Transparent nitrogen doped TiO2/WO3 composite films for self-cleaning glass applications with improved photodegradation activity

A Versatile Visual Molecular Imprinting-Driven Switchable Nanozyme Activity-Based Trimodal Assay and Logic Gate Circuits of Ethyl Carbamate

Concerns regarding the hazard of the carcinogenic ethyl carbamate (EC) have driven attempts to exploit efficient, timely, straightforward, and economic assays for warning early food safety. Here, we proposed a novel molecularly imprinted polymer Co@MOF-MIP, with a high peroxidase (POD)-like activity and a bright blue fluorescence emission, to develop a versatile visual assay for colorimetric, fluorescent, and photothermal trimodal detection and logic gate outputting of EC. Briefly, the POD-like activity of Co@MOF-MIP made it to decompose H2O2 into ·OH for oxidizing colorless 3,3',5,5'-tetramethylbenzidine (TMB) into a blue oxTMB, resulting in a 660 nm irradiated photothermal effect and bursting the blue fluorescence of Co@MOF-MIP via inner filter effect, observing a decreased fluorescence signal together with an increased colorimetric and 660 nm irradiated photothermal signals. However, EC could specifically fill the imprinted cavities of Co@MOF-MIP to block the catalytic substrates TMB and H2O2 out of Co@MOF-MIP for further reacting with the inside catalytic center of Co2+, resulting in the transformation suppressing of TMB into oxTMB, yielding an EC concentration-dependent trimodal responses in fluorescence signal enhancement, colorimetric, and 660 nm irradiated photothermal signal decreases. Assisted by the portable devices such as smartphones and hand-held thermal imagers, a visual onsite portable trimodal analytical platform was proposed for EC fast and accurate detection with the low detection limits of 1.64, 1.24, and 1.78 μg/L in colorimetric, fluorescent, and photothermal modes, respectively. Interestingly, these reactive events could be programmed by the classical Boolean logic gate analysis to offer a novel promising avenue for the big data Internet of Things monitoring and warning early residual EC in a more intelligent, dynamical, fast, and accurate manner, safeguarding food safety.

Remarkably fast and reusable photocatalysis by UV annealed Cu2O-SnO2 p-n heterojunction

Powdered micro- or nano-particles photocatalyst has separation and recovery challenges, which may create a second pollution to environment and harmful to animals. To address those issues, SnO2, Cu2O and Cu2O-SnO2 p-n heterojunction thin films are formed on glass substrates using efficient co-sputtering method that is commonly employed for large-area high-definition display panel. Using first-order kinetics, 100 °C ultraviolet (UV) annealed Cu2O-SnO2 p-n heterojunction shows the superb fast degradation rate constant of 0.21 and 0.16 min-1 for methylene blue (MB) and methyl orange (MO) organic dyes, respectively, as photogenerated electron-hole pairs is increased. Record best degradation rate constants of 0.19 and 0.11 min-1 for respective MB and MO are still achieved even after four repeated cycles. The 100 °C UV annealed Cu2O-SnO2 film catalyst displays greater degradation efficiency in both dyes, reaching 100% degradation at room temperature after 30 and 35 min of illumination for MB and MO respectively. The scavenger experiments show that hydroxyl (·OH) and superoxide radicals (·O2-) are the major active species in the degradation of dye. The 100 °C UV annealed Cu2O-SnO2 film catalyst showed stability as well as reusability towards the dye degradation. As a result, the present work delivers an effective way to enhance the photocatalytic performance and also an easy recovery of the catalyst, which can be explored for various emerging pollutants.

Development of self-cleaning polydimethylsiloxane/nano-calcium carbonate-titanium dioxide coating with fog-resistance response for building glass

Purpose

This paper introduced the simple synthesis process of self-cleaning coating with fog-resistance property using hydrophobic polydimethylsiloxane (PDMS) polymer and nano-calcium carbonate (nano-CaCO3) and titanium dioxide (TiO2).

