The effect of As(III) on the photocatalytic degradation of phenolic pollutants such as 4-chlorophenol (4-CP) and bisphenol A (BPA) in a suspension of platinized ... was investigated. In the presence ...of As(III), the photocatalytic degradation of 4-CP and BPA was significantly enhanced, and the simultaneous oxidation of As(III) to As(V) was also achieved. This positive effect of As(III) on the degradation of phenolic pollutants is attributed to the adsorption of As(V) (generated from As(III) oxidation) on the surface of ..., which facilitates the production of free OH radicals (...) that are more reactive than surface-bound OH radicals (...) toward phenolic pollutants. The generation of ... was indirectly verified by using coumarin as an OH radical trapper and comparing the yields of coumarin -- OH adduct (i.e., 7-hydroxycoumarin) formed in the absence and presence of As(V). In repeated cycles of 4-CP degradation, the degradation efficiency of 4-CP gradually decreased in the absence of As(III), whereas it was mostly maintained in the presence of As(III), which was either initially present or repeatedly injected at the beginning of each cycle. The positive effect of As(III) on 4-CP degradation was observed over a wide range of As(III) concentrations (up to mM levels) with ... However, a high concentration of As(III) (hundreds of ...M) inhibited the degradation of 4-CP with bare ... Therefore, ... can be proposed as a practical photocatalyst for the simultaneous oxidation of phenolic pollutants and As(III) in industrial wastewaters. (ProQuest: ... denotes formulae/symbols omitted.)
The effect of As(III) on the photocatalytic degradation of phenolic pollutants such as 4-chlorophenol (4-CP) and bisphenol A (BPA) in a suspension of platinized ... was investigated. In the presence ...of As(III), the photocatalytic degradation of 4-CP and BPA was significantly enhanced, and the simultaneous oxidation of As(III) to As(V) was also achieved. This positive effect of As(III) on the degradation of phenolic pollutants is attributed to the adsorption of As(V) (generated from As(III) oxidation) on the surface of ..., which facilitates the production of free OH radicals (...) that are more reactive than surface-bound OH radicals (...) toward phenolic pollutants. The generation of ... was indirectly verified by using coumarin as an OH radical trapper and comparing the yields of coumarin -- OH adduct (i.e., 7-hydroxycoumarin) formed in the absence and presence of As(V). In repeated cycles of 4-CP degradation, the degradation efficiency of 4-CP gradually decreased in the absence of As(III), whereas it was mostly maintained in the presence of As(III), which was either initially present or repeatedly injected at the beginning of each cycle. The positive effect of As(III) on 4-CP degradation was observed over a wide range of As(III) concentrations (up to mM levels) with ... However, a high concentration of As(III) (hundreds of ...M) inhibited the degradation of 4-CP with bare ... Therefore, ... can be proposed as a practical photocatalyst for the simultaneous oxidation of phenolic pollutants and As(III) in industrial wastewaters. (ProQuest: ... denotes formulae/symbols omitted.)
Display omitted
•F-TiO2 showed a higher activity for the degradation of bisphenol A than pure TiO2.•The mineralization of bisphenol A on F-TiO2 was slower than that on pure TiO2.•Surface fluorination ...enhances the OH production but reduces the O2−/HO2 production.•Fluorides reduce the interfacial electron transfer rate and the O2−/HO2 lifetime.
