Extractability of Rice Husk Waste Using Green Gamma Radiation for Dye Elimination in Laboratory-Scale Sorption System: Equilibrium Isotherm and Kinetic Analysis.

Nowadays, the use of natural materials and especially "waste" valorization has evolved and attracted the wide attention of scientists and academia. In this regard, the use of rice husk (RH) powder as a naturally abundant and cheap byproduct material is gaining superior attention. However, improving the physicochemical properties of such RH is still under research. In the current investigation, the modification of rice husk (RH) via γ-irradiation has shown to be a promising green tool to meet such a need. Clean, prepared, powdered RH samples were subjected to various γ-radiation doses, namely 5, 10, 15 and 25 kGy, and the corresponding samples were named as RH-0, RH-5, RH-10, RH-15, RH-15 and RH-25. Then, the samples were characterized via scanning electron microscopy (SEM). After irradiation, the samples showed an increase in their surface roughness upon increasing the γ-radiation up to 15 kGy. Furthermore, the sorption capacity of the irradiated RH samples was investigated for eliminating Urolene Blue (UB) dye as a model pharmaceutical effluent stream. The highest dye uptake was recorded as 14.7 mg/g, which corresponded to the RH-15. The adsorption operating parameters were also investigated for all of the studied systems and all adsorbents showed the same trend, of a superior adsorption capacity at pH 6.6 and high temperatures. Langmuir and Freundlich isotherm models were also applied for UB adsorption and an adequate fitted isotherm model was linked with Langmuir fitting. Moreover, the pseudo-second-order kinetic model provided the best fit for the adsorption data. Experimental assays confirmed that the UB dye could be successfully eradicated feasibly from the aqueous stream via a sustainable green methodology.

Cost-Effective and Efficient Cool Nanopigments Based on Oleic-Acid-Surface-Modified ZnO Nanostructured.

In this paper, as-synthesized and oleic acid (OA)-surface-treated zinc oxide (ZnO) nanocrystals were successfully synthesized and investigated for cool-nanopigment applications. ZnO nanocrystals were synthesized using the thermal decomposition method. The OA-surface-treated ZnO sample was obtained with an OA:ZnO ratio of 1:1. The structural, optical and morphological properties of the samples were characterized via X-ray diffraction (XRD), Fourier transform infrared (FTIR), UV-VIS-NIR diffused reflectance spectroscopy (DRS) and field-emission scanning electron microscopy (FE-SEM) techniques. ZnO nanocrystals possess a well-known zincate phase of ZnO, as confirmed for the as-synthesized sample with a reduction in the integrity of the ZnO crystalline structure upon the application of the OA coating. XRD peaks broadening and decreasing in crystallite size were obtained upon the surface modification of the ZnO by OA. The average crystallite size decreased from 31.5 to 17.4 nm, and the surface area changed from 23.37 to 7.48 m2/g upon OA treatment. These changes were attributed to the well-capping of the ZnO nanoparticles by OA, and, furthermore, OA increased the dispersion of the nanoparticles. The optical band gap of the investigated samples demonstrated a blue shift from 3.06 eV to 3.22 eV upon treatment. Both samples showed high NIR reflectance (RNIR∗) values, which makes them well qualified for use as cool nanopigments. Additionally, the as-synthesized sample showed an RNIR∗ value higher than that of the treated sample.

Polyaniline/Multi Walled Carbon Nanotubes-A Promising Photocatalyst Composite for Reactive Blue 4 Oxidation.

For the photocatalytic removal of the Reactive Blue 4 dye from an aqueous stream, new polyaniline/multi walled carbon nanotube nanocomposites (PANI-MWCNTs) were applied as a promising photocatalyst. The PANI-MWCNT nanocomposites were fabricated by aniline oxidation in the presence of MWCNTs using the typical direct oxidation polymerization route. The morphology, the Fourier transform infrared (FTIR) spectra and the UV-Vis absorbance spectra of the fabricated nanocomposites were studied and the attained data confirmed the good interaction between the MWCNTs and PANI matrix. The PANI-MWCNTs nanocomposites were varied according to the wt%, the MWCNTs, which ranged from 0-10 wt% and the corresponding resultant samples are labeled as P-0, P-3, P-5, P-5, P-7 and P-10, respectively. Such composites showed the high potential for the removal of the Reactive Blue 4 dye containing pollutants from wastewater. The starting concentration of the dye pollutants was halved during the first 5 min of UV illumination. The oxidation technique of Reactive Blue 4 over the prepared nanocomposites were processed in a different way and the highest catalytic activity corresponded to P-7. The process reached the complete dye removal in low concentrations of contaminants. The kinetics of the removal followed the pseudo-second order regime which possesses high correlation coefficients with the k2 in the range of 0.0036-0.1115 L.mg-1.min-1 for the Reactive Blue 4 oxidation. In this regard, the combination of the PANI and MWCNTs showed a superior novel photocatalytic activity in the oxidation of commercial textile dying wastewater, namely Reactive Blue 4. This study is the starting point for future applications on an industrial scale since the successful performances of the PANI-MWCNT on commercial dye oxidation.

