Fabrication of Tungsten Oxide Nanowalls through HFCVD for Improved Electrochemical Detection of Methylamine.

In this study, well-defined tungsten oxide (WO3) nanowall (NW) thin films were synthesized via a controlled hot filament chemical vapor deposition (HFCVD) technique and applied for electrochemical detection of methylamine toxic substances. Herein, for the thin-film growth by HFCVD, the temperature of tungsten (W) wire was held constant at ~1450 °C and gasification was performed by heating of W wire using varied substrate temperatures ranging from 350 °C to 450 °C. At an optimized growth temperature of 400 °C, well-defined and extremely dense WO3 nanowall-like structures were developed on a Si substrate. Structural, crystallographic, and compositional characterizations confirmed that the deposited WO3 thin films possessed monoclinic crystal structures of high crystal quality. For electrochemical sensing applications, WO3 NW thin film was used as an electrode, and cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were measured with a wide concentration range of 20 µM~1 mM of methylamine. The fabricated electrochemical sensor achieved a sensitivity of ~183.65 µA mM-1 cm-2, a limit of detection (LOD) of ~20 µM and a quick response time of 10 s. Thus, the fabricated electrochemical sensor exhibited promising detection of methylamine with considerable stability and reproducibility.

Microplastic contaminants detection in aquatic environment by hydrophobic cerium oxide nanoparticles.

Microplastics (MPs) poses a significant threat to ecosystems and human health, demanding immediate attention. The reported research work offers an effective and low cost method towards the detection of toxic MPs. In this study, hydrophobic cerium oxide nanoparticles (CeO2 NPs) are synthesized and applied as promising electrode material for the detection of two different types of MPs, i.e. polyethylene (PE) and polypropylene (PP). Through electrochemical analyses, such as cyclic voltammetry (CV) and linear sweep voltammetry (LSV), hydrophobic CeO2 NPs modified glassy carbon electrode (GCE) based sensor demonstrated remarkable sensitivity of ∼0.0343 AmLmg-1cm-2 and detection limit of ∼0.226 mgmL-1, with promising correlation coefficient (R2) towards the detection of PE (∼27-32 µm). Furthermore, hydrophobic CeO2 NPs modified GCE exhibited promising stability and reproducibility towards PE (∼27-32 µm), suggesting the promising potential of hydrophobic CeO2 NPs as electrode materials for an electrochemical microplastics detection.

Effects of dissolved oxygen changes in the benthic environment on phosphorus flux at the sediment-water interface in a coastal brackish lake.

In semi-enclosed coastal brackish lakes, changes in dissolved oxygen in the bottom layer due to salinity stratification can affect the flux of phosphorus (P) at the sediment-water interface, resulting in short- and long-term water quality fluctuations in the water column. In this study, the physicochemical properties of the water layers and sediments at five sites in Saemangeum Lake were analyzed in spring and autumn for four years, and phosphorus release experiments from sediments were conducted for 20 days under oxic and anoxic conditions during the same period. Sediment total phosphorus (T-P) decreased in autumn compared to spring due to mineralization of organic bound phosphorus, which was the most dominant P fraction. This may be related to the increase in the ratio of PO4-P to T-P in bottom waters in autumn, when hypoxia was frequently observed. The difference in P fluxes between oxic and anoxic conditions indicated that during autumn, as compared to spring, the release of phosphorus could have a more immediate impact on the water column during the formation of hypoxia/anoxia. The main factors influencing changes in P fluxes from sediments were identified through redundancy analysis. Additionally, based on the results of multiple regression analysis, sediment TOC, sediment non-apatite phosphorus, porewater pH, and porewater PO4-P were determined to be the most significant factors affecting P fluxes from sediments, depending on the season or redox conditions. Recently, the increased influx of seawater into Saemangeum Lake has been shown to contribute to water quality improvements in the water column due to a strong dilution effect. However, the sediment environment has shifted towards a more reduced state, leading to increased P release under anoxic conditions. Therefore, for future water quality management within the lake, it is necessary to consistently address the recurring hypoxia and continuously monitor phosphorus dynamics.

Porous MgNiO2 Chrysanthemum Flower Nanostructure Electrode for Toxic Hg2+ Ion Monitoring in Aquatic Media.

