The potential application of biochars for dyes with an emphasis on azo dyes: Analysis through an experimental case study utilizing fruit-derived biochar for the abatement of Congo red as the model pollutant

The unbridled industrialization and unrestrained expansion of modern textile facilities combined with a deficiency of adequate treatment provisions have escalated the discharge of toxic effluents rich in carcinogenic pollutants such as dyes. As a consequence, there is an alarming need for the development of financially suitable and highly efficient treatment options to protect the immaculate ecosystems, natural resources, and human health. In this respect, adsorption-based treatment options have attracted widespread attention as eco-friendly and cost-effective approach. Biochar has propelled itself to the forefront of the scientific community as a highly economical sorbent with great adsorption capabilities. Notably, biochars provide a win-win strategy by simultaneously utilizing the waste biomass during its production and a great adsorbent for pollutant removal. Although biochars have been applied for the treatment of various dyes, there have been very few reports of its application for Congo red (CR) dye. In this book chapter we analyze the application of biochar for dyes with particular focus on CR. We try to practically understand the mechanism of interaction between biochar and CR molecules (a model anionic azo dye) by elucidating an experimental case study. The case study will provide valuable insights into the importance of the utilization of locally available bio waste for economic biochar production and the mechanism of removal of anionic dyes through biochars. In brief, the adsorptive removal of CR was investigated using Arjun fruit biochar (AFB) derived from the fruit of locally grown Terminalia arjuna. The sorptive removal of CR on AFB was investigated under the following operational conditions (pH, 2–12; biochar dosage, 4–14 g/L; temperature, 30–60 °C; and contact time, 30–480 min). The sorption behavior of CR was well described through the Langmuir monolayer model (R² = 0.9985) and pseudo-second order kinetics (R² ≥ 0.9977) for all tested CR levels (20–100 mg/L). The results of thermodynamic analysis revealed that the sorption of CR onto AFB proceeded favorably and spontaneously. Copyright © 2020 Springer Nature Switzerland AG.