Synthesis, Characterization Of Several Vanadium Oxides Nanomaterials And Their Application In Catalytic Degradation Of Dyes

Textile industry effluents contain a variety of complex and hard to degrade pollutantssuch as dyes that may cause significant water pollution when they are released to ourenvironment. Therefore, to synthesize a highly effective catalyst for treating textile dyewastewater is still a challenge and has important scientific significance and applicationprospects.Semiconductor photocatalysts have been extensively studied in recent decades, andhave been applied in numerous areas, such as water treatment, air purification,decomposition of water into hydrogen, etc. However, most of photocatalysts work underultraviolet light. Thereinto, nano-TiO2has been extensively studied as an effectivephotocatalyst, but it is not a good candidate under visible light irradiation. Therefore, it isstill a challenge to synthesize a highly effective catalyst for treating textile dye wastewaterunder visible light. Vanadium oxides semiconductor materials have received significantattention recently because of their distinctive structural versatility and novel applicationsin catalysis, high-energy lithium batteries, electric field-effect transistors, chemicalsensors/actuators and electrochemical devices. Nevertheless, a few studies about usingvanadium oxides in photocatalytic degradation of organic pollutants have been reported.In this thesis, several kinds of vanadium oxide nanomaterials were synthesized viahydrothermal method, and their photocatalytic or electrochemical properties were studied.The main results are as follows:1. The ammonium vanadium oxide cross-like nanobelt arrays with bamboo matcenter were synthesized via hydrothermal method using NH4VO3as precursors inpresence of sodium carboxymethyl cellulose (CMC), the soft template, at160C for6h.The synthesized-products were characterized by XRD, FE-SEM, TEM, SA-ED, HRTEM,and FT-IR. The effects of CMC concentration, pH value and temperature on the productmorphology were investigated. It showed that pH value plays a crucial role in theformation of cross-like nanobelt arrays. Based on the results of time dependentexperiments, the growth process of the cross-like NH4V4O10nanobelt arrays is proposed.Furthermore, the mixed valance state vanadium oxide nanobelt arrays were obtained bycalcination of the cross-like NH4V4O10nanobelt arrays at400°C for40min and its capability of catalytic degradation of rhodamine B with oxygen in aqueous under UV/vislight irradiation was studied and compared with anionic dyes. Besides, the influence oftemperature on the photocatalytic degradation was also investigated. The result showedthat the degradation efficiency of rhodamine B catalyzed by the calcinated product wasabout95%at pH6.8and75C for3h and30min, suggesting it is a candidate of efficientcatalysts for the photocatalytic degradation of rhodamine B under visible light irradiation.2. Single-crystalline MnV2O6·V2O5cross-like nanobelt arrays were successfullysynthesized by hydrothermal reaction. The products were characterized by XRD, TEMand HR-TEM. The effects of the reaction conditions such as pH, V5+/Mn2+ratio,carboxymethyl cellulose concentration and reaction time on the morphology of theproducts were studied. The band gap of the as-prepared products was calculated viadiffuse reflectance spectral analysis and their activity of photocatalytic oxidation wasevaluated by photodegradation of methylene blue under visible-light irradiation. Theresults showed that the degradation efficiency of methylene blue catalyzed by thecalcinated products is remarkably enhanced due to Mn doping, suggesting thatMnV2O6·V2O5cross-like nanobelt arrays are a good candidate for visible-light-drivenphotocatalysts.3. VO2(B) hollow like-nanosphere material was synthesized via a facile one-stephydrothermal process using vanadium oxalate as precursors in the presence ofwater-benzyl alcohol. Effects of vanadium oxalate concentration, existence of benzylalcohol and its concentration, and addition of hydrogen peroxide on the morphologies ofas-prepared products were investigated. The as-synthesized products were characterizedby XRD, FE-SEM, TEM, HR-TEM and FT-IR. Based on the results of time dependentexperiments, the growth process of VO2(B) hollow like-nanosphere were proposed. Theinside-out Ostwald ripening is responsible for the growth of spherical particles and theformation of hollow like-nanosphere. In addition, the electrochemical properties of VO2(B) like-nanosphere at various reaction times were compared by using cyclicvoltammogram.