Simultaneous adsorption of heavy metals from aqueous matrices by nanocomposites: A first systematic review of the evidence

Background: Nanocomposites have received remarkable attention as effective adsorbents for removal of coexisting pollutants over the last decades. The presence of heavy metals (HMs) in wastewater has caused a global health concern. Therefore, the aim of this study was to review the most relevant publications reporting the use of nanostructures to simultaneous adsorption of HMs in mixed aqueous systems. Methods: In this systematic review, 9 studies were included through a systematic search in the three databases (ISI, Scopus, and PubMed) during 1990-2021. The optimal value of simultaneous adsorption parameters such as initial concentration, contact time, adsorbent dosage, and pH was discussed. Results: Findings indicate that the Langmuir and Freundlich models and the pseudo-second-order kinetic model have been widely used and the most popular models to describe the equilibrium of HMs by nanoadsorbents. This study confirmed that the simultaneous removal rate of HMs decreased with an increase in pH value. It was found that the major mechanisms of HMs adsorption onto nanostructures were electrostatic interactions and precipitation. Conclusion: Nanocomposites have remarkable adsorption performance for HMs with the highest adsorption capacity (qe(mg/g)). Keywords: Adsorption, Wastewater, Heavy metals, Nanocomposites, Kinetic

Study of ZnO nano particles photocatalytic process efficiency in decolorization of methylene blue and COD removal from synthetic wastewater

Background : Effluents containing synthetic dyes are hazardous to ecological systems and public health. Methylene blue is an important chemical aromatic dye which commonly used in textile industries. Due to being aromatic, it is often toxic, carcinogenic and mutagenic. The goal of this study was to investigate the efficiency of ZnO nano particles photocatalytic process for decolorization of methylene blue by UV irradiation from synthetic textile wastewater. Materials and Methods: In this study methylene blue photocatalytic decomposition using Ultraviolet (UV) irradiation and zinc oxide nano particles having less than 50 nm in diameter was surveyed. A batch-through Plexiglass reactor having two compartment used to conduct the experiments. Wastewater was flowed to the compartment which contains of nano ZnO stabilized glasses. UV lamps were installed at another compartment. The variables of the study included: exposure time, color concentration, light intensity, and lamp distance to the catalyst surface. Results: ZnO nano particles characteristics were determined by Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) analysis. Images showed that stabilizes nano particles on glass, their porosity remains in the optimal level. Optimium values for exposure time 120 minutes, color concentration 25 mg/l, light intensity 3950 μW/cm2, and distance to the catalyst surface 1 cm were achieved. At the optimal condition, methylene blue decolorization and COD removal was achieved 92.2% and 75% respectively Conclusion: Regarding the conducted experiments, the results of this studyshowed that ZnO/UV photocatalytic process has a significant efficiency in dye decolorization and COD removal. This method could be applied in the full scales

Hexavalent Chromium Adsorption onto Fire Clay

Cr (VI) as an extremely soluble and highly toxic ion is present in effluents of industries and imposes severe health-related problems. The current study aimed to provide information on Cr (VI) adsorption potential of fire clay as an abundant, cost-effective and untried material. Batch adsorption trials of Cr (VI) were performed to investigate the effects of pH, contact time, initial metal ion concentration and the adsorbent dosage. Langmuir, Freundlich and Dubinin–Radushkevich isotherm models were used to evaluate the equilibrium data at 20°C and regression coefficients were derived. Moreover, adsorption kinetics was analyzed using the pseudo-first-order and the pseudo-second-order kinetic models. Maximum chromium removal was found at pH 2.0. A kinetic study yielded an optimum equilibrium time of 90 minutes with an adsorbent dose of 2.5 g/50 mL. Results suggested that the equilibrium adsorption described by the Freundlich model. The kinetic data of the sorption showed that the pseudo second-order equation was the more appropriate. The results of the study indicated that fire clay was not a suitable adsorbent for Cr (IV). Apart from relatively long equilibrium time, the efficiency was not satisfactory. Therefore, searching for better alternative and/or modify such adsorbent is necessary in this area

