Methylene Blue Degradation Kinetics Research Articles

Statistical Design Approach for an Effective Catalyst in the Fenton Reaction in Case of Fe3O4-MOF MIL-88b (Fe) in Methylene Blue Degradation Kinetics

In this paper composites containing metal-organic framework MIL88b(Fe), nanoparticles magnetite (Fe3O4) or maghemite (γ-Fe2O3) modified by humic acids or ascorbic acid were synthesized and tested in the decomposition reaction of methylene blue. Analysis of predictive model based on multi-factor correlation analysis «physical-chemical properties — concentration of methylene blue after degradation» showed that in a line of selected parameters (initial iron concentration in sample, elemental cell parameter, Fe2+/Fe3+ ion ratio on sample surface, total iron ion released concentration, surface area specific, surface charge), a significant factor influencing Fenton reaction kinetics, is only the total concentration of the released iron ions (p-value = 0.0162). The influence of separate Fe2+ and Fe3+ ions and reaction time on the Fenton reaction kinetics was evaluated by multi-factor analysis. The results demonstrated that concentrations of released iron ions are statistically significant, with a square of the concentration of ions Fe2+ and the result of the reaction time to the concentration of ions Fe3+. A comparison of the sign and the coefficient values shows that an increase in ion concentration results in a reduction in methylene blue concentration, thereby accelerating the Fenton reaction rate, with Fe2+ ion concentration affecting more than Fe3+. The resulting model is proposed as a means of selecting a sample with the maximum Fenton reaction rate at a given point in time.

Photocatalytic Degradation of Methylene Blue Dye Using Cuprous Oxide/ Graphene Nanocomposite

Aims: The aim of this study is to evaluate the photocatalytic degradation of methylene blue dye on cuprous oxide/graphene nanocomposite. Background: Cuprous oxide (Cu2O) nanoparticles are among the metal oxides that demonstrated photocatalytic activity. However, the stability of Cu2O nanoparticles due to the fast recombination rate of electron/hole pairs remains a significant challenge in their photocatalytic applications. This in turn, leads to mismatching of the effective bandgap separation, tending to reduce the photocatalytic activity of the desired organic waste (MB). To overcome these limitations, graphene has been added to make nanocomposites with cuprous oxides. Objective: In this study, Cu2O/graphene nanocomposite was synthesized and evaluated for its photocatalytic performance of Methylene Blue (MB) dye degradation. Method: Cu2O/graphene nanocomposites were synthesized from graphite powder and copper nitrate using facile sol-gel method. Batch experiments have been conducted to assess the applications of the nanocomposites for MB degradation. Parameters such as contact time, catalyst dosage, and pH of the solution were optimized for maximum MB degradation. The prepared nanocomposites were characterized by using UV-Vis, FTIR, XRD, and SEM. The photocatalytic performance of Cu2O/graphene nanocomposites was compared against Cu2O nanoparticles for cationic MB dye degradation. Results: Cu2O/graphene nanocomposite exhibits higher photocatalytic activity for MB degradation (with a degradation efficiency of 94%) than pure Cu2O nanoparticle (67%). This has been accomplished after 180 min of irradiation under visible light. The kinetics of MB degradation by Cu2O/graphene composites can be demonstrated by the second-order kinetic model. The synthesized nanocomposite can be used for more than three cycles of phtocatalytic MB degradation. Conclusion: This work indicated new insights into Cu2O/graphene nanocomposite as highperformance in photocatalysis to degrade MB, playing a great role in environmental protection in relation to MB dye.

Synthesis of AgInS2-ZnS quantum dot/TiO2 nanocomposites as efficient photocatalysts for methylene blue degradation

