Enhancement Of Photoactivity Research Articles

Nitrogen Graphene: A New and Exciting Generation of Visible Light Driven Photocatalyst and Energy Storage Application.

The synthesis of nitrogen, boron, and nitrogen–boron-codoped graphenes was attained via mixing solutions of GO with urea, boric acid, and a mixture of both, respectively, followed by drying in vacuum and annealing at 900 °C for 10 h. These materials were thoroughly characterized employing XRD, TEM, FTIR, Raman, UV–vis, XPS, IPCE%, and electrical conductivity measurements. The nitrogen-doped graphene (NG) showed an excellent supercapacitor performance with a higher specific capacitance (388 F·g–1 at 1 A·g–1), superior stability, and a higher power density of 0.260 kW kg–1. This was mainly due to the designated N types of doping and most importantly N–O bonds and to lowering charge transfer and equivalent series resistances. The NG also indicated the highest photocatalytic performance for methylene blue (MB 20 ppm, power = 160 W, λ > 420 nm) and phenol (5 ppm) degradation under visible light illumination with rate constants equal 0.013 min–1 and 0.04 min–1, respectively. The photodegradation mechanism was proposed via determining the energy band potentials using the Mott–Schottky measurements. This determined that photoactivity enhancement of the NG is accounted for by acquisition of nitrogen-oxy-carbide phases that shared in inducing a higher IPCE% (60%) and a lower band gap value (1.68 eV) compared to boron and nitrogen–boron-codoped graphenes. The achieved photodegradation mechanism relied on scavengers performance suggesting that •OH and electrons were the main reactive species responsible for the MB photodegradation.

Enhancement of visible-light photoactivity by polypropylene coated plasmonic Au/TiO2 for dye degradation in water solution

A new approach to obtain a heterogeneous photocatalytic material with gold nanoparticles and TiO2 semiconductor was performed exploiting the reducing ability of acetylacetone, a chemical present in the TiO2 paste formulation. Gold/TiO2 heterogeneous catalyst supported on polypropylene [PP@Au-TiO2]A was prepared; composition, structure and morphology of this new material were defined by using UV–Vis spectroscopy, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray diffraction (XRD), X-ray Fluorescence (XRF), Raman Spectroscopy, Photoluminescence and Diffuse Reflectance Spectroscopy. The new material was tested in the photocatalytic degradation of Alizarin Red S in water solution, as target pollutant, under visible light and correlated with structural and spectroscopic characterizations. [PP@Au-TiO2]A showed higher photocatalytic activity respect to pure [PP@TiO2]A with an improvement of photodegradation kinetic. The best performance was obtained using [PP@Au-TiO2]A sample with 0.006 wt.% of Au and the photocatalytic improvement was correlated with the band gap energy decrease of photocatalyst.

Remarkable positive effect of Cd(OH)2 on CdS semiconductor for visible-light photocatalytic H2 production

In the past decade, photocatalytic H2 production over CdS semiconductor has garnered considerable interest due to its visible-light response, suitable band structure, and controllable morphologies. To pursue higher photocatalytic efficiency and more feasibility for practical industrial applications, Cd(OH)2 nanoparticle decorated CdS rod composites were designed and successfully fabricated in this study by a facile one-step hydrothermal method in strong alkali NaOH solution. The synthesis process followed a “mother liquor circulation” criteria since no NaOH was lost during the whole preparation course, which could greatly save costs and be conducive to the realization of large-scale production. When the content of Cd(OH)2 was 17.6 mol% in the obtained composite, the photocatalytic H2 production rate reached the highest (579.0 μmol h−1) with the help of 0.6 wt% platinum (Pt), which was more than 386 and 15 times higher than that of Pt/Cd(OH)2 and Pt/CdS, respectively. It was evidenced that such surprising and prominent enhancement of photoactivity was mainly attributed to the presence of Cd0 as an electron transport intermediary, which was produced by in-situ photoreduction of Cd(OH)2 interfacial layer between CdS and Pt. This work could not only highlight the significant roles of Cd(OH)2 on invigorating the photoactivity of CdS for H2 production, but also open an avenue of using the concept of mother liquor circulation in the photocatalyst synthesis process to satisfy the industrial manufacture requirement.

