Visible Irradiation Research Articles

α-Fe2O3 mediated periodate activation for selective degradation of phenolic compounds via electron transfer pathway under visible irradiation

Periodate (PI)-photoactivated advanced oxidation process (AOP) has recently received increasing attention for the removal of micropollutants from water. However, periodate is mainly driven by high-energy ultraviolet light (UV) in most cases, and few studies have extended it to the visible range. Herein, we proposed a new PI visible light activation system employing α-Fe2O3 as catalyst. It is completely different from traditional PI-AOP based on hydroxyl radicals (•OH) and iodine radical (•IO3). The vis-α-Fe2O3/PI system can selectively degrade the phenolic compounds via non-radical pathway under the visible range. Notably, the designed system not only shows a well pH tolerance and environmental stability, but also exhibits a strong substrate-dependent reactivity. Both quenching experiments and electron paramagnetic resonance (EPR) experiments demonstrate that photogenerated holes are the main active species in this system. Moreover, a series of photoelectrochemical experiments reveal that PI can effectively inhibit the carrier recombination on the α-Fe2O3 surface, thereby improving the utilization of photogenerated charges and increasing the number of photogenerated holes, which effectively reacts with 4-CP through electron transfer way. In a word, this work proposes a cost-effective, green and mild mean to activate PI, and provides a facile way to solve the fatal shortcomings (i.e., inappropriate band edge position, rapid charge recombination and short hole diffusion length) of traditional iron oxide semiconductor photocatalysts.

Construction of photocatalytic plates for hydrogen production from photoreforming of glycerol

The photocatalytic production of hydrogen has been reported as an attractive strategy given the possibility of using renewable sources such as sunlight and biomass. The scalability of the process involves optimizing the design of the reaction system, minimizing the cost and time spent on the stages of separation, purification and reuse of the catalyst. This work demonstrates the application of photocatalytic plates impregnated with TiO2 doped with small doses of platinum (Pt) in the photoreforming of glycerol under visible radiation. The optimized amount of catalyst was 25 mg, corresponding to an average hydrogen production rate in 3 h of reaction of 316 mmol H2.h−1.m−2, this value being independent of the platinum concentration range tested (0.1%–1.0%, w/w). The kinetic behavior of the photocatalytic plates was similar to the application of the catalyst in powder form. The presence of 0.3% platinum in the catalyst composition led to the maintenance of photocatalytic stability for 7 consecutive application cycles, indicating operational viability without appreciable loss of performance, brings good prospects for expanding the scale of the process and allowing the development of continuous flow operations.

Effect of sulfur on the solar light photoactivity of TiO2-based photocatalysts

Crude TiO2 derived from sulfate technology was used as a precursor for the novel solar light active photocatalysts with various sulfur content (S-TiO2). The effect of sulfur on the physicochemical properties of S-TiO2 and efficiency of ketoprofen photodecomposition under simulated solar light was investigated. Additionally, the activity of selected photocatalysts was evaluated under visible light and UV radiation. Moreover, different scavengers were applied to explore the mechanism of ketoprofen decomposition. Furthermore, the acute toxicity tests were performed to assess a toxicological effect of the decomposition products. It was proved that the sulfur content in a range of ∼ 0.7–1.2 wt% was a key factor affecting the photoactivity under simulated solar light. The most beneficial sulfur content was ∼ 0.9 wt%. It was revealed that the solar light induced photoactivity of the examined photocatalysts derived mainly from the visible light photocatalysis mechanism, with some contribution of the UV photocatalysis mechanism. The most important oxidizing species were h+, O2⦁− and ⦁OH, and among them h+ had the greatest impact under solar and visible light irradiation. However, the influence of e- cannot be disregarded. Based on the Aliivibrio fischeri bioluminescence assay a significant influence of the irradiation type on the treated solution toxicity was found.

