Electrocatalytic detection of l-cysteine using molybdenum POM doped-HKUST-1 metal organic frameworks
- Murinzi, Tafadzwa W, Watkins, Gareth M, Shumba, Munyaradzi, Nyokong, Tebello
- Authors: Murinzi, Tafadzwa W , Watkins, Gareth M , Shumba, Munyaradzi , Nyokong, Tebello
- Date: 2021
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/185748 , vital:44420 , xlink:href="https://doi.org/10.1080/00958972.2021.1907573"
- Description: Glass carbon electrodes (GCE) were modified with metal organic frameworks (MOFs) containing molybdenum polyoxometallates (Mo POMs) in a copper benzene tricarboxylate framework (HKUST-1). The Mo POMs were introduced via one-pot synthesis (Mo2) and post-synthetic modification (Mo1) techniques. The electrode modifiers were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermal analysis. The modified electrodes’ oxidation capacity toward L-cysteine was studied. Mo POMs significantly improved electron transfer kinetics compared to the bare GCE. The best Mo POM doped electrode (Mo1-GCE) had a catalytic rate constant of 2.2 × 104 M−1 s−1 and a limit of detection of 3.07 × 10−7 M. Under the employed experimental conditions, the detection response for L-cysteine was very fast (within 0.1 s) for all the modified electrodes and selective toward L-cysteine in the presence of other amino acids.
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Electrocatalytic detection of l-cysteine using molybdenum POM doped-HKUST-1 metal organic frameworks
- Authors: Murinzi, Tafadzwa W , Watkins, Gareth M , Shumba, Munyaradzi , Nyokong, Tebello
- Date: 2021
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/185748 , vital:44420 , xlink:href="https://doi.org/10.1080/00958972.2021.1907573"
- Description: Glass carbon electrodes (GCE) were modified with metal organic frameworks (MOFs) containing molybdenum polyoxometallates (Mo POMs) in a copper benzene tricarboxylate framework (HKUST-1). The Mo POMs were introduced via one-pot synthesis (Mo2) and post-synthetic modification (Mo1) techniques. The electrode modifiers were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermal analysis. The modified electrodes’ oxidation capacity toward L-cysteine was studied. Mo POMs significantly improved electron transfer kinetics compared to the bare GCE. The best Mo POM doped electrode (Mo1-GCE) had a catalytic rate constant of 2.2 × 104 M−1 s−1 and a limit of detection of 3.07 × 10−7 M. Under the employed experimental conditions, the detection response for L-cysteine was very fast (within 0.1 s) for all the modified electrodes and selective toward L-cysteine in the presence of other amino acids.
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Nanocomposites of sulphur-nitrogen co-doped graphene oxide nanosheets and cobalt mono carboxyphenoxy phthalocyanines for facile electrocatalysis
- Shumba, Munyaradzi, Centane, Sixolile, Chindeka, Francis, Nyokong, Tebello
- Authors: Shumba, Munyaradzi , Centane, Sixolile , Chindeka, Francis , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/239665 , vital:50753 , xlink:href="https://doi.org/10.1016/j.jelechem.2017.03.006"
- Description: Nanocomposites consisting of cobalt mono carboxyphenoxy phthalocyanine (CoMCPhPc) either covalently linked to graphene oxide nanosheets (GONS), sulphur doped graphene oxide nanosheets (SDGONS), nitrogen doped graphene oxide nanosheets (NDGONS) or sulphur/nitrogen co-doped graphene oxide nanosheets (SNDGONS) or sequentially added were used to modify glassy carbon electrode. The modified electrodes were characterised using several techniques: voltammetry, X-ray photon spectroscopy and scanning electron spectroscopy before testing their activity on the detection of hydrogen peroxide at pH 7. The presence of SNDGONS had a significant improvement on the currents as compared to CoMCPhPc modification alone in both sequentially added or covalently linked to MPcs. CoMCPhPc-SNDGONS(seq)-GCE and CoMCPhPc-SDGONS(linked)-GCE resulted in impressive limits of detection and catalytic rate constant values of 1.58 nM and 5.44 nM, 3.07 × 105 M−1 s−1 and 3.01 × 103 M−1 s−1 respectively. Gibbs energy value was determined to be −21.22 kJ mol−1 for CoMCPhPc-SNDGONS(linked)-GCE indicative of a facile spontaneous electroreduction reaction on the surface of this electrode.
