Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2022 Nov 23;7(48):43330–43336. doi: 10.1021/acsomega.2c05886

Recent Advances in Superhydrophobic Papers for Oil/Water Separation: A Mini-Review

Qingzhen He †, Zhibiao Guo †, Shiyu Ma †, Zhiwei He †,*
PMCID: PMC9730453  PMID: 36506134

Abstract

graphic file with name ao2c05886_0005.jpg

The separation of oceanic spilled oils and industrial oily wastewaters becomes a great challenge, and it is highly desirable to develop efficient materials for oil/water separation. As abundant sustainable resources, superhydrophobic papers (SPs) have drawn much attention because of low-cost and efficient oil/water separation. Herein, this mini-review summarizes recent advances of SPs in terms of design, preparation, and properties. On the basis of the many excellent properties of SPs (i.e., self-cleaning, durability, chemical corrosion resistance, and reusability), the oil/water separation performances (i.e., separation efficiency, permeation flux, and recyclability) of SPs as well as the corresponding mechanisms are discussed. The efficient oil/water separation property and recyclability of SPs make them promising candidates in the field of oily wastewater treatment.

Introduction

Oceanic oil spill incidents and the discharge of oily wastewaters have caused long-term significant threats to the environment and human health.1 To address this issue, traditional methods have been reported to remove oils from oily wastewaters, including in situ burning, bioremediation, centrifugation, coagulation, flotation, and chemical dispersion.1a−1d Unfortunately, these methods suffer from complex operations, high cost, low separation efficiency, and secondary pollution.1b−1d Therefore, efficient and energy-saving methods are highly desired for the separation of oily wastewaters.

Due to excellent liquid repellency, superhydrophobic materials have been utilized in the applications of oil/water separation,1c anti-icing,2 self-cleaning,3 anticorrosion,4 and antibacterial activity.5 Various substrate materials have been developed to obtain surface superhydrophobicity, such as papers, metals, polymers, ceramics, wood, and glass. Among them, papers have drawn much attention because of abundant sustainable resources,6 light weight,1c low cost,1a,5 flexibility,5 and environmental friendliness.6,7 For example, SPs show much better resistance to highly acidic or alkaline solutions when compared with metals (i.e., stainless steel and copper grid) and polymer (i.e., polyester) fabrics.1e Also, SPs with proper pore sizes have good performances for the separation of oil/water emulsions rather than other materials (i.e., metal meshes and glass fiber membranes).1e,7b Generally, the paper material is a type of cellulosic material, consisting of porous structures, microtextures, and rich hydrophilic functional groups. Thus, superhydrophobic papers (SPs) can be easily achieved via the decoration of nanomaterials and chemical modification. The rational design endows SPs with many excellent properties, including self-cleaning,1c mechanical and thermal durability,5 chemical resistance (i.e., acid, base, and saline solutions),1c−1e and reusability.1a,4

Recently, SPs have been used in the field of oil/water separation because oil can easily wet and penetrate SPs with low surface tension.8 For example, He et al. prepared durable TiO2/polydopamine (PDA)-based SPs and found that the TiO2/PDA-based SPs can maintain the separation efficiency of an oil/water mixture (or water-in-oil emulsions) above 94.3% (or 93.7%) after 15 cyclic separation processes.1c Yang et al. designed recyclable, magnetic, and fire-retardant SPs, and the SPs showed a separation selectivity above 99.0% and a good recycling ability for >10 times.4 Li et al. reported that a durable and sustainable superhydrophobic/superoleophilic paper can be prepared by layer-by-layer assembly and polydimethylsiloxane (PDMS) modification, and the SPs exhibited good separation efficiencies of >99% for oil/water mixtures even after 30 cycles.9 Herein, we summarize recent advances of SPs in terms of design, preparation, and properties. Then, the oil/water separation application of SPs as well as corresponding mechanisms is discussed. Due to the excellent separation properties of oil/water mixtures (or emulsions), the low-cost, sustainable, and recyclable SPs become promising candidates for the treatment of oily wastewaters.

Design and Preparation of Superhydrophobic Papers

To achieve surface superhydrophobicity, porous and microtextured pristine papers usually need to be modified to meet two necessary requirements of superhydrophobic surfaces (i.e., hierarchical structures and low surface energy). Generally, SPs can be rationally designed via two main strategies: (1) modifying cellulosic fibers with low surface energy materials (i.e., fluoroalkylsilane and stearic acid) to form nanostructured roughness on the microtextured fibers of pristine papers, and (2) decorating pristine papers with nanomaterials, followed by low surface energy modification (see Figure 1). Many preparation approaches can be used to achieve these two main strategies for SPs, including vacuum filtration,4,10 phase separation,11 colloidal deposition,12 spray-coating,13 atom transfer radical polymerization (ATRP),14 layer-by-layer assembly,5,9 self-assembly,15 dip-coating,16 immersion,1c,7b,8,17 (see Table 1), etc.

