Presence Of Heterojunction Research Articles

Evaluation of Ag@TiO2/WO3 heterojunction photocatalyst for enhanced photocatalytic activity towards methylene blue degradation

Methylene blue is a dye that is extensively used in the textile industry but it is a hazardous, carcinogenic, and mutagenic pollutant. Therefore, the treatment of wastewater containing methylene blue by photocatalytic degradation under visible light without using any sacrificial agent (H2O2) is an important method towards attaining an eco-friendly environment. Herein, the nanocomposite of Ag-doped TiO2 on WO3 nanoparticles (Ag@TiO2/WO3) was prepared by a modified sol-gel precipitation route, and their physicochemical properties were studied. The bandgap of Ag sensitized metal oxide nanocomposite in Ag@TiO2/WO3 was slightly reduced compared to the pristine titania due to the creation of interstitial energy states during colligation of titania and tungsten oxide. The ease of charge carrier transfers through the heterojunction of TiO2/WO3 increased the photocatalytic activity of the photocatalyst. Furthermore, in Ag@TiO2/WO3 the plasmonic Ag sensitization to the host semiconductor TiO2 has further boosted the rate of photocatalytic degradation because of the surface plasmon resonance (SPR) and hindrance of charge carrier recombination. Due to the synergistic effect of SPR and the presence of heterojunction in Ag@TiO2/WO3, the photocatalytic activity was found to be 25 times higher for Ag@TiO2/WO3 than that of commercial DP25 photocatalyst under visible light towards methylene blue degradation.

Facile synthesis of mesoporous graphitic carbon nitride/SnO2 nanocomposite photocatalysts for the enhanced photodegradation of Rhodamine B

In order to enhance the photocatalytic performance of carbon nitride, mesoporous graphitic carbon nitride (mpg-C3N4) nanocomposite photocatalyst (mpg-C3N4/SnO2) with high photocatalytic activity was synthesized by in situ growth method in this paper. The prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–Vis diffuse reflectance spectra (DRS). Also, the photocatalytic properties of mpg-C3N4/SnO2 nanocomposite were studied by photocatalytic degradation of Rhodamine B (RhB) solution under visible light irradiation. After 120 min of visible light irradiation, the photocatalytic activity of the synthesized mpg-C3N4/SnO2 nanocomposite increased significantly, the degradation effect of the mpg-C3N4/SnO2 composite sample can reach up to 93%, and higher than that of pure mpg-C3N4 and SnO2. The mesoporous structure of mpg-C3N4/SnO2 nanocomposite could enlarge the contact area with dye and increase light absorption, and the presence of heterojunction on the interface between mpg-C3N4 and SnO2 further enhanced the separation efficiency of photogenerated electron hole pairs, sequentially improves the photocatalytic performance of the mpg-C3N4/SnO2 nanocomposite.

Improving hole mobility with the heterojunction of graphitic carbon nitride and titanium dioxide via soft template process in photoelectrocatalytic water splitting

In this current work, we have prepared graphitic carbon nitride@titanium dioxide (g-C₃N₄@TiO2) nanocomposite material via simple one-step soft template synthesis to improve the efficacy of charge separation in photoelectrocatalytic water splitting. The g-C3N4, a photoactive component was incorporated in varying amounts into TiO2, and the resulting composites were confirmed to have improved photoelectrocatalytic activity over the bare-TiO2. Under the optimal experimental condition, the 20 wt % g-C₃N₄@TiO2 composite exhibited the highest photoelectrocatalytic activity. The g-C3N4 has an ability to absorb the incident photons, resulting in excitation of electrons between the frontier orbitals. These excited electrons move to TiO2via the interfacial border, hindering the recombination of the photo-induced electrons and holes and thus, improves the overall performance of the photocatalyst. The improved photoelectrocatalytic performance by g-C3N4@TiO2 was ascribed to the overall impact of g-C3N4 that increased its absorptive spectrum into the visible region. As such, the presence of heterojunction in the prepared composite not only aided the separation of the photogenerated charge carriers but also maintained its strong oxidation and reduction capability in the photoelectrocatalytic water splitting.

