Bull. Mater. Sci. (2020) 43:7 © Indian Academy of Scienceshttps://doi.org/10.1007/s12034-019-1981-3

Candle soot-coated egg carton material for oil water separationand detergent adsorption

PUNEET AZAD1,∗ , SAMRIDDHI RAUT1 and RAHUL VAISH2

1Department of Electronics and Communication Engineering, Maharaja Surajmal Institute of Technology,New Delhi 110058, India2School of Engineering, Indian Institute of Technology, Mandi 175 001, India∗Author for correspondence (puneet.azad@msit.in)

MS received 29 March 2019; accepted 4 July 2019

Abstract. A hydrophobic and superoleophilic adsorbent was prepared by coating candle soot (CS) on the surface of arecycled egg carton material (ECM). This waste material has been explored as a cost-effective adsorbent to remove oiland detergent from water. The surface of the material was coated with CS solution prepared by mixing soot with acetoneand characterized by scanning electron microscopy and contact angle measurements. The rate of fall of contact angle forwater and oil was evident of water rejection and oil absorption capability of the coated-waste material. Further, the effectof temperature on the contact angle between water and surface was observed. The carbon-coated ECM demonstrates goodabsorption capacity with oils of different densities, without pre-treatments and surface modifications. It also shows itscapability to absorb detergent from water with a pH value declining towards 7. Thus, a waste material can act as an effectivealternative for filtering of oil and detergent water for households and industries.

Keywords. Oil water separation; detergent adsorption; candle soot.

1. Introduction

Oil spills in the past have been biggest challenges for the sur-vival of marine life resulting in millions of oil and methanedischarge followed by dispersants in water [1,2]. Severalemergency measures have been taken for oil recovery andremoval including the use of low-density materials such aspolypropylene and hydrophobic nanocellulose aerogels as oilabsorbents [3,4]. Special superhydrophobic, superoleophilicand superoleophobic materials with stimulated wettabilityhave been used for oil–water separation [5,6]. Several materi-als such as carbon, copper, gold, octadecyltrichlorosilane andsilica nanoparticles have been used for fabricating carbon nan-otube (CNT) meshes, aerogels, steel meshes and polystyrenefor efficient oil–water separation and clean up [7–12]. How-ever, new eco-friendly and facile sorbent materials with goodabsorption capacity should be developed to meet the growingenvironmental needs. In particular, carbon-based materialssuch as CNTs, graphene and candle soot (CS) have been usedin a variety of applications such as electrode materials, lubri-cants and their additives, actuators, etc. [13–19].

These materials have also been successfully applied insuperhydrophobic and superamphiphobic coatings, as high-absorbance materials for solar collectors, and as adsorbentsfor various organic molecules, pollutants and dyes [19–26].

Among these materials, carbon has been widely exploredfor the separation of oil and water by processing various typesof sponge and foams [11,27–30]. These foams have excellent

repeatability leading to excellent performance. Active carbonhas been used for removing toxic chemicals in water filtra-tion systems during reverse-osmosis [31]. Further in orderto reduce the cost and discover eco-friendly solutions, it isimportant to explore new material systems. CS has recentlyreceived much attention and has been reported for variousapplications such as electrode materials for batteries and manymore solutions as a rich source of carbon. The use of CS mayreduce the cost. On the other hand, recycled paper used for eggpackaging and transportation is being produced drastically onthis planet. Its functional applications are not widely explored.Here, we report the fabrication of CS-coated egg carton mate-rial (ECM) and its utilization in separating oil from waterand detergent adsorption. The egg carton is manufactured byrecycling waste materials like newspaper, wrapping and officepaper and cardboard container. It was first invented in 1911in British Columbia and developed by H. G. Bennett during1950s [32]. The waste paper is hinged on a pulping machineto produce the pulp and aluminium is selected as the cast-ing material for the production of egg cartons. This articledeals with some of the water cleaning studies using ECM/CScomposition.

2. Experimental

The typical schematic of collection of CS is shown infigure 1. The CS-coated ECM was prepared by dip coating

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Figure 1. (a) Candle flame to synthesize soot and (b) collection of CS.

Figure 2. Fabrication process of the ECM.

Figure 3. SEM images of the CS: (a) uncoated and (b) coated ECM.

of the ECM in acetone. A quantity of 30 mg of CS wasmixed in 100 ml of acetone solution followed by 30 minof sonication. The ECM was dipped in CS–acetone solu-tion and left for 10 min as shown in figure 2. It was thendried under a 50 W IR lamp (Phillips) at 75 ◦C. The preparedECM was analysed using a field emission-scanning electron

microscope (FE-SEM) InspecTM S50 instrument. Contactangles between water/oil and ECM surface were measuredusing a high-resolution camera. Contact angles were alsoobserved between water and ECM at different temperatures.The ECM was further immersed in different oils such aspetrol, diesel, refined oil, coconut, engine and mustard oil

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Figure 4. Visual representation of hydrophobic and oleophilic nature of the CS-coated ECM at different time scales.

Figure 5. (a) Contact angle vs. time plot for water, (b) contact angle vs. time plots for refined oil, (c) temperature-dependent contact angle of water for the ECM and (d) variation of the contact angle for water with temperature for thecoated sample.

for absorption measurement until saturation. The absorptioncapacity (k) also known as the weight-gain ratio of the ECMwas calculated as:

k = (Wsaturated − Winitial)/Winitial (1)

where Winitial and Wsaturated absorption are the weights of theECM before and after oil absorption. To separate a deter-gent from water, the ECM was dipped in detergent waterand a change in pH was recorded. It is to note that pH canbe used to quantify detergent content in water. Detergent

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Figure 6. Oil–water separation process.

