RESUMO
The effective conversion of sunlight into H2 by photocatalytic water splitting has emerged as the most promising strategy to alleviate the energy crisis. In this work, niobium pentoxide (Nb2O5)/graphitic carbon nitride (g-C3N4) type-II heterojunctions with high photocatalytic H2 evolution rate under both visible and simulated solar light are fabricated via a novel approach involving in situ 'hydrolysis/calcination' loading of Nb2O5 nanoparticles on the g-C3N4 surface. After the optimisation, the Nb2O5/g-C3N4 heterojunctions with 5 wt% Nb2O5 content delivers high H2 evolution rates of 2.07 ± 0.03 and 6.77 ± 0.12 mmol g-1 h-1 under visible and simulated solar light exposure, respectively, which are 4.1 and 4.2 times superior to those of pure g-C3N4. According to the subsequent characterisations, the effective Nb2O5/g-C3N4 heterojunction offers sufficient contact interface, which is favourable for the efficient separation of photogenerated charges. In addition, the Nb2O5/g-C3N4 heterojunction possesses a large surface area, which contributes to the interfacial contact between photocatalyst and water. This work provides insights into the synthesis of novel g-C3N4-based hetero-photocatalysts with strong solar energy conversion capabilities.
RESUMO
Graphitic carbon nitride with nitrogen defects (g-C3N4-x) is prepared by a facile and effective solid-state chemical reduction technique at mild temperature conditions. The cyano groups and nitrogen vacancies, as evidenced by electron paramagnetic resonance (EPR), X-ray photoelectron spectrometer (XPS), Fourier transform infrared spectra (FTIR) and Solid-state 13C MAS NMR spectra, are controllable via adjusting chemical reduction temperature. Comparing to the pristine g-C3N4, the as-prepared g-C3N4-x shows much enhanced photocatalytic H2 evolution activity under visible-light irradiation. The maximum H2 evolution rate of 3068⯵mol·g-1·h-1 is achieved with g-C3N4-x after chemical reduction treatment at 400⯰C for 1â¯h, which is 4.85 times that of the pristine g-C3N4. Moreover, excellent reusability and storage stability have been shown by this photocatalyst as well. It is discovered that nitrogen defects can result in both the up-shift of the valance band and the down-shift of the conduction band, which benefit the absorption of longer wavelength photons and trapping of the photoinduced electrons, therefore reducing the recombination losses of the generated carriers. It is because of this improved visible-light absorption and charge carrier separation, g-C3N4-x displays better visible-light photocatalytic activity compared to the pristine g-C3N4. It is then concluded that the synthetic strategy presented here represents a straightforward and efficient way to synergistically optimize the chemical composition, optical response, and photocatalytic characteristics of g-C3N4-based photocatalysts.
RESUMO
Bi4Ti3O12−x nanosheet photocatalysts with abundant oxygen vacancies are fabricated by a facile solid-state chemical reduction method for the first time. This method is simple in operation, has short reaction time, and can be conducted at mild temperatures (300~400 °C). The electron paramagnetic resonance, thermogravimetric analysis, X-ray photoelectron spectrometer, and positron annihilation lifetime spectra results indicate that oxygen vacancies are produced in Bi4Ti3O12−x, and they can be adjusted by tuning the reduction reaction conditions. Control experiments show that the reduction time and temperature have great influences on the photocatalytic activities of Bi4Ti3O12−x. The optimal Bi4Ti3O12−x is the sample undergoing the reduction treatment at 350 °C for 60 min and it affords a hydrogen evolution rate of 129 μmol·g−1·h−1 under visible-light irradiation, which is about 3.4 times that of the pristine Bi4Ti3O12. The Bi4Ti3O12−x photocatalysts have good reusability and storage stability and can be used to decompose formaldehyde and formic acid for hydrogen production. The surface oxygen vacancies states result in the broadening of the valence band and the narrowing of the band gap. Such energy level structure variation helps promote the separation of photo-generated electron-hole pairs thus leading to enhancement in the visible-light photocatalytic hydrogen evolution. Meanwhile, the narrowing of the band gap leads to a broader visible light absorption of Bi4Ti3O12−x.
RESUMO
AIM: To investigate the differently expressed genes in human colorectal adenocarcinoma. METHODS: The integrated approach for gene expression profiling that couples suppression subtractive hybridization, high-throughput cDNA array, sequencing, bioinformatics analysis, and reverse transcriptase real-time quantitative polymerase chain reaction (PCR) was carried out. A set of cDNA clones including 1260 SSH inserts amplified by PCR was arrayed using robotic printing. The cDNA arrays were hybridized with fluorescent-labeled probes prepared from RNA of human colorectal adenocarcinoma (HCRAC) and normal colorectal tissues. RESULTS: A total of 86 genes were identified, 16 unknown genes and 70 known genes. The transcription factor Somult9 influencing cell differentiation was downregulated. At the same time, Heat shock protein 10 KDis downregulated and Calmoulin is up-regulated. CONCLUSION: Downregulation of heat shock protein 10 KD lost its inhibition of Ras, and then attenuated the Ras GTPase signaling pathway, increased cell proliferation and inhibited cell apoptosis. Down-regulated transcription factor Somult9 influences cell differentiation and cell-specific gene expression. Down-regulated Somult9 also decreases its binding to calmodulin, accumulates calmodulin as receptor-activated kinase and phosphorylase kinase due to the activation of PhK.
