Treatment of Trichloroethylene with Photocatalyst-Coated Optical Fiber

Titania-zeolite composite for tetracycline photocatalytic degradation under visible light: A comparison between doping and ion exchange

In this study, TiO2 supported over embryonic Beta zeolite (BEA) was prepared for the photocatalytic degradation of Tetracycline (TC) antibiotic under visible light. The immobilization of sol-gel TiO2 over the zeolite increased its surface area from 33 (m2/g) to 226 (m2/g) and enhanced its adsorption efficiency from 8 % to 18 %. In order to expand the photocatalytic activity of TiO2 towards the visible light region (i.e. λ > 380 nm), two different metal sensitization techniques with Iron ions from aqueous solution of FeCl3 were explored. In the ion-exchange method, the substitutional cations within the TiO2/BEA structure were exchanged with Fe3+. Whereas, in the doping technique, solgel TiO2 was doped with Fe3+ during its synthesis and before its immobilization over Zeolite. Four different samples with 20, 40, 60, and 100 % w/w of TiO2/BEA ratio were prepared. After testing the various ion-exchanged photocatalysts under blue and white lights, only Fe-60%TiO2/BEA showed better activity compared to pure TiO2 under white light at TC initial concentration, C o = 20 ppm. For the doped immobilized Titania with 60 wt% TiO2/BEA, three different doped photocatalysts were prepared with 3 %, 7 %, and 10 % per mole Fe/TiO2. All the Fe-doped TiO2/BEA photocatalysts showed better activity compared to pure TiO2 under white light. Under solar irradiations, the 3 % Fe-doped TiO2/BEA was able to degrade all TC within 120 min, while Fe-60%TiO2/BEA needed 200 min, and TiO2 needed more than 300 min. This enhanced performance was a result of both increased surface area due to immobilization over BEA as well as iron doping by Fe3+ that simultaneously increased the visible light absorption of TiO2 and minimized the charge carrier recombination effect.

Ag/Cr-TiO2 and Pd/Cr-TiO2 for Organic Dyes Elimination and Treatment of Polluted River Water in Presence of Visible Light

In this work, photocatalytic materials constituted by Cr-doped TiO2 (Cr-TiO2) decorated with noble metals show high effectiveness in the mineralization of Acid Orange 7 (AO7) and in the disinfection of real river water. The materials were firstly obtained by sol-gel method to get Cr-TiO2 that was subsequently modified by photochemical deposition of Ag or Pd nanoparticles (Ag/Cr-TiO2, Pd/Cr-TiO2). Chemical-physical characterization results evidenced that the noble metals were homogeneously distributed on the Cr-TiO2 surface. By using Pd(0.25%)/Cr-TiO2, the AO7 discoloration efficiency was about 91.4% after only 60 min of visible irradiation, which can be due to the lowest band gap of this material. Moreover, nitrates, chlorides, total hardness, and coliform bacteria content significantly decreased after the treatment of real river water samples (that is contaminated by industrial and domestic effluents) under UV and visible light irradiation in the presence of TiCrOx decorated with noble metals. One hundred percent of elimination rate for E. coli, total coliforms, and other enterobacteriaceae (without regrowth) was achieved by using Ag/Cr-TiO2 as photocatalyst.

UV-Vis Activated Cu2O/SnO2/WO3 Heterostructure for Photocatalytic Removal of Pesticides

A three-steps sol–gel method was used to obtain a Cu₂O/SnO₂/WO₃ heterostructure powder, deposited as film by spray pyrolysis. The porous morphology of the final heterostructure was constructed starting with fiber-like WO₃ acting as substrate for SnO₂ development. The SnO₂/WO₃ sample provide nucleation and grew sites for Cu₂O formation. Diffraction evaluation indicated that all samples contained crystalline structures with crystallite size varying from 42.4 Å (Cu₂O) to 81.8 Å (WO₃). Elemental analysis confirmed that the samples were homogeneous in composition and had an oxygen excess due to the annealing treatments. Photocatalytic properties were tested in the presence of three pesticides—pirimicarb, S-metolachlor (S-MCh), and metalaxyl (MET)—chosen based on their resilience and toxicity. The photocatalytic activity of the Cu₂O/SnO₂/WO₃ heterostructure was compared with WO₃, SnO₂, Cu₂O, Cu₂O/SnO₂, Cu₂O/WO₃, and SnO₂/WO₃ samples. The results indicated that the three-component heterostructure had the highest photocatalytic efficiency toward all pesticides. The highest photocatalytic efficiency was obtained toward S-MCh (86%) using a Cu₂O/SnO₂/WO₃ sample and the lowest correspond to MET (8.2%) removal using a Cu₂O monocomponent sample. TOC analysis indicated that not all the removal efficiency could be attributed to mineralization, and by-product formation is possible. Cu₂O/SnO₂/WO₃ is able to induce 81.3% mineralization of S-MCh, while Cu₂O exhibited 5.7% mineralization of S-MCh. The three-run cyclic tests showed that Cu₂O/SnO₂/WO₃, WO₃, and SnO₂/WO₃ exhibited good photocatalytic stability without requiring additional procedures. The photocatalytic mechanism corresponds to a Z-scheme charge transfer based on a three-component structure, where Cu₂O exhibits reduction potential responsible for O₂ production and WO₃ has oxidation potential responsible for HO· generation.