Figure 7. Oil–water separation using egg carton.

content of water can also be measured by other techniques. Inone of the recent studies, diesel soot-coated fabric was studiedfor oil–water separation, absorption of detergents, dyes andin pharmaceuticals [33]. Phenolphthalein was added initiallyin detergent water which turned pink and became colourlessshowing the adsorption of detergents using diesel soot. Simi-lar experiments can be performed using a CS-coated materialfor removing detergents and chemicals from water in thefuture study.

3. Results and discussion

The ECM surface morphology was studied using SEM.Figure 3 presents typical images for uncoated and coatedECMs. It is clearly noticed that the CS particles are distributedon the surface of the ECM. The open structure of the ECMis also clearly visible which is desirable for adsorption andseparation processes. The ECM was examined for hydropho-bicity and oleophilicity as shown in figure 4a–j. Water wasdropped over the surface of the coated ECM which remainedon the surface in a spherical shape having a contact angleof 142.2◦ as shown in figure 4a. Contrary, oil immediatelyspread and absorbed on the surface of the material with aninitial angle of 43.1◦ (figure 4f). After a duration of 133 min,the contact angle decreases to 33.3◦ (figure 4e). Also, theoleophilic behaviour was proven from the immediate fall ofthe contact angle within 6 s as shown in figure 4f–j, makingit suitable for oil–water separation. The impact of CS coat-ing on the ECM was studied by recording the contact anglebetween water drop and the ECM as shown in figure 5a. Thecontact angle between water and the coated ECM droppedfrom 100 to 80◦ in 80 min. The same drop is much bigger inthe case of the uncoated ECM and observed to be from 70to 20◦ in 80 min as shown in figure 5a. Thus, the CS greatlyenhances the hydrophobicity of the ECM and retains waterfor longer durations. Also, the contact angle for oil in thecoated sample falls quite faster from 35 to 14◦ in 5 s com-pared to water proving its oleophilic behaviour as shown infigure 5b. Slightly smaller contact angles were observed inthe coated ECM in comparison with the uncoated one, whichshows that CS has enhanced the oleophilic behaviour of the

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Figure 8. (a) Oil absorption capacity of the ECM for different oils and (b) detergent removal with a change in pH.

ECM. Further, it is observed that the contact angle falls withtemperature for both the coated and uncoated ECM as shownin figure 5c. Also, the contact angle falls slowly at room tem-perature than at 40 ◦C, proving the better hydrophobicity atroom temperature as shown in figure 5d. The demonstration ofoil separation from water is shown in figure 6a–f. Few drops ofengine oil were added to the water (figure 6b). A piece of ECMwas dipped in oil–water solution and absorption of entire oilwas noted within few seconds due to its oleophilic nature asshown in figure 6f. Also, it appeared dry after oil–water sepa-ration showing its hydrophobic nature. The oil separated fromwater is shown in figure 6f. Further, the practical utility of theECM for oil–water separation was demonstrated by slidingthe water mixed with oil through a CS-coated egg carton tray.It is observed that the oil gets absorbed inside the tray whilethe water flows down and collected in a beaker as shown infigure 7.

The oil absorption capacity (k) of the CS-coated ECM fordifferent oils was evaluated by immersing in different oils.As shown in figure 8a, the oil absorption capacity (k) of theECM for different oils lies between 1.8 and 3 g g−1 dependingon density, surface tension and viscosity of oils. The initialweight of the coated ECM before and after dipping in oilwas evaluated using a Shimadzu portable balance (ELB 300).Since density is found to be directly proportional to absorptioncapacity, i.e., the denser the oil is, the larger will be its absorp-tion capacity. The highest and lowest-absorption capacitieswere found to be 3.1 and 1.6 g g−1 for mustard oil and petrol,respectively. Thus, the ECM can absorb mustard oil threetimes more than its weight. Also, due to the low density, petrolwas least absorbed in the material. Apart from oil spills, watergets polluted due to large quantity of detergent water fromhouseholds and industries. The presence of detergent in waterretards the photosynthetic activity and produces toxic water[34]. In order to remove the detergent from water, experimentwas conducted to test the pH by immersing ECM in detergentwater. It is observed that the ECM absorbs the detergent fromwater resulting in decrease of pH towards 7. The observedchange in pH was from 11 to 9 in the case of 2:1 solution(20 g detergent mixed with 40 ml water) and from 10 to 8 in the

case of 4:1 solution (20 g detergent mixed with 80 ml water),respectively, as shown in figure 8b. This shows the decreaseof pH towards 7 leading to purification of water. Thus, theECM can be successfully used as an effective and low-costadsorbent for removing organic pollutants from waste water.

4. Conclusion

A CS-coated ECM was successfully applied for oil–water sep-aration and absorbing detergent water. Contact angles werefound to be 142 and 43◦ for water droplet and oil showingthe superhydrophobic and oleophilic nature of the ECM. It isobserved that the contact angle dropped with rising tempera-ture maintained across the ECM. It was able to absorb petrol,diesel, refined oil, coconut, engine and mustard oil success-fully with the maximum absorption capacity of 3 g g−1. It canalso absorb detergent water, thus can act as a low-cost adsor-bent for water treatment. Thus, it can be used as an effectiveabsorber for household and industrial water treatment due toits low cost, easy availability, recyclability and easy manufac-turing.

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