Performance Of Graphitic Carbon Nitride Research Articles

A well-engineered two-dimensional coral-like architecture CNWO3 for the effective removal of volatile organic compounds from indoor air

One of the promising strategies to enhance the photocatalytic performance of graphitic carbon nitride (CN) is to establish 2D photocatalysts with boosted morphology and adjusted charge transfer direction. Herein, a green and sustainable strategy (water used as solvent) is employed to fabricate a coral-like CNWO3 with highly desirable visible-light photocatalytic activity. The coral-like structure provides more atoms at the edges and corners to act as active antennae to enhance the photocatalytic activity. These new antennae generate various active sites that are short enough to drive strong visible light harvesting, while being large enough to prevent intense quantum confinement effects. Under visible-light irradiation (λ > 400 nm), the as-prepared photocatalyst effectively removes gaseous acetaldehyde (90.5 %) and toluene (73.4 %), the two most common volatile organic compounds (VOCs) in indoor air, possibly due to its unique structure. The DFT calculations clearly show that the interaction of acetaldehyde and toluene over CNWO3 is energetically more favorable than that over CN. Both the hydroxyl (OH) and superoxide (O2−) that are generated by the photocatalyst play a substantial role in VOCs degradation. This work highlights the solar-active photocatalysis development using a synergy of morphology and material nature for sophisticated gas-phase reactions to effectively solve VOCs pollution issues of the indoor environment.

Understanding the Effect of Saturated Gases on Catalytic Performance of Graphitic Carbon Nitride (g‐C3N4) for H2O2 Generation and Dye Degradation in the Presence of Ultrasound

In this article, the effect of saturated gases on H2O2 generation and dye degradation is examined using graphitic carbon nitride (g‐C3N4) as a piezoelectric catalyst. A detailed catalytic evaluation is carried out using a double‐bath sono‐reactor, where the performance of g‐C3N4 for H2O2 production and degradation of rhodamine B and indigo carmine dyes is evaluated for a range of catalyst dosage levels and saturated gases. Specific gases are selected to understand their role in the sonochemical production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) and to elucidate the catalytic mechanism. The use of an Ar–O2 gas mixture leads to the highest yield for H2O2 production and dye degradation due to the positive effect of argon and oxygen in the generation of H2O2 and ROS, respectively. The presence of nitrogen in both air and in an Ar–air mixture increases H2O2 generation since RNS improves the conversion of •OH into H2O2. In contrast, air and Ar–air negatively influences the generation of ROS, which results in a low rate of dye degradation. In this work, new insights of the mechanisms of sonochemical and piezocatalytic processes in the use of graphitic carbon nitride in catalytic applications are provided.

Polyvinyl alcohol as solid proton donor to modify g-C3N4via hydrogen bonding enabling efficient photocatalytic H2O2 production from H2O and O2.

Polyvinyl alcohol (PVA) was used as a solid proton donor to improve the photocatalytic performance of graphitic carbon nitride (CN) for hydrogen peroxide (H2O2) production. The modified CN (CN/PVA) was prepared by mixing CN and PVA at room temperature. The H2O2 production efficiency of CN/PVA was 5.65 times higher than that of CN in pure water. Photocurrent measurement, electrochemical impedance spectroscopy (EIS), and photoluminescence (PL) analysis proved that PVA increased charge separation of CN. X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared (FTIR) analyses further suggested that PVA acted as the proton donor during H2O2 production by interacting with CN via hydrogen bonds. The combination of the charge separation enhancer and proton donor from PVA promoted the sequential two-step single-electron reduction of O2 for H2O2 production. This study paves the way for the modification of g-C3N4 with hydroxyl-containing materials as solid proton donors for photocatalytic H2O2 production.

