Evaluating the efficiency of nano-sized Cu doped TiO2/ZnO photocatalyst under visible light irradiation

Recent Developments of Advanced Ti3+-Self-Doped TiO2 for Efficient Visible-Light-Driven Photocatalysis

Research into the development of efficient semiconductor photocatalytic materials is a promising approach to solving environmental and energy problems worldwide. Among these materials, TiO2 photocatalysts are one of the most commonly used due to their efficient photoactivity, high stability, low cost and environmental friendliness. However, since the UV content of sunlight is less than 5%, the development of visible light-activated TiO2-based photocatalysts is essential to increase the solar energy efficiency. Here, we review recent works on advanced visible light-activated Ti3+-self-doped TiO2 (Ti3+–TiO2) photocatalysts with improved electronic band structures for efficient charge separation. We analyze the different methods used to produce Ti3+–TiO2 photocatalysts, where Ti3+ with a high oxygen defect density can be used for energy production from visible light. We categorize advanced modifications in electronic states of Ti3+–TiO2 by improving their photocatalytic activity. Ti3+–TiO2 photocatalysts with large charge separation and low recombination of photogenerated electrons and holes can be practically applied for energy conversion and advanced oxidation processes in natural environments and deserve significant attention.

Enhanced photocatalytic degradation of xylene by blackening TiO2 nanoparticles with high dispersion of CuO

To enhance the photocatalytic activity of TiO₂, a new preparation method has been proposed to synthesize the catalysts by introducing Cu-MOF as a precursor and performing a blackening process via a mixture with NaBH₄ for TiO₂ nanoparticles (CuO-TiO₂(mb)). The results showed that the removal efficiency of xylene under ultraviolet and visible light over CuO-TiO₂(mb) was 3.45 times higher than that of the catalysts prepared by impregnation of CuO on the surfaces of TiO₂ (CuO-TiO₂(d)) and 12.12 times higher than that of pure TiO₂ nanoparticles. Analyses by the X-ray diffraction, scanning electron microscopy, and transmission electron microscopy indicated that the introduction of Cu-MOF as a precursor on the surface of the catalyst resulted in CuO-TiO₂(mb) presenting a lower grain size compared with TiO₂ nanoparticles and CuO-TiO₂(d). The results of X-ray photoelectron spectroscopy, diffuse reflectance spectrum and photoluminescence indicated that blackening process narrowed the bind gap width and shortened the band gap from 2.95 eV to 1.32 eV, introduced the coexistence of Ti⁴⁺, Ti³⁺, Cu²⁺ and Cu⁺ in CuO-TiO₂(mb) decreased the recombination rate of e^--h⁺, which greatly improved the light response of CuO-TiO₂(mb) under ultraviolet and visible light, resulting in the benefit to the photocatalytic reaction.

Mechanochemical synthesis of nanophotocatalysts SiO2/TiO2/Fe2O3: their structural, thermal and photocatalytic properties

In the study the mechanochemical synthesis was used to prepare photocatalytic materials based on TiO2, SiO2, and Fe2O3. During the preparation the impact of composition, milling speed, and calcination process on the properties of the composites was investigated. The structural and thermal properties of photocatalysts were determined using the N2 adsorption/desorption, XRD, and FT-IR/PAS methods. The thermal stability of the obtained materials was also examined (TG/DTG). Moreover, their photocatalytic activity was tested in relation to Methylene Blue at UV and Vis radiation. The results indicate that the mechanochemical synthesis in the high-energy planetary mill is an effective method for obtaining materials with photocatalytic properties at the UV and Vis radiation. It was shown that the removal process of MB may be described by the pseudo-first-order kinetics.

Trap State and Charge Recombination in Nanocrystalline Passivized Conductive and Photoelectrode Interface of Dye-Sensitized Solar Cell

The dynamic competition between electron generation and recombination was found to be a bottleneck restricting the development of high-performance dye-sensitized solar cells (DSSCs). Introducing a passivation layer on the surface of the TiO2 photoelectrode material plays a crucial role in separating the charge by preventing the recombination of photogenerated electrons with the oxidized species. This study aims to understand in detail the kinetics of the electron recombination process of a DSSC fabricated with a conductive substrate and photoelectrode film, both passivized with a layer of nanocrystalline TiO2. Interestingly, the coating, which acted as a passivation layer, suppressed the back-electron transfer and improved the overall performance of the integrated DSSC. The passivation layer reduced the exposed site of the fluorine-doped tin oxide (FTO)–electrolyte interface, thereby reducing the dark current phenomenon. In addition, the presence of the passivation layer reduced the rate of electron recombination related to the surface state recombination, as well as the trapping/de-trapping phenomenon. The photovoltaic properties of the nanocrystalline-coated DSSC, such as short-circuit current, open-circuit voltage, and fill factor, showed significant improvement compared to the un-coated photoelectrode film. The overall performance efficiency improved by about 22% compared to the un-coated photoelectrode-based DSSC.

