Formation Of Mesopores Research Articles

Facile constructing ZrO2 nanoparticles equipped with high conductivity carbon networks as pseudocapacitive anodes for removing phosphorus

Phosphorus pollution can seriously disrupt water quality and endanger ecosystem sustainability. Nonetheless, a few typical methods have been employed to remove phosphorus, but there are still challenges in controlling phosphorus from sewage. Capacitive deionization (CDI) displays the merits of having eco-friendliness and low energy consumption when capturing phosphorus. However, traditional carbon electrodes often suffer from the limitation that phosphorus uptake sites are insufficient. Herein, a novel ZrO2 nanoparticle equipped with a highly conductive carbon network (NZrC) was fabricated by a facile co-pyrolysis process. Na2EDTA can provide additional carbon backbones, N species, and metal chelation sites. Zr-MOF was applied as the ZrO2 precursor with abundant phosphorus trapping sites. The results suggested that Na2EDTA favors improving the ZrO2 dispersion, mesoporous channel formation, and pseudocapacitive behavior. NZrC-21 at 1.2 V displays low energy consumption and the optimal phosphorus uptake capacity of 10.99 mg P/g because of its rich mesoporous structure, abundant pyrrolic-N, graphitic-N, and ZrO2 active sites, and outstanding electrochemical properties. Furthermore, several key parameters were investigated for their effect on phosphorus removal performance. The mechanism revealed that hydrogen bonds, ligand exchange, and electrostatic attraction are the main uptake processes. This work presents a novel perspective for the facile construction and utilization of metal oxide nanoparticles equipped with a highly conductive carbon network for removing phosphorus.

CO2 Fixation via epoxide cycloaddition with a highly active and stable MOF-808/GO composite catalyst

The CO2 cycloaddition reaction effectively mitigates the greenhouse effect while producing high-value cyclic carbonates. Metal-organic frameworks (MOFs) have shown promise for CO2 cycloaddition with epoxides; however, the aggregation of MOFs due to high surface energy hinders mass transfer and catalytic performance. By pre-coordinating graphene oxide (GO) to regulate the dispersion of MOF-808, the resulting MOF-808/GO-100 composite catalyst exhibits twice the activity of pristine MOF-808, achieving 92.6% conversion of epichlorohydrin (ECH) with 98.2% selectivity to ECH carbonate without adding any co-catalysts. The incorporation of GO introduces numerous hydroxyl groups on the catalyst surface, serving as hydrogen bonding donors. The oxygen-containing groups on GO can compete with ligands for Zr coordination, generating defective Zr sites. The synergistic effect between defective Zr sites and hydrogen bonding donors collectively promotes epoxide opening. Notably, GO correspondingly enhances the dispersion of MOF-808 and induces mesopore formation through its stacking effect at the interface with MOF-808. Across various epoxide cycloaddition reactions, MOF-808/GO-100 consistently demonstrated optimal performance and maintained high stability over multiple reaction cycles.

Fe oxide modification of yerba mate waste-derived biochar and activated biochar via three methodologies: Effects of material surface properties on the Fe oxides grown and implications for paracetamol and atenolol sorption

