Wide Light Absorption Range Research Articles

Integration of Plasmonic Effects and Schottky Junctions into Metal–Organic Framework Composites: Steering Charge Flow for Enhanced Visible‐Light Photocatalysis

AbstractA wide range of light absorption and rapid electron–hole separation are desired for efficient photocatalysis. Herein, on the basis of a semiconductor‐like metal–organic framework (MOF), a Pt@MOF/Au catalyst with two types of metal–MOF interfaces integrates the surface plasmon resonance excitation of Au nanorods with a Pt‐MOF Schottky junction, which not only extends the light absorption of the MOF from the UV to the visible region but also greatly accelerates charge transfer. The spatial separation of Pt and Au particles by the MOF further steers the formation of charge flow and expedites the charge migration. As a result, the Pt@MOF/Au presents an exceptionally high photocatalytic H2 production rate by water splitting under visible light irradiation, far superior to Pt/MOF/Au, MOF/Au and other counterparts with similar Pt or Au contents, highlighting the important role of each component and the Pt location in the catalyst.

Bismuth Tantalum Oxyhalogen: A Promising Candidate Photocatalyst for Solar Water Splitting

AbstractAs wide range of light absorption and suitable redox potentials are prerequisites for photocatalytic water splitting, exploring new semiconductor‐based materials with proper band structures for water splitting still calls for longstanding efforts. In this work, a series of photocatalysts, bismuth tantalum oxyhalide, Bi4TaO8X (X = Cl, Br), with valence band and conduction band positions at ≈−0.70 and ≈1.80 eV versus the reversible hydrogen electrode (RHE), respectively, are found to be capable for both water oxidation and reduction under visible light irradiation. Using flux synthetic methods, Bi4TaO8X (X = Cl, Br) with microplatelet morphology can be successfully prepared. The photocatalyst based on these materials shows an apparent quantum efficiency as high as 20% at 420 nm for water oxidation. In addition, a Z‐scheme system coupling Bi4TaO8Br with Ru/SrTiO3:Rh is successfully achieved for overall water splitting with a stoichiometric ratio of H2 and O2 evolutions. This work demonstrates a new series of semiconductors Bi4TaO8X (X = Cl, Br) with the promising application in the field of solar energy utilization.

Constructing the novel ultrafine amorphous iron oxyhydroxide/g-C3N4 nanosheets heterojunctions for highly improved photocatalytic performance

Ultrafine particles, more heterojunction interfaces and amorphous materials can effectively enhance the photocatalytic activity of photocatalysts. In this work, a facile in-situ precipitation method was developed to prepare ultrafine amorphous iron oxyhydroxide/ultrathin g-C3N4 nanosheets heterojunction composites. The amorphous iron oxyhydroxide possessed an ultrafine particle size and a wide range of visible light absorption. In this process, the ultrafine particles not only shortened the diffusion distance of photogenerated carriers, but also facilitated the formation of more heterojunctions with ultrathin g-C3N4 nanosheets. The photocatalytic activities were evaluated using rhodamine B, methylene blue, and methyl orange as pollution models under visible light irradiation. Notably, the optimal photocatalytic activity of a-FeOOH/CNNS-800 composite is ~17.8 times higher than that of CNNS towards the degradation of rhodamine B under visible light. The outstanding photocatalytic activities were ascribed to the narrower band gap, the enhanced visible light absorbance, abundant heterojunction interfaces, and the effective separation of the photogenerated charges driven by the matched band edge in the heterostructures. We trusted that the facile and easy-to-extend synthesis method can be further expanded to synthesize other ultrafine semiconductors coupled with g-C3N4 for enhancing the photocatalytic activities.