Improved photocatalytic disinfection performance of graphitic carbon nitride through hybridization with humic acid /zinc peroxide: A synergistic generation of antimicrobial reactive oxygen species

Photocatalytic disinfection of bacteria using photosensitive nanomaterials is an efficient method for bacteria inactivation and is considered a beneficial alternative to chemical disinfectants that produce harmful by-products. However, due to the limited application scope of photocatalysts, the antibacterial efficiency remains unsatisfactory. To enhance the photocatalytic efficiency of the non-metal photosensitizer, graphitic carbon nitride (g-C3N4) nanosheets, they were composited with a metal-based photosensitizer, zinc peroxide (ZnO2) nanoparticles, with the aim of humic acid (HA). Besides the self-generating ability of H2O2 by ZnO2 in an aqueous medium, its deposition over g-C3N4 nanosheets enhances visible light harvesting and increases both surface area and active sites, thereby enhancing photocatalytic efficiency. The resulting composite, g-C3N4/ZnO2, produced more H2O2, •OH, and O2•- radicals than either component when exposed to visible light. Moreover, the photocatalyst demonstrated enhanced photocatalytic disinfection efficacy against Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis) under dark conditions compared to pure g-C3N4 nanosheets. However, a notably greater antibacterial activity was observed when the nanocomposites were subjected to light irradiation. FESEM images and live-dead assays revealed the physical contact of the nanocomposite with the surface of bacterial cells and the loss of cell membrane integrity. Furthermore, it was observed that there was greater cellular uptake of nanocomposites into cells and the generation of reactive oxygen species (ROS) under light irradiation compared to similar conditions in the dark, leading to an increased photoinactivation rate of bacteria. The enhanced photocatalytic and antibacterial activities of g-C3N4/ZnO2 nanocomposites make them attractive for a range of applications, including use in nanomedicine and environmental surface disinfection.

Enhancing photocatalytic performance of Graphitic carbon nitride through deep eutectic system synthesis

Graphitic carbon nitride (GCN) has emerged as a promising semiconductor for visible-light photocatalysis owing to its favorable electronic band structures and stability. However, conventional GCN materials face challenges such as limited light absorption and specific surface area. The choice of precursors significantly influences GCN properties. Mixing different precursors, such as urea and ammonium thiocyanate, in a deep eutectic system (DESys) enables the formation of a homogeneous liquid and the synthesis of GCN with unique structures, enhancing photochemical activity. Through adjustments to the DESys composition and synthesis conditions, the synthesis of GCN-DESys has been optimized, with the optimal conditions being a mixture of ammonium thiocyanate and urea at a ratio of 1:4, heated at 550 °C for 3 h. Characterization of GCN-DESys revealed a mixed layered and velvety structure, forming a heterojunction distinct from traditional GCN. With a degradation mechanism investigation, GCN-DESys demonstrated superior photocatalytic activity in degrading ciprofloxacin under visible light, outperforming traditional GCNs. GCN-DESys, synthesized through the new approach, shows outstanding photocatalytic performance owing to its unique structure and enhanced charge separation. Mechanism analysis revealed the pivotal involvement of hydroxyl radicals (·OH) and superoxide radicals (·O2–) in the photocatalytic degradation process. The formation of these radicals on the surface of the GCN-DESys contributes to the efficient degradation of ciprofloxacin. This study contributes to understanding the preparation of advanced photocatalytic materials through the formation of DESys-based liquid mixture, highlighting the potential of GCN-DESys as an efficient solution for pollutant degradation.

A comparative study of H2O2 production over g-C3N4 photocatalysts made from different sources

The photocatalytic performance of graphitic carbon nitride (g-C3N4) in H2O2 production has been constantly studied, however, whether g-C3N4 made from different raw materials possess distinct photocatalytic ability is not fully explored. In this work, a comparative study of g-C3N4 made from urea, melamine, thiourea, and dicyandiamide respectively under the same thermal process condition was carried out to distinguish their photocatalytic activities. By determining the yield of H2O2 produced under the same light conditions, the ability of the above four g-C3N4 photocatalysts was compared and the amount of H2O2 produced within 5 h was 55.8, 112.7, 101, and 134 µmol/L respectively. Photoelectrochemical and electrochemical impedance spectroscopy measurements indicated that g-C3N4 photocatalysts made from melamine and dicyandiamide with higher H2O2 production had higher photocurrent and lower charge transfer impedance. This might relate to the differences in material crystallinity and the band gap, which influenced their effective carrier concentration.

