Enhancement Of Visible Light Photocatalytic Activity Research Articles

Construction of Magnetically Retrievable g-C3N4/CeO2-Fe3O4-Reduced Graphene Oxide Composites With Enhanced Visible-Light Photocatalytic Activity And Antibacterial Properties

Construction of Magnetically Retrievable g-C3N4/CeO2-Fe3O4-Reduced Graphene Oxide Composites With Enhanced Visible-Light Photocatalytic Activity And Antibacterial Properties

Removal of Organic Dye by Ti-Doped Bi2O3/MMT with Enhanced Visible-Light Photocatalytic Activity

Removal of Organic Dye by Ti-Doped Bi2O3/MMT with Enhanced Visible-Light Photocatalytic Activity

Enhancing visible light photocatalytic activity of holmium doped g-C3N4 and DFT theoretical insights

In the search of novel photocatalysts to increase the effect of visible light in photocatalysis, g-C3N4 (CN) has become a shining star. Rare earth metals have been used as dopant material to reinforce the photocatalytic activity of CN due to their unique electron configuration recently. In this present study, the pure and different amounts of Ho-doped g-C3N4 (HoCN) photocatalysts were successfully synthesized using urea as a precursor by the one-pot method. Morphological, structural, optical, and vibrational properties of the synthesized photocatalysts were characterized by SEM, EDX, XRD, TGA, XPS, FTIR, PL, TRPL, Raman, DRS, and BET analyses. In addition, theoretical calculations using density functional theory (DFT) were meticulously carried out to delve the changes in the structural and electronic structure of CN with holmium doping. According to calculations, the chemical potential, electrophilicity, and chemical softness are higher for HoCN, while HOMO–LUMO gap, dipole moment, and the chemical hardness are lower for the pure one. Thus, holmium doping becomes desirable with low chemical hardness which indicates more effectivity and smaller HOMO–LUMO gap designate high chemical reactivity. To determine the photocatalytic efficiency of the pure and doped CN photocatalysts, the degradation of methylene blue (MB) was monitored under visible light. The results indicate that holmium doping has improved the photocatalytic activities of CN samples. Most strikingly, this improvement is noticeable for the 0.2 mmol doped CN sample that showed two times better photocatalytic activity than the pure one.

Hydrothermal Synthesis of Bismuth Ferrite Hollow Spheres with Enhanced Visible-Light Photocatalytic Activity.

In recent years, semiconductor hollow spheres have gained much attention due to their unique combination of morphological, chemical, and physico-chemical properties. In this work, we report for the first time the synthesis of BiFeO3 hollow spheres by a facile hydrothermal treatment method. The mechanism of formation of pure phase BiFeO3 hollow spheres is investigated systematically by variation of synthetic parameters such as temperature and time, ratio and amount of precursors, pressure, and calcination procedures. The samples were characterized by X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and UV-vis diffuse reflectance spectroscopy. We observe that the purity and morphology of the synthesized materials are very sensitive to synthesis parameters. In general, the chemically and morphologically very robust hollow spheres have diameters in the range of 200 nm to 2 μm and a wall thickness of 50-200 nm. The synthesized BiFeO3 hollow spheres were applied as catalysts in the photodegradation of the model pollutant Rhodamine B under visible-light irradiation. Notably, the photocatalyst demonstrated exceptionally high removal efficiencies leading to complete degradation of the dye in less than 150 min at neutral pH. The superior efficiencies of the synthesized material are attributed to the unique features of hollow spheres. The active species in the photocatalytic process have been identified by trapping experiments.

A Study of the Degradation of LEV by Transparent PVA/NCD-TiO2 Nanocomposite Films with Enhanced Visible-Light Photocatalytic Activity

In recent years, antibiotics (such as levofloxacin (LEV)) have been detected widely in the environment. Semiconductor photocatalysis has been recognized as a promising technology for removing pollutants in the environment. In this work, nitrogen and carbon codoped titanium dioxide nano-catalyst (NCD-TiO2) was immobilized in polyvinyl alcohol (PVA) matrix to form PVA/NCD-TiO2 films through solution casting and thermal treatment, which exhibited good photocatalytic efficiency for LEV degradation. The results showed that about 42% LEV can be degraded after 2 h in the presence of PVA/NCD-TiO2 nanocomposite film (the weight ratio of NCD-TiO2 to PVA is 8% and thermal treatment is 120 °C) under visible light. Moreover, possible pathways of photocatalytic degradation of LEV according to the detected intermediates are proposed, which provide insight into the degradation mechanism of LEV by using PVA/NCD-TiO2 photocatalytic films. Finally, the synthesized PVA/NCD-TiO2 films exhibited excellent reusability and stability in photocatalysis. This work provides fundamental support for the design of a high-stability, excellent photocatalyst for practical application.

