A review of recent advancement in covalent organic framework (COFs) synthesis and characterization with a focus on their applications in antibacterial activity

The primary objective of this review is to present a comprehensive examination of the synthesis, characterization, and antibacterial applications of covalent organic frameworks (COFs). COFs represent a distinct category of porous materials characterized by a blend of advantageous features, including customizable pore dimensions, substantial surface area, and adaptable chemical properties. These attributes position COFs as promising contenders for various applications, notably in the realm of antibacterial activity. COFs exhibit considerable potential in the domain of antibacterial applications, owing to their amenability to functionalization with antibacterial agents. The scientific community is actively exploring COFs that have been imbued with metal ions, such as copper or silver, given their observed robust antibacterial properties. These investigations strongly suggest that COFs could be harnessed effectively as potent antibacterial agents across a diverse array of applications. Finally, COFs hold immense promise as a novel class of materials for antibacterial applications, shedding light on the synthesis, characterization, and functionalization of COFs tailored for specific purposes. The potential of COFs as effective antibacterial agents beckons further exploration and underscores their potential to revolutionize antibacterial strategies in various domains.

Evaluation of multiscale mechanisms of ultrasound-assisted extraction from porous plant materials: Experiment and modeling on this intensified process

Ultrasound-assisted extraction (UAE) is an intensified mass transfer process, which can utilize natural resources effectively, but still lacks detailed mechanisms for multiscale effects. This study investigates the mass transfer mechanisms of UAE combined with material's pore structure at multiscale. Porous material was prepared by roasting green coffee beans (GCB) at 120 °C (RCB120) and 180 °C (RCB180), and their UAE efficiency for phytochemicals (caffeine, trigonelline, chlorogenic acid, caffeic acid) were evaluated by experiment and modeling. Besides, the physicochemical properties, mass transfer kinetics, and multi-physical field simulation were studied. Results indicated that positive synergy effects on extraction existed between ultrasound and material's pore structure. Higher mass transfer coefficients of UAE (GCB 0.16 min-1, RCB120 0.38 min-1, RCB180 0.46 min-1) was achieved with higher total porosity (4.47 %, 9.17 %, 13.52 %) and connected porosity (0 %, 3.79 %, 5.98 %). Moreover, simulation results revealed that micro acoustic streaming and pressure difference around particles were the main driving force for enhancing mass transfer, and the velocity (0.29-0.36 m/s) increased with power density (0.64-1.01 W/mL). The microscale model proved that increased yield from UAE-RCB was attributed to internal convection diffusion within particles. This study exploited a novel benefit of ultrasound on extraction and inspired its future application in non-thermal food processing.

Biodegradation-affected fatigue behavior of extrusion-based additively manufactured porous iron-manganese scaffolds

Additively manufactured (AM) biodegradable porous iron-manganese (FeMn) alloys have recently been developed as promising bone-substituting biomaterials. However, their corrosion fatigue behavior has not yet been studied. Here, we present the first study on the corrosion fatigue behavior of an extrusion-based AM porous Fe35Mn alloy under cyclic loading in air and in the revised simulated body fluid (r-SBF), including the fatigue crack morphology and distribution in the porous structure. We hypothesized that the fatigue behavior of the architected AM Fe35Mn alloy would be strongly affected by the simultaneous biodegradation process. We defined the endurance limit as the maximum stress at which the scaffolds could undergo 3 million loading cycles without failure. The endurance limit of the scaffolds was determined to be 90 % of their yield strength in air, but only 60 % in r-SBF. No notable crack formation in the specimens tested in air was observed even after loading up to 90 % of their yield strength. As for the specimens tested in r-SBF, however, cracks formed in the specimens subjected to loads exceeding 60 % of their yield strength appeared to initiate on the periphery and propagate toward the internal struts. Altogether, the results show that the extrusion-based AM porous Fe35Mn alloy is capable of tolerating up to 60 % of its yield strength for up to 3 million cycles, which corresponds to 1.5 years of use of load-bearing implants subjected to repetitive gait cycles. The fatigue performance of the alloy thus further enhances its potential for trabecular bone substitution subjected to cyclic compressive loading. STATEMENT OF SIGNIFICANCE: Fatigue behavior of extrusion-based AM porous Fe35Mn alloy scaffolds in air and revised simulated body fluid was studied. The Fe35Mn alloy scaffolds endured 90 % of their yield strength for up to 3 × 106 loading cycles in air. Moreover, the scaffolds tolerated 3 × 106 loading cycles at 60 % of their yield strength in revised simulated body fluid. The Fe35Mn alloy scaffolds exhibited a capacity of withstanding 1.5-year physiological loading when used as bone implants.

Fabrication of porous adsorbents from eco-friendly aqueous foam for high-efficient removal of cationic dyes and sustainable utilization assessment

Porous materials applied in environmental remediation have received researchers' extensive attention recently, but the related green and convenient preparation method is rarely reported. Here, we recommended a green and convenient strategy for the fabrication of porous material via aqueous foam templates, which was synergistically stabilized by Codonopsis pilosula (CP) and clay minerals of attapulgite (APT). The characterization results revealed that the APT was modified by organic molecules leached from CP and anchored at the air-water interface, which improved the foam stability significantly. The novel porous material of polyacrylamide/Codonopsis pilosula/attapulgite (PAM/CP/APT) templated from the aqueous foam via a polymerization reaction had excellent adsorption capacity for the cationic dyes methyl violet (MV) and methylene blue (MB), and the adsorption capacity can reach 755.85 mg/g and 557.64 mg/g, respectively. More importantly, the adsorption capacity of spent adsorbent material was still over 200 mg/g after being recycled five times through a simple carbonization process, and then it was added to the plant pot, the total biomass was increased by about 86.42%. This study provided a green and sustainable pathway for the preparation, application and subsequent processing of porous materials.

