Substrate Mass Transfer Research Articles

Ultrasound assisted enzymatic synthesis of OPO structured lipids by covalent organic framework immobilized lipase

In this study, the covalent organic framework immobilized Rhizomucor miehie lipase COF@RML as a novel biocatalyst was applied in the enzymatic synthesis of OPO structured lipids (1, 3-dioleoyl-2-palmitoylglycerol). The impact of reaction medium, substrate molar ratio, enzyme addition amount, reaction time and temperature on the enzymatic synthesis of OPO structured lipids were studied. Furthermore, the effects of ultrasonic power and ultrasonic time on the synthesis of OPO structural lipids were studied. The results showed that ultrasonication could increase the yeild of OPO structured lipids by improving substrate mass transfer and enzyme particle dispersion. The optimal process for the synthesis of OPO structured lipids was obtained. When the ultrasonic power was set at 90 W, ultrasonic time at 12 minutes, enzyme addition amount at 10 wt%, substrate molar ratio at 1:8, reaction temperature at 45 °C, and reaction time at 6 hours, the yield of OPO structured lipids reached a remarkable 51.27 %. Finally, the commercial lipase Lipozyme RM IM was compared with the COF@RML. The findings indicated that COF@RML immobilized enzyme had better application value in the synthesis of OPO structured lipids.

Pickering Emulsions Biocatalysis: Recent Developments and Emerging Trends.

Biocatalysis within biphasic systems is gaining significant attention in the field of synthetic chemistry, primarily for its ability to solve the problem of incompatible solubilities between biocatalysts and organic compounds. By forming an emulsion from these two-phase systems, a larger surface area is created, which greatly improves the mass transfer of substrates to the biocatalysts. Among the various types of emulsions, Pickering emulsions stand out due to their excellent stability, compatibility with biological substances, and the ease with which they can be formed and separated. This makes them ideal for reusing both the emulsifiers and the biocatalysts. This review explores the latest developments in biocatalysis using Pickering emulsions. It covers the structural features, methods of creation, innovations in flow biocatalysis, and the role of interfaces in these processes. Additionally, the challenges and future directions are discussed in combining chemical and biological catalysts within Pickering emulsion frameworks to advance synthetic methodologies.

Metal-organic-framework-derived boron and nitrogen dual-doped hollow mesoporous carbon for photo-thermal catalytic conversion of CO2

The facile fabrication of hollow materials with rich defects is highly desired for photothermal conversion of CO2. Herein, we successfully prepared Zn, B, and N co-doped hollow mesoporous carbon (BHNC) by directly pyrolyzing phenylboronic acid/melamine/ZIF-8. The hollow porous structure of the resulting BHNC material can not only achieve high photothermal conversion efficiency but also effectively promote substrate mass transfer. Moreover, the introduction of B extends the light absorption scope of the material, offers active sites for chemical adsorption and further activation of CO2, significantly promoting the cycloaddition reaction. Benefiting from their high specific surface area, hollow mesoporous nanoarchitecture and rich defects, the optimized BHNC can be employed as a high-efficiency catalyst for the CO2 cycloaddition reaction under light irradiation and ambient conditions, affording 3 times higher yield of 4-(chloromethyl)-1,3-dioxolan-2-one (97%) than that of ZIF-8-800. This study provides a new strategy for the design of efficient catalysts for CO2 conversion under mild conditions.

Effect of biofilm thickness on the activity and community composition of phosphorus accumulating bacteria in a moving bed biofilm reactor

Can biofilms enhance the rates of phosphorus removal in wastewater treatment? In order to narrow the scientific gap on the effect of biofilm thickness on the activity and microbial community of phosphorus-accumulating bacteria, this study investigated biofilms of 30 to 1000 µm thickness in a moving bed biofilm reactor. Measurements on 5 different biofilm carriers showed that biomass-specific phosphorus release and uptake rates increased as a function of biofilm thickness for biofilms thinner than about 110 µm but were lower for thicker biofilms of about 550–1000 µm. The reduced phosphorus uptake and release rates in the thickest biofilms can result from substrate mass transfer limitations whereas the low activity in the thinnest biofilms can be related to a too high turnover rate in the biofilm due to heterotrophic growth. Additionally, the microbial ecology of the different biofilms confirms the observed phosphorus uptake and release rates. The results from the full-length 16S rRNA gene sequencing of the bacterial community showed that the thicker biofilms were characterized by higher relative abundance (40–58%) of potential phosphorus accumulating genera Zoogloea, Acinetobacter, Dechloromonas and Ca. Accumulibacter. In contrast, the thinner biofilms were dominated by the genus Ferribacterium (34–60%), which might be competing with phosphorus-accumulating bacteria as indicated by the relatively high acetate uptake rates in the thinner biofilms. It is concluded that there is an optimal biofilm thickness of 100–500 µm, at which the phosphorus accumulating bacteria have the highest activity.

