Green Self-Activating Synthesis System for Porous Carbons; Celery Biomass Wastes as a Typical Case for CO2 Uptake with Kinetic, Equilibrium and Thermodynamic Studies

A green self-activating synthesis system (SASS) has been introduced for porous carbons. In the presented system, there is no external support for the activation process, and the activating agents are the circulating gases released during the pyrolysis treatment. As a typical case, this system was used for the synthesis of hierarchical porous carbons from celery wastes in hydroponic greenhouses. Based on the adsorption-desorption results, the optimal porous carbons were synthesized at 700°C, providing a surface area as high as 1126 m2g−1 and micropore volume of approximately 0.7 cm3g−1. X-ray photoelectron spectroscopy indicated the presence of graphitic nitrogen in the synthesized porous carbon structure. The synthesized porous carbons were applied as an adsorbent for CO2 capture. CO2 adsorption was performed at low and high pressures at various temperatures. Under low pressures (0-1 bar), the synthesized carbons adsorbed 5 mmolg−1 at 0°C and 2.03 mmolg−1 at 25°C. The adsorption capacity of the synthesized carbon at 25°C and a relatively high pressure of 9.5 bar was 9.57 mmolg−1. Based on the thermodynamic and kinetic models, it was clarified that the adsorption process can be regarded as physisorption with an adsorption enthalpy of 23.2 kJ.mol−1. Additionally, the fractional-order kinetic model was found to be the best match in the kinetic curves. The synthesis system described herein represents a promising strategy for producing green porous carbon from various waste organic precursors.

Surface Functionalized Halloysite with N-[3-(Trimethoxysilyl)Propyl] Ethylenediamine for Chromium and Nickel Adsorption from Aqueous Solution

In this study, -[3-(trimethoxysilyl)propyl] ethylenediamine - modified Indonesian natural halloysite was applied for Cr(III) and Ni(II) adsorption from aqueous solution. The studies include the physicochemical characterization of the synthesized material by using XRD, SEM, gas sorption analyzer, and FTIR analyses. Furthermore, the adsorption experiments were performed at a batch system for investigating the adsorption kinetics and thermodynamic. The results showed no significant changes in either the material crystallinity or specific surface area, but the changes of surface functional groups identified the anchored ammine modifier. Kinetic modeling showed pseudo-second-order model best fitted the experimental data for both adsorbents. Moreover, the thermodynamic studies represented the chemisorption interaction of modified halloysite with the adsorbate since the average adsorption enthalpy values are at 44.3 kJ/mol and 41.70 kJ/mol for Cr(III) and Ni(II), respectively.

Insight into the Mechanisms of Low Coverage Adsorption of N-Alcohols on Single Walled Carbon Nanohorn

We report for the first time the chromatographic study of n-alcohols (from methanol to butanol) adsorption on single walled carbon nanohorn (SWCNH). Using measured temperature dependence of adsorption isotherms (373–433 K) the isosteric adsorption enthalpy is calculated and compared with the data reported for a graphite surface. It is concluded that a graphite surface is more homogeneous, and the enthalpy of adsorption on SWCNHs at zero coverage correlates well with molecular diameter and polarizability, suggesting leading role of dispersive interactions, i.e., no heteroatoms presence in the walls of SWCNH structures. Next using modern DFT approach we calculate the energy of n-alcohols interactions with a graphene sheet and with a single nanocone finally proposing a more realistic—double nanocone model. Obtained results suggest alcohols entrapping between SWCNH with OH groups located toward nanocones ends, leading to the conclusions about very promising future applications of SWCNHs in catalytic reactions with participation of n-alcohols.

