Strong Visible Light Absorption Research Articles

Few-Layer β - SnSe with Strong Visible Light Absorbance and Ultrahigh Carrier Mobility

Compared with traditional bulk materials, two-dimensional materials can exhibit exotic optoelectronic properties and especially provide large photoreactive contact areas, making them more attractive for designing alternative optoelectronic devices. In this work, we use first-principles methods based on density-functional theory to study the electronic and optical properties of few-layer $\ensuremath{\beta}$-$\mathrm{Sn}\mathrm{Se}$. It is found that single-layer, double-layer, and triple-layer $\ensuremath{\beta}$-$\mathrm{Sn}\mathrm{Se}$ are semiconducting with direct band gaps of 1.38, 1.20, and 1.05 eV, respectively, which fall within the optimum band gap for solar cells. For triple-layer $\ensuremath{\beta}$-$\mathrm{Sn}\mathrm{Se}$, the optical absorbance reaches 56% and the upper limit of the energy-conversion efficiency is 15.4%, which is comparable to the current efficiency record. Furthermore, few-layer $\ensuremath{\beta}$-$\mathrm{Sn}\mathrm{Se}$ has very high carrier mobility, reaching ${10}^{7}\phantom{\rule{0.1em}{0ex}}{\mathrm{cm}}^{2}/\mathrm{V}\phantom{\rule{0.1em}{0ex}}\mathrm{s}$ for triple-layer $\ensuremath{\beta}$-$\mathrm{Sn}\mathrm{Se}$. The strong visible-light absorption and high carrier mobility of few-layer $\ensuremath{\beta}$-$\mathrm{Sn}\mathrm{Se}$ provide promising opportunities for applications in solar cells.

Enhanced photocatalytic activity of silver vanadate nanobelts in concentrated sunlight delivered through optical fiber bundle coupled with solar concentrator

To date, sunlight driven photocatalytic process for wastewater treatment is a great challenge. Herein, the photocatalytic methylene blue (MB) dye degradation activity of silver vanadate nanobelts has been enhanced using concentrated sunlight irradiation. The MB dye degradation factor in normal and concentrated sunlight irradiation is 0.57 and 0.25 respectively after 120 min of light exposure. Therefore, degradation of MB dye in concentrated sunlight occurs more than two times faster than normal sunlight. The silver vanadate nanobelts have been prepared by simple hydrothermal method. The prepared nanobelts are very thin having length ranging between 5 and 10 μm and width is in the 100–300 nm range. The optical band gap of the synthesized silver vanadate nanobelts is 1.96 eV (632.5 nm), which indicates strong absorption of visible light. This work will open new technological aspects for cost-effective sustainable wastewater treatment using solar energy.

Plasmonic Ag/N-doped Graphene Nanoflakes as Electrocatalyst for Oxygen Reduction Reaction Enhanced by Solar Energy

Plasmonic Ag nanoparticles have strong spectral absorption in ultraviolet and visible light due to unique localized surface plasmon resonance effects. Meanwhile, nitrogen-doped graphene (NG) incorporates nitrogen (N) atoms into graphene lattice through a hydrothermal process, thereby providing active oxygen reduction reaction (ORR) sites. Herein, N-doped graphene decorated with plasmonic Ag nanoparticles (Ag/NG) is synthesized and utilized as ORR catalyst. The ORR performance of Ag/NG greatly exceeds that of pure NG. Its half-wave potential is 0.86 V, exceeding that of commercial Pt/C (0.83 V). Under the AM 1.5G simulated sunlight, Ag/NG demonstrates photo-enhanced electrocatalytic performance with right shifting of onset potential and half-wave potential. In this case, the half-wave potential increases by 10 mV, while the current density also rises significantly. Therefore, the Ag/NG composite provides a potential strategy for the development of solar-enhanced electrocatalysts for fuel cells and metal-air batteries.