This work presents, for the first time, the development of magnetic composites using activated biochar (BC-Act) derived from yerba mate waste. It includes an analysis of the effect of the activation process on the formation of iron oxides using the most applied methodologies, an aspect that has not been studied before. Three methodologies have been considered for Fe oxides grown: coprecipitation (COP), impregnation-pyrolysis (IP), and alkaline oxidation in the presence of nitrates (AOPN). The materials with magnetic response and good enough BET area have been used to sorb Paracetamol (PCT) and Atenolol (ATE) from aqueous solutions. The activation process has resulted in the formation of mesopores, an increase of surface area due to the destruction/release of impurities, the transformation of whewellite to calcite, and changes in magnetic behavior. These changes seem to affect the formation of Fe oxides. The COP and IP methods allow the development of magnetic composites based on BC-Act, BC-Act-COP and BC-Act-IP, with saturation magnetization of 3.1 Am2/kg and 1.5 Am2/kg, respectively, attributed to magnetite/maghemite formation and a minimal distance for manipulation by a magnetic field of 12.1 mm and 7.9 mm, respectively. These distances must be considered when developing efficient removal systems using magnetic composites. PCT was sorbed faster and more efficiently than ATE, associated with its smaller molecular size. This presents a valuable contribution to environmental sustainability and advancements in water purification, highlighting the dual advantage of converting the widely available waste product, predominantly found in South America, into an effective sorbent with magnetic characteristics, capable of removing pharmaceutical contaminants from aqueous solutions. This is done in the circular economy, avoiding the final deposition of yerba mate waste in landfills, increasing their lifespan, and safeguarding other natural and non-renewable resources, such as clays, whose preservation rather than exploitation improves environmental quality and saves energy.

The Influence of Thermal Treatment of Activated Carbon on Its Electrochemical, Corrosion, and Adsorption Characteristics

Activated carbons can be applied in various areas of our daily life depending on their properties. This study was conducted to investigate the effect of thermal treatment of activated carbon on its properties, considering its future use. The characteristics of activated carbon heat-treated at temperatures of 1500, 1800, and 2100 °C based on its future use are presented. The significant effect of the treatment temperature on morphological, adsorption, electrochemical, and corrosion properties was proved. Increasing the temperature above 1800 °C resulted in a significant decrease in the specific surface area (from 969 to 8 m2·g−1) and material porosity—the formation of mesopores (20–100 nm diameter) was observed. Simultaneously, adsorption capability, double layer capacity, and electrochemically active surface area also decreased, which helped to explain the shape of cyclic voltammograms recorded in 2,4-dichlorophenoxyacetic acid and in supporting electrolytes. However, a significant increase in corrosion resistance was found for the carbon material treated at a temperature of 2100 °C (corrosion current decreased by 23 times). Comparison of morphological, adsorption, corrosion, and electrochemical characteristics of the tested activated carbon, its applicability as an electrode material in electrical energy storage devices, and materials for adsorptive removal of organic compounds from wastewater or as a sensor in electrochemical determination of organic compounds was discussed.

Impact of Asymmetric Microstructure on Ion Transport in Ti3C2Tx Membranes.

Consolidation or densification of low-dimensional MXene materials into membranes can result in the formation of asymmetric membrane structures. Nanostructural (short-range) and microstructural (long-range) heterogeneity can influence mass transport and separation mechanisms. Short-range structural dynamics include the presence of water confined between the 2D layers, while long-range structural properties include the formation of defects, micropores, and mesopores. Herein, it is demonstrated that structural heterogeneity in Ti3C2Tx membranes fabricated via vacuum-assisted filtration significantly affects ion transport. Higher ion permeabilities are achieved when the dense "bottom" side of the membrane, rather than the porous "top" side, faces the feed solution. Characterization of the membrane reveals distinct differences in flake alignment, surface roughness, and porosity across the membrane. The directional dependence on permeability suggests that one region of the membrane experiences stronger internal concentration polarization, potentially suppressing permeability through the porous side of the membrane.

Rapid yet Controlled Synthesis of 2D Covalent Organic Framework Nanocapsules as High-Performance Photocatalytic Carriers.

