Assessment of micro and nanosize C-based adsorbents for methylene blue uptake: A review

Abstract

Carbon-based adsorbents, including activated carbon, multiwalled carbon nanotubes, and graphene oxide, have received great attention for removing pollutants, including dyes, from solution. In this review, the overall performance of high-grade C-based adsorbents for removing methylene blue was evaluated for the first time through three criteria: maximum uptake capacity, reaction rate, and equilibrium time of the process. For this, data on adsorption of methylene blue by thirty C-based adsorbents was collected from the literature and analyzed in the framework of the aforementioned criteria. The statistical analysis showed that the equilibrium time of methylene blue uptake on graphene oxide composites is much faster compared to other adsorbents (such as activated carbon and multiwalled carbon nanotubes). Among MWCNTs, Fe3O4-Alginate-MWCNTs is the most practical to remove methylene with an uptake capacity of 906 mg g− 1, equilibrium time of 60 minutes, and simple isolation from solution using an external magnet. Graphene oxide composites outperform other adsorbents, with an average adsorption capacity of 896 mg g− 1, a mean reaction rate of 870 mg g− 1 min− 1, and a median equilibrium time of 50 minutes. Among these, diethylenetriamine-modified graphene oxide was found the best adsorbent with an uptake capacity of 3036 mg g− 1, a reaction rate of 3025 mg g− 1 min− 1, and an equilibrium time of only five minutes. The outputs of the current work will be helpful when choosing the most practical adsorbent for dyes. Unfortunately, the performance of these adsorbents under continuous flow conditions has not been examined to date, which cannot permit a comprehensive practical assessment. The adopted selection strategy is applicable for other classes of adsorbents toward pollutants, especially non-conventional materials. The estimated cost index of C-adsorbent for removing 1.0 g MB was 0.003, 38.3, and 42.3 $ for AC, MWCNTs and GO, respectively. The high production costs of MWCNTs and GO-composites may reduce their utilization on a large scale.