Efficient adsorption of tetracycline hydrochloride on biochar-ceramsite composite: Optimization of response surface methodology and investigation of adsorption mechanism

In this study, to improve the adsorption performance and recovery of biochar in tetracycline hydrochloride (TCH) adsorption, a new biochar adsorbent, biochar-ceramsite composites (OBCC), were prepared by one-step synthesis using response surface methodology to optimize the preparation conditions. The error between the predicted adsorption capacity and the actual tested adsorption capacity was only 1.9% for the optimal preparation conditions. The maximum adsorption capacity (obtained by the Langmuir model) of TCH onto OBCC (30.72 mg/g) is 1.5 times that of ceramsite (CS, 20.86 mg/g) and 1.9 times that of the raw biochar (RBC, 16.47 mg/g). The better adsorption performance of OBCC can be mainly attributed to its more mesopores distribution (average pore size is 14.58 nm) and larger surface area (1.4 and 4.8 times higher than that of CS and RBC, respectively). The TCH adsorption mechanism by OBCC involves various interactions and mechanisms, including electrostatic interactions, π-π interactions and hydrogen bonding. OBCC is non-toxic, easy to solid-liquid separation, and can be potentially reused for 22 times before completely losing its activity, exhibiting great potential to antibiotic elimination.