This paper reviews the engineering design of an electrochemical biosensor, particularly the main concepts of electrodes and the type of material selections, design, and fabrication method. Furthermore, the related theories and practical examples from existing literature are reviewed. Research is now directed toward the development of biosensors as important bioanalytical tools in the pharmaceutical, biotechnology, food, and other consumer‐oriented industries. Currently, comprehensive guidelines on the selection of electrodes for electrochemical biosensors are unavailable. Factual options are important in determining the real‐time response of biosensors. Attempts to determine the best material and design for electrodes have no results because of the complexity of fabrication and the lifespan of the material chosen for the electrodes. This paper summarizes the trends in numerous studies on developing electrochemical biosensors. A better understanding of biosensors will greatly assist in the design of new and improved biosensors.
Directional solvent extraction is one of the promising membrane-less seawater desalination method. This technique was not extensively investigated due the poor mixing and separation performances of its bench-scale system. It is believed that, overcoming these drawbacks is possible now with the rapid development of microfluidics technology that enabled high-precession micro mixing and separation. This work presents microfluidics chip for extracting and separating salt from seawater. The chip was designed with two sections for extraction and separation. In both sections, the liquids were separated using capillary channels perpendicular to the main stream. The main channels were designed to be 400 µm in width and 100 µm in height. Two streams inlets were introduced through a Y-junction containing octanoic acid as the organic phase and saltwater as the aqueous phase. The desalination performance was investigated at four different temperatures and five different solvent flow rates. Water product salinity was recorded to be as low as 0.056% (w/w) at 60 °C and 40 mL/h. A maximum water yield of 5.2% was achieved at 65 °C and 40 mL/h with a very low solvent residual (70 ppm). The chip mass transfer efficiency was recorded to be as high as 68% under similar conditions. The fabricated microfluidic desalination system showed a significant improvement in terms of water yield and separation efficiency over the conventional macroscale. The high performance of this microsystem resulted from its ability to achieve a high mixing efficiency and separate phases selectively and that will provide a good platform in the near future to develop small desalination kits for personal use.
The present work reports titanium dioxide (TiO2) photocatalyst composite based on human hair that can operate efficiently under visible light. The human hair melanin structure contains active sites, which can be described as a carbon compound derived from a Quinone where one of two oxygen atoms is bonded to a hydrogen radical and that can be reversibly photogenerated under visible or ultraviolet irradiation. The human hair‐derived microfibers (HHDMs) were created by the pyrolyzing hair at 850 °C, resulting in a rod‐like hollow structure. TiO2 was immobilized on the pyrolyzed hair by a simple self‐template method. The resulting composite was calcined at five different temperatures (150 to 350 °C). The HHDM and HHDM‐TiO2 morphologies and the chemical compositions were characterized using scanning electron microscopy (SEM), Energy‐dispersive X‐ray spectroscopy (EDX), X‐ray photoelectron spectroscopy (XPS), Fourier‐transform infrared spectroscopy (FTIR), and X‐ray powder diffraction (XRD). The HHDM‐TiO2 photocatalytic efficiency in degrading methylene blue was investigated and compared to that of a conventional TiO2 catalyst (P25). HHDM‐TiO2 was more effective for methylene blue degradation under visible light than the conventional P25 catalyst suspension due to the unique photosensitivity and porous structure of the composite. The catalyst calcined at 300 °C showed the best performance, which was 71% higher than that of the P25 catalyst.
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BACKGROUND The wide bandgap and low activity under visible light of titanium dioxide (TiO2) have limited its use in many industrial processes. This limitation is associated with the inadequate solar spectrum that activates its surface, where most of the photoexcited electron–hole pairs recombine thus, leading to a drop in the photocatalytic performance. Immobilization of TiO2 on the surface of other materials such as silicon is a suitable approach to overcome these drawbacks. However, the known immobilization methods require either high‐temperature or high‐pressure conditions. The objective of the present work is to introduce and evaluate a low power‐consumption electrodeposition method for creating a new photocatalyst that can act in visible light using electrochemical anodization for immobilizing the TiO2 on a silicon wafer surface. Two methods were utilized for immobilization which is electrodeposition and sol–gel. The prepared photocatalyst surface and composition were characterized by scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS). RESULTS The laser‐aided electrodeposition method created a unique porous silicon surface after the itching process, where the TiO2 was successfully immobilized on the silicon surface. The resulting SEM images confirmed the formation of three‐dimensional (3D)‐like structures on the silicon surface that resulted in a higher light absorption efficiency. The methylene blue degradation rate was higher by 60% using the 3D structured surface when compared with that prepared by the sol–gel method. CONCLUSION Unique microstructures were created on the silicon surface by the laser‐aided electrodeposition method that enables photocatalysis in visible light. © 2019 Society of Chemical Industry
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