Fabrication of novel SnWO4/ZnO using Muntingia calabura L. leaf extract with enhanced photocatalytic methylene blue degradation under visible light irradiation

In this study, SnWO₄/ZnO heterostructure has been successfully constructed using Muntingia calabura L. leaf extract (MCE). We conducted phytochemical tests to qualitatively detect the presence of secondary metabolites such as alkaloids, saponins, flavonoids, and tannins, which play an essential role in the formation of SnWO₄/ZnO. The photocatalytic activities of pristine SnWO₄, pristine ZnO, and SnWO₄/ZnO heterostructure were evaluated for the degradation of methylene blue (MB) under visible light irradiation. To investigate the photocatalytic activity of SnWO₄/ZnO heterostructure in the visible region, the adsorption effect of SnWO₄/ZnO was also studied. SnWO₄/ZnO heterostructure shows the highest degradation percentage of 82.86% within 120 min compared to pristine SnWO₄ and ZnO, which exhibit the degradation percentage of 69.48 and 40.41%, respectively. The enhanced photocatalytic of MB degradation is attributed to the formation of SnWO₄/ZnO heterostructure as a result of the decreased optical bandgap from 3.06 to 2.68 eV due to the low recombination rate of photogenerated electron-hole pairs. SnWO₄/ZnO shows a remarkable photocatalyst for dyes degradation with remarkable stability after four consecutive cycles. Importantly, this work demonstrates a simple eco-friendly, and low-cost green synthesis method to produce SnWO₄/ZnO with excellent photocatalytic activity and stability for dyes degradation under visible light irradiation.     

Adsorption and photocatalytic decomposition of methylene blue on mesoporous metallosilicates

Mesoporous silica and mesoporous metallosilicates with Al, Ti and Fe as foreign metal species were successfully synthesized by the rapid room temperature method. Mesoporous metallosilicates with low contents of foreign metals possessed high surface area (S_a), large mesopore volume (V_mp) and highly ordered hexagonal mesoporous structure. Increases in foreign metal contents caused disordering the mesoporous structures and lowering the S_a and V_mp values. Bleaching of aqueous methylene blue (MB) by mesoporous silica and metallosilicates was investigated. Mesoporous aluminosilicate and ferrosilicate with cation-exchangeable ability showed the excellent property for the adsorption of MB of cationic dye, while mesoporous ferrosilicate and titanosilicate which absorbed UV lights catalyzed the photocatalytic decomposition of MB under UV-illumination.     

Development of niobium doped tin oxide nanostructure via hydrothermal route for photocatalytic degradation of methylene blue and antimicrobial study

In this work, we discuss the effect of niobium (Nb) doping concentrations of 2% and 4% on the physicochemical characteristics and photocatalytic properties of tin dioxide nanostructure, which were successfully developed by a basic hydrothermal route. Nb-doped SnO₂ were characterized with regards to their optical, structural and photocatalytic features. X-ray diffraction (XRD) analyses display that both pristine and doped tin dioxide had a fine crystalline structure having tetragonal structure. Scanning electron microscopy (SEM) analysis shows that materials exhibited the irregular shaped nanoparticles morphology. Optical absorption analysis using UV–visible spectroscopy revealed a redshift in the bandgap energy for Nb³⁺ doped SnO₂ nanoparticles. Methylene blue aqueous (MB) dye was degraded by 93.78% in 120 min when exposed to 4% Nb doped SnO₂ NPs under visible light. The 4% Nb doped SnO₂ shows elevated photocatalytic activity owing to their greater surface area containing greater active zones responsible for adsorption of larger dye species and good structural stability. Similarly, the 4% Nb doped SnO₂ photocatalysts maintained their excellent stability and photodegradation efficiency over 89% even after being subjected to 5th cycles. The scavenger analysis demonstrates that the superoxide (O₂) radical, a major active substance, performed a crucial role in the mineralization of the aqueous MB dye. The 4% Nb doped SnO₂ also shows remarkable antimicrobial activity. Our finding suggests that doping strategy considered as efficient method that can help to increase the photocatalytic and antimicrobial activity.     

Adsorption of methylene blue on kaolinite

Methylene blue was adsorbed on kaolin from a local deposit. The raw kaolin itself was a relatively good adsorbent. The adsorption capacity was improved by purification and by treatment with NaOH solution. Calcination of the kaolin reduced the adsorption capacity. The adsorption data could be fitted by the Freundlich and Langmuir equations. Also, the thermodynamic parameters such as ΔH⁰, ΔS⁰ and ΔG⁰ were determined.     

