Photocatalysis has been widely applied in various areas, such as solar cells, water splitting, and pollutant degradation. Therefore, the photochemical mechanisms and basic principles of ...photocatalysis, especially TiO2 photocatalysis, have been extensively investigated by various surface science methods in the last decade, aiming to provide important information for TiO2 photocatalysis under real environmental conditions. Recent progress that provides fundamental insights into TiO2 photocatalysis at a molecular level is highlighted. Insights into the structures of TiO2 and the basic principles of TiO2 photocatalysis are discussed first, which provides the basic concepts of TiO2 photocatalysis. Following this, details of the photochemistry of three important molecules (oxygen, water, methanol) on the model TiO2 surfaces are presented, in an attempt to unravel the relationship between charge/energy transfer and bond breaking/forming in TiO2 photocatalysis. Lastly, challenges and opportunities of the mechanistic studies of TiO2 photocatalysis at the molecular level are discussed briefly, as well as possible photocatalysis models.
The basic principles and fundamental processes of TiO2 photocatalysis are highlighted. Recent progress made on the studies of the nature of TiO2 photocatalysis, in particular whether photocatalytic reactions are driven by separated charges or by energy produced via nonadiabatic exciton decay or nonadiabatic charge recombination, is summarized and discussed in detail.
Functionally Graded Porous Scaffold (FGPS) becomes an attractive candidate for bone graft due to its combination of better mechanical and biological requirements with the scaffold gradient to better ...mimic host tissue. This paper focuses on the graded change requirements of bio-porous scaffolds in terms of physical and mechanical properties. Gradients in three patterns (density, heterostructure and cell-size gradients) with Gyroid and Diamond unit cells were proposed based on Triply Periodic Minimal Surfaces (TPMS), and fabricated by Selective Laser Melting (SLM) using Ti-6Al-4V. Among them, cell-size gradient was described for the first time, realizing a variation of graded pore size on a specific way. Morphological properties of porous samples were characterized by micro-CT and SEM, followed by compressive tests for determining their mechanical behaviors. It was found that the TPMS method is an effective way to achieve gradients in multiple patterns which are comparable to natural tissue with respect to both continuous topology and interconnectivity. The porous surface area and pore size, could be controlled by the cell-size gradient without relatively density alteration, stabilizing the modulus and strength within 11% and 20%, respectively. Both Gyroid and Diamond structures possess a superior strength (152.6 MPa, 145.7 MPa) and comparable elastic modulus (3.8GPa) with natural cortical bone.
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•Cell-size gradient porous scaffold was designed based on triply periodic minimal surfaces (TPMS).•Cell-size gradient can adjust surface area and pore size of scaffolds without relative density alteration.•TPMS is a feasible way to achieve gradient scaffolds in multiple patterns with continuous topology and interconnectivity.•The studied scaffolds of TC4 have a superior strength and comparable elastic modulus with cortical bone.
•Design method of sheet based functionally graded Gyroid structure based on the mathematical expression of triply periodic minimal surfaces.•Sheet based functionally graded Gyroid exhibited failure ...mechanism of layer-by-layer buckling deformation.•Superior energy absorption capability of sheet based functionally graded Gyroid structure.•The Johnson-Cook models were implemented to simulate the deformation response of the lattice structures.
The triply periodic minimal surfaces (TPMS) have caught a lot of attention to many applications recently such as biomaterials, lightweight components with high strength and functionally graded material (FGM). In this study, the designing methods of the network based functionally graded Gyroid (N-FGG) and sheet based functionally graded Gyroid (S-FGG) structures were presented. The specimens of N-FGG and S-FGG based structures were fabricated by selective laser melting (SLM) with Ti-6Al-4V powder, then followed by quasi-static compression tests to measure the mechanical properties. The S-FGG based structure showed higher elastic modulus, yield strength and more stable stress fluctuation than N-FGG based structure with the same range of volume fraction gradient. The dominated deformation behaviors of both graded lattice structures were layer-by-layer. However, the S-FGG based structure showed more of buckling failure while the N-FGG based structure exhibited more of brittle fracture. Furthermore, the finite element analysis (FEA) with the Johnson-Cook plastic and damage models was implemented to simulate the plastic deformation and the failure behavior of the lattice materials at the post-yield stages. The simulated results illustrated that the compressive stress concentrated in the middle area of struts which connected the two adjacent layers of N-FGG based structures, while the stress in S-FGG based structures was distributed much uniformly in the middle connection region. S-FGG based structure also showed higher ultimate stress with the increase of compressive strain. Finally, the energy absorption capability of lattice structures was investigated, and the results indicated that the S-FGG based structure showed more total energy absorption per unit volume and higher energy efficiency, which means good prospects especially in the applications of relatively high allowable stress.
