Surface modification of TiO2/ZnO nanoparticles by organic acids with enhanced methylene blue and rhodamine B dye adsorption properties

The United Nations Organization (UNO) has revealed that approximately 2.1 billion people do not have access to treated water. Methylene blue (MB) and rhodamine B are produced as water pollutants in textile, plastic, and dye industries. In this study, oxalic acid or lactic acid surface-modification were applied to TiO₂/ZnO nanoparticles aiming to improve antibacterial and adsorption properties. The mixtures containing the corresponding acid and nanoparticles in 0.25 : 1/0.5 : 1 ratios of ZnO and TiO₂ correspondingly were subjected to ultrasonic treatment with a catenoidal ultrasonic probe coupled to a homemade ultrasonic generator with an output power of 750 W, wave amplitude of 50% and variable frequency in the range of 15-50 kHz. To verify the influence of the ultrasonic treatment, different treatment times of 30, 45, 60, and 90 min were applied. Unmodified and modified TiO₂/ZnO nanoparticles were characterized by FTIR, TGA, XRD, SEM, and XPS. From the results, obtained from the physicochemical characterization, in the ZTO90 and ZTL90 samples a greater modification was shown. The SEM images showed that a coating was present on the surface of the ceramic particles of the ZTL90 sample. The O 1s deconvolution in the XPS spectra indicates a greater presence of C[double bond, length as m-dash]O bonds in the ZTL90 sample. In parallel, the sample ZTL90 presented 85 and 89% adsorption efficiency for MB and rhodamine B dyes in a time of 12 min, and important antibacterial activity against E. coli and S. epidermis could be evidenced.

Columnar nitrogen-doped ZnO nanostructured thin films obtained through atomic layer deposition

The present study was aimed to develop nitrogen-doped nanostructured ZnO thin films. These films were produced in a sequential procedure involving the atomic layer deposition technique, and a hydrothermal process supported by microwave heating. Employing the atomic layer deposition technique, through self-limited reactions of diethylzinc (DEZn) and H₂O, carried out at 3.29 × 10^-4atm and 190 °C, a high-quality ZnO seed was grown on a Si (100) substrate, producing a textured film. In a second stage, columnar ZnO nanostructures were grown perpendicularly oriented to the silicon substrate on those films, using a solvothermal process in a microwave heating facility, employing Zn(NO₃)₂as zinc precursor, while hexamethylenetetramine (HMTA) was used to produce the bridging of Zn²⁺ions. The consequence of N-doping concentration on the physicochemical properties of ZnO thin films was studied. The manufactured films were structurally analyzed by scanning electron microscopy and x-ray diffraction. Also, x-ray photoelectron spectroscopy, Raman, and UV-vis spectroscopies were used to provide further insight on the effect of nitrogen doping. The N-doped films displayed textured wurtzite-like structures that changes their preferential growth from the (002) to the (100) crystallographic plane, apparently promoted by the increase of nitrogen precursor. It is also shown that nitrogen-doped films undergo a reduction in their bandgap, compared to ZnO. The methodology presented here provides a viable way to perform high-quality N-ZnO nanostructured thin films.

Photocatalytic performance of nitrogen doped ZnO structures supported on graphene oxide for MB degradation

In the present work, the photocatalytic efficiency of a novel system based on ZnO doped with nitrogen (ZT) and supported on graphene oxide (GO) is investigated. ZnO synthesis and their N doping were carried out in a microwave reactor using thiourea as nitrogen source, while the GO was prepared through a variation of the Hummers' method. Structural, morphological and photochemical characterization of the developed material was performed by X-ray diffraction (XRD), UV-Vis spectroscopy, energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), analysis by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The compounds were used to photodegrade the methylene blue molecule, which confirms the efficiency of nitrogen doped supported system compared to pristine ZnO. The degradation percentage of MB under UV energy using nitrogen-doped ZnO/GO, in a time of 35 min, reached 98% degradation; while using visible light 93% of degradation was reached.

Graphene Nanoplatelets Modified with Amino-Groups by Ultrasonic Radiation of Variable Frequency for Potential Adsorption of Uremic Toxins

Chronic kidney disease (CKD) is a worldwide public health problem. In stages III and IV of CKD, uremic toxins must be removed from the patient by absorption, through a treatment commonly called hemodialysis. Aiming to improve the absorption of uremic toxins, we have studied its absorption in chemically modified graphene nanoplatelets (GNPs). This study involved the reaction between GNPs and diamines with reaction times of 30, 45 and 60 min using ultrasound waves of different amplitudes and frequencies. Functionalized GNPs were analyzed by Fourier Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy and energy dispersitive spectroscopy (SEM-EDS), and Thermogravimetric analysis (TGA). The analysis of the functional groups confirmed the presence of amide and hydroxyl groups on the surface of the GNPs by reactions of diamines with carboxylic acids and epoxides. Adsorption of uremic toxins was determined using equilibrium isotherms, where the maximum percentage of removal of uremic toxins was 97%. Dispersion of modified graphene nanoplatelets was evaluated in water, ethanol and hexane, as a result of this treatment was achieved a good and effective dispersion of diamines-modified graphene nanoplatelets in ethanol and hexane. Finally, the results of hemolysis assays of the modified graphene with amine demonstrated that it was not cytotoxic when using 500 mg/mL. The samples of modified graphene demonstrated low degree of hemolysis (<2%), so this material can be used for in vivo applications such as hemodialysis.

