UVA Light Irradiation Research Articles

Facile synthesis and light-induced antibacterial activity of ketoprofen functionalized bacterial cellulose membranes

Bacterial cellulose (BC) has already attracted tremendous interests from researchers especially those working in the area of functional nanomaterials. In this work, the chemical grafting of BC with ketoprofen (KP) was performed through eco-friendly and simple SolReact method. Surface functionalization of BC was confirmed by FTIR, XRD, XPS, TG, SEM, and TEM. Meanwhile, the stress-strain and water contact angle were also measured simultaneously. The results showed that surface functionalization was achieved under the mild reaction condition. The three-dimensional (3D) microstructure and crystalline structure of BC were maintained without being destroyed. The thermal stability of BC-KP was improved while retaining hydrophilic property and mechanical property. The photochemical property of BC-KP showed that the ROS generation was positively correlated with the time of light irradiation. The results of antibacterial tests on E.coli and S.aureus showed that the BC-KP possessed best antibacterial performance after 30 min UVA light irradiation, reaching to 72.7% and 81.6%, respectively. SEM studies displayed the cell morphology changed and membrane damaged resulting from the ROS produced under the light irradiation, which was a potential approach to prevent the bacteria resistance to conventional antibiotics. The antibacterial BC-based membranes grafting with photodynamic antimicrobial agents may be utilized as an efficient healthcare product for prevention of infectious disease.

Development of Cd3(PO4)2/rGO Coupled Semiconductor System for Effective Mineralization of Basic Violet 10 (BV 10) under UV-A Light

Abstract Initially, novel Cd3(PO4)2 was prepared via precipitation method. It was loaded with different concentration of rGO to form rGO/CdP composites. The prepared rGO/CdP were used to degrade Basic Violet 10 (BV 10) dye under UV-A light irradiation. The optimized rGO/CdP composite was characterized along with pristine CdP and rGO by XRD, FT-IR, FT-Raman, BET, HR-SEM with EDX, HR-TEM, and UV-DRS analysis. The effect of initial dye pH in the degradation was studied. The coupled semiconductor system enhanced the photocatalytic activity and used for multiple runs, due to its remarkable stability.

Antimicrobial polypropylene with ε-poly(lysine): Effectiveness under UV-A light and food storage applications

Polypropylene (PP) was mixed with polypropylene-graft-maleic anhydride (PP-g-MA) to obtain a reactive blend (PP/PP-g-MA) and render it antimicrobial by the application of ε-poly(lysine) and styrene maleic anhydride copolymer (SMA) onto its surface through reactive blending. Infrared spectroscopy confirmed covalent attachment through imide ring coupling between ε-poly(lysine), SMA, and PP/PP-g-MA. The resulting antimicrobial plastic (PP-SMA-PL) was effective in aqueous suspensions against Escherichia coli K12 ATCC 47009 with or without UV-A light irradiation providing > 99.99% reduction, and against the same bacterium in apple juice providing ∼ 90% reduction under UV-A light. Fluorometric assays suggested that this enhanced effect may be caused by reactive oxygen species (ROS) generation. In addition, PP-SMA-PL showed effectiveness against Listeria innocua L2 inoculated in milk in a storage study under refrigeration for 21 days, providing ∼90% reduction as compared to the starting level of inoculum and 99.99%–99.999% lower microbial load as compared to the control inoculated milk at the end of the storage study. Scanning electron microscopy, energy dispersive X-Ray spectroscopy, infrared spectroscopy, and colorimetric analyses confirmed no deposition of bacteria or organic matter onto PP-SMA-PL during the storage period with milk, as well as no release of ε-poly(lysine) from the surface of PP-SMA-PL.

