Artifacts and misinterpretations in gas physisorption measurements and characterization of porous solids

Preparation of biochar from anaerobic digested sludge for enhancement of sludge dewatering

Effective dewatering is vital for both sludge treatment and resource recovery. This study focuses on converting post-anaerobic digested sludge into biochar to enhance sludge dewatering. The sludge-derived biochar is further modified with polyacrylamide (PAM-ADBC) and applied with sulfuric acid-modified montmorillonite (HMTS) for better performance. Significant advancements in dewatering were noted, even at reduced HMTS (0.1 g/g DS) and PAM-ADBC (25 g/kg DS) dosages. These improvements resulted in a remarkable 41.96% enhancement in capillary suction time (17.2 s) and a notable 20.26% reduction in moisture content (66.33%), respectively, all while maintaining a stable pH level. HMTS, with leached cations, improved dewatering by decomposing the extracellular polymeric substance structure through electro-neutralization to release the internal bound water within sludge flocs. Simultaneously, PAM-ADBC coagulated decomposed sludge particles into larger flocs to form a skeletal structure with itself to discharge internal water in compression dewatering. This study introduces a resource recovery method for anaerobically digested sludge and highlights its potential for sustainable utilization.

Weakened Mn-O bond in Mn-Ce catalysts through K doping induced oxygen activation for boosting benzene oxidation at low temperatures

K-doped Mn-Ce solid solution catalysts were synthesized using a combination of coprecipitation and hydrothermal methods, demonstrating excellent performance in benzene oxidation. The catalyst K1Ce5Mn5 exhibited comparable activity to noble metal catalysts, achieving a 90 % benzene conversion at approximately 194 ℃. Durable tests under dry and moist conditions revealed that the catalyst could maintain its activity for 50 h at 218 ℃ and 236 ℃, respectively. Characterization results indicated that the catalyst's enhanced activity resulted from the weakened Mn-O bonding caused by the introduction of K+, facilitating the activation of oxygen and its involvement in the reaction. CeOx, the main crystalline phase of Mn-Ce solid solutions, provided abundant oxygen vacancies for capturing and activating oxygen molecules for the weakened Mn-O structures. This conclusion was further supported by partial density of state analysis from density functional theory computations, revealing that the introduction of K+ weakened the orbital hybridization of Mn3d and O2p. Finally, in situ diffuse reflectance infrared Fourier-transform spectroscopy (in situ DRIFTS) studies on Ce5Mn5 and K1Ce5Mn5 catalysts suggested that the introduction of K+ promoted the conversion of adsorbed benzene. Furthermore, intermediate products were transformed more rapidly for K1Ce5Mn5 compared to Ce5Mn5.

The design of high-efficient MOFs for selective Ag(I) capture: DFT calculations and practical applications

Recovering silver from wastewater not only significantly reduces environmental harm but also meets the growing demand for silver in modern industry. Here, a novel metal-organic framework adsorbent (MOF-RD) using rhodanine derivatives as linkers is introduced for the efficient and selective capture of silver ions in real wastewater. The adsorption of MOF-RD followed pseudo-second-order and Sips models, and thermodynamic investigations revealed the process to be endothermic. MOF-RD demonstrated a remarkable adsorption capacity of 707.2 mg·g-1 for Ag(I) at pH 5 and 318 K. The interaction between silver ions and MOF-RD was mainly electrostatic attraction and coordination, with coordination primarily occurring at the CO and CS sites within the rhodanine motif. The practical applicability of MOF-RD for selective adsorption of Ag(I) was validated in actual wastewater with high-concentration competing metal ions. Furthermore, after 10 adsorption-desorption cycle experiments, MOF-RD still retained a strong regenerative capability. The results reveal the good potential of MOF-RD as an adsorbent for selectively recovering Ag(I) from industrial wastewater. Additionally, the strategies and methods adopted in this article also provide new perspectives and technical paths for the separation and recovery of other metal ions in wastewater.

The influence of HKUST-1 and MOF-76 hand grinding/mechanical activation on stability, particle size, textural properties and carbon dioxide sorption

In this study, we explore the mechanical treatment of two metal-organic frameworks (MOFs), HKUST-1 and MOF-76, applying various milling methods to assess their impact on stability, porosity, and CO2 adsorption capacity. The effects of different mechanical grinding techniques, such as high-energy ball milling and hand grinding, on these MOFs were compared. The impact of milling time, milling speed and ball size during high-energy ball milling was assessed via the Design of Experiments methodology, namely using a 33 Taguchi orthogonal array. The results highlight a marked improvement in CO2 adsorption capacity for HKUST-1 through hand milling, increasing from an initial 25.70 wt.% (5.84 mmol g-1) to 41.37 wt.% (9.40 mmol g-1), marking a significant 38% increase. In contrast, high-energy ball milling seems to worsen this property, diminishing the CO2 adsorption abilities of the materials. Notably, MOF-76 shows resistance to hand grinding, closely resembling the original sample's performance. Hand grinding also proved to be well reproducible. These findings clarify the complex effects of mechanical milling on MOF materials, emphasising the necessity of choosing the proper processing techniques to enhance their stability, texture, and performance in CO2 capture and storage applications.

