Sunlight Photocatalytic Activity Research Articles

A simple and low-cost approach to fabricate TiO2-NO2 hollow spheres with excellent simulated sunlight photocatalytic activity

Nitryl surface functionalized TiO2 hollow spheres (TiO2-NO2 HSs) composite material was successfully fabricated by a simple sol-gel combined with solvothermal and concentrated HNO3 treatment strategy using carbon microspheres obtained from hydrothermal carbonization of waste Camellia oleifera shells as a template. The microstructure, surface property, compositional and structural information, and optical and electronic property of as-prepared TiO2-NO2 HSs were well characterized. Compare with conventional g-C3N4 and TiO2 photocatalysts, the as-prepared TiO2-NO2 HSs exhibited excellent simulated sunlight photocatalytic activity toward aqueous organic pollutants degradation and hydrogen evolution from water-splitting, which can be attributed to their unique hollow spherical microstructure and the introduction of -NO2 groups.

In situ loading of Ag2WO4 on ultrathin g-C3N4 nanosheets with highly enhanced photocatalytic performance

The g-C3N4 nanosheets (g-C3N4NS) exhibit more excellent property than common bulk g-C3N4 (g-C3N4-B) due to their large surface areas, improved electron transport ability and well dispersion in water. In this work, ultrathin g-C3N4NS with a thickness of about 2.7nm have been synthesized by a simple thermal exfoliation of bulk g-C3N4, and then Ag2WO4 nanoparticles are in situ loaded on their surface to construct the Ag2WO4/g-C3N4NS heterostructured photocatalysts. Due to their unique physicochemical properties, the as-prepared heterostructures possess a fast interfacial charge transfer and increased lifetime of photo-excited charge carriers, and exhibit much higher photocatalytic activity. Under visible light irradiation, the optimum photocatalytic activity of Ag2WO4/g-C3N4NS composites is almost 53.6 and 26.5 times higher than that of pure g-C3N4-B and Ag2WO4/g-C3N4-B heterostructures towards the degradation of rhodamine B, respectively, and is almost 30.6 and 9.8 times higher towards the degradation of methyl orange, respectively. In addition, the natural sunlight photocatalytic activities of the as-prepared samples are also investigated.

Preparation and characterization of sphere-shaped BiVO4/reduced graphene oxide photocatalyst for an augmented natural sunlight photocatalytic activity

Sphere-shaped bismuth vanadate (BiVO4) was synthesized by a simple and cost-effective low temperature hydrothermal method. In order to improve the photo-response of the prepared sphere-shaped BiVO4 in natural sunlight, the as-synthesized BiVO4 incorporated with graphene oxide (GO) was assembled into sphere-shaped BiVO4/reduced graphene oxide (RGO) composites. For studying their morphological, physical, optical, and photo-chemical properties, the obtained composites were well characterized with the aid of various physicochemical techniques, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflectance, N2 adsorption/desorption and electrochemical measurements. In addition, the photocatalytic performance of the prepared BiVO4 and BiVO4/RGO composites were evaluated by monitoring the degradation of Rhodamine B (RhB)-contained wastewater under natural sunlight irradiation, where the highest photocatalytic degradation efficiency can be achieved for the BiVO4/RGO composites with 3 wt% RGO dosage (approx. 68.85% increase compared with that of pure sphere-shaped BiVO4) The improved photocatalytic activity of BiVO4/RGO composite is attributed to the formation of well-defined BiVO4-RGO interfaces, which greatly enhances the charge separation efficiency.

Ionic-liquid assisted ultrasonic synthesis of BiOCl with controllable morphology and enhanced visible light and sunlight photocatalytic activity

Ionic liquid assisted ultrasonic method was developed to prepare BiOCl at room temperature in a short time. Through this method, BiOCl with different controllable morphologies can be easily obtained via the simple change of the reaction solvents. The flowerlike microspheres, sheet and plate morphologies have been prepared in DMF, ethanol and water, respectively. And the as-prepared BiOCl samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), N2 absorption-desorption isotherms and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of the as-prepared samples was evaluated towards degradation of Rhodomine B (RhB), Quinoline blue (QB) and methyl orange (MO). The results indicate that the as-prepared BiOCl samples have high photoactivities for the degradation of dyes both under the visible light irradiation and sunlight irradiation.

