The work explores the green synthesis of defective TiO2 photocatalyst using a microwave-assisted method with L-ascorbic acid as the reducing agent. This green synthesis method produces TiO2 NPs with different levels of defects and brownness by varing concentrations of L-ascorbic acid. These defects, primarily Ti3+ and oxygen vacancies, enhance the photocatalytic properties of TiO2 by extending light absorption into the visible and near-infrared regions, reducing electron-hole recombination rates, and improving photocurrent response and charge transfer resistance. Among the synthesized samples, the one with a 1:0.25 weight ratio of TiO2 to L-ascorbic acid (PAs0.25) showed the highest hydrogen production rate under fluorescence irradiation. The study concludes that the presence of an optimal amount of defects and good porous properties significantly enhances the photocatalytic efficiency of TiO2 for hydrogen production, offering an eco-friendly and efficient synthesis route for scalable production.
Comments below address a few points which the authors should respond to before the paper is considered for publication.

1. In figure 4b, the Raman spectra show that, with the increase of L-ascorbic acid concentration, the intensity of band in 14000-1690 cm-1 significantly increases. Since this band could be assigned to C=O group, the results mean that the generated C=O carbonaceous materials are increased with more L-ascorbic acid. However, in figure 6d, the XPS spectra show that the C=O peak intensity decreases with the increase of ascorbic acid concentration. These two pieces of information seem to be contradictory. An explanation needs to be added.

2. In figure 8a, the pristine TiO2 shows relatively lower photocurrent density. The authors ascribed it to the low visible light response of pristine TiO2 (line 313). However, based on PL spectra (figure 5d) and EIS plot (figure8 a), the pristine TiO2 exhibits a higher recombination rate and higher charge transfer resistance. Thus, should the low efficiency of charge transfer or charge separation of pristine TiO2 be considered as the possible reason to account for lower photocurrent?

3. In figure 9, The authors compared the H2 production efficiency of the as prepared catalysts. PAs0.25 shows slightly between performance than that of pristine TiO2. Other than that, the other catalysts with more defects showed lower H2 production efficiency. These results indicated that the H2 production performance is not related to the number of defects, although the electron-hole separation and charge transfer is facilitated with the increased number of defects. One possible concern is that, although the charge transfer is accelerated by the introduction of defects, there might be some side reactions occurring with carbonaceous substances, limiting the overall efficiency. The GC or NMR measurement are suggested to be carried out to test if there are a lot of side products generated from the carbonaceous substances.

4. The corresponding characterization of the catalysts (Raman spectroscopy, XRD, EPR, XOS, etc.) after photocatalytic H2 production are recommended to check if the catalysts undergo the structure transformation. The comparison between the catalysts before and after reaction might be able to provide some clues about why the H2 production efficiency decreases with increases of defects amounts and charge transfer.

The response explains all the questions in the appropriate way. This paper is publishable subject to minor revisions noted. Further review is not needed.

1) The fitting parameters of XPS data (peak position and band width) for each elements are suggested to be provided in a table.