Preparation of KOH-modified poplar biochar by pyrolysis and its adsorption properties for five pesticides

To explore the adsorption performance and mechanism of poplar biochar (PBC) for pesticides in water environment, five insecticides including imidacloprid, acetamiprid, clothianidin, dinotefuran and sulfoxaflor were selected for this study. Using poplar powder as raw material, the parameters including pyrolysis temperature, time, and the concentration of KOH solution were investigated by single factor optimization method in the preparation of PBC. The poplar biochar modified with 30% KOH (30-KOH-PBC) was selected as the optimal material using batch adsorption test, and the adsorption properties and mechanism of the 30-KOH-PBC were investigated by using imidacloprid and dintefuran as target compounds. The results showed that with the pyrolysis temperature increasing, the specific surface area and pore volume of PBC greatly increased. The modification of KOH further significantly increased the specific surface area and pore volume. Compared with the PBC without modification, the 30-KOH-PBC had the highest micropore ratio, and showed the best enhancement effect, with the specific surface area and pore volume increased by 6.7 times and 7.3 times, respectively. It also had the strongest adsorption capacity for the target pesticides, and the maximum adsorption capacity of imidacloprid and dintefuran was 438.6 mg/g and 161.6 mg/g, respectively. The adsorption mechanism was mainly pore filling. It could be applied to the water samples with a wide range of pH and ionic strength, and maintained excellent adsorption capacity after 5 times of regeneration cycle. This study provides a reference for the treatment of pesticide polluted water and the resource utilization of poplar waste.