Mineralization Of Methyl Orange Research Articles

Enhanced Photocatalytic Degradation of Methyl Orange by Metal‐Tio2 Nanoparticles

AbstractIn this study, a series of transition metal‐doped TiO2 was prepared by a simple sol‐solvothermal method. Mix an ethanol solution of tetrabutyl titanate and metal nitrate solution to obtain a homogeneous sol, which is then subjected to solvothermal treatment. After calcination, the metal‐TiO2 naoncomposite was obtained. Selected transition metal precursors, including Cu, Fe, Ag, Cr, Co and Zn, were doped into TiO2 nanocatalysts to assess photocatalytic degradation activities. The results show that 1 mol % Ag−TiO2 photocatalyst has a larger specific surface area, a stable anatase phase and the narrowest forbidden band energy (3.00 eV). In photocatalytic degradation of methyl orange (MO) tests, 1 mol % Ag−TiO2 could reach 100 % decolourisation after 70 min and 75.43 % mineralisation after 90 min. ESR analysis confirmed that Ag doping significantly increased the content of ⋅O2− and ⋅OH for the TiO2 catalyst, which are responsible for the oxidation reactions and consequently degradation of pollutants. The photocatalytic degradation mechanism of MO was also proposed. The TOC analyses confirmed the mineralization of MO. The excellent thermal and chemical stability of 1 mol % Ag−TiO2 has also been demonstrated by thermogravimetric analysis and cycling experiments. Electrochemical tests have also demonstrated the excellent electrochemical properties of 1 mol % Ag−TiO2.

Potential of novel dual Z-scheme carbon quantum dots decorated MnIn2S4/CdS/Bi2S3 heterojunction for environmental applications.

In this work, CQDs decorated MnIn2S4/CdS/Bi2S3 heterojunction was prepared successfully by hydrothermal technique for photocatalytic disinfection of Escherichia coli (E. coli) and mineralization of methyl orange (MO) dye. The charge transferal route and mineralization process in CQDs-MnIn2S4/CdS/Bi2S3 heterojunction were comprehensively investigated by advanced spectroscopic techniques. The improved visible-light activity and enhanced photo-generated charge transferal efficacy caused dual Z-scheme CQDs-MnIn2S4/CdS/Bi2S3 heterojunction to achieve boosted photodegradation ability. The catalytic degradation trend was followed as CQDs-MnIn2S4/CdS/Bi2S3 > MnIn2S4 > CdS > Bi2S3. The dye was mineralized within 180min under visible light irradiation. The effect of reaction parameters, pH effect, catalyst dosage, and H2O2 addition on MO degradation was also investigated. The degradation rate was maximal at pH 4 with a pseudo-first-order rate constant, 0.0438min-1. The assessment of antibacterial properties revealed that CQDs-MnIn2S4/CdS/Bi2S3 composite effectively inactivated E. coli under visible light. Scavenging experiments, transient photocurrent response, and electron spin resonance spectroscopy suggested that •[Formula: see text] and holes were the dominant reactive species. The Z-scheme heterojunction is recyclable up to ten photocatalytic cycles according to recycling experiments. This research indicates the importance of dual Z-scheme CQDs decorated MnIn2S4/CdS/Bi2S3 heterojunction in wastewater remediation.

A Novel Shift in the Absorbance Maxima of Methyl Orange with Calcination Temperature of Green Tin Dioxide Nanoparticle-Induced Photocatalytic Activity

