## 3 Artificial Intervention in the Degradation of Antibiotics
### Physical Chemistry Methods  
#### 3.3.1 Adsorption Method  
Adsorption is a widely utilized method for the removal of antibiotics from water. Based on different adsorption mechanisms, it can be categorized into physical adsorption and chemical adsorption. This method involves the development of functional materials with a porous structure and effective adsorption performance, such as activated sludge, nanoadsorbents, surface-modified zeolites, biochar, etc. These materials purify water by adsorbing emerging pollutants, including antibiotics, through mechanisms such as electrostatic attraction, van der Waals forces, intermolecular forces, hydrogen bonding, and ion exchange. This technology is widely adopted and effectively utilized in the field of water treatment, both domestically and internationally, due to its advantages, including the simple equipment, ease of operation, mild reaction conditions, and cost-effectiveness, as well as its environmental friendliness. The adsorption of antibiotics in activated sludge primarily involves hydrophobic and electrostatic interactions. Hydrophobic interactions occur when non-polar groups in antibiotic molecules bind to lipids or hydrophobic organic matter, such as extracellular polymeric substances (EPSs) present in sludge, through van der Waals forces. The logarithm of the partition coefficient (\(\log\mathrm{P}_{\mathrm{ow}}\)) between octanol, which simulates biological membranes and organic matter, and water serves as a reference indicator. A \(\log\mathrm{P}_{\mathrm{ow}}\) greater than 3.2 indicates a high hydrophobicity, facilitating the adsorption onto organic matter in sludge, including lipids and EPSs. Conversely, a \(\log\mathrm{P}_{\mathrm{ow}}\) less than 0 indicates hydrophilicity, as exemplified by tetracycline, which has a \(\log\mathrm{P}_{\mathrm{ow}}\) of \(-1.3\). Although tetracycline exhibits low hydrophobicity, its adsorption can be enhanced by forming complexes with divalent metal ions, such as Ca\({}^{2+}\) and Mg\({}^{2+}\), or with EPSs in the sludge [94]. In activated sludge systems, the adsorption behavior of fluoroquinolone antibiotics, such as ciprofloxacin and nonfloxacin, is highly dependent on the pH, which is closely related to the pKa values of the ionizable groups in their molecular structures. For instance, fluoroquinolones exhibit amphoteric properties, containing ionizable groups such as a carboxyl (-COOH, pKa \(\approx\) 6) and amino (-NH2, pKa \(\approx\) 8). When the system pH is below the pKa of the carboxyl group (approximately 6.0), the amino group in the molecule becomes protonated (-NH3+), resulting in the entire molecule carrying a positive charge. Since the surfaces of microorganisms and organic matter in activated sludge are typically negatively charged, a strong electrostatic attraction occurs between the two [95]. In addition, the high specific surface area of the nanoadsorbent demonstrates an excellent adsorption capacity for antibiotics. [PERSON] et al. reviewed the comprehensive research advancements in recent years regarding graphene-based nanoadsorbents for the removal of various antibiotics [96]. They discussed the application value of these nanoadsorbents in water and wastewater treatments, particularly summarizing their adsorption capabilities for different antibiotics. The authors evaluated the effects of key water quality parameters, such as the pH, temperature, and ionic strength, on the adsorption efficiency of various antibiotics. They conducted a comprehensive analysis of the factors influencing the adsorption mechanisms of nanoadsorbents and discussed their potential for regeneration and reusability. Biochar, as a porous carbon material obtained from the pyrolysis of biomass, has a rich variety of surface functional groups and shows significant advantages in the adsorption of pollutants, including antibiotics, heavy metals, and organic pollutants. [PERSON] et al.