Recent Advances in Enzyme Immobilization in Nanomaterials

Chapter 5 - Nanobiocatalysts: the promising alternatives for conventional biocatalysts used in lignocellulosic biomass hydrolysis

Recent advances in nano-carrier immobilized enzymes and their applications

The application of enzymes as biocatalyst is well recognized in the field of green engineering. Due to their outstanding properties such as inconsumable in chemical reaction, highly specific in action, and speeding up the reaction rate, they are widely used in the conversion of various renewable sources into biofuel. Biofuel, in recent years, had shown such great potential in becoming the alternative for the petrol-derived fuel since it is generated from biomass origins. Researchers currently had introduced few enzyme modifications such as gene editing and supercritical fluid extraction techniques in order to maximize their catalytic performances. However, all of those methods are more tedious and still lack in maintaining the regenerative ability of the enzymes as well as their stabilities. Hence, the technique of enzyme immobilization is currently applied in the biofuel production in improving the enzymes’ performances by providing extra physical support known as backbone to the enzyme to speed up the reaction. Thus, this review aims to provide better insight on the current immobilization technology as well as the enzyme immobilization itself in biofuel generation. Different types of biofuel produced in the industry is also reviewed. The working principles, mechanisms, characteristics, and advantages of the enzyme immobilization technique is also conferred. Besides, comparisons between mobilized, extracellular immobilized and intracellular immobilization will also be reviewed along with the types of matrices used in the adsorption immobilization methods. Lastly, some issues regarding this technique are also highlighted in improving the enzyme performance itself.

Technological road map of Cellulase: A comprehensive outlook to structural, computational, and industrial applications

In recent years, enzyme immobilization technology has been developed, and studies on immobilized enzyme materials have become very prominent. With the immobilization technique, enzymes and compatible carrier materials are combined or enzyme crystals/aggregates are used in a carrier-free fashion, by physical, chemical, or biochemical methods. As a kind of biocatalyst, immobilized enzymes can catalyze certain chemical reactions with high selectivity and high efficiency under relatively mild reaction conditions and eliminate pollution to the environment. Considering the current status and applications of immobilized enzyme technology and materials emerging in the last 5years, this mini-review introduces the advantages and disadvantages of various enzyme immobilization techniques with carriers as well as the pros and cons of different materials for immobilization. The future prospects of immobilization technology and carrier materials are outlined, aiming to provide a reference for further research and applications of sustainable technology.

