Red Dye Concentration Research Articles

Biodecolorization of Reactive Red Using Bacillus cereus Isolated from Oil Contaminated Soil

Manufacturing and using organic dyes produce a variety of hazardous organic compounds which can be harmful to living organisms. Azol dyes, one of the most important synthetic organic components, are widely used in a variety of industries, particularly in the textile industry. As azo dyes breakdown, aromatic amines produce mutagenic products that can cause cancer in humans and aquatic life. In order to protect the environment, it was imperative to find a biological method for degrading these dyes. In recent years, microbial biodegradation has emerged as a promising method. Different bacterial isolates from oil-contaminated soil were investigated for their ability to decolorize reactive red. Under aerobic conditions at pH 7.0 and 35 °C with 0.1 mg/mL reactive red dye concentration, the isolated potential strain showed maximum decolorization of 84 % within 24 hr. Based on the 16S rRNA gene sequence analysis, the isolate was identified as Bacillus cereus strain BIOS MD2. A variety of agricultural wastes were supplemented along with medium to reduce the costs of the process, and extracts of apple and chikoo peels showed better decolorization rates. UV-visible spectroscopy was used to analyze the biodegradation property of reactive red, which confirmed that Bacillus cereus successfully degraded reactive red. The present study provides a valuable insight into practical applications for the removal of textile dye from the environment.

Synthesis, characterization and performance of quaternized cellulose based flocculant derived from office paper waste for dye removal

Abstract The quaternized cellulose derivatives (QCs) were synthesized by reacting extracted cellulose from office paper waste with 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTAC) in an aqueous solution of sodium hydroxide (NaOH) – urea. The characterization results by using Fourier-Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicate that the office paper waste properties changed after chemical treatment and the extract product was confirmed cellulose. In addition, the FT-IR and SEM results confirmed the successful introduction of cationic quaternary ammonium groups into the main chain of cellulose. Meanwhile, the XRD results revealed that the crystalline structure was destroyed during etherification reaction. By using synthetic Congo red dye, the flocculation performance of the QCs was evaluated via standard jar test method at different QC dosages, initial Congo red dye concentration and pH values. It was found that the QC10 exhibited a more effective flocculation capability as compared to other synthesized QCs for over a wide pH value. The QC10 performed the best at pH 7, 100 mg/L of Congo red dye concentration and 50 mg/L of QC dosage, with percentage removal of 89.09 %. These findings demonstrated the potential application of QC in dye removal.

Efficient Adsorption and Catalytic Reduction of Phenol Red Dye by Glutaraldehyde Cross-Linked Chitosan and Its Ag-Loaded Catalysts: Materials Synthesis, Characterization and Application

In this study, glutaraldehyde cross-linked chitosan support, as well as the catalysts obtained after loading Ag metal (Ag/Chitosan), were synthesised and applied for adsorption and reduction of phenol red dye in an aqueous solution. The Ag/chitosan catalysts were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis techniques. The catalytic reduction and adsorption performance of phenol red dye with Ag/chitosan and cross-linked chitosan, respectively, was performed at ambient reaction conditions. The reduction of dye was carried out using sodium borohydride (NaBH4) as the reducing agent, while the progress of adsorption and reduction study was monitored with ultraviolet-visible (UV-vis) spectrophotometry technique. The reduction of the phenol red dye varied with the amount of catalyst, the concentration of NaBH4, Ag metal loading, reaction temperature, phenol red dye concentration and initial pH of the dye solution. The dye solution with a nearly-neutral pH (6.4) allowed efficient adsorption of the dye, while acidic (pH = 4) and alkaline (pH = 8, 11, 13.8) solutions showed incomplete or no adsorption of dye. The reusability of the Ag/chitosan catalyst was applied for the complete reduction of the dye, where no significant loss of catalytic activity was observed. Hence, the applicability of cross-linked chitosan and Ag/catalyst was thus proven for both adsorption and reduction of phenol red dye in an aqueous solution and can be applied for industrial wastewater treatment.

