Methylene Blue Photooxidation Research Articles

Green synthesis of tellurium-doped SnO2 nanoparticles with sulfurized g-C3 N4 : Insights into methylene blue photodegradation and antibacterial capability.

The construction of SnO2 nanoparticles (NPs), specifically Te-doped SnO2 NPs, using a simple and economical co-precipitation technique has been thoroughly described in this work. NH3 served as the reducing agent in this procedure, whilst polyethylene glycol served as the capping agent. The primary goals of our work were to investigate the physicochemical properties of the synthesized SnO2 NPs and assess their potential use as antibacterial agents and photocatalysts. Scanning electron microscopy-energy dispersive X-ray, ultraviolet light, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), and other analytical techniques were used to thoroughly analyze the NPs. Based on the full width at half maximum of the most noticeable peaks in the XRD spectrum, the Debye-Scherrer equation was used to calculate the crystallite sizes, which indicated the presence of a single tetragonal SnO2 phase. Particularly noteworthy was the exceptional photocatalytic activity of graphene-assisted Te-doped SnO2 NPs, achieving an impressive decomposition efficiency of up to 98% in the photo-oxidation of methylene blue. Furthermore, our investigation delved into the antibacterial attributes of the synthesized SnO2 NPs against Escherichia coli and Staphylococcus aureus, demonstrating inhibitory effects on both bacteria strains. This suggests potential applications for these NPs in various environmental and medical contexts.

The Influence of Hibiscus tiliaceus Leaf Extract as Capping Agent on the Zinc Oxide Properties and its Photo-simultaneous Performance

Polyol method, as one alternative in ZnO synthetic methods, have been developed and generated a nano-ZnO. However, the produced nano-ZnO is unstable due to its small particle size. To overcome the problems, we added Hibiscus tiliaceus leaves’ extract during the ZnO (EZnO) synthesis to change the water content and hydrolysis ratio of Zn2+/water. The addition of H. tiliaceus extract resulted in a shifting peak at (101) plane compared to ZnO synthesized without extract addition (WZnO). The use of H. tiliaceus extracts leads to the formation of large and non-uniform particles compared to the one prepared without the extract, which is in agreement with the intensity of diffraction pattern. The use of H. tiliaceus extracts shifted the bandgap energy to visible range. The performance of WZnO and EZnO samples was tested for simultaneous photo-oxidation of methylene blue and photo-reduction of Cr(VI) ions under UV-C irradiation. The EZnO is equally active as WZnO for Cr(VI) ion photo-reduction but less active for photo-oxidation of methylene blue. The presence of retained organic material in EZnO is plausibly affected by the adsorption and subsequent photo-oxidation of the bulky MB leading to a lower photo-oxidation performance. However, the activity of EZnO was a little bit lower than that of WZnO, revealing that the synergistic of particle size and band gap energy is a crucial factor in photo-removal process. In addition, the presence of phenolic compounds on the EZnO surface might change the nature properties of WZnO, which influence its performance.

The electronic structure modification and photocatalytic ability improvement of Rb0.9Nb1.625Mo0.375O5.62 β-pyrochlore compound

The photocatalytic ability of Rb0.9Nb1.625Mo0.375O5.62 UV-photocatalyst has been improved by electron structure modifications. The Rb0.75Cu0.15Nb1.625Mo0.375O5.6 and Rb0.8Mn0.1Nb1.625Mo0.375O5.7 modified compounds and Rb0.9Nb1.625Mo0.375O5.62/SnO2 heterostructure photocatalyst have been obtained under hydrothermal conditions. The crystal structure and elemental composition have been confirmed by X-ray diffraction analysis and X-ray microanalysis. The electron structure of the obtained samples has been investigated in comparison to initial one by diffuse reflection spectroscopy. All prepared samples possess the absorption in visible light range; however significant photocatalytic activity shows only Rb0.9Nb1.625Mo0.375O5.62/SnO2 heterostructure. The kinetic study of methylene blue photooxidation for Rb0.9Nb1.625Mo0.375O5.62/SnO2 at neutral pH have been investigated. It has been observed that the main oxidative species for dye oxidation are holes, hydroxyl radicals and superoxide radicals. The products of MB degradation have been determined by HPLC-MS method, and possible pathway of oxidation has been proposed.