Open AccessCCS ChemistryRESEARCH ARTICLE1 May 2021Regulating Electronic Status of Platinum Nanoparticles by Metal–Organic Frameworks for Selective Catalysis Yu Shen†, Ting Pan†, Peng Wu, Jiawei Huang, Hongfeng Li, Islam E. Khalil, Sheng Li, Bing Zheng, Jiansheng Wu, Qiang Wang, Weina Zhang, Wei David Wei and Fengwei Huo Yu Shen† Key Laboratory of Flexible Electronics (KLOFE), Institute of Advanced Materials (IAM), Nanjing Tech University, Nanjing 211816 , Ting Pan† Key Laboratory of Flexible Electronics (KLOFE), Institute of Advanced Materials (IAM), Nanjing Tech University, Nanjing 211816 , Peng Wu Key Laboratory of Flexible Electronics (KLOFE), Institute of Advanced Materials (IAM), Nanjing Tech University, Nanjing 211816 , Jiawei Huang Department of Chemistry, Center for Catalysis, University of Florida, Gainesville, FL 32611 , Hongfeng Li Key Laboratory of Flexible Electronics (KLOFE), Institute of Advanced Materials (IAM), Nanjing Tech University, Nanjing 211816 , Islam E. Khalil Key Laboratory of Flexible Electronics (KLOFE), Institute of Advanced Materials (IAM), Nanjing Tech University, Nanjing 211816 , Sheng Li Key Laboratory of Flexible Electronics (KLOFE), Institute of Advanced Materials (IAM), Nanjing Tech University, Nanjing 211816 , Bing Zheng Key Laboratory of Flexible Electronics (KLOFE), Institute of Advanced Materials (IAM), Nanjing Tech University, Nanjing 211816 , Jiansheng Wu Key Laboratory of Flexible Electronics (KLOFE), Institute of Advanced Materials (IAM), Nanjing Tech University, Nanjing 211816 , Qiang Wang Department of Applied Chemistry, College of Chemistry and Molecular Engineering, Nanjing Tech University, Nanjing 211816 , Weina Zhang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory of Flexible Electronics (KLOFE), Institute of Advanced Materials (IAM), Nanjing Tech University, Nanjing 211816 , Wei David Wei *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Department of Chemistry, Center for Catalysis, University of Florida, Gainesville, FL 32611 and Fengwei Huo *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory of Flexible Electronics (KLOFE), Institute of Advanced Materials (IAM), Nanjing Tech University, Nanjing 211816 https://doi.org/10.31635/ccschem.020.202000278 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Selective hydrogenation of alkynes to alkenes remains challenging in the field of catalysis due to the ease of over-hydrogenated of alkynes to alkanes. Favorably, the incorporation of metal nanoparticles (MNPs) into metal–organic frameworks (MOFs) provides an opportunity to adjust the surface electronic properties of MNPs for selective hydrogenation of alkynes. Herein, we used different metal-O clusters of MOFs to regulate the electronic status of platinum nanoparticles (Pt NPs) toward overhydrogenation, semihydrogenation, and unhydrogenation of phenylacetylene. Specifically, Pt/Fe-O cluster-based MOFs are found to reduce the electronic density on Pt NPs and inhibit the overhydrogenation of styrene, leading to an 80% increase in selectivity toward a semihydrogenation product (styrene). Meanwhile, Cu-O cluster-based MOFs generate high oxidation states of Pt NPs and release Cu2+ ions, which worked together to deactivate Pt NPs in the hydrogenation reaction entirely. Thus, our studies illustrate the critical role of metal-O clusters in governing chemical environments within MOFs for the precise control of selective hydrogenation of alkynes, thereby, offering appealing opportunities for designing MNPs/MOFs catalysts to prompt a variety of reactions. Download figure Download PowerPoint Introduction Selective hydrogenation of alkynes to alkenes is a key transformation reaction in industrial manufacturing of fine chemicals, pharmaceuticals, polymers, and others.1–3 Achieving high selectivity of partial hydrogenation products in an economical, mild, and environmentally benign way is still a challenge because it is easy to overhydrogenate alkynes into alkanes.4,5 Heterogeneous metal catalysts are brought into the spotlight due to their high activity and stability.6 A traditional Lindlar catalyst, composed of palladium nanoparticles (Pd NPs) modified by lead ions and quinolone additives, has been used widely in the semihydrogenation industry for decades.7 However, toxic lead ions in Lindlar catalysts hamper their applications in the green chemical industry. Recently, metal oxides, organic molecule- or metal ion-modified metal nanoparticles (MNPs), multimetallic alloys, and single-atom catalysts have been developed for improving the selectivity of semihydrogenation.8–11 However, all those materials require complicated procedures to tune the electronic status of MNPs to achieve selective hydrogenation. Thus, developing new strategies to regulate the electronic status of MNPs remains a critical issue in the field of selective hydrogenation of alkynes. As an emerging porous material, metal–organic frameworks (MOFs) offer intriguing properties, including diverse organic–inorganic compositions, facile functionalization, and uniform yet tunable cavities, showing promising application prospects in gas separation, sensor platforms, heterogeneous catalysis, and so on.12–14 Besides, MOFs have been used as hosts for MNPs, and those hybrid catalysts combine both the molecular sieving effect of MOFs matrix and the high catalytic activity of MNPs.15–21 Recently, scientists found that MOFs could be used to modulate the electronic status of MNPs.22–24 For instance, Zhao et al.25 demonstrated that controlling the electron transfer in Pt/MOFs improved the catalytic selectivity for hydrogenation of α,β-unsaturated aldehydes. Also, Xiao et al.26 observed that tuning the electron transfer between platinum nanoparticles (Pt NPs) and porphyrinic MOFs allowed an increase in