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Open research questions in Advanced Photocatalysis Techniques

45 unresolved questions extracted from the limitations and future-work sections of 1,120 Advanced Photocatalysis Techniques papers in our library. Each links back to the study that raised it.

What the literature leaves open

  • Despite remarkable achievements, several critical challenges must be addressed to bridge the gap between laboratory research and the practical deployment of g-C 3N 4-based photocatalytic technologies. Future research should focus on the following key directions (Table 5). The future development of photocatalytic materials will increasingly rely on a “rational design” paradigm, moving beyond trial-and-error approaches. Leveraging AI and machine learning (ML) for high-throughput screening of optimal doping element combinations, defect configurations, and heterojunction pairings is poised to revolutionize the field. Establishing accurate © Science China Press 2026 21 REVIEWS SCIENCE CHINA Materials Figure 17 (a) An optimized structural model of the ternary composite comprising α-Fe 2O 3, BiOBr and g-C 3N 4. (b, c) Electron density difference distributions, where yellow regions indicate areas of electron accumulation and blue regions denote areas of electron depletion. Copyright 2024, Elsevier. Band structure and corresponding DOS for (d) pristine monolayer g-C 3N 4 and (e) Pt 2@g-C 3N 4, as calculated using the HSE06 functional. (f) Work function for Pt 1@g-C 3N 4. Copyright 2022, Elsevier. Gibbs free energy profiles and adsorption energies for the photocatalytic CO 2 reduction (g) and (h) process over g- C 3N 4, CuFe 2O 4, ZnIn 2S 4, and the CNCZ(x) heterojunction. Copyright 2024, American Chemical Society.

    Emerging trends of g-C3N4-based photocatalysts from 2020 to 2025 · 2026 · DOI

  • From trial-and-error to rational design Utilize AI/ML for high-throughput screening of optimal material configurations Establish predictive structure–performance models to accelerate discovery of next-generation catalysts Atomic-scale control and long-term stability Achieve precise control over active-site coordination and defect distribution; investigate deactivation mechanisms Develop robust, self-healing architectures with high environmental…

    Emerging trends of g-C3N4-based photocatalysts from 2020 to 2025 · 2026 · DOI

  • ABSTRACT While extensive efforts have focused on enhancing photocatalytic (PC) activity via promoting charge separation, the correlation of internal charge transfer on PC selectivity has not been established, primarily due to the challenges in directly exploring the origins of surface catalysis.

    Regulating Surface Energetics via Hetero‐Interfacial Charge Transfer for Selective Photocatalytic Glycerol Oxidation · 2026 · DOI

  • The photocatalytic generation of hydroxyl radicals (•OH) represents a green and powerful route for bacterial inactivation, yet its efficiency is often limited by the sluggish kinetics of the stepwise single‐electron oxygen reduction pathway.

    Asymmetric Zn─N <sub>3</sub> O <sub>1</sub> Single‐Atom Sites Promote Hydroxyl Radical Generation for Natural‐Light‐Driven Inactivation of Drug‐Resistant Bacteria · 2026 · DOI

  • Recent advances in artificial photosynthesis have improved catalyst performance and integrated system efficiencies, bringing laboratory prototypes closer to practical applications. Future research should explicitly target the development of durable, earth-abundant catalysts, design optimized multi-component interfaces for efficient light harvesting and charge transfer, scalable fabrication of device architectures, and mechanistic studies combining experimental and computational approaches. Focusing on these areas (Scalable Synthesis, Device Integration, Product Selectivity) will accelerate the development of sustainable, high-efficiency artificial photosynthetic technologies. 8. CONCLUSIONS In the last three to five years (2020–2025), chemical research in artificial photosynthesis has achieved meaningful advances in both catalyst design and integrated systems. Researchers have developed self-photosensitizing molecular catalysts and robust hybrid assemblies that improve light absorption and charge transfer, while new earth-abundant catalysts show enhanced activity and selectivity for CO2 reduction and water oxidation. Progress in artificial leaf architectures and photoelectrochemical cells has also demonstrated higher solar-to-chemical conversion efficiencies under practical conditions, narrowing the gap between fundamental chemistry and functional prototypes. Despite remaining challenges in longterm stability, material cost, and scale-up, recent studies highlight promising strategies such as bio-inspired catalyst motifs, optimized ligand environments, and coupled catalytic interfaces. Key takeaways from this review: • Main progress: Self-photosensitizing molecular catalysts (Ru and Co) eliminate the need for separate photosensitizers, simplifying system design. MOF and COF frameworks have improved catalyst stability by 10–20× compared to homogeneous analogs. • Main bottleneck – stability: Most advanced catalysts still degrade within 12–100 h of continuous operation. Commercial viability requires >1000 h (or >1 year) of stability.