TiO2–CdS supported CuNi nanoparticles as a highly efficient catalyst for hydrolysis of ammonia borane under visible-light irradiation

TiO2–CdS nanotubes (NTs) were used for the first time as a support to load metal nanoparticles (NPs) for the hydrolysis of ammonia borane (AB) which is a new strategy. The TiO2–CdS NTs support was first synthesized using a hydrothermal method, and then the CuNi NPs were loaded using a liquid-phase reduction method. The synthesized samples were characterized by XRD, SEM-EDS, TEM, XPS, ICP, UV–Vis, and PL analyses. The characterization results show that the CuNi NPs existed in the form of an alloy with a size of ~1.2 nm and uniformly dispersed on the support. Compared with their single metal counterparts, the bimetallic CuNi-supported catalysts showed a higher catalytic activity in the hydrolysis of AB under visible-light irradiation: Cu0·45Ni0·55/TiO2–CdS catalyst had the fastest hydrogen evolution rate with a high conversion frequency (TOF) of 25.9 molH2·molcat−1 min−1 at 25 °C and low activation energy of 32.8 kJ mol−1. Cu0.45Ni0.55/TiO2–CdS catalyst showed good recycle performance, maintaining 99.3% and 85.6% of the original hydrogen evolution rate even after five and ten recycles, respectively. Strong absorption of visible light, improved electron–hole separation efficiency, and metal synergy between Cu and Ni elements played a crucial role in improving the catalytic hydrolysis performance of AB. The catalyst prepared in this study provides a new strategy for the application of photocatalysts.

A facile fabrication of Ag2O-Ag/ZnAl-oxides with enhanced visible-light photocatalytic performance for tetracycline degradation

A facile and low-cost method to prepare novel Ag2O-Ag/LDO photocatalysts was demonstrated, where the Ag2O/Ag nanoparticles were decorated on the ZnAl oxide (LDO) supports. The LDO supports were obtained by calcining their ZnAl layered double hydroxide precursor (LDH) at different temperatures. The structure, composition, morphology and optical and electrochemical properties of the as-prepared Ag2O-Ag/LDO were characterized using various techniques. Under visible light irradiation, the Ag2O-Ag/LDO showed higher photoactivity and stability of tetracycline (TC) degradation than pure Ag2O-Ag. Especially, the Ag2O-Ag/LDO5 (Ag2O-Ag/LDO calcined at 500 °C) had the most excellent photoactivity with the highest rate constant k (0.0242 min−1), suggesting that the photocatalytic activity depended on the calcination temperature. The enhancement of the photocatalytic performance was attributed to the formation of the heterostructure between Ag2O/Ag and ZnO, the strong visible-light absorption and outstanding separation efficiency of photoinduced electron-hole pairs under visible light irradiation.

Highly efficient heterojunction solar cells enabled by edge-modified tellurene nanoribbons.

Tellurene, a two-dimensional (2D) semiconductor, meets the requirements for optoelectronic applications with desirable properties, such as a suitable band gap, high carrier mobility, strong visible light absorption and high air stability. Here, we demonstrate that the band engineering of zigzag tellurene nanoribbons (ZTNRs) via edge-modification can be used to construct highly efficient heterojunction solar cells by using first-principles density functional theory (DFT) calculations. We find that edge-modification enhances the stability of ZTNRs and halogen-modified ZTNRs showing suitable band gaps (1.35-1.53 eV) for sunlight absorption. Furthermore, the band gaps of ZTNRs with tetragonal edges do not strongly depend on the edge-modification and ribbon width, which is conducive to experimental realization. The heterojunctions constructed by halogen-modified ZTNRs show desirable type 2 band alignments and small band offsets with reduced band gaps and enhanced sunlight absorption, resulting in high power conversion efficiency (PCE) in heterojunction solar cells. In particular, the calculated maximum PCE of designed heterojunction solar cells based on halogen-modified ZTNRs can reach as high as 22.6%.