Fe-ZrO2 imbedded graphene like carbon nitride for acarbose (ACB) photo-degradation intermediate study

Fe-ZrO2 imbedded g-C3N4 was successfully prepaid by solvo-thermal method for the photo-degradation of anti-diabetic drug, acarbose (ACB). The synthesized material were characterized with the help of FT-IR-Spectroscopy, X-ray diffraction, UV–vis-Spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, HPLC-MS and scanning electron microscopy. These characterization results indicated that the target materials was well prepared and photo-catalytically active. The target catalyst (Fe-ZrO2/g-C3N4) showed very high photo-degradation rate against acarbose (ACB) and rhodamine (RhB). Presence of heterojunction between FZ and GCN increased the surface area and light absorbance capability. HPLC-MS scrutiny indicated that photo-degradation process, under visible light, split the ACB into lot of intermediates and finally degraded completely.

(Invited) Development and Integration of Heterojunctions for Enhanced Solar Energy Conversion

Photoelectrochemical applications of semiconducting metal oxides are continuously growing and gaining a considerable interest in view of enhanced production of renewable energy. However, overcoming intrinsic limitations of well-known and recognized towards specific action semiconducting oxides such as iron oxide, titanium oxide, tungsten oxide or copper oxide requires development of new nanoarchitectures. Given the band edges positions are not always suitable for a desired solar driven process, of primary importance is to enhance the intrinsic properties of the building materials and couple them with a catalytic modification of the surface. Therefore, efforts including development of new hetero-nanostructures and their implementation to the different type of junctions employed in solar arrangements, are continuously devoted to minimization of the required bias voltage, improvement of light capture or charge separation and collection. Recently, these approaches allowed to develop a highly active catalytic system consisting of a mesoporous semiconducting metal oxide (tungsten trioxide, titanium dioxide or iron oxide) and attached thereto polyoxometalate based WOC. The stable and reproducible water splitting photocurrents reached 4.5 mA cm-2 for WO3 based working system and were attained at standard conditions. In this scenario, incorporated in small amount polyoxometalates act as highly effective molecular OER catalysts leading to very large enhancement of water oxidation photocurrents [1]. These findings have also been transferred to other semiconducting systems relying onto engineered low sub-stoichiometric disorder in TiO2 or hexagonal WO3 conjugated to copper (I) oxide, enhanced and stabilized by the presence of heterojunction [2]. A special attention will be paid to their stabilization, intentional modification, as well as optimization of experimental conditions, permitting control and diversification of the reaction products. [1] M. Sarnowska, K. Bienkowski, P. J. Barczuk, R. Solarska, J. Augustynski, Adv. Energy Mater. (2016), 1600526 [2] E. Szaniawska, K. Bienkowski, I. Rutkowska, P. Kulesza, R. Solarska, Cat. Today (2017) doi.org/10.1016/j.cattod.2017.05.099

UV Induced Zener Diode Characteristic in a Single <I>n</I>-ZnO/<I>p</I><SUP>++</SUP>-Si Nanoheterojunction

Rectification is observed in a single n-ZnO/p++-Si nanoheterojunction using ultra high vacuum compatible scanning tunneling microscope. The nanohetrojunctions have been grown using catalyst free vapor-solid growth of ZnO nanorods on p++-Si substarte. A high rectification ratio approximately 100 at 2 V is observed in the current voltage measurements. Temperature dependent study in these nanohetero-junctions showed activation energy for carrier conduction approximately 66 meV, which is primarily associated to the presence of heterojunction induced interface states. Role of ultra violet excitation on these finite sized (approximately 500 nm) nanoheterojunction is also studied with photo-generated electron-hole pairs. A Zener breakdown is observed in this photo-excitation process. Increase in the concentration of minority carriers and corresponding decrease in barrier width and height at the junction have been identified for the observed tunneling behavior under UV illumination. The large carrier concentration in the finite sized device with large diffusion length of electron (approximately 2 microm) is made responsible for the observed voltage regulation.

High Doping Density/High Electric Field, Stress and Heterojunction Effects on the Characteristics of CMOS Compatible p-n Junctions

This paper critically reviews the different mechanisms impacting the current-voltage and capacitance voltage characteristics of complementary metal oxide semiconductor (CMOS) compatible p-n junctions. Special attention is given to the influence of high doping density/high electric fields, mechanical stress and the presence of a hetero-junction either at the junction or in the depletion region. The basic mechanisms reported in the literature are checked for their validity for state-of-the-art structures and processing techniques. Critical issues are pointed out and illustrated for advanced CMOS compatible hetero-junctions, where high-field effects, like trap-assisted tunneling (TAT) and band-to-band-tunneling (BTBT) play a prominent role. The presence of an isotype hetero-junction gives rise to frequency dispersion in the depletion layer capacitance, which becomes more pronounced in combination with grown-in or processing-induced defects at the hetero-interface. Finally, the challenges and opportunities for future devices are addressed.