Model Dye Solutions Research Articles

The worthy green heterogeneous Fenton degradation process for removal of E102 in foodstuffs and industrial waste-waters using Cypress arizonica leaves based magnetic nanocomposite (CA-Fe3O4-MNc)

A new, green magnetic nanocomposite (MNc) was synthesized based on framework of Cypress arizonica (CA) leaves and then used as Fenton catalyst for removal of tartrazine (E102) in foodstuffs and industrial waste-waters. Characterization of the synthesized magnetic nanocomposite (CA-Fe3O4-MNc) was performed with IR, EDX, FESEM, XRD and pHpzc analyses. The average particle size and pHpzc of the CA-Fe3O4-MNc were determined to be 24.36 nm and 6.8, respectively. CA-Fe3O4-MNc was composed of C (15.08 %), Fe (51.86 %), O (31.80 %) and Ca (1.26 %) elements. The parameters effecting heterogeneous Fenton dye removal process including pH, catalyst amount, reaction time, H2O2 and initial dye concentrations were investigated to achieve the best removal efficiency for E102. Under optimal conditions, the matrix effect was investigated, the reusability of CA-Fe3O4-MNc was tested, degradation products and mechanism were elucidated, and green analytical procedure index (GAPI) and analytical eco-scale (AES) of the proposed Fenton degradation process were evaluated. E102 removal values were obtained between 93 and 99 % in the applications of some foodstuffs, water samples and artificial model dye solutions. Proposed heterogeneous Fenton removal process with using CA-Fe3O4-MNc catalyst exhibited quantitative removal efficiency for E102. E102 concentrations between 5 and 50 mg/L were removed successfully. It was observed that the synthesized CA-Fe3O4-MNc material could be used at least 5 times to obtain quantitative removal values. The percent removal efficiency value decreased to 93 after five uses. Defined GAPI parameters and calculated AES scores indicated that the proposed CA-Fe3O4-MNc based heterogeneous Fenton degradation process could be considered that a valuable green removal method.

Photo-response range extension of Z-scheme ZnO/CdS for LED-light-driven photo-active catalyst

Zinc oxide (ZnO) photocatalysts are suitable for wastewater treatment via photocatalytic processes. However, they are hindered by fast e− and h+ recombination, a large bandgap, and the need for a high-energy light source for activation. Thus, this study was aimed to synthesize a photocatalyst that operates under a low-energy consumption. We introduced cadmium sulphide (CdS) heterojunction to ZnO photocatalyst, and successfully reducing their bandgap from 3.30 eV to 2.46 eV. This modification allows activation with a 21-Watt light-emitting diode (LED) visible light source. The surface structure characteristics of the ZnO/CdS photocatalyst was analyzed using XRD, HRTEM, FESEM, and N2 adsorption-desorption isotherms. UV-NIR was used for bandgap analysis and the DFT simulation method to compute the atomic properties of the materials. Catalytic evaluation showed that the ZnO/CdS photocatalyst completely degraded the model dye solution (100%) using 0.5 g of Z3C1 (3:1 M ratio) of 100 mg L−1 MB solution at pH 9 within only 90 min. A scavenger test confirmed that the hydroxyl OH• and superoxide •O2− radicals proved were the major active species responsible for degradation process. The reusability of Z3C1 was demonstrated over 4 reaction cycles, proving that CdS significantly enhances visible light absorption by extending the photo-response range and promoting superior formation of e− and h+. This delays their recombination due to the Z-scheme type, making it highly potential for wastewater treatment.

