Laboratory-scale characterization of slow-release permanganate gel (SRP-G) for the in-situ treatment of chlorinated-solvent groundwater plumes.

Significant challenges remain for the remediation of chlorinated-solvent plumes in groundwater, such as trichloroethene (TCE) and tetrachloroethene (PCE). A novel slow-release permanganate gel (SRP-G) technique may show promise for the in-situ treatment (remediation) of chlorinated contaminant plumes in groundwater. A series of laboratory experiments were conducted to characterize the primary physical factors that influence SRP-G gelation processes to optimize SRP-G performance for plume treatment. Specifically, experiments were conducted to quantify gel zeta potential, particle size distribution, and viscosity to determine SRP-G gelation characteristics and processes. These experiments tested various concentrations of two SRP-G amendment solutions (NaMnO4 and KMnO4) prepared with 30-wt.% and 50-wt.% colloidal silica to determine such influences on zeta potential, particle size distribution, and viscosity. The results of this study show that SRP-G solutions with low zeta potential and relatively high pH favor more rapid SRP-G gelation. The concomitant interaction of the predominantly negatively charged colloidal silica particles and the positively charged dissociated cations (Na+ and K+) in the SRP-G solution had the effect of stabilizing charge imbalance via attraction of particles and thereby inducing a greater influence on the gelation process. Gel particle size distribution and changes in viscosity had a significant influence on SRP-G solution gelation. The addition of permanganate (NaMnO4 or KMnO4) increased the average particle size distribution and the viscosity of the SRP-G solution and decreased the overall gelation time. SRP-G amendments (NaMnO4 or KMnO4) prepared with 50-wt.% colloidal silica showed more effective gelation (and reduced gelation time) compared to SRP-G amendments prepared with 30-wt.% colloidal silica. Under the conditions of these experiments, it was determined that both the 7-wt.% NaMnO4 solution and 90 mg/L KMnO4 solution using 50-wt.% colloidal silica would be the optimal injection SRP-G solution concentrations for this in-situ treatment technique.

A juxtaposed review on adsorptive removal of PFAS by metal-organic frameworks (MOFs) with carbon-based materials, ion exchange resins, and polymer adsorbents.

The removal of poly- and perfluoroalkyl substances (PFAS) from the aquatic environment is a universal concern due to the adverse effects of these substances on both the environment and public health. Different adsorbents, including carbon-based materials, ion exchange resins, biomaterials, and polymers, have been used for the removal of short-chain (C < 6) and long-chain (C > 7) PFAS from water with varying performance. Metal-organic frameworks (MOFs), as a new generation of adsorbents, have also been recently used to remove PFAS from water. MOFs provide unique properties such as significantly enhanced surface area, structural tunability, and improved selectivity compared to conventional adsorbents. However, due to various types of MOFs, their complex chemistry and morphology, different PFAS compounds, lack of standard adsorption test, and different testing conditions, there are inconclusive and contradictory findings in the literature. Therefore, this review aims to provide critical analysis of the performance of different types of MOFs in the removal of long-chain (C > 7), short-chain (C < 6), and ultra-short-chain (C < 3) PFAS and comprehensively study the efficiency of MOFs for PFAS removal in comparison with other adsorbents. In addition, the adsorption mechanisms and kinetics of PFAS components on different MOFs, including Materials of Institute Lavoisier (MIL), Universiteit of Oslo (UiO), Zeolitic imidazolate frameworks (ZIFs), Hong Kong University of Science and Technology (HKUST), and other hybrid types of MOF were discussed. The study also discussed the effect of environmental factors such as pH and ionic strength on the adsorption of PFAS on MOFs. In addition to the adsorption process, the reusability and regeneration of MOFs in the PFAS removal process are discussed. Finally, challenges and future outlooks of the utility of MOFs for PFAS removal were discussed to inspire future critical research efforts in removing PFAS.

Functionalized-MXene Thin-Film Nanocomposite Hollow Fiber Membranes for Enhanced PFAS Removal from Water.