Hypercrosslinked waste polycarbonate to remove heavy metal contaminants from wastewater

In this research, the waste polycarbonate was hypercrosslinked during the Friedel-Crafts reaction to eliminate metallic ions from the wastewater solution. The experiments for inspecting the adsorption behavior of lead and cadmium ions were conducted at the initial concentration of 20-100 mg/L, contact time of 10-80 min, temperature of 20-80 °C, and pH of 6-11. The isotherm, kinetic, and thermodynamic models have been used to explain the behavior of the metal ions removal process. The correlation coefficient and adsorption capacity of the kinetic model for cadmium ion have obtained 0.995 and 160.183 mg/g, respectively, and the correlation coefficient and adsorption capacity of the kinetic model for lead ion has obtained 0.998 and 160.53 mg/g, respectively, which declared that the cascade was not monolayer. The correlation coefficient of the Freundlich is calculated at 0.995 and 0.998 for Cd and Pb, respectively, indicating the resin plane was not homogenized. The n constant for cadmium and lead ions has been calculated at 2.060 and 1.836, respectively, confirming that the resin is not homogenized, and the process has performed well. Afterward, the values of enthalpy and Gibbs free energy changes were obtained at - 7.68 kJ/mol and - 0.0231 kJ/mol.K for lead ions, respectively, which implies the exothermic and spontaneous state of the process. The values of enthalpy and Gibbs free energy changes have been obtained at - 6.62 kJ/mol and - 0.0204 kJ/mol.K for cadmium ions, respectively, which implies the exothermic and spontaneous nature of the adsorption. Also, the optimal empirical conditions for lead and cadmium ions have been found at a time of 60 min, temperature of 20 °C, initial concentration of 100 mg/L, and pH of 10. At a time of 45 min, the diffusion coefficient and mass transfer coefficient for lead ions have been calculated at 0.1269 × 1020 m2/s and 0.2028 × 1015 m/s, respectively. In addition, at a time of 45 min, the diffusion coefficient and mass transfer coefficient for cadmium ions have been calculated at 0.1463 × 1020 m2/s and 0.1054 × 1015 m/s, respectively. Moreover, the mechanism study explains that the C-O-C and C-H in the aromatic groups have a crucial aspect in the bond formation among metallic ions and resin.

Construction of hydroxyl-functionalized hyper-crosslinked networks from polyimide for highly efficient iodine adsorption

The rapid development of nuclear energy posed a great threat to the environment and human health. Herein, two hydroxyl-functionalized hyper-crosslinked polymers (PIHCP-1 and PIHCP-2) containing different electron active sites have been synthesized via Friedel-Crafts alkylation reaction of the polyimides. The resulting polymers showed a micro/mesoporous morphology and good thermal and chemical stability. Rely on the high porosity and multi-active sites, the PIHCPs show an ultrahigh iodine uptake capacity reached 6.73 g g-1 and the iodine removal efficiency from aqueous solution also reaches 99.7%. Kinetic analysis demonstrates that the iodine adsorption on PIHCPs was happened on the heterogeneous surfaces in the form of multilayer chemisorption. Electrostatic potential (ESP) calculation proves the great contribution of hydroxyl groups on the iodine capture performance. In addition, the iodine capture efficiency of both adsorbents can be maintained over 91% after four cyclic experiments which ensures their good recyclability for further practical applications.

A review of sustainable utilization and prospect of coal gasification slag

Currently, the storage of coal gasification slag (CGS) is continuously increasing, as the coal gasification technology develops, posing significant environmental hazards. Due to its volcanic ash characteristics and rich residual carbon, CGS has great potential for resource utilization, which has attracted the attentions of many scholars. This paper firstly introduces the compositions and properties of CGS. Then, it reviews the existing utilization methods of CGS, including Preparation of building materials, carbon-ash separation technology, ecological restoration, and cyclic blending. The advantages and disadvantages of various methods are compared. Subsequently, some high-value utilization methods of coal gasification slag are introduced, such as the preparation of high-performance activated carbon and zeolite, of which the feasibility and advantages are evaluated. Finally, some suggestions are put forward for future developing technologies. This paper aims to provide some references and inspiration for the utilization and environmental protection of CGS.

Retention properties and mechanism of agricultural waste maize whisker on atmospheric mercury

Mercury (Hg) is a global pollutant transmitted mainly through the atmosphere, posing a serious threat to biological survival and human health. Porous materials, with high specific surface area, high porosity, and high adsorption, are particularly suitable for the purification of atmospheric Hg mixtures. However, plant porous materials are rarely directly used for atmospheric Hg purification. In this study, the properties and mechanism of maize whisker in removing atmospheric Hg were analyzed. The results show that the Hg content in the whiskers increases significantly as the initial Hg concentration increases, and 79.38% Hg can be removed by 0.2 g maize whiskers after 1 h exposure when the initial Hg concentration is 0.1 μg m-3, indicating that maize whiskers can accumulate atmospheric Hg rapidly and effectively. The hole diameter of the maize whisker is between 0.83 and 3.06 μm, which is suitable for the adsorption of small substances. Correlation analysis shows that maize whiskers have a significant correlation between atmospheric Hg retention and its specific surface area, pore size, medium pore ratio, and micropore ratio, suggesting that the maize whisker hole feature has a significant influence on its ability to retain atmospheric Hg. Compared with the energy profiles before and after Hg treatment, the peak of Mg decreased after Hg adsorption. Fourier infrared spectrometer analysis suggests that functional groups such as -OH, -COOH, and -O- are involved in the adsorption process. The change in pH value shows an obvious effect on the overall change in zeta potential in the adsorption process. Therefore, a variety of mechanisms, including physical adsorption, electrostatic adsorption, complexation, chelation, and ion exchange, are involved in Hg retention with the maize whisker. This study reveals the important potential value of agricultural waste maize whiskers in the purification of atmospheric heavy metal Hg.

