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

Abstract

Toxicity characteristic leaching procedure (TCLP) leached biochar is studied for adsorption of methylene blue (MB). Rice straw biochar obtained from slow pyrolysis at 400, 500, and 600 °C, respectively, is TCLP leached to furnish leached biochar, BL4, BL5, and BL6. The leached biochar BL4-6 have been characterized for pH, CHN analysis, ash, zeta potential, surface area morphology and functional groups. Batch adsorption studies are optimized for pH (3-9), adsorbent dose (0.5-4 g L −1 ), and initial MB concentration (20-135 mg L −1 ). Nonlinear fitting to Langmuir, Freundlich, and Redlich-Peterson adsorption isotherm with due statistical treatment and error function analysis is carried out. Leached biochar, BL4, BL5, and BL6, is characterized by the dominance of carboxylic acid, lactone, and phenols moieties, respectively. The MB adsorption on leached biochar exhibits maximum adsorption of 26.87, 51.34, and 18.83 mg g −1 for BL4, BL5, and BL6, respectively. The underlying mechanism for adsorption of MB using BL5, is characterized by non-ionic lactone ring opening in presence of MB under alkaline conditions that is supported by X-ray photoelectron spectroscopy(XPS) and Fourier transformed infrared spectroscopy (FTIR) studies. Desorption of MB and regeneration from BL5 is studied with methanol and 0.1 m HCl as stripping solvent for four cycles. Recovery of MB is better with methanol in comparison to 0.1 m HCl.

Effect of temperature and fly ash content on the catalytically pyrolyzed rice straw biochar–fly ash composites for methylene blue adsorption

“…The N 2 adsorption–desorption isotherms behavior of the composites are shown in Figure S3. As depicted from Figure S3, the BET type IV isotherm with a type H3 hysteresis loop is observed for the composites indicating mesoporous structure of the adsorbents 33 . The corresponding volumetric pore size distribution of the composites is shown in Figure S4.…”

“…However, only organic oxygen/nitrogen functionalized composites like chitosan/sepiolite showed good adsorption efficiency for MB in comparison to the biochar–fly ash composite used in the present study. Moreover, a comparison of the MB adsorption using TCLP leached biochar 33 shows that the BFA4 1 composite with up to 50% of fly ash shows significant adsorption for MB. Thus, inorganic components of the fly ash do contribute towards the adsorption of MB either by its own contribution and by the increased functional moieties on the biochar surface due to catalytic effect of fly ash.…”

“…As depicted from Figure S3, the BET type IV isotherm with a type H3 hysteresis loop is observed for the composites indicating mesoporous structure of the adsorbents. 33 The corresponding volumetric pore size distribution of the composites is shown in Figure S4. The average pore diameter of biochar-fly ash composite BFA4 1 , BFA5 1 , and BFA6 1 , respectively, was 16.38, 4.98, and 6.50 nm, respectively.…”

“…Bhardwaj et al investigated the role of leaching on the functional groups changes in biochar and its impact on dye adsorption. 33 On the contrary, it is hypothesized that the fly ash leachable nutrients could significantly improve functional group density by catalysis and/or ionexchange capacity, improving the adsorption of MB. Thus, in continued efforts for sustainable biopolymers 34,35 and biopolymer-based composites as adsorbents, 36,37 the present investigation studies the catalytic pyrolysis of rice straw in presence of higher proportion of fly ash and influence of surface physicochemical characteristics and inorganic minerals on adsorption of methylene blue (MB) dye.…”

“…In Indian scenario, it is observed that the unutilized fly ash and rice straw waste are similar in magnitude; thus, high fly ash containing biochar–fly ash composite with increased mineral content would take center stage for sustainable management of unutilized rice straw and fly ash. Bhardwaj et al investigated the role of leaching on the functional groups changes in biochar and its impact on dye adsorption 33 . On the contrary, it is hypothesized that the fly ash leachable nutrients could significantly improve functional group density by catalysis and/or ion‐exchange capacity, improving the adsorption of MB.…”