Enhanced performance of NaOH-modified Pt/TiO2 toward room temperature selective oxidation of formaldehyde

Alkali modified P25 with enhanced CO2 adsorption for CO2 photoreduction

To improve the CO2 adsorption on the photocatalyst, which is an essential step for CO2 photoreduction, solid solutions were fabricated using a facile calcination treatment at 900 °C. Using various alkalis, namely NaOH, Na2CO3, KOH, K2CO3, the resulted samples presented a much higher CO2 adsorption capacity, which was measured with the pulse injection of CO2 on the temperature programmed desorption workstation, compared to the pristine Evonik P25. As a result, all of the fabricated solid solutions produced higer yield of CO under UV light irradiation due to the increased basicity of the solid solutions even though they possessed only the rutile polymorph of TiO2. The highest CO2 adsorption capacity under UV irradiation was observed in the sample treated with NaOH, which contained the highest amount of isolated hydroxyls, as shown in the FTIR studies.

Oxidation of NO x Using Hydrogen Peroxide Vapor over Mo/TiO2

xMo/TiO₂ catalysts (x = 1, 2, 3, and 4%) were prepared using the coprecipitation method in the present study. The coprecipitation method was used in the thermal catalytic decomposition of H₂O₂ steam to treat NO _x at a low temperature range (80-160 °C). Several characterization techniques have been employed, such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller measurements, transmission electron microscopy (TEM), scanning electron microscopy and energy-dispersive X-ray spectrometry (SEM-EDXS), and Fourier transform infrared spectroscopy. The activity tests showed that the incorporation of molybdenum into TiO₂ led to a significant increase in the catalytic oxidation of NO, and under the condition of H₂O₂/NO = 6:1 (molar ratio), the NO _x removal rate of 2% Mo/TiO₂ is the highest, reaching 92.56%. XRD, TEM, and SEM-EDXS analyses showed that Mo was well dispersed on the surface of an anatase-phase TiO₂. XPS analysis indicated that Mo mixed with slag mainly existed in the form of Mo⁶⁺. Moreover, in comparison with the mostly reported SCO catalysts, used for the elimination of NO, the prepared Mo/TiO₂ catalyst showed excellent stability and sulfur resistance.

Efficient removal of formaldehyde by polyethyleneimine modified activated carbon in a fixed bed

Polyethyleneimine modified activated carbon (PEI-AC) was prepared through a treatment of immersion, and used for the adsorption of formaldehyde. The adsorption capacity of formaldehyde by unmodified AC is 190.1 mg g^-1, and the adsorption capacity of formaldehyde can reach to 317.6 mg g^-1 after 10 g L^-1 of PEI modified, being about 1.67 times than unmodified activated carbon (AC: 191.2 mg g^-1). And the 10 g L^-1 of PEI modified AC (PAC-30) has the highest adsorption capacity of formaldehyde, reached to 650 mg g^-1, with an increasing magnitude of 240% in comparison with that without modified AC. This is mainly due to changes in the pore structure and surface functional groups after modification. However, as the PEI concentration increases, the adsorption performance is inhibited. Through kinetic studies, it was found that all adsorption curves follow the second-order kinetics, and the breakthrough curves follow the Boltzmann model, and the adsorption process can also be described by the intraparticle diffusion model.

Isolated Pt single atomic sites anchored on nanoporous TiO2 film for highly efficient photocatalytic degradation of low concentration toluene

