Photocatalysis In Terms Research Articles

Impact of structural defects on the photocatalytic properties of ZnO

ZnO photocatalytic materials have been prepared using three precursors (Zinc Acetate, Zinc Hydroxide, and Zinc Peroxide), and the effect of calcination temperature on structural and photocatalytic properties of ZnO has been investigated. XRD, UV–Vis, BET, XPS, Time-Resolved Microwave Conductivity (TRMC), Raman, and Electron Paramagnetic Resonance (EPR) have been used to correlate the impact of the surface area, the introduction of oxygen and/or zinc vacancies, and the charge carrier dynamics, with their photocatalytic properties. The main objective is to provide a new approach to the impact of structural defects on ZnO semiconductors determined by using Raman and EPR techniques, and by coupling with the important role of the surface area considered as one of the most relevant characteristics in photocatalysis in terms of performance. The fewer surface defects, the more photoactive the catalyst is. The results are discussed for the model degradation of formic acid and phenol under UV-irradiation.

Surface activation of calcium tungstate by europium doping for improving photocatalytic performance: Towards lanthanide site photocatalysis

• The Eu doping on surface of CaWO 4 raises the d -band center to improve the adsorption. • The better crystallization promotes the charge mobility to the surface of CaWO 4 . • The surface adsorption and charge mobility synergistic ally improve the photocatalysis. Lanthanides doping can improve the performance of photocatalysts due to the enhanced optical absorption or charge separation. Here, we demonstrate the important role of lanthanide in photocatalysis in terms of surface reactivity. The Eu 3+ on the surface of CaWO 4 , especially for the 1st-layer lattice, substantially raised the surface energy by heightening the d -band center, so that the adsorption ability at the surface was improved. Calcination at a proper temperature promoted the mobility of more excited charge carrier to the Eu 3+ sites on the catalyst surface. The synergistic effect of the enhanced adsorption ability and carrier mobility improved the photocatalytic performance as in the case of CaWO 4 calcined at 600 °C, where Rhodamine B, Ciprofloxacin and nitroblue tetrazolium were degraded at the highest rate among all the CaWO 4 samples. Our study provides important insights into lanthanide site photocatalysis (i.e. migration of Eu 3+ into the inner part of the crystal contributed to photoluminescence rather than catalysis).

Bi2Se3, Bi2Te3 quantum dots-sensitized rutile TiO2 nanorod arrays for enhanced solar photoelectrocatalysis in azo dye degradation

Rutile TiO2 nanorod arrays vertically aligned on conductive fluorine-doped tin oxide glass are optimized for photocatalysis in terms of the density and diameter of nanorods by tuning the concentration of Ti precursor and reaction time during the hydrothermal process. Quantum dots (QDs) of V2VI3( V = Bi; VI = Se, Te) topographic insulators are then employed as sensitizers to enhance the visible-light response of TiO2. Electrochemical measurements show that the decoration of Bi2Se3 or Bi2Te3 significantly increases the photocurrent due to the enhanced light harvesting properties and the charge carrier separation capability mediated by the topographic isolation effect of V2VI3 QDs. Photoelectrocatalytic (PEC) activity evaluation is conducted towards the decoloration of azo dyes, including methyl orange and methylene blue under the sunlight irradiation. The elaborated Bi2Se3/TiO2 nanorod array exhibits the superior PEC performances, presenting shows great potentials in environmental remediation.

Enhanced Plasmonic Electron Transfer from Gold Nanoparticles to TiO2 Nanorods via Electrochemical Surface Reduction

The transport of charge carriers across the heterojunction of an optoelectronic device plays a crucial role in the performance of the device. This issue is particularly important in the area of heterogeneous metal-semiconducting photocatalysis in terms of harvesting the hot carriers generated under plasmonic resonance. This paper presents the results of a case study on the impact of electrochemical surface reduction on the transport properties of plasmonic electrons, which are generated on gold nanoparticles (Au NPs) under visible light irradiation to TiO2 nanorods (TiO2 NRs). Based on microscopic and spectroscopic characterizations, this study examined the subtle changes in the structural and the optical properties of the Au NPs/TiO2 NRs upon surface reduction of the oxygen layer which is ubiquitous on TiO2 NRs. These results suggest that the oxygen layer works as a blocking layer that limits the charge transfer efficiency of plasmonic electrons from Au to TiO2 and, consequently, reduces the device performance. The main thesis was verified directly by comparing the photocatalytic activities of pristine Au NPs/TiO2 NRs and Au NPs/reduced TiO2 NRs with methylene blue as a reference. The photocatalytic performance of the Au NPs/reduced TiO2 NRs was two times higher than that of the pristine one owing to the efficient charge transfer across the Au/TiO2 interface. This simple surface treatment can be employed widely to enhance the charge transport efficiency of various optoelectronic materials and devices derived from metal-semiconducting heterostructures.

