Electrospun Ceramic Nanofibers for Photocatalysis

Ceramic fiber photocatalysts fabricated by electrospinning hold great potential in alleviating global environmental and energy issues. However, many challenges remain in improving their photocatalytic efficiencies, such as the limited carrier lifetime and solar energy utilization. To overcome these predicaments, various smart strategies have been invented and realized in ceramic fiber photocatalysts. This review firstly attempts to summarize the fundamental principles and bottlenecks of photocatalytic processes. Subsequently, the approaches of doping, surface plasmon resonance, and up-conversion fluorescent to enlarge the light absorption range realized by precursor composition design, electrospinning parameter control, and proper post heat-treatment process are systematically introduced. Furthermore, methods and achievements of prolonging the lifetime of photogenerated carriers in electrospun ceramic fiber photocatalysts by means of introducing heterostructure and defective composition are reviewed in this article. This review ends with a summary and some perspectives on the future directions of ceramic fiber photocatalysts.

Experimental Study of the Effect of Precursor Composition On the Microstructure of Gallium Nitride Thin Films Grown by the MOCVD Process

Chemical vapor deposition (CVD) is a widely used manufacturing process for obtaining thin films of materials like silicon, silicon carbide, graphene and gallium nitride that are employed in the fabrication of electronic and optical devices. Gallium nitride (GaN) thin films are attractive materials for manufacturing optoelectronic device applications due to their wide band gap and superb optoelectronic performance. The reliability and durability of the devices depend on the quality of the thin films. The metal-organic chemical vapor deposition (MOCVD) process is a common technique used to fabricate high-quality GaN thin films. The deposition rate and uniformity of thin films are determined by the thermal transport processes and chemical reactions occurring in the reactor, and are manipulated by controlling the operating conditions and the reactor geometrical configuration. In this study, the epitaxial growth of GaN thin films on sapphire (AL2O3) substrates is carried out in two commercial MOCVD systems. This paper focuses on the composition of the precursor and the carrier gases, since earlier studies have shown the importance of precursor composition. The results show that the flow rate of trimethylgallium (TMG), which is the main ingredient in the process, has a significant effect on the deposition rate and uniformity of the films. Also the carrier gas plays an important role in deposition rate and uniformity. Thus, the use of an appropriate mixture of hydrogen and nitrogen as the carrier gas can improve the deposition rate and quality of GaN thin films.

Morphological Influence of Precursor Composition Characteristics During Ceramic Membrane Fabrication

In this work, the influence of inorganic low-cost precursor compositions (viz. kaolin, feldspar, saw dust, sodium metasilicate and boric acid) has been investigated on the morphological characteristics (such as average pore size and porosity) of the ceramic membranes that were fabricated using dry compaction method and saw dust as the pore forming agent. In order to do so, kaolin to feldspar ratio has been varied from 0.48 – 2.05 and binder composition has been varied from 10 – 15 wt.%. For an inorganic precursor formulation of kaolin 38.77 wt.%, feldspar 23.03 wt.%, saw dust 8.19 wt.%, sodium metasilicate 15 wt.% and boric acid 15 wt.%, the sub-micron range low-cost ceramic membranes (95.8 nm average pore size and 13.95% porosity) have been achieved as a key novelty. With minor variations in the precursor composition, the microfiltration membranes could be converted to ultrafiltration membranes without undergoing any complex surface reactions or polymeric coatings. An empirical model has been as well developed to quantify the variation of dependent variables on the membrane characteristics.

Effect of Different Selenium Precursors on Structural Characteristics and Chemical Composition of Cu2ZnSnSe4 Nanocrystals

In the presented work Cu2ZnSnSe4 nanocrystals have been synthesized by the polyol method. The chemical composition, morphological, structural, and microstructural properties of Cu2ZnSnSe4 nanocrystals depending on synthesis temperature and time as well as precursor composition have been thoroughly investigated using scanning and transmission electron microscopies, energy dispersive X-ray analysis, X-Ray diffraction, FTIR spectroscopy. We compared the properties of nanocrystals synthesized from different precursors containing selenourea or amorphous selenium as a source of selenium and then determined the optimal conditions for nanocrystals synthesis. It was found that the optimal synthesis time for nanocrystals obtained using the first approach was t = (30-45) min, and for the second approach t = 120 min. It was also found that the optimal composition for the synthesis of single-phase Cu2ZnSnSe4 nanocrystals by the second approach is the molar ratio of precursors 2:1.5:1:4 and synthesis temperature T = 280 оС. Cu2ZnSnSe4 nanocrystals synthesized under optimal conditions were used to develop nanoinks for printing solar cell absorbers by 2D and 3D printers.