Carbonization of methylene blue adsorbed on palygorskite for activating peroxydisulfate to degrade bisphenol A: An electron transfer mechanism

As a natural and environmentally friendly adsorbent, palygorskite (Pal) has been approved to be excellent for the adsorption of dyes. However, the spent Pal is difficult to be regenerated through normal desorption methods, and thus, becoming a solid waste. In this study, methylene blue (MB) was adsorbed by Pal, and the MB absorbed on palygorskite (MP) was carbonized at different temperatures. The carbonized MP (CMP) was used for peroxydisulfate (PDS) activation to degrade bisphenol A (BPA). The effects of carbonization temperature, pH values, PDS concentration, and catalysts dosage on BPA degradation were investigated. The results show that the MP carbonized at 800 C (CMP800) has the best activation performance due to the high degree of carbon defectivity and high specific surface area. The CMP800 can effectively degrade BPA over a wide pH range from 3 to 9 and is extremely resistant to the effects of various anions, such as Cl-, NO3-, HCO3-, and H2PO4- . Based on quenching experiments, electron spin resonance (ESR), and electrochemical analysis results, a non-radical pathway involving electron transfer from BPA to PDS is responsible for the degradation of pollutants. Moreover, the CMP800 has a high total organic carbon (TOC) removal efficiency of 83%, high stability in three cycles, and low PDS consumption. This study demonstrates the feasibility of the treatment and utilization of the waste Pal, which also provides a carbon-based activator for the activation of PDS to degrade organic contaminants.