Cellulose/chitosan/g-C3N4 nano-architectured films for visible light induced photocatalytic removal of methylene blue and Cr (VI) from water

The adverse impact of aggravating water pollution levels has exponentially trickled down to each and every component of the biosphere. The engineering of naturally occurring materials such as biopolymers has become an attractive solution for wastewater treatment. In this work, we have fabricated cellulose-based films hybridized with chitosan and g-C3N4 for visible light-induced removal of methylene blue and Cr (VI) ions from water. FE-SEM and X-ray diffraction data revealed a strong association of g-C3N4 in the cellulose chitosan network. The high porosity and specific surface area of cellulose and chitosan in the g-C3N4 network led to an increase in both its adsorption and degradation efficiency. The maximum efficiency of 98% and 96% for both methylene blue photooxidation and Cr (VI) photoreduction process, respectively was observed with the formulation containing 50 wt% g-C3N4. In addition to that, films retained their activity for 5 consecutive cycles showing their high reusability potential. Besides, the proposed films also showed excellent antibacterial properties towards S. aureus bacteria. Therefore, looking at the magnificent green, cost-effective, and simple operational nature of the films, it is anticipated that these films will play a key role in various wastewater treatment technologies.

Antibacterial and photocatalytic activity of visible-light-induced synthesized gold nanoparticles by using Lantana camara flower extract

Abstract A facile synthesis method of gold nanoparticles (AuNPs) utilizing Lantana camara flower extract (LFE) using visible light illumination towards the bio-reduction system has been conducted. The systematic characterizations of AuNPs were employed using transmission electron microscopy, X-ray powder diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The nanoparticles having a particle size of ranging 4.8–25 nm were obtained with dependence on the LFE concentration of the extract and time of light irradiation. The antibacterial activity of AuNPs was evaluated against Escherichia coli, Staphylococcus aureus, Propionibacterium acnes, and Pseudomonas aeruginosa, and the photocatalytic activity was examined in methylene blue photooxidation. The overall results point to a promising photochemical synthesis of AuNPs utilizing plant extract and the potential activities of synthesized nanoparticles as antibacterial agents and photocatalysts.

A New Insight into the Mechanisms Underlying the Discoloration, Sorption, and Photodegradation of Methylene Blue Solutions with and without BNOx Nanocatalysts.

Methylene blue (MB) is widely used as a test material in photodynamic therapy and photocatalysis. These applications require an accurate determination of the MB concentration as well as the factors affecting the temporal evolution of the MB concentration. Optical absorbance is the most common method used to estimate MB concentration. This paper presents a detailed study of the dependence of the optical absorbance of aqueous methylene blue (MB) solutions in a concentration range of 0.5 to 10 mg·L-1. The nonlinear behavior of optical absorbance as a function of MB concentration is described for the first time. A sharp change in optical absorption is observed in the range of MB concentrations from 3.33 to 4.00 mg·L-1. Based on the analysis of the absorption spectra, it is concluded that this is due to the formation of MB dimers and trimers in the specific concentration range. For the first time, a strong, thermally induced discoloration effect of the MB solution under the influence of visible and sunlight was revealed: the simultaneous illumination and heating of MB solutions from 20 to 80 °C leads to a twofold decrease in the MB concentration in the solution. Exposure to sunlight for 120 min at a temperature of 80 °C led to the discoloration of the MB solution by more than 80%. The thermally induced discoloration of MB solutions should be considered in photocatalytic experiments when tested solutions are not thermally stabilized and heated due to irradiation. We discuss whether MB is a suitable test material for photocatalytic experiments and consider this using the example of a new photocatalytic material-boron oxynitride (BNOx) nanoparticles-with 4.2 and 6.5 at.% of oxygen. It is shown that discoloration is a complex process and includes the following mechanisms: thermally induced MB photodegradation, MB absorption on BNOx NPs, self-sensitizing MB photooxidation, and photocatalytic MB degradation. Careful consideration of all these processes makes it possible to determine the photocatalytic contribution to the discoloration process when using MB as a test material. The photocatalytic activity of BNOx NPs containing 4.2 and 6.5 at.% of oxygen, estimated at ~440 μmol·g-1·h-1. The obtained results are discussed based on the results of DFT calculations considering the effect of MB sorption on its self-sensitizing photooxidation activity. A DFT analysis of the MB sorption capacity with BNOx NPs shows that surface oxygen defects prevent the sorption of MB molecules due to their planar orientation over the BNOx surface. To enhance the sorption capacity, surface oxygen defects should be eliminated.

