Decrease In Specific Surface Area Research Articles

Hydrogen-rich syngas upgrading via CO2 adsorption by amine-functionalized Cu-BTC: the effect of different amines.

Syngas produced from supercritical water gasification typically contain a high amount of CO2 along with H2. In order to improve the quality of syngas, amine-functionalized copper benzene-1,3,5-tricarboxylate (Cu-BTC) was synthesized as an effective adsorbent for selective removal of CO2 from syngas to increase the concentration of H2. The amines used in this study included monoethanolamine (MEA), ethylenediamine (EDA), and polyethyleneimine (PEI). The fundamental physicochemical character of adsorbents, CO2 adsorption capacity, and CO2/H2 selectivity were analyzed. The physicochemical characterization indicated that the structure of amine-functionalized Cu-BTC was partially damaged, which resulted in a decrease in specific surface area and pore volume. On the other hand, the enlarged pore size was beneficial for the mass transfer of gas in the adsorbent. Among these adsorbents, Cu-BTC/PEI exhibited the maximum CO2 adsorption capacity of 3.83mmol/g and the highest CO2/H2 selectivity of 19.74. It was found that the adsorption pressure is the most significant factor for the CO2 adsorption capacity. Lower temperature and higher pressure were favored for CO2 adsorption capacity and CO2/H2 selectivity, so physical adsorption by Cu-BTC played a dominant role. Moreover, Cu-BTC/PEI can be well-regenerated with stable adsorption efficiency after five consecutive cycles. These findings suggested that Cu-BTC/PEI could be a promising alternative adsorbent for CO2 capture from syngas.

STUDY OF CATALYTIC BEHAVIOURS OF THE SPINEL STRUCTURE NdxMg1- xAl2O4 COMPOSITION WITH ZSM-5 ZEOLITE IN ETHYLBENZENE DISPROPORTIONATION

Nanosized (10–15 nm) powders of spinel structures NdxMg1–xAl2O4 were obtained by low-temperature combustion of aluminium, magnesium, neodymium nitrate solutions, diethylmalonate, and hydrazine monohydrate with further calcination of nanopowders at 1000 °C, which were used in the preparation of catalytic compositions with ZSM-5 zeolite. The obtained catalytic compositions were characterized by X-ray diffraction, pyridine adsorption, and low-temperature nitrogen adsorption. The acidic properties and porosity of the catalysts were altered by controlling the concentration of nanopowder (1.0–7.0 wt.%) in the catalytic composition. The interaction of the modifier with HZSM-5 zeolite leads to a decrease in specific surface area and pore volume, as well as reduse of strong Bronsted acid sites (B) and an increase in the concentration of medium Lewis acid sites (L), resulting in a change in the B/L ratio from 3.61 to 0.23. The ongoing variations contributed mainly to an enhancement of the para-selectivity of the catalytic composition in the ethylbenzene disproportionation reaction. The catalytic composition of 5% Nd0.1Mg0.9Al2O4 with a pore volume of 0.15 cm3/g and an acid site B/L ratio of 0.27 demonstrates a maximum selectivity to p-diethylbenzene of 75.6% with a conversion of ethylbenzene of 23.7%.

The Removal of Phosphorus from Wastewater Using a Sewage Sludge Biochar: A Column Study

This scientific study investigated the adsorption capabilities of biochar samples derived from municipal sewage sludge pellets. Sewage sludge was pyrolyzed at various temperatures (400, 500, and 600 °C), and the biochar’s properties, including specific surface area, pore volume, and pore size distribution, were assessed. The results indicate that the sewage sludge biochar samples are mesoporous materials with significant potential for good adsorption performance. Despite showing a decrease in specific surface area compared to that achieved with pyrolysis at 400 °C, samples pyrolyzed at 600 °C demonstrated an increase in mesopore surface area, enhancing their adsorption potential. Two filtration experiments, conducted at a flow rate of 8 mL/min, revealed that the column containing sewage sludge pyrolyzed at 600 °C retained phosphorus the most effectively during the first and second experiments (with retention efficiencies of 87% and 78%, respectively). The study concludes that municipal sewage sludge biochar could be a promising material for the removal of phosphorus from wastewater and represents a viable solution for sustainable environmental development.

