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Superhydrophobic, photothermal, and UV-resistant coatings obtained by polydimethylsiloxane treating self-healing hydrophobic chitosan-tannic acid surface for oil/water separation
... The prepared coating provided a new strategy to develop reproof and waterproof cotton fabrics. 134 UV resistant and photothermal cotton fabric coating using chitosan, tannic acid and polydimethylsiloxane was developed by Zheng et al. (2023) superhydrophobic. Initially, polytannic acid (PTA) was coated on cotton surface (Cot@PTA) followed by deposition of PTA and chitosan mixture on the (Cot@PTA) surface. ...
... To further increase hydrophobicity they introduced polydimethylsiloxane in the coating which resulted into (Cot@PTA@PTA-CS@PDMS) exhibited a contact angle of about 153.0 ± 0.5°and sustained the contact angle up to 135.7 ± 3.9°and 137.2 ± 4.3°aer 120 cycles of sandpaper abrasion and 600 times of Taber-type abrasion (Fig. 22). 135 An ecofriendly strategy was developed by Thirumalaisamy Suryaprabha et al. (2023) where they successfully synthesized chitosan-PAni-ZnO-STA composites and coated it on the cotton bers. Chitosan was utilized to provide antimicrobial property, polyaniline was introduced to help generate reactive oxygen species, ZnO to construct surface roughness and low surface energy was achieved by stearic acid (STA). ...
... Preparation demonstration of SH coating on cotton fabric using chitosan, tannic acid and polydimethylsiloxane.135 Reproduced from ref.135 with permission from Chemical Engineering Journal, copyright 2023. ...
Superhydrophobic coatings with remarkable water repellence have emerged as an increasingly prominent field of research with the growth of the material engineering and coating industries. Superhydrophobic coatings address the requirements of several application areas with characteristics including corrosion resistance, drag reduction, anti-icing, anti-fogging, and self-cleaning properties. Furthermore, the range of applications for superhydrophobic coatings has been substantially broadened by the inclusion of key performance features such as flame retardancy, thermal insulation, resistance to water penetration, UV resistance, transparency, anti-reflection, and many more. Numerous research endeavours have been focused on biomimetic superhydrophobic materials because of their distinct surface wettability. To develop superhydrophobic coatings with a long lifespan, scientists have refined the processes of material preparation and selection. To accomplish water repellency, superhydrophobic coatings are usually fabricated using harmful fluorinated chemicals or synthetic polymers. Utilising materials derived from biomass offers a sustainable alternative that uses renewable resources in order to eliminate the consumption of these hazardous substances. This paper provides an insight of several researches reported on the construction of superhydrophobic coatings using biomass materials such as lignin, cellulose, chitosan and starch along with the techniques used for the constructing superhydrophobic coatings. This study is a useful resource that offers guidance on the selection of various biobased polymers for superhydrophobic coatings tailored to specific applications. The further part of the paper put a light on different application of superhydrophobic coatings employed in various disciplines and the future perspectives of the superhydrophobic coatings.
... Raeisi et al. 101 preparation a superhydrophobic cotton fabric using chitosan and nano TiO 2 , and found that the cotton fabric with added chitosan solution changed from superhydrophilic (WCA=0°) to hydrophilic (WCA=62°). Furthermore, the unpredictable surface hydrophobicity created by hydrophilic chitosan and tannic 16 acid, 102 this novel method can replace the traditional fluorine-free or fluorine hydrophobic materials. In this process, chitosan not only improves the surface roughness but also reduces the surface free energy of the fabric. ...
The application of fluorinated coatings on textiles has garnered substantial research interest over the past years, owing to their ability to endow fabrics with exceptional hydrophobic characteristics, thereby mitigating issues associated with high moisture absorption and susceptibility to contamination. Nevertheless, the deployment of fluorinated substances has been proscribed due to concerns regarding their ecological impact and potential human toxicity. Consequently, there has been a burgeoning demand for hydrophobic textile alternatives derived from non-fluorinated, natural materials that are both sustainable and environmentally benign. This paper presents a thorough overview of the advancements in the development and functionalization of eco-friendly, hydrophobic textiles. Initially, the natural materials and their derivatives utilized in the creation of superhydrophobic textiles are delineated, including cellulose, lignin and chitosan, among others. Subsequently, methodologies for crafting efficient, stable, and resilient hydrophobic textiles are elucidated, encompassing conventional techniques as well as novel, inventive concepts. Furthermore, the current state of research and the obstacles faced in the evolution of multifunctional textiles based on superhydrophobic fabrics are examined. In conclusion, this discussion presents incisive insights into the impending direction of advancements in functional textiles.
Keywords: Eco-friendly; Superhydrophobic; Bioinspired; Multifunctional textiles; Natural materials.
... The surface morphologies of cotton fabric before and after finishing were shown in Figure 2. As illustrated by the scanning electron microscopy (SEM) images in Figure 2, COT cotton fibers exhibited a smooth surface texture and a curved structure, while there were some noticeable creases and a tiny number of particle protrusions 25 for the treated fabric C(3PA + 3TA). This indicated that TA and PA were successfully deposited on the surface of cotton fabric. ...
The ultraviolet/flame retardant protection cotton fabric is successfully prepared using a spray baking process with tannic acid (TA) and phytic acid (PA) as key ingredients to address the issues of cotton fabric such as high flammability and lack of ultraviolet (UV) resistance. With respect to the treated fabric by 4 wt% PA solution and 3 wt% TA solution, it presented 29.5% limited oxygen index (LOI) value, 8.0 cm damaged length and 26.4 ultraviolet protection factor (UPF), while they were 28.3%, 7.5 cm and 30.6 for treated fabric by 3 wt% PA solution and 4 wt% TA solution, which indicated that in the mixed system, although TA primarily acted as an anti‐UV agent, it also exhibited flame retardant properties, and PA primarily functioned as a flame retardant and could provide a certain degree of UV protection. The prepared cotton fabric through this facile method presented excellent UV/flame retardant protection capabilities, and improved the functional efficiency of TA and PA materials. Moreover, as‐prepared fabric showed great application potential, especially in outdoor‐applied fields such as sportswear, sunshade tents, sunshade hats, and so on.
... The same self-cleaning performance was found by Zheng et al. to the hydrophobization of cotton fabrics coated with chitosan and tannic acid treated with polydimethylsiloxane. The self-cleaning fabric remained stable after 8 cycles [94]. ...
... The appearance of characteristic peaks at 554 cm − 1 (S -S stretching vibration), 1272 cm − 1 (C --S stretching vibration), and 1498 cm − 1 (N-C --S stretching vibration) indicates the successful loading of DSF onto the nanoparticle carrier [45,46]. The peak at 1710 cm − 1 (C --O stretching vibration) and 3450 cm − 1 (O -H stretching vibration) arises from TA, providing evidence for the successful modification of AH with TA/Cu [47,48]. XRD patterns are shown in Fig. 2c. ...
The Cu2+ complex formed by the coordination of disulfiram (DSF) metabolite diethyldithiocarbamate (DTC), Cu (DTC)2, can effectively inhibit tumor growth. However, insufficient Cu2+ levels in the tumor microenvironment can impact tumor-suppressive effects of DTC. In this study, we proposed a Cu2+ and DSF tumor microenvironment-targeted delivery system. This system utilizes hollow mesoporous silica (HMSN) as a carrier,after loading with DSF, encases it using a complex of tannic acid (TA) and Cu2+ on the outer layer. In the slightly acidic tumor microenvironment, TA/Cu undergoes hydrolysis, releasing Cu2+ and DSF, which further form Cu (DTC)2 to inhibit tumor growth. Additionally, Cu2+ can engage in a Fenton-like reaction with H2O2 in the tumor
microenvironment to form •OH, therefore, chemodynamic therapy (CDT) and Cu(DTC)2 are used in combination for tumor therapy. In vivo tumor treatment results demonstrated that AHD@TA/Cu could accumulate at the tumor site, achieving a tumor inhibition rate of up to 77.6 %. This study offers a novel approach, circumventing the use of traditional chemotherapy drugs, and provides valuable insights into the development of in situ tumor drug therapies.
An electroflotation coupled membrane separation (ECM) strategy is developed for cationic surfactant-stabilized emulsion treatment, demonstrating high separation efficiency and long-term antifouling capability.
