Nonthermal plasma-irradiated polyvalent ferromanganese binary hydro(oxide) for the removal of uranyl ions from wastewater

Tetracycline (TC) removal from wastewater with activated carbon (AC) obtained from waste grape marc: activated carbon characterization and adsorption mechanism

In this study, activated carbons were obtained from grape marc for tetracycline removal from wastewater. Activated carbons were obtained by subjecting them to pyrolysis at 300, 500, and 700 °C, respectively, and the effect of pyrolysis temperature on activated carbons was investigated. The physicochemical and surface properties of the activated carbons were evaluated by SEM, FTIR, XRD, elemental analysis, N2 adsorption/desorption isothermal, thermal gravimetric (TG) and derivative thermogravimetric (DTG), and BET surface area analysis. When the BET surface areas were examined, it was found that 4.25 m2/g for activated carbon was produced at 300 °C, 44.23 m2/g for activated carbon obtained at 500 °C and 44.23 m2/g at 700 °C, which showed that the BET surface areas increased with increasing pyrolysis temperatures. The pore volumes of the synthesized activated carbons were 0.0037 cm3/g, 0.023 cm3/g, and 0.305 cm3/g for pyrolysis temperatures of 300, 500, and 700 °C, respectively, while the average pore size was found to be 8.02 nm, 9.45 nm, and 10.29 nm, respectively. A better adsorption capacity was observed due to the decrease in oxygen-rich functional groups with increasing pyrolysis temperature. It was observed that the activated carbon obtained from grape skins can easily treat hazardous wastewater containing tetracycline due to its high carbon content and surface functional groups. It was also shown that the activated carbon synthesized in this study has a higher pore volume despite its low surface area compared to the studies in the literature. Thanks to the high pore volume and surface active groups, a successful tetracycline removal was achieved.

Structural simulation and performance evaluation of a novel synthesized ZIF in the adsorption of MO from aqueous solutions

Zeolitic imidazolate frameworks (ZIFs) are desirable materials widely applied as adsorbent for wastewater treatment. This study synthesizes and applies a novel structured ZIF with organic ligand of 2-methyl imidazole and metal salt of copper (II) sulfate as adsorbent. Its morphology and structure were investigated using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscope, field emission scanning electron microscope, energy dispersive X-ray spectrometry, and mapping analysis. After structural analysis, the adsorbent structure was simulated and determined using Avogadro and Gaussian software. The removal efficiency of prepared ZIF in the removal of methyl orange from aqueous solution was evaluated. The effect of pH, the concentration of the dye in solution, dosage of the adsorbent, and the contact time between adsorbent and solution on the methyl orange removal were examined using central composite design of response surface methodology in five levels. The maximum dye removal of 99% was obtained for 2 g adsorbent/L, pH of 3.3, and initial dye concentration of 121 mg/L after 127 min contact time. In addition, to reduce the economic costs and energy consumption, the synthesis time was also reduced and used to show the applicability of the adsorbent prepared and understand its advantages and disadvantages in removing methyl orange dye from aqueous solutions. This molecular adsorbent is stable, and it can be stored for months. On the other hand, this ZIF can be easily recovered and reused many times. In this research, after five times of recovery, there was no significant change in the effectiveness of the adsorbent.

Cold plasma turns mixed-dye-contaminated wastewater bio-safe

The excessive and uncontrollable discharge of diverse organic pollutants into the environment has emerged as a significant concern, presenting a substantial risk to human health. Among the advanced oxidation processes used for the purification of wastewater, cold plasma technology is superior in fast and effective decontamination but often fails facing mixed pollutants. To address these issues, here we develop the new conceptual approach, plasma process, and proprietary reactor that ensure, for the first time, that the efficiency of treatment (114.7%) of two mixed organic dyes, methylene blue (MB) and methyl orange (MO), is higher than when the two dyes are treated separately. We further reveal the underlying mechanisms for the energy-efficient complete degradation of the mixed dyes. The contribution of plasma-induced ROS and the distinct degradation characteristics and mechanism of pollutants in mixed treatment are discussed. The electron transfer pathway revealed for the first time suggest that the mixed pollutants reduce the overall redox potentials and facilitate electron transfer during the plasma treatment, promoting synergistic degradation effects. The integrated frameworks including both direct and indirect mechanisms provide new insights into the high-efficiency mixed-contaminant treatment. The degradation products for mixed degradation are revealed based on the identification of intermediate species. The plasma-treated water is proven safe for living creatures in waterways and sustainable fishery applications, using in vivo zebrafish model bio-toxicity assay. Overall, these findings offer a feasible approach and new insights into the mechanisms for the development of highly-effective, energy-efficient technologies for wastewater treatment and reuse in agriculture, industry, and potentially in urban water networks.

