# MnOx-Coffea arabica Husk and Catha edulis Leftover Biochar Nanocomposites for Removal of Methylene Blue from Wastewater

## TL;DR

This study explores using biochar nanocomposites from coffee husks and khat leftovers to efficiently remove methylene blue from wastewater.

## Contribution

The novel use of MnOx-biochar nanocomposites from coffee husk and khat leftover for methylene blue removal is introduced.

## Key findings

- MnOx-CHBNC and MnOx-KLBNC removed over 98% of methylene blue, significantly better than their pristine biochar forms.
- The adsorption process followed the Langmuir isotherm and pseudo-second-order model, indicating monolayer adsorption.
- The nanocomposites retained high efficiency after multiple reuse cycles, suggesting practical wastewater treatment potential.

## Abstract

In this study, we investigated the use of manganese oxide-biochar nanocomposites (MnOx-BNC), synthesized from coffee husk (CH) and khat leftover (KL) for the removal of methylene blue (MB) from wastewater. Pristine biochars of each biomass (CH and KL) as well as their corresponding biochar-based nanocomposites were synthesized by pyrolyzing at 300°C for 1 h. The biochar-based nanocomposites were synthesized by pretreating 25 g of each biomass with 12.5 mmol of KMnO4. To assess the MB removal efficiency, we conducted preliminary tests using 0.2 g of each adsorbent, 20 mL of 20 mg·L−1 MB, pH 7.5, and shaking the mixture at 200 rpm and for 2 h at 25°C. The results showed that the pristine biochar of CH and KL removed 39.08% and 75.26% of MB from aqueous solutions, respectively. However, the MnOx-BNCs removed 99.27% with manganese oxide-coffee husk biochar nanocomposite (MnOx-CHBNC) and 98.20% with manganese oxide-khat leftover biochar nanocomposite (MnOx-KLBNC) of the MB, which are significantly higher than their corresponding pristine biochars. The adsorption process followed the Langmuir isotherm and a pseudo-second-order model, indicating favorable monolayer adsorption. The MnOx-CHBNC and MnOx-KLBNC demonstrated satisfactory removal efficiencies even after three and six cycles of reuse, respectively, indicating their potential effectiveness for alternative use in removing MB from wastewater.