Anion-exchange-mediated internal electric field for boosting photogenerated carrier separation and utilization

Heterojunctions modulated internal electric field (IEF) usually result in suboptimal efficiencies in carrier separation and utilization because of the narrow IEF distribution and long migration paths of photocarriers. In this work, we report distinctive bismuth oxyhydroxide compound nanorods (denoted as BOH NRs) featuring surface-exposed open channels and a simple chemical composition; by simply modifying the bulk anion layers to overcome the limitations of heterojunctions, the bulk IEF could be readily modulated. Benefiting from the unique crystal structure and the localization of valence electrons, the bulk IEF intensity increases with the atomic number of introduced halide anions. Therefore, A low exchange ratio (~10%) with halide anions (I–, Br–, Cl–) gives rise to a prominent elevation in carrier separation efficiency and better photocatalytic performance for benzylamine coupling oxidation. Here, our work offers new insights into the design and optimization of semiconductor photocatalysts.

be more illustrative. 12. Line 329-330, 'The introduction of I-would lead to a more pronounced alteration in the bandgap,' Does this sentence refer to Table 1? 13. Figure 6. Explicit numbers corresponding to the colors of the legend would be beneficial. 14. In the introduction, it is emphasized that low efficiency of carriers separation hampers development of sophisticated organic reactions. It was expected that in this work, using the developed semiconductors, authors would give an example of 'sophisticated organic reaction'. However, application of the material is limited to oxidation of benzylamine only, which is rather a trivial reaction.
Once the abovementioned comments are positively addressed, the manuscript may be considered for publication in Nature Communications.
Reviewer #2 (Remarks to the Author): The manuscript entitled "Anion-Exchanged-Mediated Internal Electric Field: Boosting Photogenerated Carrier Separation and Utilization" presents the synthesis of bismuthoxy-hydroxyde as nanorods and the effect of halogen substitution of the hydroxides on its photocatalytic abilities. The authors claim that the partial substitution of OH-by halogen atoms enhance the photocatalytic conversion due to the formation of a strong internal electric field. This is an interesting work, but the results and hypothesis are too preliminary for publication in Nature Communication.
Here is the list of my remarks: 1-One main reason of the formation of an IEF presented by the author is the decrease of the photoluminescence efficiency. But a decrease of photoluminescence efficiency in solids is more attributed to trap states in the bandgap than an efficient charge carrier dissociation. Thus, this argument cannot be used as it is to prove the existence of an IEF. 2-Another argument given to support the idea of an IEF comes from the computations. But these computations are not at the state of the art. The author should look at the literature about the most appropriate computational protocol to characterize a semiconductor for photocatalytic application. They should use the range separated hybrid functional HSE06 for their calculation and deeply characterize their materials (bandgap, dielectric constant, effective masses). Furthermore, the Figure 6 is absolutely unclear. What information do we extract from the charge density? Figure 6f is to small to see the differences. From the Table 1, it appears that the DOS is almost unchanged upon halogen substitution. How do the authors explain the apparition of an IEF? Clearly, the DFT part could be much stronger and, if placed earlier in the paper, could support more the conclusion. 3- Figure 4d, the authors should give the band positions with respect to an electrode reference. 4-The authors should provide the response spectra as a function of the wavelength to see if the increase of efficiency of the BOH-I is not only due to a redshift of the absorption spectra. 5-On figure 5a, the nitrile group on the side product is linear. Please correct the structure and the TOC that also contains this structure.

