Construction Of Heterostructures Research Articles

Construction of rare-metal neodymium-doped ZnO and g-C3N4 Z-type heterostructures enhance the photocatalytic efficiency of methylene blue removal

Herein, Nd-ZnO/g-C3N4 (NZCN) composites were obtained by doping rare-earth element Nd with ZnO using a hydrothermal method, coupled with g-C3N4 (CN) electrostatic ultrasonic self-assembly. The NZCN composite exhibited an impressive methylene blue (MB) removal rate of 94.88 %, with a degradation rate of 0.02637 min−1 after 105 min exposure to 500 W xenon lamp irradiations. Comparatively, the degradation rate of MB by the NZCN composite was five and twice times higher than ZnO and CN samples, respectively. This significant improvement can be attributed to the synergistic effect of Nd, ZnO, and CN, which not only widened the light absorption range but also enhanced the density, separation, and transport of photogenerated electrons (e−) and holes (h+), thus improving the photocatalytic performance of the NZCN composites. An in-depth investigation into the photocatalytic reaction process was carried out using free-radical active-species capture experiments, confirming the critical role of h+. Furthermore, the reproducibility and stability of the NZCN composites were assessed over five experimental cycles, demonstrating consistent and stable MB degradation rates of 90.1 % while retaining the crystal structure unchanged. Overall, the construction of rare-earth-metal-doped ZnO and Z-type heterojunctions synergistically improves photocatalytic activity and provides a green and environmentally friendly approach for the removal of organics from wastewater.

Tuning the metal–semiconductor contact nature in MXene-based van der Waals heterostructures

Two-dimensional (2D) transition metal carbides, nitrides, or carbonitrides (MXenes) have emerged as promising ultrathin materials for nanoelectronics and optoelectronics. However, the contact barrier at metal–semiconductor (MS) junctions still significantly limits the device's performance. Here, we propose a novel strategy—functionalizing accompanied with external electric fields—to tune the MS contact nature in MXene-based van der Waals (vdW) heterostructures, taking 2D Ti2C as an example, by means of first-principles calculations. Different Ti2CO2/Ti2CX2 (X = OH or S) vdW heterostructures are designed via functionalizing Ti2C metals to contact with 2D Ti2CO2. We reveal that OH functionalized vdW MS heterostructure (Ti2CO2/Ti2C(OH)2) can be tuned to the Ohmic contact owing to the strong interlayer interaction inducing a large number of interlayer transferred electrons; while for the sulfurized vdW MS heterostructure (Ti2CO2/Ti2CS2), its Schottky barrier height and contact type can be effectively tuned by external electric field due to the rather weak interlayer interaction. Our work paves a new way for the construction of 2D MXene-based vdW MS heterostructures and demonstrates the great potential of 2D MXenes in future nanoelectronics and optoelectronics.

Electrochemical Nitrate Reduction to Ammonia – Recent Progress

AbstractThe presence of nitrate in industrial, domestic and agricultural wastewater has a detrimental impact on both ecosystem and human health, as remediation and purification efforts are slow, challenging and difficult, given the high solubility and stability of this pollutant. Taking nitrate into high value‐added ammonia by electrochemical reduction can overcome high pollution and energy consumption limit of Haber‐Bosch process with long‐term significance of environmental protection and energy saving. This review summarized the research progress on the electrocatalytic reduction of nitrate to ammonia, with a focus on the reaction mechanisms, influencing factors, product detection methods, performance evaluation methods and the research status of electrocatalysts up to now. The review reported the latest strategies employed to design efficient electrocatalysts, such as pore structure regulation, alloying, heterostructure construction, defect and interface engineering, crystal surface regulation and microenvironment modulation of single‐atom catalysts. It highlights critical factors that determin the performance in terms of nitrate adsorption, exposed active sites, mass transfer rate, intermediates barrier and side reactions, as well as the stability of electrocatalysts and recovery of ammonia. In addition, the future direction of technology for electrocatalytic reduction of nitrate to ammonia has also been proposed.