Enhanced sunlight photocatalytic activity and recycled Ag–N co-doped TiO2 supported by expanded graphite C/C composites for degradation of organic pollutants

Removing organic pollutants from wastewater is urgent for developing a sustainable ecological environment. A highly efficient visible light photocatalyst was synthesized through a sol–gel method using C/C composites (expanded graphite dipping in the phenol formaldehyde resin, EGC) coated with Ag, N co-doped TiO2. The as-prepared composites were characterized through scanning electron microscopy (SEM), X-ray diffraction (XRD), N2 adsorption–desorption (BET), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible light diffuse reflectance spectroscopy (UV–Vis-DRS). The XRD and N2 adsorption–desorption (BET) results revealed that the photocatalysts were composed of mesoporous structures mainly with anatase TiO2. The effects of Ag content and calcination temperature on the photocatalytic activity of Ag–N-TiO2/EGC photocatalysts were studied. The results showed that under visible light, the photocatalytic efficiencies of Ag1.0-N-TiO2/EGC (550 °C) obtained for the degradation of Rhodamine B (RB) and diesel are 7.4 times and 3.9 times higher, respectively, than those of N-TiO2/EGC with high mineralization. The enhanced photocatalytic activity of the Ag–N-TiO2/EGC composites was attributed to the porosity and flexible electron transport paths for formation of superoxide radicals. These characteristics assured Ag–N-TiO2/EGC photocatalyst as a high-efficiency photocatalytic material for organic pollutant degradation under visible light.

Mild synthesis of {001} facet predominated Bi2O2CO3 clusters with outstanding simulated sunlight photocatalytic activities

Bi2O2CO3 clusters built up of ultrathin nanosheets with predominated {001} facets were facilely synthesized via a template-free hydrothermal strategy at a mild temperature of 60 °C and exhibit excellent photocatalytic activity.

Facile ethanol/water solvothermal synthesis of {001} facet oriented WO3architectures with superior simulated sunlight photocatalytic activities

Flower shaped WO3 architectures weaved up of ultrathin nanorods with oriented {001} facets were successfully prepared via a facile ethanol/water solvothermal strategy, at a low temperature of 100 °C for 4 h. Characterizations of phase, morphology, microstructure, optical absorption, BET surface area, photoluminescence, photoelectrochemical properties and photocatalytic behavior were systematically explored. The volume ratio of ethanol and water was confirmed to be a key parameter in regulating the morphology and microstructure of WO3 by tuning the dielectric properties of the mixed solvent. The {001} faceted WO3 structures exhibit improved photocatalytic activity for the degradation of methyl orange with the reaction rate constant k enhanced by 2.1 fold, compared to the hydrothermal counterpart assembled by thick, individual WO3 nanorods. The active {001} facets with faster charge migration and enhanced surface area with more adsorption sites account for the excellent photocatalytic behavior. In addition, the active species in the photocatalytic reaction were investigated in detail, using terephthalic acid capture, ESR and radical scavengers. Combining the band edge positions of WO3 and the redox potentials of the active species, a possible migration mechanism of photogenerated e−/h+ pairs on the surface of WO3 is proposed. This work provides some new insights into the rational design and synthesis of facet-dependent 3D semiconductor photocatalysts.

Liquid phase-based ultrasonic-assisted synthesis of G–ZnO nanocomposites and its sunlight photocatalytic activity

The graphene (G)–ZnO (G–ZnO) nanocomposites with high photocatalytic activity have been successfully prepared by a simple and inexpensive liquid phase-based ultrasonic-assisted method with different doping amounts of graphene oxide. The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV–visible diffuse reflectance spectroscopy (UV–vis/DRS) and Brunauer–Emmett–Teller (BET) analysis. The results indicate that the assistance of ultrasonic can effectively decrease the size of ZnO nanostructure and increase the uniformity of the mixture of graphene and ZnO particles. Meanwhile, the sunlight absorption of the G–ZnO nanocomposite is gradually improving with the increase of the ratio of graphene. The obtained G–ZnO-30 photocatalyst shows the best photocatalytic activity for methylene blue (MB) and methyl orange (MO) under sunlight irradiation. The degradation rates of MB and MO in the presence of G–ZnO-30 reached up to 98.1% and 95.7%, respectively, under solar radiation for 1h and 6h. In addition, the photocatalyst exhibits outstanding separability and high stability.

Improved Sun light photocatalytic activity of α-Fe2O3 prepared with the assistance of CTAB

In this paper, α-Fe2O3 photocatalyst with enhanced solar-driven photocatalytic activity was prepared by a facile hydrothermal routine with the assistance of cetyltrimethylammonium bromide (CTAB). The surface parameters, the distribution of particle size, structure, morphology, and the photo-induced charge separation rate of the photocatalyst prepared (CTAB-Fe2O3) were characterized by the Brunauer-Emmett-Teller (BET) method, particle size analyzer, X-ray diffraction (XRD), scanning electron microscopy (SEM) and surface photovoltage (SPV) spectroscopy, respectively. The results reveal that CTAB alters the surface parameter and the morphology, decreases the particle size, and enhances the photo-induced charge separation rate of α-Fe2O3. The photocatalytic activity of CTAB-Fe2O3 for decolorization of methyl orange (MO) solution was evaluated. The results show that the photocatalytic activity of CTAB-Fe2O3 is more than five times of that of the reference Fe2O3 and the possible reason was discussed.