Fabrication porous adsorbents templated from aqueous foams using astragalus membranaceus and attapulgite as stabilizer for efficient removal of cationic dyes

The water-based foam stabilized by the natural surfactant applied in the fabrication of porous materials has attracted extensive attention, as the advantages of cleanness, convenience and low cost. Particularly, the development of a green preparation method has became the main research focus and frontier. In this work, a green liquid foam with high stability was prepared by synergistic stabilization of natural plant astragalus membranaceus (AMS) and attapulgite (APT), and then a novel porous material with sufficient hierarchical pore structure was templated from the foam via a simple free radical polymerization of acrylamide (AM). The characterization results revealed that the amphiphilic molecules from AMS adsorbed onto the water-air interface and formed a protective shell to prevent the bubble breakup, and APT gathered in the plateau border and formed a three-dimensional network structure, which greatly slowed down the drainage rate. The porous material polyacrylamide/astragalus membranaceus/attapulgite (PAM/AMS/APT) showed the excellent adsorption performance for cationic dyes of Methyl Violet (MV) and Methylene Blue (MB) in water, and the maximum adsorption capacity could reach to 709.13 and 703.30 mg/g, respectively. Furthermore, the polymer material enabled to regenerate and cycle via a convenient calcination process, and the adsorption capacity was still higher than 200 mg/g after five cycles. In short, this research provided a new idea for the green preparation of porous materials and the treatment of water pollution.

Diffusion of gold nanoparticles in porous silica monoliths determined by dynamic light scattering

HYPOTHESIS

The applicability of the dynamic light scattering method for the determination of particle diffusivity under confinement without applying refractive index matching was not adequately explored so far. The confinement effect on particle diffusion in a porous material which is relevant for particle chromatography has also not yet been fully characterized.

EXPERIMENTS

Dynamic light scattering experiments were performed for unimodal dispersions of 11-mercaptoundecanoic acid-capped gold nanoparticles. Diffusion coefficients of gold nanoparticles in porous silica monoliths were determined without limiting refractive index matching fluids. Comparative experiments were also performed with the same nanoparticles and porous silica monolith but applying refractive index matching.

FINDINGS

Two distinct diffusivities could be determined inside the porous silica monolith, both smaller than that in free media, showing a slowing-down of the diffusion processes of nanoparticles under confinement. While the larger diffusivity can be related to the slightly slowed-down diffusion of particles in the bulk of the pores and in the necks connecting individual pores, the smaller diffusivity might be related to the diffusion of particles near the pore walls. It shows that the dynamic light scattering method with a heterodyne detection scheme can be used as a reliable and competitive tool for determining particle diffusion under confinement.

Mechanistic insight into gel formation of co-amorphous resveratrol and piperine during dissolution process

Different from previous co-amorphous systems, co-amorphous resveratrol and piperine (namely RES-PIP CM) showed much lower dissolution in comparison to the original two crystalline drugs owing to its gel formation during dissolution. The purpose of this study is to investigate the mechanism of gel formation and seek strategies to eliminate such gelation. It was found that the dissolution performance of RES-PIP CM and the properties of formed gels were significantly affected by the medium temperature and stoichiometric ratio of components. Multiple characterization results confirmed that the gelation process underwent the decrease of T_g caused by water plasticization, and then entered into its supercooled liquid state with high viscosity, accompanied by self-assembly of molecules. Furthermore, the study answered the question that whether such gelation of RES-PIP CM could be eliminated by porous carrier materials. The materials, mesoporous silica (MES) and attapulgite (ATT), provided barrier and well separation between molecules and particles of RES-PIP CM by the pore steric hindrance, and impeded the self-assembly and aggregation, hence achieving the degelation and dissolution improvement. The present study highlights the importance of recognizing gelation potential of some co-amorphous formulations, and provides an effective strategy to eliminate gelation in developing high quality co-amorphous drug products.

Modeling liquid penetration into porous materials based on substrate and liquid surface energies

HYPOTHESIS

The widely used Lucas-Washburn (LW) equation depends on the contact angle as the driving force for liquid penetration. However, the contact angle depends on both, the liquid and the substrate. It would be desirable to predict the penetration into porous materials, without the requirement to measure the solid-liquid interaction. Here, we propose a novel modeling approach for liquid penetration from mutually independent substrate- and liquid properties. For this purpose, the contact angle in the LW-equation is replaced by polar and dispersive surface energies, utilizing the theories of Owens-Wendt-Rabel-Kaelble (OWRK), Wu, or van Oss, Good, Chaudhury (vOGC).

EXPERIMENTS

The proposed modelling approach is validated exhaustively by measuring penetration speed for 96 substrate-liquid pairings and comparing the results to model predictions based on literature- and measured data.

FINDINGS

Liquid absorption is predicted very well (R² = 0.8-0.9) with all three approaches, spanning a wide range of penetration speed, substrate- and liquid surface energy, viscosity, and pore size. The models for liquid penetration without measurement of solid-liquid interaction (contact angle) performed well. Modeling calculations are entirely relying on physical data of the solid and the liquid phase (surface energies, viscosity and pore size), which can be measured or retrieved from databases.

Porous material based on modified carbon and the effect of pore size distribution on the adsorption of methylene blue dye from an aqueous solution

Carbon porous materials obtained through KOH activation of a furfural + hydroquinone + urotropine mixture were applied as adsorbent for the remediation of methylene blue (MB). The impact of porous structure with special attention to pore size distribution along with well-known pore volume and specific surface area on the remediation of MB was well investigated and elucidated. Findings obtained revealed that pore size distribution plays a crucial role in the liquid-phase adsorption of organic dyes like MB. By varying the synthesis mode parameters, in particular, the activating agent/precursor mass ratio, with the composition and initial components ratios remaining unchanged, samples with different pore size distribution were obtained. It was found that the material predominantly containing pores with an average equivalent diameter of ~ 3.5 nm appears to be the efficient MB adsorbent. The resulting highly porous carbon materials demonstrated high MB adsorption capacity (up to 2555 mg/g). Furthermore, to fully elucidate the adsorption mechanisms occurring on the obtained materials, a comprehensive mathematical processing of experimental data was performed out using the known kinetic and diffusion models (pseudo-first- and pseudo-second order, and intraparticle diffusion), as well as adsorption equilibrium isotherm models (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich).It can be concluded that the porous carbon materials obtained and described in the present work are effective adsorbents for the removal of MB and may possess great potential for the treatment of dye-containing wastewater.