Single atom catalysts with atomically distributed active metal centers have attracted great attention owing to their maximum atom efficiency and excellent activity. Herein, we report a novel photocatalyst with isolated Pt single atomic sites anchored on nanoporous TiO₂ film prepared by a facile immersion and reduction method. HAADF-STEM, XPS, XANES and EXAFS results confirmed the anchoring of Pt single atomic sites on nanoporous TiO₂ film. The effects of immersion concentration of Pt, reduction temperature, relative humidity, inlet toluene concentration and residence time on photocatalytic degradation of low concentration toluene under UV and VUV irradiation were investigated. The results showed that the as-prepared catalyst had considerably high photocatalytic activity. The removal rate of toluene reached 45.88% under VUV irradiation when the inlet toluene concentration and residence time were 200 ppb and 0.3 s, respectively, which was 5.94 times that of pristine nanoporous TiO₂ film. The by-product ozone removal was greatly improved and the corresponding energy consumption was 0.01 kW·h/m³. While the removal rate of toluene increased with the decrease of inlet toluene concentration under UV irradiation. The Pt single atom catalyst exhibits significant potential for photocatalytic degradation of low concentration VOCs in indoor environments.

Highly Efficient Catalysts of Bimetallic Pt-Ru Nanocrystals Supported on Ordered ZrO2 Nanotube for Toluene Oxidation

ZrO₂ nanotube arrays and their supported bimetallic platinum and ruthenium (Pt_xRu_y/ZrO₂; x + y = 1 mmol %, x/y = 1:0, 0.9:0.1, 0.8:0.2, 0.7:0.3, 0.5:0.5, 0:1) nanocomposites were fabricated by employing SBA-15-OH as a hard template and an impregnation method, respectively. A controlled ordered nanotube array structure formed from the fabricated catalysts, and it showed a good performance for toluene oxidation. The specific physicochemical properties of the catalysts were examined through various analytical means. The Pt_xRu_y/ZrO₂ possessed a high surface area, and the Pt-Ru nanoparticles were dispersed uniformly on the ZrO₂ nanotube surface. The Pt_0.7Ru_0.3/ZrO₂ catalyst performed best among all of the samples, with T_90% and T_100% (temperatures for 90 and 100% conversion of toluene) of 140 and 160 °C, respectively, at a weight hourly space velocity of 36 000 mL/(h·g). These bimetallic catalysts exhibit excellent characteristics for toluene oxidation, such as higher turnover frequencies and lower apparent activation energy (E_a) values, which probably result from the synergistic effect of the Pt-Ru noble metals that leads to a high reducibility and oxygen adsorption capacity. The excellent activity, stability, and economics of the Pt_0.7Ru_0.3/ZrO₂ catalyst allow for its application in toluene removal.

The Effect of Carbon Content on Methanol Oxidation and Photo-Oxidation at Pt-TiO2-C Electrodes

The oxidation of methanol is studied at TiO2-supported Pt electrodes of varied high surface area carbon content (in the 30-5% w/w range) and C÷Ti atom ratio (in the 3.0-0.4 ratio). The Pt-TiO2 catalyst is prepared by a photo-deposition process and C nanoparticles (Vulcan XC72R) are added by simple ultrasonic mixing. The optimum C÷Ti atom ratio of the prepared catalyst for methanol electro-oxidation is found to be 1.5, resulting from the interplay of C properties (increased electronic conductivity and methanol adsorption), those of TiO2 (synergistic effect on Pt and photo-activity), as well as the catalyst film thickness. The intrinsic catalytic activity of the best Pt-TiO2/C catalyst is better than that of a commercial Pt/C catalyst and could be further improved by nearly 25% upon UV illumination, whose periodic application can also limit current deterioration.

Different effects of fluoride and phosphate anions on TiO2 photocatalysis (rutile)

At the same amounts adsorbed on Pt/rutile, fluoride was approximately 3 times more active than phosphate. A radical mechanism is proposed.

Alkaline treatment as a means to boost the activity of TiO2 in selective photocatalytic processes

In this work, the activity enhancement of TiO₂ photocatalysts by alkaline treatment has been investigated.