Synthesis and Characterization of CH<sub>3</sub>NH<sub>3</sub>Pb<sub>1-x</sub>Sn<sub>x</sub>I<sub>3</sub> Crystal

The CH3NH3PbI3 light-absorbing layer shows preferably photovoltaic performance. However, comparing with CH3NH3PbI3 film, the CH3NH3SnI3 film show smaller band gap and wider light absorption range, meanwhile, it is non-toxic and environmental friendly solar cell material. In this paper, different proportions of tin (Sn) was doped into CH3NH3PbI3 film, the atomic ratio of lead-tin strictly controlled to form CH3NH3SnI3 from CH3NH3PbI3. The five different proportions of doping CH3NH3Pb1-xSnxI3 perovskite powders were studied. The morphology of powders was observed by scanning electron microscopy (SEM). X-ray diffraction (XRD) and energy dispersive spectrum (EDS) were used to analyze the crystallization and the proportion composition of powders, respectively. The experimental results show that the powder crystal orientation was very obvious at the ratio of lead-tin around 1:1.99 and the atomic ratio close to the ideal stoichiometric ratio of doped atoms.

Effects of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>(3-x)</sub>Cl<sub>x</sub> Perovskite Layer on the Performance of Inverted Type Hybrid Organic Solar Cells Based on ZnO/P3HT

This paper reports the effect of perovskite layer on enhancing the inverted type hybrid organic solar cell performance. The mixtures of methylammonium iodide (CH3NH3I) and lead (II) chloride (PbCl2) were dissolved in N,N-Dimethylformamide (DMF) solvent and was spin-coated onto fluorine-doped tin oxide (FTO) glass substrate coated with zinc oxide nanorod arrays (ZnONRAs). The poly (3-hexylthiophene-2,5-diyl) (P3HT) film was then spin-coated onto CH3NH3I(3-x)PbClx perovskite layer, followed by silver (Ag) deposition using magnetron sputtering technique. The FTO/ZnO seed/ZnONRAs/CH3NH3PbI(3-x)Clx /P3HT/Ag device was fabricated. A device without perovskite layer was also fabricated for comparison. A power conversion efficiency (PCE) of 0.56% was achieved with the introduction of perovskite layer. The PCE was approximately six times greater than the device without perovskite layer, as a result of wider light absorption range and higher exciton dissociation efficiency.

Surface Defects Enhanced Visible Light Photocatalytic H2 Production for Zn-Cd-S Solid Solution.

In order to investigate the defect effect on photocatalytic performance of the visible light photocatalyst, Zn-Cd-S solid solution with surface defects is prepared in the hydrazine hydrate. X-ray photoelectron spectra and photoluminescence results confirm the existence of defects, such as sulfur vacancies, interstitial metal, and Zn and Cd in the low valence state on the top surface of solid solutions. The surface defects can be effectively removed by treating with sulfur vapor. The solid solution with surface defect exhibits a narrower band gap, wider light absorption range, and better photocatalytic perfomance. The optimized solid solution with defects exhibits 571 μmol h(-1) for 50 mg photocatalyst without loading Pt as cocatalyst under visible light irradiation, which is fourfold better than that of sulfur vapor treated samples. The wavelength dependence of photocatalytic activity discloses that the enhancement happens at each wavelength within the whole absorption range. The theoretical calculation shows that the surface defects induce the conduction band minimum and valence band maximum shift downward and upward, respectively. This constructs a type I junction between bulk and surface of solid solution, which promotes the migration of photogenerated charges toward the surface of nanostructure and leads to enhanced photocatalytic activity. Thus a new method to construct highly efficient visible light photocatalysts is opened.

Modifying Poly(Vinyl Alcohol) (PVA) from Insulator to Small-Bandgap Polymer: A Novel Approach for Organic Solar Cells and Optoelectronic Devices

An innovative method has been used to reduce the bandgap of poly(vinyl alcohol) (PVA) polymer by addition of a nontoxic, inexpensive, and environmentally friendly material. The resulting materials are small-bandgap polymers, hence opening new frontiers in green chemistry. The doped PVA films showed a wide range of light absorption of the solar spectrum from 200 nm to above 800 nm. Nonsharp absorption behavior versus wavelength was observed for the samples. The refractive index exhibited a wide range of dispersion. Shift of the absorption edge from 6.2 eV to 1.5 eV was observed. The energy bandgap of PVA was diminished to 1.85 eV upon addition of black tea extract solution, lying in the range of small-bandgap polymers. Increase of the optical dielectric constant was observed with increasing tea solution addition. The results indicate that small-bandgap PVA with good film-forming ability could be useful in terms of cost–performance tradeoff, solving problems of short lifetime, cost, and flexibility associated with conjugated polymers. The decrease of the Urbach energy upon addition of black tea extract solution indicates modification of PVA from a disordered to ordered material. X-ray diffraction results confirm an increase of the crystalline fraction in the doped samples.