Modulating the photocatalytic activity of TiO2 (P25) with lanthanum and graphene oxide

The modulation and tuning of the photocatalytic activity of commercial titanium dioxide (TiO2) P25 nanoparticles is demonstrated through the incorporation of lanthanum (La) and/or graphene oxide (GO). These composite materials, which could have applications in commercial products, were prepared by a two-step hydrothermal method from the corresponding precursors. The effect of La (0.05–2 mol%) and GO (5 m%) content on the crystal structure, morphology and photocatalytic activity of TiO2 was investigated by XRS, SEM, EDS, TEM, UV–vis DRS, point of zero charge, photoluminescence and the decolorization of methylene blue. Lanthanum modified the recombination rate of the photogenerated electron-hole charges on TiO2 by inducing an increase in the structural defects, which resulted in a significant suppression, up to 90%, of the photocatalytic activity in the UVA light region. In contrast, the addition of GO enhanced the photocatalytic activity of TiO2. Materials with tuned intermediate photoactivity within the entire range from high to very low were prepared by dosing appropriate amounts of La and GO species. The strategy of combining La and GO represents a useful and simple method for tuning or for suppressing the photocatalytic activity of TiO2 under UVA light irradiation in materials and consumer products using TiO2.

Silver and manganese co-doped titanium oxide aerogel for effective diclofenac degradation under UV-A light irradiation

The photodegradation of diclofenac from aqueous medium under UV-A light condition has been essayed using co-doped with manganese and silver TiO2 photocatalysts. X-ray diffraction, Raman spectroscopy, Scanning electron microscopy, Transmission electron microscopy, High resolution transmission electron microscopy, Energy dispersive X-ray, N2 adsorption-desorption measurements at 77 K, UV–Visible diffuse reflectance, X-ray photoelectron spectroscopy and photoluminescence analyses were used to characterize the materials. A high surface specific area of 165 m2/g, low band gap energy (2.7 eV) and effective charge separation were obtained for the 0.5%Ag-0.6%Mn/TiO2 photocatalyst. The results of the photocatalytic experiments showed that co-doping improved the photocatalytic activity of TiO2. In particular, TiO2 co-doped with 0.6 mol% Mn and 0.5 mol% Ag exhibited the maximum diclofenac removal (86%) after 4 h under UV-A light irradiation. The photodegradation rates followed a first order kinetics according to the Langmuir-Hinshelwood model, being the highest apparent rate of 0.0064 min−1. The photocatalytic performance appears as related to the specific surface area, the low optical band gap energy, the creation of surface oxygen vacancies and the efficient separation of photogenerated electron-hole pairs.

H2O2-assisted photoelectrocatalytic degradation of Mitoxantrone using CuO nanostructured films: Identification of by-products and toxicity

CuO nanostructured thin films supported on silicon with 6.5 cm2 area (geometric area greater than the studies reported in the literature) were synthesized by a chemical bath deposition technique. The electrodes were characterized by MEV, XRD, XPS, contact angle, cyclic voltammetry and electrochemical impedance spectroscopy analyses. To evaluate the photoelectrochemical properties of the CuO films, photocurrent–voltage measurements were performed using linear voltammetry. The catalytic activities of CuO nanostructures were evaluated by monitoring photodegradation of Mitoxantrone (MTX) under UV-A light irradiation. The method of photoelectrocatalysis (PEC), applying a voltage of 1.5 V and assisted by adding H2O2, was undertaken. To the best of our knowledge, no studies on the degradation of anticancer agents using PEC process have been found in the literature. For comparison purposes, experiments were performed under the same conditions by assisted photocatalysis (PC) with H2O2 and direct photolysis. CuO deposits consist of a needle-like morphology. The presence of CuO in the tenorite phase was evidenced by XRD and the XPS spectra showed the presence of copper(II) oxide. The increase in current under illumination shows that CuO exhibits photoactivity. The PEC system showed a 75% level of MTX degradation, while the level achieved using PC was 50%. Under UV-A light alone only 3% removal was obtained after 180 min. Up to 10 by-products were identified by chromatography-mass spectrometry (LC-MS) with m/z values ranging between 521 and 285 and a plausible degradation route has been proposed. It is worth mentioning that 9 by-products identified in this work, were not found in the literature in other studies of degradation or products generated as metabolites. The toxicity tests of MTX before and after PEC treatment with Artemia Salina and Allium cepa showed a decrease in the acute toxicity of the medium as the antineoplastic was degraded.

