External Surface Area Research Articles

Experimental Study on the Influence of Gas-Solid Heat Transfer in a Mesoscale Counterflow Combustor

ABSTRACT Combustion at small scales is inhibited by the large amount of external surface area leading to excessive heat losses and extinguishment. This limitation is diminished by transferring heat from the products to the reactants through solid surfaces leading to the development of heat recirculating reactors. A promising design is the counterflow configuration in which reactants in one channel are preheated by energy transferred through the wall from the products in the adjacent channel. In the lean equivalence ratio limit of the reactor, this arrangement encourages the stabilization of the flame. In the high equivalence ratio limit, the enhanced heat transfer may encourage blow-off. Therefore, it is important to understand the relationship between heat transfer and the operating range of the reactor. In this paper, the importance of the channel surface area-to-volume ratio is investigated analytically and experimentally in a mesoscale combustor. Reactors with different channel shapes were fabricated via additive manufacturing and studied. The change in heat transfer area affected the stable operating range, maximum temperature, and location of flame stabilization. The emission measurements showed low CO and NOx emissions. For all reactors, the stable range was limited by flashback when the burning rate exceeded the flow velocity and by blow-off when the burning rate was insufficient. This work quantifies the importance of heat transfer surface area to the operation of the counterflow reactor and guides the optimization of reactor design.

Fe Single‐Atom Catalysts on MOF‐5 Derived Carbon for Efficient Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells

AbstractThe development of Fe single‐atom catalysts (Fe SACs) with abundant, accessible Fe sites is a key step toward enhancing the efficiency of the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). In this study, Zn4O(1,4‐benzenedicarboxylate)3 (MOF‐5), which has a 3D microporous cubic structure, is used as the precursor to prepare highly‐porous carbon (denoted as C‐MOF‐5) with an ultrahigh specific surface area (2751 m2 g–1) and high external surface area (1651 m2 g–1). C‐MOF‐5 is demonstrated as an effective carbon support to yield Fe SAC‐MOF‐5 with a large amount of accessible FeNx sites (2.35 wt%). Fe SAC‐MOF‐5 delivers a half‐wave potential of 0.83 V (vs RHE) in a 0.5 m H2SO4 electrolyte, and achieves a peak power density of 0.84 W cm–2 in a 0.2 MPa H2‐O2 PEMFC. This excellent performance originates from the ultrahigh specific surface area of C‐MOF‐5 for the formation of a high density of single Fe atoms, and high external surface area for the increased exposure of active sites. This work may inspire the rational design of metal single‐atom catalysts derived from a wider range of MOF precursors with ultrahigh specific area to improve the performance of the oxygen reduction reaction in PEMFCs.

Structured cobalt–manganese oxides on SiC nano-whisker modified SiC foams for catalytic combustion of toluene

This work presents a two-step method for preparing structured Cobalt-Manganese Oxides nano-sheet (CMO) on SiC nano-whisker (SNW) modified SiC foam support (i.e. CMO@SNW@SiC) and its application to catalytic combustion of toluene. Firstly, SiC nano-whiskers were synthesized on the surface of SiC foam via carbothermal reduction to increase the specific surface area of the resulting structured support (SNW@SiC). Then, CMO were grown on SNW@SiC by hydrothermal synthesis. SNW@SiC provide more surface area, and the nano-sized SiO2/SiCxOy layer on the surface of the SNW promotes the redox reaction of the reactants on the surface, thereby ensuring the directional growth of CMO on SNW@SiC. Compared to the bare SiC foam, CMO loading was increased 67.5% on SNW@SiC. Analysis methods such as H2-TPR, O2-TPD and XPS prove that the redox ability of the CMO on SNW is similar to that of the powder CMO. Toluene catalytic combustion was used as a probe reaction to evaluate catalytic activity. The results show that the CMO@SNW@SiC catalyst could lower the light-off temperature compared to the CMO supported on SiC foam catalyst, which was equivalent to the bulk catalyst (CMO-24h). At the same time, in comparison with the bulk CMO catalyst, the CMO@SNW@SiC catalyst possessed a higher geometric external surface area, which promoted complete conversion of toluene at lower temperatures. In addition, the stability test shows that the CMO@SNW@SiC catalyst also had very good thermal stability and hydrothermal stability as well. The work provided not only the highly performed catalytic oxidation catalyst, but also presented a generic strategy for improving the design of structured catalysts.