Porous Ag3VO4/KIT-6 composite: Synthesis, characterization and enhanced photocatalytic performance for degradation of Congo Red

Novel Ag3VO4/KIT-6 nanocomposite photocatalyst has been successfully fabricated by a newly-designed simple hard-template induction process, in which the particles of Ag3VO4 were grown on the KIT-6 surface and inside the porous framework of the silica matrix. The developed porous framework nanocomposite was characterized by several techniques including N2-Physiosorption analysis. The obtained nanocomposite revealed a high surface area (273.86 m2/g) along with the possession of monoclinic Ag3VO4, which is highly responsive to visible light (with distinct intensity at about 700 nm). The UV-Vis DRS reveals that the Ag3VO4/KIT-6 photocatalyst bears a bandgap of 2.29 eV which confirms that the material has a good visible light response. The synthesized nanocomposite was tested for its superior physicochemical properties by evaluating its degradation efficiency for Congo Red (CR). The novel composite exhibited superior degradation capability of CR, reaching up to 96.49%, which was around three times the pure Ag3VO4. The detailed kinetic study revealed that the as-prepared material followed a pseudo first order kinetic model for the CR degradation. The study includes a comprehensive parametric study for the formulation of the optimized reaction conditions for photocatalytic reactions. The commercial applicability of the composite material was investigated by a regeneration and recyclability test, which revealed extraordinary results. Furthermore, the possible degradation pathway for CR was also proposed.

Novel Ni foam catalysts for sustainable nitrate to ammonia electroreduction

Electrochemical nitrate reduction (NO₃^-RR) is considered a promising approach to remove environmentally harmful nitrate from wastewater while simultaneously producing ammonia, a product with high value. An important consideration is the choice of catalyst, which is required not only to accelerate NO₃^-RR but also to direct the product selectivity of the electrolysis toward ammonia production. To this end, we demonstrate the fabrication of novel Ni foam catalysts produced through a dynamic hydrogen bubble template assisted electrodeposition process. The resulting foam morphology of the catalyst is demonstrated to crucially govern its overall electrocatalytic performance. More than 95% Faradaic efficiency of ammonia production was achieved in the low potential range from -0.1 to -0.3 V vs. RHE. Hydrogen was found to be the only by-product of the nitrate reduction. Intriguingly, no other nitrogen containing products (e.g., NO,N₂O, or N₂) formed during electrolysis, thus indicating a 100% selective (nitrate→ammonia) conversion. Therefore, this novel Ni foam catalyst is a highly promising candidate for truly selective (nitrate→ammonia) electroreduction and a promising alternative to mature copper-based NO₃^-RR benchmark catalysts. Excellent catalytic performance of the novel Ni foam catalyst was also observed in screening experiments under conditions mimicking those in wastewater treatment.

Porous biomorphic silica@ZnO nanohybrids as the effective photocatalysts under visible light

In this study, zinc oxide nanohybrids based on functionalized bio-silica were synthesized and used for the degradation of Congo red under visible light. Diatom was used as a Si natural source with hierarchical nanostructures to produce porous silica support. Functionalized porous silica is a good candidate for direct immobilization of metal oxide and therefore of interest as the catalyst. Here, six hybrids of functionalized bio-silica and ZnO were synthesized and characterized by FT-IR, XRD, SEM/EDX, BET/BJH, and UV-Vis spectroscopy. Then, the synthesized catalysts were subjected to degradation of different anionic azo dyes (Congo red, methyl orange, and methyl red) under visible light irradiation. The results show the decrease of band gap in bio-silica@ZnO hybrids which enhance the photocatalytic properties of hybrids due to the shifting to visible light adsorption. The best photocatalytic result of SiO₂@ZnO hybrid was obtained from chitosan-based amino-functionalized silica due to the best functionalization, highest loading of ZnO, low band gap, and filling of diatom pores with functional groups.

Construction of Pd Single Site Anchored on Nitrogen-Doped Porous Carbon and Its Application for Total Antioxidant Level Detection

Natural enzymes have excellent catalytic activity. However, due to their unstable nature and high cost, current research has turned to the synthesis and development of enzyme-like nanomaterials and single-atomic nanozymes. In this study, a single-atomic palladium-loaded nitrogen-doped porous carbon catalyst (SA-Pd/NPC) was prepared and used as a mimetic peroxidase to catalyze the substrates oxidation. The catalytic capability of the SA-Pd/NPC was tested by the TMB-H₂O₂ system, and it expressed a superior catalytic capability owing to the plentiful catalytic centers of the single-atom Pd, its high porosity, the large specific surface area, and the strong electron transfer capability of the NPC. For the color reaction of TMB, thiol antioxidants (e.g., glutathione, GSH) and non-thiol antioxidants (e.g., ascorbic acid, AA) are suitable for different inhibition mechanisms. GSH and AA are typical substances of these two main antioxidant types, respectively. Here, we demonstrate that this prepared catalyst could be used to simultaneously determine a variety of major known physiologically relevant thiol-containing and thiol-free antioxidants, accompanied by a blue color gradient change with UV-Vis spectra at 652 nm through the SA-Pd/NPC-catalyzed TMB-H₂O₂ system. Linear responses to GSH and AA could be obtained in the concentration ranges of 0.01-0.10 mM and 1-13 μM (both R² values were greater than 0.970), respectively, while the limits of detection were 3 μM and 0.3 μM, respectively. The ability of the nanozyme to detect overall antioxidant levels (TAL) was also confirmed in subsequent tests on artificial saliva and biological samples.

Adsorption and photocatalytic properties of porphyrin loaded MIL-101 (Cr) in methylene blue degradation

In this study for the very first time, zinc tetraphenylporphyrin (ZnTPP) was loaded into MIL-101 (Zn[TPP]@MIL-101) to perform an adsorptive and photocatalytic dye removal. The physicochemical attributes of the catalyst were thoroughly determined by the usage of XRD, FTIR, FESEM, BET, UV-vis, and inductively coupled plasma (ICP). The obtained XRD pattern exhibited the phase purity of MIL-101 and its structural stability. The solid-phase diameter of the catalyst was observed to be ~ 270.76 ± 119.95 nm, while its gas adsorption data was indicative of a decrease in the specific surface area after the loading of ZnTPP. The ICP analysis displayed the amount of encapsulated Zn[TPP] (~ 17%) in MIL-101. The UV-vis confirmed the presence of Zn[TPP] in MIL-101 with the lack of any interferences or overlaps with the λ_max of methylene blue (MB) with the support. The dye removal of MB was investigated under dark conditions (adsorption) and UV light (photodegradation). The observed adsorption under dark conditions using Zn[TPP]@MIL-101 (99.27% yield) demonstrated a superior dye removal in comparison to the cases of photodegradation of MB by MIL-101 and Zn[TPP]@MIL-101 or adsorption by MIL-101. In conformity to the gathered results, [ZnTPP] was able to increase the adsorption capacity at pH = 7 at room temperature.

