Preparation, characterization and photodegradation of methylene blue based on TiO2 microparticles modified with thiophene substituents

Abstract

The new microparticles, 2-formylthiophene (FT)/TiO 2 and (E)-1,2-bis(5-formyl-2-thienyl) ethylene (EBFTE)/TiO 2 were synthesized with a silane coupling agent. The prepared TiO 2 composites were characterized using Ultraviolet-Vis absorption (UV-Vis), X-ray diffraction (XRD), scanning electron microscope (SEM) and thermogravimetric analyzer (TGA). Methylene blue was used as a model material to examine the photocatalytic activities of the prepared catalysts under both Ultraviolet-Vis (UV) and visible (Vis) light. The enhanced photocatalytic activities were observed in the presence of (FT)/TiO 2 and EBFTE/TiO 2 under Vis light. It suggests that FT or EBFTE plays a block or active role in the photodegradation mechanisms under UV and Vis light irradiation, respectively. Organic dyes are widely used in textile industry and the released industrial waste has caused serious damages to the water system [1][2][3][4][5]. In 1976, Carey et al. [6] first reported that TiO 2 was used as a photocatalyst in the degradation of biphenyl and chlorobiphenyls. Frank and Bard [7] studied the photocatalysis oxidation of cyanide ion with oxygen in the presence of TiO 2 powders as a heterogeneous photocatalyst. TiO 2 with the non-toxicity, chemically stability and low cost is a dramatic photocatalyst in degradation of colored water. However, TiO 2 can only make use of ultraviolet (UV) light that accounted for about 3%-5% of sunlight due to its rather broad band-gap (3.2 eV) [1]. Therefore, researches have been done to explore the mechanism of photocatalytic degradation with TiO 2 [8][9][10][11][12][13][14][15] and improvement of the degradation efficiency. Thus, some effective methods have been developed, such as dye-sensitization, ion doping and semiconductor coupling [16][17][18]. In particular, dye-sensitization is utilized to expand the spectral response region extending from UV light to visible (Vis) light. Sensitizers that showed a better energy match with the conduction band (CB) and the valence band (VB) of TiO 2 are introduced to improve the utilization efficiency of sunlight. The composites are desired to be active, Vis-responsive and highly stable [12]. For example, porphyrin/TiO 2 [19] and poly(acrylamide-co-(acrylic acid))/TiO 2 [20] were applied in photodegradation and showed high degradation efficiency. In addition, thiophene and its derivatives are considered as a kind of promising sensitizers due to its high absorption in Vis light region. Zhu et al. [21] and Lu and Yang [22] reported that polythiophene/TiO 2 and poly(3-hexylthiophene)/TiO 2 microparticles were synthesized and provided an apparent additive effect on their adsorption capacities under both UV light and Vis light.However, small molecule organic compounds modified TiO 2 are seldom reported. On the other hand, (E)-1,2-bis-(2-thienyl) ethylene [23] was reported as a kind of high performance material in Vis light region with narrow energy

Photocatalytic Activity of Ag-TiO2 Composites Deposited by Photoreduction under UV Irradiation

“…Furthermore, Figure 6 shows that Ag-TiO 2 thin films showed an important increase in the photocatalytic activity under UV (near 35%); these results could be due to the silver aggregates deposited on the TiO 2 surface that can accumulate charge and accept electrons inside the semiconductor. The accumulation of electrons can reduce the carrier's recombination increasing generation of reactive oxygen species, and besides, Ag particle on TiO 2 can change and a collective oscillation can be generated, which is known as localized surface plasmon resonance (SPR) [49]; according to other reports, silver particles exhibit collective oscillation of their electrons in the conduction band, and it is suggested that the association between the semiconductor and the metal can increase photocatalytic activity, which coincides with the results obtained in this work [50]. Pseudo-first-order model was applied to kinetic data of Figure 6.…”