The characterization of biochar obtained by pyrolysis of rice husk and investigation of its effectiveness in removal enviromental contaminants

In this study, the biochar product obtained as a result of the pyrolysis of rice husk (RHB) was chemically activated by using a basic activating agent (KOH). The activation process was carried out to increase the surface area of the RHB product and to obtain a more porous adsorbent (RHB-KOH). While the characterization of the raw rice husk was done by TGA and elemental analysis, the prepared RHB-KOH product was characterized by SEM, BET and FT-IR analyses. The BET surface area and pore volume of the RHB-KOH product were measured as 2,298 m2/g and 0.812 cm3/g, respectively. The CO2 adsorption capacity was determined using the thermogravimetric analysis method at 25 °C, and the maximum adsorption capacity was calculated as 152 mg/g. The high CO2 holding capacity obtained has shown that the prepared activated biochar product with a porous carbon skeleton structure is a low-cost and effective adsorbent that can be used for the removal of this gas that causes global climate change. The prepared activated biochar was also used for the removal of methyl red (MR) dyestuff from the aqueous solution and various working parameters such as pH, contact time, temperature, initial dyestuff concentration and adsorbent dose were optimized in the batch adsorption system. Optimum adsorption conditions for MR removal from aqueous solutions; pH = 6.0, T=25 °C, Co=50 mg/L and adsorbent dosage was determined as 0.1 g/250 mL solution. Under these conditions, the maximum equilibrium adsorption capacity value reached in 140 minutes was 62.06 mg/g, and the maximum MR removal efficiency was calculated as 99.31%. Freundlich, Langmuir and Temkin adsorption models were used for the mathematical description of the adsorption equilibrium. Experimental data showed the best compatibility with the Temkin isotherm model. In order to examine the adsorption kinetics, adsorption models based on the assumption of the mechanisms of pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models were applied to the experimental data. The kinetic data fit better with the pseudo-second-order kinetic model. The calculated thermodynamic parameters showed the spontaneous, exothermic and incremental random nature of the methyl red adsorption.