Room Temperature Synthesis of V-Doped TiO₂ and Its Photocatalytic Activity in the Removal of Caffeine under UV Irradiation

Recent advances in biopolymer-based advanced oxidation processes for dye removal applications: A review

Over the past few years, synthetic dye-contaminated wastewater has attracted considerable global attention due to the low biodegradability and the ability of organic dyes to persist and remain toxic, causing numerous health and environmental concerns. As a result of the recalcitrant nature of those complex organic dyes, the remediation of wastewater using conventional wastewater treatment techniques is becoming increasingly challenging. In recent years, advanced oxidation processes (AOPs) have emerged as a potential alternative to treat organic dyestuffs discharged from industries. The most widely employed AOPs include photocatalysis, ozonation, Fenton oxidation, electrochemical oxidation, catalytic heterogeneous oxidation, and ultrasound irradiation. These processes involve the generation of highly reactive radicals to oxidize organic dyes into innocuous minerals. However, many conventional AOPs suffer from several setbacks, including the high cost, high consumption of reagents and substrates, self-agglomeration of catalysts, limited reusability, and the requirement of light, ultrasound, or electricity. Therefore, there has been significant interest in improving the performance of conventional AOPs using biopolymers and heterogeneous catalysts such as metal oxide nanoparticles (MONPs). Biopolymers have been widely considered in developing green, sustainable, eco-friendly, and low-cost AOP-based dye removal technologies. They inherit intriguing properties like biodegradability, renewability, nontoxicity, relative abundance, and sorption. In addition, the immobilization of catalysts on biopolymer supports has been proven to possess excellent catalytic activity and turnover numbers. The current review provides comprehensive coverage of different AOPs and how efficiently biopolymers, including cellulose, chitin, chitosan, alginate, gelatin, guar gum, keratin, silk fibroin, zein, albumin, lignin, and starch, have been integrated with heterogeneous AOPs in dye removal applications. This review also discusses the general degradation mechanisms of AOPs, applications of biopolymers in AOPs and the roles of biopolymers in AOPs-based dye removal processes. Furthermore, key challenges and future perspectives of biopolymer-based AOPs have also been highlighted.

V-doped TiO2 photocatalysts and their application to pollutant degradation

V-doped TiO₂ materials (0.01, 0.05, 0.10, and 1.00 nominal atomic %) were synthesized by the sol-gel method and characterized by X-ray diffraction, Raman spectroscopy, UV-visible diffuse reflectance spectroscopy, N₂ adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and H₂-temperature programmed reduction. Two vanadium precursors (vanadyl acetylacetonate and ammonium metavanadate) and three calcination temperatures (400, 500, and 600 °C, with and without air circulation) were assayed. The efficiency of the materials as photocatalysts was studied by the degradation of phenol with UV and visible lamps. The photocatalyst prepared from vanadium acetylacetonate, with a vanadium content of 0.01 nominal atomic %, calcination at 400 °C without air circulation (0.01VTi-400), showed the best performance, reaching 100% and 30% degradation of phenol (50 μM) by irradiation with UV lamps (3 h) and visible lamps (5 h), respectively. To evaluate the efficiency of this catalyst in the degradation of other structurally related compounds, two substituted phenols were selected: 4-chlorophenol and 4-nitrophenol. The 0.01VTi-400 photocatalyst showed to be applicable to the degradation of phenolic compounds when the substituent was an activating group or a weakly deactivating group (for electrophilic reactions). Additionally, the selectivity of 0.01VTi-400 for phenol degradation in the presence of Aldrich humic acid was tested: phenol degradation reached 68% (3 h, UV lamps). The performance of 0.01VTi-400 indicated that it is a promising material for further applications.

Highly crystalline anatase TiO2 nanocuboids as an efficient photocatalyst for hydrogen generation

Highly crystalline anatase titanium dioxide (TiO2) nanocuboids were synthesized via a hydrothermal method using ethylenediamine tetraacetic acid as a capping agent. The structural study revealed the nanocrystalline nature of anatase TiO2 nanocuboids. Morphological study indicates the formation of cuboid shaped particles with thickness of ∼5 nm and size in the range of 10-40 nm. The UV-visible absorbance spectra of TiO2 nanocuboids showed a broad absorption with a tail in the visible-light region which is attributed to the incorporation of nitrogen atoms into the interstitial positions of the TiO2 lattice as well as the formation of carbonaceous and carbonate species on the surface of TiO2 nanocuboids. The specific surface areas of prepared TiO2 nanocuboids were found to be in the range of 85.7-122.9 m2 g-1. The formation mechanism of the TiO2 nanocuboids has also been investigated. Furthermore, the photocatalytic activities of the as-prepared TiO2 nanocuboids were evaluated for H2 generation via water splitting under UV-vis light irradiation and compared with the commercial anatase TiO2. TiO2 nanocuboids obtained at 200 °C after 48 h exhibited higher photocatalytic activity (3866.44 μmol h-1 g-1) than that of commercial anatase TiO2 (831.30 μmol h-1 g-1). The enhanced photoactivity of TiO2 nanocuboids may be due to the high specific surface area, good crystallinity, extended light absorption in the visible region and efficient charge separation.

