SYNTHESIS OF EFFICIENT IRON (II) BASED METAL–ORGANIC FRAMEWORKS FOR REMOVAL OF FLUORIDE FROM WATER SAMPLE

ABSTRACT Water quality has an absolute influence on human health. High concentrations of fluoride in drinking water have a serious effect on human teeth and bones resulting in dental or skeletal fluorosis especially in the Rift Valley of Ethiopia region. The permissible limit of fluoride concentration in drinking water is 1.5 mg/L according to WHO guidelines. The various adsorbents such as, carbon based materials, biomass-based adsorbents, and synthetic compounds were attempting to keep up the standard limit of fluoride concentration in drinking water by adsorption method. Limitations of those adsorbents are the surface area is low, for this reason, the material becomes saturated wet quickly, poor physical integrity, needs pre treatment, lack of selectivity for fluoride and unwanted effects on water quality. Therefore, MOFs are a new class of metal-organic polymers which have an effective adsorbent of treatment technology for removal of fluoride in water samples due to its porosity nature, high surface area, tolerable charge characteristic and higher fluoride adsorption capacity. In this study synthesis of efficient iron (II) based metal–organic frameworks as an adsorbent for removal of fluoride from water sample prepared from reaction of ferrous sulfate heptahydrate as metallic cluster with oxalic acid as linker under hydrothermal conditions by adsorption method was investigated. The as synthesize Fe-Ox-MOF was characterized using iodine test, FTIR, and X-RD techniques. The fluoride removal efficiency of the Fe-Ox-MOF was determined for real water Samples which were collected in clean plastic bottles from Boricha district, sidama Zone by using grab sampling techniques. The effects of various experimental parameters such as adsorbent dose from (0.5 – 3 g/L), contact time (30 – 1440 min.), pH from (2 – 12), and initial fluoride concentration (5 – 30 mg/L) were studied by a series of batch adsorption experiments for fluoride removal from synthetic water sample at room temperature (25 ± 3 ºC). Real water samples were determined before and after treatment using ISE with initial fluoride concentration of 2.83 and 1.78 mg/L at adsorbent dose 0f 2 g/L, reported in a final concentration of both case 0.47 and 0.24 mg/L, the limit accepted by WHO. The removals of fluoride increased with increased adsorbent dose from (0.5 – 2 g/L) for a given initial fluoride concentration of 10 mg/L, whereas adsorbent dose increase from (2.5–3 g/L) removal efficiency was decreased with increasing initial concentration of fluoride. xvi The results showed that Fe-Ox-MOF, at an adsorbent dose of 2 g/L could remove 89.3 % of fluoride from an initial concentration of 10 mg/L within 360 minute and pH 7. Even though significant maximum fluoride adsorption was found in acidic range, at (pH = 2), the removal efficiency was 95.5% for adsorbents of 2 g/L from initial fluoride concentrations of 10 mg/L observation. At optimum conditions, the initial concentration of fluoride 5 mg/L, the removal efficiency was 91.5% of Fe-Ox-MOF, which is meet the standard. The equilibrium adsorption information is designed with two isotherm equations applicable to adsorption process. The removed Fe-Ox-MOF Langmuir isotherm having correlation coefficients (R2) equal to 0.9962 and 0.9638 for Freundlich isotherm, respectively. Langmuir isotherm was the better fitted for the adsorption of fluoride on Fe-Ox-MOF. Generally, from the study it was found that synthesis of iron (II) based metal-organic framework could be effectively, used to remove of fluoride into standard permissible limit.