Engineering Polyheptazine and Polytriazine Imides for Photocatalysis

Abstract

As organic semiconductor materials gain increasing prominence in the realm of photocatalysis, two carbon‐nitrogen materials, poly (heptazine imide) (PHI) and poly (triazine imide) (PTI), have garnered extensive attention and applications owing to their unique structure properties. This review elaborates on the distinctive physical and chemical features of PHI and PTI, emphasizing their formation mechanisms and the ensuing properties. Furthermore, it elucidates the intricate correlation between the energy band structures and various photocatalytic reactions. Additionally, the review outlines the primary synthetic strategies for constructing PHI and PTI, along with characterization techniques for their identification. It also summarizes the primary strategies for enhancing the photocatalytic performance of PHI and PTI, whose advantages in various photocatalytic applications are discussed. Finally, it highlights the promising prospects and challenges of PHI and PTI as photocatalysts.

This Minireview introduces the generation methods, physical and chemical properties, band structures, synthetic strategies, characterization methods, modification strategies and advantages of poly (heptazine imide) (PHI) and poly (triazine imide) (PTI) in various photocatalytic reactions. The current challenges and potential opportunities for using PHI/PTI as photocatalysts are presented.

1. Introduction

The energy problem and environmental pollution have risen to the forefront of global concerns, prompting nations worldwide to urgently seek sustainable and eco‐friendly energy solutions to address these pressing issues. ^[1] Solar energy has garnered substantial attention due to its clean, abundant, and cost‐effective nature. Meanwhile, photocatalysis technology has emerged as an advanced oxidation method with considerable potential in solving environmental and energy challenges. ^[34] Currently, the cornerstone of photocatalytic energy conversion and environmental remediation lies in the design and fabrication of efficient photocatalysts. ^[46] As a result, the development of novel photocatalysts (robust photoredox capabilities, efficient charge separation and migration, and rapid directional surface reactions) becomes a focal point of research in the pursuit of solutions to these pivotal global issues. ^[53]

Carbon‐nitrogen materials have been recognized as influential organic polymer semiconductors due to their diverse and exceptional properties. Among these materials, PHI and PTI, distinguished by their unique structures, are derivatives stemming from the formation process of carbon nitride materials (Figure 1). Both PHI and PTI not only possess inherent properties of carbon nitride materials, such as electronic structure, thermal stability, and graphite‐like skeleton, but also exhibit their own distinctive attributes, such as tunable crystal structure, unique charge characteristics, and phototaxis, which play pivotal roles in photocatalytic reactions. ^[64] Furthermore, the exceptional adjustability of PHI and PTI enables the construction of a wide range of highly customizable composite photocatalysts, offering control over composition, crystal facets, crystallinity, morphology, and more. ^[75] These distinctive features position PHI and PTI as promising semiconductor materials with compelling potential in various photocatalysis applications.

Figure 1.

Basic material structure diagram. PHI (left), PTI (right).

Recently, Pelicano and Antonietti published a review article on metal PHI photocatalysts, ^[79] focusing on their synthesis and structural characterizations as well as applications in photocatalytic H₂O splitting, H₂O₂ synthesis, and CO₂ reduction reactions. However, the reaction mechanisms and selection principles for molten salts during the synthesis process remain undiscussed. Moreover, the overview of the applications in the fields beyond artificial photosynthesis like photocatalytic organic transformation, N₂ fixation and environmental remediation is still in lack. Additionally, the related comparative and comprehensive discussion on PTI materials with different structures in the same family as PHI is scarce. In this review, we supplement these aspects to the recently published work. In particular, we discussed the novel physicochemical properties and electronic structures of both PHI and PTI as well as key characterization techniques, and theoretical calculations, which will offer new perspectives and approaches for further optimization and application of PHI and PTI materials.

This review aims to delve deeply into the structural intricacies and underlying principles of PHI and PTI, elucidating their correlation with photocatalytic reactions. Specifically, it explores the formation mechanisms of PHI and PTI, and reveals their electronic and crystal structure, piezoelectricity, π–π interactions, charge characteristics, phototaxis and other essential attributes. The review summarizes current synthesis strategies, characterization methods, and theoretical calculations of PHI and PTI. Moreover, it provides an overview of strategies for enhancing their photocatalytic performance, encompassing adjustments in layered structure, morphology, crystal facet, crystallinity, doping variations, and the construction of composite materials. Furthermore, the review highlights the advantages of PHI and PTI across diverse photocatalytic systems and subsequently discusses their prospects and challenges within this field.

2. Synthesis of PHI and PTI

Based on the routes for synthesizing PHI and PTI from melamine in Figure 2, melamine will be converted into Melam after calcination, and Melem will be formed by further condensation. PTI can be formed in one step if there is an intervention of molten salt in the subsequent process. Melem can also be converted into PHI through the intermediary of Melon, and finally converted into PTI by prolonging the reaction time. ^[81] In general, the desired PHI and PTI structures can be formed by adjusting the reaction temperature, atmosphere, type and ratio of molten salt, and other factors.

Figure 2.

Schematic diagram of the main synthetic routes. The synthesis routes of PHI and PTI are based on melamine as the initial raw material.

At present, the synthesis of PHI and PTI mainly uses molten salt‐assisted strategy due to the following advantages. Its high thermal stability allows for the synthesis to proceed at higher temperatures compared with that at traditional solvent‐reaction system, speeding up the process and promoting the growth of polymer chains. Additionally, precursors or intermediates have higher solubility in the molten salt than in conventional solvents, which improves the contact of the reactants and the uniformity of the reaction. Molten salt‘s high ionic conductivity also facilitates the modulation of microstructure and performance of the material. The use of molten salts can avoid the use of organic solvents and water, thereby reducing the possible introduction of impurities. By adjusting the types of molten salts, one can fine‐tune the nature of the reaction medium like pH and polarity. Besides, molten salt synthesis is more environmentally friendly compared to methods using organic solvents. Finally, synthesis in molten salt media promotes the formation of highly crystallized PHI and PTI. To sum up, the molten salt synthesis offers a controllable strategy with significant advantages for the preparation of PHI and PTI materials with excellent photocatalytic properties.