Background: The photocatalytic degradation of toxic organic compounds has received great attention for the past several years. Dyes, such as methyl orange (MO), are one of the major pollutants which create environmental hazards in the hydrosphere, living organisms and human beings. During photocatalytic degradation, NPs are activated in the presence of UV–Vis radiation which in turn creates a redox environment in the system and behaves as a sensitizer for light-induced redox mechanisms. Tin oxide (SnO2) is one of the prominent, but less investigated, nanomaterials compared to titanium oxide (TiO2) and Zinc oxide (ZnO) nanoparticles (NPs). Methods: Herein, Buxus wallichiana (B. wallichiana) leaf extract was utilized as a reducing and capping agent for the biosynthesis of SnO2 NPs. The effects of the calcination temperature on their photocatalytic, structure and surface properties were then examined. The degree of crystallinity and the crystallite size were determined through X-ray diffraction (XRD) analysis. The pore size and surface area were calculated by Burnett–Emmitt–Teller (BET) and Barrett–Joyner–Halenda (BJH) methods based on nitrogen desorption data. Morphological changes were assessed by scanning electron microscopy (SEM). The optical behavior was analyzed through UV–Vis diffuse reflectance spectroscopy (DRS) data and the band gap subsequently calculated. The photocatalytic efficiency of SnO2 NPs was evaluated by double beam UV–Vis spectrophotometry under the influence of initial MO concentration, catalyst dose and pH of MO solution. The surface functional moieties were identified using Fourier transform infrared (FTIR) spectroscopy. All the calcined SnO2 NPs were used as photocatalysts for the mineralization of MO in aqueous media. Results: The degree of crystallinity and the crystallite size increased with the calcination temperature. The transmittance edge obtained for all the calcined SnO2 NPs shows a maximum absorbance in the visible range (λ-max = 464 nm). Moving toward higher wavelengths, a sudden intense red shift (from 464 nm to 500 nm), attributed to the incorporation of a hydroxyl radical at the ortho-position in the benzene ring associated with the dimethylamine group of MO, was observed in the absorbance of the samples calcined up to 300 °C. The percentage degradation of MO was found to decrease with increasing calcination temperatures. The optimal photocatalytic activity toward MO (15 ppm) in a solution of pH = 6 was obtained with 15 mg SnO2 NPs calcined at 100 °C. Conclusions: UV–Vis absorption spectroscopy demonstrates that the absorption spectra of MO are strongly modified by the calcination temperature. This work opens new avenues for the use of SnO2 NPs as photocatalysts against the degradation of industrial effluents enriched with different dyes.

Enhancing the optical properties of immobilized TiO2/polyaniline bilayer photocatalyst for methyl orange decolorization

Several strategies had been employed to enhance the photocatalytic efficiency of titanium (IV) oxide/polyaniline (TiO2/PANI). In this particular study, ferric (Fe3+) ion was incorporated on the PANI sub-layer backbone instead of TiO2 purposely to improve the removal of methyl orange (MO) dye during the photocatalysis by means of optical properties. The framework of present work involves three stages of preparation which was synthesis of PANI crosslinked with polyvinyl alcohol-glutaraldehyde, doping with Fe3+ ion before coating with TiO2 to form a bilayer photocatalyst. The adhesive and Fe3+ ion solution were added via in-situ and ex-situ of PANI polymerization, respectively. The Fe3+-PANI-polyvinyl alcohol-glutaraldehyde (Fe-PPG) composite solution was then immobilized on the glass support using a facile brushing technique. The presence of Fe3+ ion enhanced the electron-hole separation as well as visible light response of the PPG when coupled with TiO2 in the form of layer by layer assemblage. The properties of light harvesting of the bilayer assemblage were then improved by simple photo-etching under light irradiation which produced more porous TiO2 layer on the sub-layer adsorbent. The thickness increased proportionally with loading in which the best loading of TiO2 on top of Fe-PPG was found to be 1.3 mg cm−2 whereas the photocatalytic-adsorption removal was the highest when MO solution was adjusted to pH 6. The mineralization of MO was also faster when TiO2-Fe-PPG was used to treat the dye as compared to single TiO2 layer. With robust mechanical strength and excellent photocatalytic activity, TiO2/Fe-PPG can possibly find its potential application in the real wastewater treatment plant.

