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Barium-Encapsulated Biodegradable Polycaprolactone for Sulfate Removal

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Barium-Encapsulated Biodegradable Polycaprolactone for Sulfate Removal water Article Barium-Encapsulated Biodegradable Polycaprolactone for Sulfate Removal Changseok Han 1,* and Mallikarjuna N. Nadagouda 2,* 1 Department of Environmental Engineering, Inha University, Incheon 22212, Korea 2 Center for Nanoscale Multifunctional Materials, Mechanical & Material Engineering, Wright State University, Dayton, OH 45431, USA * Correspondence: [email protected] (C.H.); [email protected] (M.N.N.); Tel.: +82-32-860-7505 (C.H.); +1-513-569-7232 (M.N.N.) Received: 14 September 2018; Accepted: 28 November 2018; Published: 6 December 2018 Abstract: Various compositions of barium carbonate (BaCO3) loaded polycaprolactone (PCL) composites were prepared, including 2.5/97.5, 10/90, 30/70, 50/50 and 90/10 (PCL/BaCO3), via re-precipitation technique. Small-scale column tests were conducted to study the efficiency of sulfate removal using the PCL/BaCO3 composites. The composites before and after their use to remove sulfate were extensively characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), and thermogravimetric analysis (TGA). As PCL is a biodegradable polymer, these composites are environmentally friendly and have several advantages over barium sulfate precipitation in overcoming clogging issues in filters or resins due to collection of natural organic matter (NOM). The media used in this study exhibited high capacity and was able to remove more than 90% sulfate from synthetic sulfate containing waters and NOM samples collected from the Ohio River. Keywords: barium sulfate; biodegradable polymer; polycaprolactone; environmental remediation; water treatment 1. Introduction Environmental remediation methods often employ the use of synthetic composites due to their enhanced material properties [1–5]. Sulfate is one of commonly found anions in sources of water supplies, due the presence of atmospheric sulfur dioxide and many high water-soluble minerals containing sulfate, such as sodium sulfate, potassium sulfate, and magnesium sulfate in the environment [6]. Recently, the removal of sulfate from drinking water has been targeted due to deleterious effects of sulfate on the environment [7,8]. Sulfates affect not only the environment but also human health. Abnormal changes resulting from sulfate consumption from drinking water may include diarrhea and dehydration. These ill effects are more prominent during infant years and decline with age [6]. Previously, a novel composite made of polyvinyl chloride (PVC) loaded with barium carbonate (BaCO3) was reported for sulfate removal [9]. The implementation of such a material in a small-scale column test (SST) yielded promising results. However, reports indicate that potential contamination and leaching from conventional plastic like PVC can pose a severe threat to human health and the environment [10,11]. Monomethyl-, dimethyl-, monobutyl-, and dibutyl levels have been found at values up to 291 ng Tin (Sn)/L, 49.1 ng Sn/L, 28.5 ng Sn/L, and 52.3 ng Sn/L, respectively, in drinking water distributed through PVC pipes [12,13]. Successful remediation must involve the reduction of hazardous materials without introducing any further complications. Although the previously synthesized PVC/BaCO3 composite [10] showed promising results, the necessity for a benign and environmentally friendly remediation method still exists [14]. Water 2018, 10, 1789; doi:10.3390/w10121789 www.mdpi.com/journal/water Water 2018, 10, 1789 2 of 13 TheWater 2018 hydrolytic, 10, x FOR PEER degradation REVIEW of several common polyesters has provided an attractive2 of 13 new platform for composite synthesis. In particular, polycaprolactone (PCL) has become a focus of various medicalThe hydrolytic device applications,degradation of including several common drug and polyesters bacterial encapsulationhas provided an [15 attractive,16], antimicrobial new film developmentplatform for composite [17], and synthesis. scaffolding In particular, in tissue po engineeringlycaprolactone [18 (PCL)]. PCL has exhibitsbecome a not focus only of various significant medical device applications, including drug and bacterial encapsulation [15,16], antimicrobial film biocompatibility but also undergoes slow degradation to produce harmless byproducts. Additionally, development [17], and scaffolding in tissue engineering [18]. PCL exhibits not only significant the glass transition temperature of −60 ◦C and a low melting temperature near 60 ◦C result in PCL’s biocompatibility but also undergoes slow degradation to produce harmless byproducts. substantialAdditionally, amorphous the glass thermoplastic transition temperature properties. of The−60 °C simple