TiO₂-Embedded Biocompatible Hydrogel Production Assisted with Alginate and Polyoxometalate Polyelectrolytes for Photocatalytic Application

Round 1

Reviewer 1 Report

 

The authors reported the synthesis of two hydrogel composites including Alg-Ca@PAAm@TiO₂ and PAAm@TiO₂@Mo₁₃₂ as photocatalysts for methyl orange degradation. Photostability of the composites and the role of each component are fully discussed. I found the manuscript interesting and recommend its publication in Inorganics after minor revision. The comments:

 

1-    Can the hydrogel composites be recycled and reused for methyl orange degradation?

2-    Is it possible to add a scheme for Alg-Ca@PAAm@TiO₂ concerning the synthesis and mechanism of the photocatalytic degradation?

Author Response

Dear referee,

 

Thanks for consideration and decision you made.

Concerning your questions:

1. In principal, because the composite hydrogel Alg-Ca@PAAm@TiO₂ does not undergo photodegradation after UV iiradation, this materials can be used during the long time. When methyl orange dye being removed, one can dry and reused this composite hydrogel again. However, as we found the dried sample lost the swelling ability at least on 40% that is caused with the irreversible collapse of Alg-Ca matrix where the polymer chains are attached to each other by multiple hydrogen bonds in addition to Ca²⁺ cations.

2. Thanks for your comment. We added the synthetic scheme in Fig.1. Concerning the photodegradation of Alg-Ca@TiO₂ we did not examine the exact mechanism from the chemical point of view. This is why we do not want to illustrate this process without sufficient evidences of that. However, here, we can assume that the main photodestruction mechanism of the Alg-Ca@TiO₂ is simple oxidative cleavage of glycosidic bond.

 

Reviewer 2 Report

Renat Mansurov et al. reported syntheses of TiO2-embedded hydrogels with alginate and polyoxometalate polyeletrolytes, and studied their photocatalytic activities on methyl orange dye decompositions. The products were properly characterized. The gels show interesting photocatalytic behaviors. This MS should attract interest from the readers of this journal and should be published.

Author Response

Dear referee,

 

We are appreciated for your time and thankful for the decision you made.

 

Sincerely,

Dr. Kirill Grzhegorzhevskii

Reviewer 3 Report

In this work, the authors look at the preparation of two types of PAAm-based hydrogels for photocatalytic application. Two scenarios of polyacrylamide-TiO2 (PAAm@TiO2) composite hydrogel design were constructed by using calcium alginate (Alg-Ca) or Keplerate type polyoxometalates (POM) {Mo132} tuning the polymer network structure. Swelling behavior was further explored to avoid the aggregation of hybrid hydrogel materials in aqueous suspensions. The unexpected stabilization of the PAAm@Mo132@TiO2 hydrogel production was also investigated and explained comprehensively.

I think this manuscript will be of interest to those who synthesize new hybrid hydrogel materials that can be used for photocatalytic reactions in the energy storage field. Overall, this manuscript represents a contribution to the field and is recommended for publication in the Inorganics with the following minor revisions.

 

1) The structural characterization of hybrid hydrogel materials should be included. For example, the authors should show the figures of PXRD of Hydrogel Alg-Ca@PAAm@TiO2 and Hydrogel PAAm@TiO2@Mo132.

2) The structural characterization of after swelling behavior measurement, and after long-time UV irradiation should be included in the manuscript to show its structural change or stability.

3) The authors should add some literature descriptions to make the manuscript more convincing. I would like to suggest the authors cite the following relevant articles.

a. Co2+-Linked [NaP5W30O110]14−: A Redox-Active Metal Oxide Framework with High Electron Density, J. Am. Chem. Soc. 2019, 141, 4553−4557

 

b. Immobilization of TiO2 Nanoparticles in Hydrogels Based on Poly(methyl acrylate) and Succinamide Acid for the Photodegradation of Organic Dyes Catalysts 2021, 11, 613

Author Response

Dear referee,

 

Thanks for consideration and decision you made.

Concerning your questions:

1. The IR spectra were measured for the structural characterization of the produced hydrogels. The Powder X-ray diffraction is not appropriate technique for such amorphous materials as hydrogel. Separately, the TiO₂ nanoparticles were examined with PXRD that is mentioned in Experimental Section:

“The phase composition of titanium dioxide was characterized via X-ray phase analysis on a Bruker D8 Discover diffractometer using CuK_α band and a graphite monochromator on a diffracted beam. Data were processed using the TOPAS 2.1 program with Ritveld’s refinement of the parameters. The anatase phase, the content of which was 88 wt. %, was found to predominate (CSR size = 25 nm, lattice parameters: a = 3.786 Å, c = 9.507 Å). The rutile phase (12 wt. %) was detected in addition to the anatase phase (CSR size = 36 nm, lattice parameters: a = 4.594 Å, c = 2.959 Å).”

The PXRD for {Mo₁₃₂} cannot be measured at such small concentration in hydrogel.

 

2. The IR spectrum of the PAAm@Mo₁₃₂@TiO₂ hydrogel after long-time UV irradiation is presented in Fig.S7 (data for gel#8). The obtained data show the stability of hydrogel structure during the exposition under UV light. The IR spectra of swelled Alg-Ca@PAAm@TiO₂ and Alg-Ca@PAAm hydrogels (with PAAm 90% of content) after one-year storage in distilled water were measured (please, see Fig.S6). These spectra demonstrate both the stability of hydrogel structure and that the addition of TiO₂ does not change the hydrogel structure significantly that is in line with thermodynamic data we obtained.

 

3. Thanks for your suggestion. Both articles have been cited in references.