Acceleration of biotic decolorization and partial mineralization of methyl orange by a photo-assisted n-type semiconductor

In this study, a n-type semiconductor perylene diimide (PDI) was coupled with biodegradation to accelerate the biotic decolorization and mineralization of methyl orange (MO) under light condition. The decolorization rates (k1) of MO in pure and mixed cultures with PDI were promoted by 1.35 and 1.79 folds, respectively, comparing to the cultures without PDI. The total mineralization efficiency of 4-aminobenzenesulfonic acid (4-ABA) was achieved to 22.10 ± 0.84% when in the presence of PDI. The quinone-like group and oxidation-reduction capacity of PDI were detected by Fourier transform infrared spectroscopy and cyclic voltammetry, respectively, but the enhancement on the biotic decolorization of MO was not promoted under dark condition indicating that microbial extracellular electron transfer was not promoted. The 4-ABA was confirmed to be partially mineralized when the PDI exposure to light. The generated free radicals i.e., h+, ⸱OH, was demonstrated as active species to accelerate the decolorization and mineralization of MO by ESR test and radical quenching experiments. The bond breaking of MO and 4-ABA molecules were successfully predicted by density functional theory calculations and were further proven by liquid-chromatography mass spectra. The synergistic mechanism of decolorization and mineralization of MO by microorganism and photocatalysis was proposed. Moreover, High-throughput sequencing and Live/dead cell results indicated that the presence of PDI has no obvious toxicity to the microorganisms and will not change the microbial communities during the short-term treatment period. The results of study provided a biological intimate photocatalytic material and suggested a feasible way for its combination with biodegradation of azo dyes.

A stepwise processing strategy for treating highly acidic wastewater and comprehensive utilization of the products derived from different treating steps

A stepwise processing strategy, including initial neutralization, chemical mineralization, and complete neutralization treating steps, was developed to effectively treat and utilize the highly acidic wastewater derived from titanium dioxide production. Approximately 94.6% of SO42−, 100% of Fe, and most of other metals were recovered to produce white gypsum, schwertmannite, and Fe0/Fe3O4@biochar (Fe0/Fe3O4@BC) composite in the corresponding treating steps. The resulting effluent with neutral pH and a small amount of metal ions could be discharged to general sewage treatment plant for further processing. Schwertmannite was applied as a heterogeneous Fenton-like catalyst to stimulate H2O2 to produce active radicals for effective degradation and mineralization of methyl orange (MO) in solution. The MO removal of 100% and total organic carbon removal of 91.1% were achieved in schwertmannite/H2O2 reaction system, and schwertmannite exhibited good stability and reusability. Fe0/Fe3O4@BC composite was applied to remove Cr(VI), with the adsorption capacity of 67.74 mg g−1. The removal of Cr(VI) using Fe0/Fe3O4@BC composite was a chemisorption process, including the adsorption of Cr(VI), reduction of Cr(VI) to Cr(III), and co-precipitation of Cr(III)/Fe(III) oxides/hydroxides. This stepwise treating strategy is a promising technology for effective treatment of highly acidic industrial wastewater and comprehensive utilization of the related products.

The CdS/g-C3N4 nano-photocatalyst: Brief characterization and kinetic study of photodegradation and mineralization of methyl orange

The CdS/g-C3N4 hybrid was prepared mechanically and characterized by different techniques including XRD, SEM, DRS, FTIR, and cyclic voltammetry (CV). The SEM study showed that CdS nanoparticles (NPs) have been randomly dispersed on the surface of graphitic carbon nitride (g-C3N4). The CV results showed better charge carriers' transfer for the modified carbon paste electrode (CPE) by the CdS/g-C3N4 system concerning the modified CPE by single CdS or g-C3N4 modifier. The band gap (Bg) energies of 1.7, 2.7, and 1.9 eV were obtained from DRS results for CdS, g-C3N4, and CdS/g-C3N4 systems, respectively. The photocatalytic activity of the single and hybrid systems was tested towards methyl orange (MO). The degradation extents of 16%, 22%, and 34% were respectively obtained for CdS NPs, g-C3N4, and CdS/g-C3N4 systems at initial steps. To enhance the degradation efficiency, the mole ratio of the component was changed in the second step. The work was then focused on the kinetic study of both photodegradation and mineralization processes. For this goal, the degradation extents of the photodegraded MO solutions were calculated based on the recorded absorbance of the solutions in the visible-light and the results were then subjected to the Hinshelwood equation. Then the solutions were subjected to COD experiment to follow the mineralization extent of MO. Form the slopes of the Hinshelwood plots, the rate constants of 0.024 and 0.025 min−1 were obtained for the degradation and mineralization of MO molecules, respectively. TOC results confirmed the mineralization of 187.5 μmoles of MO molecules in a 50 ppm MO solution.

