Synthesis and Characterization of Water Stable Polymeric Metallo Organic Composites for Purification of Brackish Water

Abstract

Highly water stable new series of polymeric metallo-organic composites (PMOCs) were successfully synthesized at ambient temperature. The physico-chemical properties of MOFs and polymeric composites were elucidated using various advanced spectroscopic techniques such as BET, XRD, SEM, FTIR and AAS. Maximum porosities values were exhibited by IM based Co-MOF, IM based Zn MOF, CA based Co-MOF and IM based Co-PMOC as 1889 m 2 /g, 1370 m 2 /g, 575 m 2 /g and 798 m 2 /g respectively. Powder XRD and SEM were used to explain the crystallinity and morphology. IM based Co-MOF and IM based Zn-MOF exhibited cubic while CA based Co-MOF and PANI showed layered geometries. IM based Co PMOC displayed exfoliated layers which enhanced porosity character. Interactions of heavy metals before and after adsorption were explained on the basis of FTIR. FTIR spectra showed the presence of heavy metals after adsorption interactions at values like 3749 cm -1 and 821 cm -1 for arsenic 3648 cm-1 and 932 cm-1 for lead, 3629 cm-1 and 749 cm-1 for mercury metal ions ligation from brackish water. Several factors like pH, conc. and contact time, quantity of adsorbate and adsorbent and effect of anionic strength were also studied. Adsorption analysis including kinetic and isotherms were also investigated. Pseudo 1st and 2nd order equations, Freundlich and Langmuir Models were applied for adsorptive removal of heavy metals from brackish water. The maximum adsorption capacities using MOFs and PMOCs were 1978.63 mg/g, 1436.11 mg/g, 1271.92 mg/g, 157.11 mg/g for Pb2+, Hg2+, As3+ and As5+ respectively. Malachite green (MG), methylene blue (MB) and methyl orange (MO) were also studied that represented maximum adsorption capacities 15610 mg/g, 14721 mg/g and 5083 mg/g respectively. For the adsorptive removal of heavy metals and azo/organic dyes Pseudo second order and Langmuir Model were well-fitted as determined by kinetic/isothermal investigation. Moreover to appraise the ratio for regeneration, four adsorption and desorption cycles were also conducted out which unveiled up to 96 % adsorption capacities for these metals and dyes. In particular recycling adsorption and comparative investigation of our composites as adsorbent disclosed outstanding stability which point out towards a huge development prospective of the composites in adsorbing heavy metals from waste and brackish water that established the number of porosity which increases adsorption capacity for elimination of heavy metal ions etc. xvi Furthermore fifty samples of brackish water were collected from different areas of Bahawalpur (BWP) and stored at room temperature for further studies having pH, TDS, EC and turbidity in the range of 6.8-7.3, 350-2175 ppm, 1421-1937 µS/cm and 6-10 NTU respectively. Out of these fifty samples 11 samples having higher TDS values were treated with MOFs and composites. Using adsorption method, samples having TDS values more than 600 ppm, these samples TDS value reduces to 210 for samples having TDS 600-800 ppm while samples having TDS value more than 1500 ppm when treated they showed 570 ppm TDS value but when again treated their TDS value further reduced to 250 ppm which is according to standard values as recommended by WHO (600 ppm). EC values were obtained after treatment 421 – 1173 µS/cm (WHO = max 2500), turbidity values were dropped to almost zero (WHO = max 5 NTU) and hardness of these samples were reduced to calcium = 132 and magnesium = 239 ppm (WHO = 300 max). Other ions like iron, chloride and sodium were 0.009, 35 and 38 ppm respectively. Maximum potential shown by these MOFs and composites is given as: CA based Co-PMOC > IM based Zn-PMOC > IM based Co-PMOC > IM based Zn-MOF > IM based Co MOF > CA based Co-MOF > Morpholine based Co-MOF > Morpholine based Co PMOC. Furthermore all heavy metals like lead, arsenic, mercury, cadmium were also decreased to WHO recommended values (Pb = 0-15 µg/L, Hg = 1-10 µg/L and As = 10 ppb) while before adsorption these values were more than recommended values (RV) which represented that these MOFs and PMOCs are very effective for purification of brackish water. From these outcomes it was proved that these MOFs and PMOCs can be effectively used for purification of brackish water as well as confiscation of heavy metals like arsenite, arsenate, lead, mercury, calcium, magnesium, chlorides and cadmium ions from brackish water as well as from polluted water.