Biogas Upgrading via Cyclic CO2 Adsorption: Application of Highly Regenerable PEI@nano-Al2O3 Adsorbents with Anti-Urea Properties

Adsorption behaviour of cationic and anionic dyes on new chitosan-activated carbon@metal oxide hydrogels beads: Effect of the metal nature and comparative study

The present work concerns the preparation of hydrogel composite beads based on activated carbon@metal oxide (M: CaO, Al2O3, CaO/Al2O3) from the calcination of olive stones biomass encapsulated by chitosan as a cross-linking matrix. The biocomposites were characterized by SEM, BET, Zeta potential, TGA, XRD and FTIR in order to investigate the morphological, thermal, textural and structural properties of these solids. The encapsulation of activated carbon-based nanocomposites leaded to obtain a porous structure. The nanocomposite beads were used as biosorbents for the MB and OG dyes removal. Several parameters affecting the adsorption process were investigated such as effect of the pH, dyes concentration, temperature and time. The adsorption process follows the Langmuir isotherm with R2 ≈ 1 and the pseudo-second order model confirming the uniform, monolayer, endothermic and chemisorption nature of the dye's adsorption. All biosorbents showed a higher affinity to anionic dye "Orange G (OG)" due to their positive surface charge. The CSAC@Ca showed the best adsorption capacity Qmax = 323.625 mg/g against OG while the CSAC@Al showed the best adsorption capacity Qmax = 134.589 mg/g against methylene blue. Finally, the hydrogel beads were reused in five successive cycles and showed very good efficiency even at the last cycle contrary to the parent chitosan.

Exploration of structured solid amine adsorbents for CO2 capture: PEI-loaded composite foam material

Solid amine adsorbents are widely employed for CO2 capture due to their high selectivity and renewability. However, most existing adsorbents are in powdered form, and current shaping methods often suffer from poor universality, complex synthesis procedures, low mechanical strength, or pore structure degradation-factors that significantly hinder industrial application. To address these challenges, a scalable and cost-effective strategy is proposed for fabricating structured solid amine adsorbents by combining porous materials (e.g. biochar), industrial waste-based sulfur-aluminum cementitious binders, and H2O2-assisted chemical foaming. This process integrates micro-mesopores derived from the porous materials with macropores generated through foaming and hydration, resulting in a 3D interconnected hierarchical pore structure. The structured adsorbent exhibits excellent compressive strength (∼77.33 N), competitive CO2 adsorption capacity (60.04 mg/g at 90°C), high amine utilization (68.52%), and good reusability (only a 7.59% reduction after five cycles). Kinetic analysis reveals that 76.38% of the total CO2 adsorption capacity occurs within the first 2 min, indicating a rapid initial adsorption rate despite structural shaping. Moreover, the proposed method is successfully extended to other carriers such as synthetic resin and nano-fumed silica, demonstrating strong material adaptability. In addition to adsorption capacity, this study emphasizes amine utilization as a key performance metric and introduces a novel evaluation chart for the simultaneous assessment of both parameters. Overall, this work addresses pressing challenges in shaping, mechanical strength, and cost, and offers an effective, scalable pathway for the practical deployment of solid amine adsorbents in CO2 capture technologies.

Design of Ultra-Stable Solid Amine Adsorbents and Mechanisms of Hydroxyl Group-Dependent Deactivation for Reversible CO2 Capture from Flue Gas

Although supported solid amine adsorbents have attracted great attention for CO2 capture, critical chemical deactivation problems including oxidative degradation and urea formation have severely restricted their practical applications for flue gas CO2 capture. In this work, we reveal that the nature of surface hydroxyl groups (metal hydroxyl Al-OH and nonmetal hydroxyl Si-OH) plays a key role in the deactivation mechanisms. The polyethyleneimine (PEI) supported on Al-OH-containing substrates suffers from severe oxidative degradation during the CO2 capture step due to the breakage of amine-support hydrogen bonding networks, but exhibits an excellent anti-urea formation feature by preventing dehydration of carbamate products under a pure CO2 regeneration atmosphere. In contrast, PEI supported on Si-OH-containing substrates exhibits excellent anti-oxidative stability under simulated flue gas conditions by forming a robust hydrogen bonding protective network with Si-OH, but suffers from obvious urea formation during the pure CO2 regeneration step. We also reveal that the urea formation problem for PEI-SBA-15 can be avoided by the incorporation of an OH-containing PEG additive. Based on the intrinsic understanding of degradation mechanisms, we successfully synthesized an adsorbent 40PEI-20PEG-SBA-15 that demonstrates outstanding stability and retention of a high CO2 capacity of 2.45 mmol g-1 over 1000 adsorption-desorption cycles, together with negligible capacity loss during aging in simulated flue gas (10% CO2 + 5% O2 + 3% H2O) for one month at 60-70 °C. We believe this work makes great contribution to the advancement in the field of ultra-stable solid amine-based CO2 capture materials.

