Superhydrophobic 304 Stainless Steel Mesh for the Removal of High-Density Polyethylene Microplastics

Eco-friendly lily bulb-derived polysaccharide aerogel for efficient microplastics and nanoplastics removal

Microplastics that eventually convert into nanoplastics are emerging global pollutants and the development of efficient adsorbents for their removal is urgently needed. For sustainability and eco-friendliness, in the current study, a polysaccharide aerogel (LPA) was prepared with lily bulbs as the raw material by following water bath extraction, purification and freeze-drying processes. The prepared porous LPA was then applied as a packing material in a mini adsorption column for removing polystyrene (PS) microplastics and nanoplastics. Results revealed that LPA was over 90 kDa in size and consisted mainly of glucomannan and the removal efficiencies for microplastics and nanoplastics were 93.68 % and 96.98 %, respectively, mainly due to hydrogen bonding interactions and porous structure. The adsorption column was robust and maintained a remarkable removal efficiency (over 90 %) for 3 months. In addition, the effects of other extraction methods and pre-freezing conditions before the freeze-drying process were studied. Compared with water bath extraction, ultrasonic-assisted extraction and microwave-assisted extraction transformed the LPA structure, resulting in reduced adsorption ability, while the pre-freezing temperature could be used to adjust the specific surface area. Meanwhile, the effects of temperature and pH of adsorbates were also investigated. The LPA was heat sensitive and not stable under strongly acidic (pH 4) or strongly alkaline (pH 10) conditions, resulting in a sharp decline in removal efficiency. The adsorption behaviour of LPA was further described via adsorption kinetic models, showing that the microplastics and nanoplastics adsorptions could be fitted by pseudo-second-order and pseudo-first-order models, respectively. Moreover, the adsorption performance of LPA was compared with some other aerogels and had a better result. This research provides a promising, sustainable alternative for microplastic and nanoplastic removal that has potential for pollutant adsorption and sample purification as well as a low preparation cost.

Durably Superhydrophobic Magnetic Cobalt Ferrites for Highly Efficient Oil-Water Separation and Fast Microplastic Removal

Microplastic pollution has become a primary global concern in the 21st century. Recyclable magnetic particles with micro-nanostructures are considered an efficient and economical way to remove microplastics from water. In this study, superhydrophobic magnetic cobalt ferrite particles were prepared by using a simple coprecipitation method combined with surface functionalization. The micromorphology, chemical composition, hysteresis loop, and surface contact angle of the functionalized cobalt ferrite were characterized. The separation efficiency and absorption capacity of cobalt ferrite particles in water-oil separation and microplastic removal were investigated. The results showed that the saturation magnetic field intensity of cobalt ferrite was 65.52 emu/g, the residual magnetization intensity (Mr) was 18.79 emu/g, and the low coercivity was 799.83 Oe. Cobalt ferrites had stable superhydrophobicity in the pH range of 1-13. The separation efficiency of cobalt ferrite powder for four oil-water mixture separations was higher than 94.2%. The separation efficiency was as high as 99.6% in the separation of the hexane and water mixtures. Due to the synergistic effect of the hydrophobic effect and van der Waals force, the functionalized magnetic cobalt ferrite had a high and stable microplastic removal efficiency and capture capacity. The removal efficiency of microplastics was close to 100%, and the capture capacity was 2.56 g/g. After ten microplastic removal cycles, the removal efficiency reached more than 98%, and the surface contact angle was still greater than 150°.

Deriving Superhydrophobicity Directly and Solely from Molecules: A Facile and Emerging Approach

Nature-inspired superhydrophobic surfaces have gained significant attention due to their various potential applications. Artificial superhydrophobic surfaces were fabricated through co-optimization of topography and low-surface-energy chemistry. In the conventional approach, artificial superhydrophobic surfaces are developed through associating mostly polymer, metal, alloys, nanoparticles, microparticles, etc. and commonly encounter several challenges related to scalability, durability, and complex fabrication processes. In response to these challenges, molecule-based approaches have emerged as a promising alternative, providing several advantages such as prolonged shelf life of depositing solution, higher solvent compatibility, and a simple fabrication process. In this Perspective, we have provided a concise overview of traditional and molecule-based approaches to fabricating superhydrophobic surfaces, highlighting recent advancements and challenges. We have discussed various molecule-based strategies for tailoring water wettability, customizing mechanical properties, developing substrate-independent coatings, prolonging the shelf life of deposition solutions, and so on. Here, we have illustrated the potential of molecule-based approaches in overcoming existing limitations and its importance to diverse and prospective practical applications.

