High-efficiency Visible-light Photocatalyst Research Articles

Tuning the optoelectronic properties of graphene monoxide by electric field, strain and heterostructure with Cd[formula omitted] ([formula omitted]=S, Se or Te)

Hydrogen production via photocatalytic water splitting has become a promising technique for developing clean and sustainable energy system. Low-dimensional carbon-based materials are under focus to develop high efficiency visible-light photocatalysts. Among the various 2D graphene-based materials, graphene oxides (GO) attracted attention in recent years. Recently identified GO such as graphene monoxide (GMO) shows promising electronic structure characteristics such as direct band gap behavior, high optical absorption, and well-dispersed band edges to use them in higher efficiency optoelectronic applications. Nevertheless, its valence band edge is distant from the water oxidation potential, and band gap value exceeds the ideal band gap required to effectively harvest solar energy, which minimizes its practical application in photocatalytic water splitting. Here, using hybrid density functional theory calculations, we are exploring the effect of applied electric field/strain on the photocatalytic water splitting and photovoltaic properties of GMO. We found that even after applying an electric field or strain, GMO retains the desirable direct band gap behavior, well-dispersed bands at the band edges, and high optical absorption in the visible range. Further, the band alignment analysis suggests that the application of compressive strain enhances the efficiency of photocatalytic water splitting by straddling the band edges with water redox potentials. Additionally, we explored the optoelectronic properties of GMO by designing its heterostructure with CdS, CdSe, and CdTe monolayers. Remarkably, the studied heterostructures demonstrated superior optical absorption in the visible spectrum and a low recombination rate of charge carriers by separating them across different layers with type-II band alignment; suggesting that these heterostructures will be efficient candidates for visible energy photocatalytic water splitting and higher-efficiency solar cells.

Synthesis of polyaniline modified FeWO4 nanoparticles for superior visible-light photocatalysis

This communication reports the development of a new high-efficiency visible-light photocatalyst by coupling p-type FeWO4 with n-type polyaniline (PANI). PANI/FeWO4 nanocomposite was synthesized through a facile composition-controllable solid liquid mixing-evaporation of solvent method. The composition and structure of the synthesized PANI/FeWO4 nanocomposite were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The photoabsorption and photogenerated charge separation and transfer performance of PANI/FeWO4 nanocomposite were compared with those of FeWO4 nanoparticles. The photocatalytic properties of PANI/FeWO4 nanocomposite and FeWO4 nanoparticles were tested in the reduction of aqueous Cr(VI) under visible-light (λ > 420 nm). The results showed that the photocatalytic activity of PANI/FeWO4 was significantly elevated compared to FeWO4. Coupling with PANI can increase the adsorption of Cr(VI), enhance the absorption of visible-light, and promote the separation and transfer of photogenerated charges of FeWO4, thus contributing to the better photocatalytic activity of PANI/FeWO4.

Fabrication of multi-component heterojunction Ag/AgCl/g-C3N4/Sn-In3O2 for enhanced degradation of RhB under visible light

High-efficiency visible-light photocatalysts have been recognized as a cost-effective approach for the degradation of organic pollutants in wastewater. In this study, we constructed a novel multi-component heterojunction photocatalyst Ag/AgCl/g-C3N4/Sn-In2O3 through a simple thermal polymerization and photo-assisted reduction processes. The photocatalytic activity of Ag/AgCl/g-C3N4/Sn-In2O3 was remarkably improved compared to other samples in the degradation of Rhodamine B (RhB). The degradation of RhB by 5 % Ag/AgCl/g-C3N4/Sn-In2O3 reached 98.5 % within 60 min, while the degradation rates under g-C3N4, g-C3N4/Sn-In2O3, and Ag/AgCl/g-C3N4 were found to be 41.8 %, 73.6 %, and 85.9 %, respectively. Electron spin resonance (ESR) signals trapping and radical scavenging confirmed that the h+ and ·O2− were the two main reactive species in photodegradation RhB. The result provides innovative insights that could inform the future design and development of photocatalysts with exceptional efficiency.