Synthesis and assembly of two-dimensional (2D) polymeric materials present a tricky trade-off between the high reaction rate and precise morphology control. Here we report a nanoconfined synthesis of imine-based 2D covalent organic frameworks (COFs) at the interface of oil-in-water (O/W) emulsion droplets stabilized by cationic surfactants. Highly uniform nanocapsules (NCs) could be prepared without adding extra catalysts at room temperature in just 4.5 h at a yield of 86%. The NCs have tunable average diameters and shell thicknesses, depending on the monomer and surfactant types/concentrations. Their BET-specific surface areas are up to 139.0 m2/g, mainly contributedby narrowly-distributed mesopores at ~5.0 nm and micropores at 1.4 nm.The surfactant plays the role of a catalyst during the reaction and interestingly, it also regulates the formation of mesopores and their sizes. Both theoretical and experimental studies confirm that the reaction has been accelerated by two orders of magnitude at the microdroplet interface, compared to that without emulsification. The resulting NCs could be well dispersed in water, and they have been demonstrated to be highly efficient nanocatalystsin application of water-based hydrogen evolution.Such microdroplet interface-confined synthesis may facilitate the future development of 2D polymeric materials for more advanced applications.

Rapid yet Controlled Synthesis of 2D Covalent Organic Framework Nanocapsules as High‐Performance Photocatalytic Carriers

Synthesis and assembly of two‐dimensional (2D) polymeric materials present a tricky trade‐off between the high reaction rate and precise morphology control. Here we report a nanoconfined synthesis of imine‐based 2D covalent organic frameworks (COFs) at the interface of oil‐in‐water (O/W) emulsion droplets stabilized by cationic surfactants. Highly uniform nanocapsules (NCs) could be prepared without adding extra catalysts at room temperature in just 4.5 h at a yield of 86%. The NCs have tunable average diameters and shell thicknesses, depending on the monomer and surfactant types/concentrations. Their BET‐specific surface areas are up to 139.0 m2/g, mainly contributed by narrowly‐distributed mesopores at ~5.0 nm and micropores at 1.4 nm. The surfactant plays the role of a catalyst during the reaction and interestingly, it also regulates the formation of mesopores and their sizes. Both theoretical and experimental studies confirm that the reaction has been accelerated by two orders of magnitude at the microdroplet interface, compared to that without emulsification. The resulting NCs could be well dispersed in water, and they have been demonstrated to be highly efficient nanocatalysts in application of water‐based hydrogen evolution. Such microdroplet interface‐confined synthesis may facilitate the future development of 2D polymeric materials for more advanced applications.

Silica surface modification using cellulose as a renewable organosilane derived from coconut coir fiber for carbon capture

The properties of silica surface modification for carbon capture were studied, utilizing cellulose-amine as a modification agent derived from dissolved coconut coir fiber. To form bonds with NH2 functional groups through amination processes, cellulosic biomass waste is utilized, which is analogous to replacing alkoxy ligands. The dual-function mixture reagents dimethyl sulfoxide (DMSO) and ammonium hydroxide (NH4OH) were employed in the same system as the amine sources and solvents. Waterglass is used as a source of silica, and the modified particles are formed using a one-step consecutive sol-gel spray drying process used in a direct condensation route. Changes in the concentration of sodium lauryl sulfate (SLS) were examined to determine how they affected the essential parameters of the particles. The template is removed during particle formation without further physical or chemical processing. The particle morphology changed from donut-shaped to spherical after SLS application, as evidenced by the increase in SLS concentration. This also shows that the increase in the particle surface area is directly influenced by the increase in the formation of new pore structures with increasing SLS concentration. Through this mechanism, it is possible to extend the pore size distribution to the meso-macropore regime and initiate the formation of new mesopores. This has a direct impact on the capacity to absorb CO2 gas by increasing the cellulose-amine mass fraction that can be grafted to as high as 32.35 %wt. At an operating pressure of 6 bar, a maximum CO2 gas adsorption capacity of 5.32 mmol/g silica was attained by adding SLS 3 CMC to the silica particles. This value is 2.3 times higher than that obtained when using an aminosilane-based modification agent.

