Photocatalytic degradation of methylene blue over MIL-100(Fe)/GO composites: a performance and kinetic study

Adsorption coupled with photocatalytic degradation is proposed to fulfill the removal and thorough elimination of organic dyes.Herein,we report a facile hydrothermal synthesis of MIL-100(Fe)/GO photocatalysts.The adsorption and photocatalytic degradation process of methylene blue(MB)on MIL‐100(Fe)/GO composites were systematically studied from performance and kinetic perspectives.A possible adsorption‐photocatalytic degradation mechanism is proposed.The optimized 1M8G composite achieves 95%MB removal(60.8 mg/g)in 210 min and displays well recyclability over ten cycles.The obtained MB adsorption and degradation results are well fitted onto Langmuir isotherm and pseudo‐second order kinetic model.This study shed light on the design of MOFs based composites for water treatment.

TiO_2/polyaniline composites:An efficient photocatalyst for the degradation of methylene blue under natural light

Polyaniline （PAn） sensitized nanocrystalline TiO2 composites （TiO2/PAn） were successfully prepared and used as an efficient photocatalyst for the degradation of dye methylene blue （MB）. The results showed that PAn was able to sensitize TiO2 efficiently and the composite photocatalyst could be activated by absorbing both the ultraviolet and visible light （λ： 190 ～ 800 nm）, whereas pure TiO2 absorbed ultraviolet light only （λ 〈 380 nm）. Under the irradiation of natural light, MB could be degraded more efficiently on the TiO2/PAn composites than on the TiO2 Furthermore, it could be easily separated from the solution by simple sedimentation.

Kinetics of Photocatalytic Degradation of Methylene Blue Over CaTiO_3

Kinetics of photocatalytic degradation of methylene blue(MB) over Ca Ti O3 was studied. Effects of the solution p H, the MB concentration, the Ca Ti O3 dosage, and the type of light source on photocatalytic degradation rate of MB over Ca Ti O3 were investigated in detail. The results show that photocatalytic degradation of MB over Ca Ti O3 followed the first-order reaction. The apparent rate constant(kobs) of MB significantly increased with increasing solution p H while it greatly decreased with increasing MB concentration. The kobs of MB increased with increasing Ca Ti O3 dosage from 0.05 to 0.1 g, whereas it slightly decreased with increasing Ca Ti O3 dosage in the range of 0.1-0.4 g. The kobs of MB under UV-visible light irradiation was larger by factors of 2.2 than that under visible light irradiation. The kobs of MB was(4.8±0.3)×10-1h-1 under optimal conditions with the solution p H of 11, the MB concentration of 1 ppm, the Ca Ti O3 dosage of 0.1 g, and UV-visible light irradiation.

Photocatalytic degradation of methylene blue by nanostructured Fe/FeS powder under visible light

The photocatalytic performance of mechano-thermally synthesized Fe/FeS nanostructures formed from micron-sized starting materials was compared with that of a thermally synthesized nanostructure with nano-sized precursors in this paper. The properties of as-synthesized materials were studied by X-ray diffraction（XRD）, transmission electron microscopy（TEM）, vibrating sample magnetometry（VSM）, diffuse reflectance spectroscopy（DRS）, and ultraviolet–visible（UV-Vis） spectroscopy. The effects of irradiation time, methylene blue（MB） concentration, catalyst dosage, and p H value upon the degradation of MB were studied. Magnetic properties of the samples showed that both as-synthesized Fe/FeS photocatalysts are magnetically recoverable, eliminating the need for conventional filtration steps. Degradation of 5 ppm of the MB solution by mechano-thermally synthesized Fe/FeS with a photocatalyst dosage of 1 kg/m^3 at pH 11 can reach 96% after 12 ks irradiation under visible light. The photocatalytic efficiency is higher in alkaline solution. The kinetics of photocatalytic degradation in both samples is controlled by a first-order reaction. However, the rate-constant value in the thermally synthesized Fe/FeS photocatalyst sample is only 1.5 times greater than that of the mechano-thermally synthesized one.