Photocatalytic degradation has been demonstrated to be an efficient and eco-friendly method for the removal of dye pollutants. Herein, we report the synergetic effect of glutathione (GSH)-capped AgInS2-ZnS (AIS-ZnS) core–shell quantum dots (QDs) and titanium dioxide (TiO2) as a novel nanocomposite for the efficient photocatalytic treatment of methylene blue (MB). The AIS-ZnS core–shell QDs and the corresponding QD/TiO2 nanocomposites were synthesized directly in an aqueous medium followed by annealing. The optical properties of the AIS-ZnS core–shell QDs showed strong yellow photoluminescence, which decreased gradually with the addition of TiO2. Fourier transform infrared (FTIR) spectroscopy confirmed the GSH capping on the QDs and nanocomposites. X-ray diffraction and transmission electron microscopy revealed the nanocrystalline nature and shape of the as-synthesized materials and showed the integration of the QDs (3.9 nm) on the TiO2 particles after annealing. These materials were then investigated as a photocatalyst for MB degradation using visible light irradiation. The effect of TiO2 content in the catalyst, calcination, photoirradiation period, catalyst dose, and initial MB concentration on photodegradation of MB was studied. The results indicated that the AIS-ZnS QD/TiO2 nanocomposite exhibited better photodegradation performance compared to AIS-ZnS QDs and TiO2. The increasing TiO2 concentration in the nanocomposite also enhanced MB degradation efficiency (up to 99%). The kinetics of MB degradation follows a pseudo-first-order process. The prepared AIS-ZnS QD/TiO2 nanocomposite would serve as an effective and eco-friendly photocatalyst for MB degradation.

High Performance Carbon Material Prepared from Phalsa Using Mild Pyrolytic Process towards Photodegradation of Methylene Blue under the Irradiation of UV Light

In this study, we have used a mild pyrolytic process for the synthesis of luminescent carbon material from phalsa (Grewia asiatica Linn) and utilized it for the photodegradation of methylene blue (MB) in aqueous solution under the irradiation of ultraviolet (UV) light. The carbon material was found to be graphitic in nature and with carbon dot-like properties as demonstrated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DLS), and UV-visible techniques. The prepared carbon material was further studied for the elucidation of functional groups through Fourier transform infra-red (FTIR) spectroscopy. The carbon material exhibits the nanostructured phase which makes it a high surface area material for useful surface reactions. Different photodegradation aspects were investigated, such as initial dye concentration, catalyst dose, effect of pH of dye solution, reusability, electrochemical active surface area (ECSA), and charge transfer and scavenger. Optimum conditions of 15 mg carbon material, initial dye concentration of 2.3 × 10−5 M solution, and pH 5 of dye solution gave the highest outperformance degradation efficiency. The degradation mechanism of MB in aqueous solution was dominated by the hydroxyl radicals as verified by the scavenger study. The reaction kinetics of MB degradation was followed by the pseudo first order kinetics and highest values of rate constants in the low initial dye concentration and the acidic pH of the MB solution. Significantly, the carbon material prepared from phalsa was found to be highly stable, as proven by the reusability experiments. Furthermore, the high ECSA and low charge transfer resistance of carbon material enabled it to have better performance. The use of mild pyrolytic process for the preparation of high performance luminescent carbon material from the biomass could be a great roadmap for the synthesis of a new generation of carbon materials for a wide range of applications including bio-imaging, catalysis, energy conversion and environmental applications.

ZnO Nanostructures Doped with Various Chloride Ion Concentrations for Efficient Photocatalytic Degradation of Methylene Blue in Alkaline and Acidic Media.

In this study, chloride (Cl−) ions were successfully doped into ZnO nanostructures by the solvothermal method. The effect of various Cl− concentrations on the photocatalytic activity of ZnO towards the photodegradation of methylene blue (MB) under the illumination of ultraviolet light was studied. The as-prepared Cl−-doped ZnO nanostructures were analyzed in terms of morphology, structure, composition and optical properties. XRD data revealed an average crystallite size of 23 nm, and the XRD patterns were assigned to the wurtzite structure of ZnO even after doping with Cl−. Importantly, the optical band gap of various Cl ion-doped ZnO nanostructures was successively reduced from 3.42 to 3.16 eV. The photodegradation efficiency of various Cl− ion-doped ZnO nanostructures was studied for MB in aqueous solution, and the relative performance of each Cl ion-doped ZnO sample was as follows: 20% Cl−-doped ZnO > 15% Cl−-doped ZnO > 10% Cl−-doped ZnO > 5% Cl−-doped ZnO > pristine ZnO. Furthermore, the correlation of the pH of the MB solution and each Cl ion dopant concentration was also investigated. The combined results of varying dopant levels and the effect of the pH of the MB solution on the photodegradation process verified the crucial role of Cl− ions in activating the degradation kinetics of MB. Therefore, these newly developed photocatalysts could be considered as alternative materials for practical applications such as wastewater treatment.