the surface electron densities of Pt NPs and enhanced the alcohol oxidation. Herein, we demonstrate the use of metal-O clusters within MOFs to regulate precisely the interfacial electronic status of Pt NPs for promoting the selective hydrogenation of phenylacetylene (Scheme 1). Specifically, Cr-O, Fe-O, and Cu-O cluster-based MOFs, which had similar ligands and coordination structures, were exploited to create different chemical environments for Pt NPs. We found that Pt/Fe-O cluster-based MOFs catalysts exhibited >99% conversion of phenylacetylene and ∼80% selectivity to styrene. Meanwhile, Pt/Cr-O cluster-based MOFs catalysts showed no influence on the selectivity, and thus, resulted in overhydrogenation, with the formation of ethylbenzene. Surprisingly, Cu-O cluster-based hybrid catalysts were found to lose catalytic activity totally in the hydrogenation reaction. Further, studies using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and density functional theory (DFT) confirmed the essential role of metal-O clusters within MOFs in modulating the electronic status of Pt NPs in promoting the activity and selectivity of alkyne hydrogenation. Scheme 1 | Precise control of selective hydrogenation of phenylacetylene using distinct metal-O cluster-based MOFs as modulators to regulate the electronic status of Pt NPs. MOFs, metal–organic frameworks; Pt NPs, platinum nanoparticles. Download figure Download PowerPoint Experimental Methods Preparation of Pt/MOFs catalysts About 30 mL as-synthesized Pt NPs solution (0.6 mM) and 50 mg MOFs powder were stirred under 500 rpm at room temperature for 6 h. Subsequently, Pt/MOFs were collected by centrifugation at 8000 rpm for 5 min and washed twice with ethanol or methanol. Finally, the obtained Pt/MOFs powder was dried at room temperature in a vacuum oven for 12 h. Catalytic hydrogenation of phenylacetylene In a typical procedure, 10 mg of the Pt NPs catalyst was dispersed in 5 mL of methanol solution, and then 100 μL phenylacetylene was added to the above solution. Subsequently, the solution was purged with a H2 balloon. During the catalytic process, the reaction solution was stirred magnetically at room temperature for the desired reaction time. After that, the catalysts were separated by centrifugation, and the solution was analyzed by gas chromatography (GC). Results and Discussion Catalysts preparation To actualize the concept while avoiding the interference of pore size within MOFs and MNPs morphology, the hybrid Pt/MOFs catalysts were rationally designed and synthesized, where presynthesized MNPs were deposited on the MOFs surface. Pt NPs with an average size of 2.8 nm were synthesized by established methods ( Supporting Information Figure S1).27 Several stable MOFs were selected as supports to explore the effect of distinct metal-O clusters on regulating the electronic status of Pt NPs, namely, Cr-based MIL-100(Cr) and MIL-101(Cr); Fe-based MIL-100(Fe), MIL-101(Fe), and MIL-88(Fe); and Cu-based MOF, HKUST-1, and MOF nanosheets, Cu-TCPP.28–30 Pt NPs were dispersed uniformly on the MOFs surface, as revealed by transmission electron microscopy (TEM) images and energy-dispersive X-ray spectroscopy (EDS) elemental mapping data (Figures 1a–1d). As shown in the large-scale TEM images from Supporting Information Figures S2–S8, no free Pt NPs were observed in the catalysts. Additionally, powder X-ray diffraction (PXRD) patterns of Pt/MOFs composites were identical to those of the corresponding simulated MOFs, indicating that MOFs maintained their original crystal structures after the deposition of Pt NPs ( Supporting Information Figures S9–S15). An inductively coupled plasma mass spectrometry (ICP-MS) measurements confirmed the similarity of Pt concentration in the composites ( Supporting Information Table S1). Figure 1 | TEM, high-angle annular dark-field scanning TEM (HAADF-STEM), and the corresponding EDS elemental mapping images of Pt NPs anchored on different MOFs supports. (a) Pt/MIL-101(Cr), (b) Pt/MIL-101(Fe), (c) Pt/MIL-88(Fe), (d) Pt/HKUST-1. TEM, transmission electron microscopy; EDS, energy-dispersive X-ray spectroscopy, Pt NPs, platinum nanoparticles; MOFs, metal–organic frameworks. Download figure Download PowerPoint Catalytic performance Various Pt/MOFs catalysts were utilized in exploring the chemoselectivity of phenylacetylene hydrogenations (Figure 2a). In a typical catalytic reaction, Pt/MIL-100(Cr) and Pt/MIL-101(Cr) with Cr-O clusters generated mostly overhydrogenation products (ethylbenzene), which were similar to the Pt NPs catalysts (Figure 2b and Supporting Information Table S2). Surprisingly, Pt/MIL-100(Fe), Pt/MIL-101(Fe), and Pt/MIL-88(Fe) with Fe-O clusters showed a high conversion (>99%) and selectivity (∼80%) toward the semihydrogenation product (styrene; Figure 2b), while suppressing the overhydrogenation of styrene to ethylbenzene (Figure 2c). No significant decay in the selectivity was noticed even when the reaction time was prolonged to 24 h ( Supporting Information Figure S16). Pt/HKUST-1 and Pt/Cu-TCPP composite of Cu-O clusters in MOFs showed no activity of phenylacetylene and styrene hydrogenations (Figures 2b and 2c). For comparison, MOFs and the corresponding metal oxide supports were also tested for the phenylacetylene and styrene hydrogenation. As shown in Supporting Information Table S2, all MOFs support exhibited no hydrogenation activity, and Pt/metal oxide catalysts showed no hydrogenation selectivity. The evaluation of Pt/MOFs catalytic performance was based on the similar Pt NPs loading (2%) and full conversion of phenylacetylene ( Supporting Information Figure S17 and Table S1). In short, Pt/MOFs catalysts showed three distinct hydrogenation results: overhydrogenation, semihydrogenation, and unhydrogenation, indicating