Layer-by-Layer Assembly of Molecular Metal Oxide Catalysts for Photoelectrochemical Water Splitting

Department of Energy EngineeringArtificial photosynthesis is considered one of the most promising solutions to modern energy and environmental crises. Considering that it is enabled by multiple components through a series of photoelectrochemical processes, the key to successful development of a photosynthetic device depends not only on the development of novel individual components but also on the rational design of an integrated photosynthetic device assembled from them. However, most studies have been dedicated to the development of individual components due to the lack of a general and simple method for the construction of the integrated device. In the present study, we report a versatile and simple method to prepare an efficient and stable photoelectrochemical device via controlled assembly and integration of functional components using the layer-by-layer (LbL) assembly technique. As a proof of concept, we could successfully build a photoanode for photocatalytic water oxidation by modifying the surface of various photoelectrode materials (e.g., Fe2O3, BiVO4, and TiO2) with diverse cationic polyelectrolytes and anionic polyoxometalate (molecular metal oxide) water oxidation catalysts. It was found that the performance of photoanodes was significantly improved after the deposition in terms of stability as well as photocatalytic properties, regardless of types of photoelectrodes and polyelectrolytes employed. Considering the simplicity and universal nature of LbL assembly techniques, we believe that our approach can provide a general and simple method for the design and realization of a novel photosynthetic device.ope

Amine???Rich Hydrogels Enhance Solar Water Oxidation via Boosting Proton???Coupled Electron Transfer

Photoelectrochemical (PEC) water oxidation is a highly challenging task that acts as a bottleneck for efficient solar hydrogen production. It is because each cycle of water oxidation is composed of four proton-coupled electron transfer (PCET) processes and conventional photoanodes and cocatalysts have limited roles in enhancing the charge separation and storage rather than in enhancing catalytic activity. In this study, a simple and generally applicable strategy to improve the PEC performance of water oxidation photoanodes through their modification with polyethyleneimine (PEI) hydrogel is reported. The rich amine groups of PEI not only allow the facile and stable modification of photoanodes by crosslinking but also contribute to improving the kinetics of PEC water oxidation by boosting the PCET. Consequently, the PEC performance of various photoanodes, such as BiVO4, Fe2O3, and TiO2, is significantly enhanced in terms of photocurrent densities and onset potentials even in the presence of notable cocatalyst, cobalt phosphate. The present study provides new insights into and strategies for the design of efficient photoelectrodes and PEC devices

Superaerophobic hydrogels for enhanced electrochemical and photoelectrochemical hydrogen production

The efficient removal of gas bubbles in (photo)electrochemical gas evolution reactions is an important but underexplored issue. Conventionally, researchers have attempted to impart bubble-repellent properties (so-called superaerophobicity) to electrodes by controlling their microstructures. However, conventional approaches have limitations, as they are material specific, difficult to scale up, possibly detrimental to the electrodes' catalytic activity and stability, and incompatible with photoelectrochemical applications. To address these issues, we report a simple strategy for the realization of superaerophobic (photo)electrodes via the deposition of hydrogels on a desired electrode surface. For a proof-of-concept demonstration, we deposited a transparent hydrogel assembled from M13 virus onto (photo)electrodes for a hydrogen evolution reaction. The hydrogel overlayer facilitated the elimination of hydrogen bubbles and substantially improved the (photo)electrodes' performances by maintaining high catalytic activity and minimizing the concentration overpotential. This study can contribute to the practical application of various types of (photo)electrochemical gas evolution reactions

