Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Core-Shell Nanowires

Plant-Based Phytochemicals for Synthesis of Z-Scheme In2O3/CdS Heterostructures: DFT Analysis and Photocatalytic CO2 Reduction to HCOOH and CO

Photocatalytic CO2 reduction shows potential for mitigating industrial emissions. Z-scheme In2O3/CdS(bio) heterostructures (25 nm, 217.0 m2 g-1 surface area) with a more negative conduction band synthesized using phytochemicals present in Aegle marmelos with short microwave irradiation inhibit CdS(bio) photocorrosion forming SO42-. In2O3/CdS(bio) increased the photocurrent density (0.82 μA cm-2) and CO2 adsorption (0.431 mmol g-1) significantly compared to CdS(bio) and In2O3(bio) NPs. Heterostructures increased decay time and reduced PL intensity by 46.28 and 61.80% over those of CdS(bio) and In2O3(bio) NPs. Density functional theory (DFT)-optimized geometry, band structure analysis, and density of states (DOS) studies indicate that the DOS of CdS is modified with In2O3 incorporation, enhancing charge separation. Optimal 0.4In2O3/CdS(bio) heterostructures exhibit remarkable CO2 conversion to HCOOH/CO production of 514.4/162 μmol g-1 h-1 (AQY 4.44/2.45%), surpassing CdS(bio) and In2O3(bio) by 9 and 6.5 times, and retain their morphological and structural stability. This study provides valuable insight for developing bio-based CdS heterostructures for photocatalytic CO2 reduction.

An interfacial C-S bond bridged S-scheme ZnS/C3N5 for photocatalytic H2 evolution: Opposite internal-electric-field of ZnS/C3N4, increased field strength, and accelerated surface reaction

An interfacial C-S bond bridged ZnS/C3N5 heterojunction was constructed for photocatalytic H2 evolution. Different from traditional type-II ZnS/C3N4 heterojunction, the electron transfer followed S-scheme pathway, due to opposite internal-electric-field (IEF) directions in these two heterojunctions. The C-S bond formation was carefully investigated, and they were susceptive to the preparation temperatures. In photocatalytic reaction, C-S bond was functioned as the "high-speed channel" for electron separation and transfer, and the IEF strength in ZnS/C3N5 was 1.86 × 108 V/m, 2.6 times higher than that in ZnS/C3N4. Moreover, the C-S bond also altered the surface molecular structure of ZnS/C3N5, and hence the surface reaction was accelerated via improving H2O adsorption and activation behaviors. Benefiting from the S-scheme pathway, enhanced IEF strength, and accelerated surface reaction, the photocatalytic H2 production over ZnS/C3N5 reached up to 20.18 mmol/g/h, 3.2 and 2.5 times higher than those of ZnS/C3N4 and ZnS/C3N5-300 without C-S bond.

C3N5-based nanomaterials and their applications in heterogeneous catalysts, energy harvesting, and environmental remediation

Over the past few decades, the global reliance on fossil fuels and the exponential growth of human population have escalated global energy consumption and environmental issues. To tackle these dual challenges, metal catalysts, in particular precious metal ones, have emerged as pivotal players in the fields of environment and energy. Among the numerous metal-free and organic catalyst materials, C3N5-based materials have a major advantage over their carbon nitride (CxNy) counterparts owing to the abundant availability of raw materials, non-toxicity, non-hazardous nature, and exceptional performance. Although significant efforts have been dedicated to synthesising and optimising the applicable properties of C3N5-based materials in recent years, a comprehensive summary of the immediate parameters of this promising material is still lacking. Given the rapid development of C3N5-based materials, a timely review is essential for staying updated on their strengths and weaknesses across various applications, as well as providing guidance for designing efficient catalysts. In this study, we present an extensive overview of recent advancements in C3N5-based materials, encompassing their physicochemical properties, major synthetic methods, and applications in photocatalysis, electrocatalysis, and adsorption, among others. This systematic review effectively summarises both the advantages and shortcomings associated with C3N5-based materials for energy and environmental applications, thus offering researchers focussed on CxNy-materials an in-depth understanding of those based on C3N5. Finally, considering the limitations and deficiencies of C3N5-based materials, we have proposed enhancement schemes and strategies, while presenting personal perspectives on the challenges and future directions for C3N5. Our ultimate aim is to provide valuable insights for the research community in this field.

