Metal-free heteroatom doping of carbon nitride for enhanced photocatalytic hydrogen peroxide production

Bruna F. Gon\c{c}alves; Eneko Sebastian-Garate; Hugo Salazar; Ivan Infante; Jordi Llusar; Pawel Gluchowski; Qi Zhang; Senentxu-Lanceros Mendez

arxiv: 2605.17897 · v1 · pith:MVVTRQTPnew · submitted 2026-05-18 · ❄️ cond-mat.mtrl-sci

Metal-free heteroatom doping of carbon nitride for enhanced photocatalytic hydrogen peroxide production

Eneko Sebastian-Garate , Bruna F. Gon\c{c}alves , Jordi Llusar , Pawel Gluchowski , Ivan Infante , Senentxu-Lanceros Mendez , Qi Zhang , Hugo Salazar This is my paper

Pith reviewed 2026-05-20 10:01 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci

keywords carbon nitrideheteroatom dopingphotocatalysishydrogen peroxidemetal-freecharge separationsolar-to-chemical

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The pith

Sulfur-doped carbon nitride multiplies hydrogen peroxide production by over 16 times under solar light

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper tests the addition of boron, oxygen, phosphorus, or sulfur atoms into graphitic carbon nitride to see how these metal-free changes affect its structure and its ability to make hydrogen peroxide from water using simulated sunlight. All four doped versions produce far more hydrogen peroxide than the plain material, with the sulfur version reaching the highest rate and holding most of its performance after repeated use. A sympathetic reader would care because this points to a straightforward way to turn sunlight into a useful chemical without needing scarce metals or large amounts of energy. The results tie the gains to better movement of electric charges inside the material and a preferred two-electron reaction path.

Core claim

Metal-free heteroatom doping modifies the stacked nanosheet structure of graphitic carbon nitride, producing disorder, partial exfoliation, and altered interlayer spacing that improve electronic and optical properties. The sulfur-doped material reaches a hydrogen peroxide production rate of 3022.1 μmol h⁻¹ g⁻¹ and an apparent quantum yield of 8.1 percent, a 16.4-fold increase over the undoped case, while keeping more than 95 percent of its activity after five cycles. The reaction proceeds mainly through a two-electron oxygen activation pathway in which singlet oxygen and photogenerated holes dominate.

What carries the argument

Heteroatom doping of C3N4 that induces structural disorder and electronic modification to enhance charge separation and reaction selectivity

Load-bearing premise

The measured rises in hydrogen peroxide output come from the heteroatom-induced improvements in charge separation and electronic structure rather than from differences in surface area, light absorption, or other unmeasured experimental factors.

What would settle it

Repeating the experiments with doped and undoped samples that have been matched for surface area, light-absorption spectra, and verified doping concentrations would show whether the activity differences remain or vanish.

read the original abstract

The photocatalytic production of hydrogen peroxide (H$_2$O$_2$) from water is a promising strategy for solar-to-chemical energy conversion. Herein, we investigate the effect of metal-free heteroatom doping (B, O, P, and S) on the structural, electronic, and photocatalytic properties of graphitic carbon nitride (C$_3$N$_4$) for H$_2$O$_2$ production under simulated solar irradiation. While pristine C$_3$N$_4$ exhibits stacked nanosheets, doping induces disorder, partial exfoliation, and changes in interlayer spacing, confirming successful heteroatom incorporation and modification of the electronic and optical properties. Photocatalytic experiments reveal that H$_2$O$_2$ production strongly depends on the sacrificial agent, pH, and reactive-species scavengers. All doped catalysts show enhanced activity compared to pristine C$_3$N$_4$, with 9.6-, 14.8-, 11.0-, and 16.4-fold increases for B-, P-, O-, and S-doped C$_3$N$_4$, respectively. S-doped C$_3$N$_4$ achieved the highest H$_2$O$_2$ production rate of 3022.1 $\mu$mol h$^{-1}$ g$^{-1}$ and an apparent quantum yield of 8.1\%, attributed to improved charge separation and optimized selectivity. Mechanistic studies indicate that oxygen activation mainly follows a two-electron (2e$^{-}$) pathway driven by charge-carrier modulation and reactive oxygen species dynamics, with singlet oxygen and photogenerated holes playing a dominant role. In addition, S-doped C$_3$N$_4$ retained over 95\% of its activity after five cycles. These results highlight metal-free heteroatom doping as an effective strategy for sustainable photocatalytic H$_2$O$_2$ generation.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

