Visible Light Responsive Photocatalysis Research Articles

Neodymium-doped nickel cobaltite reinforced with 2D MXene nanocomposite (Nd-NiCo2O4/MXene) for enhanced photocatalytic degradation of the organic pollutants

In the quest for sustainable strategies for environmental remediation and wastewater treatment, composite material-based visible light-responsive photocatalysis has emerged as a highly efficient method that is not only facile but also economical. Herein, we have synthesized pure (NiCo2O4) and Nd-doped (Nd-NiCo2O4) nickel cobaltite nanoparticles and incorporated doped material on 2D MXene to fabricate nanocomposite (Nd-NiCo2O4/MXene). The prepared samples were characterized to exploit the effect of Nd-doping and composite formation on structural, electrical, and optical properties. The photocatalytic potential of composite material was investigated by targeting malachite green and pendimethalin. In comparison to pure and doped materials, the nanocomposite demonstrated superior photocatalytic efficiency for the degradation of targeted pollutants. This enhanced catalytic activity is attributed to the synergism of rare earth metal doping and composite formation which result in enhanced absorption in visible light and lower coupling of charge carriers. Systematic studies revealed the promising potential of the Nd-NiCo2O4/MXene nanocomposite for solar light harvesting in wastewater remediation applications.

Synthesis of novel muscovite loaded nano Ag/Cu2-xFexO composites with excellent visible-light responsive photocatalysis

Muscovite loaded Cu2O nanosphere composites with Fe3+ doping and Ag deposition were successfully synthetized by a simple chemical reduction method. The composites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectrometer, scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) technique, transmission electron microscope (TEM), photoluminescence spectra (PL) and UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). Meanwhile, the photocatalytic performance and photocatalytic mechanism of the samples were investigated by photodegradation of methyl orange (MO) dye under visible light irradiation. The Cu2O nanosphere composites co-modified by Ag, Fe3+ and muscovite showed the best photocatalytic activity, which may originate from both the enhancement of utilization of Cu2O photocatalyst and the reduction of recombination of electrons and holes in the natural environment.

Facile synthesis of Super-paramagnetic Au @α-Fe2O3 hybrid nanoparticle and its assembly on graphene substrate for visible light Photo-catalysis

We report a simple interface modified strategy to self-assemble the as-synthesized Au@Fe2O3 nano structures by facile chemical synthesis route on graphene substrate (AFG) fo r substrate mediated photo-catalytic dye degradation. The substrate modification, film formation, photo induced charge transfer mechanism and the physico-chemical properties of the AFG has been systematically analysed using different analytical techniques. The alteration in light absorption capacity and band gap of the hybrid with respect to the individuals have been observed using diffuse reflectance spectroscopy. Moreover, the broad absorption in the visible range and squeeze in band gap of the hybrid from 2.3 to 1.97 eV confirms the ability of the hybrid and the intention of hybridization for visible light-responsive photo-catalysis. Additionally, interesting superparamagnetic behaviour of the hybrid and its magnetic separation ability has been explored. Further, the applicability, repeatability and versatility of this AFG hybrid material in catalytic degradation of different dyes in presence of visible light have been analysed. This AFG catalyst exhibits excellent photocatalytic activity against the decolouration of the both cationic and anionic dyes. A systematic study in the photo-catalytic degradation behaviour, kinetic of degradation and the postulated mechanism has been proposed.

Novel Dyadic Amorphous-Crystalline Nano-Titania Hybrids for Sacrifiers-Stored Photocatalysis

Sacrifiers-promoted photocatalysis is a useful way to achieve high efficiency photoreduction and photocatalytic hydrogen production for photocatalysts of weak reductive power such as TiO2. Herein we report a new method to fabricate a unique dyadic hybrid consisting of closely compacted crystalline (anatase) and titanium glycerolate (TiG)-derived organic group-retained amorphous nanoparticles to validate adsorption-stored sacrifiers-promoted photocatalysis instead of using sacrifiers in bulk solution. It was found that ascorbic acid (AA)-modified TiG prepared at a small fraction of glycerol, characterized by peculiar cocoon/open nanocontainer-type morphologies, varieties of oxygen containing groups, and remarkably high specific surface area, is suitable for precursing such hybrids. AA can change crystallization processes and particle morphologies by terminating chain linkages in TiG structure, which increases porosity and brings about visible light responsive photocatalysis for the dyadic hybrid. Benefiting from good adsorption affinity to organic sacrifiers, the sacrifier-prestored hybrid can catalyze significantly enhanced photoreduction with good reproducibility toward dye molecules via the synergy of sacrifier enrichment and photocatalysis. AA modified TiG also exhibits good self-reducibility enabling pre-loading of highly dispersed and localized platinum nanoparticles, and the resulted dyadic hybrid facilitates photocatalytic hydrogen production of extremely higher turn-off frequency and better impurities interference-resistivity compared to the P25-based commercial catalyst.

