry.chemical_classification ,Ligand ,Intermolecular force ,chemistry.chemical_element ,Hydrogen transfer ,General Medicine ,General Chemistry ,Hydrogen atom ,Nitride ,Photochemistry ,Medicinal chemistry ,Catalysis ,Ruthenium ,chemistry - Abstract
Kinetic and mechanistic studies on the intermolecular activation of strong C-H bonds of alkanes by a (salen)ruthenium(VI) nitride were performed. The initial, rate-limiting step, the hydrogen atom transfer (HAT) from the alkane to Ru(VI)≡N, generates Ru(V)=NH and RC·HCH(2)R. The following steps involve N-rebound and desaturation.
- Published
- 2012
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.