Design/methodology/approach

The synthesis method of PDMS/nano-CaCO3-TiO2 is based on sol-gel process. The crosslinking between PDMS and nanoparticles is driven by the covalent bond at temperature of 50°C. The 3-Aminopropyltriethoxysilane is used as binder for nanoparticles attachment in polymer matrix. Two fabrication methods are used, which are dip- and spray-coating methods.

Findings

The prepared coated glass fulfilled the requirement of standard self-cleaning and fog-resistance performance. For the self-cleaning test BS EN 1096-5:2016, the coated glasses exhibited the dust haze value around 20%–25% at tilt angle of 10°. For the antifog test, the coated glasses showed the fog haze value were below 2% and the gloss value were above 85%. The obtained results completely achieved the standard antifog value ASTM F659-06 protocol.

Research limitations/implications

Findings will provide an infrastructure support for the building glass to enhance building’s energy efficiency, cleaning performance and friendly environment.

Practical implications

This study proposed the simple synthesis method using hydrophobic polymer and nano-CaCO3 and nano-TiO2, which can achieve optimum self-cleaning property at low tilt angle and fog-resistance performance for building glass.

Social implications

The research findings have high potential for building company, cleaning building company and government sector. The proposed project capable to reduces the energy consumption about 20% per annum due to labor cost, time-consuming and safety during manual cleaning.

Originality/value

The novel method to develop self-cleaning coating with fog-resistance using simple synthesis process and fabrication method for building glass application.

Preparation, Microstructural Characterization and Photocatalysis Tests of V5+-Doped TiO2/WO3 Nanocomposites Supported on Electrospun Membranes

Metal oxide nanocomposites (MON) have gained significant attention in the literature for the possibility of improving the optical and electronic properties of the hybrid material, compared to its pristine constituent oxides. These superior properties have been observed for TiO2 — based MON, which exhibit improved structural stability and photoactivity in environmental decontamination processes. In addition, the use of polymer membrane-supported MON is preferable to prevent further aggregation of particles, increase the surface area of the semiconductor in contact with the contaminant, and enable material reuse without considerable efficiency loss. In this work, V5+-doped TiO2/WO3 MON nanostructures were prepared by the sintering process at 500 °C and supported in electrospun fiber membranes for application as photocatalyst devices. Microstructural characterization of the samples was performed by XRD, SEM, EDS, Raman, and DSC techniques. The reflectance spectra showed that the bandgap of the MON was progressively decreased (3.20 to 2.11 eV) with the V5+ ions doping level increase. The fiber-supported MON showed photoactivity for rhodamine B dye degradation using visible light. In addition, the highest photodegradation efficiency was noted for the systems with 5 wt% vanadium oxide dispersed in the fibers (92% dye degradation in 120 min of exposure to the light source), with recyclability of the composite material for use in new photocatalysis cycles. The best results are directly related to the microstructure, lower bandgap and aggregation of metal oxide nanocomposite in the electrospun membrane, compared to the support-free MON.

Preparation of TiO2/WO3/C/N Composite Nanofibers by Electrospinning Using Precursors Soluble in Water and Their Photocatalytic Activity in Visible Light

Extending the absorption range of TiO₂ nanofibers to visible light is a great improvement of the photocatalytic property of TiO₂. In this study, TiO₂/WO₃/C/N nanofibers were prepared by electrospinning using precursors soluble in water then annealing in argon. Titanium(IV) bis(ammonium lactato)dihydroxide (TiBALDH) and ammonium metatungstate (AMT) were used as the precursor for TiO₂ and WO₃ respectively. Different volume ratios of the precursors were added to a solution of PVP before electrospinning. The fibers were studied by XPS, SEM-EDX, TEM, FTIR, XRD, Raman spectroscopy and UV–VIS diffuse reflectance spectroscopy (DRS). The photocatalytic degradation of methylene blue by the fibers in visible light was investigated. The fibers had anatase TiO₂ and monoclinic WO₃. Based on UV–VIS DRS and Kubelka-Munk function the fibers could absorb visible light. Moreover, 100% TiBALDH had an indirect band gap of 2.9 eV, and the band gap decreased with increase in AMT, i.e., for 0% TiBALDH, band gap was 2.4 eV. The fibers degraded methylene blue dye in visible light, and 90% TiBALDH had the highest photocatalytic activity, i.e., it degraded 40% of the dye after 240 min.

