Investigation of Interaction Between Phenol and Cetylpyridinium Chloride Micelle in the Absence and in the Presence of Electrolyte by 1H NMR Spectroscopy
Total Page：16
File Type：pdf, Size：1020Kb
Colloids and Surfaces A: Physicochem. Eng. Aspects 356 (2010) 150–155 Contents lists available at ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa Investigation of interaction between phenol and cetylpyridinium chloride micelle in the absence and in the presence of electrolyte by 1H NMR spectroscopy Ke Xu a, Hong-qiang Ren a,∗, Guang-ming Zeng b, Li-li Ding a, Jin-hui Huang b a State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, Jiangsu, PR China b College of Environmental Science and Engineering, Hunan University, Changsha 410082, Hunan, PR China article info abstract Article history: In recent years, the micellar enhanced ultrafiltration (MEUF) of phenol in wastewater using cetylpyri- Received 3 December 2009 dinium chloride (CPC) as surfactant has gained many attentions. However, so far no research has focused Received in revised form 2 January 2010 on the interaction between phenol and CPC micelle. In this study, the interaction between phenol and CPC Accepted 6 January 2010 micelle with and without electrolyte was investigated by using 1H NMR spectroscopy. In the absence of Available online 13 January 2010 electrolyte, at low phenol concentrations (0.5 mM and 1 mM) phenol was solubilized at the micelle–water − + interface by the ion interaction between C6H6O and C5H5N , and in the hydrophilic head group region Keywords: of CPC micelle by the polar interaction between phenol and CPC micelle. When phenol concentration Phenol range was from 1 mM to 8 mM, the micelle–water interface and the hydrophilic head group region of CPC CPC − Electrolyte micelle saturated with C6H5O and phenol, then phenol penetrated into the palisade layer deeper but was Micelle still close to the hydrophilic head group of CPC micelle. The presence of NaCl and Na2SO4 had almost no Solubilization influence on the solubilization of phenol in CPC micelle, however, the presence of Na2CO3 promoted the − Interaction solubilization of phenol in CPC micelle significantly. In the presence of Na2CO3, more C6H5O ions were − + solubilized at the water–micelle interface by the ion interaction between C6H6O and C5H5N .Atlow − Na2CO3 concentration the micelle–water interface of CPC micelle saturated with C6H5O , and benzene ring penetrated into the palisade layer of CPC micelle, but deeper penetration was not observed with the 2− − increase of Na2CO3 concentration. Excessive CO3 could make some C6H5O transfer from CPC micelle to water, resulting in the decrease of the solubilization extent of phenol in CPC micelle. © 2010 Elsevier B.V. All rights reserved. 1. Introduction and water of hydration. Solubilization is known to occur at four sites in micelle: (i) at the micelle–water interface, (ii) between the In recent years, the micellar enhanced ultrafiltration (MEUF) has hydrophilic head groups, (iii) in the palisade layer of the micelle, been studied as a viable alternative technique which is effective and namely, between the hydrophilic groups and the first few carbon economical to remove phenol in wastewater. In MEUF of phenol, atoms of the hydrophobic groups that comprise the outer core of the phenol in aqueous solution is solubilized by micelle of surfactant micelle interior, and (iv) in the inner hydrophobic core of micelle then an appropriate ultrafiltration membrane is employed to reject [6]. These solubilization sites can be determined by using nuclear both micelle and phenol. Therefore, the ability of micelle to sol- magnetic resonance (NMR) [7], ultraviolet (UV) spectroscopy [8], ubilize phenol has a key influence on the performance of MEUF and X-ray diffraction [9]. NMR chemical shifts depend on the molec- of phenol. Until now many researches about the MEUF of phenol ular environment of the nuclei, so changes in chemical shifts of in aqueous stream have been conducted [1–5], but they have not surfactants as a function of solubilizate concentration provide pre- focused on the interaction between phenol and micelle. cise information on the location of a solubilizate with respect to the The location in the micelle where the solubilization of phenol micelle nuclei. In the field of colloid and interface science, some occurs can reflect the type of the interaction between micelle and researches have been conducted to investigate the solubilization phenol, and the ability of micelle to solubilize phenol. Generally, sites of phenol in micelles by using NMR. Suratkar and Mahapatra micelle consists of two parts: one is the core of micelle which is [6] investigated the site of incorporation of phenol in sodium dode- composed of hydrophobic hydrocarbon chains; the other is the cyl sulfate (SDS) micelle by 1H NMR spectroscopy and concluded surface of micelle which is composed of hydrophilic head groups that at higher concentration phenol penetrates into the palisade layer of SDS micelle. Jacobs et al. [10] using 1H NMR spectroscopy concluded that phenol orients itself in anionic SDS micelles in such ∗ Corresponding author. Tel.: +86 025 83596781; fax: +86 025 83707304. a manner that the hydroxyl group is close to the polar surface. Mata E-mail address: [email protected] (H.