Replies to the Reviewer #1
Li et al. report fabrication of nanorods of layered structure composed of (Bi2O2) 2+ and charge compensating hydroxyl ions with high cross-section-to-length aspect ratio via solvothermal approach employing polyvinylpyrrolidone and mannitol as directing agents.
Using ion exchange reaction, hydroxyl groups have been partially replaced by halide anions (ca 10%). The manuscript is well structured and written. It has been concluded that substitution of hydroxyls with halide ions induces formation of the internal electric field in the bulk of the material and, as a result leads to improved charge separation and improved performance in photocatalysis. This is the main point that authors appeal in the present work and which may, in principle, justify publication in top chemistry journal such as Nature Communications.
However, evidences supporting such claims have been derived mainly from steady state and time resolved emission spectroscopy. Despite materials have been characterized by a set of techniques, some questions related to the structure remain open. Overall, the manuscript offers synthesis, characterization and application of inorganic semiconductor of peculiar morphology in photocatalysis. However, authors should provide more evidences supporting formation of IEF as claimed in this manuscript.

Reply:
We really appreciate your positive feedback and constructive suggestions for our manuscript. Following your advices and suggestions, we have revised the manuscript carefully.
The lack of solid IEF evidence is indeed the deficiency of the original manuscript. Therefore, we conducted supplementary experiments to explore the internal electric field intensity for BOH and BOH-X, hoping to provide direct evidence for the existence of IEF. The method of measuring IEF intensity reported by Kanata et al. has been widely adopted, according to Photoreflectance signal amplitude R1-R6 . It was based on the effect of internal electric field disturbance on the dielectric constant of the semiconductor so that the photoreflectance signal was generated.

2
The formula is as follows: Fs=(-2Vsρ/εε0) 1/2 Where Fs is the internal electric field magnitude, Vs is the surface voltage, ρ is the surface charge density, ε is the low-frequency dielectric constant, and ε0 is the permittivity of free space.
As ε and ε0 are constants, the IEF intensity is mainly determined by the surface voltage (Vs) and the surface charge density (ρ). Therefore, we could qualitatively compare the internal electric field intensity of BOH and BOH-X according to the (Vsρ) 1/2 values.
Based on that, we first applied the open-circuit potentials measurements to evaluate the surface voltages of BOH and BOH-X. As shown in Figure R1, the surface voltage of BOH-I is 0.268 V, which is greater than that of BOH-Br (0.198 V), BOH-Cl (0.175 V), and BOH (0.142 V), indicating the enhanced IEF. Figure R1. The open-circuit potentials of BOH (a) and BOH-X (b-d).
As Le Formal and Gratzel et al. reported, the accumulated positive charge on the surface   is proportional to the integral value, calculated from the transient photocurrent density minus the steady-state photocurrent density in the same time R7 . Therefore, the transient photocurrent density measurements were conducted, controlling the same contact areas with ITO of every sample. The surface charge densities of BOH and BOH-X were then obtained by the integral of the transient anodic photocurrent peaks ( Figure R2). As expected, the integral value of the photocurrent response of BOH-I (148.1μcꞏcm -2 ) is the maximum among all specimens, which is even twice as magnitude as that of BOH (70.4 μcꞏcm -2 ), and also higher than that of BOH-Br (123.8 μcꞏcm -2 ) and BOH-Cl (105.4 μcꞏcm -2 ).
It can be found that the internal electric field intensity of BOH, BOH-Cl, BOH-Br, and BOH-I gradually increased ( Figure R3). Taking the IEF intensity of BOH as the "1", the IEF intensity of BOH-I is double BOH's, while these of BOH-Br and BOH-Cl are "1.6" and "1.4" respectively. Moreover, the increase of the internal electric field intensity is basically consistent with the photocatalytic performance of these catalysts for benzylamine oxidation (that is, the photocatalytic activity of BOH is "1", the catalytic activities of BOH-Cl, BOH-Br, and BOH-I are "1.6", "1.8" and "2.0" respectively). It further proves the validity of our strategy to regulate the IEF intensity through the exchange of halogen ions and directly demonstrates the positive correlation between the IEF intensity and the photocatalytic performance.
The above-related content has been supplemented in "Results: Synthesis strategy and characterization of BOX nanorods (X = Cl, Br, I)." and the corresponding SI section. Figure R2. The transient photocurrent density of BOH (a) and BOH-X (b-d). Figure R3. The internal electric field intensity and catalytic performance of BOH and BOH-X (assuming both the IEF intensity and the catalytic activity of BOH to be "1").  R8 . And the altered symmetry for BOH also results in diffraction peaks located at different angles from those for Bi2O2(OH)(NO3), as well as more diffraction peaks.
This new structure of BOH has never been reported, so we did not find a suitable standard XRD pattern corresponding to it. According to the reviewer's suggestion, we fitted the XRD pattern of Bi2O2(OH)2, as shown in Figure R4. It is observed that the BOH is basically in line with the fitted figure, and the prominent diffraction peaks (marked as peak 1-5) are consistent one-to-one match. Furthermore, a weaker diffraction peak shoulder near peak 1 might arise from the lattice distortion R9 . In addition, the diffraction peaks * do not exist in the simulated results. However, it disappeared after drying (dissolving BOH powder in a small amount of ethanol and redrying the sample at 100˚C for 15h) ( Figure R5), so we speculate the diffraction peak * might come from the hydrate impurity. However, the catalytic experiment shows that impurity has no noticeable effect on the catalytic activity ( Figure R6). These results indicate that the structure we inferred ([Bi2O2] 2+ is connected by OHbetween layers) is reasonable.
Combined with the XPS experiments and the TEM data, we further clarify that the basic composition of the BOH structure is Bi2O2(OH)2.
The above-related content has been supplemented in "Results: Synthesis strategy and characterization of BOH nanorods." and the corresponding SI section.           Electronegativity of all halides is lower compared to oxygen, while for iodide it is comparable to carbon.