A simple hydrothermal synthesis approach was used to synthesize porous MgNiO2 Chrysanthemum Flowers (CFs) nanostructures and applied as a sensing electrode for quick detection of hazardous mercury (Hg2+ ions). The morphological, structural, and electrochemical properties of MgNiO2 CFs were investigated. The morphological characteristic of MgNiO2 CFs, with a specific surface area of 45.618 m2/g, demonstrated strong electrochemical characteristics, including cations in different oxidation states of Ni3+/Ni2+. Using a three-electrode system for electrochemical detection, the MgNiO2 CFs based electrode revealed a good correlation coefficient (R2) of ~0.9721, a limit of detection (LOD) of ~11.7 µM, a quick response time (10 s), and a sensitivity of 8.22 µA∙µM-1∙cm-2 for Hg2+ ions over a broad linear range of 10-100 µM. Moreover, the selectivity for Hg2+ ions in tap water and drinking water was determined, and a promising stability of 25 days by MgNiO2 CFs electrode was exhibited. The obtained results indicate that the developed MgNiO2 CFs are a promising electrode for detecting hazardous Hg2+ ions in water and have the potential to be commercialized in the future.

Catalytic oxidation of ibuprofen over bulk heterojunction photocatalysts based on conjugated donor-acceptor configured benzoselenadiazole molecule.

The use of photocatalysts for acquiring direct photon energy from sunlight is a promising way to clean the environment, particularly the remediation of contaminants from water. In this work, firstly π-conjugated organic semiconductor configuring benzoselenadiazole, 4-(3,5-bis(trifluoromethyl) phenyl)-7-(5'-hexyl-[2,2'-bithiophen]-5-yl)-benzo [c] (Kümmerer, 2009; Chen et al., 2018; Randeep et al., 201) selenadiazole, abbreviated as (RTh-Se-F), was synthesized. The designed RTh-Se-F with an extended π-conjugation showed good optical properties in the visible region and estimated a low optical band gap of ∼2.02 eV . The molecular orbitals i.e. HOMO (-5.33 eV) and LUMO (-3.31 eV) for RTh-Se-F organic semiconductor were suitably aligned to energy levels of (Madhavan et al., 2010Madhavan et al., 2010)-Phenyl-C71-butyric acid methyl esters (PC71BM) which resulted in the broadening of absorption and covering of entire visible region. RTh-Se-F was integrated with varied weight percentages (wt %) of PC71BM to obtain bulk heterojunction (BHJ) and applied as efficient visible light driven BHJ photocatalyst for an effective oxidation of ibuprofen. RTh-Se-F@PC71BM (1:2, wt %) BHJ photocatalyst showed the superior ibuprofen degradation of ∼93% within 90 min under visible light illumination. The maximum degradation rate by BHJ photocatalyst might be accredited to the broadening of absorption capacity and improved lifetime of photogenerated electron-hole pairs which might be resulted from high absorption properties of RTh-Se-F organic semiconductor.

Experimental application of a zero-point charge based on pH as a simple indicator of microplastic particle aggregation.

Micro/nanoplastics - a useful but threatening material - continuously require fundamental research on its behaviors and properties for aggregation. Zeta potential (ζ) has been using as an indicator to determine the optimal aggregation for particle removal in water treatment processes. In the field work, however, an alternative method for streamlining these tasks and reducing the variability in processing efficiency is necessary. To improve practical utility in the field work, this study aimed at investigating applicability of the zero-point charge (ZPC) of the isoelectric point (IEP; ψpI) as an alternative indicator for aggregation in place of ζ. For the purpose, this study conducted laboratory experiments and model simulations. The experiments measured ψpI of microplastics in a trivalent-electrolyte aqueous solution using various concentrations of polyaluminum chloride (PAC) for reproducing the behavior of microplastics in natural water environments. As a result, ψpI for polyethylene (PE) and polyvinylchloride (PVC) were found to be pH 6.59 and 6.43, respectively. The removal rates (r) depended on the aggregation at the initial pH and optimal PAC concentration. The experimental attachment efficiency (αE), 0.14 to 0.4, showed a good correlation of over 95% with r, 0.04 to 0.84, both based on the pH change and PAC concentration and differing slightly with the type and size of the plastic. The highest αE was achieved with the highest r when ψpI was close to zero in the pH range of 6-8 using the optimized PAC concentration. Based on the experimental results, the model confirmed the applicability of ψpI instead of ζ as an indicator of the aggregation by simulating αE based on ψpI and ionic strength, which are themselves based on the change in pH. Therefore, this study provides some insights into behaviors of microplastics by using the isoelectric point (IEP, ψpI) as an indicator of aggregation of microplastics in place of ζ. The IEP method is limited by initial pH, optimal dosage of coagulant, and type and size of microplastics, but it will increase practical utility in the field.

