A review on g-C3N4-based photocatalysts

Catechols are found in nature taking part in a remarkably broad scope of biochemical processes and functions. Though not exclusively, such versatility may be traced back to several properties uniquely found together in the o-dihydroxyaryl chemical function; namely, its ability to establish reversible equilibria at moderate redox potentials and pHs and to irreversibly cross-link through complex oxidation mechanisms; its excellent chelating properties, greatly exemplified by, but by no means exclusive, to the binding of Fe(3+); and the diverse modes of interaction of the vicinal hydroxyl groups with all kinds of surfaces of remarkably different chemical and physical nature. Thanks to this diversity, catechols can be found either as simple molecular systems, forming part of supramolacular structures, coordinated to different metal ions or as macromolecules mostly arising from polymerization mechanisms through covalent bonds. Such versatility has allowed catechols to participate in several natural processes and functions that range from the adhesive properties of marine organisms to the storage of some transition metal ions. As a result of such an astonishing range of functionalities, catechol-based systems have in recent years been subject to intense research, aimed at mimicking these natural systems in order to develop new functional materials and coatings. A comprehensive review of these studies is discussed in this paper.

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Catechol-Based Biomimetic Functional Materials

Many reviews are written on this interesting visible light active polymeric semiconductor material, the graphitic carbon nitride (g-C3N4). Yet the ever-expanding volume of the ongoing research on this materials has inspired us to compile this review, especially on its nanoscale architectures of noble-metal-free photocatalyst systems. From the viewpoint of sustainable development, an economical photocatalyst which is made up of abundant elements e. g. C and N has a good prospect for large scale applications. Stability of the photocatalyst material under the experimental conditions is essential for its repeated usage, however, many semiconductors sought for visible-light-driven reaction, particularly sulfides and nitrides are in a compromising situation. However, g-C3N4 has high chemical- and photo-stability besides its high activity under visible light irradiation. Furthermore, solely semiconductor materials have the intrinsic problem of recombination of photogenerated electron-hole pairs. To overcome this problem, loading of the semiconductor with a co-catalyst, usually a noble metal is a common practice for transfer of electron and thus avoiding the recombination. Development of a noble-metal-free photocatalyst systems is essentially important for sustainable applications. Hence, the construction of a hybrid composite structure is interesting in the separation of photogenerated charge carriers. Besides diminishing the rate of recombination, the heterostructures are constructed for harnessing a wider spectrum of sunlight. In contrast to bulk semiconductors, their nanoscale counterpart offers a larger number of active sites along with interesting electrical and optical properties. Importantly, construction of extensive junctions between nanomaterials greatly enhance the separation of charges and consequently improve their photocatalytic efficiency. Usually, the stability of materials is compromised with the reduction of size to nano level, however, g-C3N4 and its nanomaterials demonstrate exceptional recycling in photocatalytic testing. One of the most important interests in controlling nanoparticle size, shape and composition is to develop noble-metal-free photocatalyst systems. Here in this review, we have compiled research on all the various applications of noble-metal-free nanoscale photocatalyst systems based on g-C3N4. By the end, we conclude the research topic and put forward future perspectives for further developments in designing practicable photocatalyst systems.

Graphitic C3N4 based noble-metal-free photocatalyst systems: A review

The electrocatalytic properties of multi-walled carbon nanotube modified electrodes toward the oxidation of NADH are critically evaluated. Carbon nanotube modified electrodes are examined and compared with boron-doped diamond and glassy carbon electrodes, and most importantly, edge plane and basal pyrolytic graphite electrodes. It is found that CNT modified electrodes are no more reactive than edge plane pyrolytic graphite electrodes with the comparison with edge plane and basal plane pyrolytic graphite electrodes allowing the electroactive sites for the electrochemical oxidation of NADH to be unambiguously determined as due to edge plane sites. Using these highly reactive edge plane sites, edge plane pyrolytic graphite electrodes are examined with cyclic voltammetry and amperometry for the electroanalytical determination of NADH. It is demonstrated that a detection limit of 5 µM is possible with cyclic voltammetry or 0.3 µM using amperometry suggesting that edge plane pyrolytic graphite electrodes can conveniently replace carbon nanotube modified glassy carbon electrodes for biosensing applications with the relative advantages of reactivity, cost and simplicity of preparation. We advocate the routine use of edge plane and basal plane pyrolytic graphite electrodes in studies utilising carbon nanotubes particularly if ‘electrocatalytic’ properties are claimed for the latter.

