Unexpected Photocatalytic Activity of Simple and Platinum Modified Tubular SiO2 for the Oxidation of Oxalic Acid to CO2

The photocatalytic mineralization of oxalic acid over SiO₂-based materials was investigated in the 200–800 nm range. The photocatalytic activity was found to be strongly related to the morphology of SiO₂ materials. The simple as well as the Pt-modified SiO₂ particles having a predominant spherical shape exhibited null photocatalytic activity. In contrast, the tubular shaped SiO₂ particles revealed an interesting photocatalytic activity, the rate of CO₂ evolvement being 45 µmol g _cat ^?1  h^?1. The initial activity was significantly enhanced (428 µmol CO₂ g _cat ^?1  h^?1) by platinum photodeposition on the outer and inner surface of tubular SiO₂. The catalytic materials were characterized by TEM, UV–VIS and XPS to obtain rational explanations for the phocatalytic activity that was noticed. The experiments revealed that SiO₂ tubes behave as efficient photooxidation microreactors. The morphology-dependent photocatalysis can be an efficient tool in future for the abatement of pollutants in liquid phase.     

Preparation and photocatalytic activity of hierarchically mesoporous-macroporous TiO2−xNx

Hierarchically mesoporous-macroporous N-doped titania materials were fabricated by the thermal treatment of spontaneously formed hierarchical mesoporous-macroporous titanias with urea solution, in order to extend their photocatalytic applications from ultraviolet to visible-light range. The resultant meso-macroporous TiO_2−xN_x exhibited a bicrystalline (anatase and brookite) framework with high surface area and large porosity. The content of the doped nitrogen increased with the urea solution and the nitridation temperature, and the band gaps narrowed from 3.14 to 2.48 eV. The formation of OTiN bonds in the meso-macroporous TiO_2−xN_x was confirmed by the XPS and FT-IR spectra. The photocatalytic activity was evaluated by the photodegradation of methyl orange and rhodamine B under UV and visible-light irradiation, respectively. The significant improvement of photocatalytic activity for water contaminant decomposition under both UV and visible-light irradiation was observed, which is due to the incorporation of nitrogen into the titania lattice and the presence of the hierarchical meso-macroporous structure.     

Boosting the photoconversion efficiency of TiO2 nanotubes using UV radiation-assisted anodization as a prospective method: An efficient photocatalyst for eliminating resistant organic pollutants

1D TiO₂ nanotube arrays (TNTs), as versatile nanostructures, have attracted a considerable amount of scientific attention, particularly in photocatalytic applications. In the present study, UV radiation-assisted anodization method with various irradiation times (30–120 min) was employed as a preferable approach to fabricating TNTs with remarkable optical property and photocatalytic activity. The results revealed that in situ irradiation not only improved the surface area (from 30.10 to 48.5 m²), but also increased the roughness factor (from 77.27 to 124.73). Furthermore, UV radiation had a significant impact on optical property and by altering elemental composition, led to a red shift in absorption edge (from 3.2 to 1.4eV). Meanwhile, voltammetric experiments showed that 120 min UV radiation during anodization was able to substantially cause a surge of the photocurrent density and the photoconversion efficiency of TNTs from 0.15 to 0.55 mA cm⁻² and from 13% to 40%, respectively. As a consequence of the improvement in optical property and photochemical features, anodic TNTs fabricated under 120 min UV radiation could increase the photocatalytic degradation of 2,4-DCP from 75% to 100%. Moreover, the kinetics study showed that all photocatalytic reactions followed zero-order kinetics which rate constant over the synthesized TNTs under 120 min UV radiation was about 5.1 times greater than that of conventionally fabricated TNTs. Likewise, the pathway of photocatalytic degradation and the proportion of reactive species in this process were assessed by scavenging tests. The results confirmed that holes (h⁺) play the main role that 53% of photocatalytic degradation occurred via both direct and indirect reactions with h⁺ species. The rest of the degradation pathways were also allocated to e⁻ and ^•O₂⁻ species by accounting for 37% and 10%, respectively.     

