Preparation of Acid- and Alkali-Modified Biochar for Removal of Methylene Blue Pigment

Abstract

Walnut shell biochar (WSC) and wood powder biochar (WPC) prepared using the limited oxygen pyrolysis process were used as raw materials, and ZnCl2, KOH, H2SO4, and H3PO4 were used to modify them. The evaluation of the liquid-phase adsorption performance using methylene blue (MB) as a pigment model showed that modified biochar prepared from both biomasses had a mesoporous structure, and the pore size of WSC was larger than that of WPC. However, the alkaline modified was more conducive to the formation of pores in the biomass-modified biochar materials; KOH treatment resulted in the highest modified biochar-specific surface area. The isothermal adsorption of MB by the two biomass pyrolysis charcoals conformed to the Freundlich equation, and the adsorption process conformed to the quasi-second-order kinetic equation, which is mainly physical adsorption. The large number of oxygen-containing functional groups on the particle surface provided more adsorption sites for MB adsorption, which was beneficial to the adsorption reactions. The adsorption effects of woody biomass were obviously higher than that of shell biomass, and the adsorption capacities of the two raw materials’ pyrolysis charcoal were in the order of WPC > WSC. The adsorption effects of different treatment reagents on MB were in the order ZnCl2 > KOH > H3PO4 > H2SO4. The maximum adsorption capacities of the two biomass treatments were 850.9 mg/g for WPC with ZnCl2 treatment and 701.3 mg/g for WSC with KOH treatment.

Impacts of temperatures and phosphoric-acid modification to the physicochemical properties of biochar for excellent sulfadiazine adsorption

“…Moreover, the enriched functional groups, P=O and P=OOH for example, could impact the charge distribution of the adsorbent and the H-bonding formation thanks to the lone pair electrons, and therefore tend to lead to the stronger surface complexation for adsorption (Peng et al 2017). Compared to sulfuric acid, nitric acid, zinc chloride and other modification methods, phosphoric acid modification can protect the carbon skeleton and exhibit greater advantages in micropore formation (Chen et al 2018;Kang et al 2018;Liu et al 2020a). Moreover, considering their environmental effect, equipment corrosion and chemical recovery, phosphoric acid is most preferred (Chu et al 2018;Prahas et al 2008).…”

Effect of Pyrolysis Temperature on Mechanistic Transformation for Adsorption of Methylene Blue on Leached Rice‐Straw Biochar

“…Further, the adsorption capacity of biochar is improved post pyrolysis either by modification, [20] pyrolytic activation of biomass, [21] and/or by varying reaction atmosphere using different gases. [22] Post-pyrolysis modifications of biochar with various common reagents like KOH, [23] H 2 SO 4 , [23] H 3 PO 4 , [24] HCl, [25] and ZnCl 2 [23] are known to improve the surface adsorption of adsorbates including dyes. This surface activation of biochar is accounted to modification of surface functional groups and structure/porosity of biochar.…”

Biochar for agronomy, animal farming, anaerobic digestion, composting, water treatment, soil remediation, construction, energy storage, and carbon sequestration: a review

“…Acids such as sulphuric, hydrochloric, nitric, and phosphoric acid, as well as weak acids such as oxalic and citric acid, are frequently used in acid treatment to modify biochar (Yang et al 2019a ; Deng et al 2020 ; Wang and Wang 2019 ). Alkali modification or chemical reduction refers to the process of activating the surface of biochar with reducing agents such as sodium hydroxide, sodium carbonate, potassium carbonate (Anthonysamy et al 2021 ), and potassium hydroxide (Anthonysamy et al 2021 ; Liu et al 2020a ) . Furthermore, alkaline materials containing hydroxide ions or an amino group react with the functional groups on the surface of biochar, enhancing the sorption of negatively charged species (Ahmed et al 2016 ), such as nitrate and phosphate ions, which are critical in the field of plant nutrition.…”

“…Furthermore, alkaline materials containing hydroxide ions or an amino group react with the functional groups on the surface of biochar, enhancing the sorption of negatively charged species (Ahmed et al 2016 ), such as nitrate and phosphate ions, which are critical in the field of plant nutrition. Additionally, alkali treatment significantly alters the specific surface area and porosity of biochar (Liu et al 2020a ; Kumar et al 2021b ).…”