Photodegradation Of Acetaldehyde Research Articles

Construction of 3D-graphene/NH2-MIL-125 nanohybrids via amino-ionic liquid dual-mode bonding for advanced acetaldehyde photodegradation under high humidity

The development of metal organic framework (MOF)-based π-π conjugated structures capable of effectively transforming H2O from humid air to •OH radicals for VOCs photodegradation is a significant but difficult task. Herein, an amino-ionic liquid (NH2-IL) based dual-mode bridging strategy was proposed to connect 3D-graphene with NH2-MIL-125 forming IL-3DGr/NM(Ti) nanohybrids for advanced acetaldehyde photodegradation. The rational integration of these components was responsible for: (1) maintaining π-π conjugated electron transport system; (2) generating abundant coordinatively unsaturated sites and oxygen vacancies; (3) increasing surface area of the nanohybrids. With these attributes, IL-3DGr/NM(Ti) demonstrated enhanced charge separation and transportation electrochemical impedance spectroscopy (EIS): 7-times), acetaldehyde adsorption (22 %), light absorption (bandgap: 1.51 eV). The rapid H2O adsorption and photoconversion to •OH radicals by IL-3DGr/NM(Ti) enabled it to demonstrate superior CH3CHO photodegradation rate under high humidity, surpassing many state-of-the-art photocatalysts by 9 to 187 times under static air conditions and with nearly similar catalyst dosages* (photocatalyst weight and initial acetaldehyde concentration (mg ppm−1) ratio). Interestingly, the IL-3DGr/NM(Ti) photocatalytic activity was enhanced by increasing RH% up-to 80 %. Besides, the nanohybrids demonstrated tremendous stability, with only a 3.9 % decline observed after 5 consecutive-cycles. This strategy provides new prospects to improve the compatibility of graphene/MOF materials for futuristic photoelectrical applications under high humidity.

Core/Shell Nitrogen-Doped TiO2@SiO2 Nano-Catalyst as an Additive in Photocatalytic Paint for Gaseous Acetaldehyde Decomposition

A nitrogen-doped TiO2@SiO2 core/shell nano-photocatalyst (N-TiO2@SiO2) was used as an additive in photocatalytic paint and applied for the photocatalytic degradation of gaseous acetaldehyde under light-emitting diode (LED) visible light irradiation. N-TiO2 was synthesised via the solvothermal method and then encapsulated by SiO2 via the sol-gel method. The incorporation of the N atom into the TiO2 structure was observed by X-ray photoelectron spectroscopy. The N-TiO2@SiO2 core/shell structure was determined by TEM images. The photodegradation of gaseous acetaldehyde using the prepared N-TiO2@SiO2 photocatalytic paint was examined in a closed chamber under LED light irradiation. The photodegradation of acetaldehyde by N-TiO2@SiO2 photocatalytic paint (31%) was significantly higher than that of TiO2 paint (5%) and N-TiO2 paint (20%) within 16 h. The chemical resistance and adhesion ability of N-TiO2@SiO2 photocatalytic paint were investigated following Thai Industrial Standards (TIS) no. 2321 and standard test methods for rating adhesion by tape test (ASTM D 3359-22). The N-TiO2@SiO2 paint showed good acid and alkali resistance, as well as high adhesion ability comparable with commercial paint (without a photocatalyst).

Ligand-sharing growth of upconversion UCNP(NaYbF4:Tm3+)/NMIL(Ti) nanohybrids with extended light absorbance for acetaldehyde photodegradation under high humidity

