# Evaluation of Silkworm Cocoon-Derived Biochar as an Adsorbent for the Removal of Organic and Inorganic Contaminants from Rainwater

## TL;DR

This study explores using biochar made from silkworm cocoons to remove pollutants like heavy metals and benzotriazole from rainwater.

## Contribution

The novelty lies in using waste silkworm cocoons to create an effective adsorbent for both organic and inorganic contaminants.

## Key findings

- Silkworm cocoon biochar effectively removed up to 96% of Cu(II) and 97% of benzotriazole from rainwater.
- Adsorption of Cu(II) followed the Langmuir/Freundlich model, while Ni(II) and benzotriazole adsorption fit the Freundlich model.
- The biochar showed rapid adsorption of benzotriazole within the first minute of contact.

## Abstract

This study presents evaluation of biochar derived from silkworm cocoons for the adsorption of organic and inorganic contaminants from rainwater. The material was characterised using BET surface area analysis, scanning electron microscopy (SEM), and the point of zero charge (pHPZC). The prepared biochar exhibited a well-developed surface area and demonstrated adsorption capacity toward both heavy metals and benzotriazole. The model rainwater was prepared by spiking real rainwater samples with Cu(II), Ni(II), Zn(II) ions, and benzotriazole (BT). Adsorption experiments were carried out under laboratory conditions to evaluate the effects of contact time, pH, and sorbent dosage. The experimental data were fitted to pseudo-first-order and pseudo-second-order kinetic models, as well as Langmuir/and Freundlich isotherms. The results showed that the adsorption of Cu(II) followed the Langmuir/Freundlich model, while the adsorption of Ni(II) benzotriazole was more consistent with the Freundlich model. Adsorption kinetics were best described by the pseudo-second-order model. The highest removal efficiencies were observed for Cu(II) (96%) and Ni(II) (88.8%), while Zn(II) removal was limited. Benzotriazole was also effectively adsorbed (97%), rapid adsorption occurred mainly within the first minute. Overall, the study highlights the selective adsorption behaviour of silkworm cocoon biochar and provides a comparative insight into the removal of organic and inorganic pollutants using a waste-derived adsorbent with surface properties comparable to those of activated carbon.