Micro- and nanoporous materials capable of absorbing solvents and oils reversibly: the state of the art
Micro- and nanoporous materials capable of absorbing solvents and oils reversibly: the state of the art
Javier S. Acevedo Cortez 0
Boris I. Kharisov 0
Thelma E. Serrano Quezada 0
Toma´s C. Herna´ndez Garc´ıa 0
0 Facultad de Ciencias Qu ́ımicas, Universidad Auto ́noma de Nuevo Leo ́n , Ave. Universidad s/n, 66455 San Nicola ́s de los Garza, NL , Mexico
Treatment of petroleum spills and organic solvent pollution in general is an important issue; several techniques are under development to remove oil from water. The use of absorbents is one of the most common techniques to tackle this problem. These absorbents can be classified based on their characteristics of recyclability into irreversible and reversible ones. In this review, we discuss the application of several materials as oil absorbents, according to their classification and characteristics such as hydrophobicity, surface area and oil absorption capacity. Also, the fabrication methods for some materials are presented and analyzed.
Oil spills; Composites; Reversibility; Aerogels; Natural absorbents; Micro- and nanoporous materials
Treatment of oil spills is an important issue for
environmental science and technology. In the last decades, the
environmental pollution caused by oil spills on rivers and
oceans has been a great concern (Fingas 2012). Several
techniques have been developed for oil removal from
water; among them are the uses of chemical dispersants
and sorbents, bioremediation, skimmers, burning, etc. (Ge
et al. 2014; Liu et al. 2015a; Teisala et al. 2014). Highly
efficient absorbents are mainly used in these processes
(Ceylan and Dogu 2009; Radetic et al. 2008; Yang et al.
2015b). High capacity of absorbents for oil absorption is
commonly correlated with the porosity of the materials
(Adebajo et al. 2003; Rengasamy et al. 2011); for this
reason, highly porous materials are regularly used as oil
absorbents. Syntheses of materials with specific pore
diameters (mesoporous and macroporous) for their use as
oil absorbents have been offered (Lei et al. 2013; Li et al.
Hydrophobicity is one of the most important properties
of oil absorbents. Highly hydrophobic absorbents (Feng
et al. 2015; Wang et al. 2015; Yang et al. 2015b) exhibit a
better efficiency for oil absorption than low-hydrophobic
absorbents. The cost of the absorbents might be low due to
the large amounts required for cleaning oil spills. Besides,
the development of absorbents capable of being recycled
would be an interesting achievement in oil spills treatment.
Absorbents with highly porous structures and
superhydrophobicity would be capable of very efficient removal of
oil spills. For this purpose, efforts are needed to find
ecofriendly materials with superhydrophobicity properties,
making them selective for the absorption of oil as well as
enhancing their buoyancy, recyclability and price
(Korhonen et al. 2011).
2 A brief summary on the materials absorbing organic phase irreversibly
The most common method for irreversible removal of oil
from water is the use of hydrophobic absorbents. Earlier
(Adebajo et al. 2003; Al-Haddad et al. 2007; Carmody
et al. 2007) and recent (Ge et al. 2014; Yang et al. 2015a)
Fig. 1 Surface morphology of 20% EPS electrospun at A1 11.5 kV, 20% PS; A2 15 kV, 20% PS; B1 20% PS/zeolite at 9500; B2 950,000.
Reproduced with permission of Elsevier from (Alayande et al. 2016)
Fig. 2 Surface morphology of C1 EPS/zeolite film; C2 EPS film. Reproduced with permission of Elsevier from (Alayande et al. 2016)
works on absorbents indicated the importance of the
employment of these materials. One of these methods is
based on carbon-containing nanomaterials. Thus, syntheses
of carbon nanotubes and nanofibers on expanded
vermiculite (EV) surface were carried out by chemical vapor
deposition (CVD) (Moura and Lago 2009). The growth of
carbon nanotubes and nanofibers was catalyzed by
nanoparticles of Fe and Mo, producing a resulting sponge
structure. The final product showed high hydrophobicity
and buoyancy making it a potential oil absorbent, showing
an increase of 600% of its absorption capacity compared
with the initial material. Also, enhancing the
Fig. 3 Water contact angle of a 20% PS/zeolite and b 20% PS. Reproduced with permission of Elsevier from (Alayande et al. 2016)
Fig. 4 Microscopic structure of the native nanocellulose aerogels. SEM micrographs of a freeze-dried nanocellulose aerogels, and b a
magnification of a sheet. c TEM micrograph of a nanocellulose fibril with a uniform 7 nm TiO2 coating. Reproduced with permission of ACS
from (Korhonen et al. 2011)
hydrophobicity of this material, the amount of absorbed
water per gram of absorbent decreases dramatically (from
3.5 g of water to 0.5 g). This type of synthesis was
demonstrated to be very successful in avoiding any damage
to the porous structure of the EV. CVD is a relatively
lowcost method that can be used in large-scale production of
this type of absorbent. In a related report (Angelova et al.
