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Design of visible-light photocatalysts by coupling of inorganic semiconductors
摘要： The design of advanced photocatalytic systems, effectively working under visible-light, is essential for practical application of photocatalysts in removing environmental pollutants. To achieve high efficiency, the required properties for the photocatalysts are profound solar light absorption in the visible-range, efficient charge-separation, suitable energy band locations for redox reactions, and extended photostability. As a single semiconductor-based photocatalyst cannot satisfy all of these requirements, a potential strategy will be construction of coupled structures between two or more semiconductors. In the present study, we explore various types of photocatalytic systems constructed by coupling semiconductors and their working mechanisms. When two narrow bandgap semiconductors (NBSs) absorbing visible-light are coupled to form heterojunction structures, they can be classified as p-n junction or Z-scheme systems, according to the charge-flow pathway between the two semiconductors. When a NBS that absorbs visible-light is coupled with a wide bandgap semiconductor (WBS) functioning as the main photocatalyst, the fabricated catalytic systems can be classified as Type-A or Type-B heterojunction systems dependent on their relative energy band locations. Herein various semiconductor composites reported to be visible-light photocatalysts in the literature are classified using these categories, and their photocatalytic mechanisms, including charge-flow pathways, are discussed in depth. In addition, recent progress and future perspectives for heterojunction systems are reviewed and discussed.
关键词： Oxidation reaction,Coupling of semiconductors,Type-B heterojunction,Heterojunction,Visible light,Photocatalyst
更新于2025-09-09 09:28:46
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Visible-light optical coherence tomography-based multimodal system for quantitative fundus autofluorescence imaging
摘要： Fundus autofluorescence (FAF) imaging is commonly used in ophthalmic clinics for diagnosis and monitoring of retinal diseases. Lipofuscin in the retinal pigment epithelium (RPE), with A2E as its most abundant component and a visual cycle by-product, is the major fluorophore of FAF. Lipofuscin accumulates with age and is implicated in degenerative retinal diseases. The amount of lipofuscin in RPE can be assessed by quantitative measurement of FAF. However, the currently available FAF imaging technologies are not capable of quantifying the absolute intensity of FAF, which is essential for comparing images from different individuals, and from the same individual over time. One major technical difficulty is to compensate the signal attenuation by ocular media anterior to the RPE (pre-RPE media). FAF intensity is also influenced by fluctuations in imaging conditions such as illumination power and detector sensitivity, all of which need to be compensated. In this review, we present the concept and research progress of using visible-light optical coherence tomography-based simultaneous multimodal retinal imaging to compensate signal attenuation by pre-RPE media and the influence of parameters of the acquisition system for accurate measurement of FAF intensities.
关键词： fundus autofluorescence imaging,multimodal imaging,retinal pigment epithelium lipofuscin,Visible-light optical coherence tomography,retinal imaging,fluorescence quantification
更新于2025-09-09 09:28:46
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Visible light enhanced black NiO sensors for ppb-level NO2 detection at room temperature
摘要： Although extensive studies have been carried out on n-type semiconductors for room-temperature gas sensor applications, some intrinsic problems remain. Therefore, other interesting attempts should be adopted to solve these issues, like p-type semiconductors. Previous studies have demonstrated that p-type semiconductor gas sensors exhibit better selectivity and less humidity dependence due to the distinctive oxygen adsorption and surface reactivity. Visible light is used as the external activation source to accelerate the sensing kinetics instead of heating. Stoichiometric NiO cannot absorb visible lights. Inspired by the works of black TiO2, we adopted three methods to prepare black NiO. XPS characterizations reveal that the presence of Ni3+ ions leads to the formation of black NiO. However, not all black NiO samples show good responses to NO2 at room temperature. Three main routes: synthesizing specific morphology with large specific surface area and porosity, introduction of Ni3+ ions and oxygen vacancies, are needed to get the enhanced sensing performance. The black NiO samples with large specific surface area and oxygen vacancies and Ni3+ ions show obvious response towards ppb-level NO2 with visible light irradiation at room temperature. Furthermore, light wavelength is found to play a vital role in the sensing characteristics, and blue light is the optimal choice. Different from traditional NiO sensors operated at high temperatures exhibiting superior response to reducing gases, the black NiO show excellent selectivity towards oxidizing gas, ppb-level NO2, at room temperature illuminated by blue light. In contrast with n-type semiconductors, the black NiO samples also exhibit less humidity dependence.