Due to adverse health effects and the broad sources of per- and polyfluoroakyl substances (PFAS), PFAS removal is a critical research area in water purification. We demonstrate the functionalization of thin-film composite (TFC) hollow fiber nanofiltration (HFN) membranes by MXene nanosheets during the interfacial polymerization (IP) process for enhanced removal of perfluorooctane sulfonic acid (PFOS) from water. A MXene-polyamide (PA) selective layer was fabricated on top of a polysulfone (PSF) hollow fiber support via IP of trimesoyl chloride (TMC) and a mixture of piperazine (PIP) and MXene nanosheets to form MXene-PA thin-film nanocomposite (TFN) membranes. Incorporating MXene nanosheets during the IP process tuned the morphology and negative surface charge of the selective layer, resulting in enhanced PFOS rejection from 72% (bare TFC) to more than 96% (0.025 wt % MXene TFN), while the water permeability was also increased from 13.19 (bare TFC) to 29.26 LMH/bar (0.025 wt % MXene TFN). Our results demonstrate that both electrostatic interaction and size exclusion are the main factors governing the PFOS rejection, and both are determined by PA selective layer structural and chemical properties. The lamella structure and interlayer of MXene nanosheets inside the PA layer provided different transport mechanisms for water, ions, and PFAS molecules, resulting in enhanced water permeability and PFAS rejection due to traveling through the membrane by both diffusions through the PA layer and the MXene intralayer channels. MXene nanosheets showed very promising capability as a 2D additive for tuning the structural and chemical properties of the PA layer at the permeability-rejection tradeoff.

The computational quantum mechanical study of sulfamide drug adsorption onto X12Y12 fullerene-like nanocages: detailed DFT and QTAIM investigations.

In the current work, the adsorption of sulfamide drug onto the exterior surface of four fullerene-like nanocages, including Al12N12, Al12P12, B12N12, and B12P12, was studied by employing density functional theory (DFT) and the quantum theory of atom in the molecule (QTAIM) calculations. Our calculations revealed that the sulfamide drug connects to the Al, B, P, and N atoms of Al12N12, Al12P12, B12N12, and B12P12 nanocages through the oxygen and hydrogen atoms with releasing energies of -47.27, -34.59, -28.13 and -9.45 kcal/mol, respectively. Upon the sulfamide drug adsorption onto the stated nanocages, the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were significantly changed, resulting in a decrease in the values of bandgap (Eg) that caused enhance in their electrical conductivity. This trend illustrated that all the stated nanocages may be potential electronic sensors as well as suitable candidates for the delivery of sulfamide drug in the biological system. Finally, The QTAIM analysis was investigated for both types of structural aspects and electronic properties (such as ρ, "∇" ^"2" ρ, G(r), V (r) and H(r)) associated with adsorption of sulfamide molecule on the stated nanocages.

DFT calculations towards the geometry optimization, electronic structure, infrared spectroscopy and UV-vis analyses of Favipiravir adsorption on the first-row transition metals doped fullerenes; a new strategy for COVID-19 therapy.

With the global epidemic of the COVID-19 virus, extensive and rapid research on drug therapy is underway around the world. In this regard, one of the most widely studied drugs is Favipiravir. Our aim in this paper is to conduct comprehensive research based on the Density Functional Theory (DFT) on the potential of metallofullerenes as suitable drug carriers. The surface interaction of Favipiravir with organometallic compound resulted by doping of the five transition metals of the first row of the periodic table (Ti, Cr, Cr, Fe, Ni, and Zn) was examined in depth to select the most suitable metallofullerenes. First, the adsorption geometries of Favipiravir drug onto each metallofullerene were deeply investigated. It was found that Cr-, Fe-, and Ni-doped fullerenes provide the excellent adsorbent property with adsorption energies of -148.2, -149.6, and -146.6 kJ/mol, respectively. The Infrared spectroscopy (IR) study was conducted to survey the stretching vibration of bonds involving in the systems, specialty the CO in the drug, CM in the metallofullerene, and MO in the metallofullerene-drug complex. Finally, the UV-vis analysis showed that the absorption spectra for the studied systems may be attributed to the transition from π-π* and/or n-π*.