Figure 1.

Figure 1

Open in a new tab

Schematic overview of preparation and oil/water separation of SPs.

Table 1. Preparation and a Comparison of SPs for Oil/Water Separation.

preparation methods decorated materials absorbed materials separation efficiency (%) permeation flux (L m–2 h–1) cycles (times) ref
vacuum filtration HAP, Fe3O4, PDMS chloroform, 50% (v/v) 99.6 2924.3 10 (4)
  HAP, TiO2, SA oil/water mixtures >99.4   10 (10b)
  HAP, ZnO, PFDS oil/water emulsions   66–185 10 (10a)
drop-coating SiO2, PS n-hexane, 50% (v/v) 79     (18)
spray-coating EP, PDMS, SiO2, Fe3O4 oil/water mixtures >98 41.5–129 30 (13c)
  CNFs, ODA oil/water mixtures >98   10 (13a)
  SiO2 DCE/water emulsion >99.9 >600   (13b)
ATRP cellulose, PFOEMA oil/water mixtures >95   10 (14a)
  C18-FP-g-SAN oil/water mixtures >98.5   10 (14b)
solution casting SiO2, LLDPE petroleum ether, 50% (v/v) 99.9   10 (19)
layer-by-layer assembly PDMS, Cu-MOFs oil/water mixtures >98 4.24–55.8 30 (5)
  ZnO oil/water mixtures >99 14.2–132.7 30 (9)
in situ growth PDA, Ag, n-DM oil/water mixtures >97 24–95.3 30 (20)
self-assembly PPP oil/water mixtures >97   2 (15)
phase separation SiO2, PS crude oil/water mixture 99     (11)
dip-coating SiO2, TMCS oil/water mixtures >82     (16)
colloidal deposition PTFE, PS oil/water mixtures >99   30 (12)
wire rod coating TiO2, KH550, PDMS dichloromethane/water mixture >98   10 (21)
freeze-drying CNF, MTMS chloroform, 50% (v/v) >96.8   10 (22)
  SA oil/water emulsions >98.5   10 (1a)
immersion Cu(OH)2 diesel oil/water mixture >99 1452.7 100 (17g)
  OTS, MTS diesel oil, 50% (v/v) >97   4 (17e)
  SiO2, PS diesel oil, 50% (v/v) 98.2     (8)
  SiO2, PDMS chloroform emulsion 93.4   5 (17b)
  TiO2, EP diesel/water mixture 98.2   5 (17c)
  BTCA, SHP oil/water emulsions   25.8–4920   (7b)
  SA chloroform, 30% (v/v) >95   10 (17a)
  Cu(OH)2, SA oil/water emulsions   >5500 5 (17d)
  TiO2, FDTS oil/water emulsions >93.7   15 (1c)
  SiO2, PDMS soybean oil/water mixture 93.8 >10000 10 (17f)
Open in a new tab

As for the chemical modification of cellulosic fibers, low surface energy materials need to be elaborately chosen to react with the surface functional groups of cellulosic fibers of papers. For example, Zhang et al. reported that a superhydrophobic poly(styrene-co-acrylonitrile) grafted filter paper can be prepared by combining octadecanoyl chain bonding and polymer grafting via surface-initiated atom transfer radical polymerization (ATRP).14b Yun et al. developed a facile and eco-friendly approach to prepare SPs by immersing the pristine paper in an ethanol solution of stearic acid.17a These studies obtained SPs by simply modifying both inner and outer cellulosic fibers with low surface energy materials (i.e., stearic acid). However, the control of reaction conditions between cellulosic fibers and low surface energy materials is very important, which greatly influences the homogeneous coverage of low surface energy materials on SPs.

The introduction of nanoparticles to the cellulosic fibers of pristine papers is an alternative strategy to obtain SPs. To achieve superhydrophobicity, inorganic nanomaterials (i.e., TiO2, SiO2, ZnO, Cu(OH)2, Fe3O4, and hydroxyapatite nanowires) have been used to decorate cellulosic fibers, followed by low surface energy modification. For example, Li et al. introduced hydroxyapatite nanowires (or TiO2 nanoparticles) to Kevlar fiber-reinforced papers via a vacuum filtration method and lowered the surface energy by a chemical modification of stearic acid (Figure 2a).10b He et al. achieved SPs by immersing polydopamine-decorated filter papers in the TiO2 nanoparticle suspension under magnetic stirring and modifying with a 0.5 wt % perfluorodecyltrichlorosilane (FDTS) solution (Figure 2b).1c Zhang et al. prepared SPs by drop-coating a tetrahydrofuran (THF) mixture solution of polystyrene (PS) and silica particles on filter paper (Figure 2c).18 Bai et al. used a nonsolvent vapor self-assembly method to prepare poly-p-phenylene micro/nanostructures decorated SPs for oil/water separation (Figure 2d).15 Li et al. obtained robust and magnetic SPs by spray-coating a suspension consisting of epoxy resin, PDMS, Fe3O4, and SiO2 (Figure 2e).13c Shi et al. fabricated superhydrophobic waste cardboards by combining Ca2+ cross-links via freeze-drying and postmodification with stearic acid (Figure 2f).1a In short, the introduction of nanomaterials to porous microtextured cellulosic fibers can enhance the roughness and hierarchical structures of pristine papers and thus form micro/nanostructured roughness. When modifying with low surface energy materials, SPs finally can be obtained.

