Benign Synthesis of Metal-Organic Framework (MIL-101-Cr) and Evaluation of Carbon-dioxide Adsorption Behaviour Employing Adsorption Isotherm Models

BACKGROUND

In today's world, rising temperature due to global warming is caused by higher concentration of carbon dioxide (CO₂ ) emissions in the atmosphere. Metal-Organic Framework (MOF) materials have Objective: The purpose of this work is to prepare metal-organic framework materials by a benign synthesis method using water as the solvent, followed by the characterization and property evaluation for CO₂ adsorption study.

METHODS

MIL-101-Cr metal-organic framework and its derivatives with alkali ion dopants were prepared by benign hydrothermal synthesis route, which were characterized by powder X-ray diffraction method. The adsorption isotherms of CO2 for MIL-101-Cr and its derivatives were studied to comprehend the influence of alkali dopants on CO2 sorption behaviour. The equilibrium uptakes of CO2 were further evaluated by fitting the isotherms with Langmuir, Toth and Dubinin - Astakohv adsorption models to determine the adsorption parameters.

RESULTS

The crystalline structural integrity of MIL-101-Cr is not affected by doping with alkali ions. The isosteric heat of CO2 adsorption is diminished with an increase in alkali dopant size, while the induced surface structural heterogeneity increases with increasing alkali dopant size.

CONCLUSION

The equilibrium and thermodynamic parameters calculated from this study are useful for applications in carbon dioxide capture and utilization technology.

Surface Heterogeneity-Involved Estimation of Sample Size for Accuracy Assessment of Land Cover Product from Satellite Imagery

Sample size estimation is a key issue for validating land cover products derived from satellite images. Based on the fact that present sample size estimation methods account for the characteristics of the Earth’s subsurface, this study developed a model for estimating sample size by considering the scale effect and surface heterogeneity. First, we introduced a watershed with different areas to indicate the scale effect on the sample size. Then, by employing an all-subsets regression feature selection method, three landscape indicators describing the aggregation and diversity of the land cover patches were selected (from 14 indicators) as the main factors for indicating the surface heterogeneity. Finally, we developed a multi-level linear model for sample size estimation using explanatory variables, including the estimated sample size (n) calculated from the traditional statistical model, size of the test region, and three landscape indicators. As reference data for developing this model, we employed a case study in the Jiangxi Province using a 30 m spatial resolution global land cover product (Globeland30) from 2010 as a classified map, and national 30 m land use/cover change (LUCC) data from 2010 in China. The results showed that the adjusted square coefficient of R² is 0.79, indicating that the joint explanatory ability of all predictive variables in the model to the sample size is 79%. This means that the predictability of this model is at a good level. By comparing the sample size N_S obtained by the developed multi-level linear model and n as calculated from the statistics model, we find that N_S is much smaller than n, which mainly contributes to the concerns regarding surface heterogeneity in this study. The validity of the established model is tested and is proven as effective in the Anhui Province. This indicates that the estimated sample size from considering the scale effect and spatial heterogeneity in this study achieved the same accuracy as that calculated from a probability statistical model, while simultaneously saving more time, labour, and money in the accuracy assessment of a land cover dataset.

Nanoscale Functionalized Particles with Rotation-Controlled Capture in Shear Flow

Important processes in nature and technology involve the adhesive capture of flowing particles or cells on the walls of a conduit. This paper introduces engineered spherical microparticles whose capture rates are limited by their near surface motions in flow. Specifically, these microparticles are sparsely functionalized with nanoscopic regions ("patches") of adhesive functionality, without which they would be nonadhesive. Not only is particle capture on the wall of a shear-chamber limited by surface chemistry as opposed to transport, but also the capture rates depend specifically on particle rotations that result from the vorticity of the shear flow field. These particle rotations continually expose new particle surface to the opposing chamber wall, sampling the particle surface for an adhesive region and controlling the capture rate. Control studies with the same patchy functionality on the chamber wall rather than the particles reveal a related signature of particle capture but substantially faster (still surface limited) particle capture rates. Thus, when the same functionality is placed on the wall rather than the particles, the capture is faster because it depends on the particle translation past a functionalized wall rather than on the particle rotations. The dependence of particle capture on functionalization of the particles versus the wall is consistent with the faster near-wall particle translation in shearing flow compared with the velocity of the rotating particle surface near the wall. These findings, in addition to providing a new class of nanoscopically patchy engineered particles, provide insight into the capture and detection of cells presenting sparse distinguishing surface features and the design of delivery packages for highly targeted pharmaceutical delivery.

