Effect of NOM on copper sulfide nanoparticle growth, stability, and oxidative dissolution

Abstract

Natural organic matter (NOM) impedes the growth of colloidally stable CuxS nanoparticles and slows down their morphological development, but also drives their oxidative dissolution.

Effects of natural organic matter (NOM), metal-to-sulfide ratio and Mn2+on cadmium sulfide nanoparticle growth and colloidal stability

“…On that account, the striking difference between aggregating CdS suspensions from this study and well-dispersed Cu x S suspensions of very high colloidal stability from an earlier study in our lab, both formed at the same conditions, can be conceived. 93 For instance, a 7 nm small, irregularly-shaped particle with temporary surface defects (typical pure CdS nanoparticle in this study), and a 4 nm small, hexagonallyshaped particle without considerable surface imperfections (typical pure Cu x S nanoparticle in our former study), both residing in the same solvent medium, will be subject to fairly different surface energy regimes. 93,95 The effect of NOM on CdS nanoparticles at sulfide excess conditions…”

“…In this formation process, the actual supply rate of the reactants in the system is crucial for particle development. 92,93 In the formation of CdS particles in our experiments, the reactant supply was not limited by kinetic constraints (e.g., template growth from other pre-existing mineral phases). 93 Hence, the Cd 2+ and (bi-)sulfide ions were readily available for cluster generation.…”

“…In our earlier study on Cu x S nanoparticle formation, we found that chemical speciation of the metal ion in the precursor solution can control the reaction rate of the nucleating and growing particles via formation of intermediate phases, thus indirectly affecting final particle characteristics such as particle size. 93 Therefore, we performed thermodynamic calculations on CdS suspensions in the absence and presence of SRFA to determine Cd speciation before sulfide addition. While in the SRFA-free suspensions, Cd 2+ was predicted to be present predominantly as aqueous CdCl 2 complex (Table S1a †), Cd 2+ speciation was different at low (5 mg C per L) and high (50 mg C per L) SRFA concentration with 21% (Table S1b †) and 91% (Table S1c † Despite this seemingly high stabilization potential from the SRFA for the subsequently formed CdS nanoparticles, aggregation was not completely inhibited.…”

“…In a previous study, we found a similar effect of SRFA in restricting the particle size of Cu x S nanoparticles formed at the same experimental conditions as the CdS here. 93 However, Cd 2+ ions form much weaker complexes with fulvic acids than Cu 2+ , [104][105][106] implying a less efficient capping of the CdS particle surface if surface complexation is assumed to be the only sorption mechanism. This weaker SRFA surface protection of CdS modulates the attachment efficiency in the suspension medium.…”

“…As seen in the previous section and also in other studies on metal sulfides, the presence of SRFA functional groups available for capping of the metal sulfide surfaces will additionally affect the terminal size of the particles. 72,93 The proportion of Cd present as SRFA-Cd complexes before the initiation of Environmental Science: Nano Paper particle formation (before sulfide addition) was predicted to be 21% in dilute and 35% in concentrated suspensions. In both suspensions, this would require similar fractions of SRFA sites for Cd 2+ complexation (16.2% in dilute and 18.4% in concentrated suspensions).…”