Enhancement of microwave absorption bandwidth of MXene nanocomposites through macroscopic design

MXene, the new family of two-dimensional materials having numerous nanoscale layers, is being considered as a novel microwave absorption material. However, MXene/functionalized MXene-loaded polymer nanocomposites exhibit narrow reflection loss (RL) bandwidth (RL less than or equal to −10 dB). In order to enhance the microwave absorption bandwidth of MXene hybrid-matrix materials, for the first time, macroscopic design approach is carried out for TiO2-Ti3C2Tx MXene and Fe3O4@TiO2-Ti3C2Tx MXene hybrids through simulation. The simulated results indicate that use of pyramidal meta structure of MXene can significantly tune the RL bandwidth. For optimized MXene hybrid-matrix materials pyramid pattern, the bandwidth enhances to 3–18 GHz. Experimental RL value well matched with the simulated RL. On the other hand, the optimized Fe3O4@TiO2-Ti3C2Tx hybrid exhibits two specific absorption bandwidths (minimum RL value - −47 dB). Compared with other two-dimensional nanocomposites such as graphene or Fe3O4-graphene, MXene hybrid-matrix materials show better microwave absorption bandwidth in macroscopic pattern.

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Dear Dr Tan: Title: Enhancement of microwave absorption bandwidth of MXene nanocomposites through macroscopic design Manuscript ID: RSOS-200456 Thank you for submitting the above manuscript to Royal Society Open Science. On behalf of the Editors and the Royal Society of Chemistry, I am pleased to inform you that your manuscript will be accepted for publication in Royal Society Open Science subject to minor revision in accordance with the referee suggestions. Please find the reviewers' comments at the end of this email.
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1. In figure 1, more material characterizations are required to support the claimed composite materials of TiO2-Ti3C2Tx, and Fe3O4@TiO2-Ti3C2Tx. For example, XPS mapping is necessary to be used to present the element distribution. The SEM image can not show the presence of Fe.
2. The references of MXene based functional devices need to be updated, see a recent review "X. Jiang, A.V. Kuklin, A. Baev, et al. Physics Reports 848 (2020) 1-58" 3. The experimental pictures of the MXene coated pyramid matrix are missing and should be presented in the manuscript. How is the quality of the coating? The performance of the devices highly depends on the fabrication process and outcome.
4. The authors claimed ultra-light MXene devices, which might be inaccurate and lack of experimental evidence. The Ti3C2Tx multi-layer devices are not necessarily lighter than graphene-based devices.

Reviewer: 2
Comments to the Author(s) As a novel type of 2D materials, Mexene possesses important application prospect in field of microwave absorption materials. To enhance the microwave absorption width of Mexene-hybrid matrix materials, two types of Mexene hybrid materials were fabricated for the first time by macroscopic design approach through simulation method. The results are beneficial for the successful production of Mexene hybrid-matrix materials with wide microwave absorption bandwidth. I thus recommend its publication in this journal after minor revision as followings: 1) In the as-obtained Fe3O4@TiO2-Ti3C2Tx, please provide the particular size of Fe3O4 nanoparticles, distribution, and proportion? 2) What is the interaction type between the Fe3O4 nanoparticles and Mexene matrix?
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Dear Dr Tan  Reply: The fabrication of pyramidal and multi-layered pyramidal structure was carried out by a solution process and was schematically shown in the Fig.S1 and S2 (Supporting information). Since it was fabricated through an in-situ solution process, so the intrinsic electromagnetic parameters ought to be predominant in the material.
However, there might be some minor structural errors in the fabrication. As suggested, we provided the experimental sample picture of multi-layered MXene coated pyramid matrix in the revised manuscript (Supporting information). We also agree with the reviewer and mentioned the point of structure fabrication error in the revised manuscript. Following modifications have been made in the revised manuscript: The variation of experimental results as compared to the simulated results is believed to be due to the errors in raw data fitting and structure fabrication.

The authors claimed ultra-light MXene devices, which might be inaccurate and lack of experimental evidence.
The Ti3C2Tx multi-layer devices are not necessarily lighter than graphene-based devices.
Reply: We thank the reviewer for pointing out this typographical error in the manuscript. We have modified the sentence in the revised manuscript. Following modifications have been made in the revised manuscript, MXene, the new family of 2D materials having numerous nanoscale layers, is being considered as a novel microwave absorption material.

Reviewer: 2
Comments to the Author(s): We thank the reviewer for appreciating this work and recommending its publication.

1) In the as-obtained Fe3O4@TiO2-Ti3C2Tx, please provide the particular size of Fe3O4 nanoparticles, distribution, and proportion?
Reply: We thank the reviewer for this valuable suggestion. The size of Fe3O4 nanoparticles was obtained to be ~ 8 nm. As suggested, histogram was provided in the supporting information. Following modification have been made in the revised manuscript.
The Fe3O4 nanoparticle size was recorded using ImageJ software from SEM image and histogram was shown in the Figure S2 (Supporting information). The average particle size of the Fe3O4 nanoparticles was found to be ~ 8 nm. Figure S2. Particle size distribution of Fe3O4 nanoparticles in the TiO2-Ti3C2Tx MXene.

2) What is the interaction type between the Fe3O4 nanoparticles and Mexene matrix?
Reply: The interaction between Fe3O4 nanoparticles and MXene matrix as synthesized composite was explained elaborately in the references [17] and [18]. Since the objective of this work is towards application point of view, not synthetic oriented, we did not explain it previously. As suggested, the following modification have been made in the revised manuscript: The interaction of Fe3O4 nanoparticles with MXene was explained in Ref.
[17]. The exposed hydroxyl groups offer the possibility of binding with MXenes along with blending metal-oxygen stretching modes such as .