Unrefined and Milled Ilmenite as a Cost-Effective Photocatalyst for UV-Assisted Destruction and Mineralization of PFAS.

Per- and polyfluoroalkyl substances (PFAS) are fluorinated and refractory pollutants that are ubiquitous in industrial wastewater. Photocatalytic destruction of such pollutants with catalysts such as TiO2 and ZnO is an attractive avenue for removal of PFAS, but refined forms of such photocatalysts are expensive. This study, for the first time, utilized milled unrefined raw mineral ilmenite, coupled to UV-C irradiation to achieve mineralization of the two model PFAS compounds perfluorooctanoic acid (PFOA) and perfluoro octane sulfonic acid (PFOS). Results obtained using a bench-scale photocatalytic reactor system demonstrated rapid removal kinetics of PFAS compounds (>90% removal in less than 10 h) in environmentally-relevant concentrations (200-1000 ppb). Raw ilmenite was reused over three consecutive degradation cycles of PFAS, retaining >80% removal efficiency. Analysis of degradation products indicated defluorination and the presence of shorter-chain PFAS intermediates in the initial samples. End samples indicated the disappearance of short-chain PFAS intermediates and further accumulation of fluoride ions, suggesting that original PFAS compounds underwent mineralization due to an oxygen-radical-based photocatalytic destruction mechanism induced by TiO2 present in ilmenite and UV irradiation. The outcome of this study implies that raw ilmenite coupled to UV-C is suitable for cost-effective reactor operation and efficient photocatalytic destruction of PFAS compounds.

Preparation and Characterization of Photoluminescent Graphene Quantum Dots from Watermelon Rind Waste for the Detection of Ferric Ions and Cellular Bio-Imaging Applications.

Graphene quantum dots (GQDs) were synthesized using watermelon rind waste as a photoluminescent (PL) agent for ferric ion (Fe3+) detection and in vitro cellular bio-imaging. A green and simple one-pot hydrothermal technique was employed to prepare the GQDs. Their crystalline structures corresponded to the lattice fringe of graphene, possessing amide, hydroxyl, and carboxyl functional groups. The GQDs exhibited a relatively high quantum yield of approximately 37%. Prominent blue emission under UV excitation and highly selective PL quenching for Fe3+ were observed. Furthermore, Fe3+ could be detected at concentrations as low as 0.28 µM (limit of detection), allowing for high sensitivity toward Fe3+ detection in tap and drinking water samples. In the bio-imaging experiment, the GQDs exhibited a low cytotoxicity for the HeLa cells, and they were clearly illuminated at an excitation wavelength of 405 nm. These results can serve as the basis for developing an environment-friendly, simple, and cost-effective approach of using food waste by converting them into photoluminescent nanomaterials for the detection of metal ions in field water samples and biological cellular studies.

Investigation of Functionalized Surface Charges of Thermoplastic Starch/Zinc Oxide Nanocomposite Films Using Polyaniline: The Potential of Improved Antibacterial Properties.

Improving the antibacterial activity of biodegradable materials is crucial for combatting widespread drug-resistant bacteria and plastic pollutants. In this work, we studied polyaniline (PANI)-functionalized zinc oxide nanoparticles (ZnO NPs) to improve surface charges. A PANI-functionalized ZnO NP surface was prepared using a simple impregnation technique. The PANI functionalization of ZnO successfully increased the positive surface charge of the ZnO NPs. In addition, PANI-functionalized ZnO improved mechanical properties and thermal stability. Besides those properties, the water permeability of the bionanocomposite films was decreased due to their increased hydrophobicity. PANI-functionalized ZnO NPs were applied to thermoplastic starch (TPS) films for physical properties and antibacterial studies using Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The PANI-functionalized ZnO bionanocomposite films exhibited excellent antibacterial activity for both E. coli (76%) and S. aureus (72%). This result suggests that PANI-functionalized ZnO NPs can improve the antibacterial activity of TPS-based bionanocomposite films.

Alkali/zinc-activated fly ash nanocomposites for dye removal and antibacterial applications.

Fly ash (FA), obtained as waste materials from industrial power plants, is generated in large quantities and low recycling. In this study, re-generation of waste FA as cost-effective materials with adsorbent and antibacterial applications was assessed. Alkaline/zinc-activated fly ash nanocomposite (A-FA/Zn) was prepared using one-pot hydrothermal technique. Those nanocomposites are characterized by high surface area and negatively surface charge, which are important influences contributing to an enhancement in adsorption capacity via increase in the number of adsorptive sites and electrostatic interaction between dye molecules-nanocomposites. Additionally, the presence of Zn ions in the prepared nanocomposites represents a key advantage with respect to enhancing antibacterial activity. The feasibility of further enhancing adsorption and antibacterial mechanisms was also examined. It is anticipated that the findings of this study will provide useful information with respect to the development of simple, eco-friendly and low-cost A-FA/Zn with multifunctional applications as organic dye removal and antibacterial purposes.

Effect of GO Additive in ZnO/rGO Nanocomposites with Enhanced Photosensitivity and Photocatalytic Activity.

Zinc oxide/reduced graphene oxide nanocomposites (ZnO/rGO) are synthesized via a simple one-pot solvothermal technique. The nanoparticle-nanorod turnability was achieved with the increase in GO additive, which was necessary to control the defect formation. The optimal defect in ZnO/rGO not only increased ZnO/rGO surface and carrier concentration, but also provided the alternative carrier pathway assisted with rGO sheet for electron-hole separation and prolonging carrier recombination. These properties are ideal for photodetection and photocatalytic applications. For photosensing properties, ZnO/rGO shows the improvement of photosensitivity compared with pristine ZnO from 1.51 (ZnO) to 3.94 (ZnO/rGO (20%)). Additionally, applying bending strain on ZnO/rGO enhances its photosensitivity even further, as high as 124% at r = 12.5 mm, due to improved surface area and induced negative piezoelectric charge from piezoelectric effect. Moreover, the photocatalytic activity with methylene blue (MB) was studied. It was observed that the rate of MB degradation was higher in presence of ZnO/rGO than pristine ZnO. Therefore, ZnO/rGO became a promising materials for different applications.