Effective adsorption of direct Red 23 by sludge biochar-based adsorbent: adsorption kinetics, thermodynamics and mechanisms study

Using solid adsorbents, such as biochar, has been a potential practice to remove the pollutants from water bodies to render the water safer for potential usage. A potential application of sludge biochar-based adsorbent (SBA) obtained by pyrolysis with hydrothermal treatment was developed to adsorb Direct Red 23 (DR23) from wastewater. The results showed that the synthesized SBA (0.5 g/L) in the adsorption of DR23 at low concentration (<20 mg/L), the DR23 were totally removed from the aqueous solution. PH had a limited effect on the adsorption, while an increase in temperature was shown to have a large enhancing effect. The adsorption kinetics were the best fit by the pseudo-second-order kinetic model, while the equilibrium data were best fitted by the Langmuir isotherm. A maximum saturation adsorption capacity of SBA of 111.98 mg/g was achieved. SBA could then be regenerated by pyrolysis, and after three cycles, SBA still retained the good adsorption ability of DR23, a removal rate exceeding 97% was achieved. Functional groups, pores, pi-pi bond, and electrostatic interactions are the key to the adsorption mechanisms. The results proved that SBA would be a promising material in the removal application of dyes in printing and dyeing wastewater.

Automated summary

The use of modified biochar (SBA) has shown great potential in adsorbing dyes from wastewater, achieving a removal rate exceeding 97%. Higher temperature significantly enhances the adsorption effect, with adsorption kinetics following the pseudo-second-order model and equilibrium data fitting the Langmuir isotherm.