2010), a carbon/SiO2 composite was prepared from rice
husks as precursor using the pyrolysis technique (450 C/
3 h). The obtained product contained 98% SiO2. The
absorption tests showed its higher oil absorption capacity
(2–3.5 times) compared with the material before
performing pyrolysis, showing its potential use for water clean-up
from oil spills.
Silica-based nanocomposites are known not only for this
composite above with carbon nanotubes (CNTs), but also
in combination with polymers. For example, materials
capable of gelling oil in oil spills were similarly
synthesized by CVD resulting in polydimethylsiloxane (PDMS)
on silica nanoparticles (Cho et al. 2014). These
PDMScoated silica nanoparticles showed high hydrophobicity,
stability, and oil gelation selectivity, being able to gelate 15
times the capacity of the uncoated silica nanoparticles.
These features make it a gelating agent for different types
of oils. On the other hand, the use of absorbents based on
natural products has been growing in recent years.
Absorption studies of oil, water, and buoyancy were
performed testing these features in natural absorbents (Rotar
Fig. 5 Schematic diagram for synthesis of the graphene–CNT
aerogels: a GO sheets, b CNT bundles, c the mixture of GO and
CNT prepared for d the graphene–CNT hydrogel, and e the formation
of graphene–CNT aerogel by freeze-drying from hydrogel.
Reproduced with permission of Elsevier from (Kabiri et al. 2014)
et al. 2015). Absorbents such as Nature Sorb (mixture of
sphagnum peat moss, charcoal, and sawdust) and
Sphagnum Dill (Russian peat moss) demonstrated high
absorption capacity and a long period of buoyancy compared with
sawdust. The use of this kind of natural absorbent for
removing oil in water can achieve levels of 0.03 g of oil
per liter of water. As the material is environmentally
friendly, its use as potential oil absorbent is interesting.
Heat treatment (150–250 C) was performed on sawdust to
increase specific absorption of high viscosity oil
derivatives. Although a practical and easy extraction of the
absorbed material is not possible, the oil absorbents can be
used as fuel by burning them directly after oil absorption.
3 Materials capable for multiple reversible absorption/desorption processes
3.1 Zeolites Previous works (Carmody et al. 2007; Alayande et al. 2016) focused on the synthesis of hydrophobic zeolites as
an alternative for activated carbon absorbents. Natural
zeolites are aluminosilicate minerals with a 3-D structure.
Their wide pores and large surface area make possible the
removal of impurities from water and air (Al-Haddad et al.
2007). The absorption of petroleum hydrocarbons, heavy
metals, and sulfur or ammonia compounds has been studied
using zeolites (natural and synthetic) as absorbents. Natural
and manufactured zeolites have been tested in wastewater
where zeolites performed a better absorption process of
several ammonia compounds (84.4% of removal) than
activated carbons (15.6% of removal). The selective
absorption of metals and ammonia makes zeolite a
potential absorbent for wastewater treatment, but not for refinery
wastewater due to high content of oil derivatives.
In a related report (Carmody et al. 2007), Wyoming
Namontmorillonite, octadecyltrimethylammonium bromide
(ODTMA), dodecyldimethylammonium bromide
(DDDMA), and di(hydrogenated tallow)
dimethylammonium chloride (commercial name Arquad 2HT-75) were
used to synthesize organo-clays which might present
hydrophobic or organophilic surface depending on the
exchanging ions. The absorption capacity of the
synthetized organo-clays was tested using three types of oil
(diesel, hydraulic oil, and engine oil). It was observed that
with increasing content of long chain hydrocarbon, the
absorption capacity of the organo-clay was found to be
higher. Organo-clay with certain hydrophobicity,
absorption and retention capacities might be synthesized through
the control of variables and their combinations. However,
organo-clays exhibit some disadvantages including high
cost, low biodegradability and low recyclability.