Reply:
Thanks for pointing it out. The expression of "electronegativity" is indeed not appropriate, and we have deleted the relevant expression in the manuscript. Photoelectrochemical measurements were carried out on BOH and BOH-X with acetonitrile solvent ( Figure R14), and carriers separation efficiency could be evaluated by comparing the photoelectric response. The photocurrent density of BOH-I, BOH-Br, BOH-Cl, and BOH decreases successively, indicating the gradually decreasing separation efficiency of carriers.
The above-related content has been supplemented in "Results: Structure-activity relationship of BOH and BOH-X." and the corresponding SI section. Reply: Thanks for pointing it out. In the previous manuscript, several studies suggest that the CBM values for n-type semiconductors can be approximated as the Fermi level R14 , and thus the band structures can be estimated. However, based on your comment, we have redesigned the experiment regarding some research to obtain more accurate BOH and BOH-X band structures. The specific methods are as follows: First, we measured the XPS valence band spectrum of each catalyst ( Figure R15(a-c)) and obtained the distances from the VBM of materials to the Fermi level as 1.92 eV, 1.90 eV, 1.88 eV, and 1.62 eV corresponding to BOH, BOH-Cl, BOH-Br, and BOH-I respectively.
According to the Tauc plot ( Figure R15 BOH-X relative to the normal hydrogen electrode are finally obtained as Figure R16.
The above-related content has been supplemented in "Results: Structure-activity relationship of BOH and BOH-X." and the corresponding SI section. plots. Figure R16. The schematic diagram of band structure of BOH and BOH-X.
Comment 6: Line 261. In this manuscript authors study synthesis of imines rather than imides.