Yttrium -barium oxide as a robust photocatalyst for photocatalytic degradation of organic dyes under visible light

Based on the structure related to the high-temperature superconductor yttrium-barium-copper oxide, two novel high-efficiency visible light photocatalysts were created in this study. The yttrium-barium oxide (YBO) semiconductors Y2Ba3O6 (YB3O) and Y2Ba4O7 (YB4O) were prepared by a copper-free solid-phase sintering method. They were applied for the effective treatment of dye-containing wastewater by photocatalysis under visible light irradiation. The degradation efficiency of methylene blue (MB) reached more than 95% within 10 min. Stable visible light degradation of methyl orange (MO) was achieved in the presence of YB3O and YB4O. The electron spin resonance technique and active substance capture technique confirmed the presence of superoxide radicals (·O2−), hydroxyl radicals (·OH) and holes (hVB+) under visible light illumination. UV–Vis diffuse reflectance spectroscopy analysis showed that the direct optical band gaps of YB3O and YB4O were 2.550 eV and 2.583 eV, respectively, which resulted in their high visible absorption at 486.27 nm and 480.06 nm. After five cycles, the recoveries of YB3O and YB4O reached 67.15% and 72.98%. Therefore, YB3O and YB4O are considered as powerful semiconductor catalysts for the photocatalytic degradation of organic dyes in wastewater.

Silver-modified MoS2 nanosheets as a high-efficiency visible-light photocatalyst for water splitting

One of the major challenges that the human beings are facing is the shortage of the fossil fuels. Hydrogen is considered as the most attractive renewable energy because of its abundant high energy density. Semiconductor photocatalytic technology for water decomposition is a promising method for converting sunlight into hydrogen energy, which has attracted considerable attention. Compared with bulk materials, two-dimensional (2D) materials exhibit remarkable photocatalytic properties. In this work, the pristine high-quality hexagonal molybdenum disulfide (MoS2) nanosheets and Ag-doped MoS2 nanosheets were synthesized by hydrothermal method, and the thickness of nanosheets was ranged from 0.9 to 1.1 nm. In addition, the absorption spectra of Ag-doped MoS2 nanosheets increased with the increase of Ag content. What's more, the photocatalytic properties of Ag-doped MoS2 nanosheets were tested, and the results show that Ag-doped MoS2 nanosheets have good stability, high hydrogen production efficiency and strong photocatalytic activity. It is worth mentioning that the photocatalytic hydrogen production rate of Ag-doped MoS2 nanosheets can reach 2695 μmol h−1 g−1. Meanwhile, density functional theory was used to calculate the optical properties, electronic structure of pristine and Ag-doped monolayer MoS2. These calculated results indicate that the absorption intensity of Ag-doped MoS2 in the ultraviolet–visible and visible light region increases significantly, and the conduction band of Ag-doped monolayer MoS2 is downshift compared with pristine MoS2. Therefore, Ag-doped MoS2 can optimize the band structure and promote the absorption of visible light, thereby improving the photocatalytic activity.

Fabrication and characterization of novel Ag2O-polyimide composites with enhanced visible-light photocatalytic activity

Novel high-efficiency visible-light photocatalyst, silver oxide (Ag2O)-polyimide (PI) photocatalyst is synthesized by a liquid phase reaction method. The obtained samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR) and photoluminescence (PL). The photocatalytic activity of the Ag2O-PI composites are evaluated by the decomposition of Rhodamine B (RhB) under visible-light irradiation. All Ag2O-PI composite possesses higher photocatalytic activity than pure Ag2O and PI. It could be found that RhB was photodegraded with the highest degradation efficiency of 97.9% when the mass ratio of Ag2O and PI reached to 2:1. This enhancement can be attributed to the efficient separation of photogenerated electron and holes. Furthermore, the possible mechanism for the photocatalytic activity of Ag2O-PI composites was also proposed.