Atom-level interaction design between amines and support for achieving efficient and stable CO2 capture

Amine-functionalized adsorbents offer substantial potential for CO2 capture owing to their selectivity and diverse application scenarios. However, their effectiveness is hindered by low efficiency and unstable cyclic performance. Here we introduce an amine-support system designed to achieve efficient and stable CO2 capture. Through atom-level design, each polyethyleneimine (PEI) molecule is precisely impregnated into the cage-like pore of MIL-101(Cr), forming stable composites via strong coordination with unsaturated Cr acid sites within the crystal lattice. The resulting adsorbent demonstrates a low regeneration energy (39.6 kJ/molCO2), excellent cyclic stability (0.18% decay per cycle under dry CO2 regeneration), high CO2 adsorption capacity (4.0 mmol/g), and rapid adsorption kinetics (15 min for saturation at 30 °C). These properties stem from the unique electron-level interaction between the amine and the support, effectively preventing carbamate products' dehydration. This work presents a feasible and promising cost-effective and sustainable CO2 capture strategy.

Deep insights into biodegradability mechanism and growth cycle adaptability of polylactic acid/hyperbranched cellulose nanocrystal composite mulch

The widespread use of petroleum-based plastic mulch in agriculture has accelerated white and microplastic pollution while posing a severe agroecological challenge due to its difficulty in decomposing in the natural environment. However, endowing mulch film with degradability and growth cycle adaptation remains elusive due to the inherent non-degradability of petroleum-based plastics severely hindering its applications. This work reports polylactic acids hyperbranched composite mulch (PCP) and measured biodegradation behavior under burial soil, seawater, and ultraviolet (UV) aging to understand the biodegradation kinetics and to increase their sustainability in the agriculture field. Due to high interfacial interactions between polymer and nanofiler, the resultant PCP mulch significantly enhances crystallization ability, hydrophilicity, and mechanical properties. PCP mulch can be scalable-manufactured to exhibit modulated degradation performance under varying degradation conditions and periods while concurrently enhancing crop growth (wheat). Thus, such mulch with excellent performance can reduce labor costs and the environmental impact of waste mulch disposal to replace traditional mulch for sustainable agricultural production.

The Morphologically Controlled Synthesis and Application of Mesoporous Alumina Spheres

The control of alumina morphology is crucial yet challenging for its various applications. Unfortunately, traditional methods for preparing alumina particles suffer from several limitations such as irregular morphology, poor dispersibility, and restricted application areas. In this study, we develop a novel method for preparing spherical mesoporous alumina using chitin and Pluronic P123 as mixed templates. The effects of reaction temperature, time, and the addition of mixed templates on the phase structure, micromorphology, and optical absorption properties of the samples were investigated. The experimental results indicate that lower temperature and shorter reaction time facilitated the formation of spherical mesoporous alumina with excellent CO2 adsorption capacity. The periodic density functional theory (DFT) calculations demonstrate that both the (110) and (100) surfaces of γ-Al2O3 can strongly adsorb CO2. The difference in the amount of CO2 adsorbed by Al2O3 is mainly due to the different surface areas, which give different numbers of exposed active sites. This approach introduces a novel strategy for utilizing biological compounds to synthesize spherical alumina and greatly enhances mesoporous alumina's application efficiency in adsorption fields. Moreover, this study explored the electrochemical performance of the synthesized product using cyclic voltammetry, and improved loading of electrocatalysts and enhanced electrocatalytic activity were discovered.