Structural insights into diketone-mediated high-rate photobleaching of dyeing wastewater

Acetylacetone (AA), which has two tautomers (diketo and enol), has been found to be a potent photo-activator for wastewater treatment. However, the crucial structural characteristics in the photo-activity remained unclear. Herein, the performance of 16 AA derivatives and structural analogues (AAs) was extensively evaluated for a real dyeing wastewater and a model dye solution under UV irradiation. The results indicate that the straight-chain aliphatic 1,3-diketone structure was crucial in the high-rate photobleaching. Photo-induced direct electron transfer by enolic AAs and indirect electron transfer with free radicals generated from the cleavage of ketone AAs were the two main mechanisms. The substituents affect the keto-enol tautomerization and the charge population, thereby influencing the photochemical activity of AAs. Electron-donating groups (e.g., -CH3, -(CH3)2, -CH2CH3) at the central carbon in AAs would increase the content of the diketone form and promote the generation of organic radicals from α-cleavage. By contrast, the presence of electron-withdrawing groups (such as -Cl, -(F)3, and -C2H4Br) might lead to the hydrolysis or hydration of AAs, and consequently depressed the photobleaching rate. The results here are valuable for the design of more efficient and eco-friendlier photo-activators for environmental remediation based on diketone photochemistry.

Optical band gap engineering of phosphotungstic acid upon hybridization with hexamine-nickel and -cobalt for solar/visible light photocatalysis: a combined experimental and theoretical approach

Two new organic hybrids of phosphotungstic acid (PTA) were prepared by means of hexamine complexes of nickel and cobalt. The effects of complexes were studied on the photocatalytic activity of PTA. The hybrids were characterized by elemental analyses, FTIR, powder XRD and TGA. The optical band gaps of phosphotungstate-hexamine-nickel and phosphotungstate-hexamine-cobalt were estimated from the diffuse reflectance spectra using the Tauc plots. Dye adsorption and photocatalytic properties of hybrids were tested by decolorizing of model dye solutions methylene blue, rhodamine B and methyl orange. Band gap engineering of the hybrids was investigated using the quantum chemical calculations based on density functional theory through variation in the composition. Theoretical analysis demonstrates how the band gap of these hybrids can be adjusted with variation in their composition. The scavengers were used to suggest photodegradation mechanism. The degradation advanced through the excitation of hybrid by light, followed the oxidation of dye by superoxide radicals.

Fluorescence saturation imaging microscopy: molecular fingerprinting in living cells using two-photon absorption cross section as a contrast mechanism.

Imaging of molecular-specific photophysical parameters such as fluorescence intensity, emission band shape, or fluorescence decay is widely used in biophysics. Here we propose a method for quantitative mapping of another molecular-specific parameter in living cells, two-photon absorption cross section, based on the fluorescence saturation effect. Using model dye solutions and cell culture, we show that the analysis of the fluorescence signal dependencies on the intensity of two-photon excitation within the range typical for routine two-photon microscopy experiments allows one to reconstruct two-photon absorption cross section maps across the sample. We believe that the absorption cross section contrast visualized by the proposed fluorescence saturation imaging microscopy could be a new tool for studying processes in living cells and tissues.

Enhanced photocatalytic oxidation of reactive dye using manganese catalyst complex

In this work, the treatment efficiency of advanced oxidation processes H2O2/UV enhanced by the addition of a manganese catalyst complex (MnTACN) was investigated on a model dye solution and a real dye-house effluent. The experimental results were evaluated in terms of absorbance (A) and total organic carbon (TOC) reduction. The major degradation products of the model dye solution were identified by high resolution gas chromatography/mass spectrometry analyses. In addition, the toxicity of the final reaction solution after H2O2/UV/MnTACN treatment to Vibrio fischeri bacteria was determined. The results showed that the addition of the H2O2/UV/MnTACN system at different concentrations of the catalyst solution increased the decolourisation rate compared to H2O2/UV for both the model dye solution and real dye-house effluent.

Mn2+ concentrations creating defects in chromium sesquioxide (Cr2O3) influenced the enhanced optical properties and photocatalytic activities: Synthesized via the facile precipitation process

Chromium sesquioxide (Cr2O3) nanomaterials were successfully synthesized via the facile precipitation process with different (1–3 mol %) concentrations of a Mn2+ metal ion as a dopant. The effects of the metal ion dopant concentrations creating defects in the chromium sesquioxide nanoparticles were analyzed by different techniques. The structural, morphological and optical properties of the products were studied by using XRD, FTIR, SEM, EDX, TEM, UV–vis and PL techniques. The Photocatalytic degradation performances of the products were comparatively discussed with pure chromium sesquioxide nanoparticles methyl orange as a model dye solution.

