Clay minerals in sediments have strong adsorption capacities for pollutants, but their role in the distribution of antibiotics in estuaries and nearby coastal areas is unclear. We evaluated the clay mineral montmorillonite (SWy-2) adsorption capacity for tetracycline (TC). We assessed the adsorption capacity of SWy-2 for TC by measuring the removal percentage of 30 mg/L TC over time. The effects of pH and ionic strength on the TC adsorption onto SWy-2 were investigated. We analyzed the kinetics of TC adsorption using a pseudo-second-order model and determined the adsorption isotherm using the Langmuir equation. SWy-2 particles were characterized using zeta potential, Fourier transform infrared (FTIR), and X-ray diffraction (XRD) analyses before and after TC adsorption. The removal percentage of 30 mg/L TC by SWy-2 reached 70.76% within 0.25 h and gradually increased to 78.64% at 6 h. TC adsorption was influenced by pH and ionic strength, where low pH enhanced and high ionic strength reduced the adsorption. The kinetics of TC adsorption followed a pseudo-second-order model, and the adsorption isotherm adhered to the Langmuir equation. The saturated adsorption capacity (q_max) of SWy-2 for TC was 227.27 mg/g. Zeta potential, FTIR, and XRD analyses confirmed that electrostatic interactions and chemical bonds played a significant role in the TC adsorption by SWy-2. SWy-2 clay mineral exhibits a substantial adsorption capacity for TC, indicating its potential as an effective sorbent to mitigate antibiotic contamination in estuaries and nearby coastal areas. The observed effects of pH and ionic strength on TC adsorption have implications for the environmental fate and transport of antibiotics. The pseudo-second-order kinetic model and Langmuir isotherm equation provide valuable insights into the adsorption behavior and capacity of TC on SWy-2. Characterization analyses support the involvement of electrostatic interactions and chemical bonds in the SWy-2-TC adsorption mechanism.

The preparation of magnetic biochar usually requires additives and additional synthesis steps, which leads to a significant increase in preparation costs. In this study, self-endowed magnetic biochar derived from iron-rich sludge was prepared via one-step pyrolysis to adsorb carbamazepine in water. The results show that when the initial concentration of carbamazepine is 5 mg L⁻¹ and the dosage of self-endowed magnetic biochar is 0.9 g L⁻¹, the removal efficiency of carbamazepine by self-endowed magnetic biochar can reach 90.1%, and the adsorption performance is excellent in a wide pH range. The adsorption of carbamazepine by self-endowed magnetic biochar can be well fitted by Langmuir an adsorption isotherm and pseudo-second-order adsorption kinetic model, which indicates that the adsorption process is single molecular layer chemisorption. In addition, self-endowed magnetic biochar has good magnetic properties, and can be effectively separated and recovered by an external magnetic field after use, and the adsorption rate of carbamazepine can still reach 81.4% after repeated use for 5 times. The adsorption mechanism of carbamazepine by self-endowed magnetic biochar includes pore filling, complexation, π–π interaction and hydrogen bonding.

Persulfate (PS) activated by Fe(II) has been widely investigated for degradation of contaminants. However, the Fe(II)/PS systems used for actual contaminated groundwater remediation have been restricted by circulation of Fe(III)/Fe(II). Herein, an ascorbic acid (AA) enhanced Fe(II)/PS system was developed for degradation of tetracycline (TC) contaminated groundwater. The influence of Fe(II), AA, PS dosage and pH on degradation of TC was investigated, the free radicals produced in the reaction were identified and the reusability of Fe(II) in the Fe(II)/PS/AA system for degradation of TC was also evaluated. The results showed that AA significantly promoted the degradation of TC in the Fe(II)/PS system, and a degradation rate of 86% for TC was achieved at 60 min. The dominant oxidant species for contaminant degradation in the Fe(II)/PS/AA system is ˙OH. Appropriate Fe(II), AA and PS dosage can improve the degradation rate of TC. Moreover, the degradation rate of TC in the Fe(II)/PS/AA system under acidic conditions is higher than that under alkaline conditions. With the increase of reaction time, TC can also be completely degraded even with a little Fe(II) or under alkaline conditions in the Fe(II)/PS/AA system, and Fe(II) showed a good reusability for the degradation of TC. Thus, the AA-enhanced Fe(II)/PS system for the degradation of contaminants displays the advantages of less Fe(II) consumption and a wide range of pH. This method provides a new strategy for in situ remediation of contaminated groundwater.