S-doping lifts H2O2 rates in g-C3N4 by 16x to 3022 μmol h⁻¹ g⁻¹ with 8.1% AQY and solid cycling, but the gains may trace more to unnormalized surface area or exfoliation than to the claimed electronic tweaks.

read the letter

The paper's clearest contribution is the head-to-head performance data on B-, O-, P-, and S-doped carbon nitride for photocatalytic H2O2. S-doping comes out on top with a 16.4-fold rate increase over pristine material, an absolute 3022 μmol h⁻¹ g⁻¹, 8.1% apparent quantum yield, and >95% retention after five cycles. The other dopants deliver 9.6- to 14.8-fold gains under the same conditions. They also map how each dopant alters interlayer spacing, disorder, and optical response, which lines up with the observed activity ranking. That set of quantitative benchmarks and stability numbers is new enough to be worth citing in follow-up optimization work within the photocatalysis community. The scavenger tests point to a dominant 2e⁻ route with singlet oxygen and holes involved, which is consistent with prior g-C3N4 literature but now tied to specific dopant effects here. The structural characterization (XRD, TEM, XPS) is straightforward and supports successful incorporation without metals. The main soft spot is the lack of surface-area normalization. The abstract itself notes partial exfoliation and spacing changes from doping, yet all rates are reported per gram only. If the S-doped sample simply has higher BET area or better light penetration from those morphological shifts, the ranking and fold improvements could be driven by accessibility rather than the electronic-structure story. Doping levels are not shown to be equivalent across samples either, which leaves room for concentration effects. No error bars or replicate counts appear in the summary data, so the precision of the 3022 number is hard to judge from what is given. This is a practical materials paper aimed at groups already working on carbon-nitride photocatalysts for H2O2 or related solar fuels. Readers looking for new mechanistic theory or large-scale process data will not find it, but those needing concrete dopant-performance numbers will. The work is coherent on its own terms and shows honest experimental engagement, so it merits a full referee pass to check the missing controls and raw data rather than a desk reject.

Referee Report

2 major / 1 minor

Summary. The manuscript investigates metal-free heteroatom doping (B, O, P, S) of graphitic carbon nitride (C3N4) to enhance photocatalytic H2O2 production from water under simulated solar irradiation. It reports that doping induces structural disorder, partial exfoliation, and interlayer spacing changes, leading to modified electronic and optical properties. All doped catalysts exhibit enhanced activity, with fold increases of 9.6 (B), 14.8 (P), 11.0 (O), and 16.4 (S) over pristine C3N4; S-doped C3N4 achieves the highest rate of 3022.1 μmol h⁻¹ g⁻¹ and 8.1% apparent quantum yield, attributed to improved charge separation and a dominant 2e⁻ oxygen activation pathway involving singlet oxygen and photogenerated holes. The S-doped material retains >95% activity after five cycles.

Significance. If the activity enhancements are confirmed to arise from electronic and charge-separation effects rather than unaccounted structural variables, this would represent a useful contribution to metal-free photocatalysis for H2O2 synthesis, demonstrating a straightforward doping approach that yields high rates, good selectivity, and reasonable stability. The explicit reporting of fold improvements and cycle retention provides a clear benchmark for future work in sustainable solar-to-chemical conversion.

major comments (2)