A strategy to boost the cell performance of CdSexTe1−x quantum dot sensitized solar cells over 8% by introducing Mn modified CdSe coating layer

CdSexTe1−x alloyed colloidal quantum dots show great potential application on quantum dot-sensitized solar cells (QDSCs) due to its relatively wide light absorption range and high chemical stability. In this respect, a thin Mn modified CdSe layer is introduced into TiO2/CdSexTe1−x alloyed QDs surface via a simple chemical bath deposition method (CBD) in order to further improve the cell performance. The power conversion efficiency of CdSexTe1−x QDSCs has been improved to 8.14%. Detailed investigation on the influence of this modification toward the TiO2/CdSexTe1−x interface on the cell performance reveals that introduction of Mn into CdSe QDs is found to facilitate the Mn-doped CdSe deposition and improve the light absorption of the device. In the meantime, the existence of the (Mn-)CdSe layer can also work as a passivation layer to reduce charge recombination.

Solution-Processed Gold Nanorods Integrated with Graphene for Near-Infrared Photodetection via Hot Carrier Injection.

Graphene-based photodetectors have attracted wide interest due to their high-speed, wide-band photodetection and potential as highly energy-efficient integrated devices. However, the inherently low-absorption cross-section and nonselective spectra response hinder its utilization as a high-performance photodetector. Here, we report a solution-processed and high-spectral-selectivity photodetector based on a gold nanorods (Au NRs)-graphene heterojunction with near-infrared (NIR) detection. Au NRs are used as a subwavelength scattering source, and nanoantennas with wide light absorption range from ultraviolet to near-infrared via tuning their geometry. Photons couple into Au NRs, exciting resonant plasmas and generating hot carriers that pump into graphene, resulting in selective NIR photodetection. A flexible NIR photodetector is also demonstrated based on this simple structure. Au NRs can achieve variable resonance frequencies by the design of different aspect ratios as nanoantennae for graphene, which promises the selective amplifying of the photoresponsivity and enables highly specific detection.

G-C3N4 decorated ZnO nanorod arrays for enhanced photoelectrocatalytic performance

Heterojunction can not only offer a wide range of solar light absorption but also facilitate the separation of photoinduced charge carriers, and thereby lead to enhanced photoelectrochemical efficiency. Herein, we report the heterostructured g-C3N4/ZnO nanorod arrays (NRAs) for enhanced photoelectrocatalytic performance. The g-C3N4 shell layer of about 20–30nm was coated on the surface of ZnO nanorod uniformly through thermal annealing the melamine precursor. Compared to the pristine ZnO and g-C3N4, the as-prepared g-C3N4/ZnO NRAs exhibit enhanced photoelectrocatalytic activity for methylene blue (MB) decolorization under visible light illumination. This enhancement of photoelectrocatalytic performance may be mainly attributed to improved separation efficiency of charge carriers from photoexcited g-C3N4 to ZnO across the g-C3N4/ZnO interfaces.

Photocatalytic application of Z-type system

Z-type photocatlytic system, reflembling natural photosynthesis, consists of two different photocatalysts and a shuttle redox mediator, involving two-photon excitation process for photocatlysis. One photocatalyst as a photoreduction system offers the reduction sites by conduction band (CB) electrons, and the other photocatalyst as a photooxidation system provides the oxidation sites by valence band (VB) holes. A shuttle redox mediator as an electron conductor transfers the electrons from the CB of the photooxidation system to the VB of the photoreduction system. On the one hand, the separation of photocatalytic reactive sites is advantageous for spatial separation of the electrons and holes, which is beneficial for enhancing the photocatlytic activities. On the other hand, photoreduction system and photooxidation system of different materials effectively inhibit the reflerse reaction involvement of photoreductive and photooxidative products. The Z-type photocatlytic system simultaneously possesses a wide light absorption range and strong redox ability.