Preparation and application of porous materials from coal gasification slag for wastewater treatment: A review

In recent years, coal gasification has been gradually promoted as clean technology, and coal gasification slag (CGS) emissions have increased accordingly. CGS, including coarse slag and fine slag, is rich in SiO₂ and Al₂O₃ and has pozzolanic activity, and thus CGS can be regarded as a cheap source of aluminosilicate. Also, CGS, especially the fine slag, usually contains higher contents of residual carbon which has a large specific surface area and low volatility and hence can be considered as a favorable precursor of activated carbon. Benefiting from these characteristics, CGS can be used to prepare high value-added porous materials, such as zeolite, mesoporous silica, carbon-silicon composite, and porous ceramics, and the obtained structures accommodate both sufficient adsorption capacity and low cost. Here, we review the research advances in characteristics of CGS and preparation methods of CGS-based porous materials, as well as their adsorption performance of heavy metal ions, organic dyes, ammonia nitrogen, and other water pollutants. The current studies indicate that CGS-derived adsorbents are effective and economical alternatives for removing aqueous pollutants. In addition, further research prospects on CGS-based porous materials are proposed.

Hierarchical, Highly Open Microtubes and Columnar Liquid Crystals Self-Assembled from Symmetrical and Asymmetrical Colloidal Rings

The use of simple building blocks to produce hierarchical and porous structured materials is highly desired. Rings are simple colloidal particles but unique for their internal cavities. Here we report the self-assembly (SA) of colloidal rings with tunable asymmetry mediated by a depletion force and demonstrate that a variety of porous colloidal superstructures from microtubes, flexible chains, (plastic) crystals to highly open liquid crystals (LCs) can be formed along the predesigned SA paths. In particular, the SA is staged in binary or ternary systems. Large rings first form complex ring-in-ring and ring-in-ring-in-ring assemblies by capturing smaller rings, which, as new building blocks, can further form multi-walled microtubes and open columnar LCs. Moreover, a plastic columnar LC with alternating intracolumnar stacking is found from asymmetrical rings. The SA with colloidal rings opens a new avenue to construct hierarchical and porous ordered metamaterials.

Elucidating the mechanisms of Paraffin-Olefin separations using nanoporous adsorbents: An overview

Light olefins are the precursors of all modern-day plastics. Olefin is always mixed with paraffins in the time of production, and therefore it needs to be separated from paraffins to produce polymer-grade olefin. The state-of-the-art separation technique, cryogenic distillation, is highly expensive and hazardous. Adsorption could be a novel, sustainable, and inexpensive separation strategy, provided a suitable adsorbent can be designed. There are different types of mechanisms that were harnessed for the separation of olefins by adsorption, and in this review, we have focused our discussion on those mechanisms. These mechanisms include, (a) Affinity-based separation, like pi complexation and hydrogen bonding, (b) Separation based on pore size and shape, like size-exclusion and gate-opening effect, and (c) Non-equilibrium separation, like kinetic separation. In this review, we have elaborated each of the separation strategies from the fundamental level and explained their roles in the separation processes of different types of paraffins and olefins.

Porous Co3O4 nanodisks as robust peroxidase mimetics in an ultrasensitive colorimetric sensor for the rapid detection of multiple heavy metal residues in environmental water samples

The current method for rapid and ultrasensitive detection of multiple heavy metals in environmental water still face challenge. Herein, the porous Co₃O₄ nanodisks with robust peroxidase-mimicking activity were prepared, and its catalytic activity can be significantly inhibited by the heavy metals like Cd(II), Hg(II), Pb(II) and As, which makes us to establish an ultrasensitive and rapid colorimetric sensor for the detection of multiple heavy metals. Further investigation reveals the anticompetitive inhibition effect of heavy metals on peroxidase-mimicking activity. The colorimetric sensor displays excellent sensitivity and selectivity, and the limits of detection (LOD) for Cd(II), Hg(II), Pb(II) and As are 0.085 μg·L^-1, 0.19 μg·L^-1, 0.2 μg·L^-1 and 0.156 μg·L^-1, respectively. Notably, the absorbance variation will be greater than 0.5 as the concentration of heavy metals exceeds 5 μg·L^-1, which can be clearly discriminated by the naked eyes. Moreover, the average recovery range of heavy metals in actual water samples is from 86.9% to 98.3%. The above results indicate that the proposed sensor exhibits excellent practical applicability for the rapid and ultrasensitive detection of multiple harmful heavy metals in several environmental water samples, which has potential bright application in protecting the environment and human health.

Nanocellulose-based lightweight porous materials: A review

Nanocellulose has been widely concerned and applied in recent years. Because of its high aspect ratio, large specific surface area, good modifiability, high mechanical strength, renewability and biodegradability, nanocellulose is particularly suitable as a base for constructing lightweight porous materials. This review summarizes the preparation methods and applications of nanocellulose-based lightweight porous materials including aerogels, cryogels, xerogels, foams and sponges. The preparation of nanocellulose-based lightweight porous materials usually involves gelation and drying processes. The characteristics and influencing factors of three main drying methods including freeze, supercritical and evaporation drying are reviewed. In addition, the mechanism of physical and chemical crosslinking during gelation and the effect on the structure and properties of the porous materials in different drying methods are especially focused on. This contribution also introduces the application of nanocellulose-based lightweight porous materials in the fields of adsorption, biomedicine, energy storage, thermal insulation and sound absorption, flame retardancy and catalysis.

