Peroxymonosulfate Activation by BaTiO3 Piezocatalyst
Round 1
Reviewer 1 Report
this manuscript studied systematically BTO piezocatalysts activated PMS by ultrasonic power. I think accept is necessary. there are some comments for authors in the attachment.
Comments for author File: 
Comments.pdf
Author Response
Reviewer #1
In this study, barium titanate (BTO) piezoelectric catalysts were selected for activation of PMS driven by ultrasonic power. The degradation of rhodamine B (RhB) by BTO single component, PMS single component and BTO/PMS two components was studied. The results showed that ·O2-, ·OH, ·SO42- were the main active substances, so BTO could effectively activate PMS under the effect of ultrasound. The degradation rate of RhB was 98% within 20 min, and it had high environmental applicability to AMX. BTO/PMS showed 80% AMX removal efficiency. In addition, ultrasound also plays a certain role in performance. Ultrasound not only promotes the activation of PMS itself, but also induces BTO surface charge carriers, thus contributing to the activation of PMS. This work provides a promising strategy to improve the utilization of ultrasonic energy and apply it to the field of environmental pollutants treatment. Although its representation method is innovative, there are still many problems in this paper:
Comment 1: First of all, the context is not closely connected in many parts of the text, resulting in unclear meaning expression, for example: “Taking ultrasonic PMS activation as an example, ultrasound in the frequency range of 20- 1000 kHz causes cavitation phenomenon. The high temperatures (5000 K) and high pressures (10 Atm.) at the moment the bubble bursting facilitate PMS activation.”
Answer:
Thanks for your suggestion. We reorganized the introduction part to make it readable.
See Introduction part:
“At present, the main activation methods of PMS mainly include ultraviolet activation, ultrasonic activation, metal/metal oxide activation and carbon-based material activation [15-17]. Physical activation processes such as light or vibration activation provide very limited PMS activation efficiency [18-20]. Catalytic approaches, whatever homogeneous or heterogeneous one, provide a more efficient PMS activation process.”
Comment 2: Secondly, this paper presents the auxiliary role of ultrasound in the abstract, but does not discuss the specific influence of ultrasound on its role, such as ultrasonic time or power. In addition, the characterization of piezoelectric properties is rarely proved.
Answer: We supplemented this part and discussed the effect of ultrasonic power on the degradation of RhB. In addition, more characterizations of BTO catalyst were given, such as HRTEM, N2 sorption, PFM image and curves.
See line 188:
“In Figure 3c, RhB was barely degraded in the absence of ultrasound, but was degraded by about 50 % at 120 min at 100 W, and by about 80% at 200 W and 400 W, with the best effect at 300 W, and faster degradation rates. Considering the removal efficiency and economic benefits, 300 W was finally selected as the ultrasonic power of this system.”
Figure 3. (a) Effect of PMS concentration on RhB degradation. (b) Reaction kinetics. (c) Effect of Ultrasound power on RhB degradation.
See line 147:
“To further investigate the structure of the BTO-180 catalyst, some other characterizations were carried out. BTO-180 presented a rod-like structure via TEM, consistent with the results obtained in SEM (Figure 2a). Clear lattice stripes with 0.41 nm spacing was observed (Figure 2b), which corresponded to the (100) crystal surface. The SEAD diagram showed a large number of diffraction spots with parallel regular arrangement, indicating that the BTO catalyst was a single crystal structure. N2 adsorption-desorption isotherm of the catalyst complied with the type Ⅲ isotherm. Rapid rise near P/P0=1 demonstrated the presence of large holes (Figure 2c), which was due to the overlapping of nanorods. The specific surface area of BTO-180 was 7.1 m2/g calculated by BET method. The topography image on the left shows the morphology of the polycrystalline material. The PFM phase signal was shown on the right revealing the ferroelectric domains in this sample. Figure 2d shows rod-like BTO-180 PFM phase image. Under the ±10 V DC bias electric field, the typical butterfly curve (Figure 2e) and reverse of piezoelectric hysteresis loop (Figure 2f) were measured. The test results showed the catalyst with large displacement and phase change 180, which showed that the BTO-180 showed good piezoelectric response.”
Figure 2. (a-b) TEM images and corresponding SEAD pattern of BTO-180. (c) N2 adsorption curve of BTO-180. (d) PFM images of BTO-180. (e-f) Butterfly curves and reverse piezoelectric hysteresis loop of BTO-180.
Comment 3: Finally, there are some small problems in the text, such as bold fonts, the number of XRD diffraction peaks does not match, and the picture size is different (the font in the picture is not the same size, and there is no English font space).
