Effect of Chromium (VI) on the Oxidation of Methylene Blue Dye by Fe3O4/ Chitosan Composite

: Heavy metal ion removal from industrial wastewater treatment systems is still difficult because it contains organic contaminants. In this study, functional composite hydrogels with photo Fenton reaction activity were used to decompose organic contaminants. Fe 3 O 4 Nanoparticle, chitosan (CS), and other materials make up the hydrogel. There are different factors that affected Photo-Fenton activity including (pH, H 2 O 2 conc., temp., and exposure period). Atomic force microscopy was used to examine the morphology of the composite and its average diameter (AFM). After 60 minutes of exposure to UV radiation, CS/ Fe 3 O 4 hydrogel composite had degraded methylene blue (M.B.) dye by 92 percent. In the meantime, following an 1hour of visible irradiation, COD (Chemical Oxygen Demand) dropped to 6.1 mg/l.


Introduction:
The introduction of toxins into the natural environment is referred to as pollution.There are many types of pollution (air pollution noise pollution, water pollution, soil pollution thermal pollution radiation pollution).The majority of illnesses are caused by environmental pollutants.Water is the primary source of contamination and pollution, which has a level of medical influence on human health.Harmful chemicals, dyes, oils, and other substances damage water.All effluent containing hazardous substances is discharged into neighboring bodies of water.This pollutes the water and produces a variety of health issues for the flora and wildlife.Dyes are a major contributor to water pollution.The majority of dyes emitted by the pharmaceutical and textile industries are carcinogenic, poisonous, and teratogenic, posing substantial health risks to humans and cattle.The evolution of modern, hygienic, and environmentally friendly purification technology has been prompted by environmental degradation and industrialization.Advanced oxidation mechanisms are extremely effective at consuming various hazardous, organic pollutants and completely destroying new contaminants such as naturally occurring poisons, pesticides, dyes, and other harmful contaminants.
Whereas One of the most essential strategies for breaking down pollutants and forming environmentally beneficial goods is to use advanced oxidation processes (AOPs) 1 .There are various types of AOP; non-photochemical AOP procedures including ozonation or the Fenton reaction to generate hydroxyl radicals in the absence of light.UV light, H2O2, O3, and/or Fe 2+ are used in photolysis AOPs to create reactive hydroxyl radicals but photochemical methods are utilized when traditional O3 and H2O2 are unable to thoroughly oxidize organic contaminants.The most important process in oxidation is Phot-Fenton, where it works on the generation of free radicals and in the presence of UV light 2 , hydrogen peroxide and iron ions 3 .The treatment of non-biodegradable wastewater in the field of AOPs has made extensive use of Fenton and (Photo-Fenton) process 4 .Principled (AOP's) are based on the generation of OH radicals in the solution.These OH radicals then will be responsible for the oxidation of organic compounds and act with non-selectivity.The photo reaction will cause the formation of OH radicals 5 .AOPs have benefits and drawbacks, but the benefits outweigh the drawbacks for the most part.1-There is a rapid reaction time.
2-There is a modest footprint.3-The potential for reduced toxicity and total mineralization in the case of treated organics 6 .

Experimental Part Determination of Maximum Absorption (λ max)
M.B. dye is usually used because it can have used to calculate the surface area of any catalyst 7 , to know the rate of degradation through photo Fenton reaction and considering the dye as a pollutant instead of polluted water.The M.B. was prepared at a concentration of 7 ppm by dissolving the solid powder from it with distilled water.The calibration curve of the dye was found and taken as plank for the next study.An ultraviolet visible absorption spectrum was performed for methylene blue (M.B.).The absorption spectrum is shown as peaks between absorbance and wavelength.The wavelength of (M.B.) dye's absorbance value was 661 nm. as shown in Fig. 1, which was conducted in several studies to find out the concentration before and after the reaction.

Figure 1. The absorption spectrum for M.B. dye by UV-Visible
The following Fig. 2 shows the calibration curve through which a linear equation is found through Beer-Lambert's law and the curve is represented between concentration and absorbance (A) using a spectrophotometer with a wavelength range 190-1100 nm.

