Plasmon-induced photonic and energy-transfer enhancement of solar water splitting by a hematite nanorod arra

Plasmonic metal nanostructures offer a promising route to improve the solar energy conversion efficiency of semiconductors. Here we show that incorporation of a hematite nanorod array into a plasmonic gold nanohole array pattern significantly improves the photoelectrochemical water splitting performance, leading to an approximately tenfold increase in the photocurrent at a bias of 0.23 V versus Ag|AgCl under simulated solar radiation. Plasmon-induced resonant energy transfer is responsible for enhancement at the energies below the band edge, whereas above the absorption band edge of hematite, the surface plasmon polariton launches a guided wave mode inside the nanorods, with the nanorods acting as miniature optic fibres, enhancing the light absorption. In addition, the intense local plasmonic field can suppress the charge recombination in the hematite nanorod photoanode in a photoelectrochemical cell. Our results may provide a general approach to overcome the low optical absorption and spectral utilization of thin semiconductor nanostructures, while further reducing charge recombination losses

Plasmon-Induced Photonic And Energy-Transfer Enhancement Of Solar Water Splitting By A Hematite Nanorod Array

Plasmonic metal nanostructures offer a promising route to improve the solar energy conversion efficiency of semiconductors. Here we show that incorporation of a hematite nanorod array into a plasmonic gold nanohole array pattern significantly improves the photoelectrochemical water splitting performance, leading to an approximately tenfold increase in the photocurrent at a bias of 0.23 V versus Ag|AgCl under simulated solar radiation. Plasmon-induced resonant energy transfer is responsible for enhancement at the energies below the band edge, whereas above the absorption band edge of hematite, the surface plasmon polariton launches a guided wave mode inside the nanorods, with the nanorods acting as miniature optic fibres, enhancing the light absorption. In addition, the intense local plasmonic field can suppress the charge recombination in the hematite nanorod photoanode in a photoelectrochemical cell. Our results may provide a general approach to overcome the low optical absorption and spectral utilization of thin semiconductor nanostructures, while further reducing charge recombination losses

Exploring the shared molecular mechanism of microvascular and macrovascular complications in diabetes: Seeking the hub of circulatory system injury

BackgroundMicrovascular complications, such as diabetic retinopathy (DR) and diabetic nephropathy (DN), and macrovascular complications, referring to atherosclerosis (AS), are the main complications of diabetes. Blindness or fatal microvascular diseases are considered to be identified earlier than fatal macrovascular complications. Exploring the intrinsic relationship between microvascular and macrovascular complications and the hub of pathogenesis is of vital importance for prolonging the life span of patients with diabetes and improving the quality of life.Materials and methodsThe expression profiles of GSE28829, GSE30529, GSE146615 and GSE134998 were downloaded from the Gene Expression Omnibus database, which contained 29 atherosclerotic plaque samples, including 16 AS samples and 13 normal controls; 22 renal glomeruli and tubules samples from diabetes nephropathy including 12 DN samples and 10 normal controls; 73 lymphoblastoid cell line samples, including 52 DR samples and 21 normal controls. The microarray datasets were consolidated and DEGs were acquired and further analyzed by bioinformatics techniques including GSEA analysis, GO-KEGG functional clustering by R (version 4.0.5), PPI analysis by Cytoscape (version 3.8.2) and String database, miRNA analysis by Diana database, and hub genes analysis by Metascape database. The drug sensitivity of characteristic DEGs was analyzed.ResultA total of 3709, 4185 and 8086 DEGs were recognized in AS, DN, DR, respectively, with 1820, 1666, 888 upregulated and 1889, 2519, 7198 downregulated. GO and KEGG pathway analyses of DEGs and GSEA analysis of common differential genes demonstrated that these significant sites focused primarily on inflammation-oxidative stress and immune regulation pathways. PPI networks show the connection and regulation on top-250 significant sites of AS, DN, DR. MiRNA analysis explored the non-coding RNA upstream regulation network and significant pathway in AS, DN, DR. The joint analysis of multiple diseases shows the common influenced pathways of AS, DN, DR and explored the interaction between top-1000 DEGs at the same time.ConclusionIn the microvascular and macrovascular complications of diabetes, immune-mediated inflammatory response, chronic inflammation caused by endothelial cell activation and oxidative stress are the three links linking atherosclerosis, diabetes retinopathy and diabetes nephropathy together. Our study has clarified the intrinsic relationship and common tissue damage mechanism of microcirculation and circulatory system complications in diabetes, and explored the mechanism center of these two vascular complications. It has far-reaching clinical and social value for reducing the incidence of fatal events and early controlling the progress of disabling and fatal circulatory complications in diabetes

