Hierarchical self-assembly of PSS/PEI/HTO on rice straw for high-affinity and selective Cu(II) capture toward deep water purification

Deep purification of heavy metals from complex aqueous matrices is a critical challenge in water remediation. In this study, a novel hierarchical adsorbent (RS-PSS/PEI-HTO) was developed by self-assembling poly(sodium 4-styrenesulfonate) (PSS), polyethyleneimine (PEI), and hydrated titanium oxide (HTO) onto rice straw. This ternary coating transformed the low-value biomass into a high-performance sequestration platform with enhanced structural integrity. System characterization (SEM-EDS, FTIR, and TGA) confirmed the successful formation of a stable interface with uniformly dispersed HTO nanoparticles mediated by the amine-rich PEI layer. Batch equilibrium studies revealed that the adsorption process followed the Langmuir model with an exceptionally high affinity constant (K L = 31.16 L/mg), enabling the capture of trace Cu(II) to near-zero residual levels. The adsorption mechanism was driven by the synergistic interaction of the ternary components: electrostatic pre-enrichment by PSS, high-density amine chelation by PEI, and specific metal–oxygen coordination by HTO. The composite maintained high selectivity for Cu(II) despite a 20-fold molar excess of Ca 2+ and Mg 2+ . Fixed-bed column studies validated its efficacy, reaching a breakthrough point of 225 Bed Volumes (BV) while keeping effluent Cu(II) below 0.1 mg/L, a five-fold improvement over binary RS-HTO. The exhausted adsorbent was easily regenerated with HCl-NaCl, demonstrating excellent stability and reusability. This research provides a sustainable "waste-to-wealth" paradigm for engineering high-affinity materials tailored for the deep purification of heavy-metal-contaminated wastewater. Download: Download high-res image (249KB) Download: Download full-size image