Phosphoramidic acid functionalized silica microspheres for simultaneous removal of Cr(VI), As(V) and Se(VI) from aqueous solutions based on molecular geometry match

The phosphoramidic acid functionalized silica (SiO2@NH2@H2PO3) were successfully synthesized to remove chromate (Cr(VI)), arsenate (As(V)), and selenate (Se(VI)) from aqueous solutions based on the molecular geometry of phosphoramidic acid is complementary to the target oxoanions shape and coordination geometry. The adsorption equilibration can be reached within 10 min. The maximum adsorption capacities of Cr(VI), As(V), and Se(VI) by SiO2@NH2@H2PO3 were 29.7, 25.6, and 38.8 mg/g, respectively. SiO2@NH2@H2PO3 is capable of removing Cr(VI), As(V) and Se(VI) in source water from 1 mg/L to 35, 584, and 94 mu g/L, where the residual of Cr(VI) and Se(VI) was well below the discharge standard of total Cr and Se (< 100 mu g/L) for municipal wastewater treatment plant in China. The reusability test showed that SiO2@NH2@H2PO3 can be successfully regenerated and reused. The analysis of pH effect, FT-IR and X-ray photoelectron spectroscopy demonstrated that removal of Cr(VI) and Se(VI) was mainly attributed to the formation of OP-O-Cr and OP-O-Se. The removal of As(V) was mainly ascribed to the formation of hydrogen bond with As(V). These results indicated that SiO2@NH2@H2PO3 could be a promising adsorbent in removal of Cr(VI) and Se(VI) from aqueous solutions, and the relatively low removal of As(V) warranting further design of adsorbents are needed.