Photocatalytic hydrogen production using TiO2 coated iron-oxide core shell particles

Photocatalytic water splitting plays a challenging role as it is one of the most important reactions for solving energy, environmental problems and sustainability. Photocatalytic water splitting was improved by using a novel kind of magnetically separable core shell nano photocatalyst TiO2/Fe2O3, prepared by co-precipitation method. It was characterised for particle size (XRD), band gap (UV-DRS), morphology (SEM), particle size (HRTEM), elemental composition (EDS) and electrochemical studies. Photocatalytic splitting of water was examined in tubular reactor of 500 mL capacity with various sacrificial agents viz., methanol, ethanol, acetic acid, lactic acid, EDTA and triethanolamine. To enhance the hydrogen production, various operating parameters viz., effect of sacrificial agents, catalytic dosage, light irradiation and recycle flow rate were optimized. With the optimized operating parameters (0.2 g catalyst dosage, 60 mL/min recycle flow rate, 96 W/m2 light irradiation and EDTA as sacrificial agent) the maximum hydrogen achieved was 2700 μmol/h for the quantum yield of 3.86% at 550 nm. The reusability studies were conducted and the TiO2 coated Fe2O3 core shell particles were found to be stable than the plain TiO2 nano particles. Effective charge transfer from TiO2 to Fe2O3 and the suppression of e−/h+ pair recombination attributed significant enhancement in photoactivity, thereby increasing the hydrogen production.

Fabrication of novel AgBr/Bi24O31Br10 composites with excellent photocatalytic performance.

Novel porous AgBr/Bi24O31Br10 (AB/BOB) heterojunction composites were prepared by a hydrothermal calcination-ion exchange route and their physico-chemical properties were characterized by XRD, XPS, SEM, EDX, UV-vis DRS, BET and electrochemical measurements. The photocatalytic activity of the composites consisting of different AB/BOB mass ratios was evaluated by degradation of methylene blue (MB) under visible light irradiation. Compared with pure AB and BOB, the porous 20% AB/BOB composite exhibits much enhanced photocatalytic activity with good cycling stability. The significant enhancement in photoactivity is contributed to by both a high adsorption capacity and the separation efficiency of photo-generated electron–hole (e−–h+) pairs via a Z-scheme mechanism. In addition, radical scavenging experiments confirm that the reactive ·OH radicals play an important role in the photocatalytic reaction. The novel (AB/BOB) heterojunction composites could have a promising application in treatment of various dyestuff wastewaters on a large scale.

Pillaring and NiOx co-catalyst loading as alternatives for the photoactivity enhancement of K2Ti4O9 towards water splitting

Combining TiO2 pillaring with the loading of the NiOx co-catalyst can boost the water splitting hydrogen production over K2Ti4O9 66 times.

Plasmon-mediated charge dynamics and photoactivity enhancement for Au-decorated ZnO nanocrystals

Correlations among Au content, SPR-mediated charge transfer and electromagnetic response, and the resultant photoactivity enhancement for ZnO–Au nanocrystals were established.

Effect of carbon-interaction on structure-photoactivity of Cu doped amorphous TiO2 catalysts for visible-light-oriented oxidative desulphurization of dibenzothiophene

Amorphous TiO2 (AT) was successfully prepared via the sol-gel technique, using different titanium sources followed by incorporation of copper via the electrochemical method to give CuO/TiO2 (CAT) catalysts. The catalysts were characterized via XRD, N2 physisorption, FTIR, TEM, EDX, XPS, ESR and UV–Vis DRS. The results verified that the use of different titanium precursors have profound effect on the physicochemical properties of the AT catalysts. Further one-pot self-doping carbon from titanium precursor during the addition of copper could greatly enhanced the photocatalytic activity of CAT on the oxidative desulphurization of dibenzothiophene (DBT). 15 CATTBOT exhibited the best performance mainly due to the narrowest band gap and higher numbers of O–Ti–C and Ti–O–C bonds, as well as appropriate amount of Ti3+ surface defects (TSD). These abovementioned properties offered good mobility of electron-hole pairs and/or trap the electrons for enhancement of photoactivity under irradiation of visible light. Kinetic studies showed that the photocatalytic oxidative desulphurization of DBT followed the pseudo-first order Langmuir-Hinshelwood model, where the adsorption was the controlling step. It is believed that these results could contribute to the synthesis of various supported catalysts for numerous applications specifically in removal of sulphur containing compounds in fuel oils.

