Photocatalytic Oxidation Of Gaseous Toluene Research Articles

Assembling an S-type heterojunction comprising vacancy-rich CeO2-x and CuBi2O4 for improved photocatalytic oxidation of gaseous toluene

The exploration of highly efficient methods for degrading VOCs, with concurrent low energy consumption and lasting reusability, holds significant appeal. In this regard, an S-type CuBi2O4/CeO2-x heterojunction with the robust interfacial interactions is presented as an active photocatalyst for the efficient decomposition of gaseous toluene under full-spectrum irradiation. The optimal sample CC15 effectively degrades gaseous toluene at a high concentration of 1800 ppm within 2 h, achieving a notable CO2 yield of 87.05 %, and a TOC (total organic carbon) removal rate of 89.33 %. Furthermore, CuBi2O4/CeO2-x exhibits exceptional stability, maintaining its 100 % degradation capability over 32 cycles for nearly 64 h. Comparative characterization reveals that the superior performance derives from an abundance of oxygen vacancies and effective pre-adsorption capabilities, which facilitate rapid adsorption of VOCs on the catalyst surface, thereby increasing the likelihood of degradation reactions. Additionally, the formation of an S-type heterojunction, valence pairing between Bi3+ and Ce3+/4+ ions, and strong interfacial interactions serve as the primary pathways for the efficient separation of photogenerated carriers, contributing to the high CO2 production rate and prolonged cycle stability. The present investigation underscores the significant potential of vacancy-rich S-type heterojunctions and interfacial interactions between composite components, offering excellent activity and long-term availability for VOCs removal.

Insights into the surface Structure-Sensitive photocatalytic oxidation of gaseous toluene on Pd/TiO2 catalysts

Indoor volatile organic compounds (VOCs), represented by toluene, can pose a serious threat to human health. In this work, a series of Pd/TiO2 catalysts with different surface structures (i.e., dispersion/valence of Pd species, surface Ti3+/oxygen defect concentration and Pd-TiO2 interactions, etc.) was constructed by various methods. It was found that the Pd/TiO2 catalyst prepared by one-step reduction of NaBH4 method (Pd/TiO2-N) with metallic Pd particles possessed more surface Ti3+/oxygen defects and stronger Pd-TiO2 interaction than Pd/TiO2 catalysts prepared by ethylene glycol reduction loading method (Pd/TiO2-E) and incipient wetness impregnation method (Pd/TiO2-I). Further photochemical characterizations and reaction mechanism study revealed that the relatively higher concentration of Pd0 species on Pd particles, stronger Pd-TiO2 interaction, and more surface Ti3+/oxygen defects on Pd/TiO2-N could facilitate the generation of more reactive oxygen species (ROS) under light irradiation. The partial oxidation of toluene to benzyl alcohol/benzaldehyde/benzoic acid and the subsequent ring-opening process were found to be highly determined by the valence states of Pd particles and the concentration of surface Ti3+/oxygen defects. This work provides instructive insights into the construction of highly efficient Pd/TiO2 catalysts for the removal of indoor VOCs.

Developing of reticulated ceramic photocatalyst for efficient photocatalytic oxidation of gaseous toluene

In this study, a reticulated ceramic photocatalyst was developed to conduct the photocatalytic oxidation of gaseous toluene at high concentration. Toluene was used as a target pollutant to be degraded mainly due to its high toxicity and health effect. It was aimed to prove the potential of reticulated ceramic material with open and interconnected porous structure, high mechanical property, high surface area and low cost for toxic gaseous removal. As a result of immobilizing the TiO2 catalyst on the reticulated ceramic material with three different sintering temperatures, the best photocatalytic performance was observed at 800 °C of sintering temperature due to the anatase to rutile ratio of TiO2 catalyst. Photocatalytic oxidation of toluene was conducted at continuous and periodic illumination and resulted in similar removal efficiency of toluene under both conditions. However, the removal efficiency of toluene was found as 71.21 % under continuous illumination, whereas it was 60.55 % under periodic illumination. The ceramic photocatalysts showed excellent stability in the photocatalytic oxidation of toluene for six cycles totally 9120 min.