Regulating of MnO2 photocatalytic activity in degradation of organic dyes by polymorphic engineering

Different phase nanostructured MnO2, including α-, β-, γ-, and δ-MnO2, were prepared by a hydrothermal route. Their photocatalytic activities in the degradation of cationic (methylene blue) and anionic (methyl orange) dyes were compared for the first time. The as-prepared oxides were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and low-temperature nitrogen adsorption-desorption techniques. It was shown that the highest efficiency was achieved in the degradation of cationic methylene in the presence of the δ-MnO2 photocatalyst (conversion of methylene blue was 90.4% after 180 min). These results are explained by unique physicochemical properties of the δ-MnO2 polymorph. It was observed that there is a synergetic effect between various physicochemical properties of δ-MnO2 which allows to obtain the high photodegradation efficiency: high adsorption ability towards methylene blue, unique 2D morphology, lower Mn–O bond strength, and high surface Mn4+/Mn3+ molar ratio. The reaction mechanism as well as the main products of the methylene blue photooxidation process over δ-MnO2 were also investigated.

Features of the electronic structure and photocatalytic properties under visible light irradiation for RbTe1.5W0.5O6 with β-pyrochlore structure

The compound RbTe1.5W0.5O6 with β-pyrochlore structure has been recently obtained as visible-light photocatalysts material, which is capable for dye decomposition. The refinement of electron structure has been performed based on transmittance and diffuse reflectance spectra. The ability for visible light absorbance is related to impurity defect absorbance band (∼2.5 eV) in the electron structure, despite the wide band gap (∼3.4 eV). The active radical species, led to methylene blue photooxidation, have been predicted using electronic structure and confirmed experimentally using radical's scavengers. The significant impact of electron-hole pair's recombination process on photocatalytic efficiency has been found out for powder with average size particle of 700 nm, and it has been improved by decreasing the particles size up to 300 nm. The apparent quantum efficiency has been calculated and compared for prepared samples with different particles size. Moreover, the oxidized products of methylene blue have been defined and the possible oxidation pathway has been proposed.

Fabrication of coatings based on strontium-bismuth-silicate photocatalyst for water purification from organic pollutants

Strontium-bismuth containing photocatalytic active coatings on a silicate carrier using sorbite-nitrate pyrolytic synthesis were obtained. The effect of strontium-bismuth molar ratio in the precursor mixture on the phase composition, boundaries of the visible light absorption region and photocatalytic activity of the coatings obtained were studied. The best photocatalytic activity is achieved by coatings obtained from the precursor mixture at Sr:Bi molar ratio of (1:3) and (1:4) in the experiment with a model organic pollutant — methylene blue (MB). The obtained photocatalytically active coatings on silicate carrier (Sr:Bi-1:4) were tested in a water purification unit (WPU) at different rotation speeds. The effective range of rotation of samples without loss of photocatalytic properties at photo-oxidation of MB (15–35 rpm) was established.

Hierarchical TiO2 Nanoflower Photocatalysts with Remarkable Activity for Aqueous Methylene Blue Photo-Oxidation.