Synergistic effect of CuO and Sr doped g-C3N4 for CO2 photoreduction into hydrocarbon fuels

This study investigates the enhancement of the CO2 photocatalytic reduction (CO2 PR) process, which plays a critical role in sustainable fuel production and alleviates the environmental greenhouse gas emissions. Overcoming the challenges posed by CO2 inertness and sluggish charge carrier kinetics is imperative for efficient CO2 PR. Herein, we explore the role of copper oxide (CuO) and strontium (Sr) nanoparticles as cocatalysts in enhancing the photocatalytic performance of graphitic carbon nitride (g-C3N4) for CO2 reduction. With an emphasis on the often-overlooked selectivity of photo-excited electrons for CO2 reduction with H2O, we find that Sr improves electrical transport characteristics and effectively extracts photo-excited electrons, resulting in an increased CH4 yield rate (0.25 μmol g−1h−1) compared to CN (0.11 μmol g−1h−1). However, Sr decreases CO2 reduction selectivity by accelerating H2O reduction to H2. In addition, introducing CuO in Sr-doped g-C3N4 (SrCN) further enhances CH4 yield while increasing the selectivity for CO2 reduction. The optimized 5CuO@SrCN nanocomposite exhibits a superior CH4 selectivity of 90.34 % with a yield rate of 1.87 μmol g−1h−1, demonstrating the combined effects of CuO coupling and Sr doping in improving light absorption, surface reaction sites, and charge carrier transfer and separation efficiency in CO2 reduction.

Enhancing photocatalytic hydrogen evolution of g-C3N4 via oxygen-containing groups

This study investigates the impact of three oxygen-containing functional groups (–COOH, –CO, and –OH) on the photocatalytic performance of graphitic carbon nitride (g-C3N4) in the context of the hydrogen evolution reaction (HER) using first principles calculations. Our analysis of the Gibbs free energy of HER reveals that functionalized g-C3N4 in quadrant III exhibits a significantly reduced overpotential of −1.19 eV compared to pristine g-C3N4. Moreover, g-C3N4–(OHQI + OQII + COOHQIII) and g-C3N4–(OQI + OHQII + COOHQIII) demonstrate exceptional light harvesting capabilities in the 350–800 nm range, attributed to anisotropic and steric hindrance effects. Furthermore, g-C3N4–OHQIII and g-C3N4–(OHQI + COOHQIII) exhibit favorable band alignment and narrower band gaps of 2.55 and 2.39 eV, respectively, indicating suitable band edge positions for catalytic HER activities. This work offers valuable insights into the photocatalytic mechanisms and electronic properties of oxygen-containing functional groups modified g-C3N4, paving the way for new applications in solar water splitting with tailored and desirable properties.

W18O49/crystalline g-C3N4 layered heterostructures with full solar energy harvesting towards efficient H2O2 generation and NO conversion

