RESUMO
Considering the widespread production of Cr(vi) from various industrial processes and its damaging toxicity as a carcinogenic agent, it is imperative to investigate stable and efficient adsorbents with a rapid performance towards Cr(vi) adsorption. Zirconium-containing metal-organic frameworks (Zr-MOFs) have been recently used as environmentally friendly adsorbents for the reduction of metallic contaminants in aqueous media. Preparation from nontoxic metal sources, remarkable stabilities and distinguished physicochemical features, such as the high tendency of Zr-clusters to adsorb oxo-anions, beneficial structural defects, and modification of their properties via modulator synthesis, can be enumerated as the advantages of Zr-MOFs. In this study, we improved the adsorption capacity of UiO-66 as the most stable Zr-MOF for Cr(vi) adsorption from aqueous solutions through the gradual addition of an N-O functional group. This strategy ultimately led us to afford a new Zr-MOF structure (TMU-66) with a maximum Cr(vi) adsorption capacity of 60.241 mg g-1, which is 4 times the absorption capacity of UiO-66, and very fast kinetics (<3 min) that followed the pseudo-second-order kinetics. This study demonstrates that a conceptual design can be helpful in synthesizing safe and stable adsorbents with appropriate capacity and kinetics for adsorption.
RESUMO
Synthesis of new porous materials has been developed for efficient capture of pollutants in environmental sciences. Here, the application of a new metal-organic framework (TMU-30) has been reported based on isonicotinate N-oxide as an adsorptive site for fast and highly efficient aqueous phase adsorption of Cr(VI). The adsorption process showed no remarkable effect over a pH range of 2-9. The maximum capacity of the adsorption was reached in just less than 10 min and followed the pseudo-second-order kinetics. The maximum capacity of 2.86 mol mol(-1) (145 mg/g) was obtained according to Langmuir model at 298 K. The spontaneous adsorption and an endothermic process were controlled by positive entropy changes. XPS analysis revealed electrostatic interactions between N-oxide groups of TMU-30 and Cr(VI) species, which were responsible for the adsorption process.
RESUMO
Two new lead(II) mixed-ligand coordination polymers, [Pb(PNO)(SCN)]n (1) and [Pb(PNO)(N3)]n (2), (HPNO=picolinic acid N-oxide) were synthesized by a sonochemical method and characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analysis. Compounds 1 and 2 were structurally characterized by single crystal X-ray diffraction. The thermal behavior of 1 and 2 were studied by thermal gravimetric analysis. Structural transformations of compounds 1 and 2 were evaluated through anion-replacement processes by mechanochemical method. Moreover, the effect of sonication conditions including time, concentrations of initial reagents and power of irradiation were evaluated on size and morphology of compounds 1 and 2.
RESUMO
Nano-structured three-dimensional lead(II) coordination polymer, [Pb(µ(6)-Fum)](n) (1); {Fum=Fumarate}, has been synthesized by sonochemical method and characterized by scanning electron microscopy, X-ray powder diffraction, elemental analyses and IR spectroscopy. Solvent effects on size and morphology of nano-structured compound 1 have been studied. Calcination of the nano-sized compound 1 at 600°C under air atmosphere yields PbO nanoparticles. The thermal stability of compound 1 both its bulk and nano-size has been studied by thermal gravimetric (TG) and differential thermal (DTA) analyses and compared each other.