Figure 2.

Figure 2

Open in a new tab

Preparation methods of SPs: (a) vacuum filtration, (b) immersion, (c) drop-coating, (d) self-assembly, (e) spray-coating, and (f) freeze-drying. (a) Adapted with permission from ref (10b). Copyright 2019 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique. (b) Adapted with permission from ref (1c). Copyright 2022 American Chemical Society. (c) Adapted with permission from ref (18). Copyright 2012 Elsevier. (d) Adapted with permission from ref (15). Copyright 2018 Elsevier. (e) Adapted with permission from ref (13c). Copyright 2022 Elsevier. (f) Adapted with permission from ref (1a). Copyright 2021 American Chemical Society.

Properties of Superhydrophobic Papers

Except for surface superhydrophobicity, other properties are also very important for a reliable use of SPs in practical applications, including thermal stability, chemical resistance, durability, antiaging, and regeneration of superhydrophobicity. For example, the thermal stability is an important parameter for the real application of SPs. Generally, water contact angle (WCA) before and after heating (or boiling water) has been used to evaluate the thermal stability of SPs in terms of heating and boiling water (Figure 3). Yang et al. found that the superhydrophobic HAP@Fe3O4@PDMS (HAP = hydroxyapatite) paper can well-maintain its superhydrophobicity after treatment in a wide temperature range from −198 to 250 °C.4 Du et al. showed that the WCA of a superhydrophobic filter paper can remain unchanged when the paper is placed in an oven and heated at 180 °C for 72 h.12 Piltan et al. reported that the superhydrophobicity of the as-prepared filter paper can be retained (WCA = 158° ± 3°, SA = 8°) when placed in an oven at 200 °C for 2 h.11 Therefore, the thermal stability of SPs enables the maintenance of surface superhydrophobicity and then extends their potential applications under different heating conditions (i.e., ∼200 °C).

Figure 3.

Figure 3

Open in a new tab

Properties of superhydrophobic papers.

Immersing SPs in boiling water for a certain time is another approach to evaluate the thermal stability of SPs. For example, He et al. found that the WCA of TiO2/PDA-based superhydrophobic paper is still >158° after being immersed in boiling water for 120 s.1c Wen and Guo showed that the superhydrophobic paper can tolerate boiling water for 120 s with WCAs >150°, while the shape of the paper was damaged.10a Besides, to verify the thermal stability, the thermogravimetric analysis (TGA) curves of pristine paper and SPs are characterized based on the weight loss.1c,10,21 The weight loss of SPs is due to the absorbed water, dehydration of the silane group, and degradation of the silane coupling agent, which is usually >90%. Thus, the good thermal stability of SPs can extend their applications in relatively high-temperature fields (i.e., fire-resistant materials).

In real application, the degradation of SPs is inevitable. The maintenance of superhydrophobicity for SPs becomes a great challenge. There are many methods to evaluate the durability of SPs, including finger wipe,4 tape peeling,4,5,19 knife scratching,4,19 sandpaper abrasion,4,5,7b,13c,20,21 bending,5,13c,20,21 ultrasonic treatment,5,13c,17b,20,23 flexural rigidity,23 breaking (or bursting),23 and scrubbing24 (see Figure 3). For example, Yang et al. found that the superhydrophobicity of HAP@Fe3O4@PDMS paper is well-preserved after several mechanical damage tests, including finger wipe, adhesive tape peeling, knife scratching, and sandpaper abrasion.4 Li et al. investigated the mechanical durabilities of several types of SPs and found that the superhydrophobicity of SPs can be maintained after sandpaper abrasion, bending, and ultrasonic treatment.5,13c,20 Yang et al. reported that, compared with untreated papers, the flexural rigidity and breaking strength of SiO2-decorated SPs can be enhanced by 22.0% and 20.9%, respectively.23 For versatile applications, the mechanical durability is a critical parameter that determines the stability of surface superhydrophobicity of SPs and thus influences practical applications.