Superhydrophobic materials can solve the problem of oil pollution in water resources. In this paper, superhydrophobic PDMS-SiO2 with macro-micro-nano multi-level structures was prepared by impregnation method. The superhydrophobic PDMS-SiO2 material has good physical and chemical stability, and retains its superhydrophobicity after sandpaper abrasion, tape peeling, water immersion, acid or alkali immersion, and high temperature baking. The superhydrophobic PDMS-SiO2 material has a high oil-water separation efficiency, with the highest oil-water separation efficiency reaching more than 99%, and the oil-water separation efficiency of different oils all exceeding 96%. The preparation of superhydrophobic PDMS-SiO2 material is simple, inexpensive and environmentally friendly, which can achieve fast and large-area preparation, with good engineering application prospects.
The discharge of oily wastewater in daily life and industrial production has inflicted severe damage on the natural environment and human health. Therefore, it is urgent to separate oily wastewater. Herein, a rosin-based polymer (poly(DR-DMP)) was prepared by polymerization of double-bond functionalized rosin acid (DR) and diethyl(methacryloyloxymethyl)phosphonate (DMP). And a novel superhydrophobic cotton fabric was constructed by poly(DR-DMP) and nano-hydroxyapatite (HAP). The water contact angle (WCA) and sliding angle (SA) of poly(DR-DMP)@HAP fabric achieved values of 162° and 8°, respectively. Meanwhile, the poly(DR-DMP)@HAP fabric had excellent separation performance for several oil/water mixtures, with oil fluxes up to 8941.83 L·m−2·h−1 and separation efficiency (more than 95.35 %). Furthermore, the poly(DR-DMP)@HAP fabric exhibited excellent separation performance for various emulsions, and also had excellent superhydrophobicity and oil/water separation performance after mechanical and chemical treatment. Through the vertical flame test (VFT) and thermogravimetric analysis (TG), the results showed that poly(DR-DMP)@HAP fabric had a certain flame retardancy. Overall, poly(DR-DMP)@HAP fabric had excellent superhydrophobicity, self-cleaning, oil/water separation and flame retardancy, which had great application potential in oil/water separation.
Plant polyphenols is a type of a natural substances widely present in plants, which can form a three-dimensional metal-phenolic networks (MPNs) via chelation with metal ions, thereby enabling the construction of functional material coatings. Herein, a novel and straightforward approach was employed to prepare superhydrophobic wood by utilizing a naturally-inspired strategy. The main component of wood polyphenols, rutin, was employed to create MPNs with various metal ions (Fe (III), Fe (II), Al (III), and Cu (II)), resulting in the formation of a rough hierarchical structure on the wood surface, followed by a polydimethylsiloxane (PDMS) modification. For polyphenol-free wood, it was impregnated with rutin solution and then complexed with metal ions. Taking rutin-Fe (III)-based superhydrophobic poplar as an example, it had excellent performance in self-cleaning and anti-fouling. In addition, it showed excellent resistance to acid and alkali and organic solution impregnation. The superhydrophobic coating maintained robust mechanical durability under the action of long-term placing, ultrasonic washing, tape peeling and sandpaper grinding as well. We believe that the superhydrophobic wood modified with rutin-metal complexes and PDMS is considered environmentally friendly, cost-effective, sustainable, and easily scalable. Thus, it exhibits immense potential for practical applications in indoor and outdoor decoration as well as building materials.
Developing nanomedicines with superior reactive oxygen species (ROS) scavenging capability has emerged as a promising strategy in treating ROS‐related diseases, for example, drug‐induced liver injury. However, designing nanoscavengers with the self‐propelling ability to scavenge ROS actively remains challenging. Here, a self‐propelled silica‐supported ultrasmall gold nanoparticles‐tannic acid hybrid nanozyme (SAuPTB) is designed that can effectively alleviate acetaminophen (APAP)‐induced liver injury by scavenging excessive ROS and regulating inflammation. SAuPTB exhibits multienzyme activity and displays significantly enhanced diffusion under hydrogen peroxide (H2O2). This in vitro research shows that SAuPTB can effectively eliminate ROS, increasing the viability of H2O2‐stimulated cells and reducing the cytotoxicity of APAP/H2O2‐treated AML12 cells. The in vivo studies show that SAuPTB can accumulate at inflammatory sites in mouse liver, resulting in the decrease of alanine aminotransferase, aspartate aminotransferase, and ROS, reduction in pro‐inflammatory cytokines and chemokines, hence reduced hepatocyte necrosis, liver injury, and mortality. Furthermore, SAuPTB activates the nuclear erythroid 2‐related factor 2 pathway to upregulate antioxidative genes and reduce oxidative stress. Finally, the liver shows decreased high mobility group box 1 and F4/80⁺ macrophages, suggesting an anti‐inflammatory response. This work provides a novel design strategy of nanozymes for ROS‐related disease treatment.
Fabricating controllable superhydrophobic surfaces remains challenging in various fields ranging from chemical industries to biomedical engineering. Conventional methods commonly require volatile organic solvents and the assistance of special surface deposition and modification equipment, which are detrimental to environment and limit their applications in micro‐devices. Herein, an equipment‐free method is reported to directly transform fluorinated monomer micro‐droplets into hydrophobic polymer particles on flat substrate surfaces in water, simultaneously depositing hydrophobic coatings with tunable surface structures. The as‐prepared surfaces show superior superhydrophobicity and great stability in extreme conditions (e.g., varying acidity, basicity, and heating conditions), and excellent anti‐fouling property. Meanwhile, surface hydrophobicity can be manipulated by adjusting emulsion droplet number density and reaction time. Hence, superhydrophobic surfaces with tunable hydrophobicity gradients have been successfully fabricated in one pot. This study provides an equipment‐free method to facilely fabricate controllable superhydrophobic surfaces, with great potential in the development of smart superhydrophobic materials in various engineering and industrial applications.
Superhydrophobic textiles are important superhydrophobic materials because of their low cost and high demand. In this work, low surface energy substance, dodecyltrimethoxysilane (DTM), was used to modify the hydrolyzed tetrabutyl titanate (Ti(OH)4) to obtain DTM@Ti(OH)4 particles and realize the surface organic modification of Ti(OH)4 particles. Then, functional cotton fabric was prepared by loading DTM@Ti(OH)4 particles onto the fabric based on the adhesion of natural polyphenols. The static contact angle of finished cotton fabric was up to 169.9°, the rolling contact angle was less than 8°, and the UPF value was generally greater than 70. Due to the excellent adhesion of polyphenols, the superhydrophobic cotton fabric showed great stability and durability under harsh environmental conditions. By various treatments, the water contact angles (CA) of the finished fabrics can still be greater than 155° and the UPF value was still greater than 50. The preparation process is simple, efficient and low-cost, which is suitable for large-scale industrial production. Encouragingly, this modification method is universal and can be applied to other kinds of fabrics. It has broad application prospects in outdoor textiles, oil and water separation, metal corrosion prevention and other fields.
Graphic abstract
Superhydrophobic materials have been widely reported throughout the scientific literature. Their properties originate from a highly rough morphology and inherently water repellent surface chemistry. Despite promising an array of functionalities, these materials have seen limited commercial development. This could be attributed to many factors, like material compatibility, low physical resilience, scaling-up complications, etc. In applications where persistent water contact is required, another limitation arises as a major concern, which is the stability of the air layer trapped at the surface when submerged or impacted by water. This review is aimed at examining the diverse array of research focused on monitoring/improving air layer stability, and highlighting the most successful approaches. The reported complexity of monitoring and enhancing air layer stability, in conjunction with the variety of approaches adopted, results in an assortment of suggested routes to achieving success. The review is addressing the challenge of finding a balance between maximising water repulsion and incorporating structures that protect air pockets from removal, along with challenges related to the variant approaches to testing air-layer stability across the research field, and the gap between the achieved progress and the required performance in real-life applications.
Oily wastewater seriously pollutes the environment, and is difficult to separate. In this work, superhydrophobic cotton fabrics were fabricated through the combination of micro–nano-binary structure of polydopamine (PDA) and grafting of octadecylamine (ODA). Herein, fluorine-free compounds were used. The PDA binary structure was rapidly deposited on cotton fabric under the catalysis of metal salts and oxidants. Then, the ODA was grafted onto the cotton fabric through Schiff base reaction with o-quinone formed by oxidation of the catechol structure of PDA, which covered the surface of PDA coated cotton fabric. The superhydrophobic cotton fabric with contact angle up to 163.7° and scroll angle around 9° was obtained. Due to the excellent adhesion of polydopamine, the superhydrophobic cotton fabric demonstrated great stability and durability under a variety of harsh environmental conditions. After coating the polyurethane (PU) sponge with the prepared superhydrophobic cotton fabric, an oil absorbing bag was made and it showed good oil–water separation even after being reused 20 times, and the prepared cotton fabric also had excellent self-cleaning performance. This facile strategy of preparation of superhydrophobic materials for continuous oil–water separation is quick, efficient and environmentally friendly, which has great prospect for application in removal of marine oil spills.
