An improved sparrow search algorithm and CNN-BiLSTM neural network for predicting sea level height.

Accurate prediction of sea level height is critically important for the government in assessing sea level risk in coastal areas. However, due to the nonlinear, time-varying and highly uncertain characteristics of sea level change data, sea level prediction is challenging. To improve the accuracy of sea level prediction, this paper uses a new swarm intelligence algorithm named the sparrow search algorithm (SSA), which can imitate the foraging behavior and antipredation behavior of sparrows, to determine optimal solutions. To avoid the algorithm falling into a local optimal situation, this paper integrates the sine-cosine algorithm and the Cauchy variation strategy into the SSA to obtain an algorithm named the SCSSA. The SCSSA is used to optimize the parameter values of the CNN-BiLSTM (convolutional neural network combined with bidirectional long short-term memory neural network) model; finally, a combined neural network model (named SCSSA-CNN-BiLSTM) is proposed. In this paper, the time series data of seven tidal stations located in coastal China are used for experimental analysis. First, the SCSSA-CNN-BiLSTM model is compared with the CNN-BiLSTM model to predict the time series data of SHANWEI Station. With respect to the training and test sets of data, the SCSSA-CNN-BiLSTM model outperforms the other models on all the evaluation metrics. In addition, the remaining six tide station datasets and five neural network models, including the SCSSA-CNN-BiLSTM model, are used to further study the performance of the proposed prediction model. Four evaluation indices including the root mean squared error (RMSE), mean absolute error (MAE), mean absolute percentage error (MAPE) and coefficient of determination (R2) are adopted. For six stations, the RMSE, MAE, MAPE and R2 of SCSSA-CNN-BiLSTM model are ranged from 20.9217 ~ 27.8427 mm, 9.4770 ~ 17.8603 mm, 0.1322% ~ 0.2482% and 0.9119 ~ 0.9759, respectively. The experimental analysis results show that the SCSSA-CNN-BiLSTM model makes effective predictions at all stations, and the prediction performance is better than that of the other models. Even though the combination of SCSSA algorithm may increase the complexity of the model, indeed the proposed model is a new prediction method with good accuracy and robustness for predicting sea level change.

Rational modification of hydroxy-functionalized covalent organic frameworks for enhanced photocatalytic hydrogen peroxide evolution.

Covalent organic frameworks (COFs), a class of flexibly tunable crystalline materials, have fascinating potential in photocatalytic hydrogen peroxide (H2O2) evolution under visible light irradiation. However, achieving efficient catalytic activity by tuning the composition of COFs and the linkages of building blocks is still a challenge. Herein, four imine-linked COFs with different numbers of hydroxy-functionalized are constructed to unveil the latent structure-activity relationship between the reversibility of bonding in supramolecular chemistry and the photocatalytic H2O2 performance. As the optimized material, TAPT-HTA-COF (1H-COF) containing single hydroxy group in aldehyde node exhibits a highest ordered structure and conjugation degree along and across the plane in the extended frameworks originating from the flexibly reversible iminol-to-ketoenamine tautomerism than others, which broadens the visible light absorption and accelerates the dissociation of photogenerated carriers in 1H-COF. These merits ensure that 1H-COF has the highest H2O2 yield (44.5 µmol L-1) and O2 two-electron reduction pathway among the four COFs under visible light irradiation (λ > 420 nm, 10 vol% isopropanol aqueous solution). At the same time, the long-range ordered framework of 1H-COF is well preserved during the photocatalytic H2O2 evolution process assisted by the proton-induced tautomerization. This work facilitates the design and development of COF-based photocatalysts in the evolution of H2O2.

In situ intercalation of Au nanoparticles and magnetic γ-Fe2O3 in the walls of MCM-41 with abundant void defects for highly efficient reduction of 4-nitrophenol and organic dyes.

Nowadays, agglomeration and leaching of metal active sites during reaction and recycle processes are considered to be a thorny problem for noble metal-based catalysts. Therefore, to make improvements, nano-gold was selected as a representative research object for many noble metals. In this study, Au nanoparticles (NPs) and magnetic γ-Fe2O3 were intercalated in situ in the walls of MCM-41 via a one-pot hydrothermal method, in which the intercalation process was preceded by co-condensation of tetraethyl orthosilicate (TEOS) with MPTS-Au complexes ((3-mercaptopropyl)-trimethoxysilane (MPTS), HAuCl4·3H2O), and a Fe3O4 sol. By the confinement of silica, Au NPs and γ-Fe2O3 were well dispersed in the walls of MCM-41, the sintering and loss of Au NPs was highly restricted, and the magnetic property of γ-Fe2O3 facilitated the recycling of Au-based catalysts. Additionally, abundant void defects appeared in MCM-41 by assembly of micelles in different sizes and shapes, greatly improving the surface area of target catalysts (>1800 m2 g-1), which provided more opportunities for contact and collision between reactors and gold active sites, effectively solving the problem of mass transportation. As expected, a series FeAu@MCM-41 catalysts showed superior catalytic activity in the reduction of 4-nitrophenol (4-NP) and organic dyes (MB, RhB, and MO), and these catalysts were recycled five times without significant loss of metal species or catalytic activity. This is attributed to the confinement effect of the silica walls and the excellent magnetic properties of γ-Fe2O3. This special structure of FeAu@MCM-41 catalysts provides more insights for designing and fabricating noble metal-based catalysts with desirable performances.

A metal-assisted templating route (S°M⁺I⁻) for fabricating thin-layer CoO covered on the channel of nanospherical-HMS with improved catalytic properties.