Visible-light-enhanced photoactivity of perovskite-type W-doped BaTiO3 photocatalyst for photodegradation of tetracycline

The aim of this work is to synthesize tungsten-doped BaTiO3 (W-BaTiO3) nanocomposite photocatalyst by hydrothermal method using various W amounts (0–20 wt%) and investigate their photocatalytic activity by the degradation of tetracycline under UV-A light and visible light irradiation. The nanocomposite photocatalysts were characterized by XRD, SEM-EDAX and XPS analysis. XRD analysis revealed that the W-BaTiO3 nanocomposite showed high crystallinity of TiO2 anatase phase. Lower amounts of W-doping exhibited higher photocatalytic activity than non-doped and highly doped BaTiO3. Decrease in photocatalytic activity may be due to recombination of electrone-hole pairs by increasing W-doping amount. Also, the first-order reaction rate constant, kapp, was calculated using Langmuir-Hinshelwood (L-H) equation. The kapp values were found as 3.95 × 10−2, 8.33 × 10−2, 4.87 × 10−2, and 5.43 × 10−2 min−1 and 3.72 × 10−2 for BaTiO3, W-BaTiO3-5, W-BaTiO3-10, W-BaTiO3-15 and W-BaTiO3-20 photocatalysts, respectively. According to stability tests, after the first cycle tetracycline degradation was found as 82%, while it was 73% after fifth cycle.

A new route for the synthesis of highly-active N-doped TiO2 nanoparticles for visible light photocatalysis using urea as nitrogen precursor

Nitrogen-doped TiO2 nanoparticles with high specific surface area and photocatalytic activity under visible light were successfully produced using a modified sol-gel method with urea introduced as the nitrogen source. Different synthesis approaches and parameters such as doping temperature and urea to TiO2 molar ratio were tested to examine the best outcome regarding photocatalytic activity for both UV-A and visible light irradiation. UV–vis diffuse reflectance characterization revealed a decrease in band gap from 3.24 to a minimum of 2.79 eV with the N-doping process. The photocatalytic Methylene Blue dye degradation assays suggests that the introduction of nitrogen in the TiO2 lattice cell can provide a higher efficiency under both UV-A and visible irradiation. The maximum photocatalytic activity was achieved for the nitrogen-doped powders prepared with the lowest urea:TiO2 molar ratio (1.5) as it was the formulation that promoted an enhancement in N-doping and particle specific surface area to 182 m2 g−1, despite the fact that the highest specific surface area was registered for undoped TiO2 nanoparticles (228 m2 g−1). A synthesis step variation was performed to enhance the specific surface area of nanoparticles and consequently the photocatalytic activity. This modification promoted an increase in specific surface area by a factor of ∼5. XPS spectra confirmed a successful introduction of nitrogen in the TiO2 lattice up to 1.5 at.% for optimized powders, which is strongly dependant of the type of synthesis and the amount of dopant species added during the doping process.

Nature and photoreactivity of TiO2-rGO nanocomposites in aqueous suspensions under UV-A irradiation