Microbial Electrochemical Treatment of Methyl Red Dye Degradation Using Co-Culture Method

Methyl red, a synthetic azo dye, was reported for not only being mutagenic but also its persistence has severe consequences on human health, such as cancer, alongside detrimental environmental effects. In the present study, the Pseudomonas putida OsEnB_HZB_G20 strain was isolated from the soil sample to study the catalytic activity for the degradation of methyl red dye. Another isolated strain, the Pseudomonas aeruginosa PA 1_NCHU strain was used as an electroactive anodophile and mixed with the Pseudomonas putida OsEnB_HZB_G20 strain to see the effect of co-culturing on the power generation in single-chambered microbial fuel cells (MFCs). The Pseudomonas putida OsEnB_HZB_G20 and Pseudomonas aeruginosa PA 1_NCHU strains were used as co-culture inoculum in a 1:1 ratio in MFCs. This work uses isolated bacterial strains in a co-culture to treat wastewater with varying methyl red dye concentrations and anolyte pH to investigate its effect on power output in MFCs. This co-culture produced up to 7.3 W/m3 of power density with a 250 mgL−1 of dye concentration, along with 95% decolorization, indicating that the symbiotic relationship between these bacteria resulted in improved MFC performance simultaneous to dye degradation. Furthermore, the co-culture of Pseudomonas putida and Pseudomonas aeruginosa in a 1:1 ratio demonstrated improved power generation in MFCs at an optimized pH of 7.

Industrial dye removal from tannery wastewater by using biochar produced from tannery fleshing waste: a road to circular economy

In this study, the capacity of biochars, derived from the pyrolysis of tannery fleshing waste (TFW) at 400 °C; 500 °C and 600 °C, in removal of red dye Sella Fast Red (SFR) from aqueous solutions and tannery wastewater was investigated under various experimental conditions in batch mode. Results show that for all applied biochars, the removed kinetics data were well fitted by the pseudo-second-order model, and the equilibrium state was obtained after 240 min of contact time. For an aqueous pH of 6 and a red dye concentration of 75 mg·L -1 , the removed amounts increased from 26 mg·g -1 to 39.86 mg·g -1 when the used pyrolysis temperature was increased from 400 °C to 600 °C. Moreover, SFR adsorption data at equilibrium were well fitted by Langmuir model suggesting a probable monolayer adsorption process with a maximal removal capacity of 62.7 mg·g -1 for BTFW-600 °C. The thermodynamic study demonstrated that SFR adsorption was endothermic for the three tested biochars. Desorption experiments with distilled water proved that SFR was significantly desorbed from the tested biochars, which offers possible reusability. On the other hand, BTFW-600 °C has demonstrated an important ability in removing SFR from real wastewater since only one dosage of 15 g·L -1 was enough to ensure more than 97% of dye removal. According to pH ZC and FTIR analysis, the possible mechanism toward SFR dye removal was attributed to electrostatic interactions that occurred between biochar and functional groups of SFR. This work could provide guidance for the value-added utilization of tannery solid waste and a practical way to remove dyes from tannery wastewater.

Anionic Dye Removal from Aqueous Solution Using Chitosan Modified Irind Mine Pumice

In this paper, the adsorption of Congo red dye from an aqueous solution using chitosan-coated pumice (CCP) has been studied. The abundant natural pumice from Irind mine (Republic of Armenia) was successfully activated by an acid activation method and modified with chitosan. The adsorbent was applied as a low-cost, and environmentally-friendly adsorbent for Congo red dye removal from aqueous solution. The modified pumice samples were characterized by Fourier-transform infrared spectroscopy (FT-IR). To study the adsorption behavior of Congo red dye on modified pumice, the batch adsorption method was used. The effects of operating parameters on Congo red dye adsorption on modified pumice were examined, including adsorbent dose, pH, contact time, and starting concentration. Solutions of Congo red dye concentrations before and after adsorption were measured by UV-Vis Spectrophotometer (Cary-60). The wavelength of 3.799 nm-1 corresponds to the dye's maximum absorbance, and the obtained spectra revealed that no peak was found above the threshold after modifications.

