Mesoporous Biopolymer Architecture Enhanced the Adsorption and Selectivity of Aqueous Heavy-Metal Ions

Abstract

Halloysite nanotubes (HNT) and ball-milled biochar (BC) incorporated biocompatible mesoporous adsorbents (HNT-BC@Alg) were synthesized for adsorption of aqueous heavy-metal ions. HNT-BC@Alg outperformed the BC, HNT, and BC@Alg in removing cadmium (Cd), copper (Cu), nickel (Ni), and lead (Pb). Mesoporous structure (∼7.19 to 7.56 nm) of HNT-BC@Alg was developed containing an abundance of functional groups induced from encapsulated BC and tubular HNT, which allowed heavy metals to infiltrate and interact with the adsorbents. Siloxane groups from HNT, oxygen-containing functional groups from BC, and hydroxyl and carboxyl groups from alginate polymer play a significant role in the adsorption of heavy-metal ions. The removal percentage of heavy metals was recorded as Pb (∼99.97 to 99.05%) > Cu (∼95.01 to 90.53%) > Cd (∼92.5 to 55.25%) > Ni (∼80.85 to 50.6%), even in the presence of 0.01/0.001 M of CaCl 2 and Na 2 SO 4 as background electrolytes and charged organic molecule under an environmentally relevant concentration (200 μg/L). The maximum adsorption capacities of Ni, Cd, Cu, and Pb were calculated as 2.85 ± 0.08, 6.96 ± 0.31, 16.87 ± 1.50, and 26.49 ± 2.04 mg/g, respectively. HNT-BC@Alg has fast sorption kinetics and maximum adsorption capacity within a short contact time (∼2 h). Energy-dispersive X-ray spectroscopy (EDS) elemental mapping exhibited that adsorbed heavy metals co-distributed with Ca, Si, and Al. The reduction of surface area, pore volume, and pore area of HNT-BC@Alg (after sorption of heavy metals) confirms that mesoporous surface (2–18 nm) supports diffusion, infiltration, and interaction. However, a lower range of mesoporous diameter of the adsorbent is more suitable for the adsorption of heavy-metal ions. The adsorption isotherm and kinetics fitted well with the Langmuir isotherm and the pseudo-second-order kinetic models, demonstrating the monolayer formation of heavy-metal ions through both the physical sorption and chemical sorption, including pore filling, ion exchange, and electrostatic interaction.

Green Ambient-Dried Aerogels with a Facile pH-Tunable Surface Charge for Adsorption of Cationic and Anionic Contaminants with High Selectivity

“…According to the United States Environmental Protection Agency, the permissible total amounts of Cr and Pb in drinking water is below 0.1 and 0.015 mg L –1 , respectively . Therefore, different technologies have been proposed for the decontamination of these pollutants including membrane separation, chemical precipitation, biodegradation, photodegradation, and adsorption. , Among these methods, adsorption is recognized as one of the most promising approaches owing to its low cost, simple implementation, and the absence of secondary pollutants . It has been reported that the cost of water treatment with nonadsorption technologies is in the range of 10 to 450 USD/m 3 of purified water, whereas adsorption-based approaches range from 5 to 200 USD/m 3 with approximately 70% of the cost related to the production of the adsorbent material .…”

Waste to resource: Utilization of waste bagasse as an alternative adsorbent to remove heavy metals from wastewaters in sub-Saharan Africa: A review

“…Sugarcane bagasse based adsorption removal shows selectivity based on physicochemical properties of HMs (Homagai et al 2010;Saxena et al 2017;Hassan et al 2021;Mondal et al 2022). Also, the literature shows that SCB adsorption removal of different heavy metals under similar experimental setups, shows different adsorption capacity (Kong et al 2014;Tran et al 2017;Ighalo et al 2022).…”

“…However, pseudo second order kinetics of initial rapid adsorption is due to the large binding sites of bagasse functional groups. In contrast, slow adsorption onto residual binding sites and diffusion of heavy metals into the porous surface follows pseudo first order kinetic models (Hassan et al 2021). Most adsorption kinetics of modified and unmodified SCB for metal ion removal have been reported as pseudo first and pseudo second order kinetic models (Irawan et al 2021;Iwuozor et al 2021a).…”

“…However, the aforementioned treatment methods are challenged by high initial costs, membrane fouling and high sludge production. In comparison with other processes, adsorption is a potential alternative treatment to existing technologies due to its low cost, simplicity of operation, low energy demand, recovery of heavy metals, good selectivity, and adsorbent regeneration options (Yu et al 2020;Hassan et al 2021;Younas et al 2021).…”

Cadmium and lead adsorption and desorption by coffee waste-derived biochars

“…1 and 2). The presence of mesopores favors ions transportation to active sorption sites (Cuong et al 2019), increasing the effectiveness and speed of the sorption process (Hassan et al 2021). The surface area plays an important role in metal sorption since this is a surface phenomenon (Nascimento et al 2014) and can vary widely, even among close feedstocks.…”