Fabrication of broad-spectrum response photocatalysts in a controllable manner that can efficiently utilize solar light as much as possible remains a top priority target yet a challenging task. In this work, a facile approach of synchronous bottom-up growth was employed to construct UCNP/NMIL(Ti) nanohybrids via NH2-BDC (NH2-MIL-125-ligand) linkage between upconversion NaYbF4:Tm3+ nanoparticles (~13-nm) and NH2-MIL-125. The ligand sharing integration strategy generated abundant oxygen vacancies and coordinatively-unsaturated-metal sites, efficiently enhanced light absorption, energy-transfer upconversion (UC-PL), photo-induced e-/h+ generation, and their separation (CV, EIS, Photocurrent-density). Consequently, UCNP/NMIL(Ti) exhibited excellent acetaldehyde photodegradation activity, with 12.5–77.0-folds higher rate constants (ka) than those of state-of-the-art photocatalysts under visible light and high humidity. Furthermore, the photocatalytic activity of UCNP/NMIL(Ti) only declined from 96.0% to 92.5% after five cycling-runs, demonstrating its remarkable photo-catalytic stability. Considering these attributes, the current strategy provides an avenue to synthesize efficient UCNPs/MOF composites for widespread usage in a variety of commercial applications.

UNDERSTANDING THE PHOTODEGRADATION MECHANISM OF GASEOUS ACETALDEHYDE OVER BI2WO6 — MODIFIED ZNWO4 PHOTOCATALYST UNDER UV LIGHT IRRADIATION

Indoor air quality has a significant impact on human health as people spend more time indoors. As a common indoor air pollutant, acetaldehyde is considered toxic when exposed to it for a prolonged period. The aim of this study is the enhancement of the photocatalytic activity of ZnWO4 with a monoclinic wolframite structure for degradation of gaseous acetaldehyde by modifying its surface with Bi2WO6 layered structure. The mechanisms behind the enhanced photocatalytic activity and the pathways for acetaldehyde photodegradation over the Bi2WO6-modified ZnWO4 photocatalyst are discussed

Cost-Effective Production of TiO2 with 90-Fold Enhanced Photocatalytic Activity Via Facile Sequential Calcination and Ball Milling Post-Treatment Strategy.

Titanium dioxide (TiO2), the golden standard among the photocatalysts, exhibits a varying level of photocatalytic activities (PCA) amongst the synthetically prepared and commercially available products. For commercial applications, superior photoactivity and cost-effectiveness are the two main factors to be reckoned with. This study presents the development of simple, cost-effective post-treatment processes for a less costly TiO2 to significantly enhance the PCA to the level of expensive commercial TiO2 having demonstrated superior photoactivities. We have utilized sequential calcination and ball milling (BM) post-treatment processes on a less-costlier KA100 TiO2 and demonstrated multi-fold (nearly 90 times) enhancement in PCA. The post-treated KA100 samples along with reference commercial samples (P25, NP400, and ST01) were well-characterized by appropriate instrumentation and evaluated for the PCA considering acetaldehyde photodegradation as the model reaction. Lattice parameters, phase composition, crystallite size, surface functionalities, titanium, and oxygen electronic environments were evaluated. Among post-treated KA100, the sample that is subjected to sequential 700 °C calcination and BM (KA7-BM) processes exhibited 90-fold PCA enhancement over pristine KA100 and the PCA-like commercial NP400 (pure anatase-based TiO2). Based on our results, we attribute the superior PCA for KA7-BM due to the smaller crystallite size, the co-existence of mixed anatase-srilankite-rutile phases, and the consequent multiphase heterojunction formation, higher surface area, lattice disorder/strain generation, and surface oxygen environment. The present work demonstrates a feasible potential for the developed post-treatment strategy towards commercial prospects.