A comparison of Photocatalytic silica-zinc oxide and zinc Oxide processes for the removal of dye and COD in the synthetic wastewater

Background : One of the major disadvantages of zinc oxide in aqueous solution is the light unstability of this catalyst due to the light corrosion which causes substantial reduction of photocatalytic activity of zinc oxide and application of it for environment purification. In this study, the performance of photocatalytic of UV/Silica-ZnO was compared in dye and COD removal by UV/ZnO. Materials and Methods: This study was conducted in the lab scale. The various percentages of silica nanoparticles in the combination of zinc oxides nanoparticles were fixed onto the glass by UV/Silica-ZnO process and were examined at optimum condition in the UV/ZnO process. XRD patterns of zinc oxide nanoparticles alone and accomplished by silica were conducted. Results: X-ray diffraction, confirm that there is no impurity in nanoparticles. The different percentages of silica (5, 10 and 15%) were tested in combination with zinc oxide nanoparticles. The findings showed that the value of dye and COD removal with contact time of 90 min and 10% silica loading in UV/Silica-ZnO process were 100 % and 81%, respectively and UV/ZnO process were 66% and 44% respectively. Conclusion: According to the obtained results, 10% of silica, in combination with zinc oxide nanoparticles, was the best percentage. Thus, UV/Silica-ZnO process can be used as an effective method for removing dye from textile waste waters

Adsorption of diclofenac on mesoporous activated carbons: physical and chemical activation, modeling with genetic programming and molecular dynamic simulation

This work aims at the preparation of AC from chemical activation (H3PO4, KOH, and HCl)and physical activation (thermal treatment under N2atmosphere at 500 and 700◦C) of Astra-galus Mongholicus (AM) (a low-cost bio-adsorbent and agro-industrial waste), used as carbonprecursor. The obtained materials were further applied in the adsorption of diclofenac(DCF) from water/wastewater. The physicochemical properties of the as-prepared ACs andcommercial activated carbons (CAC) were evaluated by SEM, XRD, FT-IR, and BET analyses,revealing the high surface area and mesoporous proportion of AC when compared to CAC. Adsorption results showed that the efficiency of AC-700◦C (774 m2g−1) for DCF removal(92.29%) was greater than that of AC-500◦C (648 m2g−1, 83.5%), AC-H3PO4(596 m2g−1, 80.8%),AC-KOH (450 m2g−1, 59.3%), AC-HCl (156 m2g−1, 29.8%) and CAC (455 m2g−1, 67.8%). The opti-mization of effective parameters in adsorption was examined at a laboratory-scale using theselected AC-700◦C. The Langmuir isotherm and the pseudo-second-order model fitted wellthe experimental data. The regeneration efficiency was maintained at 96% (DI-water) and97% (heating) after three cycles. Besides, genetic programming (GP) and molecular dynam-ics (MD) simulations were applied to predict the adsorption behavior of DCF from aqueousphase as well as in the ACs structure. It was found that the adsorption mechanisms involvedwere electrostatic interaction, cation–pi interaction, and pi–pi electron interaction.This research project was submitted to Ilam University of Medical Sciences, Ilam, Iran (Grant No.: 99R001/25). The authorswould like to thank Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.info:eu-repo/semantics/publishedVersio

Enhanced photocatalytic performance of milkvetch-derived biochar via ZnO–Ce nanoparticle decoration for reactive blue 19 dye removal