Synthesis and Characterization of Various Doped TiO2 Nanocrystals for Dye-Sensitized Solar Cells

Few works are reported on solvothermal preparation of nanoparticles by utilizing acetone alone without a surfactant. This synthesis approach is found to be prominent for producing the mesoporous structure, which is crucial in improving the dye loading of the photoanode. In addition, doping of metal ions is advantageous in order to bring down the excitation energy, which is promising for boosting the performance of the doped oxides. This research aims to synthesize various kinds of doped-TiO2 nanocrystals to serve as photoanode materials in dye-sensitized solar cells (DSSCs). An X-ray diffraction study evidenced the existence of the crystalline phase in pure and doped-TiO2 nanocrystals. Rietveld refinement study showed the mixed phases of crystalline TiO2 in the CrT, CuNT, and ST as compared to a single anatase phase in the samples PT, AgT, BT, CoT, FeT, SnT, ZT, VT, and ZMT. The absorption spectroscopy analysis demonstrated the reduced optical band gap from 3.10 to 2.79 eV. Scanning electron microscopy investigation endorsed the formation of TiO2 mesoporous microspheres with a mean diameter ranging from 200 to 331 nm along with a nanocrystal diameter ranging from 10 to 20 nm. Doping with the different dopants enhanced the conversion efficiency of DSSCs from 1.31 to ∼6%. Furthermore, we have performed the electrochemical impedance spectroscopy of DSSCs, and the findings are presented.

Enhanced Photocatalytic Degradation of Caffeine Using Titanium Dioxide Photocatalyst Immobilized on Circular Glass Sheets under Ultraviolet C Irradiation

This work presents the development of titanium dioxide (TiO2) film immobilized on circular glass sheets for photocatalytic degradation of caffeine under ultraviolet C (UVC) irradiation. TiO2 was synthesized through the ultrasonic-assisted sol–gel method and immobilized on circular glass sheets by the doctor blade technique. Polyvinylpyrrolidone (PVP) was used to mix with the TiO2 precursor solution to enhance film adhesion on the glass surface. TiO2 film was mainly composed of anatase phase with a small amount of rutile phase. Caffeine removal was found to increase with increasing irradiation time. Caffeine (20 mg/L) in the synthetic wastewater could not be detected after 3 h of UVC irradiation. The reaction rate of caffeine degradation followed the pseudo-first-order model. The concentrated caffeine solutions required a longer irradiation time for degradation. The used TiO2-coated glass sheets could be easily separated from the treated wastewater and reusable. The caffeine removal efficiency of TiO2-coated glass sheets in each cycle maintained a high level (~100%) during fifteen consecutive cycles.

The Influence of Light Irradiation on the Photocatalytic Degradation of Organic Pollutants

The design of a photocatalytic process must consider intrinsic and extrinsic parameters affecting its overall efficiency. This study aims to outline the importance of balancing several factors, such as radiation source, total irradiance, photon flux, catalyst substrate, and pollutant type in order to optimize the photocatalytic efficiency. Titanium oxide was deposed by the doctor blade technique on three substrates (microscopic glass (G), flour-doped tin oxide (FTO), and aluminum (Al)), and the photocatalytic properties of the samples were tested on two pollutants (tartrazine (Tr) and acetamiprid (Apd)). Seven irradiation scenarios were tested using different ratios of UV-A, UV-B + C, and Vis radiations. The results indicated that the presence of a conductive substrate and a suitable ratio of UV-A and Vis radiations could increase the photocatalytic efficiency of the samples. Higher efficiencies were obtained for the sample Ti_FTO (58.3% for Tr and 70.8% for Apd) and the sample Ti_Al (63.8% for Tr and 82.3% for Apd) using a mixture of three UV-A and one Vis sources (13.5 W/m² and 41.85 μmol/(m²·s)). A kinetic evaluation revealed two different mechanisms of reaction: (a) a one-interval mechanism related to Apd removal by Ti_FTO, Ti_Al (scenarios 1, 4, 5, and 7), and Ti_G samples (scenario 7) and (b) a two-interval mechanism in all other cases.

Titania-Coated Alumina Foam Photocatalyst for Memantine Degradation Derived by Replica Method and Sol-Gel Reaction

In the present work, alumina (Al₂O₃) foam was prepared by the replica method where a polyurethane (PU) foam (30 pores per inch (ppi)) template was impregnated with a 60 wt.% Al₂O₃ suspension. Sintered Al₂O₃ foam was used as substrate for the deposition of sol-gel derived titania (TiO₂) film using dip coating. For the preparation of TiO₂ sol, titanium(IV) isopropoxide (Ti-iPrOH) was used as the precursor. The common problem of qualification and quantification of a crystalline coating on a highly porous 3D substrate with an uneven surface was addressed using a combination of different structural characterization methods. Using Powder X-ray Diffraction (PXRD) and synchrotron Grazing Incidence X-ray Diffraction (GIXRD) on bulk and powdered Al₂O₃ foam and TiO₂-coated Al₂O₃ foam samples, it was determined Al₂O₃ foam crystallizes to corundum and coating to anatase, which was also confirmed by Fourier Transformed Infrared Spectroscopy (FTIR). Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM/EDS) revealed the structural and microstructural properties of the substrate and coating. Differential Thermal Analysis (DTA) and Thermogravimetric Analysis (TGA) were used to clarify the evolution of the porous microstructure. The Al₂O₃-TiO₂ composite was evaluated as a photocatalyst candidate for the degradation of the micropollutant medication memantine. The degradation rate was monitored using a light-emitting diode (LED) lamp operating at electromagnetic (EM) wavelength of 365 nm. The photocatalytic activity of sol-gel-derived TiO₂ film immobilized on the Al₂O₃ foam was compared with commercially available TiO₂ nanoparticles, P25-Degussa, in the form of a suspension. The levels of memantine were monitored by High-Performance Liquid Chromatography–Tandem Mass Spectrometry (HPLC–MS/MS). The efficiency and rate of the memantine photodegradation by suspended TiO₂ nanoparticles is higher than the TiO₂-coated Al₂O₃ foam. But, from the practical point of view, TiO₂-coated Al₂O₃ foam is more appropriate as a valuable photocatalytic composite material.