CoFe2O4/MoS2@Au: Multifunction Z-Scheme Heterojunction for SERS Monitoring and Photocatalytic Degradation of Fungicides

Efficient detection and degradation of fungicides are greatly concerned with aquatic food safety. Herein, a multifunction CoFe2O4/MoS2@Au (ACMS) composite was synthesized for crystal violet (CV) and malachite green (MG) photocatalytic degradation and SERS determination. As the construction of the Z-scheme heterostructure of ACMS, which enhanced the light absorption capability and the separation efficiency of photoexcited carrier significantly, ACMS possessed an excellent photocatalytic performance with a degradation rate of 94.76% for CV under simulated solar light irradiation. Furthermore, the multifunction ACMS exhibited superior SERS capability with a detection limit (LOD) of 4.309 × 10−2 μg L−1 for MG residues in water. And the ACMS substrates could be utilized to determine the MG residues in crucian carp extract, resulting in a recovery rate of 96.00~116.00%. In addition, such multifunction heterojunctions were performed for in situ monitoring of the photodegradation process. This research opened up a novel perspective on the applications of heterojunction-based multifunction materials for food safety control.

Constructing heterostructure of WP/WP2 to enhance catalytic activity and stability toward hydrogen generation

Transition metal phosphides (TMPs) have been identified as potential electrocatalysts for the hydrogen evolution reaction (HER) due to their unique structural and electronic properties. However, TMPs have not yet achieved the desired HER performance, and further improvements are required. Herein, we fabricate heterostructured tungsten phosphide/tungsten diphosphide (WP/WP2) composite microrods grown on carbon cloth (WP/WP2/CC) as an efficient self-supported electrocatalyst, which is proven to be highly efficient and stable for the HER. Various experimental results and density functional theory calculations reveal that the formation of WP/WP2 heterostructures can regulate the electronic structure of active sites and optimize hydrogen adsorption free energy on active sites, which accelerates the electron transfer and boosts the HER performance to WP/WP2/CC. By tuning the phosphidation temperatures, the optimized WP/WP2/CC electrocatalyst shows a superior HER performance with low overpotentials of 92 mV and 146 mV at 10 mA cm−2 in 0.5 M H2SO4 and 1.0 M KOH solutions. Meanwhile, it maintains a stable activity at 100 and 150 mV for at least 12 h in 0.5 M H2SO4 and 1.0 M KOH media, respectively. This study demonstrates that the construction of heterostructures can serve as an efficient strategy to improve the electrocatalytic performance of metal phosphide-based electrocatalysts.

Forging Fenton-like system to functionalize electron/hole enrichment regions for ATZ photocatalytic degradation

Independent functional regions for electrons and holes enrichment are usually driven by the construction of multiple heterostructures, which is difficult to achieve fine-controlling, resulting in the limited photocatalytic activity. TiO2-based photocatalysts with suitable forbidden band widths are promising for wide application prospects, where the construction of Schottky heterojunctions is the trick to achieve directional migration of electrons and holes. Here, a regionalized surface modification method of H–TiO2 with oxygen vacancy (Ov) and defects for efficient carrier separation was reported, in which interspersed Ag nanoparticles and SiO2 layers serve as electron/hole enrichment regions, respectively. Meanwhile, SiO2 can be served as adsorption sites for photocatalytic oxidation of small-molecule pollutants, while Ag nanoparticles with H+ adsorption capacity and reasonable guide band position can be used as an engine of Fenton-like reactions to cyclically generate the active substance H2O2 to participate in the reduction reaction. The degradation efficiency of Ag–SiO2–H–TiO2 (ASHT) can be increased by 159% for pesticide atrazine (ATZ). The superoxide radicals generated by electrons and oxygen in ASHT also generate H2O2, which promotes the centralized generation of hydroxyl radicals to improve photocatalytic performance. The structural design strategy of ASHT provides a new concept for the process of ring-opening reactions of benzene-containing contaminants in water and conversion to small molecules which will eventually be rapidly mineralized.

Construction of oxygen-vacancy-rich Z-scheme polypyrrole/Bi2SiO5 heterojunction for efficient degradation of antibiotics under simulated sunlight

A Z-scheme polypyrrole/Bi2SiO5 heterojunction rich in oxygen vacancies was prepared by combining the organic polymer polypyrrole with Bi2SiO5 via a hydrothermal method and an oxidative polymerization reaction. The photocatalyst exhibited good stability in water and effectively degraded tetracycline, oxytetracycline, ciprofloxacin, norfloxacin, and doxycycline under simulated sunlight, indicating its excellent potential for wastewater treatment. In particular, the efficiency of tetracycline removal by the optimized polypyrrole/Bi2SiO5 composite after 120 min of irradiation was 93.1%, approximately 2.1 times that of Bi2SiO5. The exceptional photocatalytic performance of polypyrrole/Bi2SiO5 stemmed from the construction of a Z-scheme heterostructure and generation of oxygen vacancies induced by the introduction of polypyrrole. Furthermore, liquid chromatography–mass spectrometry (LC-MS) was used to investigate the intermediate products of tetracycline degradation, and possible degradation pathways were deduced. Finally, a possible photocatalytic mechanism was proposed based on the results of electron paramagnetic resonance and free radical capture experiments.

