Amine-modified mesoporous silica for quantitative adsorption and release of hydroxytyrosol and other phenolic compounds from olive mill wastewater

•Solid phase extraction was used to recover phenolic compounds from olive mill wastewater.•Activated carbon adsorbed 87% of total phenols versus 67-75% for triamine-grafted mesoporous silicas.•Quantitative adsorption and recovery of hydroxytyrosol was achieved over triamine-grafted SBA-15.•The adsorption performance did not change over adsorption-regeneration cycling.

A series of synthesized and commercial adsorbents were used for the treatment of olive mill wastewater (OMW). SBA-15 and P-10 silicas functionalized by post-synthesis grafting with 3-trimethoxysilylpropyl diethylenetriamine (TRI) and commercially available activated carbon (AC) were used for the removal and recovery of phenolic compounds from actual olive mill wastewater. Using UV spectrophotometric and HPLC analyses, the concentrations of total phenols, hydroxytyrosol and tyrosol in OMW were found to be 8.21 g L-1, 2.14 g L-1 and 0.50 g L-1, respectively. The recovery of phenolic compounds after adsorption was performed by solvent extraction using 0.1 M HCl in ethanol. Under otherwise the same conditions, all three adsorbents removed hydroxytyrosol quantitatively, but activated carbon showed the highest uptake of total phenols, i.e. 87% versus 75% and 67% for TRI-SBA-15 and TRI-P-10. The overall efficiencies for adsorption and recovery of hydroxytyrosol were 100%, 91% and 37% for TRI-SBA-15, TRI-P-10 and AC, respectively. Recycling experiments revealed that no loss of efficiency occurred after three consecutive adsorption-regeneration cycles. Furthermore, triamine-functionalized SBA-15 gave the highest discoloration percentage of 61% compared to the other materials.

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