Thermochromatographic behavior of iodine in 316L stainless steel columns when evaporated from lead–bismuth eutectic

Iodine evaporated from lead–bismuth eutectic (LBE) has been examined with respect to its adsorption behavior on stainless steel in various gases to establish a base for safety evaluations on LBE based nuclear reactors. In inert conditions the iodine forms a single species with an adsorption enthalpy between − 97 and − 106 kJ/mol. The adsorbed species is tentatively identified as bismuth monoiodide, BiI. Addition of moisture to the inert gas has no substantial influence on the adsorption behaviour. For the reducing hydrogen carrier gas depositions with adsorption enthalpies ranging from − 87 to − 134 kJ/mol were observed in dry and water saturated conditions. The larger variation of adsorption enthalpies compared to analogous experiments in helium likely result from surface effects induced by the reactive gas. Formation of highly volatile species such as hydrogen iodide HI was not observed. In oxidizing conditions multiple iodine species with adsorption enthalpies ranging from − 67 to − 83 kJ/mol were observed, with the exception of one experiment where only a lower limit of –ΔHads < 64 kJ/mol could be determined due to high volatility. The species occurring in oxidizing atmosphere are most likely monatomic iodine, iodine oxides and hydroxides. While oxygen as a carrier gas changes the speciation of iodine to more volatile compounds, it also introduces a retentive effect on the evaporation of iodine from the LBE sample. These results provide important information that establish a better understanding of safety related aspects pertaining to iodine transport in an LBE reactor. The determined thermodynamic data can be used for safety assessments of LBE-based nuclear facilities in normal operation conditions as well as for accident scenarios.

Adsorption of Crystal Violet Dye Using Activated Carbon of Lemon Wood and Activated Carbon/Fe3O4 Magnetic Nanocomposite from Aqueous Solutions: A Kinetic, Equilibrium and Thermodynamic Study

Activated carbon prepared from lemon (Citrus limon) wood (ACL) and ACL/Fe3O4 magnetic nanocomposite were effectively used to remove the cationic dye of crystal violet (CV) from aqueous solutions. The results showed that Fe3O4 nanoparticles were successfully placed in the structure of ACL and the produced nanocomposites showed superior magnetic properties. It was found that pH was the most effective parameter in the CV dye adsorption and pH of 9 gave the maximum adsorption efficiency of 93.5% and 98.3% for ACL and ACL/Fe3O4, respectively. The Dubinin–Radushkevich (D-R) and Langmuir models were selected to investigate the CV dye adsorption equilibrium behavior for ACL and ACL/Fe3O4, respectively. A maximum adsorption capacity of 23.6 and 35.3 mg/g was obtained for ACL and ACL/Fe3O4, respectively indicating superior adsorption capacity of Fe3O4 nanoparticles. The kinetic data of the adsorption process followed the pseudo-second order (PSO) kinetic model, indicating that chemical mechanisms may have an effect on the CV dye adsorption. The negative values obtained for Gibb’s free energy parameter (−20 < ΔG < 0 kJ/mol) showed that the adsorption process using both types of the adsorbents was physical. Moreover, the CV dye adsorption enthalpy (ΔH) values of −45.4 for ACL and −56.9 kJ/mol for ACL/Fe3O4 were obtained indicating that the adsorption process was exothermic. Overall, ACL and ACL/Fe3O4 magnetic nanocomposites provide a novel and effective type of adsorbents to remove CV dye from the aqueous solutions.