Enhancement of visible-light photocatalytic activity of ZnO/ZnS/g-C3N4 by decreasing the bandgap and reducing the crystallite size via facile one-step fabrication

Ternary ZnO/ZnS/g-C3N4 (ZZGC) nanocomposites were synthesized via a modified high-pressure solvent-free thermal method and subsequently used as highly efficient visible-light-driven photocatalysts to degrade organic pollutants. ZZGC composites were prepared at different temperatures and characterized by several microscopic and spectroscopic techniques. The best composite (named ZZGC-1, prepared at 400℃) exhibited 98.39% photocatalytic efficiency of methylene blue (MB) dye within 70 min under visible-light illumination. In addition, ZZGC-1 showed 1185% and 222% greater activity compared with similar reactions involving no catalyst and involving the corresponding binary composite (ZnO/ZnS prepared at 400℃), respectively. Under the same experimental conditions, ZZGC-1 demonstrated 89.04% efficiency for the deterioration of Congo red dye. The enhanced photocatalytic activity of ZZGC-1 may be due to its greater specific surface area compared with that of other composite photocatalysts. No substantial loss of activity or structural arrangement of ZZGC-1 was detected after five successive cycles. Overall, ZZGC nanocomposites can be used for practical and quick visible-light-driven photocatalytic wastewater treatment.

Construction of Direct Z-Scheme Ag2o/Bi2moo6 Heterostructured Microsphere with Enhanced Visible-Light Photocatalytic Activity

Construction of Direct Z-Scheme Ag2o/Bi2moo6 Heterostructured Microsphere with Enhanced Visible-Light Photocatalytic Activity

Enhancing visible light photocatalytic activity by transformation of Co3+/Co2+ and formation of oxygen vacancies over rationally Co doped ZnO microspheres

As a typical semiconductor, ZnO is considered as a favorable photocatalyst due to its excellent photoelectrochemical properties. However, low response of visible light and the recombination of photoinduced carriers limits its application in photocatalysis. Herein, a novel, robust and recyclable heterogeneous photocatalyst based on flower-like Co doped ZnO microspheres was presented without changing the hierarchical morphology. The crystal structure, light absorption, and electrochemical performance were systematically investigated, and the response of Co doped ZnO to visible light significantly enhanced with the gap band reduced from 3.20 eV to 2.54 eV. Due to the transformation of Co2+ to Co3+, more oxygen vacancies were produced, with more photoinduced electrons transferring to Co3+ which would greatly inhibit the recombination of photoinduced electrons and holes and improve photocatalytic activity. 2-Mercaptobenzothiazole (MBT) which is considered as a long half-life intermediate of antibiotic medicine is chosen as a target. As a result, the 7% Co-ZnO photocatalyst exhibited excellent photocatalytic activity for the degradation of MBT with the rate constant of 0.1498 min−1 and removing ratio of 97.3% in 50 min. The formation of excess oxygen vacancies and the conversion between Co2+ to Co3+ were further identified by XPS analysis. This work provides new sights for doping transition metal with different chemical valence in semiconductors for producing oxygen vacancy and improving the photocatalytic efficiency.

Enhancing visible-light photocatalytic activity of hard-biotemplated TiO2: From macrostructural morphology replication to microstructural building units design

Biotemplating technique using hard templates is an effective strategy to prepare visible light-activated TiO2 inherited macrostructural morphologies and self-doping elements from templates. However, conventional hard biotemplating method for preparing TiO2 focused only on replicating the macrostructural morphology of templates via the sol-gel method, and neglected the effect of microstructural building units for artificial macrostructure assembly. Generally, the microstructural building units of the final macrostructural morphology are tightly packed nanoparticles. This paper presents a newly designed solvothermal method to replace the microstructural building units from tightly packed nanoparticles to convex nanowires or concave pores. This strategy can achieve the leap of conventional hard biotemplating method from macrostructure replication to microstructural building units design. The hard-biotemplated TiO2 with designed microstructure exhibited significantly further enhanced visible-light photocatalytic efficiency in tetracycline degradation due to the increase of active sites, high separation efficiency of photo-generated electrons and reducing the charge-transfer resistance. Biotemplated TiO2 with concave porous microstructural building units is 22.0, 5.5 and 4.4 times higher than those of pure TiO2 and the two biotemplated TiO2 samples prepared via conventional sol-gel method and solvothermal method without glycerol or HF added, respectively. The enhanced visible-light photocatalytic efficiency by microstructure design was also demonstrated by using ciprofloxacin.