Different studies to unravel the nature of the activity of TiO2 photocatalysts modified with rGO were carried out. The band edge potentials and the band gap energy of the nanocomposites were determined by performing electrochemical impedance and UV–vis diffuse reflectance measurements, respectively. However, no changes were observed when TiO2 is modified with rGO. Nevertheless, the presence of rGO in the hybrid composite led to a low charge transfer resistance across the electrode-electrolyte interface, observing even a tenfold increase in the photocurrent values in methanol photo-oxidation for P25-rGO 1%. Moreover, a higher oxygen reduction current was found when increasing the rGO concentration that could lead to a higher ROS formation. In order to analyze the beneficial properties of the hybrid materials, the influence of rGO doping ratio on oxalic acid photocatalytic degradation and on oxalic acid adsorption onto the nanocomposites surface was studied, both of them under UV-A light irradiation. In addition, the photoactivity of the conduction band electrons and the valence band holes was investigated by performing EPR and transient absorption spectroscopy measurements under UV-A illumination in O2 or N2 atmospheres. It was demonstrated that rGO behaved as an electron acceptor. Finally, TAS results under O2 and N2 atmospheres proved that the role played by rGO was not as crucial in excess of dissolved O2 as in N2 atmosphere. These findings agree with the observed photocatalytic activity and EPR measurements. Nevertheless, generation of HO in N2 saturated suspensions was highly increased with the addition of rGO.

Plate-Like Bi4Ti3O12 Particles and their Topochemical Conversion to SrTiO3 Under HydrothermalConditions

Plate-like Bi 4 Ti 3 O 12 particles were synthesized using a one-step, molten-salt method from Bi 2 O 3 and TiO 2 nanopowders at 800 °C. The reaction parameters that affect the crystal structure and morphology were identified and systematically investigated. The differences between various Bi 4 Ti 3 O 12 plate-like particles were examined in terms of the ferroelectric-to-paraelectric phase transition and the photocatalytic activity for the degradation of Rhodamine B under UV-A light irradiation. The results encouraged us to conduct further testing of the as-prepared Bi 4 Ti 3 O 12 plate-like particles as templates for the preparation of plate-like SrTiO 3 perovskite particles using a topochemical conversion under hydrothermal conditions. The characteristics of the Bi 4 Ti 3 O 12 plates and the reaction parameters for which the SrTiO 3 preserved the shape of the initial Bi 4 Ti 3 O 12 template particles were determined.

Reinforced photocatalytic reduction of CO2 to fuel by efficient S-TiO2: Significance of sulfur doping

The photocatalytic reduction of CO2 to valuable chemicals and fuels is an efficient approach to control the ever-rising CO2 level in the atmosphere. The present paper describes a significant improvement in photoreduction of carbon dioxide (CO2) using sulfur (S) doped titania (S-TiO2) nanoparticles as a photocatalyst under UV-A and visible light irradiation. The sulfur doping was done by following a simple sonothermal method, and a series of photocatalysts were synthesized with the varied amount of S doping. Various characterization techniques were employed for the photocatalysts such as XRD, surface area, UV–Visible, SEM, TEM, and XPS. The XPS reveals that S is predominantly present as S4+ in S-TiO2. The electronic structure for S-TiO2 anatase was calculated with the Vienna ab initio simulation package (VASP) code in the framework of spin-polarized density functional theory. Additional states closer to the valence band are produced inside the band gap as a result of doping. In situ reductive reaction conditions can partially reduce the catalyst, and results in the shift of Fermi level into the conduction band. It is suggested that S-doping increases catalyst surface conductivity, improves the charge transfer rate and the rate of photocatalytic reactions. The prepared series of catalysts have shown excellent activity under UV-A and visible light for photocatalytic reduction of CO2. The effect of the different base including K2CO3, Na2CO3, NaOH and KOH; catalyst amount; sulfur doping amount; and light wavelength were monitored. Methane, ethylene, propylene, and propane were observed as reaction products. In 24 h, S-TiO2 exhibited the highest photoactivity in KOH aqueous solution with a maximum yield of 6.25 μmol g−1 methane, 2.74 μmol g−1 of ethylene, 0.074 μmol g−1 of propylene and 0.030 μmol g−1 of propane under UV-A irradiation. The catalysts were active in visible light and able to generate methane and methanol in acetonitrile-H2O mixture with/without TEOA as sacrificial donor producing 846.5 μmol g−1 of methane and 4030 μmol g−1 of methanol for the former and 167.6 μmol g−1 of methane and 12828.4 μmol g−1 of methanol for the latter case. An estimate demonstrates that mass transfer does not limit the CO2 reaction.

