The colony size expansion and the reduction of cell density of wild Microcystis were attempted to accelerate its buoyancy. Culture experiments of Microcystis exhibited that the colony size expansion was observed after 24 h preculture with higher Ca2+ concentration (1,000 mg L-1) in medium, while the preculture with the addition of tightly-bound extracellular polysaccharides (TB-EPS) extracted from cyanobacterial blooms into the same medium did not largely expand the colony size compared to the Ca2+ added medium. Surface analysis of TB-EPS indicated the presence of negatively charged carboxy groups, and the added TB-EPS and the EPS originally surrounding Microcystis would be repulsed, causing prevention of colony size expansion. The floating velocity of Microcystis precultured with light exposure for 24 h was 8.19 x 10(-3) cm s(-1) at Ca2+ = 1,000 mg L-1, which was 1.4 times higher than that in the control. Furthermore, in case of the preculture without light exposure, the velocity had a remarkable acceleration (5.49 x 10(-2) cm s(-1)), which was ca. 9.1 and 5.7 times greater than the control with and without light exposure, respectively (p < 0.05). These results suggest that the reduction of cell density of Microcystis by respiration in dark would further enhance the buoyancy of Microcystis.

Artificial acceleration of Microcystis buoyancy was attempted by manipulating temperature (15-35 degrees C) to reduce intracellular polysaccharides and increase gas vesicles, as well as varying the amount of Ca2+ (500 and 1,000 mg/L) and tightly bound extracellular polysaccharides (TB-EPS) (200 mg/L) to expand the colony size in preculture. In preculture, changes in temperature affected the floating velocity of Microcystis, and the floating velocity was 4.9 and 6.4 times higher at 35 degrees C than that at 15 and 25 degrees C in dark conditions, respectively. Since the content of intracellular polysaccharides at each temperature condition was not largely different (range: 9.9-11.1 pg/cell, p > 0.05), gas vesicle volume would be concerned with the buoyancy, whereas in dark conditions at 35 degrees C, the addition of Ca2+ (1,000 mg/L) and TB-EPS (200 mg/L) into the medium containing Microcystis enlarged colony size from 280 mu m as the mean for the control to 390 mu m, which resulted in 1.9 times faster floating velocity. It was expected that Ca2+ could promote colony size expansion of Microcystis by forming cross-linking structures with the negatively charged functional groups originally present, and externally added TB-EPS. These findings provide new insights into strategies for more efficient removal of Microcystis in lakes. [GRAPHICS]

Dengue fever, caused by the dengue virus (DENV), remains a major global health challenge in tropical regions. To date, no officially approved antiviral drug has been specifically targeted at DENV infections. Graphene-based materials, composed of carbon, have demonstrated antiviral potential against various viruses. In this study, graphene oxide-niclosamide (GO-Nic) hybrid material was developed by modifying GO with niclosamide, an antiparasitic anthelmintic drug that has recently shown broad-spectrum antiviral activity, including against DENV. GO was synthesized using the Hummers method and functionalized with niclosamide through a simple mixing process. The antiviral activity of GO-Nic was evaluated in vitro against DENV serotype 3 (DENV-3) using RT-qPCR and indirect immunofluorescence assay, as well as TEM to assess viral morphology and its interaction with GO-Nic. GO-Nic exhibited enhanced antiviral activity of 60.5 % DENV-3 inhibition compared to 47.2 % inhibition of GO. Notably, this GO-Nic antiviral activity was achieved at 200-fold lower concentration compared to unmodified GO. The synergistic effect between GO and niclosamide contributed to the inhibition of viral replication. These findings highlight GO-Nic potential as a novel antiviral candidate for dengue infection.

