The study reports the preparation of activated carbon from spent coffee grounds, and the use of AC as potential adsorbend for organic dyes. The paper is well written, the experiments and their analysis and the conclusions look correct, therefore the paper can be suitable for publication in Materials, after a major revision. The weak part of the manuscript is the lack of clear presentation of the actual results of the batch sorption experiments, which consitute the main part of the work.

Major remarks

1. Present detailed plots of the experimental adsorption isotherms at all temperatures, in non-linearized form, and the fitted theoretical curves.
2. Present kinetic plots, and the fitted kinetic model curves.

Minor remarks

1. unify the use of period "." as decimal separator.
2. replace period by centered dot as multiplication operator symbol.
3. check and correct upper/lower indexes (e.g. line 162)

1. In the response letter, authors show adsorption isotherms only at room temperature, while it was explicitely asked to present isotherms at all three temperatures at which the experiments were performed, as stated in the article. These must be provided in the revised version.

2. The model fitting is apparently wrong, since the Langmuir isotherm does not fit the three higher C_e data points, while a conventional least squares fit should necessarily lye very close to the nearly horizontal experimental data, in that C_e range. Analysis should be repeated, with the appropriate software. (Figure 8)

3. in Equation 7, K_c is defined as a dimensionless constant. However, the right hand side of the equation does not seem to be dimensionless, K_L * M_w product is not dimensionless.