Highly efficient photocatalytic activity and mechanism of Yb3+/Tm3+ codoped In2S3 from ultraviolet to near infrared light towards chromium (VI) reduction and rhodamine B oxydative degradation

The Yb3+/Tm3+ codoped flower−like tetragonal In2S3 photocatalysts were synthesized through a hydrothermal route, and the crystal phases, morphologies, chemical compositions and optical properties were characterized. The results shown that the doping with Yb3+/Tm3+ did not significantly change the crystallinity of In2S3, but induced the generation of intermediate energy states for efficient charge separation. The Yb3+/Tm3+ codoped In2S3 presented a significant enhancement of photoactivity towards chromium (VI) reduction and rhodamine B oxidation from UV to NIR light. The best photocatalytic synergism was obtained for the sample with the mole ratio of In3+:Yb3+:Tm3+ at 159:40:1, in which the chromium (VI) reduction efficiency was 97.9% (NIR, 100min), 99.3% (vis, 10min) and 98.3% (UV, 10min), while the rhodamine B degradation efficiency was 98.4% (NIR, 100min), 97.3% (vis, 14min), and 96.3% (UV, 14min). The favorable NIR photoactivity was mainly attributed to the upconversion mechanism via energy level transition of Yb3+/Tm3+. Under the full−spectra−light irradiation for 6min and 7min, the removal efficiency of chromium (VI) and rhodamine B could reach to 99.4% and 94.8%, the corresponding rate constant was 2.17 and 5.60 times of pure In2S3, respectively. The improved photocatalytic efficiency might be attributed to the enhanced light absorption and favorable charge separation resulted from the intermediate energy states and/or sulfur vacancies. In addition, the free radical capture and electron spin resonance experiments were also performed to determined the role of O2− and h+ species during photocatalytic oxidation process.

Significance of a Noble Metal Nanolayer on the UV and Visible Light Photocatalytic Activity of Anatase TiO2 Thin Films Grown from a Scalable PECVD/PVD Approach.

UV and visible light photocatalytic composite Pt and Au-TiO2 coatings have been deposited on silicon and glass substrates at low temperature using a hybrid ECWR-PECVD/MS-PVD process. Methylene blue, stearic acid, and sulfamethoxazole were used as dye, organic, and antibiotic model pollutants, respectively, to demonstrate the efficiency of these nanocomposite coatings for water decontamination or self-cleaning surfaces applications. Raman investigations revealed the formation of anatase polymorph of TiO2 in all synthesized coatings with a shifting of the main vibrational mode peak to higher wavenumber in the case of Au-TiO2 coating, indicating an increase number of crystalline defects within this coating. Because of the difference of the chemical potentials of each of the investigated noble metals, the sputtered metal layers exhibit different morphology. Pt sputtered atoms, with high surface adhesion, promote formation of a smooth 2D layer. On the other hand, Au sputtered atoms with higher cohesive forces promote the formation of 5-10 nm nanoparticles. As a result, the surface plasmon resonance phenomenon was observed in the Au-TiO2 coatings. UV photoactivity of the nanocomposite coatings was enhanced 1.5-3 times and 1.3 times for methylene blue and stearic acid, respectively, thanks to the enhancement of electron trapping in the noble metal layer. This electron trapping phenomenon is higher in the Pt-TiO2 coating because of its larger work function. On the other hand, the enhancement of the visible photoactivity was more pronounced (3 and 7 times for methylene blue and stearic acid, respectively) in the case of Au-TiO2 thanks to the surface plasmon resonance. Finally, these nanocomposite TiO2 coatings exhibited also a good ability for the degradation of antibiotics usually found in wastewater such as sulfamethoxazole. However, a complementary test have showed an increase of the toxicity of the liquid medium after photocatalysis, which could be due the presence of sulfamethoxazole's transformation byproducts.