With the rapid development of agriculture and industrialization, nitrate (NO3-) contamination has become an increasingly severe global environmental issue. In this study, a nitrogen-doped porous carbon material (Cf-U1Z1-450) was synthesized using coffee grounds as the carbon precursor, with quaternary nitrogen (N-Q) species successfully incorporated via urea-assisted doping. Structural characterization confirmed the effective introduction of N-Q groups, which significantly enhanced the material's adsorption performance. Batch adsorption experiments revealed that Cf-U1Z1-450 exhibited a maximum nitrate adsorption capacity of 0.62 mmol/g under acidic conditions (pH 3). Even under neutral to alkaline conditions (pH 7-11), it still showed considerable uptake, suggesting that N-Q groups remained active at higher pH. Furthermore, fixed-bed column adsorption experiments demonstrated regeneration ability and adsorption stability, with the saturated adsorption capacity remaining nearly unchanged after five adsorption-desorption cycles. These results indicate the crucial role of N-Q functional groups in improving nitrate removal and biomass-derived carbon materials modified with N-Q hold potential for application in nitrate-contaminated water treatment.

Developing effective nitrate removal methods is crucial for addressing water pollution. A nitrogen-doped glucose-derived carbonaceous adsorbent (UrGlu-4.5Z0.6-2nd) was prepared to enhance nitrate adsorption from wastewater. The optimization process of the adsorbent revealed the interaction principles among the raw materials, wherein the special brown porous foam-like intermediate formed after pre-treatment plays a decisive role in enhancing the adsorption performance of the adsorbent. UrGlu-4.5Z0.6-2nd exhibited a point of zero charge (pHpzc) at the pH of 3.0 and a specific surface area (SBET) of 6.13 m2/g. It was shown that the nitrogen-doped modified adsorbent exhibited a considerable capacity for adsorbing nitrate over a wide pH range of 2.0-10.0. The Langmuir isotherm model and the pseudo-second-order kinetic model can accurately describe the nitrate adsorption process of UrGlu-4.5Z0.6-2nd, and the maximum adsorption capacity (Xm) predicted by the Langmuir isotherm model was 1.18 mmol/g. Additionally, UrGlu-4.5Z0.6-2nd demonstrated an excellent adsorption capacity in practical applications using a fixed-bed column adsorption mode, with a breakthrough time of 136 min. It still exhibited preferential adsorption of nitrate in the coexisting ions solution. The results of nitrate adsorption studies and surface characterization indicate that the introduction of active quaternary nitrogen (N-Q) adsorption sites after nitrogen-doped is the primary mechanism for enhancing the adsorption capacity of nitrate.

Pyridinic nitrogen (N-6) in flame resistant polyacrylonitrile (PAN) fiber was converted to positively charged quaternary nitrogen (N-Q) of methyl pyridine using methyl iodide at 40 degrees C to prepare carbon fiber adsorbents to remove a negatively charged pollutant of nitrate from aqueous solution. The prepared PAN fiber adsorbent could uptake nitrate above 0.3 mmol/g from 3 mmol/L nitrate solution, whereas only 0.03 mmol/g of nitrate was captured with the unmodified PAN fiber. Some reaction conditions for methylation were examined to maximize nitrate and above 0.6 mmol/g of nitrate adsorption could be achieved at equilibrium solution pH (pHe) 3. Langmuir adsorption isotherm could be applied to the nitrate adsorption at solution pHe 3 and calculated adsorption affinity (Ke) and capacity (Xm) of nitrate were 0.24 L/mmol and 2.39 mmol/g, respectively, for the optimum prepared conditions for the adsorbent. Influence of pHe on nitrate adsorption was also inspected for the modified PAN adsorbent and above 0.3 mmol/g at pHe 1-3 was maintained and above 0.15 mmol/g in a constant value at pHe 6-10 under standard conditions indicating that 0.15 mmol/g or greater number of quaternary nitrogen (N-Q) might be exposed to the PAN surface. XPS N1s analysis and Boehm titration support the presence of N-Q species on the modified PAN sample to adsorb nitrate.

