بررسي قابليت سيستم الكتروفنتون با استفاده از الكترود گرافيت با پوشش نانو لوله كربن در حذف رنگزاي اسيد اورانژ 7

Analysis of degradation of Acid Orange 7 by Electro-Fenton process with graphite cathode coated by carbon nanotubes

رنگزاهاي آزو در صنايعي مانند نساجي و رنگرزي كاربرد بسياري دارند. با توجه به خصوصيات ويژه اين تركيبات از قبيل پتانسيل بالاي سرطان زايي و جهش زايي روشهاي گوناگوني به منظور تصفيه آنها به كار گرفته شده است. به تازگي كاربرد فرايند الكتروفنتون به دليل كاهش مصرف انرژي، قدرت اكسندگي بالا و توليد محصولات جانبي دوستدار محيط زيست در حذف رنگزا از محلولهاي آبي به صورت گستردهاي افزايش يافته است. اين فرايند شامل واكنش غير انتخابي تركيبات آلي و راديكال هيدروكسيد توليدي طي الكتروليز H2O2 و يون آهن به عنوان كاتاليزور است. همچنين ميتوان به منظور افزايش راندمان توليد پراكسيد هيدروژن و در نهايت كارايي اين فرايند، ذرات كربن فعال و نانو لوله كربني را در سطح الكترود كربني تثبيت كرد. در اين پژوهش فرايند الكتروفنتون با استفاده از كاتدي از جنس گرافيت با پوشش نانو لوله كربني و آندي از جنس فولاد زنگ نزن براي حذف رنگ از فاضلاب سنتزي انجام شد. نتايج روي فاضلاب سنتزي نشان داد كه فرايند الكتروفنتون تحت شرايط بهينه غلظت اوليه رنگزا 100 ميلي گرم بر ليتر، چگالي جريان 1 ميلي آمپر بر سانتي متر مربع، بدون هوادهي، pH، معادل با 6/5، سطح الكترود 90 سانتي متر مربع، غلظت الكتروليت 0/01 مولار و با مصرف انرژي 0/13 كيلووات ساعت به ازاي هرppm رنگزاي حذف شده پس از360 دقيقه به ترتيب به راندمان حذف 98 و 95 درصد براي رنگزا و COD رسيد. در اين پژوهش نشان داده شد كه سيستم الكتروفنتون با استفاده از الكترودهاي گرافيت با پوشش نانو لوله كربني و فولاد زنگ نزن در عين كاهش هزينه هاي اجرايي از كارايي بالايي در حذف رنگزاي اسيد اورانژ 7 برخوردار است. بر اساس نتايج به دست آمده، فرايند الكتروفنتون براي تجزيه فاضلاب حاوي رنگزا و آلايندههاي مقاوم ميتواند به عنوان پيش تصفيه مورد استفاده قرار گيرد. اين تكنولوژي قابل اجراء موجب بهبود قابليت تصفيه پذيري زيستي فاضلاب نساجي ميشود.

Azo dyes constitute the largest class of dyes and contains one or various azo groups conjugated with aromatic systems such as acid azo dyes which have sulfonic groups causing strong attachment to the cationic groups of fibers. The characteristics of these materials are high color intensity and visibility in very low concentrations, complex chemical structures, and light resistance and hard to biodegradability, variability in pH range and above of these they have high carcinogenic and mutagenic potential. Generally, the physical, chemical and biological methods are considered as textile wastewater treatment techniques such as electrocoagulation, absorption, advanced oxidation, Fenton, photoFenton, photoelectrochemical and photoelectrocatalytic. ElectroFenton is an indirect oxidation process and is based on in situ electrochemical generation of peroxide hydrogen due to electrochemical reduction of dissolved oxygen next to graphite cathode. In this process hydroxide radicals are generated by reaction of hydrogen peroxide and iron ions in acidic condition. Hydroxide radicals are the most powerful radicals with high oxidation potential lead to degrade organic matters into simple compounds like water and carbon dioxide. Recently carbonic material like carbon felt, graphite, activated carbon fibers, carbon nanotubes, carbonic sponge and graphitePTFE are used to improve electroFenton process. Enhancement of surface area, reaction rate and electron transfer are the main reasons which Carbon nanotubes are used to improve electrochemical production of hydrogen peroxide in electroFenton process. Dye removal increased at initial reaction time by increasing current intensity, aeration rate and electrode surface due to enhancing electroFenton regents, meanwhile it decreased with increasing pH and electrolyte concentration. Reduction in dye degradation is usually caused by scavenging role of hydrogen peroxide and iron ions due to reaction of these compounds with hydroxyl radicals which decreased its concentration in reactor. Dye degradation increase by enhancement of Initial dye concentration from 35 to 100 mg/L but when initial dye concentration increased further to 200 mg/L, degradation rate was reduced. On the other hand energy consumption reduced by decreasing current intensity from 2 to 1 mA/cm2 and enhancing electrode surface from 30 to 90 cm2. It has been shown that carbon nanotubes coated on graphite cathode could enhance dye removal rate by increasing hydrogen peroxide concentration due to increase electrode surface area, electron transfer and reaction rate. The results showed that dye and COD removal efficiency was obtained 98% and 95% after 180 and 360 minutes respectively at the optimal condition of effective parameters such as current density of 1 mA/cm2, pH of 6.5, no aeration, initial dye concentration of 100 mg/L, electrode surface of 90 cm2, electrolyte concentration of 0.01 M, temperature of 25 ◦C and energy consumption of 0.13 KWhpm. ElectroFenton process seems to be an economic and environmental friendly process to remove the toxicity of the persistent organic pollutants from water due to generation of hydrogen peroxide and hydroxyl radicals. It has been demonstrated that electroFenton process with the use of stainless steel anode and graphite cathode coated with carbon nanotube is a very effective and operative method to degrade Acid Orange 7.