Hydrothermal Synthesis of Carbon Dot-Modified Multiwalled Carbon Nanotube Composites for Advanced Treatment of Oxytetracycline in Water

To prevent the proliferation of the OTC resistance genes in wastewater and their spread in the environment, advanced treatment of the OTC-containing wastewater has become necessary. In this study, an adsorbent material consisting of CDs/o-MWCNTs was synthesized using a combination of DBD technology and a hydrothermal method. The material was characterized by TEM, SEM, FT-IR, XRD, XPS, BET, TGA, and surface ζ-potential analysis. The effects of the adsorbent dosage, adsorption temperature, solution pH, adsorption time, and ionic interference on the adsorption of the OTC by CDs/o-MWCNTs were investigated. The results showed that the material contains 73.42% C, 6.39% O, and 5.78% N, with abundant active sites, a specific surface area of 148.48 m2/g, and a maximum adsorption capacity of 12.619 mg/g. The adsorption process followed the pseudo-second-order kinetic model and the Freundlich isotherm model. A series of analyses indicated that the adsorption and removal of OTC from water by CDs/o-MWCNTs occur through the synergistic effects of hydrogen bonding, π–π interactions, and van der Waals forces. After 10 adsorption–desorption cycles, the adsorption efficiency of CDs/o-MWCNTs remained above 91%. Moreover, for aquaculture wastewater with the OTC concentration below 0.1 mg/L, the material achieved a removal efficiency close to 100%. It also exhibited good salt tolerance and is suitable for the advanced treatment of OTC in high-salinity (1.0 mol/L NaCl) wastewater.