Elucidation of fungal dye-decolourizing peroxidase (DyP) and ligninolytic enzyme activities in decolourization and mineralization of azo dyes.

The aim of the study is to investigate the efficiency of Geotrichum candidum in the decolourization and mineralization of synthetic azo dyes. It includes screening of enzymes from G. candidum and its optimization, followed by decolourization and mineralization studies. Decolourization was observed to be maximum in methyl orange (94·6%) followed by Congo red (85%), trypan blue (70·4%) and Eriochrome Black T (55·6%) in 48h, suggesting the plausible degradation of the azo dyes by G. candidum. The enzyme activity study showed that DyP-type peroxidase has highest activity of 900mUml-1 compared to that of laccase (405mUml-1 ) and lignin peroxidase (LiP) (324mUml-1 ) at optimized pH (6) and temperature (35°C). Moreover, the rate of decolourization was found to be directly proportional to the production of laccase and LiP, unlike DyP-type peroxidase. Furthermore, mineralization study demonstrated reduction in aromatic amines, showing 20% mineralization of methyl orange. Geotrichum candidum with its enzyme system is able to efficiently decolourize and mineralize the experimental azo dyes. The efficient decolourization and mineralization of azo dyes makes G. candidum a promising alternative in the treatment of textile effluent contaminated with azo dyes.

Mixed oxide-polyaniline composite-coated woven cotton fabrics for the visible light catalyzed degradation of hazardous organic pollutants

Clean water and sea free of organic pollutants are among the 17 United Nation Sustainable Development Goals (SDGs). In this global concern, the design of efficient, stable and recyclable catalytic materials remains challenging. In this context, we designed a series of mixed oxide-modified cotton fabrics and their related composites and interrogated their propensity to catalyze the degradation of methyl orange (MO) (a model pollutant). More specifically, functional cotton fabrics (CF) coated with RuO2–TiO2 based-photocatalysts were obtained by dip-coating method at neutral pH. A layer of Polyaniline (PANI) was prepared by in situ oxidative polymerization of the aniline monomer on 4-diphenylamine diazonium salt (DPA) modified-RuO2–TiO2 nanoparticles (NPs) coated-CF. The modified CFs catalyzed photodegradation and mineralization of MO under visible light, which depended on polyaniline mass loading. The CF/RuO2–TiO2/DPA@PANI obtained by in situ polymerization was the best catalyst due to DPA adhesive layer for polyaniline to RuO2–TiO2, and the strong attraction force between cellulose OH groups and anilinium during polymerization. The photodegradation rate constant was 0.101, 0.0532, 0.0775 and 0.0828 min−1 for RuO2–TiO2/DPA@PANI, RuO2–TiO2, RuO2–TiO2/PANI and RuO2–TiO2/DPA/PANI coated-CFs, respectively. The catalytic activity is favored by the photoactive species (OH·, $${\mathrm{O}}_{2}^{-}$$ ) which are formed by the excitation of electrons under visible light but also by the electronic exchanges at the RuO2//TiO2, RuO2–TiO2//PANI and RuO2–TiO2/PANI//CF interfaces. CF/RuO2–TiO2/DPA/PANI photocatalyst was stable under simulated sunlight and reusable three times. A mechanism is proposed to account for the efficient CF catalytic properties.

