The extent of change in the physicochemical characteristics and pollutants sequestration of date palm stones after microemulsion modification

Date palm stones (DPS) can be used as inexpensive adsorbents, which are inferior to commercial activated carbons, but their potential low cost makes them competitive. The promising microemulsion modification process has the potential to improve the adsorption performance of DPS. In this study, the extent of change in the physicochemical properties of DPS due to the microemulsion modification and the removal of methylene blue (MB) and hexavalent chromium Cr(VI) have been investigated. Fourier transform infrared (FTIR) analysis showed that DPS surface contains non-polar/hydrophobic and polar/hydrophilic functional groups, whilst the microemulsion attachment to DPS surface is either by its hydrophilic or by its hydrophobic part. The microemulsion modification increased the basicity of the surface, causing an increase in the zero point of charge (pH_ZPC) and significantly reduced the surface area and total pore volume of DPS. The sequestration of MB and Cr(VI) from aqueous solutions by DPS and microemulsion-modified DPS (MDPS) showed that the solution pH had the most noticed effect on Cr(VI) removal. The sequestration of MB by DPS was endothermic but changed to exothermic after modification, whilst the sequestration of Cr(VI) by both solid adsorbents was endothermic. The sequestration capacity of MB was higher but lower for Cr(VI) by MDPS compared with DPS. Overall, microemulsion modification of DPS had changed their physicochemical properties and altered their capacity of sequestrating different pollutants from aqueous solutions.