SiO2/carbon nitride composite materials: The role of surfaces for enhanced photocatalysis

Porous graphitic carbon nitride with high concentration of oxygen promotes photocatalytic H2 evolution

Porous structure design and the content regulation of heteroelements have been proved to be effective strategies to boost photocatalytic H₂ generation activity of graphitic carbon nitride (g-C₃N₄) based photocatalyst. Herein, a series of porous graphitic carbon nitride with high concentration of oxygen (g-C₃N₄-O) photocatalysts were synthesized via in situ polymerization process using colloidal SiO₂ as oxygen source. The content of oxygen within the g-C₃N₄-O photocatalysts could be tuned by adjusting the amount of added colloidal SiO₂ during the preparation procedure. The introduced oxygen replaced two-coordinated nitrogen atom, influencing band edge position and localized electron distribution, thereby enhancing visible light harvesting and photoelectric conversion. As a result, the g-C₃N₄-O photocatalyst with an optimal oxygen content (8.39 wt%) showed 10.5 fold enhancement in H₂ evolution rate compared to that of bulk g-C₃N₄, attributed to the porous structure and high concentration of incorporated oxygen.

Visible-light-induced photocatalytic response of easily recoverable Mn2O3/SiO2 monolith in centimeter-scale towards degradation of ofloxacin: Performance evaluation and product analysis

Monolithic-photocatalysts being easily recoverable are a suitable alternative to powdered materials for pollutant treatment. This study was conducted to prepare Mn₂O₃/SiO₂ monoliths by wet-impregnating Mn(NO₃)₂^․4H₂O in SiO₂ monoliths. The crystallinity of oxide was affirmed via XRD analyses, whereas EDS and elemental-mapping, and XPS studies revealed the constituent elements and their oxidation states. FESEM images confirmed porous morphology, while BET-analysis confirmed its mesoporous nature (∼8.44 nm) and enormous surface area (∼241 m²/g). The DRS and PL studies disclosed that Mn₂O₃/SiO₂ monoliths consisted of narrow band-gap of ∼2.14 eV and had suitable electron/hole separation. The photocatalytic effectiveness of the monolith had been checked by degrading model dye methylene blue (MB) and antibiotic ofloxacin (OF). The influence of various reaction parameters for degradation, i.e., monolith dose, solution-pH, illumination-area, scavengers, etc., was noted. At optimal reaction conditions, outstanding competence was achieved for MB (95.23%; 0.0225 min^-1) and decent results were obtained for OF-degradation (73.2%; 0.0096 min^-1). The recyclable nature of the catalyst (∼12.7%-reduction in effectiveness after 10 successive cycles) was vindicated by several characterization studies after reusability. The O₂^•-radicals participated majorly in the degradation reaction. The reaction intermediates plus products, generated after the degradation of had been identified via LC/MS study. The mineralization extent of the OF and MB was also gauged through TOC analyses. The photocatalytic treatment of raw textile wastewater manifested ∼57.8% COD and 53% TOC-removal. This study emphasizes the competence of Mn₂O₃/SiO₂ monoliths for the photocatalytic abatement of refractory organic contaminants.

Incorporation of SiO2 functionalized gC3N4 sheets with TiO2 nanoparticles to enhance the anticorrosion performance of metal specimens in aggressive Cl- environment

Nowadays, carbon-based nano-structured materials are widely preferred for composite coating as anti-corrosive reinforcement mainly due to its enhanced physical, chemical and mechanical properties. Herein we develop highly efficient Graphitic carbon nitride-Silica-Titania (gC₃N₄/SiO₂/TiO₂) ternary nanocomposite are synthesized and it is used as a nanofillers in the corrosive protection layer on the proposed metal specimen (i.e., mild steel specimen) in an aggressive chloride environment. Size, structural and morphological analysis were analysed for the confirmation of presence of particles. gC₃N₄ is currently earning quite drastic attention, owing to its affordable cost compared to carbon nanotubes and other carbon-based materials, when gC₃N₄ incorporated with SiO₂ and TiO₂, the composite matrix greatly improves the mechanical strength of the coating mixture. XRD, XPS, EDS analysis projects excellent formation and presence of the ternary nanocomposites. The particles are well-dispersed in epoxy and organic resin and deposited on the mildsteel panels and it is examined using various surface and structural characterization techniques. The obtained results are very encouraging and the ternary composite coatings can be recommended for real world applications.