Quantitative sulfur poisoning of nanocrystal PtO2/KL-NY and its deactivation mechanism for benzene catalytic oxidation

The present study involved the synthesis of a kaolin-based NaY zeolite (KL-NY) supported nanocrystal PtO2 (5–10 nm) catalyst, which exhibited complete benzene conversion at 195 °C. However, a certain amount of sulfur species led to severe deactivation of the catalyst. This deactivation was mainly caused by the reduction of active lattice oxygen. XPS, H2-TPR and HRTEM results confirmed that adsorbed sulfur species competitively consumed active lattice oxygen, resulting in a transition of partial PtO2 to PtO. Generated PtO cannot actively participate in the oxidation reaction due to its weaker oxidation property, indicating a decrease of active species induced by sulfur poisoning. Furthermore, Al2O3 outside the KL-NY framework can adsorb sulfur species and form Al2(SO4)3, leading to an increase in acid sites. Due to the weak acid-tolerance of KL-NY, partial porous structure destruction occurred with a decrease in specific surface area and pore volume, thereby negatively impacting catalyst performance.

Enhancing interfacial synergies for the preparation of high mechanical strength and interconnected porosity of alumina extrudates through pre-wetting method

The forming of catalyst supports is a crucial step in the application of industrial catalysts. Alumina, a widely employed catalyst support, is often shaped using nitric acid as a peptizer to enhance mechanical strength. However, the use of large amounts of nitric acid typically results in a decrease in specific surface area and damage to the pore structure due to chemical corrosion. In this work, we present a more practical approach that is pre-filling the open pores of pseudo-boehmite powder with water instead of directly filling them with nitric acid solution. The binder with a small quantity of nitric acid plays a synergistic role in functioning as a glue on the particle surfaces. And through this method, high-strength (231 N cm−1) alumina support can be prepared more efficiently through extrusion. Besides, the pore structure of the extrudates was characterized by multi-scale methods, including nitrogen physical sorption and XRM (X-ray microscopy), which revealed abundant interconnected hierarchical pores deriving from the pre-wetting shaping process. This proposed approach enables the attainment of high mechanical strength and interconnected porosity for alumina extrudates with less use of acid, which holds a significant practical application value.

Removal of COD from petroleum refinery wastewater by adsorption using activated carbon derived from avocado plant

In the present work, removing of COD from wastewater generated via Al-Diwanya petroleum refinery plant located in Iraq by adsorption with activated carbon (AC) derived from avocado seeds was successfully performed via a two-step approach. In the first step, AC was prepared from avocado seeds via impregnating with H3PO4 at 400 °C where effects of H3PO4 concentration and calcination time on the specific surface area of AC were studied. Additionally, properties of the prepared AC were examined by XRD, SEM, and FTIR to knowledge the features of the internal structure of AC. Results showed that the prepared AC has mesopores structure with pore diameters in the range between 30.07 and 50.8 µm. Increasing the weight percent of H3PO4 led to an increase in the specific surface area of AC to reach a maximum value beyond which a decrease in the specific surface area was happened with further increasing in H3PO4 percent. Increasing the time resulted in an increase in the AC specific surface area to reach a maximum value beyond which a decrease in specific surface area was happened. The best value of AC specific surface area was 436.6 m2/g which obtained at 70 %H3PO4 and 4 h. At the second step, the performance of the prepared AC in removing of COD by adsorption process was evaluated via studying the effects of three operating parameters, namely adsorbent dosage (1–5 g/L), pH (3–9), and shaking speed (100–400 rpm) on the removal of COD(RE%) using a response surface methodology (RSM). Increasing AC dosage led to an increase in RE% while increasing each of pH and shaking speed resulted in lowering RE%. The optimum conditions for higher RE% were AC dosage of 5 g/L, pH of 3, and shaking speed of 100 rpm in which a removal efficiency of 94.54 % was obtained. The degradation of COD with time was found to obey a second order kinetic confirming the chemisorption is the rate limiting step in the adsorption process.