Scalable synthesis of water-dispersible 2D manganese dioxide monosheets

2D nanomaterials with atomic thickness usually exhibit high specific surface areas and atom exposure rates, which are suitable for surface reaction related applications. In this study, we selected the oxalate ions as the structure-inducing agent to synthesize δ-MnO₂ ultrathin nanosheets (~4.5 nm) via a facile hydrothermal method. Subsequently, an efficient exfoliation method to prepare single-layer MnO₂ nanosheets (~0.9 nm) with the major exposed {0 0 1} facets was successfully developed. We found that the oxalate ions play a major role in the growth and formation of δ-MnO₂ ultrathin nanosheets, and the formation process of the ultrathin structure was also investigated. The resulting single-layer MnO₂ nanosheets (monosheets) with exposed {0 0 1} facets showed much higher catalytic performance for carcinogenic airborne formaldehyde, better than few-layer ultrathin nanosheets and nanoflowers with exposed {1 0 0} facets. The reasons for the high catalytic activity of MnO₂ monosheets can be attributed to its higher surface areas and oxygen vacancy concentration. Moreover, the density-functional-theory (DFT) theoretical calculations showed that the oxygen vacancy in single-layer {0 0 1} facets exhibited the strongest adsorption/activation ability to O₂ and H₂O, which was very favorable for catalytic oxidation of formaldehyde. The synthesis strategy of ultrathin nanosheets described in this article may serve as reference and guidance for the preparation of other 2D ultrathin nanomaterials.

Hydroxyapatite-Supported Low-Content Pt Catalysts for Efficient Removal of Formaldehyde at Room Temperature

Indoor environmental quality directly affects the life quality and health of human beings, and therefore, it is highly vital to eliminate the volatile organic compounds especially formaldehyde (HCHO), which is regarded as one of the most common harmful pollutants in indoor air. Hydroxyapatite (HAP)-supported Pt (Pt/HAP) catalysts with a low content of Pt (0.2 wt %) obtained via hydrothermal and chemical reduction processes could effectively remove gaseous HCHO from the indoor environment at room temperature. The influence of modifier in the preparation on the catalyst activity was investigated. The HAP and HAP modified by sodium citrate and hexamethylenetetramine-supported 0.2 wt % Pt could completely decompose HCHO into CO2 and water, while HAP modified by sodium dodecyl-sulfate-supported Pt removed HCHO primarily via adsorption. The HAP modified by the sodium citrate catalyst exhibited superior catalytic performance of HCHO compared to the HAP and HAP modified by hexamethylenetetramine and sodium dodecyl-sulfate-supported Pt catalysts, which was mainly because of its higher surface Ca/P ratio providing more Lewis acidic sites (Ca2+) for co-operational capture of HCHO molecules and a larger amount of active oxygen species. Our results indicate that an optimized combination of functional supports and low-content noble metal nanoparticles could be a route to fabricate effective room-temperature catalysts for potential application in indoor air purification.

In Situ Generated Plasmonic Silver Nanoparticle-Sensitized Amorphous Titanium Dioxide for Ultrasensitive Photoelectrochemical Sensing of Formaldehyde

Trace concentration of formaldehyde can damage human health and environment. Consequently, it is of great significance to develop an ultrasensitive sensor for its determination. Herein, an ingenious and efficient photoelectrochemical sensor for formaldehyde was constructed by amorphous TiO₂ hollow spheres incorporated with Ag⁺ ions, which were brought about by silica template etching and then the exchange of Ag⁺/Na⁺ ions. The amorphous TiO₂ acted the dual role of Ag⁺ ion probe carriers and photoelectric materials. Upon exposure to the increased concentration of formaldehyde, the Ag nanoparticles were produced in situ, and photocurrent amplification was then achieved in a proportional manner. It is attributed to the injection of hot electrons from plasmonic Ag nanoparticles into the conduction band of amorphous titanium dioxide and therefore enhanced the photocurrent. The linear relationship between 1 and 400 pmol L^-1 resulted from the enhanced photocurrent and increased concentration of formaldehyde, and the detection limit was 0.4 pmol L^-1. Benefiting from an in situ and unique sensitization strategy, this photoelectrochemical sensor exhibited many advantages such as sensitivity, selectivity, cost-effectiveness, convenience of fabrication, low power consumption, and stability.