Polyethyleneimine-induced in-situ chemical epitaxial growth ultrathin 2D/2D graphene carbon nitride intralayer heterojunction with elevating photocatalytic activity: Performances and mechanism insight

Integrating 2D carbon nitride (CN) photocatalyst with 2D graphene into a lateral heterojunction can decrease energy loss within interlayer space, which is an intriguing strategy for tailoring photocatalyst for energy and environmental applications. Herein, a polyethyleneimine (PEI) induced in-situ chemical epitaxial growth strategy was adopted to tailor graphene-oxide CN (GO-CN) intralayer heterostructure photocatalyst, where PEI was served as chemical inducer and crosslinker to construct polymerization precursor, and a one-pot self-assembly followed in-situ thermal-polymerization and thermal-etching method was conducted. Series characterizations manifest the successful construction of ultrathin 2D-2D GO-CN intralayer heterostructure, which possesses ameliorated specific surface area, visible-light harvest and charge behaviors. Quench tests, ESR and LC-MS explored photodegradation active species, intermediate and route, while online FTIR real-time and in-situ monitor the variation of functional groups. In the end, DFT theoretical analysis further affirm the charge transfer between GO and CN, and unveil conceivable elevated mechanism.

Post‐Treatment of Metal Halide Perovskites: From Morphology Control, Defect Passivation to Band Alignment and Construction of Heterostructures

AbstractMetal halide perovskite solar cells (PSCs) have witnessed a swift increase in power conversion efficiency in the past decade, emerging as one of the most promising next‐generation photovoltaic technologies for commercialization and low‐carbon energy generation. Through significant efforts in optimizing the processing techniques, high‐quality perovskite thin films can now be prepared with polycrystalline morphologies consisting of monolayer grains. Nevertheless, defects and microstructural disorders still form at the surface/heterointerface and in the bulk of the films. Post‐treatment of the as‐crystallized films has been intensively investigated for passivating these defects, being proved effective for improving the device performance. In this review, the versatile strategies for post‐treating the surface of perovskite thin films toward morphology control, defect passivation, and band alignment are discussed. The tailored surface properties are correlated to charge dynamics at interfaces and photovoltaic performance of PSCs. Since the perovskite heterostructures prepared by simple post‐treatments may suffer from degradation at high temperatures, the recent advances in preparing phase‐pure and stable perovskite heterostructures are also discussed. Finally, a perspective elaborating future opportunities for further enhancing the efficiency and stability of PSCs is provided.

3D heterostructure constructed by few-layer 1T MoS2 and MXene under high electrostatic fields for high-performance supercapacitors

Electrostatic spray deposition (ESD) is a promising technique for preparing high-quality heterostructure materials to achieve high electrochemical performance. Moreover, the materials obtained by ESD possesses well-dispersed, bonder-free and easy-control advantages. Herein, we firstly report that 1T MoS2/Ti3C2Tx heterostructure material is successfully constructed by few-layer 1T MoS2 and Ti3C2Tx MXene through ESD. The construction of heterostructure by high electrostatic fields is able to solve problem of agglomeration of layered materials, improve conductivity and stabilize 1T MoS2 to realize outstanding electrochemical performance of supercapacitor. As expected, the binder-free 1T MoS2/Ti3C2Tx heterostructure displays an excellent specific capacitance (1198 mF cm−2 at 3 mA cm−2), a high rate performance (45% as current density from 3 to 20 mA cm−2) and long-cycle life (73.8% capacity retention after 7000 cycles at 20 mA cm−2). More interestingly, a simple and efficient route to prepare 2D/2D heterostructure electrode for storing energy can be extended to other materials.