As shown in Figure 3, the main raw material for the synthesis of PHI is melamine (or urea) and LiCl/KCl acting as molten salt, while melamine (or dicyandiamide) is used for PTI. Other carbon‐ and nitrogen‐containing chemicals can also be used as raw materials. A diverse range of molten salts have been used to synthesize PHI. During the formation of PHI and the associated Coulombic salts (such as Na‐PHI or K‐PHI), the hydrogen from the imide bond must be released as a counterionic volatile acid (HCl). This process is crucial for the formation of PHI. In contrast, the synthesis of PTI typically involves lithium‐containing halogen salts. LiCl, a necessary salt template, is retained in the PTI structure along with the chloride. Although this salt can be partially extracted, the inclusion complex introduced by LiCl is essential for the stability of the main PTI structure. In general, the proportion of halogen salts used in the synthesis of both PHI and PTI remains quite significant. In the synthesis of PHI, the most common molten salts are LiCl and KCl. While other types of salts or bases can also be utilized to simplify the synthesis process, the focus remains predominantly on salts and bases of alkali metals. This approach ensures ease of synthesis and effective results. For PTI synthesis, the preferred molten salt is also a combination of LiCl and KCl. However, LiCl is essential in most of the synthesis processes. This inclusion is critical for the stability and formation of PTI. This is primarily due to the advantages of halogen salts, including their high thermal stability, good melting properties, robust chemical stability, environmental friendliness, and high safety.

Figure 3.

Schematic diagram of the synthesis process. Currently the most important methods for synthesizing PHI and PTI (Calcination method).

3. Advantages and Features of PHI and PTI

3.1. Structural Properties of PHI and PTI

3.1.1. Crystal Structure

Despite sharing nitrogen‐containing cyclic building blocks, PHI and PTI differ in their crystal structures, with PHI adopting a triclinic crystal system and PTI a hexagonal one, as depicted in Figure 4a. ^[83] Nevertheless, both PHI and PTI usually tend to form amorphous or semi‐crystalline polymer networks. This network architecture provides an abundance of active sites and channels that are conducive to photocatalytic reactions, while ensuring excellent light absorption and charge transport properties. However, the synthesis conditions can be meticulously manipulated to encourage the formation of a highly ordered structure under specific conditions, thereby improving their performance in designed applications. ^[85] Typically, obtaining regular morphology and smooth crystal facets is more straightforward in PTI than PHI, although its synthesis conditions of PTI are more stringent.[ ⁸¹ , ⁹² ]

Figure 4.

Structural Properties of PHI and PTI. a) Crystal structure. b) π–π interaction. c) Piezoelectric properties. d) Charging characteristics. e) Phototaxis.

3.1.2. π–π Interaction

PHI and PTI are nitrogen‐containing polymers, characterized by their cyclic nitrogen‐containing heptazine and triazine units, which are connected by imine bonds (−NH−). This structural arrangement endows both PHI and PTI with abundant π‐electron systems at the molecular level (Figure 4c). The genesis of π–π interactions in PHI and PTI stem primarily from the overlap of the π‐electron systems and the mutual attraction among intermolecular π‐electron clouds. This interaction not only optimizes the molecular spacing, but also enhances the polymers stability, optical, and electronic properties.[ ⁶⁷ , ⁷⁷ , ⁹³ ] In essence, the formation of π–π interactions in polymers like PHI and PTI relies on their containing cyclic nitrogen‐containing units with extended π‐electron systems. These interactions facilitate intermolecular ordering, self‐assembly, and the overall optimization of material properties. However, to date, no studies have directly compared the strengths of π–π interaction between PHI and PTI themselves, or between their reaction substrates.

3.1.3. Piezoelectric Properties

Both PHI and PTI display a distinct two‐dimensional layered network structure, enabling them to exhibit internal polarization under mechanical deformation, thus inducing a piezoelectric effect (Figure 4b). ^[98] In addition, the piezoelectric properties of PHI and PTI can be tailored through specific molecular design and structural modulation. This includes the introduction of specific functional groups, the creation of non‐centrosymmetric molecular arrangements, or the inducement of internal polarization via external fields, such as an electric field. Currently, the piezoelectric properties of PHI and PTI are sparsely documented in the research literature, yet their crystal structures are predominantly recognized by their unique two‐dimensional networked polymer configurations. These unique structures endow them with exceptional properties and application potential in piezoelectric fields.

3.1.4. Charging Characteristics

Synthesized PHI and PTI commonly incorporate metal ions such as Li⁺, Na⁺, and K⁺. These ions interact closely with the electrons presented within the polymers, resulting in a modulation of their electron storage capacity. This modulation is facilitated by the cationic materials themselves, the surrounding solution, or a combination of both. The channels of PHI and PTI are designed to accommodate these structural ions, making their photoelectric response more intrinsic (Figure 4d). It is noteworthy that under light irradiation, a small number of alkali metal ions within the PHI and PTI structures can detach from their original coordination sites. This detachment facilitates the migration of cations within the structure and molecular structural changes caused by electron density redistribution, resulting in photochromic changes (such as transitions from yellow to blue or other colors). ^[101] Additionally, the photocharging phenomenon, facilitated by the optoionic effects in these structures, can also induce the insertion of additional alkali metal ions from high‐concentration alkali metal salt solutions into the material‘s structure. ^[117] This opens up more possibilities for the development of photocharged semiconductors. The current research results have fully demonstrated the powerful advantages of PHI in storing charges. However, despite its structural similarity, PTI remains relatively underreported in the literature, offering the untapped potential for future exploration.

3.1.5. Phototaxis

The phototaxis exhibited by PHI and PTI as photocatalytic materials for microswimmer applications allows them to navigate toward the desired position by simply directing the light irradiation. At the same time, these materials possess the remarkable ability to harness light energy and transform it into chemical energy or power, enabling the microswimmers to propel themselves independently within a liquid medium (Figure 4e).[ ⁶⁴ , ¹¹⁷ , ¹¹⁸ , ¹¹⁹ , ¹²⁰ ] The sources of these remarkable properties are diverse: PHI and PTI are able to capture light energy and convert it into energetic charge carriers, creating a driving force to facilitate the energy conversion process when encountering chemical reactions substrate such as H₂O₂ or certain organics that can trigger bubble formation (or chemical gradients);[ ¹¹⁷ , ¹¹⁸ , ¹¹⁹ , ¹²⁰ ] the integration of metal cations within the PHI and PTI structure, as well as cations in solution during photocatalysis, leads to localized changes in ion concentration, forming an ionic concentration gradient that can drive the autonomous motion of the micro‐swimmers; under light exposure, these materials may induce a localized thermal effect, affecting the properties of the surrounding fluid (such as viscosity and density), thus generating a sufficient hydrodynamic gradient to propel the micro‐swimmers; their optical propertiesthat encompass light‐absorbing and photo‐charge‐transferring characteristics, are crucial in achieving effective light‐driven dynamics. Overall, while the bubbles, chemical gradient changes, and photothermal effects generated by the photocatalytic activity of PHI and PTI themselves provide the basic driving force for the micro‐swimmers, the actual construction of the micro‐swimmers requires fine engineering, both in terms of the shapes and sizes of the materials, as well as their integration with other components to achieve the specific motion characteristics and functionality.

