@article {35754,
	title = {Coprecipitation of Fe/Cr Hydroxides at Organic{\textendash}Water Interfaces: Functional Group Richness and (De)protonation Control Amounts and Compositions of Coprecipitates},
	journal = {Environmental Science \&amp; Technology},
	volume = {58},
	year = {2024},
	pages = {8501-8509},
	abstract = {ron/chromium hydroxide coprecipitation controls the fate and transport of toxic chromium (Cr) in many natural and engineered systems. Organic coatings on soil and engineered surfaces are ubiquitous; however, mechanistic controls of these organic coatings over Fe/Cr hydroxide coprecipitation are poorly understood. Here, Fe/Cr hydroxide coprecipitation was conducted on model organic coatings of humic acid (HA), sodium alginate (SA), and bovine serum albumin (BSA). The organics bonded with SiO2\&nbsp;through ligand exchange with carboxyl ({\textendash}COOH), and the adsorbed amounts and pKa\&nbsp;values of {\textendash}COOH controlled surface charges of coatings. The adsorbed organic films also had different complexation capacities with Fe/Cr ions and Fe/Cr hydroxide particles, resulting in significant differences in both the amount (on HA \&gt; SA({\textendash}COOH) >> BSA({\textendash}NH2)) and composition (Cr/Fe molar ratio: on BSA({\textendash}NH2) >> HA \&gt; SA({\textendash}COOH)) of heterogeneous precipitates. Negatively charged {\textendash}COOH attracted more Fe ions and oligomers of hydrolyzed Fe/Cr species and subsequently promoted heterogeneous precipitation of Fe/Cr hydroxide nanoparticles. Organic coatings containing {\textendash}NH2\&nbsp;were positively charged at acidic pH because of the high pKa\&nbsp;value of the functional group, limiting cation adsorption and formation of coprecipitates. Meanwhile, the higher local pH near the {\textendash}NH2\&nbsp;coatings promoted the formation of Cr(OH)3. This study advances fundamental understanding of heterogeneous Fe/Cr hydroxide coprecipitation on organics, which is essential for successful Cr remediation and removal in both natural and engineered settings, as well as the synthesis of Cr-doped iron (oxy)hydroxides for material applications.},
	url = {https://doi.org/10.1021/acs.est.4c01245},
	author = {Yandi* Hu and Jiang, Xulin and Zhang, Suona and Cai, Dawei and Zhou, Zehao and Liu, Chuan and Zuo, Xiaobing and Lee, Sang Soo}
}
