Influences of anion concentration and valence on dispersion and aggregation of titanium dioxide nanoparticles in aqueous solutions

Photocatalytic degradation of ciprofloxacin from water with waste polystyrene and TiO2 composites

Ciprofloxacin (CIP) is one of the widely used antibiotics with a broad antimicrobial spectrum in the fluoroquinolone type. Its concentration in water bodies has increased over the years due to its frequent use. Since ciprofloxacin in the aquatic ecosystem adversely affects human health as well as other organisms, it must be removed from wastewater. The aim of this study was to develop Polystyrene (PS) and Titanium dioxide (TiO2) composites that can be used as catalysts in CIP removal by photocatalytic process. Waste PS (obtained from disposable cutlery) was used in the synthesis of these composites. In this study, PS-TiO2 composites with different PS content (C20, C50, C80; the numbers in the names indicate the PS percentage in the composite by weight) were synthesized. This is important in terms of the use of one waste in the removal of another waste. This process was optimized using Box-Behnken design, one of the response surface method. Parameters such as the amount of polymer in the composite, pH and initial CIP concentration were studied and their effects on CIP removal were found. The validity and adequacy of the selected model were evaluated according to the relevant statistical data. These are R2 = 0.9751, adjusted R2 = 0.9565, the model's p-value <0.05 and the lack of fit-value 0.246. Optimum conditions for CIP removal were obtained when the C50 was used, with a pH value of 3 and an initial CIP concentration of 5 mg/L. In the process carried out under these conditions, the CIP removal was found to be 95.01 % at the end of 180 min. This value was predicted as 94.37 % in the model. According to these results, C50 composite synthesized with waste PS can be used effectively for CIP removal.

Dispersion and transport of microplastics in three water-saturated coastal soils

The coastal area is one of the key zones for transport and fate of microplastics (MPs). This study investigated the transport behaviors of different sized MPs in three water-saturated coastal soils, with the aim to explore effects of properties of three different coastal soils on the dispersion and migration of three-sized MPs (0.3, 0.5, and 1 µm). All three-sized MPs had the strongest dispersion in Soil 3 solution, followed by that in Soil 1 solution and then that in Soil 2 solution. The strongest dispersion of MPs in Soil 3 solution was attributed to the lowest ionic strength. Such a high dispersion favored MPs movement in soil solution but readily be sorbed and fixed by rich Fe and Al oxides in Soil 3 solid through strong electrostatic attraction, leading to the lowest transport rate (20.5-41.2%). The high ionic strength in the Soil 1 solution decreased the dispersion of MPs, but the presence of high content of humic acid enhanced the electrostatic repulsion and steric hindrance between MPs and soil particles, resulting in the highest transport ability of MPs in Soil 1 (39.4-72.5%). The large amount of dissolved Ca²⁺ and Mg²⁺ in Soil 2 solution favored MPs bridged with fulvic acid, resulting in the highest aggregation of MPs and relatively lower transport ability (34.1-49.6%). Large-sized MPs had higher electrostatic repulsion between the particles, thus increasing the dispersion and transport capacity of MPs in soil. Modeling showed the experiment-consistent results that Soil 3 had the lowest MPs transport after 600 mm of heavy rainfall, with the maximum migration distance of 7.50-10.5 cm, which was smaller than that in Soil 2 (8.10-12.0 cm) and that in Soil 1 (9.00-18.3 cm). These results indicated that MPs transport in coastal soil is significant and soil solution and solid composition plays an important role in the dispersion and transport of MPs, respectively. These findings afforded a great basis for the assessment of the fate and risk of MPs in coastal areas.