Removing of Cadmium Ions and Reactive red Dye from Simulated Wastewater Using Eggshell as an Eco-Friendly Material

The research aims to use eggshells (ES) as civilian residues in the process of removing cadmium ions and reactive red dye according to international standards limits. Synthetic solutions were prepared for cadmium ions and reactive red dye using 0.2 g non-calcined and calcined ES at various temperatures (25, 250, 500, 750, and 1000 ℃) as an adsorbent. The result showed the removal of cadmium ion was (60, 100%) for non-calcined and calcined ES, respectively, with the initial concentration of cd2+ (10 ppm). The removal of reactive red dye was (18.5, 98%) using non-calcined and calcined ES, respectively, at a concentration of red dye (50 ppm). The best removal time was 90 min. XRD and FTIR spectroscopy were performed and the results were identical to the main components of ES and changed with temperature increasing due to dissolution of calcium carbonate (CaCO3).

Preparation of NiFe2O4 Nanoparticles by Solution Combustion Method as Photocatalyst of Congo red

NiFe2O4 nanoparticles had been successfully synthesized by solution combustion method using urea fuel (organic precursor). The synthesized NiFe2O4 were characterized by X-ray diffraction (XRD), Scanning electron microscopy-Electron Dispersive X-ray Spectroscopy (SEM-EDs), Transmission Electron Microscopy (TEM), Fourier Transform Infra-Red (FTIR), Vibrating Sample Magnetometer (VSM), UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis DRS), and Point of Zero Charge (pHpzc). NiFe2O4 nanoparticles irradiated with visible light were employed to degrade Congo red dye with the following variable: solution pH (3–8), H2O2 concentration (0.5–3 mM), and Congo red concentration (100–600 mg/L). XRD analysis results showed that the NiFe2O4 nanoparticles had a cubic spinel structure. The particle sizes are in the range of 10–40 nm. The magnetic properties of NiFe2O4 nanoparticles determined using VSM showed a magnetization saturation value of 47.32 emu/g. UV-Vis DRS analysis indicated that NiFe2O4 nanoparticles had an optical band gap of 1.97 eV. The success of synthesis was also proven by the EDS analysis results, which showed that the synthesized NiFe2O4 nanoparticles composed of Ni, Fe, and O elements. The removal efficiency of Congo red dye was 96.80% at the following optimum conditions: solution pH of 5.0, H2O2 concentration of 2 mM, Congo red dye concentration of 100 mg/L, and contact time of 60 min. The study of the photodegradation kinetics follows a pseudo-first order reaction with a rate constant value of 0.0853 min−1. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Experimentally and theoretically approaches for Congo red dye adsorption on novel kaolinite-alga nano-composite

ABSTRACT A comprehensive study combining experimental, computational, and field experiments was conducted to find out the most suitable catalysis method to assist industries using Congo red dye to get rid of this waste from industrial wastewater in Beni-Suef area. The adsorption potential of kaolinite, Liagora farinose (Egyptian marine macroalgae) and kaolinite modified by Liagora farinose macroalgae assessed for the removal of Congo red dye from aqueous solutions. The kaolinite/alga nano-composite with a crystal size of 40 nm was fabricated using a wet impregnation technique. Our results indicate that surface modification of kaolin with Liagora farinose results in an obvious increase in adsorption of toxic dye for nano-composite than individuals. Batch experiments were applied and both kinetics and isotherms of Congo red dye adsorption were also explored in order to find out the influence of different experimental factors. Congo red removal percentage is highly affected by adsorbent dose, working temperature, and pH value. The best temperature for Congo red adsorption onto kaolinite/alga nano-composite is 40°C at pH > 7. The maximum adsorption capacities were found to be 5.0, 7.0 and 10 mg/g for kaolinite, alga and kaolinite/alga nano-composite, respectively. Computational simulations studies have shown that the adsorption of the Congo red molecule on Kaolinite surfaces is exothermic, energetically favourable and spontaneous. Congo red adsorption on kaolinite/alga nano-composite is well handled with the first-order diffusion model, while kaolin and Liagora farinose follow two different kinetic adsorption models depending on the Congo red dye concentration. Finally, the field tests showed optimistic results with nearly 94% efficiency for kaolinite/alga nano-composite in removing mixed dyes from industrial wastewater, which in turn verified the foundation of new eco-friendly nano-adsorbents to help reuse industrial wastewater.