Preparation of Bi_(2)O_(3)/BiOI Step-scheme Heterojunction Photocatalysts and Their Degradation Mechanism of Methylene Blue

Bi_(2)O_(3)/BiOI step-scheme(S-scheme) heterojunction photocatalyst was synthesized by green calcination method, its degradation ability of methylene blue was investigated, and the photocatalytic performance of the Bi_(2)O_(3)/BiOI heterojunction, Bi_(2)O_(3) and BiOI was compared. The structure and morphology of the samples were characterized by X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM), and UV-vis diffuse reflection spectrum (UV-vis DRS). The degradation rate of methylene blue was analysised by spectrophotometry, and the calculation result showed that the degradation rate of methylene blue was 97.8% in 150 minutes. The first order kinetic rate constant of 10%Bi_(2)O_(3)/BiOI is 0.021 8 min^(-1), which are2.37 and 2.68 times of BiOI(0.009 18 min^(-1)) and Bi_(2)O_(3) (0.008 03 min^(-1)) respectively. The calculation result shows that the work function of Bi_(2)O_(3) and BiOI are 3.0 e V and 6.0 e V, respectively, by density functional theory(DFT). When this S-scheme heterojunction is used as a photocatalyst, the weaker electrons in the conduction band of BiOI will be combined with the weaker holes in the Bi_(2)O_(3) valence band under combined effect with built-in electric field and band bending, which will retain stronger photoelectrons and holes between Bi_(2)O_(3) and BiOI. This may be the internal reason for the efficient degradation of tetracycline by Bi_(2)O_(3)/BiOI S-scheme heterostructures.

Silicalite-1 zeolite encapsulated Fe nanocatalyst for Fenton-like degradation of methylene blue

Encapsulation of Fe nanoparticles in zeolite is a promising way to significantly improve the catalytic activity and stability of Fe-based catalysts during the degradation process of organic pollutants.Herein,Fe nanocatalysts were encapsulated into silicalite-1(S-1)zeolite by using a ligand-protected method(with dicyandiamide(DCD)as a organic ligand)under direct hydrothermal synthesis condition.High-resolution transmission electron microscopy(HRTEM)results confirmed the high dispersion of Fe nanocatalysts which were successfully encapsulated within the voids among the primary particles of the S-1 zeolite.The developed S-1 zeolite encapsulated Fe nanocatalyst(Fe@S-1)exhibited significantly improved catalytic activity and reusability in the catalytic degradation process of methylene blue(MB).Specifically,the developed Fe0.021@S-1 catalyst showed high catalytic degradation activity,giving a high MB degradation efficiency of 100%in 30 min,outperformed the conventional impregnated catalyst(Fe/S-1).Moreover,the Fe@S-1 catalyst afforded an outstanding stability,showing only ca.7.9%activity loss after five cycling tests,while the Fe/S-1 catalyst presented a significantly activity loss of 50.9%after only three cycles.Notably,the encapsulation strategy enabled a relatively lower Fe loading in the Fe@S-1 catalyst in comparison with that of the Fe/S-1 catalyst,i.e.,0.35%vs.0.81%(mass).Radical scavenging experiments along with electron spin resonance(ESR)measurements confirmed that the major role of
OH in the MB degradation process.Specifically,Fe@S-1 catalyst with high molar ratio of[Fe(DCD)]Cl3 is beneficial to form Fe complexes/nanoclusters in the voids(which has large pore size of 1–2 nm)among the primary particles of the zeolite,and thus improving the diffusion and accessibility of reactants to Fe active sites,and thus exhibiting a relatively higher degradation efficiency.This work demonstrates that zeolite-encapsulated Fe nanocatalysts present potential applications in the advanced oxidation of wastewater treatment.

