Synergistic sono-adsorption and adsorption-enhanced sonochemical degradation of dyes in water by additive manufactured PVDF-based materials.

The present study proposes the first mechanistic model accounting for the most meaningful physico-chemical phenomena taking place in liquid phase adsorption processes under ultrasound. Initially, this study was aimed at developing an easy-to-make and easy-to-recover piezocatalyst for the degradation of RhB in water by combining the high piezocatalytical performance of BaTiO3 with a compatible piezoelectric support such as PVDF, manufactured by a customised additive manufacturing - direct ink writing system with in-situ poling. However, initial results showed that the resulting PVDF-BaTiO3 composite slabs performed worse than BaTiO3 piezocatalysts on their own, and that poling did not have any effect on their performance (82% RhB removal after 2 h when using either poled or unpoled PVDF-BaTiO3 composite slabs compared to 92% RhB removal after 2 h in presence of BaTiO3 piezocatalysts). Further investigation with pure PVDF materials demonstrated that, instead of piezocatalysis, synergistic ultrasound-assisted adsorption and sonochemical degradation were taking place, enabling the removal of >95% of the dye within 40 min of ultrasound treatment in the presence of 4 g L-1 of additive manufactured PVDF slabs. The results of this study and their evaluation with the mechanistic model proposed for liquid phase adsorption under ultrasound suggest that the adsorption of RhB on additive manufactured PVDF slabs was enhanced by the structure, higher specific surface ratio and higher volume of mesopores achieved through the 3D-printing process, as well as the minimisation of film resistance to mass transport due to ultrasound. Moreover, adsorption on additive manufactured PVDF enhanced the sonochemical degradation of the dye due to its high concentration in the adsorbed phase. This study demonstrates that adsorption processes, especially in the presence of PVDF materials, may be significantly more important in piezocatalysis than what has been reported to date, to the point that the synergistic combination of sono-adsorption and sonochemical degradation in presence of additive-manufactured PVDF slabs may be enough to achieve high removal rates of dyes in water.

The Rigid Adsorbent Lattice Fluid Model: Thermodynamic Consistency and Relationship to the Real Adsorbed Solution Theory.

The Rigid Adsorbent Lattice Fluid model has been shown to comply with all the requirements for thermodynamic consistency in the case of an adsorbent that does not undergo structural changes. This is achieved by introducing a correction to the reduced density function that multiplies the combinatorial term. A procedure to calculate the predicted adsorbed mixture activity coefficients has been presented that allows the production of excess Gibbs energy plots at a constant reduced grand potential. The predicted nonideality is structurally consistent with the Non-Ideal Adsorbed Solution Theory of Myers in terms of both its dependence on concentration and reduced grand potential. The ability to generate excess Gibbs energy values allows linking the new Rigid Adsorbent Lattice Fluid model to the traditional Real Adsorbed Solution Theory providing an alternative approach to predicting multicomponent adsorption based solely on pure component data.

Performance-Based Screening of Porous Materials for Carbon Capture.

Computational screening methods have changed the way new materials and processes are discovered and designed. For adsorption-based gas separations and carbon capture, recent efforts have been directed toward the development of multiscale and performance-based screening workflows where we can go from the atomistic structure of an adsorbent to its equilibrium and transport properties at different scales, and eventually to its separation performance at the process level. The objective of this work is to review the current status of this new approach, discuss its potential and impact on the field of materials screening, and highlight the challenges that limit its application. We compile and introduce all the elements required for the development, implementation, and operation of multiscale workflows, hence providing a useful practical guide and a comprehensive source of reference to the scientific communities who work in this area. Our review includes information about available materials databases, state-of-the-art molecular simulation and process modeling tools, and a complete catalogue of data and parameters that are required at each stage of the multiscale screening. We thoroughly discuss the challenges associated with data availability, consistency of the models, and reproducibility of the data and, finally, propose new directions for the future of the field.

Cation Ordering and Exsolution in Copper-Containing Forms of the Flexible Zeolite Rho (Cu,M-Rho; M=H, Na) and Their Consequences for CO2 Adsorption.