The photocatalytic performance of graphitic carbon nitride (g-C3N4) heterostructures related to the charge carrier separation and transport efficiency is often governed by the interfaces. Herein, in-situ growth of W18O49 nanobelts is attained on amorphous and crystalline g-C3N4 nanosheets to study the effects of the interfaces on photocatalytic oxidation activities. The horizontal growth of W18O49 on g-C3N4 nanosheets is the key in formation of two dimensional (2D)/2D W18O49/g-C3N4 heterostructures. The growth of W18O49 nanobelts on crystalline g-C3N4 nanosheets shows well-developed interfaces (sample W18O49-CCN) in comparison with heterostructures constructed using amorphous g-C3N4 base (sample W18O49-ACN). Characterizations on the structure, components, and properties of the samples demonstrate that these heterostructures reveal extended photo-absorption in visible to near infrared region, with sample W18O49-CCN showing much higher photogenerated charge carrier separation and transport efficiency. A H2O2 evolution rate of 5550 µMg−1h−1 is observed for sample W18O49-CCN under full solar-spectrum illumination (and 398 µMg−1h−1 observed for pristine crystalline g-C3N4), which is ∼ 2.4 times of that of sample W18O49-ACN prepared using amorphous g-C3N4. In addition, a NO removal rate of 72.1% is observed for sample W18O49-CCN with a NO2 selectivity of 6.2%. These results provide inspiration for construction of g-C3N4 homojunctions for practical photo-redox reaction applications.

Probing the role of H-ZSM-5 zeolite in the hydrogen evolution performance of graphitic carbon nitride

Graphitic carbon nitride (CN) hold great promise as a photocatalyst for generating hydrogen energy via water splitting, owing to its remarkable ability to respond to visible light and its strong reduction capacity. However, the photocatalytic water splitting for H2 evolution performance of pure CN was impeded by its low surface area, inadequate hydrophilicity, and unsatisfactory photoelectric conversion efficiency. Here we tackled these challenges by synthesizing a series of CN/H-ZSM-5 composites with varying amount of H-ZSM-5 zeolite using a straightforward thermal copolymerization method. The contact angle and N2 adsorption-desorption measurements confirmed that the incorporated hydrophilic and porous H-ZSM-5 zeolite contribute to increased surface area and improved hydrophilicity of the CN/H-ZSM-5 composites. Meanwhile the resulting CN/H-ZSM-5 composites exhibited significant separation and migration enhancement of photoexcited charge carriers. Consequently, the optimized CN/H-ZSM-5 composite, containing 50 mg of H-ZSM-5 zeolite, demonstrated 13 times increase in photocatalytic H2 production rate than that of pure CN. This work not only provided a competitively universal approach on the design of high-efficiency CN based photocatalyst, but also clarified the role of H-ZSM-5 zeolite in the H2 evolution enhancement.

A Breakthrough in Photocatalytic Wastewater Treatment: The Incredible Potential of g-C3N4/Titanate Perovskite-Based Nanocomposites.

Water pollution has emerged as a major global environmental crisis due to the massive contamination of water resources by the textile dyeing industry, organic waste, and agricultural residue. Since water is fundamental to life, this grave disregard puts lives at risk, making the protection of water resources a serious issue today. Recent research has shown great interest in improving the photocatalytic performance of graphitic carbon nitride (g-C3N4) for wastewater treatment. However, the photocatalytic removal activity of pure g-C3N4 is poor, owing to its minimal surface area, fast recombination of photo-generated electron-hole pairs, and poor light absorption. Recently, titanate perovskites (TNPs) have attracted significant attention in both environmental remediation and energy conversion due to their exceptional structural, optical, physiochemical, electrical, and thermal properties. Accordingly, TNPs can initiate a variety of surface catalytic reactions and are regarded as an emerging category of photocatalysts for sustainability and energy-related industries when exposed to illumination. Therefore, in this review article, we critically discuss the recent developments of extensively developed g-C3N4/TNPs that demonstrate photocatalytic applications for wastewater treatment. The different synthetic approaches and the chemical composition of g-C3N4/TNP composites are presented. Additionally, this review highlights the global research trends related to these materials. Furthermore, this review provides insight into the various photocatalytic mechanisms, including their potential impact and significance. Also, the challenges faced by such materials and their future scope are discussed.