that metal-O clusters within MOFs functioned as modulators of Pt NPs and altered the catalytic performance of phenylacetylene hydrogenation reaction in Pt NPs. Figure 2 | Performance of various Pt/MOFs catalysts for the hydrogenation reaction yielding phenylacetylene and styrene. (a) Schematic of hydrogenation of phenylacetylene. (b) The yield of phenylacetylene hydrogenation on various catalysts. (c) The yield of styrene to ethylbenzene on various catalysts. MOFs, metal–organic frameworks. Download figure Download PowerPoint Mechanistic studies We sought to gain an understanding of how metal-O clusters within MOFs affected Pt NPs' activity and selectivity in the hydrogenation of phenylacetylene by exploring the mechanism of the electronic effects and the coordination environments of Pt NPs on MOFs. The electronic properties were experimentally confirmed by XPS and XAS spectra. The Pt 4f spectra of Pt/MIL-101(Cr) and Pt/MIL-101(Fe) showed two main peaks at 71.3 ± 0.1 and 74.6 ± 0.1 eV, corresponding to Pt 4f7/2 and Pt 4f5/2, respectively (Figure 3a).31 Interestingly, an 0.3 eV shift of Pt 4f toward the high-energy side was observed on Pt/HKUST-1, revealing the difference in the electronic status of the Pt NPs supported on HKUST-1, compared with that on MIL-101(Cr) and MIL-101(Fe). Furthermore, the Pt 4f7/2 was fitted with two components, including the predominant metallic Pt0 located in the binding energy of 71.3 eV in the spectra (denoted as red peaks) and Pt2+ at 72.3 eV (denoted as blue peaks).32 Pt/MIL-101(Cr) showed 28% amount of Pt2+ species, which was similar to that of the bare Pt NPs (27%), indicating a weak electronic interaction between Pt NPs and MIL-101(Cr).25 We speculated that this weak electronic interaction was mainly due to the less overlap of the d orbitals between Pt NPs and Cr-O clusters in MIL-101(Cr).23 Notably, the Pt2+ species ratio in Pt/MIL-101(Fe) and Pt/HKUST-1 catalysts increased to 32% and 36%, respectively, revealing that Pt NPs on these two MOFs became electron deficient, compared with the bare Pt NPs. In comparison with the Cr 2p, Fe 2p, and Cu 2p XPS spectra of MIL-101(Cr), MIL-101(Fe), HKUST-1, and Pt/MOFs composites (Figures 3b–3d), the Cr 2p states remained unchanged after the deposition of Pt NPs, whereas noticeable increases in Fe2+ species (from 61.3% to 67.7%) and Cu+ species (from 22% to 41%) were observed. These phenomena suggested that electrons from Pt NPs were transferred to Fe-O and Cu-O clusters-based MOFs across the heterogeneous interface. As shown in the normalized X-ray absorption near-edge structure (XANES) at the Pt L-edge ( Supporting Information Figure S18), Pt/HKUST-1 exhibited a higher white line intensity than Pt/MIL-101(Fe), MIL-101(Cr), and bore Pt NPs, further confirming the electron deficiency of Pt NPs in Pt/HKUST-1.31 The local coordination environment of Pt in Pt/MOFs catalysts was further characterized by extended X-ray absorption fine structure (EXAFS; Supporting Information Figure S19). The stronger peaks at 2.6 and 1.6 Å could be assigned to Pt–Pt and Pt–O coordination, respectively (Figure 3e).33 The intensity of Pt–O peaks exhibited a gradual increase upon the deposition of Pt NPs on MIL-101(Fe), and HKUST-1 supports. The quantitative EXAFS curve fitting analysis revealed that the coordination number of Pt–O bond in Pt/MIL-101(Cr) was 0.4, while in Pt/MIL-101(Fe) and Pt/HKUST-1, it increased to 0.8 and 1.2, respectively ( Supporting Information Table S3). The formation of abundant Pt–O bonds and charge-transfer interactions demonstrated that MOFs matrix shared the same function as inorganic and organic materials to regulate the surface electronic status of Pt NPs. DFT calculations further proved that the exposed metal-O clusters on MOFs could withdraw electrons from Pt atoms in the order of MIL-101(Cr) < MIL-101(Fe) < HKUST-1 and consequently increased the Bader charge of Pt atoms (Figure 3f and Supporting Information Figure S20 and Table S4). Figure 3 | Electronic status of Pt on various Pt/MOFs catalysts for phenylacetylene hydrogenation reaction. (a) XPS profiles of Pt 4f for Pt NPs supported on a series of MOFs. The metallic Pt0 located at the binding energy of 71.3 and 74.6 eV, and oxidation state Pt2+ located at 72.3 and 75.5 eV. The ratio of Pt2+/Pt0 in various catalysts was marked. (b–d) XPS profiles of Cr 2p, Fe 2p, and Cu 2p in pure MOFs and Pt/MOFs catalysts. The ratio of reduction state of Fe2+ and Cu+ within Fe-O and Cu-O cluster-based MOFs was marked. (e) EXAFS spectra of Pt foil, PtO2, and Pt/MOFs catalysts. (f) DFT calculations of Bader charge of Pt atoms on different MOFs. (g) DFT calculations of the binding energy of H atoms on the Pt surface. (h) Photographs of 5 mg Pt/MOFs catalysts mixed with 45 mg of WO3 before and after treatment with H2 gas at 25 °C for 5 min. MOFs, metal–organic frameworks; XPS, X-ray photoelectron spectroscopy; EXAFS, extended X-ray absorption fine structure; DFT, density functional theory; WO3, tungsten oxide. Download figure Download PowerPoint The surface electronic status of Pt NPs directly correlated to the interaction with active H atoms and unsaturated molecules, thus, delivering different catalytic activities and selectivities of alkyne hydrogenation.34,35 The binding energy of active H atoms on Pt(111) (2 × 2) surface with different charges was explored by DFT calculations (Figure 3g and Supporting Information Figure S21 and Table S5). The small binding energy (−0.42 eV) of H atoms on the neutrally charged Pt surface indicated that active H atoms could readily migrate to the adsorbed phenylacetylene and/or styrene, resulting in overhydrogenation on Pt NPs and Pt/MIL-101(Cr) catalysts. When the Pt(111) surface charge increased to a positive value through the interfacial electron