Review and new data on the surface properties of palygorskite: A comparative study

Palygorskite is a mineral used in a wide number of industrial sectors. Currently, there are hundreds of studies in which palygorskite is a part of different nanocomposites and bionanocomposites. The surface properties are essential for these applications, and in this work, an in-depth revision of these properties is done, showing that the high variability found cannot be explained only by the number of impurities or by differences in the analysis conditions. To further deepen the knowledge of the surface properties of palygorskite and palygorskitic clays, a comparative study of a wide group of high purity samples is also performed, and new data on these surface properties are provided with the determination of the specific surface area (SSA), micropore surface area (SSAμp), micropore volume (Vμp), external surface area (SSAEx), and mean equivalent pore diameter. Both the bibliographic data and new data show that SSA varies from a few tens of m2g−1 to almost 300 m2g−1, and the microporosity and external surface proportions also vary greatly. The experimental data obtained show that 1) ordinary soft vacuum conditions produce structural folding, which limits the accessibility to the inner part of the structural tunnels; 2) microporosity is related to the intra- and inter-fibre microporosity, depending first on the fibre size, because the shorter the fibre, the higher the partial accessibility to the entrance of the channels; 3) the crystal chemistry of the samples also influences the SSA because the Mg-rich terms, which have higher content of sepiolite polysome proportions in their structure as well as wider and more accessible intracrystalline channels than palygorskite polysomes.

Semi-continuous fermentation of chopped rice straw in a solid-state anaerobic digester: Influences of the tank height-to-diameter ratio, solid-state bed concentration, and leachate recirculation ratio

Chopped rice straw fermentation in solid-state anaerobic digesters (SS-ADs) is a viable path for biogas generation. Thus, three fermentation test series in typical anaerobic digesters were operated to investigate the effects of the external surface area, permeability, and liquid fluidity of the solid-state bed (SSB) in improving anaerobic digestion, as determined by varying the tank height-to-diameter (H:D) ratio, SSB concentration, and leachate recirculation ratio (RR), respectively. In Series A, the H:D ratio impacted the modulation of digestion progress, including biogas generation, volatile fatty acids release, and lignocellulosic degradation. In Series B, the use of an SSB concentration below the inflection threshold (10.7 %–13.3%) for biogas production decline resulted in the highest methane yield and average methane content. In Series C, a 25.0% RR increased methane production significantly (P < 0.01) in both the semi-continuous fermentation SS-AD and downward plug-flow anaerobic digester (DPAD). Accordingly, energy flow analysis revealed that the DPAD produced 19.3% more net energy than the liquid anaerobic digester.

Modification of ZSM-5 mesoporosity and application as catalyst support in hydrodesulfurization of dibenzothiophene: Experimental and DFT studies

The hydrodesulfurization (HDS) efficiency of NiMoS supported on modified H-ZSM-5 was investigated. The support modification was achieved via desilication (DS) in 3 – 5 M NaOH solution for 0.5 – 1 h, at 65 °C. The desilication of H-ZSM-5 increased both its mesoporosity and external surface area. The catalysts acidity and active phase formation and dispersion were influenced by the desilication of the zeolite supports. The NM/B-Z1/2 catalyst shows better HDS performance with dibenzothiophene (DBT) conversion of 87% after 4 h of reaction, while the catalyst formed from pristine ZSM-5 support (NM/Z) recorded the least DBT conversion of 38%. The DFT simulation energetics revealed that the hydrodesulfurization (HDS) process proceeded via the direct desulfurization (DDS) pathway in good correlation with the experimental findings. Extensive characterization techniques were adopted to gain insight into the physico-chemical properties of the support and the catalysts. Surface area and porosity analyzer was used for textural properties information of both the support and the catalyst. The information about surface and type of acidity, the metal-support interaction, morphology, metal charge content and dispersion of active species NiMo-S was explored by FESEM, FETEM, TPD, Pyr-FTIR, FTIR, XRD and XPS

