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Heavy metals in water are critical global environmental problems. In particular, the anionic heavy metal chromium (Cr) has carcinogenic and genotoxic risks on human health. To this end, an ultralight and flexible nanofibrillated cellulose (NFC)/chitosan (CS) aerogel was developed only by freeze-drying combined with physical thermal cross-linking for efficient one step co-removal of Cr(VI) and Cr(III). The maximum adsorption capacity of Cr(VI) and total Cr calculated according to the Langmuir model was 197.33 and 134.12 mg/g, respectively. Even in the presence of competing soluble organics, anions and oil contaminants, the resulting NFC/CS-5 aerogels showed excellent selectivity. The aerogel exhibited outstanding mechanical integrity, remaining intact after 17 compressions in air and underwater. Meanwhile, after 5 adsorption-desorption cycles, the aerogel was easy to regenerate and maintained a high regeneration efficiency of 80.25%. Importantly, self-assembled NFC/CS-5 aerogel filter connected with the peristaltic pump could purify 752 mL of industrial wastewater with Cr(VI) pre-concentration capacity of 49.71 mg/g. XPS and FT-IR verified that electrostatic interactions, reduction and complexation acted as the main driving forces for the adsorption process. Moreover, such aerogel possessed broad application prospects for alleviating heavy metal pollution in agriculture. [Display omitted] • An ultralight & flexible nanofibrillated cellulose/chitosan aerogel was synthesized. • The maximum adsorption capacities of Cr(VI) and total Cr were 197.33 and 134.12 mg/g. • Aerogels exhibited superior antifouling, selectivity and recyclability. • Self-assembled aerogel filter could purify 752 mL of industrial wastewater. • Adsorption coupled reduction and chelation mechanism was revealed by FTIR and XPS. [ABSTRACT FROM AUTHOR]

[Display omitted] • Elastic brushite/polyethyleneimine/nanofibrillated cellulose aerogel was developed. • The coupling of brushite and polyethyleneimine enhanced adsorption property. • PNFCA/BRU-0.2 exhibited high selectivity for Cu(II) with 332.66 mg/g. • The continuous flow purification of copper-containing wastewater was realized. • PNFCA/BRU-0.2 could block the toxicity of heavy metals to crops. To achieve efficient removal of copper(II) from heavy metal wastewater, designing an eco-friendly and low-cost adsorbent is highly desirable. Here, a novel air- and underwater shape-memory cellulose aerogel was reported via coupling brushite and polyethyleneimine (PEI)-modified nanofibrillated cellulose (NFC) for selectively adsorbing Cu(II) ions. The adsorption kinetic and isotherm studies were consistent with pseudo-second-order model and Langmuir model, indicating the removal of Cu(II) was a monolayer chemisorption process. Benefiting from the open three-dimensional (3D) framework structure and abundant exposed active sites, such compressible aerogel exhibited excellent adsorption capacity of 332.66 mg/g for Cu(II). In addition, the developed aerogel could be conveniently used as a continuous flow filter for successive purification of industrial wastewater, where the up-to-standard treatment volume was about 5.6 L. The Cu(II)-loaded aerogel could be regenerated after being eluted by 0.1 M EDTA-2Na, and its structure, shapeability and selective adsorption properties were hardly affected even after 8 consecutive cycles. Mechanistic analysis confirmed that the surface complexation, ion exchange and chemical deposition were the main driving forces for the superior adsorption performance. Finally, PNFCA/BRU could inhibit the contamination of crops by heavy metals, which was a great safeguard for wheat growth. [ABSTRACT FROM AUTHOR]

[Display omitted] • SA/PEI-0.25 aerogel showed high elastic, stability and adsorption performance. • The maximum adsorption capacities of Cr(VI) and Cd(II) were 678.67 and 464.23 mg/g. • The fixed-bed continuous filtration of Cr(VI) and Cd(II) wastewater was realized. • SA/PEI-0.25 aerogel reduced the toxicity of heavy metal ions to rice. • The adsorption mechanisms of Cr(VI) and Cd(II) were investigated. Herein, an elastic polyethyleneimine/sodium alginate aerogel was designed by a one-step freeze-drying method. The 3D honeycomb-like structure endowed it excellent compressibility and plentiful exposed adsorption sites to accelerate Cr(VI) and Cd(II) adsorption. The adsorption processes matched the pseudo-second-order and Langmuir models, and the saturated adsorption capacity for Cr(VI) and Cd(II) was 678.67 and 464.23 mg/g, respectively. The obtained aerogel still expressed superior removal performance for Cr(VI) and Cd(II) even in the coexistent of multiple interfering factors and maintained stable adsorption capacity at least after 5 cycles. Importantly, the elastic cylindrical aerogel (∼0.59 g) could achieve dynamic filtration of industrial wastewater containing Cr(VI) and Cd(II) in fix-bed column system with corresponding effective treatment volume of 4.47 and 3.25 L, respectively. The reasonable mechanisms for the adsorption behaviors of heavy metals on the as-prepared aerogel was investigated via FTIR, XPS and Density functional theory (DFT), which could be attributed to the surface electrostatic adsorption, chelation and reduction effects. Eventually, the ecological assessment verified that eco-friendly SA/PEI aerogel had a powerful auxiliary effect on the anti-fouling growth of rice. Overall, such novel biomass aerogel adsorbent possessed great application potential and theoretical guiding significance for the purification of heavy metal wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • A functionalized carboxymethyl chitosan aerogel is explored for Cu(Ⅱ) adsorption. • The maximum capacity of PCCSA-1.0 for absorbing Cu(Ⅱ) is 175.56 mg/g. • Continuous filtration of industrial wastewater with fixed bed columns is achieved. • PCCSA-1.0 is conducive to inhibit the enrichment of Cu(Ⅱ) ions in rice. • The generated waste after adsorption is converted into a material for secondary use. Copper ions (Cu(II)) in water pose a huge threat to human health and ecosystem security. Therefore, developing eco-friendly and sustainable strategies to eliminate the toxicity risk of Cu(II) in the aqueous environment remains a great challenge. In this work, an elastic polyethyleneimine-modified carboxymethyl chitosan aerogel was developed via a freeze-drying process for the adsorption of Cu(II). The adsorption kinetic and isotherm experiments demonstrated that the adsorption process was monolayer chemisorption and the maximum adsorption capacity calculated from Langmuir model was 175.56 mg g−1. The obtained aerogels exhibited preferential selectivity for Cu(II) even when the competing cations and organics existed. Besides, about 0.93 g of aerogel realized continuous fixed-bed column filtration of industrial wastewater with an effective purification volume of 4.14 L. Mechanistic analysis via FTIR and XPS revealed that the excellent adsorption performance for Cu(II) might be attributed to the strong electrostatic force, Vander Waals' force and coordination of N/O -containing functional groups. It is worth mentioning that the adsorbed Cu(II) ions in the aerogel were converted into a reusable photocatalyst, avoiding the secondary leakage of heavy metals. This work opened a door to synthesize carboxymethyl chitosan aerogel, promising for heavy metal wastewater treatment and realizing the concept of waste utilization. [ABSTRACT FROM AUTHOR]