Core-size regulated aggregation/disaggregation of citrate-coated gold nanoparticles (5-50nm) and dissolved organic matter: Extinction, emission, and scattering evidence.

Knowledge of the interactions between gold nanoparticles (GNPs) and dissolved organic matter (DOM) is significant in the development of detection devices for environmental sensing, studies of environmental fate and transport, and advances in antifouling water treatment membranes. The specific objective of this research was to spectroscopically investigate the fundamental interactions between citrate-stabilized gold nanoparticles (CT-GNPs) and DOM. Studies indicated that 30 and 50nm diameter GNPs promoted disaggregation of the DOM. This result-disaggregation of an environmentally important polyelectrolyte-will be quite useful regarding antifouling properties in water treatment and water-based sensing applications. Furthermore, resonance Rayleigh scattering results showed significant enhancement in the UV range which can be useful to characterize DOM and can be exploited as an analytical tool to better sense and improve our comprehension of nanomaterial interactions with environmental systems. CT-GNPs having core size diameters of 5, 10, 30, and 50nm were studied in the absence and presence of added DOM at 2 and 8 ppm at low ionic strength and near neutral pH (6.0-6.5) approximating surface water conditions. Interactions were monitored by cross-interpretation among ultraviolet (UV)-visible extinction spectroscopy, excitation-emission matrix (EEM) spectroscopy (emission and Rayleigh scattering), and dynamic light scattering (DLS). This comprehensive combination of spectroscopic analyses lends new insights into the antifouling behavior of GNPs. The CT-GNP-5 and -10 controls emitted light and aggregated. In contrast, the CT-GNP-30 and CT-GNP-50 controls scattered light intensely, but did not aggregate and did not emit light. The presence of any CT-GNP did not affect the extinction spectra of DOM, and the presence of DOM did not affect the extinction spectra of the CT-GNPs. The emission spectra (visible range) differed only slightly between calculated and actual mixtures of CT-GNP-5 or -10 with DOM, whereas emissions for mixtures of CT-GNP-30 or -50 with DOM were enhanced at the surface plasmon resonance (SPR) wavelength. The emission spectra (ultraviolet range) for protein-like constituents of DOM were quenched. Resonance Rayleigh scattering (RRS) was more intense for the CT-GNP-30 and -50 than for the CT-GNP-5 and -10 controls. Intensity-based DLS particle size distributions (PSDs) of DOM controls, CT-GNP-5 and -10nm controls, and 5- and 10nm GNP-DOM mixtures exhibited multimodal aggregation. Analyses of CT-GNP-5 and CT-GNP-10nm mixtures with DOM indicated overcoating of DOM molecules occurred in close proximity (<10nm) to GNPs, whereas similar overcoating was not supported for the CT-GNP-30 or -50 mixtures with DOM. These fundamental observations can be exploited to improve our comprehension of nanomaterial interactions with environmental systems.

Exploiting Synergetic Effects of Graphene Oxide and a Silver-Based Metal-Organic Framework To Enhance Antifouling and Anti-Biofouling Properties of Thin-Film Nanocomposite Membranes.

Thin-film composite (TFC) membranes still suffer from fouling and biofouling. In this work, by incorporating a graphene oxide (GO)-silver-based metal-organic framework (Ag-MOF) into the TFC selective layer, we synthesized a thin-film nanocomposite (TFN) membrane that has notably improved anti-biofouling and antifouling properties. The TFN membrane has a more negative surface charge, higher hydrophilicity, and higher water permeability compared with the TFC membrane. Fluorescence imaging revealed that the GO-Ag-MOF TFN membrane kills Escherichia (E.) coli more than the Ag-MOF TFN, GO TFN, and pristine TFC membranes by 16, 30, and 92%, respectively. Forward osmosis experiments with E. coli and sodium alginate suspensions showed that the GO-Ag-MOF TFN membrane by far has the lowest water flux reduction among the four membranes, proving the exceptional anti-biofouling and antifouling properties of the GO-Ag-MOF TFN membrane.