IM-5 zeolite with abundant narrow mesopores and modulated acidity as stable and selective cracking catalyst

High-performance IM-5 was prepared by tetrapropylammonium hydroxide (TPAOH) and NaOH alkaline treatment. The modification of combined alkaline treatment on the pore and acidity were systematically characterized. The 29 Si NMR results indicated that Si(4Si, 0Al) sites were protected by tetrapropylammonium cation (TPA + ) at low TPAOH/(NaOH + TPAOH) molar ratio, while the protection effect extended to some Si(3Si, 1Al) sites at TPAOH/(NaOH + TPAOH) ratio of 75%. And, the amount of strong Brønsted acid sites decreased significantly from 255 μmolg −1 to 119 μmolg −1 under the optimal TPAOH/NaOH alkaline treatment conditions. Compared to NaOH treatment alone, the mesopore volume and external surface area of IM-5 were further increased with TPAOH introduced, meanwhile, the mesopore size was shrunken into the range of 2–10 nm centered at 5 nm. Compared to NaOH treated IM-5 catalyst, the TPAOH/NaOH treated one exhibited higher initial light olefins yield (53.4% vs. 45.2% for n -heptane cracking) and better catalytic stability and regeneration properties. The abundant narrow mesopores contributed into high tolerance ability to coke deposition in IM-5 catalysts, as confirmed by TGA results. • TPAOH/NaOH treatment led to abundant well-spread mesopores in IM-5. • TPAOH/NaOH treatment lowered the amount of strong Brønsted acid sites. • TPA + extended protection effect to framework aluminum at high TPAOH concentration. • TPAOH/NaOH treated IM-5 reached high light olefins yield of 53.4%. • TPAOH/NaOH treated IM-5 kept stable in 5 regeneration cycles.

New data on the microporosity of bentonites

This comparative study on a very wide group of samples shows that the crystal size and crystalline defects of smectites influence microporosity of bentonite considerably more than previously considered. The smectite crystals and surface properties, including microporosity and micropore volume, were studied using high resolution transmission electron microscopy and N2 adsorption, respectively. The specific surface area obtained varied between 25 and 278 m2g−1. The micropore area ranged between 6 and 76 m2g−1, and the external area ranged from 18 to 208 m2g−1. The external surface area was related to the size of the crystals in [001] direction because of the smaller particles with few stacked 2:1 layers have more basal surfaces accessible to the N2 molecules. However, the microporosity can be related to 1) the size of the crystals, owing to the partial ability of N2 to penetrate into the interlayer space, 2) the abundance of crystalline defects affecting the stacking of the 2:1 layers, and 3) the arrangement of the crystals forming particles, in which sub-parallel aggregates generate micro and mesopores. The study shows that these bentonites have pores in the full range, from smaller micropores (related to the crystalline structure in the interior of the interlayer) to micrometric macropores. The amounts of micro, meso, and macropores varied between samples but were similar and characteristic for samples from the same geological area.

Defect Level and Particle Size Effects on the Hydrolysis of a Chemical Warfare Agent Simulant by UiO-66.

Defect engineering in metal-organic frameworks (MOFs) has recently become an area of significant research due to the possibility of enhancing material properties such as internal surface area and catalytic activity while maintaining stable 3D structures. Through a modulator screening study, the model Zr4+ MOF, UiO-66, has been synthesized with control of particle sizes (100-1900 nm) and defect levels (2-24%). By relating these properties, two series were identified where one property remained constant, allowing for independent analysis of the defect level or particle size, which frequently change coincident with the modulator choice. The series were used to compare UiO-66 reactivity for the hydrolysis of a chemical warfare agent simulant, dimethyl 4-nitrophenylphosphate (DMNP). The rate of DMNP hydrolysis displayed high dependence on the external surface area, supporting a reaction dominated by surface interactions. Moderate to high concentrations of defects (14-24%) allow for the accessibility of some interior MOF nodes but do not substantially promote diffusion into the framework. Individual control of defect levels and particle sizes through modulator selection may provide useful materials for small molecular catalysis and provide a roadmap for similar engineering of other zirconium frameworks.

