Tannin Industry Waste-Derived Porous Carbon: An Effective Adsorbent from Black Wattle Bark for Organic Pollutant Removal

Abstract

In Brazil, a significant part of the biomass is unused, contributing to environmental pollution. The tannin industry commonly extracts tannins from the bark of Acacia mearnsii or black wattle, leaving a significant residue of 70% (w w−1). This study investigates the conversion of black wattle bark into a porous carbonaceous material to efficiently remove organic pollutants. Using ZnCl2 as a chemical activation reagent, the experiments varied the impregnation time, carbonization rates, and temperatures. Additional experiments aimed to increase the specific surface area (SSA). X-ray diffraction (XRD) analysis showed the formation and removal of ZnO, which increased porosity. Scanning electron microscopy (SEM) showed an irregular morphology with pores. Fourier-transform infrared (FTIR) spectroscopy indicated characteristic bands, and electron paramagnetic resonance (EPR) detected organic free radicals. The SSAs exceeded 1000 m2 g−1, averaging 1360 m2 g−1, with a maximum of 1525 m2 g−1. Micropores (1.4 nm) were consistent. The structure of the material and the high SSA suggest a potential for efficient removal of aromatic impurities by π–π interactions. This approach addresses the issue of biomass waste, provides a solution for environmental remediation, and represents a transformative strategy for biomass utilization.