Graphic abstract
The ability of superhydrophobic surfaces to stay dry, self-clean and avoid biofouling is attractive for applications in biotechnology, medicine and heat transfer1,2,3,4,5,6,7,8,9,10. Water droplets that contact these surfaces must have large apparent contact angles (greater than 150 degrees) and small roll-off angles (less than 10 degrees). This can be realized for surfaces that have low-surface-energy chemistry and micro- or nanoscale surface roughness, minimizing contact between the liquid and the solid surface11,12,13,14,15,16,17. However, rough surfaces—for which only a small fraction of the overall area is in contact with the liquid—experience high local pressures under mechanical load, making them fragile and highly susceptible to abrasion¹⁸. Additionally, abrasion exposes underlying materials and may change the local nature of the surface from hydrophobic to hydrophilic¹⁹, resulting in the pinning of water droplets to the surface. It has therefore been assumed that mechanical robustness and water repellency are mutually exclusive surface properties. Here we show that robust superhydrophobicity can be realized by structuring surfaces at two different length scales, with a nanostructure design to provide water repellency and a microstructure design to provide durability. The microstructure is an interconnected surface frame containing ‘pockets’ that house highly water-repellent and mechanically fragile nanostructures. This surface frame acts as ‘armour’, preventing the removal of the nanostructures by abradants that are larger than the frame size. We apply this strategy to various substrates—including silicon, ceramic, metal and transparent glass—and show that the water repellency of the resulting superhydrophobic surfaces is preserved even after abrasion by sandpaper and by a sharp steel blade. We suggest that this transparent, mechanically robust, self-cleaning glass could help to negate the dust-contamination issue that leads to a loss of efficiency in solar cells. Our design strategy could also guide the development of other materials that need to retain effective self-cleaning, anti-fouling or heat-transfer abilities in harsh operating environments.
We investigate wetting and water repellency characteristics of Colocasia esculenta (taro) leaf and an engineered surface, bioinspired by the morphology of the surface of the leaf. Scanning electron microscopic images of the leaf surface reveal a two-tier honeycomb-like microstructures, as compared to previously-reported two-tier micropillars on a Nelumbo nucifera (lotus) leaf. We measured static, advancing, and receding angle on the taro leaf and these values are around 10% lesser than those for the lotus leaf. Using standard photolithography techniques, we manufactured bioinspired surfaces with hexagonal cavities of different sizes. The ratio of inner to the outer radius of the circumscribed circle to the hexagon (b/a) was varied. We found that the measured static contact angle on the bioinspired surface varies with b/a and this variation is consistent with a free-energy based model for a droplet in Cassie-Baxter state. The static contact angle on the bioinspired surface is closer to that for the leaf for b/a ≈ 1. However, the contact angle hysteresis is much larger on these surfaces as compared to that on the leaf and the droplet sticks to the surfaces. We explain this behavior using a first-order model based on force balance on the contact line. Finally, the droplet impact dynamics was recorded on the leaf and different bioinspired surfaces. The droplets bounce on the leaf beyond a critical Weber number (We ~ 1.1), exhibiting remarkable water-repellency characteristics. However, the droplet sticks to the bioinspired surfaces in all cases of We. At larger We, we recorded droplet breakup on the surface with larger b/a and droplet assumes full or partial Wenzel state. The breakup is found to be a function of We and b/a and the measured angles in full Wenzel state are closer to the predictions of the free-energy based model. The sticky bioinspired surfaces are potentially useful in applications such as water-harvesting.
Natural and artificial super-repellent surfaces are frequently textured with pillar-based discrete structures rather than hole-based continuous ones because the former exhibits lower adhesion from the reduced length of the three-phase contact line. Counterintuitively, here, we discover the unusual topographic effects on hot-water super-repellency where the continuous microcavity surface outperforms the discrete microneedle/micropillar surface. This anomaly arises from the different dependencies of liquid-repellency stability on the surface structure and water temperature in the two topographies. We interpret this unexpected wetting dynamics by determining timescales for droplet evaporation, vapor condensation, and droplet bouncing. The associated heat transfer process is unique to the wetting states and remarkably distinct from each other in the two topographies. We envision that hot-water super-repellent microcavity surfaces would be advantageous for a variety of applications, especially when both self-cleaning and thermal insulation are imperative, such as clothing for scald protection and digital microfluidics for exothermic reactions.
Since bacterial infections seriously threaten human's health, considerable attention is devoted to the design of nanoscale antibacterial materials. Among them, metal nanoparticles cannot meet the requirements of durable antibacterial effects and are harmful to biological environments. In this study, environmentally friendly nanogels with durable antibacterial and antiadhesion properties are prepared by copolymerization of styrene, polycaprolactone‐hydroxyethyl methacrylate, and polyhexamethylene guanidine hydrochloride methacrylate. The resultant nanogels possess regular spherical morphologies with the size of about 200 nm. The nanogels exhibit a strong ability to kill bacteria and the mechanism is different from that of conventional antibacterial agent loaded nanoparticles. In addition, anti‐infection experiments explored by a wound model confirm the nanogels have the capability to prevent infection. Furthermore, the nanogels grafted on the surface of cotton fibers display good thermal stability, which is essential for finishing of fabrics. The cotton fabrics finished with nanogels can prevent the adhesion of bacteria by enhancing the hydrophobicity and the bacteriostatic rate. The antibacterial fabrics against Staphylococcus aureus and Escherichia coli are still more than 86% active after 50 times of mechanical washing. The biocompatible nanogels are unleachable from the antibacterial fabrics which demonstrate that they are ideal candidates for durable and environmental‐friendly nanoscaled antimicrobial materials.
The nitration reaction of nitrite and phenolic substances was first used to identify and detect NO2- by taking fluorescent poly (tannic acid) nanoparticles (FPTA NPs) as sensing platform. With the low cost, good biodegradable and convenient water-soluble FPTA NPs, a fluorescent and colorimetric dual modes detecting assay was realized. In fluorescent mode, the linear detection range of NO2- was 0-36 μM, the LOD was as low as 3.03 nM, and the response time was 90 s. In colorimetric mode, the linear detection range of NO2- was 0-46 μM, and the LOD was as low as 27 nM. Besides, a smartphone with FPTA NPs@ agarose hydrogel formed a portable detection platform to test the fluorescent and visible color changes of FPTA NPs for NO2- sensing as well as for accurate visualization and quantitative detection of NO2- in actual water and food samples.
Thin film coatings are widely applicable in materials for consumer products, electronics, optical coatings, and even biomedical applications. Wet coating can be an effective method to obtain thin films of functional materials, and this technique has recently been studied in depth for the formation of bioinspired polyphenolic films. Naturally occurring polyphenols such as tannic acid (TA) have garnered interest due to their roles in biological processes and their applicability as antioxidants, antibacterial agents, and corrosion inhibitors. Understanding the adsorption of polyphenols to surfaces is a core aspect in the fabrication processes of thin films of these materials. In this work, the adsorption of TA to gold surfaces is measured using a quartz crystal microbalance with dissipation monitoring (QCMD) and surface plasmon resonance (SPR) for a wide range of TA concentrations. The adsorption kinetics, aggregation, and stability of TA solutions in physiological-like conditions are studied. Unexpectedly, it is found that the adsorption rates depend only weakly on concentration because of the presence of TA aggregates that do not adsorb. The mechanism of layer formation is also investigated, finding that TA monolayers readily adsorb onto gold with flat or edge-on molecular orientations dependent on the solution concentration. A mix of orientations in the intermediate case leads to slow multilayer adsorption.