In-situ preparation of Ti3C2/Ti3+-TiO2 composites with mosaic structures for the adsorption and Photo-degradation of flowing acetaldehyde under visible light

Photocatalytic degradation has been proven to be an effective way in the elimination of gaseous acetaldehyde. This work provided a facile in-situ method for the fabrication of Ti3C2/Ti3+-TiO2 photocatalysts by oxidizing Ti3C2 with H2O2. A novel mosaic structure formed by small Ti3+-TiO2 nanoparticles embedded in Ti3C2 layers was obtained by adjusting the synthesis parameters. Compared with pure Ti3C2, a 60-fold increase in the BET-SSA was observed in Ti3C2/Ti3+-TiO2 composites, which benefits the capture of the flowing acetaldehyde gas. Self-doped TiO2 nanoparticles induced by the incomplete oxidation process enabled the photodegradation of acetaldehyde under visible light. Besides, the closely contact between the two components helps the transfer of photon-induced charge carriers from TiO2 to Ti3C2, which suppressed the recombination of electron-hole pairs and promoted the generation of active radicals. Compared with commercial P25, which has almost no catalytic activity under the irradiation of visible light, a degradation efficiency of around 27% was achieved by applying Ti3C2/Ti3+-TiO2 as the photocatalyst. This work provided a new facile method for the in-situ fabrication of heterogeneous structures for the photocatalytic elimination of acetaldehyde under visible light.

A novel ternary mica-titania@rGO composite pearlescent pigment for the photocatalytic degradation of gaseous acetaldehyde

The photocatalytic application of TiO2 is limited due to low light harvesting abilities in the whole solar spectrum and fast recombination of the photoinduced electron-hole pairs. Herein, we report a TiO2-based ternary composite photocatalyst (MT@rGO-x; x = 0.05–0.2) with a pearlescent color effect, which incorporates a mica reflection core and a rGO multifunctional shell as cocatalysts. The micro flake composites were synthesized by a facile precipitation route and applied first to photodegrade gaseous acetaldehyde. MT@rGO-0.1 composite has optimal performance, which is 2.5 times photodegradation efficiency and 3 times CO2 mineralization efficiency higher than those of pure TiO2. The enhanced photocatalytic performance of MT@rGO composite is associated with effectively improved light harvesting of TiO2 by mica reflection. The presence of rGO facilitates the separation of electron-hole pairs and pollutant absorption. In addition, the superoxide radical was proved as the decisive active species for the photodegradation of acetaldehyde by electron spin resonance analyses and radical quenching tests. Our MT@rGO photocatalyst is expected to be applied as a functional and decorative additive of car paint, which is subject to photodegradation due to air pollutants.

Mesoporous TiO2 from poly(N,N-dimethylacrylamide)-b-polystyrene block copolymers for long-term acetaldehyde photodegradation

Although already some mesoporous (2–50 nm) sol–gel TiO2 synthesis strategies exist, no pore size control beyond the 12 nm range is possible without using specialized organic structure-directing agents synthetized via controlled anionic/radical polymerizations. Here, we present the use of reversible addition–fragmentation chain transfer (RAFT) polymerization as a straightforward and industrial applicable alternative to the existing controlled polymerization methods for structure-directing agent synthesis. Poly(N,N-dimethylacrylamide)-block-polystyrene (PDMA-b-PS) block copolymer, synthesized via RAFT, was chosen as structure-directing agent for the formation of the mesoporous TiO2. Crack-free thin layers TiO2 with tunable pores from 8 to 45 nm could be acquired. For the first time, in a detailed and systematic approach, the influence of the block size and dispersity of the block copolymer is experimentally screened for their influence on the final meso-TiO2 layers. As expected, the mesoporous TiO2 pore sizes showed a clear correlation to the polystyrene block size and the dispersity of the PDMA-b-PS block copolymer. Surprisingly, the dispersity of the polymer was shown not to be affecting the standard deviation of the pores. As a consequence, RAFT could be seen as a viable alternative to the aforementioned controlled polymerization reactions for the synthesis of structure-directing agents enabling the formation of mesoporous pore size-controlled TiO2. To examine the photocatalytic activity of the mesoporous TiO2 thin layers, the degradation of acetaldehyde, a known indoor pollutant, was studied. Even after 3 years of aging, the TiO2 thin layer retained most of its activity.