关键词： Room temperature,NO2 sensor,NiO,Visible light irradiation
更新于2025-09-09 09:28:46
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Polyaniline based hybrid bionanocomposites with enhanced visible light photocatalytic activity and antifungal activity
摘要： Nickel doped polyaniline/cellulose bionanocomposites have been synthesized via in-situ polymerization of aniline and hydrothermally prepared nickel nanoparticles. The as prepared materials were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV-vis) spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). Cyclic Voltammetry (CV) was used to determine the electrochemical surface area (ECSA) of the materials by using the electrochemical double layer capacitance (EDLC) data. SEM images reveal that synthesized nanocomposites contain spherical Ni nanoparticles scattered uniformly within PANI-Cellulose matrix. The as prepared materials exhibited significant degradation of reactive orange (RO-16) dye under visible light. Incorporation of Ni nanoparticles in to the polymer matrix causes strong adsorption of dye in case of PANI/C/Ni, PANI/Ni as compared to that of PANI. The photodegradation of RO-16 was achieved by the electron-hole pair separation and formation of reactive species by trapping of the photo generated electron from the surface of photo catalyst. Scavengers were added to identify the primary reactive species. Fluorescence spectroscopy was to study the recombination behavior of charge carriers (electron-hole pair) during photodegradation. Moreover, the anti-fungal nature of the bionanocomposites was also examined and the materials were found to be effective in growth control of two pathogenic fungal strains- Rhizoctonia solani and Alternaria alternate.
关键词： Visible light,Capacitance,Antifungal,Absorption,Nanoparticle,Electron-hole pair
更新于2025-09-09 09:28:46
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Multiple Access Design for Ultra-Dense VLC Networks: Orthogonal v.s. Non-Orthogonal
摘要： Small cell aided ultra-dense networks (UDN) constitute an efficient solution to the ever-increasing thirst for more data. Thanks to the vast untapped high-frequency spectrum of visible light, visible light communications (VLC) is a natural candidate for UDN. In this paper, layered asymmetrically clipped optical OFDM (LACO-OFDM) aided ultra-dense VLC (UD-VLC) is investigated in terms of its user-association, multiple access (MA) and resource allocation. To handle the severe inter-cell interference (ICI) amongst the densely-deployed access points (AP), we propose a novel overlapped clustering technique relying on a hybrid non-orthogonal MA (NOMA) and orthogonal MA (OMA) scheme for enhancing the performance, with the aid of our dynamic resource allocation conceived. Our simulations show that the proposed LACO-OFDM aided UD-VLC using our hybrid MA scheme is more robust against the ICI, at a price of modestly decreasing the sum-throughput.
关键词： visible light communications (VLC),resource allocation,non-orthogonal multiple access (NOMA),Ultra-dense network (UDN),multiple access (MA)
更新于2025-09-09 09:28:46
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Noise Analysis and Modeling in Visible Light Communication Using Allan Variance
摘要： Visible Light Communication (VLC) is a rising communication technology which uses Light-Emitting Diode (LED) luminaries for high-speed data transferring; however, the optical signal is usually degraded by the noise in the practical VLC system. In this article, Allan Variance is introduced for noise analysis and modeling in VLC for the first time, which provides an efficient method to measure different kinds of noise in the VLC systems. By applying Allan variance to analyze the signals collected from the real-world environment, both white noise and random walk are observed in the VLC systems. The observed white noise and random walk are also modeled by using the Allan variance. The noise analysis and modeling based on Allan variance provide a method to improve the performance of VLC.