-q. Ren). et al. [11] studied a phenol-induced structural transition in aque- 0927-7757/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2010.01.011 K. Xu et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 356 (2010) 150–155 151 ous cetyltrimethyl ammonium bromide (CTAB) solution by using To investigate the interaction between phenol and CPC micelle, 1H NMR and considered that phenol is located at micelle–water the CPC concentration was fixed at 20 mM and the phenol con- interface and do not penetrate the micellar core even at high con- centration varied to be 0.5 mM, 1 mM, 2 mM, 3 mM and 8 mM. centrations of phenol. Chaghi et al. [12] studied the interaction of To investigate the interaction between phenol and CPC micelle in phenol with cationic micelles of CTAB by 1H NMR in the range of the presence of electrolyte, the CPC concentration and the phenol low additive and surfactant concentrations, and concluded that the concentration were 20 mM and 2 mM, and the concentrations of preferential location of phenol is in the outer micelle parts then Na2CO3, NaCl and Na2SO4 were the same (10 mM). It was further additional phenol molecules are located increasingly deeper within investigated the interaction between phenol and CPC micelle in the micelle core. the presence of Na2CO3 from the dependence of chemical shifts on In the most of researches about the MEUF of phenol, CPC was Na2CO3 concentration. When the CPC concentration and the phenol usually used to form micelle to solubilize phenol. In our previous concentration were 20 mM and 2 mM, the Na2CO3 concentration work [13], in order to promote the performance of MEUF of phe- varied to be 1 mM, 3 mM, 5 mM, 10 mM and 20 mM. nol, electrolyte including sodium chloride (NaCl), sodium sulfate The size of CPC micelle in the presence of Na2CO3, NaCl and (Na2SO4) and sodium carbonate (Na2CO3) was added into the phe- Na2SO4 had been determined by DLS (Dynamic light scattering) nol/CPC system. Compared with NaCl and Na2SO4,Na2CO3 could with Zetasizer Nano-Zs (Malvern Instruments, UK). improve the performance of MEUF of phenol greatly. As a result, the aim of this study is to investigate the interaction between phe- 3. Results and discussion nol and CPC micelle with and without electrolyte by using 1HNMR. 1 H NMR studies primarily focused on elucidating the nature of the Fig. 1 represents the 1H NMR spectra of CPC with and with- interaction between phenol and CPC micelle, and the solubilization out phenol. It is shown seven proton signals of CPC in 1HNMR site of phenol in CPC micelle, mainly from the dependence of chem- spectrum: (a, a)-CH, (b, b)-CH and c-CH, ␣- and -methylene, ical shifts of all the CPC protons on phenol or Na2CO3 concentration. 13 bulk methylene as well as the terminal methyl proton (–CH3). Interestingly, the 13 bulk methylene protons of CPC resolved 2. Materials into two well-defined peaks. The downfield signal of this doublet was assigned to the two methylene groups (␥-(CH2)2) which are  The cationic surfactant cetylpyridinium chloride (CPC) attached to the -methylene group; the upfield signal was assigned (purity > 99%) was purchased from Sinopharm Chemical to the 11 methylene groups ( -(CH2)11) which are attached to the Reagent Co., Ltd. (Shanghai, China) and recrystallized twice terminal methyl group. The signals of CPC except -(CH2)11 and from ethanol/acetone (weight ratio of 1:3). The CMCs of CPC in –CH3 were found to shift to the upfield in the presence of phenol. This phenomenon indicated that the presence of phenol changed H2O and D2O were 0.91 mM and 0.66 mM determined by using surface tension method at 25 ◦C. Phenol and electrolytes were the molecular environment of CPC nuclei. Ring current-induced 1 analytical pure and not further purified. shifts of the H resonance signals of micelles have been admitted as the evidence for the interaction between aromatic molecules and micelles [6,11,12,14]. Further experiments show details. 2.1. Instrument and methods As shown in Fig. 2, in the presence of increasing concentrations of phenol, all group protons of CPC except -(CH2)11 and –CH3 shift 1 H NMR spectra were recorded on a Varian INOVA400 apparatus to higher magnetic field but to varying extents, whereas -(CH2)11 ◦ in D2Oat25± 0.5 C. Chemical shifts were obtained in ı unit (ppm). and –CH3 remain downfield shifts. For chemical shift measurements, a carbon tetrachloride solution Fig. 3 shows the dependence of shift extents (ı0–ı) of all the CPC of tetramethylsilane (10%) contained in a capillary was used as an protons on the phenol concentration.