Reply:
We thank the reviewer for the careful examination of our paper. In the Page X, Line X, "Imides" was corrected to "imines". Besides, we have re-examined our manuscript and the supporting information and made some revisions to the wording and grammar. The revised parts are listed below.
Corresponding changes: Reply: Thanks for your recommendation for these two references. In the supplementary, we added some typical electron sacrificial agents to the reaction system with only substrate and solvent (without photocatalyst) and repeated the benzylamine oxidation experiment ( Figure   R17 left). It is found that these electron scavengers themselves could promote the conversion of benzylamine to a certain extent, and the conversion of benzylamine with K2S2O8 used in the manuscript is 23.8%.
Then we selected CCl4, which has the worst catalytic performance of benzylamine oxidation with the conversion of 8.5%, as the electron quenching agent to explore the role of electrons in photocatalysis ( Figure R17, right). For BOH, the oxidation of benzylamine is promoted with CCl4 added, while for BOH-X, the reactions are inhibited to different degrees.
Nevertheless, inhibition is weaker than that with K2S2O8 added. In combination with the catalytic performance of these two electron scavengers, it can be considered that electrons also participate in benzylamine oxidation for ion-exchanged catalysts. However, it is indeed not rigorous to directly conclude that "the role of holes is more outstanding than that of electrons in the catalytic process of BOH and BOH-X, and the effect of holes is stronger for BOH-X than that of BOH" only from previous experiments with sacrificial agents. ". It is generally believed that for the photo-oxidation with oxygen participated in organic solvents, the utilization of electrons lies in the fact that the superoxide radicals, which are obtained by electron reduction of oxygen, have excellent oxidizing ability R15 . The EPR experiments on superoxide radical show that all the samples can generate superoxide free radicals ( Figure R18 left), but BOH-X produce more superoxide free radicals. According to the comparative experiment of superoxide radicals quenching (right of Figure R18), after superoxide dismutase (SOD) was added, the benzylamine conversion didn't decline significantly (74.1% with SOD added). It proves that the oxidation by superoxide radicals is not the main pathway. Therefore, we have concluded that direct hole oxidation is dominant to a certain extent, which is consistent with the original manuscript.
The above-related content has been supplemented in "Results: Photocatalytic performances and mechanism." and the corresponding SI section. Reply: We thank the reviewer for the valuable suggestion. In order to explore the influence of specific surface areas of BOH and BOH-X in the process of photocatalysis, we performed the BET tests ( Figure R19). The specific surface area of BOH nanorods increased from 11.7 m 2 /g to 31.7 m 2 /g compared with the hydrothermal sheet product without PVP (BOH-NPVP).
However, the specific surface areas of the catalyst before and after ion exchange are the same (BOH：31.7 m 2 /g；BOH-Cl：30.9 m 2 /g；BOH-Br：29.4 m 2 /g；BOH-I：30.1 m 2 /g), so the influence of specific surface area change on BOH-X-ray catalytic performance can be excluded.  Reply: Thank you for pointing this out. We are sorry for missing such important information in the previous manuscript. In order to enable the theoretical calculation results more in line with the actual situation, as well as to make the intrinsic differences of halogen ion exchange more intuitive, 20% halogen ion exchange was chosen for the theoretical study (while the halogen ion exchange capacity measured in our experiment is about 10%).
To investigate the influence of halogen ions more professionally, we adopted the suggestion of reviewer #2 and recalculated with the HSE06 function, which is more suitable for photocatalysis. The amount of halogen ion exchange is still 20%. The proportion of halogen ions in the calculation model has been supplemented in the calculation part of the manuscript.
According to calculation using the HSE06 function, the hybridization of p orbital of halogen atom with p orbital of Bi and O is more pronounced, contributing halogen atoms to the valence band more prominent, which more powerfully proves that the introduction of halogen could further strengthen the IEF intensity of the materials.     We are sorry that we have omitted the detailed description of Table 1 in the previous manuscript, which may cause misunderstanding among readers. Table 1 shows the contributions of each element to VBM and CBM for BOH and BOH-X (After applying the new calculation function, Table 1 has also been updated, see Table R1    Comment 13: Figure 6. Explicit numbers corresponding to the colors of the legend would be beneficial. Reply: Thanks for your suggestion. The original manuscript did not properly mark the IEF strength, so the difference in the IEF intensity among samples was not noticeable, which was indeed easy to cause readers confusion. In order to study the role of the IEF more professionally, we recalculated with the HSE06 function. The new calculation results show more pronounced distinctions of the IEF intensity of BOH and BOH-X ( Figure R24), which is also consistent with the catalytic activity of the materials ( Figure R25). Accordingly, we have updated the calculation content and illustration of the manuscript (changing the original figure 6 to the current figure 5), marked the value in the local IEF in Figure 5 with the corresponding legend color. Figure R24. DFT calculated the local internal electric field for the four catalysts. Figure R25. Superimposed plots of benzylamine conversion and calculative IEF intensity for the four catalysts.