Enhancing photocatalytic degradation efficiency via the construction of organic/inorganic S-scheme supramolecular hybrid heterostructures

This study demonstrates the successful construction of a hybrid van der Waals heterostructure (vdWH) consisting of 3D supramolecular networks and 2D semiconductor Ag3PO4, using hydrogen-bonded 3D networks H12SubPcB-OPh2OH self-assembled onto Ag3PO4. The resulting organic/inorganic vdWH exhibits significantly enhanced photocatalytic degradation efficiency for oxytetracycline (OTC) and tetracycline (TC) under visible light irradiation, with apparent rate constants 1.8 and 1.5 times higher than those of pristine Ag3PO4, respectively. Moreover, after five photocatalytic cycles, the photocatalytic activity of vdWH was still much higher than that of pristine Ag3PO4. Molecular dynamics simulations indicate that the SubPc-3 supramolecular assembly is more prone to forming a 3D hydrogen bonding network rather than a 1D columnar stacking. In-situ irradiated X-ray photoelectron spectroscopy analyses and theoretical calculations confirm that the charge transfers between H12SubPcB-OPh2OH and Ag3PO4 are consistent with the S-scheme mechanism. This work provides a promising strategy for designing and fabricating efficient and stable supramolecular self-assembled semiconductor-based photocatalysts.

Synergy Between Surface Confinement and Heterointerfacial Regulations with Fast Electron/Ion Migration in InSe-PPy for Sodium-Ion Storage.

Layered indium selenide (InSe)is a new 2D semiconductor material with high carrier mobility, widely adjustable bandgap, and high ductility. However, its ion storage behavior and related electrochemical reaction mechanism are rarely reported. In this study, InSe nanoflakes encapsulated in conductive polypyrrole (InSe@PPy) are designed in consideration of restraining the severe volume change in the electrochemical reaction and increasing conductivity via in situ chemical oxidation polymerization. Density functional theory calculations demonstrate that the construction of heterostructure can generate an internal electric field to accelerate electron transfer via additional driving forces, offering synergistically enhanced structural stability, electrical conductivity, and Na+ diffusion process. The resulting InSe@PPy composite shows outstanding electrochemical performance in the sodium ion batteries system, achieving a high reversible capacity of 336.4mAhg-1 after 500 cycles at 1Ag-1 and a long-term cyclic stability with capacity of 274.4mAhg-1 after 2800 cycles at 5Ag-1 . In particular, the investigation of capacity fluctuation within the first cycling reveals the alternating significance of intercalation and conversion reactions and evanescent alloying reaction. The combined reaction mechanism of insertion, conversion, and alloying of InSe@PPy is revealed by in situ X-ray diffraction, ex situ electrochemical impedance spectroscopy, and transmission electron microscopy.

Unveiling the Structural Self-Reconstruction and Identifying the Reactive Center of a V, Fe Co-Doped Cobalt Precatalyst toward Enhanced Overall Water Splitting by Operando Raman Spectroscopy.

The development of efficient and stable bifunctional electrocatalysts based on non-noble metals for water electrolysis is both urgent and challenging. However, unresolved issues remain regarding the challenge of identifying the active phase and gaining a comprehensive understanding of its surface reconstruction and functionality throughout the reaction process. In this study, we have combined doping and heterostructure construction by a one-step electrodeposition and a subsequent activation treatment to synthesize Fe, V co-doped Co3O4/Co(OH)2 and Co/Co(OH)2 heterointerfaces (referred to as A-Co60Fe1.1V). These heterointerfaces, composed of Co/Co(OH)2 and Co3O4/Co(OH)2, are proposed to facilitate charge transfer process during catalysis. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the introduction of V and Fe dopants increases the valence state of Co centers in Co3O4 and Co(OH)2. Further operando Raman spectroscopy reveals that Co(OH)2 and Co3O4 with the high-valence Co centers remain stable during the hydrogen evolution reaction (HER) process. These high-valence Co centers are believed to promote the crucial water dissociation step and therefore enhance the overall HER catalysis. On the other hand, during the oxygen evolution reaction (OER), Fe, V co-doping leads to an earlier formation of the active CoOOH species, while Fe doping can further help stabilize the more reactive β-CoOOH species instead of the less reactive γ-CoOOH. As a result, the A-Co60Fe1.1V catalyst exhibits significantly improved catalytic activity for both HER and OER that it requires low overpotentials of 51 and 250 mV, respectively, to attain a current density of 10 mA cm-2. Moreover, when utilized as both the cathode and anode in alkaline water electrolysis, the A-Co60Fe1.1V catalyst can operate at a mere 1.54 V voltage while maintaining 10 mA cm-2, surpassing the majority of non-noble metal catalysts. Remarkably, it also exhibits stability for at least 40 h at ∼100 mA cm-2.

