Doping of carbon into boron nitride to get the increased adsorption ability for tetracycline from water by changing the pH of solution

• Carbon-doped boron nitride (BCN) is synthesized via oxygen-limited method. • BCN can capture protons and exist in protonated form in solution. • BCN can increase the pH of tetracycline (TC) solution from 3.80 to 7.87. • TC adsorption by BCN is 76.74 mg·g −1 in pH 7.87, and 63.08 mg·g −1 in pH 3.80. • Some of the captured protons by BCN can transfer to TC during adsorption process. A series of carbon-doped boron nitride (BCN) are synthesized via oxygen-limited method, in which BCN-0.6 has the best adsorption quantity for tetracycline (TC). BCN-0.6 can capture protons and increase the pH of TC solution from 3.80 to 7.87, which makes that TC changes to negative state (pH 7.87) from neutral state (pH 3.80). BCN-0.6 exists in protonated form in solution. TC adsorption quantity by BCN-0.6 in pH 7.87 is higher than that in pH 3.8 (76.74 mg·g −1 vs. 63.08 mg·g −1 ), being due to that these captured protons can also interact with these oxygen-containing groups in TC via hydrogen bonding. The hydroxyl numbers of BCN-0.6 have been determined via Boehm titration method for clarifying the contribution of these surface hydroxyl for TC adsorption. In addition, some of the captured protons by BCN-0.6 can transfer to TC during adsorption process, increasing the electrostatic interaction between BCN-0.6 and TC. Experimental and theoretical studies support that hydrogen bonding, electrostatic interaction and π…π stacking are main driving force for TC adsorption by BCN-0.6. Langmuir isotherm model and pseudo-second-order kinetic model are suitable to describe the adsorption of TC by BCN-0.6. And, this adsorption is an endothermic process. The adsorption performance of BCN-0.6 for TC is easily regenerated by washing with water. Furthermore, the per unit specific surface adsorption capacity (4.102 mg·m −2 ) of BCN-0.6 for TC is far higher than that of commercial activated carbon for TC (0.163 mg·m −2 ), suggesting that BCN-0.6 is a good adsorbent for water purification.