Theoretical Investigations on MIL-100(M) (M=Cr, Sc, Fe) with High Adsorption Selectivity for Nitrogen and Carbon Dioxide over Methane

The removal of impurity gases (N₂ , CO₂ ) in natural gas is critical to the efficient use of natural gas. In this work, the selective adsorption for N₂ and CO₂ over CH₄ on MIL-100 (M) (M=⁴ Cr, ¹⁰ Cr, ⁶ Fe, ¹ In, ¹ Sc, ³ V) is studied by density functional theory (DFT) calculations. The calculated adsorption energy of the large-size cluster model (LC) of MIL-100 (M) shows that the ⁴ MIL-100 (⁴ Cr) is the best at the refinement of natural gas due to the lower adsorption energy of CH₄ (-2.58 kJ/mol) in comparison with that of N₂ (-21.49 kJ/mol) and CO₂ (-23.82 kJ/mol). ¹ MIL-100 (¹ Sc) and ¹ MIL-100 (⁶ Fe) can also achieve selective adsorption and follows the order ⁴ MIL-100 (⁴ Cr)>¹ MIL-100 (¹ Sc)>¹ MIL-100 (⁶ Fe). In the research of the selective adsorption mechanism of MIL-100 (M) (M=⁴ Cr, ¹ Sc, ⁶ Fe), the independent gradient model (IGM) indicates that these outstanding adsorbents interact with CO₂ and N₂ mainly through the electrostatic attractive interaction, while the van der Walls interaction dominates in the interaction with CH_4. The atomic Projected Density of State (PDOS) further confirms that CH₄ contributes least to the intermolecular interaction than that of CO₂ and N₂ . Through the scrutiny of molecular orbitals, it is found that electrons transfer from the gas molecule to the metal site in the adsorption of CO₂ and N₂ . Not only does the type of the metallic orbitals, but also the delocalization of the involved orbitals determines the selective adsorption performance of MIL-100. Both Cr and Sc share their d z 2 ${{d}_{{z}^{2}}}$ orbitals with the gases, making ¹ MIL-100 (¹ Sc) another potential effective separator for CH₄ . Additionally, the comparison of adsorption energy and PDOS shows that the introduction of ligands such as benzene impedes the electron donation from gas molecules (CO₂ , N₂ ) to the metal site, indicating electron-withdrawing ligands will further favor the adsorption.

Carbon Nanostructures Doped with Transition Metals for Pollutant Gas Adsorption Systems

The adsorption of molecules usually increases capacity and/or strength with the doping of surfaces with transition metals; furthermore, carbon nanostructures, i.e., graphene, carbon nanotubes, fullerenes, graphdiyne, etc., have a large specific area for gas adsorption. This review focuses on the reports (experimental or theoretical) of systems using these structures decorated with transition metals for mainly pollutant molecules' adsorption. Furthermore, we aim to present the expanding application of nanomaterials on environmental problems, mainly over the last 10 years. We found a wide range of pollutant molecules investigated for adsorption in carbon nanostructures, including greenhouse gases, anticancer drugs, and chemical warfare agents, among many more.

Equilibria and Isosteric Heat of Adsorption of Methane on Activated Carbons Derived from South African Coal Discards

Isosteric heat of adsorption (H _st) is critical for evaluating the thermal effects of adsorption-based storage systems. Poor management of the thermal effects of an adsorptive storage system often alters the overall performance of the storage system. In this study, methane equilibrium uptake on activated carbons derived from coal discards and isosteric heat of adsorption were evaluated. The methane adsorption capacity of the produced activated carbons was measured using a high-pressure volumetric analyzer. The isotherm results in temperature ranges of 0-50 °C and pressure of up to 40 bar are analyzed using the Langmuir, Tóth, and Dubinin-Astakhov (DA) isotherm models. The results showed that, for the two activated carbons, the DA model was the best fit. In addition, we evaluated the isosteric heat of adsorption using two theoretical frameworks, Maxwell's thermodynamic relations and the modified Polanyi potential function. The Tóth potential function and Clausius-Clapeyron equations were applied to the Dubinin-Astakhov adsorption model to obtain an analytical expression of H _st. Both methods were compared, and the result showed an overall error margin between 6 and 12%. The values of H _st obtained are over a range of 10-17 kJ/mol. It was observed that H _st decreases with an increase in methane fractional load. The H _st values obtained are useful in designing an efficient thermodynamic scheme for the ANG storage system.

Synthesis of MgO micro-rods coated with charred dextrose and its application for the adsorption of selected heavy metals from synthetic and real groundwater

MgO micro-rods supported on porous carbon were synthesized by an economical method and applied for the adsorption of three different heavy metals ions (As (III), Cd (II) and Pb (II)). Here, we used dextrose as the source of carbon during the synthesis. The synthesized material has been characterized by different techniques like XRD, TEM, FE-SEM, BET and FT-IR for the determination of various physical properties. Compared with MgO synthesized without dextrose, the carbon-supported MgO or C-MgO demonstrated consistent rod-shaped morphology, higher surface area and better absorptivity. The adsorption data were analysed using various isotherm models and the Freundlich isotherm model seemed to provide the best fit to the data. The adsorption kinetics data on the other hand was well explicated by the pseudo second-order kinetic model. The maximum adsorption capacity of C-MgO was 508.47 mg g^-1 for As (III), 566.01 mg g^-1 for Cd (II) and 476.19 mg g^-1 for Pb (II), respectively after 6 h of reaction. To check the real-life usability and efficiency of C-MgO, it was added to a groundwater sample which had 169.55 ppb of As (III) and within 20 min it was adsorbed with 99% efficiency. Reusability studies reveal that C-MgO could be used up to 6 times with more than 60% efficiency. This study shows that C-MgO has high adsorptive ability, is an economic and non-toxic material with versatile applications and can be used for groundwater remediation in real life.