VFe@Ni/Ni3N Mott-Schottky heterojunction induced electronic modulation for efficient alkaline water splitting

Designing affordable and productive bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has been a long-term goal of anion exchange membrane water electrolysis (AEMWE). Heteroatoms doping and heterostructure construction are generally considered as effective methods for electrocatalysts modification. Herein, V and Fe co-doped Ni/Ni3N (VFe@Ni/Ni3N) electrocatalyst with a Mott-Schottky heterostructure was prepared by hydrothermal and NH3 reduction methods. The formation of Ni/Ni3N Mott-Schottky heterojunction can effectively trigger the self-driven carrier transfer on the heterointerfaces, thus accelerating charges achievement to the surface active sites and advancing the catalytic efficiency. Meanwhile, the co-doping of V and Fe lowers the flat-band potential of Ni/Ni3N, leading to greater electron density, which increases the electron transport potentiality and facilitates the adsorption and reduction of H* in the HER process. Therefore, a remarkable performance for HER with overpotentials of 47 and 180 mV at 10 and 200 mA cm−2 in alkaline solution was achieved. Significant progress has also been made in OER and the full water electrolysis. Furthermore, for the AEMWE with VFe@Ni/Ni3N, a low applied cell voltage of only 1.75 V was needed to reach a high current density of 600 mA cm−2 with an impressive long-term stability of 100 h. This study supplies an innovative strategy of electronic modulation by co-doping and Mott-Schottky heterojunction construction, which is referential for the advancement of economic electrocatalysts for sustainable energy systems.

Metal-organic gel derived ZnO/α-Fe2O3 heterostructures for sensitive NO2 detection

Fabrication of metal oxide semiconductor heterostructures is an important means to improve sensor performance. However, the design of efficient heterostructures to reduce the operating temperature of metal oxides and obtain high sensitivity and selectivity remains a challenge. In this work, ZnO/α-Fe2O3 heterostructures were prepared by pyrolysis of Fe-based organic gel on ZnO nanorods, and their NO2 sensing properties were systematically studied. The α-Fe2O3 nanoparticles transformed from Fe-organic gel are evenly dispersed on the surface of ZnO nanorods, endowing the materials with a large specific surface area and remarkable charge modulation at the ZnO/α-Fe2O3 interface. The ZnO/α-Fe2O3 sensor shows superior selectivity and repeatability for NO2 detection at 175 °C, as well as short response-recovery time (24/32 s), low detection limit (79 ppb) and reliable stability. This study provides a useful strategy for the construction of core-shell heterostructure sensing materials.

DNA Linked Mixed-Dimensional Heterostructures: The Designing, Nanoscale Control and Device Applications of Tmdc-Quantum Dot Nanohybrids

DNA Linked Mixed-Dimensional Heterostructures: the Designing, Nanoscale Control and Device Applications of TMDC-Quantum Dot Nanohybrids Kai Chen,a Teymour Talha-Dean,b Tingting Zheng, a Stoichko Dimitrov, a Jan Mol b and Matteo Palma a aDepartment of chemistry, Queen Mary University of London, London E1 4NS, United Kingdom bDepartment of Physics, Queen Mary University of London, London E1 4NS, United KingdomThe construction of mixed-dimensional heterostructures is a promising approach for the development of biosensing and optoelectronic systems and devices. The accurate nanoscale control of the heterostructures interface is a key challenge, for instance to tune the distance between the individual components and their stoichiometry, that in turn affect their electronic coupling. In this regard, DNA can be a powerful structural and functional linker for nano-hybrids assembly, due to its tunability down to sub-nanometer control.Our current interest is focused on the fabrication of TMDC-based nanohybrids using double stranded (ds) DNA as both a linker and templating moiety. In particular, we recently employed three different approaches to functionalize the surface of MoS2 nanoflakes and assembled 0D (quantum dots)/2D (MoS2 flakes) hybrids using DNA as a connection moiety (see figure).[1] DNA allowed us to control the distance between QDs and MoS2 with sub-nanoscale accuracy, allowing the fine tuning of the electronic coupling between the two nanostructures.We will further discuss the construction of mixed-dimensional nanohybrids i) via the use different DNA nanotechnology strategies, and ii) for the fabrication of responsive optoelectronic devices. [1] T. Talha-Deam, K. Chen, G. Mastroianni, F. Gesuele, J. Mol and M. Pamla. “Nanoscale Control of DNA-Linked MoS2-Quantum Dot Heterostructures”. Bioconjugate Chemistry, 2022, DOI: 10.1021/acs.bioconjchem.2c00285

Recent Progress in Design Strategy of Anode for Seawater Electrolysis

Direct electrolysis of inexhaustible seawater to generate green hydrogen represents a more environment‐friendly technology relative to freshwater electrolysis. However, current seawater splitting suffers from a low catalytic efficiency and poor operation stability caused by anodic competition between the oxygen evolution reaction and the chlorine oxidation reaction as well as the severe chloride corrosion. This article provides a comprehensive overview of the latest achievements in promoting the selectivity and stability in seawater electrolysis. Beginning with the fundamentals of the anode reactions during seawater splitting, various strategies to design advanced anodic electrocatalyst including surface selective layer engineering, structural regulation by heteroatoms doping and vacancies, and heterostructure construction are discussed in detail. Finally, the conclusion and the challenges in developing seawater electrolysis technology are highlighted.