Validating an Evaporative Calibrator for Gaseous Oxidized Mercury

Understanding atmospheric mercury chemistry is the key for explaining the biogeochemical cycle of mercury and for improving the predictive capability of computational models. Increased efforts are being made to ensure comparable Hg speciation measurements in the air through establishing metrological traceability. While traceability for elemental mercury has been recently set, this is by no means the case for gaseous oxidized mercury (GOM). Since a calibration unit suitable for traceable GOM calibrations based on evaporation of HgCl2 solution was recently developed, the purpose of our work was to extensively evaluate its performance. A highly specific and sensitive 197Hg radiotracer was used for validation over a wide range of concentrations. By comparing experimental and calculated values, we obtained recoveries for the calibration unit. The average recoveries ranged from 88.5% for 1178 ng m−3 HgCl2 gas concentration to 39.4% for 5.90 ng m−3 HgCl2 gas concentration. The losses were due to the adsorption of oxidized Hg on the inner walls of the calibrator and tubing. An adsorption isotherm was applied to estimate adsorption enthalpy (ΔHads); a ΔHads value of −12.33 kJ mol−1 was obtained, suggesting exothermal adsorption. The results of the calibrator performance evaluation suggest that a newly developed calibration unit is only suitable for concentrations of HgCl2 higher than 1 µg m−3. The concentration dependence of recoveries prevents the system from being used for calibration of instruments for ambient GOM measurements. Moreover, the previously assessed uncertainty of this unit at µg m−3 level (2.0%, k = 2) was re-evaluated by including uncertainty related to recovery and was found to be 4.1%, k = 2. Calibrator performance was also evaluated for HgBr2 gas calibration; the recoveries were much lower for HgBr2 gas than for HgCl2 gas even at a high HgBr2 gas concentration (>1 µg m−3). As HgBr2 is often used as a proxy for various atmospheric HgBr species, the suitability of the unit for such calibration must be further developed.

Novel, Environment-Friendly Cellulose-Based Derivatives for Tetraconazole Removal from Aqueous Solution

In this study, cellulose-based derivatives with heterocyclic moieties were synthesized by reacting cellulose with furan-2-carbonyl chloride (Cell-F) and pyridine-2,6-dicarbonyl dichloride (Cell-P). The derivatives were evaluated as adsorbents for the pesticide tetraconazole from aqueous solution. The prepared adsorbents were characterized by SEM, TGA, IR, and H1 NMR instruments. To maximize the adsorption efficiency of tetraconazole, the optimum conditions of contact time, pH, temperature, adsorbent dose, and initial concentration of adsorbate were determined. The highest removal percentage of tetraconazole from water was 98.51% and 95% using Cell-F and Cell-P, respectively. Underivatized nanocellulose was also evaluated as an adsorbent for tetraconazole for comparison purpose, and it showed a removal efficiency of about 91.73%. The best equilibrium adsorption isotherm model of each process was investigated based on the experimental and calculated R2 values of Freundlich and Langmuir models. The adsorption kinetics were also investigated using pseudo-first-order, pseudo-second-order, and intra-particle-diffusion adsorption kinetic models. The Van’t Hoff plot was also studied for each adsorption to determine the changes in adsorption enthalpy (∆H), Gibbs free energy (∆G), and entropy (∆S). The obtained results showed that adsorption by Cell-F and Cell-P follow the Langmuir adsorption isotherm and the mechanism follows the pseudo-second-order kinetic adsorption model. The obtained negative values of the thermodynamic parameter ∆G (−4.693, −4.792, −5.549 kJ) for nanocellulose, Cell-F, and Cell-P, respectively, indicate a spontaneous adsorption process. Cell-F and Cell-P could be promising absorbents on a commercial scale for tetraconazole and other pesticides.

Isothermal Titration Calorimetry as a Method for Analyzing Protein Adsorption in Ion Exchange Chromatography

Ion exchange chromatography is a widely used method for purification of all types of biomolecules in current biotechnological downstream processes. Knowledge on the binding behavior of proteins provides valuable insight for understanding the molecular mechanisms of protein interactions in a biological context. However, thermodynamic parameters such as enthalpy and entropy changes that characterize protein adsorption are still unknown. Isothermal titration calorimetry applications in biosciences has gained its merit to study binding of soluble molecules, protein inhibition, conformational changes, reaction kinetics, and protein adsorption. However, in the case of protein adsorption, a lot of complications arise since the usual models used to study protein interactions in solution are no longer valid. This work explains a detailed methodology for the obtention of adsorption enthalpy, entropy and Gibbs energy of protein adsorption, by using ITC together with equilibrium adsorption isotherms.