Preparation of a new green magnetic Fe3O4 @TiO2-P25 photocatalyst for solar advanced oxidation processes in water

A novel green method has been investigated to obtain a magnetic recoverable photocatalyst. Fe3O4 particles formed in situ by aerial oxidative precipitation of aqueous Fe(II) in the presence of terephthalate were bonded to TiO2-P25 nanoparticles, giving rise to a coupled semiconductor heterostructure with superparamagnetic behavior at room temperature (Fe3O4 @TiO2-P25). The synthesis method is carried out in water at room temperature with almost full recovery and recycling of terephtalic acid. The prepared samples were fully characterized by XRD, TGA-DTA-MS, ATR-FTIR, WDXRF, TEM, SEM/EDX, N2 adsorption-desorption, elemental analysis, XPS, DRS, PL spectroscopy and SQUID. Photo-stability tests showed that Fe3O4 @TiO2-P25 does not undergo photodissolution under simulated solar radiation. The photocatalytic performance of Fe3O4 @TiO2-P25 was examined based on its ability to degrade aqueous metoprolol under UV–vis radiation in the presence of O2 and O3/O2. Also, the catalyst was successfully reused in six solar photocatalytic ozonation runs with negligible loss of photocatalytic activity.

Construction of α-MnO2/g-C3N4 Z-scheme heterojunction for photothermal synergistic catalytic decomposition of formaldehyde

Formaldehyde (HCHO), as the most common indoor air pollutant, undoubtedly poses a huge threat to people's health. It is of practical importance to achieve complete decomposition of HCHO to harmless CO2 at room temperature. Herein, α-MnO2/g-C3N4 Z-scheme heterojunction was constructed through the in-situ growth of α-MnO2 nanowires on the surface of g-C3N4 nanosheets. Owing to the construction of Z-scheme heterojunction, α-MnO2/g-C3N4 composite exhibits excellent photothermal catalytic activity, achieving complete mineralization of HCHO with the illumination of 191 mW/cm2 solar-light at GHSV of 180 L/gcat·h. Particularly, even under one sun and visible light radiation, the α-MnO2/g-C3N4 composite can still maintain 60% and 68% HCHO conversion, respectively. The formation of α-MnO2/g-C3N4 Z-scheme heterojunction not only effectively inhibits the photogenerated electron-hole pairs recombination, but also overcomes the band defects of the individual component. Furthermore, the mechanism of the photothermal catalysis of α-MnO2/g-C3N4 composite was discovered to be thermal-assisted photocatalytic process rather than solar-light driven thermalcatalysis. On the one hand, the thermal energy generated from light radiation can accelerate the migration of photo-generated carriers and improve the separation efficiency of photogenerated electrons from vacancies; on the other hand, it can decrease the activation energy of lattice oxygen and produce more surface-active oxygen species. This work provides cost-effective strategies and suggestions for decomposing HCHO and other VOCs in indoor air at room temperature.

Persulfate promoted visible photocatalytic elimination of bisphenol A by g-C3N4–CeO2 S-scheme heterojunction: The dominant role of photo-induced holes

In the last few years, coupling heterogeneous photocatalysis with persulfate (PDS) activation process is an efficient approach to generate abundant reactive oxidative species towards organic contaminant removal in water, however, the key role of PDS in photocatalytic process remains ambiguous. Herein, a novel g-C3N4–CeO2 (CN–CeO2) step-scheme (S-scheme) composite was constructed to photo-degrade bisphenol A (BPA) with the presence of PDS under visible irradiation. At 2.0 mM PDS, 0.7 g/L CN–CeO2 and natural pH 6.2, 94.2% of BPA could be eliminated in 60 min under visible light (Vis) illumination. Aside from the previous view of free radical generation, it tends to assume that most of PDS molecules acted as electron sacrificial agents for capturing photo-induced e− to form sulfate ions, greatly improving the charge carrier separation and thus enhancing the oxidation capacity of nonradical hole (h+) for the removal of BPA. Good correlations are further found between the rate constant and descriptor variables (i.e., Hammett constant σ−/σ+ and half-wave potential E1/2), exhibiting selective oxidation for organic pollutants in the Vis/CN–CeO2/PDS system. The study brings more insights into mechanistic understanding of persulfate-enhanced photocatalytic process for addressing water decontamination.