Extinction, emission, and scattering spectroscopy of 5-50 nm citrate-coated gold nanoparticles: An argument for curvature effects on aggregation.

The interaction of macromolecules with gold nanoparticles (GNPs) is of interest in the emerging field of biomedical and environmental detection devices. However, the physicochemical properties, including spectra, of GNPs in aqueous solution in the absence of metal-macromolecular interactions must first be considered before their activity in biological and environmental systems can be understood. The specific objective of this research was to experimentally illuminate the role of nanoparticle core size on the spectral (simultaneous consideration of extinction, emission, and scattering) versus aggregation behaviors of citrate-coated GNPs (CT-GNPs). It is difficult to find in the literature systematic simultaneous presentation of scattering, emission, and extinction spectra, including the UV range, and thus the present work will aid those who would use such particles for spectroscopic related separations or sensors. The spectroscopic behavior of CT-GNPs with different core sizes (5, 10, 30, and 50nm) was studied in ultra-pure water at pH6.0-6.5 employing UV-visible extinction, excitation-emission matrix (EEM), resonance Rayleigh scattering, and dynamic light scattering (DLS) spectroscopies. The CT-GNP-5 and CT-GNP-10 samples aggregated, absorbed light, and emitted light. In contrast, the CT-GNP-30 and CT-GNP-50 samples did not aggregate and did not emit light, but scattered light intensely. Multimodal peaks were observed in the intensity-based DLS spectra of CT-GNP-5 and CT-GNP-10 samples. Monomodal peaks in the volume-based DLS spectra overestimated particle diameters by 60% and 30% for the CT-GNP-5 and CT-GNP-10 samples, respectively, but underestimated diameters by 10% and 4% for the CT-GNP-30 and CT-GNP-50 samples. The volume-based DLS spectra indicated that dimer and trimer aggregates contributed most to the overall volume of particles in the 5- and 10-nm CT-GNPs, whereas the CT-GNP-30 and CT-GNP-50 samples did not aggregate. Here, we discuss the potential influence that differences in preparation, ionic strength, zeta potential, and conformation of adsorbed citrate anions (due to surface curvature of corona) may exert on the aggregation and spectral observations in these data. In particular, the severe surface curvature of the 5- and 10-nm GNP corona may affect the efficiency of the di-/tribasic citrate compatiblizer molecule to shield the core from interactions with light and from GNP-GNP homoaggregation.

Abiotic reversible self-assembly of fulvic and humic acid aggregates in low electrolytic conductivity solutions by dynamic light scattering and zeta potential investigation.

The aggregation of humic substances and their interaction with filtration media (membranes, soils) has implications for our understanding of membrane fouling during water treatment, the facilitated transport of contaminants, and the transport of organic matter through the microbial loop. To investigate the aggregation of fulvic and humic acids in low electrolytic conductivity solutions, laboratory studies of simulated environmental water samples as well as actual environmental water samples were examined. Intensity-, volume-, and number-based particle size distributions (PSDs) were obtained by dynamic light scattering. Aggregates were categorized into three ranges, i.e., 10-100 nm, 100-1000 nm, and >1 µm. Individual biomacromolecules and the aggregates between 10 nm and 1 µm were presumed to be precursors for the formation of a large 5-µm-sized-particle. The self-assembly of the large-in-volume, few-in-number, 5-µm-sized particle was observed in real-time and occurred in unfiltered samples and in samples filtered (0.45 µm) at a nominal size one order of magnitude smaller. The supramicrometer-sized particle formed, dissipated, and spontaneously re-formed over turbulent/quiescent cycles in the presence of sodium azide indicating reversible abiotic self-assembly. Zeta potential analyses demonstrated that colloidal stability increased as concentration increased. DLS studies of the environmental water samples were comparable to those of the simulated laboratory samples. The operational range of the instrumentation used in these experiments was 0.6 nm-6 µm; therefore, aggregates larger than 6 µm may exist in these solutions.