Preparation and characterization of TiO2 generated from synthetic wastewater using TiCl4 based coagulation/flocculation aided with Ca(OH)2

This study focused on the preparation of undoped and Ca-doped titania from flocculation generated sludge. Initially, TiCl4 was utilised to perform coagulation and flocculation in synthetic wastewater and an optimised dose of coagulant was determined by evaluating the turbidity, dissolved organic carbon (DOC) and zeta potential of the treated water. Later, using Ca(OH)2 as a coagulant aid, the effects on effluent pH, turbidity and DOC removal were investigated. Both Ca-doped and undoped anatase TiO2 were prepared from the flocculated sludge for morphological and photocatalytic evaluation. During the standalone use of TiCl4, maximum turbidity and DOC removal were found at 11.63 and 14.54 mg Ti/L, respectively. At the corresponding coagulant dose, rapid deprotonation of water caused the pH of the effluent to reach below 3.77 mg Ti/L. Whereas, when using Ca(OH)2 as a coagulant aid, a neutral pH (7.26) was attained at a simultaneous dosing of 32.40 mg Ca/L and 14.54 mg Ti/L. When aided with Ca(OH)2, the turbidity removal was further increased by 54.28% and the DOC removal was somewhat similar to the standalone use of TiCl4. TiO2 was prepared by incinerating the collected sludge at 600 °C for 2 h. Both XRD and SEM analysis were conducted to observe the morphology of the prepared titania. The XRD pattern of the TiO2 showed only an anatase phase along with the presence of a high atomic proportion of Ca (4.14%). Consequently, a high amount of Ca atoms inhibited the level of TiO2 phase and no obvious presence of CaO was observed. The prepared Ca-doped TiO2 at the optimised dose of Ca(OH)2 was found to be inferior to the undoped TiO2 during the photodegradation of acetaldehyde. However, a reduced dose of Ca(OH)2 (<15 mg Ca/L) exhibited a substantial increase in photoactivity under UV irradiance.

Adsorption and Photodegradation of Acetaldehyde and Ethylene on TiO2 (001) Surface: Experimental and First Principle Studies

In this work, the adsorption and photodegradation of acetaldehyde and ethylene on TiO2 nanoparticles (NPs) with dominant {001} facets were studied. Additionally, the first principle calculation was used to complement the experimental results. TiO2 NPs were synthesized by using a hydrothermal method. The experimental results indicated that adsorption amount of acetaldehyde on TiO2 {001} facets is higher than ethylene, with the initial concentration as 500 ± 10 ppm. Photodegradation efficiency of 88% was achieved for acetaldehyde in contrast to 17% for ethylene at flow rate of 10 sccm. The first principle calculations show that the adsorption energy (Eads) for acetaldehyde is 0.603 eV and that of ethylene is 0.251 eV. This study is imperative for understanding the adsorption and photodegradation process of acetaldehyde and ethylene, two typical VOCs, and helpful to design the photocatalysts with high efficiency.

Solid-state synthesis, characterization, UV-induced coloration and photocatalytic activity – The Sr6Bi2O11, Sr3Bi2O6 and Sr2Bi2O5 bismuthates