This study systematically evaluates the performance of a series of TiO2 nanoflower (TNF) photocatalysts for aqueous methylene blue photo-oxidation under UV irradiation. TNF nanoflowers were synthesized from Ti(IV) butoxide by a hydrothermal method and then calcined at different temperatures (T = 400–800 °C) for specific periods of time (t = 1–5 h). By varying the calcination conditions, TNF-T-t photocatalysts with diverse physicochemical properties and anatase/rutile ratios were obtained. Many of the TNF-T-1 photocatalysts demonstrated remarkable activity for aqueous methylene blue photo-oxidation at pH 6 under UV excitation (365 nm), with activities following the order TNF-700-1 > TNF-600-1 > TNF-500-1 > TNF-400-1 ∼ P25 TiO2 ≫ TNF-800-1. The activity of the TNF-700-1 photocatalyst (99% anatase, 1% rutile) was 2.3 times that of P25 TiO2 at pH 6 and 14.4 times that of P25 TiO2 at pH 4. Prolonged calcination of the TNFs at 700 °C proved detrimental to dye degradation performance due to excessive rutile formation, which reduced the photocatalyst surface area and suppressed OH• generation. The outstanding activities of TNF-700-1 and TNF-600-1 are attributed to their hierarchical nanoflower morphology which benefitted UV absorption, a near-ideal anatase crystallite size for efficient charge separation, and their unusually low isoelectric point (IEP = 4.3–4.5).

Synthesis, optical and photo-electrochemical properties of NiBi2O4 and its photocatalytic activity under solar light irradiation

NiBi2O4 was synthesized by sol gel method using citric acid as a complexing reagent. The formed gel was dried and calcined for 9 h at three temperature steps (400, 600, 800 °C) to get a single phase with the spinel structure. The as-prepared NiBi2O4 was characterized by X-ray diffraction, FT-IR spectroscopy, and UV–vis diffuse reflectance. The optical band gap (Eg =1.76 eV) was obtained from optical absorption spectroscopy. The thermal variation electrical conductivity, measured in the range (300–473 K), is characteristic of semiconductor, with a conduction mechanism by low polaron hopping and activation energy of 0.2 eV. As application, the methylene blue (MB) was successfully oxidized upon solar light. A removal conversion of 40 % was obtained after 2 h at room temperature. The total photo-oxidation of MB (30 mg/L) was obtained on the new hetero-junction NiBi2O4/ZnO at natural pH in less than 2 h. A photocatalytic degradation mechanism occurred through (electron-hole) pairs generation and the redox reactions taking place on the NiBi2O4/ZnO surface of MB are proposed to explain the high activity under solar light irradiation. The degradation kinetics followed a first order with an apparent constant rate of 0.15 h-1.

Impact of the anodization time on the photocatalytic activity of TiO2 nanotubes.

Titanium oxide nanotubes (TNTs) were anodically grown in ethylene glycol electrolyte. The influence of the anodization time on their physicochemical and photoelectrochemical properties was evaluated. Concomitant with the anodization time, the NT length, fluorine content, and capacitance of the space charge region increased, affecting the opto-electronic properties (bandgap, bathochromic shift, band-edge position) and surface hydrophilicity of TiO2 NTs. These properties are at the origin of the photocatalytic activity (PCA), as proved with the photooxidation of methylene blue.

Highly reactive anatase nanorod photocatalysts synthesized by calcination of hydrogen titanate nanotubes: Effect of calcination conditions on photocatalytic performance for aqueous dye degradation and H2 production in alcohol-water mixtures

A series of anatase TiO2 nanorod photocatalysts, denoted herein as xTiO2(t) where x = calcination temperature and t = calcination time, were successfully synthesized by calcination of H2Ti3O7 nanotubes at 500–700 °C for 10–240 min. SEM, TEM, XRD and BET analyses demonstrated that nanorods with different aspect ratios, crystallite sizes and surface areas (15–93 m2 g−1) could be obtained by varying the calcination conditions. The 600TiO2(t) and 700TiO2(t) nanorods demonstrated superior photocatalytic activity to Degussa P25 TiO2 for methylene blue photo-oxidation at pH 6, and also superior activity for H2 production in alcohol-water systems following decoration with Pd, Au or Pd-Au co-catalysts. Under UV excitation (365 nm, 6.5 mW cm−2), Pd-Au/600TiO2(20) afforded H2 production rates of 37.2, 44.0 and 45.6 mmol g−1 h−1 in 10 vol.% ethanol-water, ethylene glycol-water and glycerol-water mixtures, respectively. Co-catalyst activity for the 600TiO2(t) and P25 TiO2 photocatalysts followed the order Pd-Au > Pd > Au.