    A A Short Review of Recent Advances in ArtificialP hotosynthesis Chemistry · 2026 · DOI

  • Mott-Schottky analysis has revealed that excessively high ultrasonic power induces conduction band position shifts that suppress photocatalytic hydrogen evolution, but the quantitative relationships between ultrasonic power intensity and piezoelectric potential-induced band structure changes across different material compositions remain uncharacterized.

    A review: recent progress of piezoelectric effect coupled photocatalytic reaction: diverse mechanisms, system/structure design, characterization and application · 2026 · DOI

  • The in situ ultraviolet testing method for characterizing piezoelectric field modulation of band structure has been developed, but integration with other advanced characterization techniques such as Electron Paramagnetic Resonance and X-ray Photoelectron Spectroscopy coupled with external piezoelectric excitation devices remains unexplored.

    A review: recent progress of piezoelectric effect coupled photocatalytic reaction: diverse mechanisms, system/structure design, characterization and application · 2026 · DOI

  • Applications of piezoelectric-photocatalytic systems have been demonstrated for pollutant degradation and hydrogen evolution, but extensions to emerging fields such as plastic conversion and H2O2 production have not been experimentally validated or mechanistically characterized.

    A review: recent progress of piezoelectric effect coupled photocatalytic reaction: diverse mechanisms, system/structure design, characterization and application · 2026 · DOI

  • Emerging piezoelectric-photocatalytic material systems with single-atom/cluster loading, Janus architectures, and phase-structure modulation require systematic prediction of catalytic performance; artificial intelligence approaches have not been employed to summarize material parameters and predict performance of materials with similar characteristics.

    A review: recent progress of piezoelectric effect coupled photocatalytic reaction: diverse mechanisms, system/structure design, characterization and application · 2026 · DOI

  • The mechanisms underlying piezoelectric potential switching effects and orthogonal charge transport in composite piezoelectric-photocatalytic systems have been proposed but require fine-scale structural design using layer-by-layer assembly, interface engineering, or epitaxial growth to control spatial positions and orientations of components and enable directed charge carrier migration.

    A review: recent progress of piezoelectric effect coupled photocatalytic reaction: diverse mechanisms, system/structure design, characterization and application · 2026 · DOI

  • Most high-precision spectroscopic and microscopic characterization instruments (such as Electron Paramagnetic Resonance and X-ray Photoelectron Spectroscopy) are limited by small sample chamber environments incompatible with mechanical force conditions required to induce piezoelectric effects; dedicated in situ characterization platforms compatible with ultrasonic excitation and flowing media have not been constructed.

    A review: recent progress of piezoelectric effect coupled photocatalytic reaction: diverse mechanisms, system/structure design, characterization and application · 2026 · DOI

  • The interactions among multiple physical fields under diverse electric field distributions and multi-physical coupling in different classes of piezoelectric-photocatalytic material systems remain unclear; the commonalities and distinctive features across material systems have not been comprehensively elucidated.

    A review: recent progress of piezoelectric effect coupled photocatalytic reaction: diverse mechanisms, system/structure design, characterization and application · 2026 · DOI

  • Current piezoelectric-photocatalytic systems predominantly rely on high-frequency ultrasonic excitation, but practical material systems capable of efficiently coupling with alternative stress sources such as water flow, gravity, wind, and natural mechanical vibrations have not been systematically developed or characterized.

    A review: recent progress of piezoelectric effect coupled photocatalytic reaction: diverse mechanisms, system/structure design, characterization and application · 2026 · DOI

  • While the study focuses on non-covalent interactions at the CdS-GO interface, the role of potential defects and surface modifications in affecting photocatalytic performance is not addressed.

    Molecular Study of Cadmium Sulfide and Graphene Oxide Interfaces for Photocatalytic Water Splitting Using Sunlight · 2026 · DOI

  • The study focuses on sulfamerazine degradation and E. coli inactivation, but the applicability of Ag/AgCl/BMO to other emerging pollutants (pharmaceuticals, dyes, pesticides) and diverse bacterial species remains unexplored.