Synthesis and characterizations of Ce2Zr2O7–TiO2 for increased photocatalytic activity toward degradation of methylene blue

Herein, novel Ce2Zr2O7–TiO2 was synthesized by the green method using Annona Squamosa L. peels extract (ASE). ASE contains alkaloids as hydrolyzing and capping agents for the formation of Ce2Zr2O7–TiO2. Various characterizations were conducted to elucidate the vibrational, optical, structural, morphological, elemental composition and photocatalytic properties of Ce2Zr2O7–TiO2. The photocatalytic activity of TiO2, Ce2Zr2O7, and Ce2Zr2O7–TiO2 was evaluated for methylene blue degradation under irradiated visible light. The degradation percentage using Ce2Zr2O7–TiO2 was higher than that of both TiO2 and Ce2Zr2O7. TiO2 modification with Ce2Zr2O7 increased the photocatalytic activity due to the increased light absorption in the visible region and a low electron-hole recombination rate. The reaction kinetics of methylene blue degradation over Ce2Zr2O7–TiO2 was found to be a pseudo-first-order rate with kapp value of = 1.1 × 10−2 min−1, which was around 4-fold higher than that of TiO2. Importantly, this research suggests the preparation of a novel TiO2-based photocatalyst with good photoresponse in the visible region for potential water treatment application.

Modification of sludge biochar by MnO2 to degrade methylene blue: Synergistic catalysis and degradation mechanisms

In this study, sludge biochar (SBC) was prepared by pyrolysis method, MnO2 and MnO2@SBCs with different MnO2/SBC mass ratios (3%, 5%, 10% and 20%) were synthesized by co-precipitation method. The catalytic performance was examined by activating peroxymonosulfate (PMS) for methylene blue (MB) degradation. MB can be completely removed within 30 min when the mass ratio of MnO2/SBC is greater than 5% and the degradation kinetics of MB is more in line with the pseudo-first-order kinetic model in the MnO2@SBC/PMS system. Besides, the pseudo-first-order kinetic constants (k) in MnO2@SBC/PMS are significantly higher than that in SBC/PMS and MnO2/PMS, and the largest degradation rate of MB is in 5% MnO2@SBC/PMS system. MnO2@SBC exhibited excellent PMS activation ability in a wide range of pH (5–9) with complete degradation of MB in 30 min. Furthermore, MnO2@SBC has good stability after five usages still activating PMS for complete degradation of MB in 180 min. The quenching experiments and EPR spectrum indicated that both SO4−, OH and 1O2 were the main reactive oxygen species. Finally, the probable MB degradation pathway was proposed in the MnO2/PMS system. This study provides a reliable insight into sludge resource utilization, sludge biochar modification and its catalytic performance improvement.

Integrating Photocatalysis and Microfiltration for Methylene Blue Degradation: Kinetics and Cost Estimation

AbstractMethylene blue degradation by the UV/TiO2 and UV/TiO2/H2O2 photocatalysis in a suspended photocatalytic reactor coupled with a microfiltration (MF) module is described. The kinetics of methylene blue degradation, cake layer formation on the membrane surface, and the energy consumption of the system are evaluated and discussed. In addition, cost estimation of the treatment of methylene blue by different processes is implemented. The investment and operating costs of the photocatalytic membrane reactors are calculated and compared with the UV systems and UV/TiO2‐MF.

Degradation of aqueous organic dye pollutants by heterogeneous photo-assisted Fenton-like process using natural mineral activator: Parameter optimization and degradation kinetics

Degradation of organic pollutants by heterogeneous Fenton-based advanced oxidation processes has been proved to be an efficient method. The use of naturally occurring catalysts as H2O2 activators is of particular interest in environmental remediation. This work applied a low-cost and eco-friendly natural mineral under UV-light irradiation to degrade organic dye in water. To study the performance of the natural mineral in photo-Fenton oxidation, methylene blue (MB) was employed as a model dye pollutant. The morphology and chemical composition of the natural mineral were characterized using various techniques. The effects of different experimental conditions such as the initial pH of the solution, the amount of catalyst, and initial dye concentrations on the degradation efficiency were investigated. The degradation of methylene blue reached 91.3% at optimum reaction conditions; 0.1g catalyst and 100 mg L‒1 H2O2 concentrations for 10 mg L‒1 initial dye concentration after 180 min of treatment. The pseudo-first-order kinetic model exhibited a better correlation coefficient (R2 > 0.98) in explaining the degradation kinetics of MB. The applied natural mineral showed good catalytic activity and will open a door towards large-scale wastewater purification from dyes. Furthermore, the plausible mechanism of the heterogeneous photo-Fenton oxidation is discussed.