Comment 14:
In the introduction, it is emphasized that low efficiency of carriers' separation hampers development of sophisticated organic reactions. It was expected that in this work, using the developed semiconductors, authors would give an example of 'sophisticated organic reaction'. However, application of the material is limited to oxidation of benzylamine only, which is rather a trivial reaction.
Reply: Thanks for your comment. It needs to be emphasized that the core point of our manuscript is to introduce an ion-exchange strategy to increase the IEF intensity and then achieve efficient separation and utilization of carriers. Therefore, we chose the model reaction of benzylamine oxidation to verify our design strategy. After proving the strategy's effectiveness, we used BOH-I as a catalyst and designed experiments to oxidize a series of complex imines under the same reaction conditions. The experimental results show that BOH-I is effective for the oxidation of these imines substrates (conversion ≥ 85%, selectivity ≥93%) ( Figure R25). Therefore, it can be seen that the carrier separation efficiency caused by IEF control is greatly improved, and the complex photocatalytic organic reactions can indeed be realized.
The above-related content has been supplemented in "Results: Photocatalytic performances and mechanism." and the corresponding SI section.

Replies to the Reviewer #2
The manuscript entitled "Anion-Exchanged-Mediated Internal Electric Field: Boosting Photogenerated Carrier Separation and Utilization" presents the synthesis of bismuthoxyhydroxyde as nanorods and the effect of halogen substitution of the hydroxides on its photocatalytic abilities. The authors claim that the partial substitution of OH-by halogen atoms enhance the photocatalytic conversion due to the formation of a strong internal electric field. This is an interesting work, but the results and hypothesis are too preliminary for publication in Nature Communication.

Reply:
We would like to thank the reviewer for commenting "This is an interesting work." Based on your suggestions, we have conducted more experiments and changed the computational function to improve this manuscript.

