Ultrathin LayCoOx Nanosheets with High Porosity Featuring Boosted Catalytic Oxidation of Benzene: Mechanism Elucidation via an Experiment-Theory Combined Paradigm.

Designing transition-metal oxides for catalytically removing the highly toxic benzene holds significance in addressing indoor/outdoor environmental pollution issues. Herein, we successfully synthesized ultrathin LayCoOx nanosheets (thickness of ∼1.8 nm) with high porosity, using a straightforward coprecipitation method. Comprehensive characterization techniques were employed to analyze the synthesized LayCoOx catalysts, revealing their low crystallinity, high surface area, and abundant porosity. Catalytic benzene oxidation tests demonstrated that the La0.029CoOx-300 nanosheet exhibited the most optimal performance. This catalyst enabled complete benzene degradation at a relatively low temperature of 220 °C, even under a high space velocity (SV) of 20,000 h-1, and displayed remarkable durability throughout various catalytic assessments, including SV variations, exposure to water vapor, recycling, and long time-on-stream tests. Characterization analyses confirmed the enhanced interactions between Co and doped La, the presence of abundant adsorbed oxygen, and the extensive exposure of Co3+ species in La0.029CoOx-300 nanosheets. Theoretical calculations further revealed that La doping was beneficial for the formation of oxygen vacancies and the adsorption of more hydroxyl groups. These features strongly promoted the adsorption and activation of oxygen, thereby accelerating the benzene oxidation processes. This work underscores the advantages of doping rare-earth elements into transition-metal oxides as a cost-effective yet efficient strategy for purifying industrial exhausts.

Hydroxyl-Decorated Pt as a Robust Water-Resistant Catalyst for Catalytic Benzene Oxidation.

In catalytic oxidation reactions, the presence of environmental water poses challenges to the performance of Pt catalysts. This study aims to overcome this challenge by introducing hydroxyl groups onto the surface of Pt catalysts using the pyrolysis reduction method. Two silica supports were employed to investigate the impact of hydroxyl groups: SiO2-OH with hydroxyl groups and SiO2-C without hydroxyl groups. Structural characterization confirmed the presence of Pt-Ox, Pt-OHx, and Pt0 species in the Pt/SiO2-OH catalysts, while only Pt-Ox and Pt0 species were observed in the Pt/SiO2-C catalysts. Catalytic performance tests demonstrated the remarkable capacity of the 0.5 wt % Pt/SiO2-OH catalyst, achieving complete conversion of benzene at 160 °C under a high space velocity of 60,000 h-1. Notably, the catalytic oxidation capacity of the Pt/SiO2-OH catalyst remained largely unaffected even in the presence of 10 vol % water vapor. Moreover, the catalyst exhibited exceptional recyclability and stability, maintaining its performance over 16 repeated cycles and a continuous operation time of 70 h. Theoretical calculations revealed that the construction of Pt-OHx sites on the catalyst surface was beneficial for modulating the d-band structure, which in turn enhanced the adsorption and activation of reactants. This finding highlights the efficacy of decorating the Pt surface with hydroxyl groups as an effective strategy for improving the water resistance, catalytic activity, and long-term stability of Pt catalysts.

A superwetting stainless steel mesh with Janus surface charges for efficient emulsion separation.

Design of charged materials for demulsification of ionic surfactant-stabilized oil-in-water emulsions is emerging in recent years. Herein, a superwetting stainless steel mesh with Janus surface charges (Janus SSM) was prepared by respectively brush-coating polyethyleneimine/aminated carbon nanotubes (PEI/CNTs-NH2) coating and polyacrylic acid (PAA) coating on its two sides. Two demulsification mechanisms, i.e., electrostatic attraction-repulsion and electrostatic repulsion-attraction based on the synergism of two oppositely charged sides were proposed. Combined with the superwettability and optimized pore size, the Janus SSM can successfully be used to demulsify, coalesce and separate emulsions. In detail, the Janus SSM exhibited separation efficiencies of up to 99.29%, 97.12% for SDS- and DTAC-stabilized oil-in-water emulsions respectively under the electrostatic attraction-repulsion mechanism, and up to 97.10%, 98.57% under the electrostatic repulsion-attraction mechanism. The results indicated that the electrostatic attraction-repulsion mechanism proposed in this study is conductive to achieving higher efficiency in emulsion separation. Furthermore, excellent durability extend the operation life of Janus SSM. This Janus SSM, which combines opposite charges on its two sides, may advance the development of charged materials for emulsion separation.

A novel Janus sponge fabricated by a green strategy for simultaneous separation of oil/water emulsions and dye contaminants.

A novel Janus sponge with the ability to remove complex contaminants from water is reported. Firstly, a superhydrophilic sponge (PA@PEI-sponge) is prepared via synthesizing negatively charged phytic acid@polyethyleneimine (PA@PEI) nanoparticles and assembling them on the surface of polydopamine (PDA) and PEI-modified polyurethane (PU) sponge through electrostatic adsorption. The Janus sponge is generated by modifying one side of the PA@PEI-sponge with PDMS, which exhibits superior separation efficiency and high filtration flux toward both water-in-oil and oil-in-water emulsions due to its multiplex selective wettability and the interconnected and tortuous 3D porous channels. The numerous negatively charged active sites of PA@PEI nanoparticles and PDA layer impart the superhydrophilic PA@PEI-sponge with the removal efficiency of 39.95 ± 0.27% for malachite green (MG) via simple flow-through filtration, which can be improved to 99.92 ± 0.07% by Janus modification. More importantly, the Janus sponge exhibits an excellent treatment capacity for complex mixtures containing emulsified oil and dye, with the separation efficiency above 99.59%. The Janus sponge also demonstrates the effective separation of real industrial wastewater collected from an acrylic dyeing plant. Together with a facile and green preparation strategy, this Janus sponge shows excellent application potential for simultaneous dye removal and oil/water emulsion separation.

