g-C3N4 Photocatalyst Research Articles

Atomically dispersed Fe boosting elimination performance of g-C3N4 towards refractory sulfonic azo compounds via catalyst-contaminant interaction

Herein, an oxygen-doped porous g-C3N4 photocatalyst modified with atomically dispersed Fe (Fe1/OPCN) is successfully prepared and exhibits significant superiority in removing refractory sulfonic azo contaminants from water via catalyst-contaminant interaction. The elimination performance of Fe1/OPCN towards acid red 9, acid red 13 and amaranth containing similar azonaphthalene structure and increasing sulfonic acid groups increases gradually. The amaranth degradation rate of Fe1/OPCN is 17.7 and 6.1 times as that of homogeneous Fenton and OPCN, respectively. In addition, Fe1/OPCN also has more outstanding removal activities towards other contaminants with sulfonic acid and azo groups alone. The considerable enhancement for removing sulfonic azo contaminants of Fe1/OPCN is mainly ascribed to the following aspects: (1) The modified Fe could enhance the adsorption towards sulfonic azo compounds to accelerate the mass transfer, act as e- acceptor to promote interfacial charge separation, and trigger the self-Fenton reaction to convert in-situ generated H2O2 into •OH. (2) Fe(Ⅲ) could coordinate with —N=N— to form d-π conjugation, which could attract e- transfer to attack —N=N— bond. Meanwhile, the inhibited charge recombination could release more free h+ to oxidize sulfonic acid groups into SO4-•. (3) Under the cooperation of abundant multiple active species (•O2-, h+, e-, •OH, SO4-•) formed during the degradation reaction, sulfonic azo compounds could be completely mineralized into harmless small molecules (CO2, H2O, etc.) by means of —N=N— cleavage, hydroxyl substitution, and aromatic ring opening. This work offers a novel approach for effectively eliminating refractory sulfonic azo compounds from wastewater.

Enhanced degradation of Procion Red MX-5B using Fe-doped corn cob ash and Fe-doped g-C3N4

ABSTRACT Procion Red MX-5B (PRM) is harmful to both human health and the environment, and it is resistant to degradation through conventional wastewater treatment methods. In this study, solar-Fenton-like oxidation was used to treat it, employing Fe-doped corn cob ash and Fe-doped g-C₃N₄ (CN) photocatalysts. First, a characterization study (SEM, XRD, BET, PL, and XPS) was performed and its results proved that they were successfully synthesized and the most promising one was 20 wt. % Fe containing Fe/g-C3N4 ;(%20FeCN). Then, the influence of reaction parameters was studied and the optimal conditions were determined to be 0.2 g/L of %20FeCN, 10 mm of HPC, and pH = 3. At these reaction conditions, complete degradation of PRM was observed. Lastly, a kinetic study was performed and the reaction was found to follow the first-order kinetics, with an activation energy calculated to be 40.88 kJ/mol. This suggests that the 20% FeCN catalyst is highly effective and holds great promise for PRM degradation.

Construction of S-scheme g-C3N4/PbTiO3 heterojunction and its highly efficient photocatalytic degradation of organic pollutants under simulated sunlight.

This study successfully synthesized a composite photocatalyst g-C3N4/PbTiO3 through hydrothermal and calcination methods using PbTiO3 and g-C3N4. The catalyst was characterized by XRD, FTIR, Raman, XPS, SEM, TEM, UV-vis DRS, PL, and other techniques. The results indicate that the composite photocatalyst exhibits efficient electron transfer, enhanced light absorption, effective separation and utilization of photogenerated electron-hole pairs, demonstrating superior photocatalytic activity. Under simulated sunlight, the removal efficiency of methyl blue (MB) with an initial concentration of 10mg/L reaches 93.0% after 120min. After five cycles, the degradation efficiency of MB is 79.2%, still maintaining 85% of the initial catalytic activity. The pH values in the range of 4.0-7.0, inorganic anions, and water quality have a minimal impact on the photocatalytic degradation of MB. Additionally, the composite photocatalyst exhibits strong removal capabilities for other pollutants, such as tetracycline. Therefore, the prepared catalyst demonstrates good feasibility for practical applications. Free radical quenching experiments indicate that hydroxyl radicals (·OH) are the primary active groups in the photocatalytic degradation of MB. Based on this, a photocatalytic mechanism involving a S-scheme heterojunction has been proposed. This study provides new insights into preparing PbTiO3 composite semiconductors and constructing novel S-scheme heterojunctions.