The flexibility of the zeolite Rho framework offers great potential for tunable molecular sieving. The fully copper-exchanged form of Rho and mixed Cu,H- and Cu,Na-forms have been prepared. EPR spectroscopy reveals that Cu2+ ions are present in the dehydrated forms and Rietveld refinement shows these prefer S6R sites, away from the d8r windows that control diffusion. Fully exchanged Cu-Rho remains in an open form upon dehydration, the d8r windows remain nearly circular and the occupancy of window sites is low, so that it adsorbs CO2 rapidly at room temperature. Breakthrough tests with 10 % CO2 /40 % CH4 mixtures show that Cu4.9 -Rho is able to produce pure methane, albeit with a relatively low capacity at this pCO2 due to the weak interaction of CO2 with Cu cations. This is in strong contrast to Na-Rho, where cations in narrow elliptical window sites enable CO2 to be adsorbed with high selectivity and uptake but too slowly to enable the production of pure methane in similar breakthrough experiments. A series of Cu,Na-Rho materials was prepared to improve uptake and selectivity compared to Cu-Rho, and kinetics compared to Na-Rho. Remarkably, Cu,Na-Rho with >2 Cu cations per unit cell exhibited exsolution, due to the preference of Na cations for narrow S8R sites in distorted Rho and of Cu cations for S6R sites in the centric, open form of Rho. The exsolved Cu,Na-Rho showed improved performance in CO2 /CH4 breakthrough tests, producing pure CH4 with improved uptake and CO2 /CH4 selectivity compared to that of Cu4.9 -Rho.

Ionogels at the Water-Energy Nexus for Desalination Powered by Ultralow-Grade Heat.

Industrial processes emit enormous amounts of waste heat below 40 °C into the environment as it is cannot be used in other processes. Adsorption desalination can be driven by low-grade heat but has never been proven at temperatures below 40 °C as current adsorption materials require heat sources of 50-150 °C. Here, we present the first experimental study on adsorption desalination using a novel class of ionogel adsorption materials, which can be regenerated at 25 °C or a driving temperature difference of 5 °C. This outstanding property contrasts with the benchmarking silica gel, which requires heat sources of at least 50 °C. Ionogels are solid-state ionic materials retaining the sorption properties of the constituent ionic liquid. Thermodynamic vapor-liquid equilibrium data of water sorption on commercial ionic liquids reveal 1-ethyl-3-methylimidazolium acetate as the best fluid for this specific application. A full experimental characterization of the material is performed from imaging at the nanoscale to testing on a real adsorption desalinator. At 25 °C, the material achieves a specific daily water production of 6.7 kgwater/(kgionogel d), increasing to 17.5 kgwater/(kgionogeld) at 45 °C, outperforming silica gel by a factor of 2.

Triggered Gate Opening and Breathing Effects during Selective CO2 Adsorption by Merlinoite Zeolite.

Zeolites with flexible structures that adapt to coordinate extraframework cations when dehydrated show a rich variety of gas adsorption behavior and can be tuned to optimize kinetics and selectivity. Merlinoite zeolite (topology type MER) with Si/Al = 3.8 has been prepared in Na, K, and Cs forms and its structural response to dehydration measured: the unit cell volumes decrease by 9.8%, 7.7%, and 7.1% for Na-, K-, and Cs-MER, respectively. Na-MER adopts Immm symmetry, while K- and Cs-MER display P42/nmc symmetry, the difference attributed to the preferred locations of the smaller and larger cations. Their performance in CO2 adsorption has been measured by single-component isotherms and by mixed gas (CO2/CH4/He) breakthrough experiments. The differing behavior of the cation forms can be related to structural changes during CO2 uptake measured by variable-pressure PXRD. All show a "breathing" transition from narrow to wide pore forms. Na- and Cs-MER show non-Type I isotherms and kinetically-limited CO2 adsorption and delivery of pure CH4 in CO2/CH4 separation. However, K-MER shows good uptake of CO2 (3.5 mmol g-1 at 1 bar and 298 K), rapid adsorption and desorption kinetics, and promising CO2/CH4 separation. Furthermore, the narrow-to-wide pore transition occurs rapidly and at very low pCO2 via a "triggered" opening. This has the consequence that whereas no CH4 is adsorbed from a pure stream, addition of low levels of CO2 can result in pore opening and uptake of both CO2 and CH4, although in a continuous stream the CH4 is replaced selectively by CO2. This observed cation size-dependent adsorption behavior derives from a fine energetic balance between different framework configurations in these cation-controlled molecular sieves.