Comment 1:
One main reason of the formation of an IEF presented by the author is the decrease of the photoluminescence efficiency. But a decrease of photoluminescence efficiency in solids is more attributed to trap states in the bandgap than an efficient charge carrier dissociation. Thus, this argument cannot be used as it is to prove the existence of an IEF.
Reply: Thanks for pointing it out. The lack of solid IEF evidence is indeed the deficiency of the original manuscript. Therefore, we carried out supplementary experiments to explore the internal electric field intensity for BOH and BOH-X, hoping to provide direct evidence for the existence of IEF. The method of estimate IEF intensity reported by Kanata et al. has been widely adopted, according to Photoreflectance signal amplitude R1-R6 . It was based on the effect of internal electric field disturbance on the dielectric constant of the semiconductor so that the photoreflectance signal was generated.
The formula is as follows: Fs=(-2Vsρ/εε0) 1/2 Where, Fs is the internal electric field magnitude, Vs is the surface voltage, ρ is the surface charge density, ε is the low-frequency dielectric constant, and ε0 is the permittivity of free space.
As ε and ε0 are constants, the IEF intensity is determined by the surface voltage (Vs) and the surface charge density (ρ). Therefore, we could qualitatively compare the IEF intensity of BOH and BOH-X according to their (Vs ρ) 1/2 values.
Based on that, we first applied the open-circuit potentials measurements to evaluate the surface voltages of BOH and BOH-X. As shown in Figure R1,  areas with ITO of every sample. The surface charge densities of BOH and BOH-X were then obtained by the integral of the transient anodic photocurrent peaks ( Figure R2). As expected, the integral value of the photocurrent response of BOH-I (148.1 μcꞏcm -2 ) is the maximum among all specimens, which is twice as magnitude as that of BOH (70.4 μcꞏcm -2 ), and also higher than that of BOH-Br (123.8 μcꞏcm -2 ) and BOH-Cl (105.4 μcꞏcm -2 ).
It can be found that the internal electric field intensity of BOH, BOH-Cl, BOH-Br, and BOH-I gradually increase ( Figure R3). Taking the internal electric field intensity of BOH as the "1", the internal electric field intensity of BOH-I is double BOH's, while these of BOH-Br and BOH-Cl are "1.6" and "1.4", respectively.  (c) (d) Figure R3. The internal electric field intensity of BOH and BOH-X (assuming the IEF intensity of BOH to be "1").
The enhancement of the IEF intensity endows the photocatalysts with great potential for efficient charge separation and migration. Then, the different carrier separation behaviors of BOH and BOH-X were studied. It is widely known that the transient photocurrent tests ( Figure   R4) can directly reflect the number of residual electrons and holes after recombination and can qualitatively express the separation efficiency of carriers. The results show that the carrier separation efficiency of BOH is the weakest and that of BOH-Cl, BOH-Br, and BOH-I gradually increase, which is consistent with the results of steady-state fluorescence spectroscopy. Figure R4. The photocurrent density of BOH and BOH-X.
It can be seen that the variation range of IEF intensity is consistent with the above data for BOH and BOH-X ( Figure R5). Therefore, it can be considered that the most crucial reason for the improvement of carrier separation and utilization in BOH-X is the promotion of IEF intensity. Combined with the IEF intensity measurements and the calculation results, we believe that as the atomic number of the introduced halide species goes higher, the ionic radius becomes larger, and the charge distribution between the layers become more uneven; the larger electrostatic potential difference between the layers intensifies the interlayer IEF, and thus promotes the carrier separation and utilization.
The above-related content has been supplemented in "Results: Synthesis strategy and characterization of BOH nanorods. & Structure-activity relationship of BOH and BOH-X." and the corresponding SI section. Figure R5. Effects of ion exchange on the IEF intensity, carrier separation efficiency, and photocatalytic activity of benzylamine oxidation (assuming all the BOH value to be "1").