Preparation and Characterization of Tubelike g-C3N4/Ag3PO4 Heterojunction with Enhanced Visible-Light Photocatalytic Activity

Water pollution caused by dye wastewater is a potential threat to human health. Using photocatalysis technology to deal with dye wastewater has the advantages of strong purification and no secondary pollution, so it is greatly significant to look for new visible-light photocatalysts with high photocatalytic ability for dye wastewater degradation. Semiconductor photocatalyst silver phosphate (Ag3PO4) has high quantum efficiency and photocatalytic degradation activity. However, Ag3PO4 is prone to photoelectron corrosion and becomes unstable during photocatalysis, which severely limits its application in this field. In this study, a tubelike g-C3N4/Ag3PO4 heterojunction was constructed by the chemical precipitation method. An Ag3PO4 nanoparticle was loaded onto the surface of the tubelike g-C3N4, forming close contact. The photocatalytic activity of the photocatalyst was evaluated by the degradation of RhB under visible-light irradiation. The tubelike g-C3N4/Ag3PO4-5% heterojunction exhibited optimal photocatalytic performance. In an optimal process, the degradation rate of the RhB is 90% under visible-light irradiation for 40 min. The recycling experiment showed that there was no apparent decrease in the activity of tubelike g-C3N4/Ag3PO4-5% heterojunction after five consecutive runs. A possible Z-type mechanism is proposed to explain the high activity and stability of the heterojunction.

PDI Supermolecule-Encapsulated 3D BiVO4 toward Unobstructed Interfacial Charge Transfer for Enhanced Visible-Light Photocatalytic Activity

PDI Supermolecule-Encapsulated 3D BiVO₄ toward Unobstructed Interfacial Charge Transfer for Enhanced Visible-Light Photocatalytic Activity

One-Step Microwave-Assisted Synthesis and Visible-Light Photocatalytic Activity Enhancement of BiOBr/RGO Nanocomposites for Degradation of Methylene Blue.

In this study, bismuth oxybromide/reduced graphene oxide (BiOBr/RGO), i.e. BiOBr-G nanocomposites, were synthesized using a one-step microwave-assisted method. The structure of the synthesized nanocomposites was characterized using Raman spectroscopy, X-ray diffractometry (XRD), photoluminescence (PL) emission spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), and ultraviolet-visible diffuse reflection spectroscopy (DRS). In addition, the ability of the nanocomposite to degrade methylene blue (MB) under visible light irradiation was investigated. The synthesized nanocomposite achieved an MB degradation rate of above 96% within 75 min of continuous visible light irradiation. In addition, the synthesized BiOBr-G nanocomposite exhibited significantly enhanced photocatalytic activity for the degradation of MB. Furthermore, the results revealed that the separation of the photogenerated electron–hole pairs in the BiOBr-G nanocomposite enhanced the ability of the nanocomposite to absorb visible light, thus improving the photocatalytic properties of the nanocomposites. Lastly, the MB photo-degradation mechanism of BiOBr-G was investigated, and the results revealed that the BiOBr-G nanocomposites exhibited good photocatalytic activity.

One-Pot Synthesis of C-Modified and N-Doped TiO <sub>2</sub> for Enhanced Visible-Light Photocatalytic Activity

One-Pot Synthesis of C-Modified and N-Doped TiO <sub>2</sub> for Enhanced Visible-Light Photocatalytic Activity

Stannates, titanates and tantalates modified with carbon and graphene quantum dots for enhancement of visible-light photocatalytic activity