On the other hand, the synthesis of functionalized
nanosorbents with residues from the distillation of oil
(vacuum residue) and alumina nanoparticles have a great
potential due to their low cost and high hydrophobicity
(Franco et al. 2014). The materials were tested under
different conditions where high absorption capacity and
retention of oil can be achieved at neutral pH and a 4%
load of vacuum residue. The synthesis of this material has
the economic advantage of the use of an industrial residue
as precursor; however, its use requires specific conditions
to obtain the maximum absorption capacity restricting the
adaptability. In a similar report (Alayande et al. 2016), an
expanded polystyrene (EPS) and zeolite were used to
synthetize beaded fibers with a zeolite matrix by
electrospinning, as shown in Figs. 1 and 2. The material presents
t = 0 s
Saturated oil system
t = 10 s
t = 20 s
Fig. 6 Digital photographs showing the adsorption of vegetable oil on a water surface using prepared graphene–CNT aerogels at different times:
a t = 0 s, b t = 10 s, and c t = 20 s. d Adsorption capacity graph of graphene–CNT for oils and several organics using pure oil and solvent and
their mixtures with water. e The relationship of adsorption capacity with density of oil and organic solvents without water in the system. The
inset shows the contact angle (CA) measurements of graphene (GN), CNT, and graphene–CNT aerogel (GN–CNT), respectively. Reproduced
with permission of Elsevier from (Kabiri et al. 2014)
t = 0 s
t = 60 s
t = 90 s
t = 120 s
Fig. 7 Digital photographs showing a the packed plastic tube of graphene–CNT aerogels and b–e the progress of the continuous adsorption and
removal of gasoline from a non-turbulent water–oil system. Reproduced with permission of Elsevier from (Kabiri et al. 2014)
Fig. 8 Pillow-type sorbent (P-M17) consisting of clay polymer aerogel (M-17) surrounded by hydrophobic polypropylene (PP) nonwoven fabric
as containment barrier. a Top view. b Cross-sectional view. Reproduced with permission of Elsevier from (Rotaru et al. 2014)
Fig. 9 Pictures showing the application of the pillow-type sorbent (P-M17) for oil spill clean-up. a Sudan IV dyed dodecane spilled onto water
surface (oil slick layer of 2.5 mm). b Addition of P-M17 pillow sorbent and dodecane sorption after 10 s contact time. c Dodecane sorption after
15 min contact time. d After separation. Reproduced with permission of Elsevier from (Rotaru et al. 2014)
superhydrophobic properties (Fig. 3) and high absorption
capacity of oil due to the zeolite porous matrix.
Concluding this section, such properties of zeolites as
high porosity and large surface area are key features in the
processes of oil removal from water. However, other
properties as hydrophobicity, absorption capacity, and
retention of oil are also important in order to achieve a
complete cleaning of impurities in wastewater, seawater or
other aquatic systems.
The term ‘‘aerogel’’ is a gel material, in which its liquid
component has been replaced with gas to leave an intact
solid micro- or nanostructure without pore collapse;
aerogels contain *99% air by volume (Zuo et al. 2015).
Different types of aerogels are known, for instance
silicabased aerogel (Rao et al. 2007; Wang et al. 2010, 2012;
Olalekan et al. 2014), cellulose-based aerogels (Korhonen
Fig. 10 TEM images (a, b) and SEM images (c, d) of hollow Fe3O4 nanoparticles. Reproduced with permission of Elsevier from (Chen et al.
Fig. 12 Photographs of the removal of lubricating oil from a water surface by Fe3O4@PS nanocomposites under the magnetic field. The
lubricating oil was labeled by Sudan I dye for clarity. Reproduced with permission of Elsevier from (Chen et al. 2013)
Fig. 13 Scanning electron microscopy (SEM) images of sugar particles and PDMS oil absorbents. a–c CGS, FGS, and SS, respectively. d–
h PDMS oil absorbents prepared by CGS, FGS, SS, a mixture of CGS and SS, and a mixture of FGS and SS, respectively. Reproduced with
permission of ACS from (Zhang et al. 2013)
et al. 2011), clay-based aerogels (Rotaru et al. 2014),
carbon-based aerogels (Kabiri et al. 2014; Yang et al.