transfer from Pt to MOFs, the higher Pt–H binding energy (−1.2 eV) prevented the migration of active H atoms toward the adsorbed phenylacetylene and/or styrene, suppressing the overhydrogenation on Pt/MIL-101(Fe) and Pt/HKUST-1 catalysts. These DFT results were evaluated further by the color change in tungsten oxide (WO3), since active H atoms could react readily with the yellow WO3 to form dark blue HxWO3.36 As depicted in Figure 3h, the Pt/HKUST-1 with WO3 powder mixture exhibited no change in color after the H2 treatment, whereas mixing Pt/MIL-101(Cr) and Pt/MIL-101(Fe) with WO3 powders showed a different extent of color changes, which revealed the distinct binding energies of active H atoms on the Pt surface. These differences in the color change of WO3 were consistent with DFT simulations and the performance of phenylacetylene hydrogenation on distinct Pt/MOFs catalysts. Furthermore, the partially oxidized Pt could adsorb phenylacetylene tightly on its surface, while weakening its interaction with styrene molecules,34 as verified by the lower catalytic activity (5%) of Pt/MOFs(Fe) catalysts for styrene (Figure 2c). The electronic environment of Pt NPs created by Fe-O clusters allowed for the semihydrogenation of phenylacetylene while styrene intermediates preferred desorption from the Pt surface. The results mentioned above demonstrated that the chemical environment of metal-O clusters within MOFs could regulate the catalytic performance of Pt NPs in the hydrogenation of phenylacetylene. It is known that the metal ions also affect the catalytic activity and selectivity of MNPs in the hydrogenation reaction.37 Therefore, we wondered whether the trace of metal ions released during the catalytic process would affect the catalytic performance. As shown in Supporting Information Figure S22, even when Fe3+ ions were increased to 6 ppm, no apparent decay of Pt NPs in the hydrogenation activity was observed. The high conversion (99%) of phenylacetylene to ethylbenzene indicated that the Fe3+ ions could hardly modify Pt NPs to realize alkyne semihydrogenation. In contrast, 6 ppm Cu2+ ions could hinder the hydrogenation activity completely, suggesting that the activity of Pt NPs was sensitive to Cu2+ ions. Considering the potential influence of metal ions on the activity of Pt NPs, we built a core–shell structure [email protected](Cr) as catalysts to better evaluate the influences of metal ions released from MIL-101(Fe) and HKUST-1 on phenylacetylene hydrogenation reaction ( Supporting Information Figure S23). [email protected](Cr) catalysts reached 99% conversion of phenylacetylene to ethylbenzene, and the reduced reaction rate was mainly a result of the diffusion of the reactant through the MOFs channel from the surface to the active sites ( Supporting Information Figure S24). When HKUST-1 powders were introduced to the reaction, the conversion of phenylacetylene only reached 35% within 1 h, after which no further increase occurred ( Supporting Information Figure S24, red dots). This result indicated that the synergistic effect of Cu-O metal clusters and released Cu2+ ions could poison Pt NPs. However, when the MIL-101(Fe) was added to the reaction, the conversion of phenylacetylene reached 100%, and the selectivity was similar to [email protected](Cr) ( Supporting Information Figure S24, blue dots). These results confirmed that the metal-O clusters within MOFs could regulate the catalytic chemoselectivity of Pt NPs in the hydrogenation of alkynes. Furthermore, the catalytic stability of Pt/MIL-101(Fe) catalyst for phenylacetylene hydrogenation was evaluated by PXRD, TEM, and XPS characterizations. There was a slight decrease in Pt NPs content of Pt/MIL-101(Fe) after three reaction cycles (from 2.2% to 2.0%; Supporting Information Figure S25) and negligible influence on catalytic performance ( Supporting Information Figure S26), indicating the catalytic stability of Pt/MIL-101(Fe) catalyst. The crystallinity of MIL-101(Fe) changed slightly ( Supporting Information Figure S27) as the sizes, and electronic status of Pt NPs were retained ( Supporting Information Figures S28 and S29), which confirmed the stability of the Pt/MIL-101(Fe) catalyst. Conclusion We successfully demonstrated that employing different metal-O clusters within MOFs enabled the regulation of interfacial electronic structures of Pt NPs for significant improvement of selective hydrogenation of phenylacetylene. We found that Pt/Fe-O cluster-based MOFs catalysts highly favored the semihydrogenation of phenylacetylene to form styrene while Pt/Cr-O cluster-based MOFs facilitated overhydrogenation to an alkane. More importantly, Pt NPs were deactivated completely when Cu-O metal cluster-based MOFs were used as supports. Our studies affirmed that the electronic status of MNPs modified by metal-O clusters and trace poisonous metal ions released from MOFs is crucial in regulating the hydrogenation of unsaturated molecules, thus, opening up new paths for designing a series of suitable MNP/MOFs catalysts to boost other selective hydrogenation reactions of alkynes. Supporting Information Supporting Information is available. Conflict of Interest The authors declare no conflict of interest. Funding Information This study was supported by the National Key R&D Program of China (no. 2017YFA0207201), the National Natural Science Foundation (nos. 21727808, 21574065, 21604038, 21971114, 21604040, and 51702155), the National Science Foundation for Distinguished Young Scholars (no. 21625401), and the Jiangsu Provincial Funds for Natural Science Foundation (nos. BK20160975, BK20160981, and BK20170975). Acknowledgments The authors are grateful to the Synchrotron Radiation Research Center (NSRRC) in Taiwan for their help on X-ray absorption spectroscopy measurements.

