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

Abstract

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.

3-Aminopropyl-triethoxysilane-Functionalized Tannin-Rich Grape Biomass for the Adsorption of Methyl Orange Dye: Synthesis, Characterization, and the Adsorption Mechanism

“…The overall percentage removal was calculated considering the area under the curve of the UV–vis (190–800 nm) spectra of the two synthetic effluents before and after the treatment ,,,− (see Figure ). The results exhibited satisfactory percentage removals for both effluents: Effluent A’s and Effluent B’s percentage removal was 40.0 and 48.0%, respectively.…”

Fabrication and Characterization of Effective Biochar Biosorbent Derived from Agricultural Waste to Remove Cationic Dyes from Wastewater

“…Phosphoric acid and Zinc chloride are two of the most often used activating agents in chemical activation, aside from NaOH and KOH [20,21]. Therefore, many research studies have been published during the last couple of years investigating the use of biochar to adsorb dyes and in wastewater treatment processes [22][23][24][25][26][27][28][29][30][31][32][33]. CV and/or MB dyes were adsorbed from aqueous media by various types of biochar such as eucalyptus camaldulensis biochar (Ec-bio) [22], porous biochar [23], mesoporous seaweed biochar [24], castor biomass-based biochar [25], adsorbents from orange peel residues [26], biochar at different carbonization times [28], date palm fronds biochars [31], and rice husk-mediated magnetic biochar (RH-MBC) [33].…”

Preparation and Characterization of Pulp and Paper Mill Sludge-Activated Biochars Using Alkaline Activation: A Box–Behnken Design Approach

“… 13 , 33 , 38 Indeed, carbon-based materials are expected to be more hydrophobic than hydrophilic. 13 , 38 , 39 However, Guy et al 40 prepared biochars by alkaline activation (KOH) using Norway spruce bark as a precursor and found that most biochars were hydrophilic. This contradiction could be related to the differences in the precursor; bark is more homogeneous with abundant oxygen and hydrogen groups, while paper and pulp sludge has been subjected to several extraction methods that may remove many of these hydrophilic groups, which in turn might impact the final biochar characteristics.…”

“…Hydrophobic–hydrophilic behavior of the 15 biochar samples was evaluated, and n -heptane:water adsorption ratios are exhibited in Figure . All biochars had a ratio >1, meaning a higher affinity for n -heptane, meaning that the surfaces were predominantly hydrophobic. ,, Indeed, carbon-based materials are expected to be more hydrophobic than hydrophilic. ,, However, Guy et al prepared biochars by alkaline activation (KOH) using Norway spruce bark as a precursor and found that most biochars were hydrophilic. This contradiction could be related to the differences in the precursor; bark is more homogeneous with abundant oxygen and hydrogen groups, while paper and pulp sludge has been subjected to several extraction methods that may remove many of these hydrophilic groups, which in turn might impact the final biochar characteristics.…”