Ultrafine Bi3TaO7 Nanodot-Decorated V, N Codoped TiO2 Nanoblocks for Visible-Light Photocatalytic Activity: Interfacial Effect and Mechanism Insight

Bi₃TaO₇ is a potential photocatalyst because of its high chemical stability, defective fluorite-type structure, and superior mobility of photoinduced holes. However, few studies have focused on the interfacial effects of Bi₃TaO₇-based photocatalysts. In this work, 0D Bi₃TaO₇ nanodot-hybridized 3D V and N codoped TiO₂ nanoblock (B/VNT) composites were first synthesized for the photocatalytic removal of oxytetracycline hydrochloride, 2,4,6-trichlorophenol, and tetrabromobisphenol A. The fabricated B/VNT had a photocatalytic performance superior to that of pristine components, and probable degradation pathways were proposed according to the primary intermediates identified by a gas chromatography-mass spectrometer. Interestingly, on B/VNT, the transfer of interfacial electrons was observed from V/N-TiO₂ to Bi₃TaO₇, and the formed built-in electronic field led to a direct Z-scheme structure, rather than type II, as confirmed by the generated ^•OH and ^•O₂^- radicals and band structures from the density functional theory calculation. Therefore, the strong interfacial electronic interaction on the B/VNT was significant, which drove faster photogenerated charge transfer, more visible-light adsorption, and active ^•OH and ^•O₂^- generation, thus improving the photocatalytic activity.

Active Site-Directed Tandem Catalysis on Single Platinum Nanoparticles for Efficient and Stable Oxidation of Formaldehyde at Room Temperature

The application of tandem catalysis is rarely investigated in degrading organic pollutants in the environment. Herein, a tandem catalyst on single platinum (Pt) nanoparticles (Pt⁰ NPs) is prepared for the sequential degradation of formaldehyde (HCHO) to carbon dioxide gas [CO₂(g)] at room temperature. The synthesis approach includes coating of uniform Pt NPs on SrBi₂Ta₂O₉ platelets using a photoreduction process, followed by calcination of the sample in the atmosphere to tune partial transformation of Pt⁰ atoms to Pt²⁺ ions in the tandem catalyst. The conversion of HCHO to CO₂(g) is monitored by in situ Fourier transform infrared spectroscopy, which shows first conversion of HCHO to CO₃^2- ions onto Pt⁰ active sites and subsequently the conversion of CO₃^2- ions to CO₂(g) by neighboring Pt²⁺ species of the catalyst. The later process with Pt²⁺ species does not allow CO₃^2- poisoning of the catalyst. The enhanced activity of the prepared tandem catalyst to oxidize HCHO is maintained continuously for 680 min. Comparatively, the catalyst without Pt²⁺ shows activity for only 40 min. Additionally, the tandem catalyst presented herein performs better than the Pt/titanium dioxide (TiO₂) catalyst to degrade HCHO. Overall, the tandem catalyst may be applied to degrade organic pollutants efficiently.

Enhanced performance of alkali-modified Bi2WO6/Bi0.15Ti0.85O2 toward photocatalytic oxidation of HCHO under visible light

Photocatalytic oxidation of formaldehyde (HCHO) is considered as one of the promising ways to resolve indoor air HCHO pollution. TiO₂ has been well known as the most extended application in photocatalysis due to its strong oxidizing ability and stability. Owing to high activity under visible light irradiation, TiO₂ and Bi₂O₃ doping mixed with Bi₂WO₆ was analyzed in this study. The formation of two kinds of heterojunction caused efficient charge separation, leading to the effective reduction in the recombination of photo-generated electron and hole. The special structure and enhanced performance of these catalysts were analyzed. For the first time, the loading of alkali salts was researched for photocatalytic oxidation. In order to understand the reaction mechanism of alkali salts enhanced effects, the catalysts were investigated by using BET, XRD, UV-Vis, FT-IR, SEM, and XPS. The results found more than 2 wt% of Na₂SO₄ loading and the mixed methods with different solutions were key factors affecting the performance of catalysts. Nearly 92% HCHO conversion could be completed over Bi₂WO₆/Bi_0.15Ti_0.85O₂ (Na₂SO₄), and the concentration of HCHO was only 0.07 mg/m³ for 24 h, which was below the limit of specification in China. The results also indicated that the solution mixing method was more favorable to increase the HCHO conversion due to decrease the size of Bi_0.15T_i0.85O₂ particles. The catalysts with Na₂SO₄ loading provided more surface-adsorbed oxygen that facilitated the desorption of CO₂ and markedly increased the photocatalytic oxidation of HCHO. Graphical abstract Plausible mechanism over W-Bi2WO6/ Bi0.15Ti0.85O2-Na2SO4 (1:4) catalysts.