Abstract: The H2O2 production rates are reported only on a per-gram basis (e.g., 3022.1 μmol h⁻¹ g⁻¹ for S-doped) without normalization to BET surface area or confirmation of comparable doping concentrations across samples. The abstract itself states that doping induces disorder, partial exfoliation, and interlayer spacing changes; these structural modifications can independently increase accessible surface area and light absorption, raising the possibility that the observed 9.6- to 16.4-fold enhancements are driven at least partly by these factors rather than solely by the claimed improvements in charge separation and electronic structure.
Mechanistic studies section (as summarized in abstract): The assertion that oxygen activation follows a dominant two-electron (2e⁻) pathway driven by charge-carrier modulation rests on scavenger experiments, yet the abstract provides no quantitative details on scavenger specificity, the exact impact on H2O2 yields when particular species (e.g., holes or singlet oxygen) are quenched, or controls ruling out alternative 1e⁻ routes. This weakens the mechanistic attribution central to explaining the selectivity and activity ranking.

minor comments (1)

Abstract: The dependence of activity on sacrificial agent, pH, and reactive-species scavengers is noted qualitatively but without specific numerical conditions or values; adding these details in the main text would improve reproducibility.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments on our manuscript. We have carefully reviewed the concerns regarding rate normalization and the level of detail in the mechanistic discussion. We address each point below and indicate the revisions planned for the next version of the manuscript.

read point-by-point responses

Referee: Abstract: The H2O2 production rates are reported only on a per-gram basis (e.g., 3022.1 μmol h⁻¹ g⁻¹ for S-doped) without normalization to BET surface area or confirmation of comparable doping concentrations across samples. The abstract itself states that doping induces disorder, partial exfoliation, and interlayer spacing changes; these structural modifications can independently increase accessible surface area and light absorption, raising the possibility that the observed 9.6- to 16.4-fold enhancements are driven at least partly by these factors rather than solely by the claimed improvements in charge separation and electronic structure.

Authors: We agree that mass-normalized rates alone do not fully isolate electronic effects from structural ones. In the revised manuscript we will add BET surface area values for all samples (pristine and doped) and report H2O2 production rates normalized to both catalyst mass and specific surface area. We have performed XPS and CHNS elemental analysis confirming heteroatom incorporation levels of 2–5 at.% that are comparable across the B-, O-, P-, and S-doped materials; these data and the corresponding spectra will be included in the revised Supporting Information. While the abstract notes structural changes, the full text already presents PL quenching, EIS, and transient photocurrent results that demonstrate improved charge separation beyond what surface area alone would explain. We will strengthen the discussion to explicitly separate these contributions. revision: yes
Referee: Mechanistic studies section (as summarized in abstract): The assertion that oxygen activation follows a dominant two-electron (2e⁻) pathway driven by charge-carrier modulation rests on scavenger experiments, yet the abstract provides no quantitative details on scavenger specificity, the exact impact on H2O2 yields when particular species (e.g., holes or singlet oxygen) are quenched, or controls ruling out alternative 1e⁻ routes. This weakens the mechanistic attribution central to explaining the selectivity and activity ranking.

Authors: We accept that the abstract is too concise on the scavenger data. The full manuscript already contains quantitative results from experiments using EDTA (holes), furfuryl alcohol (¹O₂), and benzoquinone (O₂•⁻), showing >70 % suppression of H2O2 yield for holes and singlet oxygen while the superoxide scavenger has minimal effect. We will revise the abstract to include these percentage reductions and add a concise summary table of scavenger effects with appropriate control experiments. EPR spectra confirming ¹O₂ generation and additional control runs that exclude significant 1e⁻ contribution will be highlighted in the revised mechanistic section. revision: yes

Circularity Check

0 steps flagged

No circularity: purely experimental performance study with direct measurements

full rationale

This paper reports experimental synthesis, characterization, and photocatalytic testing of B-, O-, P-, and S-doped C3N4 for H2O2 production. All central claims (fold increases in rate, highest value of 3022.1 μmol h⁻¹ g⁻¹ for S-doped, 8.1% AQY, stability after five cycles) rest on measured quantities under controlled conditions rather than any derivation, equation, or prediction that reduces to its own inputs. No self-referential equations, fitted parameters renamed as predictions, or load-bearing self-citations appear in the provided text or abstract. The study is therefore self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The paper rests on standard domain assumptions of photocatalysis rather than new postulates or fitted constants.

axioms (1)

domain assumption Photocatalytic H2O2 formation proceeds via charge-carrier-mediated oxygen reduction following established two-electron or four-electron pathways.
Invoked when attributing activity to 2e⁻ pathway and reactive oxygen species dynamics.

pith-pipeline@v0.9.0 · 5908 in / 1357 out tokens · 45176 ms · 2026-05-20T10:01:26.463413+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Foundation/RealityFromDistinction.lean reality_from_one_distinction unclear

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unclear
Relation between the paper passage and the cited Recognition theorem.