Nanospherical hexagonal mesoporous silica (HMS) with a functional mesochannel covered with thin-layer-dispersed cobalt oxide species was directly fabricated via a novel metal-assisted templating method (S(0)M(+)I(-)). In this special method, cobalt ions would be enriched on the surface of the pore wall by physicochemical interactions among the surfactant, cobalt ions and silica. Typically, a metallomicelle template (S(0)M(+)) formed from the coordinative assembly of metal cations (Co(2+), M(+)) with neutral surfactant dodecyl amine (DDA, S(0)) would match with negatively charged silicate oligomers (I(-)) by counter-ion interactions to assemble into the Co-modified HMS nanosphere. The metallization of DDA micelles and the role of cobalt ions in the assembly process can be demonstrated. Interestingly, the addition of amounts of cobalt apparently affects the size of the HMS nanosphere. Additionally, the coverage of CoO species on the mesochannel is increased with cobalt ions coordinated on the micelles. Finally, the functional Co-HMS with dispersed catalytic active phase and improved structure exhibits a special catalytic activity (yield of ca. 65%) for direct oxidation of phenol to p-benzoquinone with the assistance of a sulfate radical stimulated from cobalt in the presence of peroxymonosulfate.

A highly reactive and enhanced thermal stability nanocomposite catalyst based on Au nanoparticles assembled in the inner surface of SiO2 hollow nanotubes.

A novel hollow tubular SiO2-Au catalyst with a mesoporous structure (HTMS) was successfully fabricated by a combination of the sol-gel and calcination processes. This method involves the preparation of modified MWCNTs, the sequential deposition of Au and then silica layers through the sol-gel processes, and finally the calcination at the desired temperature to remove the MWCNTs. The obtained samples were characterized by several techniques, such as N2 adsorption-desorption isotherms, transmission electron microscopy, energy-dispersive X-ray spectroscopy analysis, UV-Vis spectra, X-ray diffraction and Thermogravimetric Analysis (TGA). The results established that a different calcination temperature has an obvious influence on the morphology and structure of the final hollow tubular. When the temperature is 550 °C, the obtained materials exhibit the distinctly tubular structure because of the decomposition of MWCNTs and the preservation of hollow tubes. Furthermore, in the catalyst system, the mesoporous silica layer can act as the physical barrier to resist the agglomeration and sintering of Au nanoparticles even after being subjected to harsh treatments up to 650 °C. In our experiments, the catalytic activities of HTMS SiO2-Au were investigated by photometrically monitoring the reduction of p-nitrophenol (p-NPh) by an excess of NaBH4. It was found that the prepared HTMS SiO2-Au catalysts exhibited a high catalytic activity and this sample could be easily recycled without a decrease of the catalytic activities in the reaction.

Synthesis and characterization of a novel Au nanocatalyst with increased thermal stability.

We report the synthesis of a new Au nanocatalyst with increased thermal stability. This catalyst system consisted of gold nanoparticles attached to functionalized TiO2/SiO2 core-shell nanocomposites, together with the encapsulation of mesoporous silica. The synthesis process mainly involved four steps, which included the synthesis of the TiO2/SiO2 core-shell composites, synthesis of the Au/TiO2/SiO2 particles, coating of Au/TiO2/SiO2 with silica, and etching the outer silica layer. TEM images were used to confirm the success of each of the synthesis steps, and both UV-vis adsorption spectra and the catalytic activity evaluation were employed to investigate the degree of re-exposure of Au nanoparticles after the etching treatment. In our experiments, the obtained mesoSiO2/Au/TiO2/SiO2 catalyst showed a superior thermal stability and higher activity for CO conversion compared to the mesoSiO2/Au/SiO2 one. It resisted sintering during the calcination at 500 °C, whereas the unprotected one was found to sinter. Moreover, it was found that on the mesoSiO2/Au/TiO2/SiO2 sample, the outside silica material could hinder the phase transformation of titania to some extent. Thus, small crystalline particles of TiO2 anchored on the silica beads of the core-shell composites, leading to a better dispersion of small Au nanoparticles and improved catalytic capacity to resist sintering.

Well-crystallized mesoporous TiO2 shells for enhanced photocatalytic activity: prepared by carbon coating and silica-protected calcination.

Mesoporous anatase-phase TiO2 hollow shells were successfully fabricated by the solvothermal and calcination process. This method involves preparation of SiO2@TiO2 core-shell colloidal templates, sequential deposition of carbon and then silica layers through solvothermal and sol-gel processes, crystallization of TiO2 by calcination and finally removal of the inner and outer silica to produce hollow anatase TiO2 shells. The prepared samples were characterized by transmission electron microscopy, X-ray diffraction, N2 adsorption-desorption isotherms and UV-vis absorption spectroscopy. The results show that a uniform carbon layer is coated on the core-shell particles through the solvothermal process. The combustion of carbon offers the space for the TiO2 to further grow into large crystal grains, and the outer silica layer serves as a barrier against the excessive growth of anatase TiO2 nanocrystals. Furthermore, the initial crystallization of TiO2 generated in the carbon coating step and the heat generated by the combustion of the carbon layer allow the crystallization of TiO2 at a relatively low temperature without changing the uniform structure. When used as photocatalysts for the oxidation decomposition of Rhodamine B in aqueous solution under UV irradiation, the hollow TiO2 shells showed enhanced catalytic activity. Moreover, the TiO2 hollow shells prepared with optimal crystallinity by this method showed a higher performance than commercial P25 TiO2.