Effect of PAM on Surface Hydrophobicity of Montmorillonite and Difference of Interface Adsorption: An Experimental and Simulation Study.

How to realize efficient treatment of coal slime generated by a coal washing operation is an urgent problem to be solved in this industry. The presence of clay minerals, especially highly hydrophilic montmorillonite (MMT), is the key to the poor treatment effect of coal slime. Polyacrylamide (PAM) is very popular as a polymer agent to improve the treatment of coal slime. However, when it is used to treat coal slime with a high content of MMT, the selection of PAM type and the mechanism of action are still lacking. In this study, the effects of different types of PAM on the treatment of coal slime water containing MMT are considered by sedimentation and press filtration tests. The interaction mechanism of PAM on the MMT surface is studied by using ζ-potential, Brunauer-Emmett-Teller (BET) analysis, low-field nuclear magnetic resonance, density functional theory (DFT), and molecular dynamics (MD) simulations. The results show that the three PAM can improve the sedimentation and filtration effect of coal slime water, and the performance is CPAM > NPAM > APAM. The ζ-potential of the MMT (001) surface increases under the action of three PAM, and the effect of CPAM is the most significant. The adsorption of PAM on the MMT (001) surface has the ability to neutralize the surface charge of MMT. The flocculation of MMT particles under PAM results in an increase of particle size and a decrease of specific surface area. Meanwhile, the pore volume of MMT decreases, and the average pore size increases. In addition, PAM mainly removes vicinal water on the MMT surface. The active sites of the MMT surface and PAM are calculated by DFT. The adsorption of three PAM structural units on the MMT Na-001 surface and non-001 surface is nonbonding interaction, and the adsorption energy of CPAM is the largest. And the left shift of εp of the O atom on the MMT surface is conducive to the stable adsorption of CPAM. The MD results show that the concentration of water molecules on the surface of MMT Na-001 decreases after PAM is adsorbed on the MMT Na-001 surface, indicating that PAM can keep water molecules away from the surface of MMT, which means that the hydrophobicity of the MMT surface is enhanced. This study has guiding significance for the selection of PAM and the development of new flocculants in the treatment of coal slime with a high content of MMT.

Application of Infrared Pyrolysis and Chemical Post-Activation in the Conversion of Polyethylene Terephthalate Waste into Porous Carbons for Water Purification.

In this study, we compared the conversion of polyethylene terephthalate (PET) into porous carbons for water purification using pyrolysis and post-activation with KOH. Pyrolysis was conducted at 400-850 °C, followed by KOH activation at 850 °C for samples pyrolyzed at 400, 650, and 850 °C. Both pyrolyzed and post-activated carbons showed high specific surface areas, up to 504.2 and 617.7 m2 g-1, respectively. As the pyrolysis temperature increases, the crystallite size of the graphite phase rises simultaneously with a decrease in specific surface area. This phenomenon significantly influences the final specific surface area values of the activated samples. Despite their relatively high specific surface areas, pyrolyzed PET-derived carbons prove unsuitable as adsorbents for purifying aqueous media from methylene blue dye. A sample pyrolyzed at 650 °C, with a surface area of 504.2 m2 g-1, exhibited a maximum adsorption value of only 20.4 mg g-1. We propose that the pyrolyzed samples have a surface coating of amorphous carbon poor in oxygen groups, impeding the diffusion of dye molecules. Conversely, post-activated samples emerge as promising adsorbents, exhibiting a maximum adsorption capacity of up to 127.7 mg g-1. This suggests their potential for efficient dye removal in water purification applications.

Towards a low-cost solid oxide electrolyte based on local mineral

The demand for critical minerals is showing significant growth as a response to various applications in energy transition devices such as those involving solid oxide electrolytes. Thus, in the present work a dense and conductor material was prepared following appropriate sintering of a low-cost local natural mineral (NM). Comprehensive morphological, textural, and microstructural characterizations were carried out in order to study the densification of NM samples shaped as thin layers obtained by casting method using polyethylene oxide (PEO) as a plasticizer and distilled water. It was found that sintering at 1000 °C was enough to achieve densification without any change of material structure, as indicated by significant decrease of specific surface area and porosity. Furthermore, the effect of temperature on electrical conductivity was measured by impedance spectroscopy (IS) under dry air by increasing temperatures and total conductivity value at about 8.48 × 10−2 S cm−1 was reached at 950 °C. Such promising intrinsic electrical conductivity, in addition to appropriate material densification, paves the way for possible application of such an available and low-cost natural minerals as solid oxide electrolyte.