Effects of Defects on Photocatalytic Activity of Hydrogen-Treated Titanium Oxide Nanobelts

Previous studies have shown that hydrogen treatment leads to the formation of blue to black TiO_2, which exhibits photocatalytic activity different from that of white pristine TiO_2. However, the underlying mechanism remains poorly understood. Herein, density functional theory is combined with comprehensive analytical approaches such as X-ray absorption near edge structure spectroscopy and transient absorption spectroscopy to gain fundamental understanding of the correlation among the oxygen vacancy, electronic band structure, charge separation, charge carrier lifetime, reactive oxygen species (ROS) generation, and photocatalytic activity. The present work reveals that hydrogen treatment results in chemical reduction of TiO_2, inducing surface and subsurface oxygen vacancies, which create shallow and deep sub-band gap Ti(III) states below the conduction band. This leads to a blue color but limited enhancement of visible light photocatalytic activity up to 440 nm at the cost of reduced ultraviolet photocatalytic activity. The extended light absorption spectral range for reduced TiO_2 is ascribed to both the defect-to-conduction band transitions and the valence band-to-defect transitions. The photogenerated charge carriers from the defect states to the conduction band have lifetimes too short to drive photocatalysis. The Ti(III) deep and shallow trap states below the conduction band are also found to reduce the lifetime of photogenerated charge carriers under ultraviolet light irradiation. The ROS generated by the reduced TiO_2 are less than those generated by pristine TiO_2. Consequently, the reduced TiO_2 exhibits ultraviolet-responsive photocatalytic activity worse than that of pristine TiO_2. This report shows that increasing the light absorption spectral range of a semiconductor by doping or introduction of defects does not necessarily guarantee an increase in photocatalytic activity

Effects of Defects on Photocatalytic Activity of Hydrogen-Treated Titanium Oxide Nanobelts

Previous studies have shown that hydrogen treatment leads to the formation of blue to black TiO_2, which exhibits photocatalytic activity different from that of white pristine TiO_2. However, the underlying mechanism remains poorly understood. Herein, density functional theory is combined with comprehensive analytical approaches such as X-ray absorption near edge structure spectroscopy and transient absorption spectroscopy to gain fundamental understanding of the correlation among the oxygen vacancy, electronic band structure, charge separation, charge carrier lifetime, reactive oxygen species (ROS) generation, and photocatalytic activity. The present work reveals that hydrogen treatment results in chemical reduction of TiO_2, inducing surface and subsurface oxygen vacancies, which create shallow and deep sub-band gap Ti(III) states below the conduction band. This leads to a blue color but limited enhancement of visible light photocatalytic activity up to 440 nm at the cost of reduced ultraviolet photocatalytic activity. The extended light absorption spectral range for reduced TiO_2 is ascribed to both the defect-to-conduction band transitions and the valence band-to-defect transitions. The photogenerated charge carriers from the defect states to the conduction band have lifetimes too short to drive photocatalysis. The Ti(III) deep and shallow trap states below the conduction band are also found to reduce the lifetime of photogenerated charge carriers under ultraviolet light irradiation. The ROS generated by the reduced TiO_2 are less than those generated by pristine TiO_2. Consequently, the reduced TiO_2 exhibits ultraviolet-responsive photocatalytic activity worse than that of pristine TiO_2. This report shows that increasing the light absorption spectral range of a semiconductor by doping or introduction of defects does not necessarily guarantee an increase in photocatalytic activity

Correlation of Photocatalytic Activity with Band Structure of Low-dimensional Semiconductor Nanostructures