Study of TiO2/Ti4O7 photo-anodes inserted in an activated carbon packed bed cathode: Towards the development of 3D-type photo-electro-Fenton reactors for water treatment

In this work, commercially available Polymethyl-meta-acrylate (PMMA) spectroscopy cells were modified on the external walls with films of TiO2, Ti4O7 or TiO2/Ti4O7 mixtures. Film characterization was carried out using SEM and UV–vis spectroscopy. The results of photocatalytic (PC), electro-oxidation (EO), and photoelectrochemical (PEC) experiments on the decolorization of a methyl orange (MO) model dye solution showed that while anatase provides better photocatalytic properties and the partially reduced Ti4O7 larger electronic conductivity, the TiO2/Ti4O7 composite film behaves as a semiconductor substrate that combines the advantages of both materials (for PEC experiments for instance, decolorization values for the model dye solution using TiO2, Ti4O7 and a TiO2/Ti4O7 mixed film, corresponded to 35%, 46% and 53%, respectively). In order to test this film as an effective photoanode material in a 3-D type reactor for water treatment processes, a TiO2/Ti4O7 modified PMMA spectroscopy cell was inserted in an activated carbon (AC) bed so that the semiconductor material could be illuminated using an external UV source positioned inside the PMMA cell. The connected AC particles that were previously saturated with MO dye were used as cathode sites for the oxygen reduction reaction so that the photoelectrochemical reactions that take place in the anode could be complemented with coupled electro-Fenton processes in the cathode. As expected, the combination resulted in an effective decolorization of the dye solution that results from a complex combination of processes. The experimental decolorization data was successfully fitted to a pseudo-first order kinetic model so that a deeper understanding of the contribution of each process in the reactor could be obtained.

Bouncing Droplets: A Hands-On Activity To Demonstrate the Properties and Applications of Superhydrophobic Surface Coatings

Here we report a hands-on activity addressed to master’s students in Physical Chemistry and Materials Science courses on the properties and applications of superhydrophobic surfaces. This simple and intuitive experience can also be used to teach undergraduate and high school students, thanks to its application-oriented approach and tangible results. Superhydrophobicity was achieved by the functionalization of oxide powders with alkylsilanes and their subsequent deposition on a glass substrate. The film’s superhydrophobicity was assessed by different application tests and compared with the behaviors of model hydrophobic, hydrophilic, and superhydrophilic surfaces. Its antistain properties were tested with both model dye solutions and everyday liquids. Films were fouled with graphite and dye powders to compare the self-cleaning capabilities of the different surfaces, and single droplet transport was achieved by adding magnetic particles. This engaging and adaptable experience introduces students to basic concepts of surface science in an intuitive and tangible way.

Valorisation of Waste Wood Biomass as Biosorbent for the Removal of Synthetic Dye Methylene Blue from Aqueous Solutions

