Efficient Visible-light Activity Research Articles

Synthesis and design strategies of codoped titanium dioxide with band alignment and multiple reflections of incident light for efficient visible light activity

To increase the visible-light photocatalytic performance of Titania, it was codoped with specific elements and was effectively synthesized. The goal of enhancing visible-light photocatalytic performance was achieved by broadening its absorption spectrum in the visible light range and enhancing the quantum efficiency of the photocatalytic reaction toward the degradation of the hazardous dye methyl orange. Mixed phase photocatalyst with different percentage hierarchical secondary nanostructure has been synthesized by the combination of chemical bath deposition methods and hydrothermal. The density of the sprout-like branches changes from the concentration levels of titanium butoxide in the precursor solution. Based on the experimental analysis, a mechanism was proposed to interpret the evolution of the secondary growth. The band edge difference between anatase and TiO2(B) phases induces transfer of charge at the interface. The result revealed that in the TiO2 crystal some O-sites were substituted by N and S anions resulting in band mixing and incorporation of extra energy states in between the valence band maxima and conduction band minimum, which caused a shift towards longer wavelengths in the absorption edge. Compared with pure TiO2 nanobelt, the surface modified doped samples exhibited good visible light activity. The combined effect of fast charge transfer in the atomic level contact between two phases and localized N 2p and S 3p band above valence-band edge in the same material makes titanium dioxide suitable for use in the presence of visible light.

In situ growth of BiVO4–Bi2O3 p-n heterojunction nanocomposite via facile green combustion method: Efficient photocatalytic activity under visible light, photoluminescence and biosensing applications

The easiest and simplest green combustion approach was successfully used to synthesize the pn Heterojunction BiVO4/Bi2O3 nanocomposites (NCs) with efficient visible light activity. Different stoichiometric ratios of butea monosperma leaf powder were used as the green fuel. Using XRD, SEM, EDAX, FTIR, UV–visible, and PL spectroscopy, the phase and surface structure, composition, and optical properties of synthesized NCs are characterised. In comparison to other ratios, it was found that the 1:1.5 ratio of BiVO4/Bi2O3 NCs exhibits good photocatalytic performance for the degradation of rose bengal dye. The outcome demonstrated that the formation of a p-n heterojunction between p-type Bi2O3 and n-type BiVO4 is responsible for the improved photocatalytic activity. It resulted from the separation of electron and hole pairs and the improvement of the interfacial charge transfer efficiency, both of which were made possible by the heterojunction. In addition, the BVO 15 photocatalyst exhibits good stability across 4 degradation cycles. The glassy carbon electrode (GCE) was modified with BVO NCs for the electrochemical detection of dopamine (DA). By using CV and LSV, the electrochemical behaviour of the fabricated electrode was examined. The outcomes demonstrate that BVO NCs have strong electrocatalytic activity. The limit of detection (LOD) was determined to be 33 μM. The current work is also a beneficial effort for developing new visible light photocatalysts with heterojunction architectures and biosensors.

Hollow core-shell LDH@N-HCS/CN S-scheme photocatalyst with the enhanced visible-light activity

It is a great challenge to effectively increase the charge separation and active sites of earth-abundant graphitic carbon nitride (CN) semiconductors to improve the photocatalytic performance. Looking for a highly active cocatalyst has attracted attention because of their potential to resolve the issues of low charge separation and low specific surface area of CN. A core-shell cocatalyst composed of nitrogen doped hollow carbon spheres (N-HCS) as the core and LDH nanoplates as the photoactive shell has been designed to increase the pristine CN active sites and charge separation. N-HCS acted as the support for LDH nanoplates to prevent particle agglomeration and served as the fast electron transfer channels to enhance the photoinduced charge separation efficiency. The ternary nanocomposites exhibited superior activity for nonyl phenol and Acid Blue 92 degradation compared to the unmodified CN under the visible light. The optimized deposition of LDH@N-HCS (15 wt%) on the CN surface resulted in 7-fold higher activity than without the cocatalyst. The improved photocatalytic activity of the ternary composite compared to CN could be attributed to two factors: efficient electron-hole pair separation due to LDH nanoplates and CN interface, and the presence of the N-HCS as an electron collector. The porous hollow structure of the cocatalyst exposes the numerous surface-active sites that favor visible light photocatalytic performance and supplies multiple reflection of photons into the cavity, increasing the usage ratio of light. This work will supply a novel strategy to rationally fabricate a noble metal-free binary cocatalyst for efficient visible light activity.