Facile synthesis of novel calcium silicate hydrated-nylon 6/66 nanocomposites by solution mixing method

In this article a facile and green procedure for the synthesis of novel calcium silicate hydrated-nylon 6/66 nanocomposites is proposed. Calcium silicate hydrate (CSH) was synthesized by a hydrolysis technique assisted by ultrasound and using sodium dodecyl sulphate (SDS) as surfactant. CSH-nylon 6/66 nanocomposites were obtained by a solution mixing method at CSH loadings of 2.5, 25, 50 and 75 weight percent (samples CA, CD, CB and CC, respectively). The synthesis of CSH was confirmed by DRX and ATR-FTIR techniques; the CSH sample presents as mesoporous with a diameter between 3.34 nm and 52.68 nm and an average size of 27.07 nm; the specific surface area of the CSH sample was 343.99 m² g⁻¹. The formation of the CSH-nylon 6/66 nanocomposites was confirmed by ATR-FTIR, SEM, XRD, TGA, DSC and XPS techniques. The crystallization and melting temperatures (T_m and T_c, respectively) of CSH-nylon 6/66 nanocomposites occur at a slightly lower temperatures than those of neat Ny 6/66. These results suggest a slight decrease of the crystallite size and crystallization rate of nylon 6/66. The fusion enthalpy (ΔH_f) decreases with increase in CSH content in nylon 6/66, which can be associated to a good dispersion. The XRD peaks of the nylon 6/66 at 19.99° and 23.77° were displaced at slightly higher values of 2θ with the incorporation of CSH in the polymer forming nanocomposite materials.

In this work it was possible to synthesize novel CSH-nylon 6/66 nanocomposites using a simple and easy methodology such as the solution mixing method and using green solvents like water, formic acid and ethanol.

Degradation studies on segmented polyurethanes prepared with HMDI, PCL and different chain extenders

Biodegradable segmented polyurethanes (BSPUs) were prepared with poly(caprolactone) as a soft segment, 4,4'-methylene bis (cyclohexyl isocyanate) and either butanediol (BSPU1) or dithioerythritol (BSPU2) as a chain extender. BSPU samples were characterized in terms of their physicochemical properties and their hemocompatibility. Polymers were then degraded in acidic (HCl 2N), alkaline (NaOH 5M) and oxidative (H(2)O(2) 30wt.%) media and characterized by their mass loss, Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Undegraded BSPU1 and BSPU2 exhibited different properties, such as the glass transition temperature T(g) of the soft segment (-25 vs. 4 degrees C), mechanical properties (600% vs. 900% strain to break) and blood coagulating properties (clotting time=11.46 vs. 8.13min). After acidic and alkaline degradation, the disappearance of the 1728cm(-1) band of polycaprolactone (PCL) on both types of BSPU was detected by FTIR. However, the oxidative environment did not affect the soft segment severely as the presence of PCL crystalline domains were observed both by DSC (melting temperature T(m)=52.8 degrees C) and XRD (2theta=21.3 degrees and 23.7 degrees ). By TGA three decomposition temperatures were recorded for both BSPU samples, but the higher decomposition temperature was enhanced after acidic and alkaline degradation. The formation of the porous structure on BSPU1 was observed by SEM, while a granular surface was observed on BSPU2 after alkaline degradation.

Characterization of extracellular polymers synthesized by tropical intertidal biofilm bacteria

AIM

This study was performed to determine the potential of tropical intertidal biofilm bacteria as a source of novel exopolymers (EPS).

METHODS AND RESULTS

A screening procedure was implemented to detect EPS-producing biofilm bacteria. Isolates MC3B-10 and MC6B-22, identified respectively as a Microbacterium species and Bacillus species by 16S rDNA and cellular fatty acids analyses, produced different EPS, as evidenced by colorimetric and gas chromatographic analyses. The polymer produced by isolate MC3B-10 displays significant surfactant activity, and may chelate calcium as evidenced by spectroscopic analysis.

CONCLUSIONS

Polymer MC3B-10 appears to be a glycoprotein, while EPS MC6B-22 seems to be a true polysaccharide dominated by neutral sugars but with significant concentrations of uronic acids and hexosamines. EPS MC3B-10 possesses a higher surfactant activity than that of commercial surfactants, and given its anionic nature, may chelate cations thus proving useful in bioremediation. The chemical composition of polymer MC6B-22 suggests its potential biomedical application in tissue regeneration.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of a Microbacterium species producing EPS with surfactant properties, which expands our knowledge of the micro-organisms capable of producing these biomolecules. Furthermore, this work shows that tropical intertidal environments are a nonpreviously recognized habitat for bioprospecting EPS-producing bacteria, and that these molecules might be involved in ecological roles protecting the cells against dessication.