3.2. Electronic Structure of PHI and PTI

3.2.1. Light Harvesting Properties

The light absorption properties of PHI and PTI mainly originate from their abundant π‐electron systems and conjugated structures, which empower them to effectively harness light energy to drive the photocatalytic reactions. The Heptazine unit in the structure of PHI boasts a broad range of light absorption, spanning from visible to near‐ultraviolet regions, with its maximum absorption edge extending to ~500 nm. In comparison, PTI displays a narrower light absorption range, with its maximum absorption edge usually not exceeding 450 nm (Figure 5a). A broad light absorption range is usually necessary to effectively harness sunlight, which is beneficial in photocatalysis. Notably, the light absorption properties of PHI and PTI can be further optimized by chemical modification and doping, which allows for tuning the absorption peaks position or increasing of the absorption intensity for the sake of specific applications.

Figure 5.

The relationship between the light absorption properties of materials and their energy bands. a) Light absorption range of PHI and PTI. b) Schematic diagram of the photoexcitation process. c) Appropriate Energy Levels for PHI and PTI (pH=0). d) Redox potential of some common photocatalytic reactions.

3.2.2. Light Excitation Mechanism

Both PHI and PTI are polymeric carbon nitrides belonging to the carbon nitride material family, characterized by suitable band gaps for metal‐free photocatalysts. ^[75] PHI is polymerized from heptazine (C₆N₇) monomers, which consist of three fused triazine rings forming a central ring with one graphitic nitrogen at the centre and six pyridinic nitrogen atoms at the periphery. ^[75] PTI, on the other hand, is polymerized from triazine (C₃N₃) monomers, which consist of a single six‐membered triazine ring with alternating carbon and nitrogen atoms. ^[75] The polymeric structures of both PHI and PTI are linked through imide groups (−NH−), with heptazine and triazine units serving as the linking components, respectively. ^[75] In both PHI and PTI monomers, carbon and nitrogen atoms are sp² hybridized, forming three sp² hybrid orbitals and one unhybridized p orbital. The unhybridized p orbitals on each carbon and nitrogen atom overlap, creating the π‐electron delocalization across the heptazine and triazine units.[ ⁷⁵ , ⁷⁹ , ⁸⁵ , ⁹⁵ , ¹²³ ] In PHI and PTI, the VB primarily arises from N 2p orbitals, while the CB mainly originates from C 2p and N 2p orbitals. Vacancies or dopants can induce intermediate band gap energy levels (Figure 5b).[ ⁷⁵ , ¹³⁰ ] Moreover, the excitation within the energy band structures of PHI and PTI are closely related to their unique electronic configurations. ^[75] Therefore, PHI and PTI can effectively absorb light energy and generate electron‐hole pairs under light illumination, and thus participate in various photocatalytic reactions. The energy band structures and electronic properties of these materials can be optimized by chemical modification to meet specific photocatalytic applications.

3.2.3. Band Structure

By analyzing the positions of the PHI and PTI energy bands (Figure 5c), it becomes evident that only H‐PHI and certain PTI structures possess a band gap greater than 3.00 eV, and most of the PHI and PTI materials have bandgaps within the range of 2.40 eV to 3.00 eV. The specific band gaps ensure exceptional light absorption capabilities and allow for better utilization of visible light. Additionally, the energy level structures of PHI and PTI align well with the thermodynamic requirements for a wide array of photocatalytic reactions (Figure 5d). This compatibility provides strong support for their diverse applications, including water splitting,[ ⁶⁷ , ¹⁴⁰ ] CO₂ reduction, ^[147] N₂ fixation, ^[149] H₂O₂ production, ^[150] removal of pollutants, ^[155] antimicrobial, ^[157] Cr(VI) reduction, ^[72] U(VI) reduction, ^[28] organic transformation,[ ²³ , ⁷³ ] NO oxidation ^[75] and more. The adaptability and functionality of the PHI and PTI across such a broad range of reactions highlight their significant potential in various photocatalytic applications.

4. Structural Analysis of PHI and PTI

4.1. Structural Characterization of PHI and PTI

To establish a definitive connection with photocatalytic activity, it becomes crucial to accurately identify the characteristic structures of PHI and PTI becomes imperative. Fortunately, the emergence of cutting‐edge technologies in recent years, particularly those enabling the analysis of materials′ internal electronic structures at the atomic level, has elevated our understanding of the materials. In light of this advancement, our discussion will centre on several atomic‐level characterizations that provide evidence of the characteristic structures of PHI and PTI (Figure 6). These include techniques of High‐Resolution Transmission Electron Microscopy (HRTEM), Scanning Transmission Electron Microscopy (STEM), X‐ray Absorption Near Edge Structure (XANES), Aberration‐corrected integrated Differential Phase Contrast (AC‐iDPC), and Convergent Beam Electron Diffraction (CBED).

Figure 6.

Characterization test methods of PHI and PTI. a) HRTEM, from ref. ^[34] Copyright 2023 Wiley. b) STEM, from ref. ^[76] Copyright 2021 Wiley. c) XANES, from ref. ^[77] Copyright 2022 Springer. d) AC‐iDPC, from ref. ^[55] Copyright 2023 Wiley. e) CBED, from ref. ^[78] Copyright 2023 Royal Society of Chemistry. f) Electronic structure, from ref. ^[81] Copyright 2022 Science. g) Adsorption energy, from ref. ^[54] Copyright 2023 Wiley. h) Interface energy, from ref. ^[82] Copyright 2023 Elsevier. i) Reaction path analysis, from ref. ^[81] Copyright 2022 Science.

HRTEM can provide information such as crystal plane spacing and atomic arrangement, and its resolution has reached the atomic level. As displayed in Figure 6a, HRTEM reveals the PHI's lattice structures, with a d (−110) spacing of 1.08 nm corresponding to triclinic PHI. ^[34] STEM can reveal geometric structures within a sample. Figure 6b shows that the PTI exhibits a hexagonal lattice structure. ^[76] XANES can determine the valence states, electron distribution, coordination environment, and other crucial information. Figure 6c highlights the chemical environment of C atoms in the PHI. In addition to the typical characteristic peaks of π* (C−C/C=C) and π* (C−N−C), there are also new C−N structures and residuals. The presence of K⁺ ions offers strong evidence for the internal chemical interaction of the PHI. ^[77] As for AC‐iDPC, aberration correction provides a piece of clearer and more accurate phase information, which is used by iDPC technology to generate high‐contrast and high‐resolution images. The AC‐iDPC results shown in Figure 6d unveil the regular stacking directional growth of PTI within a specific plane. ^[55] CBED, with its high spatial resolution, can provide plentiful information, such as crystal symmetry, intricate crystal structure details, layer thickness, and electron optical properties. As seen in Figure 6e, CBED illustrates the corrugated structure of PTI, a result of dipole interactions between adjacent layers, and its triazine‐based structure. ^[78] In general, combined with above characterization results, we can achieve a detailed recognition on the crystal structure, chemical structure and electronic structure of PHI and PTI. This comprehensive understanding is crucial for furthering our knowledge of these materials and their potential applications.

