Adsorption of tetracycline in water by humic acid modified biochar derived from walnut green husk

Developing adsorbent materials with higher performance for tetracycline (TC) organic pollutants in wastewater is still accounted for a hot topic in environmental remediation. As an agricultural waste, walnut green husk is often piled up in the field at will, which not only seriously affects the surrounding ecological environment, but also overlooks its potential value for practical application. Therefore, three types composite adsorbents of HA-HF300, HA-HF500 and HA-HF700 were fabricated by loading humic acid onto walnut green husk biochar (HF) prepared under different pyrolysis temperature, so as to investigate their performance for TC adsorption. The experiment results showed that HA-HF700 exhibited the highest adsorption performance for TC. The characterization results confirmed that HA-HF700 combined the advantages of both materials, and more surface functional groups and aromaticity were observed, which improved the adsorption performance of fabricated materials. In addition, HA-HF700 obtained the strongest performance for TC at solution pH of 3 with dosage of 1 g·L^-1, as the tested adsorption capacity reaching 76.20 mg·g^-1. Nonetheless, the adsorption process of HA-HF700 for TC would be inhibited when co-existing with Mg²⁺, Ca²⁺, Na⁺ and K⁺. The Pseudo-second-kinetic and Langmuir isotherm model descripted the adsorption process of HA-HF700 for TC more accurately. By integrating the results of characterization, it is believed that the adsorption mechanisms of HA-HF700 for TC mainly include electrostatic interaction, hydrogen bonding, π-π EDA interaction, and hydrophobic interaction. To conclude, this study offered a new adsorbent for tetracycline contaminated wastewater treatment.