Improving H2S remediation efficiency through metal-free biochar modification: Nitrogen introduction and mesopore formation

Hydrogen sulfide (H₂S) poses substantial risks to human safety and infrastructure due to its toxicity and corrosive properties. In this study, we present a novel approach to enhance the selective catalytic oxidation of H₂S by synthesizing a nitrogen-doped mesoporous carbon catalyst (denoted as M/B-X-PZ-T) through pyrolysis at 600–800 °C. Our catalyst, derived from commercial biochar, incorporates melamine as a nitrogen source and employs KCl and ZnCl₂ as porogens via the salt-templating method. The resulting catalyst, M/B-1-PZ-700, exhibits an impressive specific surface area of up to 1269.77 m²/g and a high mesopore ratio, with effective nitrogen doping reaching up to 15.35 at%. Remarkably, M/B-1-PZ-700 demonstrated exceptional performance, achieving 100 % H₂S conversion and 94 % sulfur selectivity at 170 °C, surpassing previous nitrogen-doped carbon catalysts. Furthermore, our optimized catalyst maintained over 95 % H₂S conversion and superior sulfur yield for 36 h, indicating excellent long-term stability. This metal-free catalyst derived from biochar offers a promising, sustainable, and eco-friendly solution for effectively mitigating hazardous H₂S emissions.

Swelling-assisted surface grafting strategy for multichannel antifouling membranes: Reconstruction of surface pore structure and applications in microalgae harvesting and blood purification

Membrane fouling remains a major challenge in membrane separation. The modification of hydrophilic membrane surfaces can mitigate irreversible fouling deposition, thereby improving antifouling properties. Effective surface modification strategies are essential techniques for developing highly efficient antifouling membranes. In this work, a swelling-assisted surface grafting strategy was proposed for multichannel antifouling membranes, where various lengths of polyvinylpyrrolidone (PVP) brushes were grafted on the surface of polysulfone membrane using reversible addition-fragmentation chain transfer polymerization. The successful grafting of PVP polymer brushes was confirmed using Fourier transform infrared spectrometer and X-ray Photoelectron Spectroscopy. Changes in membrane morphology and pore structure were observed via scanning electron microscope and atomic force microscope. During the grafting process, the amphiphilic macromolecules formed through grafting were selectively swelled by graft solvent, leading to the formation of mesopores in both the surface layer and sublayer of the membrane, which formed additional water transport channels. The introduction of hydrophilic polymer brushes and the change of pore structure significantly boosted the hydrophilicity and permeability of the membranes. As a result, the water contact angle decreased from 85° to 42°, accompanied by an approximate 3.24-fold increase in pure water flux (PWF). Due to superior hydrophilicity, modified membranes demonstrated exemplary performance in microalgae harvesting, boasting a microalgae retention rate nearing 100 % and low fouling resistance (2.12 × 1012 m−1). In algal filtration experiments, a confocal laser scanning microscope was employed to assess the activity of filtered algae on the membrane surface. The prepared membranes effectively maintained the bioactivity of algae while also achieving a high flux recovery rate (90.7 %) following filtration and cleaning. Furthermore, in blood cell compatibility tests, the modified membranes exhibited resistance to blood cell adhesion and sustained a low hemolysis rate (0.06 %). Overall, this strategy offers unique insights into the fabrication of antifouling surfaces and shows considerable promise for large-scale applications in microalgae harvesting and blood purification.

The effect of pyrolysis heating rate on the mesoporosity of Pluronic F-127 templated carbon xerogels

This study explored the impact of pyrolysis heating rates ranging from 1 to 20 K min−1 (final temperature 500 °C) on the porosity of resorcinol-formaldehyde based carbonaceous xerogels soft-templated with Pluronic F-127. We primarily utilized thermoporometry (differential scanning calorimetry technique) and, to a lesser extent, conventional nitrogen adsorption at −196 °C to analyze the porosity of the resulting carbons. Additionally, we examined the effects of particle size and the scale of the pyrolysis experiment, comparing a laboratory furnace with a thermal analyzer. At lower heating rates, particularly in a thermal analyzer, mesopores approximately 7–8 nm in size were observed. An increase in the heating rate resulted in larger mesopores, from 7 to 17 nm, widened pore size distribution (PSD), and a rise in mesopore volume from 0.21 to 0.53 cm3g−1. Higher heating rates (> 5 K min-1) also accelerated the decomposition of the Pluronic F-127, leading to fast gas release, which subsequently caused cracking of the carbon skeleton and widening of the pores. Pyrolysis heating rate had no significant effect on the degree of graphitization in the pyrolyzed samples. Particle size showed minimal influence on porosity when xerogels were pyrolyzed at either the minimal or maximal heating rates in the thermal analyzer. However, experiments conducted in a laboratory furnace at the lowest heating rate demonstrated that imprecise temperature control and fluctuations can lead to the formation of larger mesopores.

