Zeolite Y-supported carbon-doped TiO2 nanocomposites: Efficient solar photocatalysts for the purification of medicinal wastewater.

The existence of antibiotics in aquatic streams destroys water quality and thereby poses serious ecological hitches. Photocatalysis involving nanosemiconductors is an environmentally benign technique for the mineralization of antibiotics. Herein, we prepared a new visible light-sensitive photocatalyst, zeolite Y-supported carbon-doped TiO2 nanocomposite (zeolite Y-c-TiO2), for the elimination of cefazolin antibiotic in wastewater systems. The structural and optical properties of the synthesized nanocomposites were investigated by Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller surface area analysis (BET) as well as diffuse reflectance spectroscopy (UV-DRS) and photoluminescence spectroscopy (PL). The UV-Vis absorbance spectrum of zeolite Y-c-TiO2 exhibited a red shift towards longer wavelength with an increase in visible light absorption as compared to pure TiO2 nanoparticles and zeolite Y-supported TiO2 nanocomposites (zeolite Y-TiO2). Accordingly, the photocatalytic action of the zeolite Y-c-TiO2 for the degradation of methylene blue was evaluated under solar simulator, and it turned out to be highly efficient (100%) mineralization as compared to TiO2-nanoparticles (42%) and zeolite Y-TiO2 (62%) after 70 min irradiation for a 50mg L-1 methylene blue solution. Radical scavenging experiments revealed the involvement of hydroxyl radicals, superoxide radicals, and photogenerated holes in the degradation process. Consequently, zeolite Y-c-TiO2 was applied for the photocatalytic degradation of the cefazolin antibiotic in water, and complete degradation of cefazolin (50 mg L-1) was observed within 6 h of solar light irradiation on zeolite Y-c-TiO2. The degradation pathway of cefazolin was proposed by considering various intermediates detected via LC-MS analysis. The study points to the significant potential of zeolite Y-c-TiO2 photocatalyst for the purification of medicinal wastewater under sunlight.

Kaolin-graphene carboxyl incorporated TiO2 as efficient visible light active photocatalyst for the degradation of cefuroxime sodium.

A novel solar light active photocatalyst, TiO2/kaolin-graphene carboxyl nanocomposite was synthesized by hydrothermal method for the degradation of cephalosporin antibiotic, cefuroxime sodium. The synthesized photocatalyst was characterized by various analytical and spectroscopic techniques, including Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) thermogravimetry (TG), UV-Vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL). The prepared TiO2/kaolin-graphene carboxyl nanocomposite exhibited efficient photocatalytic degradation of methylene blue (MB) upon illumination with the solar simulator as compared to unmodified TiO2. The incorporation of both kaolin and graphene carboxyl was found to immobilize TiO2, enhancing the visible light absorption range of TiO2. Scavenger study revealed that hydroxyl radicals act as the main active species in the photocatalytic degradation process. The hydroxyl group present on kaolin surface reacts with photo-generated holes to increase the amount of hydroxyl radical, and further the graphene carboxyl plays a role to impede the recombination of photo-generated electron-hole pairs. Furthermore, the synthesized photocatalyst was found to degrade cefuroxime sodium within 90 min of sunlight illumination, indicating that TiO2/kaolin-graphene carboxyl nanocomposites would be very beneficial for pharmaceutical waste management through the advanced oxidation process. Mass spectral analysis was also carried out for elucidating the photocatalytic degradation pathway of cefuroxime sodium.

Photoinduced electron transfer upon supramolecular complexation of (porphyrinato)Sn-viologen with cucurbit[7]uril.

The synthesis of (porphyrinato)Sn-viologen, 1, and its supramolecular complexation with cucurbit[7]uril (CB[7]) were studied. 1H NMR spectroscopic studies obviously reveal that 1 forms a 1 : 2 supramolecular complex with CB[7] through the inclusion of viologen moieties of 1 into the cavity of CB[7]. The cyclic voltammetric study supports that the binding affinity of the radical cation forms is comparable to that of the di-cation viologen toward CB[7]. The fluorescence arising from the porphyrin moiety is significantly quenched upon the complexation of 1 with CB[7]. The ps-time-resolved fluorescence and ns-transient absorption spectroscopic studies reveal that the photoinduced electron transfer (PET) between viologen and Sn(iv) porphyrin of 1 takes place from the first excited singlet (S1) state and the second excited triplet (T2) state of the porphyrin moiety upon complexation with CB[7], while the PET from the S1 state is negligible in the absence of CB[7].