Improving the Degradation Kinetics of Industrial Dyes with Chitosan/TiO2/Glycerol Films for the Sustainable Recovery of Chitosan from Waste Streams

This study investigates the potential of a combined photocatalysis–adsorption approach to effectively degrade near wash yellow (NWY), a commonly used and highly persistent dye in the textile industry, notorious for its challenging treatment and removal from wastewater due to its colorfastness. A chitosan–glycerol (CTiG) film combined with titanium dioxide was examined in both batch and continuous-flow experiments under visible solar irradiation. The results show that this combination was more effective than a pure chitosan film (60%) or chitosan–glycerol film (63%), with up to 83% degradation of NWY achieved in just 60 min of visible solar irradiation. The kinetics of the film were evaluated using both pseudo-first-order and Langmuir–Hinshelwood kinetic models. The rate constant values (k, min−1) decreased with increasing NWY concentration from 20 to 80 mg/L, and k was found to be greater than twice as high under visible solar irradiation as it was in the dark. The Langmuir–Hinshelwood model’s KLH (reaction rate constant) and KL (adsorption coefficient) values were 0.029 mg/L·min and 0.019 L/mg, respectively. The optimal conditions for NWY degradation were found to be 4% TiO2 to chitosan ratio, glycerol/chitosan ratio of 40%, and a pH of 7. In the continuous-flow model, the CTiG film was submerged in an 8 L NWY solution (80 mg/L) and degraded at a rate of 22.6 mg NWY/g film under natural sunlight. This study contributes to the development of effective and sustainable methods for the degradation of dyes from textile industry wastewater.

Effect of Chromium (VI) on the Oxidation of Methylene Blue Dye by Fe3O4/ Chitosan Composite

Heavy metal ion removal from industrial wastewater treatment systems is still difficult because it contains organic contaminants. In this study, functional composite hydrogels with photo Fenton reaction activity were used to decompose organic contaminants. Fe3O4 Nanoparticle, chitosan (CS), and other materials make up the hydrogel. There are different factors that affected Photo-Fenton activity including (pH, H2O2 conc., temp., and exposure period). Atomic force microscopy was used to examine the morphology of the composite and its average diameter (AFM). After 60 minutes of exposure to UV radiation, CS/ Fe3O4 hydrogel composite had degraded methylene blue (M.B.) dye by 92 percent. In the meantime, following an 1hour of visible irradiation, COD (Chemical Oxygen Demand) dropped to 6.1 mg/l.

Application of Polymeric Micelles for Cancer Treatment: A Review

Polymeric micelles have been considered a promising development in chemotherapies to treat cancer diseases in recent decades. Bearing a structure of hydrophilic outer shell and hydrophobic core, these micelles possess many advantages like their nano-size structure, self-assembly synthesis, physical and chemical stability, biocompatibility, prolonged blood circulation time, and high drug loading and release capacity. The increased availability of building block copolymers that produce polymeric micelles also enables researchers to create the ideal drug delivery system. The formation of these polymeric micelles depends on various non-covalent interactions, the used concentration and temperature, block lengths, and methods of preparation. Among these polymeric micelles, stimuli-sensitive micelles have been developed and begun to attract more attention in recent years for their high on-site specificity and enhanced drug release efficacy. To accommodate the complex microenvironment in tumors, such as the internal changes in pH, reductive responses, and enzyme activities, or the external factors like visible lights, UV irradiations, and temperature, the stimuli-sensitive micelles exhibit strong stability, high drug loading, efficient drug delivery, specific site release, and mild side effects in recent studies. This research also discusses dual or multi-stimuli-sensitive polymeric micelles that are under high research nowadays, dictating a more novel and efficient way of cancer treatments and clinical practices.

Cocatalyst loaded Al-SrTiO3 cubes for Congo red dye photo-degradation under wide range of light