5. Theoretical Simulation of PHI and PTI

Density Functional Theory (DFT) enables to reveal the electronic structure and the interactions based on PHI and PTI. Significant attention has been devoted to exploring the electronic structure, adsorption energy, interface charge transfer with other materials, and speculating substrate reaction pathways. ^[79] Upon doping with boron (B) atoms, the planar structure of PTI remains intact, indicating that B atoms may establish chemical bonds with nitrogen (N) atoms in the PTI structure. The newly‐formed structure facilitates a lower‐energy reaction pathway in the reaction of ammonia synthesis (Figure 6f and i). ^[81] Figure 6g offers the model diagram of O₂ adsorption on the PTI surface. The adsorption energy of O₂ on lithium (Li) atoms is −0.99 eV, considerably lower than that on chlorine (Cl) atoms (−0.10 eV), suggesting that O₂ molecules can readily adsorb and activate on Li atoms within the PTI framework. ^[54] Figure 6h displays the interface charge transfer between platinum (Pt) and potassium‐modified PHI (K‐PHI), which indicates that Pt gains electrons from K‐PHI, thus enhancing the photocatalytic performance. ^[82] The structural and reaction pathway analysis by theoretical calculation offers valuable insights for optimizing material systems and exploring reaction mechanisms.

6. Strategies to Improve the Photocatalytic Performance of PHI and PTI

Semiconductor photocatalysis initiates a series of continuous and intricate interface reactions, where the charge generation, charge transfer, and consumption of charge carriers play pivotal roles in photocatalysis (Figure 7a). ^[83] In general, semiconductor photocatalysts become active when the energy of excitation light exceeds their band gap (Eg). Electrons and holes must overcome Coulombic attraction to separate and become long‐lived dissociated charges, facilitating efficient energy transfer. ^[84] Previous studies have demonstrated that the generation of electrons and holes occurs within femtoseconds, but it takes hundreds of picoseconds to migrate from the bulk to the surface, and takes even nanoseconds or microseconds to reach the active sites where chemical reactions occur with the adsorbents. ^[84] Due to this disparity in time scales, a significant number of electrons and holes undergo rapid recombination within the bulk or on the surface, releasing energy in the form of light or heat. Consequently, only a small fraction of electrons and holes successfully reach the surface to participate in chemical reactions. ^[85] Hence, promoting the separation of electron‐hole pairs and enhancing interfacial charge transfer are crucial in enhancing photocatalytic activity.

Figure 7.

Strategies to adjust PHI and PTI–Thin layer structure adjustment. a) Basic process of photocatalysis. b) Schematic diagram of the formation process of a general thin layer structure. c) Photocatalytic hydrogen evolution activity of BPHI and PHINs. d) The photocatalytic mechanism of BPHI and PHINs. c–d from ref. ^[92] Copyright 2023 Elsevier.

6.1. Thin Layer Structure Adjustment

The high specific surface area of layer‐structured materials and their potential charge transfer in layers benefit photocatalytic reactions. As a result, there is growing interest in tailoring the thin‐layer structure of semiconductor photocatalysts. Current strategies for constructing thin‐layer photocatalysts primarily include mechanical exfoliation such as ultrasonication, the intercalation of small liquid molecules, and ion intercalation (Figure 7b). ^[60] Paolo Giusto et al. synthesized a series of ultra‐thin carbon nitride materials via chemical vapor deposition (CVD). A notable outcome of their work is the creation of a carbon nitride film with a diamond‐like refractive index, formed on a 2‐inch fused quartz sheet, demonstrating excellent optical properties. ^[86] Their group also utilized this carbon nitride film for photocatalytic organic conversion, indicating its potential application in photocatalysis fields. ^[90] Additionally, T. Aida's team developed a carbon nitride polymer (CNP) film actuator that autonomously responds to small humidity changes. ^[91] This actuator, synthesized through vapor deposition polymerization (VDP) using guanidine carbonate as a precursor, features adjustable thickness, ultraviolet light absorption, and a fast photothermal response. The film exhibits high mechanical strength, rapid response, and efficient driving capabilities under ambient conditions. These findings highlight that ultra‐thin carbon nitride material layers possess excellent optical, piezoelectric, and electromechanical properties. This has significant implications for the development of new ultra‐thin carbon nitride materials, such as PHI and PTI, and their effective utilization in the field of photocatalysis. Wang et al. achieved poly (heptazine imide) thin‐layer structures of PHI (PHINs) through an ion‐exchange assisted method, ^[92] and the photocatalytic hydrogen production rate of PHINs is higher that of bulk PHI (Figure 7c). This enhancement is mainly attributed to the ultrathin structure of PHINs, which increases the surface area and facilitates electron transfer, thereby promoting photocatalytic hydrogen production performance (Figure 7d).

6.2. Size Adjustment

Reducing the size of photocatalysts can lead to an increase in the number of active sites and potentially trigger a quantum size effect. ^[93] Kröger et al. employed ultrasound treatment to reduce the particle size of PHI by sonicating it in water for 2 h (or 24 h), followed by the fractional centrifugation of aggregates to isolate the desired particle sizes. ^[93] It was observed that PHI with smaller sizes exhibited a higher concentration of O−H/N−H groups on their surfaces. The average size of particles with these surface groups in PHI was less than 200 nm (Figure 8a). The results presented in Figure 8b demonstrate that the appropriate reduction of catalyst size can indeed enhance its photocatalytic performance. However, it is worth noting that too small a size may lead to a large optical band gap and deep trap states, which will have an adverse effect on photocatalysis, while the remaining effects of size reduction (such as increased wettability) will improve the photocatalytic efficiency.

Figure 8.

Strategies to adjust PHI and PTI–Size adjustment and morphological control. a) Relative area of NH and OH vibrations of FTIR of H‐PHI as a function of particle size. b) Hydrogen evolution of H‐PHI (different sizes). a–b from ref. ^[93] Copyright 2021 Wiley. c) MX→PHI nanotube synthesis process and photocatalytic mechanism diagram. c from ref. ^[98] Copyright 2022 American Chemical Society.

6.3. Morphological Control

Tailoring the morphology of a photocatalyst holds the key to tuning its charge separation properties, thus affecting its catalytic performance. ^[94] The main advantages of such modulation include the ability to provide specific morphologies like nanowires, nanotubes, or porous structures, which can not only offer more active sites but also enhance light scattering and reflection. Additionally, morphology tailoring enables to tune the charge separation property, making the photogenerated charges separate and transfer in specific directions. ^[95] For instance, Sharma et al. engineered nanotube‐shaped poly (heptazine imide) (MX→PHI), which exhibited a hydrogen peroxide production activity that was significantly higher than traditional g‐C₃N₄ photocatalyst. ^[98] This was primarily due to the efficient combination of light absorption, charge separation, and O₂ capture in MX→PHI, rendering it an exceptionally photoactive molecular catalyst.