Efficient visible light photocatalysis enabled by the interaction between dual cooperative defect sites

Modifying photocatalyst with defects offers effective pathway to tailor light absorption properties, but may result in more sluggish kinetics. Therefore, enhanced light absorption often could not guarantee increased activity. Here, we report a dual defect strategy to extend light absorption with minimal loss in charge dynamics. Fine-tuned amount of dual defect, i.e., nitrogen defects and single-site copper, is simultaneously generated in polymer carbon nitride(PCN) through in-situ vapor diffusion method. Surface nitrogen defect extends the light absorption to long-wavelength via sub-band absorption. The interaction between nitrogen and single-site copper at certain concentration retains the charge dynamics by making the photogenerated electrons more delocalized through the newly-formed copper-nitrogen bonds. As a result, champion modified PCN exhibits robust hydrogen production activity, roughly 4.5-fold greater than the pristine counterpart in both visible and full light ranges. More intriguingly, this synergism provides PCN with efficient visible light activity even in faint tailing optical absorption region(>450 nm).

Visible light responsive Bi2S3-graphene/TiO2 nanocomposites: one pot-hydrothermal synthesize and improved photocatalytic properties

Herein, we obtained chemically bonded Bi2S3-Graphene/TiO2 composites using a facile one pot-hydrothermal method. During the hydrothermal reaction, both of the reduction of graphene oxide to graphene and loading of Bi2S3 and TiO2 particles on graphene nanosheet were achieved. The resulting composites are characterized by X-Ray diffraction (XRD), Raman spectroscopy and Transmission Electron Microscopy (TEM). The optical properties are studied using UV–visible diffuse reflectance spectroscopy (DRS), which confirms that the spectral responses of the composite catalysts are extended to the visible light region. The dramatically enhanced activity of Bi2S3-Graphene/TiO2 composite photocatalysts can be attributed to great adsorptivity of dyes, extended light absorption range, and efficient charge separation properties, simultaneously. This work may provide new insights into the design of novel composite photocatalysts system with efficient visible light activity.

Rare earth co-doped ZnO photocatalysts: Solution combustion synthesis and environmental applications

A novel europium (Eu) and terbium (Tb) co-doped ZnO nanoparticles had been synthesized by a facile, cost efficient and rapid combustion method. The physical and chemical properties of the as-synthesized nanoparticles were determined by XRD, SEM, EDS, BET, FTIR, XPS, UV–vis DRS, PL, EIS and photocurrent density. XRD patterns confirm that Eu and Tb ions are stably inserted into the framework of ZnO, and the crystallite size decreases to 21 nm compared to that of pure ZnO (32 nm) as the amount of co-dopants increases to optimal value (3 mol% of each). With the insertion of Eu and Tb ions into ZnO, the recombination rate of photo generated charge carriers is found to be low. It is observed that doped Eu and Tb ions can enter the lattice structure of ZnO with a suitable doping concentration, and the obtained doped ZnO have ordered hexagonal wurtzite structures and nearly spherical morphology with high specific surface area and high porosity. Meanwhile, the introduction of Eu and Tb ions can effectively extend the spectral response from UV to visible region for the catalysts, thus reducing the band gap from 3.25 to 2.91 eV. Further analysis by means of XPS measurement showed that the existence of mixture of Eu2+/Eu3+ and Tb3+/Tb4+ oxidation states and high content of the surface chemisorbed oxygen species also contributed to the high photocatalytic activity. It was found that Eu and Tb co-doped ZnO shows highly efficient and stable visible light activity and provides a 100% MB degradation within 15 min, while the degradation time for Eu doped ZnO and Tb doped ZnO is reduced gradually to 50 and 42 min, respectively to obtain the 100% MB degradation. It was also found that the photocatalytic hydrogen evolution activity over Eu and Tb co-doped ZnO can be significantly increased to 533.8 and 792 µmol with 0.2 wt% catalyst dose and initial solution pH 9, respectively under similar conditions with good stability. Moreover, simultaneous introduction of Eu and Tb effectively promoted the yield of CH4 to 4.59 µmol, which was 3.4 fold higher in comparison to pure ZnO. Thus the present approach could provide a versatile strategy for the synthesis of novel and efficient visible light activated photocatalysts.