Photocatalytic mineralization of phenol catalyzed by pure and mixed phase hydrothermal titanium dioxide

The photocatalytic mineralization of phenol catalyzed by pure (anatase, rutile) and mixed phase hydrothermal TiO₂ was studied in aqueous solution employing different oxidative agents, H₂O₂ and O₂. In the case of H₂O₂, rutile particles, having large dimensions and high aspect ratio (size: 30–70 nm × 150–350 nm), display the highest catalytic activity due to their low tendency to recombine electrons and holes generated by UV irradiation. By using water dissolved gaseous O₂, the catalytic TiO₂ activity generally decreases and rutile displays the lowest efficacy. In fact, oxygen preferentially chemisorbs at the surface of the nanosized particles of anatase (5–15 nm) and acts as effective electron scavenger, inhibiting the electron-hole recombination. The number of electron and hole traps (Ti³⁺, O₂⁻ and O⁻) and the rate of formation of the short-lived hydroxyl radicals OH under UV irradiation, were evaluated by electron paramagnetic resonance (EPR). A correlation was suggested among the amount of the charge carrier centers, the rate of formation of OH radicals and the catalyst photoactivity. This confirms that the photocatalytic properties depend on the possibility that electrons and holes separately interact with the oxidative agents at the TiO₂ surface, inducing the formation of OH radicals.     

In situ FTIR study of photocatalytic NO reaction on photocatalysts under UV irradiation

The photocatalytic reaction of nitric oxide (NO) on TiO₂ and transition metal-loaded M (Cu, V, and Cr)/TiO₂ catalysts was studied using in situ FTIR spectroscopy under UV irradiation. TiO₂ and M/TiO₂ catalysts were prepared by the sol–gel method via controlled hydrolysis of titanium (IV) butoxide. Copper, vanadium, or chromium was loaded onto TiO₂ during the sol–gel procedure. After treatment at 500 °C under air flow, a large amount of surface peroxo species and OH groups were detected on the TiO₂ and M/TiO₂ catalysts. Nitric oxide was adsorbed on TiO₂ and M/TiO₂ in the form of bidentate nitrites and nitrates by reacting with OH groups, peroxo, or MO species. In addition, NO can also be adsorbed on Mⁿ⁺ in the form of nitrosyls. Under UV irradiation, bidentate nitrite was oxidized to either monodentate or bidentate nitrate. Such oxidation was suggested to be induced by superoxo species generated by oxidizing peroxo species via photogenerated holes. The existence of nitrosyls deferred the oxidation of nitrites to nitrates due to the prior oxidation of nitrosyls by superoxo. The XRD and UV–vis spectra showed that the structures and the abilities of absorbing UV light of all catalysts were not influenced by the photocatalytic NO reaction. Possible mechanisms were proposed for the photocatalytic NO oxidation on TiO₂ and M/TiO₂ based on the intermediates found from the in situ FTIR study.     

Water purification and toxicity control of chlorophenols by 3D nanofiber membranes decorated with photocatalytic titania nanoparticles

Highly photocatalytic water purification three-dimensional nanofiber membranes were fabricated. We identified the optimal fabrication process of nylon-6 nanofiber membranes suspending titania nanoparticles for potential water purifications and toxicity control of chlorophenols. Nanofibers and nanoparticles were deposited on a soda lime glass substrate by electrospinning and electrospraying, respectively. Titania nanoparticles were used to induce the UV light driven photocatalytic effect and nanofibers were used to tightly suspend the nanoparticles in air. Both batch and continuous deposition processes were introduced in the membrane fabrication process and their water purification performances were compared and quantified using a methylene blue solution, which is often used as a model pollutant. Surface morphologies and characteristics of the membranes fabricated at various process conditions were also provided. The membrane fabricated by the continuous means yielded 100% degradation of the methylene blue solution within 90 min under a relatively weak UV irradiation (0.6 mW/cm²), which promises its potential indoor application. The nano-textured membranes developed in this work was also applied to the real pollutants, such as chlorophenols, and showed a promising performance in their toxicity control.     

Mg3Y2Ge3O12:Bi3+ UV fluorescent phosphor as the TiO2 “sensitizer” for enhancing the heavy oil viscosity reduction

Nowadays, visible fluorescent materials based on rare earth (RE) and non-RE ions doping have been extensively explored for white LEDs. As for the UV fluorescent materials, it is well known that they are not suitable for the lighting applications. As a result, when compared to the visible fluorescent materials, previous works paid little attention to the UV fluorescent materials. In this work, we report a type of Mg₃Y₂Ge₃O₁₂:Bi³⁺ UV fluorescent phosphor. To understand the crystal structural information and photoluminescence (PL) properties of samples, we have used the X-ray diffraction (XRD), scanning electronic microscope (SEM), UV–visible diffuse reflectance and PL spectra to characterize them. The structural results reveal that the Bi³⁺ doped sample show their particle size at about 30 μm. The PL results show that the Bi³⁺ doped sample upon excitation at 230 nm can show a broad emission band that can almost cover the whole UV spectral region from 290 nm to 410 nm. Since this UV fluorescent band is exactly in agreement with the UV absorption region of TiO₂ semiconductor, we have fabricated several Mg₃Y₂Ge₃O₁₂:Bi³⁺/TiO₂-based ceramic plates and proposed used them to serve as an efficient UV irradiation source for photocatalytic application. As a result, we find that the TiO₂ can exhibit the significantly enhanced photocatalytic property for the heavy oil viscosity reduction after adding the Mg₃Y₂Ge₃O₁₂:Bi³⁺ UV fluorescent phosphor.     