Synergistic photocatalytic activity of Bi2O3/g-C3N4/ZnO ternary heterojunction with dual Z-scheme charge transfer towards textile dye degradation

It is clear that a wide range of organic substances, including synthetic textile dyes, have the potential to negatively impact the environment. It is crucial to rationally develop highly effective photocatalysts for the degradation of such type of pollutants. In this regard, a heterostructured photocatalyst comes with enhanced charge separation and extended light absorption ability that improves photocatalytic performance. Therefore, In this study, a Bi2O3/g-C3N4/ZnO (BCNZ) ternary heterojunction photocatalyst was synthesized for the degradation of methylene blue (MB) textile dye.. Thermal polycondensation method was opted to synthesize g-C3N4, while ZnO and Bi2O3 photocatalysts were fabricated using co-precipitation method. Similarly, ternary heterojunction of BCNZ was constructed through co-precipitation method. The ternary heterojunction photocatalyst demonstrated better photodegradation ability due to dual Z-scheme charge transfer route. The dual Z-scheme heterojunction enabled the ternary heterojunction to exhibit enhanced light absorption capabilities with reduced recombination rates as well as enhanced charge separation and migration efficiency (confirmed via transient photocurrent response) that resulted in improved photocatalytic performance. The BCNZ dual Z-scheme photocatalyst displayed 92 % of degradation efficiency which was much higher than that of other (binary and pristine) photocatalysts. Scavenging tests and electron spin resonance spectroscopy revealed the significant role of the •O2−, and •OH radicals in the photodegradation of MB. Furthermore, the reusability test presented good stability and recyclability of the ternary photocatalyst with 80 % degradation efficiency after five catalytic cycles.

Simultaneous bulk and surface modifications of g-C3N4 via supercritical CO2-assisted post-treatment towards enhanced photocatalytic activity

A high-temperature supercritical CO2 (ScCO2)-assisted post-treatment strategy is developed to simultaneously modify the bulk and surface structures of graphitic carbon nitride (g-C3N4) using ScCO2 as penetrant and a small amount of methanol/acetonitrile mixture as modifiers. Specifically, the product of modified g-C3N4 is obtained through the post-treatment of pristine g-C3N4 in a homogeneous ScCO2/methanol/acetonitrile system, continuously heating to reach a target temperature (330 °C, 15.2 MPa) without a residence time. With the assistance of ScCO2, organic molecules penetrate the interlayers of g-C3N4 and subsequently modify the in-plane structure of g-C3N4. Methanol induces the partial transformation of g-C3N4 into a carbon nitride with a poly(heptazine imide)-like structure and with abundant methyl and hydroxyl groups. Simultaneously, acetonitrile polymerizes into 2,4,6-trimethyl-1,3,5-triazine, which is then covalently grafted onto the surface of modified g-C3N4. Remarkably, the entire post-treatment process is completed within 5 min, achieving a final product yield of 92.3 %. The modified g-C3N4 photocatalyst achieves an H2-evolution rate of 2126.1 μmol·h−1·g−1 and a CO2-to-CO conversion rate of 874.1 µmol·h−1·g−1. This work provides a green, efficient, high-yield, and scalable strategy for preparing layered and porous non-metallic photocatalysts using supercritical fluids technology.