Intensified Photocatalytic Degradation of Solophenyl Scarlet BNLE in Simulated Textile Effluents Using TiO2 Supported on Cellulosic Tissue

The Heterogeneous photocatalysis, increasingly used in effluent purification, is attracting more and more attention by the development of new photocatalytic materials based on semiconductors deposited on various supports. In this work, TiO2 supported on cellulosic fiber was prepared and characterized by different analytical techniques such as X-ray Photoelectron Spectrometry and Brunauer-Emmett-Teller surface area. Its photocatalytic activity was investigated for the degradation of Solophenyl Scarlet BNLE (SS), an organic pollutant present in textile effluents. Several conditions were investigated such as adsorption under UV and visible irradiation, catalyst recyclability, the simulated effluent pH and the presence of H2O2 as an oxidant agent. Results showed that under UV light, the removal of SS decreased significantly with increasing initial dye concentration. For an initial concentration of 5 mg/L, SS degradation was reached more than 95 % after 2 hours of treatment (neutral pH, T = 20 °C). The supported TiO2 on cellulose remains effective over four cycles of dye treatment. In the presence of H2O2, the degradation process was inhibited with increasing the molar ratio [H2O2]/[SS]0 from 5 to 30. The kinetic modeling showed that the removal of this pollutant followed a pseudo-first-order model (Langmuir-Hinshelwood) with a regression coefficient (R2) value of 0.984.

Photocatalytic degradation and kinetic modeling of azo dye using bimetallic photocatalysts: effect of synthesis and operational parameters

Industrial wastewaters are the major source polluting the surface and ground water resources. Pollutants released along with the untreated textile industry wastewaters are responsible for the great damage to the natural resources like water. Considering the hazardous effects of the azo dyes (textile coloring agents) and their byproducts, there is a need to develop cost-effective and efficient treatment method for the textile wastewaters as such dyes have been reported as toxic, mutagenic, and carcinogenic and can cause direct demolition of aquatic communities. One of the possible and effective treatment methods is the use of TiO₂ photocatalysis due to its chemical stability, low cost, and non-toxic nature. The present study explored the photocatalytic potential of anatase-type of bimetallic Cu-Ni/TiO₂ photocatalysts under visible light irradiation for possible photocatalytic degradation and mineralization of Methyl Orange (MO), as model azo dye. The focus was to correlate the synthesis (different calcination temperatures, phase composition of TiO₂ either anatase or rutile, and metal ion loading in terms of concentration and composition (Cu:Ni)) and operational parameters (photocatalyst loading, pollutant concentration, and irradiation time) that were believed responsible for the enhanced photocatalytic performance. Blank experiments were carried out to check the effect of metal loading in comparison to bare TiO₂ and effect of absence or presence of light and photocatalysts on MO photodegradation. Results obtained using bimetallic photocatalysts are promising as compared to bare TiO₂ as 100% MO removal and ~ 90% %COD removal were obtained in 90 min of irradiation, obeying a pseudo-first-order kinetics with photocatalytic reaction via the Langmuir-Hinshelwood mechanism with a good linear fit. Photocatalysts synthesized using anatase TiO₂ were reported with improved performance compared to rutile phase. It is evident that synthesis parameters influence photocatalyst performance directly. The higher rate constant (> 1) that proves the excellent adsorption capacity of the tested photocatalysts for tested pollutants on the surface may have a great prospective for photocatalytic water purification at neutral pH.

An overview of photocatalytic degradation: photocatalysts, mechanisms, and development of photocatalytic membrane

Photocatalysis is an ecofriendly technique that emerged as a promising alternative for the degradation of many organic pollutants. The weaknesses of the present photocatalytic system which limit their industrial applications include low-usage of visible light, fast charge recombination, and low migration ability of the photo-generated electrons and holes. Therefore, various elements such as noble metals and transition metals as well as non-metals and metalloids (i.e., graphene, carbon nanotube, and carbon quantum dots) are doped into the photocatalyst as co-catalysts to enhance the photodegradation performance. The incorporation of the co-catalyst which alters the photocatalytic mechanism was discussed in detail. The application of photocatalysts in treating persistent organic pollutants such as pesticide, pharmaceutical compounds, oil and grease and textile in real wastewater was also discussed. Besides, a few photocatalytic reactors in pilot scale had been designed for the effort of commercializing the system. In addition, hybrid photocatalytic system integrating with membrane filtration together with their membrane fabrication methods had also been reviewed. This review outlined various types of heterogeneous photocatalysts, mechanism, synthesis methods of biomass supported photocatalyst, photocatalytic degradation of organic substances in real wastewater, and photocatalytic reactor designs and their operating parameters as well as the latest development of photocatalyst incorporated membrane.