What’s the Key Factor to Ensure the Photoactivity Enhancement of Fe2O3 Films with Ni(OH)2 Loading: Clues from a Structural Modification with Flagella Nanowires

A much higher photoactivity enhancement of Fe2O3 photoanode films was achieved by loading flagella-nanowire-modified Ni(OH)2 than by loading pure Ni(OH)2. Cyclic voltammetry curves and coupled i–t/potential step chronoamperometry measurements under super band gap irradiation revealed a much heavier hole accumulation in a pure Ni(OH)2 layer. Electrochemical impedance and coupled i–t/open circuit potential transient measurements were applied to explore the dynamics of hole transfer through the Fe2O3|Ni(OH)2|electrolyte multiple interface systems, finding that the structural modification of Ni(OH)2 with flagella nanowires can speed up the charge transfer at both the Fe2O3|Ni(OH)2 and Ni(OH)2|electrolyte interfaces. Based on a recent discovery that the ion-permeable Ni(OH)2 electrocatalyst acts as a surface-attached redox system, a theoretical model was proposed to explain the influence of hole accumulation in Ni(OH)2 layer on the photoactivity of Fe2O3 films. The outcome of this work implies that the key fac...

Ni/MMT-promoted TiO2 nanocatalyst for dynamic photocatalytic H2 and hydrocarbons production from ethanol-water mixture under UV-light

Photocatalytic H2 evolution from ethanol-water mixture over Ni and montmorillonite (MMT)-loaded TiO2 nanocomposite has been investigated. The samples, prepared by a single step sol-gel method, were characterized by XRD, SEM, TEM, FTIR, XPS, UV–Vis and PL spectroscopy. The TiO2 crystal growth was controlled by Ni/MMT, thus produced anatase phase TiO2. The nickel presented over the TiO2 as Ni2+, thus promoted charges separation. The photocatalytic H2 production activity was conducted in a gas phase continuous flow photoreactor system under UV-light. A significant enhancement in photoactivity of Ni-promoted MMT/TiO2 catalyst was detected for selective H2 production with appreciable amounts of C1-C3 hydrocarbons. The highest amount of H2 evolved over 3 wt% Ni-10 wt% MMT/TiO2 composite was 3470 μmole g-cat. −1 h−1 at selectivity 99%, 2.62 order of magnitude higher than pure Ni/TiO2, 6.48 fold more than MMT/TiO2 and 6.45 times the amount of H2 produced the over the pure TiO2 catalyst. Among the hydrocarbons, MMT promoted CH4/C2H6 production, while Ni/MMT was favorable for CH4/C3H6 production. The activity and selectivity of Ni-MMT/TiO2 was reduced at higher catalyst loading due to mass transfer limitations. In addition, significantly improved and stable cyclic performance was detected over the irradiation time for dynamic and selective H2 evolution. The enhanced performance of the Ni-MMT/TiO2 composite for H2 production is mainly associated with efficient charges separation due to synergistic effect of Ni/MMT and appropriate redox potentials. The reaction mechanism to understand the production of H2 and hydrocarbons in a gas phase system is critically deliberated.

Growth and characterization of n-AlGaN 1-D structures with varying Al composition using u-GaN seeds

Like all the ternary alloys in III-nitride materials family, aluminum gallium nitride (AlGaN) has unique band gap tuning property which enables the alloy to be suitable for many opto-electronic applications. The direct band gap of AlGaN can be tuned from 3.4 to 6.2 eV by changing the composition. In this article, the growth of ternary n-AlGaN micro and nano structures on Si (1 1 1) substrate is demonstrated via 2-step growth method employing metal organic chemical vapor deposition. During the growth flow of Trimethygallium is varied to modulate the final Al/Ga ratio. After the growth, various morphological, crystalline and optical characterizations are carried out to probe in the properties of the grown structures. Recorded X-ray diffraction patterns reveal that the realized structures are wurtzite single crystalline n-AlGaN having a near homogeneous Al distribution and validated by energy dispersive X-ray spectroscopy. Low temperature cathodoluminescence spectra show band edge emission in deep UV region which enables the grown n-AlGaN structures to efficiently find opto-electronic applications in the aforementioned region. Finally, planar photoconductive devices are fabricated using the grown 1-D structures and photocurrent evolution is measured. Structure bearing highest Al content shows a manifold enhancement in photo activity compared to other grown samples. Absolute photoresponsivities of the grown samples are calculated to be 301.47, 116 and 38.13 mA/W which is in accord with the findings of low temperature cathodoluminescence investigation. Therefore, it can be concluded that the successful realization of n-AlGaN 1-D structures varying Al content facilitates the further developments of the field concerning nano- and opto-electronic devices.