Numerical Analysis of the Porous Structure of Activated Carbons Derived from Synthetic Polymers

This paper presents original results from the unique analysis of the porous structure of activated carbons (ACs) produced through the chemical activation of polyethylene terephthalate (PET) and polyacrylonitrile (PAN), as well as from a physical mixture of both polymers. An advanced method of adsorbent surface analysis-more specifically, the new method of numerical clustering-based adsorption analysis regarding the surface heterogeneity, pore geometry and adsorption energy distribution parameters-allowed us to obtain information about the porous structure of the ACs from the synthetic polymers mentioned above. As the results showed, ACs obtained with PAN were characterised by a first adsorbed layer with the highest volume. When the surface heterogeneity, highly desirable in most advanced adsorption processes, is taken into account, the materials with the best surface properties in both potassium carbonate (K2CO3) and potassium hydroxide (KOH) activation processes were the ACs obtained with a mass proportion of PET to PAN of 1:3, which were characterised by a low degree of surface heterogeneity and a first adsorbed layer presenting a relatively large volume.

Ultrastable Organic Anode Enabled by Electrochemically Active MXene Binder toward Advanced Potassium Ion Storage

Conjugated carbonyl compounds are regarded as promising organic anode materials for potassium ion batteries (PIBs) due to their rich redox sites, excellent reversibility, and structural tunability, but their low electrical conductivity and severe solubility in organic electrolytes have substantially restricted their practical application. Herein, 2D MXene is utilized as an electrochemically active binder to fabricate perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) electrodes for high-performance PIBs. MXene, coupled with Super-P particles, served as a binder and conductive matrix to facilitate rapid ion and electron transport, restrain the solubility of PTCDA, promote potassium adsorption, and alleviate the volume expansion of PTCDA during potassiation. Consequently, the PTCDA electrode bonded by the MXene/Super-P system delivers excellent potassium storage performance in terms of a high capacity of 462 mAh g-1 at 50 mA g-1, superior rate capability of 116.3 mAh g-1 at 2000 mA g-1, and stable cycle performance over 3000 cycles with a low capacity decay rate of ∼0.0033% per cycle. When configured with the PTCDA@450 cathode, an all-PTCDA potassium ion full cell delivers a maximum energy density of 179.5 Wh kg-1, indicating the superiority of MXene as an electrochemically active binder to promote the practical application of organic anodes for PIBs.

Synthesis of metal-organic frameworks with multiple nitrogen groups for selective capturing Ag(I) from wastewater

As a noble metal with extremely high economic benefits, the recovery of silver ions has attracted a particular deal of attention. However, it is a challenge to recover silver ions efficiently and selectively from aqueous solutions. In this research, the novel metal-organic frameworks (MOFs) adsorbent (Zr-DPHT) is prepared for the highly efficient and selective recovery of silver ions from wastewater. Experimental findings reveal that Zr-DPHT's adsorption of Ag(I) constitutes an endothermic process, with an optimal pH of 5 and exhibits a maximum adsorption capacity of 268.3 mg·g-1. Isotherm studies show that the adsorption of Ag(I) by Zr-DPHT is mainly monolayer chemical adsorption. Kinetic studies indicate that the internal diffusion of Ag(I) in Zr-DPHT may be the rate-limiting step. The mechanism for Ag(I) adsorption on Zr-DPHT involves electrostatic interactions and chelation. In competitive adsorption, Ag(I) has the largest partition coefficient (9.64 mL·mg-1), indicating a strong interaction between Zr-DPHT and Ag(I). It is proven in the adsorption-desorption cycle experiments that Zr-DPHT has good regeneration performance. The research results indicate that Zr-DPHT can serve as a potential adsorbent for efficiently and selectively capturing Ag(I), providing a new direction for MOFs in the recycling field of precious metals.

On the Low-Pressure Hysteresis (LPH) in Gas Sorption Isotherms of Porous Carbons

This study investigates the origin of low-pressure hysteresis (LPH) in the adsorption and desorption of three different probe molecules: carbon dioxide, nitrogen, and argon, across various adsorption temperatures (from cryogenic to room temperature), and within five different carbon materials: synthetic carbons (pristine and one post-synthetically oxidized) and natural coal. Significant attention is dedicated to elucidating LPH in oxidized samples outgassed at various temperatures (120-350 °C). Experimental results show that insufficient outgassing temperature can lead to unreliable data due to artificial LPH and significantly underestimated textural properties, primarily caused by porosity blockage from substances like moisture. Conversely, in samples where heteroatoms have a stabilizing effect on texture, such as natural coal, careful consideration of outgassing temperature is crucial due to the risk of thermal degradation. Other factors contributing to LPH are adsorption temperature, and especially, kinetic limitations at cryogenic temperatures for cellulose-based carbons. Minor factors responsible for LPH are the physical state of the sample (monolith vs powder) and the flexibility of the porous system, both studied by carbon dioxide sorption. This study constitutes an important piece in the evaluation of LPH, providing practical recommendations and underlining the importance of experimental design, with implications for further research in this complex field.