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Characterized by high thermal-electrical conductivity and reasonable specific strength, lattice structures of copper alloy have great potential in industrial applications. However, they have been ...rarely studied due to their complicated structures and difficulty in fabrication. Based on the ability of selective laser melting to produce near net shape parts with any complex geometry directly, Cu-Cr-Zr copper alloy lattice structures with high density were manufactured and studied for the first time. A series of lattice structures were designed by a mathematical approach named Triply Periodic Minimal Surfaces and their mechanical properties, microstructures and deformation behaviors were systematically studied. The effects of cell size and volume fraction on their mechanical properties and energy absorptions were analyzed and evaluated. The results demonstrate that the mechanical and energy absorption properties of the lattice structures varied dramatically with the changes of cell size and volume fraction. Due to the good plasticity of the copper alloy, stress-strain curves of the lattice structures exhibit a long stress plateau without stress collapses, which is very beneficial for energy absorption. The deformation of the lattice structures occurred uniformly and was caused by the struts bending without cell breaking and struts fracturing.
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•Cu-Cr-Zr copper alloy lattice structures were well fabricated via selective laser melting for the first time.•The compression deformations of the lattice structures occurred uniformly without cell breaking and strut fracturing.•The stress-strain curves exhibit a long and rising stress plateaus without stress collapses.•Properties of the lattice structures with lower volume fraction are more sensitive to cell size.•Explicit equations depict the relations of the volume fractions and the mechanical properties.
The combination of selective laser melting (SLM) and Cu-based alloys has attracted attention in recent years due to the increasing requirements for components characterized by complicated structures ...and high electrical and thermal conductivity. In this paper, to investigate the forming properties of a Cu–Cr–Zr alloy in SLM, a statistical model regarding the impacts of the processing parameters on the density was established via an experimental approach (response surface method and analysis of variance). Furthermore, based on the acquired optimal processing parameters, samples with nearly full density and standard tension specimens were fabricated, and their microstructures and mechanical properties were analyzed. X-ray diffraction results indicate that the phase composition of the as-built sample by SLM contains only α-Cu phase and the Bragg peaks of the α-Cu phase in SLMed sample distinctly differs from those of powders and of wrought copper alloy. Compared with wrought copper alloy, SLMed Cu–Cr–Zr shows a comparable ultimate tensile strength (∼321 MPa); however, its elongation at break (25%) is much higher than that of wrought sample (15%). In addition, according to electron back-scattered diffraction analysis, a strong texture with respect to the direction parallel to the building direction arose during SLM process.
•Near fully density Cu–Zr–Cr copper alloy was successfully fabricated by SLM.•Grain morphologies were different in parallel and perpendicular to building direction.•The SLMed samples showed much higher plasticity compared with the wrought ones.•A strong texture with direction parallel to the building direction was found.
We have investigated the photocatalysis of partially deuterated methanol (CD3OH) and H2O on TiO2(110) at 400 nm using a newly developed photocatalysis apparatus in combination with theoretical ...calculations. Photocatalyzed products, CD2O on Ti5c sites, and H and D atoms on bridge-bonded oxygen (BBO) sites from CD3OH have been clearly detected, while no evidence of H2O photocatalysis was found. The experimental results show that dissociation of CD3OH on TiO2(110) occurs in a stepwise manner in which the O–H dissociation proceeds first and is then followed by C–D dissociation. Theoretical calculations indicate that the high reverse barrier to C–D recombination and the facile desorption of CD2O make photocatalytic methanol dissociation on TiO2(110) proceed efficiently. Theoretical results also reveal that the reverse reactions, i.e, O–H recombination after H2O photocatalytic dissociation on TiO2(110), may occur easily, thus inhibiting efficient photocatalytic water splitting.