WO3 nanoparticles decorated on both sidewalls of highly porous TiO2 nanotubes to improve UV and visible-light photocatalysis

The hybrid structure of nanoparticle-decorated nanotubes has the advantage of both large specific surface areas of nanoparticles and anisotropic properties of nanotubes, which is desirable for many applications. In this study, WO3 nanoparticles decorated on highly porous TiO2 nanotubes along both internal and external sidewalls (WO3@TiO2@WO3 heterostructures) were synthesized through emulsion electrospinning, thermal evaporation, and thermal annealing. The WO3@TiO2@WO3 heterostructures had large specific surface areas, high porous structure and excellent interface (between WO3 nanoparticles and TiO2 nanotubes). Three other samples, TiO2 nanofibers, TiO2 nanotubes, and TiO2 nanofibers decorated by WO3 nanoparticles, were prepared in order to compare with the WO3@TiO2@WO3 heterostructures for photocatalysis with both UV and visible light irradiation. The new material (WO3@TiO2@WO3 heterostructures) had a wide range of light absorption and demonstrated the best photocatalytic performance. The possible growth mechanism and reasons for high photocatalysis are discussed in detail.

Effect of ZnS coatings on the enhancement of the photovoltaic properties of PbS quantum dot-sensitized solar cells

We have studied the effect of ZnS coatings on the photovoltaic properties of PbS quantum dot-sensitized solar cells (QDSSCs). PbS QDs are suitable materials for QDSSCs because of their wide light absorption range; however, their high photochemical reactivity is a problem that needs to be overcome for solar cell applications. In this paper, a ZnS passivation layer was applied to PbS QDs adsorbed onto electrodes using a successive ionic layer adsorption and reaction (SILAR) method for different numbers of cycles in both aqueous and methanol solutions. It was demonstrated that, as a consequence of the low viscosity of methanol, the performance of the PbS QDSSCs was greatly enhanced when a methanol, rather than aqueous, solution was used in the SILAR method. The optical absorption properties of PbS QDs adsorbed on TiO2 electrodes with or without ZnS surface passivation were studied. An increase in size of the PbS QDs after coating with ZnS was confirmed by a red shift in the optical absorption spectra measured using photoacoustic spectroscopy. The photovoltaic properties of a sandwich structure of PbS QDSSCs were studied under “one sun” illumination using a polysulfide (S/S2−) redox system as the electrolyte and Cu2S on brass as the counter electrode. The short-circuit current density dramatically increased from 0.50 mA/cm2 to 11.2 mA/cm2 after the electrodes were modified with the ZnS coating. The maximum conversion efficiency that was achieved for PbS QDSSCs with a ZnS coating under one sun illumination was 1.92%.

Preparation of Cr-doped Ba4In2O7/In2O3 nanocomposite and its photo-assisted chargeability in hydrogen storage alloy/photocatalyst electrode

Abstract Homogeneously mixed Cr-doped Ba 4 In 2 O 7 /In 2 O 3 nanocomposite (Cr–BIO) was synthesized by a simple sol–gel method. The Cr–BIO powder was characterized by thermogravimetric (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectrometry. The as-prepared Cr–BIO powder shows the morphology comprised of Cr-doped Ba 4 In 2 O 7 nanorods and Cr-doped In 2 O 3 nanoparticles and a wide light absorption range with a main absorption edge around 480 nm. The hydrogen storage alloy/Cr–BIO photoelectrode was then fabricated and the photo-assisted electrochemical behavior was investigated by charge–discharge tests. The electrode exhibited obvious photo-assisted chargeable properties in KOH aqueous solution as the discharge time increased remarkably under the xenon light irradiation. The photo-assisted chargeability of HSA/Cr–BIO electrode was then discussed.