Novel multimethod approach for the determination of the colloidal stability of nanomaterials in complex environmental mixtures using a global stability index: TiO2 as case study

A systematic study on the colloidal behavior of uncoated and polyvinylpyrrolidone (PVP) coated TiO₂ engineered nanomaterials (ENMs) in simulated aqueous media is herein reported, in which conditions representative for natural waters (pH, presence of divalent electrolytes (i.e. Ca²⁺/Mg²⁺ and SO₄^2-), of natural organic matter (NOM) and of suspended particulate matter (SPM)) were systematically varied. The colloidal stability of the different dispersions was investigated by means of Dynamic and Electrophoretic Light Scattering (DLS and ELS) and Centrifugal Separation Analysis (CSA), and a global stability index based on these three techniques was developed. The index allows to quantitatively classify the nano-based dispersions according to their colloidal stability affected by the different parameters studied. This multimethod approach clearly identifies inorganic SPM followed by divalent electrolytes as the main natural components destabilizing TiO₂ ENMs upon entering in simulated natural waters, while it highlights a moderate stabilization induced by NOM, depending mainly on pH. Moreover, the PVP coating was found to attenuate the influence of these parameters on the colloidal stability. The obtained results show how the global stability index developed is influenced by the complexity of the system, suggesting the importance of combining the information gathered from all the techniques employed to better elucidate the fate and behavior of ENMs in natural surface waters.

Impact of montmorillonite clay on the homo- and heteroaggregation of titanium dioxide nanoparticles (nTiO2) in synthetic and natural waters

The homoaggregation of titanium dioxide nanoparticles (nTiO₂) and their heteroaggregation with ubiquitous natural clay colloids are crucial processes affecting the environmental transport and fate of nTiO₂, whereas the latter has received less attention. In this study, the effects of pH, electrolytes, natural organic matter (NOM), and montmorillonite on the homo- and heteroaggregation of nTiO₂ were systematically investigated. The isoelectric point of bare nTiO₂ was 6.98, whereas TiO₂-montmorillonite mixtures remained negative charged due to the reduced particle surface potential by heteroaggregation. Homoaggregation of nTiO₂ was mainly affected by anions, whereas heteroaggregation in TiO₂-montmorillonite mixtures was mainly affected by cations. Heteroaggregation between nTiO₂ and montmorillonite involved the adsorption of CC/CH. Intensive aggregation of nTiO₂ was observed with 4 mg/L montmorillonite, whereas with 20 mg/L montmorillonite, the aggregation was significantly inhibited by the over-coverage of montmorillonite. NOM was attached to the surface of nTiO₂ with the adsorption of functional groups involving CC/CH and OCO. The addition of NOM effectively reduced the homo- and heteroaggregation of nTiO₂, and the stabilizing effect was enhanced with the increased molecular weight and aromatic/aliphatic fraction in NOM. Besides electrostatic repulsion, steric repulsion could also be one of the main stabilization mechanisms of NOM. With Ca²⁺ in the solutions, the stabilizing effect of NOM was significantly weakened through cation bridging. The addition of montmorillonite could facilitate the aggregation of nTiO₂ in the presence of NOM. The homo- and heteroaggregation of nTiO₂ were also observed in 7 different types of natural waters. Homoaggregation predominated in waters with high ionic strength and low NOM contents (seawater and groundwater), whereas heteroaggregation predominated in surface freshwater and wastewater systems. The results reflect the instability of nTiO₂ in natural aquatic environments and the potential risk they pose to benthic organisms.

Effective Inclusion of Sizable Amounts of Mo within TiO2 Nanoparticles Can Be Obtained by Reverse Micelle Sol-Gel Synthesis

Six Mo/TiO2 samples (with 0, 1.0, 2.5, 5.0, 7.5, and 10 wt % Mo nominal contents) were obtained by reverse micelle sol-gel synthesis, followed by calcination at 500 °C. The samples were characterized by means of powder X-ray Diffraction (PXRD), quantitative phase analysis as obtained by Rietveld refinement, field-emission scanning electron microscopy (FE-SEM) coupled with energy-dispersive X-ray analysis, N2 adsorption/desorption at -196 °C, X-ray photoelectron spectroscopy, and diffuse reflectance (DR) UV-vis spectroscopy. As a whole, the adopted characterization techniques showed the inclusion of a sizeable Mo amount, without the segregation of any MoO x phase. Specifically, PXRD showed the occurrence of anatase and brookite with all the studied samples; notwithstanding the mild calcination temperature, the formation of rutile occurred at Mo wt % ≥2.5 likely due to the presence of brookite favoring, in turn, anatase to rutile transition. DR UV-vis and XP spectroscopies allowed determining the samples' band gap energy (E g) and valence band energy, respectively, from which the conduction band energy was calculated; and the observed E g value increase at 10 wt % Mo was ascribed to the Moss-Burstein effect.

