Disulfide polymer grafted polypropylene/polyethylene filter media for selective cadmium removal

Simultaneous oxidation of As(III) and reduction of Cr(VI) by NiS-CdS@biochar through efficient oxalate activation: The key role of enhanced generation of reactive oxygen species

The reutilization of exhausted biochar is attracting extensive interest among researchers. In this study, the biochar generated from Chinese fir with natural regular porous structure that adsorbed Cd²⁺/Ni²⁺ at different concentration levels was used as the precursor, and then combined with simple hydrothermal vulcanization and ion deposition to generate the p-n heterojunction between NiS and CdS compounds (NiS-CdS@C) in situ. The hybrids with 3 cycles of NiS deposition reduced the interfacial transmission resistance from 80 Ω to 40 Ω, and increased photocurrent density by 5 times, thus effectively promoting the separation of photogenerated electrons and holes. The simultaneous removal of As(III) and Cr(VI) was selected to evaluate the oxidation and reduction capacity of the visible light/NiS-CdS@C/oxalate system. The results indicated that 10 mg/L As(III) and Cr(VI) were completely and simultaneously removed with 0.75 mM oxalate addition within 40 min in the system, and the NiS-CdS@C presented good durability and stability for oxalate activation. Electron paramagnetic resonance (EPR) and quenching experiments demonstrated that oxalate was activated by holes under light to produce •CO₂^- and enhanced the generation of additional •OH and •O₂^-, further contributing to the oxidation of As(III) and reduction of Cr(VI).

Competitive sorption of Cd, Cr, Cu, Ni, Pb and Zn from stormwater runoff by five low-cost sorbents; Effects of co-contaminants, humic acid, salinity and pH

For a comprehensive estimation of metals removal by sorbents in stormwater systems, it is essential to evaluate the impacts of co-contaminants. However, most studies consider only metals (single or multiple), which may overestimate performance. This study employed a batch method to investigate the performance of five low-cost sorbents - coconut coir fiber (CCF), blast furnace slag (BFS), waste tire crumb rubber (WTCR), biochar (BC), and iron coated biochar (FeBC) - for simultaneous removal of Cd, Cr, Cu, Ni, Pb and Zn from simulated stormwater (SSW) containing other contaminants (nutrients and polycyclic aromatic hydrocarbons). BFS and CCF demonstrated the highest sorption capacity of all metals (> 95% removal) in all systems (single and multi-contaminant). However, the presence of other contaminants in solution reduced metals removal for other sorbents, as follows (highest to lowest removal): single-metal > multi-metal > multi-contaminant solutions, and removal efficiency ranking among metals was generally Cr~Cu~Pb > Ni > Cd > Zn. Humic acid (HA) negatively affected the metal sorption, likely due to the formation of soluble HA-metal complexes; NaCl concentration did not impact removal, but alkaline pH improved removal. These findings indicate that sorbents need to be tested under realistic stormwater solution chemistry including co-contaminants to appropriately characterize performance prior to implementation.

Recognizing adsorption of Cd(Ⅱ) by a novel core-shell mesoporous ion-imprinted polymer: Characterization, binding mechanism and practical application

A novel monodispersed Cd(II) ion-imprinted polymer (IIP) was synthesized inside core-shell mesoporous silica (C-SMS) particles to improve the diffusion kinetics of the polymer. The synthesized IIP@C-SMS was characterized and subsequently used in solid-phase extraction (SPE) for the selective adsorption of Cd(II) in aquatic samples. The results indicated that IIP had been successfully assembled inside the C-SMS particles with a high specific surface area (546.3 m² g^-1) and uniform mesoporous size (2.07 nm). The obtained IIP@C-SMS takes only 15 min to reach the adsorption equilibrium due to the highly developed mesoporous structure. IIP@C-SMS also presented a maximal adsorption capacity (201.9 μmol g^-1) for Cd(II), which was much higher than that of NIP@C-SMS (80.3 μmol g^-1). The relative selectivity coefficient of IIP@C-SMS for Cd(II)/M(II) (M = Cu(II), Pb(II), Cr(II), and Ni(II)) were 7.15, 8.70, 7.18, and 7.36, respectively, further confirming the satisfactory selectivity of IIP@C-SMS. The adsorption isotherms of IIP@C-SMS toward Cd(II) could be described by Langmuir model; whereas the adsorption kinetics could be fitted by the pseudo-second-order model, indicating chemisorption was the rate-limiting step. The FT-IR, ITC and XPS analysis further confirmed that the Cd(II)-induced cavities during the ion-imprinting process and the coordination between Cd(II) and -SH groups were the main adsorption mechanism. Furthermore, in real samples, IIP@C-SMS-SPE adsorbed approximately 93-104% of Cd(II). This work provides new insights for the design of novel macroporous sorbents for Cd(II).