The ever-increasing amount of oily wastewater from industries poses a serious threat to the ecological environment and human health, and separation of oil and water remains a worldwide challenge. Because there is a requirement to develop green, efficient and low-cost oil/water separation materials, biomass materials, including cellulose, lignin, chitosan, and wood, are widely used in oil/water adsorption and separation because of their unique spatial structure and abundant active functional groups. In this review, the current design and fabrication process of biomass-based adsorption/separation materials for oi/water separation applications are summarized and highlighted. We focus on the oil/water separation performance and material design concept of the biomass membrane, biomass aerogel, and biomass carbon aerogel from the oil/water separation mechanism and the physical morphology of oil/water separation materials. Furthermore, we propose new future directions for the functional improvement and structural design direction of new biomass-based oil/water separation materials based on the characteristics of biomass.
Development of efficient absorbent materials for detection and treatment of offshore oil spillages remained a challenge. In this work, C-shaped polypropylene oil-absorbent fibers with sub-micron internal pores were prepared by combining spun-bonding technique and thermally induced phase separation (TIPS). The effect of drawing speed on the phase separation and the porous morphology of the shaped fiber non-woven fabric (NWF) was investigated. C-shaped NWF with porous morphology had large water contact angle, higher porosity, larger specific surface area, and increased oil absorption speed and capacity. An online oil spillage detection system was developed using porous C-shaped NWF and an oxygen sensing probe, showing shorter response time and higher signal-to-noise (STN) ratio. The response time for detecting the spillage of soybean oil and diluted crude oil (0.5 mL/0.8 L) in water were only 24 s and 10 s, respectively. The reliable oil detection low detection limit (RLDL) of the oxygen sensing probe was reduced 173 times (from 36.5 g/L to 0.21 g/L) when combined with C-shaped porous fiber NWF.
Polyvinyl alcohol (PVA) and chitosan (CS) are attractive polymeric feedstocks for developing eco-environmental materials. In this work, a biodegradable and antibacterial film was developed based on PVA blending with different long-chain alkyl and different contents of quaternary chitosan through solution casting, in which quaternary chitosan not only acted as an antibacterial agent but also improved hydrophobicity and mechanical properties. A novel peak appeared at 1470 cm−1 in Transform Infrared Spectroscopy (FTIR) and a new Csingle bondCl bond spectral peak at 200 eV in X-ray photoelectron spectroscopy (XPS) spectra suggested that CS was successfully modified by quaternary. Besides, the modified films have better antibacterial effects against Escherichia (E. coli) and Staphylococcus (S. aureus) and present stronger antioxidant properties. Optical properties demonstrated that the light transmittance on both UV and visible light showed a decreasing trend with the increase of the quaternary chitosan contents. Whereas the composite films have enhanced hydrophobicity than PVA film. Furthermore, the composite films had higher mechanical properties, in which Young's modulus, tensile strength, and elongation at break were 344.99 MPa, 39.12 MPa, and 507.09 %, respectively. This research demonstrated that the modified composite films could extend the shelf of life on antibacterial packaging.
Two-dimensional graphene oxide (GO) nanosheets have emerged as ideal nano-fillers in anticorrosive epoxy coatings, but their poor dispersion because of π-π interaction, high hydrophilicity, and low compatibility with epoxy resin limit their application. In this work, to conquer these obstacles, the hydrophobic and anticorrosive GO based epoxy composite coating was developed via the synergistic enhancement effect of binary nano-fillers. To achieve this goal, the graphene oxide and nano-silica (SiO2) were hydrophobically functionalized by the 1H,1H,2H,2H-perfluoro-decyl triethioxy silane (PFDS) via a simple grafting method (SiO2-P: mSiO2:mPFDS=1:1), GO-P3: mGO:mPFDS=1:3), which were applied as binary fillers to reinforce the epoxy coating with enhanced dispersion and compatibility with matrix. Benefiting from the hierarchical micro-/nano- structure, regulated surface energy, good dispersion, and synergy of SiO2-P and GO-P3 binary fillers, the epoxy composite coating showed greatly enhanced hydrophobicity (The water contact angle increased from 70.45° to 126.84°) and anti-corrosion performance. With the synergetic enforcement of 1.5 wt % SiO2-P and 0.5 wt % GO-P3, the prepared epoxy composite coating exhibited the best anticorrosive performance with impedance of 2.74 × 10⁹ Ω·cm² (0.01 Hz) after immersion in 3.5 % NaCl medium for 30 days, which was confirmed by the salt spray test results. Meanwhile, the anti-corrosion mechanism including hydrophobicity and prolonged diffusion path of water-soluble corrosive medium was tentatively discussed.
This study investigates the effect of addition of tannic acid on nisin encapsulated in chitosan matrices. Composite materials were prepared using a mild, environmentally friendly procedure, ionotropic gelation of chitosan by sodium tripolyphosphate in the presence of nisin (N) at different concentrations. In two parallel sets of preparations, tannic acid (TA) was added at 10:1 and 5:1 N:TA, respectively. The obtained particles were characterized by FTIR, SEM, size, zeta potential, encapsulation efficiency, loading capacity, and ratio of residual free amino groups. The kinetics of nisin release from the particles was studied to assess the role of TA as a potential modulator thereof. Its addition resulted in enhanced release, higher at lower N:TA ratio. An additional benefit was that TA, a strong antioxidant, imparted antioxidant activity to the composites. Antimicrobial turbidimetric tests were performed against one gram-positive bacterium (Staphylococcus aureus) and two gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa), all relevant for the food, pharmaceutical, and cosmetic industries. All the composites showed synergistic effects against all the bacteria tested. The positive coaction was stronger against the gram-negative species. This is remarkable since nisin by itself has not known activity against them.
Hybrid organic-inorganic materials are attracting enormous interest in materials science due to the combination of multiple advantageous properties of both organic and inorganic components. Taking advantage of a simple, scalable, solvent-free hard-sacrificial method, we report the successful fabrication of three-dimensional hybrid porous foams by integrating two types of fillers into a poly(dimethylsiloxane) (PDMS) framework. These fillers consist of hydrophobic electrically conductive graphene (GR) nanoplatelets and hydrophobic bactericidal copper (Cu) microparticles. The fillers were utilized to create the hierarchical rough structure with low-surface-energy properties on the PDMS foam surfaces, leading to remarkable superhydrophobicity/superoleophilicity with contact angles of 158 and 0° for water and oil, respectively. The three-dimensional interconnected porous foam structures facilitated high oil adsorption capacity and excellent reusability as well as highly efficient oil/organic solvent-water separation in turbulent, corrosive, and saline environments. Moreover, the introduction of the fillers led to a significant improvement in the electrical conductivity and biofouling resistance (vs whole blood, fibrinogen, platelet cells, and Escherichia coli) of the foams. We envision that the developed composite strategy will pave a facile, scalable, and effective way for fabricating novel multifunctional hybrid materials with ideal properties that may find potential use in a broad range of biomedical, energy, and environmental applications.
Given that the membrane emulsification process involves the interaction between the membrane surfaces and two different phases (i.e., oil and water), separately manipulating the wettability of each surface would be crucial to achieve the high emulsification efficiency. Herein, the Janus silicon carbide (SiC) membranes were designed and prepared by using an emerging reactive sintering method and the subsequent chemical grafting modification on one of the hydrophilic surfaces. The surface wettability was selectively controlled by using hexadecyltrimethoxysilane (HDTMS) and 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (FOTS) as the hydrophobic or amphiphobic modifiers, respectively. Meanwhile, the modified side of Janus SiC membranes showed super-hydrophobicity under oil. It was found that the hydrophobic surface can inhibit the spread of water on membrane surface and the oleophobic surface can reduce the pollution of the membrane, which both affected the membrane emulsification performance. The water-in-oil (W/O) emulsions with mean water droplet size of 1.26–1.57 μm can be prepared using amphiphobic-hydrophilic Janus membranes at a high emulsification flux (1910 L·m⁻²·h⁻¹). Importantly, the pure water permeance only declined 15.6% of the original value after three times of membrane emulsification. Moreover, the polluted membranes can be easily and effectively regenerated by ultrasonic cleaning in ethanol with a flux recovery ratio of 95.8%. Therefore, the amphiphobic Janus SiC membranes showing improved anti-fouling ability can be effectively utilized in the emulsification of high-viscosity oil.