Investigation of photoelectrocatalytic degradation mechanism of methylene blue by a-Fe_(2)O_(3) nanorods array

Efficiently and thoroughly degrading organic dyes in wastewater is of great importance and challenge.Herein,vertically oriented mesoporous a-Fe_(2)O_(3)nanorods array(a-Fe_(2)O_(3)-NA)is directly grown on fluorine-doped tin oxide(FTO)glass and employed as the photoanode for photoelectrocatalytic degradation of methylene blue simulated dye wastewater.The Ovsites on the a-Fe_(2)O_(3)-NA surface are the active sites for methylene blue(MB)adsorption.Electrons transfer from the adsorbed MB to Fe-O is detected.Compared with electrocatalytic and photocatalytic degradation processes,the photoelectrocatalytic(PEC)process exhibited the best degrading performance and the largest kinetic constant.Hydroxyl,superoxide free radicals,and photo-generated holes play a jointly leading role in the PEC degradation.A possible degrading pathway is suggested by liquid chromatography-mass spectroscopy analysis.This work demonstrates that photoelectrocatalysis by a-Fe_(2)O_(3)-NA has a remarkable superiority over photocatalysis and electrocatalysis in MB degradation.The in-depth investigation of photoelectrocatalytic degradation mechanism in this study is meaningful for organic wastewater treatment.

Effects of Magnetic Field on Photodegradation of Methylene Blue over ZnO and TiO2 Powders using UV-LED as a Light Source

The magnetic field effects （MFEs） are studied on photocatalytic degradation of methylene blue （MB） solution using ZnO and TiO2 particles. The UV-VIS-NIR spectrometer is used to monitor the MB concentrations, and the dependence of the reaction rate on the initial dye concentration and settling duration is studied under UV light irradiation. It is found that the MFEs exist on the heterogeneous reaction systems for both ZnO and TiO2 powders and that the extraordinary phenomenon is reproducible. For ZnO powder, the results are in good agreement with the second-order reaction kinetics following the Langmuir-Hinshelwood （L-H） model, while the reaction for TiO2 follows first-order kinetics. It enhances the photodegradation for ZnO, while it reduces or enhances the reaction for TiO2 depending on the initial dye concentrations. The MFEs become small or negligible when the same photodecomposition experiment is carried out after settling the MB solution for more than three hours for both ZnO and TiO2. It is suggested that the key factors of MFEs on photocatalytic degradation is the condition of the MB solution as well as the characteristics of photocatalysts. The alteration of the MFEs ascribed to the solution condition caused by variation of the settling time.

Characterization and photocatalytic activity for methylene blue degradation of iron-deposited TiO_2 photocatalyst

Iron deposited TiO 2 was prepared by photo reducing ferric ions. The photocatalytic activity of methylene blue degradation was enhanced after TiO 2 was deposited with iron, and the optimum n (Fe)/ n (Ti) is 0.25%. TiO 2 and iron deposited TiO 2 are anatase and rutile, and anatase is the dominant crystalline phase. In all samples, the XRD patterns indicate that there are no characteristic peaks of iron to be detected. XPS confirms that Fe 3+ and Fe 2+ are present on the surface of 0.5% iron deposited TiO 2, however they are not susceptible to XRD detection. The thermodynamics analysis shows that the alternative possibility of reduction from the Fe 3+ /Fe 2+ couple seems plausible, but Fe 2+ can not be reduced to Fe. The fluorescence intensity weakens after iron is deposited on TiO 2, because iron deposited traps photo generated electrons and holes. The fluorescence intensity order of TiO 2 and iron deposited TiO 2, from strong to weak, is in good agreement with that of photocatalytic reactiveness TiO 2 and iron deposited TiO 2, from low to high.

Facile Synthesis of Ag/TiO2 by Photoreduction Method and Its Degradation Activity of Methylene Blue under UV and Visible Light Irradiation

