SYNTHESIS AND CHARACTERIZATION OF FUNCTIONALIZED SILICA FOR ADSORPTION OF PHOSPHATE AND NITRITE IONS IN WETLAND WATERS

Abstract

Quality and functions of wetlands have been affected adversely by factors such as deforestation, fertilizers, and pesticides. Pollution by nitrites and phosphates affect aquatic life as these anions have serious side effects even at low levels. Wetlands play a vital role as a supply of water for domestic and farming. Pollution in wetlands leads to eutrophication, reduce dissolved oxygen among others. These objectives of this project was to prepare and characterize silica molybdate and diazonium silica adsorbents; determine optimal conditions for adsorption of PO4 3- and NO2 - fromwater; determine the adsorption capacity, kinetics and thermodynamic parameters; compare adsorption capacities with activated carbon and examine the adsorption efficiency of the adsorbents in wetland waters. Silica based adsorbents were prepared by chlorination of raw silica followed by amination using ethylenediamine (EDA). Silica molybdate adsorbent was-prepared by adding sodium molybdate to aminated silica. Diazonium silica was prepared by reacting aminated silica with sodium nitrite. Adsorbents were characterized using FT-IR. Adsorption optimization was carried out by varying pH, temperature, contact time and initial concentration. Levels of PO4 3- and NO2 - ionson water samples were determined using UV-visible spectrophotometer. The adsorption capacities of the adsorbents were compared with activated carbon. The adsorbents were used to remove PO4 3- and NO2 - ions from water collected from wetlands. FT-IR results showed adsorption bands at 854cm-1 and 542cm-1 attributed to Mo=O and Mo-O stretching in molybdate. Diazonium silica showed a spectra band at 1587 cm-1 assign to open chain azo (N=N) group. Optimum pH for biosorption of PO4 2- was 6.0 and NO2 - was 3.0. Optimal contact time for PO4 3- and NO2 - was 60 minutes, optimum temperature for PO4 2- was 45℃ and that of NO2 - was 30℃. Biosorption isotherm fitted well in Freundlich isotherm model for adsorption of phosphates. For adsorption of nitrites biosorption isotherm fitted well in Langmuir model. For sorption of phosphates pseudo-first order kinetics model was best obeyed while for adsorption of nitrites pseudo-second order kinetic model was best obeyed. Thermodynamic parameters revealed that the sorption of phosphates was endothermic and for nitrites was exothermic. Adsorption capacity of phosphate was 194.53mg/g and 6.892 mg/g for nitrites as compared to activated carbon which was 8.241 mg/g for phosphates and 0.07985 mg/g for nitrites. Results obtained indicate that silica molybdate and diazonium silica are better adsorbents as compared to activated carbon. Adsorption efficiency of silica molybdate was 94.72% and diazonium silica was 50.2% compared to raw silica which was 10% for both phosphates and nitrites. Adsorption efficiency of phosphates and nitrites in wetland waters, were 55.9% for phosphates and 44.7% for nitrites. The study revealed that prepared adsorbents are efficient adsorbents for removal of phosphates and nitrites ion in wetland waters.