What makes carbon nitride so attractive begins with its chemistry. Graphitic carbon nitride is a metal-free polymer built from carbon and nitrogen atoms arranged in heptazine or triazine units, stacked into layers that resemble the architecture of graphite. This arrangement gives the material a set of properties that catalyst designers prize: it is chemically stable in acids, bases and organic solvents, it tolerates high temperatures, and it possesses a band gap of roughly 2.7 electronvolts, wide enough to drive photochemical reactions yet narrow enough to absorb a meaningful slice of visible sunlight. Because it contains only abundant elements, it is inexpensive and scalable in ways that many metal-based catalysts are not. Its surface is also rich in nitrogen-containing sites, including pyridinic and amino functionalities, which can anchor metal atoms, activate small molecules and participate directly in bond-forming chemistry.

The volume devotes substantial attention to how synthesis choices ripple through to catalytic performance. Carbon nitride can be prepared by thermal condensation of inexpensive precursors such as melamine, urea, thiourea or dicyandiamide, and the choice of precursor, the heating profile and the atmosphere all leave fingerprints on the final material. Thermal polycondensation at moderate temperatures tends to yield highly polymerized, well-ordered frameworks, while routes from urea can produce defect-rich structures with enhanced surface area. Post-synthetic treatments, including exfoliation into two-dimensional nanosheets, protonation, and the introduction of vacancies or heteroatom dopants, further tune the electronic structure. Each of these levers changes how the material absorbs light, how charge carriers migrate through its framework and how substrates adsorb to its surface, which in turn governs activity and selectivity in the reactions it catalyzes.

In organic synthesis, carbon nitride-based catalysts have proven capable of mediating reactions that traditionally demand stoichiometric reagents or precious-metal complexes. The book surveys their roles in carbon–carbon and carbon–heteroatom bond formation, the two workhorse transformations of synthetic chemistry, as well as in oxidation reactions and the construction of heterocyclic scaffolds that underpin much of pharmaceutical and agrochemical chemistry. Because the catalyst is heterogeneous, it can be recovered by filtration and reused, addressing one of the persistent criticisms of homogeneous catalysis. The nitrogen-rich surface can act as a Lewis base, a hydrogen-bonding platform or an electron-transfer mediator, and when combined with light absorption it enables photocatalytic variants of classical reactions that proceed under mild conditions, often at ambient temperature and pressure with molecular oxygen or water as the terminal oxidant.

Photocatalysis is arguably where carbon nitride first made its name, and the volume gives this field careful treatment. When g-C₃N₄ absorbs a photon, an electron is promoted from the valence band to the conduction band, leaving behind a hole. These charge carriers can reduce or oxidize species adsorbed on the catalyst surface before they recombine, and the art of photocatalyst design lies largely in preventing that recombination. Strategies covered in the book include coupling carbon nitride with other semiconductors to form heterojunctions that separate charges across an interface, decorating the surface with co-catalysts such as metals that act as electron sinks, and doping the framework to shift band edges. Applications range from the degradation of organic pollutants in water to the photosynthesis of value-added organic compounds, and the editors emphasize that rational functionalization, rather than trial and error, is increasingly the route to high activity and selectivity.

Water splitting, the light-driven decomposition of water into hydrogen and oxygen, receives particular scrutiny as a flagship application for sustainable energy conversion. Carbon nitride’s conduction band sits at a potential sufficiently negative to reduce protons to hydrogen, making it a candidate photocatalyst for solar fuel production. The material’s limitations, including modest visible-light absorption beyond a certain wavelength and rapid charge recombination, are precisely the problems that doping, defect engineering and composite formation are designed to solve. Alongside water splitting, the book examines oxygen reduction, the cathodic half-reaction central to fuel cells and metal–air batteries, where carbon nitride-based materials can serve as metal-free electrocatalysts or as supports that stabilize single metal atoms in highly active configurations.

Electrocatalysis and electrochemical sensing form a second major pillar of the volume. The same conductive and adsorptive properties that make carbon nitride useful for driving reactions make it valuable for detecting them. The book highlights electrochemical sensors built on carbon nitride platforms for monitoring environmental pollutants, exploiting the material’s ability to accumulate analytes at nitrogen-rich sites and transduce their presence into measurable electrical signals. Such sensors target contaminants in water and air, offering routes to monitoring tools that are inexpensive, robust and potentially deployable outside specialized laboratories. The editors frame this sensing capability as a natural companion to the materials’ environmental remediation roles: the same chemistry that destroys pollutants can be harnessed to detect them.

Threaded through all of these applications is a unifying theme that the editors return to repeatedly: the relationship between catalyst design and catalytic outcome. Activity and selectivity in carbon nitride catalysis are not fixed properties of a formula but consequences of structure at multiple scales, from the polymerization degree of the framework to the density of surface defects to the geometry of metal sites deposited upon it. A metal-decorated derivative may behave entirely differently from its pristine parent, and a composite with a second semiconductor can open reaction pathways unavailable to either component alone. The volume’s chapters collectively argue that understanding these structure–performance relationships is the key to moving carbon nitride catalysts from laboratory demonstrations to technologies that compete with, and in some cases outperform, conventional metal-based systems.