Removal of hexanal in cooking fume by combination of storage and plasma-catalytic oxidation on alkali-modified Co-Mn solid solution

Cooking oil fumes as an important source of volatile organic compounds in metropolitan areas are poisonous to the environment and human health. In this study, the removal of hexanal (a representative of cooking fume) using "storage-plasma catalytic oxidation" at ambient conditions has been investigated. Alkali-modified Co-Mn catalysts were synthesized by coprecipitation method and further characterized by XRD, SEM, N₂ adsorption-desorption, H₂-TPR, O₂-TPD and XPS techniques. It was clearly shown that the Na modification afforded a remarkable enhancement in the hexanal storage capacity, which is ascribed to the formation of surface hydroxyls that resulted in the chemical adsorption. Moreover, the plasma-catalytic oxidation results showed 99.4% hexanal removal and 85.7% CO₂ selectivity at a GHSV of 47700 h^-1. XPS results revealed that Na modification promoted the formation of more abundant Co³⁺, Mn³⁺ cations and surface adsorbed oxygen species, thus facilitated the oxidation process. In-situ FTIR results revealed that Na modification could trigger disproportionation reaction, resulting in the transformation of adsorbed hexanal into alcohol and carboxylic acid thus further speeds up the oxidation rate. This work provides a low-cost, highly efficient and energy-consuming approach for the removal of gaseous cooking fume by storage and plasma catalytic oxidation cycle at room temperature.

N-doping nanoporous carbon microspheres derived from MOFs for highly efficient removal of formaldehyde

Indoor formaldehyde (HCHO) removal is very important to reduce public health risk. Herein, we report a facile method for preparing N-doped nanoporous carbon through direct carbonization of metal-organic frameworks (ZIF-8) to remove harmful formaldehyde. The prepared N-doped nanoporous carbon exhibited uniform morphology and large specific surface area. Moreover, the type of N-functional groups on the N-doped nanoporous carbon had a dominant effect on its HCHO adsorption activity. As a result, HCHO adsorption capacity of the optimized N-doped nanoporous carbon was approximately five times higher than that of the commercially activated carbon. The detailed HCHO adsorption process, including physical adsorption and chemical adsorption, was also confirmed through in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). In addition, it should be noted that the N-doped nanoporous carbon exhibited high stability for HCHO adsorption, even after six adsorption cycles, indicating its good recyclability for long-term application. This study is expected to pave a way for expanding the environmental applications of the N-doped nanoporous carbon.

A TiO2/C catalyst having biomimetic channels and extremely low Pt loading for formaldehyde oxidation

This study presents a TiO2/C hybrid material with biomimetic channels fabricated using a wood template. Repeated impregnations of pretreated wood chips in a Ti precursor were conducted, followed by calcination at 400-600 °C for 4 hours under a nitrogen atmosphere. The generated TiO2 nanocrystals were homogenously distributed inside a porous carbon framework. With an extremely low Pt catalyst loading (0.04-0.1 wt%), the obtained porous catalyst could effectively oxidize formaldehyde to CO2 and H2O even under room temperature (conv. ∼100%). Wood acted as both a structural template and reduction agent for Pt catalyst generation in sintering. Therefore, no post H2 reduction treatment for catalyst activation was required. The hierarchal channel structures, including 2-10 nm mesopores and 20 μm diameter channels, could be controlled by calcination temperature and atmosphere, which was confirmed by SEM and BET characterizations. Based on the abundant availability of wood templates and reduced cost for low Pt loading, this preparation method shows great potential for large-scale applications.