Non-Porous versus Mesoporous Siliceous Materials for CO2 Capture.

In this study, the adsorption properties of a Stöber silica-based material towards CO2 were evaluated for the first time. The use of Stöber silica as support is interesting for real technological applications mainly due to economic factors. Furthermore, a direct comparison between the non porous Stöber sample with an ordered porous material (based on MCM-41 silica) allowed to evaluate the effect of the porosity on the CO2 adsorption properties. In order to make silica materials reactive towards CO2, they were functionalized by introducing amino groups via grafting of 3-[2-(2-aminoethyl)aminoethyl]aminopropyltrimethoxysilane. After a qualitative study of the CO2 adsorption, the quantitative determination of CO2 adsorption capacity at 35 °C revealed that the mesoporous material is more efficient compared to the Stöber-based one (adsorption capacity values of 0.49 and 0.58 mol/kg for Stöber-based and mesoporous samples). However, since the difference in the adsorption capacity is only about 15 % and the Stöber-based sample is considerably cheaper, the non-porous sample should be considered as a favourable adsorbent material for CO2 capture applications.

A Porous Carbon with Excellent Gas Storage Properties from Waste Polystyrene.

In this paper, we describe the synthesis and gas adsorption properties of a porous carbonaceous material, obtained from commercial expanded polystyrene. The first step consists of the Friedel-Craft reaction of the dissolved polystyrene chains with a bridging agent to form a highly-crosslinked polymer, with permanent porosity of 0.7 cm 3 /g; then, this polymer is treated with potassium hydroxide at a high temperature to produce a carbon material with a porous volume larger than 1.4 cm 3 / g and a distribution of ultramicro-, micro-, and mesopores. After characterization of the porous carbon and determination of the bulk density, the methane uptake was measured using a volumetric apparatus to pressures up to 30 bar. The equilibrium adsorption isotherm obtained is among the highest ever reported for this kind of material. The interest of this product lies both in its excellent performance and in the virtually costless starting material.

An experimental and modelling study of water vapour adsorption on SBA-15.

Many publications have been dedicated to the study of water vapour adsorption on the ordered silica-based material Santa Barbara Amorphous-15 (SBA-15). However, two aspects still need to be clarified: whether the solid is stable under repeated adsorption-desorption cycles and whether the experimental data can be predicted with a simple yet accurate analytical equilibrium model. In this study, SBA-15 showed good long-term structural stability when exposed to repeated adsorption-desorption cycles using water vapour as adsorptive up to 90 % relative humidity at 288 K, 298 K and 308 K. The reproducibility of the equilibrium isotherm was investigated using different commercial gravimetric instruments designed for water vapour adsorption measurements. The experimental measurements show a modification of the microporous structure of the solid after the first full isotherm measurement. Some water is strongly adsorbed and trapped during the first experiment on a fresh sample. After the first adsorption-desorption cycle, the water isotherm is characterized by a low value of the Henry law constant and by a nearly vertical capillary condensation and evaporation branches. Quite interestingly, the experimental scanning curves do not simply cross from one branch to the other as would be expected for cylindrical independent pores. The experimental data are correlated using new analytical models able to predict the amount adsorbed in the entire concentration range for the main adsorption-desorption branches and for the adsorption-desorption scanning curves.

Net, excess and absolute adsorption in mixed gas adsorption.

The formulation of a thermodynamic framework for mixtures based on absolute, excess or net adsorption is discussed and the qualitative dependence with pressure and fugacity is used to highlight a practical issue that arises when extending the formulations to mixtures and to the Ideal Adsorbed Solution Theory (IAST). Two important conclusions are derived: the correct fundamental thermodynamic variable is the absolute adsorbed amount; there is only one possible definition of the ideal adsorbed solution and whichever starting point is used the same final IAST equations are obtained, contrary to what has been reported in the literature.

Net, excess and absolute adsorption and adsorption of helium.

