Search Results

1 - 7 of 7 items

  • Author: Miroslav Černík x
Clear All Modify Search

Abstract

Contaminated mine water from the Kank site (Czech Republic) containing arsenic at a concentration of approximately 85 mg/dm3 was tested in a reaction with elemental iron nanoparticles. In a reductive environment there was a reduction of As to the more soluble and toxic form of As(III) depending on the pH of the solution. Oxidation of elemental iron creates oxyhydroxides which incorporate As into their structure in the form of mixed complexes and thereby remove and bind dissolved As from the solution. The addition of 0.5 g/dm3 nZVI to the contaminated water leads to a significant decrease in ORP and concentrations of As to around the detection limit. The pH of the solution is not significantly affected by the addition of nZVI. The main competing anion for co-precipitation is represented by phosphates whose concentration after the addition of nZVI was reduced to 6.5% of the original value. The resulting precipitates were analyzed by XPS, XRF, XRD, SEM-EDX and Mössbauer spectroscopy. The presence of jarosite, Schwertmannite and also arsenic probably in the form of skorodite was confirmed

Abstract

The recent advances and potential applications of nanoparticles and nanofibres for energy, water, food, biotechnology, the environment, and medicine have immensely conversed. The present review describes a ‘green’ method for the synthesis and stabilization of nanoparticles and ‘green electrospinning’ both using tree gums (arabic, tragacanth, karaya and kondagogu). Furthermore, this review focuses on the impending applications of both gum stabilized nanoparticles and functionalized membranes in remediation of toxic metals, radioactive effluents, and the adsorptive removal of nanoparticulates from aqueous environments as well as from industrial effluents. Besides, the antibacterial properties of gum derivatives, gum stabilized nanoparticles, and functionalized electrospun nanofibrous membranes will also be highlighted. The functionalities of nanofibrous membranes that can be enhanced by various plasma treatments (oxygen and methane, respectively) will also be emphasized.

Abstract

This article deals with combined abio-bioreductive methods for in-situ removal of chlorinated ethenes. The method is based on the use of bioremediation supported by lactate and chemical reduction using nZVI. The method is compared with the use of the individual methods alone, mainly with nZVI. In an environment with very low permeability a poor contaminant removal efficiency was achieved during repeated application of nZVI (about 50% of the original content of contamination). Separate application of lactate resulted in conversion of PCE to 1,2-cis-DCE, whose degradation occurred very slowly. When using the combined abio-bioreductive method, based on consecutive application of lactates and nZVI, over 75% of the original content of contamination was removed. This article discusses not only the changes in concentrations of contaminants but also pH and ORP. Both methods are also compared from an economic point of view.

Abstract

Amongst all of the reducing agents that can be used in environmental remediation, zero valent iron (ZVI) is one of the most common due to its environmental acceptance, high reaction rate, good availability, and long-term stability. Moreover, ZVI mobility, stability and reactivity can be enhanced by the application of a DC electric current, ie electrokinetics (EK). In the study, six various slurries containing different ZVI were tested for their efficacy for chlorinated ethenes and ethanes degradation. Chlorinated compound concentrations, pH, oxidation-reduction potential (ORP) and conductivity were determined during the long-term kinetic test. Kinetic rate constants calculated for the degradation of three chlorinated ethenes (PCE, TCE and cis-DCE) concluded that EK brings substantial contribution to chlorinated compounds degradation. Nano-scale zero valent iron STAR had the highest reaction rates compare to the other ZVI tested. The performed study could serve as a preliminary assessment of various available ZVI before in-situ application.

Abstract

Due to the extreme toxicity of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), the remediation of PCDD/F aquifer source zones is greatly needed; however, it is very difficult due to their persistence and recalcitrance. The potential degradability of PCDD/F bound to a real matrix was studied in five systems: iron in a high oxidation state (ferrate), zero-valent iron nanoparticles (nZVI), palladium nanopowder (Pd), a combination of nZVI and Pd, and persulfate (PSF). The results were expressed by comparing the total toxicity of treated and untreated samples. This was done by weighting the concentrations of congeners (determined using a standardized GC/HRMS technique) by their defined toxicity equivalent factors (TEF). The results indicated that only PSF was able to significantly degrade PCDD/F. Toxicity in the system decreased by 65% after PSF treatment. Thus, we conclude that PSF may be a potential solution for in-situ remediation of soil and groundwater at PCDD/F contaminated sites.

Abstract

Heterogeneous catalysis is one of the fastest developing branches of chemistry. Moreover, it is strongly connected to popular environment-related applications. Owing to the very fast changes in this field, for example, numerous discoveries in nanoscience and nanotechnologies, it is believed that an update of the literature on heterogeneous catalysis could be beneficial. This review not only covers the new developments of heterogeneous catalysis in environmental sciences but also touches its historical aspects. A short introduction to the mechanism of heterogeneous catalysis with a small section on advances in this field has also been elaborated. In the first part, recent innovations in the field of catalytic air, water, wastewater and soil treatment are presented, whereas in the second part, innovations in the use of heterogeneous catalysis for obtaining sustainable energy and chemicals are discussed. Catalytic processes are ubiquitous in all branches of chemistry and there are still many unsolved issues concerning them.

Abstract

Recently electrospinning has gained significant attention due to unique possibilities to produce novel natural nanofibers and fabrics with controllable pore structure. The present study focuses on the fabrication of electrospun fibres based on gum karaya (GK), a natural tree gum, with polyvinyl alcohol (PVA), and functionalization of the membrane with TiO2 nanoparticles with further methane plasma treatment. The GK/PVA/TiO2 membrane was analyzed with several techniques including: fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), and water contact angle, in order to characterize its morphological and physicochemical properties. The GK/PVA/TiO2 membrane was further successfully used for the degradation (under UV irradiation) of bisphenol A and diclofenac from aqueous solution. It was also observed that the degradation kinetics of these compounds are faster in comparison to the UV treatment alone.