Novel fabrication of a robust superhydrophobic PU@ZnO@Fe3O4@SA sponge and its application in oil-water separations

Photothermal, Magnetic, and Superhydrophobic PU Sponge Decorated with a Fe3O4/MXene/Lignin Composite for Efficient Oil/Water Separation

Frequent oil spills and the discharge of industrial oily wastewaters have become a serious threat to the environment, ecosystem, and human beings. Herein, a photothermal, magnetic, and superhydrophobic PU sponge decorated with a Fe3O4/MXene/lignin composite (labeled as S-Fe3O4/MXene/lignin@PU sponge) has been designed and prepared. The obtained superhydrophobic/superoleophilic PU sponge possesses excellent chemical stability, thermal stability, and mechanical durability in terms of being immersed in corrosive solutions and organic solvents and boiling water and being abrased by sandpapers, respectively. The oil adsorption capacities of the S-Fe3O4/MXene/lignin@PU sponge for various organic liquids range from 29.1 to 70.3 g/g, and the oil adsorption capacity for CCl4 can remain 69.6 g/g even after 15 cyclic adsorption tests. The separation efficiencies of the S-Fe3O4/MXene/lignin@PU sponge for n-hexane and CCl4 are higher than 98% in different environments (i.e., water, hot water, 1 mol/L NaOH, 1 mol/L NaCl, and 1 mol/L HCl). More importantly, the introduction of three light absorbers (i.e., Fe3O4, MXene, and lignin) into the S-Fe3O4/MXene/lignin@PU sponge shows a synergistic effect in the photothermal heat conversion performance, and the maximum surface temperature reaches 64.4 °C under sunlight irradiation (1.0 kW/m2). The separation flux of the S-Fe3O4/MXene/lignin@PU sponge for viscous LT147 vacuum pump oil reaches 35,469 L m-2 h-1 under sunlight irradiation, showing an increase of 27.3% compared to that of oil adsorption processes without the photothermal effect. Thus, the rational design of superhydrophobic sponges by introducing proper photothermal heat absorbers provides new insights into facile and cost-effective preparation of sponges for efficient oil/water separation.

Superhydrophobic MS@CuO@SA sponge for oil/water separation with excellent durability and reusability

We present a superhydrophobic material based on commercially melamine sponge (MS) with great durability, recyclability, and excellent sorption performance. The fabrication process of this sponge is facile without using toxic reagents or sophisticated equipment and therefore it is simple to scale up. The CuO layer utilized to give a rough surface of the substrate (MS) was successfully prepared in a commercial microwave to seed copper nucleuses in an alkaline medium. Stearic acid (SA) plays a role as the self-assembled monolayer on the surface of the sponge skeletons. Throughout this study, the properties of the modified sponge were fully characterized, and the changes in wettability were carefully examined. Water contact angle (WCA) measurements revealed the excellent superhydrophobicity of the material with high static WCA of 165.1° and low dynamic WCA of 8°. Furthermore, the as-prepared sponge demonstrated high efficiency in separation (over 99.0%) of different oils from water. Notably, several unique properties of as-modified material were found, consisting of ultrafast sorption capacities of up to 32-52 times of its own weight by using 80 mL of each oil, outstanding reusability with good sorption capacity even after 40 cycles. Even under various harsh environments, the novel materials proved its outstanding durability and ultrafast sorption capacity of oils. The durability, recyclability, and superhydrophobic properties of the novel superhydrophobic sponge provide it a solid basis for oil-water separation applications through an ultrafast sorption capacity of oils as well as quick recovery of the oil by easy squeezing process.

Composite Materials Based on Iron Oxide Nanoparticles and Polyurethane for Improving the Quality of MRI

Polyether urethane (PU)-based magnetic composite materials, containing different types and concentrations of iron oxide nanostructures (Fe₂O₃ and Fe₃O₄), were prepared and investigated as a novel composite platform that could be explored in different applications, especially for the improvement of the image quality of MRI investigations. Firstly, the PU structure was synthetized by means of a polyaddition reaction and then hematite (Fe₂O₃) and magnetite (Fe₃O₄) nanoparticles were added to the PU matrices to prepare magnetic nanocomposites. The type and amount of iron oxide nanoparticles influenced its structural, morphological, mechanical, dielectric, and magnetic properties. Thus, the morphology and wettability of the PU nanocomposites surfaces presented different behaviours depending on the amount of the iron oxide nanoparticles embedded in the matrices. Mechanical, dielectric, and magnetic properties were enhanced in the composites’ samples when compared with pristine PU matrix. In addition, the investigation of in vitro cytocompatibility of prepared PU nanocomposites showed that these samples are good candidates for biomedical applications, with cell viability levels in the range of 80–90%. Considering all the investigations, we can conclude that the addition of magnetic particles introduced additional properties to the composite, which could significantly expand the functionality of the materials developed in this work.

