Adsorption behavior of Congo red on a carbon material based on humic acid

Abstract

In this study, a carbon composite based on humic acid (CAH) was synthesized by partially carbonizing humic acid using aluminum sulfate with a mass ratio of 2 : 3 and a leavening agent oxalic acid with a fixed mass. The morphology and microstructure of the sample were characterized using a scanning electron microscope and a transmission electron microscope, and the composition and structure of the material were analyzed using an X-ray diffractometer, a thermal analyzer, a Raman spectrometer, an X-ray photoelectron spectrometer and an infrared spectrometer. The BET surface area of CAH was determined to be 149 m² g⁻¹. Congo red was used as a model dye for adsorption research. When the Congo red concentration is 400 mg L⁻¹ and the amount of adsorbent is 10 mg, CAH displays the highest dye removal rate. The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetic data and the Langmuir and Freundlich models were applied to describe the adsorption isotherms. The results showed that the equilibrium adsorption data were found to fit better to the Langmuir adsorption model and the kinetic process of adsorption could be described using the pseudo-second-order model. Compared with humic acid, CAH composite materials can effectively improve the adsorption rate and adsorption capacity of Congo red, and the adsorption capacity is as high as 3986 mg g⁻¹ within 30 minutes. In addition, this study selected low-cost humic acid as the carbon source to prepare composite materials, which had the advantages of low cost and good adsorption.