Multifunctional alginate-based carbon aerogels for oil–water mixture and emulsion separation

Lightweight, Elastic, and Superhydrophobic Multifunctional Organic-Inorganic Fibrous Aerogels for Efficient Oily Wastewater Purification and Electromagnetic Microwave Absorption

Lightweight and robust aerogels with multifunctionality are highly desirable to meet the technological demands of current society. Herein, we designed lightweight, elastic, and superhydrophobic multifunctional organic-inorganic fibrous hybrid aerogels which were assembled with organic aramid nanofibers and inorganic hierarchical porous carbon fibers. Thanks to the organic-inorganic fiber hybridization strategy, the optimal aerogels possessed remarkable compressibility and elasticity. Benefiting from the microscopic hierarchical porous structure of carbon fibers and the macroscopic macroporous lamellar structure of aerogels, the optimal aerogels exhibited superb lightweight property, conspicuous electromagnetic microwave absorption ability, and outstanding oily wastewater purification capacity. As for electromagnetic microwave absorption, it achieved a strong reflection loss of -41.8 dB, and the effective absorption bandwidth reached 6.86 GHz. Besides, the oil adsorption capacity for trichloromethane reached as high as 93.167 g g-1 with a capacity retention of 95.6% after 5 cycles. Meanwhile, it could act as a gravity-driven separation membrane to continuously separate trichloromethane from a trichloromethane-water mixture with a high flux of 7867.37 L·m-2·h-1, even for surfactant-stabilized water-in-n-heptane emulsions of 3794.94 L·m-2·h-1. Such a strategy might shed some light on the construction of multifunctional aerogels toward broader applications.

Facile construction of multifunctional bio-aerogel for efficient separation of surfactant-stabilized oil-in-water emulsions and co-existing organic pollutant

The deep treatment of robust oily emulsion wastewater has long been an arduous challenge. Herein, a biomass-derived PEI-TiO2@Gelatin aerogel (PEI-TiO2@GA) with honeycomb-like porous structure was fabricated. The interface wetting characteristics of PEI-TiO2@GA could be selectively switched between the superlipophilicity and superoleophobicity through the merely pre-wetting process. Combined with extraordinary structure and superwetting properties, PEI-TiO2@GA was proved to be ideal for oils absorption (17-26 g/g) and MO dye adsorption (73.549 mg/g) with high up-taking rate. Simultaneously, as-prepared PEI-TiO2@GA could realize various surfactant-stabilized oil-in-water emulsions separation simply under gravity with the separation efficiency as high as 99.25%. In addition, PEI-TiO2@GA was highly resistant toward mechanical compression (1.952 MPa), and exhibited acceptable regenerability within 5 cycles by performing solvent replacement approach. Combining with the newly developed separator and dynamic emulsion separation device, the continuous deep separation of the emulsion and the synergistic removal of co-existing pollutants can be achieved with the enhanced separation efficiency and permeation flux. Most importantly, the mechanism results show that the transition of interface wetting properties was a reversible multi-step process, and the demulsification separation of emulsion and the adsorption removal of co-existing pollutants were two independent processes. This work opens up a new avenue to customize advanced bio-aerogels for industrial effluent treatment and environmental remediation.

Recent advances in cellulose- and alginate-based hydrogels for water and wastewater treatment: A review

From the environmental perspective, it is essential to develop cheap, eco-friendly, and highly efficient materials for water and wastewater treatment. In this regard, hydrogels and hydrogel-based composites have been widely employed to mitigate global water pollution as this methodology is simple and free from harmful by-products. Notably, alginate and cellulose, which are natural carbohydrate polymers, have gained great attention for their availability, price competitiveness, excellent biodegradability, biocompatibility, hydrophilicity, and superior physicochemical performance in water treatment. This review outlined the recent progress in developing and applying alginate- and cellulose-based hydrogels to remove various pollutants such as dyes, heavy metals, oils, pharmaceutical contaminants, and pesticides from wastewater streams. This review also highlighted the effects of various physical or chemical methods, such as crosslinking, grafting, the addition of fillers, nanoparticle incorporation, and polymer blending, on the physiochemical and adsorption properties of hydrogels. In addition, this review covered the alginate- and cellulose-based hydrogels' current limitations such as low mechanical performance and poor stability, while presenting strategies to improve the drawbacks of the hydrogels. Lastly, we discussed the prospects and future directions of alginate- and cellulose-based hydrogels. We hope this review provides valuable insights into the efficient preparations and applications of hydrogels.

Adjustable Underwater Gas Transportation Using Bioinspired Superhydrophobic Elastic String

Dynamic and precise manipulation of the gas flow in a liquid environment through a facile and reliable approach is of great importance for directional gas transportation and multiphase chemical reactions. In this research, elastic superhydrophobic strings were prepared by a one-step, non-fluorinated dip-coating strategy. The surface-treatment string demonstrated a good superaerophilicity underwater. By simply elongating or shortening superaerophilic strings, the gas flux underwater was precisely manipulated in a gas-siphon underwater experiment. The result reveals that a large strain of the treated string induces a low gas flow, and a rope woven with more strings results in a larger range of gas flow regulation. The elastic superhydrophobic/superaerophilic string was utilized to adjust the reaction time of carbon dioxide and sodium hydroxide aqueous solution successfully. Furthermore, in a wet oxidation experiment for treating simulated flue gas composed of nitric oxide (NO), nitrogen and oxygen, superhydrophobic and stretched strings with a strain of 200% demonstrated a 7.9% higher NO removal efficiency than that of untreated strings. Interestingly, NO removal efficiency can be regulated by mechanical stretching of gas-conducting strings. We believe that this facile and low-cost approach provides a valid method of on-demand manipulation of the gas flow for underwater gas transportation.