Terahertz-spectroscopy for non-destructive determination of crystallinity of L-tartaric acid in smartFilms® and tablets made from paper

Newly developed active pharmaceutical ingredients (API) often experience low solubility in aqueous media and thus possess poor oral bioavailability. The SmartFilm®-technology is a novel approach to overcome poor solubility. The technique uses commercial paper in which API can be loaded in amorphous state, thus increasing dissolution rate dc/dt and solubility c_s when compared to bulk material. However, the preservation of the amorphous state is a prerequisite for an efficient use of the smartFilm-technology and thus the crystalline state needs to be inspected during storage. Preferably, this should be done non-destructively. Traditional techniques, such as x-ray diffraction (XRD) or differential scanning calorimetry (DSC), do not allow for non-destructive crystallinity investigations, whereas Terahertz (THz) spectroscopy is a non-destructive technique, that is sensitive to the crystalline state of many molecular crystals. Therefore, the potential of THz-spectroscopy for crystallinity state inspection of API in smartFilms and tablets made from smartFilms was investigated in this study. The THz results obtained were compared to results obtained from XRD and DSC measurements. Whereas DSC measurements failed to reliably detect crystalline API in the smartFilms, XRD and THz-spectroscopy showed similar results and revealed that it was possible to prepare smartFilms loaded with >23% (w/w) amorphous API. Results indicate the great potential of THz spectroscopy for the non-destructive determination of the crystalline state of APIs in smartFilms and/or tablets made from paper.

Effective adsorption of methylene blue by biodegradable superabsorbent cassava starch-based hydrogel

Superabsorbent hydrogels were synthesized from cassava starch (CS) and polyacrylamide (PAM) via radical polymerization. Scanning electron microscope revealed the porous structure of the hydrogels. Pore size was smaller at higher CS contents. Hydrogel containing 50 wt% CS (CS50) showed excellent water absorbency of >8000%, which was much greater than that of CS0 (pure PAM) hydrogel. This CS50 hydrogel removed >85% of methylene blue (MB) in <10 h with the greatest adsorption capacity of 2000 mg MB/g. The experimental results fitted the Freundlich and pseudo-second order models. After 4 cycles of use, the hydrogel could still remove >50% of MB in solution. Interestingly, the hydrogels were photodegradable and biodegradable. Buried in soil, the CS50 hydrogel was 80% degraded within 30 days whereas pure PAM was only 22% degraded.

Preparation of porous adsorbent via Pickering emulsion template for water treatment: A review

Porous materials as emerging potential adsorbents have received much more attention because they are capable of capturing various pollutants with fast adsorption rate, high adsorption capacity, good selectivity and excellent reusability. In order to prepare porous materials with decent porous structure, Pickering emulsion template method has been proved to be one of the most effective technologies to create pore structure. This paper reviewed comprehensively the latest research progress on the preparation of porous materials from various Pickering emulsions and their applications in the decontamination of pollutants (e.g., heavy metal ions, organic pollutants) and in the oil/water separation. It was expected that the summaries and discussions in this review will provide insights into the design and fabrication of new efficient porous adsorbents, and also give us a better understanding of the subject.

Biodiesel synthesis from fish waste via thermally-induced transesterification using clay as porous material

The valorization of organic waste through biodiesel synthesis was investigated to explore the concept of hazardous waste-to-energy. Fish waste (mackerel waste) was chosen as a case study because of the growing concern regarding the treatment of food waste, which is potentially hazardous to the environment. This study focused on the thermally-induced transesterification of fish waste for the production of biodiesel (i.e., fatty acid methyl esters (FAMEs)). This process requires a porous material that allows for the collision between reactants (fish waste and methanol) to increase inside its pores at high temperatures. Therefore, commercial clay (montmorillonite) was used as the porous material in this study. The optimal temperature for the thermally-induced transesterification of unpurified mackerel oil was 380 °C, and the FAME recovery reached up to ˜72 wt.%. This study also proved that thermal cracking of polyunsaturated FAME species was initiated at temperatures ≥390 °C, and that fish waste is a promising feedstock for biodiesel when it is produced via thermally-induced transesterification over clay as a porous material.

Self-Assembled Single-Crystalline GaN Having a Bimodal Meso/Macropore Structure To Enhance Photoabsorption and Photocatalytic Reactions

This paper describes the self-assembled fabrication of single-crystal GaN with a bimodal pore (meso/macropore) size distribution (BiPS-GaN). A 4.7 μm-thick BiPS-GaN layer was grown spontaneously using halogen-free vapor phase epitaxy in conjunction with boron impurity doping (>1 × 10¹⁹ atoms/cm³) on a GaN template fabricated via metalorganic chemical vapor deposition (MOCVD-GaN). The boron impurity acted as a surfactant, and its segregation generated a dense (>1 × 10¹⁰ cm^-2), homogeneous distribution of mesopores with sizes of 30-40 nm in GaN during growth. In addition, macropores with sizes of 0.1-2 μm were produced by the fusion of mesopores in close proximity to one another. As a result, BiPS-GaN exhibited a high density of both meso- and macropores, all aligned in the vertical direction (that is, along the c axis). BiPS-GaN showed good electroconductivity and almost the same high degree of crystallinity as the MOCVD-GaN template. Furthermore, the hybrid meso/macropore structure of BiPS-GaN imparted excellent photoabsorption properties and allowed this material to work as an efficient support for a nanosized IrO _x catalyst. The photocurrent density in BiPS-GaN was enhanced by as much as a factor of 5 compared to planar GaN by effective absorption due to the hybrid meso/macropore structure of BiPS-GaN. Moreover, the oxygen generation efficiency of BiPS-GaN with the IrO _x catalyst was approximately doubled, compared to that of BiPS-GaN without IrO _x, while maintaining long-term stability. These results demonstrate that BiPS-GaN fabricated in this facile manner has significant potential in applications such as photoelectrochemical reactions and catalysis.