Investigating the effect of anode materials on the performance and microbial community in an integrated chamber-free microbial fuel cell

Conventionally, there are two basic configurations for microbial fuel cell (MFC), one with anode and cathode chambers, as known as dual-chamber MFC, one with only anode chamber and a air–cathode, called single-chamber MFC. However, electrode materials' complex configuration and high resistance limit their practical applications in power generation and wastewater purification. To this end, we constructed three MFCs using carbon felt, Ni/Ti, and Ag-Ni/Ti as anodes based on our previously constructed integrated chamber-free MFC (iMFC). After 21 days of operation, the Ag-Ni/Ti-MFC performed best in bioelectricity output and removal of target pollutants. The bioelectricity output parameters were an open-circuit voltage of 0.773 V, a maximum current density of 552.1429 mA/m2, and a power density of 426.8064 mW/m2. Furthermore, the MFC achieved removals of 67.90% for the chemical oxygen demand (COD), 55.20% for total nitrogen (TN), and 61.83% for ammonia nitrogen (NH3-N). Introducing silver nanoparticles to the transmembrane and outer membrane boosted the charge extraction efficiency in the MFCs. Moreover, 16S rDNA analysis indicated that typical electricity-producing bacteria, including Comamonas, Paraclostridium, and Asaccharospora, had a higher relative abundance in the Ag-Ni/Ti-MFC anode than in other anodes. Overall, the surface structure of different anode materials plays a critical role in bioelectricity generation and wastewater purification using iMFC by affecting the mass transfer of substrates and metabolites.

A novel bienzymatic bioreactor based on magnetic hierarchical porous MOF for improved catalytic activity and stability: Kinetic analysis, thermodynamics properties and biocatalyst applications

Metal-organic frameworks (MOFs) have been regarded as ideal carriers for enzyme immobilization owing to their unique structural characteristics. Whereas, enzyme activity and catalytic efficiency are seriously influenced owing to the conformation change of enzyme molecules during immobilization and the increase of substrate mass transfer resistance during catalysis. Herein, for the first time, we designed a novel magnetic hierarchical micro- and mesoporous metal-organic framework (mH-UiO-66(Zr)) as a platform for co-immobilizing horseradish peroxidase (HRP) and glucose oxidase (GOx). The obtained mH-UiO-66(Zr) with magnetic performance and hierarchical structure can effectively inhibit enzyme leakage, and reduce the material loss caused by centrifugation and the mass transfer resistance of substrate. Notably, the bienzyme bioreactor (GOx&HRP@mH-UiO-66(Zr)) was accurately constructed online in situ by microcalorimetry, which exhibited outstanding catalytic efficiency and superior stability against organic solvents, pH and temperature and favourable reusability, maintaining 95.1% of the original activity after 1 h incubation at 70 °C and over 90% initial activity after 15 cycles. Kinetics and thermodynamics investigation revealed the enhanced affinity of GOx&HRP@mH-UiO-66(Zr) for substrates. Furthermore, GOx&HRP@mH-UiO-66(Zr) has been utilized for the rapid detection and efficient degradation of 2,4-dichlorophenol (2,4-DCP), ensuring bio-catalytic material a bright potential application in environmental remediation.

