No abstract

A simple and novel method, self-assembly of nanocellulose and nanochitin, was developed to produce high-efficiency and versatile biohybrid hydrogel (BHH) and aerogel (BHA) for water purification. The self-assembly process was driven by the electrostatic force between one-dimensional (1D) negatively charged TEMPOoxidized cellulose nanofiber (TOCNF) and positively charged partly deacetylated chitin nanofiber (PDChNF). The self-assembly process was performed at room temperature and without adding any crosslinking agents throughout the process. This results in the threedimensional (3D) BHH that physically cross-linked via both electrostatic interactions and hydrogen bonding between TOCNF and PDChNF. The obtained BHA from lyophilized BHH exhibited a highly porous interconnected structure with a specific surface area of 54 m 2 •g −1 , which assures the availability of its internal active site for the adsorption of toxic metalloid ions and organic pollutants. Consequently, the BHA displayed super-high adsorption capacities of 217 mg•g −1 for As(III) under the neutral pH conditions and 531 mg•g −1 for methylene blue (MB) under an alkaline aqueous condition with rapid adsorption kinetics, in sharp contrast to conventional biobased adsorbents. Moreover, the BHA is reusable, which still exhibited a high MB adsorption capacity of 505 mg•g −1 even after five successive adsorption−desorption cycles. This versatile BHA produced via a facile preparation strategy is proven to be a promising renewable adsorbent for water purification, offering simple and green alternatives to the conventional adsorbent from synthetic polymers.

Surface area, particle aggregation, pressure drop in columns, nanotoxicity, and commercialization difficulties limit the use of nanoparticle adsorbents. Magnetic primary nano-Fe3O4 particles (∼16.7 nm diameter) were dispersed on high-surface-area (695 m2/g) Douglas fir biochar (MBC). A cheap, commercial fast pyrolysis biochar, a syngas byproduct, was modified by chemical coprecipitation of Fe3O4 from Fe3+/Fe2+ aqueous NaOH, served as a matrix, aiding magnetite nanoparticle dispersion and reducing the extent of particle aggregation. This MBC removed ∼90.0 mg/g of phosphate from water, approximately 20 times the capacity reported for neat (∼39 nm) magnetite particles (∼5.1 mg/g). MBC was robust in fixed-bed column sorption with 82.5 mg/g (at pH 3) capacity, showing no significant equilibrium or kinetic limitations in flow versus batch sorption. The biochar support serves as an added adsorption phase for heavy metals and organic contaminants, adsorbing poorly on magnetite. MBC enables magnetic separation of exhausted adsorbent from a batch process, an alternative to filtration. The neat and phosphate-laden hybrid sorbents were was characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray, point of zero charge, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), elemental analysis, vibrating sample magnetometry, and Brunauer–Emmett–Teller surface-area and pore-volume measurements. The chemisorption mechanism versus pH, evaluated by XPS and existing literature, characterized the dominant phosphate complexes adsorbed on magnetite. The pH effect on phosphate sorption and the P 2p XPS binding energy shifts at pH from 1 to 13 are reported. A solution pH of 1–3 facilitates the formation of bidentate monoprotonated phosphate complexes [(Fe–O)2-PO2H]− at Fe–OH surface functions. H2PO4 2– predominates in solution at pH ∼4–6.5, which favors the formation of [Fe–O–PO3H]− at these pH values. At strongly basic pH (10–13) values, PO4 3– predominates and forms deprotonated chemisorbed monodentate [Fe–O–PO3]2– and bidentate [(Fe–O)2PO2]2–. Multilayer phosphate sorption and precipitation of iron phosphates were considered.

No abstract

Tea-waste biochar produced under different pyrolysis temperatures were subjected to three acid modifications and a comparative evaluation of their key physicochemical characteristics made.