The photocatalytic activity of surface fluorinated TiO2 (F-TiO2) for both the degradation and mineralization of bisphenol A (BPA) was compared with that of pure TiO2. The degradation rate of BPA (i.e., the conversion rate of BPA to intermediates) was enhanced, but the mineralization rate (i.e., the conversion rate of BPA to CO2) was reduced by surface fluorination. These behaviors are different from the general trend in photocatalysis, in which the photocatalyst with a higher activity for the degradation also shows a higher activity for the mineralization. The surface fluorination of TiO2 enhanced the production of the hydroxyl radical (OH), which is primarily responsible for the degradation of BPA, by altering the OH generation pathway. However, the lower mineralization on F-TiO2, which produced more OH, implies that the role of OH in the photocatalytic mineralization process is minor. The production of superoxide/hydroperoxyl radical (O2−/HO2), which is suggested as an essential oxidant for the mineralization of phenolic pollutants, by F-TiO2 was lower than that exhibited by pure TiO2. The reduced photocurrent (Iph) generation and the enhanced H2O2 production on F-TiO2 indicate that fluorides on the TiO2 surface reduce the interfacial electron transfer rate (i.e., the production of O2−/HO2) and enhance the reduction of O2−/HO2 to H2O2. The degradation rate increased, but the mineralization efficiency decreased with increasing the surface coverage of fluorides, which depends on the pH and fluoride concentration in the solution. The reduced mineralization efficiency of other phenolic pollutants (4-chlorophenol, phenol, methylene blue, rhodamine B, and acid orange 7) was also observed on F-TiO2. This result indicates that the negative effect of surface fluorination on the mineralization of phenolic pollutants is pervasive and is not restricted to BPA.
The thermal and hydrothermal stabilities and the structural degradation characteristics of a supported ZIF-7 membrane were studied at various temperatures (423-673 K), H
2
O vapor concentrations ...(10-40 mol%), and metal oxide supports (alumina, silica-alumina, silica, magnesia). The α-Al
2
O
3
supported ZIF-7 membrane prepared by the seeding and secondary growth method exhibited a high H
2
permeance (4.0 × 10
−7
mol m
−2
s
−1
Pa
−1
) with high H
2
selectivities (∼10) over larger CO, CH
4
, and CO
2
gases at an elevated temperature of 573 K. The thermal stability of the membrane in a dry atmosphere was determined primarily by the intercrystalline grain boundaries on the ZIF-7 overlayer, exhibiting a high thermal stability at 573 K. However, considerable cracks developed through the grain boundaries at 673 K due to excessive thermal stress. It was found that the metal oxide supports markedly affect the hydrothermal stability of the ZIF membranes. The α-Al
2
O
3
supported membrane suffered from fatal hydrothermal degradation of the ZIF-7 membrane layer even at a relatively low temperature of 473 K, and structural degradation was facilitated as the temperature and H
2
O vapor concentration increased. Surface acid/base properties of the metal oxide supports had a critical impact on the stability of the membrane; the ZIF-7 structure exhibited severe hydrothermal degradation on the acidic Al
2
O
3
and SiO
2
-Al
2
O
3
supports. Conversely, the ZIF-7 crystalline structure remained intact on the neutral SiO
2
and basic MgO supports even under highly antagonistic hydrothermal conditions (573 K, 20 mol% H
2
O). These findings provide important new insights for the effective construction of ZIF membranes with improved structural stabilities under practically relevant thermal and hydrothermal operation conditions.
The hydrothermal stability of crystalline ZIF membranes markedly depend on the surface chemistry of the metal oxide supports.
The thermochemical stability of metal organic framework (MOF) membranes is vital for the application in chemical-reaction and -separation processes, but understanding the stability of MOF membranes ...and structure–property relationships under antagonistic chemical atmosphere is still required. In this work, a supported zeolitic imidazolate framework (ZIF) membrane, ZIF-7/MgO-Al2O3, of unprecedented hydrothermal stability is obtained by a modulation of the acid–base chemistry at the membrane/support interface. The solid/solid interface acidity that has been overlooked in the fields turns out to have paramount inducing effects on the thermochemical stability of ZIF membranes, resulting in the catastrophic acid-catalyzed decomposition of ZIF frameworks at atomic level. The ZIF-7/MgO-Al2O3 of marked thermochemical stability permits the first significant application of MOF membranes for catalytic membrane reactor (MR) in severe and practical process conditions, performing water–gas shift reaction (CO + H2O ↔ CO2 + H2) at considerably high temperatures (473–673 K) and steam concentrations (20–40%). The findings and results provide significant new insights on the property and stability of ZIF membranes with extensive opportunities for thermochemical processes that have been permitted only for the inorganic membranes such as zeolites, palladium, and metal oxides.