$$\hbox {C}_{3}\hbox {N}_{4}$$ supported on chitosan for simple and easy recovery of visible light active efficient photocatalysts

To investigate the photocatalytic activities of heterogeneous systems under visible light, graphitic carbon nitride (g- $$\hbox {C}_{3}\hbox {N}_{4})$$ and chitosan (CS) were chosen as a model system. By solution cast method, $$\hbox {C}_{3}\hbox {N}_{4}$$ were embedded into a CS biopolymer matrix in this study. The purpose is to degrade methyl orange (MO) using a novel $$\hbox {C}_{3}\hbox {N}_{4}$$ /CS nanocomposite thin film. Using a visible light-equipped photoreactor with a tungsten incandescent lamp, photo-decolourization of dye was carried out. To catalyse the photodegradation of organic dye pollutant MO, a $$\hbox {C}_{3}\hbox {N}_{4}$$ /CS nanocomposite film photocatalyst was found to be successful and a recovery of 100% of the photocatalyst is achieved by a simple new hand-picking technique. Using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform-infrared spectroscopy and UV–visible diffuse reflectance spectroscopy, detailed characterization was carried out. $$\hbox {C}_{3}\hbox {N}_{4}$$ /CS has high capacity and better photocatalytic activity compared to g- $$\hbox {C}_{3}\hbox {N}_{4}$$ and CS, because $$\hbox {C}_{3}\hbox {N}_{4}$$ possesses a larger surface area and CS has high absorption efficiency which is indicated by the photocatalytic discolouration of MO under visible light irradiation. The $$\hbox {C}_{3}\hbox {N}_{4}$$ /CS nanocomposite thin film photocatalyst is regarded as an excellent catalyst with 98% degradation efficiency and is prepared by the simple solution cast method. The total organic carbon value was measured to be 86%. These values evidence that the mineralization of MO was carried out under these conditions.

Photo-Fenton oxidation and mineralization of methyl orange using Fe-sand as effective heterogeneous catalyst

A novel heterogeneous photo-Fenton catalyst, iron coated sand (Fe-sand) was synthesized by impregnation-calcination method. The catalyst Fe-sand was characterized by XRD, BET, SEM, TEM, FTIR, XRF and DRS methods. X-ray diffraction (XRD) analysis showed that the Fe-sand catalyst mainly consists of Fe2O3 and SiO2 crystallites, and the Fe concentration of the prepared catalyst measured by AAS is 135.7 mg/g. BET results revealed that Fe-sand possess a mesoporous structure with a porosity of 23%. The catalytic performance of the Fe-sand was studied in the discoloration and mineralization of methyl orange (MO). The influence of reacting conditions on degradation efficiency of the oxidation process was analyzed. At optimal conditions (200 mg/L of H2O2, 100 mg/L of initial MO concentration, pH = 3 and without added alcohol) complete discoloration of MO can be obtained within 60 min. The reaction process of MO discoloration was followed by UV–vis and GC–MS spectroscopic techniques. Based on the oxidation products formed, a probable degradation mechanism has been distinguished. Leaching tests indicated a very low concentration of dissolved iron ion and satisfactory stability of prepared catalyst. Industrial application of this catalyst in textile effluent treatment has shown that the proposed catalytic process is suitable for producing reusable water quality.

Novel Fe2V4O13/ZnO nano-heterojunction: Effective decomposition of methyl orange under solar light irradiation

A simple and efficient method was established for the synthesis of Fe2V4O13/ZnO nanocomposites. Photocatalytic degradation of Methyl Orange (MO) dye by using synthesized photocatalysts was investigated under solar irradiation. The effects of operational parameters such as pH, catalyst loading, initial dye concentration, and reusability were studied. The complete mineralization of MO was confirmed by chemical oxygen demand (COD) measurements. Moreover, the catalyst was found to be stable and reusable.

Photocatalytic degradation and kinetic modeling of azo dye using bimetallic photocatalysts: effect of synthesis and operational parameters.