Unmasking the Role of an Amorphous/Amorphous Interface and a Crystalline/Amorphous Interface in the Transition of Charge Carriers on the CN/SiO2/WO3 Photocatalyst

Making heterojunctions between semiamorphous carbon nitride (CN) and other well-matched semiconductors (or even insulators) can solve many photocatalytic problems such as the recombination of charge carriers. However, many researchers encounter intrinsic problems including the lack of detailed information on contact boundaries in their heterojunctions, particularly in the amorphous/amorphous interface. In addition, the roles of contact boundaries in the photocatalytic mechanisms of many heterojunctions are still obscure. This study synthesized a novel CN/SiO₂/WO₃ photocatalyst having two different contact features by constructing an amorphous/amorphous (CN/SiO₂) interface and a crystalline/amorphous (WO₃/CN) interface to provide deep insights into heterojunction interfaces. SiO₂ plays an exceptional role as a major component in the separation and migration of charge carriers. It not only modifies the texture but also transfers electrons. Surprisingly, the amorphous/amorphous interface shows an unpredicted capability for decreasing the recombination of electron-hole pairs. Based on capturing experiments and photoluminescence investigations, the amorphous/amorphous interface is unprecedently present in the production of hydroxyl radicals, while the crystalline/amorphous interface gives more superoxide radicals. This work provides a platform that opens a new perspective on the selection of mutual photocatalysts. It extends boundaries of conventional heterojunctions.

Universal strategy using environment-friendly inorganic compounds for the preparation of porous carbon nitride for efficient photocatalytic hydrogen production and environmental remediation

In this work, a facile strategy is proposed for the preparation of efficient porous CN for photocatalytic hydrogen production and environmental remediation.

Heterogeneous photocatalysis in flow chemical reactors

The synergy between photocatalysis and continuous flow chemical reactors has shifted the paradigms of photochemistry, opening new avenues of research with safer and scalable processes that can be readily implemented in academia and industry. Current state-of-the-art photocatalysts are homogeneous transition metal complexes that have favourable photophysical properties, wide electrochemical redox potentials, and photostability. However, these photocatalysts present serious drawbacks, such as toxicity, limited availability, and the overall cost of rare transition metal elements. This reduces their long-term viability, especially at an industrial scale. Heterogeneous photocatalysts (HPCats) are an attractive alternative, as the requirement for the separation and purification is largely removed, but typically at the cost of efficiency. Flow chemical reactors can, to a large extent, mitigate the loss in efficiency through reactor designs that enhance mass transport and irradiation. Herein, we review some important developments of heterogeneous photocatalytic materials and their application in flow reactors for sustainable organic synthesis. Further, the application of continuous flow heterogeneous photocatalysis in environmental remediation is briefly discussed to present some interesting reactor designs that could be implemented to enhance organic synthesis.

Monomer sequence design at two solvent interface enables the synthesis of highly photoactive carbon nitride

Structural modifications in carbon nitrides and related carbon-based materials have been achieved in recent years by organizing their monomers into versatile supramolecular structures that serve as reactants for the high temperature solid-state reaction. To date, the organization is usually carried out in one solvent where the building blocks must be dispersed. Here, we show the utilization of a molecule with both hydrogen bond donor and acceptor sites for constructing hydrogen bonded frameworks in interfacial systems. The chemical and electronic properties of the carbon nitride materials after calcination are strongly altered showing enhanced photocatalytic performance in different model reactions. This work shows a new large-scale pathway for the synthesis of highly photoactive carbon nitride with tailored properties and morphology by employing novel supramolecular assemblies prepared in the interface between two solvents, and furthermore opens new opportunities in the rational design of different carbon–nitrogen based materials utilizing supramolecular structures.

The design of a supramolecular assembly in a two solvent interface is used to tailor the morphology, chemical and electronic properties of carbon nitride. This approach opens many opportunities for the design of C–N based materials.

