Simultaneous removal of pollutants from sub-nanometric to nanometric scales by hierarchical dendrimers modified aerogels

Multifunctional amphibious superhydrophilic-oleophobic cellulose nanofiber aerogels for oil and water purification

Aerogels are of a popular choice for oil-water separation and water purification due to their attractive properties, such as lightweight, large surface area, and high porosity. Developing robust aerogels with multifunctional characteristics is highly desirable but remains challenging nowadays. Herein, we develop a facile one-pot condensation strategy for the fabrication of superhydrophilic-oleophobic (SHI-OP) composite aerogels using cellulose nanofibers (CNF), 3-glycidy-loxypropyl trimethoxysilane (GPTMS), polyethyleneimine (PEI) and fluorine-contained compound (FS-60). The resulted aerogels exhibit a directional lamellar structure with interconnected macropores, super-lightweight with high porosity of 98.30 % and low density of 0.0256 g·cm-3. Also, the aerogels are mechanically durable against repeated compression. Meanwhile, the amphibious SHI-OP feature of the composite aerogels in both air and water states enables them to not only absorb trace amount of water from contaminated oils, but also separate oil-water mixtures with separation efficiency of over 99 % and high permeation flux of over 9060 L/m2·h. Moreover, the aerogels also show excellent dye adsorption capability and reusability toward anionic dyes with a maximum adsorption capacity of 1245.68 mg/g. Such robust and multifunctional aerogels with special surface wettability provide good opportunity for liquid purification and dye-containing wastewater treatment.

Synthesis of salicylaldehyde tailored PAMAM dendrimers/chitosan for adsorption of aqueous Hg(II): Performance and mechanism

Water pollution caused by Hg(II) exerts hazardous effect to environmental safety and human health. Herein, a family of salicylaldehyde tailored poly(amidoamine) (PAMAM) dendrimers/chitosan composites (G0-S/CTS, G1-S/CTS, and G2-S/CTS) were prepared and used for the removal of Hg(II) from water solution. The adsorption performance of the as-prepared composites for Hg(II) was thoroughly demonstrated by determining various influencing factors. G0-S/CTS, G1-S/CTS and G2-S/CTS exhibited competitive adsorption capacity and good adsorption selective property for Hg(II). The maximum adsorption capacity of G0-S/CTS, G1-S/CTS and G2-S/CTS for Hg(II) were 1.86, 2.18 and 4.47 mmol‧g-1, respectively. The adsorption for Hg(II) could be enhanced by raising initial Hg(II) concentration and temperature. The adsorption process was dominated by film diffusion processes with monolayer adsorption behavior. The functional groups of NH2, CONH, CN, OH, CO and CN were mainly responsible for the adsorption of Hg(II). G0-S/CTS, G1-S/CTS and G2-S/CTS displayed good regeneration property and the regenerate rate maintained 95.00 % after five adsorption-desorption cycles. The as-prepared adsorbents could be potentially used for the efficient removal of Hg(II) from aqueous solution.

Flexible fabrication chitosan-polyamidoamine aerogels by one-step method for efficient adsorption and separation of anionic dyes

Chitosan in situ grown polyamidoamine (CTS-Gx PAMAM (x = 0, 1, 2, 3)) aerogels were fabricated by a facile one-step freeze-drying method, with glutaraldehyde serving as a crosslinker. The three-dimensional skeletal structure of aerogel provided numerous adsorption sites and accelerated the effective mass transfer of pollutants. The adsorption kinetics and isotherm studies of the two anionic dyes were consistent with the pseudo-second-order and Langmuir models, indicating that the removal of rose bengal (RB) and sunset yellow (SY) was a monolayer chemisorption process. The maximum adsorption capacity of RB and SY reached 370.28 mg/g and 343.31 mg/g, respectively. After five adsorption-desorption cycles, the adsorption capacities of the two anionic dyes reached 81.10% and 84.06% of the initial adsorption capacities, respectively. The major mechanism between the aerogels and dyes was systematically investigated based on using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-dispersive spectroscopy analyses, confirming that electrostatic interaction, hydrogen bonding and van der Waals interactions were the main driving forces for the superior adsorption performance. Furthermore, the CTS-G2 PAMAM aerogel exhibited good filtration and separation performance. Overall, the novel aerogel adsorbent possesses excellent theoretical guidance and practical application potential for the purification of anionic dyes.

High strength chitin/chitosan-based aerogel with 3D hierarchically macro-meso-microporous structure for high-efficiency adsorption of Cu(II) ions and Congo red

A high-strength aerogel with a 3D hierarchically macro-meso-microporous structure (HPS-aerogel) was designed based on biological macromolecules of chitin and chitosan. The macropores can be created within HPS-aerogel after CaCO₃ removal, and meso-micropores resulting from water sublimation during freeze-drying. The macro-meso-microporous structure endowed HPS-aerogel with high porosity, good mechanical properties, and excellent compression strength (1472 kPa at strain of 80 %). The HPS-aerogel exposed many adsorption sites and was used as an adsorbent to simultaneously remove Cu(II) and Congo red (CR) from water for the first time. The adsorption capability for Cu(II) and CR was 59.21 mg/g and 2074 mg/g at 303 K, respectively, and the adsorption processes matched Pseudo-second-order and Langmuir models with spontaneous and endothermic nature. Additionally, HPS-aerogel showed good anti-interference ability for coexisting pollutant. Importantly, HPS-aerogel exhibited an effective fixed-bed column adsorption performance for dynamic Cu(II) and CR with superior reusability and stability. Furthermore, HPS-aerogel showed outstanding adsorption efficiencies for Cu(II) and CR in real samples. The main adsorption mechanism for Cu(II) was attributed to the electrostatic attraction and chelation, and which was electrostatic attraction, Schiff base, and hydrogen bonding for CR. Therefore, HPS-aerogel should to be a promising adsorbent for removing both heavy-metal ions and dyes from wastewater.