The sustainability case for these materials is central to the book’s argument. Catalysis underpins the majority of industrial chemical production, and the environmental costs of precious-metal catalysts, stoichiometric oxidants and energy-intensive processes have pushed chemists toward alternatives grounded in earth-abundant elements and renewable energy inputs. Carbon nitride fits that brief unusually well: it is synthesized from cheap organic precursors, contains no metals, can harvest sunlight directly, and can drive oxidations with air or water. The editors position the material as relevant to sustainable chemistry, energy conversion and environmental monitoring simultaneously, a rare breadth that reflects the tunability of the underlying platform. For industries seeking greener routes to fine chemicals, fuels and clean water, the message is that a single material family may serve multiple points in the same sustainability pipeline.

By gathering contributions that span organic chemistry, materials science, photocatalysis and electrochemistry, the volume offers an interdisciplinary map of a field that has often advanced in disconnected pockets. The editors, Vijai Kumar Rai, Manorama Singh and Ankita Rai, have assembled a reference aimed at researchers and advanced readers in organic chemistry, materials science, catalysis, nanotechnology and chemical engineering, and its scope suggests that carbon nitride-based nanomaterials have moved decisively beyond a single-application curiosity. Whether the next breakthrough comes from a more selective organic transformation, a more efficient water-splitting device or a more sensitive pollutant sensor, the common denominator will be the same: a metal-free, nitrogen-rich framework whose properties chemists can now design with increasing precision. For a field racing toward efficient and environmentally responsible catalytic technologies, graphitic carbon nitride has earned its place at the center of the conversation.

Subject of Research: Catalytic applications of graphitic carbon nitride-based nanomaterials

Article Title: Catalytic applications of carbon nitride-based nanomaterials

Article References: Catalytic applications of carbon nitride-based nanomaterials. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: carbon nitride, g-C3N4, catalysis, photocatalysis, electrocatalysis, water splitting, organic synthesis, nanomaterials, sustainable chemistry, environmental sensing, oxygen reduction, heterogeneous catalysis

The logic of photocatalysis is elegantly simple. A semiconductor absorbs a photon, kicking an electron from its valence band into its conduction band and leaving behind a positively charged hole. If the electron survives long enough to reach the surface, it can reduce protons to hydrogen gas; the holes, meanwhile, oxidize water to oxygen. The trouble is that in most materials, the electron and hole recombine almost instantly, releasing their energy as heat and accomplishing nothing. For a photocatalyst to work well, it must absorb a broad swath of the solar spectrum, separate its charge carriers efficiently, and present abundant active sites for the redox reactions. Ideal band gaps fall between roughly 1.23 and 3 electron volts, a window that balances light harvesting against redox power.

Graphitic carbon nitride, or g-C3N4, checks many of these boxes. It is a metal-free polymeric semiconductor built from triazine and heptazine rings of carbon and nitrogen, arranged in extended sp2-hybridized sheets. Its band gap of approximately 2.7 electron volts lets it absorb visible light, it is remarkably stable in acids, bases, and a wide range of organic solvents, and it can be synthesized simply by heating cheap, nitrogen-rich precursors such as melamine, urea, or thiourea to temperatures between roughly 450 and 650 degrees Celsius. Since the landmark 2009 demonstration that g-C3N4 could evolve hydrogen under visible light, the material has become one of the most studied photocatalysts in the world. Yet its Achilles heel is well known: charge carriers in pristine g-C3N4 are mobile only with difficulty, so photogenerated electron-hole pairs recombine rapidly, and the material exploits only a modest fraction of the sunlight that strikes it.

Enter MXenes, the two-dimensional transition metal carbides, nitrides, and carbonitrides first derived from layered MAX phase precursors by selectively etching away their aluminum layers, typically with hydrofluoric acid, lithium fluoride in hydrochloric acid, or molten salts. The resulting sheets, with the general formula Mn+1XnTx, carry surface terminations of hydroxyl, oxygen, or fluorine that tune their electronic structure and hydrophilicity. Crucially, MXenes behave electrically like metals: they conduct electrons with ease, offer enormous surface areas, and can be functionalized in countless ways. In a photocatalytic composite, that metallic conductivity makes them ideal electron sinks, whisking photogenerated electrons away from a semiconductor before recombination can occur. Mandari and Kang argue that this is precisely the missing ingredient for g-C3N4, and their review systematically catalogs how the two materials have been married in type-II, Z-scheme, S-scheme, and Schottky junction architectures.