Tungsten and nitrogen co‐doped TiO2 nanobelts with significant visible light photoactivity

Tungsten and nitrogen co‐doped TiO2 nanobelts (W/N‐TNBs) have been successfully synthesized via 1‐step hydrothermal method. The structure, morphology, and composition of prepared samples were characterized by X‐ray diffraction, scanning electron microscopy, and X‐ray photoelectron spectroscopy, respectively. The prominent phase of all as‐prepared samples is anatase crystal. For samples with N doping, new energy states can be introduced on top of O 2p states which reduced the band gap by 1.1 eV. The reduced band gap leads to efficient visible light activity. The 3%‐W/N‐TNBs were found to exhibit the highest activity. The photocatalytic performance of 3%‐W/N‐TNBs under visible light is about 4.8 times than that of pure TiO2 nanobelts, which emphasizes the synergistic effect of W and N co‐doping for effectively inhibiting the recombination of photogenerated electrons and holes. In addition, our results testify the different redox potentials of the photoelectrons at different final states.

Fabrication of Bi2MoO6 nanoplates hybridized with g-C3N4 nanosheets as highly efficient visible light responsive heterojunction photocatalysts for Rhodamine B degradation

The Bi2MoO6/g-C3N4 heterojunction photocatalysts have been successfully fabricated using a simple liquid chemisorptions and thermal post-treatment. These nanostructured Bi2MoO6/g-C3N4 composites were extensively characterized by X-ray diffraction(XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR),UV–vis diffuse reflectance spectra (UV–vis DRS) and Photoluminescence (PL). The photocatalytic results show that 20wt% Bi2MoO6/g-C3N4 sample exhibits efficient visible light activity and excellent photo-stability. The kinetic constant of RhB degradation over 20wt% Bi2MoO6/g-C3N4 is about 5 and 2.5 times higher than that over pure Bi2MoO6 and g-C3N4 nanosheets, respectively. The enhanced photocatalytic performance is attributed to the construction of heterogeneous interface to promote photo-induced charge carrier pairs separation.

Fabrication of a heterostructured Ag/AgCl/Bi2MoO6 plasmonic photocatalyst with efficient visible light activity towards dyes

A ternary Ag/AgCl/Bi2MoO6 plasmonic photocatalyst was successfully fabricated through a two-step synthesis method.

Visible-light sensitive Cu(ii)–TiO2with sustained anti-viral activity for efficient indoor environmental remediation

Photocatalysts with efficient visible-light activity and sustainable function under dark conditions are desirable for indoor environmental remediation applications.

Effect of photo-corrosion of Ag2CO3 on visible light photocatalytic activity of two kinds of Ag2CO3/TiO2 prepared from different precursors

Two kinds of Ag2CO3/TiO2 nanocomposite photocatalysts, Ag2CO3/P25 (P25 refers to TiO2 of Degussa Company of Germany produced by gas-phase method) and Ag2CO3/TiO2(Vo•) (Vo• refers to single-electron-trapped oxygen vacancy (abridged as SETOV)), were prepared by precipitation method with commercial P25-TiO2 and TiO2(Vo•) as the precursors. The photocatalytic activity of as-prepared Ag2CO3/P25 and Ag2CO3/TiO2(Vo•) was compared by monitoring the oxidation of propylene under visible light irradiation with pure Ag2CO3 photocatalyst as a reference. The oxidation reaction of propylene was performed in two different reaction systems, i.e., a glass reactor combined with a home-made xenon lamp (denoted as system I) and a quartz reactor combined with a commercial xenon lamp (denoted as system II), respectively. Furthermore, X-ray photoelectron spectroscopic analysis, X-ray diffraction analysis, and diffuse reflection spectrometric analysis of Ag2CO3/P25 and Ag2CO3/TiO2(Vo•) before and after visible light irradiation were conducted to investigate the effect of Ag2CO3 photo-corrosion on the activity of the two kinds of photocatalysts, and their photocatalytic mechanisms were proposed. It was found that in system I (light intensity irradiated on to-be-tested samples at λ=420nm: about 9mW/cm2), Ag2CO3/TiO2(Vo•) shows highly efficient and stable visible light activity and provides a propylene removal rate of up to 90% which remains unchanged within 4h of irradiation, while the degradation rate of propylene over Ag2CO3/P25 is reduced gradually from 35% to nearly zero within 2.5h of irradiation. In system II (light intensity at λ=420nm: about 40mW/cm2), both Ag2CO3/P25 and Ag2CO3/TiO2(Vo•) exhibit similar photocatalytic activity of up to ca. 90%. Besides, photo-corrosion of Ag2CO3 happens during photocatalytic process to afford metallic Ag, and such a photo-corrosion is originally non-conducive to the photocatalysts. Nevertheless, metallic Ag is responsible for strong surface plasmon resonance effect of Ag2CO3/P25 and desired electron capture ability of Ag2CO3/TiO2(Vo•) as well, leading to highly efficient visible light activity of Ag2CO3/P25 in system II. As to Ag2CO3/TiO2(Vo•), a large amount of SETOV induces a new sub-band between the valence band and conduction band of TiO2(Vo•), and this sub-band synergistically functions with nascent surface metallic Ag to result in highly visible light activity. Thus the present approach could provide a versatile strategy for the synthesis of novel and efficient visible light-activated photocatalysts.