The use of auxiliaries for textile dyeing and printing and the release of residual dyeing liquor cause enormous harm to the environment, while the single function of dyed fabrics hinders their development in more advanced fields. In this work, zeolitic imidazolate framework-8 (ZIF-8) nanocrystals were grown in situ on carboxymethyl cotton fabric to absorb acid dyes without auxiliaries. To further improve its durability and color fastness, polymethylhydrosiloxane (PMHS) hydrophobic coating was used to protect its surface. The as-prepared cotton fabrics exhibited a K/S value of 21.78, a hydrophobic angle of 160.2° and a UPF value close to 50+. They showed high stability under various environmental conditions, which provided a simple and enviromental way to prepare multifunctional dyed textiles. The high hydrophobic angle of the fabric offered excellent adsorption of oil agent in the oil–water mixture, and the oil–water separation efficiency can still reach more than 95% even after 20 cycles, indicating that the fabric also had promising applications in the treatment of oiled wastewater.
The coating is an economical and convenient approach for textiles to realize multi-functionalization and broaden their applications in various fields. Polyimide (PI) is an excellent functional coating material with great thermal insulation, ultraviolet resistance, and chemical resistance; however, its coating process requires high cyclization temperature, and its inherent dark color makes it unsuitable for the preparation of functional textiles. In this study, soluble and colorless PI was successfully developed to coat onto cotton fabric via a one-step solution process, thereby effectively avoiding disrupting the substrate fabric's mechanical and color properties in the conventional two-step process. Attractively, this composite coated fabric combined various excellent properties of PI, such as high thermal resistance, water and stain resistance, UV resistance, acid resistance, etc. Especially, the warmth property of PI coated cotton fabric could improve by 3-5 folds as compared to the original cotton fabric and the PI coated cotton fabric simultaneously retained excellent air permeability. This coating method fully integrated the advantages of PI into the fabric, showing great promise for preparing multifunctional fabric in a scalable, economical, and facile way.
Climate change and global warming have increased the frequency of extreme heat stress events that severely affect plant production. Photosynthesis is an intricate heat-sensitive physiological process. Heat stress affects CO2 assimilation, photochemical reactions, D1 and D2 protein turnover, and chlorophyll biosynthesis. Heat stress-induced damage to chloroplast downregulates important chloroplast components and inactivates heat-sensitive proteins, including RuBisCo activase, causing redox imbalance, reducing photosynthetic efficiency, and possibly causing cell death. As all photochemical processes in the Calvin cycle in the stroma and thylakoid lamellae of the chloroplast are prone to heat stress injury, these organelles are the primary activators of cellular heat stress responses and signaling. This review describes approaches to protect crop plants against heat-induced photochemical damage and discusses chloroplast responses, sensitivity, and retrograde signaling that contribute to the sensitivity and tolerance of photosynthetic apparatus.
At present, the research and development of adsorbents for oil/water separation are mostly focused on polymer materials. The third generation of aerogels are made from nanocellulose prepared from abundant and sustainable cellulose. At present, there is concern regarding the use of nanocellulose aerogels (NAs) in oil/water separation. To improve the selective absorbability, the NAs should be hydrophobically modified, and in this review, we summarized the progress made in hydrophobic modification methods. Additionally, the typical materials used for hydrophobic modification of NAs in recent years were reviewed, and then, we discussed the fabrication of nanocellulose composite aerogels (NCAs) with different properties for use in oil/water separation. Moreover, the additional desirable properties of NAs used in oil/water separation processes are systematically discussed according to the different separation requirements, and the conclusions regarding the relationship between the oil adsorption capacity and different NA parameters are summarized. Finally, the outlook for and challenges faced in the construction of efficient NAs for oil/water separation were put forward.
Textile coated by natural polymer is an industrial method for enhancing the inkjet printing qualities. However, the hydrophobic modified polymer coating has been rarely reported. Here, the effect of hydrophobic methyl cellulose (MC) coating on the inkjet printing qualities of cotton fabric was investigated and compared with commonly used sodium alginate (SA) and sodium carboxymethyl cellulose (CMC) coatings. The results show that all three polymers could improve the sharpness and color depth of inkjet printing. However, the effect of the MC coating was far better than the SA and CMC coatings, which results from the different functional groups of the three polymers. Methyl groups make MC coating hydrophobic, while the SA and CMC coatings exhibit hydrophilicity. The hydrophobicity and swelling of the MC coating could synergistically reduce the spreading and penetrating of ink droplets. SA and CMC coatings rarely reduced the flow of ink droplets and only preserved part of ink by the swelling property. This work reveals the action mechanism of the polymer coating. And it is confirmed that the hydrophobic natural polymer coating is more effective than the hydrophilic coating to enhance the inkjet printing qualities.
In accord with the general trend of low carbon emissions, aiming at solving the difficulty of insoluble natural dyes pad dyeing, we innovatively proposed an efficient pad dyeing method for wool fabrics with curcumin. In this study, a color paste containing curcumin dispersion and sodium polyacrylate solution (PAAS) was used as a coloring agent to pad dyeing wool fabrics. The mixed color paste showed excellent stability and dyeing performance. The highest K/S value (16.15) can be obtained by wet steaming process under 7.5 g/L of sodium polyacrylate, 8 g/L of curcumin and steaming for 15 min. Dyeing and fixation can occur simultaneously by adding tannin, achieving an outstanding color effect. Utilization rate of natural dyes was significantly improved. This dyeing method endowed wool fabrics excellent color intensity, fastness and antibacterial activity, the wet steaming method eliminated the drying process and reduced energy consumption. It provided a feasible route for natural dyes pad dyeing and showed great potential in environmental dyeing field.
Micro/nanomotors that combine the miniaturization and autonomous motion have attracted much research interest for environmental monitoring and water remediation. However, it is still challenging to develop a facile route to produce bifunctional micromotors that can simultaneously detect and remove organic pollutants from water. Herein, we developed a novel Janus micromotor with robust peroxide-like activity for simultaneously colorimetric detection and removal of catechol from water. Such laccase (Lac) functionalized Janus micromotor consisted of calcined MgAl-layered double hydroxides (MgAl-CLDHs) nanosheets and Co3O4-C nanoparticles (Lac-MgAl-CLDHs/Co3O4-C), revealing unique 3D hierarchical microstructure with highly exposed active sites. The obtained Janus micromotors exhibited autonomous motion with a maximum velocity of 171.83±4.07 μm/s in the presence of 7 wt% H2O2 via a chemical propulsion mechanism based on the decomposition of H2O2 by Co3O4-C layer on the hemisphere surface of Janus micromotors. Owing to the combination of autonomous motion and high peroxide-like activity, Lac-MgAl-CLDHs/Co3O4-C Janus micromotors could sensitively detect catechol with the limit of detection of 0.24 μM. In addition, such Janus micromotors also could quickly degrade catechol by •OH generated from a Fenton-like reaction. It is a first step towards using autonomous micromotors for highly selective, sensitive, and facile detection and quick removal of catechol from water.
Absorbable sutures have moved to the forefront in surgical fields with a huge market. Antibacterial activity is one indispensable feature for the next generation of absorbable sutures. This study develops a simple and cost-effective coating method to endow sutures with staged control over antibacterial actions to achieve enhanced dual stages of the wound healing process. This method is achieved in aqueous solution under mild conditions without the usage of any organic solvent and reserves the fundamental properties of suture materials, based on the pH-dependent reversible self-polymerization of tannic acid (TA) together with the strong adhesion of poly (tannic acid) (PTA) not only toward the suture surface but also with TA. Just by changing pH of TA solution, a hybrid coating (MPTA) composed of PTA and TA could be readily formed on the commercialized sutures originating from synthetic and natural materials. In the initial post-surgery stage, wound sites are susceptible to aseptic and/or bacterial inflammation. The resulting acid conditions induce burst release of antibacterial TA mostly coming from the adsorbed TA monomer. In the later stage, TA release is tailored totally depending on the pH conditions determined by the healing degree of wounds, allowing the sustained antibacterial prevention in a biologically adjustable manner. Thus, antibacterial MPTA coating meets the rigid requirements that differ distinctly during two major wound healing stages. Nontoxic MPTA coating on sutures leads to excellent post-implantation outcomes regarding bacterial prevention/elimination, anti-inflammation, tissue repair and wound healing. Moreover, MPTA coating provides sutures with a robust platform for functional expansion due to the matrix-independent adhesive ability of PTA.
