Carbon nanotube- and carbon fiber-reinforcement of ethylene-octene copolymer membranes for gas and vapor separation

A comprehensive review and perspective research in technology integration for the treatment of gaseous volatile organic compounds

Volatile organic compounds (VOCs) are harmful pollutants emitted from industrial processes. They pose a risk to human health and ecosystems, even at low concentrations. Controlling VOCs is crucial for good air quality. This review aims to provide a comprehensive understanding of the various methods used for controlling VOC abatement. The advancement of mono-functional treatment techniques, including recovery such as absorption, adsorption, condensation, and membrane separation, and destruction-based methods such as natural degradation methods, advanced oxidation processes, and reduction methods were discussed. Among these methods, advanced oxidation processes are considered the most effective for removing toxic VOCs, despite some drawbacks such as costly chemicals, rigorous reaction conditions, and the formation of secondary chemicals. Standalone technologies are generally not sufficient and do not perform satisfactorily for the removal of hazardous air pollutants due to the generation of innocuous end products. However, every integration technique complements superiority and overcomes the challenges of standalone technologies. For instance, by using catalytic oxidation, catalytic ozonation, non-thermal plasma, and photocatalysis pretreatments, the amount of bioaerosols released from the bioreactor can be significantly reduced, leading to effective conversion rates for non-polar compounds, and opening new perspectives towards promising techniques with countless benefits. Interestingly, the three-stage processes have shown efficient decomposition performance for polar VOCs, excellent recoverability for nonpolar VOCs, and promising potential applications in atmospheric purification. Furthermore, the review also reports on the evolution of mathematical and artificial neural network modeling for VOC removal performance. The article critically analyzes the synergistic effects and advantages of integration. The authors hope that this article will be helpful in deciding on the appropriate strategy for controlling interested VOCs.

Geometrical and physical effects of nanofillers on percolation and electrical conductivity of polymer carbon-based nanocomposites: a general micro-mechanical model

A micro-mechanical model was developed to describe the electrical percolation and effective electrical conductivity of nanocomposites containing fillers with different shapes such as graphene nanoplatelets, carbon black, and carbon nanotubes. The fillers are considered to be an oblate or short cylindrical shape for graphene nanoplatelets, a spherical or spheroidal shape for carbon blacks, and a prolate or long cylindrical shape for carbon nanotubes. The effects of the filler shape, filler size, filler aspect ratios, the thickness of the interphase layer, the conductivity of the filler, the conductivity of the interphase layer, the conductivity of the matrix, volume fractions, quantum tunneling distance, and tunneling barrier height have been examined. This modified mean field model well describes the electrical properties of nanocomposites in the whole range of volume fractions for a variety of experimental results with various reinforcements. Also, it reproduces the very sharp behavior of the percolation transition well around the percolation threshold. The results show that nanocomposites containing fillers with an aspect ratio of 10^-2 < M < 10² and a volume fraction of ϕ_f < 0.3 show an insulating behavior while exhibiting a metallic behavior in the ranges M < 10^-2 and M > 10². This model produces variations in the percolation threshold in terms of the aspect ratio as a parabolic curve that can be used to predict the percolation threshold of nanocomposites with various fillers. The present general model can provide a new insight to design conductive polymer nanocomposites with the desired features and specific applications.

Adsorption and membrane separation for removal and recovery of volatile organic compounds

Volatile organic compounds (VOCs) are a crucial kind of pollutants in the environment due to their obvious features of severe toxicity, high volatility, and poor degradability. It is particularly urgent to control the emission of VOCs due to the persistent increase of concentration and the stringent regulations. In China, clear directions and requirements for reduction of VOCs have been given in the "national plan on environmental improvement for the 13th Five-Year Plan period". Therefore, the development of efficient technologies for removal and recovery of VOCs is of great significance. Recovery technologies are favored by researchers due to their advantages in both recycling VOCs and reducing carbon emissions. Among them, adsorption and membrane separation processes have been extensively studied due to their remarkable industrial prospects. This overview was to provide an up-to-date progress of adsorption and membrane separation for removal and recovery of VOCs. Firstly, adsorption and membrane separation were found to be the research hotspots through bibliometric analysis. Then, a comprehensive understanding of their mechanisms, factors, and current application statuses was discussed. Finally, the challenges and perspectives in this emerging field were briefly highlighted.

Role of Nanocomposite Support Stiffness on TFC Membrane Water Permeance

This paper discusses the role played by the mechanical stiffness of porous nanocomposite supports on thin-film composite (TFC) membrane water permeance. Helically coiled and multiwall carbon nanotubes (CNTs) were studied as additives in the nanocomposite supports. Mechanical stiffness was evaluated using tensile tests and penetration tests. While a low loading of CNTs caused macrovoids that decreased the structural integrity, adding higher loads of CNTs compensated for this effect, and this resulted in a net increase in structural stiffness. It was found that the Young's modulus of the nanocomposite supports increased by 30% upon addition of CNTs at 2 wt %. Results were similar for both types of CNTs. An empirical model for porous composite materials described the Young's modulus results. The nanocomposite supports were subsequently used to create TFC membranes. TFC membranes with stiffer supports were more effective at preventing declines in water permeance during compression. These findings support the idea that increasing the mechanical stiffness of TFC membrane nanocomposite supports is an effective strategy for enhancing water production in desalination operations.

Gas Transport Properties of Polybenzimidazole and Poly(Phenylene Oxide) Mixed Matrix Membranes Incorporated with PDA-Functionalised Titanate Nanotubes

Functionalised titanate nanotubes (TiNTs) were incorporated to poly(5,5-bisbenzimidazole-2,2-diyl-1,3-phenylene) (PBI) or poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) for improving the interfacial compatibility between the polymer matrix and inorganic material and for altering the gas separation performance of the neat polymer membranes. Functionalisation consisted in oxidative polymerisation of dopamine-hydrochloride on the surface of non-functionalised TiNTs. Transmission electron microscopy (TEM) confirmed that a thin polydopamine (PDA) layer was created on the surface of TiNTs. 1.5, 3, 6, and 9 wt.% of PDA-functionalised TiNTs (PDA-TiNTs) were dispersed to each type of polymer matrix to create so-called mixed matrix membranes (MMMs). Infrared spectroscopy confirmed that -OH and -NH groups exist on the surface of PDA-TiNTs and that the nanotubes interact via H-bonding with PBI but not with PPO. The distribution of PDA-TiNTs in the MMMs was to some extent uniform as scanning electron microscope (SEM) studies showed. Beyond, PDA-TiNTs exhibit positive effect on gas transport properties, resulting in increased selectivities of MMMs. The addition of nanotubes caused a decrease in permeabilities but an increase in selectivities. It is shown that 9 wt.% of PDA-TiNTs in PBI gave a rise to CO₂/N₂ and CO₂/CH₄ selectivities of 112 and 63 %, respectively. In case of PPO-PDA-TiNT MMMs, CO₂/N₂ and CO₂/CH₄ selectivity increased about 25 and 17 %, respectively. Sorption measurement showed that the presence of PDA-TiNTs in PBI caused an increase in CO₂ sorption, whereas the influence on other gases is less noticeable.