In recent years, numerous investigations have explored the use of biochar for the removal of organic and inorganic pollutants in single component systems. Biochar is a carbonaceous material produced from waste biomass, mainly by thermochemical conversion methods. This material was used as a biosorbent in various removal processes of pollutants, and its efficiency was strongly influenced by the characteristics of the biomass feedstock. This review integrates the recent works of literature to understand the biosorption behaviour of dyes onto biochar-based biosorbents. The factors influencing the biosorption process and the mechanisms describing the biosorption behaviours of the biochar have been broadly reviewed. Furthermore, the biosorption models can be used to comprehend the competence of the biochar as biosorbent for dye removal techniques. Graphical Abstract

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In this work, non-living red seaweed (Kappaphycus alvarezii) biomass was investigated as a new biosorbent of methylene blue from aqueous solution. The effect of operational parameters such as equilibrium pH, agitation time, initial dye concentrations and biosorbent dosage on the biosorption capacity of Kappaphycus alvarezii was studied. The equilibrium solution pH was found to profoundly affected methylene blue sorption capacity of Kappaphycus alvarezii with pH 8 found to be optimum. Evidence from Fourier-transform infrared spectroscopy and scanning electron microscopy pictures confirmed the dye biosorption mechanism as electrostatic interaction between the negatively charged seaweed surface and positively charged methylene blue. Biosorption isotherms indicated that Kappaphycus alvarezii exhibited methylene blue uptake of 74.4 mg/g, according to the Langmuir model. The equilibrium isotherm data were evaluated using the Freundlich, Langmuir, Redlich-Peterson and Toth models. Kinetic studies revealed that methylene blue uptake was fast with 97% or more of the uptake occurred within 60 Downloaded by [University of Cincinnati Libraries] at 21:26 03 January 2015A c c e p t e d M a n u s c r i p t 2 min of contact time. The pseudo first and second order models were applied to describe kinetic data, of which the pseudo-first order described experimental data better with high correlation coefficient and low percentage of error values.

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