Sulfur-tolerant mechanism in catalytic combustion of toluene over Co/5Mg-γ-Al2O3 catalyst: Dual functions of MgO

Using toluene catalytic combustion as a probe reaction, simulating quantitative sulfur poisoning by in situ thermal decomposition of ammonium sulfate solution, the study used MgO modified γ-Al2O3 to support cobalt-based catalyst, and the result displayed that the catalyst exhibited excellent sulfur poisoning resistance. The successful construction of MgO-Al2O3 heterogeneous interface weakened the interaction between Co and Al and reduced the production of inactive CoAl2O4. Besides that, it fixed sulfur species and formed MgSO4 to protect active components. The dual function of MgO have been proved by various characterization experiments. The modification of γ-Al2O3 by the appropriate amount of MgO could improve the catalytic activity of Co/γ-Al2O3. Meanwhile, T100 increased from 300 °C to 330 °C after 1.6 wt% sulfur poisoning and we concluded that the decrease in catalytic performance was not caused by the loss of active Co, but by the decrease of specific surface area and lattice oxygen activity.

Reducing rare earth loss by adding acetic acid in the aluminum removal process of rare earth leaching solution

The ionic-type rare earth ore, abundant in medium and heavy rare earth elements, is a strategic mineral resource. The removal of aluminum from ionic rare earth leaching solution results in over 8% loss of rare earths. Preliminary research has found that adding acetic acid (HAc) during aluminum removal process can effectively reduce the loss of rare earth elements. In this paper, through the calculation of the species distribution in the La2(SO4)3-Al2(SO4)3-HAc-H2O system, it is found that HAc forms an AlOH-Ac+ complex with aluminum ions, with a proportion of up to 70%, which will increase the initial precipitation pH of aluminum hydroxide. Furthermore, HAc and lanthanum form a LaAc2+ complex, and the proportion can reach more than 20%. Moreover, the zeta potential, FT-IR, and XPS tests of aluminum hydroxide, obtained by neutralization precipitation, revealed that the complexation of HAc and aluminum can reduce the precipitation rate of aluminum hydroxide, so that its particle size increases, the specific surface area decreases, and the van der Waals force adsorption sites are reduced. HAc can be chemically adsorbed on aluminum hydroxide, thereby increasing the zeta potential of aluminum hydroxide and ultimately reducing its electrostatic adsorption effect on rare earths. Additionally, the complexation of HAc and rare earth elements can reduce the local supersaturation of rare earth hydroxides and decline the coprecipitation of rare earth elements. Finally, under a precipitation endpoint pH of 5.2, HAc concentration of 0.006 mol/L, aluminum concentration of 0.2 g/L, rare earth concentration of 0.8 g/L, magnesium ion concentration of 0.5 g/L and magnesium oxide slurry concentration of 0.45 mol/L, the aluminum removal efficiency obtained with rare earth leaching solution reached 98.47%, and the rare earth loss efficiency was 2.62%. Compared with the control, the rare earth loss efficiency was reduced by 5.59%. This paper provides guidance for the efficient and green development of ionic-type rare earth ore.

Reactivity of kaolinitic clays calcined in the 650 °C–1050 °C temperature range: Towards a robust assessment of overcalcination

Using calcined clays as supplementary cementitious materials is one of the main solutions available for a substantial and widespread reduction of the clinker factor in cement. Thus, understanding the phenomena governing their production process and reactivity is crucial for a successful technological deployment. In this study, the mineralogical and physical changes experienced by kaolinitic clays calcined within 650 and 1050 °C were explored, with emphasis on the identification of overcalcination. It was observed that the decrease in reactivity above the optimum calcination temperature is associated with the formation of Al–Si spinel and a decrease in specific surface area, which is linked to a modification of the pore size distribution within the particles. Differential scanning calorimetry (DSC) was identified as the most robust, and repeatable technique to identify an overcalcined kaolinitic clay. In combination with thermogravimetric analysis (TGA), it can provide a complete calcination process overview, relevant for quality control purposes.