Abstract This article reports on two novel strontium bismuthate photocatalysts (Sr6Bi2O11 and Sr3Bi2O6) prepared by a solid-state synthesis for which the number of strontium atoms exceeds the number of bismuth atoms in the cation sublattice; for comparison, the bismuthate Sr2Bi2O5 was also re-examined. All three bismuthates were characterized by a variety of spectroscopic techniques (XRD, XPS, EDX, DR, Raman, SEM, and EIS). Direct bandgap energies for the three bismuthates were assessed from diffuse reflectance spectra: 2.61 eV for Sr6Bi2O11; 3.40 eV for Sr3Bi2O6; 3.17 eV for Sr2Bi2O5, while the flatband potentials (versus NHE) of the corresponding valence bands were estimated from XPS spectra: +2.22 eV for Sr6Bi2O11; +1.71 eV for Sr3Bi2O6; +1.61 eV for Sr2Bi2O5. The two novel bismuthates displayed photocatalytic activity toward the photodegradation of acetaldehyde in the gas phase and phenol in aqueous media, with the Sr6Bi2O11 system exhibiting significantly greater photoactivity vis-a-vis the Sr3Bi2O6 bismuthate; by comparison, Sr2Bi2O5 was photocatalytically inactive in this case; their photoactivity was also assessed from the photodegradation of phenol in aqueous media (in all cases using UV-Vis irradiation from a Xe light source). Detailed photocatalytic mechanisms are proposed based on UV-induced coloration studies (carried out using a high-pressure Hg lamp; 365 nm) and on the photodegradation in the presence of radical scavengers to explain how composition and structure of the three bismuthates affect their photocatalytic activity. The role of point defects (oxygen vacancies) in their crystal lattice is described as they affect photocatalytic activity by acting as electron traps and potentially as electron/hole recombination centers.

Enhanced photocatalytic performance of Ag@TiO2 for the gaseous acetaldehyde photodegradation under fluorescent lamp

The ever increasing problem of air pollution has provoked the research and development of highly-efficient photocatalysts. Herein, Ag nanowires@TiO2 composite photocatalyst with improved photocatalytic performance was fabricated by a facile one-step solvothermal procedure. The formation of one-dimensional Ag nanowires@TiO2 core-shell nanostructures could not only broaden the light-absorbing range of TiO2 catalysts through the surface plasmon resonance effect of Ag nanowires, but also enable the effective separation of photoinduced electron-hole pairs. Under the irradiation of a 260 W fluorescent lamp, the composite with 0.5 wt% Ag nanowires exhibited the highest photocatalytic activity in short contact time (4.8 min), and the corresponding gaseous acetaldehyde removal ratio was 72%, which was much higher than that of bare TiO2 (37%). The photocatalyst also showed ultrastable activity in the 15 weeks usage, which ensured their practical applications in the air purification field. An in-depth mechanism of the photodecomposition of acetaldehyde was proposed on the basis of the electron spin resonance (ESR) tests and the scavenger experiments. O2− reactive radicals was found to play a predominant role in the oxidation and decomposition of acetaldehyde. The outstanding performance of the composite materials and the thoroughly understanding of the reaction mechanism would cast light on the purposively design and optimization of TiO2-based catalysts.

Probing photon localization effect between titania and photonic crystals on enhanced photocatalytic activity of titania film

A systematic study on the photon localization of photonic-crystals (PCs) was conducted with respect to its PCs periodicity and its spatial distribution using the photo-degradation of acetaldehyde on nc-TiO2/SiO2 PCs composite films as the probe reaction. The periodicity of SiO2 PCs layer was tuned by the concentration of silica suspension in vertical deposition. The spatial distribution of photon localization was studied by inserting a SiO2 spacer with various thicknesses between the SiO2 PCs and nanocrystalline TiO2 (nc-TiO2). It was shown that the photocatalytic enhancement factor increased with the SiO2 PCs periodicity, indicating that, the more the periodicity of the PCs, the stronger the effect of its photon localization. However, when the PCs periodicity was more than 35, the enhancement factor tends asymptotically to a stationary value. In addition, the photocatalytic activity decreased with the gap distance between the nc-TiO2 catalytic layer and the PCs layer (i.e. the thickness of the SiO2 spacer), and when the gap distance is larger than 2.9μm, the PCs layer cannot enhance the photoactivity of the nc-TiO2 any longer. The effect of the photon localization of PCs can exist outside the PCs, and weakens with the distance away from the surface of the PCs. This work can offer guidance for the fabrication and application of PCs-based photocatalysts.

