From the solvothermally treated poly(vinylidenefluoride) colloidal suspension to sticky hydrophobic coating

Effect of basic and basic/acid modifications on the surface of PVDF membranes for the insertion of TiO2 and its use in environmental applications

Supporting titanium oxide (TiO2) on polymeric membrane surfaces is a strategy to increase the photocatalytic activity of this material as well as to modify membrane surface with antifouling properties or to develop hybrid processes of water treatment. The chemical characteristics of the polymeric membrane surfaces are a determining factor in the correct impregnation of TiO2 particles. In this work, the titanium oxide was immobilized on polyvinylidene fluoride (PVDF) membrane surface by direct impregnation during the synthesis of the inorganic particles by sol-gel route. The PVDF membranes were previously modified by treatments based on an alkaline attack followed by acid treatment. The final TiO2-modified membranes were characterized by infrared and Raman spectroscopy, as well as by scanning electron microscopy. In addition, the changes on the surface characteristics were determined by contact angle measurements. Finally, the membranes were tested on the photocatalytic degradation of methyl orange (MO). The results obtained indicate that the basic/acid pretreatment allows the generation of active sites in the membrane and that when carrying out the synthesis of TiO2 on the membrane, it can be anchored stably on its surface and through the pores. The microscopies indicate that the structure of the membrane is not compromised by the pretreatment. The amount of TiO2 deposited on the membrane was of 0.1580 ± 0.01773 mg TiO2/cm2 membrane. With this amount of TiO2, a degradation percentage of 98.2% is achieved after 450 min; when the membrane is used for a second cycle, a degradation percentage of 82.0% is obtained, which remains constant for 3 subsequent cycles. This method, which uses the PVDF membrane as a support for TiO2 particles, represents a low-cost and easy-to-prepare insertion procedure, with good degradation percentages, which means that the membrane can be used for subsequent studies in filtration systems in the treatment of effluents from the textile industry.

Candle Soot-Based Electrosprayed Superhydrophobic Coatings for Self-Cleaning, Anti-Corrosion and Oil/Water Separation

The interest in candle soot (CS)-based superhydrophobic coatings has grown rapidly in recent years. Here, a simple and low-cost process has been developed for the fabrication of CS-based superhydrophobic coatings through electrospraying of the composite cocktail solution of CS and polyvinylidene fluoride (PVDF). Results show that the superhydrophobicity of the coating closely relates to the loading amount of CS which results in coatings with different roughnesses. Specifically, increasing the CS amount (not more than 0.4 g) normally enhances the superhydrophobicity of the coating due to higher roughness being presented in the produced microspheres. Further experiments demonstrate that the superhydrophobicity induced in the electrosprayed coating results from the synergistic effect of the cocktail solution and electrospray process, indicating the importance of the coating technique and the solution used. Versatile applications of CS-based superhydrophobic coatings including self-cleaning, anti-corrosion and oil/water separation are demonstrated. The present work provides a convenient method for the fabrication of CS-based superhydrophobic coatings, which is believed to gain great interest in the future.

Sandwich-structured composite fibrous membranes with tunable porous structure for waterproof, breathable, and oil-water separation applications

HYPOTHESIS

In general, microporous membranes with waterproofness, breathability, and oil-water separation performance are prepared from hydrophobic raw materials and demonstrated to exhibit an interconnected porous structure. Hence, constructing porous and gradient-structured composite membranes by integrating robust hydrophobic/lipophilic polyvinylidene fluoride (PVDF) and breathable polyurethane (PU) microporous membranes could help realize a selective separation process.

EXPERIMENT

Here, novel polyvinylidene fluoride-carbon nanotube/polyurethane/polyvinylidene fluoride-carbon nanotube (PVDF-CNT/PU/PVDF-CNT) sandwich-structured microporous membranes were fabricated by sequential electrospinning. The influence of the thickness ratios of PVDF/PU/PVDF and carbon nanotube (CNT) content on the fibrous construction, porous structure, and wettability of the composite membranes was systematically studied by scanning electron microscopy (SEM), pore size, porosity and contact angle. Significantly, the effect of the fibrous construction, porous structure, and wettability on the waterproofness, breathability, and oil-water separation ability of the composite membranes was investigated.

FINDINGS

The novel separation system proved the 'complementary effect' between the PVDF and PU membranes. Further, because of the elaborate gradient construction, superior porous structure, and robust hydrophobicity-oleophilicity, the resultant membranes exhibited moderate waterproofness (38 kPa) and excellent breathability (8.63 kg m^-2 d^-1), and oil-water separation, confirming that they could be promising alternatives for numerous practical applications, such as protective clothing, treatment of oil-contaminated water, and membrane distillation.