The potential of Gd doping as a promising approach for enhancing the adsorption properties of nickel-cobalt ferrites.

The study shows that the addition of gadolinium ions has a significant impact on the structure, morphology, and adsorption properties of Ni-Co spinel ferrite that was synthesized by the sol-gel auto-combustion method. The research also indicates that the higher the Gd content, the greater the increase in the lattice parameter, which suggests that Gd3+ ions uniformly replaced the octahedral Fe3+ ions. The morphology and chemical composition of Gd-doped Ni-Co ferrites have been studied using SEM and EDS. Gd adding to the NiCoFe matrix increases the BET surface area by 50% (from 48 to 72 m2/g) and promotes the formation of mesopores with an average radius from 3.9 to 4.9nm. The pHPZC values of Gd-doped ferrites are in the range of 7.22-7.39, which means that the ferrite surface will acquire a positive charge at natural pH, so this will promote the adsorption of Congo red anionic dye through electrostatic interaction forces. Langmuir, Freundlich, and Dubinin-Radushkevich models were used to explain the mechanism of CR adsorption on the Ni0.5Co0.5GdxFe2-xO4 adsorbent surface. The ionic-covalent parameter has been estimated to describe the surface acid-base properties. Overall, this study highlights the potential of Gd3+ doping as a promising approach for enhancing the adsorption properties of nickel-cobalt ferrites.

Simple and sustainable synthesis of loosely stacked nano-H-ZSM-5 aggregates from kaolin and catalytic studies

The conversion of natural clay to crystalline zeolites has been the subject of considerable interest from both academic and industrial circles. We present an effective strategy for converting kaolin to ZSM-5 zeolite, addressing the issue of reduced mesopore formation in conventional nano-ZSM-5 aggregates due to close-packing. This strategy utilizes kaolin as the sole source of silicon and aluminum, and by decoupling the nucleation and growth of ZSM-5 crystals, loosely stacked nano-H-ZSM-5 aggregates with high crystallinity crystals can be synthesized in a solid-like system by employing a tiny amount of TPAOH (TPAOH/SiO2 = 0.064). The resulting nano-H-ZSM-5 aggregates exhibited high specific surface area (405.66 m2/g), high mesopore volume (0.64 cm3/g), and superior catalytic activity. This strategy offers a novel approach to the cost-effective synthesis of nano-H-ZSM-5 aggregates suitable for industrial applications.

Evolution of pore structure and diagenetic stages of late Permian shales in the Lower Yangtze Region, South China