Development of hierarchically porous cobalt oxide for enhanced photo-oxidation of indoor pollutants

Porous cobalt oxide was successfully prepared by precipitation of cobalt hydroxide followed by low temperature thermal decomposition. The morphologies of the resultant oxides remained as the corresponding hydroxides, although the morphology of cobalt hydroxides was greatly influenced by the precursor salts. The cobalt oxides with average crystal size less than 20 nm were characterized by X-ray diffraction, scanning electron microscope, BET surface area, and XPS analysis. The photocatalytic activities of the various cobalt oxides morphologies were investigated by comparing the photo-degradation of acetaldehyde under simulated solar illumination. Relative to their low order structures and reference titania samples, the hierarchical nanostructures of cobalt oxide showed excellent abilities to rapidly degrade acetaldehyde, a model air pollutant. This was attributed to the unique nature of these hierarchical cobalt oxide nanoassemblies, which contained many catalytically active reaction sites and open pores.

Synthesis of mesoporous titania–graphite composite templated by hypocrellins for visible-light photocatalytic degradation of acetaldehyde

A photoactive compound extracted from a fungus (Hypocrella bambuase), named hypocrellins, was used as template to synthesize thermally stable mesoporous materials. The synthesized mesoporous titania samples were characterized using a combination of various physicochemical techniques, such as N2 adsorption/desorption measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FT-IR). The results of physicochemical characterizations showed that the as-synthesized sample was a composite of highly crystalline mesoporous anatase titania and graphitic carbon (gc–MTiO2), which implies the dual function of hypocrellins as template and “dopant”. The in situ doped graphitic carbon significantly increased the visible-light absorbance of TiO2. The gc–MTiO2 exhibited efficient photocatalytic activity under visible-light for photodegradation of acetaldehyde, a common indoor air pollutant. The photophysics and electron dynamics in this photocatalytic process were studied by time-resolved FT-IR spectra, in particular on the nano- to milli-second time scale. It is observed that electrons were injected into the conduction band of gc–MTiO2 and they were decayed to deep traps caused by graphitic carbon. The reported strategies could open up new uses for mesoporous titania self-doped with carbon in applications such as solar cells, photocatalysts, photoelectrical devices, and photo-induced sensors.

Preparation of Bi2WO6– and BiOI–allophane composites for efficient photodegradation of gaseous acetaldehyde under visible light

Clays have been used in combination with various photocatalysts to enhance the removal of organic pollutants. The aim of the present work was to study the impact of allophane as the support material on photocatalytic activity of Bi2WO6 and BiOI. In this work, we report on the preparation of highly adsorptive mechanically-mixed and as-synthesized Bi2WO6– and BiOI–allophane composites by mechanical mixing and hydrothermal synthesis, respectively. The prepared composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy (Raman), ultraviolet–visible spectroscopy (UV–vis), and BET method. The allophane powders showed higher specific surface area, SSA, (SBET=263m2/g) in comparison with the Bi2WO6 (SBET=21.3m2/g) and BiOI (SBET=23.1m2/g) powders. The mechanically-mixed composites possessed higher SSA compared to the as-synthesized composites probably due to the pore collapse or pore filling during the hydrothermal synthesis of the composites. The light absorption by both composites started from 700nm; however, the Bi2WO6–allophane composites only absorbed the photons>325nm, whereas the BiOI–allophane composites absorbed the photons>500nm. The samples with higher SSA showed higher acetaldehyde adsorption. On the basis of the CO2 liberation estimated from the photodegradation experiments, the BiOI and BiOI–allophane composites decomposed acetaldehyde completely within 5–7h, whereas the Bi2WO6, mechanically-mixed and as-synthesized Bi2WO6–allophane composites decomposed 75.5%, 100%, and 85.6% within 8h, respectively. With its significant adsorption of acetaldehyde, allophane contributed to the efficient photodegradation of acetaldehyde by allophane-containing composites. The obtained results suggested that both mechanically-mixed and as-synthesized Bi2WO6– and BiOI–allophane composites can be useful material for efficient photodegradation of acetaldehyde under visible light.

