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Technetium-99 (99Tc), as one of the important high-yield fission products, is a significant threat to the environment and human health. It is produced in large amounts by nuclear fission of 235U or 239Pu in nuclear reactions, though the quantity of Tc produced by the spontaneous fission of 238U or by decay of 99Mo in the nature which is very small. 99Tc in the environment originates from nuclear weapons tests, discharges from nuclear power plants, nuclear medicine and radiobiology. These activities generate large volumes of low and intermediate radioactive waste which can cause a significant impact on the environment if disposed without suitable treatment. Immobilization of 99Tc into a relatively small volume waste is vital for long term permanent disposal. High mobility and long half-life of 99Tc considered to be one of the most important radionuclides in safety assessment of environmental radioactivity as well as nuclear waste management. Effective removal of radioactive technetium (99Tc) from contaminated water is of enormous importance from an environmental and public health perspective, yet many current methodologies are highly ineffective. This paper summarizes physico-chemical separation procedures emphasizing those that are the most used in practice. Classic sorbents such as activated carbons, ion exchange resins as well, as new materials, such as metal−organic frameworks and graphene based membranes are described in the paper.

Pollution of the environment is a serious issue nowadays, and finding a proper wastewater treatment is only small part of challenges that humans are facing. In order to find innovative ways for wastewater treatment, different techniques are applied, which lead to the production of new materials, such as ones made of polymeric nanofibers and materials with photocatalytic properties. In this study, nanofibers composite, synthetized from polyamide (PA) and UiO-66 Metal Organic Framework (MOF) by electrospinning method was used for degradation of Congo red dye from 10 ppm aqueous solution in batch conditions. Ultra-thin PA nanofiber membranes were produced with different ratios of MOF - 0.5 wt.%, 1 wt.%, 2 wt.% and 10 wt.% and prior the experiments, in order to be easily applied and removed from the solution, cut in the rectangular shape 1cm x 2 cm. FTIR, XRD and SEM are used for characterization of selected composites, prior and after sorption and photocatalytic experiments, while for determination of dye concentration UV-ViS spectrophotometer was used. The best performance in Congo red degradation was shown by membranes which contained 1 wt.% of MOF. FTIR spectra have shown that, upon the introduction of MOF particles into the PA fiber, reduction of all the peaks by the same amount in intensity indicates no interaction between MOF additive and PA matrix. Further, a new peak appeared after sorption at 590 cm-1 and disappeared after dye degradation induced by sun irradiation. XRD analysis has shown that there are no observable microstructural changes in composites upon sorption and cycling. Decreasing of the band gap of composite compared to pure MOF indicated increased photocatalytic activity. Reusability of composite membranes was investigated by performing experiments in multiple cycles, and results have shown that electrospun UiO-66/polyamide membranes have no significant changes in degradation efficiency of Congo red upon 4 cycles.

Worldwide water bodies have been affected by toxic effluents of industries, such as organic compounds, and are continuously deteriorating the environment as industrialization coupled with urbanization has caused the excess release of wastewater. Finding a proper wastewater treatment is of the greatest importance. Gamma irradiation technique, as one of the advanced oxidation techniques, has been widely investigated as a technique for degradation of organic molecules. It has been shown that this method has the potential to be effectively applied for degradation of toxic colorants which show high persistence to degradation. Although the literature abounds with degradation studies of different organic molecules using a wide range of irradiation dozes and doze rates, according to available data, no such irradiation facility exists, mostly due to high doses and expensive equipment needed to be installed. A mechanism of degradation was proposed: generated reactive species non-specifically react with organic compounds leading to their partial or complete degradation. In recent advances, gamma irradiation was coupled with other wastewater treatment technologies to reduce needed doses. Coupling of gamma irradiation was achieved with addition of oxidants which resulted in increased number of reactive species, then coupling with solid matrices, biological treatment, which all lead to additional destabilization of organic molecules. This way, combining different methods of wastewater purification opens new possibilities and may enable the design of a new modular, or even mobile, plant that will satisfy all the needs for its wide commercial application. As a result, a sustainable development goal can be more easily reachable, i.e., sustainable water resources management in future industrial zones and smart cities may be possible without generation of waste transfer into another media.

Rapid industrialization and increasing population have increased the water demand. Various wastes from industries and anthropogenic activities are discharged into aquatic bodies such as lakes, ponds, rivers, oceans. Therefore, focus is placed on the removal of the contamination from the wastewater. Organic pollutants gained extensive attention because of their toxicity, persistence and significant impacts on human health Among them, organic dyes are complex molecules and most of them are water-soluble, resistant to detergents and heat, exhibit poor biodegradability, etc. Azo dyes are used in about 70% of commercial dyes today, from textile and plastic to cosmetics and food. In this work, removal of azo-type dye Congo Red (CR) from water was performed by using UiO-66 type MOF (Metal Organic Framework), activated carbon (AC) and their composite powder mixture (MOF/AC = 50/50 wt.%). Samples were exposed to solar light irradiation for 1h and 2.5 h, respectively, centrifuged to remove solid particles, and solutions were analyzed by UV-ViS spectrophotometer in order to determine the concentration of the remaining dye. Process was repeated three times in order to explore the renewability of the photocatalysts used, with catalysts dried at 50 °C between cycles. Results revieled superior photocatalytic cycling performance of the MOF compared to the MOF/AC composite, while AC showed decline in dye removal performance due to the saturation of available adsorption sites. MOF/AC composite exhibited beneficial cost/performance ratio.