    Plasmonic Ag/AgCl/Bi <sub>2</sub> MoO <sub>6</sub> photocatalyst: Dual-functional bacteriostatic and sulfamerazine degradation via synergistic LSPR and Z-scheme charge transfer · 2026 · DOI

  • Experimental evidence interestingly shows that temperature can significantly accelerate OER, but the atomic-level mechanism remains elusive in both experiment and theory.

    Bubble-water/catalyst triphase interface microenvironment accelerates photocatalytic OER via optimizing semi-hydrophobic OH radical · 2024 · DOI

  • However, little is known about the effect of the spatial position of the heteroatoms on the photocatalytic activity of the semiconductors toward CO2 reduction.

    Isolated Cu Sites in CdS Hollow Nanocubes with Doping-Location-Dependent Performance for Photocatalytic CO<sub>2</sub> Reduction · 2024 · DOI

  • Abstract Metal nanoparticle (NP) cocatalysts are widely investigated for their ability to enhance the performance of photocatalytic materials; however, their practical application is often limited by the inherent instability under light irradiation.

    Noble‐Metal‐Free High‐Entropy Alloy Nanoparticles for Efficient Solar‐Driven Photocatalytic CO<sub>2</sub> Reduction · 2024 · DOI

  • In summary, as a traditional semiconductor photocatalyst, TiO2 has received extensive attention on its photocatalytic performance. However, the single TiO2 always presents a limited photocatalytic efficiency, which is due to its rapid photo-induced carrier recombination, confined light-harvesting ability, and insufficient reduction ability. By constructing a TiO2-based Sscheme heterojunction photocatalyst, it seems to be a very reasonable strategy to overcome the above shortcomings. In this case, this review gives a comprehensive summary of the classification of TiO2-based S-scheme heterojunction photocatalysts, including metal oxides, metal chalcogenides, organic semiconductors, and other semiconductors. Besides, the potential applications of TiO2-based S-scheme heterojunction photocatalysts in photocatalytic H2 evolution, CO2 reduction, H2O2 production, and pollutant degradation are described in detail. And, the characterization methods are also employed to explore the formation and photo-induced carrier transfer pathway of TiO2-based S-scheme heterojunction photocatalysts. Although the reported TiO2-based S-scheme heterojunction February 2024 | Vol. 67 No. 2 © Science China Press 2024 437 REVIEWS SCIENCE CHINA Materials Figure 16 XPS spectra of (a) Ti 2p, (b) C 1s for TiO2, SCN, and SCN/TiO2 with and without light illumination, (c) photocatalytic mechanism of SCN/TiO2, (d) photocatalytic Congo Red degradation efficiencies over different samples. Reprinted with permission from Ref., Copyright 2021, Elsevier. Figure 17 (a) Photocatalytic tetracycline degradation mechanism of NM(Al)/F-TiO2(B). Reprinted with permission from Ref., Copyright 2023, Elsevier. − and (c) DMPO-·OH over In2S3/TiO2(B). Reprinted with permission from Ref., Copyright 2022, The electron spin resonance spectra of (b) DMPO-·O2 Elsevier. 438 © Science China Press 2024 February 2024 | Vol. 67 No. 2 SCIENCE CHINA Materials REVIEWS photocatalysts can simultaneously obtain the broadened light absorption range, efficient photo-induced carrier separation and transfer, and strong redox capacity, thereby achieving the prominent photocatalytic efficiency. However, there are still some significant challenges in the future development of TiO2-based S-scheme heterojunction photocatalysts that need to be further concerned and overcome in the following directions: (1) Based on the formation mechanism of TiO2-based Sscheme heterojunction photocatalyst, the internal electric field, energy band bending, as well as Coulombic attraction, can act as the driving forces to facilitate efficient photo-induced carrier separation and migration. However, it is rarely reported the relationship between them on photocatalytic performance. Thus, more attention should be paid to regulating the structure of heterojunctions in future research. (2) Notably, TiO2-based S-scheme heterojunction photocatalysts usually consist of two or more semiconductors.