Gold nanorods-conjugated TiO2 nanoclusters for the synergistic combination of phototherapeutic treatments of cancer cells.

BACKGROUND: Recently, a combination of photodynamic therapy (PDT) and photothermal therapy (PTT) to generate reactive oxygen species (ROS) and heat to kill cancer cells, respectively has attracted considerable attention because it gives synergistic effects on the cancer treatment by utilizing the radiation of nontoxic low-energy photons such as long wavelength visible light and near IR (NIR) penetrating into subcutaneous region. For the effective combination of the phototherapies, various organic photosensitizer-conjugated gold nanocomplexes have been developed, but they have still some disadvantages due to photobleaching and unnecessary energy transfer of the organic photosensitizers. RESULTS: In this study, we fabricated novel inorganic phototherapeutic nanocomplexes (Au NR-TiO2 NCs) by conjugating gold nanorods (Au NRs) with defective TiO2 nanoparticle clusters (d-TiO2 NP clusters) and characterized their optical and photothermal properties. They were observed to absorb a broad range of visible light and near IR (NIR) from 500 to 1000 nm, exhibiting the generation of ROS as well as the photothermal effect for the simultaneous application of PDT and PTT. The resultant combination of PDT and PTT treatments of HeLa cells incubated with the nanocomplexes caused a synergistic increase in the cell death compared to the single treatment. CONCLUSION: The higher efficacy of cell death by the combination of PDT and PTT treatments with the nanocomplexes is likely attributed to the increases of ROS generation from the TiO2 NCs with the aid of local surface plasma resonance (LSPR)-induced hot electrons and heat generation from Au NRs, suggesting that Au NR-TiO2 NCs are promising nanomaterials for the in vivo combinatorial phototherapy of cancer.

Fabrication of ZnO nanoplates for visible light-induced imaging of living cells.

Visible light-sensitive ZnO nanoplates (ZnO NPls) were successfully synthesized using a hydrothermal sol-gel method and their structures were characterized by using techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmitting electron microscopy (TEM), atomic force microscopy (AFM) and FT-IR analysis. From these studies it was found that the nanoplates have excellent crystallinity and a perfect nanoplate morphology with diameter ranging from 50 nm to 250 nm and a thickness of ∼10 nm. Surfaces of the ZnO NPls were further conjugated with hydrophilic amino groups such as aminopropyl triethoxysilane (APTES) to enhance the biocompatibility and cell penetrations. The resultant APTES-modified ZnO NPls showed excellent colloidal stability in various aqueous media, exhibiting stable and strong red fluorescence emission (∼650 nm) under visible light-excitation at 405 nm. They also exhibited strong red emission even after being penetrated into living cells with negligible cytotoxicity. Therefore, the APTES-modified ZnO NPls should be promising alternative nanomaterials to the traditional quantum dots as well as previously reported ZnO cellular labelling agents which exhibit green emission by UV-excitation.

Preparation of an aqueous suspension of stabilized TiO2 nanoparticles in primary particle form.

To prepare stabilized TiO2 nanoparticles (TiO2 NPs) in aqueous media as a suspension of the primary particles, we attempted to optimize the conditions for dispersing stable, aggregated TiO2 NPs (A-TiO2 NPs) in aqueous HCl/NaOH solutions or 5 mM pH buffered aqueous solutions. The A-TiO2 NPs with a hydrodynamic diameter (or DLS size) of 150 +/- 20 nm could be dispersed at high concentration (63.5 +/- 0.5 mg/ml) in a 5 mM phosphate buffer (PB) solution of pH 8, and a primary TiO2 (P-TiO2) NP suspension (1.2 +/- 0.3 mg/ml) with DLS size of 30 +/- 5 nm could be separated from the highly concentrated A-TiO2 NP suspension by sonication and subsequent centrifugation. It was observed by comparing the UV-Vis absorption spectra of the A-TiO2 and P-TiO2 NP suspensions that the extinction coefficient of the TiO2 NPs in the aqueous suspension depended on the degree of aggregation. The stabilized P-TiO2 NP suspension in aqueous solution can be used to study nanotoxicity as well as to characterize the physicochemical properties of TiO2 NPs.

