Mesoporous anatase TiO₂nanoparticles are produced by employing a facile green chemistry approach at low temperature with soluble starch as the template in this work. The obtained TiO₂photocatalyst is visible-light active with good photocatalytic activities.

Photocatalytic degradation by the titanium dioxide (TiO₂) photocatalyst attracts tremendous interest due to its promising strategy to eliminate pollutants from wastewater. The floating photocatalysts are explored as potential candidates for practical wastewater treatment applications that could overcome the drawbacks posed by the suspended TiO₂ photocatalysis system. The problem occurs when the powdered TiO₂ applied directly into the treated solution will form a slurry, making its reuse become a difficult step after treatment. In this study, the immobilization of titanium dioxide nanoparticles (TiO₂ NPs) on the floating substrate (cork) employing polyvinyl alcohol (PVA) as a binder to anchor TiO₂ NPs on the surface of the cork was carried out. Characterizations such as Fourier transformer infrared, X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV–vis), zeta potential, photoluminescence spectroscopy, femtosecond to millisecond time-resolved visible to mid-IR absorption spectroscopy, ion chromatography, and scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDX) analyses were employed. XRD analysis revealed the formation of anatase-phase TiO₂ NPs. The results demonstrated that the crystallite size was 9.36 nm. The band gap energy of TiO₂ NPs was determined as 3.0 eV. PL analysis verified that TiO₂ NPs possessed a slower recombination rate of electron–hole pairs as compared to anatase TiO₂. The result was attributed by the behavior of photogenerated charge carriers on TiO₂ NPs, which existed as shallowly trapped electrons that could survive longer than a few milliseconds in this study. Furthermore, SEM–EDX analysis indicated that TiO₂ NPs were well distributed on the surface of the cork. At the optimal mole ratio of TiO₂/PVA (1:8), the TiO₂/PVA/cork floating photocatalyst degraded at 98.43% of methylene blue (MB) under a visible light source which performed better than under sunlight irradiation (77.09% of MB removal) for 120 min. Besides, the mineralization result has measured the presence of sulfate anions after photocatalytic activities, which achieved 86.13% (under a visible light source) and 65.34% (under sunlight). The superior photodegradation performance for MB was mainly controlled by the reactive oxygen species of the superoxide radical (^•O₂^–). The degradation kinetics of MB followed the first-order kinetics. Meanwhile, the Langmuir isotherm model was fitted for the adsorption isotherm. The floating photocatalyst presented good reusability, resulting in 78.13% of MB removal efficiency even after five cycles. Our TiO₂/PVA/cork floating photocatalyst fabrication and high photocatalytic performance are potentially used in wastewater treatment, especially under visible light irradiation.

Titanium dioxide nanoparticles (TiO₂ NPs) have attracted tremendous interest owing to their unique physicochemical properties. However, the cytotoxic effect of TiO₂ NPs remains an obstacle for their wide-scale applications, particularly in drug delivery systems and cancer therapies. In this study, the more biocompatible nitrogen-doped graphene quantum dots (N-GQDs) were successfully incorporated onto the surface of the TiO₂ NPs resulting in a N-GQDs/TiO₂ nanocomposites (NCs). The effects of the nanocomposite on the viability of the breast cancer cell line (MDA-MB-231) was evaluated. The N-GQDs and N-GQDs/TiO₂ NCs were synthesised using a one- and two-pot hydrothermal method, respectively while the TiO₂ NPs were fabricated using microwave-assisted synthesis in the aqueous phase. The synthesised compounds were characterised using Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM) and UV-visible spectrophotometry. The cell viability of the MDA-MB-231 cell line was determined using a CellTiter 96® AQueous One Solution Cell Proliferation (MTS) assay. The obtained results indicated that a monodispersed solution of N-GQDs with particle size 4.40 ± 1.5 nm emitted intense blue luminescence in aqueous media. The HRTEM images clearly showed that the TiO₂ particles (11.46 ± 2.8 nm) are square shaped. Meanwhile, TiO₂ particles were located on the 2D graphene nanosheet surface in N-GQDs/TiO₂ NCs (9.16 ± 2.4 nm). N-GQDs and N-GQDs/TiO₂ NCs were not toxic to the breast cancer cells at 0.1 mg mL⁻¹ and below. At higher concentrations (0.5 and 1 mg mL⁻¹), the nanocomposite was significantly less cytotoxic compared to the pristine TiO₂. In conclusion, this nanocomposite with reduced cytotoxicity warrants further exploration as a new TiO₂-based nanomaterial for biomedical applications, especially as an anti-cancer strategy.

Titanium dioxide nanoparticles (TiO₂ NPs) have been proven to be potential candidates in cancer therapy, particularly photodynamic therapy (PDT). However, the application of TiO₂ NPs is limited due to the fast recombination rate of the electron (e⁻)/hole (h⁺) pairs attributed to their broader bandgap energy. Thus, surface modification has been explored to shift the absorption edge to a longer wavelength with lower e⁻/h⁺ recombination rates, thereby allowing penetration into deep-seated tumors. In this study, TiO₂ NPs and N-doped graphene quantum dots (QDs)/titanium dioxide nanocomposites (N-GQDs/TiO₂ NCs) were synthesized via microwave-assisted synthesis and the two-pot hydrothermal method, respectively. The synthesized anatase TiO₂ NPs were self-doped TiO₂ (Ti³⁺ ions), have a small crystallite size (12.2 nm) and low bandgap energy (2.93 eV). As for the N-GQDs/TiO₂ NCs, the shift to a bandgap energy of 1.53 eV was prominent as the titanium (IV) tetraisopropoxide (TTIP) loading increased, while maintaining the anatase tetragonal crystal structure with a crystallite size of 11.2 nm. Besides, the cytotoxicity assay showed that the safe concentrations of the nanomaterials were from 0.01 to 0.5 mg mL⁻¹. Upon the photo-activation of N-GQDs/TiO₂ NCs with near-infrared (NIR) light, the nanocomposites generated reactive oxygen species (ROS), mainly singlet oxygen (¹O₂), which caused more significant cell death in MDA-MB-231 (an epithelial, human breast cancer cells) than in HS27 (human foreskin fibroblast). An increase in the N-GQDs/TiO₂ NCs concentrations elevates ROS levels, which triggered mitochondria-associated apoptotic cell death in MDA-MB-231 cells. As such, titanium dioxide-based nanocomposite upon photoactivation has a good potential as a photosensitizer in PDT for breast cancer treatment.

The optical frequency response and changes to the dielectric and optical parameters due to annealing temperature variation (200–500 °C) of sol–gel derived CuCoO_x thin film coatings were investigated. The optical constants such as absorption coefficient, band-gaps, Urbach energy, complex refractive index, complex dielectric constants, optical dispersion parameters, and energy loss functions were determined from reflectance data analysis recorded in the ultraviolet to near-infrared (190–2200 nm) range. The absorption coefficient and the broadening of absorption edge (steepness parameter), energy band-gaps, Urbach energy, loss tangent and energy loss functions decreased with the increase in annealing temperatures. The refractive index displayed normal dispersion behaviors at higher frequency with the maximum value at a temperature of 500 °C. First-principles simulations, density functional theory (DFT+U) as implemented in the Cambridge Serial Total Energy Package (CASTEP), based on a cluster structure of Cu_0.5Co_2.5O₄ system, optimized the crystalline structure and calculated the electronic structure of the framework. The calculated density of states (DOS) and associated absorption coefficient and dielectric constant results reasonably support the experimental findings.