Enzymes are a catalytic class of proteins that possess high specificity, selectivity and biocompatibility, which makes them ideal for multiple applications in industrial production and biotechnology. However, the use of enzymes in such applications is limited due to their low operational stability and increased cost attributed to difficulty of purification and reuse. Immobilization of enzymes onto nano-sized solid supports has emerged as a potential solution to these shortcomings with a trade-off of a percentage of activity loss upon immobilization. Herein, a comprehensive study of enzyme immobilization techniques with emphasis on active-surface decontamination applications is presented.;In Chapter 1, an overview of the potential uses of enzymes and enzyme immobilization techniques is given. Benefits of enzyme-nanosupport conjugates in industrial catalysis, energy production (i.e. biofuels and biofuel cells), biosensing and bioactive coatings are discussed with emphasis on enzyme-based decontamination coatings. It is emphasized that enzyme-based conjugates are capable of increasing enzyme stability at operational conditions used in industrial production of fine chemicals, pharmaceuticals and foods. Also, this Chapter emphasizes the benefits of enzyme immobilization in regard to the development of the next generation of biosensors with enhanced selectivity and specificity or biofuel cells that do not require a membrane, and thus allow miniaturization. Additionally, coatings capable of decontaminating pathogens such as bacteria and spores can be produced through the incorporation of enzymenanomaterial conjugates. Finally, the chapter provides new perspectives and future directions in enzyme-based biotechnology. A. Campbell, C. Dong, C. Xiang, N. Q. Wu and C. Z. Dinu, "Enzyme-Based Technologies: Perspectives and Opportunities" Accepted to Green Polymer Chemistry: Biocatalysis and Biomaterials, ACS Symposium Series 2012..;In Chapter 2, the impacts of the reactions that take place upon enzyme immobilization at the nanointerface are discussed and the effects of multiple variables present in the immobilization process on enzyme retained activity are identified. These variables include nanosupport characteristics (i.e. physical and chemical properties, rate of curvature), enzyme properties (i.e. surface properties, molecular weight, isoelectric point) and immobilization technique (i.e. chemical or physical binding). Prior to immobilization of the selected enzymes (i.e. soybean peroxidase (SBP), chloroperoxidase (CPO) and glucose oxidase (GOX)) all nanosupports (i.e. single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) and graphene oxide nanosheets (GON)) are chemically functionalized under user-controlled conditions through strong acids treatment and characterized in terms of structure and morphology. A comparison of how the characteristics of both the nanosupports used as well as immobilization technique employed affect retained activity in an enzyme specific manner is also presented. A. Campbell, C. Dong, J. Hardinger, F. Meng, G. Perhinschi, N. Q. Wu and C. Z. Dinu, "Activity and Kinetics of Immobilized Enzyme Depend on the Enzyme-Interface Reaction" To be submitted to Langmuir..;In Chapter 3, the development of a self-decontaminating enzyme-nanosupport hybrid system is presented. This system is based on the generation of the strong decontaminant hypochlorous acid (HOCl) by CPO. Two strategies are investigated. First, the production of the required substrate (i.e. hydrogen peroxide (H 2O2)) by photocatalytic titanium dioxide nanobelts to be used by immobilized CPO for in situ HOCl generation is tested. Secondly, the production of H2O2 by co-immobilized GOX onto MWCNTs in the presence of glucose to be further used by immobilized CPO for in situ HOCl generation is examined. Characterization of both conjugate systems as well as their capacity for HOCl generation is presented in detail. The decontaminant production capability of the CPO-MWCNTs-GOX system shows promise for the next generation of active surface decontamination coatings. A. Campbell, C. Dong, C. Xiang, N. Q. Wu, J. S. Dordick and C. Z. Dinu, "Bionano Engineering Hybrids for the Next Generation of Self- Sustainable Decontamination Coatings" Submitted to Process Biochemistry..;This thesis also contains Appendices in which supporting information in regard to the respective chapters is detailed. Also attached are other publications in which I have been a contributing author: (1) C. Dong, A. Campbell, R. Eldawud, G. Perhinschi, Y. Rojansakul and C. Z. Dinu, "Effects of Acid Treatment on Structure, Properties and Biocompatibility of Carbon Nanotubes" Applied Surface Science 2013, 264, 261-268. (2) C. Z. Dinu, I. Borkar, S. Bale, A. Campbell, R. Kane and J. S. Dordick "Perhydrolase-nanotube-paint sporicidal composites stabilized by intramolecular crosslinking" Journal of Molecular Catalysis B: Enzymatic 2012, 75,20-2..