关键词： Visible Light Communication (VLC),random walk,white noise,Allan Variance,time-correlated noise,photodiode
更新于2025-09-09 09:28:46
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Substituent Effect on Metastable‐State Photoacids: Design, Synthesis and Evaluation of their Photochemical Properties
摘要： Recently, metastable-state photoacids have been widely used to control proton transfer in numerous chemical and biological processes as well as applications with visible light. Generally, substituent groups have great influence on photochemical properties of molecules, which will further affect their applications. Yet, substituent effect on the metastable-state photoacid has not been studied systematically. In this work, sixteen metastable-state photoacid derivatives were designed and synthesized based on their substituents involving a large range of σ-π electron-donor-acceptor capability. Substituent effects main on their color display (or maximum absorption peak(s)), solubility, pKa(s), dark-/photo-acidity, photosensitivity and relaxation kinetic(s) were investigated in detail. This study will be conducive to targetedly design and synthesize promising photoacids as well as to apply their photo-controlled proton-release processes in functional materials/devices.
关键词： visible-light-response,metastable-state photoacid,pH photocontrol,substituent effect,chemical dynamics
更新于2025-09-09 09:28:46
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Visible light accelerates the ultraviolet A-induced degradation of eumelanin and pheomelanin
摘要： Exposure to excess ultraviolet (UV) A radiation induces the degradation/modification of both eumelanin and pheomelanin that may be deleterious to pigmented tissues. Although the spectral distribution of solar energy comprises nearly half of visible light (VL), few studies have been conducted to examine the role of VL in the photodegradation of both types of melanin, either VL alone or in combination with UVA. In this study, we examined the effects of physiological doses of VL (150 to 300 J/cm2) alone or in combination with a physiological dose of UVA (20 J/cm2) in normal human epidermal melanocytes. The degradation/modification of melanin structures were evaluated by our chemical degradation – HPLC methods. The results show that VL accelerates UVA-induced changes in the structural features of both eumelanin and pheomelanin, although VL or UVA alone induced only minor changes in melanin structure. The differential spectral method provides support for the additive effects of VL.
关键词： visible light,eumelanin,photodegradation,pheomelanin,ultraviolet A
更新于2025-09-09 09:28:46
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[ACM Press the 1st International Workshop - New Delhi, India (2018.10.29-2018.10.29)] Proceedings of the 1st International Workshop on Communication and Computing in Connected Vehicles and Platooning - C3VP '18 - On Feasibility of VLC Based Car-to-Car Communication Under Solar Irradiance and Fog Conditions
摘要： This paper investigates the impact of solar irradiance and fog condition on visible light communication (VLC) based car-to car (C2C) communication for two capital cities, New Delhi and London. The bit error rate (BER) variation over a day has been compared for both the cities for the month of March, June and December. It has been shown that for a given BER threshold performance, the impact of solar irradiance is more pronounced in month of June especially at New Delhi when solar irradiance reaches its peak. It has also been shown that in month of December, fog is one of the most significant climatic factors that greatly influences the VLC based C2C communication in terms of atmospheric attenuation. This paper also establishes the relationship for the minimum safety distance required between cars based on two-second rule, car speed and angle between cars. The minimum safety distance which would be required to avoid any rear-end collision especially during light or dense fog in the month of December has also been compared for New Delhi and London.
关键词： safety distance,fog conditions,solar irradiance,car-to-car communication,visible light communication,bit error rate
更新于2025-09-09 09:28:46
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Degradation of Rhodamine B Under Visible-Light by Cu-Doped ZnAl Layered Double Hydroxide
摘要： The Cu-doped ZnAl layered double hydroxides (LDH) were papered by coprecipitation. The prepared samples were characterized by mutiple techniques including X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area, scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse-re?ectance spectroscopy (UV-vis DRS). The doping of Cu2+ into the LDH sheets results in formation of the distorted CuO6 octahedrons which contribute for the excitation of electrons under visible light. The doped Cu2+ also serves as photo-generated charges separator and improves the visible-light-driven photocatalytic activity of ZnAl LDH. A degradation mechanism based on the hydroxyl radical as the active species was proposed.
关键词： RhB Degradation,Visible Light,Copper-Doping,Layered Double Hydroxides
更新于2025-09-09 09:28:46