This study examines the evolution characteristics of shale pores in the Late Permian Longtan Formation located in the Lower Yangtze region of South China. The complete process of thermal evolution of the samples was achieved through thermal simulation experiments while identifying qualitatively the pore types and their development characteristics using field emission-scanning electron microscope (FE-SEM). Quantitative analysis of pore size distribution was conducted through mercury intrusion capillary pressure (MICP), nitrogen (N2) and carbon dioxide (CO2) adsorption experiments. The paper comprehensively analyzed the pore evolution characteristics and controlling factors of shale in the study area, with an analysis of diagenetic differences. Findings reveal that during the pore evolution process, both morphology and pore size are influenced by thermal maturity. The pore volume is dominated by mesopores and macropores, while the specific surface area is mainly dominated by mesopores and micropores. Thermal evolution promotes the formation of micropores and mesopores but hinders the development of macropores. Moreover, clay minerals transformation and mineral dissolution make certain contributions to the development of micropores. The diagenesis in the study area is controlled primarily by the pyrolysis of organic matter. Pyrite and clay minerals are the first to dissolve, followed by calcite and quartz. Five stages of evolution characterization have been identified from low-mature stage (Ro = 0.88 %) to overmature stage (Ro = 3.35 %) in combination with diagenesis. The development of pore structure and its influencing factors vary across different stages. The influencing factors mainly include hydrocarbon generation from organic matter, compaction, mineral transformation, and dissolution. The process of hydrocarbon generation in organic matter occurs throughout the entire pore evolution process, resulting in the development of numerous micropores and mesopores. Compaction primarily impacts pore development during the early diagenetic stage, causing a substantial transition of primary mineral pores from macropores to mesopores. Mineral transformation and dissolution take place during and after the middle diagenetic stage. The former governs the development of mesopore-sized clay interlayer pores, while the latter primarily generates micropores.

Disassembly-reassembly-phosphating strategy to fabricate hydrothermally-stable hierarchical P@ZSM-5 zeolite for efficient methanol-to-propylene

Available hierarchization and phosphorization of ZSM-5 zeolite as one of methanol-to-propylene (MTP) catalysts have improved reactive stability and propylene selectivity, but are subjected to the problems of poor phosphorus stabilization efficiency and inhomogeneous dispersion. Herein, we fabricate a series of hierarchical P@ZSM-5 zeolites via one-step disassembly-reassembly-phosphating strategy of ZSM-5 zeolite using successfully self-created asymmetric quaternary phosphonium hydroxides and elucidate the mechanism of mesoporous formation and the interaction of phosphorus with framework aluminum. Delightfully, reconstructively tetracoordinated PIV-O-AlIV structure endows excellent hydrothermal and Brønsted acid stability of hierarchical P@ZSM-5 zeolites. The MTP tests show that the P@ZSM-5(TBuCP) catalyst prepared by disassembly-reassembly-phosphating of tributylhexadecylphosphine hydroxide (TBuCPOH) exhibits superior propylene selectivity (48.9 %) and remarkedly long lifetime (32.5 h, WHSV=6h−1). Such enviable MTP performance is benefited from the join hands of the zeolitic hierarchization and suitable Brønsted acid strength conferred by its phosphorus-aluminum interaction that are conducive to olefinic cycle process. These findings afford value-filled opportunities in novel MTP catalysts with high reactive stability and propylene selectivity, and the understandings for phosphorus-zeolite chemistry.

Research on influence laws of aggregate sizes on pore structures and mechanical characteristics of cement mortar

Aggregate plays an important role in cement-based materials. Evaluating the impact of aggregate gradation on pore structure and mechanical properties will help to optimize the mortar ratio and improve its durability. In this study, artificial sand with 5 different particle sizes was used as aggregate, and the synthetic gradation formed by their coupling was compared. The pore structure distribution of mortar was quantitatively characterized by nuclear magnetic resonance (NMR) technology. Surface-to-volume ratio (SVR) and ρd (aggregate packing density) were used to characterize the aggregate grading characteristics. The correlation between aggregate gradation characteristics and mortar parameters, such as porosity, pore structure fractal dimension, permeability coefficient, and mechanical strength, was analyzed, and a compressive modulus of mortar was established. The results indicate that the pore structure characteristics, K (permeability), and mechanical characteristics of mortar are all influenced by both SVR and ρd. The predominant pores in the mortar are micropores and movable fluid pores, and the addition of 0.1–0.5 mm aggregates reduces the formation of micropores, mesopores, macropores, and movable fluid pores in the mortar. As the number of pores increases, the complexity of the pore structure decreases, leading to higher homogeneity. Moreover, the K shows a strong power function relationship with the total porosity and the total porosity fractal. The compressive strength and Ec (compression modulus) of GM1–6 are significantly higher than those of GM7–9, correlating with the minimum aggregate size and the inherent strength of the aggregates. The regression results of the strength correlation model are significant, and the strength model established based on the porosity of micropores and Ec can accurately predict the compressive strength of mortar.