Controllable synthesis of hierarchical nanoporous ε-MnO2 crystals for the highly effective oxidation removal of formaldehyde

Hierarchical nanoporous ε-MnO₂ crystals were prepared through thermal decomposition of hydrothermally-synthesized MnCO₃ precursors without any external templates or surfactants.

Core–shell g-C3N4/Pt/TiO2 nanowires for simultaneous photocatalytic H2 evolution and RhB degradation under visible light irradiation

Core–shell structural diagram (a) and proposed photocatalytic mechanism (b) for the CN/Pt/TiO₂ composite.

MOF-derived metal oxide composite Mn2Co1Ox/CN for efficient formaldehyde oxidation at low temperature

A novel MOF-derived MnCoO_x nanoparticles embedded in porous N-doped carbon catalyst exhibits excellent catalytic activity for the low-temperature oxidation of formaldehyde.

Photocatalytic Degradation of Methylene Blue over TiO2 Pretreated with Varying Concentrations of NaOH

In this paper, different NaOH concentrations (2, 5, 10, and 15 M) were used to treat {001}TiO2. The effect of NaOH on the crystal structure, morphology, optical properties, light raw electronic-hole recombination, and degradation performance of {001}TiO2 on methylene blue were studied. The results demonstrate that rutile TiO2 appeared when the NaOH concentration was as high as 10 M, showing much better photolytic performance than others. As the concentration of sodium hydroxide increases, the morphology changes accordingly. The specific surface area increases and the optical electronic-hole recombination rate decreases. Radical scavenging tests showed that hydroxyl radical and hole are very important in photocatalysis.

Ultralow Pt Catalyst for Formaldehyde Removal: The Determinant Role of Support

Supported Pt catalyst has been intensively investigated for formaldehyde elimination owing to its superior reactivity at room temperature (RT). However, the high Pt content is challenging because of its high cost. Herein, we report PbO-supported Pt catalysts with only 0.1 wt % Pt, which can achieve complete conversion of formaldehyde and reliable stability at RT under demanding conditions. Both experiments and simulations demonstrate that PbO interacts strongly with the Pt species, resulting in tight Pb-O-Pt bonding at the metal/support interface and concomitant activation of the surface lattice oxygen of the support. Moreover, PbO exhibits an extremely high capacity of formaldehyde capture through methylene glycol chemisorption rather than the common hydroxyl-associated adsorption, presenting a different reaction mechanism because the active surface lattice oxygen in the vicinity of Pt species offers improved reactivity. This work provides a valuable example for the design of an efficient catalyst for formaldehyde and potentially oxidation of other carbohydrates.

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Pt% in catalyst for room temperature formaldehyde removal was reduced to 0.1 wt %

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100% formaldehyde removal and reliable stability was achieved at room temperature

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PbO interacts strongly with the Pt species to form tight Pb-O-Pt bonding

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The active surface lattice oxygen close to Pt species offers improved reactivity

Enhanced photocatalytic activity of rGO/TiO2 for the decomposition of formaldehyde under visible light irradiation