In recent years, membrane separation technology has been widely used in various fields. And for the increasingly severe oily wastewater system, there is an increasing demand for the anti-fouling properties of the membranes. Based on the concept of fluorine-free, non-toxic, environmental-friendly and low-cost, this study constructed a discontinuous silicon-island structure with low surface energy on the surface of the hydrophilic membrane, which endows the PVDF-CTFE membrane with fouling resistance and cleaning pH-responsiveness. The discontinuous silicon-island structures were constructed by introducing SiO2 nanoparticles on the super-hydrophilic layer of the PVDF-CTFE membrane modified by itaconic acid, and then hydrophobically treated with polydimethylsiloxane (PDMS). The experimental results exhibited that the modified membrane reached the hydrophobic and underwater super-oleophobic state when treated by PDMS for 1.0 h. The water contact angle (WCA) and the underwater oil contact angle (OCA) were 124° and 151°, respectively. Furthermore, the water flux remained at 186 L m⁻² h⁻¹ with no serious pore-plugging. Moreover, the water flux decay rate (FDR) remained below 19.6%, when modified membrane treating soybean oil/water emulsion for 6 cycles, presenting an excellent anti-fouling performance. Additionally, the water flux recovery rate (FRR) was over 99.3% after alkali cleaning, indicating the modified membrane possessed excellent cleaning pH-responsiveness. The above analysis exhibited that the synergistic effect of hydrophilic micro-domains and oleophobic micro-domains not only slows down the attachment of hydrophobic pollutants but also promotes the separation of hydrophobic pollutants during chemical cleaning, which greatly improves its anti-fouling performance and expands its application prospect.
Enzymes are versatile catalysts with high potential in various applications, and much attention has been paid to the stability improvement of native enzymes and activity modulation. Encapsulation in metal-organic frameworks (MOFs) as an efficient strategy for protecting fragile native enzymes while modulating the activity of enzymes remotely, which is practically demanded, has rarely been explored in MOF-encapsulated enzymes. Herein, Ti3C2 nanosheets exhibiting photothermal effect and biocompatibility were encapsulated in Cyt c-embedded ZIF-8 to tailor the enzymatic activity remotely by near-infrared (NIR) irradiation for the first time. By exposure to NIR light, the temperature of an aqueous solution containing Ti3C2/Cyt c@ZIF-8 increases obviously (up to 15 °C), while that of Cyt c@ZIF-8 shows no change. The enzymatic activity in the composites with a certain amount of nanosheets increases, which is attributed to the created defect and transformed microenvironment caused by the introduction of nanosheets. Importantly, the enzymatic activity in ZIF-8 can be further enhanced up to 150% under NIR light irradiation, and this enhancement can be modulated flexibly by varying laser power density. Our investigations indicate that Ti3C2 nanosheets are promising candidates for modulating the activity of encapsulated enzymes remotely.
Personal thermal management textiles that put focus on cooling human body in hot environment attracts intense research interests since the urgent requirement for adjusting human activity to save energy even when we face extreme weather more frequently. Textiles produced from petrol-based fibers have shown their effective passive cooling effects. However, regeneratable passive cooling textiles are still lacking. In this study, we report a cotton-based effective passive cooling textile by interfacial engineering by alginate modification and in-situ generated CaCO3 particles. The Alg/CaCO3-cotton fabrics not only effectively cool the underlining surface via high reflectivity over solar spectra (∼90%) and high mid-infrared emissivity (0.97) in the atmospheric window, but also present enhanced water evaporation and water vapor permeation capabilities (36.51% higher water vapor transmission rate than pristine cotton fabric). The textile avoids overheating by 5.4 °C under direct solar irradiation, comparable to the performance of the reported petrol-based textile. The Alg/CaCO3-cotton also presents high washing stability, UV protection properties, faster drying and fire resistance properties. The surface engineering process is compatible with large-scale production. This work provides enlightening insights to regeneratable and wearable passive cooling materials and sheds light on the working mechanism of personal thermal management materials.
A nanocellulose-based multiple-functional coating was fabricated with excellent superhydrophobicity, abrasion resistance, acid resistance and fluorescence. The fluorescent cellulose nanofibril (FCNF) prepared by grafting 5-(4,6-dichlorotriazinyl) aminofluorescein (DTAF) onto CNF was used to construct the 2–8 μm microparticles with many gullies by spray drying, which were hydrophobically modified by MTMS. A superhydrophobic coating was formed by combining the MTMS-modified microparticles and polydimethylsilane (PDMS), and coated on filter paper and wood block. The coated paper and the wood block had the water contact angles (WCA) 156.6° and 162° with sliding angle <10°. The coating layers remain superhydrophobic after being immersed in hydrochloric acid solution of pH 1, 4, and 0.1 M NaCl solution for 4 h. In addition, the obtained coating possessed excellent friction resistance, which remained the WCA of 150.8° after 50 frictions with 200 g weight. The good folding and crimping resistance, self-cleaning and acid corrosion resistance properties were reported as well. Interestingly, this fluorescent superhydrophobic coating is promising to be implemented as outer building materials to prevent acid corrosion, luminous decorative materials and anti-counterfeiting materials.
Innovative, green and sustainable multifunctional historical textile coating was developed. The developed coating was constructed from renewable molokhia extract and naturally deposited halloysite nanotubes in presence of chitosan chains. The halloysite nanotubes were wrapped with molokhia extract and then uniformly dispersed in chitosan solution using ultrasonication process and then, coated on linen textile fabrics surface. The thermal stability, surface morphology and structural properties of the treated linen fabrics were investigated using microscopic, spectroscopic and thermogravimetric tools. The mass loadings of molokhia extract and halloysite nanotubes in coating layer are varied. The flammability, mechanical and UV protection properties of the coated and uncoated linen fabrics were evaluated. The flame retardancy properties of developed textile fabrics was significantly improved achieved reduction in rate of burning by 50.2% (40 mm/min) compared to untreated linen fabrics (80.3 mm/min). The tensile strength and elongation properties of developed textile fabrics were improved by 22 and 35%, respectively, compared to untreated linen. Additionally, the ultraviolet rays protective properties of the developed textile fabrics were highly enhanced achieving improvement in ultraviolet protection factor (UPF) by 57%. Moreover, the developed green coating achieved good antibacterial properties for textile fabrics recording 11 mm of clear inhibition zone compared to zero for untreated fabrics. Thus, the smart and green textile coating developed in this study exhibiting a new strategy for historical textile conservation against harmful UV rays, failure in tensile strength and fire hazard properties.
In this work, a sustainable flame retardant and superhydrophobic cotton fabric was prepared by a two-step process: the cotton fabric was firstly treated with a chitosan/sodium polyborate polyelectrolyte complex water solution to obtain a flame retardant layer, and then treated with a polydimethylsiloxane (PDMS) tetrahydrofuran solution to construct a superhydrophobic layer. The phase-separated chitosan with a micro-nano roughness structure was covered by PDMS, which synergistically improved the hydrophobicity of the cotton fabric. The flammability evaluation indicated that the limiting oxygen index value of the treated fabric was increased to 40.0% from 18.2%, the peak of heat release rate was reduced by 63.8%, and the total heat release was reduced by 57.6% compared with that of the control sample. The enhanced flame retardancy was attributed to the excellent charring ability in the condensed phase. The treated fabric also showed anti-sticking, self-cleaning, and oil/water-separating properties. This coating treatment without any F, Cl, Br, P elements involved is regarded as a clean methodology for producing flame retardant and superhydrophobic cotton fabrics.
Chitosan-based materials have attracted considerable attention owing to their inherent biodegradability, biocompatibility, and antimicrobial properties. However, the establishment of a scalable technology for the fabrication of high-strength and high-toughness chitosan films remains a major challenge. Herein, a new route for the fabrication of high-strength and high-toughness chitosan films mediated by a unique hydrated chitosan crystal structure is reported, using an aqueous KOH/urea solution as a solvent and an aqueous KCl solution as a neutralization bath. The KCl concentration, neutralization temperature, and neutralization time significantly affect the self-assembly and lateral aggregation of chitosan chains and the microstructure and morphology of the chitosan hydrogels and films. Furthermore, stretching orientation endows the chitosan films with a high tensile strength, Young’s modulus, and work of fracture of 579 ± 52 MPa, 18.8 ± 1.5 GPa, and 26.7 ± 6.9 MJ m⁻³, respectively. To the best of our knowledge, the chitosan films developed in this study are the first example of extremely high-strength and high-toughness chitosan films. We believe that our findings will be useful for the fabrication of polysaccharide-based films with excellent mechanical properties and in broader applications in the fields of biomedicine, flexible bioelectronics, water treatment, and food packaging.