Exploring surface silanols in mesoporous Na-LTA zeolite to enhance its catalytic activity in knoevenagel condensation by grafting amino groups

Mesoporous Na-LTA zeolite was synthesized using the surfactant templating method with the organosilane surfactant [3-(trimethoxysilyl)propyl] octadecyldimethylammonium chloride (TPOAC). The formation of mesopores not only improved the accessibility of the basic catalytic sites but also led to the formation of isolated external silanols. These silanols were used to anchor propylamine groups by reacting with 3-aminopropyltrimethoxysilane (APTMS). The incorporation of propylamine groups in the mesoporous Na-LTA improved its catalytic activity in the Knoevenagel condensation reaction by 40 % due to the presence of extra basic catalytic sites from amino groups. The combination of mesopore generation and functionalization is an efficient strategy for enhancing the performance of Na-LTA zeolite in this reaction.

Algal-based biochar and hydrochar: A holistic and sustainable approach to wastewater treatment

Biochar and hydrochar are carbon-rich solid products of algal and terrestrial biomass obtained through various thermochemical processes, mainly hydrothermal liquefaction, pyrolysis, and hydrothermal carbonization. Both are regarded as economical, potent, and environmentally friendly adsorbents for wastewater remediation. The versatile applicability of biochar and hydrochar, which is due to their enhanced surface physicochemical properties, includes efficient metal biosorption, soil fertility enhancement, and carbon sequestration. Consequently, there has been an increase in research for producing and exploiting biochar and hydrochar from algae. Both micro- and macro-algal biomass have strong potential due to their sustainability footprint and distinct properties. This review focuses on a comprehensive account of the synthesis of algal biochar and hydrochar and use in wastewater treatment to develop innovative solutions for efficient mitigation of several aqueous pollutants and heavy metal ions. The review discusses the various thermochemical production routes, biophysical characterization techniques, and modes of mechanism for wastewater bioremediation. Algal-based biochar and hydrochar are reported to have higher porosity and more diverse functional groups such as amines, hydroxyl, and carboxyl compared to their cellulosic and waste-derived counterparts, demonstrating an increased wastewater remediation efficiency. In addition, presence of inorganic metal including sodium, potassium, magnesium, and phosphorus in algal chars facilitates the formation of mesopores and graphite structures, improving their cation exchange capacity. Moreover, algal chars may exhibit pH buffering capacity, which could help stabilize the pH during wastewater treatment processes. Notably, the low O/C content of algal hydrochars enhances the binding and removal of organic pollutants including toxic dyes and antibiotics. The review highlights the development of modified algal chars to enhance the porosity, surface area, structural integrity, and adsorption capacity enabling a higher bioremediation potential.

La-Modified SBA-15 Prepared by Direct Synthesis: Importance of Determining Actual Composition

Lanthanum (La) integration (at various nominal contents) in SBA-15 prepared under acidic medium was intended from corresponding direct nitrate addition during mesoporous silica formation. Materials were impregnated with Pt (1.5 wt%) and studied through several textural (N2 physisorption), structural (XRD, TG-DTG), and surface (FTIR, STEM-HAADF, SEM-EDS, NH3, and CO2 TPD) instrumental techniques. Pt-impregnated solids were tested in phenol hydrodeoxygenation (HDO, T = 250 °C, 3.2 MPa, batch reactor, n-decane as solvent). Catalytic activity (in pseudo-first-order kinetic constant, kHDO basis) was not directly related to Pt dispersion, which was not determined by nominal rare earth content. Determining the actual composition of modified SBA-15 materials is crucial in reaching sound conclusions regarding their physicochemical properties, especially when La modifier is directly added during mesoporous matrix formation, where efficient interaction among constituents could be difficult to get. Otherwise, results from some characterization techniques (N2 physisorption and FTIR, for instance) could be misleading and even contradictory. Indeed, extant modifier precursors, when under SBA-15 synthesis conditions, could affect the properties of prepared materials even though they were absent in obtained formulations. Performing simple compositional analysis could eliminate uncertainties regarding the role of various modifiers on characteristics of final catalysts. However, several groups have failed in doing so.