MOFs-derived CuO–Fe3O4@C with abundant oxygen vacancies and strong Cu–Fe interaction for deep mineralization of bisphenol A

A novel CuO–Fe3O4 encapsulated in the carbon framework with abundant oxygen vacancies (CuO–Fe3O4@C) was successfully prepared by thermal conversion of Cu(OAc)2/Fe-metal organic framework. The as-prepared catalyst exhibited excellent peroxymonosulfate (PMS) activation performance, good recyclability and fast magnetic separation. Under optimal conditions, the added BPA (60 mg/L) could be completely removed by CuO–Fe3O4@C/PMS system within 15 min with the degradation rate constant (k) of 0.32 min−1, being 10.3 and 246.2 times that in CuO/PMS (0.031min−1) and Fe3O4/PMS (0.0013 min−1) system. A deep mineralization rate of BPA (＞80%) was achieved within 60 min. The results demonstrated the synergistic effect of bimetallic clusters, oxygen vacancies and carbon framework was a key benefit for the exposure of more active sites, the electron donor capacity and the mass transfer of substrates, thereby promoting the decomposition of BPA. Capture experiments and EPR indicated that 1O2 was the predominant reactive oxygen species (ROSs). The degradation routes of BPA and the activation mechanism of PMS were proposed. This study offers an opportunity to develop promising MOFs-derived hybrid catalysts with tailored structures and properties for the practical application of SR-AOPs.

Modeling the microbial pretreatment of camelina straw and switchgrass by Trametes versicolor and Phanerochaete chrysosporium via solid-state fermentation process: A growth kinetic sub-model in the context of biomass-based biorefineries.

Advancing microbial pretreatment of lignocellulose has the potential not only to reduce the carbon footprint and environmental impacts of the pretreatment processes from cradle-to-grave, but also increase biomass valorization, support agricultural growers, and boost the bioeconomy. Mathematical modeling of microbial pretreatment of lignocellulose provides insights into the metabolic activities of the microorganisms as responses to substrate and environment and provides baseline targets for the design, development, and optimization of solid-state-fermentation (SSF) bioreactors, including substrate concentrations, heat and mass transfer. In this study, the growth of Trametes versicolor 52J (TV52J), Trametes versicolor m4D (TVm4D), and Phanerochaete chrysosporium (PC) on camelina straw (CS) and switchgrass (SG) during an SSF process was examined. While TV52J illustrated the highest specific growth rate and maximum cell concentration, a mutant strain deficient in cellulose catabolism, TVm4D, performed best in terms of holocellulose preservation and delignification. The hybrid logistic-Monod equation along with holocellulose consumption and delignification models described well the growth kinetics. The oxygen uptake rate and carbon dioxide production rate were directly correlated to the fungal biomass concentration; however, a more sophisticated non-linear relationship might explain those correlations better than a linear model. This study provides an informative baseline for developing SSF systems to integrate fungal pretreatment into a large-scale, on-farm, wet-storage process for the utilization of agricultural residues as feedstocks for biofuel production.

Genetic design of co-expressing a novel aconitase with cis-aconitate decarboxylase and chaperone GroELS for high-level itaconic acid production

Itaconic acid (IA) is regarded as one of the 12 important building blocks as recognized by US Department of Energy. Thus, the production of IA is crucial and urgent. In this study, we attempted to explore a new aconitase from an acidophilic E. coli Nissle 1917, denoted as ENAcnA, and was compared to Corynebacterium glutamicum for the first time. The native ENAcnA has 10 amino acid mutations and the supposed critical mutations at N397S, Q409L, S522G, and G826E in the aconitase family domain contributed to the high hydratase activity at the low pH condition. Co-expression of ENAcnA and cis-aconitate decarboxylase from Aspergillus terreus in the recombinant E. coli BL21(DE3) resulted in IA titer and productivity of 80.4 g/L and 10.1 g/L/h, respectively. Integration of GroELS chaperon to chromosome of BL21(DE3) for generating BD::7G strain even enhanced IA titer by 13 %. The cold treatment of whole-cell biocatalyst substantially assisted the mass transfer of substrate through the cell membrane, and consequently achieved the maximum IA productivity. The discovery of ENAcnA, chaperon assistance in host, and cold treatment of whole cell biocatalysts contributed to high-level IA production up to 95.5 g/L for the industrial scale.