Thermal behavior of minerals in shale and its influence on evolution of gas-flow channels under thermal shock

Thermal shock-induced damage can significantly enhance the connectivity of the rock's fracture network. Thermal Enhanced Recovery (TER) technology holds promising potential for application in shale gas production. Nevertheless, there is still a lack of direct experimental studies focusing on the evolution of shale's gas-flow channels and the mechanism of thermal fracturing in shale under the influence of thermal shock. In this study, we initially investigated the impact of thermal shock on various minerals in shale through X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) imaging, and examined the mass and heat variation with temperature using Thermogravimetry-Differential Scanning Calorimetry (TG-DSC) testing. Subsequently, we assessed the alterations in shale's internal structure due to thermal shock through low-temperature gas (N2) adsorption (LTGA) analysis, and observed the distribution and expansion patterns of shale fractures under thermal shock using computed tomography (CT). Finally, we evaluated the changes in shale permeability before and after thermal shock. The findings indicate that quartz, feldspar, and clay exhibit relatively stable behavior in shale under thermal shock, whereas carbonate and pyrite are prone to crack. Under the combined influence of mineral cracking and thermal stress, the internal pore structure of shale tends to enlarge in size while reducing in surface area. The substantial decrease in pore specific surface area highlights the considerable reduction in gas adsorption capacity. Furthermore, fractures expand along the bedding planes as surface fractures. The expansion of pores and fractures promotes the formation of primary gas-flow channels. In addition, the aforementioned test results demonstrate a high level of consistency, specifically highlighting a distinct threshold temperature (500 °C) for the alteration of various physical parameters of shale during thermal shock. This study is anticipated to offer insights into the implementation of TER technology in the oil and gas industry.

The electronic structure regulation improving xylene gas sensing properties in p-type Zn-doped α-Fe2O3 nanoparticles

Xylene is a highly carcinogenic inert gas, and achieving highly selective detection toward xylene gas is crucial for environmental protection and physical health. Herein, α-Fe2O3 nanoparticles doped with different Zn contents (ZF-0, ZF-1, ZF-2 and ZF-3) have been prepared through a feasible solvothermal and subsequent annealing treatment. The successful doping of Zn has been confirmed through EDS, XPS and XRD characterizations. After Zn doping, the baseline resistance in air reduces, the band gap and specific surface area decrease, but oxygen vacancy defects increase for α-Fe2O3 nanoparticles. When applied as gas sensors, all as-prepared α-Fe2O3 samples show typical p-type semiconductor gas sensing behaviors. Especially, the ZF-2 sample with appropriate amount of Zn doping exhibits an excellent xylene gas sensing selectivity. Meanwhile, the ZF-2 sensor shows a high response, fast response/recovery speed, well stability and repeatability and a detection limit of 5 ppm at 240 °C. The acceptor level and oxygen vacancy defects in ZF-2 nanoparticles promote the catalytic oxidation of xylene gas by p-type Zn-doped α-Fe2O3 oxide semiconductors, thereby resulting in better xylene gas sensing performance.

Improved high-temperature sintering resistance and light alkanes oxidation activity by La modification on Co3O4 nanocatalyst