Transition metal nickel nanoparticle-decorated g-C3N4 photocatalyst for improving tetracycline hydrochloride degradation

Metallic nickel nanoparticles (Ni0 NPs)-supported g-C3N4 have been developed using a solvothermal technique in N,N-dimethylformamide solvent. A uniformly dispersion of Ni0 NPs anchored on a g-C3N4 photocatalyst can improve the photocatalytic efficiency. The optimized Ni/g-C3N4 catalyst demonstrated a high photodegradation rate of TCH at 6.0 × 10−3 min−1 under LED light irradiation, which was approximately three times greater than that of the bare g-C3N4 catalyst. This superior performance originates from the capable separation of electron-hole pairs, facilitated by the strong interaction between Ni0 NPs and the host g-C3N4, as supported by optical and electrochemical property analysis. Our work provides a facile manner for the effective degradation of pollutants using heterojunction photocatalysts.

Electrostatic self-assembly of hydrotalcite-based g-C3N4 composites for adsorption and photocatalytic degradation of aqueous norfloxacin

Norfloxacin, a quinolone antibiotic pollutant, posed a significant threat to environment and human being health. In this study, hydrotalcite-based g-C3N4 composites were produced using electrostatic self-assembly and the structural memory effect of hydrotalcite to optimize their adsorption-degradation of norfloxacin under visible-light illumination. Optimized hydrotalcite and g-C3N4 composite (750°C, 40 wt% of g-C3N4) exhibited a highest photo-degradation rate constant of 1.8×10−2 min−1 with 83.98 % norfloxacin degradation achieved within 1.5 h under visible-light, surpassing that of bare g-C3N4 and hydrotalcite photocatalysts. The synergistic effects of the composite, such as uniform flower-like micro-morphology and rich mesoporous structure, resulted in a large specific surface area (58.67 m2/g), abundant active sites, and good photo-generated charge separation efficiency. All these facilitated both sorption (7.95 mg/g) and subsequent visible-light degradation of norfloxacin. Furthermore, the superior photocatalytic performance observed in the degradation of norfloxacin under visible-light illumination was assigned to the effective transport of photogenerated electrons and holes between hydrotalcite and g-C3N4 components. The work highlights the potentials of hydrotalcite and g-C3N4 composites as an excellent photocatalyst for environment remediation and water treatment.

Edge functionalized with benzenesulfonyl groups of g-C3N4 nanosheets as a highly efficient photocatalyst for water purification

Photocatalytic water purification is a promising method for environmental remediation, but it is greatly hindered by the rapid charge carrier recombination behavior of the photocatalysts. Herein, a simple wet-chemical method is developed for grafting electron-withdrawing benzenesulfonyl groups at the edges of g-C3N4 nanosheets. These exhibited a superior and versatile photocatalytic performance on the degradation of organic contaminant, as well as disinfected Escherichia coli (E. coli) bacteria under visible light illumination. Systematic studies reveal that the grafting of benzenesulfonyl groups led to the synergic effect in ultrathin g-C3N4 nanosheets of enhancing the photogenerated charge carrier separation on surface, improving light absorption, changing electronic band structure, and causing surface charge redistribution, all of which are beneficial for enhancing the photocatalytic performance. Notably, these edge-activated g-C3N4 photocatalysts also demonstrate remarkable photocatalytic activity in the real tap water and urban wastewater, indicating their promising potential for application in real wastewater treatment.