High sensitivity in quantitative analysis of mixed-size polystyrene micro/nanoplastics in one step

As emerging environmental pollutants, microplastics (MPs) and nanoplastics (NPs) pose a serious threat to human health. Owing to the lack of feasible and reliable analytical methods, the separation and identification of MPs and NPs of different sizes remains a challenge. In this study, a hyphenated method involving filtration and surface-enhanced Raman spectroscopy (SERS) for the separation and identification of MPs and NPs is reported. This method not only avoids the loss of MPs and NPs during the transfer process but also provides an excellent SERS substrate. The SERS substrate was fabricated by electrochemically depositing silver particles onto the reduced graphene oxide layer coated on stainless steel mesh. Results show that polystyrene (PS) MPs and NPs are efficiently separated on the SERS substrate via vacuum filtration, resulting in high retention rates (74.26 % ± 1.58 % for 100 nm, 81.06 % ± 1.49 % for 500 nm, and 97.73 % ±0.11 % for 5 μm) and low limit of detection (LOD). The LOD values of 100 nm, 500 nm, and 5 μm PS are 8.89 × 10-5, 3.39 × 10-5, and 1.57 × 10-4 μg/mL, respectively. More importantly, a linear relationship for uniform quantification of 100 nm, 500 nm, 3 μm and 5 μm PS was established, and the relationship is Y = 225.61 lgX + 1076.36 with R2 = 0.980. The method was validated for the quantitative analysis of a mixture of 100 nm, 500 nm PS NPs, 3 μm and 5 μm PS MPs in a ratio of 1:1:1:1, which successfully approaches the evaluation of evaluated PS NPs in the range of 10-4-10 μg/mL with an LOD value of approximately 7.82 × 10-5 μg/mL. Moreover, this method successfully detected (3.87 ± 0.06) × 10-5 μg MPs and NPs per gram of oyster tissue.

Revealing the Mechanism of Ink Flaking from Surfaces of Palm Leaves (Corypha umbraculifera)

Palm leaves are the primary literary support in South and Southeast Asia before the widespread use of paper. However, palm leaf manuscripts face the threat of information loss due to the persistent issue of ink flaking during long-term preservation. Herein, we focus on studying the botanical structure, surface properties, and surface composition of palm leaves to gain an insightful understanding of the mechanism of ink flaking. According to the surface energy analysis, the surface of palm leaves is dominated by the dispersive component due to the presence of hydrophobic substances, resulting in the weak interaction between the handwriting and palm leaves. Moreover, the accumulation of silicon on palm leaves creates a "cuticle-silicon double layer", leading to a dense structure that hinders deep ink absorption. These two main reasons are considered to cause the ink flaking easily, which is further proven by the ink flaking test with the simulated palm leaf manuscripts. To the best of our knowledge, this is the first in-depth technical study on the adhesion performance of handwriting on plant leaves. This work also provides a theoretical basis for the study of the deterioration, adhesive repair, enhancement of flexibility, handwriting reinforcement, and beyond, which contributes to the conservation of precious palm leaf manuscripts.

