Fabrication, Modification and Application of Visible Light Responsive TiO2 Nanotubes

The highly ordered TiO2 nanotube arrays have demonstrated remarkable properties that include solar cells, hydrogen sensors, drug eluting surfaces, hydrogen generation, and water purification along with numerous other applications. Built upon a suitable fabrication approach that enable significant differences in reproducibility as well as the large scale production with low cost plus investigation of the effective way to increase its visible light response so that create environmental friendly alternative energy sources were the motivations of this work, Since the field has grown so rapidly as to make it difficult to summarize the scope of all related work, some key aspects on this field have been discussed and then mainly focus on the work that has been done during my Ph.D study. This Ph.D work focuses on the most challenging issues: 1) improves the tune quality of highly ordered TiO2 nanotubes by reproducible manner as well as reduces the cost of fabrication. 2) Investigates the different methods of modification in order to increase photo response of the materials in visible light region. 3) Explore the surface superhydrophobic property of fluorinated TiO2 nanotubes layer. Following progresses have been made towards the target. An innovative technique of sonication assisted fabrication of highly ordered TiO2 nanotubes in reproducible manner was proposed and the expensive platinum cathode was replaced by titanium by which the fabrication cost was reduced. A one-step method for the fabrication of Fe–C–N-codoped TiO2 nanotubes by electrochemical anodization is reported. A maximum photocurrent efficiency of 2.7% was achieved. Highly ordered nitrogen-doped titanium dioxide (N-doped TiO2) nanotube array films with enhanced photo conversion efficiency were reported and the conditions were optimized. The optimized experiment resulted in 7.42% PCE which was within 95% confidence interval of the predicted value by the model. The structural and photo catalytic properties of Pt/ZIF-8 loaded TiO2 nanotubes (TiO2 NTs) are investigated and compared to Pt/TiO2 NTs. The Pt/ZIF-8 loaded TiO2 NTs has shown 18.6% oxidation towards phenol in 2 hours under visible light. Finally, a simple process of tailoring the surface wettability of TiO2 nanotube array surface was proposed by which any desirable degree of hydrophobicity between 100o to 170o can be achieved

Pramanicin analog induces apoptosis in human colon cancer cells: critical roles for Bcl-2, Bim, and p38 MAPK signaling

Pramanicin (PMC) is an antifungal agent that was previously demonstrated to exhibit antiangiogenic and anticancer properties in a few in vitro studies. We initially screened a number of PMC analogs for their cytotoxic effects on HCT116 human colon cancer cells. PMC-A, the analog with the most potent antiproliferative effect was chosen to further interrogate the underlying mechanism of action. PMC-A led to apoptosis through activation of caspase-9 and -3. The apoptotic nature of cell death was confirmed by abrogation of cell death with pretreatment with specific caspase inhibitors. Stress-related MAPKs JNK and p38 were both activated concomittantly with the intrinsic apoptotic pathway. Moreover, pharmacological inhibition of p38 proved to attenuate the cell death induction while pretreatment with JNK inhibitor did not exhibit a protective effect. Resistance of Bax -/- cells and the protective nature of caspase-9 inhibition indicate that mitochondria play a central role in PMC-A induced apoptosis. Early post-exposure elevation of cellular Bim and Bax was followed by a marginal Bcl-2 depletion and Bid cleavage. Further analysis revealed that Bcl-2 downregulation occurs at the mRNA level and is critical to mediate PMC-A induced apoptosis, as ectopic Bcl-2 expression substantially spared the cells from death. Conversely, forced expression of Bim proved to significantly increase cell death. In addition, analyses of p53-/- cells demonstrated that Bcl-2/Bim/Bax modulation and MAPK activations take place independently of p53 expression. Taken together, p53-independent transcriptional Bcl-2 downregulation and p38 signaling appear to be the key modulatory events in PMC-A induced apoptosis

Rational design of Pd-TiO2/g-C3N4 heterojunction with enhanced photocatalytic activity through interfacial charge transfer

A hybrid heterojunction-based photocatalyst is synthesized by an electrostatic self-assembly strategy including surface modification and controlled metal deposition. The interfacial contact was made by mixing negatively charged anatase TiO2 nanoparticles with positively charged g-C3N4. Visible-light deposition of Pd nanoparticles largely on TiO2 was made possible due to the charge transfer from C3N4 (excited by visible light) to the conduction band of TiO2 reducing Pd ions on contact with its surface. In order to further test the efficiency of this cascade of electron transfer across the conduction bands of the two semiconductors, photocatalytic H2 production from water was studied. Upon optimizing the ratio of the two semiconductors, increased H2 production rates were observed and attributed to enhanced charge separation. Catalysts were studied by a variety of techniques in order to probe into their properties and link them to activity. The reaction rate, under visible-light excitation, of the best sample showed an 8-fold enhancement when compared to that of Pd-C3N4 in identical conditions and the highest apparent quantum yield of 31% was achieved by a 0.1%Pd/20%TiO2/C3N4 sample in a 420- to 443-nm range

Dissolution-regrowth of hierarchical Fe-Dy oxide modulates the electronic structure of nickel-organic frameworks as highly active and stable water splitting electrocatalysts