Highly Efficient Amorphous Carbon Sphere-Based Superhydrophobic and Superoleophilic Sponges for Oil/Water Separation

In this experimental study, a commercially available polyurethane (PU) sponge coated with amorphous carbon spheres (ACSs) is investigated for oil/water separation. The ACSs synthesized using chemical vapor deposition are embedded in the PU sponge by a simple dip-coating method. The superhydrophobic ACS-PU sponge exhibits a water contact angle (WCA) of 156.2 ± 1° and a sliding angle <5°. The prepared sponge exhibits high absorption capacity, removal of oil spills from water, and demulsification of an oil-in-water emulsion. Absorption capacities of 32-68 times the ACS-PU sponge weight were obtained for different organic solvents and oils. It was found that the prepared ACS-PU sponge can effectively absorb oils under both static and turbulent conditions. Compared with the reported studies on the loading of different carbon materials in sponges for oil/water separation, ACSs in PU have a low loading percentage of ∼7 wt % and better absorption recyclability. The method proposes a simple and cost-effective preparation technique of highly hydrophobic and oleophilic ACS-PU sponges for effective oil/water separation.

Facile synthesis of superhydrophobic MS/TiO2/PDMS sponge for efficient oil-water separation

To obtain a kind of superhydrophobic sponge with high oil and water selectivity, the MS/TiO₂/PDMS sponge was prepared via a two-step hydrophobic fabrication based on the melamine sponge (MS), tetrabutyl titanate (TBOT), and polydimethylsiloxane (PDMS). The effects of modification time, the concentrations of TBOT and PDMS on the properties of the MS/TiO₂/PDMS sponge were studied, and the separation mechanism was also discussed based on the interaction between the oil and the surface of the MS/TiO₂/PDMS sponge. The results suggest that under optimal conditions, the MS/TiO₂/PDMS sponge show superhydrophobicity. The contact angle and adsorption capacity for oil of the MS/TiO₂/PDMS sponge are 149.2° and 98.5 g·g^-1, respectively, and they can be recycled for about 25 cycles after oil-water separation test. This study prepares a new composite material with high oil-water selectivity, which is a good foundation for the development and research of new oil adsorbents.

Dip-Coating Approach to Fabricate Durable PDMS/STA/SiO2 Superhydrophobic Polyester Fabrics

The facile, simple, highly efficient, and fluorine-free fabrication of superhydrophobic surfaces on fabrics with high durability has attracted considerable attention because of its urgent practical application. The simple dip-coating method was adopted to make a stable and durable polydimethylsiloxane/stearic acid/silica (PDMS/STA/SiO2) superhydrophobic fabric. The fabric’s surface morphology, roughness, and composition were analyzed by scanning electron microscopy, atomic force microscopy, and Fourier transform infrared spectroscopy, respectively. The PDMS/STA/SiO2-coated fabric: demonstrated strong superhydrophobicity (a water contact angle (WCA) of around 163°), efficiently repelled different liquids (milk, coffee, orange juice, Coca-Cola, and 1 M of HCl and NaOH) with a contact angle above 155°, had excellent self-cleaning performance, and retained superhydrophobicity with a WCA greater than 150° after 72 h of ultraviolet irradiation and 700 cycles of mechanical abrasion. The PDMS/STA/SiO2 coating had few influences on the color fastness of the fabric. Superhydrophobic coatings are expected to be practically applied in the textile industry.

Surface Engineering of Ceramic Nanomaterials for Separation of Oil/Water Mixtures