Modeling behaviors of permeable non-spherical micro-plastic aggregates by aggregation/sedimentation in turbulent freshwater flow.

This study developed and evaluated a behavior model for permeable non-spherical micro-plastic aggregates in a turbulent flow of freshwater based on fractal theory, as conducting experimental and modeling studies. Laboratory-scale experiments evaluated attachment efficiency α to aggregation kinetics in an aquatic environment (pH 6, 20 â„ƒ) of the electrolyte (Al3+). The experimental α was dependent on characteristics of plastics (type, size, and density) and ranged from 0.062 to 0.2772 (averaging 0.1) with a high correlation with the modeled α (R2 > 0.92). Model validation was conducted under two simulation conditions: one drawn from a previously published study of impermeable spherical aggregates and the other based on fractal theory. The simulations verified the limited primary particle size with the lowest retention rate based on the previous study but it was difficult to determine the specific particle size with the lowest retention rate as a limiting factor. The sum of residual errors for aggregation/sedimentation between the two types of structures showed an overestimation of spherical structures. Such overestimation influenced the aggregate number concentration and distribution pattern. Therefore, the model needs to more detailed express the aggregation mechanism of permeable non-spherical aggregate structures in terms of surface growth.

Estimation and evaluation of auto-flocculated algae harvesting efficiency using the population balance in turbulence model in flotation process.

Algae are considered water pollutants because they form algal blooms in stagnant water. Algae harvesting technology, however, can help convert them into a useful industrial material like biomass. The core technique (flocculation) separates microalgae from other flocculants, allowing for the harvest of clean and pure algal biomass. This study aims to estimate and evaluate algal separation (removal or harvesting) efficiency (X) to concurrently obtain the objectives of algal bloom management and algal particle collection. To simulate algal separation by auto-flocculation (no flocculants) related flotation, the population balance in turbulence (PBT) model is used. Model simulations are conducted under optimal conditions provided by previous studies about the biological impact factors of algae, operating parameters of the flotation process, and so on. This modeling study determines the efficiency (X) of separating algae from the water body in the separation zone after forming auto-flocculated bubble-floc agglomerates by making them collide and attach to each other in the contact zone of the flotation tank. The X is examined as a function of size distribution of agglomerates and bubbles and of the number of initially injected bubbles. Optimal conditions for forming and harvesting the agglomerates may be found through further modeling studies.

Enhanced phosphorus removal in the DAF process by flotation scum recycling for advanced treatment of municipal wastewater.

To remove phosphorus (P) from municipal wastewater, various types of advanced treatment processes are being actively applied. However, there is commonly a space limit in municipal wastewater treatment plants (MWTPs). For that reason, the dissolved air flotation (DAF), which is well known for small space and flexible application process, is preferred as an additive process to enhance the removal of P. A series of experiments were conducted to investigate the feasibility of flotation scum recycling for effective P removal from a MWTP using a DAF pilot plant over 1 year. The average increases in the removal efficiencies due to flotation scum recycling were 22.6% for total phosphorus (T-P) and 18.3% for PO4-P. A higher removal efficiency of T-P was induced by recycling the flotation scum because a significant amount of Al components remained in the flotation scum. The increase in T-P removal efficiency, due to the recycling of flotation scum, shifted from the boundary of the stoichiometric precipitate to the equilibrium control region. Flotation scum recycling may contribute to improving the quality of treated water and reducing treatment costs by minimizing the coagulant dosage required.

Flotation of algae for water reuse and biomass production: role of zeta potential and surfactant to separate algal particles.

The effect of chemical coagulation and biological auto-flocculation relative to zeta potential was examined to compare flotation and sedimentation separation processes for algae harvesting. Experiments revealed that microalgae separation is related to auto-flocculation of Anabaena spp. and requires chemical coagulation for the whole period of microalgae cultivation. In addition, microalgae separation characteristics which are associated with surfactants demonstrated optimal microalgae cultivation time and separation efficiency of dissolved CO2 flotation (DCF) as an alternative to dissolved air flotation (DAF). Microalgae were significantly separated in response to anionic surfactant rather than cationic surfactant as a function of bubble size and zeta potential. DAF and DCF both showed slightly efficient flotation; however, application of anionic surfactant was required when using DCF.

Evaluation of initial collision-attachment efficiency between carbon dioxide bubbles and algae particles for separation and harvesting.