The crucial role of a protein corona in determining the aggregation kinetics and colloidal stability of polystyrene nanoplastics

Nanosized plastics are considered as being a class of contaminants of emerging concern. The interaction between nanoplastics and proteins may significantly influence the environmental behavior and fate of nanoplastics. Here, we employed time-resolved dynamic light scattering to explore the aggregation kinetics and stability of polystyrene nanoparticles (PSNPs) exposed to a model globular protein (bovine serum albumin, BSA) in the presence of a number of typical electrolytes (NaCl, CaCl₂, and Na₂SO₄). With the increase of the BSA concentration, the amount of BSA adsorbed on the surface of negatively charged PS-Bare (non-modified) and PS-COOH (carboxyl-modified) increased, resulting in higher dispersibility in comparison to the treatment without BSA. This stabilization effect derived from the protein corona structure was revealed by combining characterization techniques and visualized by transmission electron microscopy. Upon addition of NaCl and CaCl₂, the aggregation of positively charged PS-NH₂ (amino-modified) was inhibited by the BSA addition possibly due to the screening of the attractive patch-charge force and the competition for adsorption of cations between PS-NH₂ and the protein. When Na₂SO₄ was present in the suspension, BSA addition significantly increased PS-NH₂ aggregation rate due to patch-charge attraction and the high performance of SO₄^2- in attaching to particles and charge neutralization. These findings shed light on the interactions between PSNPs and proteins, which were shown to vary with the composition of the surface coatings of PSNPs. The newly gained knowledge will help us to forecast the transport and fate of PSNPs in natural aqueous systems.

Removal of atrazine in catalytic degradation solutions by microalgae Chlorella sp. and evaluation of toxicity of degradation products via algal growth and photosynthetic activity

Degradation solutions containing atrazine need to be further purified before they are discharged into the aquatic environment. With the objectives of evaluating removal capacity of the microalga Chlorella sp. toward atrazine in degradation solutions and toxicity of the degradation products, we investigated the removal efficiency (RE) and bioaccumulation of atrazine in the microalgae after an 8 d exposure to diluted degraded solutions containing 40 μg/L and 80 μg/L of atrazine as well as degradation products in the present study. Moreover, pure atrazine solutions with similar concentrations were simultaneously inoculated with the microalgae in order to distinguish the influence of the products. The photocatalytic degradation results showed that 31.4% of atrazine was degraded after 60 min, and three degradation products, desisopropyl-atrazine (DIA), desethyl-atrazine (DEA), and desethyl-desisopropyl-atrazine (DEIA) were detected. After an 8-d exposure, 83.0% and 64.3% of atrazine were removed from the degraded solutions containing 40 μg/L and 80 μg/L of atrazine, respectively. In comparison with the control, i.e., pure atrazine solution with equal concentration, Chlorella sp. in the degraded atrazine solution showed lower RE and growth rate. The photosynthetic parameters, especially performance index (PI_ABS), clearly displayed the differences between treatments. The values of PI_ABS of Chlorella sp. cultured in degradation atrazine for 8 days were significantly lower (P < 0.01) than that in the corresponding pure atrazine, suggesting potential inhibitory effect of degradation products on the microalgae. Atrazine and the degradation products inhibited algal photosynthesis via depressed light absorption and electron transport, and reduced utilization of light energy via energy dissipation. Our results demonstrated that microalgae Chlorella sp. had an encouraging atrazine removal potential and the degradation products of atrazine may inhibit algal growth and removal capability. This study may be useful for the application of microalgae in herbicide wastewater treatment and understanding algal removal of atrazine in natural aquatic environment.