Hypothesis
The drop deposition technique can impact contact angle measurements. We hypothesized that the drop pinch-off, during the traditionally used pendant drop technique, significantly alters the static contact angle. The capillary waves and dynamic wetting pressure generated during the pendant drop deposition are the source for forced spreading which can be circumvented by alternative liquid-needle drop deposition techniques.
Experiments
To compare the role of drop-pinch off and resultant dynamic wetting pressure, we meticulously observed and quantified the entire drop deposition process using high speed imaging until the drop attains the static contact angle in both cases, namely pendant drop and liquid needle deposition technique. Conventionally used standard substrates are compared using both techniques and further compared using literature data. The capillary waves and corresponding drop shape variations are analysed for quantifying the dynamic wetting pressure by measuring drop base diameter, contact angle and centre of mass.
Findings
We compared three parameters - drop pinch-off, spreading behaviour and respective static contact angles along with the resultant dynamic wetting pressure for both the techniques, i.e., pendant drop and liquid-needle. For the pendant drop technique we observed a pronounced drop volume dependency of these parameters even though the corresponding Bond numbers are less than unity. In contrast, for the liquid needle there is no such dependency. With a theoretical argument corroborating experimental observations, this work highlights the importance of a well controlled drop deposition, with a minimum wetting pressure, in order to guarantee contact angle data is independent of drop deposition effects, thereby only reflecting the substrate properties.
A durable superhydrophobic photocatalytic cotton fabric was prepared by titanium composite bamboo charcoal (BC) and polydimethylsiloxane (PDMS). Through comparative experiments, the TiO2-BC composite particles proved to significantly improve the hydrophobic finishing effect of PDMS. The contact angle of cotton modified with TiO2-BC/PDMS reaches 155 °. The results show that the consumption of TiO2 particles achieves a reduction of 87.5 %, without affecting the hydrophobic effect. Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) were employed to determine the surface physical morphology and chemical properties of the cotton fabrics correspondingly. Based on the results showed in the experiment, it was confirmed that on the one hand, the increased fiber roughness plays an important role in providing a superhydrophobic surface of cotton fabric. On the other hand, the methyl (CH3) and siloxane (SiOSi) in PDMS provided for water repellency. Furthermore, the CC/CH component was found to increase by 39 %, while the CO bond was dramatically reduced by 88 %. Thermogravimetric analysis (TGA) suggests that the thermal stability of the treated fabric was improved, and the thermal mass residue increased from 12 % to 16 %. A degradation of 85.12 % of Rhodamine B (RhB) was obtained when the photocatalysis experiment was performed under the visible light, while the contact angle can still reach above 150 ° after the test. The durability experiment proves that the TiO2-BC/PDMS modified fabric maintained a contact angle of 140 ° even after 25 times of regular soaping. Given the above, the fluorine-free hydrophobic silicone materials with porous nanocomposites develop a cost-effect and eco-friendly approach for preparing durable superhydrophobic photocatalytic textile under the circumstance of reducing chemical consumption.
A novel facile and eco-friendly procedure for fabrication of multifunctional antibacterial and ultraviolet (UV) protective cotton surface was presented, including premodification of cellulose fibres with a polysiloxane matrix, followed by green in situ biosynthesis of silver nanoparticles (Ag NPs) in the presence of sumac leaf extract as a reducing and stabilising agent. During the biosynthesis, face-centred cubic Ag NPs with an average size of 52 to 105 nm were generated on the cotton fibres. Increasing the concentration of the AgNO3 precursor resulted in increased concentration of Ag NPs of 50 to 11,000 mg/kg. The chemically modified cotton surface exhibited excellent antimicrobial and UV protection properties. The additive antibacterial activity of Ag NPs and sumac leaf extract showed biocidal activity against S. aureus even at the lowest Ag NP concentration of 50 mg/kg, and in the case of E. coli, biocidal activity was achieved at a concentration of 340 mg/kg. The presence of both Ag NPs and sumac leaf extract provided UV protection factor greater than 40, irrespective of Ag NP concentration. The increase in Ag NP concentration significantly improved the durability of the coating.
Novel fluorescent poly(tannic acid) nanoparticles (FPTA NPs) were successfully synthesized via the self-polymerization reaction of tannic acid (TA) being followed by the degradation with hydrogen peroxide (H2O2). The as-prepared FPTA NPs possessed excellent intrinsic fluorescence characteristics as well as the features of low-cost, good biodegradation, convenient and large-scale preparation. It was found that picric acid (PA) could act as a strong quencher for FPTA NPs. Subsequently, the FPTA NPs-based fluorescent sensor was used for PA detection, which showed a sensitive and fast response towards PA. The utilizations of TA are mainly in the field of surface modification, and this work is the first report on utilizing the autofluorescence characteristics of FPTA NPs in sensor development, which will further broaden the application of TA. The method is of profound meanings for the excellent sensitivity and selectivity and low cost from the engineering viewpoint.
Superhydrophobic surfaces hold great prospects for extremely diverse applications owing to their water repellence property. The essential feature of superhydrophobicity is micro-/nano-scopic roughness to reserve a large portion of air under a liquid drop. However, the vulnerability of the delicate surface textures significantly impedes the practical applications of superhydrophobic surfaces. Robust superhydrophobicity is a must to meet the rigorous industrial requirements and standards for commercial products. In recent years, major advancements have been made in elucidating the mechanisms of wetting transitions, design strategies and fabrication techniques of superhydrophobicity. This review will first introduce the mechanisms of wetting transitions, including the thermodynamic stability of the Cassie state and its breakdown conditions. Then we highlight the development, current status and future prospects of robust superhydrophobicity, including characterization, design strategies and fabrication techniques. In particular, design strategies, which are classified into passive resistance and active regeneration for the first time, are proposed and discussed extensively.
Mono and di-functional benzoxazines were developed based on both sustainable bio-based cardanol and less hazardous synthetic bisphenol-F using mono and di amino derivatives with paraformaldehyde under appropriate experimental conditions. The molecular structure of the developed benzoxazines was confirmed using FTIR and ¹HNMR spectra. The ring opening polymerization of developed benzoxazines was studied using differential scanning calorimetry to ascertain their cure behaviour. The hydrophophic and oleophhilic behaviour of benzoxazines coated melamine foam developed in the present work were ascertained from the values of water contact angle determined using goniometer. The optimum concentration required to transform hydrophilic melamine foam in to hydrophobic/oleophilic nature was studied using varying weight percentage amount of benzoxazines as coating material. Based on the results of water contact angle obtained for 25 wt%, 50 wt%, 75 wt% and 100 wt% of benzoxazine coated on melamine foam, it was ascertained that 50 wt% of benzoxazine was required to obtain maximum water contact angle. The values of water contact angle obtained for 50 wt% of C-a, C-l, C-s, C-h, C-i, BF-l and BF-s are 150˚,153˚,155˚,153˚,158˚,150˚and152˚respectively. It was also noticed that, among the different benzoxazines coated melamine foam, 50 wt% C-i possesses the highest value of water contact angle of 158˚. The oil (engine oil, mineral oil and soybean oil) absorption capacity of different polybenzoxazines coated melamine foam was obtained in the range between 85 and 95 times based on the weight of melamine foam. It is concluded from the results obtained, the materials developed in the present work has great utility in the field of oil/water separation and environmental pollution control.
Oil pollution from produced water in the offshore petroleum industry is one of the most serious marine pollutants worldwide, and efficient separation technology is crucial for the control of oil pollutant emission. Medium coalescence is an efficient oil-water separation technology, but its theory is lacking and the development is slow. In this work, the microscopic mechanism of fiber coalescence was revealed, and found that the effective collision positions were the three-phase contact line and the exposed fiber surface. Further, a theoretical model for calculating the separation performance of a fiber bed was established. For a given inlet droplet size distribution and bed geometric parameters, the outlet droplet size distribution and the total separation efficiency of the fiber bed can be predicted. Then, an Ω-shaped woven method composed of oil-wet fibers and oil-phobic fibers was designed and the separation performance of the fiber beds prepared by the method and the influence law of various parameters were clarified through macroscopic experiment. Finally, the novel technology achieved its first engineering application on an offshore platform, with the average oil content of the outlet was less than 25 mg/L, which could reform the current treatment process of produced water.