Industrial wastewaters are the major source polluting the surface and ground water resources. Pollutants released along with the untreated textile industry wastewaters are responsible for the great damage to the natural resources like water. Considering the hazardous effects of the azo dyes (textile coloring agents) and their byproducts, there is a need to develop cost-effective and efficient treatment method for the textile wastewaters as such dyes have been reported as toxic, mutagenic, and carcinogenic and can cause direct demolition of aquatic communities. One of the possible and effective treatment methods is the use of TiO2 photocatalysis due to its chemical stability, low cost, and non-toxic nature. The present study explored the photocatalytic potential of anatase-type of bimetallic Cu-Ni/TiO2 photocatalysts under visible light irradiation for possible photocatalytic degradation and mineralization of Methyl Orange (MO), as model azo dye. The focus was to correlate the synthesis (different calcination temperatures, phase composition of TiO2 either anatase or rutile, and metal ion loading in terms of concentration and composition (Cu:Ni)) and operational parameters (photocatalyst loading, pollutant concentration, and irradiation time) that were believed responsible for the enhanced photocatalytic performance. Blank experiments were carried out to check the effect of metal loading in comparison to bare TiO2 and effect of absence or presence of light and photocatalysts on MO photodegradation. Results obtained using bimetallic photocatalysts are promising as compared to bare TiO2 as 100% MO removal and ~ 90% %COD removal were obtained in 90min of irradiation, obeying a pseudo-first-order kinetics with photocatalytic reaction via the Langmuir-Hinshelwood mechanism with a good linear fit. Photocatalysts synthesized using anatase TiO2 were reported with improved performance compared to rutile phase. It is evident that synthesis parameters influence photocatalyst performance directly. The higher rate constant (> 1) that proves the excellent adsorption capacity of the tested photocatalysts for tested pollutants on the surface may have a great prospective for photocatalytic water purification at neutral pH.

Magnetically separable ZnO/ZnFe2O4 and ZnO/CoFe2O4 photocatalysts supported onto nitrogen doped graphene for photocatalytic degradation of toxic dyes

Advanced oxidation processes (AOPs) counting heterogeneous photocatalysis has confirmed as one of the preeminent method for waste water remediation. In the present work, we have successfully fabricated novel visible-light-driven nitrogen-doped graphene (NG) supported magnetic ZnO/ZnFe2O4 (ZnO/ZF/NG) and ZnO/CoFe2O4 (ZnO/CF/NG) nanocomposites. ZnO synthesized via direct precipitation method. Hydrothermal method was used for the preparation of nitrogen-doped graphene supported magnetic ZnO/ZF (ZnO/ZnFe2O4) and ZnO/CF (ZnO/CoFe2O4) nanocomposites. The procured materials were scrutinized by assorted characterizations to acquire information on their chemical composition, crystalline structure and photosensitive properties. The absorption and photocatalytic performance of photocatalysts were studied via UV–Visible spectra. Photodegradation performance of the synthesized nanocomposites was estimated toward mineralization of methyl orange (MO) and malachite green (MG) dyes in aqueous solution. The high surface area of ZnO/ZF/NG and ZnO/CF/NG was suitable for adsorptive removal of MO and MG dyes. The photodegradation performance of heterojunction photocatalysts was superior to bare photocatalyst in 140 min under visible-light irradiation. Spectrophotometer, GC–MS (Gas chromatography–mass spectrometry) elucidation was carried out to expose the possible intermediates formed. Both ZnO/ZF/NG and ZnO/CF/NG were rapidly isolated from the aqueous phase by applying an external magnetic field in 20 sec and 2 min, respectively. The photocatalytic performance and stability of ZnO/ZF/NG and ZnO/CF/NG nanocomposites were confirmed by conducting 10 consecutive regeneration cycles. Owing to recyclability of ZnO/ZF/NG and ZnO/CF/NG, these heterogeneous nanocomposites might be used as cost-effective for treatment of discarded water. The observations endorse that the synthesized ternary heterogeneous nanocomposites facilitates wastewater decontamination using photocatalytic technology.