In order to improve low-temperature activity and high-temperature sintering resistance of cobalt-based catalyst in catalytic degradation of emitted light alkanes, a strategy of lanthanum modification on Co3O4 nanocrystalline is proposed in this work, aiming at efficiently degrading methane emitted from the oil and natural gas industry. The La-Co3O4 nanocatalysts were prepared by co-precipitation method, and the effects of La-doping on the structural features and catalytic activity of Co3O4 catalyst for methane oxidation were investigated. The results show that the addition of lanthanum forms a composite catalyst containing La2O3 phase and Co3O4 phase, and the interaction increases the active species, which can significantly improve the low-temperature activity of the catalyst. Among them, 5 % La-Co3O4-F catalyst shows the best catalytic activity with 48 °C decrease of the temperature of 90 % methane conversion (T90) compared with pure Co3O4. Furthermore, with thermal ageing treatment at 750 °C for 100 h, Lanthanum modification can significantly slow down the agglomeration growth and the decrease of specific surface area of cobalt oxide in long-term running, and the formation of perovskite structure (LaCoO3) on Co3O4 nanocrystal surface increases the mobility of lattice oxygen, further inhibiting the sintering deactivation of Co3O4 catalyst. The catalyst doped with 5 % La still showed better performance after thermal ageing, which is 127 °C lower than T90 of pure Co3O4. Moreover, this advantage of La doping can also be observed in the catalytic oxidation of other typical hydrocarbons such as ethane and propane. This work provides a promising strategy toward the design of advanced non-precious metal oxide catalysts for practical catalytic oxidation application with excellent high-temperature sintering resistance.

Magnetite nanoparticles obtained by solution combustion synthesis

This research presents a comprehensive investigation into the synthesis and characterization of magnetite nanoparticles through solution combustion reactions ignited by conventional means. In addition to the structural and compositional findings, this study's main investigation results include the specific surface area measurements conducted using the BET method. The analysis revealed specifi c surface area values for the synthesized magnetite nanoparticles at varying propellant-to-oxidant ratios, demonstrating a substantial decrease in specific surface area as the ratio increased. Specifically, specific surface areas of 72.203 m2/g for the 1:1 ratio, 22.240 m2/g for the 1:1.5 ratio, and 9.204 m2/g for the 1:2 ratio were determined. Furthermore, calculations based on the BET results and assuming spherical magnetite nanoparticles provided average particle sizes of 16±1 nm for the 1:1 ratio, 51±2 nm for the 1:1.5 ratio, and 125±4 nm for the 1:2 ratio. These findings highlight the impact of synthesis parameters on the nanoparticles' surface area and size, shedding light on their potential applications in various fields, including nanomedicine and magnetic diagnostics. Overall, this research contributes valuable insights into the synthesis, characterization, and tunable properties of magnetite nanoparticles, offering potential avenues for their utilization across diverse industries.

Autoclave-Induced Changes in the Physicochemical Properties and Antigen Adsorption of Aluminum Adjuvants

Aluminum hydroxide adjuvants are widely used in human vaccines, such as diphtheria, tetanus, hepatitis A and hepatitis B vaccines. The adsorption of antigens on aluminum hydroxide adjuvants determines the immune boosting effect of vaccines, but it is not clear how changes in physicochemical properties resulting from the production and formulation processes affect the adsorption of aluminum hydroxide adjuvants with antigens. In this study, the commercial aluminum hydroxide adjuvant Alhydrogel® was pretreated by commonly used processes such as autoclaving and calcination, and the changes of aluminum hydroxide adjuvant in physicochemical properties during the treatment were then comprehensively characterized. The adsorption of ovalbumin (OVA) with treated Alhydrogel®, was also investigated, it was found that the decrease in specific surface area caused by the autoclaving process reduced the adsorptive capacity of the antigen, and the adsorptive strength of antigen was decreased only when the surface hydroxyl groups and chemically bound water of adjuvant were reduced by calcination. These findings help to optimize the production and formulation process of adjuvants for the rational regulation of antigen adsorption in vaccines.