Eco-friendly and acid-resistant magnetic porous carbon derived from ZIF-67 and corn stalk waste for effective removal of imidacloprid and thiamethoxam from water

Neonicotinoids, extensively present in water environment, can adversely affect the ecological safety and human health. Herein, a low-cost magnetic porous carbon ZIF-67/CS@C derived from ZIF-67 and agricultural waste corn stalk (CS) is designed and applied for adsorptive removal of imidacloprid and thiamethoxam from water. The adsorbent is fabricated by carbonizing ZIF-67/CS hybrid pre-prepared through an in-situ decoration of ZIF-67 on the surface of CS, and then acid picking to elute the unstable constituents. In the carbonization, Co2+ ions are reduced to magnetic Co0 nanoparticles, with the result that ZIF-67/CS@C shows a strong magnetic response (saturation magnetization intensity is 12.25 emu‧g−1) and can be easily magnetically separated. Meanwhile, Co nanoparticles are protectively encapsulated in well-developed graphitized wall, which endows ZIF-67/CS@C with good acid resistance (only 0.23% of Co is leached out at pH 1.0). More importantly, reasonable pore size distribution (most pore sizes match or are 3–6 times that of imidacloprid and thiamethoxam) and high external surface area (280 m2‧g−1) are obtained, which makes ZIF-67/CS@C super adsorbent. The adsorption capacities for imidacloprid and thiamethoxam can reach as high as 189 and 133 mg‧g−1, respectively. Moreover, after six consecutive recycling processes, the adsorption efficiencies are still above 95%, which reveals excellent reusability of ZIF-67/CS@C. Mechanism analysis affirms that pore-filling, H-bond, and π-π EDA interaction are mainly responsible for driving imidacloprid and thiamethoxam adsorption. Finally, ZIF-67/CS@C with a great security towards Daphnia carinata survival and wheat growth is eco-friendly. This study can be easily adapted to different biomass wastes and MOFs, thus potentially enabling the preparation of more novel adsorbents.

Defective sites in ZSM-5 zeolite synthesized by n-butylamine template facilitating uniform meso-microporosity by alkali-treatment

Two ZSM-5 zeolites (denoted as BZ and TZ series), respectively synthesized by using n-butylamine (BA) and tetrapropylammonium (TPA+) as template, were transformed to pertinent hierarchical zeolites (BZ-AT and TZ-AT) by post-treatment via alkali-treatment. The both ZSM-5 zeolites have distinct defective sites, which are crucial importance for their properties in terms of forming meso-microporosity and performance in the methanol to olefin reaction. By alkali treating ZSM-5 zeolites (BZ-80 and TZ-80) with comparable SiO2/Al2O3 of 80, the hierarchical zeolite BZ-80-AT proves higher Desilication Efficiency than TZ-80-AT. Notably, BZ-80-AT features a uniform distributed meso-microporosity with mesopore size centered around 10 nm, larger external surface area and mesopore volume, while TZ-80-AT displays a centrally hollow structure with cavity size of more than 200 nm in diameter. Characterization results demonstrate more silanol nests in BZ-80, facilitating uniform desilication to create uniform mesopore in BZ-80-AT crystals. In contrast, the more internal silanols in TZ-80, along with the connatural distorted framework aluminium generate the hollowed structure in TZ-80-AT. Much should be owed to its specific micro/mesoporosity rendering better diffusivity, BZ-80-AT exhibits higher propylene and butylene selectivity as well as longer lifetime in the MTP reaction.