Characterization and Application of Chitosan as a Natural Coagulant in Reducing Remazol Red Dyestuff Concentration and COD Value of Batik Liquid Waste

Research on chitosan application as a natural coagulant in reducing the concentration of remazol red dye from batik liquid waste has been carried out. This study aims to study the effect of the acidity of batik wastewater on the coagulant ability to reduce the remazol red dye concentration and the COD value of batik liquid waste. In this study, chitosan compounds before and after coagulation were characterized using Fourier Transform Infrared (FTIR) Spectroscopy. The pH range used in the coagulation process was pH 2-6. Post-coagulation chitosan FTIR spectra showed a shift in the wave number in the 3400 cm-1 area, which indicated an interaction between the -OH group of chitosan and the dye remazol red. Remazol red dye was maximally coagulated by chitosan at pH 2. The percentage reduction in the dye concentration reached 100%, and the decrease in COD value at that pH was 71.69%.

Application of Immobilized Aspergillus niger in Alginate for Decolourization of Congo Red Dye by Using Kinetics Studies

Discharges of disposal of the textile industry into general water bodies can cause deterioration of aquatic ecosystems and adversely affect human health. The objective of this study is to assess the Congo red dye decolourization by immobilized Aspergillus niger obtained from textile dye wastewater. The effect of experimental parameters like pH 5, contact time (30 h) and initial dye concentration (50 mg/L) on the process of decolourization of dye in the aqueous solution was revealed 97%. The optimum dye decolourization efficiency of immobilized Aspergillus niger using central composite design was found to be 98.97%, obtained were pH 5, initial concentration 50 mg/L, temperature 30 °C and contact time 36 h. Isotherm studies showed that the experimental data better fitted with to Langmuir isotherm, the Freundlich isotherm and Tempkin isotherm for decolourization dye by immobilized Aspergillus niger. It was found that the decolourization was best evaluated by a pseudo-second-order model rather than the pseudo-first-order model. The maximum monolayer adsorption capacity of immobilized Aspergillus niger was resulted as 4325 mg/g at 303 K (R2 = 0.994). The value of separation factor (RL) from Langmuir equation and Freundlich constant (n) indicated on favorability of bioabsorption. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated and the negative value of ΔH° (− 29,671 kJ/mol) for corresponding initial Congo red dye concentrations: 50 mg/L, in the solution indicated that the bioabsorption was of exothermic reaction.. The UV–Vis and FTIR analysis of metabolites after treatment confirmed that the decolourization. Phytotoxicity test confirmed that was less toxic than original dye. The reusability of the immobilized Aspergillus niger was repeated with seven cycles and removal efficiency ranged from 98 to 42%.

Tapered Optical Fiber Detector for a Red Dye Concentration Measurement.

In this work, a detector based on optical fiber covered with Multi-Wall Carbon Nanotubes (MWCNTs) was used for sensing and removal of Alizarin from wastewaters. Alizarin is a strong anionic red dye that is part of the anthraquinone dye group. As a rule, this dye is used in the textile industry as a coloring agent. Experiments showed a good efficiency of wastewater treatment. This development could resolve the problem of water contamination with Alizarin red dye. We used a single-mode fiber SMF-28e with a core diameter of 8.2 μm and a cladding diameter of 125 μm as a base for the tapered optical fiber detector. An MWCNTs array was synthesized on the tapered optical fiber detector surface by spray pyrolysis Chemical Vapor Deposition (CVD) method at 800oC for 20 min inside a tubular furnace, using ferrocene solution in toluene as a catalyst precursor. The formed structure was applied for Alizarin detection in water. According to the patent studies, the nanotubes completely covered the optical fiber surface and the array had a high density with minimal distance between nearby nanotubes. Carbon nanotubes were oriented along the radius of the optical fiber. The average diameter of carbon nanotubes was 24 nm. The optical absorbance levels increased as the Alizarin concentration increased from 50 mg/L to 1000 mg/L. MWCNTs on the optical fiber tapered section adsorbed the dye molecules from aqueous solution. Three intensive absorption bands with the wavelength of the 700, 714 and 730 nm appeared and their intensity increased as the Alizarin concentration increased. The accumulated Alizarin can be recovered by multiple immersing clean water. This property may make tapered optical fiber detector reusable and increase the economic expediency of the sensor application. The study showed higher Alizarin adsorption efficiency of the tapered optical fiber detector compared with relative detectors. This structure can be reusable for dye detection. Removal efficiency for Alizarin reached 98.6%, which makes the tapered optical fiber detector promising for wastewater treatment and dye elimination.

