The origin of high electrocatalytic activity of hydrogen peroxide reduction reaction by a g-C3N4/HOPG sensor

Two-Dimensional Graphitic Carbon Nitride (g-C3N4) Nanosheets and Their Derivatives for Diagnosis and Detection Applications

The early diagnosis of certain fatal diseases is vital for preventing severe consequences and contributes to a more effective treatment. Despite numerous conventional methods to realize this goal, employing nanobiosensors is a novel approach that provides a fast and precise detection. Recently, nanomaterials have been widely applied as biosensors with distinctive features. Graphite phase carbon nitride (g-C₃N₄) is a two-dimensional (2D) carbon-based nanostructure that has received attention in biosensing. Biocompatibility, biodegradability, semiconductivity, high photoluminescence yield, low-cost synthesis, easy production process, antimicrobial activity, and high stability are prominent properties that have rendered g-C₃N₄ a promising candidate to be used in electrochemical, optical, and other kinds of biosensors. This review presents the g-C₃N₄ unique features, synthesis methods, and g-C₃N₄-based nanomaterials. In addition, recent relevant studies on using g-C₃N₄ in biosensors in regard to improving treatment pathways are reviewed.

Low Platinum-Content Electrocatalysts for Highly Sensitive Detection of Endogenously Released H2O2

The commercial viability of electrochemical sensors requires high catalytic efficiency electrode materials. A sluggish reaction of the sensor’s primary target species will require a high overpotential and, consequently, an excessive load of catalyst material to be used. Therefore, it is essential to understand nanocatalysts’ fundamental structures and typical catalytic properties to choose the most efficient material according to the biosensor target species. Catalytic activities of Pt-based catalysts have been significantly improved over the decades. Thus, electrodes using platinum nanocatalysts have demonstrated high power densities, with Pt loading considerably reduced on the electrodes. The high surface-to-volume ratio, higher electron transfer rate, and the simple functionalisation process are the main reasons that transition metal NPs have gained much attention in constructing high-sensitivity sensors. This study has designed to describe and highlight the performances of the different Pt-based bimetallic nanoparticles and alloys as an enzyme-free catalytic material for the sensitive electrochemical detection of H₂O₂. The current analysis may provide a promising platform for the prospective construction of Pt-based electrodes and their affinity matrix.

Electrodes and electrocatalysts for electrochemical hydrogen peroxide sensors: a review of design strategies

H₂O₂ sensing is required in various biological and industrial applications, for which electrochemical sensing is a promising choice among various sensing technologies. Electrodes and electrocatalysts strongly influence the performance of electrochemical H₂O₂ sensors. Significant efforts have been devoted to electrode nanostructural designs and nanomaterial-based electrocatalysts. Here, we review the design strategies for electrodes and electrocatalysts used in electrochemical H₂O₂ sensors. We first summarize electrodes in different structures, including rotation disc electrodes, freestanding electrodes, all-in-one electrodes, and representative commercial H₂O₂ probes. Next, we discuss the design strategies used in recent studies to increase the number of active sites and intrinsic activities of electrocatalysts for H₂O₂ redox reactions, including nanoscale pore structuring, conductive supports, reducing the catalyst size, alloying, doping, and tuning the crystal facets. Finally, we provide our perspectives on the future research directions in creating nanoscale structures and nanomaterials to enable advanced electrochemical H₂O₂ sensors in practical applications.

Nanosilver and protonated carbon nitride co-coated carbon cloth fibers based non-enzymatic electrochemical sensor for determination of carcinogenic nitrite

A novel electrochemical nitrite (NaNO₂) sensor was fabricated by combining nanosilver with protonated carbon nitride (H-C₃N₄) supported on carbon cloth (CC). H-C₃N₄ was distributed uniformly on the CC surface, providing more active sites for the electrocatalytic active center (nanosilver). CC as a substrate improved the H-C₃N₄ conductivity and provided the sensor with a flexible feature. The strong synergistic effect between CC, H-C₃N₄, and nanosilver can exert a significant electrocatalytic performance on the flexible sensor. The Ag/H-C₃N₄/CC flexible sensor electrode did not consume much more time to polish the surface of traditional electrodes, and possessed a high sensitivity of 0.85537 μA/mg, a wide linear response range that spanned 5 to 1000 μM, a low detection limit of 0.216 μM (S/N = 3), and high selectivity for nitrite in the presence of common organic and inorganic interfering species (such as CaCl₂, NaCl, MgCl₂, NaNO₃, glucose, urea, and p-nitrophenol). The Ag/H-C₃N₄/CC flexible sensor can be used for sample detection of nitrite as it has a strong anti-interference ability, good reproducibility, repeatability, and long-term stability. The Ag/H-C₃N₄/CC sensor is a promising alternative electrode to traditional ones such as ITO, gold or glassy carbon electrodes.

