Ultrathin graphitic carbon nitride (gCN) nanosheets, due to their two-dimensional graphene-like structure, regularly distributed triangular nanopores and structural defects on the laminar network, have attracted great research attention in fabricating high-performance water selective membranes. However, the poor dispersity of gCN limited its application in thin film nanocomposite (TFN) membranes. Here, we synthesized acidified graphitic carbon nitride (aCN) with smaller size and higher solubility. Both aCN and gCN were incorporated into a polyamide (PA) selective layer by interfacial polymerization. The aCN embedded TFN membrane (TFN-aCN) possessed supreme reverse osmosis (RO) performance among the prepared membranes. Compared with the reference TFC membrane, the TFN-aCN50 membrane exhibited a 79.3% increase in permeate flux accompanied by a quite high NaCl rejection of 98.6%. Moreover, the introduction of aCN and gCN generated a more hydrophilic and negatively charged membrane surface, and thus resulted in an improved antifouling performance.

•XG was used as an additive in chemical dispersant formulation.•The oil dispersion and oil droplet stabilization were both improved by XG.•The oil was easily degraded by bacteria due to the increased droplet stability by XG.It is necessary for chemical dispersant to disperse oil effectively and maintain the stability of oil droplets. In this work, Xanthan Gum (XG) was used as an environmentally friendly additive in oil dispersant formulation to enhance the stability and biodegradation of dispersed crude oil droplets. When XG was used together with chemical dispersant 9500A, the dispersion effectiveness of crude oil in artificial sea water (ASW) and the oil droplet stability were both greatly enhanced. In the presence of XG, lower concentration of 9500A was needed to achieve the effective dispersion and stabilization. In addition to the enhancement of dispersion and stabilization, it was found that the biodegradation rate of crude oil by bacteria was dramatically enhanced when a mixture of 9500A and XG was used as a dispersant. Because of the low environmental impact of XG, this would be a potential way to formulate the dispersant with lower toxicity.Download high-res image (120KB)Download full-size image

Effective oil–water phase separation from various emulsions, especially those stabilized by surfactant, is of great importance. Although superhydrophobic and superoleophilic materials have attracted considerable attention in recent years, they are incapable of directly separating all types of oil–water mixtures. To separate various types of emulsions, one of the most important features of particles is that they can be dispersed in the continuous phase for delivery and target dispersed phases. In this study, cyclodextrin-modified magnetic composite particles (M-CDs) have been fabricated for this goal, based on their special interfacial activity and response to an external magnetic field. Though M-CDs are hydrophilic, the intelligent M-CDs can switch from hydrophilicity to hydrophobicity spontaneously, due to the formation of CD–oil inclusion complexes (ICs) at the oil–water interface. Physicochemical characterization reveals that M-CDs can adsorb at the oil–water interface and locate at the droplet surface as an effective Pickering emulsifier. By applying an external magnetic field, M-CDs are removed from the droplet surface and a rapid oil–water phase separation occurs. Our M-CDs can demulsify, for the first time, surfactant-free or surfactant-stabilized oil-in-water (O/W) and water-in-oil (W/O) emulsions directly, with high separation efficiency. Furthermore, the recycled MNPs still show high demulsification efficiency. In view of the sustainability of cyclodextrin and effective recycling ability of MNPs, M-CDs provides a new opportunity to develop an environmentally friendly interfacial material for practical applications in wastewater treatment.

Effective emulsification of oil in seawater plays an important role in the marine oil spill remediation process. The negative effects of chemical surfactants have necessitated a search for alternative dispersant that are sustainable and environmentally friendly. After modifying with dodecanol, petroleum hydrocarbon degrading bacteria, Bacillus cereus S-1, was elucidated to produce an extremely stable oil-in-water (o/w) Pickering emulsion, just liking a solid particle emulsifier. In an appropriate concentration range, the presence of dodecanol improved the surface hydrophobicity and wettability of bacterial cells, which was responsible for their adsorption at the oil–water interface. When a sufficient amount of bacteria was added, only a small amount of dodecanol was required to obtain stable emulsions. However, stable emulsion was not prepared with unmodified Bacillus cereus S-1 cells. Scanning electron microscopy (SEM) and confocal laser scanning microscope (CLSM) images indicated that the effective emulsification was attributed to the formation of a dense bacterial interfacial film around oil drops, providing a steric barrier to impeding droplet coalescence. For application in emulsification of crude oil in seawater, the dodecanol-modified bacterial cells (DMB) were still very effective. In addition to emulsification, DMB remarkably facilitated the oil biodegradation compared to bacterial cells alone. By combining the emulsification and biodegradation of sustainable hydrocarbon degrading bacteria, this work showed a novel strategy for developing an alternative, environmentally friendly remediation technology for marine oil spills.Keywords: Biodegradation; Dodecanol; Oil emulsification; Oil spill dispersion; Petroleum hydrocarbon degrading bacteria;