Copper contamination of fruit orchards soils: Biotic Impacts : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Extensive use of fungicide copper (Cu) has a more recent history in New Zealand than in many other parts of the world where long-lasting Cu accumulation in soil has become a major environmental issue. However, Cu is extensively applied in New Zealand orchards, including organic orchards, with some awareness that the consequences of its current and future accumulation on soil health are relatively unknown and under-explored. This doctoral study aimed to investigate the impact on soil functional processes and plants of soil copper contamination associated with cherry, apple and kiwifruit orchards, vineyards and hops. The research encompassed experimental work on soil respiration, plant growth, earthworms, soil microbial activity, root growth and plant cell culture through a combination of fieldwork, glasshouse and laboratory studies. The central hypothesis of this study was that accumulation and persistence of Cu in orchard soils are likely to adversely affect critical aspects of soil biology and functionality. Following a detailed survey of accumulation and spatial variability of soil Cu across different fruit orchards up to 73 years old, practical investigations involved soil respirometry, analysis of microbial carbon (C) and nitrogen (N), and rhizobox and pot plant growth assays, as much as possible using in-situ field measurements or soils collected from orchards and transferred to the glasshouse and laboratory. In an earthworm behavioural and Cu-uptake study, a native anecic species was exposed to soils from the same orchard with differing histories of fungicide use. Three hop varieties (Cascade, Nelson Sauvin and Riwaka) were used for plant growth trials on the same soils. Plant stress responses were investigated using callus incubation trials on cell lines isolated from three apple cultivars (Braeburn, Fuji, and Cripps Pink) grown on a Cu-spiked growth medium. All practical work was carried out from 2020 to 2023. The results showed that soil Cu concentrations in orchards frequently and substantially exceeded most published threshold limits. Whilst soil Cu concentrations could largely be explained by modelling the age of the orchards, fruit type and soil organic matter (SOM) also had a large role in Cu retention. When SOM and existing Cu concentrations were amended in four soils from different blocks of the same cherry orchard, the ecotoxicological impact differed, and it was found that SOM could be a more powerful determinant than Cu of the biotic responses. Earthworm survivorship and growth in these soils were significantly determined by both SOM and Cu; earthworms exhibited a preference for soils with concentrations of Cu elevated substantially above background (to 160 mg kg-1), where SOM content was also high. A variable impact of Cu contamination on soil microbial activity was recorded across soils with elevated Cu concentrations (from 195 to 405 mg kg-1). Only a weak correlation was found between soil total Cu concentration and soil respiration when data for all orchards were combined, but the impact of Cu was more evident when each type of fruit orchard was evaluated separately. Microbial biomass carbon (MBC) and nitrogen (MBN) analyses similarly provided only a weak or negligible correlation with soil Cu, but artificially spiked soils provided a more consistent response to elevated Cu. Confounding factors appeared to relate to vegetation cover within and between rows and the amount of cultivation of the soils used to manage weeds (and bronze beetle in apples). The influence of management variables requires a more detailed study. Root growth in hop varieties was negatively affected at Cu concentrations exceeding 263 mg kg-1, whilst best growth was observed at 160 mg kg-1 in conjunction with abundant SOM. In callus culture assays, Cu negatively impacted the growth of Braeburn and Fuji apple varieties at concentrations exceeding 15 mg kg-1, while Cripps Pink had higher Cu tolerance. The value of using biological and ecological indices to assess the impacts of agricultural chemicals and contaminated soils is discussed. The findings have identified detrimental biotic impacts of soil Cu concentrations that already exist in orchards, which are probably reflected in a negative influence on soil health. Transfer rates of Cu to fruits through uptake from soil or from foliar absorption are negligible, but stress responses in plants and soil fauna and impacts on soil biology and ecology have been detected. Currently, the deleterious impact of elevated Cu is largely mitigated by SOM content in combination with the avoidance of low pH in orchard soils. Whilst this implies there is a potential avenue for amelioration of toxicity and maintenance or restoration of soil health, residual fungicide Cu will not significantly dissipate and is likely to continue to accumulate. Sustainable soil health management in New Zealand's orchards is not viable with longer-term continued usage of Cu fungicides

Phloretin Exerts Anti-Tuberculosis Activity and Suppresses Lung Inflammation

An increase in the prevalence of the drug-resistant Mycobacteria tuberculosis necessitates developing new types of anti-tuberculosis drugs. Here, we found that phloretin, a naturally-occurring flavonoid, has anti-mycobacterial effects on H37Rv, multi-drug-, and extensively drug-resistant clinical isolates, with minimum inhibitory concentrations of 182 and 364 μM, respectively. Since Mycobacteria cause lung inflammation that contributes to tuberculosis pathogenesis, anti-inflammatory effects of phloretin in interferon-γ-stimulated MRC-5 human lung fibroblasts and lipopolysaccharide (LPS)-stimulated dendritic cells were investigated. The release of interleukin (IL)-1β, IL-12, and tumor necrosis factor (TNF)-α was inhibited by phloretin. The mRNA levels of IL-1β, IL-6, IL-12, TNF-α, and matrix metalloproteinase-1, as well as p38 mitogen-activated protein kinase and extracellular signal-regulated kinase phosphorylation, were suppressed. A mouse in vivo study of LPS-stimulated lung inflammation showed that phloretin effectively suppressed the levels of TNF-α, IL-1β, and IL-6 in lung tissue with low cytotoxicity. Phloretin was found to bind M. tuberculosis β-ketoacyl acyl carrier protein synthase III (mtKASIII) with high affinity (7.221 × 107 M−1); a binding model showed hydrogen bonding of A-ring 2′-hydroxy and B-ring 4-hydroxy groups of phloretin with Asn261 and Cys122 of mtKASIII, implying that mtKASIII can be a potential target protein. Therefore, phloretin can be a useful dietary natural product with anti-tuberculosis benefits

