A novel monolithic amidogen-rich biomass adsorbent was successfully prepared. Corn bract (CB) was employed as adsorbent matrix, and arginine (Arg) was selected as a bonding bridge between the ...hydroxyls on cellulose that came from CB and modifier molecules to enrich reactive sites and improve reaction activity. Polyethyleneimine (PEI) was then grafted to the surface of CB in a heterogeneous reaction. The resultant CB-g-PEI (CB-grafted-PEI) held a grafting ratio of 60.6%. And the maximum adsorption for (acid red 18) AR18 was reached 506.7 mg/g. As a necessary content of adsorption behavior research, models about isotherm adsorption, adsorption kinetics and adsorption thermodynamics were all inspected. According to the research conclusions obtained, the pseudo-second-order model provides the best explanation for the kinetics of adsorption. The adsorption isotherm of AR18 is in better agreement with the Langmuir isotherm model. The adsorption and desorption experiments were conducted over 6 times. The samples were characterized using FT-IR, SEM and EDS. The study suggests that the CB-g-PEI is an available adsorbent.
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•A geopolymer is proposed based on fluidized bed fly ash–metakaolin.•Geopolymer shows relatively lower mass loss and strength loss compared to ordinary Portland cement.•Geopolymer ...possesses good heat resistance and acid resistance compared to ordinary Portland cement.•A model is proposed for microstructure development.•Durability of geopolymer is demonstrated by monitoring the pore structure.
This study aims to investigate durability and microstructure of fluidized bed fly ash and metakaolin based geopolymer exposed to elevated temperatures and acid attack. Geopolymer specimens were prepared by combination of fly ash and metakaolin activated by sodium silicate and sodium hydroxide solutions and were cured in microwave radiation environment plus a heat curing period. Compressive strength and several key durability parameters for geopolymer and ordinary Portland cement (OPC) were assessed and compared. Microstructure formation and development was characterized in terms of morphology and pore structure as well as simulation.
The experimental results reveal a dense microstructure of geopolymer compared to OPC. In terms of resistance to the acidic solution and elevated temperatures, geopolymer is superior to OPC as indicated by the relatively lower strength loss and lower mass change. Compressive strength shows a dramatic drop in OPC while geopolymer shows a strength increase after 400°C. The mass loss curves of geopolymer are similar to OPC, but it shows relatively lower mass loss compared to OPC. The result of saturated water absorption after 28days curing indicates less water absorption in geopolymer before and after thermal and acid exposure. Durability of geopolymer is demonstrated by monitoring the pore structure.
The surface pretreatment by electrochemical cyclic voltammetry (CV) in the dark was found to remarkably enhance the photocurrent of Mo-doped BiVO4 from the front side illumination. The variation of ...the samples before and after the surface pretreatment was investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, and Mott–Schottky methods. The results showed that the photocurrent enhancement came from both the removal of the surface recombination center, including Mo6+ ions, and reoxidation of the reduced species. The part of the reduced ions can be reoxidized in air. However, the photocurrent enhancement from the Mo6+ dissolution can be kept at high potential under illumination. A possible mechanism was also proposed to explain the reason for the photocurrent enhancement.
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•Progress of non-oxide semiconductors for photoelectrochemical solar fuel production is summarized.•Protection strategies to increase the operational durability of non-oxide ...photoelectrodes are highlighted.•The effects of interfacial energy diagrams on charge transfer kinetics at various interfaces are presented.•Future perspectives for development of efficient and stable non-oxide solar-fuel photoelectrodes are discussed.