When used in harsh environments, the chemical corrosion resistance is beneficial to the long-term use of SPs, including soaking in different organic solvents, saline solutions, acid solutions, and alkaline solutions (Figure 3). For example, He et al. found that the WCAs of the TiO2/PDA-based SPs are still >150° when being immersed in a HCl solution (pH = 1) for 180 min and in an alkaline solution (pH = 13) for 120 min.1c Yang et al. showed that the superhydrophobicity of HAP@Fe3O4@PDMS paper remains after soaking in organic solvents (i.e., acetone, cyclohexane, isopropanol, methanol, ethanol, n-hexane, and ethylene glycol) and being immersed in solutions with different pH values (2.35–12.98) and extremely acid condition (pH = 1.46).4 Li et al. found that the WCAs of SPs are still kept >150° after being immersed in different organic solvents (i.e., ethanol, acetone, and n-hexane) for 72 h.5 However, the gradual degradation of surface chemistry and morphologies of SPs becomes unavoidable in corrosive solutions (i.e., organic solvents, saline solutions, acid solutions, and alkaline solutions) as time elapses.

Antiaging and antiultraviolet properties of SPs are also very important when utilized in harsh outdoor conditions (Figure 3), which can be realized by the rational design of SPs. For example, Ge et al. evaluated long-term durability by a hydrothermal aging test (i.e., the aging temperature is 60 °C and the humidity is 80%), indicating the stability of SPs.17b Du et al. placed SPs under the light of a 48 W ultraviolet (UV) lamp for 72 h, and the SPs showed excellent resistance to ultraviolet irradiation.12 Gao et al. found that the WCA of SPs still remains >151° after UV exposure for >5 h, showing good UV resistance.17c Li et al. showed that the superhydrophobic PDA@Ag@n-DM paper still kept superhydrophobicity after 6 h of UV exposure, indicating good UV durability.20 On the basis of the earlier discussions, antiaging and antiultraviolet properties enable SPs’ resistance toward different environmental conditions and facilitate the maintainence of long-term stability of SPs in practical applications.

Besides, the regeneration of surface superhydrophobicity is a vital ability for the reusability of SPs (Figure 3). For example, Ren et al. reported that the superhydrophobicity can be restored by heating the coated material at 80 °C for 15 min.24 Satapathy et al. showed that the superhydrophobicity of damaged/scratched surfaces can be regenerated by the solution-casting method.19 Now that the degradation and loss of surface superhydrophobicity are unavoidable, the regeneration ability (or self-healing property) makes it possible for SPs to have stable and long-term utilization during practical applications.

Superhydrophobic Papers for Oil/Water Separation

Due to excellent surface superhydrophobicity, SPs have been utilized in various practical applications. Among them, oil/water separation is crucial to the treatment of oceanic oil spill incidents and the discharge of oily wastewaters. Thus, the performances of SPs on separating oily wastewaters are highly important when used in oil/water separation, including separation efficiency, permeation flux, recyclability, and so on (see Table 1). Recently, the mechanisms of SPs for oil/water separation have aroused much interest from researchers. Usually, SPs possess superhydrophobicity (i.e., water droplets in the Cassie–Baxter state) and superoleophilicity (i.e., oil droplets in the Wenzel state). When oil/water mixtures (or emulsions) have contact with SPs, water droplets can be blocked by surface superhydrophobicity and oil can easily permeate into the cellulosic fibers of SPs because of the superoleophilicity.1c Generally, a stable oil/paper interface can be generated during a separation process and, thus, effectively block the permeation of water droplets.1c,10a When the intrusion pressure is positive (ΔP > 0) (Figure 4a), water cannot go through cellulosic fibers. Once the intrusion pressure is negative (ΔP < 0), oil can easily enter into fibers (Figure 4b).

Figure 4.

Figure 4

Open in a new tab

Separation mechanisms of (a) oil/water mixtures and (b) oil/water emulsions. (b–e) Adapted with permission from ref (7b). Copyright 2021 Springer.

However, the efficient separation of oil/water emulsions is still a challenge for SPs due to the stability and the small droplet size of oil/water emulsions. When separating oil/water emulsions, the pore size of SPs and the droplet size of oil/water emulsions are of great importance to demulsification processes.5,13c,20,23 If the size of the oil/water emulsion droplet is smaller than the pore size of the SPs, oil droplets can be easily separated.7a When the oil droplets are larger than the pore size of the SPs, they can be held (Figure 4c).7b Because of superhydrophobicity, the liquid bridges can be formed among the fiber pores, and thus small oil droplets can leave and permeate through the cellulosic fibers (Figure 4d).7b Xi et al. thought that the existence of the liquid bridge can result in the coalescence of oil droplets and thus induce the demulsification of emulsions (Figure 4e).7b Although the separation efficiency of SPs is high, the tiny nanoemulsions are still difficult to be separated. For example, Ren et al. found that the size of the emulsions ranges from 300 to 1500 nm before separation, while the droplet sizes in the filtrate are between 3 and 12 nm after separation by using SPs.24 Shi et al. reported that the particle size of emulsions is distributed between 1000 and 2500 nm, while the particle size of emulsions in the filtrate is between 4 and 18 nm.1a Therefore, the separation of tiny nanoemulsions (i.e., size < 20 nm) needs to be fundamentally investigated by the rational design of SPs (i.e., the size of the pores).