2015a; Zeng et al. 2009; Zuo et al. 2015), etc. The
methods of synthesis for each type of aerogel vary
depending on the final application; however, supercritical
drying or freeze-drying is fundamental in order to obtain
The synthesis of silica-based aerogels is carried out by
well-known methods for advanced nanoporous materials;
however, their applications require deeper studies. Due to
Table 1 Materials on the basis of natural absorbents
The use of dried eggshell as a biosorbent of oil in water is capable of performing a removal of 100%
of oil from water in concentration of 194 mg L-1
Absorption properties of talc, montmorillonite and sepiolite were elucidated leading to the sepiolite Zadaka-Amir
with the highest removal capacity (100%) and the talc with the highest adsorption capacity et al. (2013)
(13.5 mg of oil/m2)
Studies of the adsorption capacity of luffa with different oils demonstrated that the luffa is capable
of removing 85% of oil from water and it might be recycled
Dried azolla was used as sorbent for the removal of oil from water. The azolla achieved an
absorption capacity of 5.3 g of crude oil/g of dried azolla where the optimal conditions of
absorption were 25 C and pH 9
Study of the human hair as oil absorbent, using 3 types of hair (African, Asian, and European). The Ifelebuegu et al.
absorption capacity was 3 to 9 times their own weight. The African hair exhibited the mayor (2015)
absorption capacity with 9.3 g of oil/g of hair
Table 2 Natural-based reported materials
Exfoliated vermiculite (EV)/
Carbonized cotton fibers
Cellulose aerogels composite
Carbon fiber aerogel
A composite made of exfoliated vermiculite based with growth of carbon nanotubes on the
surface by CVD presented an absorption capacity of 26.7 g g-1 for diesel oil with a CNT
content of 91% on the surface (Fig. 14)
Porous nanocellulose aerogels were synthesized by freeze-drying and coated with TiO2 making
them hydrophobic and oleophilic. This material exhibit an absorption capacity of 20–40 wt/
wt depending on the solvent used
Pyrolysis of rice husks in a temperature range of 250–700 C. The absorption capacity was
10 g of crude oil per gram of absorbent. The influence of a porous structure formed during a
pyrolysis was the main attribution for the absorption capacity
Pyrolysis of cotton fibers was performed to create hollow carbon fibers and used as absorbents.
The carbonized cotton fibers achieve an absorption capacity of 32–77 times their own weight
(Figs. 15, 16)
Deposition of modified silica particles with octadecyltrichlorosilane on sawdust achieving a
superhydrophobic (153 ) composite with an absorption capacity of 17.5 g g-1 for diesel oil
(Figs. 17, 18)
Cellulose aerogel coated with methyltrimethoxysilane by CVD had an absorption capacity of Feng et al.
95 g g-1. Concentration, cellulose/Kymene ratio, temperature and pH were the parameters (2015)
studied to achieve the maximum absorption capacity (Figs. 19, 20)
Pyrolysis of lyophilized cellulose suspension was performed to produce a carbon fiber aerogel Yang et al.