Background and Purpose: Wood and wood processing industries are generators of a substantial amount of waste wood biomass, such as wood chips, shavings and sawdust. Such waste is often unused and its disposal can be a serious environmental problem. Different lignocellulosic waste materials have been successfully used as low-cost adsorbents (biosorbents) for the removal of synthetic dyes, as well as other contaminants, from wastewater. The aim of this study was to valorise the waste wood biomass of ten tree species, out of which seven are the most represented species of the Croatian growing stock, as biosorbents for the removal of synthetic dye methylene blue (MB) from model solutions. Materials and Methods: The waste wood biomasses (shavings or sawdust) of ten tree species, namely common beech, pedunculate oak, sessile oak, common hornbeam, narrow-leafed ash, poplar, European silver fir, Norway spruce, European larch and Douglas fir, were dried and milled prior to characterisation and adsorption experiments. Characterisation of the biosorbents was performed by chemical analysis and Fourier transform Fourier transform infrared spectroscopy (FTIR). Upon characterisation, batch adsorption experiments were conducted in order to survey waste wood biomass as potential adsorbents for the removal of synthetic dye MB. The colour removal was monitored spectrophotometrically at predetermined time intervals. Further adsorption experiments were performed using poplar sawdust. The effects of contact time, biosorbent concentration, initial dye concentration, and pH on the adsorption process were investigated. The experimental data obtained by batch adsorption experiments were analysed using adsorption isotherm models (Freundlich and Langmuir). Results: All the tested biosorbents were found to be very effective for the removal of MB from model dye solution, achieving high removal percentages ranging from 93.25 to 98.50%. Poplar sawdust proved to be the most effective. It was shown that MB adsorption process onto poplar sawdust could be interpreted in terms of Langmuir and Freundlich adsorption isotherm models. Conclusions: Taken together, these results suggest that waste wood biomass has the potential to be used as a low-cost biosorbent for MB removal from aqueous solutions.

Hybrid Composite Materials Based on Natural Layered Silicates

We have prepared composite materials based on natural silicates: vermiculite modified with cellulose and nontronite modified with an alkaline rice husk hydrolysate. The materials have been characterized by X-ray diffraction, IR spectroscopy, and positron annihilation spectroscopy, and their specific surface area, sorption capacity (for model dye solutions), and tribological properties have been assessed. It has been shown that cellulose in the vermiculite-based composite material is incorporated between the aluminosilicate layers, forming a new crystalline phase. The nontronite-based composite material reduces the wear of friction pairs by a factor of 2.5 to 7.

Alternate use of sulphur rich coals as solar photo-Fenton agent for degradation of toxic azo dyes

Abstract Low grade coals with high sulphur contents are not suitable as fuels in thermal power plants due to generation of high ash content and emission of toxic sulphur oxide gases. Here we have demonstrated an alternate use of pyrite rich coal as a source for sustainable generation of hydrogen peroxide and hydroxyl radicals in aqueous medium via solar light induced photo-Fenton process which were utilized for degradation of toxic azo-dyes. The textural, compositional and morphological features of pristine pyritic coals with varying sulphur concentrations are studied by an array of characterization techniques. The dye degradation capacities of pyrite rich coal are studied using model dye solutions e.g., Basic Blue 41 containing single azo group per unit and Trypan Blue containing two azo groups per unit. The rate of degradation (k) is faster for Basic Blue-41 (0.0192 min−1, ∼99% degradation) at optimized solar radiation exposure time, pH 6 and dose of 1 g/L pyritic coal. The dye degradation is presented as a measure of solar radiation accumulation energy per unit volume, and it is attributed to in-situ generation of hydrogen peroxide and hydroxyl radicals, and re-confirmed from scavenging studies. The dye degradation mechanism by pyritic coal is discussed in the light of solar photo-Fenton mechanism with respect to (1) qualitative identification of trace quantities of degradation products by gas chromatography-mass spectrometry technique; (2) leaching of 2700 mg/L iron in the reaction medium, estimated by inductive coupled plasma optical emission spectrometry, and (3) and changes in the chemical speciation of iron, sulphur and oxygen in the used coal by X-ray photoelectron spectroscopy.

Two-dimensional bismuth oxybromide coupled with molybdenum disulphide for enhanced dye degradation using low power energy-saving light bulb

In the present work, two-dimensional bismuth oxybromide (BiOBr) was synthesized and coupled with co-catalyst molybdenum disulphide (MoS2) via a simple hydrothermal process. The photoactivity of the resulting hybrid photocatalyst (MoS2/BiOBr) was evaluated under the irradiation of 15 W energy-saving light bulb at ambient condition using Reactive Black 5 (RB5) as model dye solution. The photo-degradation of RB5 by BiOBr loaded with 0.2 wt% MoS2 (MoBi-2) exhibited more than 1.4 and 5.0 folds of enhancement over pristine BiOBr and titanium dioxide (Degussa, P25), respectively. The increased photocatalytic performance was a result of an efficient migration of excited electrons from BiOBr to MoS2, prolonging the electron-hole pairs recombination rate. A possible charge transfer diagram of this hybrid composite photocatalyst, and the reaction mechanism for the photodegradation of RB5 were proposed.