Photo-catalytic oxidation of gaseous toluene by Z-scheme Ag3PO4-g-C3N4 composites under visible light: Removal performance and mechanisms

Volatile organic compounds (VOCs) which exist widely in indoor air, are confirmed to be harmful to human health. In this study, gaseous toluene, the representative VOCs, was degraded by photo-catalytic oxidation (PCO) under visible light. The Ag3PO4-g-C3N4 composites with different weight ratios of Ag3PO4/g-C3N4 were synthesized and used as the photo-catalysts. The results indicated that the Ag3PO4-g-C3N4 composites with the weight ratio of 2.6 % exhibited the most superior photo-catalytic activity, and the removal efficiency of toluene was 87.52 % within 100 min irradiation, which was higher than that of bare g-C3N4 and Ag3PO4. The pseudo-one-order model was applied to analyzing the reaction process, and the apparent reaction rate constant of 2.6 %-APO-g-C3N4 was 0.005 min−1. After 3 cycles, the removal efficiency was still higher than 80.72 %. According to the results of PLS and ESR, the combination of Ag3PO4 and g-C3N4 could improve photo-induced carrier separation as well as OH and O2− radicals were both detected. Furthermore, the Z-scheme mechanism of Ag3PO4-g-C3N4 photo-catalysts was proposed. Therefore, the superior photo-catalytic activity of composites was significantly increased by the Z-scheme. In addition, the small proportion of Ag3PO4 in composites may be beneficial for a wide range of applications, given the cost of noble metal Ag.

Fabrication of novel Ag4Bi2O5-x towards excellent photocatalytic oxidation of gaseous toluene under visible light irradiation

In this work, a novel oxide combined with bismuth (Bi) and silver (Ag) was prepared via simple ball milling. This substance was optimized by adjusting the amount of pre-source. Preliminary characterization results confirmed the successful synthesis of Ag4Bi2O5. Subsequently, gaseous toluene was selected as model compound to evaluate the photocatalytic activity of Ag4Bi2O5 photocatalyst. According to the degradation results, Ag4Bi2O5 performed excellent visible light-driven photocatalytic activity with high stability. For the oxidation process of gaseous compound, reactive oxygen species (ROS) were responsible for the achievement, and the formation of oxygen vacancies on Ag4Bi2O5 were involved in the generation of ROS to promote the transfer of photogenerated electrons, and improving photocatalytic activity. DFT calculations revealed the theoretical band gap of Ag4Bi2O5 bulk is 1.758 eV. And the work function of Ag4Bi2O5 (112)ov was ca. at 4.447 eV. The material was easily fabricated and a reliable path was provided for the synthesis of new and efficient photocatalyst for the remediation of polluted indoor air.

Efficient photocatalytic oxidation of gaseous toluene in a bubbling reactor of water

Conventional gas-solid photocatalytic oxidation (SPCO) of VOCs has drawbacks such as accumulation of intermediates and catalytic deactivation. In this study, gas-liquid photocatalytic oxidation (LPCO) was exploited to improve the catalytic activity and stability by continuously bubbling VOCs into water. Toluene and commercial TiO2 (P25) were chosen as the representative VOC pollutant and photocatalyst, respectively. Toluene removal efficiency in LPCO was about 6 times of that in conventional SPCO, and no intermediates were detected in the exhaust of LPCO probably due to its high degradation and mineralization rates. However, plentiful intermediates were identified by GC-MS and ITMS both in the gas outlet and on the surface of catalyst in SPCO, which may lead to photocatalytic deactivation. Moreover, LPCO exhibited superior catalytic activity towards typical soluble VOCs such as formaldehyde compared to SPCO. The soluble intermediates formed from toluene degradation can be easily removed by sustaining UV irradiation to avoid water pollution and the water after purification can be reused in LPCO. This study provides a novel gas-liquid photocatalytic oxidation to replace conventional gas-solid photocatalytic oxidation for the sake of better catalytic activity and fewer by-products.

