Separation of a heavy metal from water through a membrane containing boron nitride nanotubes: molecular dynamics simulations

Removal of metals and assimilable organic carbon by activated carbon and reverse osmosis point-of-use water filtration systems

Activated carbon (AC) systems and reverse osmosis (RO) systems are commonly used point-of-use (POU) water filtration systems for removing trace-level contaminants in tap water to protect human health. However, limited research has been done to evaluate their effectiveness in removing heavy metals like manganese (Mn) and uranium (U), or to assess the potential for undesired microbial growth within POU systems, which can reduce their treatment efficiency. This study aimed to systematically evaluate the removal of metals and assimilable organic carbon (AOC) in POU systems. AC systems were operated to 200% of their designed treatment capacities and RO systems were run for three weeks. The results showed that AC systems were generally ineffective at removing metals from drinking water, while RO systems effectively removed them. Both Mn and U were poorly removed by AC systems. Calcium (Ca) and magnesium (Mg) were poorly removed by AC systems, with efficiencies of less than 1%. Iron (Fe) removal by AC systems varied between 61% and 84%. Copper (Fe), likely due to its low influent concentration (<30 μg L-1), was effectively removed by AC systems with efficiencies over 95%. In contrast, RO systems consistently removed all metals effectively. Mn and U removal in RO systems exceeded 95%, while Ca, Mn, Fe, and Cu were all removed with efficiencies greater than 98%. AOC was effectively removed from all AC and RO systems, but with high variability in removal efficiency, which is likely attributed to the heterogeneity of biofilm and microbial growth within the POU systems. The new knowledge generated from this study can improve our understanding of chemical contaminant removal in POU systems and inform the development of better strategies for designing and operating POU systems to remove chemical contaminants in drinking water and mitigate their associated health risks.

Preparation of Activated Boron Nitride and Its Adsorption Characteristics for Zn, Cu, and Cd in Flue Gas

Developing non-carbon-based adsorbents is essential for removing heavy metals from post-incineration flue gas. In this study, a new high-temperature-resistant adsorbent-activated boron nitride (BN) was prepared using precursors combined with a high-temperature activation method. The adsorption characteristics of BN for Zn, Cu, and Cd in simulated flue gas and sludge incineration flue gas were investigated using gas-phase heavy metal adsorption experiments. The results showed that BN prepared at 1350 °C for 4 h had defect structures, abundant pores, functional groups, and a high specific surface area of 658 m2/g. The adsorption capacity of BN in simulated flue gases decreases with increasing adsorption temperature, whereas it is always higher than that of activated carbon (AC). The total adsorption capacities for Zn, Cu, and Cd were the highest at 50 °C with 48.3 mg/g. BN had strong adsorption selectivity for Zn, with a maximum adsorption capacity of 54.45 mg/g, and its adsorption process occurred mainly on the surface. Cu and Cd inhibited Zn adsorption, leading to a decrease in the Zn adsorption capacity. In sludge incineration flue gas, BN can quickly reach adsorption equilibrium. The BN had a synergistic disposal capacity for heavy metals and fine particulate matter. The maximum adsorption capacity was reduced compared to the simulated flue gas adsorption capacity, which was 5.1 mg/g. However, BN still exhibited a strong adsorption selectivity for Zn, and its adsorption capacity was always greater than that of AC. The rich functional groups and high specific surface area enable BN to physically and chemically double-adsorb heavy metals.

Boron Nitride Nanotube (BNNT) Membranes for Energy and Environmental Applications