Construction of Ni3S4@ZIS@C3N5 photocatalyst with type II and Z-type heterojunctions by self-assembly for efficient photocatalytic hydrogen evolution

A novel ternary photocatalyst Ni3S4@ZIS@C3N5 with type II and Z-type heterojunctions was synthesized for the first time by hydrothermal and electrostatic self-assembly methods, effectively avoiding the thermal decomposition of C3N5 during the synthesis of the complex. The best ternary catalyst Ni3S4@ZIS@C3N5 is capable of achieving an optimal hydrogen evolution rate of 9750 mmol g-1 h-1, which is approximately 10.89 times as high as that of C3N5, indicating that the complex effectively enhanced the photocatalytic properties of the monomer. The coexistence of two types of heterojunctions in the complex effectively enhances photocatalytic performance, in which the monomer ZIS constructs type II scheme with Ni3S4 and Z-type scheme with C3N5, respectively. The two heterojunctions complement each other and jointly promote the rapid electron transfer from Ni3S4 and C3N5 to the ZIS surface. In conclusion, the cooperation of the two heterojunctions efficiently facilitates the migration of photogenerated carriers, thus enhancing the photocatalytic hydrogen generation performance of Ni3S4@ZIS@C3N5.

Isotype heterojunction: tuning the heptazine/triazine phase of crystalline nitrogen-rich C3N5 towards multifunctional photocatalytic applications

Photocatalytic technology has been well studied as a means to achieve sustainable energy generation through water splitting or chemical synthesis. Recently, a low C/N atomic ratio carbon nitride allotrope, C3N5, has been found to be highly prospective due to its excellent electronic properties and ample N-active sites compared to g-C3N4. Tangentially, crystalline g-C3N4 has also been a prospective candidate due to its improved electron transport and extended π-conjugated system. For the first time, our group successfully employed a one-step molten salt calcination method to prepare novel N-rich crystalline C3N5 and elucidate the effect of calcination temperature on the heptazine/triazine phase. Calcination temperatures of 500 °C (CC3N5-500) and 550 °C (CC3N5-550) lead to crystalline carbon nitride with both heptazine and triazine phases, forming an intimate isotype heterojunction for robust interfacial charge separation. An excellent photocatalytic hydrogen evolution rate (359.97 μmol h-1; apparent quantum efficiency (AQE): 12.86% at 420 nm) was achieved using CC3N5-500, which was 15-fold higher than that of pristine C3N5. Furthermore, CC3N5-500 exhibited improved activity for simultaneous benzyl alcohol oxidation and hydrogen production, as well as H2O2 production (AQE: 9.49% at 420 nm), signifying its multitudinous photoredox capabilities. Moreover, the recyclability tests of the optimal CC3N5-500 on a 3D-printed substrate also showed a 92% performance retention after 4 cycles (16 h). This highlights that crystalline C3N5 significantly augmented the reaction performance for diverse multifunctional solar-driven applications. As such, these results serve as a guide toward the structural tuning of 2D metal-free carbon nanomaterials with tunable crystallinity toward achieving boosted photocatalysis.

CO2 Photoreduction Activity Enhancement and Unexpected Observation of Carbon Monoxide Adsorbates on the Surface of TiO2 Nanotube Arrays Synthesized in Formamide Electrolytes