Ga-Doped ZnO Nanostructured Powder for Cool-Nanopigment in Environment Applications.

Gallium (Ga) doped zinc oxide (ZnO) nanocrystals were successfully synthesized via a γ-radiation-assisted polymer-pyrolysis route. Ga doped ZnO samples with Ga and ZnO precursor salts with molar ratios of 0%, 3%, 5%, and 10% were produced. A γ-radiation dosage of 1.5 kGy was used for polymerization initiation during the sample preparation. The properties of the obtained nanocrystal samples were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), UV-visible absorption, NIR-VIS-UV diffused reflectance, and high-resolution transmission electron microscopy (HR-TEM) characterization techniques. XRD results revealed the formation of ZnO nanocrystals with wurtzite structure for both Ga-doped and undoped ZnO samples. Noticeable increasing in the line broadening of the XRD peaks as well as pronounced decreasing of crystallite size were observed with the increasing Ga ratio in the samples. Optical peaks around Ga:ZnO samples showed a blueshift in the optical absorption peaks with increasing Ga content. These results are in good agreement with the dependency of crystallites size as well as grain size on Ga ratio obtained from XRD and TEM images, which make them fit well for the powder cool-pigment applications. The doped samples showed high values of NIR reflectance (RNIR*) with percentage varied from 84.25% to 89.05% that enabled them to qualify for cool-nanopigment applications. Furthermore, such doped samples registered low values of visible reflectance (RVIS*) that enabled to reduce the glare from the reflected visible sunlight.

Thermal Degradation of Polystyrene (PS) Nanocomposites Loaded with Sol Gel-Synthesized ZnO Nanorods.

Thermal degradation of polystyrene/ZnO (PS/ZnO) nanocomposites was investigated in this study. PS/ZnO polymer nanocomposites were prepared by using ZnO nanorods as nanofillers that were prepared via the sol-gel route. The as-prepared ZnO nanoparticles showed nanocrystallites in rod-like shapes with a non-uniform hexagonal cross-section and diameter varying from 40 to 75 nm. PS/ZnO nanocomposites with ZnO nanoparticles content ranging from 0-3 wt% are prepared via the common casting method. Even dispersion for ZnO nanoparticles within as-prepared PS/ZnO nanocomposites was verified through SEM/EDX measurements. Thermal degradation of the samples was checked by using the thermogravimetric (TG) analysis and differential scanning calorimetry (DSC) under non-isothermal conditions and a constant heating rate of 10 °C min. The thermal stability of the nanocomposite is elevated compared to that of pristine PS due to the addition of the ZnO nanoparticles. The homogeneity of the PS/ZnO nanocomposites is verified by systematic increases in thermal degradation with increasing ZnO content. The characterization degradation temperatures at different weight loss percentages of ZnO nanoparticles increase at high ZnO wt%. Static activation energy of decomposing is based on TGA data. Activation energies showed some enhancement after the addition of ZnO nanorods into the PS matrix. Enhancing the thermal stability of PS with ZnO addition within the investigated ZnO concentration range is verified by TG, DSC results.

Structural and Optical Characteristics of Highly UV-Blue Luminescent ZnNiO Nanoparticles Prepared by Sol-Gel Method.

A simple single pot sol-gel method is used to prepare ZnNiO nanoparticles at assorted Ni doping levels, 1, 3, 7 and 10 wt.%. Structural and optical properties of nanoparticles are studied by X-ray diffraction (XRD), UV-visible diffuse reflection spectroscopy (DRS), photoluminescence (PL) measurements, scanning electron microscopy (SEM), µ-Raman and X-ray photoelectron-spectroscopy (XPS). A single substitutional solid solution phase is detected in the wurtzite ZnNiO nanoparticles at various doping levels. XRD peak splitting and shifting is ascribed to reduced wurtzite character and presence of crystalline strain in nanoparticles at higher level of Ni doping. The Kubelka-Munk function of DRS data reveals the presence of the Burstein-Moss effect in the optical absorption of ZnNiO nanoparticles. Photoluminescence studies show intense UV-blue emission from ZnNiO nanoparticles. The UV PL also exhibits the Burstein-Moss blue shift in the ZnNiO luminescence. Raman analyses also confirms the wurtzite structure of ZnNiO nanoparticles; however, crystal structural defects and bond stiffness increase with Ni doping. The optical and structural studies presented in this work are pointing towards a multivalent Ni substitution in the nanoparticles.