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- Authors: Shumba, Munyaradzi , Centane, Sixolile , Chindeka, Francis , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/239665 , vital:50753 , xlink:href="https://doi.org/10.1016/j.jelechem.2017.03.006"
- Description: Nanocomposites consisting of cobalt mono carboxyphenoxy phthalocyanine (CoMCPhPc) either covalently linked to graphene oxide nanosheets (GONS), sulphur doped graphene oxide nanosheets (SDGONS), nitrogen doped graphene oxide nanosheets (NDGONS) or sulphur/nitrogen co-doped graphene oxide nanosheets (SNDGONS) or sequentially added were used to modify glassy carbon electrode. The modified electrodes were characterised using several techniques: voltammetry, X-ray photon spectroscopy and scanning electron spectroscopy before testing their activity on the detection of hydrogen peroxide at pH 7. The presence of SNDGONS had a significant improvement on the currents as compared to CoMCPhPc modification alone in both sequentially added or covalently linked to MPcs. CoMCPhPc-SNDGONS(seq)-GCE and CoMCPhPc-SDGONS(linked)-GCE resulted in impressive limits of detection and catalytic rate constant values of 1.58 nM and 5.44 nM, 3.07 × 105 M−1 s−1 and 3.01 × 103 M−1 s−1 respectively. Gibbs energy value was determined to be −21.22 kJ mol−1 for CoMCPhPc-SNDGONS(linked)-GCE indicative of a facile spontaneous electroreduction reaction on the surface of this electrode.
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Characterization and Electrocatalytic Activity of Nanocomposites Consisting of Nanosized Cobalt Tetraaminophenoxy Phthalocyanine, Multi‐walled Carbon Nanotubes and Gold Nanoparticles
- Shumba, Munyaradzi, Nyokong, Tebello
- Authors: Shumba, Munyaradzi , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188659 , vital:44773 , xlink:href="https://doi.org/10.1002/elan.201501058"
- Description: Glassy carbon electrodes were modified with composites containing cobalt tetraaminophenoxy phthalocyanine nanoparticles (CoTAPhPcNP), multi-walled carbon nanotubes (MWCNT) and gold nanorods (AuNRs). The modified electrodes were studied for their electrocatalytic behavior towards the reduction of hydrogen peroxide. Phthalocyanine nanoparticles significantly improved electron transfer kinetics as compared to phthalocyanines which are not in the nanoparticle form when alone or in the presence of multiwalled carbon nanotubes (MWCNTs). CoTAPhPcNP-MWCNT-GCE proved to be suitable for hydrogen peroxide detection with a catalytic rate constant of 3.45×103 M−1 s−1 and a detection limit of 1.61×10−7 M. Adsorption Gibbs free energy ΔGo was found to be −19.22 kJ mol−1 for CoTAPhPcNP-MWCNT-GCE.
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- Authors: Shumba, Munyaradzi , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188659 , vital:44773 , xlink:href="https://doi.org/10.1002/elan.201501058"
- Description: Glassy carbon electrodes were modified with composites containing cobalt tetraaminophenoxy phthalocyanine nanoparticles (CoTAPhPcNP), multi-walled carbon nanotubes (MWCNT) and gold nanorods (AuNRs). The modified electrodes were studied for their electrocatalytic behavior towards the reduction of hydrogen peroxide. Phthalocyanine nanoparticles significantly improved electron transfer kinetics as compared to phthalocyanines which are not in the nanoparticle form when alone or in the presence of multiwalled carbon nanotubes (MWCNTs). CoTAPhPcNP-MWCNT-GCE proved to be suitable for hydrogen peroxide detection with a catalytic rate constant of 3.45×103 M−1 s−1 and a detection limit of 1.61×10−7 M. Adsorption Gibbs free energy ΔGo was found to be −19.22 kJ mol−1 for CoTAPhPcNP-MWCNT-GCE.
