Magnetic amphiphilic composites based on carbon nanotubes and nanofibers grown on an inorganic matrix: effect on water-oil interfaces

Abstract

Novos compósitos magnéticos anfifílicos foram preparados pelo crescimento de nanotubos e nanofibras de carbono contendo partículas magnéticas através de deposição química de vapor (CVD), utilizando etanol como fonte de carbono e lama vermelha (RM, subproduto do processo Bayer de produção de alumina) como suporte e catalisador. Monitoramento da reação CVD à temperatura programada (TPCVD), difração de raios X (XRD), espectroscopia Mössbauer, espectroscopia de energia dispersiva (EDS), espectroscopia Raman, termogravimetria (TG/DTA), análise elementar (CHN), determinação de área superficial (BET), microscopia eletrônica de varredura (SEM) e de transmissão (TEM) e medidas magnéticas mostraram que etanol reduz íons de ferro na RM para formar fases magnéticas, por exemplo Fe 3 O 4 e Fe 0 , e depósitos de carbono (5-42 wt.%) na forma de nanotubos e nanofibras. A combinação de nanoestruturas hidrofóbicas de carbono com óxidos hidrofílicos de Al, Si e Ti presentes na lama vermelha produziu materiais anfifílicos com excelente interação com a interface água-óleo. Misturas de óleo de soja ou de decalina com água (completamente imiscíveis) foram emulsificadas facilmente na presença dos compósitos anfifílicos. Quando os compósitos foram adicionados a uma emulsão água-biodiesel estável, as partículas anfifílicas difundiram-se para a interface água-óleo. As partículas do compósito foram atraídas por ímãs e carregaram com elas as gotas de óleo, levando à completa desemulsificação e separação entre biodiesel e água.New magnetic amphiphilic composites were prepared by the catalytic carbon vapor deposition (CVD) growth of carbon nanotubes and nanofibers using ethanol as carbon source and red mud waste (RM, a by-product of the Bayer process of alumina production) as catalyst and support. Temperature-programmed CVD (TPCVD), analyses by X-ray diffractometry (XRD), Mössbauer spectroscopy, energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy, thermogravimetry (TG/DTA), elemental analysis (CHN), superficial area determination (BET), scanning (SEM) and transmission (TEM) electron microscopies and magnetic measurements showed that ethanol reduces the iron ions in the red mud to form magnetic phases, e.g., Fe 3 O 4 and Fe 0 , and carbon deposits (5-42 wt.%), particularly nanotubes and nanofibers. The combination of the hydrophobic carbon nanostructures with the hydrophilic Al, Si and Ti oxides present in the RM produced amphiphilic materials with excellent interaction with the water-oil interface. Soybean oil or decalin mixtures with water (completely immiscible) were easily emulsified in the presence of the amphiphilic composites. When the composites were added to stable biodiesel-water emulsions, the amphiphilic particles diffused to the interface oil-water. These composite particles were attracted by a magnet, carrying the oil droplets with them and leading to the complete demulsification and separation of the biodiesel from the water.

Iron: a versatile element to produce materials for environmental applications

“…[45][46][47][48] These amphiphilic materials are composed of a ceramic matrix (providing the hydrophilic surface) containing carbon nanostructures (responsible for the hydrophobic properties) and magnetic iron cores coated with carbon to produce the magnetic properties of the composite (Figure 14).…”

Magnetic amphiphilic hybrid carbon nanotubes containing N-doped and undoped sections: powerful tensioactive nanostructures

“…[1][2][3] In general, the use of a surfactant is necessary to improve the phase transfer, but this introduces several operational, technical and economical drawbacks. [5][6][7][8][9] Given that the development of robust amphiphilic nanostructures highly efficient in promoting emulsions has been very recently identified as an important challenge for colloidal materials, 10 we believe that further research in this area is of considerable interest. Recently, composites based on hydrophobic carbon nanomaterials supported on hydrophilic oxide particles have been used to stabilize water-oil emulsions and catalyze reactions at the liquidliquid interface.…”

The influence of asphaltenes subfractions on the stability of crude oil model emulsions

“…11,12 Emulsion destabilization can be achieved by different methods. [13][14][15] Crude oil can be demulsified by adding chemical compounds (normally at concentrations of 10 to 1000 ppm) to improve the separation rate of the W/O emulsion. These additives cause thinning of the interfacial film, allowing the droplets to coalesce more easily, thus allowing the phases to separate.…”