Oil/water mixtures are a potentially major source of environmental pollution if efficient separation technology is not employed during processing. A large volume of oil/water mixtures is produced via many manufacturing operations in food, petrochemical, mining, and metal industries and can be exposed to water sources on a regular basis. To date, several techniques are used in practice to deal with industrial oil/water mixtures and oil spills such as in situ burning of oil, bioremediation, and solidifiers, which change the physical shape of oil as a result of chemical interaction. Physical separation of oil/water mixtures is in industrial practice; however, the existing technologies to do so often require either dissipation of large amounts of energy (such as in cyclones and hydrocyclones) or large residence times or inventories of fluids (such as in decanters). Recently, materials with selective wettability have gained attention for application in separation of oil/water mixtures and surfactant stabilized emulsions. For example, a superhydrophobic material is selectively wettable toward oil while having a poor affinity for the aqueous phase; therefore, a superhydrophobic porous material can easily adsorb the oil while completely rejecting the water from an oil/water mixture, thus physically separating the two components. The ease of separation, low cost, and low-energy requirements are some of the other advantages offered by these materials over existing practices of oil/water separation. The present review aims to focus on the surface engineering aspects to achieve selectively wettability in materials and its their relationship with the separation of oil/water mixtures with particular focus on emulsions, on factors contributing to their stability, and on how wettability can be helpful in their separation. Finally, the challenges in application of superwettable materials will be highlighted, and potential solutions to improve the application of these materials will be put forward.

Selected Heavy Metals Removal From Electroplating Wastewater by Purified and Polyhydroxylbutyrate Functionalized Carbon Nanotubes Adsorbents

This research investigated the removal of heavy metals (As, Pb, Cr, Cd, Ni, Cu, Fe, and Zn) via batch adsorption process from industrial electroplating wastewater using two different nano-adsorbents; purified carbon nanotubes (P-CNTs) and polyhydroxylbutyrate functionalized carbon nanotubes (PHB-CNTs), both produced through catalytic chemical vapour deposition (CCVD) method. HRSEM, HRTEM, XRD, DLS, BET, FTIR, XPS, TGA, pH drift and Raman spectroscopy were used to characterize the developed nano-adsorbents. In the batch adsorption process, the effects of contact time, dosage, temperature and pH were studied. Both nano-adsorbents gave optimum contact time, equilibrium time, optimum dosage, and pH of 10 minutes, 70 minutes, 20 mg, and 5.63–5.65 respectively. The heavy metals removal efficiencies by the nano-adsorbents followed the order of PHB-CNTs > P-CNTs based on ion exchange and electrostatic forces mechanism. For P-CNTs and PHB-CNTs, the equilibrium sorption isotherm suits temkin model, kinetic data fitted to pseudo-second order based on the linear regression correlation coefficient, and the thermodynamic study established spontaneity and endothermic nature of the adsorption process. The findings in this research conclude that both nano-adsorbents have exceptional capacity to remove heavy metals from the adsorbate, with PHB-CNTs possessing better quality. The treated adsorbate meets the standard for industrial or irrigation re-use.

Toward Superhydrophobic/Superoleophilic Materials for Separation of Oil/Water Mixtures and Water-in-Oil Emulsions Using Phase Inversion Methods

In this study, a method that can simultaneously separate oil/water mixtures and water-in-oil emulsions were developed. Various substrates (synthetic polymers and stainless steel meshes) were coated by rough hydrophobic polymer films. The prepared materials possessed superhydrophobicity and superoleophilicity. These superhydrophobic sponges can isolate extensive amounts of oil from water when connected to a related vacuum framework. Moreover, the superhydrophobic meshes (SHM) can separate both surfactant-free and -stabilized water-in-oil emulsions via gravity with high separation efficiency (oil purity: >99.99%) and flux (up to 4760 L m−2 h−1). The extraordinary performance of our materials and their low-energy, efficient, low-cost preparation propose that they have great potential for real-time applications.

Batch and fixed-bed column studies for selective removal of cesium ions by compressible Prussian blue/polyurethane sponge

In this work, compressible Prussian blue/polyurethane sponges (PB@PUS) for selective removal of cesium ions were prepared via an in situ radiation chemical route. The characterization results indicate that uniform PB nanoparticles were successfully synthesized and well dispersed on the porous skeleton of sponge. Batch and fixed-bed column experiments were detailedly conducted to investigate their adsorption performances. Batch adsorption experiments reveal that PB@PUS exhibited good selective removal property for cesium ions in a wide range of pH, whose maximal adsorption capacity and removal efficiency reached 68.6 mg g-1 and 99%, respectively. The adsorption processes could be described by the Langmuir isotherm adsorption model and pseudo-second-order adsorption kinetic model. The fixed-bed column experiments show that the breakthrough and exhaustion time obviously increased with the decrease of flow rate and initial cesium ions concentration. The breakthrough curves could be well fitted by the Thomas model and Yoon-Nelson model. The theoretical saturated adsorption capacity of PB@PUS-3 calculated from the Thomas model was 68.2 mg g-1. The as-prepared samples were light, stable and compressible, which can be applied in radioactive wastewater treatment.