An open superstructure of hydrangea-like carbon with highly accessible Fe-N4 active sites for enhanced oxygen reduction reaction

Single-atom catalysts (SACs) have sparked intense interest in heterogeneous catalysis lately, but insufficient accessibility of active sites restricts their further applications. Herein, a hydrangea-like carbon nanoparticle possessing highly open nanospaces and enhanced external surface area that fully exposes the catalytic sites is reported. By introducing mesoporous silica nanoparticles (MSNs), Fe-doping zeolitic imidazolate framework-8 (ZIF-8) precursors are assembled into a flower-like superstructure interlaced by porous nanosheets, which expand from inside out constructing an open and interconnected architecture. This unique structure can substantially liberate the densely dispersed but deeply buried Fe-N4 sites inside carbon nanoparticles and accelerate mass transfer in the catalyst layer that increases active-site utilization. Furthermore, the physical and chemical properties of the assembled catalysts can be adjusted by the diameter (200, 300, and 500 nm) of MSNs. When the diameter was 500 nm, the optimal FeNC-F3 catalyst exhibited large specific surface area, maximum metal centers utilization, high oxygen reduction reaction efficiency, and excellent stability. The novel cathodic electrocatalyst achieved high power density of 0.32 mW cm−2 in microbial fuel cell and 288 mW cm−2 in Zn-air battery. This work established a realistic strategy for promoting the practical development of fuel cell catalysts.

Hollow porous organic polymers spheres decorated with silver nanoparticles for sterilization and oil/water separation

The exploitation of high-performance antibacterial materials is of great importance for maintain public health and sustainable development of modern society. Here, we describe a facile approach for the preparation of conjugated microporous polymer hollow spheres (CMP1-HSs and CMP2-HSs) by using SiO2 nanoparticles as a template and 1,3,5-triethynybenzene and 3,7-dibromophenothiazin-5-ium, bromide for CMP2 and 1,3,5-triethynybenzene and 1,4-dibromobenzene for CMP1-HSs as building blocks via the Sonogashira-Hagihara cross-coupling reaction. The as-synthesized CMPs-HSs possess good thermal stability with a thermal decomposition temperature of up to 588 °C, high porosity (a BET specific surface area of approximately 556 m2 g−1) and a unique hollow spherical morphology with inner diameter of ca. 380 nm. Benefit from their intrinsic lipophilicity and hydrophobicity, the CMPs-HSs could act as a kind of ‘micro-tank’ which enable to capture and absorption of organics from water. Interestingly, the CMPs-HSs also show an antibacterial property with bromide. To further improve their antibacterial performance, silver nanoparticles were doped onto the CMPs-HSs (abbreviated as [email protected]). The as-resulted [email protected] exhibit excellent antimicrobial activity both for gram-negative, e.g. Escherichia coli, The minimum inhibitory concentration (MIC) value of CMP1 is 15 μg mL−1 that is the growth of E. coli could be inhibited entirely after 3 h treatment. Taking advantages of their superior wettability, excellent absorption and separation ability, unique hollow spherical morphology makes much more accessible external surface area for doping Ag nanoparticles, such [email protected] may hold great potentials as a kind of novel porous medium for organic pollution elimination, water treatment and antibacterial applications.

Synthesis and Characterization of Sn, Ge, and Zr Isomorphous Substituted MFI Nanosheets for Glucose Isomerization to Fructose

Various metals including Sn, Ge, and Zr have been successfully incorporated into the MFI nanosheets via a one-pot synthesis. The as-synthesized zeolites exhibit high external surface area and mesopore volume without large metal oxides aggregated on zeolite surfaces. Interestingly, the successful introduction of heteroatoms in MFI nanosheets can be confirmed by shifted XRD peaks corresponding to the unit cell expansion due to the replacement of metals into the framework. In addition, the UV-Vis absorbance spectra reveal that at the suitable metal loading the incorporated tetrahedral coordination of metal species in the zeolite framework has been obtained. To illustrate the benefits of the prepared catalysts, the glucose isomerization to fructose was carried out in a water/dioxane system. Obviously, the SnMFI-NS samples, containing the high dispersion of metal isomorphous species demonstrate the outstanding catalytic behavior in term of fructose selectivity (>85 %).

