Objective Wet blue is an indispensable intermediate product in leather manufacture. However, wet blue is prone to mildew due to its high moisture content, causing widespread use of chlorophenol-based antifungal agents. Chlorophenols are strictly regulated internationally due to their high toxicity, thereby their residues in leather could significantly influence the quality of finished leather. Thus, developing efficient and eco-friendly methods for the removal of chlorophenols is crucial for enhancing ecological safety of leather products and promoting sustainable development in leather industry.

Methods In this research, we developed a novel eluting system via utilizing β-cyclodextrin (β-CD) as primary eluting agent and 2,4,5-trichlorophenol (TCP) as target pollutant to systematically investigate the removal mechanism of TCP from wet blue. The key parameters were optimized, including the type and concentration of surfactants, NaCl concentration, β-CD dosage, pH, elution time, temperature, and number of elution cycles.

Results The best TCP removal rate was achieved at 0.1 g/L of surfactant DW, 7 g/L of β-CD, 298.15 K, 60 min of elution, and pH 5, resulting in a substantial elimination of TCP from 55.42 mg/kg to 4.83 mg/kg in wet blue with a removal efficiency of 91.3%, which meets the ecological standard of leather. Mechanistic investigation results revealed that the surfactant DW significantly reduced the surface tension of the β-CD solution and improved its wettability and penetration into the hydrophobic leather surface, thereby promoting the inclusion interaction between β-CD and TCP molecules. Afterwards, β-CD formed stable inclusion complexes with TCP via its hydrophobic cavity, realizing the efficient elution of TCP. During the elution process, the TCP removal rate was increased first and then inhibited with the increase of β-CD concentration, which may be attributed to the β-CD self-aggregation at excessive content. Moreover, it was found that the TCP removal efficiency could be improved by multiple elution cycles, particularly effective in processing wet blue with low or moderate TCP contamination. In addition, the physicochemical properties of wet blue before and after treatment were analyzed. The minimal release of chromium and hydroxyproline indicated the treatment barely influenced collagen fiber structure. Physical property tests proved that tensile strength, elongation at break, and tear strength remained unchanged. Microstructure analysis further confirmed that micropores and mesopores in wet blue were slightly increased after treatment, which benefited the deep penetration and binding of chemicals in wet-end process.

Conclusions In this work, an efficient and eco-friendly treatment of TCP elimination was established via β-CD elution system, and the synergistic mechanism between β-CD and surfactant was revealed at micro level. These excellent findings are promising for practical application and provide new insights into pollutant control in leather manufacture.