Influence of yolk-shell Au@TiO2 structure induced photocatalytic activity towards gaseous pollutant degradation under visible light

Core-shell and yolk-shell Au@TiO2 NPs were successfully synthesized, and the morphology differences were observed. Its photocatalytic activity was evaluated by photocatalytic oxidation of gaseous toluene under visible light illumination. The results indicated that yolk-shell Au@TiO2 exhibited superior photocatalytic properties and demonstrated a good stability. Almost 57.3% of gaseous toluene was removed over 0.14 at% yolk-shell Au@TiO2 in 3 h. It could also be reused for several times without corrosion. Furthermore, the comprehensive effect of LSPR response of Au, high cavity volume of yolk-shell structure, larger specific surface area, more mesoporous and the existence of Ti3+ were all benefit for the photocatalytic process. ESR tests also confirmed that h+, OH, O2− and Ti3+ generated from yolk-shell Au@TiO2 were the main active species in the photocatalytic degradation progress of gaseous toluene under visible light irradiation.

Efficient photocatalytic oxidation of gaseous toluene over F-doped TiO2 in a wet scrubbing process

The application of photocatalytic oxidation (PCO) of volatile organic compounds (VOCs) is strongly limited by catalyst deactivation, low mineralization ability and mass-transfer in gas-solid phase. Wet-scrubbing coupled with PCO (WPCO) provides a novel and efficient method for VOCs degradation. Fluorine-doped TiO2 (F-TiO2) photocatalyst was prepared and applied in this coupled process for toluene degradation. Toluene removal efficiency reached 80% over F-TiO2, while it was only 25% over TiO2 in the WPCO process. As for gas-solid PCO process, F-TiO2 had a low toluene removal efficiency of 10%. Furthermore, the mineralization capability of WPCO process over F-TiO2 also remarkably increased, achieving about 92 ppmv CO2 generated from toluene oxidation. Compared with TiO2, the surface fluorinated TiO2 significantly enhanced toluene degradation since it generated mobile hydroxyl radical (OH) in the WPCO process. The F/Ti molar ratio (RF) greatly affected photocatalytic activity towards toluene degradation, and the F-TiO2 with RF at 1 obtained the best performance. The photocatalytic activity of F-TiO2 had good stability and remained highly efficient after four runs.

Photocatalytic Oxidation of Toluene on Fluorine Doped TiO2/SiO2 Catalyst Under Simulant Sunlight in a Flat Reactor

Improving the capacity of TiO2 semiconductors for visible light response is a key problem for utilization of solar energy in photo-catalytic degradation of organic pollutants. Both catalyst character and reactor conditions are important for the reaction efficiency. The fluorine ion doped TiO2/SiO2 catalyst was prepared by sol-gel method using HF solution as fluorine source. The activity test and UV–vis results indicated that this catalyst was superior to TiO2 P25 in photocatalytic oxidation of gaseous toluene under simulant sunlight irradiation due to the enhancement of visible and ultraviolet light absorbance. GC-MS results indicated that the main intermediates accumulated on active sites included benzoic acid, benzaldehyde, and phenol. A flat interlaid reactor was designed for continuous treatment of the stream with F-TiO2/SiO2 film. The results showed that coating the catalyst on the surface of both top and bottom glass substrates, through the knife coating method with an optimal reactor height, attained the highest efficiency. In addition, the presence of water and oxygen enhanced the oxidation of toluene due to the generation of hydroxyl radicals and peroxy radicals, respectively. The toluene oxidation rate increased with the increase in water vapor concentration in the range of 0~60 vol.%.