During a separation process of oil/water emulsions, a stable liquid/solid interface can be formed that effectively blocks the contact between oil (or water) and the SPs.1c,10a As for the oil/water separation, oil/water mixtures (or emulsions) be can realized via a gravity-driven separation by using SPs, while the intrusion pressures for separating different oils are usually different.1e Yang et al. found that the intrusion pressures of water and emulsions as well as the working pressure during emulsion separation are 10.39, 3.71, and 0.36 kPa, respectively.23 The small working pressure guarantees the block of water passing through SPs, achieving the efficient separation of oil/water emulsions. Thus, the intrusion pressure and working pressure should be considered when separating oil/water mixtures (or emulsions).

Viscous oil/water mixtures or emulsions (i.e., crude oils) are another challenge in the field of oil/water separation. Very recently, an external stimulus (i.e., electrothermal or photothermal heating) could be considered to enhance the oil/water separation. For example, the photothermal effect has been demonstrated to increase the surface temperature and thus facilitate the mobility of crude oils.2a,25 Once the viscosity of viscous oil/water mixtures (or emulsions) is reduced at high surface temperature, the adsorption (or separation) efficiency will increase. This photothermal effect promoted strategy provides new insights into the cleanup of viscous crude oils and other viscous oily wastewaters. Besides, the morphologies of SPs may change after several oil/water separation cycles.1c The recycling performances of SPs should also been considered for long-term use in oil/water separation.

Conclusions and Outlook

In summary, this mini-review introduces the design, preparation, and properties of SPs for their application in the field of oil/water separation. The SPs are cellulosic fiber-based materials, consisting of porous structures, microtextures, and rich hydrophilic functional groups. The excellent properties of SPs (i.e., self-cleaning, durability, chemical corrosion resistance, and reusability) enable the efficient oil/water mixtures (or emulsions). Thus, as abundant sustainable resources, SPs are promising candidates in the field of oily wastewater treatment.

In the future, the rational design of SPs needs to be realized to meet the requirements (i.e., thermal stability, chemical resistance, durability, antiaging (or anti-UV), and reusability) of practical applications (i.e., oil/water separation). When utilized in oil/water separation, two main challenges (i.e., the separation of emulsions and the separation of viscous oil/water mixtures) exist. By adjusting the pore size of the SPs and the working pressure, oil/water emulsions can be efficiently separated. However, nanoemulsions (with droplet size <20 nm) are still difficult to separate. The separation efficiency of nanoemulsions probably can be improved by the combination of the following two methods: (1) the introduction of an external stimulus (i.e., electrothermal or photothermal heating and magnetic field) in the separation of oil/water emulsions is beneficial to the demulsification processes; (2) a multistep process can be employed by utilizing SPs with different pore sizes to realize the separation of nanoemulsions. As for viscous oil/water mixtures, electrothermal or photothermal heating has been demonstrated to enhance the separation of oil/water mixtures, while the recyclability of SPs should be improved after several cycles of viscous oil/water separation. Of course, SPs also have disadvantages for oil/water separation. For example, the adsorption capacity of SPs for oil/water mixtures (or emulsions) is much lower than that of sponges and porous materials. Thus, in the practical application of oil/water separation, suitable separation materials can be selected to meet different conditions and environments (i.e., viscous oils, nanoemulsions, light oils, and heavy oils). All in all, low-cost and renewable SPs are promising candidates in the field of oily wastewater treatment, providing a great potential use in different harsh environments.

Acknowledgments

This work is financially supported by the National Natural Science Foundation of China (Grant no. 51803043), the Graduate Scientific Research Foundation of Hangzhou Dianzi University (GK228810299018), the Fundamental Research Funds for the Provincial Universities of Zhejiang (GK210701218033 and ZX220701218033), and the Science Foundation of Hangzhou Dianzi University (KYS205620119).

Biographies

Qingzhen He is currently an undergraduate student at College of Materials and Environmental Engineering of Hangzhou Dianzi University. She joined the AIM Laboratory under the supervision of Prof. Zhiwei He in 2021. Her research interest focuses on superhydrophobic materials.

Zhibiao Guo is currently a graduate student at College of Materials and Environmental Engineering of Hangzhou Dianzi University under the supervision of Prof. Zhiwei He. He joined the AIM Laboratory in 2021. His research interest focuses on superhydrophobic materials and anti-icing materials.

Shiyu Ma received her Ph.D. degree in Materials Science and Engineering from Shandong University (Prof. Jianxin Zhang) in 2018. She joined the College of Materials and Environmental Engineering at Hangzhou Dianzi University in 2018. Her research interest focuses on first-principles calculations.

