Enhanced & effective phosphate recovery from water by indium fumarate & zirconium fumarate metal-organic frameworks: Synthesis, characterization, adsorption, kinetic and isotherm studies

Abstract

Eutrophication has been an important environmental issue for the last decade. Agricultural and industrial actions cause high concentrations of phosphate discharging to surface and ground waters, and high levels of phosphate concentration causes eutrophication. The decreasing of the phosphate concentration is an essential matter and adsorption is one of the most effective solutions for this purpose. In this study, indium fumarate (In-fum) and zirconium fumarate (Zr-fum) were prepared. Surface characterizations of these adsorbents were applied by XRD, FTIR, SEM, TGA, DSC, and BET surface analysis. The surface areas of In-fum and Zr-fum were determined as 181.19 m2/g and 527.96 m2/g, respectively. Water absorption abilities of adsorbents were tested by Karl-Fischer method. The water contents inside the pores of water-treated Zr-fum and In-fum are 0.0560% (w/w) and 0.0694% (w/w), respectively. Phosphate adsorption performances of In-fum and Zr-fum particles were studied by parametric research, investigating the effects of adsorbent quantity, contact time, solution pH, initial solution concentration, adsorption temperature, and co-existing ions. The phosphate adsorption uptake (qe) of Zr-fum is 33.52 mg/g and qe value of In-fum is 31.29 mg/g when adsorbent quantity is 1 mg. The kinetic studies reveal that both adsorbents follow pseudo second-order kinetic model according to the R2 values. These values are 0.93 for In-fum and 0.98 for Zr-fum. The rate constants are 0.15 g/mg min (In-fum) and 0.14 × 10−2 g/mg min (Zr-fum). Theoretical maximum phosphate adsorption uptake (qm) of In-fum is 93.40 mg/g at 318 K. The qm value of Zr-fum is 67.44 mg/g at 308 K. Phosphate adsorption over In-fum is strongly dependent on temperature change whereas the effect of temperature on adsorption performance of Zr-fum is insignificant. The pH of the phosphate solution should be below 7 to obtain an appropriate surface and phosphate ion charge combination. The presence of co-existing chloride ions does not dramatically affect phosphate adsorption capacity.