Improved adsorption and charge transfer capacity by coupling g-C3N4 and NH2-MIL-125 for efficient degradation of sulfamethoxazole in water: Characterization, degradation efficiency, influence factors, and mechanism

Photocatalysis is an advanced oxidation process that shows excellent promise in degrading organic pollutants present in water. However, electrons and holes tend to combine easily during the transfer process, and the adsorption capacity of single-phase photocatalytic materials is weak, resulting in a low degradation rate. Therefore, a new composite semiconductor photocatalyst g-C3N4/NH2-MIL-125 was constructed using a two-step solvothermal method. The morphology, elemental composition, structure, photoelectric properties, and photocatalytic activity of g-C3N4/NH2-MIL-125 were characterized. The photocatalytic degradation of Sulfamethoxazole (SMX) in water was also carried out. Results indicated that g-C3N4/NH2-MIL-125 had been synthesized successfully, and g-C3N4/NH2-MIL-125 had a broader photoresponse range, higher adsorption capacity, and higher separation efficiency of photogenerated carriers. When pH was 4.0 and catalyst dosage was 0.15 g/L, g-C3N4/NH2-MIL-125 showed the highest degradation rate for SMX. It was confirmed that the main active groups in SMX degradation were OH, h+, and O2−. 15 kinds of intermediates of SMX and the possible degradation pathways were identified by high-performance liquid chromatography-mass spectrometry and DFT calculation. Toxicity analysis revealed that the intermediate products have a lower developmental toxicity than SMX. This work demonstrated that g-C3N4/NH2-MIL-125 has great potential in eliminating antibiotics from water.

Facile ultrasound-assisted synthesis of g-C3N4@Bi20TiO32/Bi2O2CO3 heterojunction with high photocatalytic performance for resistant-biodegradable dye

In this study, g-C3N4/Bi20TiO32/Bi2O2CO3 photocatalyst structured as a heterojunction was fabricated by an ultrasound-assisted methodology. It evaluated the activity in photocatalytic processes of g-C3N4/Bi20TiO32/Bi2O2CO3 composite material through simulated visible light-induced Rhodamine B photodegradation, demonstrating photodegradation efficiencies 5.6 and 13.84 times exceeding that of pure g-C3N4 and Bi20TiO32/Bi2O2CO3 in turn. Due to the formation of a ternary heterojunction, the g-C3N4/Bi20TiO32/Bi2O2CO3 composite material has a stronger visible light absorption capability compared to pure g-C3N4 and Bi20TiO32/Bi2O2CO3. The photocurrent density is also significantly increased (0.156 μA/cm2). The catalyst's efficiency remained a high degradation ratio (over 95 %) after five cycles, showing the composite's sustainable stability. In summary, based on its excellent performance, the ternary composite photocatalyst g-C3N4/Bi20TiO32/Bi2O2CO3 exhibits great potential for photodegradation of non-biodegradable dye.

The coexistence of highly dispersed Pt2+ and Pt0 co-catalysts on chemically oxidized g–C3N4 via metal-support interaction: The effect of reduction time on Pt species and hydrogen evolution of Pt/g-C3N4 photocatalysts

Platinum (Pt) cocatalyst greatly enhances the photoactivity of the graphitic carbon nitride (g-C3N4) photocatalyst for photocatalytic H2 evolution where the Pt properties are critical to determine the photocatalytic activity. In this study, highly dispersed Pt was successfully loaded onto chemically oxidized g–C3N4 (OCN) via a hydrogen reduction process over different reduction time. OCN photocatalysts containing highly dispersed Pt2+/Pt0 exhibited outstanding charge separation efficiency and photocatalytic performance. Symmetrical –CO groups on the OCN surface specifically interacted with atomic Pt2+, and the Pt2+ atoms were stably reduced to Pt0 atoms along with the generation of –OH groups over time. The coexistence of Pt0 and Pt2+ promoted superior photocatalytic performance because the photoinduced charge transfer was facilitated by the Pt0 atoms, which was evidenced by the DFT calculation and the EIS, PL, and photocurrent response results. Consequently, after the 24 h reduction, the highly stable and active Pt2+/Pt0 atoms were effectively distributed over OCN, resulting in the highest HER activity at 4091.3 µmol g−1 h−1.