Synthesis of Spherical TiO2 Particles with Disordered Rutile Surface for Photocatalytic Hydrogen Production

One of the most important issues in photocatalysis research has been the development of TiO2-based photocatalysts that work efficiently under visible light conditions. Here, we report the monodispersed, spherical TiO2 particles with disordered rutile surface for use as visible-light photocatalysts. The spherical TiO2 particles with disordered surface were synthesized by sol-gel synthesis, followed by sequential calcination, and chemical reduction process using Li/Ethylenediamine (Li/EDA) solution. Variation of the calcination temperature allowed the crystalline properties of the calcined TiO2 samples, such as the ratio of anatase and rutile, to be finely controlled. The content ratios of anatase phase to rutile phase leads to different degrees of disorder of the rutile surface, which is closely related to the photocatalysis activity. Chemical reduction using the Li/EDA solution enables selective reduction of the rutile surface of the calcined TiO2, resulting in enhanced light absorption. As a result, we were able to synthesize spherical TiO2 photocatalysts having a disordered rutile surface in a mixed crystalline phase, which is beneficial during photocatalysis in terms of light absorption and charge separation. When used as photocatalysts for hydrogen production under solar light conditions, the chemically-reduced TiO2 particles with both the disordered rutile surface and mixed crystalline phase showed significantly enhanced catalytic activity.

Performance of electrochemical oxidation and photocatalysis in terms of kinetics and energy consumption. New insights into the p-cresol degradation

This work reports the comparative performance of two Advanced Oxidation Processes (AOPs), electrochemical oxidation and photocatalysis, as individual technological alternatives for the treatment of effluents containing p-cresol. First, the influence of operating parameters in the oxidation and mineralization yield was carried out together with kinetic analysis. Boron Doped Diamond (BDD), RuO2 and Pt as anodic materials, Na2SO4 and NaCl as supporting electrolytes and different current densities were evaluated in electrochemical oxidation whereas the effect of TiO2 concentration and radiation was studied in the photocatalytic degradation. Then, the parameter Electrical Energy per Order (EEO) was calculated to compare the energy consumption in both AOPs, concluding that under the studied conditions the electrochemical treatment with BDD, Na2SO4 and 125 A m−2 showed the best energy efficiency, with an EEO of 5.83 kW h m−3 order−1 for p-cresol and 58.05 kW h m−3 order−1 for DOC removal, respectively.

Superior H2 production by hydrophilic ultrafine Ta2O5 engineered covalently on graphene

A H2O2-mediated hydrothermal method was developed for the fabrication of hydrophilic Ta2O5/graphene composite. The composite shows a superior H2 productivity, up to 30 mmol g−1 h−1 when used as a photocatalyst for water splitting, corresponding to an apparent quantum efficiency of 33.8% at 254 nm. This superior performance is due to the hydrophilic nature of the composite and more importantly due to the ultrafine Ta2O5 nanoparticles (about 4.0 ± 1.5 nm) which are covalently bonded with the conductive graphene. The hydrophilic property of the composite is attributed to the use of H2O2 in the hydrothermal process. The ultrafine size of the Ta2O5 particles which are covalently bonded with the graphene sheets is attributed to the use of sonication in the synthesis process. Furthermore, the hydrophilic Ta2O5/Gr composite is durable, which is beneficial to long term photocatalysis. The strategy reported here provides a new approach to designing photocatalysts with superior performance for H2 production.

Magnetic nanoparticles of core-shell structure for recoverable photocatalysts

Si doped iron-iron oxide core-shell magnetic nanoparticles are presented in this paper for photocatalysis applications. The nanoparticles were fabricated by a gas phase method with control of small size. Enhanced optical absorption was observed in them compared to the ones without Si, particularly in the 310 nm–450 nm wavelength range. This active optical property is beneficial for photocatalysis in terms of the efficient hole transfer from the catalysts to the reacting chemistry groups. The nanoparticles also possess a strong and active magnetic property which provides an easy way for recyclable usage. This work offers a route towards the improvement of a photocatalytic system which integrates a nanoparticulate structure of a large surface area with effective doping and recoverability by a magnetic field.

On the genesis of heterogeneous photocatalysis: a brief historical perspective in the period 1910 to the mid-1980s

The concept Photocatalysis and, of greater import here, Heterogeneous Photocatalysis were first introduced in the second decade (1910-1920) of the 20th century according to the CAPLUS and MEDLINE databases (SciFinder). This review reports a brief historical perspective on the origins of the two concepts, whether implied or explicitly stated, in some detail up to about the mid-1980s when heterogeneous photocatalysis witnessed the beginning of an exponential growth, with particular emphasis on the use of nanosized TiO(2) particles in powdered form as the (so-called) photocatalyst of choice in environmental applications because of its inherent properties of abundance and chemical stability in acidic and alkaline aqueous media (in the dark), in contrast to ZnO that had been the metal oxide of choice in the early days. The early workers in this area often used the term photosensitization rather than the current popular term photocatalysis, used since the early 1980s. The term Photocatalysis appeared in the literature as early as 1910 in a book by Plotnikow (Russia) and a few years later it was introduced in France by Landau. The review also reports on contributions during the early years by Terenin at the University of St. Petersburg (previously Leningrad, Soviet Union), and in the decade spanning 1975-1985 contributions by Bard's group at the University of Texas at Austin (USA) as well as those of other groups. Some activities into the conversion of light energy to chemical fuels (e.g. H(2)) during the 1975-1985 decade are also considered.

