Ultrasonic inactivation of Microcystis aeruginosa in the presence of TiO2 particles

Anti-algal activity of a fluorine-doped titanium oxide photocatalyst against Microcystis aeruginosa and its photocatalytic degradation

Fluorine-doped TiO2 was successfully synthesised and applied as algaecide. Studies on algae removal efficiencies and mechanisms illustrated that F-TiO2 was suitable for algae elimination in natural water bodies.

In-situ active formation of carbides coated with NPTiO2 nanoparticles for efficient adsorption-photocatalytic inactivation of harmful algae in eutrophic water

Harmful algae pollution in eutrophic waters represents one of the most serious problems in natural water environment. Adsorption assisted photocatalytic inactivation is often considered as a promising method to achieve the clean-up of harmful algae and the remediation of eutrophic water. Here, we synthesize the NPTiO₂ (nitrogen and phosphorous doped TiO₂)/C composites using a facile sol-gel method, and demonstrate successful achievement of efficient adsorption-photocatalytic performance via the in-situ formed carbides coated with NPTiO₂ nanoparticles. We find that the composites have rough surfaces with porous structure, which can be tuned by the calcination temperature, and that such composites can be served to efficiently capture the algal cells. The N and P are successfully doped into the TiO₂ crystal lattices, and the cooperation of carbides and NPTiO₂ particles enhances significantly light absorption, while inhibiting the recombination of the photogenerated charge carriers. Among all the NPTiO₂/C composites, the NPTiO₂/C system calcinated at 550 °C shows the best photocatalytic performance for the algal inactivation, presenting a removal rate of 92.6% following 6 h visible light irradiation. The destruction of cell structures is clearly observed in the photocatalytic process. Interestingly, the metabolic activities are also disturbed by the photogenerated radicals, which accelerates the death of algal cells. Moreover, the NPTiO₂/C composite can effectively remove the cytotoxins from water, rendering the composite and the doping strategy promising in the remediation practice for eutrophic waters.

Surface modified TiO2 floating photocatalyst with PDDA for efficient adsorption and photocatalytic inactivation of Microcystis aeruginosa

Microcystis aeruginosa, as the most common cyanobacteria, often grows uncontrollably in eutrophic lakes with the accumulation of microcystin-LR (MC-LR) in water, which heavily pollutes water and hence imposes tremendous threat to aquatic animals and human beings. To remediate the harmful algae polluted water, here we synthesize a series of poly dimethyl diallyl ammonium chloride (PDDA) modified TiO₂ floating photocatalysts, PDDA@NPT-EGC, and apply them as a visible light driven multifunctional material. The fabricated PDDA@NPT-EGC composites have a worm-like structure with PDDA particles distributed on their surfaces, and the concentration of PDDA can affect the agglomerative condition and distribution of PDDA particles and the photoelectric properties of catalysts. Among these catalysts, the PDDA@NPT-EGC with 0.2 wt% PDDA (0.2PDDA@NPT-EGC) shows the highest adsorption and photocatalytic activity. Compared with the NPT-EGC, the dark adsorption efficiency for the 0.2PDDA@NPT-EGC after 3 h increases from 70.4% to 88.9%, and the total removal efficiency after visible light irradiation for 2 h increases from 77.8% to 92.6%. In addition, the 0.2PDDA@NPT-EGC exhibits a removal efficiency of 96.55% for photocatalytic degradation of MC-LR after irradiation for 3 h. The Adda side chain of MC-LR molecule is found to degradate gradually in the photocatalytic degradation process, indicative of the elimination of biotoxicity for MC-LR molecule in the reaction. We demonstrate that the 0.2PDDA@NPT-EGC is remarkably competitive in both algae inactivation and MC-LR removal, which shall hold substantial promise in remediation of algae pollution in eutrophic waters.

Anticyanobacterial effect ofl-lysine onMicrocystis aeruginosa

Cyanobacterial blooms can cause serious environmental problems and threaten aquatic organisms and human health. It is therefore essential to effectively control cyanobacterial blooms in aquatic ecosystems. In the present study, the anticyanobacterial effect of l-lysine on Microcystis aeruginosa was examined. The results showed that the growth of M. aeruginosa (>90%) was effectively inhibited by l-lysine at dosages of 5.0, 6.5, and 8.0 mg L⁻¹ after 3 d treatment. The content of superoxide anion radicals, MDA content and SOD activity in M. aeruginosa cells increased after 1 d of treatment with l-lysine (3.0, 5.0, 6.5, and 8.0 mg L⁻¹), revealing that l-lysine induced oxidative stress in the cyanobacterial cells. The chlorophyll-a and protein contents in M. aeruginosa treated with l-lysine (3.0, 5.0, 6.5, and 8.0 mg L⁻¹) decreased after 2 d, indicating damage of the photosynthetic system by l-lysine treatment. Additionally, the production of exopolysaccharide by M. aeruginosa also increased and the expression of polysaccharide synthesis genes was upregulated by 3.0 mg L⁻¹l-lysine after 3 d of treatment. In response to the algicidal effects of l-Lysine, M. aeruginosa upregulated exopolysaccharide synthesis. Electron microscopic observations demonstrated that the cell membrane of M. aeruginosa was broken down during treatment with l-lysine (≥3.0 mg L⁻¹). Our results revealed that the effects of l-lysine on M. aeruginosa cells were comprehensive, and l-lysine is therefore an efficient anticyanobacterial reagent.

l-lysine had an anticyanobacterial effect on Microcystis aeruginosa, which involved growth inhibition, physiological and metabolic disturbance, and cell membrane damage.