Facile synthesis of Nd2Sn2O7-SnO2 nanostructures by novel and environment-friendly approach for the photodegradation and removal of organic pollutants in water

A simple and clean synthesis for Nd2Sn2O7-SnO2 nanocomposites as high-efficiency visible-light responsive photocatalyst is described applying extract of pineapple, for the first time. As novel and non-toxic biofuel, extract of pineapple, is employed to fabricate Nd2Sn2O7-SnO2 nanocomposites through an environment-friendly procedure. The findings denote that the applied biofuel can play a meaningful role as capping agent during preparation of Nd2Sn2O7-SnO2 nanocomposites. Depending on the applied dosage of pineapple extract as well as time for fabrication, the grain size, photocatalytic yield and morphology of Nd2Sn2O7-SnO2 structures changed. A suite of identification methods like XRD, TEM, EDS, DRS, BET and FESEM are utilized for investigation of the produced Nd2Sn2O7-SnO2 nanocomposites. Nd2Sn2O7-SnO2 structures are utilized as visible-light responsive photocatalyst to degrade the rhodamine B and eosin Y contaminants. The produced Nd2Sn2O7-SnO2 nanocomposites have been found to be very effective as visible-light responsive photocatalyst to degrade contaminants which may bring to environmental pollution.

A facile in situ solvothermal method for two-dimensional layered g-C3N4/SnS2 p-n heterojunction composites with efficient visible-light photocatalytic activity

To overcome the fast recombination rate of electron-hole pairs of individual SnS2, p-n heterojunction g-C3N4/SnS2 composites were fabricated as high-efficiency visible-light photocatalyst to photodegradate the organic dye MB. The morphologies, structures, compositions, and photocatalytic properties were characterized. The SnS2 shows two-dimensional layer structure with an average thickness of 20 nm and diameter size of about 2 μm, and the g-C3N4 nanoflakes were uniformly deposited on the surface of SnS2 nanosheets. In comparison with the bare g-C3N4 and SnS2, the composites show improved photocatalytic activity under visible light, which is sensitive to the content of g-C3N4. In particular, the 15% g-C3N4/SnS2 composites exhibit the highest photocatalytic activity and outstanding reusability, which can degrade 88.01% MB after only 1 h in the visible light (λ > 420 nm) range. The g-C3N4/SnS2 heterojunction composites show outstanding reusability after four times cycling experiments. The improved photocatalytic activities of composites are attributed to abundant active species, increased charge separation, and decreased electron-hole pair recombination, which originated from the large specific surface area and efficient interfacial transport of photo-induced charge carriers between SnS2 and g-C3N4. These results suggest that the two-dimensional layered g-C3N4/SnS2 p-n heterojunction composites are promised to be a high-efficiency visible-light photocatalyst.

A new high efficiency visible-light photocatalyst made of SnS2 and conjugated derivative of polyvinyl alcohol and its application to Cr(VI) reduction

This study focuses on the synthesis of a new high efficiency visible-light photocatalyst made of SnS2 and conjugated derivative (CPVA) from thermal dehydration of polyvinyl alcohol (PVA), and the evaluation of its performance in photocatalytic reduction of aqueous Cr(VI). SnS2/CPVA nanocomposites were synthesized via the procedures of (i) mixing of SnS2 nanocrystals and PVA in aqueous solution and evaporation of the aqueous solvent to generate SnS2/PVA nanocomposites, and (ii) thermal treatment of the SnS2/PVA nanocomposites for transforming their PVA into conjugated CPVA. The optimum conditions for synthesis of most efficient SnS2/CPVA nanocomposite were explored. The characterization by X-ray diffraction, Raman spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy and elemental mapping indicated the formation of SnS2/CPVA nanocomposites. The photocatalytic experiments showed that SnS2/CPVA nanocomposite synthesized under the optimum conditions (SnS2/CPVA-1%-180°C-2h) had exceptionally higher photocatalytic activity than SnS2 nanocrystals, physical mixture of SnS2 nanocrystals and CPVA, SnS2/CPVC nanocomposite and TiO2/CPVA nanocomposite in the reduction of aqueous Cr(VI) under visible-light (wavelength>420nm) irradiation. The mechanism underlying the most enhanced photocatalytic activity of SnS2/CPVA-1%-180°C-2h was elucidated, based upon comparison between the optical, photoelectric and electrochemical impedance properties of SnS2 nanocrystals and different SnS2/CPVA nanocomposites. Furthermore, the effects of photocatalytic experiment parameters (including dosage of photocatalyst, and initial pH and concentration of Cr(VI) aqueous solution) on the Cr(VI) removal efficiency by SnS2/CPVA-1%-180°C-2h were also studied.