Room-temperature fabrication of superhydrophobic covalent organic framework (COF) decorated cotton fabric for high-flux water-in-oil emulsion separation.

We report the preparation of a two-dimensional superhydrophobic covalent organic framework (COF)-coated cotton fabric via a rapid one-step method at room temperature. The COF-coated fabric was found to have stable superhydrophobicity and remarkable water-in-oil emulsion separation capacity with ultra-high flux under only gravity.

Fabrication of superhydrophilic PVDF membranes by one-step modification with eco-friendly phytic acid and polyethyleneimine complex for oil-in-water emulsions separation.

Superhydrophilic membranes with simultaneous underwater superoleophobicity are highly desirable and worth exploring for separation of emulsified oil from water. In this work, combining the strong negative charges of phytic acid (PA) and the high cationic charge density of polyethyleneimine (PEI), an eco-friendly PA@PEI polyelectrolyte complex was synthetized in aqueous solution. And then the polyelectrolyte complex was deposited onto hydrophobic PVDF membranes through a one-step assembly approach with high convenience, endowing the membranes with superhydrophilic and underwater superoleophobic property. The as-prepared PA@PEI/PVDF membrane shows outstanding static and dynamic water stability, and was successfully used to separate multiple oil-in-water emulsions, with an average rejection rate exceeding 98.5% and a water flux up to 12203.6 L m-2∙h-1∙bar-1. Furthermore, the water flux can be recovered to a high level after four separation-washing cycles, showing excellent antifouling performance and recovery capability. Together with its natural raw materials and environmentally friendly preparation strategy, the PA@PEI/PVDF membrane shows great potential in practical treatment of emulsified oily wastewater.

Microwave-Assisted Solvothermal Synthesis of Covalent Organic Frameworks (COFs) with Stable Superhydrophobicity for Oil/Water Separation.

COFs were synthesized by a microwave-assisted solvothermal route, with the building blocks containing 1,3,5-tris(4-aminophenyl) benzene and 2,3,5,6-tetra-fluoroterephthalaldehyde (or 1,4-phthalaldehyde). The -F groups introduced into the benzene ring promoted hydrophobicity and stability of the COFs. The universality and long effectiveness of oil adsorption can be realized when applying COFs as adsorbent. The powder also exhibited excellent water-in-oil emulsions separation performance, with the separation efficiency no lower than 99.5%. In this work, the use of microwave solvothermal synthesis of superhydrophobic COFs is potential to replace the conventional synthesis process and more suitable for industrial scale-up production. Furthermore, the findings provide a new strategy for solving the problem of oil spill treatment and industrial water-in-oil emulsions separation by using the emerging 2D COFs.

Nature-Inspired Strategy toward Superhydrophobic Fabrics for Versatile Oil/Water Separation.

Phytic acid, which is a naturally occurring component that is widely found in many plants, can strongly bond toxic mineral elements in the human body, because of its six phosphate groups. Some of the metal ions present the property of bonding with phytic acid to form insoluble coordination complexes aggregations, even at room temperature. Herein, a superhydrophobic cotton fabric was prepared using a novel and facile nature-inspired strategy that introduced phytic acid metal complex aggregations to generate rough hierarchical structures on a fabric surface, followed by PDMS modification. This superhydrophobic surface can be constructed not only on cotton fabric, but also on filter paper, polyethylene terephthalate (PET) fabric, and sponge. AgI, FeIII, CeIII, ZrIV, and SnIV are very commendatory ions in our study. Taking phytic acid-FeIII-based superhydrophobic fabric as an example, it showed excellent resistance to ultraviolet (UV) irradiation, high temperature, and organic solvent immersion, and it has good resistance to mechanical wear and abrasion. The superhydrophobic/superoleophilic fabric was successfully used to separate oil/water mixtures with separation efficiencies as high as 99.5%. We envision that these superantiwetting fabrics, modified with phytic acid-metal complexes and PDMS, are environmentally friendly, low cost, sustainable, and easy to scale up, and thereby exhibit great potentials in practical applications.

Inspired by Stenocara Beetles: From Water Collection to High-Efficiency Water-in-Oil Emulsion Separation.

Inspired by the water-collecting mechanism of the Stenocara beetle's back structure, we prepared a superhydrophilic bumps-superhydrophobic/superoleophilic stainless steel mesh (SBS-SSM) filter via a facile and environmentally friendly method. Specifically, hydrophilic silica microparticles are assembled on the as-cleaned stainless steel mesh surface, followed by further spin-coating with a fluoropolymer/SiO2 nanoparticle solution. On the special surface of SBS-SSM, attributed to the steep surface energy gradient, the superhydrophilic bumps (hydrophilic silica microparticles) are able to capture emulsified water droplets and collect water from the emulsion even when their size is smaller than the pore size of the stainless steel mesh. The oil portion of the water-in-oil emulsion therefore permeates through pores of the superhydrophobic/superoleophilic mesh coating freely and gets purified. We demonstrated an oil recovery purity up to 99.95 wt % for surfactant-stabilized water-in-oil emulsions on the biomimetic SBS-SSM filter, which is superior to that of the traditional superhydrophobic/superoleophilic stainless steel mesh (S-SSM) filter lacking the superhydrophilic bump structure. Together with a facile and environmentally friendly coating strategy, this tool shows great application potential for water-in-oil emulsion separation and oil purification.