Most efforts in heterogeneous photocatalysis are focused on development of new and stable photoactive materials efficient in degradation of various pollutants under visible-light irradiation. In this regard, the wide-bandgap perovskite semiconductors, i.e., SrTiO3 (titanate), SrSnO3 (stannate) and AgTaO3 (tantalate), were prepared by a solvothermal method, and then modified with carbon quantum dots (CQDs) or graphene quantum dots (GQDs) co-modified with erbium. The photocactivity was investigated for: (i) toluene degradation (gas phase), (ii) phenol decomposition (aqueous phase), and (iii) inactivation of Escherichia coli K12 bacteria. It has been found that the morphology of semiconductors depends on the synthesis conditions, resulting in the formation of spherical particles, rods and faceted particles for SrTiO3, SnSrO3 and AgTaO3, respectively. Additionally, deposition of CQDs and GQDs/erbium has resulted in an enhancement of light harvesting, thus improved photoactivity under visible-light irradiation. Samples modified with both erbium and GQDs revealed much higher photoactivity than corresponding pristine and CQDs-modified samples. Moreover, all photocatalyst modified with GQDs and Er exhibited a significant antibacterial properties under visible light irradiation (λ > 420 nm). Accordingly, it has been proposed that obtained semiconductors modified with QDs and Er are promising candidates as sustainable, clean and cheap materials for environmental purification under solar radiation.

Visible-light photocatalytic activity enhancement of red phosphorus dispersed on the exfoliated kaolin for pollutant degradation and hydrogen evolution

The semiconductor photocatalyst is crucial for dealing with the current environmental and energy crises. However, the large-scale applications of the reported semiconductor materials are hampered by the recombination of electrons and holes, low kinetic properties, and slow reaction rates. Herein, a three-dimensional structured kaolin/hydrothermally treated red phosphorus (K/HRP) composite photocatalyst was synthesized. The composition ratio was optimized, and the K7/HRP composites (contained 7%) exhibited the highest photocatalytic activity. The rhodamine B photodegradation rate constant and the hydrogen production rate were 0.25 min−1 and 252 μmol h−1 g−1, which were higher than those of HRP by 12.4 and 7.2 times, respectively. The enhancement of the HRP photocatalytic activity was attributed to the presence of K, which inhibited the overgrowth and the agglomeration of HRP and shortened the carrier migration distance. The electrostatic interaction between the K and the HRP effectively promoted the separation of photogenerated charge carriers. In addition, the three-dimensional structure of the K and the HRP construct enhanced the light absorption and provided a pollution-free and large-area transport interface for carriers. This work has paramount guiding importance in the preparation of high-efficiency, cheap, and recyclable nanocomposite photocatalyst materials.

Improvement of Bi doping in ZnO nanocrystals by co-doping with Al: crystal geometry calculations and photocatalytic activity

In this work we demonstrate enhancement in visible-light photocatalytic activity (PCA) of ZnO nanoparticles (NPs) with minimal attenuation of visible light transmittance. This approach can benefit numerous optoelectronic and photocatalytic applications. ZnO NPs were p-n co-doped with Al and Bi to improve Bi doping into the ZnO crystal. Al- and/or Bi-doped ZnO was coprecipitated by ammonia from aqueous nitrate solutions of Zn2+, Al3+, and Bi3+, followed by microwave heating. Doping concentrations in Al- and Bi- doped ZnO (AZO and BZO) and Al/Bi co-doped ZnO (ABZO) were 1, 3, 5, and 7 mole %. The resulting NPs were characterized by XRD, TEM, EDS, BET, and UV-visible absorption. While EDS shows that almost all added Bi was incorporated into the ZnO, XRD analysis of BZO reveals formation of α-Bi2O3 as a secondary phase due to the poor Bi solubility in ZnO. Co-doping of Al with Bi suppressed α-Bi2O3 formation and increased Bi solubility in ZnO. XRD-based calculations of the lattice constants and deformation strain, stress, and energy all show insertion of Al and/or Bi into the crystal with different extents according to the dopants’ solubilities into ZnO. AZO and BZO NPs had E g lowered by 0.05–1.39 eV and 0.30–0.70 eV, respectively, relative to ZnO. On the other hand, ABZO had E g reductions of only 0.01–0.20 eV due to formation of acceptor-donor complex through co-doping. ABZO gave higher PCA enhancements with respect to E g reductions (Δk photo/–ΔE g) than either AZO and BZO, with values up to 370, 126, and 13 min–1 eV–1, respectively.