A facile approach for oil-water separation using superhydrophobic polystyrene-silica coated stainless steel mesh bucket

Inspired by traditional shaduf technology in the irrigation field, we fabricated a superhydrophobic stainless steel mesh bucket by layering polystyrene and SiO2 nanoparticles through a facile dip coating technique for effective oil-water separation. The superhydrophobic steel mesh bucket could effectively lift oil as well as microplastic pollutants from the water surface. The water contact angle of a two-layered polystyrene-silica coating was 158.5° ± 2°, while the oil contact angle was nearly 0°. The oil-water separation performance of superhydrophobic mesh was tested using several kinds of oil. The separation efficiency achieved for low viscous oil was 99.33 %, while 86.66 % efficiency was recorded for high viscous oil. The superhydrophobic mesh showed high durability against mechanical tests including bending, folding, twisting, adhesive tape tearing (25 cycles), and sandpaper abrasion (20 cycles). The mesh presented admirable thermal and chemical durability. The present superhydrophobic steel mesh bucket is a suitable candidate for large-scale application.

Superhydrophobic cotton fabrics for effective removal of high-density polyethylene and polypropylene microplastics: Insights from surface and colloidal analysis

HYPOTHESIS

The use of superhydrophobic materials to remove particulate pollutants such as microplastics is still in its infancy. In a previous study, we investigated the effectiveness of three different types of superhydrophobic materials - coatings, powdered materials, and meshes - for removing microplastics. In this study, we will explain the removal process by considering microplastics as colloids and taking into account their wetting properties as well as those of a superhydrophobic surface. The process will be explained through the interactions of electrostatic forces, van der Waals forces, and the DLVO theory.

EXPERIMENTS

In order to replicate and verify the previous experimental findings on the removal of microplastics using superhydrophobic surfaces, we have modified non-woven cotton fabrics with polydimethylsiloxane. We then proceeded to remove high-density polyethylene and polypropylene microplastics from water by introducing oil at the microplastics-water interface, and we determined the removal efficiency of the modified cotton fabrics.

FINDINGS

After achieving a superhydrophobic non-woven cotton fabric (159 ± 1°), we confirmed its effectiveness in removing high-density polyethylene and polypropylene microplastics from water with a removal efficiency of 99%. Our findings suggest that the binding energy of microplastics increases and the Hamaker constant becomes positive when they are present in oil instead of water, leading to their aggregation. As a result, electrostatic interactions become negligible in the organic phase, and van der Waals interactions become more important. The use of the DLVO theory allowed us to confirm that solid pollutants can be easily removed from the oil using superhydrophobic materials.

Soft and Rigid Integrated Durable Coating for Large-Scale Deicing

Soft silicone has been widely used for anti-icing coating, but the ice adhesion strength is usually scaled with the iced area at a relatively large thickness. On the other hand, a thin rigid poly(vinyl chloride) (PVC) film could be independent of the iced area and was named a low-interfacial-toughness material. Thus, a soft and rigid integrated (SRI) coating was prepared by doping PVC particles into a silicone matrix here. The introduction of PVC particles not only served as phase II to accelerate the stress concentration but also favored the formation of a wrinkle structure. After further introducing plasticizers, this SRI coating not only has a very low ice adhesion strength at a low iced length but also tends to a limit value irrespective of the iced length, which further leads to excellent large-area deicing behavior. Furthermore, the SRI coating demonstrated outstanding chemical stability, mechanical robustness, and on-field repairability.

Removal of dyes, oils, alcohols, heavy metals and microplastics from water with superhydrophobic materials

A wide variety of pollutants can be currently found in water that are extremely difficult to remove due to their chemical composition and properties. A lot of effort has been made to tackle this issue that directly affects the environment. In this scenario, superhydrophobic surfaces, which have a water contact angle >150°, have emerged as an innovative technology that could be applied in different ways. Their environmental applications show promise in removing emerging pollutants from water. While the number of publications on superhydrophobic materials has remained largely unchanged since 2019, the number of articles on the environmental applications of superhydrophobic surfaces is still rising, corroborating the interest in this area. Herein, we briefly present the basis of superhydrophobicity and show the different materials that have been used to remove pollutants from water. We have identified five types of emerging pollutants that are efficiently removed by superhydrophobic materials: oils, microplastics, dyes, heavy metals, and ethanol. Finally, the future challenges of these applications are also discussed, considering the state of the art of the environmental applications of superhydrophobic materials.