Shock-consolidated TiO2 bulk with pure anatase phases fabricated by explosive compaction using underwater shockwave

Titanium dioxide (TiO₂) bulk with pure anatase phases was fabricated by an explosive compaction technique using an underwater shockwave. Dynamic shock pressure of 6 GPa was used to consolidate anatase TiO₂ powders. Its microstructural, crystalline structural and photocatalytic characteristics were observed and measured by various techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and photocatalytic activity measurement system. It was confirmed that the relative density of anatase TiO₂ compact is about 96% (3.73 g/cm³) of the theoretical density (3.89 g/cm³) and a strong surface bonding between particles is formed by a shock energy. In X-ray diffraction analysis, high purity anatase phases, broadened peaks due to lattice defects and decreased crystallite size were found. For the photocatalytic activities, the anatase TiO₂ compact was quite excellent compared to the commercial sintered TiO₂ bulk.     

Design of piezoelectric nanogenerator based on BiFeO3/epoxy resin with potential application for wearable electronic devices

Growing demand for electric energy in newly developed electronic systems causes increasing interest in research on piezoelectric nanogenerators (PENGs). Design and fabrication of such devices is challenging, considering cost of materials used in their construction. This is the main reason why intensive research has begun on 0-3 composites with piezoelectric properties. One of the most promising constituent materials for composites fabrication are polymers, due to their low cost and easy processing. Herein, we present fabricated wearable PENG with good impact and vibration energy conversion properties. Correlation between matrix stiffness and piezoelectric properties of 0-3 type composite is proposed. It was found that composite with 10 wt.% of BiFeO₃ particles exhibits power output density for vibrations, finger tapping, and air stream pressure P = 11.12 nW cm⁻³, P = 4.83 μW cm⁻³, and P = 769.2 μW cm⁻³, respectively. Decrease in stiffness of epoxy matrix results at least in two-times lower power output density for this same PENG. The obtained results demonstrate that the fabricated BFO/epoxy composites show the wide applicability and potential to be integrated with other functional devices, for example, as a part of wearable devices in smart shoes.     

Surface modification of ABS by photocatalytic treatment for electroless copper plating

Surface roughness of acrylonitrile–butadiene–styrene (ABS) resin prior to metallization is treated generally with sulphuric/chromic acid system. However, the presence of chrominum (VI) ion imposes serious environmental problems. In this work, TiO₂ photocatalytic treatment was used to enhance the adhesion strength between the ABS surface and the electroless copper film. Effects of the TiO₂ content, irradiation time and UV power upon the surface topography, surface characterization and the adhesion strength were investigated. The results indicated that the surface hydrophilicity of ABS resin and the adhesion strength between the electroless copper film and ABS surface increased with an increase in the UV power and a prolongation in irradiation time, and did not increase linearly with an increase of TiO₂ content. Though the surface topography of ABS changed little, the adhesion strength reached 1.25?kN/m, which was higher than that in the optimal H₂SO₄–MnO₂ colloid. The surface chemistry results indicated that –COOH and –OH groups formed with the photocatalytic treatment and the absorption strengths increased with the UV power. XPS analysis results further demonstrated that the contents of C=O and –COOH reached 6.4 and 4.9% with the photocatalytic treatment, which was much higher than that of the H₂SO₄–MnO₂ colloid (3.9 and 3.1%). The high contents of C=O and –COOH groups enhanced the surface hydrophilicity of the ABS resin and improved the adhesion strength between the electroless copper film and ABS resin. The results indicated that the photocatalytic treatment was an environment-friendly and effective method to replace the commercial wet chemical process for ABS surface modification.     