Enhanced photocatalytic decolorization of methyl orange dye and its mineralization pathway by immobilized TiO2/polyaniline

An immobilized TiO2/polyaniline (TiO2/PANI) bilayer photocatalyst was fabricated to decolorize methyl orange (MO) dye in aqueous solution. The synergistic decolorization of MO occurred via photocatalysis by TiO2 top layer and adsorption by PANI sub-layer. The fabrication of the photocatalyst was pertaining to the loading of TiO2 (0.32–2.24 mg cm−2) and PANI (0.32–1.92 mg cm−2). Increasing the loading would increase the thickness of the layer whereas an increment in the adsorption rate constant would essentially increase the synergistic photocatalytic–adsorption in the decolorization of MO. The TiO2 and PANI layer loading was optimized at 1.27 and 0.63 mg cm−2, respectively. The optimized TiO2/PANI photocatalyst removed MO dye by four and three times more effectively than the TiO2 and PANI single layer, respectively. The aeration, which supplied the dissolved oxygen, was optimized at 40 mL min−1 of flow rate. The photocatalytic degradation mechanism of MO was initiated by the demethylation followed by the aromatic ring opening and ended with a complete oxidation of the aliphatic chain to become CO2 and H2O. The TOC and IC analyses confirmed the mineralization of MO.

Sequential anaerobic and electro-Fenton processes mediated by W and Mo oxides for degradation/mineralization of azo dye methyl orange in photo assisted microbial fuel cells

The intensification of the degradation and mineralization of the azo dye methyl orange (MO) in contaminated water with simultaneous production of renewable electrical energy was achieved in photo-assisted microbial fuel cells (MFCs) operated sequentially under anaerobic - aerobic processes, in the presence of Fe(III) and W and Mo oxides catalytic species. In this novel process, the W and Mo oxides deposited on the graphite felt cathodes accelerated electron transfer and the reductive decolorization of MO. Simultaneously, the mineralization of MO and intermediate products was intensified by the production of hydroxyl radicals (HO) produced by (i) the photoreduction of Fe(III) to Fe(II), and by (ii) the reaction of the photochemically and electrochemically produced Fe(II) with hydrogen peroxide, which was produced in-situ during the aerobic stage. Under anaerobic conditions, the reductive decolorization of MO was driven by cathodic electrons, while the partial oxidation of the intermediates proceeded through holes oxidation, producing N,N-dimethyl-p-phenylenediamine. In contrast, under aerobic conditions superoxide radicals (O2−) were predominant to HO, forming 4-hydroxy-N,N-dimethylaniline. In the presence of Fe(III) and under aerobic conditions, the oxidation of the intermediate products driven by HO superseded that of O2−, yielding phenol and amines, via the oxidation of 4-hydroxy-N,N-dimethylaniline and N,N-dimethyl-p-phenylenediamine. These sequential anaerobic and electro-Fenton processes led to the production of benzene and significantly faster oxidation reactions, compared to either the anaerobic or the aerobic operation in the presence of Fe(III). Complete degradation and mineralization (96.8 ± 3.5%) of MO (20 mg/L) with simultaneous electricity production (0.0002 kW h/kg MO) was therefore achieved with sequential anaerobic (20 min) - aerobic (100 min) operation in the presence of Fe(III) (10 mg/L). This study demonstrates an alternative and environmentally benign approach for efficient remediation of azo dye contaminated water with simultaneous production of renewable energy.

