Cheap Nano-Adsorbents Based on Zno/Mineral Nanocomposites for Removal of Chloroform from Water Solution

Background: Chloroform, as a hazardous chemical, can contaminate water resources via the reaction of chlorine as an antiseptic chemical with humic acids resulted from agricultural activities. In humans, chloroform may cause dizziness, heart disorders, and disorders of the nervous system. Hence, its removal is of crucial importance. Objectives: The current study aimed to propose cheap and efficient adsorbents to remove chloroform from water. Methods: Four different nanomaterials (ZnO, ZnO/graphene oxide (ZnO/GO), ZnO/GO/Zeolite, and GO/Zeolite nanocomposites) were prepared and characterized with X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) images. Textural properties of the nano- adsorbents were evaluated using Brunauer Emmet Teller (BET) and Barrett-Joyner-Halenda (BJH) techniques. Different isotherms and kinetic models were studied. The effect of pH on the removal efficiency of the nano-adsorbents was tested. Regenerability of the nano-adsorbents towards the removal of the chloroform was also evaluated. Results: XRD patterns and FESEM images of the nanocomposites confirmed lattice structures and nanoscale particle size of the prepared nanocomposites. According to the BET and BJH models, all samples had mesoporous structures. The BJH cumulative surface area of pores of ZnO, ZnO/GO, ZnO/GO/Zeolite, and GO/Zeolite nanocomposites were 8.5, 26.4, 17.2, and 20.8 m2/g, respectively. The best removal speed and efficiency were obtained according to the different isotherm and kinetic models for the removal of chloroform ZnO/GO nanocomposites. All adsorbents revealed characteristic adsorption in the pH range of 7 to 8. Conclusion: The ZnO/GO, a cheap and efficient nanocomposite, showed the best performance to remove chloroform from water samples due to its superior textural property. Hence, it can be used to remove chloroform from water for up to 5 cycles.

Essesment of IM-50 and TOFA Adsorbed Layer on Cassiterite in Flotation of Tin Sulfide Wastes

The paper presents the results of experimental study of the adsorption characteristic of theIM-50 and tall oil fatty acids (TOFA) collector reagents on cassiterite. UV-spectrophotometric method, scanning electron and lasermicroscopy were applied to analyze the adsorption of the reagents. SHIMADZU UV 1800 was used to obtain the UV spectra of aqueous solutions of IM-50 reagents and saponified TOFA at varied concentrations. IM-50 has not got characteristic adsorption maximain ultraviolet and visible spectrum. TOFA has a weakly pronounced maximum absorption in the range of 233-244 nm. Microscopicphotographs of cassiterite sections were obtained with LEO 1420VP INCA equipped OXFORD ENERGY 350 analyzer. Reagent IM-50and TOFA collector reagent, Newly formed organic matter phases of IM-50 and TOFA were detected. X-ray spectra characterized theincreased carbon content indicating adsorption on the surface of cassiterite IM-5- and TOFA.By measuring the surface relief parameters of polished cassiterite, using KEYENCE VK-9700 scanning laser microscopy and VK-Analyzer software, a qualitative and quantitative assessment of the IM-50 and TOFA reagent layer on the cassiterite surface was performed. Measurements were performed in the several fields of view and showed the degree of IM-50 coating varied from 40.5 to 42.6%of the surface area, and TOFA average coating was 38.5%. Subsequent washing with water does not remove the reagents from thesurface of the mineral and indicates a strong fixation of IM-50 and TOFA on cassiterite, which can have a positive effect on flotationextraction of sludge tin fractions.Qualitative and quantitative results of the reagent adsorption helped to make a forecast of their floatability by the studied collectors.This study is supported by the Russian Science Foundation (project No. 17-17-01292).