Answer:
Thanks for your suggestion. The format of the entire manuscript was carefully revised.
For example, see line 120:
“The diffraction peaks of BTO samples at 21.99°, 31.56°, 38.87°, 45.20°, 50.89°, 56.09°, 65.77° corresponded well to (100), (110), (111), (200), (210), (211), (220) of standard card (JCPDS: 05-0626; tetragonal barium titanate).”
Comment 4: Please ensure that the quotation numbers in the text are correct. Such as chemical polymerization [23,24], this is wrong.
Answer:
Sorry about our mistake. The error parts have been revised accordingly.
Comment 5: If the author wants to use abbreviations for time, use the abbreviations uniformly. Some places use hours, some place use min. I think this is not very good. Please change it.
Answer:
Thanks for your suggestion. All time units have been unified as “min”.
For example, “In order to optimize the reaction conditions, the effect of BTO-180 dosage, reaction pH, RhB concentration, different anions on PMS activation were investigated. In Figure 4a, when the BTO-180 dosage was 0.08 g/L, the RhB removal efficiency was 51.5% within 120 min.”
Comment 6: Why the “BTO-180 (25 mg) was added into the” marked black?
Answer:
The black bold mark was cancelled. Thanks for your reminder.
Comment 7: The relevant studies on photocatalytic activities are suggested to be cited to enhance the introduction. Journal of Alloys and Compounds, 2022, 901: 163628. RSC advances, 2021, 11(6): 3333-3341. ACS Catal. 2014, 4, 10, 3724-3729, 10.1021/cs500794j. Chem. Eur. J. 2014, 20, 311-316, 10.1002/chem.201302679. ChemSusChem, 2018, 11, 1, 276-284, 10.1002/cssc.201701574. ACS Sustainable Chem. Eng. 2019, 7, 17, 15137-15145, 10.1021/acssuschemeng.9b04153. Journal of Colloid and Interface Science, 2020, 578, 431-440, 10.1016/j.jcis.2020.04.033. Catal. Sci. Technol., 2019, 9, 5812-5818, 10.1039/C9CY01192G. ACS Sustainable Chem. Eng. 2019, 7, 12, 10971-10978, 10.1021/acssuschemeng.9b02009. Applied Catalysis B: Environmental, 2021, 290, 120058, 10.1016/j.apcatb.2021.120058.
Answer:
Thanks for your suggestion. We cited these articles.
See line 24:
“Photocatalysts [21-28] and piezocatalysts [29-35] both show excellent PMS activation efficiency.”
[21] Bi, L.; Gao, X.; Zhang, L.; Wang, D.; Zou, X.; Xie, T. Enhanced photocatalytic hydrogen evolution of NiCoP/g‐C3N4 with improved separation efficiency and charge transfer efficiency. Chem. Sus. Chem. 2018, 11(1): 276-284.
[22] Bu, Q.; Li, S.; Wu, Q.; Lin, Y.; Wang, D.; Zou, X.; Xie, T. In situ synthesis of FeP-decorated Ti–Fe2O3: an effective strat-egy to improve the interfacial charge transfer in the photoelectrochemical water oxidation reaction. Catal. Sci. Technol. 2019, 9(20): 5812-5818.
[23] Han, B.; Zhu, P.; Liu, Y.; Qiu, Q.; Li, J.; Liang, T.; Xie, T. Enhanced photocatalytic degradation activity via a stable perovskite-type LaFeO3/In2S3 Z-scheme heterostructured photocatalyst: Unobstructed photoexcited charge behavior of Z scheme photocatalytic system exploration. J. Alloy. Compd. 2022, 901: 163628.
[24] Li, Y.; Wu, Q.; Chen, Y.; Zhang, R.; Li, C.; Zhang, K.; Li, M.; Lin, Y.; Wang, D.; Zou, X.; Xie, T. Interface engineering Z-scheme Ti-Fe2O3/In2O3 photoanode for highly efficient photoelectrochemical water splitting. Appl. Catal. B Environ. 2021, 290: 120058.
[25] Bu, Q.; Li, S.; Zhang, K.; Lin, Y.; Wang, D.; Zou, X.; Xie, T. Hole transfer channel of ferrihydrite designed between Ti–Fe2O3 and copi as an efficient and durable photoanode. ACS Sustainable Chem. Eng. 2019, 7(12): 10971-10978.
[26] Bi, L.; Zhang, R.; Zhang, K.; Lin, Y.; Wang, D.; Zou, X.; Xie, T. Sulfidization of platinum nickel bimetal-decorated g-C3N4 for photocatalytic hydrogen production: photogenerated charge behavior study. ACS Sustainable Chem. Eng. 2019, 7(17): 15137-15145.