•Electrical conductivity of SFM perovskites increased with increasing Fe content.•ODHE resulted in 16.1% C2H6 conversion and 83.1% C2H4 selectivity on SFM45.•Moderate oxygen ionic transport is a key ...factor for high selectivity to C2H6.•Fast desorption of C2H4 from SFM45 resulted in higher selectivity of C2H4.
The oxidative dehydrogenation of ethane (ODHE) was investigated using a solid oxide electrocatalytic cell with Sr2Fe2–XMoXO6–δ (SFM) double perovskite as the anode electrocatalyst. As shown in the XRD patterns, SFM perovskites maintained their cubic structure upon modifying the B-site ratios of Mo and Fe. Increasing the Mo content of the perovskite structure resulted in a lower water signal intensity at low temperatures in TPR profiles, indicative of moderate oxygen transport through the perovskite structure. Because Mo–O bonds are stronger than Fe–O bonds, the electrical conductivity of SFM perovskites decreased with increasing Mo content. When operated at 100 mA cm–2, ODHE activity improved four times compared to open circuit voltage, resulting in 16.1% conversion of C2H6 and 83.1% selectivity to C2H4. It has been demonstrated that oxygen ions provided by perovskite lattices were the key species involved in activating C2H6 based on the in-situ DRIFTS experiments. The SFM perovskite with higher Mo content showed the highest conversion and selectivity due moderate oxygen ion mobility and fast desorption of C2H4.
Display omitted
Oxidative dehydrogenation (ODH) of propane offers an attractive and feasible method for increasing propylene production to meet the growing demand. In this study, a dual phase catalyst composed of ...proton conducting SrCe0.95Yb0.05O3 (SCY) and mixed oxygen ionic and electronic conducting (La0.8Sr0.2)0.95MnO3 (LSM) has been investigated for propane ODH. TPD-DRIFTS was used to study H2O adsorption and the presence of basic lattice oxygen on the surface of SCY. The addition of 40 wt% SCY to LSM resulted in significant improvements in propane conversion and olefin selectivity. These enhancements were likely due to the highly basic nature of the SCY surface by helping rapid desorption of propylene resulting in high propylene yields. In addition, proton conductive SCY facilitated the proton abstraction from propane and its transport to the interface between SCY and LSM where an oxidation reaction occurs. It was demonstrated by TPrxn experiments using C3H8 and C3H6 that a moderate oxygen ionic conductivity and a basic surface of the catalyst are needed for the selective conversion of propane to olefins.
Display omitted
•Dual phase anode composed of SCY and LSM is examined for electrocatalytic propane ODH.•Incorporation of SCY as part of the composite anode provides higher C3H8 conversion.•Proton conductivity of SCY facilitates hydrogen abstraction from C3H8.•Proton conductivity of SCY enables transport of proton to interface of LSM/SCY.•Basicity of SCY facilitates desorption of C3H6, improving its yields.
Solid oxide electrocatalytic cell (SOEC) is a promising technology for facilitating reactions involving the removal or addition of oxide ions. By designing the appropriate electrode catalysts, ...reactions such as CO2 electrolysis, H2O electrolysis, oxidative dehydrogenation (ODH) of light alkanes (C2H6, C3H8), and oxidative coupling of methane can be efficiently carried out in an SOEC. Perovskite materials based on Fe, such as La(Sr)FeO3, possess a range of beneficial properties for use in electrocatalysis. They are compatible with electrolyte materials, have high electrical conductivity, and are stable in both oxidizing and reducing atmospheres. Additionally, the formation of exsolved B-site metal nanoparticles on the surface of the perovskite material can significantly improve its electrochemical activity when exposed to a reducing atmosphere.In chapter 1, La0.7Sr0.2Ni0.2Fe0.8O3 (LSNF), having thermochemical stability, superior ionic and electronic conductivity, and structural flexibility, was investigated as a cathode in SOECs. Exsolution of nanoparticles by reduction of LSNF at elevated temperatures can modulate the characteristics of adsorption, electron transfer, and oxidation states of catalytically active atoms, consequently improving the electrocatalytic activity. The exsolution of NiFe and La2NiO4 nanoparticles to the surface of LSNF under reducing atmosphere (5% H2/N2) was verified at various temperatures (500–800 °C) by