Enhanced solar-induced photocatalytic removal of antibiotics over molecularly reconstituted graphitic carbon nitride

Promoting the photocatalytic performance of graphitic carbon nitride (g–C3N4) for efficient removal of organic contaminants like antibiotics from wastewater has gained much consideration due to its metal-free uniqueness and environmental friendliness. In this work, the photocatalytic activity of g–C3N4 is greatly enhanced via a hydrothermally molecular dissociation and subsequent calcination reconstitution, which endows g–C3N4 with a large specific surface area, rapid separation of photogenerated electron/holes and strong redox ability. The apparent kinetic constant (k) of tetracycline hydrochloride (TCH) for the sample obtained under the optimal preparation conditions (CN–C–12) is 4.5 times that of pristine g–C3N4, companied with a stable cycling photocatalytic activity. The possible degradation pathways and the toxicological evaluation of the intermediates were analyzed by LC-MS and ECOSAR. Superoxide radicals (∙O2–) and singlet oxygen (1O2) are detected to be the primary reactive species in the photocatalytic degradation of TCH. Additionally, the practical application of CN–C–12 for TCH removal in actual sunlight and treatment of domestic printing and dyeing wastewater was also investigated. This work shows a potential application of the molecular reconstituted g–C3N4 in the photo-catalytically environmental purification.

Regulating Intermediate Concentration to Synthesize Highly Crystalline g‐C3N4 under Spontaneous Ultrahigh Pressure

AbstractImproving polymerization and crystallization properties has become a key point to maximize the intrinsic photocatalytic performance of graphitic carbon nitride (g‐C3N4), however, the critical roles of intermediates in the polymerization and crystallization process are not clear. Herein, highly crystalline g‐C3N4 is obtained by calcinating different amount of dicyandiamide in a closed environment. Ultrahigh atmospheric pressure up to 6.2 MPa can be spontaneously formed due to the produced gaseous intermediates. The best crystallization properties were achieved when 1.8 g of dicyandiamide was used. The photocatalytic hydrogen production rate reaches 9241.3 μmol ⋅ g−1 ⋅ h−1, which is improved by about 12.5 times by comparison. The crystallization and hydrogen production activities cannot be enhanced only by adding an initial gas pressure meanwhile keeping the quality of dicyandiamide constant, confirming that the intermediate concentration determines the polymerization and hydrogen production performance of g‐C3N4. This study is important to improve the intrinsic photocatalytic performance of g‐C3N4 and the composites.

Enhancing the photocatalytic performance of the g-C3N4/BiOCl heterojunction in gaseous toluene degradation via K+ decoration in g-C3N4

Doping or constructing heterojunctions by coupling with other semiconductors are effective methods to improve the photocatalytic performance of graphitic carbon nitride (g-C3N4) in toluene degradation. Herein, thermally condensed synthesized K-doped g-C3N4 (KCN) is coupled with BiOCl via a hydrothermal method, and KCN/BOC heterostructures are obtained. The optimal KCN1/BOC heterojunction exhibits approximately 85% removal of toluene after 150 min irradiation under simulated solar light, which is 12.4 and 9.6 times higher than those of g-C3N4 and BiOCl, respectively. The superior performance of KOH-modified g-C3N4 is attributed to the electron transfer channels formed by the insertion of K+ into the g-C3N4 layers, which facilitate efficient charge separation and rapid electron transfer. Furthermore, the KCN/BOC heterostructure with the Z-scheme further improves the surface charge separation efficiency, which plays a critical role in the photocatalytic process. This work provides a facile and promising strategy for dual-strategy modification of g-C3N4 to enhance photocatalytic degradation activity.

The Adsorption Behaviors and Mechanisms of Humic Substances by Thermally Oxidized Graphitic Carbon Nitride.