[27] Qiu, Q.; Zhu, P.; Liu, Y.; Liang, T.; Xie, T.; Lin, Y. Highly efficient In2S3/WO3 photocatalysts: Z-scheme photocatalytic mechanism for enhanced photocatalytic water pollutant degradation under visible light irradiation. RSC adv. 2021, 11(6): 3333-3341.
Comment 8: The degradation performance and stability of catalysts are not good enough and need to be further improved.
Answer:
Thanks for your suggestion. To investigate the degradation performance stability of the catalyst, seven cycle experiments were performed (Figure 5). At the end of each reaction, the catalyst was washed in an ultrasonic environment to better remove contaminants from the catalyst surface. Eventually, the catalyst degradation rate was maintained at around 82%. The reusability and stability of the catalyst were given.
Figure 5. (a) The reusability of BTO-180 piezocatalyst for the treatment of RhB. (b) XRD patterns of BTO-180 sample before and after use.
Author Response File: Author Response.pdf
Reviewer 2 Report
It is of the significance to develop economical and efficient AOPs. In this work, BaTiO3 piezocatalytic system was selected to activate PMS under ultrasonic condition. The synergistic effect between piezoelectric carriers and PMS facilitated the generation of active radical species, which provided a facile and safe way for environmental remediation. The present manuscript is well organized in a methodical and logical way, and experiments are systematically conducted to demonstrate the claims. revision is recommended. Here are the comments:
Comment 1: In Figure 3(c), the authors stated that the PMS/BTO system completely degrades RhB at low concentrations (concentrations less than 10mg/L), but no degradation data for lower initial RhB are available and suggest supplementation.
Comment 2: In Figure 3(d,e,f), three anions are introduced. What salt are they corresponding to? Why are these three anions selected as the study object?
Comment 3: On page 13, in Figure 4(a), the degradation rate of pollutants by catalyst decreased from 94.4% to 75.3% in four cycles of experiments, but in the description on page 12, the degradation rate decreased from 93% to 79%. Please confirm the consistency of the data.
Comment 4: Some errors should also be revised.
Page 9: The dosage of PMS, PMS/BTO should not be "0.3 mg/L, 0.2 mg/L", should be written as "0.3 g/L, 0.2 g/L".
Page 12: Figure 3, the sixth figure should be numbered "f".
Page 14: "AMX showed much higher AMX degradation rate (80%)", the catalyst is not AMX but PMS/BTO-180.
Author Response
Reviewer #2
It is of the significance to develop economical and efficient AOPs. In this work, BaTiO3 piezocatalytic system was selected to activate PMS under ultrasonic condition. The synergistic effect between piezoelectric carriers and PMS facilitated the generation of active radical species, which provided a facile and safe way for environmental remediation. The present manuscript is well organized in a methodical and logical way, and experiments are systematically conducted to demonstrate the claims. Minor revision is recommended. Here are the comments:
Comment 1: In Figure 3(c), the authors stated that the PMS/BTO system completely degrades RhB at low concentrations (concentrations less than 10mg/L), but no degradation data for lower initial RhB are available and suggest supplementation.
Answer:
Thanks for your suggestion. As shown in the figure below, we supplemented the RhB degradation experiments at lower concentrations (1 mg/L, 5 mg/L), achieving a 100% degradation rate at all the 120 min.
See line 213:
“In Figure 4c, RhB can be completely degraded within 120 min when its concentration was below 10 mg/L”
Comment 2: In Figure 3(d, e, f), three anions are introduced. What salt are they corresponding to? Why are these three anions selected as the study object?
Answer:
Cl-, HCO3-, NO3- are shown for NaCl, NaHCO3, and NaNO3, respectively. These three ions were chosen because of their abundance in wastewater.
See line 271:
“The degradation of RhB in the presence of Cl− (NaCl), HCO3− (NaHCO3) and NO3− (NaNO3) were explored.”
Comment 3: On page 13, in Figure 4(a), the degradation rate of pollutants by catalyst decreased from 94.4% to 75.3% in four cycles of experiments, but in the description on page 12, the degradation rate decreased from 93% to 79%. Please confirm the consistency of the data.
Answer:
Sorry about our mistake. We retested the stability of PMS/BTO system. The removal efficiency of RhB decreased from 95.8% to 83.5% after 7 cycles’ test.
Figure 5. (a) The reusability of BTO-180 piezocatalyst for the treatment of RhB. (b) XRD patterns of BTO-180 sample before and after use.
