Plasma & Microwaves as Greener Options for Nanodiamond Purification: Insight Into Cytocompatibility

The potential biomedical applications of nanodiamond have been considered over the last few decades. However, there is still uncertainty regarding the extent to which the surface characteristics of this material can influence potential applications. The present study investigated the effects of surface characteristics alongside the prospective of improving nanodiamond production using cold plasma and microwave technologies for the surface tailoring of the nanocarbons. Numerous approaches were applied to purify, refine and modify a group of nanosized diamonds at each step of their production cycle: from the detonation soot as the initial raw material to already certified samples. The degree of surface changes were deliberately performed slowly and kept at different non-diamond carbon presence stages, non-carbon elemental content, and amount converted superficial moieties. In total, 21 treatment procedures and 35 types of nanosize diamond products were investigated. In addition cultures of human fibroblast cells showed enhanced viability in the presence of many of the processed nanodiamonds, indicating the potential for dermal applications of these remarkable nanomaterials.

Antifouling performance of polytetrafluoroethylene and polyvinylidene fluoride ultrafiltration membranes during alkali/surfactant/polymer flooding wastewater treatment: Distinctions and mechanisms

Alkali/surfactant/polymer (ASP) flooding wastewater is highly caustic, and membrane fouling is the main obstacle during ASP ultrafiltration (UF) treatment. To maintain favorable filtration performance, polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) membranes were implemented here, and their antifouling properties and mechanisms were investigated based on the threshold flux theory. Compared with the PVDF membranes, the PTFE membranes exhibited superior antifouling properties with lower reductions in flux and smaller hydraulic resistance, and they presented a nearly identical pseudo-stable fouling rate at a later time point. In the fouling layers of the PTFE and PVDF membranes, anion polyacrylamide (APAM) was observed along with divalent/trivalent metal ions. The thermodynamic and molecular mechanisms of membrane fouling by APAM were elucidated using the Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and atomic force microscopy (AFM), respectively. The calculated total interfacial free energy (mJ/m²) of adhesion between the APAM and PTFE membranes was positive, and the value between the APAM and PVDF membranes was negative. Furthermore, the values and interaction distances of the measured intermolecular rupture and approaching forces were larger for APAM-PTFE than for APAM-PVDF. For the PTFE membranes, the positive free energies and smaller intermolecular interaction resulted in weaker APAM-PTFE adhesion and adsorption and therefore the lower levels of flux decline and the later achievement of the pseudo-stable fouling rate. Additionally, the total flux recoveries observed after physical cleaning reached 0.78-0.80 and 0.32-0.39 for the PTFE and PVDF membranes, respectively, which showed that the PTFE membranes can be cleaned easily. The PTFE membranes have considerable potential for extensive application in UF treatments for ASP wastewater. These results should promote understanding the essence of the threshold flux and the fouling control of UF membranes.

Fabrication of high-performance polytetrafluoroethylene microporous membranes filled with nano-alumina

In this article, polytetrafluoroethylene (PTFE) microporous membranes with excellent tensile strength and good wear durability were successfully fabricated by the addition of nano-alumina (Al2O3). The friction and mechanical behavior of PTFE microporous membranes with different nano-Al2O3 contents were investigated by Martindale abrasion tester, dynamic mechanical analysis, and universal testing machine. Scanning electron microscopy was applied to analyze the surface, longitudinal section, and worn surface of the microporous membranes. Results demonstrated that nano-Al2O3 particles were dispersed into the “node” structures of PTFE microporous membranes and acted as the skeleton, leading to the increasing of the tensile strength remarkably. The wear rate reduced significantly with the addition of nano-Al2O3 and was affected by nano-Al2O3 content. Additionally, the wear mechanism of the microporous membranes was also discussed based on the study results.

Sintering process investigation during polytetrafluoroethylene hollow fibre membrane fabrication by extrusion method

In this study, the effect of sintering conditions including manner, temperature and duration on properties of polytetrafluoroethylene (PTFE) hollow fibre membrane fabricated by extrusion method was intensively investigated. Different from un-sintered and relaxed sintered, the fixed sintered PTFE hollow fibre membrane was observed to generate a uniform ‘fibril–node’ porous structure and a main crystal transformation to folded chain crystal with smaller size. Consequently, it was found that for fixed setting sintering, both temperature increase from 340°C to 400°C and duration prolongation obviously improved pore size, ethanol permeation performance and mechanical strength. Additionally, the test results revealed that the membrane sintered below virgin melting point (350°C) had a noticeable higher porosity but poorer ethanol permeation performance that could be primarily attributed to increased ratio of closed pore. The sintering condition exhibited evident influence on PTFE hollow fibre membrane thermal stability, though it showed no alteration to the thermal decomposition of PTFE. The obtained PTFE hollow fibre membrane was tested to evaluate their vacuum membrane distillation (VMD) performances. It was found that PTFE membrane from lower sintering temperature delivered a better salt rejection; on the other hand, the permeate flux was improved by increased vacuum pressure during VMD operation.