AgCl co-catalyst modified g-C3N4 nanosheets for highly efficient photocatalytic hydrogen evolution

This article uses a co-precipitation method to prepare AgCl/g-C3N4 photocatalysts, and the different loading amounts of AgCl on the g-C3N4 surface photocatalysts have a major effect on the efficiency of photocatalysis. AgCl/g-C3N4 photocatalysts can reduce charge transfer efficiency and enhance photocatalytic performance by loading a significant amount of AgCl onto their surface, which results in a wide interface contact area, excellent charge transfer efficiency, and an increase in numerous surface active sites. In ideal circumstances, 15 % AgCl/g-C3N4 (15 % AgCl/CN) photocatalyst exhibits visible light in triethanolamine aqueous solution (λ > 420) the hydrogen production is as high as 721.34 μmol h−1 g−1 is 15.6 times greater than traditional g-C3N4 photocatalysts. The result show that photocatalysts based on g-C3N4 are capable of producing hydrogen with good efficiency.

Enhanced visible light-assisted photocatalytic activity of g-C3N4 decorated with ZIF-8 and AgI ternary heterojunctions

Fabrication of a suitable photocatalyst system that responds to visible light has become a requirement for photocatalytic environmental remediation processes. For better transfer/separation of photogenerated-charges, successful interfacial engineering to build photocatalytic heterojunctions is essential for improving the photodegradation performance. Herein, ternary composites of zeolitic-imidazolate-framework-8 (ZIF-8) coupled with AgI nanoparticles assembled on g-C3N4 have been fabricated, characterized using XRD, FESEM, EDX, TEM, PL, UV–visible DRS, and N2-adsorption–desorption, and used as visible-light-driven photocatalysts for photocatalytic destruction of methylene blue (MB). The ternary AgI/ZIF-8/g-C3N4 photocatalyst achieved superb photodestruction activity (94.2 %) within 120 min. Besides, the first-order degradation rate constant reached 0.02431 min−1, which was nearly 1.5, 2.5, 4.5, and 5.5 times greater than that reached by ZIF-8/g-C3N4 (0.01628 min−1), g-C3N4 (0.00941 min−1), AgI (0.00542 min−1) and ZIF-8 (0.00441 min−1), respectively. The improved photocatalytic behavior was accredited to the synergistic influence of the photo-charge carrier transfer/separation pathway and the electron mediation assisted by ZIF-8. The trapping tests supported the recommended photocatalytic mechanism, which suggested that the O2− radicals were the main reacting agents in this process. The parameters affecting the photodegradation, including the AgI/ZIF-8/g-C3N4 dose, the solution pH, and the MB concentration were systematically tested in this work. Furthermore, the AgI/ZIF-8/g-C3N4 demonstrated good degradation stability after multi-consecutive rounds (only 1 % deduction in its activity after 5 rounds), and thus, it is projected to be a promising photocatalyst in wastewater treatment.

Hydrogen generation by water splitting of formic acid assisted supramolecular self-assembled g-C3N4 nanostructures

The photocatalytic hydrolysis reaction primarily unfolds on the material's surface, making the material's morphology and microstructure critical for the catalytic efficiency of photocatalysts. In this paper, a formic acid-assisted melamine hydrothermal self-assembly method is explored to prepare g-C3N4 photocatalysts with a unique morphology. The impact of sintering temperature on the morphology of the g-C3N4 photocatalysts are explored and the effect of formic acid concentration on the XRD and FTIR was analyzed. Findings reveal that the g-C3N4 nanostructures photocatalyst possesses fibrous tubular and nanosheet structures, boasting a heightened specific surface area (32.9 m2/g) and a more refined graphite-like crystalline framework. When synthesized with a 0.15 M concentration of formic acid, the g- C3N4 nanostructured photocatalyst achieved a hydrogen production rate (1289.4 μmol h−1 g−1), which is approximately 4.8 times greater than that of bulk g-C3N4 (264.7 μmol h−1 g−1). This work provides a simple method for preparing high-performance g-C3N4 based photocatalysts for visible light hydrolysis hydrogen production.