Cu-doped TiO2 hollow nanostructures for the enhanced photocatalysis under visible light conditions

We report a synthetic strategy for fabricating Cu-doped TiO2 hollow nanostructure for visible light responsive photocatalysis. Hollow Cu-doped TiO2 photocatalysts were prepared by sol–gel coating of TiO2 on the surface of SiO2, removal of sacrificial core, Cu2+ ion exchange, and calcination followed by acid leaching. The ion exchanged Cu species allows TiO2 shell to be preferentially crystallized rutile phase, even at low calcination temperature. The acid leaching allows the excess bulk CuO to be dissolved out and Cu-doped TiO2 to expose more reactive TiO2 surface. No measurable CuO composites were observed while uniformly distributed Cu species is detected in acid treated CT–X–HCl samples indicating the Cu2+ ions were homogeneously doped into crystalline TiO2 frameworks. In particular, the CT–650–HCl catalyst that was prepared by calcination at 650°C, followed by HCl leaching, showed beneficial physio-chemical properties, such as narrow bandgap, mixed anatase-rutile crystalline phase, and more reactive TiO2 surface with high surface area, resulting in the best photocatalytic performance towards phenol degradation under visible light conditions.

Synthesis, characterization and visible light-responsive photocatalysis properties of Ce doped CuO nanoparticles: A combined experimental and DFT+U study

In this work, CuO and Ce doped CuO (Ce:CuO) nanoparticles (NPs) were prepared by the sol-gel auto-combustion process. The effect of the concentration of Ce doping (0, 2%, 4%, 6%, and 8%) on the structural properties, surface morphology, electronic properties, optical properties, and visible light assisted photocatalytic activities of NPs were studied experimentally and also with Density Functional Theory (DFT + U) simulation. The X-ray Diffraction (XRD), Raman and Fourier transform-infrared (FTIR) studies confirmed the presence of Cu-O bonding in the as-prepared nanoparticles. Incorporation of Ce was found to introduce intrinsic defects in the Ce:CuO NPs and reduces the optical bandgap from 1.72 eV to 1.40 eV. The photocatalytic performance of the NPs was assessed by studying the degradation of methylene blue (MB) under visible light irradiation. Ce:CuO NPs exhibit better photocatalytic efficiency compared to pure CuO NPs. Furthermore, DFT based simulation predicted that the incorporation of Ce narrowed down the bandgap of the NPs due to the creation of shallow doping states near the valance and conduction bands. The reduction of band gap together with the presence of shallow dopant states allows efficient charge separation together with improved photon adsorption of Ce doped CuO NPs yielding an enhanced photocatalytic activity.

Rendering Visible-Light Photocatalytic Activity to Undoped ZnO via Intrinsic Defects Engineering

It is significant to render visible-light photocatalytic activity to undoped ZnO nanostructures via intrinsic defect engineering. In this work, undoped ZnO nanocrystals were derived via co-precipitation synthesis. The resulting ZnO nanocrystals were characterized by means of X-ray diffraction, scanning electron microscopy, photoluminescence spectroscopy, and ultraviolet-visible absorption spectroscopy, respectively. The visible-light photocatalytic activity of the products were characterized by monitoring the decomposition of methyl orange in water under visible-light illumination of a 300 W halogen lamp. It is found that undoped ZnO nanocrystals exhibit visible-light photocatalytic activity with their first-order rate constant up to 4.6 × 10−3 min−1. Density functional calculations show that oxygen vacancies create deep energy levels at EV + 0.76 eV in the bandgap of ZnO. In conjunction with the density functional calculations, the photocatalytic degradation of methyl orange under visible-light irradiation provides direct evidence that oxygen vacancies in ZnO nanocrystals yield the visible-light photocatalytic activity. Our results demonstrate that visible-light photocatalytic activity can be endowed to undoped ZnO nanocrystals by manipulating the intrinsic defects in ZnO. Intrinsic defect-modulated ZnO photocatalysts thus represent a powerful configuration for further development toward visible-light responsive photocatalysis.