Polyethylene glycol-assisted sol-gel synthesis of magnetic CoFe2O4 powder as photo-Fenton catalysts in the presence of oxalic acid

The aim of the study was to prepare magnetic photo-Fenton catalysts based on CoFe2O4 by polyethylene glycol-assisted sol-gel method for the degradation of methylene blue under UVA and visible light irradiation with H2C2O4 as a radical producing source. The catalysts were synthesized at different annealing temperatures in order to investigate the influence of annealing temperature on their crystal structure, morphology, surface functional groups, magnetic properties, and their photo-Fenton catalytic activity. According to the results, when the annealing temperature increased from 600 to 800 °C, the content of CoFe2O4 cubic spinel phase was significantly enhanced, the amount of Fe3+ ions in the tetrahedral sites also increased on the surface of samples, which improved the magnetic properties as well as the photo-Fenton catalytic performance under both UVA and visible light. However, at the annealing temperature of 900 °C, the photo-Fenton activity was declined, which can be attributed to the growth of catalytic particles and the decrease of Fe3+ ions on their surface.

Antimicrobial activity of ZnO nanoplates and its Ag nanocomposites: Insight into an ROS-mediated antibacterial mechanism under UV light

We have previously shown that the bactericidal effect of ZnO nanoparticles in the absence of a light source originates from the released Zn2+ ions. The purpose of this study was to explore antibacterial activity arising from photo-induced reactive oxygen species (ROS) of ZnO nanoparticles under UV-A light irradiation. To achieve this, S. aureus and K. pneumoniae bacteria were exposed to three different ZnO nanoparticles under UV-A light. The concentrations of the ZnO nanoparticles were low, such that the antibacterial effect of the dissolved Zn2+ ions was negligible. From various empirical evidence, we found that the oxygen defects of the ZnO crystals enhanced the photogeneration of ROS and consequently, the ZnO nanoplates (NPs) with the polar facets exhibited the most pronounced antibacterial activity under UV-A stimulation. To enhance the antimicrobial activity of the NPs, we successfully synthesized silver-nanoparticle-decorated ZnO NPs and explored their antibacterial activity compared to that of the NPs.

Fog, phenolic acids and UV-A light irradiation: A new antimicrobial treatment for decontamination of fresh produce

This study evaluates synergistic interactions of food grade phenolic acids (gallic and ferulic acid) and UV-A light to achieve decontamination of fresh produce using a fog to improve dispersion of the phenolic acids on produce surface. Nonvirulent strains of Escherichia coli O157:H7 and Listeria innocua were used as model bacteria and spinach was selected as a model fresh produce. Synergistic combination of a fog deposited phenolic acid and a UV-A light treatment achieved reduction in bacterial plate count up to 2 log CFU/cm2 independently of the initial load of the bacteria (104 or 106 CFU/cm2). Following the treatment, fog deposited gallic and ferulic acid could be easily removed from the surface of produce by immersion in water and the treatment did not significantly alter the total endogenous phenolic content of spinach. The treatment also did not affect the texture, but impacted the color of the spinach leaves on a Hunter's Lab scale although the visual color changes were small. Overall, this technology may aid in developing alternative approaches for decontamination processes using food grade compounds.

Novel ZnO-Ag/MWCNT nanocomposite for the photocatalytic degradation of phenol

A novel Ag-doped ZnO nanoparticle with different amount of multi-walled carbon nano tubes (MWCNTs) was developed, aiming to shift the band edge toward longer wavelength. New particles were produced in a simple wet synthesis method and assessed toward the removal of phenol under UV-A illumination. The photocatalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) with an energy-dispersive X-ray (EDX) spectroscopy analysis, transition electron microscopy (TEM), BET surface area analyzer, UV–vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectroscopy (PL). The results indicated that all the samples containing MWCNTs exhibit higher photocatalytic activity than the bare ZnO and Ag doped ZnO nanoparticles. At a 10% MWCNT addition, the novel particle achieved a photocatalytic conversion rate of 81% in removing 100 ppm phenol under UV-A light irradiation after 240 min. The pH value, initial concentration and catalyst dosage were also found to influence the particle’s photocatalytic performance significantly.