One-pot molten salt synthesis of CdNb2O6/Cd2Nb2O7 heterojunction photocatalysts with enhanced photocatalytic properties

Abstract CdNb 2 O 6 /Cd 2 Nb 2 O 7 heterojunction photocatalysts were one-pot synthesized by a molten salt method using cadmium nitrate, niobium oxide as raw materials in Li 2 SO 4 - Na 2 SO 4 salt system at 900 °C. The as-synthesized photocatalysts were characterized by X-ray diffraction, scanning electron microscopy, photoluminescence, photocurrent, and UV–vis diffuse reflectance spectroscopy. The experimental results show that CdNb 2 O 6 /Cd 2 Nb 2 O 7 is composed of CdNb 2 O 6 rods and Cd 2 Nb 2 O 7 particles. as-synthesized CdNb 2 O 6 /Cd 2 Nb 2 O 7 composites exhibit enhanced photodegradation performances toward Rodamine and phenol under UV light irradiation compared with pure CdNb 2 O 6 and Cd 2 Nb 2 O 7 . The enhancement in photoactivity can be attributed to the construction of CdNb 2 O 6 /Cd 2 Nb 2 O 7 heterojunction and the typical mixed morphology of CdNb 2 O 6 rods and Cd 2 Nb 2 O 7 particles, which result in the effective separation of photogenerated electron/hole pairs and easy transfer of electrons to the surface through CdNb 2 O 6 rods. Moreover, the dominant active species and the photocatalytic mechanism were discussed in detail.

Significantly enhanced photocatalytic performance of zinc oxide via bismuth oxybromide hybridization and the mechanism study

A highly efficient and stable ZnO–BiOBr composite photocatalyst was prepared by a facile one-pot solvothermal method. A variety of sophisticated techniques such as X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), UV–Vis diffuse reflectance spectra, photoluminescence spectra and photoelectrochemical measurement, and so on were employed to characterize the materials. The as-prepared ZnO–BiOBr nanocrystalline showed strong photocatalytic activity for decomposition of methylene blue (MB), Orange II and biphenol A (BPA) under simulated visible light illumination. The possible working principle for the superior photocatalytic properties and reusability of the ZnO–BiOBr hybrid was surveyed to disclose contributions of various effects for the photoactivity enhancement. It was pointed out that *OH and holes take priority over ∙O2 − radicals in serving as the main oxidant in the reaction system. The experimental results indicated that the ZnO–BiOBr composite is highly photostable and valuable for real environmental applications.

Novel synthesis approaches for WO3‐TiO2/MWCNT composite photocatalysts- problematic issues of photoactivity enhancement factors

The “build-up” methodology, the importance of the order of the semiconductor layers in WO3‐TiO2/MWCNT composite materials was studied in terms of the applied synthesis pathway, morpho-structural parameters (mean crystallite size, crystal phase composition, morphology) and photocatalytic efficiency (using oxalic acid as model pollutant). The appearance of TiWOx phase in the composites contributed to the enhancement of the photocatalytic efficiencies, as different synthesis approaches led to different crystal phase compositions. Although, it was proven that a beneficial phase’s presence can be hindered if an excess of MWCNT or WO3 was applied. As the ratio of the mentioned materials was reduced, active composites were obtained, but the previously noticed TiWOx disappeared. Therefore, it was proven, that in the case of WO3-TiO2/MWCNT nanocomposite system several photocatalytic activity enhancement factors can be introduced, but not simultaneously (the disappearance of TiWOx at low MWCNT and WO3 contents and the appearance of highly crystalline anatase).