Strategy to boost catalytic activity of polymeric carbon nitride: synergistic effect of controllable in situ surface engineering and morphology

Polymeric carbon nitride (CN) is a promising metal-free catalyst plagued by a low intrinsic activity. Herein, a novel strategy based on controllable in situ surface engineering and morphology was developed to synergistically boost the catalytic activity of CN by tuning the hydroxyl groups on its surface and constructing a unique nanostructure. The controllable introduction of hydroxyl groups on CN nanoshells, prepared by the thermal condensation of oxygen-containing supramolecular precursors formed in water, led to spatial separation of the HOMO and LUMO, and effective exciton dissociation, as verified by experiments and ab initio calculations. Furthermore, the hollow hemispherical nanoshell endowed more exposed active sites, optimal mass transport, and dynamic modulations. The optimized hollow hemispherical CN nanoshells exhibited remarkable catalytic activity, with a photoelectrocatalytic OER overpotential of about 330 mV at a current density of 10 mA cm^-2, outperforming state-of-the-art precious-metal catalyst IrO₂. High activity for the visible-light photocatalytic HER and pollutant degradation were also observed. This study proposes that, through rational surface group modification, a polymer material with high catalytic activity can be practically realized, which is promising for the design of efficient metal-free catalysts.

Doping-induced enhancement of crystallinity in polymeric carbon nitride nanosheets to improve their visible-light photocatalytic activity

Structural defects can greatly inhibit electron transfer in two-dimensional (2D) layered polymeric carbon nitride (CN) unit, seriously lowering its utilization ratio of photogenerated charges during photocatalysis. Herein, we propose a new strategy based on intra-melon hydrogen bonding interactions in 2D CN frameworks to improve the crystallinity of CN. This concept was validated by removing some amino groups and connecting melon using codoped B and F atoms via a simple one-step sodium fluoroborate-assisted thermal treatment. The enhancement in crystallinity effectively promoted exciton dissociation and charge transfer in the CN nanosheets. Furthermore, the B/F dopants also improved the separation of photogenerated carriers by promoting charge capture. The highly efficient visible-light photocatalytic activity of the crystalline B/F-codoped CN nanosheets was demonstrated by degrading methyl orange, Rhodamine B, colorless phenol and tetracycline hydrochloride as models, where their degradation rate constant was more than 10, 5, 32 and 3 times higher than that of pure CN, respectively. Moreover, the B/F-codoped CN exhibited an excellent photoelectrocatalytic performance for the oxygen evolution reaction (OER), outperforming the precious-metal IrO2 catalyst. The simple and effective strategy proposed herein provides a direct route to engineer high crystallinity in 2D materials for tunable charge carrier separation and migration for electronic and optoelectronic applications.

Interfacial Engineering of Hierarchical Transition Metal Oxide Heterostructures for Highly Sensitive Sensing of Hydrogen Peroxide

Hydrogen peroxide (H₂ O₂ ) is a major messenger molecule in cellular signal transduction. Direct detection of H₂ O₂ in complex environments provides the capability to illuminate its various biological functions. With this in mind, a novel electrochemical approach is here proposed by integrating a series of CoO nanostructures on CuO backbone at electrode interfaces. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction, and X-ray photoelectron spectroscopy demonstrate successful formation of core-shell CuO-CoO hetero-nanostructures. Theoretical calculations further confirm energy-favorable adsorption of H₂ O₂ on surface sites of CuO-CoO heterostructures. Contributing to the efficient electron transfer path and enhanced capture of H₂ O₂ in the unique leaf-like CuO-CoO hierarchical 3D interface, an optimal biosensor-based CuO-CoO-2.5 h electrode exhibits an ultrahigh sensitivity (6349 µA m m^-1 cm^-2 ), excellent selectivity, and a wide detection range for H₂ O₂ , and is capable of monitoring endogenous H₂ O₂ derived from human lung carcinoma cells A549. The synergistic effects for enhanced H₂ O₂ adsorption in integrated CuO-CoO nanostructures and performance of the sensor suggest a potential for exploring pathological and physiological roles of reactive oxygen species like H₂ O₂ in biological systems.

Graphitic-phase carbon nitride-based electrochemiluminescence sensing analyses: recent advances and perspectives

This review describes the current trends in synthesis methods, signaling strategies, and sensing applications of g-C₃N₄-based ECL emitters.