Preparation of an Au-TiO2 photocatalyst and its performance in removing phycocyanin

A novel TiO₂ photocatalyst (Au-TiO₂ composite film) with enhanced photocatalytic activity has been synthesized, characterized and its performance in the removal of phycocyanin (PC) was investigated. The results show that the Au-TiO₂ composite film has a lower electron-hole recombination rate, wider optical response range and high electron transfer rate. The photocatalytic activity of the as-prepared Au-TiO₂ composite photocatalyst was observed to be enhanced with the removal efficiency of PC and dissolved organic nitrogen found to be 96.7% and 59%, respectively using the UV/Au-TiO₂ process. In addition, the combination of photocatalytic pretreatment and coagulation can achieve an enhanced removal efficiency. The Au-TiO₂ photocatalyst was found to decrease the dichloroacetonitrile formation potential (105.9 to 79.3 μg/L), however, it exacerbated the production of trichloromethane and dichloroacetamide beyond their initial levels (116.7 to 224.9 μg/L and 2.27 to 2.31 μg/L, respectively). The divergent trends of these disinfection by-products are due to the fundamental differences in the precursor material.

Ag loaded B-doped-g C3N4 nanosheet with efficient properties for photocatalysis

Three material engineering strategies in the form of doping (Boron-doping), nanostructuring (nanosheet (NS) formation) and decorating with plasmonic nanoparticles (loading with Ag metal), were integrated to improve the photocatalytic activity of graphitic carbon nitride (gC₃N₄). Concentrations of B-doping and Ag-loading were optimized to maximize the catalytic performance in the final nanocomposite of Ag-loaded B-doped gC₃N₄ NS. Combined effect of all three strategies successfully produced over 5 times higher rate towards degradation of organic dye pollutant, when compared to unmodified bulk gC₃N₄. Detailed characterization results revealed that incorporation of B in gC₃N₄ matrix reduces the band gap to increase the visible light absorption, while specific surface area is significantly enhanced upon formation of NS. Decoration of Ag nanoparticles (NPs) on B-doped gC₃N₄ NS assists in fast transfer of photogenerated electrons from gC₃N₄ to Ag NPs owing to the interfacial electric field across the junctions and thus reduces the recombination process. Investigations on individual strategies revealed that decoration of Ag NPs to induce better charge separation, is the most effective route for enhancing the photocatalytic activity.

Fabrication and characterization of ZnO-TiO2-PANI (ZTP) micro/nanoballs for the detection of flammable and toxic gases

The present paper reports the in-situ chemical polymerization of nanocomposites thin film composed by titanium dioxide (TiO₂), zinc oxide (ZnO) and polyaniline (PANI). It was found that nanocomposites sensor is highly selective and shows response to low concentration. To improve the sensing response characteristics of ZT thin film, PANI is incorporated. Thin film based LPG sensor of ZnO-TiO₂-PANI composite was fabricated by spin coating of ZnO-TiO₂ nanoparticles doped with PANI over inter digital electrodes (IDEs). The thin film was characterized by using XRD, SEM, TEM, UV-vis, BET and FTIR. It was also tested for gas sensing properties of LPG/NO₂ which are well known flammable and toxic gases. The measured response for ZnO-TiO₂-PANI based sensor was 87 for 2000 ppm of LPG and 412 for 20 ppm of NO₂ at room temperature towards other testing gases together with Acetone, IPA, NH₃ and CO₂.

Kinetics and mechanism of photocatalytic degradation of methyl orange in water by mesoporous Nd-TiO2-SBA-15 nanocatalyst

High-efficiency nanophotocatalysts with large specific surface areas have a broad range of application prospects in the catalytic oxidation treatment of organic pollutants in wastewater. A chemical method was used to synthesize a TiO₂ nanophotocatalyst with a mesoporous structure upon which a rare earth metal (Nd) was deposited, namely Nd-TiO₂-SBA-15 (NTS). The prepared NTS was characterized using X-ray diffractometry, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectrometry. The photocatalytic mechanism was explored using scavenger experiments with photoinduced carriers combined with total organic carbon and UV-Vis measurements. At the same time, the kinetic properties of the NTS photocatalytic degradation of methyl orange (MO) were evaluated. The results showed that the deposition of TiO₂ nanoparticles on the surface of the SBA-15 molecular sieve did not change the mesoporous structure, and Nd was uniformly distributed on the surface of the nanophotocatalyst. The photogenerated holes of the NTS played an important role in the photocatalysis process. In addition, the synthesized NTS had good adaptability in the range of pH 2-10. At pH 4, the reaction rate constant (k) of the MO photocatalytic degradation by NTS was 0.011825 mg·(L·min)^-1, and the adsorption equilibrium constant (K) was 0.051359 L mg^-1. In addition, the photocatalytic degradation rate of MO by NTS remained above 70%, even when the NTS was recycled four times. The NTS showed a good performance after recycling. This work provides a good foundation for the large-scale application of NTS.