Enantioseparations by Gas Chromatography Using Porous Organic Cages as Stationary Phase

The resolution of chiral compounds into optically pure enantiomers is very important in various fields, such as pharmaceutical, chemical, agricultural, and food industries. Chiral gas chromatography (GC) is one of the efficient methods for enantioseparations of volatile compounds. In recent years, porous materials as stationary phases for chromatographic separations have achieved increasing attention. Porous organic cages (POCs) represent an emerging class of porous materials, which are assembled by discrete organic molecules with shape-persistent and permanent cavities through weak intermolecular forces. This chapter describes several chiral POCs as chiral stationary phases for GC enantioseparations of racemic compounds.

Preparation and characterization of CuO catalyst for the thermolysis treatment of distillery wastewater

CuO catalyst was prepared from copper sulfate by alkali precipitation method followed by drying and calcination. Characterization of CuO catalyst using X-ray diffraction, Brunauer-Emmett-Teller, and Barrett-Joyner-Halenda surface area analysis envisaged the effectiveness of CuO as a catalyst for the treatment of biodigester effluent (BDE) emanated from distilleries. The catalytic thermolysis is an efficient advance treatment method for distillery biodigester effluent (BDE). CT treatment of BDE was carried out in a 0.5 dm³ thermolytic batch reactor using CuO as a catalyst at different pH (1-9), temperatures (80-110°C), and catalyst loadings (1-4 kg/m³). With CuO catalyst, a temperature of 110°C, catalyst loading of 4 kg/m³, and pH of 2 was found to be optimal, providing a maximum reduction in chemical oxygen demand of 65%. The settling characteristics at different temperatures of CT-treated sludge were also presented.

Upgrading the glassy slag from waste disposal by thermal plasma treatment

The paper reports on the experimental results obtained from the production of glassy slag by the plasma smelting of a mixture of two different wastes. The combination of two wastes with different chemical compositions is a promising way to optimise the energy consumption in the disposal process. Asbestos-cement roof tiles (ACRTs) and fly ash from fluidised-bed boilers (with a weight ratio of 1:1) were used for the preparation of glassy (vitrified) slag. The thermal process facilitated a 14.4% reduction of the weight of the original mixture and a 72% volume reduction of the waste. The glassy slag is then adopted as a raw material in the production of porous materials intended for various architectural applications, thus eliminating the necessity for its further disposal. The formation of a porous glass-ceramic matrix, using the vitrified slag containing CaSO₄ as the pore-forming agent, is described in detail. A glass-ceramic foam with 66% porosity is formed by the rapid heating of the mixture of glassy slag and a 1 wt% of CaSO₄, consisting of crystallised calcium aluminosilicate (Ca₂Al₂SiO₇, Ca_0.88Al_1.77Si_2.23O₈). The thermal conductivity of the prepared porous material, measured by a laser flash thermal analysis, is 0.22 W·m^-1·K^-1.

Binary gas mixture adsorption-induced deformation of microporous carbons by Monte Carlo simulation

Considering the thermodynamic grand potential for more than one adsorbate in an isothermal system, we generalize the model of adsorption-induced deformation of microporous carbons developed by Kowalczyk et al. [1]. We report a comprehensive study of the effects of adsorption-induced deformation of carbonaceous amorphous porous materials due to adsorption of carbon dioxide, methane and their mixtures. The adsorption process is simulated by using the Grand Canonical Monte Carlo (GCMC) method and the calculations are then used to analyze experimental isotherms for the pure gases and mixtures with different molar fraction in the gas phase. The pore size distribution determined from an experimental isotherm is used for predicting the adsorption-induced deformation of both pure gases and their mixtures. The volumetric strain (ε) predictions from the GCMC method are compared against relevant experiments with good agreement found in the cases of pure gases.

Direct separation of arsenic and antimony oxides by high-temperature filtration with porous FeAl intermetallic

A temperature-controlled selective filtration technology for synchronous removal of arsenic and recovery of antimony from the fume produced from reduction smelting process of lead anode slimes was proposed. The chromium (Cr) alloyed FeAl intermetallic with an asymmetric pore structure was developed as the high-temperature filter material after evaluating its corrosive resistance, structural stability and mechanical properties. The results showed that porous FeAl alloyed with 20wt.% Cr had a long term stability in a high-temperature sulfide-bearing environment. The separation of arsenic and antimony trioxides was realized principally based on their disparate saturated vapor pressures at specific temperature ranges and the asymmetric membrane of FeAl filter elements with a mean pore size of 1.8μm. Pilot-scale filtration tests showed that the direct separation of arsenic and antimony can be achieved by a one-step or two-step filtration process. A higher removal percentage of arsenic can reach 92.24% at the expense of 6∼7% loss of antimony in the two-step filtration process at 500∼550°C and 300∼400°C. The FeAl filters had still good permeable and mechanical properties with 1041h of uninterrupted service, which indicates the feasibility of this high-temperature filtration technology.

Mass Transfer in Mesoporous Microparticles Studied by Confocal Fluorescence Recovery after Photobleaching

The intraparticle diffusion of a fluorescent dye in single microparticles in an aqueous solution was analyzed using fluorescence recovery after photobleaching, with a confocal fluorescence microscope. The fluorescence depth profile of single microparticles, and the fluorescence recovery at the particle center, were measured; further, the intraparticle diffusion coefficient was determined through simulations of three-dimensional diffusion in the respective microparticles. The intraparticle diffusion of coumarin 102 in octadecylsilyl silica gel was limited by the surface diffusion.

Porous chitosan microspheres for application as quick in vitro and in vivo hemostat

Controlling massive hemorrhage is of great importance to lower transfusional medical cost, and to reduce death and mobility rate in battlefield and civilian accidents. We reported the fabrication of porous chitosan microspheres (CSMS) with tunable surface pore size by microemulsion combined with thermally induced phase separation technique, and its application as a quick hemostat. Their hemostatic property was characterized by blood clotting kinetics, adherence interaction between red blood cells/platelets and CSMS, in vitro and in vivo hemostasis by rat tail amputation and liver laceration models, and histological analysis. Their density, surface area, porosity, water absorption ratio were 0.04-0.06g/cm³, 28.2-31.5m²/g, 98%, and 15.5-23.2g/g, respectively. The surface pore was controlled to be smaller than 2.0μm. The porous CSMS showed increasing hemostatic efficacy with decreasing surface pore size. Compared to the conventional compact chitosan particles (CCSP), the porous CSMS had much improved in vitro and in vivo hemostatic potential with respect to formation of blood clot, hemostatic time, and blood loss. For instance, the hemostatic time and blood loss of CSMS in the rat liver laceration model were down to respectively 70s and 0.026g from 175s and 0.28g of CCSP. Histological examination showed that application of porous CSMS to liver laceration caused no destruction of underlying hepatocytes, inflammatory reaction, and thermal injury to liver tissue. The porous CSMS is a biodegradable, quick and safe hemostat, which can be used in various wounds including complex and non-compressive ones.