Engineering polyelectrolyte multilayer coatings as a strategy to optimize enzyme immobilization on a membrane support

This study presents a systematic design of a biocatalytic membrane reactor, where we combined physical adsorption and chemical conjugation of Alcohol Dehydrogenase (ADH) in a novel type of polyelectrolyte (PE) layer-by-layer (LbL) assembly system. The hybrid LbL structure is proposed as a strategy to simultaneously advance activity and operational stability of enzymes immobilized on a membrane surface. Using poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) sodium salt (PMAA) allowed functionalization of polysulfone (Psf) membrane for subsequent ADH immobilization with no resistance to substrate mass transfer and no decrease in water permeability (WP) (56.5 ± 8.8 Lm−2h −1bar−1) compared to the pristine membrane (50.8 ± 1.7 Lm−2h−1bar−1). Tailoring membrane surface chemistry, enzyme concentration, time, and pH during the adsorption step allowed to increase specific activity of the biocatalytic membrane from 1.13 ± 0.18 mU/cm2 for immobilization on the pristine membrane to 4.09 ± 0.53 mU/cm2 for immobilization on a PAH-modified coating. Conjugation of adsorbed ADH with PMAA layer improved reusability compared to the non-conjugated membrane (by retaining 73.4 ± 3.2% of the starting activity on the third conversion run against 58.7 ± 2.4%) and shifted pH optimum by 1 unit compared to the free ADH. The presented approach of LbL assembly synthesis provides a potential foundation for engineering of biocatalytic nanoscale reactors.

A novel inverse membrane bioreactor for efficient bioconversion from methane gas to liquid methanol using a microbial gas-phase reaction

BackgroundMethane (CH4), as one of the major energy sources, easily escapes from the supply chain into the atmosphere, because it exists in a gaseous state under ambient conditions. Compared to carbon dioxide (CO2), CH4 is 25 times more potent at trapping radiation; thus, the emission of CH4 to the atmosphere causes severe global warming and climate change. To mitigate CH4 emissions and utilize them effectively, the direct biological conversion of CH4 into liquid fuels, such as methanol (CH3OH), using methanotrophs is a promising strategy. However, supplying biocatalysts in an aqueous medium with CH4 involves high energy consumption due to vigorous agitation and/or bubbling, which is a serious concern in methanotrophic processes, because the aqueous phase causes a very large barrier to the delivery of slightly soluble gases.ResultsAn inverse membrane bioreactor (IMBR), which combines the advantages of gas-phase bioreactors and membrane bioreactors, was designed and constructed for the bioconversion of CH4 into CH3OH in this study. In contrast to the conventional membrane bioreactor with bacterial cells that are immersed in an aqueous phase, the filtered cells were placed to face a gas phase in the IMBR to supply CH4 directly from the gas phase to bacterial cells. Methylococcus capsulatus (Bath), a representative methanotroph, was used to demonstrate the bioconversion of CH4 to CH3OH in the IMBR. Cyclopropanol was supplied from the aqueous phase as a selective inhibitor of methanol dehydrogenase, preventing further CH3OH oxidation. Sodium formate was added as an electron donor to generate NADH, which is necessary for CH3OH production. After optimizing the inlet concentration of CH4, the mass of cells, the cyclopropanol concentration, and the gas flow rate, continuous CH3OH production can be achieved over 72 h with productivity at 0.88 mmol L−1 h−1 in the IMBR, achieving a longer operation period and higher productivity than those using other types of membrane bioreactors reported in the literature.ConclusionsThe IMBR can facilitate the development of gas-to-liquid (GTL) technologies via microbial processes, allowing highly efficient mass transfer of substrates from the gas phase to microbial cells in the gas phase and having the supplement of soluble chemicals convenient.

Immobilization of horseradish peroxidase on hierarchically porous magnetic metal-organic frameworks for visual detection and efficient degradation of 2,4-dichlorophenol in simulated wastewater