Visible light-sensitive APTES-bound ZnO nanowire toward a potent nanoinjector sensing biomolecules in a living cell.

Nanoscale cell injection techniques combined with nanoscopic photoluminescence (PL) spectroscopy have been important issues in high-resolution optical biosensing, gene and drug delivery and single-cell endoscopy for medical diagnostics and therapeutics. However, the current nanoinjectors remain limited for optical biosensing and communication at the subwavelength level, requiring an optical probe such as semiconductor quantum dots, separately. Here, we show that waveguided red emission is observed at the tip of a single visible light-sensitive APTES-modified ZnO nanowire (APTES-ZnO NW) and it exhibits great enhancement upon interaction with a complementary sequence-based double stranded (ds) DNA, whereas it is not significantly affected by non-complementary ds DNA. Further, the tip of a single APTES-ZnO NW can be inserted into the subcellular region of living HEK 293 cells without significant toxicity, and it can also detect the enhancement of the tip emission from subcellular regions with high spatial resolution. These results indicate that the single APTES-ZnO NW would be useful as a potent nanoinjector which can guide visible light into intracellular compartments of mammalian cells, and can also detect nanoscopic optical signal changes induced by interaction with the subcellular specific target biomolecules without separate optical probes.

Highly fluorescent peptide nanoribbon impregnated with Sn-porphyrin as a potent DNA sensor.

Highly fluorescent and thermo-stable peptide nanoribbons (PNRs) were fabricated by solvothermal self-assembly of a single peptide (D,D-diphenyl alanine peptides) with Sn-porphyrin (trans-dihydroxo[5,10,15,20-tetrakis(p-tolyl)porphyrinato] Sn(IV) (SnTTP(OH)2)). The structural characterization of the as-prepared nanoribbons was performed by transmitting electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM), FT-IR and Raman spectroscopy, indicating that the lipophilic Sn-porphyrins are impregnated into the porous surface formed in the process of nanoribbon formation through intermolecular hydrogen bonding of the peptide main chains. Consequently the Sn-porphyrin-impregnated peptide nanoribbons (Sn-porphyrin-PNRs) exhibited typical UV-visible absorption spectrum of the monomer porphyrin with a red shifted Q-band, and their fluorescence quantum yield was observed to be enhanced compared to that of free Sn-porphyrin. Interestingly the fluorescence intensity and lifetimes of Sn-porphyrin-PNRs were selectively affected upon interaction with nucleotide base sequences of DNA while those of free Sn-porphyrins were not affected by binding with any of the DNA studied, indicating that DNA-induced changes in the fluorescence properties of Sn-porphyrin-PNRs are due to interaction between DNA and the PNR scaffold. These results imply that Sn-porphyrin-PNR will be useful as a potent fluorescent protein analogue and as a biocompatible DNA sensor.

Development of multiplexed analysis for the photocatalytic activities of nanoparticles in aqueous suspension.

A multiplexed assay technique to measure the photocatalytic activity (PCA) of nanoparticles (NPs) in aqueous suspension was developed based on the observation of TiO(2) NPs-photocatalytic oxidation rate of NADH by monitoring the fluorescence intensities. 96 sample solutions of a small volume (<150 µL) could be assayed in a single run without separation of NPs within 15 min. PCA values can be measured with high sensitivity and low experimental uncertainties through the observation at various concentrations of photocatalyst, substrate, aqueous protons and pH buffer ions in a short measurement time.

Optical waveguiding and lasing action in porphyrin rectangular microtube with subwavelength wall thicknesses.