capable of absorbing 129 times its own weight and the resulting material presented great (2015a)
recyclability (Figs. 21, 22, 23, 24)
Coating of SiO2 nanoparticles with poly(dimethylsiloxane) by dip-coating and its deposition on
cotton fibers surface exhibit a superhydrophobicity and an oil absorption capacity of 20–40
times its own weight (Fig. 25)
their own properties such as high surface area,
hydrophobicity and porosity, a study of the sorption of three oils
(vegetable oil, motor oil, and crude oil) was carried out
(Wang et al. 2012). Using Cabot nanogels (silica-based
aerogels) with different particle sizes, a high capacity for
adsorption of oils was observed. Their capacity of
absorption depends on the stability of the mixture of water
and oil. In the cases where the emulsion was stable, the
absorption capacity of the aerogel decreased tenfold. In
order to avoid this issue, the use of sustainable materials
Fig. 14 Images showing the morphology of a the EV and b the as-obtained EV/CNT hybrids after a 120-min reaction; SEM images showing the
morphology of c the EV and the EV/CNT hybrids with a CNT content of d 11.4% in EV/CNT-5 for a 5-min reaction, e 33.1% in EV/CNT-30 for
a 30-min reaction, f 67.6% in EV/CNT-60 for a 60-min reaction, g 91.0% in EV/CNT-90 for a 90-min reaction and h 94.8% in EV/CNT-120 for
a 120-min reaction; i TEM and inserted high-resolution TEM images showing the tubular structure of the CNT in the EV/CNT hybrids. The EV
layers in d–h are indicated by white arrows, while the aligned CNT arrays in d–h are indicated by black arrows. Reproduced with permission of
Elsevier from (Zhao et al. 2011)
such as plants and some soils as aerogel precursors was
offered. These materials exhibit the advantages of being
renewable, natural and with low impact on environments
due to their high compatibility with nature. For example,
the functionalized cellulose aerogel with hydrophobic
coating (TiO2) and a process of freeze-drying produce
nanocellulose aerogels (Korhonen et al. 2011). Aerogel
structure is created by the connected fibers of the
nanocellulose, and Fig. 4 illustrates their resulting
morphology with and without the coating. The composite
Fig. 15 Cross-sectional FE-SEM images of cotton fibers and CCFs with hollow structures. a, b CCFs-400. c CCFs-600. d CCFs-800. e
CCFs1000. f Cotton fibers. Reproduced with permission of ACS from (Wang et al. 2013)
exhibited absorption capacity of 20–40 (wt of oil/wt of
absorbent) but also, it can be reused (10 times) since the
absorption capacity does not change. After the oil
absorption, it requires only a wash with solvent in order to
be reused as sorbent or can be incinerated in order to use it
as a fuel.
Also, the use of carbon-based aerogels is more frequent
now; in particular, ‘‘greener synthesis’’ has nowadays
Fig. 16 Floating-ability test of CCFs-400 after crude oil sorption. a Crude oil on the water surface. b CCFs-400 sorbents placed on the spill area.
c CCFs-400 starting to adsorb oil. d Crude oil adsorbed by CCFs-400. e CCFs-400 floating on the surface after crude oil sorption. f Cleaned water
surface. Reproduced with permission of ACS from (Wang et al. 2013)
Fig. 17 Photographs of a behavior of a water droplet on pristine sawdust, b behavior of a water droplet, and c oil droplet on as-prepared
superhydrophobic/superoleophilic sawdust. Reproduced with permission of Elsevier from (Zang et al. 2015)
attracted attention. The development of these
nanomaterials which do not only accomplish the final application but
also their synthesis using low-toxicity chemicals and
reducing the number of steps of the process are important.
The synthesis of graphene–carbon nanotube aerogel has
been reported by greener techniques, where the interaction
of the graphene oxide and carbon nanotubes was performed
in a one-step process (Kabiri et al. 2014). A schematic
Fig. 18 The process of resulting sawdust product as an oil sorbent for the separation of water and gasoil mixture. a As-prepared
superhydrophobic/superoleophilic sawdust. b Water and gasoil mixture (gasoil was colored with Sudan III for clear observation). c All given red
gasoil was absorbed and red sawdust floated on the water. d After adsorption, the sawdust filled with red liquid was separated. Reproduced with
permission of Elsevier from (Zang et al. 2015)
Fig. 19 a Superhydrophobic recycled cellulose aerogel. b Flexibility of the large-scale cellulose aerogel (38 cm 9 38 cm 9 1 cm) containing
0.60wt% of the cellulose fibers. SEM images of the cellulose aerogels with different ratios of cellulose fibers (wt%) and Kymene (ll): c 0.25:5,
d 1.00:5, e 0.60:5, and f 0.60:20. Reproduced with permission of Elsevier from (Feng et al. 2015)
diagram of the synthesis procedure is represented in Fig. 5.
Carbon nanotubes provide the hydrophobic and porous
property to the product (Fig. 6), promoting the absorption
of oil products. The synthesis method used is economically
attractive and simple for scalable production. A possible
absorption process to implement on a large scale is shown
in Fig. 7.
Clay-based aerogels combine the hydrophobicity of
organo-clays with the large porosity of the aerogels making
them an interesting candidate for oil spill clean-up. Various
amounts of montmorillonite (MMT), sodium dodecyl
sulfate (SDS), and polyvinyl alcohol (PVA) were tested to
synthesize clay-based aerogels (Fig. 8) (Rotaru et al.