TiO2 nanotube arrays grown through electrochemical anodization in a formamide-based electrolyte (TNTA-FA) exhibited a whole host of unusual properties compared to nanotubes grown in the conventional ethylene glycol-based electrolyte (TNTA-EG). TNTA-FA exhibited shorter phonon lifetimes, lower lattice strain, more visible light absorption, lower work function, and a highly unusual adsorbate structure consisting of physisorbed and chemisorbed CO along with linearly adsorbed CO2 and various monodentate and bidentate carbonate species. The observation of adsorbed CO in the dark is highly unusual and indicates spontaneous deoxygenation of CO2 on the surface of TNTA-FA. The significance of this finding is that the formation of CO2•- is no longer the rate-limiting bottleneck for the reduction of CO2 on TNTA-FA surfaces as it is for all TiO2 surfaces. TNTA-FA samples are strongly colored (inclusive of a fluorescent green color) and consist of rounded, vertically oriented hollow cylinders as opposed to the honeycomb-like morphology of TNTA-EG arranged in an approximate triangular lattice. The photocatalytic activity was tested through the CO2 photoreduction and dye degradation tests. Formamide-based nanotubes outperformed the EG-based nanotubes by almost 1.7 and 2 times, respectively, in CO2 reduction and dye degradation tests done on methylene blue, brilliant green, and rhodamine B dyes. These results are attributed to stronger surface band bending in TNTA-FA which facilitates more efficient separation of photogenerated electron-hole pairs.

Predicting Free Energies of Exfoliation and Solvation for Graphitic Carbon Nitrides Using Machine Learning

As a metal-free and visible-light-responsive photocatalyst, graphitic carbon nitride (g-C3N4) has emerged as a new research hotspot and has attracted broad attention in the field of solar energy conversion and thin-film transistors. Liquid-phase exfoliation (LPE) is the best-known method for the synthesis of 2D g-C3N4 nanosheets. In LPE, bulk g-C3N4 is exfoliated in a solvent via high-shear mixing or sonication in order to produce a stable suspension of individual nanosheets. Two parameters of importance in gauging the performance of a solvent in LPE are the free energy required to exfoliate a unit area of layered materials into individual sheets in the solvent (ΔGexf) and the solvation free energy per unit area of a nanosheet (ΔGsol). While approximations for the free energies exist, they are shown in our previous work to be inaccurate and incapable of capturing the experimentally observed efficacy of LPE. Molecular dynamics (MD) simulations can provide accurate free-energy calculations, but doing so for every single solvent is time- and resource-consuming. Herein, machine learning (ML) algorithms are used to predict ΔGexf and ΔGsol for g-C3N4. First, a database for ΔGexf and ΔGsol is created based on a series of MD simulations involving 49 different solvents with distinct chemical structures and properties. The data set also includes values of critical descriptors for the solvents, including density, surface tension, dielectric constant, etc. Different ML methods are compared, accompanied by descriptor selection, to develop the most accurate model for predicting ΔGexf and ΔGsol. The extra tree regressor is shown to be the best performer among the six ML methods studied. Experimental validation of the model is conducted by performing dispersibility tests in several solvents for which the free energies are predicted. Finally, the influence of the selected descriptors on the free energies is analyzed, and strategies for solvent selection in LPE are proposed.

Cobalt doped nitrogen-vacancies-rich C3N5 with optimizing local electron distribution boosts peroxymonsulfate activation for tetracycline degradation: Multiple electron transfer mechanisms

Heterogeneous photocatalysis coupled with peroxymonosulfate (PMS) activation is considered as an advanced water purification technology for emerging contaminates degradation. In this study, Cobalt (Co) doped nitrogen-vacancies-rich C3N5 photocatalysts (Co/Nv-C3N5) were designed to activate PMS for tetracycline removal. The photo-chemical oxidation system displayed superior advantage, in which the observed rate constant of tetracycline degradation (0.1488 min-1) was 10.86 and 1.82 times higher than that of photo-oxidation and chemical-oxidation systems. Density functional theory calculation results verified the reconstruction of local charge distribution during PMS activation, indicating Co doping and nitrogen-vacancy engineering not only promoted photoelectrons capture, but also boosted electron transfer from the C-N framework to PMS and the generation of active species. Furthermore, several unique multiple electron transfer mechanisms were found in nonradicals (h+, 1O2 and Co(IV)) pathways. Additionally, three possible tetracycline degradation pathways were proposed and the toxicity of the intermediates was evaluated. Overall, the findings from this study provided a novel strategy for developing high-efficient photocatalyst for the rapid degradation of organic pollutants.

