Sustainable synthesis of graphene sand composite from waste cooking oil for dye removal.

Waste cooking oil (WCO) appears to be a potential carbonaceous source for synthesizing graphene sand composite (GSC) adsorbent in removing pollutants. This study presents a green synthesis method of GSC using WCO as a sustainable carbon source for the synthesis of GSC through the thermal graphitization method. Characterization analysis conducted on GSC _WCO verified the successful coating of WCO onto the sand surface and conversion to graphene, which possessed distinct functional groups and features of graphene materials. GSC _WCO adsorbent effectiveness in removing Congo Red dye through batch adsorption was studied under the influence of different initial concentrations (20 to 100 mg/L), and the optimum pH (pH 2 to 10), contact time (5 to 240 min), and temperature (25 to 45 °C) were investigated. The GSC _WCO showed removal rates of 91.5% achieved at an initial dye concentration of 20 mg L ^-1 , 1.0 g of adsorbent dosage, a temperature of 25 °C, and 150 min of contact time. The GSC _WCO exhibited a maximum capacity of 5.52 mg g ^-1 , was well-fitted to the Freundlich isotherm model with an R ² value of 0.989 and had an adsorption mechanism that followed the pseudo-second-order kinetic model. Negative values of enthalpy (ΔH) and Gibbs free energy (ΔG) revealed that CR adsorption onto GSC _WCO was a spontaneous and exothermic process. The presence of functional groups on the surface of GSC _WCO with such interactions (π-π attractive forces, hydrophobic forces, and hydrogen bonding) was responsible for the anionic dye removal. Regeneration of GSC _WCO adsorbent declined after four cycles, possibly due to the chemisorption of dyes with GSC that resulted in inefficient adsorption. Being a waste-to-wealth product, GSC _WCO possessed great potential to be used for water treatment and simultaneously benefited the environment through the effort to reduce the excessive discharge of WCO.
(© 2023. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.)