Enhanced methylene blue photodegradation with propylene carbonate as a solvent

The role of water in the TiO2-based photocatalytic phenomenon is not yet fully understood. The photocatalysis of methylene blue dissolved in propylene carbonate and different concentrations of water was studied. It was observed that the photocatalytic activity of TiO2 (P25 from Evonik) peaks when propylene carbonate solvent is used with minute amounts of water; the maximum photodegradation rate was ca. 6.5 times higher than when just water solvent was used. The conventional interpretation of the methylene blue photooxidation intermediated by free radical OH cannot explain these results. Alternately, the experimental results were interpreted based on the recently proposed “direct–indirect” (D-I) model and a mathematical model was successfully developed and fitted to the experimental results. Finally, new insights on the role of water in the photocatalytic phenomenon were withdrawn.

Photocatalyst of Perovskite CaTiO3 Nanopowder Synthesized from CaO derived from Snail Shell in Comparison with The Use of CaO and CaCO3

Calcium titanate belongs to the important group of compounds with a perovskite structure having high dielectric loss for various applications including photocatalysis mechanism. Refer to the principles of green chemistry, in this work preparation of CaTiO3 was conducted by using CaO derived from snail shell. Aim of this research are to study the physicochemical character of perovskite derived from snail shell and its comparison with CaO and CaCO3 as Ca sources. Material preparation was performed by solid reaction of Ca sources with TiO2 under comparison with CaO and CaCO3 precursors. Mixture of Ca sources with TiO2 in certain proportion were ground and calcined at the temperature of 200 °C for 2 hs. Materials were characterized by using X-ray diffractometer (XRD), Fourier Transform-Infra Red (FTIR) and the photocatalytic activity was tested by using methylene blue photooxidation. Perovskite synthesized using CaO derived from snail shell exhibits the similar XRD pattern with that were prepared by using CaO and CaCO3. From the photooxidation activity test, it is proven that CaTiO3 shows similar photocatalytic activity correspond to that were prepared by CaO and CaCO3. Utilazation of shell as agricultural waste of the synthesis of CaTiO3 perovskite is the novelty of this work. Furthermore, the study on material structure and photoactivity is the main focuses for the application in industry and environment.

Plant Extract Mediated of ZnO Nanoparticles by Using Ethanol Extract of Mimosa Pudica Leaves and Coffee Powder

The objective of the present work is to develop a procedure for obtaining ZnO nanoparticle via complex formation with plant extracts. Mimosa pudica leaves and coffee powder were utilized as template for synthesis of ZnO nanoparticle.. After the complex formation, calcination of the complexes at the temperature related to thermal transformation was conducted. DTA-TGA, XRD and DRUV-Vis spectrophotometric analysis were utilized to study the effect of synthesis route to the physicochemical character and methylene blue photooxidation was chosen as reaction model to evaluate the photoactivity. The results show that the materials have crystallite size of around 27. 14 Å and 46.94 Å from the utilization of Mimosa pudica and coffee powder extracts respectively. Photocatalytic activity is related to the crystallite size as well as band gap energy values.

Effect of the TiO2 Crystallite Size, TiO2 Polymorph and Test Conditions on the Photo-Oxidation Rate of Aqueous Methylene Blue