Novel MoS2/C3N5 composites with extended spectral response towards highly efficient photocatalytic abatement of hazardous pollutants

Carbon nitride materials are one of the potential candidates for photocatalytic application. The present work demonstrates the fabrication of C₃N₅ catalyst from a simple, low-cost, and easily available nitrogen-containing precursor, melamine. The facile and microwave mediated method was used to prepare novel MoS₂/C₃N₅ composites (referred to as MC) with varying weight ratios (1:1, 1:3, and 3:1). This work provided a novel strategy to improve photocatalytic activity and accordingly fabricated a potential material for effective removal of organic contaminants from water. XRD and FT-IR results affirms the cryatalinity and successful formation of the composites. The elemental composition/distribution was analysed via EDS and color mapping. The elemental oxidation state and successful charge migration in hetrostructure was confirmed by XPS findings. The catalyst's surface morphology indicates tiny MoS₂ nanopetals dispersed throughout C₃N₅ sheets, while BET studies revealed its high surface area (34.7 m²/g). The MC catalysts were highly active in visiblelight, with an energy band gap value of 2.01 eV and a lowered recombination of charges. Because of the strong synergistic relationship (2.19) in the hybrid, excellent activity for methylene blue (MB) dye (88.9%; 0.0157 min^-1) and fipronil (FIP) photodegradation (85.3%; 0.0175 min^-1) with MC (3:1) catalyst under visible-light irradiation was obtained. Investigations were carried out on the effect of catalyst quantity, pH, and effectual illumination area on photoactivity. Post-photocatalytic assessment verified the high re-useable character of the catalyst with a high degradation (63% (5 mg/L MB) and 54% (600 mg/L FIP)) after five cycles. The trapping investigations demonstrated that superoxide radicals and holes were intimately enrolled in the degradation activity. Remarkable removal rates of COD (68.4%) and TOC (53.1%) demonstrate excellent photocatalytic removal of practical wastewater even without any preliminary processes. The new study, when paired with previous research, demonstrates the real-world perspective of these novel MC composites for the elimination of refractory contaminants.

Radial Nano-Heterojunctions Consisting of CdS Nanorods Wrapped by 2D CN:PDI Polymer with Deep HOMO for Photo-Oxidative Water Splitting, Dye Degradation and Alcohol Oxidation

Solar energy harvesting using semiconductor photocatalysis offers an enticing solution to two of the biggest societal challenges, energy scarcity and environmental pollution. After decades of effort, no photocatalyst exists which can simultaneously meet the demand for excellent absorption, high quantum efficiency and photochemical resilience/durability. While CdS is an excellent photocatalyst for hydrogen evolution, pollutant degradation and organic synthesis, photocorrosion of CdS leads to the deactivation of the catalyst. Surface passivation of CdS with 2D graphitic carbon nitrides (CN) such as g-C₃N₄ and C₃N₅ has been shown to mitigate the photocorrosion problem but the poor oxidizing power of photogenerated holes in CN limits the utility of this approach for photooxidation reactions. We report the synthesis of exfoliated 2D nanosheets of a modified carbon nitride constituted of tris-s-triazine (C₆N₇) linked pyromellitic dianhydride polydiimide (CN:PDI) with a deep oxidative highest occupied molecular orbital (HOMO) position, which ensures sufficient oxidizing power for photogenerated holes in CN. The heterojunction formed by the wrapping of mono-/few layered CN:PDI on CdS nanorods (CdS/CN:PDI) was determined to be an excellent photocatalyst for oxidation reactions including photoelectrochemical water splitting, dye decolorization and the photocatalytic conversion of benzyl alcohol to benzaldehyde. Extensive structural characterization using HR-TEM, Raman, XPS, etc., confirmed wrapping of few-layered CN:PDI on CdS nanorods. The increased photoactivity in CdS/CN:PDI catalyst was ascribed to facile electron transfer from CdS to CN:PDI in comparison to CdS/g-C₃N₄, leading to an increased electron density on the surface of the photocatalyst to drive chemical reactions.