Due to the low concentration of indoor air contaminants, photocatalytic technology shows low efficiency for indoor air purification. The application of TiO₂ for photocatalytic removal of formaldehyde is limited, because TiO₂ can only absorb ultraviolet (UV) light. Immobilization of TiO₂ nanoparticles on the surface of graphene can improve the visible light photocatalytic activity and the adsorption capacity. In this study, rGO (reduced graphene oxide)/TiO₂ was synthesized through a hydrothermal method using titanium tetrabutoxide and graphene oxide as precursors, and was used for the degradation of low concentration formaldehyde in indoor air under visible light illumination. Characterization of the crystalline structure and morphology of rGO/TiO₂ revealed that most GO was reduced to rGO during the hydrothermal treatment, and anatase TiO₂ nanoparticles (with particle size of 15-30nm) were dispersed well on the surface of the rGO sheets. rGO/TiO₂ exhibited excellent photocatalytic activity for degradation of formaldehyde in indoor air and this can be attributed to the role of rGO, which can act as the electron sink and transporter for separating photo-generated electron-hole pairs through interfacial charge transfer. Furthermore, rGO could adsorb formaldehyde molecules from air to produce a high concentration of formaldehyde on the surface of rGO/TiO₂. Under visible light irradiation for 240min, the concentration of formaldehyde could be reduced to 58.5ppbV. rGO/TiO₂ showed excellent moisture-resistance behavior, and after five cycles, rGO/TiO₂ maintained high photocatalytic activity for the removal of formaldehyde (84.6%). This work suggests that the synthesized rGO/TiO₂ is a promising photocatalyst for indoor formaldehyde removal.

One-step synthesis of OH-TiO2/TiOF2 nanohybrids and their enhanced solar light photocatalytic performance

TiO2/TiOF2 nanohybrids were quickly synthesized through a hydrothermal process using titanium n-butoxide (TBOT), ethanol (C2H5OH) and hydrofluoric acid as precursors. The prepared nanohybrids underwent additional NaOH treatment (OH-TiO2/TiOF2) to enhance their photocatalytic performance. In this paper, the mechanism of NaOH affecting the pathway of transformation from TBOT (Ti precursor) to TiO2 nanosheets was discussed. The synthesized TiO2/TiOF2 and OH-TiO2/TiOF2 were characterized by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction pattern (XRD), Fourier infrared spectroscopic analysis (FT-IR), Photoluminescence (PL) emission spectra and UV-visible diffuse reflection spectra (UV-vis DRS). The photocatalytic activity and stability of synthesized samples were evaluated by degradation of methylene blue (MB) under the simulated solar light. The results showed that a larger ratio of TiO2 to TiOF2 in TiO2/TiOF2 and OH-TiO2/TiOF2 nanohybrids could allow for even higher MB conversion compared with only TiO2 nanosheets. NaOH treatment can wash off the F ions from TiOF2 and induce this larger ratio. The highest efficiency of MB removal was just above 90% in 1 h. Lower electron-hole pairs recombination rate is the dominant factor that induces the photocatalytic performance enhancement of TiO2/TiOF2 nanohybrids. The synthesized OH-TiO2/TiOF2 nanohybrids exhibit great potential in the abatement of organic pollutants.

Effect of catalyst calcination temperature in the visible light photocatalytic oxidation of gaseous formaldehyde by multi-element doped titanium dioxide

The present study investigates the influence of calcination temperature on the properties and photoactivity of multi-element doped TiO₂. The photocatalysts were prepared by incorporating silver (Ag), fluorine (F), nitrogen (N), and tungsten (W) into the TiO₂ structure via the sol-gel method. Spectroscopic techniques were used to elucidate the correlation between the structural and optical properties of the doped photocatalyst and its photoactivity. XRD results showed that the mean crystallite size increased for undoped photocatalysts and decreased for the doped photocatalysts when calcination was done at higher temperatures. UV-Vis spectra showed that the absorption cut-off wavelength shifted towards the visible light region for the as-synthesized photocatalysts and band gap narrowing was attributed to multi-element doping and calcination. FTIR spectra results showed the shifting of OH-bending absorption bands towards increasing wave numbers. The activity of the photocatalysts was evaluated in terms of gaseous formaldehyde removal under visible light irradiation. The highest photocatalytic removal of gaseous formaldehyde was found at 88%. The study confirms the effectiveness of multi-element doped TiO₂ to remove gaseous formaldehyde in air by visible light photocatalysis and the results have a lot of potential to extend the application to other organic air contaminants.