Adsorption and mechanism study for phenol removal by 10% CO2 activated bio-char after acid or alkali pretreatment

Abstract

The development of an efficient bio-char used to remove phenol from wastewater holds great importance for environmental protection. In this work, wheat straw bio-char (BC) was acid-washed by HF and activated at 900 °C with 10% CO₂ to obtain bio-char (B-Ⅲ-0.1D₉₀₀). Adsorption experiments revealed that B-Ⅲ-0.1D₉₀₀ achieved a remarkable phenol removal efficiency of 90% within 40 min. Despite its relatively low specific surface area of 492.60 m²/g, it exhibited a high maximum adsorption capacity of 471.16 mg/g. Furthermore, B-Ⅲ-0.1D₉₀₀ demonstrated a good regeneration capacity for at least three cycles (90.71%, 87.54%, 84.36%). It has been discovered that HF washing, which removes AAEM and exposes unsaturated functional groups, constitutes one of the essential prerequisites for enhancing CO₂ activation efficiency at high temperatures. After 10% CO₂ activation, the mesoporous structure exhibited substantial development, facilitating enhanced phenol infiltration into the pores when compared to untreated BC. The increased branching of the bio-char culminated in a more complete aromatic system, which enhances the π-π forces between the bio-char and the phenol. The presence of tertiary alcohol structure enhances the hydrogen bonding forces, thereby promoting intermolecular multilayer adsorption of phenol. With the combination of various forces, B-Ⅲ-0.1D₉₀₀ has a good removal capacity for phenol. This work provides valuable insights into the adsorption of organic pollutants using activated bio-char.

Keywords: Adsorption; Aromaticity; Bio-char; CO(2) activation; Phenol.