Mechanistic modeling of glyphosate interaction with rice husk derived engineered biochar

• Steam activated engineered biochar used for the first time on glyphosate removal.
• Glyphosate adsorption capacity decreased significantly with increasing pH.
• Both Freundlich and Langmuir models fitted best to the equilibrium isotherm data.
• Pore diffusion, H-bonding, donor–acceptor interactions were the mechanisms involved.

Biochar (BC), a carbon-rich solid product of biomass, and its surface activation via steam have been recognized as alternative economically viable strategy to decontaminate wastewaters. Existence of glyphosate, the most extensively used non-selective herbicide, in waters at elevated concentrations has received worldwide attention due to its ill consequences. The main objective of the present study was to investigate the potential of steam activated BC produced from rice husk (RHBC) via slow pyrolysis at 700 °C to remove glyphosate from aqueous solution. Batch adsorption experiments were carried out to evaluate the effects of pH, reaction time and glyphosate loading on the RHBC adsorption process. Results showed that a maximum removal of glyphosate (82.0%) occurred at pH 4, and the adsorption capacity decreased significantly with increasing pH. Both the Freundlich and Langmuir models fitted best to the equilibrium isotherm data suggesting physisorption as well as chemisorption mechanisms governing the glyphosate adsorption. The Langmuir maximum adsorption capacity was 123.03 mg/g. The kinetics of the adsorption process was well described by the pseudo-first order indicating that the glyphosate adsorption onto RHBC would be more inclined towards physisorption depending on the initial glyphosate concentration. Pore diffusion, π–π electron donor–acceptor interaction and H-bonding were postulated to be involved in physisorption, whereas electrophilic interactions led to chemisorption type of adsorption. Overall, steam activated RHBC could be a promising remedy of glyphosate removal from aqueous solution.

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