Titanium Dioxide/Polyvinyl Alcohol/Cork Nanocomposite: A Floating Photocatalyst for the Degradation of Methylene Blue under Irradiation of a Visible Light Source.

Photocatalytic degradation by the titanium dioxide (TiO2) photocatalyst attracts tremendous interest due to its promising strategy to eliminate pollutants from wastewater. The floating photocatalysts are explored as potential candidates for practical wastewater treatment applications that could overcome the drawbacks posed by the suspended TiO2 photocatalysis system. The problem occurs when the powdered TiO2 applied directly into the treated solution will form a slurry, making its reuse become a difficult step after treatment. In this study, the immobilization of titanium dioxide nanoparticles (TiO2 NPs) on the floating substrate (cork) employing polyvinyl alcohol (PVA) as a binder to anchor TiO2 NPs on the surface of the cork was carried out. Characterizations such as Fourier transformer infrared, X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV–vis), zeta potential, photoluminescence spectroscopy, femtosecond to millisecond time-resolved visible to mid-IR absorption spectroscopy, ion chromatography, and scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDX) analyses were employed. XRD analysis revealed the formation of anatase-phase TiO2 NPs. The results demonstrated that the crystallite size was 9.36 nm. The band gap energy of TiO2 NPs was determined as 3.0 eV. PL analysis verified that TiO2 NPs possessed a slower recombination rate of electron–hole pairs as compared to anatase TiO2. The result was attributed by the behavior of photogenerated charge carriers on TiO2 NPs, which existed as shallowly trapped electrons that could survive longer than a few milliseconds in this study. Furthermore, SEM–EDX analysis indicated that TiO2 NPs were well distributed on the surface of the cork. At the optimal mole ratio of TiO2/PVA (1:8), the TiO2/PVA/cork floating photocatalyst degraded at 98.43% of methylene blue (MB) under a visible light source which performed better than under sunlight irradiation (77.09% of MB removal) for 120 min. Besides, the mineralization result has measured the presence of sulfate anions after photocatalytic activities, which achieved 86.13% (under a visible light source) and 65.34% (under sunlight). The superior photodegradation performance for MB was mainly controlled by the reactive oxygen species of the superoxide radical (•O2–). The degradation kinetics of MB followed the first-order kinetics. Meanwhile, the Langmuir isotherm model was fitted for the adsorption isotherm. The floating photocatalyst presented good reusability, resulting in 78.13% of MB removal efficiency even after five cycles. Our TiO2/PVA/cork floating photocatalyst fabrication and high photocatalytic performance are potentially used in wastewater treatment, especially under visible light irradiation.

Application of Silver-Loaded Composite Track-Etched Membranes for Photocatalytic Decomposition of Methylene Blue under Visible Light.

In this study, the use of composite track-etched membranes (TeMs) based on polyethylene terephthalate (PET) and electrolessly deposited silver microtubes (MTs) for the decomposition of toxic phenothiazine cationic dye, methylene blue (MB), under visible light was investigated. The structure and composition of the composite membranes were elucidated by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction technique. Under visible light irradiation, composite membrane with embedded silver MTs (Ag/PET) displayed high photocatalytic efficiency. The effects of various parameters such as initial dye concentration, temperature, and sample exposure time on the photocatalytic degradation process were studied. The decomposition reaction of MB was found to follow the Langmuir–Hinshelwood mechanism and a pseudo-first-order kinetic model. The degradation kinetics of MB accelerated with increasing temperature and activation energy, Ea, was calculated to be 20.6 kJ/mol. The reusability of the catalyst was also investigated for 11 consecutive runs without any activation and regeneration procedures. The Ag/PET composite performed at high degradation efficiency of over 68% after 11 consecutive uses.

