Adsorption and photocatalytic degradation of tetracycline using carbon quantum dot-CuBTC nanocomposites: isotherm, kinetics, and mechanistic studies.

Antibiotics (especially tetracycline) are being recognised as highly persistent emerging micropollutants in aquatic environments, deteriorating water quality, and exerting toxic effects on non-target microorganisms; they need cutting-edge and effective techniques to reduce environmental contamination. Herein, a CuBTC (copper benzene-1,3,5-tricarboxylate) with CQDs (carbon quantum dots), an effective nanocomposite adsorbent-photocatalyst using a hydrothermal method with different amounts of CQDs incorporated (5, 10, 15, and 20%) was synthesized. CuBTC@CQDs was analysed thoroughly by employing sophisticated analytical techniques such as XRD, FTIR, FESEM, EDS, HRTEM, UV-Vis, DRS, PL, XPS, and BET measurements to validate the successful integration of CQDs onto the CuBTC, verifying its crystallinity, shape, elemental content, charge transport characteristics, optical behavior, and porosity. Out of all the synthesised nanocomposites, CuBTC@CQDs (15%) had the best photocatalytic degradation efficiency (87.9%) for tetracycline (TC), with degradation kinetics adhering to pseudo-first-order kinetics. The adsorption behaviour of TC on CuBTC@CQDs (15%) was optimally characterised by the Freundlich and Frenkel-Halsey-Hill isotherms, whereas the adsorption kinetics adhered to a pseudo-second order model. The prepared composite exhibited enhanced reusability/durability (n = 5 cycles). Mineralisation experiments indicated a decrease in total organic carbon (63%) and chemical oxygen demand (57%), while high-resolution mass spectrometry validated the conversion of total carbon into organic intermediates via ring-opening and oxidative reactions. Overall, the synergistic combination of adsorption and photocatalysis provides an excellent platform for the remediation of antibiotics, including TC.