KOH-activated high surface area Douglas Fir biochar for adsorbing aqueous Cr(VI), Pb(II) and Cd(II).

Biochar has become a popular research topic in sustainable chemistry for use both in agriculture and pollution abatement. To enhance aqueous Cr(VI), Pb(II) and Cd(II) removal efficiency, high surface area (535 m2/g) byproduct Douglas fir biochar (DFBC) from commercial syn-gas production obtained by fast pyrolysis (900-1000 °C, 1-10 s), was subjected to a KOH activation. KOH-activated biochar (KOHBC) underwent a remarkable surface area increase to 1049 m2/g and a three-fold increase in pore volume (BET analysis). Batch sorption studies on KOHBC verses pH revealed that the highest chromium, lead and cadmium removal capacities occurred at pH 2.0, 5.0 and 6.0, respectively. KOHBC exhibited much higher adsorption capacities than unactivated DFBC. Heavy metal loadings onto KOHBC were characterized by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Sorption of Cr(VI), Pb(II) and Cd(II) all followed pseudo-second order kinetics and the Langmuir adsorption model. The highest Langmuir adsorption capacities at the respective pH's of maximum adsorption were 140.0 mg g-1 Pb(II), 127.2 mg g-1 Cr(VI) and 29.0 mg g-1 Cd(II). Metal ions spiked into natural and laboratory waste water systems exhibited high sorption capacities. Desorption studies carried out using 0.1 M HCl revealed that Pb(II) adsorption onto the KOHBC surface is reversible. Portions of Cd(II) and Cr(VI) adsorbed strongly onto KOHBC were unable to be desorbed by 0.1 M HCl and 0.1 M NaOH.

Biohybrid Hydrogel and Aerogel from Self-Assembled Nanocellulose and Nanochitin as a High-Efficiency Adsorbent for Water Purification.

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 TEMPO-oxidized cellulose nanofiber (TOCNF) and positively charged partly deacetylated chitin nanofiber (PDChNF). The self-assembly process was performed at room temperature and without adding any cross-linking agents throughout the process. This results in the three-dimensional (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 m2·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.