Transformation of polyvinyl chloride (PVC) into a versatile and efficient adsorbent of Cu(II) cations and Cr(VI) anions through hydrothermal treatment and sulfonation

The reuse of waste polyvinyl chloride (PVC) has drawn much attention as it can reduce plastic waste and associated pollution, and provide valuable raw materials and products. In this study, sulfonated PVC-derived hydrochar (HS-PVC) was synthesized by two-stage hydrothermal treatment (HT) and sulfonation, and shown to be a versatile adsorbent. The removal of Cu(II) cations and Cr(VI) anions using HS-PVC reached 81.2 +/- 1.6% and 60.3 +/- 3.8%, respectively. The first stage of HT was crucial for the dichlorination of PVC and the formation of an aromatic structure. This stage guaranteed the introduction of -SO3H onto PVC-derived hydrochar through subsequent sulfonation. HT intensities (i.e., temperature and time) and sulfonation intensity strongly determined the adsorption capacity of HS-PVC. Competitive adsorption between Cu(II) and Cr(VI) onto HS-PVC was demonstrated by binary and preloading adsorption. The proposed Cu(II) cations adsorption mechanism was electrostatic adsorption, while Cr(VI) were possibly complexed by the phenolic -OH and reduced to Cr(III) cations by C--C groups in HS-PVC. In addition, HS-PVC derived from PVC waste pipes performed better than PVC powder for Cu(II) and Cr(VI) removal (>90%). This study provides an efficient method for recycling waste PVC and production of efficient adsorbents.

Automated summary

The study synthesized a versatile adsorbent, HS-PVC, from PVC waste through two-stage hydrothermal treatment and sulfonation, showing high removal efficiency for Cu(II) and Cr(VI). The adsorption capacity of HS-PVC was strongly determined by the intensities of hydrothermal treatment and sulfonation. Competitive adsorption between Cu(II) and Cr(VI) onto HS-PVC was demonstrated, with different mechanism for their removal.