Nitrogen doped TiO2 nanoparticles decorated on graphene sheets for photocatalysis applications

Nitrogen doped TiO2 nanoparticles decorated on graphene sheets are successfully synthesized by a low-temperature hydrothermal method. The resulting GR-N/TiO2 composites are characterized by X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-Ray photoelectron spectroscopy (XPS) and Transmission Electron Microscopy (TEM). The optical properties are studied using UV–visible diffuse reflectance spectroscopy (DRS), which confirms that the spectral responses of the composite catalysts are extended to the visible-light region and show a significant reduction in band gap energy from 3.18 to 2.64 eV. Photoluminescence emission spectra verify that GR-N/TiO2 composites possess better charge separation capability than pure TiO2. The photocatalytic activity is tested by degradation of methyl orange (MO) dye under visible light irradiation. The results demonstrate that GR-N/TiO2 composites can effectively photodegrade MO, showing an impressive photocatalytic enhancement over pure TiO2. The dramatically enhanced activity of composite photocatalysts can be attributed to great adsorption of dyes, enhanced visible light absorption and efficient charge separation and transfer processes. This work may provide new insights into the design of novel composite photocatalysts system with efficient visible light activity.

Cu(II) Oxide Amorphous Nanoclusters Grafted Ti3+ Self-Doped TiO2: An Efficient Visible Light Photocatalyst

Ti3+ self-doped TiO2 was prepared by a facile one-step thermal oxidation of Ti2O3 and TiO2 mixture in air. Electron spin resonance (ESR) spectra confirmed the presence of Ti3+ in this sample. Ti3+ states caused a visible light absorption, which is originated from the isolated band in its forbidden gap. Although the photocatalytic activity of this Ti3+ self-doped TiO2 was negligible even under the UV light, its UV and visible light activities were drastically increased by the grafting of Cu(II) oxide amorphous clusters with a size of around 2 nm as a co-catalyst. Consequently, the photocatalytic decomposition of gaseous 2-propanol (IPA) into CO2 with a maximum generation rate of 0.20 μmol/h and a quantum efficiency of 10.8% is achieved, under the visible light irradiation. Its efficient visible light activity is highly stable in air and can be repeatedly used for a long term.

Enhanced visible light photocatalytic activity of novel Pt/C-doped TiO2/PtCl4 three-component nanojunction system for degradation of toluene in air

C-doped TiO2 nanoparticles prepared by partial oxidation of TiC were modified with Pt species by impregnation–calcination method in order to enhance the visible light photocatalytic activity. The physicochemical properties of as-prepared samples were characterized by various techniques in detail. The results indicated that a novel Pt/C-doped TiO2/PtCl4 three-component nanojunction system was formed, where C-doped TiO2 and PtCl4 behaved as two visible light responsive components, and Pt metal as electron-transfer system. The three-component nanojunctioned photocatalyst system exhibited six times higher visible light activity than that of the pristine C-doped TiO2 in degradation of toluene in air. The dramatically enhanced activity can be attributed to the increased utilization of visible light, the enhanced charge carrier separation and transfer process. Further more, the band structure and photocatalysis mechanism over the three-component nanojunction system was proposed and discussed. This work may provide new insights into the design of novel multi-component photocatalyst system with efficient visible light activity.