Studies on the heterogeneous electron transport and oxygen reduction reaction at metal (Co, Fe) octabutylsulphonylphthalocyanines supported on multi-walled carbon nanotube modified graphite electrode

Colloidal metal nanocatalysts to advance orange II hydrogenolysis tracked by a microplate reader

The thermal reduction method was applied to synthesize metal nanoparticles using poly(1-vinyl-2-pyrrolidone) as an organic stabilizer to control metal nanoparticle agglomeration. Colloidal metal nanoparticles, gold, palladium, and gold–palladium nanoparticles were synthesized, and UV–visible spectrophotometry and high-resolution transmission electron microscopy analyses were conducted to characterize them. The metal nanoparticle micrographs showed well-dispersed particles with an average size of 9.6 nm (Au), 15.4 nm (Pd), and 10.6 nm (AuPd). All the colloidal metal nanoparticles served as nanocatalysts to advance a reductive degradation of orange II in presence of borohydride ions. For a prompt screening of catalytic activity, the microplate reader system was considered at a fixed maximum absorbance wavelength of λ 489 nm respected by orange II. Excess borohydride ions were used to construct pseudo-first kinetic conditions. The Langmuir–Hinshelwood model allowed the finding of kinetic activity on the surface of metal nanoparticles. AuPd nanocatalyst interface exhibited low activation energy (5.38 kJ mol−1) compared to the one on Au (8.19 kJ mol−1) and Pd (7.23 kJ mol−1).

Graphical Abstract

Electrochemical biosensor with aptamer/porous platinum nanoparticle on round-type micro-gap electrode for saxitoxin detection in fresh water

Cyanotoxins are toxins produced by cyanobacteria; they negatively impact water resources used by humans and disrupt ecosystems worldwide. Among cyanotoxins, saxitoxin (STX) is a small molecule that causes paralysis in humans and contamination in freshwater resources. To monitor low concentration of STX levels, a sensitive and high fidelity detection system is required. In this study, a round-type micro-gap electrode (RMGE) was fabricated that provides the high signal fidelity for STX detection in real freshwater sample. The RMGE has the 15 pairs of identical electrode wire length between gap that gives the high signal fidelity. In addition, the sensitivity for STX detection was improved by introducing the porous platinum nanoparticle (pPtNP) that enahced the electrochemical sensitivity and the STX aptamer was used as the bioprobe. An electrochemical measurement method (square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS)) was introduced to construct STX biosensor. To evaluate the biosensor performance, the limit of detection (LOD) and selectivity test were performed on real freshwater samples. The biosensor demonstrated high selectivity even in freshwater samples over a wide linear concentration range of 10 pg/mL to 1 μg/mL and a detection limit of 4.669 pg/mL. These results suggest that the designed biosensor shows a wide range of possibilities for the detection of toxicants in freshwater that provide the new direction to the biosensor electrode design.

Mononuclear Fe in N-doped carbon: computational elucidation of active sites for electrochemical oxygen reduction and oxygen evolution reactions

First principles simulations show that in Fe and N co-doped carbon, Fe coordination controls the activity for oxygen reduction and oxygen evolution reactions, and that including the electrostatic potential has a major influence at high potential.

Electrocatalytic behavior of single walled carbon nanotubes with alkylthio-substituted cobalt binuclear phthalocyanines towards oxidation of 4-chlorophenols

This work describes the adsorption of synthesized cobalt mono (CoPc) and binuclear phthalocyanines (CoBiPc) with single walled carbon nanotubes (SWCNT) to form SWCNT-CoPc or SWCNT-CoBiPc as non-covalent conjugates onto glassy carbon electrodes (GCE). The cobalt complexes and their SWCNT-conjugate-modified electrodes were studied for their electrocatalytic oxidation towards 4-chlorophenol. All modified electrodes showed improved catalytic current and stability towards the detection of 4-chlorophenol. The best activity was observed for the SWCNT-CoBiPc2 system in terms of current response and the SWCNT-CoBiPc1 system in terms of resistance to electrode fouling.

Relevance of the Interaction between the M-Phthalocyanines and Carbon Nanotubes in the Electroactivity toward ORR

In this work, the influence of the interaction between the iron and cobalt-phthalocyanines (FePc and CoPc) and carbon nanotubes (CNTs) used as support in the electroactivity toward oxygen reduction reaction (ORR) in alkaline media has been investigated. A series of thermal treatments were performed on these materials in order to modify the interaction between the CNTs and the phthalocyanines. The FePc-based catalysts showed the highest activity, with comparable performance to the state-of-the-art Pt-Vulcan catalyst. A heat treatment at 400 °C improved the activity of FePc-based catalysts, while the use of higher temperatures or oxidative atmosphere rendered the decomposition of the macrocyclic compound and consequently the loss of the electrochemical activity of the complex. CoPc-based catalysts performance was negatively affected for all of the tested treatments. Thermogravimetric analyses demonstrated that the FePc was stabilized when loaded onto CNTs, while CoPc did not show such a feature, pointing to a better interaction of the FePc instead of the CoPc. Interestingly, electrochemical measurements demonstrated an improvement of the electron transfer rate in thermally treated FePc-based catalysts. They also allowed us to assess that only 15% of the iron in the catalyst was available for direct electron transfer. This is the same iron amount that remains on the catalyst after a strong acid washing with concentrated HCl (ca. 0.3 wt %), which is enough to deliver a comparable ORR activity. Durability tests confirmed that the catalysts deactivation occurs at a slower rate in those catalysts where FePc is strongly attached to the CNT surface. Thus, the highest ORR activity seems to be provided by those FePc molecules that are strongly attached to the CNT surface, pointing out the relevance of the interaction between the support and the FePc in these catalysts.