The continued pollution, waste, and unequal distribution of the limited amount of fresh water on earth are pushing the world into water scarcity crisis. Consequently, development of revolutionary, cost-effective, and efficient techniques for water purification is essential. Herein, molten flux method was used for the preparation of micro-sized Al-doped SrTiO3 photocatalyst loaded with RhCr2O3 and CoOOH cocatalysts via simple impregnation method for the photo-assisted degradation of Congo red dye under UV and visible irradiation compared with P25 standard photocatalyst. In addition, photoelectrochemical analysis was conducted to reveal the separation and transfer efficiency of the photogenerated e−/h+ pairs playing the key role in photocatalysis. SEM and TEM analyses revealed that both P25 and the pristine SrTiO3 have spherical shapes, while Al-doped SrTiO3 and the sample loaded with cocatalysts have cubic shapes with a relatively higher particle size reaching 145 nm. In addition, the lowest bandgap is due to Al+3 ion doping and excessive surface oxygen vacancies, as confirmed by both UV–Vis diffuse-reflectance and XPS analyses. The loading of the cocatalysts resulted in a change in the bandgap from n-type (pristine SrTiO3 and Al-SrTiO3) into p-type (cocatalyst loaded sample) as exhibited by Mott–Schottky plots. Besides, the cocatalyst-loaded sample exhibited good performance stability after 5 cycles of the photocatalytic removal of Congo red dye. OH· radical was the primary species responsible for CR degradation as confirmed by experiments with radical scavengers. The observed performance of the prepared samples under both UV and visible light could foster the ongoing efforts towards more efficient photocatalysts for water purification.

Ce-doped perovskite-type catalyst derived from Ti-bearing blast furnace slag for photocatalytic removal of gaseous toluene under visible light

Since the yield of titanium-bearing blast furnace slag (TF) during the smelting of vanadium titanium magnetite is large, it is urgent to find ways to recycle it and implement its value-added utilization. In this study, a perovskite-rich photocatalyst was prepared by acid-washing of TF, and then Ce was doped to modify it for photocatalytic removal of gaseous toluene under the irradiation of visible light. XRD, XRF and XPS analyses demonstrated that the perovskite phase was enriched after the acid-washing, and the content of CaTiO3 in the acid-washed slag (AS) also increased after Ce doping. The combined N2 adsorption-desorption, UVVis DRS, EIS, PL, and ESR analysis results indicated that the photocatalytic performance of the mentioned photocatalyst was related to the Ce dopant content. The AS doped with 20% Ce (20% Ce-AS) had a lower band gap and larger specific surface area than the others catalysts. Under visible light radiation, more active radicals were produced, and the removal efficiency of toluene reached 92.08% for 20% Ce-AS. In addition, the results of the in situ DRIFTS tests indicated that toluene was gradually degraded by the Ce-doped perovskite-type photocatalyst to alcohols and aldehydes and mineralized to H2O and CO2. This study is expected to provide a new approach for the technical development of the value-added utilization of TF coupled with the efficient removal of toluene.

Enhanced degradation of diazinon in aqueous solution using C-TiO2/g-C3N4 nanocomposite under visible light: Synthesis, characterization, kinetics, and mechanism studies

Sol-gel synthesis of C-TiO2/g-C3N4 nanocomposite using carboxymethyl cellulose as a carbon source and with different contents of C-TiO2 nanoparticles for the degradation of diazinon with the use of visible radiation was investigated in this study. Characteristics of the synthesized catalyst were analyzed by FE-SEM, XRD, EDX, FT-IR, BET, PL, TGA, and DRS techniques. We obtained the degradation efficiency of diazinon with C-TiO2 (30 wt%)/g-C3N4 under optimal conditions (dose of catalyst 0.1 g L−1, diazinon initial concentration 15 mg L−1, time of reaction 30 min, pH = 5.5) 98.34%, which showed premiere photocatalytic degradation efficiency compared to carbon nitride and C-TiO2. According to the data, the degradation process of diazinon by C-TiO2/g-C3N4 nanocomposite corresponds to first-order kinetics. The catalyst showed good reusability after five consecutive cycles. In addition, we investigated the effects of several scavengers on photocatalytic degradation yield and proposed the possible mechanism of diazinon destruction by C-TiO2 (30 wt%)/g-C3N4.

Antimicrobial activity of Emodin in combination with visible light against Escherichia coli and Staphylococcus aureus: Applications for food safety technology

In order to promote the application of natural photosensitizer, the photodynamic antibacterial effect of emodin combined with visible light on Escherichia coli and Staphylococcus aureus were studied in this work. The results showed that emodin mediated photodynamic antibacterial activity was dependent on concentration, light time and pH. Confocal microscopy and scanning electron microscopy confirmed that emodin can produce reactive oxygen species to kill bacteria under visible light irradiation. After treatment with emodin and visible intermittent radiation, S. aureus inoculated on the surface of fresh-cut apples was significantly reduced to 1.5 Log CFU/mL during 5 days of storage, and the storage method had no significant effect on the weight and appearance of apples. The results indicate that photodynamic inactivation of foodborne pathogens by combining emodin with visible light is a potential food safety technology.

