تاثير اصلاح سطح كربن فعال توسط پلاسماي سرد بر ظرفيت جذب رنگ رودامين بي

Effect of surface modification of activated carbon by cold plasma on the adsorption capacity of Rhodamine B

بسياري از رنگ­هاي مورد استفاده در صنايع مختلف سمي و مضر هستند و هنگامي كه در پساب رها مي­شوند باعث بروز مشكلات زيست­ محيطي و سلامتي مي­شوند. رودامين B يكي از رنگ­هاي پر كاربرد در صنعت نساجي، چاپ و چرم است كه براي انسان و ساير جانوران مضر مي­باشد. از بين روش­هاي مرسوم فيزيكي، شيميايي و بيولوژيكي حذف رنگ، جذب يكي از روش­هاي ساده و موثر براي حذف رنگ از پساب مي­باشد. كربن­فعال جاذب مناسبي براي حذف اين نوع آلاينده­ ها از فاز مايع بوده و از صدمات زيست ­محيطي حاصل جلوگيري مي­كند. بسته به نوع آلاينده مي­توان ميل تركيبي كربن فعال را با روش­هاي اصلاح بهبود بخشيد. يكي از روش­هاي بهبود ظرفيت جذب كربن فعال، اصلاح آن با پلاسما مي­باشد. بنابراين در اين تحقيق سطح كربن فعال به منظور افزايش ظرفيت جذب نسبت به رنگ رودامين B توسط پلاسماي سرد اصلاح شد. روش بررسي: كربن فعال از چوب سالم و پوسيده راش با روش فعال­سازي شيميايي توسط ZnCl2 در دماي كربونيزاسيون ᵒC 400 و نسبت آغشته ­سازي 70 درصد تهيه شد. با استفاده از روش BET و جذب N2 در دماي k 77 سطح ويژه، حجم و ميانگين قطر حفرات اندازه ­گيري شد. اصلاح سطح كربن­ فعال­ها توسط پلاسماي تخليه سد دي­الكتريك(DBD) در يك راكتور صفحه به صفحه در سه سطح زمان و در سه سطح ولتاژ انجام گرفت. به منظور ارزيابي تغييرات ايجاد شده در ساختار كربن فعال از طيف بيني FT-IR و ميكروسكوپ روبشي الكتروني(SEM) استفاده شد. سپس قابليت حذف رنگ رودامين B از محلول آبي توسط كربن فعال اصلاح شده بررسي و نتايج با كربن فعال اصلاح نشده مقايسه شد. يافته­ ها: فعال­سازي شيميايي پيش ­تركيب­ها منجر به ساخت كربن­ هاي فعال با منافذ ميكرو شد. سطح ويژه و حجم حفرات كل كربن فعال حاصل از چوب سالم بيشتر از چوب پوسيده به دست آمد. بالعكس ظرفيت جذب رنگ رودامين كربن فعال تهيه شده از چوب پوسيده بيشتر بود. تغيير ولتاژ تاثير شگرفي بر ظرفيت جذب رنگ كربن­هاي اصلاح شده با پلاسما نداشت، با اين وجود بهبود 20 درصدي در شرايط اعمال ولتاژ kv 2 براي مدت زمان اصلاح دو دقيقه حاصل شد. با افزايش زمان اصلاح از ظرفيت جذب نمونه­ها كاسته شد. نتايج طيف­بيني FTIR نشان داد كه در اثر اصلاح كربن فعال با استفاده از روش پلاسماي سرد، گروه­هاي عاملي حاوي اكسيژن در سطح افزايش يافته و سطوح كربن ­فعال اندكي اسيدي شد. بهبود ظرفيت جذب كربن­هاي فعال اصلاح شده با پلاسما را به مي­توان به غني شدن سطح با همين گروه ­ها و در نتيجه افزايش جاذبه­ هاي الكترو استاتيكي و برهم­ كنش­ هاي واندروالسي با رنگ كاتيوني رودامين B نسبت داد. با توجه به تصاوير ميكروسكوپ روبشي تهيه شده مشاهده شد كه مرفولوژي سطوح كربن فعال در اثر تيمار با پلاسماي سرد تغيير نكرده است. نتيجه­ گيري: كربن فعال­هاي تهيه شده از پيش­ تركيب­هاي ليگنوسلولزي با منبع يكسان در صورتي­كه در معرض تخريب­هاي بيولوژيكي مثل پوسيدگي قارچي قرار گرفته باشند رفتار جذب متفاوتي در برابر رنگ­ها خواهند داشت. علاوه بر اين، عمل­آوري با پلاسماي سرد در شرايط بهينه ولتاژ و زمان تيمار مي­تواند روش اصلاح مناسبي به منظور افزايش ظرفيت جذب كربن فعال براي حذف آلاينده هاي رنگي مانند رودامين B در فاز مايع بدون ايجاد تغييرات قابل توجه در ساختار مورفولوژيكي آن باشد.

