Efficient removal of oxytetracycline from aqueous solution using magnetic montmorillonite-biochar composite prepared by one step pyrolysis.

Three adsorbents, namely, original biochar (CLB), montmorillonite (MMT)-biochar composite (MBC), and magnetic MMT-biochar composite (MMBC) were successfully fabricated by one step pyrolysis of original cauliflower (Brassica oleracea L.) leaves, mixture of cauliflower leaves and MMT, and FeCl3-laden mixture of cauliflower leaves and MMT under limited oxygen atmosphere, respectively. The characterizations of samples indicated that substantial MMT mineral particles and Fe3O4 nanoparticle were dispersed on the surface of MMBC. Due to the introduction of Fe3O4, MMBC performed excellent magnetization property. The adsorption experiments of oxytetracycline (OTC) indicated that the maximum adsorption ability of MMBC was 58.85 mg·g-1, which was 2.63 times as large as CLB, also, larger than that of MBC. Meanwhile, pH, ionic strength, and humic acid (HA) performed slight effects for adsorption of OTC on MMBC. In addition, MMBC still removed 92% OTC after five regeneration cycles. Finally, primary mechanisms of OTC adsorption onto MMBC were attributed to hydrogen bonding and π-π reaction, and ion exchange reaction was considered to exist. Meanwhile, functional groups including Si-O-Al, Si-O-Si, Si-O, and Fe3O4 nanoparticles would provide extra binding sites for OTC adsorption. Therefore, MMBC had an obvious potential to apply into water purification as a reliable, low-cost, and environmentally friendly adsorbent.