Fındık ve ceviz kabuğundan üretilen aktif karbon ile diklofenak sodyum, siprofloksasin ve sülfametoksazol adsorpsiyonunun incelenmesi = Investigation of the adsorption of diclofenac sodium, ciprofloxacin and sulfahmetoxazole by activated carbon produced from hazelnut and walnut shell

Abstract

Ülkemiz fındık ve ceviz üretiminde önemli bir paya sahip olmakta ve buna bağlı olarak yüksek miktarda fındık ve ceviz kabuğu ortaya çıkmaktadır. Fındık ve ceviz kabukları düşük maliyete sahip olmaları, yerel olarak büyük miktarlarda mevcut olmaları ve her yıl yenilenebilir olmaları gibi avantajlara sahiptir. Dolayısıyla aktif karbon üretiminde hammadde olarak kullanılmaları ve bu şekilde ekonomiye kazandırılmaları önem arz etmektedir. Bu çalışmanın amacı, fosforik asitle aktive edilmiş fındık (HSAC) ve ceviz (WSAC) kabuğu karbonunun sulu çözeltilerden ve atık sulardan diklofenak (DC), siprofloksasin (CIP) ve sülfametoksazol (SMX) giderimindeki etkinliğini belirlemektir. HSAC ve WSAC'nin karakterizasyon çalışmaları yüzey alanı, gözenek boyutu dağılımı, elementel, FT-IR, SEM ve termogravimetrik analizler gibi çeşitli analitik işlemlerle yapılmıştır. HSAC ve WSAC'nin adsorpsiyon özelliklerinin belirlenmesi amacıyla, DC, CIP ve SMX'i sulu çözeltilerden ve atık sulardan uzaklaştırma yetenekleri başlangıç konsantrasyonu, temas süresi, pH, adsorban dozu ve sıcaklık gibi çeşitli parametrelerle test edilmiştir. SEM çalışmaları, HSAC ve WSAC yüzeyinin çeşitli boyut ve şekillerde çok sayıda düzensiz çukur içerdiğini göstermiştir. HSAC ve WSAC'nin BET yüzey alanları sırasıyla 1173 m 2 g -1 ve 1428 m 2 g -1 olarak bulunmuş, WSAC'nin daha büyük bir yüzey alana sahip olduğu belirlenmiştir. DC, CIP ve SMX'in adsorpsiyon dengesini modellemek için Langmuir, Freundlich, Temkin ve Dubinin-Radushkevich izotermleri kullanılmıştır. HSAC ile elde edilen maksimum adsorpsiyon kapasiteleri DC, CIP ve SMX için sırasıyla 125, 95.2 ve 285.7 mg g -1 ; WSAC ile elde edilen maksimum adsorpsiyon kapasiteleri DC, CIP ve SMX için sırasıyla 135.1, 185.2 ve 476.2 mg g -1 olarak hesaplanmıştır. Yapılan incelemeler ile DC, CIP ve SMX adsorpsiyonunun Langmuir izoterm modeli ile uyumlu olduğu sonucuna varılmıştır ve bu durum monomoleküler yani tek tabakalı adsorpsiyonun baskın olduğunu göstermiştir. Adsorpsiyon mekanizmasının kinetik davranışının değerlendirilmesi sonucunda, yalancı ikinci dereceden modelin DC, CIP ve SMX adsorpsiyonu için en uygun kinetik model olduğu belirlenmiştir. Termodinamik çalışmalar, DC, CIP ve SMX'in HSAC ve WSAC ile adsorpsiyonunun kendiliğinden ve endotermik olduğunu ortaya koymuştur. Kentsel atık su arıtma tesisi çıkış atık suyundan alınan numunelerde HSAC ile yapılan adsorpsiyon çalışmaları sonucunda elde edilen giderim verimleri DC, CIP ve SMX için sırasıyla %61.9, %54.2 ve %63.1; WSAC ile yapılan adsorpsiyon çalışmaları sonucunda elde edilen giderim verimleri DC, CIP ve SMX için sırasıyla %74.2, %77.4 ve %60.2 olarak olarak bulunmuştur. Sonuç olarak, HSAC ve WSAC'nin atık sulardan DC, CIP ve SMX giderimi için kolay bulunabilir, çevre dostu ve etkili birer adsorban olduğu ifade edilebilir.

