Ambient-dried biomass 3D porous aerogel with “brick-mortar-binder” structure for the determination and adsorption of Cr(VI)

Biomass aerogel has broad application prospects in eradicating water pollution. However, conventional preparation methods are limited by high energy consumption, which deviates from the original intention of materials for environmental remediation. In this work, a biomass aerogel with “brick–mortar-binder” structure prepared at ambient drying is proposed firstly for the determination and adsorption of Cr(VI). This biomass aerogel consists of polyacrylonitrile (PAN) nanofibers grafted with CDs serving as “brick”, flexible 2, 2, 6, 6-tetramethyl-1-piperidinyloxy −oxidized cellulose fibers and carboxymethyl chitosan as “mortar”, and (4, 6-dimethoxy[1.3.5]triazin-2-yl)-4-methylmorpholinium chloride hydrate (DMTMM) functioning as “binder”. The gel and crosslinking of TOCNFs and CMC are initiated by DMTMM. This method produces solid hydrogels that can resist capillary force during environmental volatilization, and become aerogels through freezing, solvent thawing and exchange, and drying at room temperature. Grafting CDs onto electrospun PAN nanofibers not only provides fluorescent signal and adsorption sites, but also prevents CDs from falling off. Meanwhile, nanofibers are introduced into aerogel, which enhances mechanical strength and boosts elasticity of biomass aerogel by 6 times (from 17.60 to 98.85 KPa). This ambient-dried biomass aerogel shows excellent sensitivity and selectivity to Cr(VI), possessing a detection limit as low as 1.12 μM and a linear range of 5–50 μM. It also has an adsorption capacity of 166.25 mg/g for Cr(VI) at room temperature and pH of 2, conforming to pseudo-second-order adsorption kinetics and Langmuir models. The mechanism of detecting and adsorbing Cr(VI) by biomass aerogel is clarified. This work presents an environmentally friendly, sustainable and low-energy method for constructing functional biomass aerogels that can be utilized to detect and adsorb heavy metal ions, thereby expanding the application of ambient-dried aerogels in environmental protection.