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Electrocatalytic activity of nanocomposites of sulphur doped graphene oxide and nanosized cobalt phthalocyanines
- Shumba, Munyaradzi, Nyokong, Tebello
- Authors: Shumba, Munyaradzi , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188530 , vital:44762 , xlink:href="https://doi.org/10.1002/elan.201600226"
- Description: In this work we explore the electrocatalytic activity of nanocomposites of reduced sulphur doped graphene oxide nanosheets (rSDGONS) and cobalt phthalocyanine (CoPc) or cobalt tetra amino phthalocyanine (CoTAPc) towards hydrogen peroxide. Transmission electron microscopy, scanning electron microscopy, X-ray photon spectroscopy, X-ray diffraction, chronoamperometry, linear scan voltammetry and cyclic voltammetry were used to characterize the nanocomposites. Nanosized CoPc showed superior (in terms of currents) electrocatalytic oxidation and reduction of hydrogen peroxide compared to CoTAPc nanoparticles (CoTAPcNP). The lowest detection limit was obtained for hydrogen peroxide oxidation on electrodes modified with CoPcNP-rSDGONS at 1.49 µM. The same electrode gave a high adsorption equilibrium constant of 1.27×103 mol−1 and a Gibbs free energy of −17.71 kJ/mol, indicative of a spontaneous reaction on the electrode surface.
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- Authors: Shumba, Munyaradzi , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188530 , vital:44762 , xlink:href="https://doi.org/10.1002/elan.201600226"
- Description: In this work we explore the electrocatalytic activity of nanocomposites of reduced sulphur doped graphene oxide nanosheets (rSDGONS) and cobalt phthalocyanine (CoPc) or cobalt tetra amino phthalocyanine (CoTAPc) towards hydrogen peroxide. Transmission electron microscopy, scanning electron microscopy, X-ray photon spectroscopy, X-ray diffraction, chronoamperometry, linear scan voltammetry and cyclic voltammetry were used to characterize the nanocomposites. Nanosized CoPc showed superior (in terms of currents) electrocatalytic oxidation and reduction of hydrogen peroxide compared to CoTAPc nanoparticles (CoTAPcNP). The lowest detection limit was obtained for hydrogen peroxide oxidation on electrodes modified with CoPcNP-rSDGONS at 1.49 µM. The same electrode gave a high adsorption equilibrium constant of 1.27×103 mol−1 and a Gibbs free energy of −17.71 kJ/mol, indicative of a spontaneous reaction on the electrode surface.
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Electrode modification using nanocomposites of boron or nitrogen doped graphene oxide and cobalt (II) tetra aminophenoxy phthalocyanine nanoparticles
- Shumba, Munyaradzi, Nyokong, Tebello
- Authors: Shumba, Munyaradzi , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188699 , vital:44777 , xlink:href="https://doi.org/10.1016/j.electacta.2016.02.166"
- Description: Reduced graphene oxide nanosheets (rGONS), reduced boron doped graphene oxide nanosheets (rBDGONS) and reduced nitrogen doped graphene oxide nanosheets (rNDGONS) and their composites with cobalt tetra aminophenoxy phthalocyanine nanoparticles (CoTAPhPcNP) were employed towards the detection of hydrogen peroxide. The nanomaterials were characterized by absorption spectroscopy, transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, linear sweep voltammetry and cyclic voltammetry. rNDGONS showed excellent electrooxidation and electroreduction of hydrogen peroxide supported by superior surface coverage values. The inclusion of nanosized Pc significantly lowered the reduction overpotential. CoTAPhPcNP-rNDGONS-GCE gave a sensitivity of 39.30 mA/M, catalytic rate constant of 1 × 103 M−1 s−1 and a detection limit of 8.2 nM. An adsorption equilibrium constant and Gibbs free energy of 1.26 × 103 M−1 and −17.69 kJ mol−1 respectively were observed.
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- Authors: Shumba, Munyaradzi , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188699 , vital:44777 , xlink:href="https://doi.org/10.1016/j.electacta.2016.02.166"
- Description: Reduced graphene oxide nanosheets (rGONS), reduced boron doped graphene oxide nanosheets (rBDGONS) and reduced nitrogen doped graphene oxide nanosheets (rNDGONS) and their composites with cobalt tetra aminophenoxy phthalocyanine nanoparticles (CoTAPhPcNP) were employed towards the detection of hydrogen peroxide. The nanomaterials were characterized by absorption spectroscopy, transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, linear sweep voltammetry and cyclic voltammetry. rNDGONS showed excellent electrooxidation and electroreduction of hydrogen peroxide supported by superior surface coverage values. The inclusion of nanosized Pc significantly lowered the reduction overpotential. CoTAPhPcNP-rNDGONS-GCE gave a sensitivity of 39.30 mA/M, catalytic rate constant of 1 × 103 M−1 s−1 and a detection limit of 8.2 nM. An adsorption equilibrium constant and Gibbs free energy of 1.26 × 103 M−1 and −17.69 kJ mol−1 respectively were observed.