Lasing action by planar-, fiber-, or ring-type waveguide has been extensively investigated with different types of microcavities such as thin films, wires, cylindrical tubes, or ribbons. However, the lasing action by sharp bending waveguide, which promises efficient interconnection of amplified light in the photonic circuits, remains unexplored. Here, we report the first observation of microcavity effects in the organic rectangular microtubes (RMTs) with sharp bends (ca. 90°) and subwavelength nanoscale wall thicknesses, based on single crystalline and themostable tetra(4-pyridyl)porphyrin (H(2)TPyP)-RMTs synthesized by the VCR process. A bright tip emission is observed from the sharp bending edges of a single RMT upon laser excitation, demonstrating a clear waveguiding behavior in RMT. The appearance of a peak from the (0-1) band at a threshold tube length and the gradual decrease of its full width at half-maximum (fwhm) suggest that amplification of spontaneous emission (ASE) is developed by stimulated emission along the walls of the RMTs. The ehancement of the ASE peak together with the narrowing of its fhwm over a threshold pump power and the tube size (width and length) dependence of the mode spacing strongly support vibronic lasing action in the RMTs. The stimulated emission by the subwavelength bending waveguide demonstrates that the organic RMTs can be applied as new building blocks for micromanipulation of optical path and amplification in the integrated circuits for efficient photonic devices.

Fluorescence spectroscopic and time-dependent DFT studies for intramolecular excimer formation of Di-9H-fluoren-9-yldimethylsilane: dynamics and energetics for conformational change.

Intramolecular excimer formation of di-9H-fluoren-9-yldimethylsilane in various solvents was studied by means of steady-state and time-resolved fluorescence spectroscopies. Solvent viscosity effect on the kinetics for the monomer-excimer transition was found to be very slight, indicating that the transformation is accompanied by a slight conformational change presumably involving a transition from a near face-to-face conformer to a true sandwich conformer. The excitation energies and the corresponding oscillator strengths were derived with the time-dependent B3LYP/cc-pVTZ method. The simulated absorption spectrum involving the variation of the oscillator strengths in terms of the wavelengths accords with the experimental absorption pattern. The TD DFT calculations also reveal that excitation energy is significantly decreased with decreasing the interchromophore separation and the dihedral angle in a fluorene dimer, as an indication that the excimer state emitting the significantly red-shifted fluorescence corresponds to a sandwich conformer.

Photoluminescence properties of sonochemically synthesized gold nanoparticles for DNA biosensing.

The electronic interactions of sonochemically synthesized gold (Au) nanoparticles with AT- and GC-DNA were studied by measuring photoluminescence (PL) spectral properties and the inherent PL images of the Au nanoparticles incorporated with the single DNA molecules using a laser scanning confocal microscope. The Au-nanoparticles incorporated AT-DNA and GC-DNA exhibit confocal PL image. These results suggest a Lewis acid (Au)-Lewis base (N- or O-groups of DNA) type of interaction between Au nanoparticles and DNA.

Blinking photoluminescence properties of single TiO2 nanodiscs: interfacial electron transfer dynamics.

Blinking photoluminescence was observed in single TiO2 nanodiscs (NDs) by using a laser scanning confocal microscope (LSCM)-coupled steady-state and ps-time-resolved photoluminescence (PL) spectroscopic system, while it was not significantly observed for TiO2 quantum dots (QDs). Analysis of the PL blinking time trajectories revealed single-exponential kinetics with the average lifetimes of on-state (approximately 286 ms) and off-state (approximately 58 ms), implying the existence of inherent surface-trap sites which can be filled by photogenerated electron or hole. The PL spectra of single TiO2 NDs exhibited broad surface emissions with four decay times, which may be due to diffusion of the energies of electron or hole trap states related to surface structural changes by modification of TiO2 QDs. These results and the surface structural analysis (IR and XPS) suggests a simple model for the PL blinking of single TiO2 NDs that is based on repetitive interfacial electron transfer to the inherent surface trap sites (4Ti4+-OH) with Auger-assisted hole trapping in the multiple surface states as modified by the diffusive coordinate model and the surface-trap-filling model. Based on this blinking mechanism and kinetics, the rates of the interfacial electron transfer and the back electron transfer in TiO2 NDs were determined to be 18 ns and 58 ms, respectively, which are slow enough to keep the polarization of e-h pairs at the surface for efficient photocatalysis and photovoltaic activities. The present methodology and results may be applicable to obtain surface exciton dynamics of various photoelectronic semiconductor nanostructures.