The potential toxicity of existing chemical dispersants on the marine environment has motivated the search for environmentally friendly dispersants with excellent dispersion ability. Here, an effective Pickering emulsifier is developed based on the synergy of natural biopolymer, Xanthan Gum (XG), and silica nanoparticles. The oil–in–seawater emulsion stabilized by a combination of XG and silica demonstrates great stability and smaller droplet size, which is favorable for the following natural degradation of oil. The synergistic emulsification mechanism has been investigated systematically. The presence of XG favors the adsorption of silica nanoparticles at the oil–seawater interface and also is considerably effective in enhancing the viscosity of continuous phase. These contributions of XG slow down the droplet coalescence and creaming significantly. Confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM) images of emulsions indicate a thick layer of aggregated XG/silica particles at the oil–water interface. This thick layer provides an effective steric barrier. In this study, the synergy between XG and silica not only enhances the dispersion effectiveness, but also reduces the amount of nanoparticles dramatically. This finding opens up a new path for the development of a novel, high efficiency, ecologically acceptable, and cheaper dispersant for emulsifying crude oil following a spill.Keywords: Biopolymer; Nanoparticles; Oil spill dispersion; Pickering emulsion; Sustainable; Synergy

One remediation technique of oil spills is the application of dispersants to oil slicks, which is essentially a process of emulsification. Tetradecane and crude oil-in-seawater emulsions formed with silica nanoparticles modified in situ with rhamnolipid produced a longer stability and smaller droplet size. The interactions of silica particles with rhamnolipid were characterized by contact angle, interfacial tension, TEM, and SEM measurements. The images of confocal fluorescence microscopy and SEM showed the oil droplet microstructure and the morphology of nanoparticles at the oil droplet–water interface. The average emulsion droplet size and emulsion index were investigated. These results indicated a synergistic stabilization upon rhamnolipid addition. The synergy was even more efficient in the case of seawater with a high salinity. Here, because of the strong flocculation caused by high salinity, silica nanoparticles alone were not an effective emulsifier in seawater. The modification of silica nanoparticles by rhamnolipid changed the contact angle and promoted their adsorption at the oil–seawater interface, which provided an efficient barrier to droplet coalescence. The emulsification of rhamnolipid-modified silica nanoparticles worked well in crude oil–seawater system. So, this could be a new method to deal with the issue of the marine oil spill by environmentally benign silica particles and rhamnolipid.Keywords: Dispersants; Emulsification; Oil spill; Rhamnolipid; Seawater; Silica nanoparticles;

The effective emulsification of oil and retention of the stability of this emulsion in sea water is an important requirement for the remediation process following a marine oil spill. To identify alternate dispersants for emulsifying oil following a spill, we investigated oil-in-water emulsions stabilized by self-assembled complexes of a hydrophilic petroleum hydrocarbon degrading bacteria, Bacillus cereus S-1, with the linear polysaccharide chitosan. We found that the addition of chitosan improves the ability of hydrophilic Bacillus cereus S-1 to function as an effective emulsifier. The self-assembled complex of Bacillus cereus S-1 and chitosan is able to adsorb on the interface and stabilize oil-in-water emulsions for months. Confocal laser scanning microscope (CLSM) imagings and SEM results showed that the oil-in-water emulsions were stable against coalescence by formation of a thin film of bacteria–chitosan complex. Bacillus cereus S-1 associated with chitosan in the aqueous phase gave rise to a network, which was also responsible for the emulsion stability. The ability of this complex work in seawater was still very effective. In addition to stabilization, the addition of chitosan dramatically enhanced the oil degradation rate of Bacillus cereus S-1. Due to the sustainability and low environmental impact of chitosan and petroleum hydrocarbon degrading bacteria, this is an environmentally friendly and inexpensive way to treat marine oil spills.