Rapid mineralization of methyl orange by nanocrystalline-assembled mesoporous Cu2O microspheres

In this study, nanocrystalline-assembled mesoporous Cu2O microspheres (MCMs) with enhanced visible-light driven photocatalytic activity were synthesized by a facile one-step hydrothermal method. MCMs exhibit excellent visible-light driven photocatalytic activity with 85% removal of methyl orange (MO) (60% removal of total organic carbon (TOC)) in 40 min. The excellent photocatalytic performance is dependent on the specific morphology and excellent visible-light absorption ability. Interestingly, MCMs can efficiently remove MO with or without light. The amount and categories of active species were determined by electron paramagnetic resonance and photoluminance (PL). Reactive oxygen species (ROS) (mainly · and H2O2) and Cu (I) radicals are important in fading and further mineralization of MO. With the assistance of gas chromatography-mass spectrometer , TOC and x-ray photoelectron spectroscopy, the degradation pathways in light and dark conditions were analyzed. It has been proven that MO could be efficiently mineralized by ROS generated in light, while reaction in dark condition was more likely to be an efficient fading process.

VUV/TiO2 photocatalytic oxidation process of methyl orange and simultaneous utilization of the lamp-generated ozone

A photocatalytic reactor using an ozone-generating mercury vapor lamp with the capability to simultaneously utilize the ozone internally generated from the lamp was fabricated. The reactor included a microbubble-generating mechanism to facilitate the dissolution of ozone and oxygen in the reaction liquid. Photocatalytic and photolytic degradation were investigated using two types of mercury vapor lamps: an ozone-generating lamp emitting at both 254 nm and 185 nm as well as a germicidal lamp emitting only at 254 nm. The roles of ozone, 254 nm light and 185 nm light under the degradation of methyl orange were investigated.In particular, the mineralization of methyl orange in different processes, namely pure ozonation, photolysis under an ozone-generating lamp with or without the assistance of ozone, photolysis under a germicidal lamp, TiO2 photocatalysis under an ozone-generating lamp with or without the assistance of ozone and TiO2 photocatalysis under a germicidal lamp, were analyzed with the chemical oxygen demand and UV–visible absorption measurements.

A Facile Hydrothermal Route for Synthesis of ZnS Hollow Spheres with Photocatalytic Degradation of Dyes Under Visible Light

A facile hydrothermal method was employed for the synthesis of ZnS hollow spheres by using thioglycolic acid (TGA) as a capping agent under hydrothermal condition. The obtained products were characterized by X-ray powder diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). No diffraction peaks from other crystalline forms were detected, the synthesized ZnS hierarchical hollow spheres were relatively pure. The photocatalytic activities of as-synthesized samples were evaluated by the degradation of methyl orange (MO) and rhodamine B (RhB) under the condition of visible-light irradiation. The higher the initial MO and RhB concentrations, the longer it takes to reach the same residual concentration, implying that the apparent rates of MO and RhB degradation decrease with increase in the initial MO and RhB concentration. The increase of photocatalyst dosage from 0.2 to 0.6 g/L results in a sharp increase of the photodegradation efficiency from 68.50 to 92.66% after 180 min of visible-light irradiation for MO degradation, and the increase of photocatalyst dosage from 0.2 to 0.4 g/L results in a distinct increase of the photodegradation efficiency from 65.72 to 90.85% after 180 min of visible-light irradiation for RhB. The elution of intermediates generated in the photocatalytic mineralization of MO and RhB resulted in an increase in total organic carbon (TOC) level, leading to the difference between TOC removal rate and MO and RhB decolorization rates.

Photocatalytic degradation of trypan blue and methyl orange azo dyes by cerium loaded CuO nanoparticles

Pure and cerium loaded CuO nanoparticles (CCO NPs) were synthesized by a simple precipitation – thermal decomposition method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive spectra (EDS), diffuse reflectance spectra (DRS), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS) and BET surface area measurements. The photo catalytic activity of pure, commercial and optimized Ce-loaded CuO catalyst was studied for the degradation of azo dyes such as Methyl Orange (MO) and Trypan Blue (TB) under UV light irradiation. CCO was found to be more competent in the degradation of two azo dyes than pure and commercial CuO. The mineralization of MO and TB has been confirmed by chemical oxygen demand (COD) measurements. A possible mechanism for the degradation was proposed for CCO. This catalyst can be reused and it was more stable without loss of their activity even at third cycles.