The large amounts of the dyestuffs used in industries are toxic and whenever are released into wastewaters can lead to environmental and health problems. One of the most commonly used dyes in industries is Rhodamine B. It is widely used in printing, leather, paper and textile industries and is harmful to both human beings and animals. Thus, it is necessary to treat contaminated wastewater prior to discharging into water streams. Among all conventional physical, chemical and biological methods, adsorption is a very simple and effective method for removing dyes from wastewater even at low concentration. Activated carbons (ACs) are among the most widely used efficient absorbents which can remove these pollutants from aqueous phase and cause to prevent damages to the environments. Specific surface area, pore volume, pore-size distribution and the nature of surface are the main factors that influence AC performance. The surface modifications result in the change in the surface reactivity, chemical, physical and structural properties. Based on the type and chemical nature of the dyes, the surface of AC can be modified to enhance the affinity toward the desired contaminants. Depending on the application, there are different methods to modify AC, which can be classified as chemical, physical and biological modification. Plasma treatment is an environmental friendly method, which can introduce functional groups onto material surfaces without changing the bulk properties of the substrate. Methods: Modification of AC surfaces by means of plasma is a well-known method to enhance its adsorption capacity. Hence, in this research AC was prepared using chemical activation method from sound (SBAC) and rotted (RBAC) beech wood (Fagus orientalis) as precursors. The impregnation was carried out by ZnCl2 with the ratio of 75 percent to precursor mass and carbonization was performed at activating temperature of 400 ºC. The potential of AC treatment by plasma was then examined to introduce oxygen-containing groups onto AC surfaces and to enhance its efficiency to remove a basic dye, Rhodamine B, from aqueous solution. After carbonization step, surface modification of activated carbons was then conducted by dielectric barrier discharge (DBD) plasma in a parallel- plate reactor under different conditions of voltages (2, 4, and 6 kv) and treatment time(20, 30, and 40 min). Specific surface area, average pore diameter and pore volume of ACs were characterized from the results obtained by N2 adsorption at 77 K. In order to evaluate structure changes in plasma modified-ACs the FT-IR spectroscopy and scanning electron microscopy (SEM) were also used. Then, the capability of modified-ACs in removing of Rhodamine B was assessed and was compared with untreated ones. The batch adsorption tests have been carried out in the laboratory by contacting a 100 ml of dye aqueous solution with 0.15g of AC. The adsorption capacity of Rhodamine B in aqueous solution was measured using UV-Vis spectrometer at 555 nm. Results: The results indicated that the iodine number of ACs prepared from sound wood (SBAC) was less than RBAC that indicate more development of micropores in RBAC. Activated carbons from sound wood exhibited more specific surface area (1538 m2g -1 ), total pore volume (0.649 cm3g -1 ) and less average diameter (1.69 nm) in comparison with RBAC. As it was expected, chemical activation of precursors by ZnCl2 could successfully develop micropores through dehydrating reactions. It was found that adsorption capacity of untreated ACs prepared from rotted beech wood was higher in comparison with sound wood ACs. This may be attributed to differences in chemical compositions of precursors, which results inThe large amounts of the dyestuffs used in industries are toxic and whenever are released into wastewaters can lead to environmental and health problems. One of the most commonly used dyes in industries is Rhodamine B. It is widely used in printing, leather, paper and textile industries and is harmful to both human beings and animals. Thus, it is necessary to treat contaminated wastewater prior to discharging into water streams. Among all conventional physical, chemical and biological methods, adsorption is a very simple and effective method for removing dyes from wastewater even at low concentration. Activated carbons (ACs) are among the most widely used efficient absorbents which can remove these pollutants from aqueous phase and cause to prevent damages to the environments. Specific surface area, pore volume, pore-size distribution and the nature of surface are the main factors that influence AC performance. The surface modifications result in the change in the surface reactivity, chemical, physical and structural properties. Based on the type and chemical nature of the dyes, the surface of AC can be modified to enhance the affinity toward the desired contaminants. Depending on the application, there are different methods to modify AC, which can be classified as chemical, physical and biological modification. Plasma treatment is an environmental friendly method, which can introduce functional groups onto material surfaces without changing the bulk properties of the substrate. Methods: Modification of AC surfaces by means of plasma is a well-known method to enhance its adsorption capacity. Hence, in this research AC was prepared using chemical activation method from sound (SBAC) and rotted (RBAC) beech wood (Fagus orientalis) as precursors. The impregnation was carried out by ZnCl2 with the ratio of 75 percent to precursor mass and carbonization was performed at activating temperature of 400 ºC. The potential of AC treatment by plasma was then examined to introduce oxygen-containing groups onto AC surfaces and to enhance its efficiency to remove a basic dye, Rhodamine B, from aqueous solution. After carbonization step, surface modification of activated carbons was then conducted by dielectric barrier discharge (DBD) plasma in a parallel- plate reactor under different conditions of voltages (2, 4, and 6 kv) and treatment time(20, 30, and 40 min). Specific surface area, average pore diameter and pore volume of ACs were characterized from the results obtained by N2 adsorption at 77 K. In order to evaluate structure changes in plasma modified-ACs the FT-IR spectroscopy and scanning electron microscopy (SEM) were also used. Then, the capability of modified-ACs in removing of Rhodamine B was assessed and was compared with untreated ones. The batch adsorption tests have been carried out in the laboratory by contacting a 100 ml of dye aqueous solution with 0.15g of AC. The adsorption capacity of Rhodamine B in aqueous solution was measured using UV-Vis spectrometer at 555 nm. Results: The results indicated that the iodine number of ACs prepared from sound wood (SBAC) was less than RBAC that indicate more development of micropores in RBAC. Activated carbons from sound wood exhibited more specific surface area (1538 m2g -1 ), total pore volume (0.649 cm3g -1 ) and less average diameter (1.69 nm) in comparison with RBAC. As it was expected, chemical activation of precursors by ZnCl2 could successfully develop micropores through dehydrating reactions. It was found that adsorption capacity of untreated ACs prepared from rotted beech wood was higher in comparison with sound wood ACs. This may be attributed to differences in chemical compositions of precursors, which results in