Technological improvements enable single-cell epigenetic analyses of organ development. We reasoned that high-resolution single-cell chromatin accessibility mapping would provide needed insight into ...the epigenetic reprogramming and transcriptional regulators involved in normal mammary gland development. Here, we provide a single-cell resource of chromatin accessibility for murine mammary development from the peak of fetal mammary stem cell (fMaSC) functional activity in late embryogenesis to the differentiation of adult basal and luminal cells. We find that the chromatin landscape within individual cells predicts both gene accessibility and transcription factor activity. The ability of single-cell chromatin profiling to separate E18 fetal mammary cells into clusters exhibiting basal-like and luminal-like chromatin features is noteworthy. Such distinctions were not evident in analyses of droplet-based single-cell transcriptomic data. We present a web application as a scientific resource for facilitating future analyses of the gene regulatory networks involved in mammary development.
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•Performed single-nucleus (sn)ATAC-seq profiling of fetal and adult mammary cells•snATAC-seq reveals chromatin changes correlating with basal or luminal cell states•Cells with luminal- or basal-oriented chromatin features are evident before birth•A web resource for single-cell profile of embryonic and postnatal mammary development
The ability to deconstruct complex tissues into their constituent cell states and identify molecular mechanisms involved in cell differentiation is enabling deeper understanding of normal development and disease. Chung et al. use snATAC-seq to agnostically determine the chromatin states correlated with cell-state changes during embryonic and postnatal mammary development.
Previous observations of methyl formate (HCOOCH3) during the photo-oxidation of methanol (CH3OH) on TiO2 catalysts suggested that photocatalysis on TiO2 could be used to build up complex molecules ...from a single precursor. We have investigated the mechanism of HCOOCH3 formation by irradiating a CH3OH-adsorbed TiO2(110) surface with 400 nm light at low surface temperatures. Through the detection of volatile products after irradiation by temperature programmed desorption, we have found, as previously reported Phillips et al. J. Am. Chem. Soc. 2013, 135, 574–577 that HCOOCH3 is formed by the cross-coupling reaction of CH3O and CH2O, which are products of the first and second dissociation steps, respectively, in the stepwise photocatalysis of CH3OH on TiO2(110). Unlike the previous study, we have observed the photocatalytic production of HCOOCH3 without preoxidation of the surface, and we have concluded that the final reaction step to produce HCOOCH3 (i.e., the cross-coupling reaction of CH2O with CH3O) does not involve a transient HCO intermediate.
Jujube (
) was domesticated from wild jujube (
var.
). Here, integrative physiological, metabolomic, and comparative proteomic analyses were performed to investigate the fruit expansion and fruit ...taste components in a jujube cultivar 'Junzao' and a wild jujube 'Qingjiansuanzao' with contrasting fruit size and taste. We revealed that the duration of cell division and expansion largely determined the final fruit size, while the intercellular space in the mesocarp dictated the ratio of mesocarp volume in mature fruits. The high levels of endogenous gibbereline
(GA) and zeatin in the growing fruit of 'Junzao' were associated with their increased fruit expansion. Compared with 'Junzao,' wild jujube accumulated lower sugars and higher organic acids. Furthermore, several protein co-expression modules and important member proteins correlated with fruit expansion, sugar synthesis, and ascorbic acid metabolism were identified. Among them, GA20OX involved in GA biosynthesis was identified as a key protein regulating fruit expansion, whereas sucrose-6-phosphate synthase (SPS) and neutral invertase (NINV) were considered as key enzymes promoting sugar accumulation and as major factors regulating the ratio of sucrose to hexose in jujube fruits, respectively. Moreover, the increase of Nicotinamide adenine dinucleotide-Malate dehydrogenase (NAD-MDH) activity and protein abundance were associated with the malic acid accumulation, and the high accumulation of ascorbic acid in wild jujube was correlated with the elevated abundance of GalDH, ZjAPXs, and MDHAR1, which are involved in the ascorbic acid biosynthesis and recycling pathways. Overall, these results deepened the understanding of mechanisms regulating fruit expansion and sugar/acids metabolisms in jujube fruit.
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