Expanded Graphite-Polyurethane Foams for Water–Oil Filtration

Abstract

Herein, expanded graphite is successfully combined with waterborne polyurethane to develop porous foams with underwater oleophobic properties for the separation of surfactant-free, oil-in-water mixtures and emulsions. To obtain foams with different pore sizes and therefore with different performances in the oil−water filtration process, two solvent-free fabrication processes are adopted. In the first one, the expanded graphite granules are mixed with the waterborne polyurethane (PUEGr), and in the second method, calcium carbonate is introduced to the two-component mixture (PUEGr_t). In both cases, the obtained foams exhibit hydrophilicity and oleophilicity in air and oleophobicity underwater, and they have porous interconnected networks, while their pore size distribution differs significantly. The foams can be used as 3D filters, able to separate, through gravity, surfactant-free, oil-in-water mixtures (10% w/w oil in water) with high oil rejection efficiencies and flow rates that depend on the type of foam. In particular, in the gravitydriven filtration process using 100 mL of the feed liquid, the PUEGr foams have an oil rejection efficiency of 96.85% and flow rate of 9988 L m −2 h −1 , while for the PUEGr_t foams the efficiency is higher (99.99%) and the flow rate is lower (8547 L m −2 h −1 ) due to their smaller pore size. Although the PUEGr_t foams have slower separation performance, they are more efficient for the separation of surfactant-free emulsions (1% w/w oil in water) reaching an oil rejection efficiency of 98.28%, higher than the 95.66% of the PUEGr foams of the same thickness. The foams can be used for several filtration cycles, as well as in harsh conditions without deteriorating their performance. The nature of raw materials, the simple solvent-free preparation method, the effective gravity-driven filtration even in harsh conditions, and their reusability suggest that the herein engineered foams have great potential for practical applications in oil−water separation through highly energy-efficient filtration.

3D Photothermal Cryogels for Solar-Driven Desalination

“…MIP analysis allows for the quantification of detailed parameters about the macro-structures (>10 nm) of the materials, while N 2 physisorption analysis was adopted to investigate the structural characteristics of the mesoscopic (2–50 nm) and microscopic (<2 nm) pores. 51 The MIP pore-size distribution analysis revealed that the increasing concentration of pyrrole used to prepare the PPCs results in a shift toward a larger modal macropore-size ( Figure S7 ). Specifically, the pores with sizes between 0.01 and 1 μm, which are initially present in PSA, are absent in PPC10 and PPC20, while only pores larger than 100 μm remain for PPC30.…”

Synthesis of Castor Oil‐Based Waterborne Polyurethane with Improved Properties via Adjusting PBA/CO Soft Segment Ratio

“…[7,11] Most of the soft segments in waterbased polyurethanes are derived from petroleum-based polyols. [12,13] Therefore, there is a growing interest in using renewable resources to develop sustainable polymers. Renewable resources suitable for recycling or biodegradation as a partial or entire replacement of petroleum-based starting materials have been reported.…”

“…Polyurethane is one of the six most widely used plastic materials in the world [7,11] . Most of the soft segments in water‐based polyurethanes are derived from petroleum‐based polyols [12,13] . Therefore, there is a growing interest in using renewable resources to develop sustainable polymers.…”

Modification of Polyurethane Sponge Based on the Thiol–Ene Click Reaction and Its Application for Oil/Water Separation

“…In recent years, oil and organic solvent spills have caused worldwide concern due to the ensuing environmental pollution [1][2][3][4]. Thus, separating and recovering oil from water is becoming more and more important.…”