6.4. Crystal Facet Engineering

Crystal facet engineering holds paramount significance in the realm of photocatalysis, which enables to modulate the charge separation behaviours and surface reactions on specific facets. ^[99] Crystal facet engineering manifests in several aspects, including dictating reactivity by distinguishing between highly active and inert crystal facets, modulating the kinetics of charge transport, and influencing surface reaction kinetics or reaction selectivity. ^[101] Wang et al. manipulated the crystal structure of PTI by adjusting the type of molten salt used in the synthesis process (Figure 9a). ^[42] They further modified the PTI with cocatalysts for hydrogen production (Pt‐CrO_x) and oxygen production (CoO_x) to achieve impressive photocatalytic water‐splitting performance. Remarkably, PTI‐LiNaK exhibited superior activity compared to PTI‐LiNa and PTI‐LiK (Figure 9b). This enhancement was primarily due to the efficient separation and transport of photogenerated carriers within PTI‐LiNaK, their effective utilization at the surface, and the exposure of specific crystal facets by its 2D layered structure, all contributing to optimized photocatalytic reactions.

Figure 9.

Strategies to adjust PHI and PTI–Crystal plane control and crystallinity control. a) A proposed process for the synthesis of PTI/Li⁺Cl⁻ nanosheets catalyst in ternary molten salt (LiCl/KCl/NaCl). b) Photocatalytic water splitting rates of different PTI samples. a–b from ref. ^[42] Copyright 2023 Wiley. c) XRD patterns, d) SEM images and e) photocatalytic overall water splitting performances of PTI samples prepared by adjusting the precursor and salt weight ratio. c–e from ref. ^[55] Copyright 2023 Wiley.

6.5. Crystallinity Control

Crystallinity plays a pivotal role in fine‐tuning the electronic structure and energy band structure of a photocatalyst. ^[104] Improving the crystallinity can affect the light absorption capacity, the stability, and the kinetics of specific reactions. ^[106] Liang et al. synthesized three different PTI samples through varied processing methods. ^[55] Figure 9c shows that all the samples synthesized at different weight ratios of precursor and molten salt exhibited the characteristic PTI crystal structure. ^[55] Figure 9d illustrates the diverse morphologies of these PTI samples. ^[55] Notably, it revealed that only an optimal amount of molten salt can lead to a superior crystalline structure of PTI in a specific direction. Further loading CoO_x and Pt cocatalysts on these three PTI surfaces enables to achieve photocatalytic overall water splitting. Among them, the water splitting activity of the PTI‐1 : 10 is much hihger than that of the PTI‐1 : 1 and PTI‐1 : 50 samples (Figure 9e), which is mainly due to the efficient charge separation and surface reaction of the PTI‐1 : 10 sample. ^[55]

6.6. Tuning Active Sites via Ion Exchange

The unique structure of PHI and PTI makes the incorporated metal ions can easily exchange with those on the material surface, which provides more possibilities in photocatalytic applications. ^[109] For example, the specific metal ions embedded into the structure of PHI and PTI through ion exchange can provide new active sites for the chemical reactions. Additionally, the introduction of diverse ions regulates the band structure of photocatalysts, optimizes the light absorption ability, and improves the charge separation behaviour. ^[109] The introduction of specific ions can also enhance the structural stability of the PHI and PTI materials.[ ¹⁰⁹ , ¹¹⁰ , ¹¹¹ , ¹¹² ] As can be seen in Figure 10a, the cations used for exchange in PHI and PTI primarily consist of alkali metals, alkaline earth metals, and transition metals, while the anions are mainly halogens (molten halogen salts as reaction medium with the halogens acting as charge compensation). Notably, PHI is more widely used in ion exchange because its structure contains sites that are easy to exchange with ions. Furthermore, PHI shows superior chemical stability following ion exchange, and offers flexibility and diversity in ion exchange, enabling a broader range of adjustments and optimization according to diverse photocatalytic reactions. ^[114] Figure 10b shows that a common ion‐exchange strategy, where alkali metal ions are swapped into the original M‐PHI/PTI by introducing other metal chloride salts at room temperature, resulting in the formation of new N‐PHI/PTI photocatalytic materials. Currently, ion exchange in PHI can be achieved for nearly all the marked metal ions in Figure 10, whereas in PTI, only partial ion exchange is feasible. It is worth noting that the elements that can be used for ion exchange are still unexplored, thus leaving the potential for further investigation of photocatalysts constructed by ion exchange.

Figure 10.

Strategies to adjust PHI and PTI–Ion exchange. a) All relevant elements involved in the PHI and PTI ion exchange process. b) Schematic diagram of the reaction process of conventional PHI and PTI ion exchange.

6.7. Doping Strategy

6.7.1. Doping of Metallic Elements

Doping the additional metal or non‐metal elements is a widely adopted strategy in photocatalysis. ^[117] Its principal functionalities are diverse, encompassing modifications of the electronic structure, improvements in charge separation and transportation, and adjusting the reaction kinetics. ^[120] Ou et al. constructed two PHI‐based samples using doping Cu into the structure (CuL/PHI and CuP/PHI) as depicted in Figure 11a. ^[71] As shown in Figure 11b–c, the presence of dense white bright spots on the CuL/PHI and CuP/PHI samples proves that Cu species within both materials exist in a single‐atom dispersed state. Further comparative experiments confirm that CuL/PHI exhibits a superior antibacterial effect against Gram‐negative Escherichia coli (E. coli) and Gram‐positive MRSA (Figure 11d). This is mainly because the Cu sites on CuL/PHI enhance photoelectron migration and O₂ adsorption activation, enabling CuL/PHI to generate reactive oxygen radicals more effectively. These radicals can damage the cellular structures of bacteria, ultimately leading to their demise.

Figure 11.

Strategies to adjust PHI and PTI–Doping of metallic and non‐metallic elements. a) Scheme of the synthesis of Cu_L/PHI and Cu_P/PHI. b) HAADF‐STEM image of Cu_L/PHI and c) Cu_P/PHI. d) The representative colony forming unit images of E. coli and MRSA. a–d from ref. ^[71] Copyright 2023 Wiley. e) Schematic illustration for the fabrication process of HS‐SPHI. f) The HER measurements of HS‐SPHI‐x and BGCN. g) The wavelength‐dependent AQE of photocatalytic H₂ evolution and UV/Vis DRS of HS‐SPHI‐650. h–j from ref. ^[123] Copyright 2023 Elsevier.