Zhiwei He received his Ph.D. degree in Nanomechanics from NTNU Nanomechanical Lab under the supervision of Prof. Zhiliang Zhang in 2016 and continued to work as a postdoctoral researcher at NTNU Nanomechanical Lab in 2017. He was appointed as an associate professor at College of Materials and Environmental Engineering of Hangzhou Dianzi University in 2018 and founded the Anti-Icing Materials (AIM) Laboratory. His research interest focuses on superhydrophobic materials and anti-icing materials.

Author Contributions

‡ Q.H. and Z.G. contributed equally to this work.

The authors declare no competing financial interest.

References

  1. a Shi G.; Wu M.; Zhong Q.; Mu P.; Li J. Superhydrophobic waste cardboard aerogels as effective and reusable oil absorbents. Langmuir 2021, 37 (25), 7843–50. 10.1021/acs.langmuir.1c01216. [DOI] [PubMed] [Google Scholar]; b He Z.; Wu H.; Shi Z.; Duan X.; Ma S.; Chen J.; Kong Z.; Chen A.; Sun Y.; Liu X. Mussel-inspired durable superhydrophobic/superoleophilic MOF-PU sponge with high chemical stability, efficient oil/water separation and excellent anti-icing properties. Colloid. Surface. A 2022, 648, 129142. 10.1016/j.colsurfa.2022.129142. [DOI] [Google Scholar]; c He Z.; Wu H.; Shi Z.; Gao X.; Sun Y.; Liu X. Mussel-inspired durable TiO2/PDA-based superhydrophobic paper with excellent self-cleaning, high chemical stability, and efficient oil/water separation properties. Langmuir 2022, 38 (19), 6086–98. 10.1021/acs.langmuir.2c00429. [DOI] [PubMed] [Google Scholar]; d He Z.; Wu H.; Shi Z.; Kong Z.; Ma S.; Sun Y.; Liu X. Facile preparation of robust superhydrophobic/superoleophilic TiO2 decorated polyvinyl alcohol sponge for efficient oil/water separation. ACS Omega 2022, 7 (8), 7084–95. 10.1021/acsomega.1c06775. [DOI] [PMC free article] [PubMed] [Google Scholar]; e Fan J.-B.; Song Y.; Wang S.; Meng J.; Yang G.; Guo X.; Feng L.; Jiang L. Directly coating hydrogel on filter paper for effective oil–water separation in highly acidic, alkaline, and salty environment. Adv. Funct. Mater. 2015, 25 (33), 5368–75. 10.1002/adfm.201501066. [DOI] [Google Scholar]
  2. a He Z.; Xie H.; Jamil M. I.; Li T.; Zhang Q. Electro-/photo-thermal promoted anti-icing materials: A new strategy combined with passive anti-icing and active de-icing. Adv. Mater. Interfaces 2022, 9 (16), 2200275. 10.1002/admi.202200275. [DOI] [Google Scholar]; b He Z.; Jamil M. I.; Li T.; Zhang Q. Enhanced surface icephobicity on an elastic substrate. Langmuir 2022, 38 (1), 18–35. 10.1021/acs.langmuir.1c02168. [DOI] [PubMed] [Google Scholar]
  3. He Z.; Zhang Z.; He J. CuO/Cu based superhydrophobic and self-cleaning surfaces. Scripta Mater. 2016, 118, 60–64. 10.1016/j.scriptamat.2016.03.015. [DOI] [Google Scholar]
  4. Yang R.-L.; Zhu Y.-J.; Chen F.-F.; Qin D.-D.; Xiong Z.-C. Recyclable, fire-resistant, superhydrophobic, and magnetic paper based on ultralong hydroxyapatite nanowires for continuous oil/water separation and oil collection. ACS Sustain. Chem. Eng. 2018, 6 (8), 10140–50. 10.1021/acssuschemeng.8b01463. [DOI] [Google Scholar]
  5. Li H.; Luo Y.; Yu F.; Zhang H. In-situ construction of MOFs-based superhydrophobic/superoleophilic coating on filter paper with self-cleaning and antibacterial activity for efficient oil/water separation. Colloid. Surface. A 2021, 625, 126976. 10.1016/j.colsurfa.2021.126976. [DOI] [Google Scholar]
  6. Sriram S.; Singh R. K.; Kumar A. Preparation of superhydrophobic coatings on filter paper for oil-water separation. Mater. Sci. Forum 2020, 978, 492–98. 10.4028/www.scientific.net/MSF.978.492. [DOI] [Google Scholar]
  7. a Tang X.; Shen C.; Zhu W.; Zhang S.; Xu Y.; Yang Y.; Gao M.; Dong F. A facile procedure to modify filter paper for oil–water separation. RSC Adv. 2017, 7 (48), 30495–99. 10.1039/C7RA03754F. [DOI] [Google Scholar]; b Xi J.; Lou Y.; Jiang S.; Fang G.; Wu W. Robust paper-based materials for efficient oil–water emulsion separation. Cellulose 2021, 28 (16), 10565–78. 10.1007/s10570-021-04165-2. [DOI] [Google Scholar]