Photocatalytic hydrogen generation by water splitting is a promising technique to produce clean and renewable solar fuel. The development of effective semiconductor photocatalysts to obtain efficient photocatalytic activity is the key objective. However, two critical reasons prevent wide applications of semiconductor photocatalysts: low light usage efficiency and high rates of charge recombination. In this dissertation, several low-dimensional semiconductors were synthesized with hydrothermal, hydrolysis, and chemical impregnation methods. The band structures of the low-dimensional semiconductor materials were engineered to overcome the above mentioned two shortcomings. In addition, the correlation between the photocatalytic activity of the low-dimensional semiconductor materials and their band structures were studied.;First, we studied the effect of oxygen vacancies on the photocatalytic activity of one-dimensional anatase TiO2 nanobelts. Given that the oxygen vacancy plays a significant role in band structure and photocatalytic performance of semiconductors, oxygen vacancies were introduced into the anatase TiO2 nanobelts during reduction in H2 at high temperature. The oxygen vacancies of the TiO2 nanobelts boosted visible-light-responsive photocatalytic activity but weakened ultraviolet-light-responsive photocatalytic activity. As oxygen vacancies are commonly introduced by dopants, these results give insight into why doping is not always beneficial to the overall photocatalytic performance despite increases in absorption. Second, we improved the photocatalytic performance of two-dimensional lanthanum titanate (La2Ti2 O7) nanosheets, which are widely studied as an efficient photocatalyst due to the unique layered crystal structure. Nitrogen was doped into the La2Ti2O7 nanosheets and then Pt nanoparticles were loaded onto the La2Ti2O7 nanosheets. Doping nitrogen narrowed the band gap of the La2Ti 2O7 nanosheets by introducing a continuum of states by the valence band edge, unlike the mid-gap states introduced by oxygen vacancies, leading to an improvement in visible and UV photocatalysis. The Pt nanoparticles both enhanced separation of charge carriers and acted as reaction sites for hydrogen evolution. The photocatalytic hydrogen generation rate of the La 2Ti2O7 nanosheets was increased to ∼21 muM g-1 hr-1 from zero in visible light by nitrogen doping and Pt loading, showing the importance of the positioning of dopant energy levels within the band gap.;Third, a hematite/reduced graphene oxide (alpha-Fe2 2O3/rGO) nanocomposite was synthesized by a hydrolysis method. The photocatalytic oxygen evolution rate of the hematite was increased from 387 to 752 muM g-1 hr-1 by incorporating rGO. Photoelectrochemical measurements showed that coupling the hematite nanoparticles with the rGO can greatly increase the photocurrent and reduce the charge recombination rate, overcoming the poor charge recombination characteristics of hematite and allowing its small band gap to be taken advantage of. Fourth, a Au/La 2Ti2O7/rGO heterostructure was synthesized to further enhance the photocatalytic hydrogen generation rate of the La 2Ti2O7 nanosheets. The enhanced performance of photocatalytic water splitting was due to plasmonic energy transfer, which resulted from the plasmonic Au nanoparticles on the La2Ti 2O7 nanosheets. This heterostructure showed doping, charge extraction, and plasmonics work synergistically. Fifth, nanoscale p-n junctions on the rGO were formed by depositing the p-type MoS 2 nanoplatelets onto the n-type nitrogen-doped rGO. The p-MoS2/n-rGO heterostructure had significant photocatalytic hydrogen generation activity under solar light irradiation. The enhanced charge generation and suppressed charge recombination due to the p-n junctions led to enhance solar hydrogen generation reaction while allowing replacement of the expensive Pt nanoparticles with an eco-friendly alternative.;The research results in this dissertation are contributed to a better understanding of the relationship between the band structure tuning and photocatalytic activity of low-dimensional semiconductor nanostructures. The results lay out guidelines for the enhancement of large band gap semiconductors with poor solar utilization and small band gap semiconductors with poor charge recombination characteristics alike. Additionally, it is shown that the rare earth co-catalyst can be replaced with an earth friendly alternative, leading to a further increase in performance. The findings of this thesis can be used to guide photocatalyst selection and optimization for solar to hydrogen conversion

Design of Copper-Catalyzed Multicomponent Reactions and Applications to Natural Product Synthesis