Adsorption of Congo Red Dye from Aqueous Solutions by Wheat husk

The Wheat husk is one of the common wastes abundantly available in the Middle East countries especially in Iraq. The present study aimed to evaluate the Wheat husk as low cost material, eco-friendly adsorbents for the removal of the carcinogenic dye (Congo red dye) from wastewater by investigate the effect of, at different conditions such as, pH(3-10), amount of adsorbents (1-2.3gm/L),and particle size (125-1000) μm, initial Congo red dye concentration(10, 25 , 50 and 75mg/l) by batch experiments. The results showed that the removal percentage of dye increased with increasing adsorbent dosage, and decreasing particle size. The maximum removal and uptake reached (91%) , 21.5mg/g, respectively for 25 initial concentration, pH 6.7 and 1.5 g/l Wheat husk dosage. The experimental data fitted well to Langmuir isotherm mode. The kinetic data support the assumptions of chemisorption were indicates a good fitting to the pseudo-second-order model.

Degradation of Anionic Dye using Fe /Tio2 Composite by Photocatalysis

Dyeing industry discharges large amount of colored wastewater into water bodies without proper treatment. There are various methods to treat wastewater, but recently Photocatalytic treatment has been proven effective. So an effective Iron /Titanium Dioxide (Fe/TiO2) photocatalytic composite has been synthesized by sol-gel method. The synthesized Fe /TiO2 composite was characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), Energy Dispersive Spectroscopy (EDAX). The photocatalytic degradation study of Fe/TiO2 composite under UV light was studied using the aqueous solution of anionic dye Congo Red. The effect of various parameters such as catalyst loading, pH and initial concentration of the dye on degradation has been investigated. The maximum degradation of Congo Red dye concentration in aqueous medium was obtained at pH=5 and 200 mg/l of Fe/TiO2 composite for 10 mg/l concentration of Congo Red dye. Finally, the results prove that photodegradation of Congo Red dye in aqueous solution using composite was very effective under UV irradiation

Chrysanthemum indicum microparticles on removal of hazardous Congo red dye using response surface methodology

Biomass-derived adsorbents have been intensively studied due to their competence in reducing pollutants with conventional methods. Flowers are used as source in medicine, cosmetics and even as adsorbents for pollutant abatement. In this study, the microparticles from Chrysanthemum indicum were used as adsorbent for reducing the Congo red dye concentration from synthetic solution. Batch trials were evaluated to understand the influence of factors and optimization was carried out using central composite design. Maximum reduction (84.1%) achieved under the optimized settings of pH (1.0), adsorbent dose (300 ppm), stirring speed (150 rpm), and contact time (75 min) at initial dye concentration (150 ppm at 30 °C). Microparticle size ensured with surface morphology of the adsorbent using electron microscopy and functional groups was studied using infrared spectroscopy techniques, respectively. Regression coefficient (R2) value was obtained as 0.956 which indicates that the predicted values were in good agreement with their corresponding experimental values for the Congo red dye adsorption. Based on the investigation, it is inferred that the Chrysanthemum indicum flower has the potential for Congo red dye reduction from aqueous solution.

Adsorption of congo red using kaolinite-cellulose adsorbent

Kaolinite was impregnated with cellulose extracted from rubber wood fibers has been done. The product of impregnated kaolinite-cellulose was characterized using FT-IR spectrophotometer. Furthermore, the impregnation results are used as an adsorbent of Congo red. Adsorption of Congo red was also studied the kinetic and thermodynamic parameters. The results of characterization using FT-IR spectrophotometer shows the process of impregnation was successfully conducted. It was indicated that the presence wavenumber at 910.4 - 918.12 cm-1 and 1033.85 cm-1 become 1026.13 cm-1 and the existence of vibration at wavenumber 2931.8 cm-1. The pH of adsorption was adjusted to 4 before the adsorption process. The adsorption process of cellulose impregnated kaolinite shows the rate of adsorption (k) of 0.002 min-1, the adsorption reviews largest capacity (b) at 50 °C was 500 mol/g. The greatest adsorption energy (E) at 40 °C is 11:09 kJ/mol. The enthalpy value (ΔH) and entropy (ΔS) decreased with increasing Congo red dye concentration. Keywords: kaolinite, cellulose, impregnation, Congo red