    TiO2-based S-scheme photocatalysts for solar energy conversion and environmental remediation · 2024 · DOI

  • In summary, single-component photocatalysts cannot simultaneously possess high utilization efficiency of solar energy and strong redox abilities of photoexcited charges, thus usually suffering weak photocatalytic activity [177,178]. The star material g-C3N4 in the field of photocatalysis is no exception. In this case, February 2024 | Vol. 67 No. 2 © Science China Press 2024 465 REVIEWS SCIENCE CHINA Materials Figure 20 (a) TEM and (b) HRTEM images of CNNS/AgBiS2. (c) Photocatalytic N2 fixation activities. (d) Recycling tests and (e) photocatalytic mechanism. Reprinted with permission from Ref.. Copyright 2023, Elsevier. constructing S-scheme heterojunctions between g-C3N4 with other semiconductors can simultaneously overcome the typical shortcomings of low light energy utilization, rapid recombination, and weak redox abilities of carriers, thus prominently reinforcing its photocatalytic performance. Hence, this review comprehensively comments on the latest research progress of background, fundamental theory, design and preparation, and characterization strategies of g-C3N4-based S-scheme heterojunctions. Additionally, various photocatalytic applications of g-C3N4-based S-scheme heterojunctions have been detailly illustrated through example discussion and list comparison, involving photocatalytic H2 production, CO2 reduction, H2O2 production, pollutant degradation, and others. Although g-C3N4-based S-scheme heterojunctions have made phased progress in controllable construction and enhancement of activity, there are still some bottlenecks to overcome, which are listed as follows. (1) The dynamic process of charge transfer and the intensity, position, and direction of the built-in electric field are still lacking in-situ characterization methods to intuitively reveal. It is well-known that revealing the S-scheme mechanism in depth is the prerequisite for its further development. Therefore, there is 466 © Science China Press 2024 February 2024 | Vol. 67 No. 2 SCIENCE CHINA Materials REVIEWS an urgent need to develop new characterization technologies to effectively reveal the mechanism. Meanwhile, it is necessary to strengthen interdisciplinary integration to intuitively and efficiently detect the relevant information of the built-in electric field. (2) According to the carrier transmission path of S-scheme heterojunction, it is not difficult to conclude that the interfacial electric field is the key factor driving the transmission of photoexcitation charges in S-scheme heterojunctions. However, the current researches for the improvement of g-C3N4-based Sscheme heterojunction are primarily concentrating on the traditional cocataltyst modification, element doping, morphology regulation, etc. [180–183], and the influences of the built-in electric field of S-scheme heterojunction on its carrier separation efficiency and photocatalytic activity are rarely studied.

    g-C3N4-based S-scheme heterojunction photocatalysts · 2024 · DOI

  • In conclusion, CCNs have been a popular research topic in photocatalysis due to their extraordinary features such as high photogenerated carrier transfer capacity, improved light absorption ability and low electron–hole pair recombination rate. In this review, we summarized the recent developments of CCNs and 440 | EES Catal., 2024, 2, 411–447© 2024 The Author(s). Published by the Royal Society of ChemistryOpen Access Article. Published on 06 January 2024. Downloaded on 6/14/2026 8:39:25 AM.

    Crystalline carbon nitrides for photocatalysis · 2024 · DOI

  • For the photocatalytic process, the most important challenge is to improve the solar‐to‐fuels efficiency to at least 15 %, whereas for the electrocatalytic reduction process, even with much improved current density, cell potential, and reaction selectivity, the process will be ultimately limited by the price of solar (or other renewable) electricity.

    Assessment of Solar‐to‐Fuels Strategies: Photocatalysis and Electrocatalytic Reduction · 2016 · DOI

  • Despite the growing interest in mixed‐anion compounds, robust control of particle morphology and a clear morphology–activity relationship remain to be fully established.

    Morphology Control of a Layered Oxyhalide Bi <sub>4</sub> NbO <sub>8</sub> Cl Photocatalyst via Flux Synthesis · 2026 · DOI

  • Comparative performance evaluation with other state-of-the-art photocatalytic systems under identical conditions is lacking, limiting assessment of the material's competitive advantages.

    Plasmonic Ag/AgCl/Bi <sub>2</sub> MoO <sub>6</sub> photocatalyst: Dual-functional bacteriostatic and sulfamerazine degradation via synergistic LSPR and Z-scheme charge transfer · 2026 · DOI

  • While the Z-scheme-like electron transfer mechanism is proposed theoretically, direct experimental evidence (such as in-situ spectroscopy or time-resolved measurements) validating the proposed charge transfer pathways is not presented.

    Plasmonic Ag/AgCl/Bi <sub>2</sub> MoO <sub>6</sub> photocatalyst: Dual-functional bacteriostatic and sulfamerazine degradation via synergistic LSPR and Z-scheme charge transfer · 2026 · DOI

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