Self-cementation of gold tailings activated by nonthermal plasma irradiated calcium (hydro)oxide

The alkalinity of CaO is commonly insufficient in alkali-activating raw soils or minerals for the formation of cementation or geopolymerization. In this study, nonthermal plasma (NTP) irradiation was employed to activate traditional CaO to enhance its efficacy in alkali activation and further intensify the self-cementation of gold tailings. The solidification/stabilization (S/S) of the gold tailings-based matrix activated by NTP-CaO was better than that of CaO. The NTP irradiation enhanced the surface hydroxyl groups and oxygen atoms, decreased the binding energy, formed nanoparticles, and significantly changed the morphologies of the calcium activator. The dosage of the NTP-irradiated CaO (NTP-CaO) directly affected the self-cemented solidification/stabilization of gold tailings. The Johnson-Mehl-Avrami-Kolmogorov model was appropriate for analysing the NTP-CaO-activated geopolymerization kinetics of gold tailings. Three-dimensional (3D) structural minerals covered with small pores were determined in the NTP-CaO-activated cemented samples. The employment of NTP-CaO facilitated the formation of aluminosilicate geopolymers during the self-cementation of gold tailings according to comprehensive characterization strategies. The study achieves the efficient self-remediation of gold tailings by activating calcium precursors, which further solves the contradiction between salinization and alkali activation in the field of noncalcined cementitious materials.

B-site metal modulation of phosphate adsorption properties and mechanism of LaBO3 (B = Fe, Al and Mn) perovskites

La-based adsorbents are widely used for controlling phosphate concentration in water bodies. In order to explore the effect of different B-site metals regulating La-based perovskites on phosphate adsorption, three La-based perovskites (LaBO₃, B = Fe, Al, and Mn) were prepared using the citric acid sol-gel method. Adsorption experiments showed that LaFeO₃ exhibited the highest adsorption capacity for phosphate, which was 2.7 and 5 times higher than those of LaAlO₃ and LaMnO₃, respectively. The characterization results demonstrated that LaFeO₃ has dispersed particles exhibiting larger pore size and more pores than LaAlO₃ and LaMnO₃. Spectroscopy analysis and density functional theory calculation results showed that different B-positions cause a change in the type of perovskite crystals. Among them, the differences between lattice oxygen consumption ratio, zeta potential and adsorption energy are the main reasons for the differences in adsorption capacity. In addition, the adsorption of phosphate by La-based perovskites were well fitted with Langmuir isotherm and pursues the pseudo-second-order kinetic models. The maximum adsorption capacities were 33.51, 12.31 and 6.61 mg/g for LaFeO₃, LaAlO₃ and LaMnO₃, respectively. The adsorption mechanism was mainly based on inner-sphere complexation and electrostatic attraction. This study provides an explanation for the influence of different B sites on phosphate adsorption by perovskite.

Synthesis and application of quantum dots in detection of environmental contaminants in food: A comprehensive review

Environmental pollutants can accumulate in the human body through the food chain, which may seriously impact human health. Therefore, it is of vital importance to develop quick, simple, accurate and sensitive (respond quickly) technologies to evaluate the concentration of environmental pollutants in food. Quantum dots (QDs)-based fluorescence detection methods have great potential to overcome the shortcomings of traditional detection methods, such as long detection time, cumbersome detection procedures, and low sensitivity. This paper reviews the types and synthesis methods of QDs with a focus on green synthesis and the research progress on rapid detection of environmental pollutants (e.g., heavy metals, pesticides, and antibiotics) in food. Metal-based QDs, carbon-based QDs, and "top-down" and "bottom-up" synthesis methods are discussed in detail. In addition, research progress of QDs in detecting different environmental pollutants in food is discussed, especially, the practical application of these methods is analyzed. Finally, current challenges and future research directions of QDs-based detection technologies are critically discussed. Hydrothermal synthesis of carbon-based QDs with low toxicity from natural materials has a promising future. Research is needed on green synthesis of QDs, direct detection without pre-processing, and simultaneous detection of multiple contaminants. Finally, how to keep the mobile sensor stable, sensitive and easy to store is a hot topic in the future.