Graphite-TiO2-doped coated sand granules for efficient continuous removal of methylene blue dye: Combining adsorption and photocatalytic degradation

This manuscript focuses on the development of coated sand granules, consisting of a thin layer of graphite doped with activated carbon (AC) and titanium oxide (TiO2) for continuous removal of methylene blue dye. The coating process was carrried out by using polyvinylpyrrolidone (PVP), AC and titanium isopropoxide (TiP). The graphitic surface was activated using 1.0 M KOH solution. Increasing the sand granules' weight from 5 to 10 g considerably enhanced adsorption capacity, with minimal improvements observed at 20 g. Calcination temperatures above 500 degrees C exhibited no significant impact on adsorption capacity, as samples prepared at 650 and 800 degrees C showed similar dye removal efficiency to the 500 degrees C sample. Increasing the amounts of TiP and PVP linearly improved adsorption capacity, albeit at a modest rate. The incoorporation of AC particles distinctly enhanced dye removal process, with the highest enhancement observed at 1 g AC content, further augmented by light irradiation. Flow rate studies revealed that maintaining a flow rate of 4 ml/min.cm2 resulted in continuous and stable removal (90 % removal for 90min). Increasing the flow rate to 8 ml/min.cm2 led to a linear reduction in removal rate (77 % removal after 90min), while a flow rate of 18 ml/min.cm2 showed an S-shaped adsorption isotherm, reaching 35 % removal after 90min.