Electronic and optical properties of Cr-, B-doped, and (Cr, B)-codoped SrTiO3

Energy band engineering of semiconductors plays a crucial role in exploring high-efficiency visible-light response photocatalysts. Herein, we systematically study the electronic properties and optical response of Cr-, B-doped SrTiO3, and (Cr, B)-codoped SrTiO3 by using first-principles calculations to explore the mechanism for its superior photocatalytic activities in the visible light region. Special emphasis is placed on uncovering the synergy effects of nonmetal B dopant with metal Cr dopant at different cation sites. It is found that the electronic properties and optical absorption of SrTiO3 can be dramatically engineered by mono- or co-doping. In particular, the intermediate levels lying in the bandgap of the codoped SrTiO3 relay on the Cr impurity doped at Sr or Ti cation sites. Moreover, the (Cr@Sr, B@O)-SrTiO3 retains the charge balancing without the generation of unexpected oxygen vacancies, and is more desirable for solar light harvesting due to its higher absorption than others in the entire visible light. The findings can rationalize the available experimental results and are helpful in designing SrTiO3-based photocatalysts with high-efficiency performance.

Fe(III) modified BiOCl ultrathin nanosheet towards high-efficient visible-light photocatalyst

To pursue high photocatalytic activity in visible-light region, the Fe(III) modified BiOCl ultrathin nanosheet (Fe(III)@BOC NS) has been firstly synthesized via a facile solvothermal approach. The morphological and compositional characterizations reveal that the thickness of the as-prepared Fe(III)@BOC NS is less than 5 atomic layer with the exposure of active [001] facets. And the Fe(III) doping and surface grafting result in a 0.58eV down-shift of the BiOCl conduction band minimum extending the light absorption from ultraviolet light to visible light region, as well as a promoted interfacial charge transfer upon visible light irradiation. Meanwhile, the Fe(III) modification introduces unique active sites on the surface of ultrathin nanosheet facilitating the surface reaction. Moreover, both of the appropriate self-induced electric field of [001] facets, and the shortened charge carrier diffusion length of ultrathin nanosheet enhance the separation and transfer efficiency of charge carriers. Therefore, by taking those advantages, we experimentally demonstrate that the Fe(III)@BOC NS is a high-efficiency visible-light photocatalyst for both of environment remediation and water splitting.

ChemInform Abstract: Efficient Visible Driven Photocatalyst, Silver Phosphate: Performance, Understanding and Perspective

AbstractReview: 82 refs.

Preparation, Characterization and Photocatalytic Property of Cubic α-Fe2O3 Nanoparticles

Abstract A simple hydrothermal synthesis method has been designed for the controllable synthesis of cubic α-Fe2O3 nanoparticles. Structural and morphological characterizations of the synthesized products were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The size range of the cubic α-Fe2O3 particles is 130–150 nm. Results indicate that the α-Fe2O3 nanoparticles can be used as an efficient photocatalysts for photocatalytic degradation of Rhodamine B in the presence of hydrogen peroxide, which may provide the design and development of high-efficiency visible-light photocatalysts for removing toxic dyes from industrial wastewater with a new way and basis.