Comment 2:
Another argument given to support the idea of an IEF comes from the computations. But these computations are not at the state of the art. The author should look at the literature about the most appropriate computational protocol to characterize a semiconductor for photocatalytic application. They should use the range separated hybrid functional HSE06 for their calculation and deeply characterize their materials (bandgap, dielectric constant, effective masses). Furthermore, the Figure 6 is absolutely unclear. What information do we extract from the charge density? Figure 6f is too small to see the differences.
From the Table 1, it appears that the DOS is almost unchanged upon halogen substitution. How do the authors explain the apparition of an IEF? Clearly, the DFT part could be much stronger and, if placed earlier in the paper, could support more the conclusion.
Reply: We thank the reviewer for the valuable suggestion. In order to make the theoretical calculation more in line with the actual situation, we adopted a more suitable range separated hybrid functional HSE06 to describe the semiconductor for photocatalytic application, according to your suggestion. Compared with the PBE function, the band gaps obtained by HSB06 function increase, better aligning with the experimental results. Therefore, it can be seen that the PBE function underestimates the energy band of the materials, while the HSB06 function is more suitable for the calculation of photocatalytic materials. The calculation result with HSB06 function further demonstrates that "the introduction of halogen ions enhances the IEF intensity " in this manuscript.
First, using HSE06 function to calculate R8-R9 , we found that DOS changed more reasonably for BOH-X ( Figure R6      After calculating HSE06 functional, the IEF intensity of BOH and BOH-X changed more obviously ( Figure R10). In particular, according to the initial calculation results, the local electric field intensity of each sample is 0.42 eV (for BOH), 0.47 eV (for BOH-Cl), 0.49 eV (for BOH-Br), and 0.51eV (for BOH-I). In comparison, the local IEF intensity calculated with HSE06 function is 10.8 eV, 11.6 eV, 11.9 eV, and 12.3 eV (corresponding to BOH, BOH-Cl, BOH-Br, and BOH-I, respectively), which are consistent with the results of the IEF intensity measurement experiments (see Comments 1), as well as the catalytic activity of BOH and BOH-X ( Figure R11). The results prove that the intrinsic driving force of BOH-X performance improvement is the increase of IEF intensity caused by the introduction of halogen ions.
The above-related content has been supplemented in "Results: Structure-activity relationship of BOH and BOH-X." and the corresponding SI section.  In order to assess the Fermi levels for BOH and BOH-X, we conducted the Mott-Schottky measurements at the potential of -0.1 V to -0.7 V (at a fixed frequency of 500 Hz). Based on the Mott-Schottky formula, Csc -1 =2(sc-RT/F) (qεε0N) -1 (where sc=V-Vfb, Vfb is the flat band potential, T is the Kelvin temperature, F is the Faraday constant, R is the gas constant, ε and ε0 are the semiconductor dielectric constant and vacuum dielectric constant, respectively, q is the charge quantity, and N is the doping concentration), we plotted Csc -1 versus V ( Figure   S22), and then obtained the flat bands of BOH, BOH-Cl, BOH-Br and BOH-I through the intercept of the abscissa V0=Vfb+RT/F. Therefore, the potentials of BOH, BOH-Cl, BOH-Br and BOH-I are 0.15 eV, 0.21 eV, 0.03 eV and 0.02 eV, (versus Ag/AgCl at pH 6.80) respectively, which are -0.25 eV, -0.19 eV, -0.17 eV and -0.38 eV separately, relative to the normal hydrogen electrode at pH=0 (NHE). Since the Fermi level Ef and Vfb have the same value, combined with the valence band spectrum and UV-vis DRS test results, the energy band diagrams of BOH and BOH-X relative to the normal hydrogen electrode are finally obtained as Figure R12.
The above-related content has been supplemented in "Results: Structure-activity relationship of BOH and BOH-X." and the corresponding SI section. Figure R12. The schematic diagram of band structure of BOH and BOH-X.

Comment 4:
The authors should provide the response spectra as a function of the wavelength to see if the increase of efficiency of the BOH-I is not only due to a redshift of the absorption spectra.
Reply: Thanks for your valuable suggestion. In order to explore the redshift effect of BOH-I, we designed photocatalytic experiments with monochromatic light of different wavelengths.
According to the Tauc plot ( Figure R13(d)) and the formula λg=1240/Eg (λg is the light absorption threshold of the material; Eg is the band gap.), the light absorption threshold values Therefore, the redshift region of BOH-I is mainly concentrated in the range of 340 nm-400 nm.
Based on this, the monochromatic lights with four wavelengths (365 nm, 405 nm, 450 nm, and 500 nm) were selected ( Figure R14). The results show that whether the wavelength of the light source is in the BOH-I redshift region or not, the photoactivity still follows the previous order (BOH < BOH-Cl < BOH-Br < BOH-I), which proves that the redshift of the absorption spectrum is not an essential advantage for BOH-I. Combined with the qualitative IEF intensity measurements, we can attribute the high activity of BOH-I mainly to its more vigorous IEF intensity.
The above-related content has been supplemented in "Results: Photocatalytic performances and mechanism." and the corresponding SI section. Figure R14. Photocatalytic activity over BOH and BOH-X by introducing different single wavelength light.

Comment 5:
On figure 5a, the nitrile group on the side product is linear. Please correct the structure and the TOC that also contains this structure.