Preparation of activated carbon incorporated polysulfone membranes for dye separation

Immediate use of activated carbon incorporated polysulfone membrane application for dye separation was reported in this work. Dimethylformamide (DMF) was used as the solvent for the membrane preparation. The membrane thus prepared were characterized in terms of surface morphology, ATR-FTIR, AFM, experimental results as membrane performance. The resultant nanofiltration (NF) membranes were tested with Congo red dye concentration 200 mg/L. The water permeability was found to be considerably higher than that reported in literature. Experimental results show that the real rejection of the Congo red is 99.57% over the transmembrane pressure 100 psi using 30% activated carbon incorporated membrane. Prepared NF membranes shows the corresponding permeates fluxes were 40 Lm-2h-1 to 82 Lm-2h-1 with different activated carbon percentage incorporated in polysulfone membrane. The present study demonstrated that dye rejection enhanced NF may be a feasible method for the dye wastewater treatment. The overall observations thus indicated that toxic residual dyes can be appreciably separated from the membrane technology, provided that the accompanying polymeric membrane, activated carbon as binding agents and the process parameter levels are astutely selected.

Nile Red Staining for Oil Determination in Microalgal Cells: A New Insight through Statistical Modelling

In the wake of global warming and rapid fossil fuel depletion, microalgae emerge as promising feedstocks for sustainable biofuel production. Nile red staining acts as a rapid diagnostic tool to measure the amount of biodiesel-convertible lipid that the cells accumulate. There is a need for the development of a more uniform staining procedure. In its first phase, this study examined the dependence of microalgal Nile red fluorescence (Tetraselmis suecica) in terms of its most pertinent staining variables. A quadratic surface model that successfully described the Nile red fluorescence intensity as a composite function of its variables was generated (r2=0.86). Cell concentration was shown to have a significant effect on the fluorescence intensity. Up to a certain threshold, fluorescence intensity was shown to increase with Nile red dye concentration. In its second phase, the study reviewed findings from previous Nile red studies to elucidate some of the fundamental mechanism underlying the diffusion of Nile red dye molecules into the microalgal cells and their subsequent interaction with intracellular lipids. Through the review process, we were able to develop a simple framework that provided a set of guidelines for the standardization of the Nile red staining procedure across different microalgal species.

In vitro photoacoustic measurement of hemoglobin oxygen saturation using a single pulsed broadband supercontinuum laser source.

We have utilized a single pulsed broadband supercontinuum laser source to photoacoustically sense total hemoglobin concentration (HbT) and oxygen saturation of hemoglobin (SO2) in bloods in vitro. Unlike existing expensive and bulky laser systems typically used for functional photoacoustic imaging (PAI), our laser system is relatively cost-effective and compact. Instead of using two single wavelengths, two wavelength bands were applied to distinguish the concentrations of two different chromophores in the mixture. In addition, we have successfully extracted the total dye concentration and the ratio of the red dye concentration to the total dye concentration in mixed red and blue dye solutions in phantoms. The results indicate that PAI with a cheap and compact fiber based laser source can potentially provide HbT and SO2 in live animals in vivo.

Changes in morphology and optical properties of polyvinyl alcohol foils induced by Congo red dye concentration and stretching degree

Abstract To establish correlations between the optical and morphological properties of anisotropic polyvinyl alcohol (PVA) foils containing Congo red (CR) dye in various concentrations, characteristics such as degree of crystallinity, dichroic ratio, order parameter, birefringence, surface morphology, and three-dimensional texture parameters were estimated before and after stretching. An increase in morphological and optical anisotropy with the degree of stretching has been evidenced for both pure and CR-containing PVA foils, this behavior being facilitated by the presence of the dye. The study of these properties lays the foundation for understanding the circumstances in which PVA foils containing CR can be used as polarizing filters.