Surface-Controlled CdS/Ti3C2 MXene Schottky Junction for Highly Selective and Active Photocatalytic Dehydrogenation-Reductive Amination​.

Photocatalytic valorization and selective transformation of biomass-derived platform compounds offer great opportunities for efficient utilization of renewable resources under mild conditions. Here, the novel three-dimensional hierarchical flower-like CdS/Ti3C2 Schottky junction (MCdS) composed of surface-controlled CdS and pretreated Ti3C2 MXene is created for photocatalytic dehydrogenation-reductive amination of biomass-derived amino acid production under ambient temperature with unprecedented activity and selectivity. Schottky junction efficiently promotes photoexcited charge migration and separation and inhibits photogenerated electron-hole recombination, which results in a super-high activity. Meanwhile, CdS with the reduced surface energy supplies sufficient hydrogen sources for imine reduction and induces the preferential orientation of alanine, thus contributing superior selectivity. Moreover, a wide range of hydroxyl acids are successfully converted into corresponding amino acids and even one-pot conversion of glucose to alanine is easily achieved over MCdS. This work illustrates the mechanism of crystal orientation control and heterojunction construction in controlling catalytic behavior of photocatalytic nanoreactor, providing a paradigm for construction of MXene-based heterostructure.

Competitive assembling strategy to construct carbon nitride homojunctions for boosting photocatalytic performance

Both morphology and composition have a great influence on the properties and functions of materials, however, how to rational modulate both of them to achieve their synergistic effects has been a long-standing expectation. Herein, we demonstrate a competitive assembling strategy for the construction of metal-free graphite carbon nitride (CN) homojunctions in which morphology and composition can be easily controlled simultaneously by only changing the ratio of assembly raw materials. These homojunctions are comprised of porous nanotubular S-doped CN (SCN) grafted with CN nanovesicles, which are derived from thermal polycondensation of melamine-thiocyanuric acid (M-T)/melamine-cyanuric acid (M-C) supramolecular hybrid blocks. This unique architecture and component engineering endows the novel SCN–CN homojunction with abundant active sites, enhanced visible trapping ability, and intimate interface contact. As a result, the synthesized SCN–CN homojunctions demonstrate high photocatalytic activity for hydrogen evolution and pollutant degradation. This developed strategy opens up intriguing opportunities for the rational construction of intricate metal-free heterostructures with controllable architecture and interfacial contact for applications in energy-related fields.

Construction of Type-II Heterojunctions in Crystalline Carbon Nitride for Efficient Photocatalytic H2 Evolution.

As an encouraging photocatalyst, crystalline carbon nitride (CCN) exhibits unsatisfactory photocatalytic activity and stability due to its rapid recombination of photo-generative carriers. Herein, high-crystalline g-C3N4 was prepared, including CCN obtained in KCl (K-CCN), LiCl-KCl mixture (Li/K-CCN), and LiCl-NaCl-KCl mixture (Li/Na/K-CCN), via the molten salt strategy using pre-prepared bulk carbon nitride (BCN) as a precursor. The obtained BCN sample was formed by heptazine-based units, which convert into triazine-based units for K-CCN. Heptazine and triazine are two isotypes that co-exist in the Li/K-CCN and Li/Na/K-CCN samples. Compared with BCN and other CCN samples, the as-prepared Li/Na/K-CCN sample exhibited the optimal photocatalytic hydrogen evolution rates (3.38 mmol·g-1·h-1 under simulated sunlight and 2.25 mmol·g-1·h-1 under visible light) and the highest apparent quantum yield (10.97%). The improved photocatalytic performance of the Li/Na/K-CCN sample is mainly attributed to the construction of type-II heterojunction and the institution of the built-in electric field between triazine-based CCN and heptazine-based BCN. This work provides a new strategy for the structural optimization and heterostructure construction of crystalline carbon nitride photocatalysts.