Boundary lubrication of heterogeneous surfaces and the onset of cavitation in frictional contacts

Surfaces can be slippery or sticky depending on surface chemistry and roughness. We demonstrate in atomistic simulations that regular and random slip patterns on a surface lead to pressure excursions within a lubricated contact that increase quadratically with decreasing contact separation. This is captured well by a simple hydrodynamic model including wall slip. We predict with this model that pressure changes for larger length scales and realistic frictional conditions can easily reach cavitation thresholds and significantly change the load-bearing capacity of a contact. Cavitation may therefore be the norm, not the exception, under boundary lubrication conditions.

Surface-Mediated Protein Unfolding as a Search Process for Denaturing Sites

Surface-induced protein denaturation has important implications for the development of materials that are resistant and/or innocuous to biomolecules. Here, we studied the mechanism of lysozyme (T4L) unfolding on fused silica (FS) using single-molecule methods that provided direct insight into the cause of denaturation. Unfolding of T4L was monitored by Förster resonance energy transfer while simultaneously tracking the adsorption, diffusion, and desorption of individual molecules at the solid-solution interface. Results of high-throughput single-molecule analysis suggested that the unfolding of T4L on FS was mediated by surface diffusion and occurred on isolated nanoscale sites, which were relatively rare and distinct from the majority of the surface. These observations suggest that surface-mediated protein unfolding is a search process that is based on the exploration for denaturing sites by the protein. Ultimately, these findings have important implications for the design of protein-compatible surfaces.

Relating material surface heterogeneity to protein adsorption: the effect of annealing of micro-contact-printed OTS patterns

We have investigated the influence of micrometer- and sub-micrometer-scale surface heterogeneities in patterned octadecyltrichlorosilane (OTS) films on human serum albumin (HSA) adsorption and its spatial distribution. 5-μm-wide OTS patterns were created on glass substrates by micro-contact printing and in some instances subsequent annealing was used to alter OTS molecule distribution within the patterns. Scanning force microscopy (SFM), advancing water contact angles and water vapor condensation figures were used to characterize the OTS films and to assess the nature of the heterogeneities within the various surface areas. High-resolution fluorescence microscopy was used to record images of fluorescently labeled albumin on OTS patterned films and fluorescence intensity was quantified and converted into the adsorbed amount. Adsorbed albumin was also characterized through SFM measurements. Combined SFM topography and lateral force microscopy (LFM) imaging revealed that micro-contact printing of OTS onto glass both replicated the stamp pattern and created small islands within the non-stamped regions between the patterns. The OTS coverage within stamped regions was not fully continuous but improved with subsequent annealing. Annealing also resulted in OTS island growth within the non-stamped regions and decreased average wettability on both the stamped and non-stamped areas. The extent of albumin adsorption was not proportional to OTS coverage, but correlated with the sub-μm distribution of OTS chains. We inferred that the surface distribution of ligands such as OTS on a sub-μm length scale determines the nature of albumin adsorption and its kinetics.

How Surface Heterogeneity Affects Protein Adsorption: Annealing of OTS Patterns and Albumin Adsorption Kinetics

Fluorescence microscopy and intensity histogram analysis techniques were used to monitor spatially-resolved albumin adsorption kinetics to model heterogeneous surfaces on sub-μm scales. Several distinct protein subpopulations were resolved, each represented by a normal distribution of adsorption densities on the adsorbent surface. Histogram analyses provided dynamic information of mean adsorption density, spread in adsorption density, and surface area coverage for each distinct protein subpopulation. A simple adsorption model is proposed in which individual protein binding events are predicted by the summation of multiple protein's surface sub-site interactions with different binding energy sub-sites on adsorbent surfaces. This model is predictive of the albumin adsorption on the patterns produced by one step μ-contact printing (μCP) of octadecyltrichlorosilane (OTS) on glass but fails to describe adsorption once the same patterns are altered by a thermal annealing step.