BiVO4/sulfur-doped g-C3N4 nanocomposite as photocatalyst for degradation of ciprofloxacin under visible light irradiation

In recent years, the use of antibiotics has greatly increased, which has caused environmental pollution. We offer a photocatalyst based on BiVO4/sulfur-doped g-C3N4 nanocomposite, which was made by a one-step thermal condensation method from thiourea and bismuth vanadate to degradate ciprofloxacin (CIP). The BiVO4/sulfur-doped g-C3N4 photocatalyst was analyzed by certain techniques including XRD, FTIR, BET, FESEM, EDX, TEM, DRS, photoluminesence, and Mott-Schottky to determine various physicochemical properties. The photocatalytic degradation of CIP, as a model pollutant, under visible LED light irradiation was tested to investigate the catalytic performance of nanocomposite. Response Surface Methodology (RSM) was employed to optimize operational parameters, including photocatalyst dosage (50–150 mg), CIP concentration (10–30 mg/L), initial pH of the solution (3–11), and irradiation time (12–120 min). The BiVO4/sulfur-doped g-C3N4 nanocomposite, with a narrow bandgap of 2.15 eV, exhibited exceptional photocatalytic performance in degrading CIP. The optimal conditions for CIP removal were photocatalyst dosage of 120.9 mg, CIP concentration of 10 mg/L, and initial solution pH of 3, resulting in 93.5 % removal efficiency after 105 min of irradiation. The photocatalytic degradation kinetics of CIP followed a pseudo-first-order model with a rate constant (K) of −0.0221 L/min, indicating rapid degradation process. The photocatalyst maintained excellent performance after 5 reuses, with only a 3 % reduction in efficiency. XRD analysis confirmed the structural stability of the nanocomposite after reuse.

Modulating g-C3N4 photocatalyst for H2 production via water splitting: The impact of Schiff base incorporation

This study explores the potential for improved photocatalytic activity by tailoring the properties of two-dimensional graphitic carbon nitride (g-C3N4) through non-metallic molecule modifications. Herein, melamine monomers were thermally polymerized in the presence of organic materials, namely (E)-2-((phenylimino)methyl) phenol, (E)-4-(benzylideneamino)benzoic acid, and (E)-4-((hydroxybenzylidene)amino)benzoic acid, to produce g-C3N4-PMP, g-C3N4-BAB, and g-C3N4-HBAB nanosheet composites, respectively. The investigated Schiff bases offer a variety of functionalities capable of influencing the electronic structure, surface reactive sites, and porosity. Consequently, all of the modified composites exhibited higher efficiency in photocatalytic hydrogen generation compared to pristine g-C3N4. Notably, the highest catalytic activity was observed for g-C3N4-PMP, with a rate of 1148 µmol•g−1•h−1, which is seven times greater than that of g-C3N4. Optical and photoelectrochemical properties of the photocatalysts were analyzed to develop a workable mechanism for photocatalysis. The utilization of organic Schiff bases in conjunction with melamine for the g-C3N4 synthesis presents a versatile approach to tailor the properties and augment the photocatalytic performance of the resulting nanocomposite material for diverse environmental and energy-related applications.

Reduction of the photogenerated electron transport path by modulating the conduction band region to achieve the highest lignin β–O–4 bond photocleavage efficiency under xenon excitation