Photocatalytic Performance of Prussian Blue-loaded Tungsten Oxide for Photodegradation of Acetaldehyde

Photocatalytic Performance of Prussian Blue-loaded Tungsten Oxide for Photodegradation of Acetaldehyde

Synthesis and modification of nano-sized TiO2 for photo-degradation process under visible light irradiation; a Placket–Burman experimental design

In this research, nitrogen and iron (III) co-doped nano TiO2 (N-Fe-TiO2) was prepared by sol-gel method using ammonium chloride and iron chloride solutions as nitrogen and iron sources, respectively. The effect of synthesis parameters (weight ratios of N/TiO2 and Fe/TiO2, synthesis temperature, calcination time and temperature) was simultaneously investigated on the quality of the N-Fe-TiO2 product by a two-level Placket–Burman experimental design. The synthesized powders were characterized by XRD, XPS and UV–Vis spectroscopy techniques. The mean crystal size and anatase content were determined and evaluated as the linear functions of so-called synthesis parameters by the statistical analysis and regression. The 2%N-1%Fe-TiO2 product by 11nm mean crystal size and 78% anatase content, synthesized at 35°C and calcined at 500°C during 2h, exhibited the most significant activity during the photo-degradation of acetaldehyde under visible light irradiation and its efficiency was obtained about four times more than photocatalytic activity of Degussa TiO2-P25.

Visible-light-driven photodegradation of acetaldehyde gas catalyzed by aluminosilicate nanotubes and Cu(II)-grafted TiO2 composites

Aluminosilicate nanotubes and Cu(II)-grafted TiO2 composites were prepared, and the acetaldehyde degradation activity of the composites was evaluated at various relative humidities. The aluminosilicate nanotubes were synthesized hydrothermally and characterized by TEM, XRD, 27Al and 29Si NMR, FT-IR, N2 and water vapor isotherms. Their morphology was nanotubular with 3–5nm outer diameter, and the specific surface area was 245m2/g. The aluminosilicate had a strong affinity for water molecules, and the structure was determined to be an imogolite by 27Al and 29Si NMR. TiO2 and imogolite composites exhibited higher activity for the photodegradation of acetaldehyde under UV irradiation than TiO2, but was dependent on the relative humidity. Cu(II)-grafted TiO2 and imogolite composites exhibited higher activity for the photodegradation of acetaldehyde under visible light irradiation than Cu(II)-grafted TiO2, and were less affected by the relative humidity. These results show that Cu(II)-grafted TiO2 - imogolite composites exhibit very efficient absorption and photodecomposition of acetaldehyde in a variety of environments.

Selective synthesis of TiO2-based nanoparticles with highly active surface sites for gas-phase photocatalytic oxidation

This work demonstrated the absence of surface terminal hydroxyl groups plays a key role in the photocatalytic oxidation of low concentration volatile organic compounds. Probed by 1H MAS NMR spectroscopy, we showed the synthesis of bare and F-TiO2 nanoparticles with undetectably low content of terminal hydroxyl groups (TiOH) on the surface of TiO2 could be obtained through a sol–gel process. The characterization results by N2 adsorption, XRD, HRTEM, Raman, and XPS show that the bare TiO2 and F-TiO2 have almost identical bulk and surface structural properties. The photocatalytic activity was evaluated by photocatalytic oxidation of acetaldehyde and ethanol. Due to the absence of terminal TiOH in the bare TiO2 and F-TiO2, both materials exhibit 100% photodegradation of acetaldehyde and ethanol. No deactivation was observed during the experimental period of 8 days. The activities surpassed the photodegradation performance of the benchmarking Aeroxide P25 TiO2 under similar conditions (93%). On the bare TiO2, only stoichiometric CO2 production was observed and no detectable by-product existed in the product stream, resulting in no expanded off-odor problems. On the contrary, ethanol photodegradation on F-TiO2 produced minor acetaldehyde as a by-product, but the amount of acetaldehyde produced was still lower than that produced on Aeroxide P25.