Enhancement of Visible-Light Photocatalytic Efficiency of TiO2 Nanopowder by Anatase/Rutile Dual Phase Formation

Visible-light photocatalytically active titanium oxide (TiO2) nano-powder was synthesized by a flat-flame chemical vapor condensation method. The formation of TiO2 consisting of different ratios of anatase and rutile phases was controlled by two parameters: the acetylene flow rate (C2H2, 600 sccm and 800 sccm) and the acetylene/oxygen flow ratio (C2H2/O2, 1:3, 1:4, 1:5, and 1:6). The location of the photonic center was identified for visible-light absorption, which is in the anatase grains. The photonic center on the surface of anatase grains happens to be the nucleation site for rutile in an oxygen-deficient environment. The visible-light absorption could be attributed to the formation of defect levels related to the photonic center within the band gap of anatase. The major role of the mixed-phase structure of TiO2 in the enhancement of visible-light photocatalytic activity is in the enhancement of carrier separation and not of light harvest, for the powder produced in this study.

Enhancing visible-light photocatalytic activity of Ag-TiO2 nanowire composites by one-step hydrothermal process

TiO2 nanowires loaded with different amounts of Ag (1–5 mol%) were successfully fabricated by one-step hydrothermal process using titanium butyrate as a precursor in alkaline solution. The products were characterized using X-ray diffraction, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy and UV–Vis diffuse reflectance spectroscopy. Photocatalytic performance of all Ag-TiO2 samples was investigated by degradation of Rhodamine B dye under simulated sunlight. The result showed that Ag modification significantly improved the absorption of TiO2 nanowires in the visible region. The Ag-TiO2 nanowire composites with 3 mol% Ag demonstrated the best photocatalytic activity compared with other samples, which could be attributed to the enhancement of light harvesting and the decrease of charge recombination.

Enhancing visible-light photocatalytic activity for overall water splitting in UiO-66 by controlling metal node composition

The photocatalytic activity of a series of five UiO-66 (M: Zr, Zr/Ti, Zr/Ce, Zr/Ce/Ti, Ce) materials for overall water splitting with generation of hydrogen and oxygen has been herein measured. The most efficient photocatalyst for the overall water splitting is the trimetallic MOF UiO-66(Zr/Ce/Ti) which achieves 230 μ mol ∙ g−1 of H2 and 110 μ mol ∙ g−1 of O2, upon UV light irradiation, and 210 μ mol ∙ g−1 of H2 and 70 μ mol ∙ g−1 of O2, under visible light irradiation. These productivity data indicate that a considerable percentage of its photocatalytic activity derives from the visible region of the spectrum (λ > 450 nm). The photocatalytic activity of trimetallic UiO-66(Zr/Ce/Ti) was maintained upon reuse. Kinetics of the charge separated state monitored by transient absorption spectroscopy shows similar deactivation profiles for the five UiO-66 samples, suggesting that it is the charge separation efficiency the main factor responsible for the differences in the photocatalytic activity. The use of methanol as sacrificial agent during the photocatalytic experiments indicated that the high photocatalytic efficiency for overall water splitting in UiO-66(Zr/Ce/Ti) derives from the favorable kinetics of oxygen evolution. These results show the potential of multimetallic metal-organic frameworks as solar photocatalysts by tuning light absorption towards the visible region.

Ultrasonication-Assisted Synthesis of ZnxCd1−xS for Enhanced Visible-Light Photocatalytic Activity

ZnxCd1−xS as a solid solution photocatalyst has attracted widespread attention for its unique adjustable band gap structure and good and stable performance. A novel synthesis approach for ZnxCd1−xS is still required to further improve its performance. In this study, we synthesized a series of ZnxCd1−xS (x = 0−1) solid solutions via an ultrasonication-assisted hydrothermal route. In comparison with conventional methods of preparation, the sample prepared by our innovative method showed enhanced photocatalytic activity for the degradation of a methyl orange (MO) solution under visible light due to its high crystallinity and small crystallite size. Furthermore, the composition and bandgap of ZnxCd1−xS can be tuned by adjusting the mole ratio of Zn2+/Cd2+. Zn0.3Cd0.7S shows the highest level of activity and stability for the degradation of MO with k = 0.85 h−1, which is 2.2 times higher than that of CdS. The balance between band gap structure-directed redox capacity and light absorption of Zn0.3Cd0.7S accounts for its high photocatalytic performance, both of which are determined by the composition of the solid solution. Also, a degradation mechanism of MO over the sample is tentatively proposed. This study demonstrates a new strategy to synthesize highly efficient sulfide photocatalysts.