Synthesis of CS/Fe3O4 Nanocomposite
Good oxidizing nanocomposites was prepared in the Fenton reaction consisting of a mixture of a biopolymer, chitosan (purity:90% deacetylated) with iron(III) oxide, by suspension the chitosan in 1% acetic acid solution under continuous stirring for 10 minutes until it became well suspended.Then the iron oxide was added and the solution was dispersed in Ultrasonic device for 4 minutes to ensure that the particles are well distributed and that no agglomeration occurs.This is done at a temperature of 20 ͦ C, then the ammonium hydroxide solution was slowly added and put in the Ultrasonic device again, thus we got a homogeneous solution of magnetic composite.It was left to dry for 24 hours as shown in Fig. 3.After that we got a magnetic crystal powder and this powder was suspensed by distilled water and placed in the Fenton cell 8 .

Preparation of Photocell
Stainless steel tube with a diameter of 4 cm and a length of 15 cm was equipped with a copper coil surrounding the outer cell surface and connected to a water bath to control of the reactor heat and lamp solution.First, concentrated HF acid is used to treat the inner cell surface, creating also, the cell or photo is rough on the inside and might pick up paint.To coat the photo cell, suspension solution of Chitosan/ Fe3O4 was decanted and allowed to make stable layer on the cell inner surface for 10 minute, on air drier 500 ο C was used to dry the coated layer 9 .To start studying the effect of Cr 6+ on the photo-Fenton degradation of methylene blue dye, 20 ppm of Cr 6+ (potassium dichromate) was used.Figure 4 shows the apparatus used in degradation process and the suspension composite which coated the cell.

Characterization Study
In FTIR spectrum of CS as shown in Fig. 5, a broad band appears in CS spectrum at ⱱ 3434.98,3417.63cm -1 for (NH2 stretching) groups and ⱱ 3244.05cm -1 of O-H stretching group.A peak at ⱱ 2869.88 cm -1 can be characterized for C-H extending the aliphatic group's.C=O in amide groups ⱱ 1637.45 cm -1 .(C-H, CH2) aliphatic at ⱱ 1469.66,1415.65 cm -1 respectively.Other significant bands in CS can be found at ⱱ 1340.43 cm -1 (C-N bending), ⱱ 1149.50 cm -1 (anti-symmetrical of the C-O-C bridge), ⱱ 1047.27cm -1 (C-O bending of a saccharide structure) and ⱱ 1020.27cm -1 (O-H bending), C-C aliphatic appear at ⱱ 925.77 cm -1 .Figure 6 indicates a shift in all peaks, and this is an evidence of the interaction that took place, as frequencies a broad band appears at ⱱ 3452.34 cm -1 and 3434.98 cm -1 of NH2 stretching groups.In ⱱ 3292.26cm -1 of O-H stretching group.A peak at ⱱ 2875.67 cm -1 can be characterized for C-H extending the aliphatic group's.C=O in amide groups ⱱ 1639.38 cm -1 .the appearance of a peak at ⱱ 1413.72 cm -1 of CH2 bending the aliphatic group.Other bands in CS can be found at ⱱ 1367.4422 the pure cubic magnetite structure, which is consistent with the results The peaks were distinct, and this suggests that the structural arrangement in the lengthy bands was at its best 11 .

Figure 7. XRD pattern of CS/Fe3O4 tomic Force Microscope
The AFM study provides measurements of the average grain size and granularity cumulating distribution for the composite built of CS and Fe3O4.the most commonly used parameters are of average roughness (Sa) and square roughness (Sq).The data of CS/ Fe3O4 are (Roughness average= 8.455, average diameter= 13.65) nm, as shown in Fig. 8, average diameter to find out the diameter of the particle.When the surface area increases, number of reaction sites increases and the percentage degradation will be increased.While the roughness average has been used to compare the change of the morphology of the surface after treating with Fe3O4 12 .

Effect of Fenton Detector
At pH = 7, the effect of Fenton on the percent decomposition (% deg) of dye was studied using CS and CS/ Fe3O4 compound with Fenton reagent.The result shows that the presence of Fenton reagent with iron oxide is better than the primary coating and that it increases the degradation of M.B 7 ppm.After UV irradiation, the samples were quickly removed at different time intervals for spectrometry.A spectrophotometer was used to record the absorption spectra of the solutions produced.Using spectrophotometry, percentage degradation was calculated according to the literature 13 , % degradation =  .−.
.* % 1 It was found that after one hour of 60 minutes, the rate of smashing had stabilized, as shown in Fig. 9.