Inactivation Mechanisms of Human and Animal Rotaviruses by Solar UVA and Visible Light.

Two rotavirus (RV) strains (sialidase-resistant Wa and sialidase-sensitive OSU) were irradiated with simulated solar UVA and visible light in sensitizer-free phosphate buffered solution (PBS) (lacking exogenous reactive oxygen species (ROS)) or secondary effluent wastewater (producing ROS). Although light attenuated for up to 15% through the secondary effluent wastewater (SEW), the inactivation efficacies increased by 0.7 log10 for Wa and 2 log10 for OSU compared to those in sensitizer-free phosphate buffered solution (PBS) after 4 h of irradiation. A binding assay using magnetic beads coated with porcine gastric mucin containing receptors for rotaviruses (PGM-MB) was developed to determine if inactivation influenced RV binding to its receptors. The linear correlation between the reduction in infectivity and the reduction in binding after irradiation in sensitizer-free solution suggests that the main mechanism of RV inactivation in the absence of exogenous ROS was due to damage to VP8*, the RV protein that binds to host cell receptors. For a given reduction in infectivity, greater damage in VP8* was observed with sialidase-resistant Wa compared to sialidase-sensitive OSU. The lack of correlation between the reduction in infectivity and the reduction in binding, in SEW, led us to include RNase treatment before the binding step to quantify virions with intact protein capsids and exclude virions that can bind to the receptors but have their capsid permeable after irradiation. This assay showed a linear correlation between the reduction in RV infectivity and RV-receptor interactions, suggesting that RV inactivation in SEW was due to compromised capsid proteins other than the VP8* protein. Thus, rotavirus inactivation by UVA and visible light irradiation depends on both the formation of ROS and the stability of viral proteins.

CeO2 nanoscale particles: Synthesis, characterization and photocatalytic activity under UVA light irradiation

CeO2 nanoparticles (NPs) were synthesized in alkaline medium via the homogeneous precipitation method and were subsequently calcined at 80 °C/24 h (assigned as CeO2-80) and 500 °C/2 h (assigned as CeO2-500). The as-prepared materials and the commercial ceria (assigned as CeO2-com) were characterized using TGA-MS, XRD, SEM-EDX, UV–vis DRS and IEP techniques. The photocatalytic performances of all obtained photocatalysts were assessed by the degradation of Congo red azo-dye (CR) under UVA-light irradiation at various environmental key factors (e.g., reaction time and calcination temperature). Results reveal that CeO2 compounds crystalize with cubic phase. CeO2-500 exhibits smaller crystallite size (9 nm vs 117 nm) than that of bare CeO2-com. SEM analysis shows that the materials are spherical-like in shape NPs with strong assembly of CeO2 NPs observed in the CeO2-500 NPs. EDX analysis confirms the stoichiometry of CeO2 NPs. UV–vis DRS measurement reveals that, CeO2-500 NPs exhibits a red-shift of absorption band and a more narrow bandgap (2.6 eV vs 3.20 eV) than that of bare CeO2-com. On the contrary, Urbach energy of Eu is found to be increased from 0.12 eV (CeO2-com) to 0.17 eV (CeO2-500), highlighting an increase of crystalline size and internal microstrain in the CeO2-500 NPs sample. Zeta potential (IEP) of CeO2-500 NPs is found to be 7.2. UVA-light-responsive photocatalytic activity is observed with CeO2-500 NPs at a rate constant of 10 × 10−3 min−1, which is four times higher than that of CeO2-com (Kapp = 2.4 × 10−3 min−1) for the degradation of CR. Pseudo-first-order kinetic model gives the best fit. On the basis of the energy band diagram positions, the enhanced photocatalytic performance of CeO2-500 nano-catalyst can be ascribed to O2·−, O·H and R·+ as the primary oxidative species involved in the degradation of RC under UVA-light irradiation.