Photoregulated fluorescence switching in axially coordinated tin(IV) porphyrinic dithienylethene.

Photochromic fluorophore Sn(TTP)(DTE)2 , in which two phenolic derivatives of 1,2-dithienylethene are axially coordinated to (5,10,15,20-tetratolylporphyrinato)tin(IV) in trans position, has been synthesized and fully characterized by various spectroscopic methods. We have also investigated the photoregulated fluorescence switching behavior of Sn(TTP)(DTE)2 . The fluorescence of the porphyrin macrocycle in Sn(TTP)(DTE) 2 greatly depends on the state of the 1,2-dithienyletene photochromic switch. In the open state (Sn(TTP)(o-DTE)2), the porphyrin exhibits high fluorescence intensity at 609 and 664 nm when excited at 410 nm. When the photocyclization reaction was carried out by irradiating Sn(TTP)(o-DTE)2 with the UV light (approximately 365 nm), the fluorescence intensity of the porphyrin macrocycle decreased. Back irradiation with visible light at wavelengths greater than 500 nm regenerated Sn(TTP)(o-DTE)2 and almost restored the original fluorescence spectrum. The fluorescence intensity of the porphyrin fluorophore is efficiently regulated by photochromic switching between Sn(TTP)(o-DTE)2 and Sn(TTP)(c-DTE)2 in several cycles, clearly demonstrating that the Sn(TTP)(DTE)2 can act as a system for reversible data processing using fluorescence as the detection method.

Protic solvent effects on the photophysical properties of O=Ti(IV)TSPP: photoinduced electron transfer.

The photophysical properties of oxotitanium(IV)meso-tetra(4-sulfonatophenyl) porphyrin (O=Ti(IV)TSPP) have been investigated in water and methanol by laser spectroscopic techniques. The fluorescence emission spectrum of O=Ti(IV)TSPP in methanol exhibits two strong emission bands at 610 and 670 nm at room temperature with the decay time of ca. 310 +/- 10 ps and the rise time shorter than 30 ps, in contrast to the extremely weak emission with the decay time of ca. 27 +/- 4 ps in water, indicating that the fluorescence emissive states are different in the two solvents as supported by the solvent dependences of the excitation spectrum. The transient Raman spectra of O=Ti(IV)TSPP in water has been observed to exhibit a remarkable enhancement of phenyl-related mode at 1599 cm(-1), while in methanol, the Raman frequencies of the porphyrin skeletal modes (upsilon2 and upsilon4) are down-shifted without any apparent enhancement of the phenyl-related mode, indicating different interactions of the two solvents with the excited O=Ti(IV)TSPP. These Raman studies reveal that methanol molecule interacts with the photoexcited O=Ti(IV)TSPP more strongly than water, forming the exciplex, O=Ti(IV)TSPP(MeOH)*, suggesting that the two different emissive states are the singlet Franck-Condon state and the exciplex state in methanol and water, respectively. A broad triplet transient absorption of O=Ti(IV)TSPP has been also observed at 480 nm in water as well as in methanol, which is decreased upon addition of methyl viologen (MV2+) with appearance of a new absorption band at 620 nm. This indicates that the photoinduced electron transfer (PET) takes place from the porphyrin to MV2+ in both solvents. The kinetic analysis of the transient absorption band exhibits the PET rate constants of 4.76 x 10(5) s(-1) and 3,03 x 10(4) s(-1) in methanol and water, respectively. All these results infer that the PET takes place from the (d,pi) CT state and the triplet state of the excited porphyrin in methanol and water, respectively.