2014). The absorption capacity determined under the
Fig. 20 Oil absorption process of the recycled cellulose aerogel having 5.0wt% of the cellulose fibers in the artificial seawater (3.5% NaCl and
pH 7) mixed with the 5w40 motor oil and dyed with Sudan Red G before testing. Reproduced with permission of Elsevier from (Feng et al. 2015)
optimal conditions was 23.6 g g-1 for dodecane and
25.8 g g-1 for motor oil. The process of absorption of
dodecane on water with the synthetized aerogel is shown in
Fig. 9. The percentage of recovery of the absorbed oil was
estimated by free drainage (from 1.06% to 14.9%)
followed by centrifugation of the absorbent (from 42.3% to
66.0%). This study reveals the high absorption capacity,
hydrophobicity (116 ), and the possible recycling of the
aerogel under the optimal conditions of synthesis.
The polymeric absorbents such as polyurethane,
polypropylene, polyethylene, and cross-linked polymers
are the most commonly absorbent for oil spills. Due to their
high porosity, absorbent capacity and hydrophobicity, these
polymers have been widely used for the absorption of
organic compounds. Thus, innovations in this area have
become imperative. The creation of novel polymeric
systems like polymer-based absorbent (Keshavarz et al. 2015;
Li et al. 2012; Liu et al. 2015b; Nikkhah et al. 2015; Zhou
et al. 2015; Zhu et al. 2015), polymer absorbents (Kundu
and Mishra 2013; Lin et al. 2008; Zhang et al. 2013) and
polymeric coatings (Chen et al. 2013; Machado et al. 2006)
of different materials are reported. Thus, a common and
suitable process was creating an absorbent on the basis of
carbon nanotubes and polyurethane (Wang et al. 2015).
This absorbent presented superhydrophobicity and a high
absorption capacity (34.9 times its own weight). The
synthesis method consists of the oxidative self-polymerization
of dopamine followed by a reaction with octadecylamine.
The mechanical strength of the absorbent was improved by
the deposition of carbon nanotubes on the sponge skeleton.
The recyclability of the as-prepared absorbent was 150
times without losing its high absorption capacity.
Also, the uses of polymer-coated materials are very
common, in particular those having magnetic properties.
Thus, the two-step synthesis of magnetic nanoparticles
(Fe3O4) coated with polystyrene was carried out and the
products were tested as oil absorbents (Chen et al. 2013).
The hollow Fe3O4 nanoparticles and the
polystyrenecoated Fe3O4 nanoparticles are shown in Figs. 10 and 11,
respectively; the use of this polymer on the magnetic
nanoparticles generates a hydrophobic property that
Fig. 21 Preparation of MCF aerogel (a–d I hydrothermal treatment; II freeze-drying process; III pyrolysis), the morphologies of aerogel before
and after thermal treatment (e, f bamboo fiber aerogel; g, h MCF aerogel), and nitrogen adsorption–desorption isotherm of MCF aerogel (i).
Reproduced with permission of RSC from (Yang et al. 2015a)
Fig. 22 Surface wettability of aerogels to different probe liquids.
a Adsorption of water stained with methylene blue by fiber aerogel.
b Water droplets on a MCF aerogel. c Interaction between MCF
aerogel and liquid after immersing into water. d, e Behavior of water
and oil droplets on MCF aerogel. Reproduced with permission of
RSC from (Yang et al. 2015a)
enhances the oil absorption of the composite. The magnetic
properties of the coated nanoparticles were used to remove
oil from water using a magnet (Fig. 12). Due to its
hydrophobicity, this nanocomposite presented a selective
absorption exclusively for the oil. The absorption capacity
of its coated nanoparticles was shown to be 3 times its own
weight. Furthermore, the oil could be removed from the
nanocomposite implementing a simple treatment and does
not affect its future performances.
An easy polymerization of poly(dimethylsiloxane)
(PDMS) was achieved using sugar to make a porous
material that can absorb larger oil quantities at less time
(Zhang et al. 2013). This synthesis involves PDMS,
p-xylene, and sugar (coarsely granulated sugar, CGS; finely
granulated sugar, FGS; soft sugar, SS). A porous skeleton
was created (Fig. 13), and the absorption capacity,
hydrophobicity, and recyclability of the processes were
evaluated. The absorbent presented an absorption capacity
in the range of 4–34 g g-1 depending the oil and organic
solvent. The recycling process showed a recyclability of 20
times losing only a little of its original absorption capacity.