6.7.2. Doping of Non‐Metallic Elements

The doping of non‐metal elements is also commonly used in tuning the band structure of photocatalysts.[ ¹¹⁹ , ¹²¹ ] Gao et al. constructed a sulfur‐containing PHI material (HS‐SPHI) through the self‐templating of melamine and trithiocyanuric acid. ^[123] As shown in Figure 11e, the energy band structure of HS‐SPHI has changed significantly through the doping of sulfur element, favouring its photocatalytic capabilities. The photocatalytic hydrogen production performance of HS‐SPHI‐650 is greatly improved compared to that of the original carbon nitride material (B‐GCN) (Figure 11f–g). The above results show that optimizing the energy band structure of PHI via non‐metal doping enables is feasible to tune the photocatalytic performances.

6.7.3. Functional Group Modification

Functional group modification stands as an effective strategy for tuning the microstructure of photocatalysts. ^[124] By introducing specific functional groups onto the surface, surface properties of the photocatalysts, including hydrophilicity or lipophilicity, surface charge distribution, reactive sites, or even the microenvironment for surface reactions can be changed. ^[124] Kröger et al. employed a low‐temperature calcination approach to introduce melamine functional groups onto the surface of K‐PHI, forming a new material named Mel‐PHI (as depicted in Figure 12a). ^[129] This alteration led to a shift in its energy band structure, specifically raising both valence band edges and conduction band edges by approximately 0.4 eV (as shown in Figure 12b). With its bandgap remaining unchanged, Mel‐PHI exhibited a higher reduction potential for photogenerated electrons in the conduction band. Additionally, surface functionalization with melamine impacted carriers’ localization, consequently influencing carriers separation and extraction (depicted in Figure 12c). A comparison of the photocatalytic hydrogen production performance is presented in Figure 12d, showing that when TEoA was utilized as an electron donor, Mel‐PHI outperformed K‐PHI and H‐PHI in photocatalytic hydrogen production, which may be due to the interaction between Mel‐PHI and TEoA to promote electron transfer.

Figure 12.

Strategies to adjust PHI and PTI–Functional group modification and Links modification. a) Schematic depiction of the synthesis of Mel‐PHI. b) UPS valence band measurement and conduction band edge estimation by adding the optical band gap of Mel‐PHI and K‐PHI. c) Interaction of the Mel‐PHI model system with water molecules. Blue areas depict the interaction of water molecules with Mel‐PHI model system; Interaction of Mel‐PHI model system with TEoA and water. d) Hydrogen evolution of K‐PHI, H‐PHI, and Mel‐PHI at optimized Pt loadings with the donors MeOH and TEoA. a–d from ref. ^[129] Copyright 2022 Wiley. e) NH₃ evolution rates over as prepared catalysts. f) Plausible mechanism for the photocatalytic N₂ fixation over PCON‐2 under visible light irradiation. e–f from ref. ^[66] Copyright 2022 Elsevier.

6.7.4. Links Modification

Links modifications are critical in organic semiconductor photocatalysts, as they have a profound effect on the electronic properties of these semiconductors. ^[130] This impact is multifaceted, including the regulation the electronic structures, promotion of charge transfer, enhancement of intermolecular interactions, as well as the modulation of molecule arrangement and self‐assembly mode. ^[133] Yang et al. achieved photocatalytic ammonia synthesis by introducing C−N and N−C−O units into the structure of PHI, where the optimal sample exhibits a greatly enhanced NH₃ production than C₃N₄ (Figure 12e). ^[66] This is primarily attributed to the n‐π* transitions induced by various linkers embedded in the PHI structure, which act as charge channels and activation sites. These linkers significantly extend light absorption into the near‐infrared spectrum, enhance charge separation, and facilitate reaction activation. Furthermore, N₂ molecules adsorbed on the linkage band react with electrons and then combine with protons to produce NH₃. Simultaneously, the holes generated in the heptazine units react with water to produce O₂ (Figure 12f).

6.8. Composite Modulation

6.8.1. Surface Modification of Metal Monomer

Metal monomer modification is widely employed in organic semiconductors. ^[138] Metal monomer modification offers several advantages, including the improvement of charge separation, the enhancement of light absorption capabilities, and the modulation of reactive sites and reaction pathways.[ ¹⁰⁶ , ¹⁴⁰ ] Zhong et al. loaded multiple Cu monomers with diverse exposed crystal planes onto the PHI surface (Figure 13a). ^[142] The constructed Cu/PHI composite materials exhibit similar XRD patterns with PHI. Figure 13b–c shows photocatalytic CH₃SH removal rates over different Cu/PHI photocatalysts. Cu (111)/PHI demonstrated superior CH₃SH removal efficiency compared to other materials, likely due to the Cu (111) surface effectively accelerating the extraction and transfer of photogenerated charge carriers through its enhanced surface electron pumping effect. Additionally, the active sites on the Cu (111) surface, with their unsaturated d‐orbital electrons, can effectively adsorb H₂O, O₂, and CH₃SH. This facilitates the activation of H₂O and O₂ into reactive oxygen species (⋅OH, ⋅O₂ ⁻, and ¹O₂), which then efficiently degrade CH₃SH in proximity.

Figure 13.

Strategies to adjust PHI and PTI–Metal monomer modification. a) PHI, Cu (111)/PHI, Cu (100)/PHI and Cu (111+100)/PHI. b) Photocatalytic elimination of CH₃SH with different catalysts. c) Elimination efficiency with different catalysts. a–c from ref. ^[142] Copyright 2024 Elsevier.

6.8.2. Heterojunction

Constructing a heterojunction between different semiconductors has been widely used in photocatalysis to improve the charge separation process. Various heterojunction types are used in photocatalytic systems, including Type‐II heterojunction, S‐Scheme heterojunction, p‐n junction, as well as heterophase junction.[ ⁷⁴ , ¹⁴³ ] Cheng et al. fabricated a composite photocatalyst using PHI and cano‐modified carbon nitride (ACN), forming a Type‐II heterojunction, which was found to effectively promote the charge separation and migration (Figure 14a). ^[146] Xiong et al. constructed a g‐C₃N₅/PTI S‐Scheme heterojunction to facilitate charge separation, resulting in an improvement of photocatalytic hydrogen production (Figure 14b). ^[147] Besides, Due to the presence of particular ion channels in the PHI and PTI structures, it is possible to construct stepwise unidirectional charge transport channels when using PHI and PTI to construct composite photocatalysts. Zhang et al. Fabricated a close interface contact between PHI/PTI and proposed a stepwise transfer path for charge transportation (Figure 14c). ^[61] Rodríguez et al. utilized the dye sensitization effect of rhodamine B (RhB) to facilitate electron transfer from MIL‐125‐NH₂ to PHIK, inhibiting the reverse electron transfer (Figure 14d). ^[148] Wang et al. used ferroelectric material Ba_xSr_1‐xTiO₃ (B_xST) to increase the built‐in electric field at the interface between B_xST and KPHI (Figure 14e–f). ^[149] Combined with the K⁺ cations in K‐PHI acting as a charge transfer bridge, this strategy promoted the migration and separation of photogenerated charge carriers and ultimately achieved an improvement of photocatalytic hydrogen production.