Since hazelnuts and walnuts are produced in significant quantities in Turkey, large quantities of hazelnut and walnut shells occur every year. Cheap, locally accessible agricultural byproducts are favored for the synthesis of activated carbon (AC) to reduce commercial AC production costs. Hazelnut shell (HS) and walnut shell (WS) might be considered as acceptable precursors for AC manufacturing due to their low cost, local availability in large quantities, and renewability year after year. Other advantages of HS and WS include low economic value compared to various precursors used in AC manufacturing, no labor required for harvesting as they are field ready material, and long-term storage without deterioration. As a result, it is critical to convert discarded hazelnut and walnut shells into value-added materials and investigate their adsorption capacities for the removal of various contaminants from wastewater. The purpose of this study is to test effectiveness of phosphoric acid-activated hazelnut (HSAC) and walnut (WSAC) shell carbon for the adsorption of diclofenac (DC), ciprofloxacin (CIP), and sulfamethoxazole (SMX) from aqueous solutions and wastewater. Characterization of HSAC and WSAC was carried out using several techniques including proximate analysis, elemental analysis, Brunauer-Emmett-Teller (BET) surface area measurement, scanning electron microscopy (SEM) images, and Fourier-transform infrared spectroscopy (FT-IR). The impact of pH, contact time, dosage, initial concentration, and temperature on batch adsorption of DC, CIP, and SMX by HSAC and WSAC was investigated. The adsorption kinetics of DC, CIP, and SMX were studied using pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetic models. The adsorption equilibrium of DC, CIP, and SMX onto HSAC and WSAC was studied using Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models. The adsorption thermodynamics of DC, CIP, and SMX onto HSAC and WSAC were also calculated to assess the changes in free energy (ΔG), enthalpy (ΔH) and entropy (ΔS). For the production of HSAC and WSAC, the hazelnut and walnut shells were cleaned with deionized water, dried overnight at 105°C, then crushed to a size of 1- 1.5 mm using a steel blender. Then, equal parts of H 3 PO 4 and HS or WS (150 g) were added to 150 mL deionized water. The suspensions were kept in in a water bath at 80°C and then, dried at 105°C overnight. The impegrenated materials were then pyrolyzed at 600°C under N 2 gas flow (100 mL min –1 ) in the tube furnace. The pyrolized samples in the furnace were cooled down to ambient temperature under N 2 gas flow (100 mL min –1 ). Then, the samples were cleaned with hot deionized water. To remove any remaining acid in the products, they were submerged in a 1% NaHCO 3 solution overnight. Then, the products were washed with hot deionized water until the pH of the washing water reached 7.0. The produced AC's were dried at 105°C for 24 h, sieved to a particle size of 250-500 µm, and then stored in brown glass vials for use in the following studies. A variety of analytical techniques, including BET surface area measurement, pore size distribution, C, H, N elemental analysis, FT-IR, SEM, and thermogravimetric analysis were used to carry out the characterization studies of HSAC and WSAC. Proximate analyses of HSAC and WSAC were performed according to the requirements of the American Society for Testing and Materials (ASTM). FTIR measurements between 450 and 4,000 cm -1 were used to identify the functional groups on the surface of the HSAC and WSAC. N 2 adsorption-desorption isotherms at 77 K were used to compute the multipoint surface area of the HSAC using the BET method. The surface morphology of HSAC and WSAC was examined using SEM images. The pH pzc values of HSAC and WSAC were experimentally determined. Lactonic, phenolic, and carboxylic groups in the HSAC and WSAC were calculated after Boehm