Analytical methods and environmental processes of nanoplastics

The degradation of plastic debris may result in the generation of nanoplastics (NPs). Their high specific surface area for the sorption of organic pollutions and toxic heavy metals and possible transfer between organisms at different nutrient levels make the study of NPs an urgent priority. However, there is very limited understanding on the occurrence, distribution, abundant, and fate of NPs in the environment, partially due to the lack of suitable techniques for the separation and identification of NPs from complex environmental matrices. In this review, we first overviewed the state-of-the-art methods for the extraction, separation, identification and quantification of NPs in the environment. Some of them have been successfully applied for the field determination of NPs, while some are borrowed from the detection of microplastics or engineered nanomaterials. Then the possible fate and transport of NPs in the environment are thoroughly described. Although great efforts have been made during the recent years, large knowledge gaps still exist, such as the relatively high detection limit of existing method failing to detect ultralow masses of NPs in the environment, and spherical polystyrene NP models failing to represent the various compositions of NPs with different irregular shapes, which needs further investigation.

Interpreting the role of NO3-, SO42-, and extracellular polymeric substances on aggregation kinetics of CeO2 nanoparticles: Measurement and modeling

The early stage of aggregation of cerium oxide nanoparticles (CeO₂ NPs) in anion solutions was inspected in the absence and presence of extracellular polymeric substance (EPS) with a help of time-resolved dynamic light scattering (DLS). The aggregation kinetics and attachment efficiencies were calculated according to measured hydrodynamic diameter across a range of 1-500 mM NaNO₃ and 0.01-100. mM Na₂SO₄. The aggregation of CeO₂ NPs in both NaNO₃ and Na₂SO₄ solution conformed with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. In NaNO₃ solution, the critical coagulation concentrations (CCC) of CeO₂ NPs was calculated to be about 47 mM; in Na₂SO₄ solution, CeO₂ NPs showed a re-stabilization process and thus there was no CCC value. SO₄^2- had intenser effects on CeO₂ NPs aggregation than NO₃^- might because of the distinction between their polarization, consisting in Hofmeister series. The presence of bound EPS (B-EPS), tightly bound EPS (TB-EPS) and loosely bound EPS (LB-EPS) in NaNO₃ solutions all lead to significant decrease in CeO₂ NPs aggregation. Steric repulsive force produced by absorbed EPS on CeO₂ NPs might take main responsibility in stabilizing CeO₂ NPs. Besides, Extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) model successfully predicted the energy barrier between CeO₂ NPs with B-EPS, TB-EPS and LB-EPS as a function of NaNO₃ concentration. Furthermore, the difference in impeding the CeO₂ NPs aggregation with B-EPS, TB-EPS and LB-EPS may be caused by the divergence in molecular weight and component mass fraction especially protein content. These results might subserve the assessment on the fate and transport behaviors of CeO₂ NPs released in wastewater treatment plants.

Study on Dispersion of TiO2 Nanopowder in Aqueous Solution via Near Supercritical Fluids

In this study, we investigated the effects of near supercritical carbon dioxide (SCCO2) parameters, including pressure, temperature, and saturation time on titanium dioxide (TiO2) nanopowder dispersion in water-containing sodium hexametaphosphate (SHMP). The stability and morphology of TiO2 particles dispersed in an aqueous solution were examined using a zeta potential instrument, dynamic light scattering, and transmission electron microscopy. As shown in the results, of particular interest, it was found that near SCCO2's pressure and saturation time had the strongest impact on TiO2 dispersion in water-containing SHMP. This finding indicated that TiO2's secondary average particle size was significantly reduced with an increase in near SCCO2's pressure and saturation time. Additionally, in the presence of SHMP, the zeta potential of the as-prepared dispersion solution reached -53.7 mV because of production of the larger negative static charge repulsion force (resulting from SHMP dissociation) on the TiO2 particle surface. The secondary average size was 127 ± 68 nm, indicating good stability of TiO2 dispersed in water containing an inorganic dispersant.