A series of Ag/TiO2 with various Ag contents were prepared by photoreduction method. Commercial TiO2 from Evonik-Degussa was used as the catalyst. Ag was used as the cocatalyst. This facial synthesis method is cheap and easy. TiO2 was suspended in water with various concentrations of silver nitrate. The solution was illuminated by UV light for 36 h. Ag would deposit on the surface of TiO2. This method can deposit all Ag cation in the starting material on TiO2 after 36 h irradiation by UV light. X-ray diffraction, high resolution-TEM, and X-ray photoelectron spectroscopy were used to characterize the surface, morphology and chemical composition of the catalysts. Photocatalytic degradation of methylene blue in water on these catalysts was carried out under UV and visible light irradiation, respectively. The methylene blue concentration in water was measured by a UV-vis spectrophotometer. The results showed that the bulk structure of TiO2 did not change and some of Ag was incorporated into the surface of TiO2 lattice. The change in the electronic state of Ti on surface is attributed to the replacement of titanium atoms by silver atoms on the TiO2 surface structure which induced visible light response and enhanced the photocatalytic activity. 1 wt% Ag is the optimum loading to have high activity.

Preparation of Carbon-coated Tourmaline and the Degradation of Methylene Blue

An attempt was made to prepare carbon coated tourmaline by mixing tourmaline powders and polyvinyl alcohol (PVA), followed by heat treatment in argon atmosphere. All samples were characterized by powder X-ray diffraction, high-resolution transmission electron microscopy, UV diffuse reflectance spectroscopy. Results showed that the residual carbon content was influenced by heat treatment temperature and the amount of PVA. The degradation of methylene blue by Carbon-coated tourmaline was also studied. The experiments pointed out that the carbon coated effects are best when the heating temperature was 900℃ and the weight content of PVA was 70%. And the tourmaline prepared under 900℃ in the oxidation atmosphere has the best degrade efficiency. The results also proved that the infrared radiation of tourmaline is not effect in the degrade progress.

Facile Synthesis of Uniform Zinc-blende ZnS Nanospheres with Excellent Photocatalytic Activity toward Methylene Blue Degradation

Uniform and well-dispersed Zn S nanospheres have been successfully synthesized via a facile chemical route. The crystal structure, morphology, surface area and photocatalytic properties of the sample were characterized by powder X-ray diffraction（XRD）, scanning electron microscopy（SEM）, Brunauer-Emmett-Teller（BET） and ultraviolet-visible（UV-vis） spectrum. The results of characterizations indicate that the products are identified as mesoporous zinc-blende ZnS nanospheres with an average diameter of 200 nm, which are comprised of nanoparticles with the crystallite size of about 3.2 nm calculated by XRD. Very importantly, photocatalytic degradation of methylene blue（MB） shows that the as-prepared Zn S nanospheres exhibit excellent photocatalytic activity with nearly 100% of MB decomposed after UV-light irradiation for 25 min. The excellent photocatalytic activity of ZnS nanospheres can be ascribed to the large specific surface area and hierarchical mesoporous structure.

Enhanced photocatalytic performance of iron oxides@HTCC fabricated from zinc extraction tailings for methylene blue degradation:Investigation of the photocatalytic mechanism

Photocatalytic processes are efficient methods to solve water contamination problems,especially considering dyeing wastewater disposal.However,high-efficiency photocatalysts are usually very expensive and have the risk of heavy metal pollution.Recently,an iron oxides@hydrothermal carbonation carbon(HTCC)heterogeneous catalyst was prepared by our group through co-hydrothermal treatment of carbohydrates and zinc extraction tailings of converter dust.Herein,the catalytic performance of the iron oxides@HTCC was verified by a nonbiodegradable dye,methylene blue(MB),and the catalytic mechanism was deduced from theoretical simulations and spectroscopic measurements.The iron oxides@HTCC showed an excellent synergy between photocatalysis and Fenton-like reactions.Under visible-light illumination,the iron oxides@HTCC could be excited to generate electrons and holes,reacting with H_(2)O_(2)to produce·OH radicals to oxidize and decompose organic pollutants.The removal efficiency of methylene blue over iron oxides@HTCC at 140 min was 2.86 times that of HTCC.The enhanced catalytic performance was attributed to the advantages of iron oxides modification:(1)promoting the excitation induced by photons;(2)improving the charge transfer.Furthermore,the iron oxides@HTCC showed high catalytic activity in a wide pH value range of 2.3-10.4,and the MB removal efficiency remained higher than 95% after the iron oxides@HTCC was recycled 4 times.The magnetically recyclable iron oxides@HTCC may provide a solution for the treatment of wastewater from the textile industry.

