Monitoring of Single-Track Melting States Based on Photodiode Signal during Laser Powder Bed Fusion.

Single track is the basis for the melt pool modeling and physics work in laser powder bed fusion (LPBF). The melting state of a single track is closely related to defects such as porosity, lack of fusion, and balling, which have a significant impact on the mechanical properties of an LPBF-created part. To ensure the reliability of part quality and repeatability, process monitoring and feedback control are emerging to improve the melting states, which is becoming a hot topic in both the industrial and academic communities. In this research, a simple and low-cost off-axial photodiode signal monitoring system was established to monitor the melting pools of single tracks. Nine groups of single-track experiments with different process parameter combinations were carried out four times and then thirty-six LPBF tracks were obtained. The melting states were classified into three classes according to the morphologies of the tracks. A convolutional neural network (CNN) model was developed to extract the characteristics and identify the melting states. The raw one-dimensional photodiode signal data were converted into two-dimensional grayscale images. The average identification accuracy reached 95.81% and the computation time was 15 ms for each sample, which was promising for engineering applications. Compared with some classic deep learning models, the proposed CNN could distinguish the melting states with higher classification accuracy and efficiency. This work contributes to real-time multiple-sensor monitoring and feedback control.

In Situ Construction of Near-Infrared Response Hybrid Up-Conversion Photocatalyst for Degrading Organic Dyes and Antibiotics.

Unique nonlinear optical properties for converting low-energy incident light into high-energy radiation enable up-conversion materials to be employed in photocatalytic systems. An efficient near-infrared (NIR) response photocatalyst was successfully fabricated through a facile two-step method to load BiOBr on the Nd3+, Er3+@NaYF4 (NE@NYF) up-conversion material. The NE@NYF can transform NIR into visible and UV light and promote charge-energy transfer in the semiconductor. Consequently, the as-obtained photocatalysts exhibit excellent photodegradation performance for rhodamine B dye (RhB) and tetracycline (TC) organic pollutants. About 98.9% of the RhB was decomposed within 60 min with the 20% NE@NYF-B sample, outperforming the pristine BiOBr (61.9%). In addition, the 20% NE@NYF-B composite could decompose approximately 72.7% of the organic carbon during a 10 h reaction, which was almost two-fold more than that of BiOBr. Meanwhile, a possible charge transfer mechanism is proposed based on the recombination of electron-hole pairs and reactive oxygen species. This work provides a rational hybrid structure photocatalyst for improving photocatalytic performance in the broadband spectrum and provides a new strategy for NIR light utilization.

Highly Water-Stable and Efficient Hydrogen-Producing Heterostructure Synthesized from Mn0.5Cd0.5S and a Zeolitic Imidazolate Framework ZIF-8 via Ligand and Cation Exchange.

Developing highly water-stable zeolitic imidazolate frameworks (ZIFs) for visible-light-driven photocatalytic hydrolysis is important and challenging. Herein, the Type II heterojunction catalyst Mn0.5Cd0.5S@ZIF-8 and its derivatives (including MCS@ZIF-8-Mn, MCS@ZIF-8-Br, and MCS@ZIF-8-MB) were successfully constructed using a facile strategy. Through dual postsynthetic ligand and cation exchange (PSE) treatments of Mn(Ac)2·4H2O and 4-bromo-1H-imidazole for ZIF-8, the hydrogen production efficiency of the MCS@ZIF-8-MB heterojunction catalyst can reach 5.450 mmol·g-1·h-1 and remain at 97.11% after 9 h of the stability test. Construction of heterojunctions can effectively improve the hydrogen production performance of Mn0.5Cd0.5S while maintaining excellent water stability. X-ray photoelectron spectroscopy results show that upon successful construction of the MCS@ZIF-8-MB heterojunction an interface forms between the surface of MCS and ZIF-8-MB, effectively weakening the photocorrosion of MCS. Density functional theory calculations also indicate that the induction of Mn can increase the electronic states of p and d orbitals near the Fermi level of ZIF-8, suggesting that Mn(II) attracts more electrons than Zn(II). This provides more powerful theoretical evidence for the electron cloud shift from the electron donor S2- to Mn2+.

Metal Mesh and Narrow Band Gap Mn0.5Cd0.5S Photocatalyst Cooperation for Efficient Hydrogen Production.

A novel co-catalyst system under visible-light irradiation was constructed using high-purity metal and alloy mesh and a Mn0.5Cd0.5S photocatalyst with a narrow band gap (1.91 eV) prepared by hydrothermal synthesis. The hydrogen production rate of Mn0.5Cd0.5S changed from 2.21 to 6.63 mmol·(g·h)-1 with the amount of thioacetamide, which was used as the sulphur source. The introduction of Ag, Mo, Ni, Cu, and Cu-Ni alloy meshes efficiently improved the H2 production rate of the co-catalyst system, especially for the Ni mesh. The improvement can reach an approximately six times greater production, with the highest H2 production rate being 37.65 mmol·(g·h)-1. The results showed that some bulk non-noble metal meshes can act as good or better than some noble metal nanoparticles deposited on the main photocatalyst for H2 evolution due to the promotion of photoinduced electron transfer, increase in redox reaction sites, and prevention of the recombination of carriers.