Comment 4: Some errors should also be revised.
Page 9: The dosage of PMS, PMS/BTO should not be "0.3 mg/L, 0.2 mg/L", should be written as "0.3 g/L, 0.2 g/L".
Page 12: Figure 3, the sixth figure should be numbered "f".
Page 14: "AMX showed much higher AMX degradation rate (80%)", the catalyst is not AMX but PMS/BTO-180.
Answer:
Thanks for your suggestion. These questions we have revised. Thank you again for your valuable comments.
See line 295:
“PMS/BTO-180 showed much higher AMX degradation rate (80 %) than that of pure PMS and pure BTO systems”
Author Response File: Author Response.pdf
Reviewer 3 Report
see attachment
Comments for author File: Comments.pdf
Author Response
Reviewer #3
Yu et al. reported a method that can be used for the activation of PMS by piezocatalyst. This is an interesting piece of work since mechanical energy, i.e., ultrasonication played synergistic roles in the combined system, which provides a more efficient way for PMS activation. Overall, this work is publishable after addressing the following issues.
Comment 1: More characterizations for structure analysis of BTO should be supplemented. Only SEM and XRD were presented in the manuscript. HRTEM, piezoelectric curve by AFM, N2 nitrogen adsorption should be added.
Answer:
HRTEM, N2 adsorption curve, PFM were supplemented to characterize the structure of BTO-180 sample.
See line 147:
“To further investigate the structure of the BTO-180 catalyst, some other characterizations were carried out. BTO-180 presented a rod-like structure via TEM, consistent with the results obtained in SEM (Figure 2a). Clear lattice stripes with 0.41 nm spacing was observed (Figure 2b), which corresponded to the (100) crystal surface. The SEAD diagram showed a large number of diffraction spots with parallel regular arrangement, indicating that the BTO catalyst was a single crystal structure. N2 adsorption-desorption isotherm of the catalyst complied with the type Ⅲ isotherm. Rapid rise near P/P0=1 demonstrated the presence of large holes (Figure 2c), which was due to the overlapping of nanorods. The specific surface area of BTO-180 was 7.1 m2/g calculated by BET method. The topography image on the left shows the morphology of the polycrystalline material. The PFM phase signal was shown on the right revealing the ferroelectric domains in this sample. Figure 2d shows rod-like BTO-180 PFM phase image. Under the ±10 V DC bias electric field, the typical butterfly curve (Figure 2e) and reverse of piezoelectric hysteresis loop (Figure 2f) were measured. The test results showed the catalyst with large displacement and phase change 180, which showed that the BTO-180 showed good piezoelectric response.”
Figure 2. (a-b) TEM images and corresponding SEAD pattern of BTO-180. (c) N2 adsorption curve of BTO-180. (d) PFM images of BTO-180. (e-f) Butterfly curves and reverse piezoelectric hysteresis loop of BTO-180.
Comment 2: The mechanism for the activation of PMS needs more proof. For example, the transform process of PMS should be given. The adsorption and activation of PMS on BTO by XPS are needed.
Answer:
“To study the valence state change of the catalyst before and after the reaction, experiments under three conditions were designed by BTO, US-PMS/BTO, PMS/BTO. In Figure 6b of Ti 2p XPS, the BTO binding energies of Ti 2p3/2 were 458.5eV for BTO. When PMS was added and activated by ultrasonic power. The Ti 2p3/2 XPS shifted to higher binding energy (458.7 eV), indicating electron transfer occurred from Ti (BTO) to O (PMS), which was a strong evidence that electron coupling existed between BTO and PMS. However, for pure PMS/BTO, no obvious binding energy shift was observed, indicating ultrasound was essential for PMS activation. The S 2p XPS was shown in Figure 6c. Due to the strong noise or traces of S element contents, we did not observe any S species in PMS/BTO. A sharp peak at 167 eV appeared, which was located around S 2p5/2 XPS peak. The strong interaction between PMS and BTO under ultrasound might facilitate the generation of adsorbed species [37].”
Figure 6. (a) The effects of different free radical inhibitors on RhB degradation. (b) Ti 2p, (c) S 2p XPS of BTO, US-PMS/BTO, PMS/BTO. (d) The free radical detection of BTO, PMS, PMS/BTO. (e) Schematic illustration of PMS activation process by BTO piezocatalyst.
Comment 3: More related articles should be cited to better charity the novelty of this work. In addition, the language needs to be polished. For example, Figure 3, the numbered "f" is missing.
Answer:
Thanks for your suggestion. The introduction part was reorganized to better clarify the novelty of this work. In addition, language details were polished. The content in Figure 3 was also changed. Thank you again for making your valuable comments.