The liquid surfactant membrane technique for immobilization of enzymes in enzyme emulsions is described in this paper. This offers the combination of selective mass transport and specific enzymatic reaction. Several applications are presented to show the potential of this technique for integration of enzymatic reaction, purification, and product accumulation to one single process step. A strategy for membrane optimization is given and discussed. In addition information on the selective mass transport through liquid surfactant membranes (enzyme emulsions and solid supported liquid membranes) and on the reaction modeling are presented.

Self-Assembly Ultrathin Fe-Terephthalic Acid as Synergistic Catalytic Platforms for Selective Hydrogenation

Dispersions, novel nanomaterial sensors and nanoconjugates based on carbon nanotubes

Recent advances in enzyme immobilization techniques: Metal-organic frameworks as novel substrates

Multifunctional carbon nanotubes and their derived nano-constructs for enzyme immobilization – A paradigm shift in biocatalyst design

Cyclodextrin (CD) is a non-reducing maltooligosaccharides which able to form inclusion complexes with many hydrophobic molecules, changing their physical and chemical properties. With these properties, CD has been discovered to have numerous applications in food industries, pharmaceutical, agricultural and environmental engineering. CD is produced by the enzymatic reaction between cyclodextrin glucanotransferase (CGTase) and starch. Various enzyme immobilization techniques such as adsorption, entrapment, encapsulation and cross-linking have been applied to improve the production of CD. Some of the immobilization parameters such as contact time, agitation rate and pH of the immobilization solution play a vital role in enzyme immobilization process, in order to achieve high production of CD. In the present study, the CGTase from Bacillus licheniformis was immobilized on polyvinylidene difluoride (PVDF) hollow fiber membrane via adsorption technique. The efficiency of enzyme immobilization appears to be affected by various factors (immobilization parameters) such as contact time, agitation rate and pH. Therefore, the effect of contact time (6-72 h), agitation rate (50-250 rpm) and pH (3-10) on the immobilization of CGTase on PVDF hollow fiber membrane were investigated in this study. The immobilized CGTase exhibited the highest immobilization yield of 69.37% under the conditions of 24 h contact time, 100 rpm and pH 7.0. Therefore, the influence of the immobilization parameters during the enzyme immobilization process is vital in order to achieve the high production of CD. Hence, high immobilization yield contributed to the high production of CD which in turn may be beneficial for the industrial purposes.