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“Turn on” fluorescence enhancement of Zn octacarboxyphthaloyanine-graphene oxide conjugates by hydrogen peroxide
- Shumba, Munyaradzi, Mashazi, Philani N, Nyokong, Tebello
- Authors: Shumba, Munyaradzi , Mashazi, Philani N , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/190438 , vital:44994 , xlink:href="https://doi.org/10.1016/j.jlumin.2015.11.001"
- Description: Zn octacarboxy phthalocyanine-reduced graphene oxide or graphene oxide conjugates were characterized by absorption spectroscopy, transmission electron microscopy, fluorescence spectroscopy, X-ray diffraction, thermo gravimetric analysis and X-ray photon spectroscopy. The presence of reduced graphene oxide or graphene oxide resulted in the quenching (turn on) of Zn octacarboxy phthalocyanine fluorescence which can be explained by photoinduced electron transfer. Zn octacarboxy phthalocyaninereduced graphene oxide or graphene oxide conjugates “turned on” fluorescence showed a linear response to hydrogen peroxide hence their potential to be used as sensors. The nanoprobe developed showed high selectivity towards hydrogen peroxide in the presence of physiological interferences.
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- Authors: Shumba, Munyaradzi , Mashazi, Philani N , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/190438 , vital:44994 , xlink:href="https://doi.org/10.1016/j.jlumin.2015.11.001"
- Description: Zn octacarboxy phthalocyanine-reduced graphene oxide or graphene oxide conjugates were characterized by absorption spectroscopy, transmission electron microscopy, fluorescence spectroscopy, X-ray diffraction, thermo gravimetric analysis and X-ray photon spectroscopy. The presence of reduced graphene oxide or graphene oxide resulted in the quenching (turn on) of Zn octacarboxy phthalocyanine fluorescence which can be explained by photoinduced electron transfer. Zn octacarboxy phthalocyaninereduced graphene oxide or graphene oxide conjugates “turned on” fluorescence showed a linear response to hydrogen peroxide hence their potential to be used as sensors. The nanoprobe developed showed high selectivity towards hydrogen peroxide in the presence of physiological interferences.
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“Turn on” fluorescence enhancement of Zn octacarboxyphthaloyanine-graphene oxide conjugates by hydrogen peroxide
- Shumba, Munyaradzi, Mashazi, Philani N, Nyokong, Tebello
- Authors: Shumba, Munyaradzi , Mashazi, Philani N , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/240875 , vital:50881 , xlink:href="https://doi.org/10.1016/j.jlumin.2015.11.001"
- Description: Zn octacarboxy phthalocyanine-reduced graphene oxide or graphene oxide conjugates were characterized by absorption spectroscopy, transmission electron microscopy, fluorescence spectroscopy, X-ray diffraction, thermo gravimetric analysis and X-ray photon spectroscopy. The presence of reduced graphene oxide or graphene oxide resulted in the quenching (turn on) of Zn octacarboxy phthalocyanine fluorescence which can be explained by photoinduced electron transfer. Zn octacarboxy phthalocyanine-reduced graphene oxide or graphene oxide conjugates “turned on” fluorescence showed a linear response to hydrogen peroxide hence their potential to be used as sensors. The nanoprobe developed showed high selectivity towards hydrogen peroxide in the presence of physiological interferences.
- Full Text:
- Authors: Shumba, Munyaradzi , Mashazi, Philani N , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/240875 , vital:50881 , xlink:href="https://doi.org/10.1016/j.jlumin.2015.11.001"
- Description: Zn octacarboxy phthalocyanine-reduced graphene oxide or graphene oxide conjugates were characterized by absorption spectroscopy, transmission electron microscopy, fluorescence spectroscopy, X-ray diffraction, thermo gravimetric analysis and X-ray photon spectroscopy. The presence of reduced graphene oxide or graphene oxide resulted in the quenching (turn on) of Zn octacarboxy phthalocyanine fluorescence which can be explained by photoinduced electron transfer. Zn octacarboxy phthalocyanine-reduced graphene oxide or graphene oxide conjugates “turned on” fluorescence showed a linear response to hydrogen peroxide hence their potential to be used as sensors. The nanoprobe developed showed high selectivity towards hydrogen peroxide in the presence of physiological interferences.
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