A Review on Recent Treatment Technology for Herbicide Atrazine in Contaminated Environment

Atrazine is a kind of triazine herbicide that is widely used for weed control due to its good weeding effect and low price. The study of atrazine removal from the environment is of great significance due to the stable structure, difficult degradation, long residence time in environment, and toxicity on the organism and human beings. Therefore, a number of processing technologies are developed and widely employed for atrazine degradation, such as adsorption, photochemical catalysis, biodegradation, etc. In this article, with our previous research work, the progresses of researches about the treatment technology of atrazine are systematically reviewed, which includes the four main aspects of physicochemical, chemical, biological, and material-microbial-integrated aspects. The advantages and disadvantages of various methods are summarized and the degradation mechanisms are also evaluated. Specially, recent advanced technologies, both plant-microbial remediation and the material-microbial-integrated method, have been highlighted on atrazine degradation. Among them, the plant-microbial remediation is based on the combined system of soil-plant-microbes, and the material-microbial-integrated method is based on the synergistic effect of materials and microorganisms. Additionally, future research needs to focus on the excellent removal effect and low environmental impact of functional materials, and the coordination processing of two or more technologies for atrazine removal is also highlighted.

Effects of Ca2+ and fulvic acids on atrazine degradation by nano-TiO2: Performances and mechanisms

In this study, the adsorption and UV photocatalytic degradation of atrazine using nano-TiO₂ particles were studied systematically, and the colloidal stability of nano-TiO₂ particles in solution was also investigated to reveal the removal mechanism. Experiments which contained the first 6.0 hours darkness and 4.0 hours UV illumination later were conducted at different concentrations of Ca²⁺ and/or fulvic acids (FA) at pH = 7.0. Results showed that the adsorption rate of atrazine onto nano-TiO₂ particles decreased with the increase of Ca²⁺ and/or FA concentrations, which could be explained well by the colloidal stability of nanoparticles. When the solution contained Ca²⁺ or Ca²⁺-FA, the nanoparticles were aggregated together leading to the decrease of the contact surface area. Besides, there existed competitive adsorption between FA and atrazine on the particle surface. During photocatalytic degradation, the increase of Ca²⁺ and/or FA concentration accelerated the aggregation of nano-TiO₂ particles and that reduced the degradation efficiency of atrazine. The particle sizes by SEM were in accordance with the aggregation degree of nanoparticles in the solutions. Sedimentation experiments of nano-TiO₂ particles displayed that the fastest sedimentation was happened in the CaCl₂ and FA coexistent system and followed by CaCl₂ alone, and the results well demonstrated the photodegradation efficiency trends of atrazine by nano-TiO₂ particles under the different sedimentation conditions.

Beneficial use of ultrasound irradiation in synthesis of beta-clinoptilolite composite used in heavy oil upgrading process

A novel beta–clinoptilolite composite was prepared from beta zeolite and alkaline treated clinoptilolite by employing conventional and sonicated mixing procedures. Parent and prepared catalysts were characterized by XRD, FE-SEM, N₂ adsorption–desorption and NH₃-TPD analyses. Prepared composite of beta zeolite and treated clinoptilolite exhibited improved structural properties especially upon sonicated mixing procedure. Employing ultrasound irradiation notably improved beta distribution in the composite and increased mesoporous volume and specific surface area from 0.245 cm³ g⁻¹ and 171.3 m² g⁻¹ in conventionally mixed composite to 0.353 cm³ g⁻¹ and 232.9 m² g⁻¹ in sonicated sample. Catalytic performance of prepared composite was evaluated in heavy oil upgrading process in a continuous fixed bed apparatus. Liquid product was specified by conducting SIMDIS-GC and GC/MS analyses. Spent catalysts were characterized by TGA, FTIR and XRD. Beta–clinoptilolite composite containing only 30 wt% of beta zeolite, exhibited similar performance to beta zeolite catalyst by resulting 75.3% viscosity reduction while producing lower amount of coke. Amount of light hydrocarbons produced over beta–clinoptilolite composite was 33.51 wt% while beta zeolite catalyst produced 35.58 wt% light hydrocarbons in upgrading process. Ultrasound irradiated composite showed more stable structure in catalytic cracking procedure compared to conventionally mixed composite. After 5 h time on stream, relative crystallinity of clinoptilolite phase in the conventionally mixed composite was reduced by 34.5% while sonicated sample remarkably preserved its structure during the reaction and only 1% reduction occurred for this sample.