Surface defect engineering of mesoporous Cu/ZnS nanocrystal-linked networks for improved visible-light photocatalytic hydrogen production

Cu-doped ZnS nanocrystal-linked mesoporous frameworks possessing suitable electronic energy levels, strong visible-light absorption and large porosity with a low defective surface show efficient photocatalytic H2 evolution activity from water splitting.

A N–H functionalized perylene diimide with strong red-light absorption for green solvent processed organic electronics

The synthesis of a perylene diimide semiconductor using simple condensation chemistry that exhibits strong visible light absorption, green solvent solubility, and n-type charge mobility behavior.

Effect of Rh valence state and doping concentration on the structure and photocatalytic H2 evolution in (Nb,Rh) codoped TiO2 nanorods.

The simultaneous realization of visible light response and high photocatalytic activity remains a challenging task for TiO2 despite extensive research. Herein, (Nb,Rh) codoping is adopted to extend the absorption band of anatase TiO2 into the visible-light region. Meanwhile, the dependence of the electronic structure, visible-light absorption, and photocatalytic performance on the dopant ratio as well as doping concentration is studied. Open shell t2g5 Rh(iv) and closed shell t2g6 Rh(iii) coexist in Rh-doped TiO2, and the codoped Nb promotes a change in valence state from Rh(iv) to Rh(iii). Rh(iii) is the main active species in charge of the excellent photocatalytic performance, while Rh(iv) doping introduces electron/hole recombination centres. However, surprisingly, a trace of Rh(iv)-doping contributes to a decrease in electron transfer resistance and an increase in donor density, which help to improve photocatalytic performance. By virtue of the controlled content of Rh(iii) and Rh(iv), Ti1-2xNbxRhxO2 exhibits a high hydrogen evolution rate of ∼9000 μmol g-1 h-1 in methanol solution, along with a remarkable photocurrent density of ∼9 μA cm-2 under visible-light irradiation, which are about 170 and 30 times higher than those of pristine TiO2 nanorods, respectively.

ZnPc/TiO2 composites for photocathodic protection of 304 stainless steel

ZnPc/TiO2 composites were synthesized by a drop-coating method and used as photoanodes for photocathodic protection to slow the corrosion of 304 stainless steel (304SS). TiO2 is a wide-band-gap (3.2 eV) conductor that only absorbs UV light with a wavelength <380 nm, and the recombination rate of photogenerated carriers in TiO2 is high. Zinc phthalocyanine (ZnPc) is a material with strong visible-light absorption. The combination of ZnPc and TiO2 can increase the absorption of visible light. Furthermore, the lowest unoccupied molecular orbital (LUMO) conduction-band level of ZnPc is higher than that of TiO2; thus, the electrons in ZnPc excited by the light can migrate to the conduction band of TiO2, thereby accelerating the separation of electrons and holes. The results show that the visible-light absorption of the ZnPc/TiO2 composite is markedly improved compared with that of TiO2 alone. The open-circuit potential (OCP) of 304SS coupled with the ZnPc/TiO2 composite decreased substantially compared with that of 304SS coupled with pure TiO2, reaching approximately −700 mV. The proposed ZnPc/TiO2 composites offer superior photocathodic protection for 304SS.

Preparation of quinary CuNixZn2−xInS4 nanocrystals with wurtzite structure and tunable band gap

As the typical multifunctional materials, multinary metal chalcogenides have attracted tremendous attention due to their broad applications. In this work, quinary chalcogenide CuNixZn2−xInS4 (x = 0–2) nanocrystals with a wurtzite structure have been successfully synthesized for the first time by a solution method. The phase structure analysis suggests that the fabricated wurtzite phase has a disordered structure in which all metal cations share the same position and have a random distribution in the unit cell. The transmission electron microscopy results reveal that the products show a morphological evolution from sphere-like nanocrystals of CuZn2InS4 (x = 0) to bullet-like nanocrystals of CuNi2InS4 (x = 2) together with a growing particle size. All the as-obtained wurtzite CuNixZn2−xInS4 nanocrystals show a strong and broad visible light absorption. More importantly, the band gap energy of these nanocrystals can be readily tuned from 2.20 eV to 1.44 eV by varying the value of x from 0 to 2, which decreases almost linearly with the composition x. This work demonstrates a new series of I–II2–III–VI4 group chalcogenide semiconductors.