Mussel-inspired modification of Microporous polypropylene membranes for functional catalytic degradation

In this manuscript, an easy method of anchoring Au nanoparticles onto a polypropylene (PP) membrane to prepare a composite Au-PP membrane with catalytic activity was demonstrated. The surface of the PP membrane was first modified with a primary amine by mussel-inspired dopamine polymerization. Then, the modified PP membrane was used to reduce chloroauric acid to anchor Au nanoparticles onto the surface, forming a Au-PP membrane. The surface morphology and composition of the modified PP membrane were characterized with SEM, ATR-FTIR and XPS. The catalytic activity of the Au-PP membrane was also evaluated by the degradation of a model dye solution of methylene blue. The fabricated membrane shows excellent catalytic performance, and the catalytic activity can be effectively regenerated.

Excellent dyes removal and remarkable molecular size rejection of novel biopolymer composite membrane

ABSTRACT The κ-carrageenan mass fraction (F C) was a key factor to determine membrane character not only on mechanical strength but also on selected molecular permeability. It was defined as the following equation: F C ≡ (κC[g]/(P[g] + κC[g])) and changed in desired range (0.33–0.83). This study reports the results of mass transfer and ultrafiltration experiments on model dye solutions, indicating Methyl Orange, Indigo Carmine, Bordeaux S, Brilliant Blue, and Rose Bengal, and the reference molecular weight are from 327 to 1017 Da. The fundamental parameters influencing the transport of dye such as experimental temperature, viscosity of the feed solution, initial dye concentrations have been determined. The effective diffusion coefficient of dye molecules in the biopolymer membrane was calculated. Outstanding molecular size recognition was appeared. The molecular weight cut-off values in F C0.33 membrane were 327 Da, and for F C0.66 membrane performed the results of 466 Da, respectively. The membrane changed from the wholly compact structure to the porous structure by an increase in the F C, and then, we proved the changes of membrane formation while F C value increased scientifically based on a scanning electron microscope (SEM) observation.

The determination of performances of polysulfone (PS) ultrafiltration membranes fabricated at different evaporation temperatures for the pretreatment of textile wastewater

The effects of evaporation temperature on properties and filtration performances of polysulfone membrane were investigated with a series of experiments. Membranes were fabricated by phase inversion process at five different evaporation temperatures (25±0.4, 35±0.6, 45±0.5, 55±0.5 and 65±0.6°C). The resulted membranes were characterized by water permeability, MWCO (molecular weight cut-off), AFM, porosity, contact angle and SEM analyses and tested for filtration performances by using a model dye solution (reactive orange 16-RO16) and a real dye-bath textile wastewater. The pore size and density onto the membrane surface become smaller and the surface roughness, porosity, permeability and MWCO values of membranes considerably decreased with the increasing of evaporation temperature. At the pretreatment filtration experiments, the flux values of membranes decreased largely with the increase of the evaporation temperature while the removal efficiencies for color, COD and conductivity parameters increased. At the membrane fouling analysis, the flux reduction ratios (FRR), the filtration (Rt) and fouling (Rf) resistances and the reusable performances of membrane changed directly proportional with roughness, porosity and pore size characteristics of membranes. At the nanofiltration step (NF-270 membrane), the moderate color, chemical oxygen demand (COD) and conductivity removal were showed at permeate of PS-65 membrane (the membrane fabricated at 65±0.6°C).