  8. Wang S.; Li M.; Lu Q. Filter paper with selective absorption and separation of liquids that differ in surface tension. ACS Appl. Mater. Interfaces 2010, 2 (3), 677–83. 10.1021/am900704u. [DOI] [PubMed] [Google Scholar]
  9. Li H.; Zhang H.; Luo Y.; Shi H.; Peng L. Fabrication of durable and sustainable superhydrophobic-superoleophilic paper for efficient oil/water separation. Cellulose 2021, 28 (8), 5033–53. 10.1007/s10570-021-03862-2. [DOI] [Google Scholar]
  10. a Wen G.; Guo Z. Nonflammable superhydrophobic paper with biomimetic layered structure exhibiting boiling-water resistance and repairable properties for emulsion separation. J. Mater. Chem. A 2018, 6 (16), 7042–52. 10.1039/C8TA01920G. [DOI] [Google Scholar]; b Li Q.; Wu D.; Huang J.; Guo Z. Kevlar fiber-reinforced multifunctional superhydrophobic paper for oil–water separation and liquid transportation. New J. Chem. 2019, 43 (38), 15453–61. 10.1039/C9NJ03563J. [DOI] [Google Scholar]
  11. Piltan S.; Seyfi J.; Hejazi I.; Davachi S. M.; Khonakdar H. A. Superhydrophobic filter paper via an improved phase separation process for oil/water separation: study on surface morphology, composition and wettability. Cellulose 2016, 23 (6), 3913–24. 10.1007/s10570-016-1059-y. [DOI] [Google Scholar]
  12. Du C.; Wang J.; Chen Z.; Chen D. Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method. Appl. Surf. Sci. 2014, 313, 304–10. 10.1016/j.apsusc.2014.05.207. [DOI] [Google Scholar]
  13. a Roy S.; Zhai L.; Van Hai L.; Kim J. W.; Park J. H.; Kim H. C.; Kim J. One-step nanocellulose coating converts tissue paper into an efficient separation membrane. Cellulose 2018, 25 (9), 4871–86. 10.1007/s10570-018-1945-6. [DOI] [Google Scholar]; b Ge D.; Yang L.; Wang C.; Lee E.; Zhang Y.; Yang S. A multi-functional oil–water separator from a selectively pre-wetted superamphiphobic paper. Chem. Commun. 2015, 51 (28), 6149–52. 10.1039/C4CC09813G. [DOI] [PubMed] [Google Scholar]; c Li H.; Luo Y.; Yu F.; Peng L. Simple and scalable preparation of robust and magnetic superhydrophobic papers by one-step spray-coating for efficient oil-water separation. Colloid. Surface. A 2022, 640, 128449. 10.1016/j.colsurfa.2022.128449. [DOI] [Google Scholar]
  14. a Wu H.; Wu L.; Lu S.; Lin X.; Xiao H.; Ouyang X.; Cao S.; Chen L.; Huang L. Robust superhydrophobic and superoleophilic filter paper via atom transfer radical polymerization for oil/water separation. Carbohyd. Polym. 2018, 181, 419–25. 10.1016/j.carbpol.2017.08.078. [DOI] [PubMed] [Google Scholar]; b Zhang K.; Wang M.; Wu M.; Wu Q.; Liu J.; Yang J.; Zhang J. Fabrication of robust superhydrophobic filter paper for oil/water separation based on the combined octadecanoyl chain bonding and polymer grafting via surface-initiated ATRP. Cellulose 2020, 27 (1), 469–80. 10.1007/s10570-019-02810-5. [DOI] [Google Scholar]
  15. Bai W.; Guan M.; Lai N.; Yao R.; Xu Y.; Lin J. Superhydrophobic paper from conjugated poly(p-phenylene)s: Self-assembly and separation of oil/water mixture. Mater. Chem. Phys. 2018, 216, 230–36. 10.1016/j.matchemphys.2018.06.014. [DOI] [Google Scholar]
  16. Khan S. A.; Zulfiqar U.; Hussain S. Z.; Zaheer U.; Hussain I.; Husain S. W.; Subhani T. Fabrication of superhydrophobic filter paper and foam for oil–water separation based on silica nanoparticles from sodium silicate. J. Sol-Gel Sci. Technol. 2017, 81 (3), 912–20. 10.1007/s10971-016-4250-6. [DOI] [Google Scholar]