Among various artificial photosynthesis routes, photoelectrochemical (PEC) hydrogen (H2) production via water splitting and hydrocarbon generation via carbon dioxide (CO2) reduction are particularly intriguing for achieving a sustainable society. A simpler and potentially economical device design for PEC cells, as compared with those containing photovoltaic cells, is using semiconductor–liquid junction (SCLJ) based photoelectrodes to assemble a photoanode–photocathode tandem cell. The SCLJs form immediately upon semiconductor films immersing into electrolytes, which are then used to separate photogenerated electron–hole pairs and drive corresponding redox chemistry. To engineering these SCLJ-based photoanode–photocathode tandem PEC devices to achieving considerable solar energy conversion efficiencies, the key step is to identify suitable semiconductor materials, the core component in most solar energy conversion systems. In addition, applying effective strategies to modify these semiconductors are needed, as they cannot simultaneously meet all the requirements of efficient light absorption, charge separation and extraction, surface reaction, and operational stability at the same time. This article provides a review on promising non-oxide semiconductors for PEC conversion of solar energy into chemical fuels. The efforts to increase charge transport and separation, to accelerate the charge transfer kinetics across various interfaces, and to engender long-term durability of these non-oxide photoelectrodes are emphasized. As screening, evaluation and optimization have led to substantial improvement in both PEC performance and operational durability, non-oxide semiconductors will provide new opportunities, in addition to classical metal oxide semiconductors, to realize efficient and cost-effective PEC solar fuel production.
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•Design of crystal-facet exposed photocatalysts with various routes through altering the relative order of the surface energy.•Crystal facet-based surface junctions to promote the ...charge transfer and separation.•In situ techniques to detection of charge accumulation on crystal-faceted surfaces.•Exposed face-determined photocatalytic application from the point of the reactant adsorption and activation.
Tailoring semiconductor crystals with optimized reactive facets is considered one of effective strategies to improve photocatalytic activity and selectivity for energy conversion and environmental remediation. The arrangement of surface atom structure through crystal facet engineering could tune surface free energy, electronic band structure, charge transfer and separation, the reactant adsorption and product desorption, and surface redox sites. This progress report aims to concisely highlight recent state-of-the-art progress of crystal facet-dependent performance of promising photocatalysts beyond TiO2. It includes (1) design of crystal-facet exposed photocatalysts with various routes through altering the relative order of the surface energy; (2) crystal facet-based surface junctions to promote the charge transfer and separation; (3) in situ techniques to detection of charge accumulation on crystal-faceted surfaces; (4) exposed face-determined photocatalytic application in water splitting, photoreduction of CO2 into renewable fuels, degradation of organic contaminants from the point of the reactant adsorption and activation. The challenges and prospects for future development are also presented.
A metal‐free photoanode nanojunction architecture, composed of B‐doped carbon nitride nanolayer and bulk carbon nitride, was fabricated by a one‐step approach. This type of nanojunction (s‐BCN) ...overcomes a few intrinsic drawbacks of carbon nitride film (severe bulk charge recombination and slow charge transfer). The top layer of the nanojunction has a depth of ca. 100 nm and the bottom layer is ca. 900 nm. The nanojunction photoanode results into a 10‐fold higher photocurrent than bulk graphitic carbon nitride (G‐CN) photoanode, with a record photocurrent density of 103.2 μA cm−2 at 1.23 V vs. RHE under one sun irradiation and an extremely high incident photon‐to‐current efficiency (IPCE) of ca. 10 % at 400 nm. Electrochemical impedance spectroscopy, Mott–Schottky plots, and intensity‐modulated photocurrent spectroscopy show that such enhancement is mainly due to the mitigated deep trap states, a more than 10 times faster charge transfer rate and nearly three times higher conductivity due to the nanojunction architecture.
A B‐doped carbon nitride thin nanolayer and carbon nitride thick nanolayer were combined into a nanojunction polymer photoanode. The resulting film led to an efficient charge transport and separation in the bulk and at electrode/electrolyte interface, leading to a record IPCE of 10 % at 400 nm under one‐sun irradiation in the absence of any scavenger.