Flower-like porous hematite nanoarchitectures achieved by complexation–mediated oxidation–hydrolysis reaction

Flower-like porous hematite (α-Fe 2O 3) nanoarchitectures composed of ultra-thin nanoflakes were prepared by annealing the iron oxide precursor formed via the oxidation-hydrolysis reaction between Fe(II) ions and Tris(hydroxymethyl)aminomethane (abbreviated as Tris). The microstructure of the prepared FeOOH and hematite samples were fully characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, Fourier-transforming infrared spectra, thermogravimetric analysis, and nitrogen adsorption–desorption isotherm. Based on the influences of reactant concentrations, reaction time and reaction temperature on the morphologies of the resultant samples, a formation mechanism of etching was proposed, Fe(II)–Tris complexes were self-assembled via hydrogen bonds into brick-like building blocks, which then aggregated into rudimentary nanoparticles, and the synergistic effect between the crystallization of FeOOH and dissociation of Fe(II)–Tris complexes make the rudimentary nanoparticles evolve into the flower-like products. The as-prepared flower-like α-Fe 2O 3 nanostructures possessed a Brunauer–Emmett–Teller specific surface area of 191.63 m 2 g −1, hierarchical pore distribution ranging from micropores to macropores, and good crystallinity, and excellent visible photocatalysis in terms of removing chemical oxygen demand of dimethyl sulfoxide industrial wastewater. The current work provides a reliable approach for building functional hierarchical nanoarchitectures and the prepared iron oxide nanomaterials demonstrate an excellent ability to remove toxic pollutants in industrial wastewater.

Superior biodegradability mediated by immobilized Fe-fabrics of waste waters compared to Fenton homogeneous reactions

Pretreatment of waste waters of industrial origin has been carried out on structured silica fabrics that have been exchanged with Fe-ions. Evidence is presented that the treatment under light irradiation in the presence of added oxidant (H2O2) and the silica loaded fabric (from now on EGF/(Fe(0.4%)) involves fast recycling of the Fe-ions back on the fabric. Attenuated total reflection infrared spectroscopy (ATRIR) of intermediate products as carboxylic acids indicates very fast degradation on the EGF/Fe(0.4%) fabric without any significant concentration of detectable species in the fabric surface. The catalyst surface is shown by ATRIR not to be blocked due to adsorption of any initial or intermediate product during waste water degradation. Degradation products like anilines, phenols and chlorocarbons were present in lower amounts when EGF/Fe(0.4%) fabric was used as the photocatalyst compared to Fenton reagent added in homogeneous solution under light irradiation. The intermediates were determined in each case by GC–MS. The ratio BOD5/TOC after treatment was enhanced more favorably by the EGF/Fe(0.4%) fabric than by homogeneous Fenton reagent pointing out to higher biodegradability attained by heterogeneous photocatalysis in spite of the fact that TOC reduction was more marked in homogeneous media. The structural features of EGF/Fe(0.4%) surfaces were investigated before and after the photocatalysis of oxalates by high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and gas absorption studies (BET). Fe-clusters of ≤1nm with a fairly homogeneous size distribution were observed along Fe-silicates on the EGF-silica fabric. The state of the Fe-ion oxidation (XPS) and the pore diameter (BET) were constant during long term photocatalysis providing some evidence for the long term stability of the fabric used.

Terminology, relative photonic efficiencies and quantum yields in heterogeneous photocatalysis. Part I: Suggested protocol

Abstract The term photocatalysis is one amongst several in a quagmire of labels used to describe a photon-driven catalytic process; a simple description of photocatalysis is proposed herein. Other labels such as quantum yield and/or quantum efficiency used in solid/liquid and solid/gas hetero-geneous photocatalytic systems to express process efficiencies have come to refer (incorrectly) to the ratio of the rate of a given event to the rate of incident photons impinging on the reactor walls and typically for broadband radiation. There is no accord on the expression for process efficiency. At times quantum yield is defined; often, it is ill-defined and more frequently how it was assessed is not described. This has led to much confusion in the literature, not only because of its different meaning from homogeneous photochemistry, but also because the description of photon efficiency precludes comparison of results from different laboratories owing to variations in light sources, reactor geometries, and overall experimental conditions. The previously reported quantum yields are in fact apparent quantum yields, i.e. lower limits of the true quantum yields. We address this issue and argue that any reference to quantum yields or quantum efficiencies in a heterogeneous medium is inadvisable until the number of photons absorbed by the light harvester (the photocatalyst) is known. A practical and simple alternative is proposed for general use and in particular for processes employing complex reactor geometries: the concept of relative photonic efficiency (xr) is useful to compare process efficiencies using a given photocatalyst material and a given standard test molecule. A quantum yield can subsequently be calculated since f = xr f phenol, where f phenol denotes the quantum yield for the photocatalyzed oxidative transformation of phenol used as the standard secondary actinometer and Degussa P-25 TiO2 as the standard photocatalyst. For heterogeneous suspensions (only), an additional method to determine quantum yields f is also proposed.

Generation of catalysts by photolysis of transition metal complexes

Abstract