Comparison of Threshold Power between Methylene Blue Degradation and KI Oxidation Reaction Using Ultrasound

Ultrasound is used in various chemical reaction processes, and these reactions are influenced by ultrasonic frequency. A threshold power is required for the ultrasonic degradation reaction and oxidation reaction caused by hydroxyl radicals, and the cavitation threshold power is also influenced by frequency generally. In this study, the effects of frequency on the threshold power of methylene blue degradation and KI oxidation were investigated in the range between 22.8 kHz and 1640 kHz. The threshold power of KI oxidation reaction increased with increasing frequency. This phenomenon well agrees with previous study, and it is revealed that the generation of I-3?ion is caused by oxidation reaction of Iˉ ions with hydroxyl radicals. On the other hand, the threshold power of methylene blue degradation reaction was not affected by frequency. The ultrasonic degradation of methylene blue is considered to be caused by hydroxyl radicals, and there is a linear relationship between degradation rate constant and sonochemical efficiency value. However, it is guessed that the degradation of methylene blue is occurred inside cavitation bubble by pyrolysis at high frequency regions.

Three modes of a direct-current plasma jet operated underwater to degrade methylene blue

A direct-current air plasma jet operated underwater presents three stable modes including an intermittently-pulsed discharge, a periodically-pulsed discharge and a continuous discharge with increasing the power voltage. The three discharge modes have different appearances for the plasma plumes. Moreover, gap voltage-current characteristics indicate that the continuous discharge is in a normal glow regime. Spectral lines from reactive species（OH, N2, N2^＋, Hα,and O） have been revealed in the emission spectrum of the plasma jet operated underwater.Spectral intensities emitted from OH radical and oxygen atom increase with increasing the power voltage or the gas flow rate, indicating that reactive species are abundant. These reactive species cause the degradation of the methylene blue dye in solution. Effects of the experimental parameters such as the power voltage, the gas flow rate and the treatment time are investigated on the degradation efficiency. Results indicate that the degradation efficiency increases with increasing the power voltage, the gas flow rate or the treatment time. Compared with degradation in the intermittently-pulsed mode or the periodically-pulsed one, it is more efficient in the continuous mode, reaching 98% after 21 min treatment.

Study of the Influence of Clay in the Degradation of Methylene Blue by Photo-Fenton Process

Industrial effluents from textile, tannery or printing activities often have a significant pollutant load composed of dyes that are difficult to biodegrade. These dyes pose a threat to the environment. To overcome this problem, various processes have been developed to eliminate these dyes in wastewater before their release into nature. Conventional biological or physical processes most often prove to be ineffective and expensive. It is therefore necessary to resort to other processes such as advanced oxidation processes (POA). This work therefore focuses on the study of the influence of clay in the degradation of Methylene Blue by the photo-Fenton process which is one of the advanced oxidation processes (POA), with the source of irradiation, natural light. To do this, two clays from Côte d’Ivoire referenced AB and Aga were the subject of a physicochemical and mineralogical characterization. The results showed that Aga clay is composed of 75.43% quartz, 12.72% kaolinite, 8.75% illite and 3.12% goethite and AB clay consists of 61, 36% kaolinite, 28.6% quartz and 10.10% illite. Under natural light irradiation the optimal amounts of Fenton reagents (iron: 10 mg;H2O2: 0.1 mL) were determined. Finally, the addition of clay to the photo-Fenton process made it possible to improve the degradation of the pollutant (Methylene Blue). Indeed, the yield increased from 92% for the photo-Fenton process to 98.43% with the addition of AB clay and 98.13% for the addition of Aga clay. The results of the degradation kinetics clearly show that the degradation follows the pseudo-second order kinetics with correlation coefficients greater than 0.99.