Abstract In this research, the photocatalytic removal of reactive blue 19 (RB19) dye is investigated employing zinc oxide/cerium (ZnO@Ce) nanoparticles decorated with biochar under LED irradiation. Synthesis of ZnO@Ce nanoparticles decorated with biochar was performed utilizing the co-precipitation procedure and, then, the texture and morphology of the fabricated nanocomposite were analyzed using energy dispersive X-ray (EDX), field emission scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), and Fourier transform infrared (FTIR) spectroscopy techniques. Moreover, FE-SEM images demonstrate that ZnO–Ce nanoparticles were successfully decorated on the surface of biochar. The specific surface areas of biochar and biochar/ZnO–Ce were 519.75 and 636.52 m2/g, respectively. To achieve the maximum yield in the removal of RB19 dye, the effects of operating variables including dye concentration, LED lamp power, biochar@ZnO–Ce catalyst dose, pH and H2O2 dose were explored. Besides, the maximum percentage of RB19 dye removal was 96.47% under optimal conditions, i.e. catalyst dosage of 100 mg, H2O2 dosage of 1 mL, pH of 9, initial dye concentration of 5 ppm, LED power of 50 W, and reaction time of 140 min. Furthermore, the kinetic analysis reveals that the removal of RB19 dye follows the pseudo-first order kinetic model, with calculated values of a reaction rate constant of 0.045 min−1 and a correlation coefficient of R2 = 0.99, respectively. Moreover, the reusability and recyclability of biochar@ZnO/Ce nanocatalyst was promising over five runs, with only a 6.08% decrease in RB19 dye removal efficiency. Therefore, it can be concluded that the biochar @ZnO/Ce photocatalyst can be promisingly applied for the removal of azo dyes in aqueous solutions

Detection of different variants of SARS-CoV-2 RNA (genome) on inanimate surfaces in high-touch public environmental surfaces

Abstract Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) disease started in late 2019 and still continues as a global pandemic, spreading among people around the world. There is limited knowledge about the role of contaminated environmental surfaces, especially high-touch public surfaces, in the transmission of the disease. The objective of the present investigation was detection of different variants (Delta, UK, and Omicron) of SARS-CoV-2 RNA (genome) on inanimate surfaces in high-touch public environmental surfaces in different seasons. Automated teller machines of banks (ATM), point-of-sale (POS) machine, gas station pump nozzles, and escalator handrails of malls were selected as high-touch environmental surfaces in public places. Overall, 75 samples were collected from these places and examined for the presence of SARS-CoV-2 RNA (genome), and 21 samples (28%) were positive. Although the role of fomite transmission of COVID-19 is understood, more studies should be conducted to determine the virus survival rate as well as the required efforts to prevent the spread of SARS-CoV-2 such as frequent cleaning and the use of efficient disinfectants on environmental surfaces, especially high-touch public places. In conclusion, the results address the importance of touching contaminated inanimate objects as well as transmission through environmental surfaces, and they could be used to establish an effective protocol to prevent indirect environmental transmission of SARS-CoV-2, slow down the spread of the virus, and reduce the risk of infection

LED-light-driven over ZnO/biochar nanocomposite for activation of peroxymonosulfate to enhanced photocatalytic removal of Methyl orange dye in aqueous solutions

Organic dyes are stable and persistent toxic compounds in the aquatic environment that are refractory to decompose by different removal methods such as physico-chemical, optical and biological. Their presence in the aquatic media threatens human and wildlife. Therefore, herein, ZnO nanoparticles (NPs) due to good chemical durability, abundant availability, easy preparation, low cost and good photocatalytic performance was anchored on biochar (ZnO@biochar) nanocomposites were synthesized towards activation of peroxymonosulfate (PMS) for the photocatalytic removal of methyl orange (MO) dye. Several methods were used to characterization of the nanocomposites including FESEM, XRD, PL, EDS, FT-IR spectroscopy, and N2 adsorption/desorption. The results of the characterization techniques demonstrated that the well-dispersed ZnO NPs were loaded onto the biochar surface. According to the particle size distribution graph, the average particle size of 64 nm was obtained for the ZnO NPs. BET analyzes showed that pore volume, the specific surface area (SSA) and average pore size of the synthesized nanocomposite increased. The survey of effective operational parameters indicated that the highest photocatalytic activity for MO removal was in the pH 3 of solution, 5 ppm initial dye concentration, 30 mg ZnO/biochar nanocomposite, and 20 mg PMS dose under LED-50W lamp irradiation (97.03% in the reaction time of 80 min). During the process, the reduction of the total organic carbon (TOC) contents and chemical oxygen demand (COD) were observed. Moreover, the MO degradation kinetics under optimal operating conditions were determined. It is concluded that the ZnO@biochar nanocomposite/PMS process was an efficient degradation method for the decomposition of the dye pollutant.</p