# Polymorph II Cellulose Nanocrystals Derived from Oil Palm Empty Fruit Bunches for High-Efficiency COD Removal in Industrial Wastewater

## TL;DR

This study shows how cellulose nanocrystals from oil palm waste can efficiently remove chemical oxygen demand from industrial wastewater.

## Contribution

The paper introduces a scalable method to produce cellulose II nanocrystals from oil palm waste for high-efficiency COD removal.

## Key findings

- Cellulose II nanocrystals achieved 91.47% COD removal under optimized conditions.
- CNCs-2 outperformed CNCs-1 in adsorption tests due to their structural and chemical properties.
- The Box–Behnken design identified optimal parameters for maximum COD removal efficiency.

## Abstract

This study reports the valorization of oil palm empty fruit bunches into cellulose nanocrystals (CNCs) for the removal of the chemical oxygen demand (COD) from industrial wastewater generated by the same processing sector. Cellulose Iβ was first isolated through sequential bleaching, delignification, and mercerization, and two hydrolysis routes were evaluated to obtain CNCs: a concentrated acid route (60% v/v H2SO4, 50 °C, 60 min) for CNCs-1 and a low-acid, long-duration route (1% v/v H2SO4, 80 °C, 12 h) for CNCs-2. Rietveld refinement of the X-ray diffractograms confirmed the polymorphic transition, assigning cellulose Iβ to the intermediate materials and cellulose II to the CNC samples, with crystallite sizes of 4.99 nm for CNCs-1 and 5.43 nm for CNCs-2. Attenuated Total Reflectance–Fourier Transform Infrared (ATR-FTIR) spectroscopy analysis showed the progressive removal of lignin and hemicellulose and supported the cellulose Iβ to II transition through changes in hydroxyl bonding and crystallinity-related bands. Preliminary adsorption tests showed better COD removal with CNCs-2, which were therefore selected for optimization using a Box–Behnken design with the adsorbent mass, pH, and contact time as variables. The quadratic model was significant (R2 = 0.9675; predicted R2 = 0.8908), and the maximum COD removal reached 91.47%, decreasing the COD concentration from 2459.0 to 209.85 mg L−1 under the optimum conditions of 0.09 g CNCs-2, pH 3, and 20 min. These results highlight cellulose II nanocrystals derived from oil palm waste as a promising and scalable adsorbent for industrial wastewater treatment.