Green synthesis of reduced graphene oxide supported TiO2/Co3O4 nanocomposite for photocatalytic degradation of methylene blue and crystal violet

The hybrid rGO-TiO₂/Co₃O₄ nanocomposite was successfully synthesized through co-precipitation method. The structural, morphological, compositional and optical properties of the as synthesized nanocomposite were characterized by X-ray diffraction (XRD), Field Emission scanning electron microscopy (FESEM), energy dispersive X-Ray Spectroscopy (EDS), Fourier transformation infrared spectroscopy (FTIR), UV–visible spectrophotometer (UV–vis) and photoluminescence (PL). XRD, EDS and FTIR confirms the existence of rGO-TiO₂/Co₃O₄ in the prepared nanocomposite. FESEM confirms that the TiO₂/Co₃O₄ nanocomposite are adsorbed on the surface of the rGO. UV–Vis and PL spectra revealed that the absorbance and emission occurred at visible region, which greatly supports the photocatalytic dye degradation through the electron-hole separation. The percentage decolorization of methylene blue dye solution was higher with lesser time compared to crystal violet dye. This result concludes that the commercialization of rGO/TiO₂/Co₃O catalyst may useful for treating various dyes in industries.     

Synthesis and photocatalytic activity of Na+ co-doped CaTiO3:Eu3+ photocatalysts for methylene blue degradation

The Na⁺ co-doped CaTiO₃:Eu³⁺ powders were produced through the solution combustion method. The phase structure and optical properties of the synthesized samples were adequately characterized by X-ray diffraction (XRD), photoluminescence (PL) spectra, ultraviolet–visible (UV–vis) diffuse reflection spectroscopy and scanning electron microscopy (SEM). The XRD patterns revealed that a low level of Eu³⁺ doping could not cause lattice distortion of CaTiO₃. Photoluminescence (PL) displayed the CaTiO₃:0.5% Eu³⁺ sample synthesized at 900 °C has the weakest PL emission and the low electrons and holes recombination rate. The morphology of the sample was small nanoscale spherical particles. The UV–vis diffuse reflection spectra proved that doping Na⁺ and Eu³⁺ enlarged the absorption region and reduced band energy of pure CaTiO₃. The photocatalytic properties of Na⁺ co-doped CaTiO₃:Eu³⁺ samples were investigated via degrading methylene blue (MB) under ultraviolet light irradiation. The CaTiO₃:0.5% Eu³⁺, 0.5% Na⁺ sample, by contrast, exhibited the greatest photocatalytic property and the degradation rate was as high as 96.62%, which makes it a promising multi-functional material (photocatalytic material and red phosphor) for decreasing organic pollution in water.     

Ag-ZnO catalysts for UV-photodegradation of methylene blue

High surface area Ag-ZnO catalysts have been made by flame spray pyrolysis (FSP) and characterized by X-ray diffraction (XRD), nitrogen adsorption, UV–vis spectroscopy and electron microscopy (SEM and transmission electron microscopy (TEM)) combined with energy dispersive X-ray spectroscopy (EDXS) for elemental mapping. Silver metal clusters deposited directly on ZnO nanocrystals were obtained from this process. The Ag loading (1–5 at.%) controlled the Ag cluster size from 5 to 25 nm but did not influence the ZnO crystal size. Photodegradation of 10 ppm methylene blue (MB) solution was used to evaluate the performance of these FSP-made Ag-ZnO and was compared to wet-made Ag-ZnO and reference titania photocatalysts. The rate of photodegradation was optimal for Ag loading around 3 at.%. The best photocatalytic performance was exhibited by flame-made Ag-ZnO produced at the longest high-temperature residence times having high crystallinity as determined by XRD and UV–vis.     

Characterization and evaluation of ZnO/CuO catalyst in the degradation of methylene blue using solar radiation

Catalysts based on the combination of zinc oxide and copper oxide were synthesized at a 80:20 mass ratio by the Pechini method and calcined at 500, 600 and 700 °C for 1 h. These catalysts were characterized by XRD, SEM, FT-IR, BET, UV-Vis, TGA and XRF. They were subsequently tested for the removal of methylene blue dye by means of heterogeneous catalysis combined with solar radiation through a RCCD experimental design, analyzing the concentrations of H₂O₂ and methylene blue, as well as radiation exposure time and pH. The average crystallite size obtained was of 26.21, 28.21 and 35.91 nm for the respective calcined samples. The XRF was effective in determining the elements present in the catalyst, consisting of 75% zinc oxide and 25% copper oxide. The values of surface area were of 7.54, 7.19 and 3.92 m²/g, respectively. The experimental design showed that the catalyst calcined at 500 °C exhibited the highest removal efficiency (93%) of methylene blue with a dye concentration of 20 mg/L. Despite the need to carry out new studies to optimize the process, results suggest that the application of solar photocatalysis in the treatment of methylene blue with ZnO/CuO is a feasible alternative.     

