Efficient Hg(II) removal to ppb level from water in wider pH based on poly-cyanoguanidine/graphene oxide: Preparation, behaviors, and mechanisms

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Vol. 641; p. 128467
• Main Authors: Lin, Haiying, Duan, Yu, Zhao, Bohan, Feng, Qingge, Li, Mingzhi, Wei, Junqi, Zhu, Yifan, Li, Mingen
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20.05.2022
• Subjects: Adsorption mechanism; Column adsorption; Cyanoguanidine functionalization; Graphene oxide; Mercury removal; Mercury removal; Column adsorption; Cyanoguanidine functionalization; Graphene oxide; Adsorption mechanism
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/j.colsurfa.2022.128467

Graphene oxide keeps the high surface area and physicochemical stability, while poor adsorption capacity and selectivity limit its ability to remove mercury from water. To enhance its properties, cyanoguanidine was utilized as the modifier to synthesize the poly-cyanoguanidine/graphene oxide composite (DCDA-GO) through chlorination and cyanidation reaction, and the infrared spectrum and elemental analysis proved a successful synthesis. The prepared material has discovered a tremella-like three-dimensional structure with surface ravines, which achieved the actual maximum Hg(II) adsorption capacity to be 174.7 mg g−1 at 200 mg L−1. The DCDA-GO demonstrated a high pH-tolerance property and high removal efficiency at the wider pH (>91.5%, 1–13) and high resistance of ionic strength (>92.86%, 2000 mg L−1). Meanwhile, DCDA-GO can also complete the selective enrichment of Hg(II) in the bi-component and multi-component solution containing seven different metal ions, whose selectivity coefficient to Hg(II) was 1.7 × 105 mL g−1 and 3–5 orders of magnitude higher than other metal ions except for lead. And the composite can keep a high removal efficiency (85.5%) after 4 cycles. The adsorption process reached equilibrium after 100 min, which can be described as an endothermic, multilayer, and chemical interaction. The proposed adsorption mechanism was primarily ascribed to the chelation between Hg(II) and nitrogen-containing groups (imino and nitrile groups) while the contribution from electrostatic attraction was neglectable due to a positively charged surface. Moreover, the Hg(II) concentration was dramatically declined from 20 ppm to 1 ppb after column adsorption, the capacity could reach 108.17 mg g−1. On the whole, the DCDA-GO could be the remarkable material for removing Hg(II) from salt-abundance, pH fluctuating, or multiple heavy metals containing wastewater. [Display omitted] •DCDA functionalization can enhance the adsorption capacity of GO by pH 2–4 times.•The DCDA-GO maintained high properties in high-salinity water at a wider pH range.•The Hg(II) concentration was reduced to < 1 ppb after column adsorption.•DCDA-GO presented the tremella-like structure and it collapsed after adsorption.