Search

The purpose of the work is to establish the possibility of obtaining expanded graphite of high purity (carbon content more than 99.5 % wt.) from flotation-enriched graphite (carbon content 94–97 % wt.) by combining into one process intercalation of graphite with a solution of potassium dichromate in concentrated sulfuric acid with subsequent hydrolysis, and chemical purification using solutions of ammonium bifluoride in sulfuric or hydrochloric acid and Trilon B in an alkaline buffer as purification reagents, and to confirm this possibility by quantum chemical calculations. It has been experimentally shown that combining oxidized graphite synthesis and its chemical purification into one process allows obtaining expanded graphite of high purity, with a carbon content of 99.75–99.85 % wt. The methods of X-ray diffraction and thermogravimetry show that the interaction of oxidized graphite (the residual compound of intercalation of graphite with sulfuric acid) with cleaning reagents does not reduce the ability to expand. The magnitude of the mass loss of oxidized graphite according to various variants of chemical post-cleaning and the temperature range of such loss remain practically unchanged. Quantum chemical calculations of the adsorption energy (∆Eads) of one molecule of Trilon B on the surface of a graphene-like plane (GLP), the complexation reaction of metal sulfates, the energy effect of the interaction of Trilon B with sulfates of alkaline earth metals in an aqueous solution, and with the participation of the surface of the graphene plane were carried out using the GAMESS (US) program by the density functional theory (DFT) method with the B3LYP functional and the 6-31G(d,p) basis set, taking into account the Grimme D3 dispersion correction within the PCM polarizable continuum. The results of the analysis of quantum chemical calculations indicate that the Trilon B molecule is better physically sorbed on the oxidized GLP (–412 kJ/mol) than on its native form (–188 kJ/mol). The values of the energy effect of the complexation of magnesium and calcium cations with Trilon B have a negative value both in an aqueous solution and in the presence of the oxidized form of GLP. This indicates the thermodynamic probability of this process, which is consistent with the experimental results. Regardless of the nature of the cation, its interaction with Trilon B is thermodynamically more likely in an aqueous solution than in the adsorbed state on the surface of oxidized GLP. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) have been widely employed for metal ion adsorption owing to their inherent advantages, encompassing low crystal density, well-organized organic unit structures, adjustable pore size, and remarkable structural stability. However, it is still a great challenge to design excellent COFs with high adsorption and advanced purification capabilities for Pb2+ and Cd2+ ions. Herein, hydrazine-linked COFs (COF-TCH) were prepared for effective adsorption and advanced purification of metal ions. The adsorption capacity of COF-TCH for Pb2+ and Cd2+ ions are 395.3 and 153.5 mg/g, respectively. Moreover, the Pb2+ and Cd2+ ions in water can be treated from 75 and 30 mg L−1 to less than 0.01 and 0.003 mg L−1, respectively, indicating the excellent adsorption and advanced purification capability of COF-TCH. This is a rare example of COFs adsorbent that deeply purify water to meet the guideline values in drinking water for the World Health Organization. FT-IR, XPS and quantum mechanics calculation were performed to understand the adsorption mechanism. The remarkable adsorption and advanced purification capability of COF-TCH for Pb2+ and Cd2+ ions can be attributed to the synergistic interaction between the amine and thione groups, which can easily complex with Pb2+ and Cd2+ ions to form stable five-membered ring structure in COF-TCH. In addition, COF-TCH still remains an adsorption capacity of over 90% after ten adsorption-desorption cycles, indicating its excellent reusability and stability. COF-TCH with high adsorption and advanced purification capability, high stability, low cost and reusability has enormous practical application potential in high-performance remediation of Pb2+ and Cd2+ contaminated water. [Display omitted] [ABSTRACT FROM AUTHOR]

Biogas, a sustainable energy source, is hampered by CO 2 and N 2. Commercially purifying it to biomethane involves pressure or vacuum swing adsorption. The efficiency and cost-effectiveness of these techniques pivot on the adsorption selectivity of the employed adsorbent material. This study examined the impact of varying metal/clay ratios in porous aluminium pillared clays on adsorption selectivity. Characterization techniques, including nitrogen adsorption/desorption, XRD, FTIR, SEM, and Raman spectroscopy, were employed. High-pressure adsorption capacity for CO 2 , CH 4 , and N 2 was investigated up to 1000 kPa. Selectivity for CO 2 /CH 4 , CO 2 /N 2 , and CH 4 /N 2 binary mixtures was calculated using IAST. Results indicate that changing the metal/clay ratio altered physiochemical properties, enhancing adsorption capacity and selectivity. AlPILC-4 demonstrated maximum surface area (158 m2∙g-1) and adsorption capacity (0.35–1.13 mmol∙g-1) for all gases, while AlPILC-2 exhibited the highest selectivity (11.85–1.85) at 100 kPa. The decrease in the surface area at higher metal/clay ratio apprehends to the saturation of swelling capacity of the parent clay. However, increase in the competitive adsorption with surface area resulted in a decrease in the selectivity of the samples. Working capacity of the modified samples calculated at two different regeneration pressures (100 kPa and 0.133 kPa) help comprehend the cost layout and efficiency of the prepared materials. Notably, the results mirrored the trends observed in adsorption capacity, with values nearly 200 % higher than those of the parent clay. [Display omitted] • Aluminium PILCs with varying metal/clay ratio were prepared. • Solid-gas interaction dominates at lower pressure conditions, whereas, gas-gas interaction predominates at higher pressure. • Highest CO 2 adsorption capacity was shown by AlPILC with 4 mmol/g metal to clay ratio. • Samples with lowest metal/clay ratio shows highest selective for all the three binary mixtures. [ABSTRACT FROM AUTHOR]