The numbers emerging from laboratory studies are striking. In a type-II heterojunction, electrons flow to the semiconductor with the lower conduction band while holes migrate to the higher valence band counterpart, spatially separating the charges. Tahir and colleagues anchored g-C3N4 nanosheets onto titanium carbide MXene layers embedded with in situ grown TiO2, and found that the etching time of the MXene, varied from 24 to 96 hours, critically influenced performance. The optimized 48-hour sample delivered 310 micromoles of hydrogen per gram per hour, nearly triple the yield of bulk carbon nitride. Even more dramatic results came from a 0D/2D design in which bimetallic Mo2Ti2C3 MXene quantum dots were electrostatically self-assembled onto g-C3N4 nanosheets. Acting as electron reservoirs and cocatalysts, the quantum dots pushed the hydrogen evolution rate to 2809 micromoles per gram per hour, an order of magnitude above the bare polymer.

Type-II junctions, however, pay a hidden price: the staggered band alignment that separates charges also erodes their redox power. Z-scheme systems, modeled on the electron flow of natural photosynthesis, solve this by recombining the low-energy carriers while preserving the high-energy electrons and holes. Parida and coworkers built an all-solid-state Z-scheme from facet-exposed TiO2 derived from MXene layers, boron-doped g-C3N4, and metallic MXene sheets serving as the electron mediator. The optimized composite evolved hydrogen at 408.4 micromoles per hour with an apparent quantum efficiency of 6.7 percent, four and twenty times better than the pristine doped carbon nitride, respectively. Yuan and colleagues went further, combining Mn0.5Cd0.5S, Ti3C2 MXene flakes, and g-C3N4 into a Z-scheme that reached a remarkable 13.7 millimoles of hydrogen per gram per hour under visible light, with the MXene’s polycrystalline lattice, confirmed at a spacing of 0.28 nanometers, enabling rapid electron transport.

Schottky junctions exploit an even more direct trick: when a metallic MXene touches a semiconductor, the difference in their work functions creates a built-in electric field and a Schottky barrier that blocks backflow of electrons. A hollow-sphere photocatalyst assembled from g-C3N4 shells wrapped around Ti3C2Tx MXene achieved 982.8 micromoles per gram per hour, more than 3.5 times the output of protonated g-C3N4 alone, with the three-dimensional hollow architecture shortening electron migration distances and boosting light harvesting. Porous 3D/2D hybrids of the same pairing reached 1948 micromoles per gram per hour, while a vanadium carbide variant, V2C coupled to g-C3N4 by simple physical mixing, delivered a 4.23-fold improvement over the pristine polymer, thanks to a favorable built-in electric field at the intimate 2D/2D interface.

The review also highlights more exotic designs that blur the line between materials science and biology. An S-scheme heterojunction decorated with chlorophyll-a derivatives, whose porphyrin-like magnesium-centered rings act as molecular antennas, achieved 131 micromoles per hour per gram, outperforming the same junction without the pigment. Ternary systems push synergy further still: copolymerized carbon nitride loaded with gold nanoparticles and Ti3C2 MXene showed hydrogen evolution enhanced 99.8-fold under simulated sunlight compared with unmodified g-C3N4, driven by plasmonic light absorption from the gold and MXene-mediated electron transport. A manganese dioxide, boron and oxygen co-doped carbon nitride, and delaminated Ti3C2 hybrid produced both hydrogen at 897.2 micromoles per hour and hydrogen peroxide at 2846.4 micromoles per hour per gram, demonstrating that these platforms can generate valuable chemicals beyond fuel.

None of this means a solar hydrogen economy is around the corner. The authors are candid about the obstacles: MXenes themselves can be unstable under prolonged irradiation, long-term operational durability remains poorly characterized, and translating bench-scale milligrams into industrially relevant reactors demands reproducible, scalable synthesis. Etching MXenes with hydrofluoric acid also raises safety and environmental concerns that molten salt routes only partially resolve. Still, the trajectory is unmistakable. By combining the visible-light responsiveness and robust stability of g-C3N4 with the conductivity, tunability, and surface chemistry of MXenes, and by engineering the junction between them with increasing atomic precision, researchers are systematically dismantling the recombination problem that has plagued photocatalysis for decades. If interface engineering, defect control, and scalable manufacturing can keep pace, these two-dimensional partners may yet turn ordinary water and sunlight into the cleanest fuel on Earth.

Subject of Research: Photocatalytic hydrogen production using g-C3N4/MXene heterostructure catalysts

Article Title: g-C3N4/MXene-based heterostructures: advanced catalysts for efficient and sustainable renewable energy production

Article References: Mandari, K. K., & Kang, M. (2025). g-C3N4/MXene-based heterostructures: advanced catalysts for efficient and sustainable renewable energy production. Advances in Industrial and Engineering Chemistry, 1(1), Article 14. https://doi.org/10.1007/s44405-025-00014-z

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00014-z

Keywords: g-C3N4, MXene, photocatalysis, hydrogen production, water splitting, heterojunctions, Z-scheme, Schottky junction, S-scheme, charge separation, renewable energy, two-dimensional materials