Improved Cl2 sensing characteristics of reduced graphene oxide when decorated with copper phthalocyanine nanoflowers

A novel gas sensing platform involving a hybrid of reduced graphene oxide (rGO) sheets with unsubstituted copper phthalocyanine (CuPc) nanoflowers has been explored as a room temperature ppb level chemiresistive chlorine (Cl₂) sensor with a detection limit as low as 1.97 ppb.

Multifunctional copper dimer: structure, band gap energy, catalysis, magnetism, oxygen reduction reaction and proton conductivity

A new copper dimeric complex has been synthesized, characterized and used as a multifunctional material.

Oxygen reduction reaction at MWCNT-modified nanoscale iron(ii) tetrasulfophthalocyanine: remarkable performance over platinum and tolerance toward methanol in alkaline medium

A novel nanoscale iron(ii) tetrasulfophthalocyanine complex catalyzes oxygen reduction reaction in alkaline medium more efficiently than the expensive state-of-the-art Pt catalyst.

Electrocatalytic activity of metalloporphyrins grown in situ on graphene sheets toward oxygen reduction reaction in an alkaline medium

A series of novel non-noble-metal catalysts for ORR, based on metalloporphyrins grown on poly(sodium-p-styrenesulfonate) modified reduced graphene oxide sheets, have been successfully fabricated using an in situ solvothermal synthesis method.

Electrochemical characterization of dilithium phthalocyanine carbonaceous electrodes

Carbonaceous electrodes of dilithium phthalocyanine were prepared using graphite, carbon microspheres and multiwall carbon nanotubes. The electrochemical behavior of the dilithium bisphthalocyanine electrodes was found to be dependent on the nature of the carbonaceous material and on the nature of the electrolytic solution. The electrocatalytic properties of the dilithium phthalocyanine electrodes for oxidation of ascorbic acid were evidenced by the enhancement of the oxidation peak current, (~10 fold compared to the bare carbon electrodes) and the decrease of the oxidation potential at which oxidation of ascorbic acid takes place. The combined use of multiwall carbon nanotubes and dilithium phthalocyanine produces a synergistic effect that improves the electrocatalytic effect towards ascorbic acid.

Self-assembly of tetrakis (3-trifluoromethylphenoxy) phthalocyaninato cobalt(II) on multiwalled carbon nanotubes and their amperometric sensing application for nitrite

In this work, the soluble cobalt phthalocyanine functionalized multiwalled carbon nanotubes (MWCNTs) are synthesized by π-π stacking interaction between tetrakis (3-trifluoromethylphenoxy) phthalocyaninato cobalt(II) (CoPcF) complex and MWCNTs. The physical properties of CoPcF-MWCNTs hybrids are evaluated using spectroscopy (UV-vis, XPS, and Raman) and electron microscopy (TEM and SEM). Subsequently, an amperometric nitrite electrochemical sensor is designed by immobilizing CoPcF-MWCNTs hybrids on the glassy carbon electrode. The immobilized CoPcF complex shows the fast electron transfer rate and excellent electrocatalytic activity for the oxidation of nitrite. Under optimum experimental conditions, the proposed nitrite electrochemical sensor shows the fast response (less than 2 s), wide linear range (9.6 × 10(-8) to 3.4 × 10(-4) M) and low detection limit (6.2 × 10(-8) M) because of the good mass transport, fast electron transfer rate, and excellent electrocatalytic activity.

Direct growth of carbon nanofibers to generate a 3D porous platform on a metal contact to enable an oxygen reduction reaction

For carbon nanotube-based electronics to achieve their full performance potential, it is imperative to minimize the contact resistance between macroscale metal contacts and the carbon nanotube (CNT) nanoelectrodes. We have developed a three-dimensional electrode platform that consists of carbon nanofibers (CNFs) that are directly grown on a metal contact, such as copper (Cu). Carbon nanofiber morphology can be tailored by adjusting the annealing time of a thin electrochemically deposited nickel catalyst layer on copper. We demonstrate that increasing the annealing time increases the amount of copper infused into the nickel catalyst layer. This reduces the carbon deposition rate, and consequently a more well-defined CNF 3D architecture can be fabricated. This direct growth of CNFs on a Cu substrate yields an excellent electron transfer pathway, with contact resistance between CNFs and Cu being comparable to that of a Cu-Cu interface. Furthermore, the excellent bonding strength between CNFs and Cu can be maintained over prolonged periods of ultrasonication. The porous 3D platform affixed with intertwined CNFs allows facile surface functionalization. Using a simple solution soaking procedure, the CNF surface has been successfully functionalized with iron(II) phthalocyanine (FePc). FePc functionalized CNFs exhibit excellent oxygen reduction capability, equivalent to platinum-carbon electrodes. This result demonstrates the technological promise of this new 3D electrode platform that can be exploited in other applications that include sensing, battery, and supercapacitors.