All doped catalysts show enhanced activity... S-doped C3N4 achieved the highest H2O2 production rate of 3022.1 μmol h⁻¹ g⁻¹... attributed to improved charge separation and optimized selectivity.
IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

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unclear
Relation between the paper passage and the cited Recognition theorem.

BET specific surface areas... 61.6, 67.3, 102.1, 78.2, and 141.5 m2 g-1... higher surface upon doping suggests a higher number of catalytic sites

What do these tags mean?

matches: The paper's claim is directly supported by a theorem in the formal canon.
supports: The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends: The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
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contradicts: The paper's claim conflicts with a theorem or certificate in the canon.
unclear: Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

3 extracted references · 3 canonical work pages

[1]

INTRODUCTION The global energy transition is a pressing challenge in the 21st century, driven by the need to reduce carbon emissions, mitigate climate change, and develop sustainable alternatives to fossil fuels. As industries and governments shift toward cleaner energy solutions, hydrogen-based technologies have garnered significant attention due to thei...

work page doi:10.1016/j.scitotenv.2024.173622 2023
[2]

P. Sun, Z. Chen, J. Zhang, G. Wu, Y. Song, Z. Miao, K. Zhong, L. Huang, Z. Mo, H. Xu, Simultaneously tuning electronic reaction pathway and photoactivity of P, O modified cyano-rich carbon nitride enhances the photosynthesis of H2O2, Appl Catal B 342 (2024) 123337. https://doi.org/10.1016/j.apcatb.2023.123337. [16] W. Wang, R. Liu, J. Zhang, T. Kong, L. W...

work page doi:10.1016/j.apcatb.2023.123337 2024
[3]

Z. Zhao, Y. Long, Y. Chen, F. Zhang, J. Ma, Phosphorus doped carbon nitride with rich nitrogen vacancy to enhance the electrocatalytic activity for nitrogen reduction reaction, Chemical Engineering Journal 430 (2022) 132682. https://doi.org/10.1016/j.cej.2021.132682. [30] M. Zuo, X. Li, Y. Liang, F. Zhao, H. Sun, C. Liu, X. Gong, P. Qin, H. Wang, Z. Wu, L...

work page doi:10.1016/j.cej.2021.132682 2022

[1] [1]

INTRODUCTION The global energy transition is a pressing challenge in the 21st century, driven by the need to reduce carbon emissions, mitigate climate change, and develop sustainable alternatives to fossil fuels. As industries and governments shift toward cleaner energy solutions, hydrogen-based technologies have garnered significant attention due to thei...

work page doi:10.1016/j.scitotenv.2024.173622 2023

[2] [2]

P. Sun, Z. Chen, J. Zhang, G. Wu, Y. Song, Z. Miao, K. Zhong, L. Huang, Z. Mo, H. Xu, Simultaneously tuning electronic reaction pathway and photoactivity of P, O modified cyano-rich carbon nitride enhances the photosynthesis of H2O2, Appl Catal B 342 (2024) 123337. https://doi.org/10.1016/j.apcatb.2023.123337. [16] W. Wang, R. Liu, J. Zhang, T. Kong, L. W...

work page doi:10.1016/j.apcatb.2023.123337 2024

[3] [3]

Z. Zhao, Y. Long, Y. Chen, F. Zhang, J. Ma, Phosphorus doped carbon nitride with rich nitrogen vacancy to enhance the electrocatalytic activity for nitrogen reduction reaction, Chemical Engineering Journal 430 (2022) 132682. https://doi.org/10.1016/j.cej.2021.132682. [30] M. Zuo, X. Li, Y. Liang, F. Zhao, H. Sun, C. Liu, X. Gong, P. Qin, H. Wang, Z. Wu, L...

work page doi:10.1016/j.cej.2021.132682 2022