Application of the methylene blue test to cement raw materials

Characterisation of raw materials for Portland cement manufacture by use of the methylene blue adsorption method is discussed. The method is shown to be a simple, convenient ‘rule of thumb’ procedure. It provides a guide to the quantity and type of argillaceous minerals present in a given raw material sample.     

Electrochemical property of methylene blue redox dye immobilized on porous silica-zirconia-antimonia mixed oxide

The mixed oxide SiO₂/ZrO₂ obtained by the sol-gel processing method adsorbs Sb(V) from acid solution, forming a new phase on the matrix surface designated as SiO₂/ZrO₂/Sb₂O₅. The amount of Zr(IV) in the matrix was 8.1 wt.%, corresponding to 0.89 mmol g⁻¹, and the amount of Sb(V) incorporated in the matrix was 6.3 wt.% (0.52 mmol g⁻¹). This material presented a specific surface area, S_BET=590 m² g⁻¹. The immobilized Sb₂O₅ is a good cation exchanger and adsorbs methylene blue (MB) cationic dye with an average surface density δ=1.1×10⁻¹¹ mol cm⁻² (about 0.07 molecule nm⁻²). The dye is strongly entrapped in the pores of the matrix and it is not leached off in KCl solutions as concentrated as 1.0 M. A carbon paste of the SiO₂/ZrO₂/Sb₂O₅/MB material showed a reversible redox pair with midpoint potential E_m=−0.1 V versus SCE. This midpoint potential is not affected by solution pH change between 2 and 7. The immobilized dye mediated NADH catalytic oxidation at ca. 50 mV.     

An efficient and energy saving approach to photocatalytic degradation of opaque high-chroma methylene blue wastewater by electrocatalytic pre-oxidation

The opaque methylene blue (MB) dye wastewater hard to be degraded directly by photocatalytic (PC) oxidation was successfully decomposed by a new two-step process, in which electrocatalytic (EC) pre-oxidation was followed with photoelectric synergistic catalytic (PEC) oxidation. The SnO₂/TiO₂ NTs electrode was used as the anode, which simultaneously has superior EC and PC performance. In the pre-oxidation step, the opaque dye wastewater is decolorized by EC oxidation, and the wastewater becomes a light transmission system, which provides the necessary condition for PC oxidation. However, the individual EC oxidation will be of low current efficiency and high energy consumption for the decreasing of the pollutants concentration in wastewater. Thus, in second stage, the PC process was introduced, and the synergistic catalytic oxidation leads to high PEC oxidation efficiency, so that the complete mineralization of the MB dye wastewater was realized. The whole process is highly efficient and energy-saving, which opens a new avenue to degrade the high-chroma or opaque dye wastewater.     

Degradation of cationic dye methylene blue by ozonation assisted with kaolin

An enhanced ozonation process, methylene blue (MB) wastewater treated by MnO₂/O₃ assisted with kaolin in a slurry reactor, at room temperature and atmospheric pressure, MB wastewater can be effectively purified, a chemical oxygen demand (COD) of 88.3% and a decoloration rate of 98.9% were obtained in 10 min at pH 11. Compared with MnO₂/O₃ catalytic ozonation (16.0% of decoloration and 33.3% of COD reduction), decoloration and COD reduction were markedly increased, indicating that kaolin can significantly improve the catalytic ozonation process. According to the experimental results, the hypothetical mechanism of degradation and the reaction kinetics were also proposed. COD reduction can be described by a second-order model and the reaction rate constant in the presence of kaolin was higher than that of absence of kaolin.     

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 Fe_0.021@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.     

固定式填充复合床光催化反应器降解亚甲基蓝的研究

设计了一种固定式填充复合床光催化反应器,以普通玻璃片和玻璃螺旋圈为载体,用溶胶-凝胶法制备了负载型TiO2薄膜光催化剂。利用紫外光为光源,采用难降解物质亚甲基蓝在不同初始浓度、pH值和光强等因素下的光催化降解脱色反应速率考察了该反应器的工艺特性,试验结果表明:该种反应器的最佳操作条件为反应器中同时放置普通玻璃片TiO2薄膜光催化剂和玻璃螺旋圈TiO2薄膜光催化剂,溶液pH值为7.5,光源光强为650W,光照时间为180min。当进水亚甲基蓝的质量浓度为8.0mg/L时,在此条件下的降解脱色效率为93.83%,且其设计易于实现产业化。     