Carbon nanotubes and metalloporphyrins and metallophthalocyanines-based materials for electroanalysis

We discuss here the state of the art on hybrid materials made from single (SWCNT) or multi (MWCNT) walled carbon nanotubes and MN4complexes such as metalloporphyrins and metallophthalocyanines. The hybrid materials have been characterized by several methods such as cyclic voltammetry (CV), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and scanning electrochemical microscropy (SECM). The materials are employed for electrocatalysis of reactions such as oxygen and hydrogen peroxide reduction, nitric oxide oxidation, oxidation of thiols and other pollutants.

Electrochemical reduction of carbon dioxide in an MFC-MEC system with a layer-by-layer self-assembly carbon nanotube/cobalt phthalocyanine modified electrode

Electrochemical reduction of carbon dioxide (CO(2)) to useful chemical materials is of great significance to the virtuous cycle of CO(2). However, some problems such as high overpotential, high applied voltage, and high energy consumption exist in the course of the conventional electrochemical reduction process. This study presents a new CO(2) reduction technique for targeted production of formic acid in a microbial electrolysis cell (MEC) driven by a microbial fuel cell (MFC). The multiwalled carbon nanotubes (MWCNT) and cobalt tetra-amino phthalocyanine (CoTAPc) composite modified electrode was fabricated by the layer-by-layer (LBL) self-assembly technique. The new electrodes significantly decreased the overpotential of CO(2) reduction, and as cathode successfully reduced CO(2) to formic acid (production rate of up to 21.0 ± 0.2 mg·L(-1)·h(-1)) in an MEC driven by a single MFC. Compared with the electrode modified by CoTAPc alone, the MWCNT/CoTAPc composite modified electrode could increase the current and formic acid production rate by approximately 20% and 100%, respectively. The Faraday efficiency for formic acid production depended on the cathode potential. The MWCNT/CoTAPc composite electrode reached the maximum Faraday efficiency at the cathode potential of ca. -0.5 V vs Ag/AgCl. Increasing the number of electrode modification layers favored the current and formic acid production rate. The production of formic acid was stable in the MFC-MEC system after multiple batches of CO(2) electrolysis, and no significant change was observed on the performances of the modified electrode. The coupling of the catalytic electrode and the bioelectrochemical system realized the targeted reduction of CO(2) in the absence of external energy input, providing a new way for CO(2) capture and conversion.

Single walled carbon nanotubes functionalized with nickel phthalocyanines: effects of point of substitution and nature of functionalization on the electro-oxidation of 4-chlorophenol

In this work we report on electrochemical behavior of nickel phthalocyanine derivatives tetrasubstituted peripherally and non-peripherally with hydroxy and used to modify single walled carbon nanotubes. Nickel phthalocyanine complex octasubstituted at the peripheral positions with hydroxy groups was also used to modify single walled carbon nanotubes. Nickel phthalocyanine complex tetrasubstituted with amino groups at peripheral position was covalently and non-covalently linked to single walled carbon nanotubes. All the conjugates of nickel phthalocyanine derivatives with single walled carbon nanotubes were used for the electro oxidation of 4-chlorophenol. The nickel phthalocyanine octabsubstituted with hydroxy groups at the non-peripheral positions gave the best current response and the best resistance against electrode fouling for the oxidation of 4-chlorophenol.

CHARACTERIZATION OF QUANTUM DOTS, SINGLE WALLED CARBON NANOTUBES AND NICKEL OCTADECYLPHTHALOCYANINE CONJUGATES

In this work nickel octadecylphthalocyanine (NiPc(C10H21)8) and cadmium telluride quantum dots (QDs) capped with thioglycolic acid (TGA) are adsorbed on single walled carbon nanotubes (SWCNT) to form NiPc(C10H21)8 -SWCNT-QDs conjugate. X-ray photoelectron, ultra violet/visible and Raman spectroscopies are used to characterize the conjugate. SWCNT, poly- Ni(O)Pc(C10H21)8 , NiPc(C10H21)8 -SWCNT and NiPc(C10H21)8 -SWCNT-QDs complexes are used to modify glassy carbon electrode (GCE) and used for the electro-oxidation of pentachlorophenol as a test molecule. NiPc(C10H21)8 -SWCNT-QDs electrode gave the best detection current for pentachlorophenol.