Modeling of iron activated persulfate oxidation treating reactive azo dye in water matrix

Advanced oxidation processes (AOPs) offer effective solutions for the treatment of wastewaters containing hazardous and refractory organic pollutants. However, their efficiency is strongly influenced by varying process conditions thus the prediction of the system behavior is of an unappreciable interest. In this study iron activated persulfate oxidation was applied for degradation of reactive azo dye, C.I. Reactive Red 45 (RR45), in water matrix. Fe 2+/S 2O 8 2− and Fe 0/S 2O 8 2− processes were maintained in a dark as well as with UV light assistance. The main purpose was to develop the flexible mathematical/mechanistic model ( MM) which would (i) predict not only the conversion of parent pollutant, i.e. decolorization of model dye solution, but also the mineralization of model pollutant, and (ii) could keep the predictive power regardless the process operating conditions. Hence, the pH dependent mechanism describing both organic and inorganic ferric complexes formation as one of the major limitations of iron activated processes, as well as iron activated persulfate oxidation, was built in the model. Developed MM showed a high accuracy in predicting the degradation of RR45 considering both decolorization and mineralization, as well as the profiles of iron species, persulfate decomposition, the subsequent formation of sulfates and pH changes during the treatment. Good agreement of the data predicted and the empirically obtained was confirmed by calculated root mean square deviation (RMSD) values.

Application of ceramic membranes for the separation of dye particles

This study reports the results of ultrafiltration experiments on model dye solutions containing anionic dyes and anionic surfactant. The ceramic membrane modules CeramINSIDE (TAMI Industries) of various cut-off values (1, 5, 8, 15, and 30 kDa) were used in the experiments. The suitability of ceramic membranes for the decolourization of dye solutions was evaluated. Seven anionic organic dyes of molecular weights ranging from 327 to 1084 Da were used in the tests. The anionic surface active agent (sodium dodecyl sulphate, SDS) was added to the dye solutions. The experiments were conducted at 0.03–0.1 MPa with the use of a laboratory and semi-pilot UF installation. The effect of the molecular weight of the dyes as well as the SDS presence in the separated solutions (in the range below the CMC) on the process efficiency was studied. It was found that membrane properties (permeability and dye separation factor) were almost identical for membrane modules of cut-off equal to 1, 5, and 8 kDa. For high-molecular-weight dyes above 600 Da retention amounted to 95–98% and was slightly influenced by the SDS presence in the dye solution. Ceramic membranes with a cut-off of 15 and 30 kDa exhibited insignificantly poorer properties.

Concentration of organic contaminants by ultrafiltration

The results of concentration experiments on model dye solutions containing anionic surfactant and mineral salts were reported. The objective of the study involved recovery of valuable substances and water reuse. The membrane efficiency as well as dye and surfactant rejections during concentration tests were evaluated. The Mollsep Fiber (Nadir) modules with membranes made of polyethersulfone (10 and 30 kDa) were used in the experiments. The anionic surface active agent (sodium dodecyl sulphate) and sodium chloride (NaCl) were added to the dye (Direct Black) solutions. The concentration experiments were conducted at 0.1 MPa. The effect of concentration factor on the volume flux of dye solutions, dye and surfactant rejection was studied. It was found that membrane permeability and dye separation factor was kept constant during concentration process for all experimental solutions. Surfactant retention was highly influenced by solution composition and subjected to great variations. Nevertheless, it was possible to receive two streams in UF process: concentrated dye solutions and water containing anionic surfactant (SDS).

Membrane contactors for textile wastewater ozonation.

This paper deals with the application of a membrane contactor for the ozone treatment of textile wastewater. Ceramic (alpha-Al(2)O(3)) membranes were chosen because of their ozone resistance. A thin metal oxide (TiO(2) and gamma-Al(2)O(3)) layer was deposited on the membrane surface to eliminate large defects. Membranes were characterized by bubble pressure and gas permeability tests. Mass transfer coefficients were calculated by using the double-film theory. Decolorization kinetics were studied with model dye solutions. Decolorization experiments with a real exhausted dyebath (untreated and after biological treatment) were also carried out. The potential advantages of membrane contactors for the treatment of these types of effluents are demonstrated.