Effects of I and F codoped TiO2 on the photocatalytic degradation of methylene blue

Nanocrystalline I-F-codoped TiO₂ was prepared by a sol-gel-impregnation method, using tetrabutylorthotitanate in a mixed NH₄I-NH₄F aqueous solution. The as-prepared TiO₂ was characterized with UV-vis diffuse reflectance spectra, X-ray diffraction and nitrogen adsorption. The degradation of methylene blue (MB) over as-prepared TiO₂ in aqueous solution under simulated sunlight irradiation was remarkably enhanced by codoping with I and F. The effects of codoping and calcination temperature on the photocatalytic activity and microstructures were investigated. The photocatalytic activity of as-prepared I-F-codoped TiO₂ was remarkably higher than that of pure, I-doped, and F-doped TiO₂ when the molar ratios of I and F to Ti were kept in the value of 10. The influence of I-F-modification on the photocatalytic activity was discussed by considering the higher surface area, entire anatase phase, effective dopant content, and stronger absorbance of sunlight, corresponding to the higher quantum efficiency. In addition to a complete removal of color, the as-prepared TiO₂ was simultaneously able to oxidize MB and small amounts of intermediates such as formic acid and phenol were detected. After prolonged sunlight irradiation some intermediates almost vanished, and MB appeared to be eventually mineralized to NH₄⁺, NO₃⁻ and SO₄²⁻.     

Preparation of reusable glass hollow fiber membranes and methylene blue adsorption

In this work, the PVDF/glass as-prepared composite membrane was prepared through phase-inversion method and used to adsorb methylene blue dye. The results of SEM and BET showed that the membrane had an asymmetric nanoscale porous structure. The electronegativity on the surface of membrane was determined through zeta potential test. The adsorption properties of as-prepared composite membrane and glass membrane were studied through testing the removal ratio of methylene blue from aqueous solution. Then the effects of membranes dose, pH value, temperature and initial concentration on the removal ratio were systematically studied. The adsorption mechanism was also studied. The adsorption kinetics and adsorption isotherm fitted well with the pseudo-second-order model and Freundlich model, respectively. In addition, the adsorption efficiency of glass membrane basically remained 85% after eight repeated adsorption-calcination cycles. The obtained membranes could be reused for methylene blue removal with high efficiency for multiply times.     

Lightweight geopolymer-expanded glass composites for removal of methylene blue from aqueous solutions

In this work, monolithic geopolymer-expanded glass composites were prepared for the purpose of methylene blue removal from wastewaters. Zeolite A was found to form during geopolymerization process, e.g. sodium hydroxide solution alkali-activation of metakaolin and metakaolin with expanded glass aggregates blends, and curing at 80 °C for 24 h. The effect of expanded glass content on density and compressive strength of the obtained samples was examined and showed the decrease from 1.1 g/cm³ and 20.4 MPa (sample without expanded glass) to 0.5 g/cm³ and 1.6 MPa (sample with a 50%-replacement of metakaolin with expanded glass). The addition of expanded glass positively affected sorption capacity and removal efficiency. The sample without expanded glass reached 3.4 mg/g and 70%, while sample with a 50%-replacement of metakaolin with expanded glass reached 4.9 mg/g and 99%, respectively. The influence of methylene blue initial concentration and sorption time on the dye uptake and removal efficiency was also analyzed.     

Spectral and electrochemical studies of methylene blue and thionine encapsulated in zeolite-Y

Investigation on the spectral and electrochemical properties of methylene blue and thionine encapsulated in zeolite-Y is carried out. Both the dyes exist as monomer and H-aggregates in zeolites and the ratios for the aggregates of the dyes are different at the zeolite surface even though the dyes have similar basic structure. The electrochemical behaviour of thionine and methylene blue at zeolite modified electrode shows that both the dyes experience different environment at zeolite modified electrode and the presence of methyl groups in methylene blue plays a vital role in stabilizing the electroactive species at the electrode surface. The concentration of the supporting electrolyte is found to influence the nature of the redox process.     

Equilibrium modeling for the adsorption of methylene blue from aqueous solutions on activated clay minerals

This work reports the application of an activated clay mineral as adsorbent for the removal of a basic dye, methylene blue (MB), from aqueous solutions. The thermal treatment at 300 °C for 2 h and the acid activation with nitric acid of 0.5 mol/dm³ under reflux conditions improve the adsorption capacity of the raw clay mineral. A maximum of 500 mg/g of MB at equilibrium is achieved. Equilibrium data are mathematically modelled using the Freundlich, Langmuir and Toth isotherm adsorption models.