Immobilization of enzymes onto solid carrier is an important way to improve the stability and reusability of enzymes. However, the enzymatic activity and catalytic efficiency are severely hampered due to enzyme leaching and increased substrate mass transfer resistance. Herein, for the first time, we reported a novel strategy of co-regionalization for enzyme immobilization using hierarchically porous magnetic metal-organic frameworks (HP-Zr-MOF@Fe3O4). The HP-Zr-MOF@Fe3O4 integrate magnetic characteristics and hierarchical porous structure for supporting horseradish peroxidase (HRP) via metal-ion affinity interaction, in which the mesoporous pores are suitable for entrapping enzyme while the microporous can be used to concentrate substrate to reduce the mass transfer resistance. Significantly, the prepared HRP@HP-Zr-MOF@Fe3O4 can efficiently suppress enzyme leaching from the HP-Zr-MOF@Fe3O4 skeleton and remain superior recovered activity (96.8 %) of the initial activity of free HRP, which exhibited excellent stability and reusability. Interestingly, the HRP@HP-Zr-MOF@Fe3O4 was used efficiently in the colorimetric detection and catalytic degradation of 2,4-dichlorophenol in simulated wastewater. The excellent property of HRP@HP-Zr-MOF@Fe3O4 was investigated through the analyses of kinetics and thermodynamics, demonstrating that the HRP@HP-Zr-MOF@Fe3O4 had significant specificity and binding affinity for the substrate compared with free HRP.

Enzyme-Immobilized Metal-Organic Frameworks: From Preparation to Application.

As a class of widely used biocatalysts, enzymes possess advantages including high catalytic efficiency, strong specificity and mild reaction condition. However, most free enzymes have high requirements on the reaction environment and are easy to deactivate. Immobilization of enzymes on nanomaterial-based substrates is a good way to solve this problem. Metal-organic framework (MOFs), with ultra-high specific surface area and adjustable porosity, can provide a large space to carry enzymes. And the tightly surrounded protective layer of MOFs can stabilize the enzyme structure to a great extent. In addition, the unique porous network structure enables selective mass transfer of substrates and facilitates catalytic processes. Therefore, these enzyme-immobilized MOFs have been widely used in various research fields, such as molecule/biomolecule sensing and imaging, disease treatment, energy and environment protection. In this review, the preparation strategies and applications of enzyme-immobilized MOFs are illustrated and the prospects and current challenges are discussed.

Magnetic cross-linked lipase aggregates coupled with ultrasonic pretreatment for efficient synthesis of phytosterol oleate

In this study, coupling with substrate ultrasonic pretreatment technology, magnetic cross-linked enzyme aggregates (CRL-FIL-CLEAs@Fe3O4) was used as novel biocatalyst for efficient preparation of phytosterol oleate in solvent-free reaction system. The CRL loading was 0.16 mg protein/mg CRL-FIL- CLEAs@Fe3O4. The effects of ultrasonic parameters, catalyst dosage, substrate molar ratio, and reaction temperature on the synthesis of phytosterol esters were studied. The results showed that the catalytical properties of CRL-FIL-CLEAs@Fe3O4 (7.09±0.11 µmol phytosterol/mg protein. hour) was significantly improved compared with natural lipase from Candida rugosa (CRL, 5.13±0.21 µmol phytosterol/mg protein. hour). Simultaneously, ultrasonic pretreatment greatly enhanced substrate mass transfer, further reducing the esterification time. The max conversion rate 94.72% of phytosterol was obtained after 9 h reaction under optimum condition (the molar ratio of oleic acid to phytosterol was 6:1, the concentration of CRL-FIL-CLEAs@Fe3O4 was 10 wt% of the phytosterol mass). After five recycles, the activity of CRL-FIL-CLEAs@Fe3O4 (80.02%) was still 2.68 times higher than that of natural lipase system (29.91%). Meanwhile, the novel immobilized lipase (CRL-FIL-CLEAs@Fe3O4) before and after reaction was characterized by SEM, AFM, VSM, TEM, and TGA. The results showed that CRL-FIL-CLEAs@Fe3O4 was a robust and recyclable biocatalyst for phytosterol esterification.

CuO/g-C3N4/rGO multifunctional photocathode with simultaneous enhancement of electron transfer and substrate mass transfer facilitates microbial electrosynthesis of acetate

