Effect of solution chemistry on the sedimentation, dissolution, and aggregation of the bimetallic Fe/Cu nanoparticles pre- and post-grafted with carboxymethyl cellulose

The suitability of iron-based nanomaterials or composites for in-situ remediation hinges on their physicochemical stability. Introducing surface modifications like metal doping or polymer grafting can regulate interparticle forces, influencing particle stability. Thus, probing how grafting methods (i.e., pre- or post-grafting) tune material properties controlling interparticle forces, comprehend the synergistic effect of metal doping and polymer grafting, and evaluate stability under varying geochemical conditions are the way forward in designing sustainable remediation strategies. To this end, time-dependent sedimentation, dissolution, and aggregation of four synthesized iron-based nanoparticles (bare iron (Fe), copper doped bimetallic iron/copper (Fe/Cu), pre- and post-grafted Fe/Cu with carboxymethyl cellulose (CMC) - CMCpre-Fe/Cu and CMCpost-Fe/Cu, respectively) were carried out as a function of solution chemistry (i.e., pH - 5 to 10, ionic strength, IS - 0 to 100 mM NaCl, initial particle concentration, C-0-20 to 200 mg.L-1) mimicking geoenvironmental conditions. CMCpre-Fe/Cu exhibited markedly higher particle availability (> 91 %) against sedimentation than others (bare Fe/Cu (11.28 %) > bare Fe (7.33 %) > CMCpost-Fe/Cu (6.09 %)) - suggesting the pivotal role of grafting method on particle stability. XDLVO energy profiles revealed pre-grafting altered magnetic properties favoring surface charge-driven electrostatic repulsion over magnetic attraction, thereby limiting aggregation-induced particle settling. In contrast, superior magnetic force overrides the electrostatic behavior for bare and post-grafted particles. Unlike bare and post-grafted nanoparticles, CMCpre-Fe/Cu aggregate size correlated positively with [H+] and IS, consistent with their settling behavior. Rise in C-0 showed a visible negative effect on particle aggregation and, thereby, sedimentation except for CMCpre-Fe/Cu by facilitating particle collision through Brownian movement. Both acidic pH and copper doping promoted nanoparticle dissolution, whereas pre-grafting can provide a plausible solution against nanoparticle toxicity and loss of reactivity due to ionic release. To recapitulate, these findings are imperative in building a sustainable framework for environmental remediation application.