Reinforced photocatalytic reduction of SnO2 nanoparticle by La incorporation for efficient photodegradation under visible light irradiation

In this era of technology, evolving and understanding the physicochemical properties of a novel photocatalytic material to degrade organic species in polluted water is most needed all over the globe due to environmental production. This study reports the influence of lanthanum (La) in physicochemical properties of tin (II) dioxide (SnO2) nanoparticles and its application towards methylene blue (MB) degradation under sunlight. The SnO2, 2 mol% La incorporated SnO2 and 4 mol% La incorporated SnO2 (4 mol% La) nanoparticles were synthesized by simple co-precipitation method and characterized. X-ray diffraction patterns indicate higher angle shifts and peak broadening with respect to increase in La concentration. High-resolution transmission electron microscopic images (HR-TEM) reveal that SnO2 particle size decreases with respect to increase in La concentration. Morphological analysis shows that addition of La changes SnO2 morphology from agglomeration to segregated porous nature. Energy dispersive spectrum confirms the presence of parent and dopant elements in La incorporated SnO2 nanoparticles. UV–Visible spectrum indicates the increase in the band gap of La incorporated SnO2 due to the quantum size effect. The surface disorder, reduction in particle size and phonon confinement are identified from the Raman spectral analysis. Moreover, electrochemical analysis demonstrates the possible electrochemical activity of the materials as well as confirms that La provides higher charge transfer kinetics and stability to SnO2 nanoparticle. In addition, the calculated CBM potential confirms that La increases the redox potential of SnO2 nanoparticle, which is an ample condition to reduce O2 as ·O2−. The fast MB degradation kinetics achieved by 4 mol% La-SnO2 nanoparticle, which degrades 99% of MB within 60 min under sunlight irradiation and exhibits more than 90% photodegradation efficiency up to ten recycle. A through study of possible photocatalytic mechanism for the photocatalytic degradation is discussed.

One‐Step Hydrothermal Synthesis of ZnS Quantum Dots‐Reduced Graphene Oxide Composites with Enhanced Photocatalytic Activity

Zinc sulfur quantum dots‐reduced graphene oxide (ZnS QDs‐rGO) composites are successfully synthesized by a one‐step hydrothermal method. The ZnS QDs are well scattered on the surface of the wrinkled rGO with smaller particle size compared with initial ZnS QDs. The influence of the content of rGO in composites on the photocatalytic effect is also investigated in detail. The ZnS QDs‐1.0% rGO has the highest photocatalytic activity and the degradation kinetics of methylene blue is more consistent with the zero order kinetic model than the pseudo first order kinetic model in this experiment. The mechanism for the enhancement of photocatalytic activity is mainly due to promoting separation of the photogenerated carriers with the introduction of rGO and the increase in specific surface area of ZnS QDs due to decrease in size. These results reveal that the effective synergistic action between ZnS QDs and rGO is the key factor to determine the photocatalytic degradation efficiency of the ZnS QDs‐rGO composites.

Superior visible light photocatalytic performance of reticular BiVO4 synthesized via a modified sol-gel method.

Reticular BiVO4 catalysts were successfully synthesized via a modified sol–gel method. Here, citric acid (CA) was used as the chelating agent and ethylenediaminetetraacetic acid (EDTA) was used as the chelating agent and template. Furthermore, the effects of pH values and EDTA on the structure and morphology of the samples were studied. We determined that EDTA and pH played important roles in the determination of the morphology of the as-prepared BiVO4 samples. Photocatalytic evaluation revealed that the reticular BiVO4 exhibited superior photocatalytic performance characteristics for the degradation of methylene blue (MB) under visible-light (λ > 400 nm) exposure, about 98% of the MB was found to degrade within 50 min. Moreover, the degradation kinetics of MB was in good agreement with pseudo-first-order kinetics. The obtained apparent reaction rate constant kapp of reticular BiVO4 was much higher than that of BiVO4 synthesized by the citric acid sol–gel method.

Novel Solar Photocatalytic Reactor for Wastewater Treatment

A new solar photocatalytic reactor (photoreactor) using TiO2 nanoparticles coated onto plastic granules has been designed. Catalyst granules are placed into the cavity of a reactor panel made of glass. A pump is used to circulate wastewater in the photoreactor. Methylene blue (MB) dissolved in water was chosen as the wastewater model. The performance of the photoreactor was evaluated based on changes in MB concentration with respect to time. The photoreactor showed a good performance by degrading 10 L of MB solution up to 96.54% after 48 h of solar irradiation. The photoreactor was scaled up by enlarging the panel area to twice its original size. The increase in the surface area of the reactor panel and therefore of the mass of catalyst granules and reactor volume led to a three-fold increase of the photodegradation rate. In addition, the MB degradation kinetics were also studied. Data analysis confirmed the applicability of the pseudo-first-order Langmuir-Hinshelwood model. The proposed photoreactor has great potential for use in large-scale wastewater treatment.