Photocracking of lignin β–O–4 bonds is a green approach for the high-value modification of lignin. Graphitic carbon nitride (g-C3N4) that can photocleave the β–O–4 bond is presently the only stable, metal-free photocatalyst owing to the residual metal ions generated due to photocorrosion of metal sulfides. Herein, g-C3N4 with a N–C3 vacancy structure is prepared by etching site–engineering strategy based on the protection of C–N=C structure by chlorine atom. The N–C3 vacancy structure can reduce the transport path of the photogenerated electrons by tuning the conduction band (CB) region to the edge of the photocatalyst, which impedes the critical complexation of the photogenerated electron–hole pairs and enhances the photoelectric conversion efficiency five-fold. Combined with the unique chemisorption capacity (137.82 kJ/mol) of N–C3 vacancies for oxygen, the g-C3N4 photocatalysts with N–C3 vacancy structure can generate 9.6-fold higher superoxide radicals and 13-fold higher lignin β–O–4 bond photocleavage efficiency lignin compared with untreated g-C3N4. Based on the reaction enthalpy changes and free energies investigated through simulations, a route of lignin Cα–Cβ bonds being oxidized and dehydrogenated twice by photogenerated cavities is proposed for the first time. This work reveals the relation between the properties of g-C3N4 and the photocleavage efficiency of lignin β–O–4 bonds.

Self-assembled S-scheme In2.77S4/K+-doped g-C3N4 photocatalyst with selective O2 reduction pathway for efficient H2O2 production using water and air

Self-assembled S-scheme In2.77S4/K+-doped g-C3N4 photocatalyst with selective O2 reduction pathway for efficient H2O2 production using water and air

Enhanced degradation of tetracycline by gas-liquid discharge plasma coupled with g-C3N4/TiO2

Plasma-catalysis is considered as one of the most promising technologies for antibiotic degradation in water. In the plasma-catalytic system, one of the factors affecting the degradation effect is the performance of the photocatalyst, which is usually restricted by the rapid recombination of electrons and holes as well as narrow light absorption range. In this research, a photocatalyst g-C3N4/TiO2 was prepared and coupled with gas-liquid discharge (GLD) to degrade tetracycline (TC). The performance was examined, and the degradation pathways and mechanisms were studied. Results show that a 90% degradation rate is achieved in the GLD with g-C3N4/TiO2 over a 10 min treatment. Increasing the pulse voltage is conducive to increasing the degradation rate, whereas the addition of excessive g-C3N4/TiO2 tends to precipitate agglomerates, resulting in a poor degradation efficiency. The redox properties of the g-C3N4/TiO2 surface promote the generation of oxidizing active species (H2O2, O3) in solution. Radical quenching experiments showed that ·OH, hole (h +), play important roles in the TC degradation by the discharge with g-C3N4/TiO2. Two potential degradation pathways were proposed based on the intermediates. The toxicity of tetracycline was reduced by treatment in the system. Furthermore, the g-C3N4/TiO2 composites exhibited excellent recoverability and stability.

Visible-light driven efficient cleavage of Cα–Cβ bond in lignin models and lignin over porous tubular carbon nitride

The photocatalytic selective breaking of recalcitrant Cα–Cβ bond in real lignin to product value-added chemicals under mild conditions is intriguing but remains challenging. Herein, a sustainable strategy for the efficient and selective breakage of Cα–Cβ bond in lignin β-O-4 model compounds and lignin over porous tubular g-C3N4 (PTCN) photocatalyst was designed under ambient conditions. Compared with bulk g-C3N4, the construction of PTCN not only facilitates photogenerated charge separation and transfer, but also provides more exposed interior active sites, which is conductive to reactant adsorption on the surface of PTCN, thereby resulting in the higher photocatalytic efficiency. With this strategy, 2-phenoxy-1-phenylethanol as the typical model substrate was completely converted into aromatic monomers with Cα–Cβ bond cleavage selectivity of 97.2 %. Both mechanistic studies and theoretical calculations revealed that the photogenerated holes, electrons and O2− respectively played an essential role in the Cβ–H dehydrogenation and Cα–Cβ bond breakage. Native lignin samples (alkaline, pine and wheat straw) were applied to these photocatalytic systems and successfully depolymerized with Cα–Cβ bond cleavage under optimal reaction conditions. This work could provide an in-depth insight into photocatalyst design for the economical and efficient valorization of lignin.