titration. Batch experiments were used to assess the adsorption dynamics of DC, CIP, and SMX with HSAC and WSAC. The effects of variables including contact time, initial concentration of DC, CIP and SMX, HSAC and WSAC dosage, pH of the aqueous phase and temperature were performed. Individual aqueous solutions of DC, CIP and SMX (50 mL) were used in the batch adsorption experiments. An exact quantity of HSAC/WSAC was poured into the DC, CIP, and SMX solution at a certain concentration, and the suspensions were then shaken for a predefined period of time at 25°C (except of temperature effect experiments). A known amount of HSAC/WSAC was added to the DC, CIP and SMX solution at definite concentration and then the suspensions were shaken for predetermined time at 25°C (except of studies on the temperature effect). Following that, centrifugation was used to separate the suspensions. To determine equilibrium concentrations of DC, CIP and SMX in the supernatant phase, a UV-vis spectrophotometer was employed for DC and CIP at 276 nm, and SMX at 265 nm. The characterization results showed that HSAC and WSAC had ash contents of 13.5% and 11.9, respectively. High concentrations of activating agents and the inorganic content of hazelnut and walnut shells may be the cause of the high ash content. HSAC and WSAC were found to have 6.4% and 10.4% moisture, respectively. The amounts of volatile matter in HSAC and WSAC were calculated to be 10.9% and 17.8%, respectively. HSAC includes 81.1% C, 1.6% H, and 1.1% N, while WSAC has 71.6% C, 1.6% H, and 1.1% N, according to the results of the elemental analysis. The pH pzc of HSAC and WSAC were calculated to be 4.24 and 4.26, respectively. In the N 2 adsorption/desorption isotherm results of HSAC and WSAC, the obtained isotherms demonstrated hysteresis in I(b) and H4 according to IUPAC classification. Type I(b) isotherms have been identified for materials having a broader pore-size distribution, such as bigger micropores and possibly narrow mesopores (2.5 nm). In micro mesoporous carbons, H4-type hysteresis has been commonly documented. According to the pore-size distribution plots, HSAC and WSAC exhibit small pore- size distributions. HSAC and WSAC BET surface areas were calculated to be 1173 m 2 g -1 and 1428 m 2 g -1 , respectively. Batch adsorption studies on the DC, CIP and SMX using HSAC and WSAC showed that the adsorptions reached to equilibrium at 1440 min. Adsorbed amounts of DC, 30 CIP and SMX per gram HSAC and WSAC incresed by increasing of initial concentrations of DC, CIP and SMX. The removal of DC, CIP and SMX from real wastewater collected from the effluent of the urban wastewater treatment plant in Sakarya, Turkey was found to be 61.9%, 54.2% and 63.1% using HSAC, and 74.2%, 77.4% and 60.2% by WSAC, respectively. The adsorption equilibrium of DC, CIP and SMX onto HSAC and WSAC was modeled using Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms equations. The maximum adsorption capacities obtained with HSAC were 125.0, 95.2 and 285.7 mg g -1 for DC, CIP and SMX, respectively; the maximum adsorption capacities obtained with WSAC were calculated as 135.1, 185.2 and 476.2 mg g -1 for DC, CIP and SMX, respectively. It was also concluded that DC, CIP and SMX adsorption onto HSAC and WSAC were compatible with the Langmuir isotherm model and monolayer adsorption was dominant. As a result of the evaluation of the kinetic behavior of the adsorption mechanism, it was determined that the pseudo- second order model was the most suitable kinetic model for DC, CIP and SMX adsorption on the HSAC and WSAC. Thermodynamic studies showed that DC, CIP and SMX adsorptions onto HSAC and WSAC were spontaneous and endothermic. The obtained results in this study showed that HSAC and WSAC could be accepted as low-cost, efficient, easily accessible and environmentally friendly adsorbents for the treatment of wastewater containing DC, CIP and SMX.