Fluorine doped anatase TiO2 with exposed reactive (001) facets supported on porous diatomite for enhanced visible-light photocatalytic activity

Novel fluorine doped TiO2/diatomite (F-T/DE) composites with visible-light responding activity were fabricated through a facile sol-gel method in this study. The as-synthesized F-T/DE-1.0% (1.0% fluorine content) composite exhibited enhanced photocatalytic activity in degrading rhodamine B (RhB) under visible-light illumination, the reaction rate constant of which was nearly up to 4.4 times and 26.1 times higher than that of F-T-1.0% (fluorine doped TiO2 with 1.0% content) and pure TiO2, respectively. It is indicated that the anatase TiO2 nanoparticles were firmly and homogeneously loaded on the surface of diatomite and fluorine ions were successfully incorporated into the lattice of TiO2. In addition, the construction of composite can effectively promote the generation of oxidative radicals and reduce the recombination probability of photogenerated electron-hole pairs and thus contribute to the enhancement of photoactivity under visible light. The enhanced photocatalytic activity of F-T/DE can be attributed to the fluorine doping induced oxygen vacancies and much more exposed highly active (001) facets, as well as the carrier effect (smaller grain size, well distribution and enhanced adsorption ability).

New insights into water photooxidation on reductively pretreated hematite photoanodes.

It has been recently demonstrated that the photoactivity toward oxygen evolution of a number of n-type metal oxides can be substantially improved by a reductive electrochemical pretreatment. Such an enhancement has been primarily linked to the formation of low valent metal species that increase electrode conductivity. In this work, we report new insights into the electrochemical doping using highly ordered (110)-oriented hematite nanorods directly grown on FTO. The reductive pretreatment consists in applying negative potentials for a controlled period of time. Such a pretreatment was optimized in both potentiostatic and potentiodynamic regimes. We show that the optimized pretreatment enhances electrode conductivity due to an increase in charge carrier density. However, it additionally triggers changes in the morphologic, catalytic and electronic properties that facilitate the separation and collection of the photogenerated charge carriers causing an up to 8-fold enhancement in the photocurrent for water oxidation. The reductive pretreatment can be considered as a highly controllable electrochemical n-type doping with the amount of generated Fe2+/polaron species and the change in film morphology as the main factors determining the final efficiency for water photooxidation of the resulting electrodes.

Influence of the reduction of graphene oxide (rGO) on the structure and photoactivity of CdS-rGO hybrid systems

Solvothermal and chemical reduction of graphene oxide with N2H4 or HI affect the surface composition, rupture and delamination degree of reduced graphene oxide (rGO). Higher reduction and stacking of rGO was achieved by chemical reduction with HI, while solvothermal reduction and, especially, the chemical reduction with N2H4 lead to higher delamination of rGO. The incorporation of the different rGO to CdS implies changes in the characteristics and photoactivity of the CdS-rGO hybrids. A promoter effect was observed in all CdS-rGO hybrids respect to the photoactivity of bare CdS, observing the better photoactivity on the hybrid in which the graphene oxide was reduced with HI (CdS-rGO/HI). The variations in the photoactivity of CdS-rGO hybrids are analyzed in terms of changes in the structure, surface and light absorption ability of CdS and also analyzing the contact of CdS with rGO. The greater concentration of small CdS nanostructures with strong quantum confinement is in the origin of the enhancement in photoactivity observed in the CdS-rGO/HI hybrid.

Thiol-Capped Gold Nanoparticles Swell-Encapsulated into Polyurethane as Powerful Antibacterial Surfaces Under Dark and Light Conditions.

A simple procedure to develop antibacterial surfaces using thiol-capped gold nanoparticles (AuNPs) is shown, which effectively kill bacteria under dark and light conditions. The effect of AuNP size and concentration on photo-activated antibacterial surfaces is reported and we show significant size effects, as well as bactericidal activity with crystal violet (CV) coated polyurethane. These materials have been proven to be powerful antibacterial surfaces against both Gram-positive and Gram-negative bacteria. AuNPs of 2, 3 or 5 nm diameter were swell-encapsulated into PU before a coating of CV was applied (known as PU-AuNPs-CV). The antibacterial activity of PU-AuNPs-CV samples was tested against Staphylococcus aureus and Escherichia coli as representative Gram-positive and Gram-negative bacteria under dark and light conditions. All light conditions in this study simulated a typical white-light hospital environment. This work demonstrates that the antibacterial activity of PU-AuNPs-CV samples and the synergistic enhancement of photoactivity of triarylmethane type dyes is highly dependent on nanoparticle size and concentration. The most powerful PU-AuNPs-CV antibacterial surfaces were achieved using 1.0 mg mL−1 swell encapsulation concentrations of 2 nm AuNPs. After two hours, Gram-positive and Gram-negative bacteria were reduced to below the detection limit (>4 log) under dark and light conditions.