Efficient visible light-driven in situ photocatalytic destruction of harmful alga by worm-like N,P co-doped TiO2/expanded graphite carbon layer (NPT-EGC) floating composites

Preparation of N,P co-doped TiO₂/expanded graphite carbon layer (NPT-EGC) composites for floating algaecides.

Sonocatalytic injury of cancer cells attached on the surface of a nickel-titanium dioxide alloy plate

The present study demonstrates ultrasound-induced cell injury using a nickel-titanium dioxide (Ni-TiO2) alloy plate as a sonocatalyst and a cell culture surface. Ultrasound irradiation of cell-free Ni-TiO2 alloy plates with 1 MHz ultrasound at 0.5 W/cm(2) for 30s led to an increased generation of hydroxyl (OH) radicals compared to nickel-titanium (Ni-Ti) control alloy plates with and without ultrasound irradiation. When human breast cancer cells (MCF-7 cells) cultured on the Ni-TiO2 alloy plates were irradiated with 1 MHz ultrasound at 0.5 W/cm(2) for 30s and then incubated for 48 h, cell density on the alloy plate was reduced to approximately 50% of the controls on the Ni-Ti alloy plates with and without ultrasound irradiation. These results indicate the injury of MCF-7 cells following sonocatalytic OH radical generation by Ni-TiO2. Further experiments demonstrated cell shrinkage and chromatin condensation after ultrasound irradiation of MCF-7 cells attached on the Ni-TiO2 alloy plates, indicating induction of apoptosis.

New insight into the residual inactivation of Microcystis aeruginosa by dielectric barrier discharge

We report the new insight into the dielectric barrier discharge (DBD) induced inactivation of Microcystis aeruginosa, the dominant algae which caused harmful cyanobacterial blooms in many developing countries. In contrast with the previous work, we employed flow cytometry to examine the algal cells, so that we could assess the dead and living cells with more accuracy, and distinguish an intermediate state of algal cells which were verified as apoptotic. Our results showed that the numbers of both dead and apoptotic cells increased with DBD treatment delay time, and hydrogen peroxide produced by DBD was the main reason for the time-delayed inactivation effect. However, apart from the influence of hydrogen peroxide, the DBD-induced initial injures on the algal cells during the discharge period also played a considerable role in the inactivation of the DBD treated cells, as indicated by the measurement of intracellular reactive oxygen species (ROS) inside the algal cells. We therefore propose an effective approach to utilization of non-thermal plasma technique that makes good use of the residual inactivation effect to optimize the experimental conditions in terms of discharge time and delay time, so that more efficient treatment of cyanobacterial blooms can be achieved.

Study the toxicity to Microcystis aeruginosa induced by TiO₂ nanoparticles photocatalysis under UV light

In the present study, the biological effect of TiO2 nanoparticles on cyanobacteria cells was studied using Microcystis aeruginosa (M. aeruginosa) as a model. Nano-TiO2 as a photo-catalysts agent used for water treatment may pose a risk to ecosystems, especially for the water organisms such as cyanobacteria. Scanning electron microscope (SEM) images provided that with the increasing of photocatalytic time, slime layer on the cell surface was damaged and sunk. Attenuated total reflectance fourier transform infrared (ATR-FTIR) spectroscopy revealed that the vibration peaks of C-C, C-H, C=O, P=O weakened within 12 h. According to the dynamic analysis of the infrared peaks, the damage on the cell groups under nano-TiO2 photocatalysis with different time periods was analyzed. The concentrations of K(+), Ca(2+), Mg(2+) released from the cells were measured, which indicated that nano-TiO2 photocatalysis have changed the cell membrane permeability and fluidity of M. aeruginosa.

Targeted sonocatalytic cancer cell injury using avidin-conjugated titanium dioxide nanoparticles

In this study, we applied sonodynamic therapy to cancer cells based on the delivery of titanium dioxide (TiO2) nanoparticles (NPs) modified with avidin protein, which preferentially discriminated cancerous cells from healthy cells. Subsequently, hydroxyl radicals were generated from the TiO2 NPs after activation by external ultrasound irradiation (TiO2/US treatment). Although 30% of the normal breast cells (human mammary epithelial cells) exhibited the uptake of avidin-modified TiO2 NPs, over 80% of the breast cancer cells (MCF-7) exhibited the uptake of avidin-TiO2 NPs. Next the effect of the TiO2/US treatment on MCF-7 cell growth was examined for up to 96 h after 1-MHz ultrasound was applied (0.1 W/cm(2), 30 s) to cells that incorporated the TiO2 NPs. No apparent cell injury was observed until 24h after the treatment, but the viable cell concentration declined to 68% compared with the control at 96 h.