Evaluation of Physico-Chemical Properties Influence on Drug Product in vitro Profiles and Solubility Profile of Fourth Generation Antibacterial Drug

Moxifloxacin hydrochloride drug substance used to treat bacterial infections in many different parts of the body and most widely used worldwide. In this study, various high-end physico-chemical techniques are used like PXRD, DSC, TGA, BET SSA and PSD analysis to check the relative differences on the product behaviour. The present work reports an impact of alteration in particle size due to compaction process where increase in particle size has been observed from 15.912 μm to 751.001 μm, decrease in specific surface area from 1.89 m2/g to 0.861 m2/g, decrease in crystallinity from 91.65% to 59.15% and impact of dehydration or loss of water from 3.776% to 1.866%, which were observed during study. All the alterations in the physico-chemical properties impacting the drug manufacturing process and on the bioperformance of the finished product. This research attempt aims to investigate the effects of these modifications on in vitro experiments conducted in the office of generic drugs (OGD) media and the equilibrium solubility profile. The in vitro studies resulted about 35% release difference observed in the initial time points, whereas solubility in water observed about 17 mg/mL difference. This research work helps to demonstrate the optimization of finished product development process to meet the biofriendly formulation.

Influence of structural changes on gas transport properties of a cycled CaO/Ca(OH)2 powder bulk for thermochemical energy storage

Thermochemical energy storage using reversible gas-solid reactions has a great potential to evolve into a vital part of a future energy system. A major obstacle for technical application, however, is caused by insufficient gas transport within storage reactors leading to ineffective charging and discharging as well as lower storage densities. Although significant changes in the solid bulk structure are reported throughout the literature, the relevant material property – the bulk permeability – is rarely experimentally studied. In the presented study, the evolution of the gas permeability of a technical grade CaO/Ca(OH)2 powder bulk is studied experimentally. To this end, the pressure drop at ambient conditions is recorded before thermochemical cycling as well as after each dehydration respectively rehydration reaction. The pressure gradient and thereby the permeability is determined based on Darcy's law. The permeability of the fresh Ca(OH)2 bulk after compaction due to the gas flow is 1·10−13 m2. Due to restructuring during thermochemical cycling the permeability increases to 1.6…3.3·10−12 m2 for the cycled Ca(OH)2 bulk and 9.2·10−12 m2 to 2.4·10−11 m2 for the cycled CaO bulk. Further analysis of fresh and cycled samples shows a general increase in particle size and decrease in specific surface area as well as a reduction in reactivity due to agglomeration of the powder. Noticeable is the inhomogeneity of the cycled bulk with powder mixed with larger agglomerates at the top of the bulk and highly porous but seemingly homogeneous solid material at the bottom. Based on the experimental results, gas transport within the agglomerates is identified as a major limiting factor within thermochemical reactors. It is therefore proposed to consider cycled CaO/Ca(OH)2 bulks on a macro- and mesoscale (respectively bulk and agglomerate) simultaneously if transport properties – and their impact on effective reaction dynamics – are relevant.

Adsorption Mechanisms of Glyphosate on Ferrihydrite: Effects of Al Substitution and Aggregation State.

Ferrihydrite is one of the most reactive iron (Fe) (oxyhydr)oxides in soils, but the adsorption mechanisms of glyphosate, the most widely used herbicide, on ferrihydrite remain unknown. Here, we determined the adsorption mechanisms of glyphosate on pristine and Al-substituted ferrihydrites with aggregated and dispersed states using macroscopic adsorption experiments, zeta potential, phosphorus K-edge X-ray absorption near-edge structure spectroscopy, in situ attenuated total reflectance Fourier transform infrared spectroscopy coupled with two-dimensional correlation spectroscopy, and multivariate curve resolution analyses. Aggregation of ferrihydrite decreases the glyphosate adsorption capacity. The partial substitution of Al in ferrihydrite inhibits glyphosate adsorption on aggregated ferrihydrite due to the decrease of external specific surface area, while it promotes glyphosate adsorption on dispersed ferrihydrite, which is ascribed to the increase of surface positive charge. Glyphosate predominately forms protonated and deprotonated, depending on the sorption pH, monodentate-mononuclear complexes (MMH1/MMH0, 77-90%) on ferrihydrites, besides minor deprotonated bidentate-binuclear complexes (BBH0, 23-10%). Both Al incorporation and a low pH favor the formation of the BB complex. The adsorbed glyphosate preferentially forms the MM complex on ferrihydrite and preferentially bonds with the Al-OH sites on Al-substituted ferrihydrite. These new insights are expected to be useful in predicting the environmental fate of glyphosate in ferrihydrite-rich environments.