Chitosan is an antimicrobial, biodegradable and biocompatible natural polymer, commercially derived from the partial deacetylation of chitin. Currently modified chitosan has occupied a major part of scientific research. Modified chitosan has excellent biotic characteristics like biodegradation, antibacterial, immunological, metal-binding and metal adsorption capacity and wound-healing ability. Chitosan is an excellent candidate for drug delivery, food packaging and wastewater treatment and is also used as a supporting object for cell culture, gene delivery and tissue engineering. Modification of pure chitosan via grafting improves the native properties of chitosan. Chitosan grafted copolymers exhibit high significance and are extensively used in numerous fields. In this review, modifications of chitosan through several graft copolymerization techniques such as free radical, radiation, and enzymatic were reported and the properties of grafted chitosan were discussed. This review also discussed the applications of grafted chitosan in the fields of drug delivery, food packaging, antimicrobial, and metal adsorption as well as dye removal.
Polysaccharides were extracted from a wild species of Ornithogalum by using three methods: maceration, ultrasound-assisted extraction, and combination of maceration and ultrasound. Extraction conditions were optimized by using response surface method (RSM) with a central composite design (CCD). The optimal extraction yield was 81.7%, 82.5% and 85.7%, and the optimal polysaccharides yield was 74.7%, 75.7%, and 82.8% under the optimum conditions of maceration, ultrasound-assisted extraction and combined extraction, respectively. These results indicate that the combination method significantly improves the extraction and polysaccharides yields compared to traditional extraction methods. The combination method also allows reducing the time of ultrasound treatment and thus its adverse effects on polysaccharides. In addition, these results well corroborate with the theoretically predicted values. The NMR (¹H,¹³C, HSQC, HMBC, and COSY) analysis shows that the extract is composed of fructo-polysaccharides with a backbone of (2 → 6)-linked β-d-fructofuranosyl (Fruf) and (2 → 1)-linked β-d-Fruf branched chains, and terminated with glucose and fructose residues. The antioxidant activities of the extract were evaluated from ABTS radical scavenging activity, total antioxidant capacity, metal-chelating power and β-carotene bleaching test. Data show that the extract presents outstanding antioxidant activities.
Inspired by the defects of superoleophobic surface with poor friction resistance and the complicated preparation method, the bio-dopamine was utilized and the friction-durable superoleophobic composite coating was successfully obtained via Schiff base reaction and self-assembly. Dopamine contains the phenolic hydroxyl groups that can react with an amine group or a thiol group. Polydopamine is formed via dopamine self-polymerization under aerobic and weakly alkaline conditions. Additionally, polydopamine can adhere to the surface of virtually all materials. First, the self-polymerization of folic acid induced dopamine to form polydopamine micro-nanoparticles under weakly alkaline conditions. Second, 3,5-Bis(trifluoromethyl)aniline reacted with the phenolic hydroxyl groups of polydopamine nanoparticles via Schiff base reaction. Ammonium hexafluorosilicate was adsorbed on the surface of polydopamine microspheres via electrostatic interactions. Then, the self-assembly behavior of fs-81 and fs-63 with ammonium hexafluorosilicate occurred on polydopamine nanoparticles via electrostatic interactions. Accordingly, the surface roughness was further increased, for which the limitation of traditional methods of using additional nanoparticles to construct hierarchical rough surface was broken. Eventually, the superoleophobic composite coating was applied to the surface of cotton fabric. The results showed that the contact angles of the cotton fabric surface with edible oil, ethylene glycol and glycerol were greater than 150° in the air, respectively, after two cycles of self-assembly modification. The contact angles between the cotton fabric surface and edible oil droplets were still greater than 150°after 25 mechanical abrasion cycles. In addition, the surface free energy of cotton fabric was decreased by 64.1 % after finishing the coating.
Ni and NiW coatings with micro-nanoscale hierarchical structures were obtained by a two-step electrodeposition process. A detailed statistical analysis was performed on SEM images to clarify the effect of tungsten, as an alloying element, on surface morphology of Ni. In the presence of tungsten, the circularity parameter of Ni coating highly increased from 0.49 to 0.77 and a more regular and orderly distribution of micro colonies was obtained. The surface roughness parameters of the coatings were obtained using AFM profile analysis. The static contact angles of Ni and NiW coatings were measured by a set of four different polar/non-polar liquids. The Wu model was then used to translate the contact angle data to surface free energies. According to the obtained results, the storage time of Ni and NiW coatings in the air greatly affects the polar component of their surface free energies. This could be due to the adsorption of airborne hydrocarbons followed by gradual increase of hydrophobic carboxylic groups on coating surface.
Although superhydrophobic materials play important roles in emerging fields because of their anti-wetting behavior, they still face a series of challenges such as brittle rough structure. Herein, a mechanically durable superhydrophobic polymer material (SPM) with roughness-regenerative characteristics was synthesized by integrating acrylate-terminated polyurethane (A-PU) with precipitated silica particle (PSP) using vinyltriethoxysilane (VTES) as a bridge. With the optimization of UV curable components, the appropriate covalently cross-linking networks and hierarchical rough structure were formed in the polymer skeleton, endowing the SPM with solid mechanical strength (B hardness) and superior superhydrophobicity (CA>152°, SA<5°). Taking advantage of the roughness-regenerative characteristics across the material bulk, the SPM was capable of surviving after multi-cycle abrasion damages (>250 cycles). More importantly, the roughness-regenerative characteristics enabled the damaged SPM to repair its superhydrophobicity via sanding treatment (>40 cycles). Our findings convincingly propose a feasible approach to fabricate versatile superhydrophobic materials as promising candidates for emerging fields.
It is highly challenging to construct a durable superhydrophobic coating for practical applications since the coating is easily destroyed by mechano-chemical attack. To address this issue, a “PDMS-in-water” emulsion approach is for the first time adopted to design a mechanochemically robust superhydrophobic cotton fabric with intelligent self-healing nature, without using any fluorine-containing components. With this approach, PDMS molecules firstly penetrate into the cotton fiber, and then graft onto the surface of the cotton fabric with a strong binding force, creating hierarchical rough structures and lowering the surface energy simultaneously. Benefitting from this design, the PDMS@cotton fabric exhibits high superhydrophobicity with a water contact angle over 155°, surpassing all the PDMS-in-organic solvent based approaches. Impressively, the surface repairs its superhydrophobicity throughout the whole lifetime though damaged by machine washing or abrasion (>100 cycles), due to the self-diffusion process of PDMS molecules from the inner part to the outer surface of the cotton fibers to minimize surface free energy. Besides, the superhydrophobic coatings display superior chemical stability in strongly acidic and alkaline solution, and maintain similar textile physical properties of the cotton fabric, such as elongation at break, tensile strength, etc. Our environment-friendly “PDMS-in-water” approach can be easily integrated into industrial textile finishing treatment and is promising to apply to various substrates with robust superhydrophobic surfaces.
Mussel-inspired surface modification has been received great attention due to the universal adhesive properties of catechols for fabrication of multifunctional coatings, especially for gluing hydrophilic polymers to fabricate underwater-superoleophobic materials utilizing in oil/water separation. Despite the extensive research carried out on this topic, the similarity and discrepancy between catecholamine and catecholic amino acid on surface modification and post functionalization have not been fully addressed yet. In this work, underwater superoleophobic surfaces have been successfully developed by a two-step dip-coating method with mussel-inspired coatings and subsequent zwitterionic sulfobetaine methacrylate (SBMA) grafting onto stainless steel meshes and used in oil/water separation. Here, dopamine and 3,4-dihydroxy-L-phenylalanine were both served as mussel-adhesives. More specifically, small molecule zwitterion rather than polyzwitterion was functionalized onto mussel-inspired coatings to minimize the effect of surface topography on surface wettability. The modified surfaces were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle measurements to observe the surface morphology, estimate the surface roughness, and evaluate the wettability, respectively. It showed that SBMA modified meshes with polydopamine (PDA) or poly(3,4-dihydroxy-L-phenylalanine) (PDOPA) layer possessed quite different surface roughness, while both presented excellent oil repellency in water with underwater oil contact angles of 153°–160° indicating a less dependence on surface roughness. Although by using the small molecule as the hydrophilic functionalized groups, the as-prepared meshes exhibited good self-cleaning and oil/water separation performance (separation efficiency >98% for hexane and >97% for soybean oil) and outstanding recyclability with 98% separation efficiency after 30 cycles. This method provides insight into different properties of polycatechols and simplifies the fabrication process through the use of small molecule zwitterion rather than zwitterionic polymer. Besides, the modified meshes also exhibited excellent stability for long-term use. The resulting underwater superoleophobicity and robust self-cleaning ability promise an ideal candidate for oil/water separation and oil contamination restriction.