Facile synthesis of sheet-like N–TiO2/g-C3N4heterojunctions with highly enhanced and stable visible-light photocatalytic activities

Sheet-like N–TiO2/g-C3N4heterojunctions with well-controlled structures as high-efficiency visible-light photocatalysts were synthesized by direct co-calcination of preformed N–TiO2nanoparticles and g-C3N4nanosheets.

Diatomite coated with Fe2O3 as an efficient heterogeneous catalyst for degradation of organic pollutant

Heterogeneous catalysts have been attracted considerable attention for degradation of organic pollutions to overcome the disadvantages of the homogeneous Fenton process. Diatomite-Fe2O3 hybrid material, honeycomb structure with circular pores synthesized as a heterogeneous catalyst for photo-Fenton degradation of organic contaminants by a novel method. The existence of Fe2O3 nanoparticles in the diatomite-Fe2O3 catalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The catalytic activities of the diatomite-Fe2O3 catalyst were evaluated by the degradation of organic dye under visible light irradiation (>420 nm) in the presence of hydrogen peroxide. The results showed that the catalyst exhibited excellent catalytic property for 99.14% decoloration and 73.41% TOC removal of Rhodamine B, which could be attributed to the synergetic effects of the adsorptive power of diatomite and the hydroxyl radicals produced by heterogeneous photo-Fenton reactions. In addition, the decoloration efficiency was still higher than 90% after the catalyst being used for 5 cycles. Hence, the simplicity and cost-effectiveness of the hybrid material could be very promising for synthesizing for high-efficiency visible-light photocatalyst in the degradation of organic pollutants.

Graphene oxide–Fe2O3 hybrid material as highly efficient heterogeneous catalyst for degradation of organic contaminants

Graphene oxide–Fe2O3 (GO–Fe2O3) hybrid material was synthesized as a heterogeneous catalyst for photo-Fenton degradation of organic contaminants by an easy and scalable impregnation. X-ray diffraction analysis and high-resolution transmission electron microscope analysis confirm the existence of the Fe2O3 nanoparticles in the GO–Fe2O3 catalyst. Fourier transform infrared spectroscopy analysis proves that the combination of Fe2O3 and GO sheet is due to the metal–carbonyl coordination. The catalytic activities of the GO–Fe2O3 catalyst were evaluated by the degradation of Rhodamine B and 4-nitrophenol under visible light irradiation (>420nm) in the presence of hydrogen peroxide. The results show that the catalyst exhibited excellent catalytic property at a wide pH range of 2.09–10.09 and stable catalytic activity after seven recycles, which could be attributed to the synergetic effects of the adsorptive power of GO and the hydroxyl radicals produced by heterogeneous photo-Fenton reactions. The present results suggest that the GO–Fe2O3 hybrid material can act as an efficient heterogeneous catalyst for degradation of organic contaminants, which may provide insight into the design and development of high-efficiency visible-light photocatalyst for water treatment.

H2WO4·H2O/Ag/AgCl Composite Nanoplates: A Plasmonic Z-Scheme Visible-Light Photocatalyst

The Z-scheme has been proven to be an effective strategy to develop a high-efficiency visible-light photocatalyst. However, the visible-light-responding active component in the Z-scheme system is usually restricted to semiconductor materials sensitive to visible light. On the other hand, noble-metal nanoparticles (such as Ag) can act as an active component for the design of high-efficiency plasmonic photocatalysts due to their strong absorption in the visible light region. In this study, H2WO4·H2O/Ag/AgCl composite nanoplates were prepared by a one-step ionic reaction between Ag8W4O16/Ag nanorods and HCl aqueous solution. The photocatalytic activity experiments indicated that the H2WO4·H2O/Ag/AgCl composite nanoplates exhibited a much higher photocatalytic activity than the one-component (H2WO4·H2O) or two-component (such as Ag/AgCl and H2WO4·H2O/Ag) photocatalysts. On the basis of photocatalytic activity and band structure analysis, a plasmonic Z-scheme photocatalytic mechanism is proposed; namely, two-s...