Enhanced simulated sunlight induced photocatalytic activity by pomegranate-like S doped SnO2@TiO2 spheres

Abstract In the present study we prepared pomegranate-like S doped SnO2@TiO2 composite sphere nanoparticles with high simulated sunlight photocatalytic activity. Various characterization techniques such as TEM, HRTEM, SEM, XRD, EDX, XPS were used to check its morphology and structural properties. UV–vis spectra showed that the composite particles have broadened absorption edge and narrowed energy band gap compared with pure TiO2. The composite particles displayed enhanced photocatalytic activity compared with other photocatalysts, including TiO2, S doped TiO2, SnO2@TiO2, etc. The rhodamine B (RhB) dyes can be degraded by 97% in 200 min, by synthesizing composite particles, under the simulated sunlight irradiation. The electron scavenger (K2S2O8) can accelerate the photocatalytic activity by 62%, indicating that the holes act as the major role for the oxidization of organic pollutants. Mechanism discussion was also proposed to support that the prepared S doped SnO2@TiO2 composite nanoparticles can serve as a promising candidate for the applications in many solar catalytic fields.

Enhanced sunlight photocatalytic activity of Ag3PO4 decorated novel combustion synthesis derived TiO2 nanobelts for dye and bacterial degradation

This study demonstrates the synthesis of TiO2 nanobelts using solution combustion derived TiO2 with enhanced photocatalytic activity for dye degradation and bacterial inactivation. Hydrothermal treatment of combustion synthesized TiO2 resulted in unique partially etched TiO2 nanobelts and Ag3PO4 was decorated using the co-precipitation method. The catalyst particles were characterized using X-ray diffraction analysis, BET surface area analysis, diffuse reflectance and electron microscopy. The photocatalytic properties of the composites of Ag3PO4 with pristine combustion synthesized TiO2 and commercial TiO2 under sunlight were compared. Therefore the studies conducted proved that the novel Ag3PO4/unique combustion synthesis derived TiO2 nanobelt composites exhibited extended light absorption, better charge transfer mechanism and higher generation of hydroxyl and hole radicals. These properties resulted in enhanced photodegradation of dyes and bacteria when compared to the commercial TiO2 nanocomposite. These findings have important implications in designing new photocatalysts for water purification.

Effectiveness of a photocatalytic organic membrane for solar degradation of methylene blue pollutant

The results of a feasibility study are presented on the use of a polystyrene (PS) organic membrane as a photocatalyst support in the degradation of organic pollutants in aqueous solution. Methylene blue (MB) was employed as a model dye and commercial titanium dioxide (TiO2) was used as a photocatalyst. The MB dye which is resistant to direct photolysis especially at high concentrations was successfully eliminated by TiO2 fixed on the PS membrane in aqueous dispersion under solar irradiation. Photodegradation results of MB showed that the film with 10 wt% TiO2 exhibited a remarkable ultraviolet (sun light) photocatalytic activity over 5 h, with 68% of the pollutant being degraded. This is similar to a TiO2 slurry system. The photocatalytic degradation obeyed pseudo-first-order kinetics at low initial MB concentration. The optimum pH for efficient removal of dye was found to be 11. An increase in initial dye concentration decreased the degradation rate. The applicability of Langmuir–Hinshelwood kinetic equation revealed that the degradation of MB occurred mainly on the surface of the photocatalyst. The concept and results provide a promising platform for fabricating highly efficient organic photocatalytic membranes for water treatment.