Tailoring Adsorption Induced Switchability of a Pillared Layer MOF by Crystal Size Engineering

The pillared layer framework DUT-8(Zn) (Zn₂(2,6-ndc)₂(dabco), 2,6-ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane, DUT = Dresden University of Technology) is a prototypical switchable MOF, showing characteristic adsorption and desorption induced open phase (<i>op</i>) to closed phase (<i>cp</i>) transformation associated with huge changes in cell volume. We demonstrate switchability strongly depends on a framework-specific critical particle size (d<i>_crit</i>). The solvent removal process (pore desolvation stress contracting the framework) significantly controls the <i>cp</i>/<i>op</i> ratio after desolvation and, subsequently, the adsorption induced switchability characteristics of the system. After desolvation, the dense <i>cp</i> phase of DUT-8(Zn) shows no adsorption-induced reopening and therefore is non-porous for N₂ at 77 K and CO₂ at 195 K. However, polar molecules with a higher adsorption enthalpy, such as the polar molecules such as chloromethane at 249 K and dichloromethane (DCM) at 298 K can reopen the macro-sized crystals upon adsorption. For macro-sized particles, the outer surface energy is negligible and only the type of metal (Zn, Co, Ni) controls the DCM-induced gate opening pressure. The framework stiffness increases from Zn to Ni as confirmed by DFT calculations, X-ray crystal structural analyses, and low frequency Raman spectroscopy. The partial disintegration of the Zn based node hinges produces an overall increased stabilization of<i> cp </i>vs. <i>op</i> phase shifts the critical particle size at which switchability starts to become suppressed to even lower values (d<i>_crit</i> < 200 nm) as compared to the Ni-based system (<i>d_crit</i> ≈ 500 nm). Hence, the three factors affecting switchability (energetics of the empty host, (<i>E_op-E_cp</i>) (I), particle size (II), and desolvation stress (III)) appear to be of the same order of magnitude and should be considered collectively, not individually.

Tailoring Adsorption Induced Switchability of a Pillared Layer MOF by Crystal Size Engineering

The pillared layer framework DUT-8(Zn) (Zn₂(2,6-ndc)₂(dabco), 2,6-ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane, DUT = Dresden University of Technology) is a prototypical switchable MOF, showing characteristic adsorption and desorption induced open phase (<i>op</i>) to closed phase (<i>cp</i>) transformation associated with huge changes in cell volume. We demonstrate switchability strongly depends on a framework-specific critical particle size (d<i>_crit</i>). The solvent removal process (pore desolvation stress contracting the framework) significantly controls the <i>cp</i>/<i>op</i> ratio after desolvation and, subsequently, the adsorption induced switchability characteristics of the system. After desolvation, the dense <i>cp</i> phase of DUT-8(Zn) shows no adsorption-induced reopening and therefore is non-porous for N₂ at 77 K and CO₂ at 195 K. However, polar molecules with a higher adsorption enthalpy, such as the polar molecules such as chloromethane at 249 K and dichloromethane (DCM) at 298 K can reopen the macro-sized crystals upon adsorption. For macro-sized particles, the outer surface energy is negligible and only the type of metal (Zn, Co, Ni) controls the DCM-induced gate opening pressure. The framework stiffness increases from Zn to Ni as confirmed by DFT calculations, X-ray crystal structural analyses, and low frequency Raman spectroscopy. The partial disintegration of the Zn based node hinges produces an overall increased stabilization of<i> cp </i>vs. <i>op</i> phase shifts the critical particle size at which switchability starts to become suppressed to even lower values (d<i>_crit</i> < 200 nm) as compared to the Ni-based system (<i>d_crit</i> ≈ 500 nm). Hence, the three factors affecting switchability (energetics of the empty host, (<i>E_op-E_cp</i>) (I), particle size (II), and desolvation stress (III)) appear to be of the same order of magnitude and should be considered collectively, not individually.

Adsorption Properties of Surface Modified Carbons with Metal Nanoparticles

The effect of surface modification by nanoparticles of metal compounds was investigated by means of gas and vapor adsorption analysis. The surface of activated carbon fiber cloths was modified by loading of Li2CO3 and MgO nanoparticles. The particles on the carbon surface played as initial adsorption site of water molecules, leading to the promotion of micropore filling without diminishing the micropore volume of the porous carbon supports. The increasing characteristic adsorption energy suggested some interaction between methane molecules and the particles.