Great photoelectric properties can herald the high potentials of CsPbBr
3
nanocrystals (NCs) to function as the fluorescent probes for early tumor diagnosis. However, the intrinsic water ...vulnerability of CsPbBr
3
NCs highly restricts their biomedical applications. To conquer this challenge, we herein introduce a nature inspired "stress-response" method to tightly encapsulate CsPbBr
3
into SiO
2
nano-shells that can dramatically improve the water stability of CsPbBr
3
@SiO
2
nanoparticles for over 48 h. We further highlighted the advantageous features of CsPbBr
3
@SiO
2
by using them as the fluorescent probes for CT26 tumor cell imaging with their high water stability, biocompatibility, and low cytotoxicity. Our work for the first time exhibited the potential of lead halide perovskite NCs for tumor diagnosis, and can highly anticipate the further
in vivo
biomedical applications that light up live cells.
Two-electrode solar rechargeable device is one of the promising technologies to address the problem of solar energy storage in large scale. However, the mechanism of dark output voltage remains ...unclear and the low volumetric energy density also limits its practical applications. Herein, we report that a Si/CoO
/KBi
/MnO
Faradaic junction device exhibits a photovoltage memory effect, that is, the dark output voltage can precisely record the value of the photovoltage in the device. To investigate the mechanism of the effect, we develop an open circuit potential method to real-time monitor the photo charge and dark discharge processes in the Faradaic junction device. This effect leads to minimized interface energy loss in the Faradaic junction device, which achieves much higher performances than the devices without the effect. Moreover, we realize a portable device with a record value of the dark volumetric energy density (∼1.89 mJ cm
) among all reported two-electrode solar rechargeable devices. These results offer guidance to improve the performance of a solar rechargeable device and design other photoelectric devices for new applications.
Abstract
Energy band alignment theory has been widely used to understand interface charge transfer in semiconductor/semiconductor heterojunctions for solar conversion or storage, such as quantum-dot ...sensitized solar cells, perovskite solar cells and photo(electro)catalysis. However, abnormally high open-circuit voltage and charge separation efficiency in these applications cannot be explained by the classic theory. Here, we demonstrate a Faradaic junction theory with isoenergetic charge transfer at semiconductor/semiconductor interface. Such Faradaic junction involves coupled electron and ion transfer, which is substantively different from the classic band alignment theory only involving electron transfer. The Faradaic junction theory can be used to explain these abnormal results in previous studies. Moreover, the characteristic of zero energy loss of charge transfer in a Faradaic junction also can provide a possibility to design a solar conversion device with a large open-circuit voltage beyond the Shockley-Queisser limit by the band alignment theory.
•A novel self-evolution hourglass worm drive is proposed.•The meshing geometry theory of each evolution stages are established.•The mathematical models of the five main boundary conditions are ...established.•The evolution mechanism of meshing contact area was defined and elaborated.•Numerical analysis are simulated to verify the meshing performance evolution.
To satisfy the increasing unique characteristics of high precision and heavy-load performance in industrial equipment, a novel self-evolution hourglass worm drive is proposed in this paper. It is consisted of an involute helical beveloid (IHB) gear and an oblique planar enveloping (OPE) hourglass worm, and this worm drive gradually evolves from a local conjugate hourglass worm drive with point contact in the initial meshing state, and a middle meshing state (MES) hourglass worm drive with short-line contact with continuous operation and wear, as well as the finally evolves into a toroidal involute (TI) hourglass worm drive with line contact. According to the differential geometry theory and the spatial meshing principle, the mathematical models of this novel self-evolution hourglass worm drive are established in each evolution stage, the theory of backlash-adjustable is confirmed with introducing a pair of transition tooth surfaces, and the meshing contact area evolution mechanism was defined and elaborated. In addition, the meshing performance evolution of the contact area and the bearing capacity are simulated by numerical analysis including tooth contact analysis and finite element analysis. The analysis results show that with the continuous evolution, the contact area keeps increasing, and the bearing capacity also keeps improving. This study will provide a theoretical basis for the industrial application of this novel hourglass worm drive.
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