Highly enhanced photocatalytic degradation of methylene blue over the indirect all-solid-state Z-scheme g-C3N4-RGO-TiO2 nanoheterojunctions

In the present research work, the ternary indirect all-solid-state Z-scheme nanoheterojunctions, graphitic-C3N4/reduced graphene oxide/anatase TiO2 (g-C3N4-RGO-TiO2) with highly enhanced photocatalytic performance were successfully prepared via a simple liquid-precipitation strategy. The photocatalytic activities of indirect all-solid-state Z-scheme g-C3N4-RGO-TiO2 nanoheterojunctions were evaluated by the degradation of methylene blue (MB). The results showed that the introduction of RGO as an interfacial mediator into direct Z-scheme g-C3N4-TiO2 nanocomposites can remarkably enhance their photocatalytic activities. The as-obtained indirect all-solid-state Z-scheme g-C3N4-RGO-TiO2 nanoheterojunctions, with the optimal loading amount of 10wt% RGO, exhibited the highest rate towards the photocatalytic degradation of MB under simulated solar light irradiation. The degradation kinetics of MB can be described by the apparent first-order kinetics model. The highest degradation rate constant of 0.0137min−1 is about 4.7 and 3.2 times greater than those of the pure g-C3N4 (0.0029min−1) and direct Z-scheme g-C3N4-TiO2 (0.0043min−1), respectively. An indirect all-solid-state Z-scheme charge-separation mechanism was proposed based on the photoluminescence spectra and the trapping experiment procedure of the photo-generated active species. It was believed that the indirect all-solid-state Z-scheme charge separation mechanism in g-C3N4-RGO-TiO2 nanoheterojunctions could lead to the promoted charge separation and transfer, improved oxygen-reduction capacity of electrons in g-C3N4 and the formation of hydroxyl radicals driven by the holes in TiO2, respectively, thus achieving the highly enhanced photocatalytic degradation performance. This work might provide new insights and understanding on the graphene as electron mediators to design highly efficient all-solid-state Z-scheme nanoheterojunctions with enhanced visible-light driven photoactivity for various photocatalytic applications.

Synthesis of Cu-CuO nanocomposite in microreactor and its application to photocatalytic degradation

The nanocomposite of Cu-CuO is successfully prepared via controlled oxidation of Cu nanoparticles synthesized by liquid-phase reduction in a microreactor. The particle's morphology, size, and elemental compositions have been investigated. Experimental results demonstrate that copper nanoparticles are spherical in shape, with good dispersion and narrow particle size distribution. The surface of Cu nanoparticles was oxidized to CuO, and the size of Cu-CuO composites crystallites was around 10 nm, consistent with the size of copper nanoparticles. The prepared Cu-CuO nanocomposite along with the presence of H2O2 exhibits excellent photocatalytic activity for degradation of methylene blue (MB) under UV irradiation. An overall degradation of 98.5% could be achieved with 10 mg of Cu-CuO nanocomposite along with 1 mL of H2O2, within duration of 50 min irradiation. The MB degradation kinetics was observed to follow first order.

Preparation, kinetics, mechanism and properties of semi-transparent photocatalytic stable films active in dye degradation