Construction of novel magnetic BiFeO3/MoS2 composite for enhanced visible-light photocatalytic performance towards purification of dye pollutants

ABSTRACT This research focuses on a novel visible light-responsive photocatalysis system employing MoS2 and magnetically responsive BiFeO3 for removing dye. Novel BiFeO3/MoS2 magnetic nanocomposite was successfully synthesised by a simple method and characterised by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), Uv–Vis diffuse reflection spectra (DRS) and vibrating sample magnetometry (VSM). Comparing with pure BiFeO3 and MoS2, the prepared nanocomposite illustrated notably better photocatalytic activity. The outcome of the photocatalytic experiments depicted that nanocomposite reaches to about 89% removal of Rhodamine B in 200 min under visible light irradiation. The superior photocatalytic activity could be attributed to the high separation efficacy of the photogenerated electron-hole pairs. Moreover, the BiFeO3/MoS2 nanocomposite can be separated and collected easily by an external magnetic field and maintain high activity after three times photoreaction cycles. Trapping experiments have contributed to propose the possible mechanism for the improved photocatalytic activity of the nanocomposite.

Crafting carbon sphere-titania core–shell interfacial structure to achieve enhanced visible light photocatalysis

Anchoring titania on carbon sphere forms a core–shell structure (TiO2@CS) which shows high-performance visible light response photocatalysis. In order to further improve such photocatalysis, herein acrylic acid (AA) is employed to modify the surface chemistry of CS so as to craft the interfacial structure between CS and TiO2. It was found that AA addition leads to morphology change from smooth to rough surface or to aggregates of smaller primary nanoparticles which, however, do not impede formation of the close contact core–shell structure with TiO2. Detailed analysis demonstrates a complex change in surface functional groups of CS in which the acidic OH is the major type whose quantity shows a peak maximum and a continuous increase at small and large AA addition ranges, respectively. Photocatalysis, photocurrent, and DFT calculation certificate that rather than COOH, the acidic OH, particularly, that related to sufficiently conjugated backbone carbon contributes to the formation of the interfacial structure which facilitates better visible light responsive photocatalysis. Benefiting from the improved interfacial charge separation, the visible light photoactivity reaches the highest when the quantity of the conjugated carbon-related OH becomes the maximum. An explicit charge transfer mechanism is proposed based on both experimental and theoretical calculation results.

One-Dimensional/Two-Dimensional/Three-Dimensional Dual Heterostructure Based on MoS2-Modified ZnO-Heterojunction Diode with Silicon

Two-dimensional (2D) transition-metal dichalcogenides and their composites with metal oxides showed promising applications for visible-light responsive photocatalysis. In this work, we have synthes...

Synthesis of eco-friendly porous g-C3N4/SiO2/SnO2 composite with excellent visible-light responsive photocatalysis

Forming eco-friendly heterojunction photocatalysts is excellent method to accelerate the separation rate of photogenerated charge carriers, which is attracting more and more attention. In this study, a novel and stable disordered porous g-C3N4/SiO2/SnO2 (DOP-CSiSn) heterojunction composites was fabricated by a sol-gel hard template method, and the optimal g-C3N4 doped ratio was adjusted in DOP-CSiSn. The DOP-CSiSn photocatalyst had the much larger specific surface area and disordered porous structure, which exhibited strong photocatalytic effect to degrade Rhodamine B (RhB), Methylene blue (MB) and Methyl orange (MO) under visible light. When the g-C3N4 doping content was 30 wt%, the highest photocatalytic activities were obtained, and the degradation rate of MB and MO were 99.73% and 95.58% after 50 min, respectively. Degradation rate of RhB was 95.10% after 90 min. Photocatalytic degradation rate of organic pollutants were still more than 90% after six time consecutive cycles, the composite had wonderful stability and potential value in environmental purification.

