A comparative study of the effect of Pd-doping on the structural,optical, and photocatalytic properties of sol–gel derived anatase TiO2 nanoparticles

Pd-doped anatase TiO₂ nanoparticles were synthesized by a modified sol–gel deposition technique. The synthetic strategy is applicable to other transition and post-transition metals to obtain phase-pure anatase titania nanoparticles. This is important in the sense that anatase titania forms the most hydroxyl radicals (compared to other polymorphs like rutile, brookite, etc.) for better photocatalytic performance. XRD and Raman data confirm the phase-pure anatase formation. Doping of Pd²⁺ into Ti⁴⁺ sites (for substitutional doping) or interstitial sites (for interstitial doping) creates strain within the nanoparticles and is reflected in the XRD peak broadening and Raman peak shifts. This is because of the ionic radii difference between Ti⁴⁺(∼68 pm) and Pd²⁺(∼86 pm). XPS data confirm the formation of high surface titanol groups at the nanoparticle surface and a large number of loosely bound Ti³⁺–O bonds, both of which considerably enhance the photocatalytic activity of the doped nanoparticles. A comparative study with other metal doping (Ga) shows that TiO₂: Pd nanoparticles have more Ti³⁺–O bonds, which enhance the charge transfer rate and hence improve the photocatalytic activity compared to other transition and post-transition metal-doped titania nanostructures.     

The dependence of the photocatalytic activity of TiO2/carbon nanotubes nanocomposites on the modification of the carbon nanotubes

Nanostructural TiO₂/modified multi-wall carbon nanotubes photocatalysts were prepared by hydrolysis of Ti(iso-OC₃H₇)₄ providing chemical bonding of anatase TiO₂ nanoparticles onto oxidized- or amino-functionalized multi-wall carbon nanotubes (MWCNT). The processes of functionalization of the MWCNT and the deposition of TiO₂ influence the photocatalytic activity of the synthesized nanocomposites. The phase composition, crystallite size, and the structural and surface properties of the obtained TiO₂/modified-MWCNT nanocomposite were analyzed from XRD, FEG-SEM, TEM/HRTEM and FTIR data, as well low temperature N₂ adsorption. In the photocatalytic study, the TiO₂/oxidized-MWCNT catalyst showed the highest and the TiO₂/amino functionalized-MWCNT catalysts somewhat lower degradation rates, indicating that the enhancement of photocatalysis was supported by the more effective electron transfer properties of the oxygen- than amino-containing functional groups, which support the efficient charge transportation and separation of the photogenerated electron-hole pairs.     

Superhydrophilic Cu-doped TiO2 thin film for solar-driven photocatalysis

Nanosized Cu-doped TiO₂ film was prepared by the sol–gel spin coating technique. XPS analysis showed that Cu atoms had been successfully doped into TiO₂ lattice, which hence modified the surface chemical composition. As a result, the Cu-doped TiO₂ thin film possessed a superhydrophilic surface with a water contact angle (WCA) only 5.1° and exhibited excellent anti-fogging behavior. The Cu-doped TiO₂ thin film also exhibited a much better photocatalytic activity than the reference TiO₂ thin film, as evaluated by the degradation of 10 mg/L methylene blue (MB) solution under simulated solar-driven irradiation.     

Synthesis of ternary zinc spinel oxides and their application in the photodegradation of organic pollutant

Ternary zinc spinel oxides such as Zn₂SnO₄, ZnAl₂O₄ and ZnFe₂O₄ were synthesized and characterized, and their activities in the photodegradation of phenol molecules were investigated. Zn₂SnO₄, ZnAl₂O₄ and ZnFe₂O₄ powders were synthesized by hydrothermal, metal–chitosan complexation and solvothermal routes, respectively. The face-centered cubic spinel structure of each material was confirmed by powder X-ray diffractometry (XRD) and its porous structure by N₂ adsorption–desorption isotherms. The characterization of spinels was complemented with Fourier transform infrared spectroscopy (FTIR) and X-rays fluorescence (XRF), revealing the formation of spinel structures with high purity. The photocatalytic activity in the degradation of phenol was observed only with Zn₂SnO₄ oxide. Mineralization degree of phenol molecules by Zn₂SnO₄ photocatalyst determined by total organic carbon analysis (TOC) reached 80% at 360 min under sunlight.     

A Review of Dehydration of Various Industrial Sludges

Wastewater characteristics and sludge generation potential of point source categories are reviewed critically. Novel industry-specific sludge dewatering/drying solutions necessary to establish a sustainable model are examined through a detailed literature survey. Knowledge of sludge properties is one of the most critical issues needed to design dewatering/drying equipment. This study focuses on industrial wastewater/sludge characterization. In addition, a comprehensive review of current drying models and technologies is also presented. A summary of the results derived from a novel thin-film-based photonic sludge dewatering/drying study is outlined as an alternative approach for industrial sludge control. Sludge was dried in a tubular quartz reactor (TQR), the inner surface of which was coated with a TiO₂ thin film. The TQR was irradiated with UV A, UV B, and UV C lamps. The consumed and generated energy fluxes through endergonic and exergonic reactions driven by photolysis and photocatalysis were investigated. In addition, the variations in sludge dewatering/drying characteristics were also examined and compared with conventional methods to evaluate the energy requirements.     