Figure 14.

Strategies to adjust PHI and PTI–Heterojunction. a) Schematic mechanism of BCN‐NaK for photocatalytic H₂ production. a from ref. ^[146] Copyright 2023 Elsevier. b) The S‐Scheme electrons transfer mechanism of the g‐C₃N₅/PTI interface. b from ref. ^[147] Copyright 2023 Elsevier. c) Photocatalytic H₂ production mechanism diagram of PHI/PTI. c from ref. ^[142] Copyright 2022 Wiley. d) Electron transfer paths of PHIK/MIL‐125‐NH₂. d from ref. ^[61] Copyright 2017 American Chemical Society. e–f) Schematic diagram of photogenerated charge carrier migration and separation in poly (heptazine imide) (K‐PHI)/Ba_xSr_1–xTiO₃ (B_xST) composite. e–f from ref. ^[149] Copyright 2022 Wiley.

6.9. Other Regulatory Strategies

In addition to the primary control strategies mentioned, several novel methods have been employed to enhance the photocatalytic performance of PHI and PTI. For instance, constructing a core–shell structure cocatalyst (such as Rh/Cr₂O₃ and CoO_x) on the surface of PTI can prevent oxygen transfer while allowing protons to penetrate the oxide layer. This effectively inhibits the reverse reaction on the surface of the precious metal core, thereby improving the overall efficiency of photocatalytic water splitting. ^[150] Additionally, combining new molten salt (NaCl−CaCl₂, LiBr/NaBr) and molecular structure control methods has significantly enhanced the physical, chemical, and photocatalytic properties of PHI. ^[151] The use of a hard template (such as mesoporous SiO₂) to guide the growth of PTI regulates its crystal face exposure, leading to a substantial improvement in the total water‐splitting performance of the resulting PTI nanospheres. ^[155] Furthermore, different PHI‐based composite materials synthesized with porous carbon (Ad), carbon dots (CD), HPPT‐carbon, and KPHI have shown greatly enhanced photocatalytic hydrogen production compared to other materials. This enhancement is primarily attributed to the establishment of close interface contact between carbon materials and PHI, inducing space charge separation and extending carrier lifetime. ^[156] Overall, these emerging control methods have played a positive role in regulating the structure, physical and chemical properties, optical properties, and photocatalytic performance of PHI and PTI.

7. Photocatalytic Applications

Currently, both PHI and PTI are mainly used in various photocatalytic reactions including water splitting, organic conversion, N₂ fixation, CO₂ reduction, water purification, and hydrogen peroxide production (Figure 15a). Among them, it can be seen from the distribution diagram in Figure 15b that the photocatalytic applications of the PHI and PTI are dominant in hydrogen production, organic transformation, and degradation of environmental pollutants. For photocatalytic hydrogen production, the energy band structures of both PHI and PTI satisfy the thermaldynamic requirement for photocatalytic water splitting. In addition, the special structure of PHI and PTI may benefit the light harvesting and charge separation for photocatalytic hydrogen production. Moreover, the unique electron storage characteristics of PHI and PTI materials may benefit photocatalytic hydrogen evolution reactions. When it comes to photocatalytic organic conversion reactions, both PHI and PTI stand out due to their positive valence band level, moderate redox capability, long‐lived trap states, as well as the high exposure of C‐ and N‐ containing microstructures serving as reactive sites. High selectivity and conversion of organic transformation can be guaranteed by the characteristics of PHI and PTI, such as microporous structure, suitable thermodynamics, and high stability in the presence of electrophiles, nucleophiles, and free radicals. ^[157] For photocatalytic degradation reactions, the appropriate energy band position of PHI and PTI can generate reactive oxygen radicals, which possess a strong oxidative ability to decompose organic pollutants. In addition, both PHI and PTI have abundant π electronic systems, which can form π–π interactions with organic pollutants, particularly those possessing aromatic ring structures. This interaction significantly enhances the decomposition rate of organic pollutants, thus facilitating their removal from the environment. Additionally, both PHI and PTI participate actively in other reactions that involve direct electron transfer, such as Cr(VI) reduction, U(VI) reduction, CO₂ reduction, and H₂O₂ production. The unique characteristics of PHI and PTI make them versatile and effective photocatalysts with broad applications in photocatalysis and beyond.

Figure 15.

Various photocatalytic reactions involving PHI and PTI. a) Applications of PHI and PTI in various photocatalytic reduction and/or oxidation reactions. b) Proportion of papers on PHI/PTI in different photocatalytic applications in recent years (2013–2024.04).

8. Summary and Outlook

Compared with the conventional carbon and nitrogen materials, both PHI and PTI show excellent physicochemical properties including a distinct crystal structure, piezoelectric properties, π–π interactions, charging properties, phototaxis properties, and ion‐exchange properties. In particular, the specific crystal structure of PHI and PTI, designed for photocatalytic hydrogen production, and their ion‐exchange properties, which enable the construction of photocatalysts for specific organic reactions, are most attractive. Despite their applications in various fields of photocatalysis and the noteworthy progress made, PHI and PTI are still in their infancy and face significant challenges in the future.

8.1. Revealing Crystal Structural Properties

The modulation of the crystal structures for PHI and PTI remains elusive, hampering our ability to precisely manipulate it. This is crucial as the crystal structure significantly impacts light absorption, charge transport, and other vital functions. Furthermore, the mechanism underlying the charge storage capacity of PHI remains unclear. Given that PTI, a polymer with a triazine ring structure, abundant π‐electron system, and specific electron arrangement, exhibits structural similarities to PHI, it is likely to possess electron storage and transport channels. This underscores the need for researchers to further explore the physicochemical properties of these materials to achieve controllable storage of electrons. Currently, advanced testing methods such as neutron powder diffraction, synchrotron X‐ray diffraction, X‐ray free‐electron laser, ultrafast electron diffraction, and resonant soft X‐ray scattering have not yet provided significant discoveries in the crystal structure research of PHI and PTI. However, these techniques hold substantial value in materials science research. Typically, these methods need to be used in combination to obtain more comprehensive crystal structure information. Furthermore, the development of methods to build single atoms on PHI and PTI by ion exchange is crucial, along with enhancing their stability by means of environmental regulation of ion exchange, the introduction of organic small molecules, and post‐processing treatments. Such advancements will pave the way for the expanded utilization of these materials in various applications.

