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•Carbon nanotubes activate persulfates via nonradical mechanisms.•The CNT/persulfate system effectively oxidizes phenolic compounds.•Reactive complexes of CNT–persulfate are ...responsible for the compound degradation.
Carbon nanotubes (CNTs) have been found to activate persulfates (i.e., peroxymonosulfate and peroxydisulfate) into reactive species that are capable of oxidizing organic compounds in water. In the presence of single- or multi-walled CNTs, persulfates effectively degraded phenolic compounds and certain pharmaceuticals. Phenyl derivatives substituted with electron-withdrawing groups, such as benzoic acid and nitrobenzene, were resistant to degradation by the CNT/persulfate system. Based on observations regarding persulfate decomposition and linear sweep voltammetry using a CNT electrode, it has been suggested that persulfates bind onto the surface of CNTs, forming reactive complexes that are immediately decomposed upon reaction with organic compounds. Electron paramagnetic resonance spectroscopy with spin-trapping indicates that these reactive species are distinct from sulfate radical anions or hydroxyl radicals. The CNT-activated persulfate system shows promise as a novel treatment technology for the selective oxidation of organic contaminants in water.
Oxidation by persulfates at elevated temperatures (thermally activated persulfates) disintegrates bacterial cells and extracellular polymeric substances (EPS) composing waste-activated sludge (WAS), ...facilitating the subsequent sludge dewatering. The WAS disintegration process by thermally activated persulfates exhibited different behaviors depending on the types of persulfates employed, that is, peroxymonosulfate (PMS) versus peroxydisulfate (PDS). The decomposition of PMS in WAS proceeded via a two-phase reaction, an instantaneous decomposition by the direct reaction with the WAS components followed by a gradual thermal decay. During the PMS treatment, the WAS filterability (measured by capillary suction time) increased in the initial stage but rapidly stagnated and even decreased as the reaction proceeded. In contrast, the decomposition of PDS exhibited pseudo first-order decay during the entire reaction, resulting in the greater and steadier increase in the WAS filterability compared to the case of PMS. The treatment by PMS produced a high portion of true colloidal solids (<1 μm) and eluted soluble and bound EPS, which is detrimental to the WAS filterability. However, the observations regarding the dissolved organic carbon, ammonium ions, and volatile suspended solids collectively indicated that the treatment by PMS more effectively disintegrated WAS compared to PDS, leading to higher weight (or volume) reduction by postcentrifugation.
This study introduces graphited nanodiamond (G-ND) as an environmentally friendly, easy-to-regenerate, and cost-effective alternative catalyst to activate persulfate (i.e., peroxymonosulfate (PMS) ...and peroxydisulfate (PDS)) and oxidize organic compounds in water. The G-ND was found to be superior for persulfate activation to other benchmark carbon materials such as graphite, graphene, fullerene, and carbon nanotubes. The G-ND/persulfate showed selective reactivity toward phenolic compounds and some pharmaceuticals, and the degradation kinetics were not inhibited by the presence of oxidant scavengers and natural organic matter. These results indicate that radical intermediates such as sulfate radical anion and hydroxyl radical are not majorly responsible for this persulfate-driven oxidation of organic compounds. The findings from linear sweep voltammetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and electron paramagnetic resonance spectroscopy analyses suggest that the both persulfate and phenol effectively bind to G-ND surface and are likely to form charge transfer complex, in which G-ND plays a critical role in mediating facile electron transfer from phenol to persulfate.
The use of calcium oxide (CaO) demonstrates a superior potential for the activation of ground granulated blast furnace slag (GGBFS), and it produces a higher mechanical strength than calcium ...hydroxide Ca(OH)2. The mechanical strength differences between CaO- and Ca(OH)2-activated GGBFS binders are explored using isothermal calorimetry, powder X-ray diffraction, thermogravimetric and differential thermal analysis (TGA and DTA) as well as compressive strength testing. Calcium silicate hydrate (C–S–H), Ca(OH)2 and a hydrotalcite-like phase are found as reaction products in all samples. The TGA and DTA results indicate that the use of CaO produces more C–S–H, although this is not likely to be the primary cause of higher strength development in the CaO-activated GGBFS. Rather, other factors such as porosity may govern the strength at a higher order of magnitude. Significant reduction of Ca(OH)2 occurs only with the use of Ca(OH)2, followed by the formation of carbonate (CaCO3), indicating carbonation.
•CaO showed a better potential for the activation of GGBFS than Ca(OH)2.•Strength test, XRD, TGA/DTA and isothermal calorimetry are used.•C-S-H, Ca(OH)2, and a hydrotalcite-like phase are found in all samples.•The use of Ca(OH)2 causes some degree of carbonation.
Recent results on the underlying mechanisms initiating the transformations of engineered nanoparticles (ENPs) in the environment are reviewed.
•Collation of results concerning underlying mechanisms ...that initiate the transformation of engineered nanoparticles (ENPs).•The transformation process of ENPs is altered by a confluence of factors depending on the characteristics of ENPs and surrounding environmental matrices.•The interaction of ENPs with both, organic and inorganic ligands, results in changes at the physicochemical, macromolecular and biological levels.•ENPs show bioavailability potential dependent on the extent of transformation and aging in the environment.
The increased flux of engineered nanoparticles (ENPs) in consumer and commercial products has become a viable threat, particularly if their release affects the environment. The aim of this paper is to review the recent literature results pertaining to the underlying mechanisms initiating the transformations of ENPs for both biotic and abiotic processes. The transformation of ENPs is necessarily interrelated to multiple environmental aspects and many concepts overlap. Physicochemical, macromolecular, and biological pathways contribute to assessing the impact of the altered activities of ENPs on the surrounding environmental matrices. Transformations involving both organic and inorganic ligands are vital in soil and water systems. Energy-efficient biocatalytic pathways can easily facilitate biotransformation involving enzymatic reactions and biomolecules. The relationship between physicochemical and biological parameters triggers transformation, greatly affecting the bioavailability and aging of ENPs to various extents. Therefore, the interaction of ENPs in environmental matrices is significant in understanding the risk of potential exposure and/or uptake by biota.
