Synergistic Effect on Photocatalytic Activity of Co-Doped NiTiO3/g-C3N4 Composites under Visible Light Irradiation
Round 1
Reviewer 1 Report
Manuscript Number: catalysts-1006414
Manuscript Title:” Synergistic Effect on Photocatalytic Activity of
Co-doped NiTiO3/g-C3N4 Composites under Visible Light Irradiation”
Recommendation: Accept after minor revision
Additional comments: The target of the manuscript is study of photocatalytic properties of nano-composites produced by hetero junction between combination of Co-doped NiTiO3 and g-C3N4 and Co-doping into the NiTiO3. This target is important and actual. So, the manuscript is dedicated to an actual problem of physical chemistry.
However, there are some small problems in the manuscript that should be corrected.
- In the text of the paper described photocatalytic MB degradation experiments is written “The determination coefficients (R2 values) for the linear regression were higher than 0.97, indicating that the photodegradation reaction rate constants of all reactions followed an apparent-first-order reaction model [24]”
Comments: R2 close to 1 means only high correlation between function and variable. Linearity functional law needs other statistical confirmation.
- Based on Figure 3 XPS data, in the text that described Figure 3 is written: “In addition, the appearance of Ti-N features in the composites reconfirmed the presence of Ti-N bonding and a relatively high Ti-N atomic percentage in the C-1 composite photocatalyst compared with other composite photocatalysts.”
Comments: More detail description of this effect is needed, because in the part of Conclusions it is the central point in explanation of Synergistic effect.
- The spectrum of irradiation can be supplied or in the text of the paper or in the Supplementary materials.
Author Response
- In the text of the paper described photocatalytic MB degradation experiments is written “The determination coefficients (R2values) for the linear regression were higher than 0.97, indicating that the photodegradation reaction rate constants of all reactions followed an apparent-first-order reaction model [24]”
Comments: R2 close to 1 means only high correlation between function and variable. Linearity functional law needs other statistical confirmation.
Response)
In our study, we decide to choose the apparent first-order model for the MB degradation reaction for the reason described below.
Previous results of photocatalytic degradation kinetics indicated that the photocatalytic degradation rates of various dyes fitted the Langmuir – Hinshelwood kinetics model. The rate of reaction (mg/L min) can be expressed as:
r = dC/dt = kKC/(1+KC)
where C is the concentration of the reactant (mg/L), t is the illumination time, k is the reaction rate constant (mg/L min), and K is the adsorption coefficient of the reactant (L/mg). When the chemical concentration C is small (10 ppm in our study), the above equation can be simplified to an apparent first-order equation:
ln(C0/C) = kt
A plot of ln(Co/C) versus time results in a straight line, the slope of which upon linear regression equals the apparent first-order rate constant k. Generally, first-order kinetics is appropriate for the entire concentration range up to few ppm and several studies were reasonably well fitted by this kinetic model. It has been agreed that the expression for the rate of photo-mineralization of organic substrates such as dyes follows the Langmuir–Hinshelwood law for the four possible situations:
(a) The reaction takes place between two adsorbed substances.
(b) The reaction occurs between a radical in solution and an adsorbed substrate molecule.
(c) The reaction takes place between a radical linked to the surface and a substrate molecule in the solution.
(d) The reaction occurs with both species being in the solution.
As shown in the Figure 6 (in the main text), the plot is fitted with a straight line using linear regression techniques. The closeness of the determination coefficients (R2 values) to unity indicates that the degradation process follows an apparent-first-order kinetics, which is well represented by the Langmuir–Hinshelwood model.
Reference:
Rashed, M.N. and El-Amin, A.A. Photocatalytic degradation of methyl orange in aqueous TiO2 under different solar irradiation sources. International Journal of Physical Sciences 2007, 2(3), 73-81.
- Based on Figure 3 XPS data, in the text that described Figure 3 is written: “In addition, the appearance of Ti-N features in the composites reconfirmed the presence of Ti-N bonding and a relatively high Ti-N atomic percentage in the C-1 composite photocatalyst compared with other composite photocatalysts.”
Comments: More detail description of this effect is needed, because in the part of conclusions it is the central point in explanation of synergistic effect.
Response)
We are greatly thankful for the reviewer’s comment. In this study, we prepared the Co-doped NiTiO3/g-C3N4 composites, which can be applied for photocatalytic degradation of methylene blue (MB), using different percentage of Co. Basically, we focused on the interactions between the g-C3N4 precursors (organic) and co-doped NiTiO3 (inorganic) during the thermal formation of g-C3N4 structure and the resultant photocatalytic behaviour. The formation of the Ti-N linkages between the NiTiO3 lattice and g-C3N4 can decrease the recombination rate of the photogenerated charges in the composite photocatalysts owing to high charge separation efficiency. As a result, the Co-doped NiTiO3/g-C3N4 composite photocatalysts can have a high photocatalytic activity. The corresponding description has been added into the revised manuscript.
- The spectrum of irradiation can be supplied or in the text of the paper or in the Supplementary materials.
Response)
We have added Figure S3 (UV-Vis spectra of MB photodegraded with C-1 photocatalyst as a function of reaction time.) in the Supplementary materials and the corresponding sentence has been inserted into the text as follows:
“The concentrations were measured by UV-Vis spectra for MB (Figure S3, see Supplementary Materials).”
Reviewer 2 Report
The present manuscript reports on the fabrication of Co-doped NiTiO3/g-C3N4 composite photocatalysts which show a much higher photocatalytic activity toward methylene blue photodegradation under visible light irradiation with the respect of their single consitutents. The content of this paper is surely original and technically sound. Many characterization techniques were properly used to support the conclusions. Moreover, the discussion is clear and complete. Therefore, only minor revisions need to be made to accept this manuscript for publication in “Catalysts”.
- (Lines 83-85) The authors stated “doping of Co ions induced a 0.1° shift of the characteristic peak positions to higher diffraction angles and the peak width narrowed owing to a change in the NiTiO3 crystallite size [17,18]”. Please replace references 17 and 18, which reports on TiO2 systems, with more appropriate ones.
Author Response
- (Lines 83-85) The authors stated “doping of Co ions induced a 0.1° shift of the characteristic peak positions to higher diffraction angles and the peak width narrowed owing to a change in the NiTiO3 crystallite size [17,18]”. Please replace references 17 and 18, which reports on TiO2 systems, with more appropriate ones.
Response)
We have carefully read and replaced the previous references [17] and [18] with more appropriate references relating to NiTiO3 system:
[13] Pham, T.-T.; Shin, E.W. Inhibition of charge recombination of NiTiO3 photocatalyst by the combination of Mo-doped impurity state and Z-scheme charge transfer. Applied Surface Science 2020, 501, 143992.
[17] Pham, T.-T.; Kang, S.G.; Shin, E.W. Optical and structural properties of Mo-doped NiTiO3 materials synthesized via modified Pechini methods. Applied Surface Science 2017, 411, 18-26.
[18] Lenin, N.; Karthik, A.; Sridharpanday, M.; Selvam, M.; Srither, S.R.; Arunmetha, S.; Paramasivam, P.; Rajendran, V. Electrical and magnetic behavior of iron doped nickel titanate (Fe3+/NiTiO3) magnetic nanoparticles. Journal of Magnetism Magnetic Materials 2016, 397, 281-286.