Beta–clinoptilolite composite synthesized in the presence of ultrasound irradiation exhibited high stability in heavy oil upgrading process while producing equal amount of light fuels and lower amount of coke compared to beta zeolite catalyst.

Application of Reverse Micelle Sol⁻Gel Synthesis for Bulk Doping and Heteroatoms Surface Enrichment in Mo-Doped TiO₂ Nanoparticles

TiO₂ nanoparticles containing 0.0, 1.0, 5.0, and 10.0 wt.% Mo were prepared by a reverse micelle template assisted sol–gel method allowing the dispersion of Mo atoms in the TiO₂ matrix. Their textural and surface properties were characterized by means of X-ray powder diffraction, micro-Raman spectroscopy, N₂ adsorption/desorption isotherms at −196 °C, energy dispersive X-ray analysis coupled to field emission scanning electron microscopy, X-ray photoelectron spectroscopy, diffuse reflectance UV–Vis spectroscopy, and ζ-potential measurement. The photocatalytic degradation of Rhodamine B (under visible light and low irradiance) in water was used as a test reaction as well. The ensemble of the obtained experimental results was analyzed in order to discover the actual state of Mo in the final materials, showing the occurrence of both bulk doping and Mo surface species, with progressive segregation of MoO_x species occurring only at a higher Mo content.

Sustainable removal of pernicious arsenic and cadmium by a novel composite of MnO2 impregnated alginate beads: A cost-effective approach for wastewater treatment

There is a dire necessity of developing low cost waste water treatment systems, for the efficient removal of noxious heavy metals (and metalloids) such as Arsenic (As) and Cadmium (Cd). Magnetic biopolymer (CABs-MO) was synthesized by the entrapment of nanocrystalline MnO₂ in the polymeric microcapsules of calcium alginate (CABs). Batch experiments were conducted under constant pH (6.5), temperature (25^OC), different initial concentrations (30-300 mg L^-1) and contact times (0-48 h) to study the adsorption isotherms and removal kinetics of pristine (CABs) and hybrid biopolymer (CABs-MO) for the removal of As and Cd. The pseudo-equilibrium process was mathematically well explained by the pseudo-second-order kinetic (R² ≥ 0.99) and Langmuir isotherm model (R² ≥ 0.99) with the highest monolayer sorption capacity of 63.6 mg g^-1 for Cd on CABs-MO. The As removal rate was maximum up to 6.5 mg g^-1 after 12 h of contact period in a single contaminant system than in the mixed contaminant (As + Cd) system (0.8 mg g^-1), though the effect was non-significant for Cd (p < 0.05; t-test). The performance of the 10 mM HCl as a regenerating agent was superior (for As in comparison to Cd, p < 0.05; t-test) compared to distilled water (DW) through three to five regeneration cycles. Therefore, the obtained results clearly validate the feasibility of CABs-MO as a potential promising adsorbent for removing metal contaminants from the wastewater. Further research is required to study the decontamination of emerging contaminants with such novel composite beads characterized by varied physico-chemical properties.

The three-dimensional flower-like Bi2WO6 assisted by ethanolamine through a microwave method for efficient photocatalytic activity

The three-dimensional flower-like Bi2WO6 was synthesized through a one-step microwave method (the reaction temperature was 434 K and the reaction took 10 min) with the assistance of ethanolamine (EA). The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, ultraviolet-visible spectroscopy, PL, X-ray photoelectron spectroscopy and Brunauer-Emmett-Teller analysis. Methyl orange was used as target pollutant to evaluate the photocatalysis property of samples. Furthermore, the influence of the mechanism of EA on the structure and catalytic performance of Bi2WO6 was discussed. The detailed characterizations revealed that the three-dimensional flower-like Bi2WO6 was successfully synthesized with the assistance of EA. The results confirmed that EA significantly influenced the morphology of Bi2WO6 products. The addition of EA can effectively alter the pressure of the reaction and improve the crystal phase and structure of Bi2WO6 photocatalysts, enhancing the photocatalytic activity of samples and improving the photocatalytic efficiency. EA can serve as an assembling agent and structure-directing agent resulting in the formation of flower-like architectures. With the increase of the amount of EA, the as-prepared Bi2WO6 sample gradually forms a flower-like structure, leading to a shorter time of light holes migrating to the surface of the catalyst. It makes the compound rate significantly decreased, and improves the photocatalytic efficiency of the sample.