A frequency of cyanobacterial blooms appearance in lakes has been increasing as a consequence of eutrophication together with global warming. Although cyanobacterial blooms have been removed/collected by a suction method, there are few ways to effectively use the cyanobacterial biomass. If added values such as adsorptive function for pollutants in aqueous solution can be provided to the cyanobacterial biomass, it would be contributed to solve problems on cyanobacterial blooms and water pollution. This study aimed to prepare adsorbent from cyanobacterial bloom sample collected in a eutrophic lake for the removal of pollutants, and attempted to remove Cd2+ by cyanobacterial blooms-originated adsorbent (CBA) prepared via dehydration treatment using a concentrated sulfuric acid. As a result, CBA possessed smaller specific surface area (13.1 m2/g) and higher amount of total acidic functional groups (8.29 mmol/g), and the maximum amount of Cd2+ adsorption was 1.43 mmol/g, which was higher than oxidized activated carbons. From these values, the number of carboxy groups per unit surface area was calculated to be 1.51 × 1020 number/m2, and the distance between carboxy groups was estimated to be 8.14 × 10−2 nm, which would be one of the major reasons of higher amount of Cd2+ adsorption. Furthermore, adsorption/desorption experiments were repeatedly conducted 3 times, and the results showed that the adsorption amount and recovery rate were not largely varied, indicating that CBA can be reused for the Cd2+ adsorption. These results suggest that the preparation of adsorbent for the removal of Cd2+ would be one of the effective ways for the effective utilization of cyanobacterial biomass.

The utilization of carbon-based materials in biomedicine, especially graphene derivatives, has garnered significant interest. However, the concern about the necessity of removing oxygen containing functional groups in graphene oxide (GO) modification for biomedical applications has not been extensively studied. Here, we synthesized graphene oxide (GO) and reduced graphene oxide (rGO) modified with small gold nanoparticles (AuNPs) below 10 nm, referred to as GO-Au and rGO-Au, respectively, and subsequently their antioxidant capability, antibacterial activity, and cytotoxicity were directly compared. The rapid microwave-assisted synthesis method was employed to produce GO-Au and rGO-Au nanocomposites. Structural and compositional analyses using various characterization techniques revealed distinctive properties between GO-Au and rGO-Au. Interestingly, antioxidant assays employing DPPH and ABTS methods demonstrated that GO-Au exhibited higher antioxidant activity than rGO-Au with IC50 values of 98.5 and 202.8 μg/mL, respectively. Antibacterial assays showed that GO-Au was more effective at inhibiting E. coli growth (52

In this study, cyanobacterial bloom adsorbents (CBA) were prepared by H2SO4 treatment (sulfonic acid-treated CBA; CBA-S) at 90-95 °C and ZnCl2 activation at 100, 200 and 300 °C (zinc chloride-activated CBA; CBA-Z-100, 200 and 300). Then, practicality and reusability of CBA were examined by researching the adsorption/desorption performance of Cd(II) in batch and column methods. In batch method, the amount of 1st adsorption in CBA-S was highest (0.95 mmol/g) and more than twice CBA-Z series. The amounts of 2nd to 4th adsorption in CBA-S were higher than other three samples. The desorption rates were higher than 90% in 2nd to 4th adsorption. Adsorption capacity (Qm) and affinity (Ke) of CBA-S were 1.98 mmol/g and 8.74 L/mmol in Langmuir equation, respectively. CBA-S has many adsorption sites for Cd(II), and its adsorption power is weak. In column method, the adsorption of CBA-S was 0.705 mmol/g when the initial concentration of Cd(II) was 500 mg/L. After desorption, the amounts of 2nd and 3rd adsorption were 0.708 (100%) and 0.655 (93%) mmol/g, respectively. These results indicate that CBA-S had high adsorption performance and could be used repeatedly as clarified by batch and column experiments.