Effects of perlite and caustic soda on microorganism activities of leachate in a sequence batch reactor

The purpose of this article is to evaluate the effect of adsorbents and alkali pre-treatment on microorganism activities of activated sludge (AS) for the treatment of landfill leachate (LFL). The chemical oxygen demand (COD) and BOD5/COD ratio of LFL used in this research were 10,500 and 0.68, respectively. In order to survey the role of porous absorbent, perlite was employed as an alternative with low porosity and was compared to powdered activated carbon (PAC), which has been most widely used in the treatment process. As a result, the COD removal efficiency increased from 32% to 47.7% when alkali LFL was loaded to the sequence batch reactors (SBRs) at the optimum conditions of the biological process. Also, at the same condition, both SBRs containing PAC and perlite showed COD removals of over 81% and 72%, respectively. The specific oxygen uptake rate (SOUR) showed that alkali pre-treatment reduces the toxicity effect of heavy metals on microorganism activities. The adsorption capacity (the uptake of COD) was analyzed by Langmuir and Freundlich isotherm models. Further, the kinetic study of COD adsorption during the treatment process demonstrated that the alkali pre-treatment of LFL proceeded faster and was intensified by the presence of adsorbents.

Adsorption separation of CO from syngas with CuCl@AC adsorbent by a VPSA process

In this work, activated carbon (AC) supported CuCl (CuCl@AC) prepared with CuCl₂ as precursor is investigated for CO separation from the synthesis gas mixture. Firstly, the CuCl@AC adsorbents are investigated for their CO reversible adsorption capacity at an operation temperature of 303 K. And a vacuum pressure swing adsorption (VPSA) process of CO separation from syngas utilizing the prepared CuCl@AC adsorbent is investigated at ambient temperature and 0.79 MPa through a dynamic optimization with Aspen Adsorption software. The integrated model is closer to a realistic PSA process, making the results of the simulation and optimization more convincing. The adsorption result reveals that the obtained CuCl@AC adsorbent with the copper loading of 7 mmol g⁻¹ AC achieves a high reversible CO adsorption capacity and adsorption selectivity. The simulation result shows that, under optimal conditions, the CO product with the purity of 98.1 vol% can be separated from the syngas with the CO concentration of 32.3 vol% utilizing the prepared CuCl@AC adsorbent, and the recovery of CO is 92.9%.

High purity CO was obtained from syngas with low CO concentration utilizing CuCl@AC adsorbent by VPSA process at ambient temperature.

Adsorption–desorption of CO2 on zeolite-Y-templated carbon at various temperatures

This study aims to investigate the adsorption–desorption of CO₂ on a micro-mesoporous zeolite-Y-templated carbon (ZTC) at various temperatures. ZTC was synthesized via sucrose impregnation, carbonization, and template removal. The adsorption–desorption of CO₂ on ZTC was performed using the gravimetric method. Results showed that the CO₂ adsorption capacity was 9.51 wt%, 5.60 wt%, and 3.47 wt%, and desorbed up to 59.83%, 69.70%, 77.5% for temperatures of 30 °C, 40 °C, and 50 °C, respectively. The adsorption process of CO₂ at temperatures of 30 °C and 40 °C follow the pseudo-second order, while at 50 °C follows intra-particle diffusion. The thermodynamic analyses indicate that the adsorption was due to physisorption.

A micro-mesoporous structure of ZTC was synthesized via an impregnation method, and the structure assisted in a faster CO₂ adsorption–desorption equilibrium.

Selective CO adsorbent CuCl/AC prepared using CuCl2 as a precursor by a facile method

CuCl/AC adsorbent with high CO adsorption capacity and selectivity was prepared using CuCl₂ as precursor by monolayer dispersion method.

Study of the temperature and solvent content effects on the structure of Cu–BTC metal organic framework for hydrogen storage

A special MOF, Cu–BTC, was synthesized using ultrasonic and reflux condition technique. The effect of synthesis temperature and solvent ratio on the nanostructure and its hydrogen storage capacity was investigated.

Poly(vinylidene chloride)-based carbon with ultrahigh microporosity and outstanding performance for CH4 and H2 storage and CO2 capture

Poly(vinylidene chloride)-based carbon (PC) with ultrahigh microporisity was prepared by simple carbonization and KOH activation, exhibiting great potential to be superior CO2, CH4, and H2 adsorbent at high pressures. The CO2 uptake for pristine PC is highly up to 3.97 mmol/g at 25 °C and 1 bar while the activated PC exhibits a slightly lower uptake at 1 bar. However, the activated PC has an outstanding CO2 uptake of up to 18.27 mmol/g at 25 °C and 20 bar. Gas uptakes at high pressures are proportional to the surface areas of carbons. The CH4 uptake for the activated PC is up to 10.25 mmol/g (16.4 wt % or 147 v/v) at 25 °C and 20 bar which is in a top-ranked uptake for large surface area carbons. Furthermore, H2 uptake on the activated PC reaches 4.85 wt % at -196 °C and 20 bar. Significantly, an exceptionally large H2 storage capacity of up to 2.43 wt % at 1 bar was obtained, which is among the largest value reported to date for any porous adsorbents, to the best of our knowledge. The ease of preparation and large capture capacities endow this kind of carbon attractive as promising adsorbent for CH4, H2, and CO2 storage.