УДАЛЕНИЕ ЭКОТОКСИКАНТОВ ИЗ ВОДНЫХ РАСТВОРОВ С ПОМОЩЬЮ МЕХАНОАКТИВИРОВАННОГО АНАТАЗА ПОД ДЕЙСТВИЕМ ОСВЕЩЕНИЯ

A significant improvement in the ability to remove ecotoxicants, hexavalent chromium and methylene blue dye, from aqueous solutions under the action of short-wave visible radiation was shown for anatase modification after mechanical activation.

Palladium-modified TiO2 Photocatalysts: Synthesis, Characterization, and Environmental Application

Sol-gel method was used to prepare palladium-modified TiO2 powder photocatalysts (Pd atomic percentage range of 0–1.00). The materials were characterized by X-ray diffraction, N2 physisorption, UV–Vis diffuse reflectance spectroscopy and transmission electron microscopy. Photocatalytic activity was tested for phenol degradation, with UV and visible lamps. The optimum palladium content was determined (0.10% atomic Pd), showing phenol degradation of 100% under UV irradiation (2 h) and 68% under visible irradiation (5 h). The presence of PdO particles was revealed on this material. Furthermore, the immobilization of this material on glass slides was studied by dip-coating method to overcome the limitations of the slurry mode. This film presented photocatalytic activity under UV and visible irradiation (5 h), reaching 80% and 23% of phenol degradation, respectively. This film is a promising alternative to degradation of pollutant using solar irradiation effectively.

Metal-free hybrid nanocomposites of graphitic carbon nitride and char: Synthesis, characterisation and photocatalysis under visible irradiation

BackgroundThe hybrid nanocomposites of graphitic carbon nitride (g-C3N4) and char were synthesised from melamine and hydroxyethyl cellulose/glucose to obtain metal-free photocatalysts active under visible irradiation. The nanocomposites were tested for the degradation of phenol and ofloxacin. MethodsThe nanocomposites were characterized by elemental and thermal analysis. Their electronic properties were studied by UV–Vis and photoluminescence spectroscopy. Texture and morphology were studied by physisorption of nitrogen, X-ray diffraction, infrared spectroscopy, X-ray photoelectron spectroscopy, and by transmission electron microscopy. The photocatalytic experiments were performed under the LED irradiation of 420 nm. Significant findingsHydroxyethyl cellulose and glucose formed char which was incorporated in the g-C3N4 structure. The char acted as an electron collector enabling the separation of photoinduced electrons and holes. In this way, the photocatalytic activity of g-C3N4 increased and 96% of ofloxacin was degraded during after 120 min. In addition, in this work the total combustion of graphitic carbon nitride up to 800 oC was investigated for the first time.

Visible-light enhanced peroxymonosulfate activation on Co3O4/MnO2 for the degradation of tetracycline: Cooperation of radical and non-radical mechanisms

Advanced oxidation processes (AOPs) dominated by SO4·- species have drawn mainly attentions for the removal of persistent pollutions. Nevertheless, single radical underutilizes the oxidizing capacity of reactive oxygen species and possesses poor adaptability to the environment compared with the cooperation of radical and non-radical. Herein, a Co3O4/MnO2 heterojunction catalyst is synthesized and used to peroxymonosulfate (PMS) activation for the degradation of tetracycline (TC) via non-radical cooperates with radical under visible irradiation. The optimized 10-Co3O4/MnO2 (10-CMO) composite catalyst exhibits 99.4% TC degradation efficiency within 60 min, and theapparent rate constant is 0.1353 min−1, which is 6.77 and 45.10 times higher than that of in 10-CMO/PMS and 10-CMO/Vissystems, respectively. The PMS acts as an electron accepter and induces the non-radical pathways accelerating TC degradation. After 5 cycles, the 10-CMO catalyst can still remove 93.7% TC with low Co (0.06 mg/L) and Mn (0.20 mg/L) ions leakage. The reactive species trapping experiments and electron paramagnetic resonance analysis demonstrate that the 1O2, h+ and SO4·- species dominate the TC degradation. Theoretical calculation results further reveal the probable PMS activation mechanism and the superiority of heterojunction for the PMS activation. This work shows great potential for pollutions control with visible-light-assisted PMS activation in presence of catalyst.