The definitions of absolute, excess and net adsorption in microporous materials are used to identify the correct limits at zero and infinite pressure. Absolute adsorption is shown to be the fundamental thermodynamic property and methods to determine the solid density that includes the micropore volume are discussed. A simple means to define when it is necessary to distinguish between the three definitions at low pressure is presented. To highlight the practical implications of the analysis the case of adsorption of helium is considered in detail and a combination of experiments and molecular simulations is used to clarify how to interpret adsorption measurements for weakly adsorbed components.

In situ synchrotron IR microspectroscopy of CO2 adsorption on single crystals of the functionalized MOF Sc2(BDC-NH2)3.

Synchrotron radiation (SR) IR microspectroscopy has enabled determination of the thermodynamics, kinetics, and molecular orientation of CO2 adsorbed in single microcrystals of a functionalized metal-organic framework (MOF) under conditions relevant to carbon capture from flue gases. Single crystals of the small-pore MOF, Sc2 (BDC-NH2 )3 , (BDC-NH2 =2-amino-1,4-benzenedicarboxylate), with well-defined crystal form have been investigated during CO2 uptake at partial pressures of 0.025-0.2 bar at 298-373 K. The enthalpy and diffusivity of adsorption determined from individual single crystals are consistent with values obtained from measurements on bulk samples. The brilliant SR IR source permits rapid collection of polarized spectra. Strong variations in absorbance of the symmetric stretch of the NH2 groups of the MOF and the asymmetric stretch of the adsorbed CO2 at different orientations of the crystals relative to the polarized IR light show that CO2 molecules align along channels in the MOF.

A model for sound propagation between two adsorbing microporous plates.

A model describing the sound propagation between two infinite adsorbing plates is proposed in order to investigate the extension to the audible sound range of the Frequency Response method applied to the measurement of diffusion in micropores. The model relates adsorption parameters (i.e., diffusivity and equilibrium constant) to an acoustic quantity (i.e., propagation constant). The equations describing sound propagation in the presence of adsorbing boundaries are obtained on the basis of the classical Kirchhoff theory [(1868). Ann. Phys. (Leipzig) 134, 177-193]. The solution is derived using the Low Reduced Frequency Approximation method [Tijdeman, (1975). J. Sound Vib. 39, 1-33].

Understanding carbon dioxide adsorption on univalent cation forms of the flexible zeolite Rho at conditions relevant to carbon capture from flue gases.

A series of univalent cation forms of zeolite Rho (M(9.8)Al(9.8)Si(38.2)O(96), M = H, Li, Na, K, NH(4), Cs) and ultrastabilized zeolite Rho (US-Rho) have been prepared. Their CO(2) adsorption behavior has been measured at 298 K and up to 1 bar and related to the structures of the dehydrated forms determined by Rietveld refinement and, for H-Rho and US-Rho, by solid state NMR. Additionally, CO(2) adsorption properties of the H-form of the silicoalumino-phosphate with the RHO topology and univalent cation forms of the zeolite ZK-5 were measured for comparison. The highest uptakes at 0.1 bar, 298 K for both Rho and ZK-5 were obtained on the Li-forms (Li-Rho, 3.4 mmol g(-1); Li-ZK-5, 4.7 mmol g(-1)). H- and US-Rho had relatively low uptakes under these conditions: extra-framework Al species do not interact strongly with CO(2). Forms of zeolite Rho in which cations occupy window sites between α-cages show hysteresis in their CO(2) isotherms, the magnitude of which (Na(+),NH(4)(+) < K(+) < Cs(+)) correlates with the tendency for cations to occupy double eight-membered ring sites rather than single eight-membered ring sites. Hysteresis is not observed for zeolites where cations do not occupy the intercage windows. In situ synchrotron X-ray diffraction of the CO(2) adsorption on Na-Rho at 298 K identifies the adsorption sites. The framework structure of Na-Rho "breathes" as CO(2) is adsorbed and desorbed and its desorption kinetics from Na-Rho at 308 K have been quantified by the Zero Length Column chromatographic technique. Na-Rho shows much higher CO(2)/C(2)H(6) selectivity than Na-ZK-5, as determined by single component adsorption, indicating that whereas CO(2) can diffuse readily through windows containing Na(+) cations, ethane cannot.