Process Parameters Optimization, Characterization, and Application of KOH-Activated Norway Spruce Bark Graphitic Biochars for Efficient Azo Dye Adsorption.

In this work, Norway spruce bark was used as a precursor to prepare activated biochars (BCs) via chemical activation with potassium hydroxide (KOH) as a chemical activator. A Box-Behnken design (BBD) was conducted to evaluate and identify the optimal conditions to reach high specific surface area and high mass yield of BC samples. The studied BC preparation parameters and their levels were as follows: pyrolysis temperature (700, 800, and 900 °C), holding time (1, 2, and 3 h), and ratio of the biomass: chemical activator of 1: 1, 1.5, and 2. The planned BBD yielded BC with extremely high SSA values, up to 2209 m2·g-1. In addition, the BCs were physiochemically characterized, and the results indicated that the BCs exhibited disordered carbon structures and presented a high quantity of O-bearing functional groups on their surfaces, which might improve their adsorption performance towards organic pollutant removal. The BC with the highest SSA value was then employed as an adsorbent to remove Evans blue dye (EB) and colorful effluents. The kinetic study followed a general-order (GO) model, as the most suitable model to describe the experimental data, while the Redlich-Peterson model fitted the equilibrium data better. The EB adsorption capacity was 396.1 mg·g-1. The employment of the BC in the treatment of synthetic effluents, with several dyes and other organic and inorganic compounds, returned a high percentage of removal degree up to 87.7%. Desorption and cyclability tests showed that the biochar can be efficiently regenerated, maintaining an adsorption capacity of 75% after 4 adsorption-desorption cycles. The results of this work pointed out that Norway spruce bark indeed is a promising precursor for producing biochars with very promising properties.

Performance of aquatic weed - Waste Myriophyllum spicatum immobilized in alginate beads for the removal of Pb(II).

A new biosorbent - alginate encapsulated with Myriophyllum spicatum - MsA was investigated for lead ions removal. This biosorbent was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), zeta potential, X ray Diffraction (XRD) and size distribution analysis. FT-IR analysis demonstrated that the lead ions sequestration mechanism included ion exchange and lead complexation with the carboxyl, carbonyl and hydroxyl groups in MsA. In order to better understand the mechanisms of the binding of Pb(II) on immobilized M. spicatum beads, 3 reaction and one diffusion based kinetic models were applied on kinetic data removal lead ions on three materials: M. spicatum, Ca-alginate and MsA. Myriophyllum spicatum encapsulated with alginate - MsA have higher adsorption capacity than M. spicatum. Among examined six isotherms Redlich-Peterson and the Langmuir isotherm model exhibited the best fit to the experimental data, with capacities ranging from 230 to 268.7 mg/g. Among the various tested desorption agents, nitric acid has proven to be the best. The obtained results suggest that the immobilized M. spicatum biosorbent holds great potential for lead wastewater treatment applications.