See the introduction part:
“Photocatalysts [21-28] and piezocatalysts [29-35] both show excellent PMS activation efficiency. For example, g-C3N4-based photocatalyst exhibited excellent PMS activation. The photo-generated electrons can intact with PMS and facilitated its activation. Jiang et al. [36] proposed that the facile static interactions between host g-C3N4 and negatively charged PMS and acidic orange 7 influenced the degradation efficiency of dye. However, the direct PMS activation needs UV light, which restricted its application. Piezocatalysis has the advantage of converting mechanical energy into chemical energy by exploiting abundant low-frequency vibration energy sources. For example, Cao et al. [37] reported that PMS can be activated by MoS2 piezocatalyst with sulfur vacancies. The O–O bond length in PMS prolonged, which resulted in the generation of more abundant ·OH and ·SO4- radicals. On one hand, PMS can be directly activated by ultrasound. On the other hand, the coupling of PMS and carrier generated by piezocatalyst also promotes PMS activation. However, few studies have combined PMS activation with piezocatalyst up to now, especially for environmental remediations.”
Author Response File: Author Response.pdf
Reviewer 4 Report
This manuscript reported a method that can be used for the activation of PMS by piezocatalyst. This is an interesting piece of work since mechanical energy, i.e., ultrasonication played synergistic roles in the combined system, which provides a more efficient way for PMS activation. Overall, this work is publishable after addressing the following issues.
1: More characterizations for structure analysis of BTO should be supplemented. Only SEM and XRD were presented in the manuscript. HRTEM, piezoelectric curve by AFM, N2 nitrogen adsorption should be added.
2: The mechanism for the activation of PMS needs more proof. For example, the transform process of PMS should be given. The adsorption and activation of PMS on BTO by XPS are needed.
3: More related articles should be cited to better charity the novelty of this work. In addition, the language needs to be polished. For example, Figure 3, the numbered "f" is missing.
Author Response
Reviewer #4
This manuscript investigates the activation of PMS by BTO piezoelectric catalysts, but the explanation of the mechanism is not in-depth, revision has to be made before further consideration.
Comment 1: In the section of characterizations, author claimed that related studied also proved that effect of the morphology on the piezocatalytic performance, but didn’t cite the relevant literatures.
Answer:
Thanks for your suggestion. We cited some articles in the field of piezocatalysis, all of which claimed that the morphology of the catalyst had important effects on piezocatalytic properties.
See line 140:
“Related studies also proved the correlations between morphologies and piezoelectric properties, easier deformation corresponded higher piezopotential [3,10,12].”
Comment 2: Please compare how well the BTO/PMS system removes RhB in the absence of ultrasound to illustrate the role of ultrasound.
Answer:
Thanks for your suggestion. We compared the removal rate of BTO/PMS for RhB at different ultrasound powers. Among them, the degradation rate of RhB was negligible in the absence of ultrasound, which indicated that ultrasound plays an essential role in this system.
See line 188:
“In Figure 3c, RhB was barely degraded in the absence of ultrasound, but was degraded by about 50 % at 120 min at 100 W, and by about 80 % at 200 W and 400 W, with the best effect at 300 W, and faster degradation rates.”
Comment 3: In the mechanism discussion section, please prove that charge-hole pairs are generated under ultrasound conditions as well as the charge-hole pairs used to activate oxygen and water into superoxide and hydroxyl groups.
Answer:
Electron spin-resonance spectroscopy experiments allow accurate detection of free radicals in the reaction. In Figure 6d, ·O2− and ·OH free radicals [50] were detected on BTO solution under ultrasound This result indicated that charge-hole pairs are generated under ultrasound conditions as well as the charge-hole pairs used to activate oxygen and water into superoxide and hydroxyl groups.
Comment 4: Please provide ESR characterization to confirm the presence of superoxide, hydroxyl and ·SO42- groups in the system.
Answer:
- OH free radical were detected in the BTO system, while both ·OH and ·SO4− radicals were detected in the BTO/PMS system, indicating PMS was successfully activated.
Figure 6. (a) The effects of different free radical inhibitors on RhB degradation. (b) Ti 2p, (c) S 2p XPS of BTO, US-PMS/BTO, PMS/BTO. (d) The free radical detection of BTO, PMS, PMS/BTO. (e) Schematic illustration of PMS activation process by BTO piezocatalyst.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Thank you for addressing my comments. The authors justified the comments and included them appropriately in the revised manuscript. Therefore, I am supportive of its publication in its current form.