Equilibrium,Kinetics and Thermodynamics of the Adsorption of Methylene Blue onto a Metal-Organic Frameworks Material,Copper Coordination Polymer with Dithiooxamide

The equilibrium, kinetics and thermodynamics of the adsorption of methylene blue( MB) from aqueous solution onto copper coordination polymer with dithiooxamide( H2dtoaCu),one of the metal-organic frameworks( MOFs),were investigated in a batch adsorption system as a function of initial pH, adsorbent concentration, contact time, initial dye concentration, and temperature. The Langmuir, Freundlich, and DubininRadushkevich( D-R) isotherm models were used for modeling the adsorption equilibrium. It was found that Langmuir model yielded a much better fit than the Freundlich model under different temperatures. The maximum monolayer adsorption capacities of MB were 192. 98,229. 86,and 297. 38 mg /g at 298,308,and 318 K,respectively. The calculated mean adsorption energy( 8. 26-11. 04 kJ /mol) using D-R model indicated that the adsorption process might take place by chemical adsorption mechanism.Otherwise,the kinetic studies revealed that the adsorption process could be well explained by pseudo-second-order rate kinetics and intraparticle diffusion was not the rate-limiting step.Thermodynamic studies indicated that this system was feasible,spontaneous,and endothermic process. Based on these studies,H2dtoaCu can be considered as a potential adsorbent for the removal of MB from aqueous solution.

Kinetics and Thermodynamics of Adsorption Methylene Blue onto Tea Waste/CuFe₂O₄Composite

Tea waste/CuFe2O4 (TW/C) composite was prepared by co-precipitation method. The TW and TW/C samples are characterized by FTIR, XRD, SEM and N2 physical adsorption. The results showed that specific surface area of 350 and 570 m2·g?1 for TW and TW/C, respectively. The average pore size of TW/C is ca. 100 nm. Adsorption of methylen blue onto TW/C composite has been studied. Measurements are performed at various contact time, pH and adsorbent dosage. The adsorption kinetics of methylen blue (MB) could be described by the pseudo-second order kinetic model. The adsorption isotherms are described by means of Langmuir and Freundlich isotherms. It was found that the Freundlich model fit better than the Langmuir model. The thermodynamic constants of the adsorption were calculated to predict the nature of adsorption. The values of thermodynamic parameters indicate that a spontaneous and endothermic process was occurred.

One-pot synthesis of poly vinyl alcohol(PVA) supported silver nanoparticles and its efficiency in catalytic reduction of methylene blue

Stable silver nanoparticles were synthesized using polyvinyl alcohol （PVA） as reducing and capping agent. The method of steric stabilization was adopted for the incorporation of silver nanoparticles in the polymer matrix. The successful incorporation of silver nanoparticles in a PVA matrix was confirmed by UV–Visible spectroscopy, transmission electron microscopy （TEM） and Fourier transform infrared （FT-IR） spectroscopy. The synthesized silver nanoparticles were characterized by a peak at 426 nm in the UV–Vis spectrum. TEM studies showed the formation of spherical shaped silver nanoparticles of 10-13 nm, following the reduction by UV irradiation. Catalytic properties were studied by means of UV-Visible spectroscopic analysis. The synthesized silver nanoparticles exhibited good catalytic properties in the reduction of methylene blue.

Solution Blowing of Palygorskite-Based Nanofibers for Methylene Blue Adsorption

Palygorskite(PG)adsorbent with superior adsorption property and ion-exchange ability is highly desired in the field of dye removal.However,it generates high amounts of precipitation due to the granular form,resulting in secondary pollution after adsorption.Herein,the novel high porosity PG-based nanofibers that are easy for operating and retrieving have been fabricated using effective solution blowing and subsequent calcination.The obtained highly efficient adsorption nanofibers exhibit large specific surface area about 170.50 m^(2)/g with average diameter from 243 nm to 365 nm.Based on the abovementioned nanofibrous structure and negatively charged PG,the solution blowing of PG-based nanofibers(SBPNs)showed high adsorption capacity for methylene blue(MB)(112.36 mg/g).In addition,the adsorption of SBPNs is well described by the Langmuir isotherm model.This work provides new SBPNs forming process for the fields of dye removal,which may achieve the production of PG adsorbents at the industrial level.