and a ring-opening low melting temperature polymerization near 60 synthesis °C makesresult this polymerin PCL’s matrix substantial attractive amorphous for nanocomposite thermoplastic formation. properties. PCL The shows simple significant ring-opening solubility at roompolymerization temperature in synthesis a gamut makes of solvents, this polymer including matr chloroform,ix attractive dichloromethane,for nanocomposite carbon formation. tetrachloride, PCL benzene,shows toluene, significant cyclohexanone, solubility at androom 2-nitropropane. temperature in Such a gamut strong of propertiessolvents, including of PCL make chloroform, it a suitable alternativedichloromethane, to PVC in thecarbon previously tetrachloride, reported benzene, facile toluene, synthesis cyclohexanone, of polymer/BaCO and 2-nitropropane.3 composites Such [7]. Instrong the presentproperties work, of PCL incorporation make it a suitable of barium alternative into a biodegradableto PVC in the previously and biocompatible reported facile polymer matrixsynthesis for removal of polymer/BaCO of sulfate from3 composites contaminated [7]. waters has been investigated. The porous nature of In the present work, incorporation of barium into a biodegradable and biocompatible polymer the PCL matrix promotes the use of such a material in column packing applications for environmental matrix for removal of sulfate from contaminated waters has been investigated. The porous nature of remediation. Several issues of previous schemes were addressed in the implementation of PCL. the PCL matrix promotes the use of such a material in column packing applications for environmental Primarily,remediation. hazardous Several and issues environmentally of previous damagingschemes were PVC addressed was replaced in thewith implementation PCL as a benign of PCL. matrix. Furthermore,Primarily, thehazardous easily acceleratedand environmentally hydrolytic damaging degradation PVC was elucidates replaced a with new PCL method as a forbenign barium sulfatematrix. (BaSO Furthermore,4) recovery the following easily accelerated its use in hydr theolytic column degradation studies. elucidates The resulting a new PCL method and for BaCO 3 compositebarium (PCL/Ba) sulfate (BaSO showed4) recovery significant following sulfate its use in removal the column capacity studies. similarThe resulting to that PCL observed and BaCO in3 the previouscomposite studies (PCL/Ba) [7]. The showed process significant of precipitation sulfate remo is shownval capacity in Scheme similar1. Concernsto that observed of wall in effects the in columnprevious applications studies [7]. were The addressed, process of andprecipitation the results is shown have beenin Scheme reported 1. Concerns in this work.of wall effects in column applications were addressed, and the results have been reported in this work. SchemeScheme 1. The 1. The phase phase change change from from barium barium carbonate carbonate to barium barium sulfate sulfate in inthe the polymer polymer composite composite on on passingpassing sulfate sulfate containing containing water. water. 2. Experimental2. Experimental Section Section 2.1. Synthesis2.1. Synthesis of Polymer of Polymer Composites Composites TenTen grams grams of of PCL PCL (Aldrich; (Aldrich; Mn Mn 70–90 70–90 kDa) kDa) was wasdissolved dissolved in tetrahydrofuran in tetrahydrofuran (THF) at 10.0% (THF) at 10.0%weight weight per per volume volume ratio. ratio. The solid The solidBaCO BaCO3 powder3 powder was added was to added the resulting to the resultingsolution. solution.The The heterogeneousheterogeneous mixture mixture was was agitated agitated by byan anIKA IKA Lab Lab Egg Egg compact compact mixer mixer to create to create a milky a milky slurry. slurry. Subsequently,Subsequently, 100 mL100 methanolmL methanol was was slowly slowly added added to to the the slurry. slurry. Finally, Finally, 100 100 mL mL ofof distilleddistilled water was was added to induce precipitation. added to induce precipitation. Following the complete addition of water, solid PCL/BaCO3 precipitates settled from the Following the complete addition of water, solid PCL/BaCO precipitates settled from the solution solution to yield a clear supernatant. The composite material 3was purified by decanting organic to yieldsolvents a clear and supernatant. washing three The times composite with distilled material water. was Various purified compositions by decanting prepared organic are shown solvents in and washingTable three 1. times with distilled water. Various compositions prepared are shown in Table1. Water 2018, 10, 1789 3 of 13 Table 1. Various PCL/Ba media compositions. Sample Composition PCL/Ba(2.5/97.5) Polycaprolactone 2.5 wt% + BaCO3 97.5 wt% PCL/Ba(10/90) Polycaprolactone 10 wt% + BaCO3 90 wt% PCL/Ba(30/70) Polycaprolactone 30
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