Thermo-catalytic co-pyrolysis of ironbark sawdust and plastic waste over strontium loaded hierarchical Y-zeolite

The objective of this research is to synthesize hierarchical strontium loaded Y-zeolite and study its application for ironbark (IB) and plastic waste (PW) co-pyrolysis. Commercial parent Y-zeolite (Si/Al = 2.48) was modified via sequential dealumination-desilication using citric acid and NaOH. Further, strontium (8 wt %) was loaded into the modified Y-zeolite via wet and dry impregnation methods. The prepared catalyst was characterized by N2 adsorption-desorption isothermal, field emission scanning electron microscopy (FESEM) combined with energy dispersive x-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Thermogravimetric analyzer (TGA). After dealumination (treatment using 0.1 M of citric acid), the external surface area and Si/Al ratio increased from 53.5 to 147.4 m2/g and 2.48 to 5.36, respectively. However, the sequential desilication treatment reduced Si/Al ratio from 5.36 to 2.57. In addition, Y-zeolite enhanced the total aromatic percentage and reduced the acidic group in co-pyrolysis oil.

Prediction of water retention properties of Syrian clayey soils

Studies on clayey soils developed in temperate areas have shown that their water retention properties are related to both the clay content and the specific pore volume of the clay, the latter being related to the hydric history of the soil, that is to the drying/wetting cycles. Our objective was to discuss the validity of these results for clayey soils developed in semi-arid areas. Samples were collected in soils located in Syria. Physico-chemical properties were determined. Water content was measured at field capacity and for water potentials ranging from −10 to −15,000 hPa. X-ray diffraction analyses were performed on the clay fraction to identify the clay. Results showed that the clays have both a high cation exchange capacity (0.707–0.891 mmol+ g−1 of clay) and a high external specific surface area (112 and 178 m2 g−1 of clay). These values are consistent with the X-ray diffraction results which showed the presence of a high proportion of smectite in most horizons and secondarily of varying proportions of illite and chlorite; kaolinite, while present, was not abundant. Results also showed that the amount of water retained by the clay according to the water potential was closely related to the specific pore volume of the clay at field capacity. Regression equations established by using both the data published earlier and those of this study enabled us to predict the water retention properties of clayey soils for a larger range of clay mineralogy and climatic environments including semi-arid environments than previously discussed in the literature.

Two Coexisting Forms of Simple Molecules for Directing Sesqui-Unit-Cell Zeolite Nanosheets

Feasible strategies are desirable for preparing zeolitic nanosheets with opener porosities and more accessible active sites. Highly delaminated FER nanosheets (ECNU-17) with unit-cell scale thickness were hydrothermally synthesized using a simple, small, and low-cost imidazole molecule as the sole organic structure-directing agent (OSDA). The single OSDA directed the formation of the FER framework, while the π–π stacked OSDAs terminated the growth perpendicular to the zeolite sheets. The ECNU-17 nanosheet is only 2.9 nm in thickness, corresponding to one and a half FER unit cells along a-axis. With open hierarchical porosity and an enhanced external surface area of 253 m2 g–1, ECNU-17 is endowed with improved mass transport and a significantly increased number of active acid sites accessible to bulky organic molecules. The ultrathin sheets of ECNU-17 aluminosilicate display excellent activity and selectivity for the protection reaction of benzaldehyde with pentaerythritol as well as the cracking of 1,3,5-triisopropylbenzene.

Synthesis and microwave absorbing properties of N-doped carbon microsphere composites with concavo-convex surface