Ultralong Nanostructured Carbon Nitride Wires and Self-Standing C-Rich Filters from Supramolecular Microspheres

The rational design of ultralong carbon nitride nanostructures is highly attractive due to their high aspect ratio alongside their high surface-to-bulk ratio, which make them suitable candidates for various applications such as photocatalysts, water treatment, and sensors. However, the synthesis of ultralong, continuous carbon nitride wires is highly challenging. Here we report the synthesis of 4 cm long and large lateral size carbon nitride wires by utilizing unique supramolecular spheres composed of graphitic carbon nitride (g-CN) monomers as the reactants. In situ scanning electron microscopy studies reveal that upon calcination the g-CN wires spontaneously start to grow from the spheres, while the remaining assembly which acts as a substrate creates self-standing carbon-rich g-CN porous films. The different morphology, chemical composition, and electronic properties of the wires and carbon-rich g-CN allow their utilization as both photocatalyst and water cleaning materials. The g-CN wires exhibit excellent photoactivity for hydrogen production whereas the porous carbon-rich g-CN porous film can be efficiently used for water cleaning applications. The reported work opens opportunities for tailored design of g-CN nanostructures and their use as multifunctional materials for photocatalysis, sensing, and other energy-related applications.

Reactive Hypersaline Route: One-Pot Synthesis of Porous Photoactive Nanocomposites

Herein, porous photoactive nanocomposites are prepared by a simple one-pot synthesis approach using a salt and aqueous media. Within this reactive hypersaline route, the salt not only serves in the structuring of the composite but also becomes an integral active part of it. Here, the addition of sodium thiocyanate to a titania precursor guides, on the one hand, the formation of needle-shaped nanoparticles and, on the other hand, forms yellow compound isoperthiocyanic acid, which is homogeneously incorporated into the porous nanocomposite. Compared to a pure titania reference, this material reveals a 7-fold-increased photodegradation rate of Rhodamine B as a model compound. This reveals the reactive hypersaline route to be a promising and facile synthesis route toward photoactive porous materials.

Facile synthesis of mesoporous detonation nanodiamond-modified layers of graphitic carbon nitride as photocatalysts for the hydrogen evolution reaction

The hydrogen evolution reaction (HER) may contribute substantially to energy resources in the future through solar energy conversion.

Two isomeric solid carbon nitrides with 1 : 1 stoichiometry which exhibit strong mechanical anisotropy

Two isomeric layered carbon nitride polymorphs are characterized using reliable theoretical methods. The NCNC phase, which is predicted for the first time, has a number of differences with the isomeric NCCN polymorph in its electronic, spectral and mechanical properties.

Facile synthesis and enhanced visible-light photoactivity of a g-C3N4/mullite composite

The g-C₃N₄/mullite photocatalyst was synthesized through a simple wetting chemical method. Strong interfacial combination and electrons transfer were key factors for the enhanced photoactivity of the composite photocatalyst.

Activating Pd nanoparticles on sol–gel prepared porous g-C3N4/SiO2via enlarging the Schottky barrier for efficient dehydrogenation of formic acid

The g-C₃N₄/SiO₂ nanocomposite was prepared via a sol–gel method to activate Pd nanoparticles for hydrogen generation from formic acid.

A highly efficient g-C3N4/SiO2 heterojunction: the role of SiO2 in the enhancement of visible light photocatalytic activity

SiO₂, an insulator, hardly has any photocatalytic acitivity due to its intrinsic property, and it is generally used as a hard template to increase the surface area of catalysts.

Complementing Graphenes: 1D Interplanar Charge Transport in Polymeric Graphitic Carbon Nitrides

Charge transport in polymeric graphitic carbon nitrides is shown to proceed via diffusive hopping of electron and hole polarons with reasonably high mobilities >10(-5) cm(2) V(-1) s(-1). The power-law behavior of the ultrafast luminescence decay exhibits that the predominant transport direction is perpendicular to the graphitic polymer sheets, thus complementing 2D materials like graphene.