As the kinetically sluggish oxygen evolution reaction (OER) is considered to be a bottleneck in overall water splitting, it is necessary to develop a highly active and stable electrocatalyst to overcome this issue. Herein, we successfully fabricated a three-dimensional iron-dysprosium oxide co-regulated in-situ formed MOF-Ni arrays on carbon cloth (FeDy@MOF-Ni/CC) through a facile two-step hydrothermal method. Electrochemical studies demonstrate that the designed FeDy@MOF-Ni/CC catalyst requires an overpotential of only 251 mV to reach 10 mA cm(-2) with a small Tafel slope of 52.1 mV dec(-1). Additionally, the stability declined by only 5.5% after 80 h of continuous testing in 1.0 M KOH. Furthermore, a cell voltage of only 1.57 V in the overall water splitting system is sufficient to achieve 10 mA cm(-2); this value is far better than that of most previously reported catalysts. The excellent catalytic performance originates from the unique 3D rhombus-like structure, as well as coupling synergies of Fe-Dy-Ni species. The combination of lanthanide and transition metal species in the synthesis strategy may open entirely new possibilities with promising potential in the design of highly active OER electrocatalysts. (c) 2020, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved

Pramanicin analog induces apoptosis in human colon cancer cells: critical roles for Bcl-2, Bim, and p38 MAPK signaling.

Pramanicin (PMC) is an antifungal agent that was previously demonstrated to exhibit antiangiogenic and anticancer properties in a few in vitro studies. We initially screened a number of PMC analogs for their cytotoxic effects on HCT116 human colon cancer cells. PMC-A, the analog with the most potent antiproliferative effect was chosen to further interrogate the underlying mechanism of action. PMC-A led to apoptosis through activation of caspase-9 and -3. The apoptotic nature of cell death was confirmed by abrogation of cell death with pretreatment with specific caspase inhibitors. Stress-related MAPKs JNK and p38 were both activated concomittantly with the intrinsic apoptotic pathway. Moreover, pharmacological inhibition of p38 proved to attenuate the cell death induction while pretreatment with JNK inhibitor did not exhibit a protective effect. Resistance of Bax -/- cells and the protective nature of caspase-9 inhibition indicate that mitochondria play a central role in PMC-A induced apoptosis. Early post-exposure elevation of cellular Bim and Bax was followed by a marginal Bcl-2 depletion and Bid cleavage. Further analysis revealed that Bcl-2 downregulation occurs at the mRNA level and is critical to mediate PMC-A induced apoptosis, as ectopic Bcl-2 expression substantially spared the cells from death. Conversely, forced expression of Bim proved to significantly increase cell death. In addition, analyses of p53-/- cells demonstrated that Bcl-2/Bim/Bax modulation and MAPK activations take place independently of p53 expression. Taken together, p53-independent transcriptional Bcl-2 downregulation and p38 signaling appear to be the key modulatory events in PMC-A induced apoptosis

Generation of Multiple Excitons in Ag2S Quantum Dots: Single High-Energy versus Multiple-Photon Excitation

We explored the carrier multiplications generated by single high-energy and multiple photon absorption in Ag2S quantum dots (QDs) using femtosecond broadband transient absorption spectroscopy

Comprehensive study of all-solid-state Z-scheme photocatalytic systems of ZnO/Pt/CdZnS

We have investigated a Z-scheme based on a ZnO/Pt/CdZnS photocatalyst, active in the presence of a complex medium composed of acetic acid and benzyl alcohol, the effects of which on the catalyst stability and performance are studied. Transmission electron microscopy images showed uniformly dispersed sub-nanometer Pt particles. Inductively coupled plasma and X-ray photoelectron spectroscopy analyses suggested that Pt is sandwiched between ZnO and CdZnS. An apparent quantum yield (AQY) of 34% was obtained over the [ZnO]4/1 wt %Pt/CdZnS system at 360 nm, 2.5-fold higher than that of 1%Pt/CdZnS (14%). Furthermore, an AQY of 16% was observed using [ZnO]4/1 wt %Pt/ CdZnS, which was comparable to that of 1 wt %Pt/CdZnS (10%) at 460 nm. On the basis of these results, we proposed a charge transfer mechanism, which was confirmed through femtosecond transient absorption spectroscopy. Finally, we identified the two main factors that affected the stability of the catalyst, which were the sacrificial reagent and the acidic pH.Peer Reviewe

Transcriptional downregulation of Bcl-2 is critical to mediate PMC-A induced apoptosis.

<p>Wild type HCT116 cells were treated with indicated concentrations of PMC-A and harvested at 24 h post-exposure, lysed and immunoblotted with anti-Bcl-2 and anti-β-actin antibodies (A). β-actin was used as loading control. Downregulation of cellular Bcl-2 was amplified by increasing PMC-A dose. HCT116 wt cells were treated with indicated PMC-A concentrations, harvested after 24 h for total RNA extraction, cDNA synthesis and qRT-PCR analysis (B). A marginal (∼5-fold) decrease in Bcl-2 transcription was evident upon PMC-A treatment (p<0,01). HCT116 wt cells were transiently transfected with expression plasmids either carrying human Bcl-2 gene or mock vector only (C). Transfected cells were treated with 50 µM PMC-A before collection and flow cytometry analysis. The results from at least 3 independent experiments were shown as means ± SD. Difference of mean values between mock and Bcl-2-transfected cells were tested using paired student’s t-test; <b>**</b>P<0.01. Analysis indicates that ectopic Bcl-2 expression renders the cells more resistant against PMC-A induced apoptosis. Bcl-2 expression statuses of mock- and Bcl-2-transfected cells prior to PMC-A treatment are displayed as immunoblotting results obtained from cells that were harvested, lysed and immunoblotted with anti-Bcl-2 antibody (C). Results from one of three independent experiments are shown in immunoblotting results.</p