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

Just Soaping Them: The Simplest Method for Converting Metal Organic Frameworks into Superhydrophobic Materials

The incorporation of superhydrophobic properties into metal organic framework (MOF) materials is highly desirable to enhance their hydrolytic stability, gas capture selectivity in the presence of humidity and efficiency in oil-water separations, among others. The existing strategies for inducing superhydrophobicity into MOFs have several weaknesses, such as increased cost, utilization of toxic reagents and solvents, applicability for limited MOFs, etc. Here, we report the simplest, most eco-friendly, and cost-effective process to impart superhydrophobicity to MOFs, involving a rapid (90 min) treatment of MOF materials with solutions of sodium oleate, a main component of soap. The method can be applied to both hydrolytically stable and unstable MOFs, with the porosity of modified MOFs approaching, in most cases, that of the pristine materials. Interestingly, this approach was used to isolate superhydrophobic magnetic MOF composites, and one of these materials formed stable liquid marbles, whose motion could be easily guided using an external magnetic field. We also successfully fabricated superhydrophobic MOF-coated cotton fabric and fiber composites. These composites exhibited exceptional oil sorption properties achieving rapid removal of floating crude oil from water, as well as efficient purification of oil-in-water emulsions. They are also regenerable and reusable for multiple sorption processes. Overall, the results described here pave the way for an unprecedented expansion of the family of MOF-based superhydrophobic materials, as virtually any MOF could be converted into a superhydrophobic compound by applying the new synthetic approach.

CdO-Nanografted Superhydrophobic Hybrid Polymer Composite-Coated Cotton Fabrics for Self-Cleaning and Oil/Water Separation Applications

The current study presents a simple and cost-competitive method for the development of high-performance superhydrophobic and superoleophilic cotton fabrics coated with cadmium oxide/cerotic acid (CdO/CE)-polycaprolactone (PCL)- and cadmium oxide/stearic acid (CdO/ST)-polycaprolactone-grafted hybrid composites. X-ray powder diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy are used to characterize the CdO/CE-PCL and CdO/ST-PCL and polycaprolactone-modified cotton fabrics. Using an optical contact angle meter, the wetting behavior of corrosive liquids such as coffee, milk, tea, water dyed with methylene blue, strong acids (HCl), strong alkali (NaOH), and saturated salt solution (NaCl) on the CdO-CE/ST/PCL-modified cotton fabrics is assessed as well as the durability of CdO-CE/ST/PCL-modified cotton fabrics in corrosive liquids. Data obtained from the oil-water separation experiment indicate remarkable separation efficiency with oil purity values of ≥99.97 wt %, and high permeation flux values of up to 11,700 ± 300 L m-2 h-1 are observed for surfactant-stabilized water-in-oil emulsions via a gravity-driven technique. From the data obtained, it is concluded that the nano-CdO-grafted superhydrophobic hybrid polymer composite-coated cotton fabrics (CdO-ST/(CE)/PCL/CFs) can be utilized for self-cleaning and oil/water separation applications.

Co-exposure of microplastics and heavy metals in the marine environment and remediation techniques: a comprehensive review

Microplastics (MPs) and heavy metals are significant pollutants in the marine environment, necessitating effective remediation strategies to prevent their release into the sea through sewage and industrial effluent. This comprehensive review explores the current understanding of the co-exposure of MPs and heavy metal-enriched MPs, highlighting the need for effective remediation methods. Various mechanisms, including surface ion complexation, hydrogen bonding, and electrostatic forces, contribute to the adsorption of heavy metals onto MPs, with factors like surface area and environmental exposure duration playing crucial roles. Additionally, biofilm formation on MPs alters their chemical properties, influencing metal adsorption behaviors. Different thermodynamic models are used to explain the adsorption mechanisms of heavy metals on MPs. The adsorption process is influenced by various factors, including the morphological characteristics of MPs, their adsorption capacity, and environmental conditions. Additionally, the desorption of heavy metals from MPs has implications for their bioavailability and poses risks to marine organisms, emphasizing the importance of source reduction and remedial measures. Hybrid approaches that combine both conventional and modern technologies show promise for the efficient removal of MPs and heavy metals from marine environments. This review identifies critical gaps in existing research that should be addressed in future studies including standardized sampling methods to ensure accurate data, further investigation into the specific interactions between MPs and metals, and the development of hybrid technologies at an industrial scale. Overall, this review sheds light on the adsorption and desorption mechanisms of heavy metal-enriched MPs, underscoring the necessity of implementing effective remediation strategies.

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

HYPOTHESIS

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

EXPERIMENTS

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

FINDINGS

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

Regional Regression Correlation Model of Microplastic Water Pollution Control Using Circular Economy Tools

Water pollution caused by microplastics represents an important challenge for the environment and people's health. The weak international regulations and standards in this domain support increased water pollution with microplastics. The literature is unsuccessful in establishing a common approach regarding this subject. The main objective of this research is to develop a new approach to necessary policies and ways of action to decrease water pollution caused by microplastics. In this context, we quantified the impact of European water pollution caused by microplastics in the circular economy. The main research methods used in the paper are meta-analysis, statistical analysis and an econometric approach. A new econometric model is developed in order to assist the decision makers in increasing efficiency of public policies regarding water pollution elimination. The main result of this study relies on combining, in an integrated way, the Organisation for Economic Co-operation and Development's (OECD) data on microplastic water pollution and identifying relevant policies to combat this type of pollution.