Synthesis of amine imprinted manganese ferrite and its application in the removal of free fatty acid from waste vegetable oil
Introduction
Crude vegetable oil obtained after extraction, heating, crushing or rendering contains some unwanted substances such as free fatty acids (FFAs) [1]. The presence of FFAs deteriorates the quality of vegetable oil, making it non-edible and unfit for some applications. Vegetable oil contains mainly triglyceride, which undergoes hydrolysis to form FFAs that imparts an unpleasant taste to the oil. FFA must be removed to improve the quality of vegetable oil and make it suitable for further use.
When vegetable oil is used for cooking, it loses quality with time due to heating, which leads to hydrolysis of triglyceride to form FFA in the oil [2]. The FFA formed impart unpleasant taste in the oil, reducing its quality to generate waste vegetable oil (WVO). The FFA content is a measure of the quality of vegetable, and a high amount of this is undesired. High FFA content can make vegetable oil rancid; moreover, consumption of vegetable oil with high FFA content is capable of increasing level of low-density-lipoprotein in the blood [3] and inducing harm to the human body.
A large volume of WVO is generated annually from domestic cooking and industrial processes. Presently, there is no specific use for WVO in most countries of the world. The generated WVO contributes to environmental waste, which is a challenge requiring attention. It is essential that WVO is treated to make it suitable for reuse instead of discarding it into the environment as waste. Developing the most appropriate method for the removal of FFA from WVO is of interest as most of the known methods have one challenge or the other. Previously reported methods include liquid-liquid extraction [4], physical deacidification [5], microbial [6] and membrane technology [7]. These methods have shown limitations like low selectivity, incomplete removal, and high cost of operation. However, adsorption is an efficient method in the separation of solute from a solvent, which might be effective in the removal of FFAs from vegetable oils.
The effectiveness of adsorption may be attributed to its high kinetic update, low-cost, environmental friendliness and selectivity [8]. Despite the effectiveness of adsorption, material development as adsorbent is a challenge. Most materials used as adsorbent include resin, activated carbon and functional polymers. Some of these materials are expensive and may not be easily regenerated for long term reuse. However, nanomaterial falls into the group of materials with potentials to serve as an effective adsorbent for effective adsorption process. Therefore, this study proposes the use of metal nanoparticle as a suitable adsorbent for the removal of FFA from WVO.
Metal nanoparticle is gaining interest in adsorption due to its unusual physicochemical properties compared to bulk metals and other materials [9]. The physicochemical properties include small size high stability; large surface area to volume ratio; high reactivity; photothermal and enhanced mechanical [10]. However, these properties can be improved by simple chemical or physical modification [11]. The large surface area to volume ratio has placed metal nanoparticle at an advantage as an adsorbent for the removal of FFA in a mixture. Iron oxide nanoparticle is a suitable example that falls into this category with compatibility, chemical stability and superparamagnetic actions [12]. However, iron oxide is limited with the formation of aggregates due to its oxidation in air, which reduces its capacity as adsorbent for molecules such as FFA.
In order to address this limitation, this work proposes the synthesis of manganese ferrite (MnFe2O4) via coprecipitation and its surface imprinting with amine functional group to produce amine imprinted manganese ferrite (MnFe2O4-DEA). The concept is to reduce aggregation as well as promote the removal of FFA in WVO as a result of interaction between the carboxylic group in FFA and the amine functionality imprinted on MnFe2O4-DEA nanoparticles. This method makes use of Adansonia digitata seed oil as a capping agent to control particle growth. Fatty acid composition of Adansonia digitata seed oil has been previously reported by Adewuyi et al. [13] to predominantly contain C18:1 (36.55%) and C18:2 (28.19%) fatty acids. The thin film of MnFe2O4 has been shown to have various properties such as size-dependent saturation magnetization [14], which has granted it application in adsorption studies [15, 16]. In order to improve on its properties, the coprecipitation of iron oxide with Mn was further surface imprinted with diethylenetriamine to form MnFe2O4-DEA. Diethylenetriamine was engraved on the nanoparticles to create MnFe2O4-DEA because the molecule of diethylenetriamine contains nitrogen atoms, which are a heteroatom with nonbonding electrons that can take part in chemical bonding with FFA.
Moreover, diethylenetriamine is a weak organic acid, which when present on the surface of MnFe2O4-DEA may impose an alkaline property that is capable of promoting ionic interaction in the form of acid (FFA) - base (MnFe2O4-DEA) interaction, which may lead to the removal of FFA from WVO. Therefore, MnFe2O4-DEA was synthesised and used for the removal of FFA from WVO. The use of MnFe2O4-DEA for the removal of FFA was carried out in a batch adsorption process where MnFe2O4-DEA was brought in contact with WVO at different time interval. The effect of variables such as operation temperature, the concentration of FFA, and weight of MnFe2O4-DEA was also determined to understand the efficiency of MnFe2O4-DEA.
Section snippets
Materials
Iron (III) chloride hexahydrate (FeCl3.6H2O), manganese (II) chloride tetrahydrate (MnCl2.4H2O), sodium hydroxide (NaOH), diethylenetriamine and all other chemicals used in this study were purchased from Aldrich Chemical Co., England. Melon oil (Citrullus colocynthis) used in this study was purchased from a market in Osogbo, Nigeria. The melon oil used in this study was continuously used for deep-frying until it became deteriorated with FFA value reaching 70 g kg−1 to become WVO. The FFA value
Synthesis of MnFe2O4-DEA
The FTIR result of MnFe2O4-DEA is shown in Fig. 1a. The spectrum revealed peaks describing the functional groups present in MnFe2O4-DEA. From the spectrum, the peak at 3446 cm−1 was ascribed to the presence of OH functional group, which may have been attached to the Fe ions. It may also account for the existence of moisture on the surface of MnFe2O4-DEA [19]. The peak at 1582 cm−1 was assigned to the bending vibration of OH group from H2O molecules attached to Fe ions [20]. The peak at 3446 cm−1
Conclusions
Developing a means for the removal of FFA in WVO is a challenge. This study responded to this challenge by synthesising MnFe2O4-DEA via coprecipitation method as a means for removing FFA in WVO. The synthesised MnFe2O4-DEA was characterized using FTIR analysis, which revealed the presence of unique peaks due to the MnFe2O4-DEA. The XRD of MnFe2O4-DEA confirms the formation of manganese ferrite particle with a pattern relatively similar to crystalline spinel. The BET isotherm for MnFe2O4-DEA is
Credit author statement
Yusuf Adedoyin A: Investigation, formal analysis
CRediT authorship contribution statement
Adewale Adewuyi: Conceptualization, Visualization, Funding acquisition, Formal analysis, Writing - review & editing. Adedoyin A Yusuf: Funding acquisition, Formal analysis, Writing - original draft. Woei Jye Lau: Funding acquisition, Writing - review & editing. Mirabbos Hojamberdiev: Funding acquisition, Writing - review & editing. Rotimi A Oderinde: Conceptualization, Visualization.
Declaration of Competing Interest
The authors declared no potential conflicts of interest with respect to the research, authorship, and publication of this article.
Acknowledgements
Authors are grateful to the Department of Chemical Sciences, Redeemer's University, Nigeria for provision of research space and chemicals.
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