Synthesis and characterization of a porous and hydrophobic cellulose-based composite for efficient and fast oil–water separation
Introduction
Every year a large volume of oily wastewater is produced from various process industries (Pagidi, Saranya, Arthanareeswaran, Ismail, & Matsuura, 2014). With the characteristics of extensive sources, complex components and poor biodegradability, oily wastewater causes great harm to ecosystems (Gao et al., 2014). Therefore, oil substances must be substantially removed from the water before discharge in order to prevent the deleterious impact on ecosystems and meet progressively more stringent environmental regulations (Barron, 2012, Dalton and Jin, 2010, Montgomery and Elimelech, 2007, Schrope, 2011, Shannon et al., 2008).
Many methods have been developed to solve the problem, but in which some traditional ones, such as dissolved air flotation (Al-Shamrani, James, & Xiao, 2002), flocculation (Yang et al., 2015) and oil skimmers (Nordvik, Simmons, Bitting, Lewis, & Strøm-Kristiansen, 1996) usually have disadvantages of low separation efficiency and high operation cost. Therefore, a variety of separation materials are further developed to overcome these disadvantages. Some meshes (An et al., 2014, La et al., 2011, Liao et al., 2014, Xu et al., 2014, Yin et al., 2014) with superhydrophilicity and superoleophobicity can permeate oil while completely repelling water, and are put effectively into use for oil–water separation. Besides, some synthetic coatings, including inorganic nanoparticles (Chen, De Leon, & Advincula, 2015), polymers (Liu et al., 2015, Xue et al., 2013) and organic/inorganic nanocomposites (Gondal et al., 2014, Li et al., 2014) were used to modify the meshes to achieve a good oil–water separation efficiency of 98–99%. Although the synthetic materials can well separate the oil–water mixture, they are environmentally unfriendly, and may further lead to secondary pollution.
Recently, some biodegradable separation materials are reported, in particular based on cellulose (Mansourizadeh and Azad, 2014, Rohrbach et al., 2014, Zhou et al., 2013). Cellulose/polyvinylidene fluoride-co-hexafluoropropylene membranes were prepared for gasoline/water separation via electro-spinning and direct coating technique (Ahmed, Lalia, Hilal, & Hashaikeh, 2014). Wang and Lin (2013) fabricated a cellulose sponge with stable wettability of superoleophobicity under water and superhydrophilicity under oil which can remove crude oil from water. Ma, Kang, and Cui (2014) reported a separator using glass microfiber as coalescence medium for diesel oil/water separation. However, only a few reports focused on the separation of different types of oil–water mixture including vegetable oil–water mixture (Liu et al., 2014, Pintor et al., 2014). Till now, it still remained unclear how modified cellulose could affect separation selectivity among different oil–water mixtures. Besides, there has been more interest in cellulose-based superfast separation materials.
In this work, we presented a simple method to fabricate hydrophobic silanized cellulose by biodegradable microcrystalline cellulose (MCC) and hexadecyltrimethoxysilane (HDTMS) with long alkyl chain. Besides of rough structure caused by SiO2 nanoparticles via sol–gel reaction, porous network was formed by condensation reaction between MCC and HDTMS. To the best of our knowledge, no work has been reported on such hydrophobically modified porous MCC with HTDMS used for efficient and fast oil–water separation. These findings would provide a new insight to design oil–water separation materials.
Section snippets
Materials
Sodium hydroxide (NaOH), thiocarbamide (CH4N2S), n-hexane and acetone were analytical reagents and purchased from Zhiyuan Chemical Reagent Co. Ltd. (Tianjin, China). HDTMS and Oil Red O were obtained from Aladdin Reagent Co. Ltd. (Shanghai, China). MCC (molecular weight: 36,000) was provided by Hengxin Chemical Reagent Co. Ltd. (Shanghai, China). Methylene Blue was obtained from Shengmiao Chemical Reagent Co. Ltd. (Tianjin, China). Gasoline and diesel oil were purchased from PetroChina
The sol–gel reaction
In this study, preparation of silanized cellulose via the sol–gel method includes the hydrolysis and condensation of HDTMS in MCC solution. When HDTMS was mixed in alkaline MCC solution, hydrolysis reaction took place and three methoxyl groups of HDTMS were converted into hydroxyl groups, liberating methanol as a by-product. It is believed that methanol helps the HDTMS to be fully dissolved into water (Sankaraiah et al., 2008), thus promoting the hydrolysis reaction. With HCl added,
Conclusions
A simple approach was developed to fabricate porous and hydrophobic silanized cellulose by sol–gel reaction of HDTMS in cellulose solution. The silanized cellulose received efficient and fast oil–water separation only for vegetable oil–water mixture, not for mineral oil–water mixture. The separation efficiency reached up to 99.93% while water flux was as high as 4628.5 L m−2 h−1. The excellent separation performance was resulted by the porous structure and specific hydrophilic–hydrophobic property
Acknowledgments
The authors would like to thank Xinjiang Uygur Autonomous Region Science and Technology Project (201415101) and NSFC-Xinjiang Joint Fund for Local Outstanding Youth (U1403392) for the financial support of this work.
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