(42c) Spray Dried Hollow Carbon Spheres from Lignin: Adsorption Kinetics and Thermodynamics Study for Highly Efficient Wastewater Treatment

In recent years, the interest in hollow carbon spheres (HCSs) has increased for various applications because of their unique physicochemical properties and structure. In this work, HCSs were synthesized by spray drying lignin-KOH solution. Spray drying is an environment-friendly and scalable fabrication technique that has given rise to great HCSs size and shape uniformity. The particle size and surface morphology were characterized using a particle size analyzer and a scanning electron microscope for HCSs from two different nozzle sizes. The surface area of the HCSs carbonized at temperatures ranging from 700 to 900 °C was found to be 1100 m² g^-1 – 1500 m² g^-1. We utilized the lignin-derived HCSs as an adsorbent for wastewater treatment. Methylene blue (MB) was chosen as the model dye to investigate the effect of time, temperature, and MB concentration on adsorption. The carbonization temperature was the main control factor to tune the adsorbent microstructure. The kinetics study showed that the adsorption process occurs rapidly, with more than 95% dye removal (initial MB concentration < 150 mg L^-1) by the HCSs in less than 5 minutes at room temperature, and the pseudo-second-order model explains the experimental data very well, especially at higher initial concentrations of MB. The adsorption isotherm analysis with the Redlich-Peterson model indicated that the maximum adsorption capacity was as high as 650 mg g^-1 at room temperature. The adsorption thermodynamics studies revealed that the adsorption of MB is endothermic (∆H = 30.4 kJ mol^-1) with higher adsorption capacity at higher temperatures. In addition to adsorption kinetics and thermodynamics investigation on lignin-derived HCSs, we designed and tested an HCS-coated nylon filter unit that can effectively remove MB from flowing water.