Big-leaf hydrangea-like Bi2S3-BiOBr sensitized TiO2 nanotube arrays with enhanced photoelectrocatalytic performance.

TiO2 nanoparticles as solar cells and photocatalysts caused extensive attention in solar energy utilization and environment remediation due to the high photoelectrochemical performance. We demonstrated a novel approach to fabricate big-leaf hydrangea-like Bi2S3-BiOBr self-assembled by superthin nanosheets on TiO2 nanotube arrays (TiO2 NTs/B2S3-BiOBr). Results indicated that the Bi2S3-BiOBr co-sensitization showed higher photoelectric conversion efficiency than the single Bi2S3 or BiOBr sensitization. More remarkably, TiO2 NTs/B2S3-BiOBr showed excellent photoelectrocatalytic (PEC) removal of MB, MO, RhB and Cr(VI). The remarkable PEC performance could be attributed to the strong visible light absorption and effective electron transportation at the interface of TiO2/B2S3-BiOBr. The high photoelectrochemical performances indicate that the TiO2 NTs/B2S3-BiOBr could work as potential photoelectric materials for large-scale applications in the photoelectrochemical energy conversion and pollutant removal.

Microfluidic Reactors for Plasmonic Photocatalysis Using Gold Nanoparticles.

This work reports a microfluidic reactor that utilizes gold nanoparticles (AuNPs) for the highly efficient photocatalytic degradation of organic pollutants under visible light. The bottom of microchamber has a TiO2 film covering a layer of AuNPs (namely, TiO2/AuNP film) deposited on the F-doped SnO2 (FTO) substrate. The rough surface of FTO helps to increase the surface area and the AuNPs enables the strong absorption of visible light to excite electron/hole pairs, which are then transferred to the TiO2 film for photodegradation. The TiO2 film also isolates the AuNPs from the solution to avoid detachment and photocorrosion. Experiments show that the TiO2/AuNP film has a strong absorption over 400–800 nm and enhances the reaction rate constant by 13 times with respect to the bare TiO2 film for the photodegradation of methylene blue. In addition, the TiO2/AuNP microreactor exhibits a negligible reduction of photoactivity after five cycles of repeated tests, which verifies the protective function of the TiO2 layer. This plasmonic photocatalytic microreactor draws the strengths of microfluidics and plasmonics, and may find potential applications in continuous photocatalytic water treatment and photosynthesis. The fabrication of the microreactor uses manual operation and requires no photolithography, making it simple, easy, and of low cost for real laboratory and field tests.

Electronic, magnetism, and optical properties of transition metals adsorbed g-GaN

Abstract The electronic, magnetism, and optical absorption behaviors of transition metals adsorbed g-GaN systems were investigated by employing density functional theory based on first-principles calculations. The results demonstrate that the most stable adsorption sites of different transition metals on g-GaN are different. The observed the Ni, Pt, and Zn adsorbed g-GaN systems exbibit nonmagnetic semiconductors, whereas the Au, Co, Cr, Cu, Fe, and Mn adsorbed g-GaN systems appear magnetic semicondutors, and the Sc, Ti, and V adsorbed g-GaN systems show magnetic metal behaviours. Furthermore, the charge transfer occurs between the g-GaN and TM, demonstrating a covalent bonding features in the appeared between TM and under-coordinated atoms. The work function of the Co, Cr, Cu, Fe, Mn, Ni, Sc, Ti, and V adsorbed g-GaN systems are lower than that of pristine g-GaN. Importantly, the absorption spectrum of transition metals adsorbed g-GaN systems have many strong visible light absorption peak, which located about in 471.3 nm, 495.8 nm, 517.6 nm, 574.4 nm, 627.5 nm, 672.3 nm and 717.1 nm. The adsorption of TM on g-GaN has a wide range of adjustment in solar energy spectrum. Thus, above results indicate that transition metals adsorbed g-GaN systems will facilitate design of nano-spintronics and high efficiency photocatalysts device.