8.2. Developing Synthetic Methods

At present, the molten salt high‐temperature calcination method is the primary technique for synthesizing PHI and PTI. However, this approach involves the utilization of a large amount of salt and requires a high‐temperature environment, leading to environmental concerns and energy consumption. Therefore, there is an urgent need to develop green, energy‐saving, and cost‐effective methods to synthesize high‐quality PHI and PTI with tuneable structures. In addition, the synthesis of such highly crystalline organic polymers could be potentially extended to encompass other macrocyclic organic polymers, especially the formation of certain COFs structures, which may address the challenges of instability and poor catalytic performance.

8.3. Improving the Dynamics of Charge Carriers

Although both PHI and PTI are active in visible light, the utilized spectra range and the charge separation process are still limited. Rational design of the catalysts and optimization of the synthesis process are crucial to improve the separation and utilization of photogenerated charges. Regulating the size, crystal planes, as well as the composite photocatalysts to form heterojunctions has been demonstrated to be useful in improving the charge behaviour of PHI and PTI photocatalysts. Furthermore, the regulation of the directional growth of crystal planes with high crystalline and specific surface structures is still appealing. For surface modification of metal ions within PHI and PTI via ion exchange, it is crucial to construct controllable metal modification sites at the atomic scale and deeply investigate their intrinsic roles and mechanisms in photocatalytic reactions. Furthermore, composites modulation still holds vast potential for further development. A significant challenge remains in constructing an interface structure with atomic‐scale lattice matching, as this would greatly facilitate interface charge transfer. Overcoming this challenge would represent a significant step forward in enhancing the photocatalytic performance of PHI and PTI.

8.4. Revealing the Catalytic Mechanism

At present, there still lacks in‐depth understandings of the reaction mechanism of PHI and PTI photocatalysis. Specific areas that require further elucidation include the identification of real reaction active sites, the dynamic evolution of the structures along with the change of internal ions, the underlying mechanism of π–π interaction in various photocatalytic reactions, and the charge transfer pathways within or on the surface of PHI and PTI photocatalysts. To address these challenges, it is imperative to understand the mechanisms at the atomic scale by leveraging state‐of‐the‐art characterization techniques, such as in situ X‐ray diffraction, in situ infrared spectroscopy, in situ Raman, in situ environmental transmission electron microscopy, and in situ X‐ray absorption spectroscopy, in tandem with theoretical calculations informed by methods like machine learning. By combining multiple techniques, researchers can achieve a deeper understanding of the key steps in the photocatalytic reactions and identify the active sites of the catalysts. Enhanced fundamental understanding of these processes will pave the way for the rational design of efficient photocatalytic systems based on PHI and PTI photocatalysts.

8.5. Broaden the Application Scope

In addition to their outstanding performance in photocatalysis, PHI and PTI also exhibit immense promise in various fields, including energy storage, sensor technology, photoelectronics, and gas adsorption. These diverse applications underscore the vast potential of PHI and PTI as versatile materials in multiple areas of energy transition, environment remediation, and carbon neutralization. Looking ahead, with the steady achievements of fundamental research on PHI and PTI materials and a deeper understanding of their reaction mechanism, it is conceivable to devise efficient and stable photocatalyst systems tailored for potential scale‐up applications. Crucial to this endeavour is the transition of the PHI and PTI materials from the laboratory to practical applications. Further considerations in this transition might involve scaling up the developed devices, potentially arranging them in series or parallel configurations, and ultimately integrating them into compatible industrial systems. By leveraging the capabilities of PHI and PTI materials, we can chart a path toward a sustainable future, where these materials may play a pivotal role in addressing environmental and energy issues.

Conflict of Interests

The authors declare no conflict of interest.

Biographical Information

Liquan Jing received his PhD degree from Jiangsu University majoring in Environmental Science and Engineering in 2021. He is currently a postdoctoral researcher in the Department of Chemical and Petroleum Engineering at the University of Calgary under the guidance of Prof. Jinguang Hu and Prof. Ian D. Gates. His current research mainly focuses on the design and synthesis of functional photocatalysts for sustainable hydrogen, the conversion of biomass into other high‐value‐added biological products, and methane conversion.

Biographical Information

Zheng Li received his PhD degree from Dalian Institute of Chemical Physics. He is currently an Eyes High Post‐doctoral Research Fellow in the Department of Chemical and Petroleum Engineering at the University of Calgary under the guidance of Dr. Jinguang Hu and Dr. Zhangxin (John) Chen. His research mainly focuses on photo (electro/piezo/bio)‐catalytic conversion of biomass‐derived and energy‐related molecules for the production of sustainable hydrogen and value‐added chemicals.

Biographical Information

Zhangxin Chen is a professor in the Department of Chemical and Petroleum Engineering at the University of Calgary. He holds the NSERC/Energy Simulation Industrial Research Chair and Alberta Innovates Industrial Chair at the University of Calgary. His Ph.D. (1991), M.Sc. (1985), and B.S. (1983) are from Purdue University, Xi′an Jiaotong University, and Nanchang (formerly, Jiangxi) University, respectively. He has authored and edited 23 books and published over 900 research articles. Dr. Chen is a Fellow of both the Royal Society of Canada and the Canadian Academy of Engineering. His research interest is in reservoir engineering and renewable energy.

Biographical Information

Rengui Li received his PhD Degree from the Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences in 2014. He worked as a Visiting Research Associate in Prof. K. Domen's group at the University of Tokyo in 2011 and Prof. Harry Atwater's group at California Institute of Technology from 2019 to 2020. In 2014, he began to work at the State Key Laboratory of Catalysis in DICP as an Associate Professor. Since 2018, he was promoted as a Full Professor at DICP. His research interest is mainly focused on photocatalytic solar energy conversion.

Biographical Information

Jinguang Hu received his PhD degree in 2014 from The University of British Columbia (UBC) and did his postdoc research in UBC BioProducts Institute (Canada) and Aalto‐VTT HYBER Center (Academy of Finland's Centre of Excellence in Molecular Engineering of Biosynthetic Hybrid Materials research) respectively. He is an associate professor in the Department of Chemical and Petroleum Engineering at the University of Calgary and his current research is supported by the Canada First Research Excellence Fund (CFREF) Initiative. His research interest is utilizing photo/bio‐catalysts to design and fabricate bioinspired materials or systems for Energy, Environmental, and Medical applications.

Jing L., Li Z., Chen Z., Li R., Hu J., Angew. Chem. Int. Ed. 2024, 63, e202406398. 10.1002/anie.202406398

Data Availability Statement

Data sharing is not applicable to this article as no new data were created or analyzed in this study.