ZrO2/carbon aerogel composites: A study on the effect of the crystal ZrO2 structure on cationic dye adsorption

• ZrO2/Carbon aerogel composites were successfully prepared in the hydrothermal process.
• ZrO2 crystalline phase was successfully controlled by varying the quantity of reactant HMTA.
• The ZrO2/CA (H 1.683) sample possesses the highest adsorption capacity for RhB dyes.
• The as-prepared ZrO2/CA (H 1.683) sample is also reusable for RhB dye adsorption.

In this study, ZrO2/carbon aerogel (CA) composites with different amounts of monoclinic and tetragonal ZrO2 crystallites were successfully prepared by varying the quantity of HMTA in the hydrothermal synthesis. Monoclinic ZrO2 (m-ZrO2) structures are successfully transformed to tetragonal ZrO2 (t-ZrO2) structures by increasing the amount of HMTA from 0.187 to 1.683 g. As a result, ZrO2/CA (H 1.683) samples with the addition of 1.683 g of HMTA possess only the t-ZrO2 structure. Furthermore, ZrO2/CA (H 1.683) samples possess the highest adsorption capacity for cationic RhB dyes with positive charges, which is attributed to these samples having the largest negative surface charge (−42 mV at pH 7). As a result, ZrO2/CA (H 1.683) samples have a large potential for use in the industrial removal of the cationic RhB dye. This work provides a basis for the concept of crystalline structure design to improve organic dye adsorption.

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