Photocatalytic and semiconducting performance of La modified M-type lead hexaferrite

La0.2Pb0.7Fe12O19 (LaPbM), a traditional M-type hexaferrite with permanent magnets, was revealed to be a semiconductor by optical spectroscopy. The direct and indirect band gap energies were determined to be 1.70 eV and 0.72 eV, respectively. The Raman spectrum with nine phonon lines are indicative characterization of LaPbM and clearly distinguishes from that of α-Fe2O3 and γ-Fe2O3. Another type of expression for the semiconductor characterization of LaPbM is its photocatalytic activity upon degradation of Methylene Blue (MB) under visible light illumination. Gradually, with an increase in the duration of photodegradation reaction, the color of the MB solution changes from deep blue to pale white and the optical absorption coefficient decreases rapidly. The degradation duration was cut in half when graphen@La0.2Pb0.7Fe12O19 was used as the photocatalytic system. This structure reduced charge recombination and thus enhanced the reactivity. Graphene greatly improves the degradation rate and efficiency of LaPbM through electron transfer. These results provide a new insight into the high performance of visible-light responsive photocatalysis of LaPbM and facilitates its application in environmental protection issues.

Facile and Cost-Efficient Synthesis of Quasi-0D/2D ZnO/MoS2 Nanocomposites for Highly Enhanced Visible-Light-Driven Photocatalytic Degradation of Organic Pollutants and Antibiotics.

Nanoscale transition-metal dichalcogenide materials showed promising potential for visible-light responsive photocatalysis. Here, we report our investigations on the synthesis of heterodimensional nanostructures of two-dimensional (2D) ultrathin MoS2 nanosheets interspersed with ZnO nanoparticles by using a facile two-step method consisting of sonication-aided exfoliation technique followed by a wet chemical process. The photocatalytic activity of the nanocomposites was examined by studying the degradation of different organic dye pollutants and tetracycline, a common antibiotic, under visible-light irradiation. It is found that within 30 min more than 90 % of the model organic dye was photodegraded by the optimized quasi-0D/2D hybrid nanomaterial. The reaction rate of pollutant degradation is about five and eight times higher than those of the pristine MoS2 naonosheets and P25 photocatalysts, respectively. The outstanding photocatalytic activity of the heterodimensional hybrids can be attributed to a few beneficial features from the synergetic effects. Most importantly, the intimate junction between ZnO and MoS2 facilitates the separation of photogenerated carriers, leading to the enhancement of photocatalytic efficiency. A tentative photocatalytic degradation mechanism was proposed and tested. Overall, the present work provides valuable insights for the exploration of cost-effective nanoscale heterodimensional hybrids constructed from atomically thin layered materials.

Oxygen vacancies of the TiO2 nano-based composite photocatalysts in visible light responsive photocatalysis.

The TiO2 nano-based composite photocatalyst is best known for application in solving the recent issues related to energy and environmental purification. Due to the low cost, nontoxicity, chemical stability and high efficiency of TiO2, it is unquestionably one of the most considered materials in environmental treatment. In this systematic review, we reveal the outstanding potential of oxygen vacancy in photocatalysis, and discuss the contemporary advancement in the photocatalytic activities, productivity, preparation methods and oxygen vacancy of the TiO2 nano-based composite photocatalyst for environmental treatment and energy as well as wastewater treatment. This exposé is anticipated to enlighten researchers and engineers on the specific management and assessment of the environment, which warrants prospective research into developing appropriate mechanisms for energy, wastewater treatment and environmental purification.

Cost-effective fabrication of ZnO/g-C3N4 composite film coated stainless steel meshes for visible light responsive photocatalysis

The ZnO and ZnO/g-C3N4 composite films were deposited on stainless steel meshes having different apertures (370, 500, 780 and 1000μm) using a simple cost-effective automated tubular nebulizer spray pyrolysis technique for photocatalytic degradation of organic pollutants. Photocatalytic studies were done for the degradation of methylene blue (MB) and malachite green (MG). The photocatalytic studies reveal that the ZnO/g-C3N4 composite film having smallest aperture exhibits superior photocatalytic activity compared with other meshes. The degradation efficiency of this composite film for MB and MG dyes are 97% (irradiation time-75min) and 95% (irradiation time-45min), whereas for pristine ZnO film the corresponding efficiencies are only 88% and 87%. The aperture size related photocatalytic efficiency variations and the effect of g-C3N4 addition on the photocatalytic efficiency of ZnO films have been addressed with appropriate supporting experimental evidences and reports.