Tailoring of molecular catalysts for photoelectrochemical and electrochemical water splitting

Department of Energy Engineering (Energy Engineering)clos

Interfacial engineering of hematite photoanodes through layer-by-layer assembly for solar water splitting

Solar to chemical conversion is considered as a promising solution to energy and environmental problems because various chemicals (e.g., hydrogen, formate, and syngas) can be produced from wasted carbon dioxide and abundant water in a carbon-neutral manner. It can be enabled by a series of photoelectrochemical processes with various functional materials, which include semiconducting materials for exciton generation, conducting materials for exciton dissociation and charge transport, and redox catalysts for target-chemical reactions. For the development of efficient and stable solar to chemical energy conversion devices, it is imperative to precisely assembly these components. Here, we report that an efficient and stable photoanode for solar water oxidation can be readily fabricated by layer-by-layer (LbL) assembly. In particular, cationic graphene oxide (GO) nanosheets and anionic molecular metal oxide catalysts were readily deposited on hematite without alteration of their properties using the LbL method. It was found that their sequential deposition significantly improves the photocatalytic performance and stability of hematite for solar water oxidation. In addition, the deposition of multilayers of cationic and anionic polymer electrolyte prior to the GO and catalyst layers improve the photoanode performance even further by allowing the engineering of the flat band potential of the underlying hematite photoanode. We believe that the present study opens a new avenue for an efficient photosynthetic device, as well as an academic insight to scientists and engineers for designing novel electrochemical/photoelectrochemical devices

Interfacial Engineering of Hematite through Layer-by-Layer Assembly for Solar Water Oxidation

Artificial photosynthesis has a great attention as a promising energy solution to environmental problems. In principle, valuable chemicals can be produced from wasted carbon dioxide and abundant water, instead of using fossil fuels, through a series of photoelectrochemical processes in a carbon-neutral manner. For the successful development of efficient and stable photosynthetic devices, it is significantly required to assemble various functional materials for efficient exciton generation, exciton dissociation, charge transport, and electrocatalytic charge transfer reactions. Here, we develop an efficient and stable photoanode for solar water oxidation through deposition of artificial nacre film on hematite by layer-by-layer assembly of cationic graphene oxide nanosheets and anionic molecular metal oxide catalysts. The deposition of the film greatly improved both the photocatalytic activity and stability of hematite photoanodes. It was found that deposition of alternating layers of cationic and anionic polymers prior to the artificial nacre film allowed fine-tuning of the work-function of the hematite electrode, enhancing the photoelectrochemical performance even further

Bioinspired Materials Science: Mimicking Nature's Strategies to Build Functional Materials

One of most fascinating features of biological system is that their excellent physical and chemical properties stem from their unique structure where various organic and inorganic components are precisely assembled at nanoscale precision. They have developed their own strategies to build functional materials and systems in response to external stimuli (or environment) through evolution over millions of years. For example, excellent mechanical properties of natural bone is resulted from their unique structure where organic peptide nanofibers and calcium phosphate nanocrystals are hierarchically organized at nano- and micro-scales. Another good example is photosynthetic machinery of plants, which can produce sugars and biological fuels with sustainable resources. Spatiotemporal arrangement of light-harvesting chlorophyl dyes and redox catalysts allows efficient separation of charges and directional flow of electrons (i.e. redox power), enabling photocatalytic splitting of water and production of carbohydrates from CO2. In this presentation, we report the development of functional materials and systems, especially for energy storage and conversion devices, by mimicking Mother Nature'ss stretegies. Following topics will be covered in this presentation: 1) Synthesis of functional materials by using biological templates such as peptides and viruses, 2) Development of artiticial photosynthetic system for the production of valuable chemicals