Preparation and photoelectrochemical properties of BiFeO3/BiOI composites.

BiFeO3 thin films were spin coated onto FTO. BiFeO3/BiOI composites have been successfully synthesized by an electrochemical deposition method. The morphology, structure and optical absorption properties of the as-synthesized samples were characterized via XRD, SEM, and UV-Vis DRS. The effect of the BiOI electrodeposition cycles on the photoelectrochemical properties of the BiFeO3/BiOI composites were investigated. The results showed that the photoelectrochemical properties were enhanced under simulated solar light. The composite could achieve an optimum photocurrent density of 16.03 µA cm-2 at 0 V (vs. Ag/AgCl), which is more than twice that of pure BiFeO3 thin films (6.3 µA cm-2). In addition, the Mott-Schottky curves indicate an improvement in the carrier density of the composite. The enhanced photoelectrochemical properties of the composites can be attributed to the formation of a heterojunction at the interface and the band bending of the ferroelectric material BiFeO3.

Photocatalytic performance of Cu2O-loaded TiO2/rGO nanoheterojunctions obtained by UV reduction.

A novel dot-like Cu2O-loaded TiO2/reduced graphene oxide (rGO) nanoheterojunction was synthesized via UV light reduction for the first time. Cu2O with size of ca. 5 nm was deposited on rGO sheet and TiO2 nanosheets. The products were characterized by infrared spectroscopy, Raman spectrum, UV-Vis diffuse reflectance spectra, XPS techniques, photoluminescence spectra. The results demonstrated that Cu2O and rGO enhanced the absorption for solar light, separation efficiency of electron-hole pairs, charge shuttle and transfer, and eventually improved photoelectrochemical and photocatalytic performance for contaminants degradation. The reaction time and anion precursor could affect the final copper-containing phase. As extending UV irradiation time, Cu2+ was be first reduced to Cu2O and then transformed to metal Cu. In comparison with CH3COO- (copper acetate), NO3- (copper nitrate) and Cl- (copper chloride), SO42- (copper sulfate) was the optimum for synthesizing pure Cu2O phase.

Photocatalytic Properties of TiO2 Porous Network Film.

Three-dimensional porous network TiO2 film (PW-film) and nanoparticles film were synthesized on surface of the Ti foil by a facile method to investigate both the photoelectrochemical and photocatalytic properties. The prepared samples were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM) and X-ray diffraction spectroscopy (XRD) techniques. Methylene blue was used as a target molecule to estimate the photocatalytic activity of the films. Results revealed that the hydrothermal temperature and time have great influence on the crystal type and film morphology of TiO2 catalysts. A higher hydrothermal temperature is benefit for the formation of anatase phase of TiO2 nanotubes with PW-film, which had a large number of nodes. After investigation of the photoelectrochemical properties, a maximum photoconversion efficiency of 4.79% is observed for nanoparticles film with rutile phase of TiO2 under UV light illumination, which was incredible 2 times higher than that of the PW-film with anatase phase. It was shown that the morphology of TiO2 film contributes more significant effect on photocatalytic and photoelectric performance than its crystal type.

Controllable Nd2Fe14B/α-Fe nanocomposites: chemical synthesis and magnetic properties.

It is extremely desirable but challenging to develop exchange-coupled magnets with well-dispersed hard/soft phase and confined size to meet the high energy requirements of advanced magnets in modern industry and information technology. Here, we report a novel bottom-up strategy with two-step thermal decomposition and reductive annealing process to synthesize Nd2Fe14B/α-Fe nanocomposites, in which effective control of the hard/soft magnetic phase size and proportion was achieved. It is worth noting that the composition, as well as phase distribution, can be readily tuned by changing the ratio between Nd-Fe-B-oxide and α-Fe. This work provides an effective approach to adjust the phase size and distribution for exchange-coupled, rare-earth nanomagnets, which can be fundamental for high energy magnets.

Controlled doping of carbon nanotubes with metallocenes for application in hybrid carbon nanotube/Si solar cells.

There is considerable interest in the controlled p-type and n-type doping of carbon nanotubes (CNT) for use in a range of important electronics applications, including the development of hybrid CNT/silicon (Si) photovoltaic devices. Here, we demonstrate that easy to handle metallocenes and related complexes can be used to both p-type and n-type dope single-walled carbon nanotube (SWNT) thin films, using a simple spin coating process. We report n-SWNT/p-Si photovoltaic devices that are >450 times more efficient than the best solar cells of this type currently reported and show that the performance of both our n-SWNT/p-Si and p-SWNT/n-Si devices is related to the doping level of the SWNT. Furthermore, we establish that the electronic structure of the metallocene or related molecule can be correlated to the doping level of the SWNT, which may provide the foundation for controlled doping of SWNT thin films in the future.