Highly stable binder free CNTs/rGO aerogel electrode for decolouration of methylene blue & palm oil mill effluent via electro-Fenton oxidation process

In this study, single wall carbon nanotubes (CNTs)/reduced graphene oxides (rGO) aerogels were prepared by a one-pot hydrothermal process without using a binder.

Fine particle attachment to quartz sand in the presence of multiple interacting dissolved components

In natural aquatic systems water chemistry is complicated and fine particles encounter multiple water components simultaneously, yet the combined effects of some multiple components on the fate and transport of these particles have not been elucidated. In this study nTiO₂ and illite colloid attachment to quartz sand was investigated in 1 mM NaCl and 0.5 mM CaCl₂ background solutions using a range of phosphate concentrations (0 to 10 mg/L) at pH 5 and 9. The results obtained from the batch experiments indicated that without using phosphate, nTiO₂ aggregation and attachment was strongly influenced by pH and Ca²⁺, both of which modified nTiO₂ surface charges. nTiO₂ attachment was high in CaCl₂ solution at pH 9 due to attractive forces between nTiO₂ and sand, as well as ripening. Furthermore, phosphate adsorption to nTiO₂ was higher in CaCl₂ solution at pH 9 than that at pH 5 due to attractive forces between nTiO₂ and phosphate anions, and also potential surface precipitation of Ca-P minerals at pH 9. Phosphate adsorption to illite was low owing to strong repulsive forces between illite and phosphate. The effect of phosphate on nTiO₂ and illite attachment to sand was influenced by pH and cation valency. A decreasing trend in nTiO₂ attachment with phosphate addition was observed in NaCl solution at pH 5 and 9, and in CaCl₂ solution at pH 5; however, in CaCl₂ solution at pH 9, the surface charge of nTiO₂ reversed from negative to positive and a substantial amount of nTiO₂ attached to sand. Moreover, illite attachment to sand was much lower than that of nTiO₂ under all the conditions tested in this study. These findings are important for understanding of the fate and transport of nTiO₂ and illite colloids in natural aquatic systems where various anions and cations co-exist.

Preparation, performances and mechanisms of magnetic Saccharomyces cerevisiae bionanocomposites for atrazine removal

Saccharomyces cerevisiae and nanoparticles of iron oxide (Fe₃O₄) which were linked with chitosan (CS) through epichlorohydrin (ECH) were encapsulated in calcium alginate to prepare a novel type of bionanocomposites. Characterization results showed that the Fe₃O₄-ECH-CS nanoparticles were quasi-spherical with an average diameter of 30 nm to which chitosan was successfully attached through epichlorohydrin. The saturation magnetization value of the nanoparticles was 21.88 emu/g, and ferrous and ferric irons were simultaneously observed in the magnetic nanoparticles. Data of atrazine removal by yeasts showed that both inactivated and live yeasts could decrease the concentration of atrazine effectively. The inactivated yeasts achieved 20% removal rate, which indicated that adsorption by the yeasts also played a role in the removal. Removal efficiency of atrazine was maximized at 88% under 25 °C, pH of 7 and an initial atrazine concentration of 2 mg/L. When the magnetic bionanocomposite was recycled and reused twice, only 12% and 20% drop in removal efficiency was observed at the first time and the second time severally. So, atrazine could be used by the yeasts as the sole carbon source for growth and multiplication, and both adsorption and biodegradation by the bionanocomposite contributed to atrazine removal.