Preparation of BiOCl/Bi2S3 composites by simple ion exchange method for highly efficient photocatalytic reduction of Cr6+

A series of hollow spherical BiOCl/Bi2S3 composites were fabricated via a simple ion exchange method under 80 °C water bath. Based on BiOCl's hollow spherical morphology, a reasonable formation process was proposed. Interestingly, the as-prepared BiOCl/Bi2S3 composites maintained the morphology of the BiOCl precursor well. Compared with pure BiOCl, the BiOCl/Bi2S3 composites have excellent photocatalytic activity for the reduction of hexavalent chromium (Cr6+). Remarkably, BiOCl/Bi2S3-4h exhibits the highest reduction efficiency (kapp = 0.400 min−1), which could be mainly attributed to the construction of BiOCl/Bi2S3 composites. The hollow spherical BiOCl/Bi2S3 composites have strong visible light absorption, high separation rate of electron-hole pairs, fast electronic transmission and a relatively large specific surface area. Meanwhile, the feasible mechanism of photocatalytic reduction was further discussed in detail.

Single-band near-infrared upconversion emission and visible-light absorption in highly doped pseudo-perovskite oxides

Currently, concentration-induced near-infrared upconversion quenching at highly doped levels of lanthanide ions poses a significant constraint for their practical applications. In this work, the fabricated Tm3+/Yb3+ codoped Na0.5Bi2.5Nb2O9 (NBN) materials with a layered structure exhibited a single-band near-infrared to near-infrared upconversion emission (808 nm emission, 980 nm excitation) with no obvious concentration quenching even with a higher Yb3+ content of 90 mol%, while maintaining excellent thermal stability. Meanwhile, the Tm3+/Yb3+ co-doped NBN materials showed strong visible-light absorption at 400-800 nm under the irradiation with sunlight (AM1.5), and the absorbed light can be released via a thermal stimulus, showing a typical photochromic reaction. The near-infrared upconversion emission intensity was effectively tuned after and before sunlight irradiation. This research provides a new strategy for designing high-efficiency near-infrared upconversion and visible photoresponsive oxides for near-infrared modulation, solar energy conversion, and other multifunctional applications.

Synthesis and degradation kinetics of TiO2/GO composites with highly efficient activity for adsorption and photocatalytic degradation of MB

Poriferous TiO2/GO (denoted as TGO-x%) photocatalysts with ultrathin grapheme oxide (GO) layer were prepared by a hydrothermal method, the adsorption and photocatalytic degradation and its kinetics about Methylene blue(MB) were studied systematically. All the TGO-x% showed improved adsorption and photodegradation performance. TGO-25% had excellent adsorptivity while TGO-20% exhibit the highest visible light photocatalytic degradation activity. The adsorption capacity for TGO-25% was 20.25 mg/gcatalyst along with the k1 was about 0.03393 min·gcatalyst/mg, this enhancement was mainly owing to the strong adsorption capacity of GO and the stacking structure of sheets and nanoparticles. GO sheets prevented the agglomeration of TiO2 particles and TiO2 nanoparticles also prevented the agglomeration of GO sheets, which could provides greater surface area. Besides, the remarkably superior photodegradation activity of TiO2/GO composites is mainly attribute to the strong absorption of visible light and the effective charge separation revealed by the photoluminescence, the total removal rate of MB is 97.5% after 35 min adsorption and 140 min degradation, which is 3.5 times higher than that of TiO2.