Furthermore, this synthesis method could be used to design
novel polymeric absorbents.
3.4 Natural and natural-based products
The study of hydrophobic properties, absorption capacity,
and buoyancy in absorbents has been increased over time
since these properties are key features in the treatment of
oil spills. Most common absorbent materials are based on
polymers, which are oil-based. The aim of these
innovations is to produce absorbents based on cheap and
commercially available natural products. This area can be
divided into two large groups, natural absorbents
(Abdelwahab 2014; Behnood et al. 2013; Chen et al. 2013;
Ifelebuegu et al. 2015; Machado et al. 2006; Muhammad
et al. 2012; Rotar et al. 2014; Ribeiro et al. 2003; Sayyad
Amin et al. 2015; Wahi et al. 2013; Zadaka-Amir et al.
2013) and natural-based absorbent products (Fu and Chung
2011; Galblaub et al. 2016; Raj and Joy 2015;
Kudaybergenov and Ongarbayev 2012; Nwadiogbu et al. 2016;
Okiel et al. 2011; Uzunov et al. 2012; Wang et al. 2013;
Zang et al. 2015; Zhao et al. 2011). Natural absorbents are
those that can be obtained in nature and are used without
modifying their hydrophobicity properties, absorption
capacity, buoyancy, etc. These materials are commonly
used after a drying process to eliminate the water adsorbed
on the structure of the material. Some selected works
reporting the use of natural absorbents are listed in Table 1.
The natural-based absorbents are natural absorbents
with a modified surface using different types of materials or
by a change on the chemical composition of their surface to
achieve a better hydrophobicity and, oil absorption
Fig. 23 Recyclability of MCF aerogel using different methods and corresponding morphologies after cyclic operation for 6 times. a, b
Hexaneadsorbed MCF aerogel recycled by distillation. c, d Hexadecane-adsorbed MCF aerogel recycled by combustion. e, f Gasoline adsorbed MCF
aerogel recycled by squeezing). Reproduced with permission of RSC from (Yang et al. 2015a)
Fig. 24 Photographs showing the regeneration of MCF aerogel via combustion (a) and squeezing (b). Reproduced with permission of RSC from
(Yang et al. 2015a)
capacity. The modification of these materials can be carried
out by methods such as CVD, dip-coating, pyrolysis, etc. In
Table 2 are presented several reports in this field (Figs. 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25).
4 Conclusions and further outlook
Oil spill removal is a serious issue where the well-being of
the environment is placed at risk due to the toxicity of these
compounds causing critical effects to the sea flora and
fauna, human health, and also economic losses. In this
regard, advanced and ‘‘smart’’ materials are required in
order to offer products capable of attending to this
problem. Distinct materials have been used for oil absorption
with different properties that make them suitable for certain
conditions or oil residues due to their properties such as
large surface area, porosity and hydrophobicity. Although,
in recent years, the search for eco-friendly and low-cost
materials promotes the investigation of methods of
synthesis with low-impact on the environment, some
researchers proposed the use of natural materials such as
plants and clays for the development of novel absorbents
with reversible oil absorption properties. Additional
treatments can improve their hydrophobicity, leading to
lowcost absorbents possessing high absorption capacity, and
reusability. The use of CVD and deposition of thin layers
of hydrophobic nanoparticles on the internal surface of
these materials is useful for their conversion from
hydrophilic to hydrophobic materials, as well the oil absorption
capacity of the material can be increased.
Even though much development has been achieved in
this field, many materials are not applicable in the real field
due to the limits of mass production and price. There are
some materials which have potential for scale-up and
commercialization. As future works in this area, plants
with naturally porous structures and large surface area
seem to be very promising source to create new reversible
Fig. 25 Selective oil sorption from the oil/water mixture by
PDMScoated absorbent cotton. a The set-up of home-built oil-filter. b Oil
remained on the SiO2 layer after the sorption process pump oil (dyed
red) without filter. c–e The sorption process using the filter fabricated
with the dip-coated absorbent cotton. f Filtered clean water in the
beaker after the sorption process. Reproduced with permission of
Elsevier from (Lee et al. 2016)
absorbents based on natural materials using the CVD or
Acknowledgements The authors are grateful to the Universidad
Auto´noma de Nuevo Leo´n (Monterrey city, Mexico) for financial
support (Project Paicyt-2015).
Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://crea
tivecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
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