内建电场调控光生电荷分离效率的研究进展

光催化技术是解决现今环境污染和能源危机的重要手段之一,然而大部分催化剂的光催化效率较低,提高光生电荷的分离是提高光催化效率的一种有效方法.首先对催化剂的光催化原理进行了概述;结合近年来国内外在提高光生电荷分离效率方面取得的最新成果及进展,从内建电场的产生机理入手,综述了半导体p-n结、异相结、极化表面和铁电材料极化对光...     

Facet engineered TiO2 hollow sphere for the visible-light-mediated degradation of antibiotics via ligand-to-metal charge transfer

Efficient removal of tetracycline (TC) under visible-light irradiation over TiO₂-based photocatalysts remains a challenge based on the fact that the reported photocatalytic systems still suffer from weak visible-light absorption and/or inefficient charge separation. Herein, we constructed {101} and {001} facets co-exposed TiO₂ hollow sphere (001-HT) via a gentle NaF treatment, in which the hollow mesoporous feature can trap incident light for a long time to improve photons efficiently. Meanwhile, the as-formed facet heterojunction significantly facilitates the charge separation. As a result, the 001-HT exhibits a high removal rate (~90.1%) of TC under visible-light irradiation, beyond the values of many reported TiO₂-based photocatalysts. Most importantly, we further expound the ligand-to-metal charge transfer mechanism towards TiO₂-assisted degradation of TC under visible-light irradiation, which effectively clarifies the confusion about the origin of pure TiO₂ visible-light activity towards TC degradation because both TiO₂ and TC do not exhibit any visible-light catalytic activity. Therefore, this work provides a new insight in revealing the mechanism of visible-light-mediated TC degradation over pure TiO₂ photocatalyst.     

Metal oxide mesocrystals and mesoporous single crystals: synthesis,properties and applications in solar energy conversion

Metal oxide mesocrystals (MCs) and mesoporous single crystals (MSCs) exhibit superior carrier transport ability,high specific surface area,shortened photo-carrier diffusion lengths to interfaces and enhanced absorbance of the incident sunlight.These advanced features make metal oxide MCs and MSCs be a promising candidate material in photocatalysis,photoelectrocatalysis,dye sensitized solar cells (DSSCs) and perovskite solar cells (PSCs).Recently,remarkable advances of applying metal oxide MCs and MSCs in these areas have been achieved.Therefore,it is extremely important to deeply understand the influence of the unique properties of metal oxide MCs and MSCs on solar energy conversion systems.Herein,we presented a brief introduction on the synthesis and carrier transfer behavior of metal oxide MCs and MSCs.Then,the rational structure design and modification of metal oxide MCs and MSCs for photocatalysis,photoelectrocatalysis,DSSCs and PSCs are systematically discussed.Finally,the perspectives on extending the application of metal oxide MCs and MSCs are addressed.     

Enhance photocatalysis of TiO2 and ZnO ceramics by addition of fused silica as a UV guiding medium

We report a facile method to prepare porous TiO₂ and ZnO photo-catalytic ceramics in which colloidal silica was added to yield nano fused silica (FS). The colloidal silica forms continuous media within the porous ceramic structure, and when calcined at 550 °C, it converted to fused silica phase which is an excellent UV wave-guiding material. With light wave guiding effect of FS and capillary effect of reaction solution in the porous channels, the photo-catalytic reactions could occur at the vast active sites at interface inside the porous bulks, as well as at the external surfaces. Photo-catalysis experiments and kinetics were investigated and analyzed. The photo-catalytic efficiencies tested for methylene blue were enhanced by a factor of 4.1 for TiO₂/FS system and, astonishingly, by a factor of 34.6 for ZnO/FS system, when compared with pure TiO₂ and ZnO under identical testing conditions. A model of UV-waveguide ceramic systems was proposed and discussed. This study proposes a practical approach to construct UV-waveguide porous structures, of which the principle is also potentially applicable to other types of photo-catalytic materials, including visible light active photo-catalysts.     

Cost-effective large-scale synthesis of oxygen-defective ZnO photocatalyst with superior activities under UV and visible light

A cost-effective solution method was developed to produce ZnO photocatalyst in large quantity, through the conversion of ε-Zn(OH)₂ to ZnO in NaOH solutions. Experimental results indicated that the concentrated NaOH solution (4 mol L⁻¹) promoted the rapid formation of ZnO owing to the enhanced dissolution-precipitation reactions. The large-scale synthesis was also achieved with high-yield and solvent-recyclability. Structural analysis based on X-ray photoelectron spectroscopy, electron spin resonance and photoluminescence revealed that the as-prepared ZnO photocatalyst was rich in oxygen vacancies (V_O). The V_O-rich ZnO photocatalyst exhibited improved visible-light absorption, higher photocurrent responses and superior activities toward the degradation of rhodamine B under both UV (λ~254 nm) and visible-light illumination (λ>420 nm) compared to commercial ZnO and P25 TiO₂ powders, as well as good cycle stability. Based on the results of photoluminescence and active species detection, the V_O-enhanced photocatalytic activity was attributed to the generation of V_O-isolated level in the band structure. Under UV light, the V_O-level could promote charge separation by trapping the photoinduced electrons, while under visible-light, the V_O-level improved visible-light absorption and facilitated the charge generation. The presently developed synthesis may potentially benefit the large-scale production and low-cost application of ZnO photocatalyst for solar energy utilization.