IFFT from ETEM, TPR and in situ XRD. The exsolved nanoparticles obtained uniform size distribution (4.2–9.2 nm) and dispersion (1.31 to 0.61 × 104 particle per μm2 ) depending on the reduction temperature (700–800 °C) and time (0–10 h). The reoxidation of the reduced LSNF (Red-LSNF) was verified by the XRD patterns, indicative of its redox ability, which allows for redistribution of the nanoparticles between the surface and the bulk. TPD-DRIFTS analysis demonstrated that Red-LSNF had superior H2O and CO2 adsorption behavior as compared to unreduced LSNF, which we attributed to the abundance of oxygen vacancy sites and the exsolved NiFe and La2NiO4 nanoparticles. After the reduction of LSNF, the decreases in the oxidation states of the catalytically active ions, Fe and Ni, were characterized on the surface by XPS as well as in the bulk by XANES. The electrochemical performance of the Red-LSNF cell was superior to that of the LSNF cell for electrolysis of H2O, CO2, and H2O/CO2.In chapter 2, oxidative coupling of methane (OCM), which is a fundamentally challenging reaction due to low selectivity of C2+ hydrocarbons, was investigated using a solid oxide electrocatalytic cell. This study presents in-situ reduction of lanthanum strontium cobalt ferrite (LSCF) perovskite as an effective method for modifying its surface properties and enhancing its electrocatalytic reactivity for OCM. The evolution of hetero-phases during the reduction of LSCF resulted in CoFe nanoparticles being formed at the surface. The in-situ reduced LSCF cell for OCM could be operated in either an ion pump or a fuel cell mode. High selectivity of 63% and 10.2% were reported for C2+ hydrocarbons and C3H6, respectively. DFT calculations on LSCF and CoFe revealed that the high selectivity of C2+ hydrocarbons on the LSCF primarily stems from the presence of CoFe nanoparticles. In addition, elemental analysis of the surface and bulk LSCF by XPS and XANES verified the reduced oxidation state of Co and Fe ions. In-situ TPD-DRIFTS spectra using CO2 as a probe molecule indicated enhanced basicity on the reduced LSCF. Temperature-programmed experiments and in-situ DRIFTS conducted under CH4 flow proved that complete oxidation of CH4 can be effectively inhibited by reducing LSCF, and control of oxygen supply is an important parameter for selective conversion of CH4 to higher order hydrocarbon.In chapter 3, La0.7Sr0.2Ni0.2Fe0.8O3 (LSNF) perovskite was used an effective anode for OCM with co-feeding of water. Its surface characteristics and electrocatalytic activity can be improved by reduction and the resultant exsolution of bimetallic NiFe nanoparticles from its bulk. X-ray diffraction (XRD) and environmental transmission electron microscopy proved that the evolution of hetero-phases under reducing environment resulted in bimetallic NiFe nanoparticles being formed on the surface. A 36% improvement in C2+ hydrocarbon production rate was achieved due to the reduction of LSNF and the formation of exsolved NiFe nanoparticles. Co-feeding of H2O enhanced selective conversion of CH4 resulting in the production rate of C2+ hydrocarbons being increased by 56%. Analysis of impedance spectra and in-situ DRIFTS under a CH4 + H2O atmosphere provided an understanding for the enhancement on the electrocatalytic OCM. Chapter 4 investigates the exsolution of metal nanoparticles from perovskite oxide as a method to enhance the electrochemical performance in solid oxide electrocatalytic cells. The process can be electrochemically triggered by applying cathodic polarization to the perovskite oxide electrode for a short period of time. The electrochemical reduction of the perovskite oxide electrode and the resultant exsolution of B-site metal nanoparticles are investigated by scanning the cell voltage to provide an insight into the electrochemical behavior during electrolysis. A user-designed X-ray absorption spectroscopy operando cell is used to identify the edge energy change of B-site atoms during electrolysis. The electrochemical switching point is identified as a point where the incremental area-specific resistance changes to a decrease, providing valuable insight into the electrochemical exsolution process of metal nanoparticles in perovskite oxide electrodes.Chapter 5 explored oxidative dehydrogenation (ODH) of propane which offers an attractive and feasible method for increasing propylene production to meet the