Structural parameters, optical band gap, and catalytic performance of anodized molybdenum

In this work, a nanopowder of porous molybdenum (Mo) oxides with different polymorphs were prepared by anodizing the Mo sheet in ethylene glycol solution containing fluoride at 60, 70, and 80 V for 30 min. Synthesized Mo oxides showed remarkable changes in their structural parameters and morphology upon the anodization voltage which were confirmed using X-ray diffraction, energy dispersive X-ray, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, N2 adsorption-desorption, and field emission scanning electron microscopic. Anodized Mo is composed of α-MoO3, β-MoO3, β-MoO2, and β-Mo9O26 phases. Synthesized Mo oxides were used, as a catalyst, for the photodegradation of methylene blue (MB), and results were compared to the literature. The maximum observed efficiency, ∼65%, towards MB was achieved using anodized Mo at 70 V (MO70) under UV–visible irradiation for 85 min. The N2 adsorption-desorption analysis revealed that MO70 exhibits the smallest particle size and greatest surface area among other samples. The performance of MB adsorption was investigated using several kinetic adsorption models and the pseudo-second-order model being the ideal one. The maximum adsorption constant is 1.4 × 10−2 g/(mg min) and the amount of MB that degraded at equilibrium is 5.52 mg/g for MO70. The anodization of Mo generated various polymorphs semiconductors which provide an excellent platform for the removal of toxic organic dyes from the wastewater.

Ceramic ZnO-SnO2-Fe2O3 Powders and Coatings -Effective Photogenerators of Reactive Oxygen Species

Ceramic ZnO-SnO2-Fe2O3 powders and transparent coatings on glasses prepared using the non-isothermal polymer-salt method demonstrate a strong ability to generate chemically active oxygen species under UV and visible irradiation. Crystal structures and morphologies of these materials were studied using the XRD and the SEM analysis. It was found that there are significant differences in the crystal structure of ceramic powders and thin coatings. The powders consist of randomly oriented oxide nanocrystals of size ~47 nm. The strong orientation of the ZnO nanocrystals due to their interaction with the glass substrate is observed in the coating structure. Experimental data show that thin ceramic coatings are transparent (~90%) in the visible spectral range and the band gap of the ceramic material is 3.44 eV. The band gap value of this multi-component ceramic material is described sufficiently using Verlag’s law. Ceramic powders and coatings demonstrate the intensive photogeneration of reactive oxygen species, both in liquid and air. High photocatalytic activity of ZnO-SnO2-Fe2O3 ceramic coatings and powders was observed upon the oxidation of the diazo dye, Chicago Sky Blue. In the presence of transparent photocatalytic coating, the value of the constant rate of the dye photodecomposition was high (k = 0.056 min−1). It was found that, in spite of their short life time, photogenerated reactive oxygen species demonstrate the ability to decompose dye molecules located up to a distance of 0.5 mm from the surface of ceramic coating. Obtained experimental results suggest that the prepared ceramic materials are promising for different practical applications of the photocatalytic materials.

Photocatalytic degradation of model pollutants using ZnO/Ag3PO4 heterostructure thin films under visible and solar irradiation

ZnO/Ag3PO4 heterostructure-based thin films were prepared by hydrothermal and SILAR deposition processes. The prepared samples were characterized for their morphology, structure, and optical properties using SEM, XRD, EDS, UV–Vis spectroscopy, and PL spectroscopy. Ag3PO4 modifies the light absorption characteristics significantly, with a considerable absorbance in the visible region found for ZnO. Under visible light and sunlight irradiation, Ag3PO4–ZnO nanorod-based heterostructure displayed substantially more substantial photocatalytic activity toward MB degradation, as well as superior recyclability and stability than pure ZnO nanorods. The Ag3PO4–ZnO nanorod combination with a 5 times dip of Ag3PO4 had the excellent photodegradation efficiency of MB (86%) compared to pure ZnO nanorods (60%) under visible irradiation.