This study systematically re-examines the titania-catalysed photo-oxidation of methylene blue (MB) in aqueous solution at 20 °C, placing particular emphasis on the effects of TiO2 crystallite size, TiO2 polymorph (anatase, brookite, rutile and combinations thereof) and experimental test conditions on the rate of MB photo-oxidation. For all TiO2 samples tested, the highest rate of MB photo-oxidation was observed at pH 6, slightly above the isoelectric point of TiO2 (~5.8 for P25 TiO2). Increasing the ionic strength at pH 6 induced MB dimer formation in solution, and lowered the rate of MB photo-oxidation by TiO2. For all TiO2 polymorphs, the surface area normalised rate increased with crystallite size reflecting the corresponding reduction in surface and bulk defects (electron–hole pair recombination sites). The optimum crystallite sizes were ~20–25 nm for anatase and ~50 nm for brookite. The photocatalytic activity of the different TiO2 powders followed the general order P25 > anatase > brookite ≫ rutile, with the high activity of P25 TiO2 providing strong evidence that anatase–rutile heterojunctions act as “hotspots” for MB photo-oxidation. Mixed phase anatase–rutile or brookite–rutile powders, each containing ~5 wt% rutile, demonstrated superior area normalized photocatalytic activities for MB photo-oxidation compared to pure phase anatase or brookite powders of comparable crystallite size. Finally, deposition of Pd, Pt or Au nanoparticles decreased the activity of P25 TiO2 for MB photo-oxidation. This paper clarifies long-standing confusion in the scientific literature about the photo-oxidation of aqueous MB over TiO2 and M/TiO2 (M = Pd, Pt and Au) photocatalysts.

Tailoring preparation, structure and photocatalytic activity of layer-by-layer films for degradation of different target molecules

Photocatalytic thin films composed of titanium dioxide and poly(styrene sulfonate) with hierarchical porosity and high transparency were prepared by the layer-by-layer self-assembly method. The influence of preparation conditions on the structure and photocatalytic activity of the films was investigated. It was found there is no need to reach adsorption equilibrium during layer deposition. Using very short deposition times, films with better transparency and higher activity for methylene blue photo-oxidation were obtained. Diffusion limitations due to strong adsorption of dye molecules and ammonia to the polyelectrolyte were revealed. These results indicate that films could be devised to selectively degrade specific target molecules in a mixture. The films were deposited on a three-dimensional carbon substrate and successfully demonstrated in a photoelectrochemical water splitting experiment.

Elucidation of the Binding Properties of A Photosensitizer to Salmon Sperm DNA and Its Photobleaching Processes by Spectroscopic Methods

Methylene blue (MB) is a tricyclic heteroaromatic photosensitizer with a promising application in the photodynamic therapy (PDT) for anticancer treatment. The binding properties of MB to salmon sperm DNA have been investigated by the measurements of absorption spectra, quenching experiments and the photobleaching processes. Remarkable hypochromic and bathochromic effects of MB in the presence of increasing amounts of DNA have been observed in the absorption spectra. The quenching of MB by the DNA bases obeys the Stern-Volmer equation and ferrocyanide quenching of MB in the absence and presence of DNA is also measured as extended experiments. Results from the above spectral measurements are all consistent with the intercalative binding mode of MB to DNA with the K b value of 5.6 × 10(3) M(-1). The photobleaching processes of MB and its DNA complex have also been studied, which indicate that the photobleaching of MB and its DNA complex proceed with different mechanisms and the reactive oxygen species are responsible for the self-sensitized photooxidation of MB.

Synthesis and characterization of activated carbon-coated SiO2/TiO2−xCx nanoporous composites with high adsorption capability and visible light photocatalytic activity

High thermal stability C-doped SiO2/TiO2 coated with activated carbon (AC) nanoporous composites that exhibit high absorption capability and efficient visible light photocatalytic activity were synthesized. The silica particles serve as the cores, glycerol used as the carbon source and pore-forming promoter, and TiCl4 used as the source of TiO2. The structure, crystallinity, morphology and other physical–chemical properties of the samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform-infrared spectroscopy (FT–IR), N2 adsorption–desorption isotherms and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). Composition of the composites was also analyzed by energy dispersive x-ray spectra (EDX). The formation mechanism of the nanoporous composites was extensively discussed. Methylene blue (MB) solution was used as a pollution model to evaluate the adsorption capability and photocatalytic activity of the samples under visible light. The as-synthesized nanoporous composites exhibit both much higher absorption capability and better photocatalytic activity for the photooxidation of MB than pure titania. The higher absorption capability and better photocatalytic activity of as-synthesized nanoporous composites are attributed to their high surface area, well conductivity and higher visible light absorption intensity.