The photocatalytic activity, mechanism and characterization of polyethylene-TiO2 films (PE-TiO2) during the discoloration/degradation of methylene blue (MB) are reported in this study. PE-TiO2 films were prepared at moderate temperatures (∼90°C). TiO2 did not leach out during discoloration/degradation of MB. This is a significant finding for a low temperature catalyst-polymer preparation leading to a stable repetitive MB degradation kinetics. MB discoloration on PE-TiO2 films proceeded showing a quantum yield of 0.25%. Band-gap irradiation of TiO2 was applied by way of a mercury medium pressure lamp to excite only TiO2 and avoid MB photosensitization. The nature of the oxidative radicals intervening in MB discoloration was investigated by scavenging experiments. The relative importance of the oxidative species during MB discoloration is: TiO2vbh+>HO2/O2−>1O2>OH. Evidence is presented for the superoxide anion-radical O2− at pH 6, as the main radical species leading to MB-discoloration. The MB- discoloration kinetic trend on PE-TiO2 followed the behavior observed for diffusion-controlled reactions. The diffusion distance of the HO2 and OH radicals during the discoloration of a solution MB 1×10−5molL−1 were estimated as 71 and 2.2μm respectively. The OH formation was assessed quantitatively during MB degradation by fluorescence measurements. The PE-TiO2 film at time zero presented a contact angle (CA) of ∼92°, decreasing within the five hour MB discoloration period to <5°. Reversibility from the hydrophilic nature of the film to the initial hydrophobic state proceeded in the dark within few days. The implications of the reversibility time on the MB-discoloration performance are discussed. Evidence for redox catalysis during MB-discoloration was found by XPS measurements. The surface properties of the (PE-TiO2) films were characterized by X-ray fluorescence (XRF), UV–vis spectroscopy, X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass-spectrometry (ICP-MS).

Accelerated methylene blue (MB) degradation by Fenton reagent exposed to UV or VUV/UV light in an innovative micro photo-reactor

This study presents the accelerated discoloration/degradation of methylene blue (MB) in solution by Fenton reagent under exposure to ultraviolet (UV) or Vacuum-UV/UV (VUV/UV) light in an innovative micro photo-reactor. The MB degradation was kinetically faster when using VUV/UV light at 254/185nm compared to UV-irradiation at 254nm. Oxidative radicals produced by the photo-Fenton process were identified with appropriate scavengers. The addition of benzoquinone (BQ) at millimolar (mM) concentrations to MB solutions precluded completely the MB photo-induced bleaching, while tert-butanol hindered to a lesser extent the MB degradation suggesting that HO2 was the predominant intermediate leading to MB degradation. The VUV/UV micro photo-reactor comprised mercury resonance lines at 185 and 254nm. The photon percentages absorbed by water were estimated to be 16.8% at 254nm and 78.3% at 185nm by water, while those absorbed by H2O2 were 0.9% and 2.2%, correspondingly. The solution parameters affecting the features of MB degradation, such as MB, Fe, and H2O2 concentrations, were explored and reaction mechanism was proposed. The lifetimes of OH and HO2 were estimated to be 2ns and 0.38s under an optimized solution with 0.016mM MB, 0.147mM H2O2 and 0.05mM Fe3+. Moreover, an estimation of the mean free paths of these radicals in solution provided the evidence that it was the radical lifetimes and mean-free paths, not their oxidation potentials that controlled the MB degradation kinetics. This study shows the potential of this VUV/UV assistant photo-Fenton process for the degradation of diluted organic compounds in aqueous solution.

Enhanced photocatalytic degradation and adsorption of methylene blue via TiO2 nanocrystals supported on graphene-like bamboo charcoal

In this study, a novel efficient photocatalytic nanomaterial, TiO2 nanocrystals supported on graphene-like bamboo charcoal, has been successfully synthesized via a facile multi-step process. The structural and optical properties of the as-prepared samples were characterized by different techniques, such as X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis absorption spectroscopy, photoluminescence spectra (PL), Raman spectra and nitrogen adsorption–desorption isotherms. The photocatalytic activities under sunlight were evaluated by the degradation of methylene blue (MB). The results indicated that the ternary hybrid photocatalysts exhibited much higher photocatalytic activities toward the degradation of MB than the pure TiO2 under UV light irradiation. Moreover, the optimum weight content of graphene-like bamboo charcoal in composite photocatalysts was 6wt% for achieving the maximum photocatalytic degradation rate. The apparent rate constant of the best sample (0.0509min−1) was about 3 times greater than that of the commercial P25 (0.0170min−1). The adsorption and degradation kinetics of MB can be described by the pseudo-first-order model and apparent first-order kinetics model, respectively. The highly enhanced photocatalytic performance was attributed to the synergetic effect of graphene-like carbon and bamboo charcoal, which lead to the promoted charge separation and reduction reaction of oxygen, and enhanced adsorption capacities of MB, respectively. The composite photocatalysts displayed a high photochemical stability under repeated irradiation. This work may provide new insights and understanding on the graphene-like bamboo charcoal as an excellent support for photocatalyst nanoparticles to enhance their visible-light photocatalytic activity.