Concavo-convex surface can increase the external surface area and provide multi-directional reflective surface, which has significant advantages in improving the microwave absorbing performance of materials. In this paper, a series of N-doped carbon microsphere composites with concavo-convex surface (NCMCCS) and their preparation method have been reported. The precursors organic-inorganic hybrid microspheres with concavo-convex surface (OHMCS) are synthesized by solvothermal method. NCMCCS with different ZnS and ZnO loadings are prepared by calcining OHMCS at different temperatures. Their microwave absorbing properties have been evaluated. NCMCCS obtained at different temperatures exhibit excellent microwave absorbing performance under optimal filler content. The samples calcined at lower temperature have significant advantages in low frequency. The maximum reflection loss (RLmax) of the sample obtained at 750 °C is −60.4 dB@7.2 GHz@3.7 mm, and the effective absorption bandwidth (EAB) is 2.6 GHz. The higher temperature calcined sample shows the characteristic of ultra-low filler content, the RLmax of the sample prepared at 900 °C reaches −46.8 dB@10.4 GHz@2.7 mm under a filler content of only 6%. Meanwhile, the microwave attenuation mechanism has been systematically analyzed and explained. This work provides a new way for constructing high efficiency microwave absorbers with complex surface.

Fabrication of magnetic bimetallic Co–Zn based zeolitic imidazolate frameworks composites as catalyst of glycolysis of mixed plastic

With the increasing awareness of environmental protection, the degradation of waste plastic has attracted more and more attention. In this study, the glycolysis of PET and PBT which are widely used in daily life were investigated using CoFe2O4@ZIF-8/ZIF-67 composite as catalyst. Moreover, the glycolysis of PET/PBT mixed plastic was also studied. The result showed that CoFe2O4@ZIF-8/ZIF-67 has ideally catalytic effect in glycolysis of plastic, especially in glycolysis of PET/PBT mixed plastic. PET/PBT (5 g), CoFe2O4@ZIF-8/ZIF-67 (0.05 g) and ethylene glycol (25 g) were at 200 °C for 60 min, plastic conversion is up to 100% and BHET yield reached 84.3%. The main product of glycolysis of PBT and PET/PBT was characterized and confirmed to be bis(hydroxyalkyl) terephthalate (BHET). The result of UPLC indicated that purity of main product of glycolysis of PET/PBT was 92%. The as-synthesized catalysts were characterized by XRD, FT-IR, SEM, TGA, N2 adsorption–desorption and VSM. The catalytic performance of catalysts was significantly influenced by external BET surface area. More importantly, the magnetic catalyst could be collected quickly by external magnetic field. The catalytic performance of CoFe2O4@ZIF-8/ZIF-67 did not obviously decrease and element content of Zn and Co in catalyst was just decreased by less than 10% after it was reused for five times.

APTES modified SBA15 and meso-macro silica materials for the immobilization of aminoacylases from Streptomyces ambofaciens

Aminoacylases from a crude extract from Streptomyces ambofaciens were described as attractive way for the synthesis of amino acids biobased surfactants. The aim of this study is to investigate the influence of the porosity and the APTES functionalization of the silica support on the immobilization and the activities of these aminoacylases. To reach this goal, a mesoporous (SBA-15) and of meso -macroporous (MMS) silica material without and with functionalization with APTES were used. The results show that the use of non-functionalized supports led to a poor enzyme loading due to electrostatic repulsion between the enzyme and the silica support. The APTES functionalization of the silica materials allow a better enzyme loading by favouring enzyme-support interactions with an increase of the immobilization rate by increasing the APTES functionalization rate from 0 to 10% especially when using MMS. However, the measurement of the catalytic performances of the enzymes immobilized on the materials shows a significant improvement of the conversion rate by increasing the APTES percentage in the case of SBA-15 unlike the enzymes immobilized on the functionalized MMS. This behaviour can be explained by the better substrate accessibility to the enzyme immobilized on the SBA-15-based materials which is mainly located on the external surface area of the functionalized materials. The cross linking of the aminoacylases by using glutaraldehyde led to a loss of the activity due to enzyme inactivation. The LC-MS-MS analysis of the product of lysine acylation reaction shows that the regioselectivity of the enzymes after immobilization is not modified. • Improvement of the immobilization rate and the activity of the immobilized enzymes by increasing the APTES concentration. • No effect of the porosity on the immobilization performance. • Collapse of the structure of the mesomacroporous material after immobilization led to a diffusional limitation. • Structural stability of the SBA-15 material after immobilization. • Decrease of the activity after the addition of glutaraldehyde.