Microbial electrosynthesis (MES) is a potential CO2 fixation technique in which biocatalysts obtain electrons from electrodes as a driving force to reduce CO2 to more valuable multi-carbon products. In this study, a novel CuO/g-C3N4/rGO multifunctional photocatalyst was developed, and an MES system was constructed using mixed culture as a biocatalyst. Compared with CuO/g-C3N4, the introduction of rGO into CuO/g-C3N4 can enhance light absorption capacity and improve photogenerated electron–hole separation migration efficiency. Under the action of increasing reducing power, CuO/g-C3N4/rGO can accelerate electron transport rate to microbes in three ways (indirect via formate, indirect via hydrogen, and direct electron transfer). Furthermore, CuO/g-C3N4/rGO was beneficial for enriching electroautotrophic microorganisms and increasing the abundance of Acetobacterium and Arcobacter. In addition, the CO2 adsorption capacity of the photocatalyst can be improved. At a potential of −0.9 V (versus Ag/AgCl), the acetate production of MES with the CuO/g-C3N4/rGO photocathode was 0.27 g/L/d, which was 4.2 times higher than that of the control. This study provides an idea for the design of a multifunctional photocathode for reducing energy consumption and improving MES efficiency by simultaneously enhancing electron transfer and substrate mass transfer.

Bionic mineralization growth of UIO-66 with bovine serum for facile synthesis of Zr-MOF with adjustable mesopores and its application in enzyme immobilization

A metal–organic frameworks (MOFs) with adjustable mesopores was prepared through bionic mineralization using protein as template in this paper. By regulating the content of bovine serum, pore structures of different sizes (6.46, 7.55, 10.80 nm) were obtained, used for the immobilization of enzymes (HRP, laccase and cellulase). It was found that the UIO-66 with a pore size of 6.46 nm exhibited the highest loading capacities for the investigated three enzymes. Under optimized conditions for immobilization, the maximum loading capacity of HRP, laccase and cellulase was 205.7, 214.2 and 203.9 mg g−1, respectively. It should be noted that the stabilities of the three immobilized HRP@UIO-66, laccase@UIO-66 and cellulase@UIO-66 were significantly improved due to the favorable fitting between the pore size of the carrier material and the enzyme molecular size. In particular, the substrate affinity of the immobilized HRP@UIO-66 (0.120 g L−1) is similar to that of free HRP (0.122 g L−1). It is mainly due to that the appropriate porous structure of the carrier could avoid the obstruction of the substrate mass transfer channel after the adsorption of enzyme molecules. Moreover, the porous structure has a certain enrichment effect on the substrate, which promotes the catalytic efficiency of immobilized enzymes.

Construction of Ti-containing zeolite with highly enhanced catalytic activity by active species surface implanting strategy

Herein, highly efficient Ti-containing zeolite catalyst (Ti/Al-HSZ) has been prepared by an active catalysis species surface implanting strategy (ACS-SIS) through the combination of precedent acid treatment and subsequent recrystallization. Compared with commercial titanosilicate zeolite catalysts and Ti-HSZ catalyst synthesized by one-step method, Ti/Al-HSZ-c-3.5d-AT catalyst presents highly enhanced catalytic activity and turnover number values in the epoxidation of linear and cycloalkenes by using 30% H2O2 as oxygen agent under mild reaction conditions. Particularly for the conversion of bulky linear alkene and cycloalkene (1-dodecene and cycloheptene), the catalytic activity of Ti/Al-HSZ-4M‐3.5d‐AT can attained more than three times than that over Ti-HSZ-3.5d-AT. Based on systematical comparison and analysis, on one hand, the excellent catalytic performance of Ti/Al-HSZ is ascribed to its unique hollownest morphology that acts as ideal reaction space by providing with plenty of hierarchical porous structure and high external surface, which is beneficial for the diffusion and mass transfer of bulky substrate. On the other hand, the high content of active open Ti species locating on the surface of catalyst is particularly beneficial for the formation of transition state to accelerate the epoxidation reaction. Not only the Ti source utilization rate but also the Tiopen incorporated rate of Ti/Al-HSZ-4M‐3.5d‐AT prepared by ACS-SIS is much higher than that of Ti-HSZ prepared by one-step hydrothermal synthesis route. The effects of acid treatment and recrystallization on the zeolite framework, morphology, chemical composition, and Ti coordination states have been thoroughly discussed. The ACS-SIS is believed to be an effective route to construct excellent solid heterogeneous catalyst to meet the urgent need of green chemistry for sustainable development.