Visible light driven MoS2/α-NiMoO4 ultra-thin nanoneedle composite for efficient Staphylococcus aureus inactivation

MoS2/α-NiMoO4 ultra-thin nanoneedle composite was synthesized by microwave hydrothermal process in one step. The nanocomposite revealed the complete destruction of multidrug resistant Staphylococcus aureus (S. aureus) within 150 min under visible light irradiation. According to electron spin resonance measurement and radical trapping experiment, it has been established that O2¯ acts as a major active species for bacterial inactivation in visible light. The bacterial inactivation was further proved by membrane deformities in bacterial cell membrane, DNA fragmentation, and protein destruction. TEM- elemental mapping confirms the inactivation of S. aureus by reactive oxygen species (ROS) but not the toxicity of photocatalyst. Transient photocurrent responses, electrochemical impedance spectroscopy, and cyclic voltammetry measurements reveal the efficient separation of electron-hole pairs in the composite photocatalyst. The composite photocatalyst shows greater ROS production, higher degree of DNA fragmentation and protein degradation, detrimental effects on the morphology of the bacterial cell wall, outstanding transient photocurrent responses, reduction of interfacial charge transfer resistance, superb oxidation/reduction potential, strong visible light absorption, and adequate separation of photogenerated electron-hole pairs as compared to host photocatalyst. The photocatalytic inactivation mechanism was explained. So, this promising composite photocatalyst can be applied for inactivation of multidrug resistant bacteria in biological waste water.

Indoor Photovoltaics: Photoactive Material Selection, Greener Ink Formulations, and Slot-Die Coated Active Layers.

Strong visible light absorption is essential to achieve high power conversion efficiency in indoor organic photovoltaics (iOPVs). Here, we report iOPVs that exhibit high efficiency with high voltage under excitation by low power indoor lighting. Inverted type organic photovoltaic devices with active layer blends utilizing the polymer donor PPDT2FBT paired with fullerene, perylene diimide, or ring-fused acceptors that are 6.5-9.1% efficient under 1 sun are demonstrated to reach efficiencies from 10 to 17% under an indoor light source. This performance transcends that of a standard silicon photovoltaic device. Moreover, we compared iOPVs with active layers both spin-cast and slot-die cast from nonhalogenated solvents and demonstrate comparable performance. This work opens a path towards high-efficiency iOPVs for low power electronics.

Mineralogical characteristics and photocatalytic properties of natural sphalerite from China

Different natural sphalerites have a range of photocatalytic properties that can potentially be exploited for environmental remediation purposes. To develop value in the exploitation of sphalerite, samples were collected from 19 ore deposits in China and characterized for their mineralogical and photocatalytic properties. X-ray diffraction (XRD) and electron probe micro analysis (EPMA) measurements indicated that all the natural sphalerites from various localities crystallized in cubic phases with various chemical compositions. The substitution of Fe for Zn ranged from 0.235% to 14.826% by weight, Mn from 0.004% to 4.868%, Cu from 0.009% to 5.529% and Cd from 0.133% to 1.576%. As Fe became more abundant, the color of natural sphalerite darkened, becoming almost black; and higher Fe content was associated with stronger visible light absorption. Photoluminescence spectra showed emission mainly related to S-vacancies and progressively decreasing fluorescence intensity with increasing Fe content. Tests of the photocatalytic degradation of methyl orange indicated that the sample with the highest Cd content but moderate Fe content had the highest photocatalytic activity. Specifically, the degradation of Methyl Orange (30 mg/L) attained 82.11% efficiency under visible light irradiation for 4 hr of natural sphalerite with 4.262% Fe and 1.576% Cd. Overall, the Fe content in sphalerite was found to contribute to the visible light absorption ability and the recombination rate of photo-generated electrons and holes, while substitution by Cd was observed to have a greater effect on the photocatalytic properties. These findings provide a scientific basis for the profitable utilization of base metal resources like sphalerite.