Fabrication of Co + F Doped ZnO Films for Improved Visible Light Responsive Photocatalysis

The aim of this work is to investigate the efficacy of nebulizer sprayed ZnO–Co–F thin films for degrading the methylene blue (MB) aqueous solution under visible light irradiation. The physical properties of the prepared samples like structural, surface morphological and optical properties are studied using X-ray diffractometer (XRD), Scanning Electron Microscope (FESEM), UV-vis NIR spectrometer, spctroflurometer (PL) and Fourier Transform Infrared spectrometer (FTIR). The photocatalytic studies revealed that ZnO–Co–F film exhibited superior degradation efficiency over ZnO–Co and ZnO against MB as evinced by the degradation rate constants, 0.0782, 0.0475 and 0.0289 min–1, respectively. This study showed that Co + F doping helps to remove the major limitations of ZnO and thereby leads towards better visible light activity. The structural and optical studies revealed the proper incorporation of Co2+ and F– ions into the ZnO lattice and the reduction in band gap. PL emission confirmed that Co + F doping reduces the electronhole recombination rate and increases the availability of free carriers.

Enhanced visible light responsive photocatalysis by ZnO:Mg/RGO nanocomposites

Mg and RGO activated ZnO nanocomposites were prepared using a low-cost soft chemical method. As per the structural studies the samples exhibit wurtzite structure of ZnO with hexagonal crystal system. No secondary phases were observed. The photocatalytic activity of the prepared samples were assessed through the degradation of cationic dyes, methylene blue (MB) and malachite green (MG) under visible light irradiation. The studies revealed that the ZnO:Mg/RGO nanocomposite exhibits enhanced photocatalytic as well as antibacterial behavior compared to bare ZnO. The optical, structural and surface morphological studies support the reports on the photocatalytic and antibacterial activities of the synthesized samples.

Copper and Nitrogen Co-Doping Effect on Visible-Light Responsive Photocatalysis of Plasma-Nitrided Copper-Doped Titanium Oxide Film

In order to clarify the visible-light responsive photocatalysis of TiO2 co-doped with Cu and N atoms, plasma-nitridation was taken place to Cu-doped TiO2 film. Cu-doped TiO2 films were prepared by dip-coating method and they were nitrided by nitrogen plasma in the plasma-enhanced CVD system. Cu-doped TiO2 films before and after plasma-nitridation show similar X-ray diffraction peaks of anatase TiO2. XPS analysis reveals that the ionic states of Ti and Cu in the Cu-doped TiO2 films are Ti4+ and Cu+, respectively. After nitrogen plasma treatment, oxygen atoms are released by substitution of nitrogen atoms in the TiO2 matrix, so that Cu+ is oxidized to generate Cu2+ and at the same time oxygen vacancy is formed. The absorption edge of both Cu-doped and plasma-nitrided Cu-doped TiO2 did red shift. Visible-light responsive photocatalytic activity of the Cu-doped TiO2 film degraded after nitrogen plasma treatment.

Electrospinning, solvothermal, and self-assembly synthesis of recyclable and renewable AgBr[sbnd]TiO2/CNFs with excellent visible-light responsive photocatalysis

Novel carbon nanofibers (CNFs) modified by AgBrTiO2 composite nanoparticles (NPs) would be the most desirable nanostructure materials in preparing visible-driven catalysts because of its efficient charge separation and transport properties as well as superior light harvesting efficiency. In this study, TiO2 nanoparticles grown directly on Ag/CNFs were prepared by a simple solvothermal synthesis. The formation of AgBr, which derived from Ag NPs, was carried out by the gas/solid oxidization reaction. The characterization results indicate that AgBr-sensitized TiO2 NPs were uniformly covered on the surface of CNFs. Under visible light irradiation, the degradation efficiency of MO in the presence of AgBrTiO2/CNFs was much higher than that of TiO2/CNFs or AgTiO2/CNFs, and the as-prepared catalysts showed a universal degradation ability for different organics. Meanwhile, AgBrTiO2/CNFs had a certain photochemical stability and could be regenerated easily. The as-prepared composites could be easily separated from the solution phase due to the large length-diameter ratio of CNFs, suggesting that the AgBr-sensitized TiO2 nanoparticles loading on carbon nanofibers had a potential application in the field of dye degradation.

Magnetic BiFeO3 grafted with MWCNT hybrids as advanced photocatalysts for removing organic contamination with a high concentration

This work focuses on a novel visible light responsive photocatalysis system for removing organic contamination employing MWCNTs as a scaffold and an efficient electron relay mediator and visible light and magnetically responsive BiFeO3.