Transformation of Glass Fiber Waste into Mesoporous Zeolite-Like Nanomaterials with Efficient Adsorption of Methylene Blue
Round 1
Reviewer 1 Report
The authors have synthesized mesoporous zeolite-like nano-material from the glass fiber wastes and utilized these materials to remove methylene blue from solutions. The optimal processing parameters were determined by applying Taguchi approach to achieve the maximum adsorption capacity. The experiments are well-designed and results are thoroughly discussed.
- Page 2, line 53. “to data” might be a typo.
- Page 3, lines 123-128. The authors used both y_i and q_e to denote the MB adsorption capacity. q_e is also seen in other equations. Suggest using the same symbol in the equations in order to make them consistent.
- Page 4, lines 181-183. The second sentence of this paragraph is hard to read. Consider rephrasing.
- Figure 6 (b). First and secondary axes are not indicated in the plot.
- Page 13, lines 457-462. Another possible cause could be the closure of pores due to sintering effect as the calcination temperature is much higher than the hydrothermal temperature.
- The authors used both degree K and degree C in the text, tables and figures. Consider using uniform unit in the manuscript.
Author Response
Point 1. Page 2, line 53. “to data” might be a typo.
Reply: We thank the reviewer’s comment. We have re-checked the manuscript thoroughly. Several typos have been corrected.
Page 2, line 53: To date, there has been a growing tendency…….
Point 2. Page 3, lines 123-128. The authors used both y_i and q_e to denote the MB adsorption capacity. q_e is also seen in other equations. Suggest using the same symbol in the equations in order to make them consistent.
Reply: We thank the reviewer for the insightful suggestion. We have used qe to denote the MB adsorption capacity to the revised manuscript and follow:
Page 3, line 120: The follows Eq.1
Page 3, line 123-124: …. n is the repetitions number under the same experimental conditions and qe represents the results of MB adsorption capacity.
Point 3. Page 4, lines 181-183. The second sentence of this paragraph is hard to read. Consider rephrasing.
Reply: We thank the reviewer for the insightful suggestion. For this sentence has been rephrased to the revised manuscript and follows:
Page 4, line 189-192: ……….. the hydrothermal-alkaline reaction because of its have significant tunneling effect on cleavage of the tetrahedrally coordinated cages of Si-O-Si linkage connected via bridging oxygens (BO) into reactive Si-O- clusters, where an alkali metal cation establishes charge neutrality for the negatively charged nonbridging oxygens (NBOs) [34], resulting in a high surface area with functional activate sites on the mesoporous zeolite-like surface.
Point 4. Figure 6 (b). First and secondary axes are not indicated in the plot.
Reply: We thank the reviewer for the comment. We have redrawn and indicated the first and secondary axes in Figure 6 (b) in the revised manuscript.
Page 12: The follows Figure 6 (b)
Point 5. Page 13, lines 457-462. Another possible cause could be the closure of pores due to sintering effect as the calcination temperature is much higher than the hydrothermal temperature.
Reply: We thank the reviewer for the insightful suggestion. For this sentence has been adjusted to the revised manuscript and follows:
Page 13, lines 462-464: Those possible causes could be the closure of pores due to the sintering effect as the calcination temperature is much higher than the hydrothermal temperature, and the desorption of bottleneck effect.
Point 6. The authors used both degree K and degree C in the text, tables, and figures. Consider using uniform unit in the manuscript.
Reply: We thank the reviewer’s comment. We have used the uniform unit of Kelvin (K) in the text, tables, and figures in the revised manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This is an interesting and well-written paper. It is a good attempt to convert the glass fiber waster into the mesoporous materials. However, two pieces of crucial information are missing in the manuscript:
- The fibers were subjected to activation at 150 C in sodium hydroxide, and to subsequent acid leaching, in order to generate the hydroxyl groups and porosity on the surface. However, the chemistry of the reacted layers on the fiber surface was not explained in detail. This is important for understanding the mechanisms of the meso-pores in the final materials. If the authors have not done such characterizations, they could discuss this aspect based on the recent paper: Barly et al. Chem. Res. Toxicol. 2019, 32, 2398−2410. This paper describes the dissolution of basaltic glass fibers under different pH conditions and the dissolution induced change of surface layer chemistry. The composition of such fibers is Ca-Mg aluminosilicate with only a little alkali content, and thus is similar to the E-glass fibers that the authors studied.
- The E-glass fibers were extremely fast quenched (cooling rate >10^5 K/s) and hence their network structure possess much higher potential energy. They were subjected to large drawing force during fiberization and thus involve anisotropic structure. These two features of E-glass fibers have been described in M. Ya et al J. Am. Ceram. Soc., 91 [3] 745–752 (2008). These two factors make the fibers are more easily activated at 150 C Na(OH)2, and the acid leaching compared to bulk E glass. This aspect could be discussed in their manuscript.