Metal-organic frameworks (MOFs), an exciting class of porous crystalline materials, are suitable for adsorptive removal of toxic heavy metal-ethylenediaminetetraacetic acid (M-EDTA) complexes from wastewater. In this paper, water-stable UiO-66(Zr) with well-defined morphology was successfully synthesized through a facile microwave-assisted solvothermal method and employed as nanotraps for the efficient capture of the three M-EDTA complexes, Cu-EDTA, Pb-EDTA, and Ni-EDTA. The adsorption behaviors, effects of solution pH and co-existing anions, as well as the eluant and desorption were investigated. The obtained UiO-66(Zr) showed good stability and excellent uptake capacity of M-EDTA in a wide pH range (3.0-10.0). UiO-66(Zr) exhibited a higher removal efficiency of Cu-EDTA (57.56 mg/g), Pb-EDTA (120.6 mg/g), and Ni-EDTA (54.27 mg/g). Based on the overall analysis results, our findings show that EDTA-metal complex ions can be adsorbed inside UiO-66(Zr) mainly through the Lewis-acid/-base interactions and possible anion-πinteraction with strong binding energies. Size-matching EDTA-metal complexes confined in the UiO-66(Zr) with flexible geometry would also contribute to the fast adsorption kinetics as well as the selective adsorption of different M-EDTA complexes. © 2020 Elsevier Ltd.

Development of method for the complete conversion of Cr-containing electroplating sludge (ES) into the black inorganic pigment was presented. Difficulties related to the ES complex, variable composition and inhomogeneity, where the dominant presence of Cr was followed by: Fe, P, Zn, Ni, Cu, etc., can be overcome by determination of the precise amount of Fe2O3 necessary to be added in order to firmly embed all the heavy metals into the pigment structure (i.e. the Fe0.7Cr1.3O3/FePO4 nanocomposite), taking care not only about weight/molar ratios, but also about average particle size, apparent densities, and volume fraction of the starting materials. As a source of Fe2O3, commercial (p.a.) Fe2O3 and two different Fe-wastes were used, thus completely fulfilling the principles of the circular economy. The obtained black inorganic pigments have consistent composition, no leaching of toxic metals, color (CIE L-a-b-values) comparable with those of commercial pigments and thus have the potential commercial large scale application. © 2021 Elsevier Ltd.

Most heavy metals, such as Cr (chromium), Pb (lead), Cd (cadmium), Ni (nickel), Cu (copper) and Fe (iron), are extremely toxic above a tolerance limit. These heavy metals in wastewater are not biodegradable and can cause serious harm to human health and ecological environments.1 One of the top-priority toxic heavy metal in wastewater is chromium.2 In natural waters, chromium exists in both trivalent Cr(III) and hexavalent Cr(VI) forms. Cr(VI) is the most toxic one and have the tolerance limit 0.1 mg/L into surface water and 0.05 mg/L in potable water.3 Various methods, such as ion exchange, sedimentation, electrochemical process, cementation, coagulation, adsorption and solvent extraction have been developed for the removal of Cr(VI) and other toxic metals from wastewater.4 Among these methods, in some papers,5-8 adsorption has been used as one of the most effective method for the removal of Cr(VI) from aqueous solutions. Characteristics of adsorption, such as low cost, easy to perform, efficient and reversible method with high operating speed, make this method as most commonly used for the removal of Cr(VI) from aqueous solutions.9 Several adsorbents, like activated alumina,10 zeolites,11 natural bisorbents such as chitosan,12 but also activated carbon13 have been used for the removal of Cr(VI) from aqueous solutions. Due to the high cost, commercial activated carbon is not available in less developed countries and there is a considerable attention to produce activated carbon from less expensive and available materials. As a low-cost adsorbent, activated carbon can be produced from materials such as rice husk, seeds husk, tea leaves, sawdust, oil palm shell, coconut husk and coconut shell.14 Activated carbon is one of the most important adsorbents which is applied in different areas. In these areas it is important to determine and remove low concentrations of some pollutants, such as heavy metals. Very good features of this adsorbent are the main reason why it is u, Praškast ugljenični materijal proizveden iz kokosove ljuske korišćen je kao adsorbent za uklanjanje Cr(VI) jona iz vodenih rastvora. Karakterizacija adsorbenta rađena je primenom dve analitičke tehnike, skenirajućom elektronskom mikroskopijom (SEM) i BET metodom. Eksperimenti adsorpcije rađeni su u šaržnom režimu, kako bi se istražili uticaji pH rastvora, vremena kontakta i početne koncentracije Cr(VI) jona. Eksperimentalni rezultati su pokazali da je efikasnost uklanjanja Cr(VI) najveća u pH intervalu od 2,0 do 3,5, a da se ravnoteža uspostavlja nakon 60 minuta. Dva ravnotežna adsorpciona modela, Langmirov i Frojndlihov, korišćena su za fitovanje dobijenih podataka. Frojndlihova izoterma je obezbedila najbolju korelaciju za adsorpciju Cr(VI) jona na ugljeničnom materijalu proizvedenom iz kokosove ljuske. Na osnovu dobijenih rezultata može se zaključiti da ugljenični materijal proizveden iz kokosove ljuske predstavlja jeftin i efikasan adsorbent koji bi potencijalno mogao biti korišćen za tretman otpadnih voda koje sadrže toksični Cr(VI).