In-situ pyrogenic production of biodiesel from swine fat

In-situ production of fatty acid methyl esters from swine fat via thermally induced pseudo-catalytic transesterification on silica was investigated in this study. Instead of methanol, dimethyl carbonate (DMC) was used as acyl acceptor to achieve environmental benefits and economic viability. Thermo-gravimetric analysis of swine fat reveals that swine fat contains 19.57wt.% of water and impurities. Moreover, the fatty acid profiles obtained under various conditions (extracted swine oil+methanol+NaOH, extracted swine oil+DMC+pseudo-catalytic, and swine fat+DMC+pseudo-catalytic) were compared. These profiles were identical, showing that the introduced in-situ transesterification is technically feasible. This also suggests that in-situ pseudo-catalytic transesterification has a high tolerance against impurities. This study also shows that FAME yield via in-situ pseudo-catalytic transesterification of swine fat reached up to 97.2% at 380°C. Therefore, in-situ pseudo-catalytic transesterification can be applicable to biodiesel production of other oil-bearing biomass feedstocks.

Mass release curves as the constitutive curves for modeling diffusive transport within biological tissue

In diffusion governed by Fick's law, the diffusion coefficient represents the phenomenological material parameter and is, in general, a constant. In certain cases of diffusion through porous media, the diffusion coefficient can be variable (i.e. non-constant) due to the complex process of solute displacements within microstructure, since these displacements depend on porosity, internal microstructural geometry, size of the transported particles, chemical nature, and physical interactions between the diffusing substance and the microstructural surroundings. In order to provide a simple and general approach of determining the diffusion coefficient for diffusion through porous media, we have introduced mass release curves as the constitutive curves of diffusion. The mass release curve for a selected direction represents cumulative mass (per surface area) passed in that direction through a small reference volume, in terms of time. We have developed a methodology, based on numerical Finite Element (FE) and Molecular Dynamics (MD) methods, to determine simple mass release curves of solutes through complex media from which we calculate the diffusion coefficient. The diffusion models take into account interactions between solute particles and microstructural surfaces, as well as hydrophobicity (partitioning). We illustrate the effectiveness of our approach on several examples of complex composite media, including an imaging-based analysis of diffusion through pancreatic cancer tissue. The presented work offers an insight into the role of mass release curves in describing diffusion through porous media in general, and further in case of complex composite media such as biological tissue.

Towards accurate porosity descriptors based on guest-host interactions

For nanoporous materials at the characterization level, geometry-based approaches have become the methods of choice to provide information, often encoded in numerical descriptors, about the pores and the channels of a porous material. Examples of most common descriptors of the latter are pore limiting diameters, accessible surface area and accessible volume. The geometry-based methods exploit hard-sphere approximation for atoms, which (1) reduces costly computations of the interatomic interactions between the probe guest molecule and the porous material framework atoms, (2) effectively exploit applied mathematics methods such as Voronoi decomposition to represent and characterize porosity. In this work, we revisit and quantify the shortcoming of the geometry-based approaches. To do so, we have developed a series of algorithms to calculate pore descriptors such as void fraction, accessible surface area, pore limiting diameters (largest included sphere, and largest free sphere) based on a classical force field model of interactions between the guest and the framework atoms. Our resulting energy-based methods are tested on diverse sets of metal-organic frameworks and zeolite structures and comparisons against results obtained from geometric-based method indicate deviations in the cases for structures with small pore sizes. The method provides both high accuracy and performance making it suitable when screening a large database of materials.

Porous materials produced from incineration ash using thermal plasma technology

This study presents a novel thermal plasma melting technique for neutralizing and recycling municipal solid waste incinerator (MSWI) ash residues. MSWI ash residues were converted into water-quenched vitrified slag using plasma vitrification, which is environmentally benign. Slag is adopted as a raw material in producing porous materials for architectural and decorative applications, eliminating the problem of its disposal. Porous materials are produced using water-quenched vitrified slag with Portland cement and foaming agent. The true density, bulk density, porosity and water absorption ratio of the foamed specimens are studied here by varying the size of the slag particles, the water-to-solid ratio, and the ratio of the weights of the core materials, including the water-quenched vitrified slag and cement. The thermal conductivity and flexural strength of porous panels are also determined. The experimental results show the bulk density and the porosity of the porous materials are 0.9-1.2 g cm(-3) and 50-60%, respectively, and the pore structure has a closed form. The thermal conductivity of the porous material is 0.1946 W m(-1) K(-1). Therefore, the slag composite materials are lightweight and thermal insulators having considerable potential for building applications.

Lead and zinc removal from aqueous solutions by aminotriphosphonate-modified converted natural phosphates

Apatite particles prepared from natural phosphate rock and grafted with nitrilotris(methylene)triphosphonate (NTP) were evaluated for Pb²⁺ and Zn²⁺ sorption from aqueous solutions. Sorption capacities as high as 640 mg.g^-1 and 300 mg.g^-1 could be obtained for the highest organic content (10 wt%). Analysis of the sorption isotherms using Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich models revealed that Pb²⁺ ions have a larger affinity for apatite (sorption energy ≈ 8 kJ.mol^-1) than for NTP so that organo-modified surfaces led to a heterogenous adsorption process. In contrast, Zn²⁺ interacts weakly (sorption energy ≈ 1 kJ.mol^-1) and similarly with the mineral surface and the organic moieties following a homogenous sorption process. Such an association of organic metal ligands with reactive apatite surfaces within porous materials appears as a promising strategy to obtain efficient adsorbents at low cost and limited environmental impact.