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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] • 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]

[Display omitted] • Polyethyleneimine functionalized chitosan aerogel is prepared via a facile pathway. • PCA-3 possesses 3D network structure and reversible compressibility. • PCA-3 has superior adsorption ability to Cr(VI) with maximum capacity of 445.3 mg/g. • PCA-3 can filter 7.4 L of real Cr wastewater with a concentration of 52.88 mg L−1. • PCA-3 can reduce the accumulation of Cr(VI) in wheat roots and leaves. Here we unveiled a novel polyethyleneimine (PEI) functionalized chitosan (CS) aerogel (PCA) with three-dimensional (3D) porous network structure and superior reversible compression property and investigated its adsorption behavior toward Cr(VI). The kinetic study displayed that the adsorption of Cr(VI) ions followed the pseudo-second-order model, indicating the adsorption was such as to depend on the chemical reaction between Cr(VI) ions and PCA. Notably, the maximum adsorption capacity fitted according to the Langmuir model was 445.29 mg/g, exceeding those of most previous chitosan-based adsorbents. The major reaction mechanism involving the capture and reduction of Cr(VI) has been systematically investigated based on FTIR, XPS and DFT analyses. Particularly, the fixed-bed column experiments illustrated that the effective treatment volume of PCA was 36367 mL and 7453 mL in simulated chromium wastewater and real chromium wastewater with initial concentrations of 2 mg L−1 and 52.88 mg L−1, respectively, suggesting the promising potential of PCA for large-scale practical applications. More interestingly, the current aerogel adsorbents could significantly reduce the accumulation of heavy metal ions in wheats, which meant that heavy metal wastewater had great prospects for agricultural irrigation after being treated by the aerogel of this work. In summary, this strategy could provide valuable and promising contribution towards the development of scalable and sustainable chitosan-based aerogels for Cr(VI) removal from practical wastewater. [ABSTRACT FROM AUTHOR]