Characteristics, application and modeling of solid amine adsorbents for CO2 capture: A review

In recent years, global warming has become an important topic of public concern. As one of the most promising carbon capture technologies, solid amine adsorbents have received a lot of attention because of their high adsorption capacity, excellent selectivity, and low energy cost, which is committed to sustainable development. The preparation methods and support materials can influence the thermal stability and adsorption capacity of solid amine adsorbents. As a supporting material, it needs to meet the requirements of high pore volume and abundant hydroxyl groups. Industrial and biomass waste are expected to be a novel and cheap raw material source, contributing both carbon dioxide capture and waste recycling. The applied range of solid amine adsorbents has been widened from flue gas to biogas and ambient air, which require different research focuses, including strengthening the selectivity of CO₂ to CH₄ or separating CO₂ under the condition of the dilute concentration. Several kinetic or isotherm models have been adopted to describe the adsorption process of solid amine adsorbents, which select the pseudo-first order model, pseudo-second order model, and Langmuir isotherm model most commonly. Besides searching for novel materials from solid waste and widening the applicable gases, developing the dynamic adsorption and three-dimensional models can also be a promising direction to accelerate the development of this technology. The review has combed through the recent development and covered the shortages of previous review papers, expected to promote the industrial application of solid amine adsorbents.

Influence of ultra-micropore volume of activated carbons prepared from noble mung bean on the adsorption properties of CO2, CH4, and N2

In this study, mung bean-based nanoporous activated carbons with different pore properties were prepared by varying the mass ratio of activating agent (KOH) and activation temperature.

Insights into the Critical Role of Abundant-Porosity Supports in Polyethylenimine Functionalization as Efficient and Stable CO2 Adsorbents

The emerging polyethylenimine (PEI)-functionalized solid adsorbents have witnessed significant development in the implementation of CO₂ capture and separation because of their decent adsorption capacity, recyclability, and scalability. As an indispensable substrate, the importance of selecting porous solid supports in PEI functionalization for CO₂ adsorption was commonly overlooked in many previous investigations, which instead emphasized screening amine types or developing complex porous materials. To this end, we scrutinized the critical role of different commercial porous supports (silica, alumina, activated carbon, and polymeric resins) in PEI impregnation in this study, taking into account multiple perspectives. Hereinto, the present results identified that abundant larger pore structures and surface functional groups were conducive to loading a considerable amount of PEI molecules. Various supports after PEI functionalization had great differences in adsorption capacities, amine efficiencies, and the corresponding optimal temperatures. In addition, more attention was paid to the role of porous supports in long-term stability during the consecutive adsorption-regeneration cycles, while N₂ and CO₂ purging as regeneration strategies, respectively. Especially, CO₂-induced degradation due to urea species formation was specifically recognized in a SiO₂-based adsorbent, which would induce serious concerns in CO₂ cyclic capture. On the other side, we also confirmed that adopting conventional porous supports, for example, HP20, could achieve superior adsorption performance (above 4 mmol CO₂/g) and cyclic stability (around 1% loss after 30 cycles) rather than the ones synthesized through complex approaches, which ensured the availability and scalability of PEI-functionalized CO₂ adsorbents.

On the state of the art of crystalline structure reconstruction of coal fly ash: A focus on zeolites

Coal fly ash (CFA) is fine particles generated from coal combustion, and large amount of CFA causes environmental pollution. Traditionally, CFA is added into construction materials, which has realized effective reduction. As the exploration of CFA properties goes deeper, finer utilization has been studied to maximize the recycling of CFA. Summarized from plenty of investigations, structure reconstruction has become the most crucial part for re-production as well as pre-treatments. Various zeolites and other complex materials have been synthesized by structure reconstruction. In this work, the state of the art of structure reconstruction were technically collated in the order of pre-treatments, mechanisms, specific techniques, and novel optimizing strategies. It has been found the crystalline types are closely related to the reaction conditions, that certain types of products could be obtained via accurate condition controls, especially the ratio of Si to Al. The current as-synthesized products were listed as well as their crystalline structure characteristics. Recently, combined materials and techniques have been innovatively investigated. However, the challenge remains as low purity, not only impurities in CFA but also different types of zeolites formed in one process.