Owing to their extraordinary thermal, mechanical, optical, and electrical properties, boron nitride nanotubes (BNNTs) have been attracting considerable attention in various scientific fields, making it more promising as a nanomaterial compared to other nanotubes. Recent studies reported that BNNTs exhibit better properties than carbon nanotubes, which have been extensively investigated for most environment-energy applications. Irrespective of its chirality, BNNT is a constant wide-bandgap insulator, exhibiting thermal oxidation resistance, piezoelectric properties, high hydrogen adsorption, ultraviolet luminescence, cytocompatibility, and stability. These unique properties of BNNT render it an exceptional material for separation applications, e.g., membranes. Recent studies reported that water filtration, gas separation, sensing, and battery separator membranes can considerably benefit from these properties. That is, flux, rejection, anti-fouling, sensing, structural, thermal, electrical, and optical properties of membranes can be enhanced by the contribution of BNNTs. Thus far, a majority of studies have focused on molecular simulation. Hence, the requirement of an extensive review has emerged. In this perspective article, advanced properties of BNNTs are analyzed, followed by a discussion on the advantages of these properties for membrane science with an overview of the current literature. We hope to provide insights into BNNT materials and accelerate research for environment-energy applications.

Large-scale molecular dynamics modeling of boron-doped amorphous SiCO ceramics

At high temperature, silicon oxycarbide (SiCO) exhibits excellent mechanical properties and thermal stability. The incorporation of boron in SiCO results in improved performance in creep temperatures. In this work, large-scale molecular dynamics calculations were applied to obtain amorphous SiCO structures containing boron. Phase separation of C-C, B-C and Si-O was achieved for three compositions, and silicon-centered mixed-bond tetrahedrons were reproduced successfully. As the boron content increases, the boron atoms tend to form B-C and B-Si bonds in the voids, which stretches the free carbon network in some instances, causing a increase in C-C distance. Young's modulus remains stable at high temperature for the high-carbon case, which indicates that the free carbon network plays a critical role in the structural and thermal stability of SiBCO. Graphical Abstract Three major typical structures in the cooling down process for silicon boron oxycarbide (Si₅BC₂O₈). Bonds: red Si-O, blue Si-C, black C-C, green B-C, purple Si-B.

Separation of cyanide from an aqueous solution using armchair silicon carbide nanotubes: insights from molecular dynamics simulations

Separation of cyanide, as a model contaminant, from aqueous solution was investigated using molecular dynamics simulations.

Oriented Clay Nanotube Membrane Assembled on Microporous Polymeric Substrates

Organized arrays of halloysite clay nanotubes have great potential in molecular separation, absorption, and biomedical applications. A highly oriented layer of halloysite on polyacrylonitrile porous membrane was prepared via a facile evaporation-induced method. Scanning electronic microscopy, surface attenuated total reflection Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy mapping indicated formation of the nanoarchitecture-controlled membrane. The well-ordered nanotube coating allowed for the excellent dye rejection (97.7% for reactive black 5) with high salt permeation (86.5% for aqueous NaCl), and thus these membranes were suitable for dye purification or concentration. These well-aligned nanotubes' composite membranes also showed very good fouling resistance against dye accumulation and bovine serum albumin adsorption as compared to the pristine polyacrylonitrile or membrane coated with disordered halloysite layer.

Molecular Dynamics Study of Carbon Nanotubes/Polyamide Reverse Osmosis Membranes: Polymerization, Structure, and Hydration

Carbon nanotubes/polyamide (PA) nanocomposite thin films have become very attractive as reverse osmosis (RO) membranes. In this work, we used molecular dynamics to simulate the influence of single walled carbon nanotubes (SWCNTs) in the polyamide molecular structure as a model case of a carbon nanotubes/polyamide nanocomposite RO membrane. It was found that the addition of SWCNTs decreases the pore size of the composite membrane and increases the Na and Cl ion rejection. Analysis of the radial distribution function of water confined in the pores of the membranes shows that SWCNT+PA nanocomposite membranes also exhibit smaller clusters of water molecules within the membrane, thus suggesting a dense membrane structure (SWCNT+PA composite membranes were 3.9% denser than bare PA). The results provide new insights into the fabrication of novel membranes reinforced with tubular structures for enhanced desalination performance.

Removal of heavy metals from water through armchair carbon and boron nitride nanotubes: a computer simulation study

Number of heavy metals permeation from the (7,7) CNT and the (7,7) BNNT in the applied voltages.

Water desalination through armchair carbon nanotubes: a molecular dynamics study

Separation of ions from water using armchair carbon nanotubes.