Removal of acetylsalicylate and methyl-theobromine from aqueous environment using nano-photocatalyst WO3-TiO2 @g-C3N4 composite

Highly efficient, visible light-driven and a novel ternary hybrid photocatalyst WO₃-TiO₂-g-C₃N₄ with robust stabilities and versatile properties has been synthesized through facile hydrothermal method. This study considers the photo-degradation of aspirin (acetylsalicylate) and caffeine (methyl-theobromine) via photocatalysts (WO₃, WO₃/TiO_2, and WO₃/TiO₂/g-C₃N₄ (WTCN) composite) under visible-light irradiation. The SEM and TEM images show the formation of WO₃ nanoparticles with orthorhombic structure and average particle size of 65 nm. The photocatalyst WTCN composite possesses higher-catalytic activity when compared to that of WO₃ and WO₃/TiO₂ for degradation of aspirin and caffeine. The incorporation of g-C₃N₄ in WO₃/TiO₂ composite exhibited significant influence on the photocatalytic performance for both pollutants. Excellent photocatalytic performance of WTCN composite was observed owing to hydroxyl radical (OH) and superoxide radical (O₂^-) as main active species. The enhanced photocatalytic activity of WTCN composite can be attributed to following three reasons: (1) extended visible-light absorption; (2) extended surface area; (3) efficient charge-separation due to synergistic effects between g- and WO₃/TiO₂ composite. The removal efficiency of aspirin and caffeine (Methyl theobromine) could be achieved as much as 98% and 97% for acetylsalicylate and methyl-theobromine using WTCN composite material, respectively. This study could provide new insights into the synthesis of novel WO₃-based materials for environmental and energy applications.

Engineering nanomaterials for water and wastewater treatment: review of classifications, properties and applications

Based on their characteristics and applicability, a new category of NMs is proposed for water and wastewater treatment.

Mesoporous TiO2 with WO3 functioning as dopant and light-sensitizer: A highly efficient photocatalyst for degradation of organic compound

The suitable doping or modification on TiO₂ holds promise for improving charge separation and extending light absorption range. Here, WO₃ modifying reduced band gap mesoporous TiO₂ (WO₃/RM-TiO₂) due to WO₃ doping was successfully fabricated by immersing mesoporous TiO₂ nanoparticles in the peroxotungstic acid sol with controllable reaction time (0-1 h). The W⁶⁺ ions were first incorporated into the TiO₂ lattice to form WOTi bonds, resulting in the formation of WO₃ doping TiO₂. Then, WO₃ nanoparticles gradually formed and attached on the TiO₂ surface, constructing a novel heterojunction catalyst with WO₃ serving as both dopant and light-sensitizer for TiO₂. Photocatalytic activity of the resulting WO₃/RM-TiO₂ depends on the immersing duration in the peroxotungstic acid. The BET analysis shows that 0.5 h-WO₃/RM-TiO₂ has the largest pore volume of 0.491 cm³ g^-1 and the highest surface area of 82.3 m² g^-1, whereas these values decline with prolonged immersing duration. As expected, the optimal efficiency in removing p-nitrophenol (PNP) is achieved over 0.5 h-WO₃/RM-TiO₂ under visible light irradiation, which is 2.33 times that of the unmodified M-TiO₂. This should be attributed to the suitable WO₃ doping and WO₃ modification.

TiO₂-ZnO Binary Oxide Systems: Comprehensive Characterization and Tests of Photocatalytic Activity

A series of TiO₂-ZnO binary oxide systems with various molar ratios of TiO₂ and ZnO were prepared using a sol-gel method. The influence of the molar ratio and temperature of calcination on the particle sizes, morphology, crystalline structure, surface composition, porous structure parameters, and thermal stability of the final hybrids was investigated. Additionally, to confirm the presence of characteristic surface groups of the material, Fourier transform infrared spectroscopy was applied. It was found that the crystalline structure, porous structure parameters, and thermal stability were determined by the molar ratio of TiO₂ to ZnO and the calcination process for the most part. A key element of the study was an evaluation of the photocatalytic activity of the TiO₂-ZnO hybrids with respect to the decomposition of C.I. Basic Blue 9, C.I. Basic Red 1, and C.I. Basic Violet 10 dyes. It was found that the TiO₂-ZnO material obtained with a molar ratio of TiO₂:ZnO = 9:1 and calcined at 600 °C demonstrates high photocatalytic activity in the degradation of the three organic dyes when compared with pristine TiO₂. Moreover, an attempt was made to describe equilibrium aspects by applying the Langmuir-Hinsherlwood equation.