Sunlight responsive WO3/ZnO nanorods for photocatalytic degradation and mineralization of chlorinated phenoxyacetic acid herbicides in water

Highly effective WO3/ZnO nanorods (NRs) were synthesized via a hydrothermal–deposition method for degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) under natural sunlight. The structural properties of WO3/ZnO NRs such as morphology, crystal structure, porous properties and light absorption characteristics were investigated in detail. The X-ray diffraction and X-ray photoelectron spectroscopy results indicated that the prepared samples were two-phase photocatalysts consisted of WO3 and ZnO NRs. The UV–vis diffuse reflectance spectroscopy result showed that the addition of WO3 altered the optical properties of the photocatalysts. In contrast with the pure ZnO NRs, commercial anatase TiO2 and commercial WO3, the WO3/ZnO NRs showed excellent sunlight photocatalytic activities in degrading 2,4-D. The optimal WO3 loading and calcination temperature were also determined. Based on the band position, the synergetic effect of WO3 and ZnO NRs was the source of the enhanced photocatalytic activity as validated by PL and terephthalic acid-photoluminescence measurements. The reaction intermediates and degradation pathways of 2,4-D were elucidated by a HPLC method. In addition, the extent of mineralization during the 2,4-D degradation was also estimated using total organic carbon (TOC) and ion chromatography (IC) analyses.

Fabrication and enhanced simulated sunlight photocatalytic activity of metallic platinum and indium oxide codoped titania nanotubes

Pt/In2O3–TiO2-NTs were fabricated by a multicomponent assembly-solvothermal treatment, and showed excellent activity originating from an improved quantum yield and nanotubular geometries.

Effect of synthesis medium on aggregation tendencies of ZnO nanosheets and their superior photocatalytic performance

A simple soft chemical method has been suggested for large-scale production of zinc oxide (ZnO) nanosheets at room temperature using two synthesis mediums: aqueous (H2O) and non-aqueous (C2H5OH). In H2O medium, nanosheets interwoven group wise in flower-like structures revealing the strong inter-hydrogen bonding among initially nucleated ZnO nanocrystals, whereas weak hydrogen bonding in C2H5OH medium leads to the formation of un-aggregated interwoven’ nanosheets. The growth of ZnO flower-like and interwoven nanosheets proceeded via anisotropic oriented attachment of ZnO nanocrystals. Obtained nanosheets were faceted, possessing large surface area, width hundreds of nanometers, and thickness in tens of nanometer, as characterized by scanning electron microscopy and transmission electron microscopy. These nanosheets show high sunlight photocatalytic activity toward the degradation of an organic pollutant ‘methylene blue dye.’ The enhancement in photodegradation efficiencies, interwoven sheets 99.94 %, and flower-like nanosheets 79.76 % for 120 min of irradiation is attributed to the surface oxygen vacancies narrowing the band gap as confirmed by photoluminescence spectra, faceted geometry, and large surface area of ZnO nanosheets.

Sunlight assisted photocatalytic mineralization of nitrophenol isomers over W6+ impregnated ZnO

The synthesis, characterization and sunlight photocatalytic activity of W6+ impregnated ZnO for the degradation of nitrophenol isomers (2-nitrophenol, 3-nitrophenol, and 4-nitrophenol) is reported. Compared to pure ZnO, the impregnated catalysts exhibited a relatively improved spectral response in the visible region. The significant decrease in luminescence intensity for W6+ impregnated catalysts, relative to pure ZnO, established the effective trapping of charge carriers by surface bonded W6+ states. The characterization of the impregnated catalysts by FESEM, XRD and XPS revealed the presence of impregnated W6+ entities at the surface without affecting the morphology of ZnO. The synthesized catalysts exhibited superior activity for the mineralization of three nitrophenol isomers under sunlight exposure. Based on HPLC analysis, ∼99% of 2- and 4-nitrophenol was degraded in a short span of 120min while a degradation of >80% was observed in 3-nitrophenol in the same period. Time scale TOC measurements ratified the mineralization capability of impregnated catalysts. The release of NO2−, NO3− ions in the solution, pH measurements and non-existence of hydroxylated aromatic intermediates revealed that superoxide anion radicals (O2−) are the major contributors in the degradation process. Besides the traces of coupling products, major intermediates identified by GC–MS analysis were either aliphatic dihydroxy alcohols, carboxylic acids or other oxygen containing species depicting that the degradation process proceeds through ring opening mechanism. The W6+ impregnated catalyst also furnished high activity in the visible portion of sunlight. Suitable kinetic models were applied to estimate the rate constants (k) of various processes involved in the degradation process. The stability of the photocatalyst against photocorrosion and the possible decrease in the activity of the catalyst in the successive use was also monitored.

Solid-Phase Synthesis of Mesoporous ZnO Using Lignin-Amine Template and Its Photocatalytic Properties

Nanoparticles of zinc oxide (ZnO) with high sunlight photocatalytic activity were synthesized by a solid-phase method using lignin-amine (LA) template. The prepared ZnO was characterized using UV–visible diffuse reflectance spectroscopy (UV–vis/DRS), thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), Brunauer–Emmett–Teller (BET) analysis, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. XRD confirmed the formation of hexagonal wurtzite structural ZnO, and the SEM results indicated the porous surface characteristic of the products. The average ZnO crystallite size determined by XRD was 15–44 nm. Room-temperature PL spectra exhibited a strong ultraviolet emission band centered at about 383 nm. The BET isotherms were of type IV with a type H3 hysteresis loop, suggesting the presence of abundant mesoporous structures in the architectures of the as-prepared ZnO. The sample calcined at 400 °C (ZL4) showed a PL emission peak of weak...