growing demand. A dual phase catalyst composed of proton conducting SrCe0.95Yb0.05O3 (SCY) and mixed oxygen ionic and electronic conducting (La0.8Sr0.2)0.95MnO3 (LSM) has been investigated for propane ODH. TPD-DRIFTS was used to study H2O adsorption and the presence of basic lattice oxygen on the surface of SCY. The addition of 40 wt% SCY to LSM resulted in significant improvements in propane conversion and olefin selectivity. These enhancements were likely due to the highly basic nature of the SCY surface by helping rapid desorption of propylene resulting in high propylene selectivity. In addition, proton conductive SCY facilitated the proton abstraction from propane and its transport to the interface between SCY and LSM where an oxidation reaction occurs. It was demonstrated by TPrxn experiments using C3H8 and C3H6 that a moderate oxygen ionic conductivity and a basic surface of the catalyst are needed for the selective conversion of propane to olefins. Chapter 6 proposes potential future research on enhancing the structural stability of perovskite oxide through the incorporation of oxyphilic atoms like Mo or Cr. This is in response to the exsolution of B-site atoms, which creates oxygen vacancies in the lattice and potentially undermines stability. This stability issue caused by exsolution of b-site atoms could be addressed by oxyphilic atom inversion. In addition to this, it is suggested that double perovskite oxides can serve as superior electrode materials due to their enhanced stability in both reducing and oxidizing environments compared to traditional perovskite oxides. This provides a promising alternative to ferrite-based perovskites.
The jawless vertebrates (agnathans/cyclostomes) are ancestral animals comprising lampreys and hagfishes as the only extant representatives. They possess an alternative adaptive immune system (AIS) ...that uses leucine-rich repeats (LRR)-based variable lymphocyte receptors (VLRs) instead of the immunoglobulin (Ig)-based antigen receptors of jawed vertebrates (gnathostomes). The different VLR types are expressed on agnathan lymphocytes and functionally resemble gnathostome antigen receptors. In particular, VLRB is functionally similar to the B cell receptor and is expressed and secreted by B-like lymphocytes as VLRB antibodies that bind antigens with high affinity and specificity. The potential repertoire scale of VLR-based antigen receptors is believed to be at least comparable to that of Ig-based systems. VLR proteins inherently possess characteristics that render them excellent candidates for biotechnological development, including tractability to recombinant approaches. In recent years, scientists have explored the biotechnological development and utility of VLRB proteins as alternatives to conventional mammalian antibodies. The VLRB antibody platform represents a non-traditional approach to generating a highly diverse repertoire of unique antibodies. In this review, we first describe some aspects of the biology of the AIS of the jawless vertebrates, which recognizes antigens by means of unique receptors. We then summarize reports on the development of VLRB-based antibodies and their applications, particularly those from the inshore hagfish (Eptatretus burgeri) and their potential uses to address microbial diseases in aquaculture. Hagfish VLRB antibodies (we call Ccombodies) are being developed and improved, while obstacles to the advancement of the VLRB platform are being addressed to utilize VLRBs effectively as tools in immunology. VLRB antibodies for novel antigen targets are expected to emerge to provide new opportunities to tackle various scientific questions. We anticipate a greater interest in the agnathan AIS in general and particularly in the hagfish AIS for greater elucidation of the evolution of adaptive immunity and its applications to address microbial pathogens in farmed aquatic animals and beyond.
•The agnathan adaptive immune system uses leucine-rich repeats-based variable lymphocyte receptors (VLRs) to recognize antigens.•VLRB proteins secreted by B-like cells are analogous to gnathostome antibodies.•VLRB proteins have been developed as alternatives to immunoglobulin antibodies.•VLRB antibodies from the hagfish Eptatretus burgeri have been developed as immunological tools in aquaculture.•Difficulties need to be tackled to effectively develop and utilize VLRB antibodies as immunological reagents.
PDF