Nanosized zerovalent iron (nFe0) loaded with a secondary metal such as Ni or Cu on its surface was demonstrated to effectively activate periodate (IO4-) and degrade selected organic compounds at ...neutral pH. The degradation was accompanied by a stoichiometric conversion of IO4- to iodate (IO3-). nFe0 without bimetallic loading led to similar IO4- reduction but no organic degradation, suggesting the production of reactive iodine intermediate only when IO4- is activated by bimetallic nFe0 (e.g., nFe0-Ni and nFe0-Cu). The organic degradation kinetics in the nFe0-Ni(or Cu)/IO4- system was substrate dependent: 4-chlorophenol, phenol, and bisphenol A were effectively degraded, whereas little or no degradation was observed with benzoic acid, carbamazepine, and 2,4,6-trichlorophenol. The substrate specificity, further confirmed by little kinetic inhibition with background organic matter, implies the selective nature of oxidant in the nFe0-Ni(or Cu)/IO4- system. The comparison with the photoactivated IO4- system, in which iodyl radical (IO3•) is a predominant oxidant in the presence of methanol, suggests IO3• also as primary oxidant in the nFe0-Ni(or Cu)/IO4- system.
Zero-valent iron nanoparticles (nano-Fe0) in aqueous solution rapidly inactivated Escherichia coli. A strong bactericidal effect of nano-Fe0 was found under deaerated conditions, with a linear ...correlation between log inactivation and nano-Fe0 dose (0.82 log inactivation/mg/L nano-Fe0 x h). The inactivation of E. coli under air saturation required much higher nano-Fe0 doses due to the corrosion and surface oxidation of nano-Fe0 by dissolved oxygen. Significant physical disruption of the cell membranes was observed in E. coli exposed to nano-Fe0, which may have caused the inactivation or enhanced the biocidal effects of dissolved iron. The reaction of Fe(II) with intracellular oxygen or hydrogen peroxide also may have induced oxidative stress by producing reactive oxygen species. The bactericidal effect of nano-Fe0 was a unique property of nano-Fe0, which was not observed in other types of iron-based compounds.
A substrate-immobilized (SI) TiO2 nanofiber (NF) photocatalyst for multiple uses was prepared through electrospinning and hot pressing. The rate of furfuryl alcohol degradation under UV irradiation ...was found to be the highest when the anatase to rutile ratio was 70:30; the rate did not linearly increase as a function of the NF film thickness, mainly due to diffusion limitation. Even after eight repeated cycles, it showed only a marginal reduction in the photocatalytic activity for the degradation of cimetidine. The effects of pH and different organic matter characteristics on the photodegradation of cimetidine (CMT), propranolol (PRP), and carbamazepine (CBZ) were investigated. The pH-dependence of the photocatalytic degradation rates of PRP was explained by electrostatic interactions between the selected compounds and the surface of TiO2 NFs. The degradation rates of CMT showed the following order: deionized water > l-tyrosine > secondary wastewater effluent (effluent organic matter) > Suwannee River natural organic matter, demonstrating that the characteristics of the dissolved organic matter (DOM) can affect the photodegradation of CMT. Photodegradation of CBZ was affected by the presence of DOM, and no significant change was observed between different DOM characteristics. These findings suggest that the removal of CMT, PRP, and CBZ during photocatalytic oxidation using SI TiO2 NFs is affected by the presence of DOM and/or pH, which should be importantly considered for practical applications.
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•A multiusable photocatalyst was prepared by electrospinning and hot pressing.•The anatase to rutile ratio of 70:30 was optimal for photocatalysis.•Photodegradation of cimetidine was affected by DOM characteristics.•Photodegradation of propranolol was affected by the surface charge of SI TiO2 NFs.•Photodegradation of carbamazepine was greatly retarded by the presence of DOM.
Morphology-controlled materials at the micro- and nanoscale levels are of great significance to the design and application of materials. Stable and well-dispersed boehmite and alumina with different ...morphologies were fabricated under hydrothermal conditions. The nitrate, chloride, and sulfate aluminum salts yielded nanoplate, microspindle, and microsphere morphologies, respectively. Calcination of the prepared boehmite samples yielded alumina samples with retention of the morphologies. In comparisons of samples with identical morphologies, alumina exhibited better uptake of As(V) than boehmite; the As(V) concentration was analyzed by the standard molybdenum blue method. The adsorption capabilities of the morphologically controlled materials are ranked microspindle > microsphere > nanoplate. The impacts of process parameters, such as reaction time; initial As(V) concentration; solution pH; competing ions (Ca2+, Mg2+, NO3−, PO43-), which are common in most aquatic ecosystems; and co-contaminants (Cr(VI), Pb(II)), on removal efficiencies were examined. A well-defined mesostructure, superior surface area, chemical and electrostatic interaction, and surface charge distribution over the aluminol surface sites could be factors in the uptake of As(V). The design and synthesis of functional hierarchical micro- and nanostructured materials with the desired adsorptive properties, which are suitable for water treatment applications, can be achieved through environmentally benign hydrothermal fabrication.
•Hierarchical boehmite and alumina were synthesized by a simple hydrothermal method.•Use of different aluminum salts induced different morphologies in the materials.•The synthesized materials were superior in As(V) adsorption to commercial alumina.
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