In the present study, the glucose-based carbonaceous adsorbent was prepared from glucose, melamine and urea by using ZnCl2 activation and heated at 550ºC under N2 flow. The sample was treated for the 1st, 2nd and 3rd activation process, and they were characterized by N2 adsorption and desorption isotherms, elemental analysis and X-ray photoelectron spectroscopy (XPS). The results showed that the content of nitrogen increased and that of oxygen decreased with the increasing of the number of activation process. The adsorbent obtained after the 2nd activation showed the best adsorption properties and was used in batch and fixed-bed column adsorption studies. In batch adsorption experiments, we investigated the factors affecting nitrate adsorption such as initial concentration, solution pH, adsorption isotherms and adsorption kinetics. The isotherm data and kinetic data were fitted well to the Langmuir isotherm model and pseudo-second-order model, respectively, and the maximum adsorption capacity calculated by Langmuir model was 1.58mmol/g at pH 3. The adsorption performance of the adsorbent in industrial application mode was also investigated by fixed-bed column experiments. The breakthrough time of the packed column was 160min for the initial nitrate concentration of 200mg/L at pH 3. The saturated column could be regenerated by 1mol/L HCl and reused for at least 5 adsorption-desorption cycles. The column showed good adsorption performance in both coexisting ions solution and real contamination water.

We report two evaporator tube failures that took place in the same boiler owing to hydrogen damage within an interval of approximately one year. Notably, hydrogen damage occurred selectively on recently repaired tubes. In contrast, some of the original tubes that had been operating for 18 years or longer remained intact under the same environment. Comprehensive metallurgical investigation and chemical analysis revealed that the older tubes slowly developed a thin film of evaporation residue on their inner surface, which had a protective effect and suppressed the progress of corrosion. Hydrogen damage is more likely to proceed in the electric resistance welding (ERW) part than in the other parts. Kinetic consideration proved the rapid (within 18 hours) progression of hydrogen damage in evaporator tubes. Moreover, it confirmed that the hydrogen damage could be stemmed by instantaneous shutdown without improving the water quality immediately. The cleaning test suggested that tubes that already suffered hydrogen damage may be further damaged during acid cleaning. These results can help identify the cause of hydrogen damage in evaporator tubes due to poor water quality and determine the area of tube renewal/repair.

Sucrose was mixed with melamine and urea, and the mixture was activated by zinc chloride to increase the number of amine functional groups and quaternary nitrogen (N–Q) atoms on the sample surface and to improve phosphate ion adsorption. The highest amount of phosphate ion adsorption (0.40 mmol/g) was obtained when melamine, urea, sucrose, and zinc chloride were mixed in 1 : 1 : 2 : 2 weight ratios and activated three times at 550 °C. The total amount of nitrogen in the sample decreased as the number of activation cycles increased, but the number of protonated amine functional groups and N–Q that contributed to phosphate adsorption increased. The specific surface area increased with the number of activation cycles, with a maximum value of approximately 278 m2/g. This was due to the removal of hydrogen and oxygen ions from the raw materials by the dehydration reaction using zinc chloride at high temperatures, resulting in the formation of pores. Maximum adsorption was observed when the equilibrium solution pH (pHe) was 4.0, indicating that the adsorbent has a high adsorption performance in acidic regions. The adsorption isotherm was fitted to the Langmuir model, indicating monolayer adsorption, with an estimated maximum amount of phosphate adsorption (Xm) of 0.61 mmol/g.

This study investigated the relationship between nitrogen (N) and phosphorus (P) mass ratio in the medium and cellular N (Nc) and P (Pc) mass ratio in Microcystis cell. Monoculture experiments were conducted with the phosphorus concentration fixed at 0.110 mg L–1 and the initial N:P mass ratios of 1, 10, 18, 50, 70, and 100. The results showed that the cell density of Microcystis sp. was highest at the initial N:P mass ratio of 50. Although it has been disputed that a low total N:P (TN:TP) ratio (< 29) in water was a cause of the development of cyanobacterial blooms or a result of its occurrence, this study could support the latter trend. This assumption could be supported by the results of elemental analysis (i.e., cellular Nc:Pc mass ratio of Microcystis sp.). At the end of the culture experiment, the Nc:Pc ratios ranged from 13.2 to 20.3, which were similar to the initial value (12.7). In general, the dissolved N and P concentrations in lake water are completely consumed when cyanobacterial blooms occur. Therefore, the present study suggests that the low TN:TP ratio may reflect the cellular Nc:Pc ratio of Microcystis sp. following assimilation of N and P in lake water.