Characterization and photocatalytic activity of new photocatalysts based on Ag, F-modified ZnO nanoparticles prepared by thermal shock method

Ag-modified ZnO, F-modified ZnO and (Ag, F)-modified ZnO nanoparticles were prepared by thermal shock method in order to study the effects of doping agents on their crystal structure, morphology, optical properties, surface structure and photocatalytic activity. The catalysts were characterized by XRD, FE-SEM, TEM, FTIR, UV–Visible diffuse reflectance and XPS spectroscopy. The photocatalytic activity was evaluated via the degradation of methylene blue under UVA and visible light irradiation. According to the results, the thermal shock process with AgNO3 did not modify the morphology but successfully created silver species on the surface of ZnO, which induces the visible light absorption and then increases the photocatalytic activity. The enhanced phototcatalytic performance was also observed in F-modified ZnO sample owing to the increase of surface hydroxyl groups and the formation of zinc vacancies. Among three modified ZnO samples, (Ag, F)-modified ZnO was found to be the best sample with the photocatalytic activity enhanced by the factor of 3 under both UVA and visible light, which may be attributed to the synergic effects of AgNO3 and KF used in thermal shock process.

Influence of the preparation method and ZnO/(ZnO + TiO2) weight ratio on the physicochemical and photocatalytic properties of ZnO-TiO2 nanomaterials

In this work, ZnO-TiO2 nanomaterials with various ZnO/(ZnO + TiO2) weight ratios (0.1–0.9) were synthesized by using sol-gel and precipitation methods The influence of the ZnO weight ratio (R) and the preparation method on the structural, optical, morphological and photocatalytic properties of the prepared nanomaterials has been studied. The obtained physicochemical characterization results indicated that the crystalline structure, the morphological and the optical properties of the ZnO-TiO2 nanomaterials are strongly influenced by the preparation method as well as the ZnO weight ratio. The results of the photocatalytic degradation of Methyl Orange (MO) in the presence of the synthesized photocatalysts and UV-A light irradiation showed the existence of two domains of ZnO weight ratio. The first is between 0.2 and 0.5 in which the ZnO-TiO2 nanomaterials prepared by sol-gel method exhibited the lowest MO conversion values in comparison with those prepared by precipitation method. These low MO conversion values were due to the intervention of a combination of various parameters that are the particles’ agglomeration, the poor crystallinity and the high Eg values. The second corresponds to R ≥ 0.67 in which the sol-gel method leads to the fabrication of ZnO-TiO2 materials with better photocatalytic efficiencies. The kinetic study showed that the Zn(Pr)-Ti-0.1 sample exhibited the best final MO conversion (99.5%) with the highest apparent rate constant value (0.01763 mn−1).

Synthesis and Charcterization of Coupled ZnO/SnO2 Photocatalysts and Their Activity towards Degradation of Cibacron Red Dye

ABSTRACTA series of coupled ZnO-SnO2 photocatalyst was successfully synthesized in the Zn:Sn molar ratio of 20:1, 10:1, 5:1 and 2:1 via co-precipitation method followed by calcination at different temperatures. The synthesized materials were characterized by X-ray diffraction, diffuse reflectance spectra, scanning electron microscope and transmission electron microscope. Photocatalytic activitiy of synthesized materials was applied for the degradation of cibacron red dye in aqueous solution under UV-A light irradiation. Experimental results revealed that the coupled ZnO-SnO2 photocatalyst with Zn:Sn molar ratio 10:1, calcined at 600oC for 1 h was the most efficient photocatalyst among synthesized samples for the degradation of cibacron red. Superoxide anion radical (•O2–) was found to be the prominent active species responsible for degradation comparative to hole (h+), hydroxyl radical (•OH).