Microalgae have been regarded as a pollutant causing algal blooms in lakes or reservoirs but have recently been considered as a useful source of biomass to produce biofuel or feed for livestock. For the algae particle separation process, carbon dioxide (CO2), one of the main greenhouse gases, is dissolved into a body of water rather than being emitted into atmosphere. This study aims at determining the feasibility of CO2 bubbles as an algae particle separation collector in a flotation process and providing useful information for effective algae harvesting by describing optimal operating conditions of dissolved carbon dioxide flotation or dissolved air flotation. The first step is to develop a flotation model for bi-functional activity, algae control and algae harvesting at the same time. A series of model simulations is run to investigate algae particle separation possibilities such as an initial collision-attachment efficiency that depends upon separation characteristics due to an algae life cycle, including: pH, size distribution, zeta potential, cell surface charge, density, electric double layer, alkalinity, and so on. Based on the separation characteristics, conditions required to form flocculation are predicted in order to obtain the optimal flotation efficiency.

Characterization and application of electrospun alumina nanofibers.

Alumina nanofibers were prepared by a technique that combined the sol-gel and electrospinning methods. The solution to be electrospun was prepared by mixing aluminum isopropoxide (AIP) in ethanol, which was then refluxed in the presence of an acid catalyst and polyvinylpyrolidone (PVP) in ethanol. The characterization results showed that alumina nanofibers with diameters in the range of 102 to 378 nm were successfully prepared. On the basis of the results of the XRD and FT-IR, the alumina nanofibers calcined at 1,100°C were identified as comprising the α-alumina phase, and a series of phase transitions such as boehmite → γ-alumina → α-alumina were observed from 500°C to 1,200°C. The pore size of the obtained γ-alumina nanofibers is approximately 8 nm, and it means that they are mesoporous materials. The kinetic study demonstrated that MO adsorption on alumina nanofibers can be seen that the pseudo-second-order kinetic model fits better than the pseudo-first-order kinetic model.

An advanced oxidation process using ionized gas for wastewater treatment.

This study on removing non-degradable materials in wastewater focused primarily on advanced oxidation methods such as ozone, ozone/UV and ozone/H2O2. Wastewater treatment using an ionized gas from plasma has been actively progressing. The ionized gas involves reactive species such as O2+, O2- cluster, O radical and OH radical. Since the ionized gas method has such outstanding characteristics as relatively simple structures, non-calorification, non-toxicity and low electricity consumption, it evidently of interest as a new process. A series of experiments were conducted to demonstrate the feasibility of ionized gas as a useful element for the diminution of nondegradable organic matters. On the other hand, a large amount of organic matters were changed to hydrophilic and the compounds containing aromatic functional group gradually decreased. The results implied that the ionized gas has been able to degrade the non-biodegradable organic matters. Therefore, the oxidation process by using an ionized gas process could be considered as an effective alternative unit in water and wastewater treatment plants.

Adsorption of dichloromethane from water onto a hydrophobic polymer resin XAD-1600.

Dichloromethane is one of the chlorinated volatile organic compounds (CVOCs) that contaminate the waters. Especially, the dichloromethane used as a solvent in polycarbonate synthesis, is dissolved in wastewater with the saturated solubility of 17,220 mg L(-1), which is several times that of other CVOCs. Thus, it is reasonable to recover the dichloromethane dissolved in water instead of destruction based on the economic point of view. To study on the recovery of the dichloromethane, adsorption equilibrium and column dynamics were investigated using a hydrophobic polymer resin (XAD-1600) without the ion-exchange functional groups. In addition, a hydrophilic polymer resin (XAD-7) and an activated carbon (DY-GAC) were chosen for comparison. Conventional two- or three-parameter models such as the Langmuir, Freundlich, or Sis equations could not fit the adsorption equilibrium data of two polymer resins obtained over the entire range of concentration (1-200 mol m(-3)). They were well fitted by a hybrid model consisting of Langmuir and BET (Brunauer-Emmett-Teller) equations. The adsorption amount at high concentration was in the order of XAD-1600>XAD-7>DY-GAC on a mass basis. To confirm the possibility of using resin as a sorbent for the removal of dichloromethane, adsorption breakthrough curves were measured under key operating conditions such as the concentration, the flow rate, and the column length. Moreover, desorption from polymer resins adsorbed with dichloromethane was conducted by using pure water only as a desorbate. A simple dynamic model was also formulated to describe the adsorption breakthrough curves of dichloromethane from XAD-1600, XAD-7 and DY-GAC columns.