Synthesis of three-dimensional ordered macroporous TiO2, Gd/TiO2 and their photocatalytic activity

In this paper, three-dimensional ordered macroporous (3DOM) TiO₂ and Gd/TiO₂ materials were synthesized by colloidal crystal templating process. The obtained samples were analyzed by field-emission scanning electron microscope, transmission electron microscopy, X-ray diffraction, diffuse reflectance spectra and Brunauer–Emmett–Teller method. The photocatalytic activity of various samples was evaluated by degradation of methyl orange in aqueous solution under UV and visible light irradiation. At the same time, Degussa P25 (a commercial Titania) powders were used for comparison. The results indicated that 3DOM Gd/TiO₂ samples showed a significant shift in the onset absorption towards the longer wavelength compare to pure 3DOM TiO₂, and displayed excellent photocatalytic activity under both UV and visible light irradiation.     

Preparation of titanium dioxide/tungsten disulfide composite photocatalysts with enhanced photocatalytic activity under visible light

Titanium dioxide/tungsten disulfide (TiO₂/WS₂) composite photocatalysts were fabricated via a one-step hydrothermal synthesis process, using TiCl₄ as titanium source and bulk WS₂ as sensitizer. The morphology, structure, specific surface area and optical absorption properties of the composite photocatalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), specific surface area analyzer and ultraviolet-visible diffuse reflection spectrum (UV-vis DRS), respectively. The photocatalytic activity of as-prepared photocatalysts was evaluated by the degradation of methyl orange (MO) under illumination of 500W Xenon lamp. The results indicated that TiO₂/WS₂ composite photocatalysts possessed excellent photocatalytic activity, and ～95% of the degradation rate for MO was reached when molar ratio of WS₂ to TiO₂ was 0.004 and the irradiation time was 60 min. Moreover, the carrier trapping experiment and fluorescence spectra showed that ·O ₂ ^? was the key component in the photocatalytic degradation process and O₂ was reduced to be ·O ₂ ^? by the electrons from the conduction band of TiO₂ and WS₂ for the degradation of MO.     

Mixtures of l-Amino Acids as Reaction Medium for Formation of Iron Nanoparticles: The Order of Addition into a Ferrous Salt Solution Matters

Owing to Mössbauer spectroscopy, an advanced characterization technique for iron-containing materials, the present study reveals previously unknown possibilities using l-amino acids for the generation of magnetic particles. Based on our results, a simple choice of the order of l-amino acids addition into a reaction mixture containing ferrous ions leads to either superparamagnetic ferric oxide/oxyhydroxide particles, or magnetically strong Fe⁰-Fe₂O₃/FeOOH core-shell particles after chemical reduction. Conversely, when ferric salts are employed with the addition of selected l-amino acids, only Fe⁰-Fe₂O₃/FeOOH core-shell particles are observed, regardless of the addition order. We explain this phenomenon by a specific transient/intermediate complex formation between Fe²⁺ and l-glutamic acid. This type of complexation prevents ferrous ions from spontaneous oxidation in solutions with full air access. Moreover, due to surface-enhanced Raman scattering spectroscopy we show that the functional groups of l-amino acids are not destroyed during the borohydride-induced reduction. These functionalities can be further exploited for (i) attachment of l-amino acids to the as-prepared magnetic particles, and (ii) for targeted bio- and/or environmental applications where the surface chemistry needs to be tailored and directed toward biocompatible species.     

Direct hydrolysis synthesis of BiOI flowerlike hierarchical structures and it's photocatalytic activity under simulated sunlight irradiation

BiOI flowerlike hierarchical structure was synthesized via direct hydrolysis from BiI₃ and characterized by powder X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) spectra, and transmission electron microscopy (TEM). As-synthesized BiOI showed higher photocatalytic activity in aqueous RhB photodegradation system than P25 TiO₂ under simulated sunlight irradiation. The trapping experiments of active species and electron spin resonance (ESR) experiment during the photocatalytic reaction showed that the photocatalytic degradation of organic pollutants in BiOI system proceeds through direct hole transfer and O₂⁻ rather than OH.     

TiO<Subscript>2</Subscript> porous ceramic/Ag–AgCl composite for enhanced photocatalytic degradation of dyes under visible light irradiation

TiO₂ porous ceramic/Ag–AgCl composite was prepared by incorporating AgCl nanoparticles within the bulk of TiO₂ porous ceramic followed by reducing Ag⁺ in the AgCl particles to Ag⁰ species under visible light irradiation. The porous TiO₂ ceramic was physically robust and chemically durable, and the porous structure facilitated the implantation of AgCl NPs. Compared with the bare TiO₂ ceramic, TiO₂ porous ceramic/Ag–AgCl composite exhibited higher photocatalytic performance for the degradation of MO and RhB under visible light irradiation. The reaction rate constants k of MO and RhB degradation over TiO₂ porous ceramic/Ag–AgCl composite was respectively 6.25 times and 3.62 times higher than those recorded over the bare TiO₂ porous ceramic. The photocatalytic activity showed virtually no decline after four times cyclic experiments under visible light irradiation. Scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, UV–Vis diffuse reflectance spectroscopy, photoluminescence spectra and X-ray photoelectron spectroscopy were used to characterize the TiO₂ porous ceramic/Ag–AgCl composite.     