In Ukrainian

The CMs were obtained in argon in three stages: 1) heating (4 grad/min) to the specified temperature t in the range of 350–825 °С; 2) isothermal exposure 1 h; 3) cooling, washing from alkali and drying. Samples are denoted as CM(t). The CM yield (Y, %) and CMs elemental composition are determined. Based on low-temperature (77 K) nitrogen adsorption-desorption isotherms, integral and differential dependences of the specific surface area SDFT (m2/g) and pore volume V (cm3/g) on the average pore diameter (D, nm) were calculated by 2D-NLDFT-НS method (SAIEUS program). They were used to define volumes of ultramicropores (Vumi), supermicropores (Vsmi) and micropores (Vmi). The total pore volume V was calculated from the nitrogen amount adsorbed at a relative pressure p/p0 ~ 1.0. The S values of ultramicropores (Sumi), supermicropores (Ssmi) and micropores (Smi) were similarly determined. The CM yield was established to decrease linearly (R2 = 0.979) from 70.2 to 45.3 % with an increase in temperature from 350 to 825 °С. The carbon content decreases to a minimum value at 500 °С (72.6 %), and then increases to a maximum value (87.5 %) at 825 °С; the oxygen content changes antibatically. Two temperature regions were identified: region I (≤ 500 °С) of increasing the oxygen content due to reactions in which KOH acts as a donor of O atoms; region II (≥ 500 °C) of dominating the thermal destruction of functional groups (carboxyl, lactone, ester) with the release of CO and CO2, and condensation increasing the size of polyarenes of the CM secondary framework and formsng single Сar-Саr bonds between them. The CM(350) sample was found to contain only mesopores (D ≥ 10 nm) and macropores. An activation temperature increase to 400 °C initiates the additional formation of small-diameter micropores and mesopores. In samples CM(400) - CM(825), the main portion of newly formed pores falls on pores with D ≤ 5 nm. With increasing temperature, the micropores volume increases almost linearly (R2 = 0.992). The Vumi and Vsmi volumes increase up to 600 °C. At higher temperatures the ultramicropores volume decreases due to transforming ultramicropores (D ≤ 0.7 nm) into supermicropores (D = 0.7–2.0 nm). Portion of the ultramicropores volume changes with a maximum (23.9 %) in the CM(600) sample. The SBET specific surface area linearly (R2 = 0.992) increases with temperature up to 1729 m2/g. The SDFT values are close to SBET, but noticeably lower (1514–1530 m2/g) for CM(785)-CM(825). The micropores specific surface area increases to 1415 m2/g, and ultramicropore surface Sumi changes extremely with a maximum (526 m2/g) for the CM(600) sample, which should be expected based on the temperature dependence of the Vumi parameter. The decrease in Sumi values after the maximum is compensated by an increase in the supermicropore surface. Such an effect - the redistribution of pores by size in the microporous range (D ≤ 2 nm) with an increase in the alkaline activation temperature is not described in the literature. The portion of the micropores surface is dominant (92.6–97.0 %) in samples prepared at t ≥ 450 °C. The portion of the ultramicropore surface is maximum (56.3 %) in CM(500). Pores are revealed that do not form at all at 450–750 °C. These are supermicropores (D = 0.96–2.00 nm) and mesopores of small diameters (D = 2.0–2.82 nm). This effect was assumed to be due to the properties of the CM supramolecular framework, which is formed from polyarene fragments of the initial and activated coals having polyarenes with diameters of the same order (1.68–2.54 nm).