Mechanistic, Energetic and Structural Aspects of the Adsorption of Carmustine on the Functionalized Carbon Nanotubes

Using density functional theory, noncovalent interactions and two mechanisms of covalent functionalization of drug carmustine with functionalized carbon nanotube（CNT） have been investigated. Quantum molecular descriptors of noncovalent configurations were studied. It was specified that binding of drug carmustine with functionalized CNT is thermodynamically suitable. NTCOOH and NTCOCl can bond to the NH group of carmustine through OH（COOH mechanism） and Cl（COCl mechanism） groups, respectively. The activation energies, activation enthalpies and activation Gibbs free energies of two pathways were calculated and compared with each other. The activation parameters related to COOH mechanism are higher than those related to COCl mechanism, and therefore COCl mechanism is suitable for covalent functionalization. COOH functionalized CNT（NTCOOH） has more binding energy than COCl functionalized CNT（NTCOCl） and can act as a favorable system for carmustine drug delivery within biological and chemical systems（noncovalent）. These results could be generalized to other similar drugs.

An improved theoretical procedure for the pore-size analysis of activated carbon by gas adsorption

Amorphous carbon materials play a vital role in adsorbed natural gas(ANG) storage. One of the key issues in the more prevalent use of ANG is the limited adsorption capacity, which is primarily determined by the porosity and surface characteristics of porous materials. To identify suitable adsorbents, we need a reliable computational tool for pore characterization and, subsequently, quantitative prediction of the adsorption behavior. Within the framework of adsorption integral equation(AIE), the pore-size distribution(PSD) is sensitive to the adopted theoretical models and numerical algorithms through isotherm fitting. In recent years, the classical density functional theory(DFT) has emerged as a common choice to describe adsorption isotherms for AIE kernel construction. However,rarely considered is the accuracy of the mean-field approximation(MFA) commonly used in commercial software. In this work, we calibrate four versions of DFT methods with grand canonical Monte Carlo(GCMC) molecular simulation for the adsorption of CH_4 and CO_2 gas in slit pores at 298 K with the pore width varying from 0.65 to 5.00 nm and pressure from 0.2 to 2.0 MPa. It is found that a weighted-density approximation proposed by Yu(WDA-Yu) is more accurate than MFA and other non-local DFT methods. In combination with the trapezoid discretization of AIE, the WDA-Yu method provides a faithful representation of experimental data, with the accuracy and stability improved by 90.0% and 91.2%, respectively, in comparison with the corresponding results from MFA for fitting CO_2 isotherms. In particular, those distributions in the feature pore width range(FPWR)are proved more representative for the pore-size analysis. The new theoretical procedure for pore characterization has also been tested with the methane adsorption capacity in seven activated carbon samples.

Structures, Stabilities and Work Functions of Alkali-metal-adsorbed Boron α1-Sheets

In this study, we employed the density functional theory method to simulate Li-, Na- and K-adsorbed boron α1-sheets（al-BSTs）. After optimizing possible structures, we investigated their thermodynamic stabilities, barriers for metal atom diffusion on the substrate, and work functions. The computed results indicate that the work function of α1-BST decreases significantly after the adsorption of Li, Na and K. Furthermore, under high hole coverage, these alkali-metal-adsorbed α1-BSTs have lower work functions than the two-dimensional materials of greatest concern and the commonly used electrode materials Ca and Mg. Therefore, the Li-, Na- and K-adsorbed α1-BSTs are potential low-work-function nanomaterials.

Regeneration performance and carbon consumption of semi-coke and activated coke for SO_2 and NO removal

To decrease the operating cost of flue gas purification technologies based on carbon-based materials, the adsorption and regeneration performance of low-price semi-coke and activated coke were compared for SO2 and NO removal in a simulated flue gas. The functional groups of the two adsorbents before and after regeneration were characterized by a Fourier transform infrared（FTIR） spectrometer, and were quantitatively assessed using temperature programmed desorption（TPD） coupled with FTIR and acid–base titration. The results show that semi-coke had higher adsorption capacity（16.2% for SO2 and 38.6% for NO） than activated coke because of its higher content of basic functional groups and lactones. After regeneration, the adsorption performance of semi-coke decreased because the number of active functional groups decreased and the micropores increased. Semi-coke had better regeneration performance than activated coke. Semi-coke had a larger SO2 recovery of 7.2% and smaller carbon consumption of 12% compared to activated coke. The semi-coke carbon-based adsorbent could be regenerated at lower temperatures to depress the carbon consumption, because the SO2 recovery was only reduced a small amount.

Adsorptive removal of As(Ⅲ) ions from water using spent grain modified by polyacrylamide

In order to enhance the removal efficiency of As（III）, a pre-oxidation process is generally applied first to convert As（III） to As（V）, which may cause unwanted new contaminants. To overcome this problem, efforts were made to develop an effective way to remove As（III）directly without an oxidation step. The effect of polyacrylamide polymers（PAMs） such as anionic PAM, cationic PAM and nonionic PAM, on As（III） ion adsorption by spent grain（SG）was investigated. The physico-chemical properties of the three PAM-polymerized SGs（APSG（anionic PAM-polymerized modified spent grain）, CPSG（cationic PAM-polymerized spent grain） and NPSG（nonionic PAM-polymerized spent grain）） were analyzed using Fourier transform infrared（FT-IR）, scanning electron microscope（SEM） and zeta potential.Batch experimental data showed that the sequence of preferential adsorption for As（III） was APSG 〉 CPSG 〉 NPSG. Active functional groups such as amino group（NH2）, carbonyl group（C_O）, C–N bond of the amide group（CONH2）, and hydroxyl group（O–H） were responsible for As（III） adsorption. Many tubular structures occurring on the surface of APSG possibly increase the specific surface areas and favor the adsorption of As（III） ions. A fixed-bed study was carried out by using APSG as an adsorbent for As（III） from water. Three factors such as bed height, initial concentration and flow rate were studied, and breakthrough curves of As（III） were obtained. The Adams–Bohart model was used to analyze the experimental data and the model parameters were evaluated.

A combined DFT and molecular dynamics study of U(Ⅵ)/calcite interaction in aqueous solution

Here we present a combined DFF and molecular dynamics study of uranyl （U（VI）） interaction mecha- nisms with the calcite （104） surface in aqueous solution. The roles of three anion ligands （CO2 , HCO3, OH ） and solvation effect in U（VI） interaction with calcite have been evaluated. According to our calculations, water adsorbed on the calcite （104） surface prefers to exist in molecular state rather than dis- sociative state. Energy analysis indicate that the positively charged uranyl species prefers to form surface complexes on the surface, while neutral uranyl species may bind with the surface via both surface complexing and ion exchange reactions of U（VI） → Ca（II）. In contrast, the negatively charged uranyl species prefer to interact with the surface via ion exchange reactions of U（VI）→ Ca（II）, and the one with UO2（CO3）2（H2O）^2- as the reactant becomes the most favorable one in energy. We also found that uranyl adsorption increases the hydrophilicability of the （104） surface to different extents, where the UO2（CO3）3Ca2 species contributes to the largest degree of energy changes （ 53 kcal/mol）. Our calcula- tions proved that the （104） surface also has the ability to immobilize U（VI） via either surface complexing or ion exchange mechanisms under different pH values.