  17. a Yun T. T.; Tong H.; Wang Y. L.; Qian F.; Cheng Y.; Lv Y. N.; Lu J.; Li M. J.; Wang H. S. Fabrication of the superhydrophobic natural cellulosic paper with different wettability and oil/water separation application. J. Appl. Polym. Sci. 2021, 138 (19), 50371. 10.1002/app.50371. [DOI] [Google Scholar]; b Ge B.; Zhu X.; Li Y.; Men X.; Li P.; Zhang Z. The efficient separation of surfactant-stabilized water-in-oil emulsions with a superhydrophobic filter paper. Appl. Phys. A: Mater. Sci. Process. 2015, 121 (3), 1291–97. 10.1007/s00339-015-9509-1. [DOI] [Google Scholar]; c Gao Z.; Zhai X.; Liu F.; Zhang M.; Zang D.; Wang C. Fabrication of TiO2/EP super-hydrophobic thin film on filter paper surface. Carbohyd. Polym. 2015, 128, 24–31. 10.1016/j.carbpol.2015.04.014. [DOI] [PubMed] [Google Scholar]; d Cao C.; Cheng J. A novel Cu(OH)2 coated filter paper with superhydrophobicity for the efficient separation of water-in-oil emulsions. Mater. Lett. 2018, 217, 5–8. 10.1016/j.matlet.2018.01.026. [DOI] [Google Scholar]; e Wang J.; Wong J. X. H.; Kwok H.; Li X.; Yu H.-Z. Facile preparation of nanostructured, superhydrophobic filter paper for efficient water/oil separation. PLoS One 2016, 11 (3), e0151439. 10.1371/journal.pone.0151439. [DOI] [PMC free article] [PubMed] [Google Scholar]; f Ruan X.; Xu T.; Chen D.; Ruan Z.; Hu H. Superhydrophobic paper with mussel-inspired polydimethylsiloxane–silica nanoparticle coatings for effective oil/water separation. RSC Adv. 2020, 10 (14), 8008–15. 10.1039/C9RA08018J. [DOI] [PMC free article] [PubMed] [Google Scholar]; g Belal A. S.; Nady J. E.; Shokry A.; Ebrahim S.; Soliman M.; Khalil M. Superhydrophobic functionalized cellulosic paper by copper hydroxide nanorods for oils purification. Sci. Rep. 2021, 11 (1), 16261. 10.1038/s41598-021-95784-z. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Zhang M.; Wang C.; Wang S.; Shi Y.; Li J. Fabrication of coral-like superhydrophobic coating on filter paper for water–oil separation. Appl. Surf. Sci. 2012, 261, 764–69. 10.1016/j.apsusc.2012.08.097. [DOI] [Google Scholar]
  19. Satapathy M.; Varshney P.; Nanda D.; Panda A.; Mohapatra S. S.; Kumar A. Fabrication of superhydrophobic and superoleophilic polymer composite coatings on cellulosic filter paper for oil–water separation. Cellulose 2017, 24 (10), 4405–18. 10.1007/s10570-017-1420-9. [DOI] [Google Scholar]
  20. Li H.; Wu L.; Zhang H.; Yu F.; Peng L. Mussel-inspired fabrication of superhydrophobic cellulose-based paper for the integration of excellent antibacterial activity, effective oil/water separation and photocatalytic degradation. Colloid. Surface. A 2022, 640, 128490. 10.1016/j.colsurfa.2022.128490. [DOI] [Google Scholar]
  21. Teng Y.; Wang Y.; Shi B.; Li X.; Chen Y. Robust superhydrophobic surface fabrication by fluorine-free method on filter paper for oil/water separation. Polym. Test. 2020, 91, 106810. 10.1016/j.polymertesting.2020.106810. [DOI] [Google Scholar]
  22. Zhang F.; Ren H.; Shen L.; Tong G.; Deng Y. Micro–nano structural engineering of filter paper surface for high selective oil–water separation. Cellulose 2017, 24 (7), 2913–24. 10.1007/s10570-017-1292-z. [DOI] [Google Scholar]
  23. Yang X.; Liu S.; Zhao Z.; He Z.; Lin T.; Zhao Y.; Li G.; Qu J.; Huang L.; Peng X.; Liu D. A facile, clean construction of biphilic surface on filter paper via atmospheric air plasma for highly efficient separation of water-in-oil emulsions. Sep. Purif. Technol. 2021, 255, 117672. 10.1016/j.seppur.2020.117672. [DOI] [Google Scholar]
  24. Ren J.; Tao F.; Liu L.; Wang X.; Cui Y. A novel TiO2@stearic acid/chitosan coating with reversible wettability for controllable oil/water and emulsions separation. Carbohyd. Polym. 2020, 232, 115807. 10.1016/j.carbpol.2019.115807. [DOI] [PubMed] [Google Scholar]
  25. Li Q.; Sun Q.; Li Y.; Wu T.; Li S.; Zhang H.; Huang F. Solar-heating crassula perforata-structured superoleophilic CuO@CuS/PDMS nanowire arrays on copper foam for fast remediation of viscous crude oil spill. ACS Appl. Mater. Interfaces 2020, 12 (17), 19476–82. 10.1021/acsami.0c01207. [DOI] [PubMed] [Google Scholar]

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES