Novel thiol-grafted composite of chitosan and rice straw biochar (TH@CT-BC): A two-step fabrication for highly selective adsorption of cadmium from contaminated water

This study followed the one-step and two-step technologies to produce rice straw biochar (BC), chitosan-modified rice straw biochar (CT-BC), and thiol grafted chitosan-modified biochar (TH@CT-BC) for cadmium (Cd) removal from contaminated water. Here, chitosan and thiol were introduced by two-step combination to enhance the adsorption ability of biochar. Our results revealed the maximum Cd adsorption at pH 5.5 with TH@CT-BC (261.47 mg g⁻¹) followed by CT-BC (103.14 mg g⁻¹) and BC (29.64 mg g⁻¹). Obtained data was best fitted by the Langmuir and pseudo-second-order kinetic models (with R² values of 0.997 for TH@CT-BC) as compared to Freundlich and Temkin models (0.949 and 0.925, respectively). TH@CT-BC retained its efficiency in spiked river water system, removing up to 89% of Cd in river water spiked with 30 mg⁻¹ L Cd. The experimental investigations and data calculations demonstrated the surface complexation and electrostatic interaction as dominant underlying mechanisms for Cd removal by TH@CT-BC. Moreover, it is essential to utilize the large amount of produced rice straw to develop new materials which would help in converting the waste to useable product for environmental remediation. Thus, this study demonstrates the production of TH@CT-BC from rice straw as an effective adsorbent of Cd from aqueous systems which can be studied as a potential candidate for practical wastewater treatment applications.