Cellulose-Amine Porous Materials: The Effect of Activation Method on Structure, Textural Properties, CO2 Capture, and Recyclability

CO2 capture via physical adsorption on activated porous carbons represents a promising solution towards effective carbon emission mitigation. Additionally, production costs can be further decreased by utilising biomass as the main precursor and applying energy-efficient activation. In this work, we developed novel cellulose-based activated carbons modified with amines (diethylenetriamine (DETA), 1,2-bis(3-aminopropylamino)ethane (BAPE), and melamine (MELA)) with different numbers of nitrogen atoms as in situ N-doping precursors. We investigated the effect of hydrothermal and thermal activation on the development of their physicochemical properties, which significantly influence the resulting CO2 adsorption capacity. This process entailed an initial hydrothermal activation of biomass precursor and amines at 240 °C, resulting in C+DETA, C+BAPE and C+MELA materials. Thermal samples (C+DETA (P), C+BAPE (P), and C+MELA (P)) were synthesised from hydrothermal materials by subsequent KOH chemical activation and pyrolysis in an inert argon atmosphere. Their chemical and structural properties were characterised using elemental analysis (CHN), infrared spectroscopy (IR), scanning electron microscopy (SEM), and thermogravimetric analysis (TG). The calculated specific surface areas (SBET) for thermal products showed higher values (998 m2 g-1 for C+DETA (P), 1076 m2 g-1 for C+BAPE (P), and 1348 m2 g-1 for C+MELA (P)) compared to the hydrothermal products (769 m2 g-1 for C+DETA, 833 m2 g-1 for C+BAPE, and 1079 m2 g-1 for C+MELA). Carbon dioxide adsorption as measured by volumetric and gravimetric methods at 0 and 25 °C, respectively, showed the opposite trend, which can be attributed to the reduced content of primary adsorption sites in the form of amine groups in thermal products. N2 and CO2 adsorption measurements were carried out on hydrothermal (C) and pyrolysed cellulose (C (P)), which showed a several-fold reduction in adsorption properties compared to amine-modified materials. The recyclability of C+MELA, which showed the highest CO2 adsorption capacity (7.34 mmol g-1), was studied using argon purging and thermal regeneration over five adsorption/desorption cycles.

Effect of synthesis conditions on the porous texture of activated carbons obtained from Tara Rubber by FeCl3 activation

This paper presents the results of an unique analysis of the influence of the mass ratio of activator FeCl3 to precursor and the temperature of the activation process on the formation of the porous structure of activated carbons obtained from Tara Rubber by FeCl3 activation. The study used the new numerical clustering based adsorption analysis method and the quenched solid density functional theory, taking into account, among other things, the heterogeneity of the analysed surface which is a new approach rarely used in the analysis of the porous structure of adsorbents. On the basis of the calculation results, it was concluded that the activated carbon with the most developed porous texture was obtained at a mass ratio (FeCl3:Tara Rubber) of 2, at an activation process temperature of 800 °C. This activated carbon is also characterised by the lowest degree of surface heterogeneity and at the same time, however, the widest range of micropores compared to activated carbons obtained at other mass ratios. The analyses carried out further demonstrated the valuable and complementary information obtained from the structure analysis methods and their high utility in practical applications, especially in the development of new industrial technologies for the production of adsorbents and the selection of optimal conditions for their production.

Numerical analysis of the porous structure of spherical activated carbons obtained from ion-exchange resins

This paper presents the results of an analysis of the porous structure of spherical activated carbons obtained from cation-exchange resin beads subjected to ion exchange prior to activation. The study investigated the effects of the type of cation exchange resin, the concentration of potassium cations in the resin beads and the temperature of the activation process on the adsorption properties of the resulting spherical activated carbons. The numerical clustering-based adsorption analysis method and the quenched solid density functional theory were used to analyse the porous structure of spherical activated carbons. Based on original calculations and unique analyses, complex relationships between preparation conditions and the porous structure properties of the obtained spherical activated carbons were demonstrated. The results of the study indicated the need for simultaneous analyses using advanced methods for the analysis of porous structures, i.e., the numerical clustering-based adsorption analysis method and the quenched solid density functional theory. This approach allows a reliable and precise determination of the adsorption properties of the materials analysed, including, among other things, surface heterogeneities, and thus an appropriate selection of production conditions to obtain materials with the expected adsorption properties required for a given industrial process.