Exploring the electrocatalytic sites of carbon nanotubes for NADH detection: an edge plane pyrolytic graphite electrode study

A generalization of the recent version of the statistical associating fluid theory for variable range Mie potentials [Lafitte et al., J. Chem. Phys. 139, 154504 (2013)] is formulated within the framework of a group contribution approach (SAFT-γ Mie). Molecules are represented as comprising distinct functional (chemical) groups based on a fused heteronuclear molecular model, where the interactions between segments are described with the Mie (generalized Lennard-Jonesium) potential of variable attractive and repulsive range. A key feature of the new theory is the accurate description of the monomeric group-group interactions by application of a high-temperature perturbation expansion up to third order. The capabilities of the SAFT-γ Mie approach are exemplified by studying the thermodynamic properties of two chemical families, the n-alkanes and the n-alkyl esters, by developing parameters for the methyl, methylene, and carboxylate functional groups (CH3, CH2, and COO). The approach is shown to describe accurately the fluid-phase behavior of the compounds considered with absolute average deviations of 1.20% and 0.42% for the vapor pressure and saturated liquid density, respectively, which represents a clear improvement over other existing SAFT-based group contribution approaches. The use of Mie potentials to describe the group-group interaction is shown to allow accurate simultaneous descriptions of the fluid-phase behavior and second-order thermodynamic derivative properties of the pure fluids based on a single set of group parameters. Furthermore, the application of the perturbation expansion to third order for the description of the reference monomeric fluid improves the predictions of the theory for the fluid-phase behavior of pure components in the near-critical region. The predictive capabilities of the approach stem from its formulation within a group-contribution formalism: predictions of the fluid-phase behavior and thermodynamic derivative properties of compounds not included in the development of group parameters are demonstrated. The performance of the theory is also critically assessed with predictions of the fluid-phase behavior (vapor-liquid and liquid-liquid equilibria) and excess thermodynamic properties of a variety of binary mixtures, including polymer solutions, where very good agreement with the experimental data is seen, without the need for adjustable mixture parameters.

Group contribution methodology based on the statistical associating fluid theory for heteronuclear molecules formed from Mie segments

Electrocatalytic oxidation of hydrazine at a pyrocatechol violet (PCV) chemically modified electrode

Photocatalytic degradation of different pollutants by the novel gCN-NS/Black-TiO2 heterojunction photocatalyst under visible light: Introducing a photodegradation model and optimization by response surface methodology (RSM)

Electrocatalytic oxidation of nicotinamide adenine dinucleotied (NADH) at a glassy carbon electrode modified with electrodeposited film derived from pyrocatechol violet (PCV) has been studied. The PCV modified glassy carbon electrode shows excellent electrocatalytic activity toward NADH oxidation in phosphate buffer solution (pH 7.0) with an overpotential of about 447 mV lower than that of the bare electrode. The apparent charge transfer rate constant and charge transfer coefficient for electron transfer between the electrode surface and immobilized PCV were calculated as 5.3 s−1 and 0.49, respectively. The catalytic rate constant of the modified glassy carbon electrode for the oxidation of NADH is determined by cyclic voltammetry and rotating disk electrode measurements. Also, it has been shown that using the PCV modified electrode, NADH can be estimated by amperometry with high sensitivity and good limit of detection.

Electrochemistry and Electrocatalytic Activity of Pyrocatechol Violet (PCV) Film on a Glassy Carbon Electrode Towards the Oxidation of Reduced Nicotinamide Adenine Dinucleotide(NADH)

Majid Hamzehloo

Papers

Electrocatalytic oxidation of hydrazine at a pyrocatechol violet (PCV) chemically modified electrode

Photocatalytic degradation of different pollutants by the novel gCN-NS/Black-TiO2 heterojunction photocatalyst under visible light: Introducing a photodegradation model and optimization by response surface methodology (RSM)

Electrochemistry and Electrocatalytic Activity of Pyrocatechol Violet (PCV) Film on a Glassy Carbon Electrode Towards the Oxidation of Reduced Nicotinamide Adenine Dinucleotide(NADH)

Direct C-H trifluoromethylthiolation of (hetero)arenes: A review

RSM optimized adsorptive removal of erythromycin using magnetic activated carbon: Adsorption isotherm, kinetic modeling and thermodynamic studies