In recent years, researchers have focused on developing simple and efficient methods based on electrochemical biosensors to determine hydroxycinnamic acids from various real samples (wine, beer, propolis, tea, and coffee). Enzymatic biosensors represent a promising, low-cost technology for the direct monitoring of these biologically important compounds, which implies a fast response and simple sample processing procedures. The present review aims at highlighting the structural features of this class of compounds and the importance of hydroxycinnamic acids for the human body, as well as presenting a series of enzymatic biosensors commonly used to quantify these phenolic compounds. Enzyme immobilization techniques on support electrodes are very important for their stability and for obtaining adequate results. The following sections of this review will briefly describe some of the laccase (Lac) and tyrosinase (Tyr) biosensors used for determining the main hydroxycinnamic acids of interest in the food or cosmetics industry. Considering relevant studies in the field, the fact has been noticed that there is a greater number of studies on laccase-based biosensors as compared to those based on tyrosinase for the detection of hydroxycinnamic acids. Significant progress has been made in relation to using the synergy of nanomaterials and nanocomposites for more stable and efficient enzyme immobilization. These nanomaterials are mainly carbon- and/or polymer-based nanostructures and metallic nanoparticles which provide a suitable environment for maintaining the biocatalytic activity of the enzyme and for increasing the rate of electron transport.

The development of energy storage and conversion devices provides a beneficial approach for the renewable energy application, which can help relieve the severe reliance on fossil fuels and also address problems related to global climate change. Currently, the efficiencies of energy conversion devices such as the metal–air batteries and fuel cells are mainly limited by the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) processes. Developing catalytically active and cost effective catalyst for the ORR and OER is of prime importance. So far, noble metals and their alloys, such as Pt and Pt-Pd, have been exclusively used as electrochemical bifunctional catalyst in ORR and OER due to their superior catalytic activity. However, the high cost, limited availability, poor durability and sluggish electron transfer kinetics of noble metal based bifunctional catalysts have impeded the practical application of metal-air batteries. Therefore, the discovery of cost effective, catalytically active alternative bifunctional catalyst such as non-precious metals, carbonaceous materials, and transition metal oxides is highly desirable. Perovskite oxide (ABO3) possesses a unique electronic structure and chemical defect properties, and has been demonstrated to be a promising non-precious metal catalyst among the transition metal oxides in the application of metal air batteries and alkaline fuel cells. It is known that the intrinsic electrochemical catalytic activity is mainly determined by the B site cation in perovskite oxide. Extensive research conducted by Yang et al. demonstrated that the ORR and OER catalytic activities of perovskite oxides follow a volcanic relationship with the filling of electrons in antibonding orbitals [1]. Among the typical LaMO3 (M= Mn, Co, Fe, Ni, Cr), LaMnO3 and LaCoO3 have exhibited highest ORR and OER catalytic activities, respectively. In addition, due to the desirable electronic properties of the perovskite oxides, strategies such as cation partial substitution and oxygen non-stoichiometry formation could, therefore, be utilized as the effective approaches to fine-tune the catalytic properties and to achieve a better bifunctional activity [2,3]. To enhance the bifunctional catalytic performance, improved specific surface area as well as enhanced oxygen channel are desired. Researchers have found that electrochemical catalysts with porous nanofiber structures could favor the ORR and OER pathways by providing uniform O2 electrolyte distribution, and beneficial oxygen diffusion channels. Zhao et al. have synthesized mesoporous La0.5Sr0.5CoO2.91 nanowires through the multistep microemulsion method, showing significant enhanced catalytic performance [4]. Xu et al. have demonstrated that the porous La0.75Sr0.25MnO3 nanotube catalyst fabricated through facile electrospinning technologies provides favorable advantages to the availability of the catalytic active sites in the organic solvent electrolyte in Li-O2 batteries [5].Herein, we developed a bifunctional perovskite catalyst towards both ORR and OER in alkaline solution. Cobalt cations were doped into Pr0.5Ba0.5MnO3-δ perovskite to achieve the higher intrinsic ORR and OER activities by engineering the structure symmetry, electronic and the oxygen vacancy defects of the material. The bifunctional catalyst with a unique porous nanofiber structure was fabricated by electrospinning technology (Figure.1). A single phase perovskite oxide Co doped Pr0.5Ba0.5MnO3-δ was obtained after sintering the electrospun precursor at high temperature. The ORR and OER activities of the composite catalysts consisting 50 wt% of the as-synthesized perovskite oxides and 50 wt% carbon black were investigated in 0.1 KOH with rotating disk electrode (RDE). Significant enhancement in ORR and OER performance was achieved via using the composite catalyst with Co doped Pr0.5Ba0.5MnO3-δ nanofiber/carbon black with respect to the reduced overpotential and improved current density. In particular, the Co doped Pr0.5Ba0.5MnO3-δ nanofiber/carbon black composite demonstrated enhanced electron transfer number in the ORR process, indicating preferable dominance of four electron transfer pathway. Moreover, the Co doped Pr0.5Ba0.5MnO3-δ composite exhibited high stability during the cycling tests, indicating its promising applications in metal-air batteries.