High-efficient removal and adsorption mechanism of organic dyes in wastewater by KOH-activated biochar from phenol-formaldehyde resin modified wood

The treatment of wastewater contaminated with organic dyes has become an intricate challenge in water pollution control. Currently, sophisticated chemical modifications and synthetic methods are frequently needed to enhance the adsorption capacity of biochar for removing dyes during the treatment process. In order to develop a facile, low-cost and efficient biochar absorbent, an activated biochar (KOH/PF-WB) was successfully synthesized from phenol-formaldehyde (PF) resin modified wood via pyrolysis and potassium hydroxide (KOH) activation. Based on the joint effect of PF resin and wood, KOH/PF-WB-700-2 exhibited a remarkable porous structure and abundant oxygen-containing functional groups, which resulted in a substantially high specific surface area (SBET = 2301.61 m2/g) and total pore volume (Vtotal = 1.205 cm3/g). Additionally, the PF resin modification led to increased disorder and more defect sites of activated wood biochar. As a result, KOH/PF-WB-700-2 demonstrated superior adsorption capacity for congo red (3472.22 mg/g) and methylene blue (1112.35 mg/g) dyes compared to some reported adsorbents. The adsorption process could be better described by the pseudo-second-order kinetic model and Langmuir isotherm model, while the overall process was spontaneous and feasible. The primary adsorption mechanism involved pore filling through the modulation of PF resin, along with the cooperative effects of electrostatic attraction, hydrogen bonding and pi-pi interaction. This finding provides a viable strategy for the waste PF-modified wood cyclic application, and offer technical support for the prospect of KOH/PF-WB for the removal of organic dyes.