Synthesis of a benzyl-grafted alginate derivative and its effect on the colloidal stability of nanosized titanium dioxide aqueous suspensions for Pickering emulsions

TiO₂ nanoparticles (nano-TiO₂) as one of the most extensively used nanoscale materials easily undergo spontaneous aggregation and gravity sedimentation ascribed to their high adsorption energy, which significantly restricts their actual applications. For this reason, a benzyl-grafted alginate derivative (BAD) with good colloidal interface activity, prepared by a bimolecular nucleophilic substitution (S_N2) reaction, was used as the dispersant to stabilize nano-TiO₂. The structure and colloidal properties of BAD was evaluated by FT-IR spectroscopy, ¹H NMR spectroscopy, thermal gravimetric analysis (TGA) and dynamic light scattering (DLS). The effects of pH and ionic strength on the dispersion stability of BAD/nano-TiO₂ suspensions were also examined by DLS. To further probe its feasibility as a drug delivery system, the BAD/nano-TiO₂ complex was applied as particulate emulsifiers to fabricate drug-loaded Pickering emulsions. Meanwhile, the morphology properties and the sustained release performance of the drug-loaded Pickering emulsions were also investigated. Experimental results showed that the adsorption of BAD on nano-TiO₂ was achieved by an intermolecular hydrogen bond between the carboxylic functional groups of BAD and the Ti–OH of TiO₂. The adsorption of BAD enhanced the electrostatic repulsion and steric hindrance between nano-TiO₂ improving the dispersion stability of nano-TiO₂ at different pH and ionic strength. Additionally, the obtained Pickering emulsions displayed good drug-loading capacity and sustained release performance with the release mechanism of non-Fickian transport, which exhibited great potential in the pharmaceutical field.

TiO₂ nanoparticles (nano-TiO₂) easily undergo spontaneous aggregation and gravity sedimentation ascribed to their high adsorption energy, which significantly restrict their actual applications.

miR-96-5p and miR-101-3p as potential intervention targets to rescue TiO2NP-induced autophagy and migration impairment of human trophoblastic cells

Autophagy induced by titanium dioxide nanoparticles (TiO₂NPs) has been realized nowadays, but the underlying mechanisms remain largely unknown.

Yield cultivation of magnetotactic bacteria and magnetosomes: A review

Magnetotactic bacteria (MTB) have started to be employed for the biosynthesis of magnetic nanoparticles, due to the rapidly increasing demand for nanoparticles in biomedical, biotechnology and environmental protection. MBT are the group of prokaryotes that have the ability to produce bio-magnetic minerals or bio-magnetic crystals of either magnetite (Fe₃ O₄ ) or greigite (Fe₃ S₄ ) in numerous shapes and size ranges, known as magnetosomes (MS). MS compel MTB to respond to the applied external magnetic field. However, it is extremely difficult to grow MTB and produce high yield of MS under artificial environmental conditions, thus creating a major hurdle to relocate MTB technology from laboratory scale to industrial or commercial level. Therefore, to best of our knowledge this review is the first attempt to highlight existing research developments about the laboratory scale and mass production of MS by MTB. Moreover, the optimum culture media and environmental conditions used for the cultivation of MTB were also considered. Finally, future research is encouraged for the improvement of MS yield which will result in the development of advanced nanotechnology/magnetotechnology.

The impact of zeta potential changes on Ceratium hirundinella cell removal and the ability of cells to restore its natural surface charge during drinking water purification

The removal efficacy ofCeratiumcells from source water was evaluated. The best ZP for coagulation were achieved with organic polymer and Ca(OH)₂. Cells were able to restore their ZP after 120 and 240 minutes settling time.

Fate and transformation of nanoparticles (NPs) in municipal wastewater treatment systems and effects of NPs on the biological treatment of wastewater: a review

Fate, transformation of NPs in WWTP & effects on wastewater treatment.

DNA assembled metal nanoclusters: synthesis to novel applications

In this review, we have discussed the emergence of promising environmental-benign DNA assembled fluorescent metal nanoclusters and their unique electronic structures, unusual physical and chemical properties.