Polymeric photocatalysts based on graphitic carbon nitride

Semiconductor-based photocatalysis is considered to be an attractive way for solving the worldwide energy shortage and environmental pollution issues. Since the pioneering work in 2009 on graphitic carbon nitride (g-C3N4) for visible-light photocatalytic water splitting, g-C3N4 -based photocatalysis has become a very hot research topic. This review summarizes the recent progress regarding the design and preparation of g-C3N4 -based photocatalysts, including the fabrication and nanostructure design of pristine g-C3N4 , bandgap engineering through atomic-level doping and molecular-level modification, and the preparation of g-C3N4 -based semiconductor composites. Also, the photo-catalytic applications of g-C3N4 -based photocatalysts in the fields of water splitting, CO2 reduction, pollutant degradation, organic syntheses, and bacterial disinfection are reviewed, with emphasis on photocatalysis promoted by carbon materials, non-noble-metal cocatalysts, and Z-scheme heterojunctions. Finally, the concluding remarks are presented and some perspectives regarding the future development of g-C3N4 -based photocatalysts are highlighted.

Graphitic carbon nitride based nanocomposites: a review

Graphitic carbon nitride (g-C(3)N(4)), as an intriguing earth-abundant visible light photocatalyst, possesses a unique two-dimensional structure, excellent chemical stability and tunable electronic structure. Pure g-C(3)N(4) suffers from rapid recombination of photo-generated electron-hole pairs resulting in low photocatalytic activity. Because of the unique electronic structure, the g-C(3)N(4) could act as an eminent candidate for coupling with various functional materials to enhance the performance. According to the discrepancies in the photocatalytic mechanism and process, six primary systems of g-C(3)N(4)-based nanocomposites can be classified and summarized: namely, the g-C(3)N(4) based metal-free heterojunction, the g-C(3)N(4)/single metal oxide (metal sulfide) heterojunction, g-C(3)N(4)/composite oxide, the g-C(3)N(4)/halide heterojunction, g-C(3)N(4)/noble metal heterostructures, and the g-C(3)N(4) based complex system. Apart from the depiction of the fabrication methods, heterojunction structure and multifunctional application of the g-C(3)N(4)-based nanocomposites, we emphasize and elaborate on the underlying mechanisms in the photocatalytic activity enhancement of g-C(3)N(4)-based nanocomposites. The unique functions of the p-n junction (semiconductor/semiconductor heterostructures), the Schottky junction (metal/semiconductor heterostructures), the surface plasmon resonance (SPR) effect, photosensitization, superconductivity, etc. are utilized in the photocatalytic processes. Furthermore, the enhanced performance of g-C(3)N(4)-based nanocomposites has been widely employed in environmental and energetic applications such as photocatalytic degradation of pollutants, photocatalytic hydrogen generation, carbon dioxide reduction, disinfection, and supercapacitors. This critical review ends with a summary and some perspectives on the challenges and new directions in exploring g-C(3)N(4)-based advanced nanomaterials.

Ag3PO4 nanoparticle decorated on SiO2 spheres for efficient visible light photocatalysis

Light irradiation on Ag₃PO₄ decorated SiO₂ generates three reactive species (˙OH, O₂⁻˙, and hole) leading to efficient photocatalysis.

One-step synthesis of SnO2 nanoparticles-loaded graphitic carbon nitride and their application in thermal decomposition of ammonium perchlorate

SnO₂NPs/g-C₃N₄ hybrids can effectively catalyze NH₄ClO₄ molecules by the aid of a synergistic reaction of SnO₂.

Template free synthesis of graphitic carbon nitride/titania mesoflowers

Multifunctional solar active graphitic carbon nitride–titania mesoflowers with surface area of 147 m² g⁻¹ are synthesized by a one-step solvothermal process for environmental remediation.

Synthesis of a visible-light active V2O5–g-C3N4 heterojunction as an efficient photocatalytic and photoelectrochemical material

Synergistic enhancement of the photocatalytic degradation of DR81 using V₂O₅–g-C₃N₄ is due to an increase in visible-light absorption efficiency and rapid photoinduced charge separation.

Photocatalytic and photoelectrochemical studies of visible-light active α-Fe2O3–g-C3N4 nanocomposites

Synergistic enhancement in photocatalytic degradation of α-Fe₂O₃–g-C₃N₄ due to an increase in visible-light absorption efficiency and rapid photoinduced charge separation.