Reduced graphene oxide on a dumbbell-shaped BiVO4 photocatalyst for an augmented natural sunlight photocatalytic activity

A simple and efficient route for the controllable synthesis of dumbbell-shaped BiVO4 hierarchical structures at a large scale with uniform size and shape distributions was demonstrated, where the as-synthesized BiVO4 products were then incorporated with prepared reduced graphene oxide (RGO) sheets to form dumbbell-shaped BiVO4/RGO composites. The obtained composites were well characterized with the aid of various techniques to study their morphological, physical, optical, and photo-chemical properties. Photocatalytic capacities of the pure BiVO4 dumbbells and BiVO4/RGO composites have been evaluated by investigating the degradation of Rhodamine B (RhB)-contained wastewater under natural sunlight irradiation, where a noticeable augmentation in the natural-sunlight-driven decolorization efficiency (approx. 26% increase compared with that of pure BiVO4) of RhB could be achieved on the prepared BiVO4/RGO composites under experimentally optimum conditions. The cycle-stabilized photocatalytic performances of the BiVO4/RGO composites have also been probed.

Highly efficient and recyclable triple-shelled Ag@Fe3O4@SiO2@TiO2 photocatalysts for degradation of organic pollutants and reduction of hexavalent chromium ions

Herein, we demonstrate the design and fabrication of the well-defined triple-shelled Ag@Fe3O4@SiO2@TiO2 nanospheres with burr-shaped hierarchical structures, in which the multiple distinct functional components are integrated wonderfully into a single nanostructure. In comparison with commercial TiO2 (P25), pure TiO2 microspheres, Fe3O4@SiO2@TiO2 and annealed Ag@Fe3O4@SiO2@TiO2 nanocomposites, the as-obtained amorphous triple-shelled Ag@Fe3O4@SiO2@TiO2 hierarchical nanospheres exhibit a markedly enhanced visible light or sunlight photocatalytic activity towards the photodegradation of methylene blue and photoreduction of hexavalent chromium ions in wastewater. The outstanding photocatalytic activities of the plasmonic photocatalyst are mainly due to the enhanced light harvesting, reduced transport paths for both mass and charge transport, reduced recombination probability of photogenerated electrons/holes, near field electromagnetic enhancement and efficient scattering from the plasmonic nanostructure, increased surface-to-volume ratio and active sites in three dimensional (3D) hierarchical porous nanostructures, and improved photo/chemical stability. More importantly, the hierarchical nanostructured Ag@Fe3O4@SiO2@TiO2 photocatalysts could be easily collected and separated by applying an external magnetic field and reused at least five times without any appreciable reduction in photocatalytic efficiency. The enhanced photocatalytic activity and excellent chemical stability, in combination with the magnetic recyclability, make these multifunctional nanostructures promising candidates to remediate aquatic contaminants and meet the demands of future environmental issues.

Sunlight photocatalytic activity enhancement and mechanism of novel europium-doped ZnO hierarchical micro/nanospheres for degradation of phenol

Europium-doped ZnO hierarchical micro/nanospheres (Eu/ZnO) were synthesized for the first time via a facile and surfactant-free chemical solution route. The as-synthesized products were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy dispersion X-ray analysis, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, UV–visible diffuse reflectance spectroscopy, nitrogen adsorption–desorption and photoluminescence spectroscopy. The results showed that the as-synthesized products were well-crystalline and accumulated by large amount of interleaving nanosheets. It was also observed that the Eu doping increased the light absorption ability of Eu/ZnO and a red shift for Eu/ZnO appeared when compared to pure ZnO. Under natural sunlight irradiation, the Eu/ZnO exhibited much higher photocatalytic activity than those of pure ZnO, Eu-doped ZnO nanorods (Eu/ZNRs) and commercial TiO2 for the degradation of phenol. The photocatalytic enhancement of Eu/ZnO products was attributed to their high charge separation efficiency and hydroxyl radical generation ability as evidenced by the photoluminescence spectra. By using several radical scavengers, hydroxyl radical was determined to play a pivotal role for the phenol degradation. Furthermore, the Eu/ZnO could be easily separated and reused, showing great potential for practical applications in environmental cleanup and solar energy conversion.