Fast adsorptive and photocatalytic purification of air from acetone and dimethyl methylphosphonate by TiO2 aerosol

A high concentration (1.5 × 10⁶ cm⁻³) TiO₂ aerosol of the average particle size 0.5 μm was generated by a sonic method inside 0.1 m³ Plexiglas chamber and applied for the adsorptive and adsorptive-photocatalytic purification of air from vapors of acetone and chemical agents’ model dimethyl methylphosphonate (DMMP). The adsorptive capture of acetone over the TiO₂ aerosol results in establishing equilibrium adsorption state and is limited by the rate of the aerosol admission into the chamber. A model derived from the Langmuir isotherm describes well the acetone concentration vs. aerosol mass curve and allows obtaining the adsorption constant and monolayer coverage of acetone in a 10 min experiment. The UV irradiation of TiO₂ aerosol accelerates dramatically the purification from acetone at the high relative humidity (RH) of the air. Increased RH of air decreases the rate of the acetone adsorption but has a little positive effect on the rate of photocatalytic oxidation of acetone over aerosol particles. The DMMP adsorption over TiO₂ aerosol is accompanied by the immediate (τ < 10 s) and irreversible hydrolysis of DMMP with the formation of gas phase methanol and adsorbed methyl methylphosphonic acid. The irreversible reactive adsorption results in the very fast air purification (τ = 20–40 s) due to very small diffusion distances of substrate to the TiO₂ surface in aerosol. The increase of the air RH from 4 to 37% (296 K) decreases the rate of adsorption but accelerates significantly the rate of photocatalytic oxidation. The complete air purification from organic compounds within 10 min is possible only with the photocatalytic oxidation because the adsorption alone does not remove methanol. The time needed for the air purification over the nanosized TiO₂ aerosol is directly determined by the rate of the aerosol generation which allows a further optimization of the TiO₂ aerosol air purification. The obtained results approve experimentally a suggestion that the photocatalytic oxidation over solid atmospheric aerosols actually takes part in the Earth atmosphere and serves as an important sink for airborne organics.     

Effect of sputtering parameters on the self-cleaning properties of amorphous titanium dioxide thin films

The aim of this work was to assess the effect of the direct current magnetron sputtering parameters on the photocatalytic activity and photoinduced wettability of amorphous TiO₂ films. TiO₂ films were deposited on glass using the direct current magnetron sputtering technique, without heating, at different total working pressures. Qualitative analysis using in situ X-ray photoelectron spectroscopy confirmed the TiO₂ stoichiometry of the deposited films. Surface structure was studied as a function of working pressure using scanning electron microscopy. The hydrophilicity of the TiO₂ surfaces was investigated macroscopically using measurements of the water contact angle. A threshold working pressure was observed, with a strong dependence on the film thickness. A super hydrophilic surface was observed after less than 1 h of UV irradiation. The photocatalytic activity of the films was evaluated under UV light through the degradation of methylene blue (\(\lambda_{\hbox{max} } \approx 660\;{\text{nm}}\)). The effect of UV irradiation on the photocatalytic activity was rapid, strong, and dependent on film thickness and total working pressure. Fifty percent of organic compounds were photodegraded by films with a thickness of 60 nm deposited at 10 mTorr.     

A DRIFTS study of the morphology and surface adsorbate composition of an operating methanol synthesis catalyst

The nature of the species adsorbed on a Cu/ZnO/Al₂O₃ catalyst while it was producing methanol has been elucidated in this study using DRIFTS. The species are carbonates, formate, CO, oxygen atoms ( 2% of a monolayer) and methoxy on the Cu and methoxy on the ZnO. The frequencies observed for the C-O stretch on Cu, 2076, 2092, 2105 and 2132 cm^–1, have revealed the morphology of the copper component of the operating catalyst. The surface of the copper is predominantly the (111) face ( 65%) (the 2076 cm^–1 peak) with the (755) (the 2092 cm^–1 peak) and the (311) (the 2105 cm^–1 peak) faces occupying roughly 20% and 15%, respectively, of the copper area. The 2132 cm^–1 peak derives from CO adsorbed on Cu⁺ site on the copper which is 2% of a monolayer.