Author Response
Point 1. The fibers were subjected to activation at 150 C in sodium hydroxide, and to subsequent acid leaching, in order to generate the hydroxyl groups and porosity on the surface. However, the chemistry of the reacted layers on the fiber surface was not explained in detail. This is important for understanding the mechanisms of the meso-pores in the final materials. If the authors have not done such characterizations, they could discuss this aspect based on the recent paper: Barly et al. Chem. Res. Toxicol. 2019, 32, 2398−2410. This paper describes the dissolution of basaltic glass fibers under different pH conditions and the dissolution induced change of surface layer chemistry. The composition of such fibers is Ca-Mg aluminosilicate with only a little alkali content, and thus is similar to the E-glass fibers that the authors studied.
Reply: We thank the reviewer’s comment. We has been discuss this reference to ref 29 to the revised manuscript and follow:
Page 2, lines 87-96: In this study, the chemical composite of glass fiber waste (GFW) is a content aluminosilicate glass system, similar to the stone wool fiber as Ca-Mg aluminosilicate with less alkali content. Its surface layer has significant dissolution rates with sodium-based lung fluid and preferential leaching of matrix on the low pH of 4.5 [29]. Therefore, this study proposed transforming a valuable waste from the glass fibers into the mesoporous zeolite-like nanomaterial (MZN) to adsorb methylene blue in an aqueous solution. The GFW surface layer could expect higher dissolution rates with an alkali solution to enhance activation reaction at 423 K and then apply the low pH to leaching sodium aluminosilicate matrix to produce the hydroxyl groups and porosity on the surface for improving the adsorption efficiency.
Point 2. The E-glass fibers were extremely fast quenched (cooling rate >10^5 K/s) and hence their network structure possess much higher potential energy. They were subjected to large drawing force during fiberization and thus involve anisotropic structure. These two features of E-glass fibers have been described in M. Ya et al J. Am. Ceram. Soc., 91 [3] 745–752 (2008). These two factors make the fibers are more easily activated at 150 C Na(OH)2, and the acid leaching compared to bulk E glass. This aspect could be discussed in their manuscript.
Reply: We thank the reviewer’s comment. We has been discuss this reference to ref 37 to the revised manuscript and follow:
Page 7, lines 243-247: This is mainly because the glass fibers were extremely fast quenched (cooling rate >10^5 K/s), and their network structure possesses much higher potential energy [37]. The glass fiber of quartz SiO2 is more easily alkali-activated to a breaking reaction between the Si-O and Al-O bond under the hydrothermal process at a low temperature of 423K.
Author Response File: Author Response.pdf
Reviewer 3 Report
I am not very comfortable with this subject, so I am not in a position to do a substantive review.
The article seems interesting and well constructed to me.
Few comments :
- L103 - I suggest presenting glass fibers in more detail (chemistry, appearance ...)
- L166 - I am not sure I understood the usefulness of the Taguchi approach. Maybe we need to add a few lines in the introduction. Reference 22 (L73) may be insufficient.
- L484 - is it possible to reprocess mineral wool glasses by this method? Maybe you can go further in the discussion, look at the results obtained in projects such as "Wool to Loop" in Europe.
Author Response
Point1. L103 - I suggest presenting glass fibers in more detail (chemistry, appearance ...)
Reply: We thank the reviewer’s comment. We have been presented chemistry, the appearance of glass fiber in the revised manuscript and follows:
Page 3, lines 108-111: The industrial glass fiber (GFW) is a pure aluminosilicate containing 69.8wt% SiO2, 13.1wt % Al2O3,15.7 wt% CaO and 0.64 % wt MgO by the ASTM C169-16 method in this study, and the appearance is needle-like with a diameter of about 11-13 um. The GFW was initially obtained from the local glass fiber manufacturer (Yunlin, Taiwan) in the absence of plastic polymer resin organic matter. It required no further treatment before it was used.
Point 2. L166 - I am not sure I understood the usefulness of the Taguchi approach. Maybe we need to add a few lines in the introduction. Reference 22 (L73) may be insufficient.
Reply: We thank the reviewer’s comment. We has been discussion of the Taguchi approach reference to ref 22- 25 to the revised manuscript and follow:
Page 2, lines 71-76: The Taguchi method, an orthogonal array design, is combined with statistical analysis and engineering practice. It is widely applied in the material manufacturing fields to determine the optimum process parameters such as sintering [22], milling [23], casting [24], and melting [25]. The above studies showed that the Taguchi approach could be efficiently applied to solve process parameters, improve product quality [26], reduce energy consumption and pollutant emission [25].
Point 3. L484 - is it possible to reprocess mineral wool glasses by this method? Maybe you can go further in the discussion, look at the results obtained in projects such as "Wool to Loop" in Europe.
Reply: We thank the reviewer for the insightful suggestion. We have been discussing reprocess mineral wool glasses to the revised manuscript and follow:
Page 14, lines 489-492: As well, this sustainable reusability method being alkali-activation could be a wide range applied to reprocess glasses-based waste (such as waste mineral wool glasses and lamp glasses) to save as an environmentally friendly nanomaterial in the future.
Author Response File: Author Response.pdf