Thermal oxidation is efficient for enhancing the photocatalysis performance of graphitic carbon nitride (g-C3N4), while its effect on adsorption performance has not been fully studied, which is crucial to the application of g-C3N4 as adsorbents and photocatalysts. In this study, thermal oxidation was used to prepare sheet-like g-C3N4 (TCN), and its application for adsorption of humic acids (HA) and fulvic acids (FA) was evaluated. The results showed that thermal oxidation clearly affected the properties of TCN. After thermal oxidation, the adsorption performance of TCN was enhanced significantly, and the adsorption amount of HA increased from 63.23 (the bulk g-C3N4) to 145.35 mg/g [TCN prepared at 600 °C (TCN-600)]. Based on fitting results using the Sips model, the maximum adsorption amounts of TCN-600 for HA and FA were 327.88 and 213.58 mg/g, respectively. The adsorption for HA and FA was markedly affected by pH, alkaline, and alkaline earth metals due to electrostatic interactions. The major adsorption mechanisms included electrostatic interactions, π-π interactions, hydrogen bonding, along with a special pH-dependent conformation (for HA). These findings implied that TCN prepared from environmental-friendly thermal oxidation showed promising prospects for humic substances (HSs) adsorption in natural water and wastewater.

Bioinspired Z-scheme In2O3/C3N4 heterojunctions with tunable nanorod lengths for enhanced photocatalytic hydrogen evolution

Inspired by natural photosynthesis, Z-scheme heterojunction fabrication has been developed as an effective approach to improve the photocatalytic H2 evolution performance of graphitic carbon nitride (g-C3N4) based photocatalysts. In this work, we fabricated the Z-scheme In2O3 nanorod/C3N4 heterojunction and tailored the length of the In2O3 nanorod, by which the carriers' behavior of the In2O3/C3N4 heterojunctions could be subtly regulated. By employing finite difference time domain simulation and photoelectric characterization, we clarified the mechanism of the length-dependent regulation for photoelectric conversion efficiency. Due to the compromise between photoinduced exciton generation, dissociation, and migration as the nanorod length increased, the photoelectric conversion efficiency was maximized at an optimal length (53 nm) of the In2O3 nanorod, and the corresponding maximum H2 evolution rate of Z-scheme In2O3/C3N4 heterojunctions was 12.9 times higher than that of the pristine g-C3N4. This work provides a direct guideline for designing the optimal geometrical configuration of g-C3N4 based heterojunctions.

Sn-doped g-C3N4 as a novel photoelectrocatalyst for water oxidation

The photocatalytic performance of graphitic carbon nitride can be enhanced multifold by introducing suitable dopants. Here we report incorporating a cost-effective, non-toxic and abundant element, i.e., tin, in elongated semiconducting carbon nitride (g-C3N4). A novel procedure was used to introduce varying amounts of tin to the g-C3N4 framework. The new photocatalysts (Sn–CN) were characterized by X-Ray Diffraction (XRD) and FT-IR measurements, confirming the absence of tin oxide and incorporation of tin in the g-C3N4 backbone. The SEM, EDX, TEM and XPS measurements demonstrated the elongated morphology and the presence of tin in the composite materials. BET measurements showed a relative increase in the specific surface area for the composites. The optical measurements showed enhanced solar light absorption and promoted the charge carrier's separation after the insertion of Sn to g-C3N4. Photoelectrochemical water dissociation measurements showed that 10% tin doping increased the activity of g-C3N4 to water photo-oxidation about four times. This improvement was analyzed by electrochemical impedance spectroscopy measurements.

Controllable synthesis for carbon self-doping and structural defect co-modified g-C3N4: Enhanced photocatalytic oxidation performance and the mechanism insight

For the purpose of improving the photocatalytic performance of graphitic carbon nitride (g-C3N4) in the field of contaminant elimination, an in-situ malonamide-assisted strategy is provided to prepare carbon self-doping and structural defect co-modified g-C3N4 (CDCN) via preprocessing of the mixture of urea and malonamide followed by thermal copolymerization. Changing the initial malonamide dosage can precisely adjust the carbon doping level and structural defect concentration of CDCN. The characteristic results confirm that the doped C derived from malonamide was successfully implanted into the g-C3N4 framework by replacing sp2 hybrid N atoms (C−N=C) in the heptazine units, simultaneously forming some structural defects. Additionally, the preprocessing endows CDCN with good textural properties. So, the optimal CDCN20 shows remarkably enhanced visible-light photocatalytic activity in eliminating acetaminophen (APAP) and methylparaben (MPB) in water than pristine g-C3N4. By combining experimental and theoretical calculating results, the synergistic effect of C self-doping and structural defect promoting the photocatalytic performance of g-C3N4 is revealed thoroughly. This work provides a controllable strategy for synthesizing effective C self-doped g-C3N4 and a new insight into electronic structure and band structure-regulated photocatalytic oxidation mechanisms.