Engineered g-C3N5-Based Nanomaterials for Photocatalytic Energy Conversion and Environmental Remediation

Photocatalysis plays a vital role in sustainable energy conversion and environmental remediation because of its economic, eco-friendly, and effective characteristics. Nitrogen-rich graphitic carbon nitride (g-C₃N₅) has received worldwide interest owing to its facile accessibility, metal-free nature, and appealing electronic band structure. This review summarizes the latest progress for g-C₃N₅-based photocatalysts in energy and environmental applications. It begins with the synthesis of pristine g-C₃N₅ materials with various topologies, followed by several engineering strategies for g-C₃N₅, such as elemental doping, defect engineering, and heterojunction creation. In addition, the applications in energy conversion (H₂ evolution, CO₂ reduction, and N₂ fixation) and environmental remediation (NO purification and aqueous pollutant degradation) are discussed. Finally, a summary and some inspiring perspectives on the challenges and possibilities of g-C₃N₅-based materials are presented. It is believed that this review will promote the development of emerging g-C₃N₅-based photocatalysts for more efficiency in energy conversion and environmental remediation.

In Situ Coupling Carbon Defective C3N5 Nanosheet with Ag2CO3 for Effective Degradation of Methylene Blue and Tetracycline Hydrochloride

The development of novel catalysts for degrading organic contaminants in water is a current hot topic in photocatalysis research for environmental protection. In this study, C₃N₅ nanosheet/Ag₂CO₃ nanocomposites (CNAC-X) were used as efficient photocatalysts for the visible-light-driven degradation of methylene blue (MB), and tetracycline hydrochloride (TC-HCl) was synthesized for the first time using a simple thermal oxidative exfoliation and in situ deposition method. Due to the synergistic effect of nanosheet structures, carbon defects, and Z-scheme heterojunctions, CNAC-10 exhibited the highest photocatalytic activity, with photodegradation efficiencies of 96.5% and 97.6% for MB (60 mg/L) and TC-HCl (50 mg/L) within 90 and 100 min, respectively. The radical trapping experiments showed that ·O₂^- and h⁺ played major roles in the photocatalytic effect of the CNAC-10 system. Furthermore, intermediates in the photodegradation of MB and TC-HCl were investigated to determine possible mineralization pathways. The results indicated that C₃N₅ nanosheet/Ag₂CO₃ photocatalysts prepared in this work could provide an effective reference for the treatment of organic wastewater.

Colloidal-ALD-Grown Hybrid Shells Nucleate via a Ligand-Precursor Complex

Colloidal atomic layer deposition (c-ALD) enables the growth of hybrid organic-inorganic oxide shells with tunable thickness at the nanometer scale around ligand-functionalized inorganic nanoparticles (NPs). This recently developed method has demonstrated improved stability of NPs and of their dispersions, a key requirement for their application. Nevertheless, the mechanism by which the inorganic shells form is still unknown, as is the nature of multiple complex interfaces between the NPs, the organic ligands functionalizing the surface, and the shell. Here, we demonstrate that carboxylate ligands are the key element that enables the synthesis of these core-shell structures. Dynamic nuclear polarization surface-enhanced nuclear magnetic resonance spectroscopy (DNP SENS) in combination with density functional theory (DFT) structure calculations shows that the addition of the aluminum organometallic precursor forms a ligand-precursor complex that interacts with the NP surface. This ligand-precursor complex is the first step for the nucleation of the shell and enables its further growth.

TiO2-HfN Radial Nano-Heterojunction: A Hot Carrier Photoanode for Sunlight-Driven Water-Splitting

The lack of active, stable, earth-abundant, and visible-light absorbing materials to replace plasmonic noble metals is a critical obstacle for researchers in developing highly efficient and cost-effective photocatalytic systems. Herein, a core–shell nanotube catalyst was fabricated consisting of atomic layer deposited HfN shell and anodic TiO2 support layer with full-visible regime photoactivity for photoelectrochemical water splitting. The HfN active layer has two unique characteristics: (1) A large bandgap between optical and acoustic phonon modes and (2) No electronic bandgap, which allows a large population of long life-time hot carriers, which are used to enhance the photoelectrochemical performance. The photocurrent density (≈2.5 mA·cm−2 at 1 V vs. Ag/AgCl) obtained in this study under AM 1.5G 1 Sun illumination is unprecedented, as it is superior to most existing plasmonic noble metal-decorated catalysts and surprisingly indicates a photocurrent response that extends to 730 nm. The result demonstrates the far-reaching application potential of replacing active HER/HOR noble metals such as Au, Ag, Pt, Pd, etc. with low-cost plasmonic ceramics.