Effect of H2O2 Concentration
One of the operating factors that greatly affects the final mineralization extent is hydrogen peroxide concentration.When a specific ideal Fenton reagent ratio reaches, degradation efficiency also increases with additional increases in (H2O2 conc.).The effect of (H2O2 conc.) on the M.B degradation was studied at temperature 298 K, pH= 7 after 60 min in the presence of catalyst CS, CS/ Fe3O4 composite, and the % deg.increase with (H2O2 conc.)increased 14 as shown in Fig. 10.

Effect of pH on Degradation Process
pH had an impact on the degradation of 7 ppm M.B after 60 minutes in the presence of CS Biomass and H2O2 5*10 -3 M. The photolysis procedure was also carried out at altered pH settings using HCl 0.5M and NaOH 0.5M, while composites maintained constant levels of dye solutions.While when using the CS/Fe3O4 compound, the study of the effect of pH failed because deposition superimposed with the pollutant.

Effect of Cr 6+ Ion Concentration
Chromium ion concentration had an effect on the % deg. at 7 ppm of MB after 60 minutes in the presence of CS and CS/ Fe3O4, hydrogen peroxide 5 * 10 -3 M. The photolysis procedure was carried out using pH 7 and a temperature of 298 K, while the compounds maintained stable levels of the dye solutions.Where the chromium solution was placed with the pollutant which is the dye.During the use of the compound CS/ Fe3O4, the rate of deterioration was higher than that of chitosan.It was found that the optimum concentration of chromium used in this process was 20 ppm, Fig. 12 indicates that.

Kinetic Degradation Study
Using a CS/ Fe3O4 composite and 7 ppm M.B and 5*10 -3 M of H2O2, the concentration of M.B. was followed with time according to different orders of reaction, the first-order equation was applied as shown in Fig. 14, according to equ. 2 15 ln Ct = ln C0kt 2 Where: C0: initial concentration of methylene blue.Ct: concentration of M.B after exposing to UV at specific.k: rate constant.t: time.The degradation percentage (deg.%) with using CS/ Fe3O4 decreased with increasing temperature from 293-323 K and the value of Ea changed from 16.628 to 25.038 J/mol and (A) values (which related the number of sites) decreased from 0.031 to 0.014.This result shows the Anti-Arrhenius behavior, which may be related to formation of on complex between M.B. and empty d-orbital for (Cr 6+ ).

Test of Chemical Oxygen Demand (COD)
For detecting pollutants in wastewater and natural rivers, one widely used metric approach is COD 17 .After 60 minutes of irradiation, CS/ Fe3O4 composite reduced the carbon content to 83.6%, and the resulting solution was digested by potassium dichromate for 2 hours.The solution had a concentration of 7 ppm of MB at pH= 7, and the temperature was 298 K and 5*10 -3 M H2O2 as detailed in Table 2.

Conclusion:
In conclusion, methylene blue dye has the ability to degrade chitosan/Fe3O4 composite as catalyst in the presence of hexavalent chromium ion.AFM was successful in characterizing composites by measuring their average diameter and shape.After adding Cr to the CS/ Fe3O4 composite, the AFM image showed that the particle size increased and the efficiency of (M.B.) degradation increased.CS /Fe3O4 composite was used as a catalyst in the Photo-Fenton process, which was successful in removing the pollutants dye.The most effective irradiation period was determined to be 60 minutes.The results of the pH effect demonstrated that PH= 7 provided the best M.B dye degradation on CS/ Fe3O4 composite.The degradation of M.B dyes on the CS/ Fe3O4 composite was demonstrated to be temperature-dependent, increasing with in293 K temperature.The color was taken out, and the dye was changed into an organic.The degradation of M.B dyes on the CS/Fe3O4 composite was demonstrated to be temperature-dependent, increasing within 293 K temperature.The highest percentage of dye breaking down in the best studied conditions was 92%, This is an excellent percentage compared to the literature 18 .After the dye solution has been subjected to radiation for a longer amount of time, the color has been eliminated and the dye has been transformed into organic material (COD test after 2 hours is low or under range).According to the findings of the kinetic investigation, the M.B dye degradation on the CS/ Fe3O4 composite was well understood.Last but not least, it is advised to use the employed method (the photo Fenton process) to treat wastewater that contains organic compounds.

Figure 4 .
Figure 4. Setup for image degradation using the full system.

Figure 14 .
Figure 14.relation between Ln Ct and time for 7 ppm of methylene blue by a) CS, b) CS/ Fe3O4 composite at different temperatures