Biodegradation dynamics disparity between n‐alkanes and polycyclic aromatic hydrocarbons in the vadose zone: A critical review

AbstractIn the shallow terrestrial subsurface, bioavailability often controls biodegradation rates of various hydrophobic organic pollutants, such as hydrocarbons. Microorganism‐mediated depletion of n‐alkanes and polycyclic aromatic hydrocarbons (PAHs) in the vadose zone proceeds with distinctively different rates and kinetics. The observed disparity in biodegradation dynamics between these two classes of hydrocarbons are described here in terms of the Best equation, which allows for a complex process of hydrocarbon contaminant depletion to be explained in terms of the physically relevant processes. This equation combines terms describing contributions of two key elements of hydrocarbon biodegradation—the intrinsic catabolic activity of microorganisms and the mass transfer process delivering substrate to active microorganisms. If substrate supply is slow, biodegradation process is availability‐limited because microorganisms consume the substrate faster than it can be delivered. Conversely, when the mass transfer of substrate is faster than the microbial consumption, biodegradation rate tends to be controlled by metabolic kinetics.The evaluation conducted in this study ascertains that the critical factor limiting the rate and extent of PAH biodegradation is the mass transfer rather than the intrinsic microbial activity that appears to govern the rate of n‐alkane biodegradation. The specifics of mass transfer are determined by the magnitude of the substrate–soil interactions. Whereas sorption of n‐alkanes is controlled by weak hydrophobic and van der Waals forces, PAHs tend to bind to the soil matrix by much stronger electron‐donor–acceptor interactions. Stronger interactions between aromatic compounds and soil components translate into the higher activation energies for desorption of PAHs and therefore a slower mass transfer process. This aspect of the substrate–soil interaction explains a more prominent effect of mass transfer limitation on biodegradation dynamics of PAHs compared to that of the corresponding n‐alkanes.

Matrimid substrates with bicontinuous surface and macrovoids in the bulk: A nearly ideal substrate for composite membranes in CO2 capture

Scalable fabrication of thin-film composite (TFC) membrane for post-combustion carbon capture is often limited by the availability of high-performance nanoporous substrate. Ideally, the substrate should allow for fast gas transport at the selective layer/substrate interface as well as in the bulk of the substrate. In this study, highly permeable Matrimid substrates were prepared via vapor- and nonsolvent-induced phase separations. The phase separation mechanism of the Matrimid®/N-methyl-2-pyrrolidone casting solution was modulated by the addition of LiCl to control the solution thermodynamic stability, and nanoporous Matrimid substrates were formed with a bicontinuous surface and macrovoids in the bulk. This hierarchically optimized structure resulted in a CO2 permeance of 2.60 × 105 GPU (1 GPU = 1 × 10−6 cm3(STP) cm−2 s−1 cmHg−1 = 3.349 × 10−10 mol m−2 s−1 Pa−1), which was ca. 11 times more permeable than a benchmark polyethersulfone substrate with cellular pores. The benefit of using this new substrate was demonstrated by coating a 170-nm amine-containing polymer to form a TFC facilitated transport membrane. The membrane exhibited a CO2 permeance of 932 GPU at 57 °C, which was 72 GPU higher than the counterpart coated on the benchmark substrate. Meanwhile, the CO2/N2 selectivity was remained at 158. This permeance improvement could be well explained by the resistance-in-series model, where the improved permeance was attributed to the reductions in substrate and lateral diffusion mass transfer resistances. The upper bound (UB) analysis indicates that the Matrimid substrate is nearly ideal for the state-of-the-art polymers for CO2/N2 separation. The substrate improvement could also reduce the parasitic energy associated with the membrane process due to the reduced membrane cost and flue gas compression requirement.

Droplet motion on chemically heterogeneous substrates with mass transfer. II. Three-dimensional dynamics

We consider a thin droplet that spreads over a flat, horizontal and chemically heterogeneous surface. The droplet is subjected to changes in its volume though a prescribed, arbitrary spatiotemporal function, which varies slowly and vanishes along the contact line. A matched asymptotics analysis is undertaken to derive a set of evolution equations for the Fourier harmonics of nearly circular contact lines, which is applicable in the long-wave limit of the Stokes equations with slip. Numerical experiments highlight the generally excellent agreement between the long-wave model and the derived equations, demonstrating that these are able to capture many of the features which characterize the intricate interplay between substrate heterogeneities and mass transfer on droplet motion.