Synchronized wet-chemical development of 2-dimensional MoS2 and g-C3N4/MoS2 QDs nanocomposite as efficient photocatalysts for detoxification of aqueous dye solutions

The photocatalytic performance of graphitic carbon nitride (g-C3N4) is improved by the introduction of molybdenum disulfide (MoS2) quantum dots (QDs), aiming the enhanced visible light absorbance in resultant 2-dimensional g-C3N4/MoS2, termed as GCN/MoS2 hereafter. A novel synthetic approach i.e., pseudo-successive ionic layer adsorption and reaction (p-SILAR) was employed to deposit MoS2 QDs on g-C3N4 and to salvage 2-dimensional MoS2 concomitantly. The results of the photocatalytic activity affirm that GCN/MoS2 worked as a better photocatalyst than the pure g-C3N4, while salvaged MoS2 also showed reasonable degradation of Rhodamine-B (RhB) dye. The average pore size (measured with BET analysis) of GCN/MoS2 was reduced to 31.91 nm from 33.11 nm (for g-C3N4), indicating effectual nanoscale deposition of MoS2 which resulted in a decrease in the overall bandgap alignment of the composite from 2.8 eV to 2.2 eV. In-depth material characterization and photocatalytic analysis was carried out to affirm that p-SILAR serves as a suitable synthesis route for the development of GCN/MoS2 nanocomposite as well as salvaged MoS2.

Molten salt-assisted synthesis of nitrogen-vacancy crystalline graphitic carbon nitride with tunable band structures for efficient photocatalytic overall water splitting

The photocatalytic overall water splitting performance of graphitic carbon nitride (g-C3N4) has still been restricted by its inefficient charge separation efficiency. Herein, nitrogen-vacancy crystalline g-C3N4 nanosheets (g-C3N4-D) with tunable band structures were successfully prepared by the alkali-molten salt-assisted method for efficient photocatalytic overall water splitting. Among them, g-C3N4-D2 not only combines the advantages of the amorphous and crystalline state of two-dimensional g-C3N4 nanosheets, but also introduces nitrogen vacancy to adjust the bandgap structures of crystalline g-C3N4 by an alkali etching, thus improving the light energy utilization and charge separation efficiency. TEM and EPR spectrum prove the existence of N defects in the crystalline g-C3N4. The excellent and stable photocatalytic overall water splitting activity with H2 and O2 evolution rate of 49.60 μmol g−1 h−1 and 24.71 μmol g−1 h−1 was obtained over g-C3N4-D2 with Pt and Co3O4 nanorods as cocatalysts (Pt/g-C3N4-D2/3%Co3O4 NRs) under AM 1.5G simulated light irradiation. In the half-reaction experiments, the maximum H2 evolution rate of Pt/g-C3N4-D2/3%Co3O4 NRs is 3.78 mmol g−1 h−1 with a significant quantum efficiency of 11.94 % at 400 nm, and the solar-hydrogen conversion efficiency (STH) is 1.48 %. The photocatalytic water oxidation activity of Pt/g-C3N4-D2/5%Co3O4 NRs is 42.34 μmol g−1 h−1. Additionally, the potential mechanism of photocatalytic overall water splitting was testified by in-situ XPS. This work provides a simple strategy for further advancing the potential application of g-C3N4 by molten salt-assisted alkali etching to introduce N vacancies to regulate the band gap of crystalline g-C3N4 for photocatalytic overall water splitting.