Enhanced visible light photocatalytic activity of Fe2O3 modified TiO2 prepared by atomic layer deposition

In this work, commercial anatase TiO2 powders were modified using ultrathin Fe2O3 layer by atomic layer deposition (ALD). The ultrathin Fe2O3 coating having small bandgap of 2.20 eV can increase the visible light absorption of TiO2 supports, at the meantime, Fe2O3/TiO2 heterojunction can effectively improve the lifetime of photogenerated electron-hole pairs. Results of ALD Fe2O3 modified TiO2 catalyst, therefore, showed great visible light driven catalytic degradation of methyl orange compared to pristine TiO2. A 400 cycles of ALD Fe2O3 (~ 2.6 nm) coated TiO2 powders exhibit the highest degradation efficiency of 97.4% in 90 min, much higher than pristine TiO2 powders of only 12.5%. Moreover, an ultrathin ALD Al2O3 (~ 2 nm) was able to improve the stability of Fe2O3-TiO2 catalyst. These results demonstrate that ALD surface modification with ultrathin coating is an extremely powerful route for the applications in constructing efficient and stable photocatalysts.

Photoelectrocatalytic Hydrogen Production Using a TiO2/WO3 Bilayer Photocatalyst in the Presence of Ethanol as a Fuel

Photoelectrocatalytic hydrogen production was studied by using a photoelectrochemical cell where the photoanode was made by depositing on FTO electrodes either a nanoparticulate WO3 film alone or a bilayer film made of nanoparticulate WO3 at the bottom covered with a nanoparticulate TiO2 film on the top. Both the electric current and the hydrogen produced by the photoelectrocatalysis cell substantially increased by adding the top titania layer. The presence of this layer did not affect the current-voltage characteristics of the cell (besides the increase of the current density). This was an indication that the flow of electrons in the combined semiconductor photoanode was through the WO3 layer. The increase of the current was mainly attributed to the passivation of the surface recombination sites on WO3 contributing to the limitation of charge recombination mechanisms. In addition, the top titania layer may have contributed to photon absorption by back scattering of light and thus by enhancement of light absorption by WO3. Relatively high charge densities were recorded, owing both to the improvement of the photoanode by the combined photocatalyst and to the presence of ethanol as the sacrificial agent (fuel), which affected the recorded current by “current doubling” phenomena. Hydrogen was produced under electric bias using a simple cathode electrode made of carbon paper carrying carbon black as the electrocatalyst. This electrode gave a Faradaic efficiency of 58% for hydrogen production.

TiOxNy Modified TiO2 Powders Prepared by Plasma Enhanced Atomic Layer Deposition for Highly Visible Light Photocatalysis

In this work, TiN film deposited by plasma enhanced atomic layer deposition (PEALD) is adopted to modify the commercial anatase TiO₂ powders. A series of analyses indicate that the surface modification of 20, 50 and 100 cycles of TiN by PEALD does not change the morphology, crystal size, lattice parameters, and surface area of TiO₂ nano powders, but forms an ultrathin amorphous layer of nitrogen doped TiO₂ (TiO_xN_y) on the powder surfaces. This ultrathin TiO_xN_y can facilitate the absorption of TiO₂ in visible light spectrum. As a result, TiO_xN_y coated TiO₂ powders exhibit excellent photocatalytic degradation towards methyl orange under the visible light with good photocatalytic stability compared to pristine TiO₂ powders. TiO_xN_y (100 cycles PEALD TiN) coated TiO₂ powders exhibit the excellent photocatalytic activity with the degradation efficiency of 96.5% in 2 hours, much higher than that of pristine TiO₂ powder of only 4.4%. These results clearly demonstrate that only an ultrathin surface modification layer can dramatically improve the visible light photocatalytic activity of commercial TiO₂ powders. Therefore, this surface modification using ALD is an extremely promising route to prepare visible light active photocatalysts.