This study aimed to control the buoyancy of Microcystis by increasing the growth rate and simultaneously reducing the cellular carbohydrate content under various light and temperature regimes. Microcystis was precultured in continuous dark (0 µmol·m−2·s−1) or light conditions (135 µmol·m−2·s−1) for 48 hours at 30°C and 35°C. After preculture, Microcystis was cultivated in a burette to observe the difference in the buoyancy. The buoyancy was evaluated by relative buoyancy of 25% (RB25), defined as the percentage of Microcystis cell number in the upper 25% layer to the total cell number in the burette. The result showed that preculture under the dark condition at 30°C had higher RB25 (43.8 ± 3.5%), than under the light condition (23.8 ± 2.8%). In addition, Microcystis precultured in the dark condition at 30°C also had the lowest cellular carbohydrate (3.1 ± 0.3 pg/cell). The reduction of cell ballast would promote the buoyancy of Microcystis. These results indicate that the buoyancy of Microcystis can be controlled by reducing cellular carbohydrate using preculture under the dark condition at high temperature. Thus, artificial control to increase Microcystis buoyancy could be a useful method for removal of Microcystis blooms, especially in water purification plants.

In this study, aiming to address the issue of phosphate contamination in water, a novel activated carbon adsorbent with excellent adsorption performance for phosphate ions was de-signed and synthesized through a nitrogen-doped surface modification method. The adsorption experiment results revealed that the sample obtained after the second activation at 600 degree celsius (MeUrGlu-6.0Z0.5-2nd) exhibited a high adsorption capacity of up to 0.42 mmol/g for phosphate ions. The surface modi-fication method using nitrogen-doping significantly enhanced the adsorption capacity of the adsorbent for phosphate anions. The surface characteristics of the sample were analyzed by Brunauer-Emmett-Teller method, elemental analysis, and X-ray photoelectron spectroscopy (XPS). The characterization results indicated that the increase in adsorption capacity primarily attributed to the successful introduction of quaternary nitrogen (N-Q) onto the activated carbon surface. Additionally, the adsorbent demonstrated high adsorption capacity for phosphate ions in acidic solution (pH <4.5), overcoming the limitation of commercial anion exchange resin HP555 which cannot be used effectively in acidic environment. The Langmuir isotherm model was found to accurately describe the adsorption process which is a monolayer adsorption. Finally, the regenerability of MeUrGlu-6.0Z0.5-2nd and the recovery of phosphate ions were investigated in a continuous flow adsorption mode.

This study investigates the correlation between the damage distribution in the evaporator tube and thermal-hydraulic properties of a boiler with hydrogen damage caused by a decrease in the pH of the boiler water. The hydrogen damage in the vertical upward flow tube of the boiler was located in the transition region from the slightly subcooled boiling region to the saturated boiling region. Thermal-hydraulic analysis suggested that this region may have an environment with a gentler flow and a higher concentration of chemical species on the heat transfer surface than that in a fully saturated boiling region. Based on these findings, in the vertical upward flow tube downstream (upper part) from the damaged part of the boiler furnace, material diffusion on the surface becomes more active owing to the acceleration and stirring effect caused by bubbling in the main stream. Therefore, the concentration on the heat transfer surface is moderated. In addition, in the upper part, the effect of decreasing the heat flux due to the distance from the burner is compounded, and the risk of hydrogen damage is further reduced.