Thesis advisor: Amir H. HoveydaChapter 1. Ligand-Controlled Site-Selective NHC–Cu-Catalyzed Protoboration of Monosubstituted Allenes. Site-selective proto–boryl additions to monosubstituted allenes promoted by NHC–Cu complexes are disclosed. Synthetically useful 1,1-disubstituted and Z-trisubstituted alkenylboron compounds are afforded in high efficiency (71%–92% yield) and site selectivity (88% to >98%) through proper choice of NHC ligands. Mechanistic study with the assistance of DFT calculations indicates that protonation of 2-boron-substituted allylcopper complex occurs through six-membered cyclic transition state. The utility of this protocol is demonstrated through application to fragment synthesis of an antibiotic macrolide natural product elansolid A. Chapter 2. Cu-Catalyzed Chemoselective Copper–Boron Additions to Monosubstituted Allenes Followed by Allyl Additions to Carbonyl Compounds. The first examples of catalytic generation of 2-boron-substituted allylcopper species and their in situ use for C–C bond formation are described. The reactions are performed in the presence of bisphosphine– or NHC–Cu complexes at 22 oC. High-value alcohol-containing alkenylboron compounds are provided in high efficiency (68–92% yield after oxidation) and stereoselectivity (88:12 to >98:2 dr). The reactions proceed with exclusive γ-addition mode through a cyclic six-membered transition state. Enantioselectivity can be achieved with chiral bisphosphine ligands in up to 97:3 enantiomeric ratio. Chapter 3. Chemo-, Site- and Enantioselective Copper–Boron Additions to 1,3-Enynes Followed by Site- and Diastereoselective Additions of the Resulting Allenylcopper Complexes to Aldehydes. Catalytic enantioselective multicomponent reactions involving 1,3-enynes, aldehydes and B2(pin)2 are described. The resulting products contain a primary C–B(pin) bond, as well as alkyne- and hydroxyl-substituted tertiary stereogenic centers. A critical feature is high enantioselectivity of the initial Cu–B addition to an alkyne-substituted terminal alkene. The key mechanistic issues are investigated by DFT calculations. Reactions are promoted in the presence of the Cu complex of an enantiomerically pure C1-symmetric bisphosphine and are complete in 8 h at ambient temperature. Products are generated in 66–94% yield (after oxidation or catalytic cross-coupling), 90:10 to >98:2 diastereomeric ratio, and 85:15–99:1 enantiomeric ratio. Aryl-, heteroaryl-, alkenyl-, and alkyl-substituted aldehydes and enynes are suitable substrates. Utility is demonstrated through catalytic alkylation and arylation of the organoboron compounds as well as applications to synthesis of fragments of tylonolide and mycinolide IV. Chapter 4. Multifunctional Alkenylboron Compounds through Single-Catalyst-Controlled Multicomponent Reactions and Their Applications in Scalable Natural Product Synthesis. A facile multicomponent catalytic process that begins with a chemo-, site- and diastereoselective copper–boron addition to a monosubstituted allene followed by addition of the resulting boron-substituted organocopper intermediate to an allylic phosphate, generating products that contain a stereogenic center, a monosubstituted alkene and an easily functionalizable Z-trisubstituted alkenylboron group in up to 89% yield with >98% branch selectivity and stereoselectivity and an enantiomeric ratio greater than 99:1. The copper-based catalyst is derived from a robust heterocyclic salt that can be prepared in multigram quantities from inexpensive starting materials and without costly column chromatography purification. The utility of the method is demonstrated through enantioselective synthesis of gram quantities of two natural products, rottnestol and herboxidiene/GEX1A. Chapter 5. Cu-Catalyzed Enantioselective Allyl and Propargyl 1,6-Conjugate Additions through 3,3’-Reductive Elimination. Catalytic enantioselective 1,6-conjugate additions of allyl-type nucleophiles promoted by NHC–Cu complexes are reported. Propargyl and 2-boron allyl 1,6-conjugate products are formed in high efficiency, diastereo- and enantioselectivity. The unique mechanistic feature is that the transformations proceed through Cu-catalyzed 3,3’-reductive elimination, that is unprecedented for copper catalysis. Further mechanistic study and application to complex molecule synthesis will be conducted.Thesis (PhD) — Boston College, 2015.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Chemistry

Model‐driven neural network based for HPO‐MIMO channel estimation

Abstract Integrated Sensing and Communications (ISAC) need to process data streams in high‐speed sensor data acquisition or high‐speed wireless communications. To process the data can require more computing and communication resources, resulting in higher power consumption. Halved‐Phase Only Multiple Input Multiple Output (HPO‐MIMO) communication technology can solve this problem by using low‐power nonlinear detection devices. In ISAC, Channel Estimation (CE) technology can provide key channel characteristics and state information for sensing and collaborative work of perception and communication tasks. However, HPO‐MIMO system cannot realize CE using traditional receiver schemes because of the missing amplitude. In order to solve this problem, two HPO‐MIMO CE schemes based on model‐driven deep learning are proposed in this paper. The proposed schemes include a Densely Residual Network (DRN) and a Inception‐Resnet (IR), which is suitable for the case of sufficient data and insufficient data, respectively. The simulation results show that the performance of DRN based scheme is better than that of IR based scheme when the data amount is sufficient, and the performance of IR based scheme is better when the dataset is small. In addition, the proposed CE schemes work well with a range of antenna sizes and distances

Pathway-divergent coupling of 1,3-enynes with acrylates through cascade cobalt catalysis

Abstract Catalytic cascade transformations of simple starting materials into highly functionalized molecules bearing a stereochemically defined multisubstituted alkene, which are important in medicinal chemistry, natural product synthesis, and material science, are in high demand for organic synthesis. The development of multiple reaction pathways accurately controlled by catalysts derived from different ligands is a critical goal in the field of catalysis. Here we report a cobalt-catalyzed strategy for the direct coupling of inexpensive 1,3-enynes with two molecules of acrylates to construct a high diversity of functionalized 1,3-dienes containing a trisubstituted or tetrasubstituted olefin. Such cascade reactions can proceed through three different pathways initiated by oxidative cyclization to achieve multiple bond formation in high chemo-, regio- and stereoselectivity precisely controlled by ligands, providing a platform for the development of tandem carbon-carbon bond-forming reactions