Chitosan and its modified forms have received great attention as potential adsorbents due to its outstanding adsorption characteristics toward removal of vaious toxic heavy metal ions from aqueous solutions. In this work, a porous chitosan hydrogel beads (CHB) and CHB cross-linked with glutaraldehyde (GLA) and citric acid (CA) were synthesized and used for investigation of its adsorption performances toward the removal of Pb(II), Cu(II), Zn(II), Cd(II) and Cr(VI) ions from water in batch and dynamic systems. Maximum removal was achieved in the pH ranges of 4.0 - 6.5 and 2.0 - 3.5 for divalent cations and Cr(VI) oxyanion, respectively. The equilibrium adsorption data were best fitted by the Langmuir isotherm model. Based on the optimal conditions, the fixed-bed breakthrough curves for the removal of the studied metal ions from the aqueous solutions using fixedbed columns were experimentally evaluated, as well as theoretically predicted using COMSOL Multiphysics software.

An analytical method based on solid-phase extraction (SPE) using coconut shell activated carbon (CSAC) as a low-cost adsorbent and high performance liquid chromatography with diode array detector (HPLC-DAD) was developed and validated for the determination of four varying polarity pesticides in water samples. SPE procedure was optimized and under the optimized conditions the proposed method was validated. The method exhibited good linearity, satisfactory precision (1.4 – 5.1%), high enrichment factor, good recovery and low limits of detection (0.025 – 0.039 g/dm3 ). Optimized method was used to determine selected pesticides in tap water samples. The recoveries ranged from 58.2% to 105.3%, with low relative standard deviations. The obtained results indicated that the proposed SPE-HPLC-DAD method could be efficiently used for the determination of the selected pesticides in environmental water samples at trace levels.

The recycling of heavy metals from solid wastes and transforming these metals into useful materials, such as metal oxides, nanocomposites, and metal–organic frameworks (MOFs), are beneficial for both sustainable development and environmental protection. MOFs are promising for adsorptive desulfurization, owing to their extremely high surface areas and tunable structures. In this paper, for the first time, MIL-53(Cr) was successfully fabricated from electroplating sludge (EPS) as a metal source through a facile hydrothermal method with and without HF. Our synthetic method is novel, green, scalable, and time-efficient. The obtained MIL-53(Cr) was employed as an adsorbent for adsorptive dibenzothiophene removal from liquid fuel. MIL-53(Cr) with HF exhibits a higher desulfurization capacity (40.11 mg g–1) than that of MIL-53(Cr) without HF (32.80 mg g–1). The improved adsorption performance of MIL-53(Cr) with HF is attributed to adding a small amount of HF, which produces highly crystalline and relativity pure MIL-53(Cr) microrods with a high surface area and porosity, and is due to a robust metal–sulfur interaction. Furthermore, the regenerated adsorbent can retain 94% of its initial sulfur adsorption capability even after 5 cycles, implying that MIL-53(Cr) prepared from Cr-EPS is an efficient adsorbent for fuel desulfurization. This study provides new insight for the production of high-value-added MOF materials from solid wastes following the principle of “resource reuse”.

Modified activated carbon cloth is prepared by mechanochemical modification of viscose rayon carbon cloth. The effects of different milling atmospheres, in the air and inert conditions, were investigated. Changes in kind and number of acidic and basic surface groups on the surface of activated carbon cloth, upon modification, as well as before and after the sorption of arsenic were determined. Higher number of basic groups responsible for the removal of arsenic ions was achieved by modification under inert conditions. Breakage and collapse of cylindrical fibers, decrease of particle sizes, change in the shape and consistency of the particles, as well as increase of microstructural disorder i.e. the loss of turbostratic structure occurred upon milling. pHPZC values increased from 4.46 to 5.04 and 5.77 after the air and inert milling, respectively. Adsorption followed pseudo second order kinetics with chemisorption as rate-controlling step. Langmuir isotherm best fit the equilibrium data and maximum adsorption capacity is 5.5 mg g−1 at a pH value close to 7.0, typical for groundwater. The mechanism of arsenic adsorption onto activated carbon cloth milled in inert atmosphere involved electrostatic and dispersive interactions between arsenic ions and carbon particles in wide pH range (from 2 to 10).