Layered MoSe2/Bi2WO6 composite with P-N heterojunctions as a promising visible-light induced photocatalyst

In this paper, layered MoSe2/Bi2WO6 composites were fabricated by a simple bath sonication method for photocatalytic applications. Their photocatalytic performances were then investigated via the photocatalytic oxidation of gaseous toluene under visible-light irradiation. As a result, 1.5%-MoSe2/Bi2WO6 catalyst showed the highest activity with a degradation rate of nearly 80% during three-hour visible-light irradiation. The k value determined of 1.5%-MoSe2/Bi2WO6 was approximately 6 times higher than that of pure Bi2WO6 and 7 times higher compared with pure MoSe2. After a series of characterizations, it was concluded that the p-n heterojunctions of MoSe2/Bi2WO6 composites with strong interlayer interactions could effectively prolong the life time of photoinduced electron-hole pairs. And both the contents of surface superoxide and hydroxyl radicals were thereby increased, benefitting the photocatalytic process. Furthermore, the hydroxyl radicals and holes were found to be the major active species. This work provided a way to design photocatalyst with enhanced visible-light driven photoactivity toward indoor air pollutants purification.

Photocatalytic Oxidation of Gaseous Toluene by Visible-Light-Driven CoCuMnO x : Performance and Mechanism

CoCuMnO x as one solar energy absorbing coating was synthesized by a facile co-precipitation approach for photocatalytic oxidation of gaseous toluene under visible light, and characterized by UV–Vis-DRS, BET, SEM, XRD and XPS, respectively. It demonstrated that CoCuMnO x owned photocatalytic activity and 57% of toluene with an initial concentration of 400 mg/m3 was degraded by 1 g CoCuMnO x under 6 h irradiation with a 100 W halogen tungsten lamp. The degradation of toluene was mainly attributed to photolysis and photocatalysis, and the thermal effect of CoCuMnO x had little effect. The degradation efficiency of toluene decreased gradually from 57 to 32% after five consecutive cycles. High active spinels like Cu1.5Mn1.5O4, CuMn2O4, CuCoO2 and Co2MnO4 existed onto the CoCuMnO x surface, which accelerated electron transfer so as to form various free radicals, such as h+, .OH, and ·O2 − etc. Toluene was oxidized evidently by these radicals so that the aromatic ring itself was cleaved to generate alcoholic, aldehydic and acidic intermediates.

Fabricate and characterization of Ag/BaAl2O4 and its photocatalytic performance towards oxidation of gaseous toluene studied by FTIR spectroscopy

Porous and rod-shaped nanostructure of BaAl2O4 was successfully synthesized by using a simple hydrothermal method. Ag-doped BaAl2O4 catalyst based on the porous BaAl2O4 was prepared by incipient wetness impregnation strategy, which showed excellent photoelectric property and catalytic activity. The structural properties of the samples were systematically investigated by XRD, BET, SEM, EDX, TEM, DRS, XPS and FT-IR techniques. The results revealed that the prepared Ag/BaAl2O4 nanorods were more active than BaAl2O4 and commercial TiO2 in photocatalytic oxidation of gaseous toluene. The photodegradation ratio of toluene over Ag/BaAl2O4 reaches to 88%. The toluene was not complete degradation over these catalysts which only partial oxidations were achieved under UV illumination. The weakly adsorbed benzaldehyde is formed during photocatalysis. Hydroxyl groups on the surface of the catalyst are able to react with benzaldehyde which played a key role in the photocatalytic process.

Phase transformation-induced crystal plane effect of iron oxide micropine dendrites on gaseous toluene photocatalytic oxidation

Hematite (α-Fe2O3), magnetite (Fe3O4), and maghemite (γ-Fe2O3) micropine dendrites were synthesized by a facile hydrothermal method and oxidation-reduction process. The samples have been thoroughly characterized by various physicochemical techniques. The adsorption ability, quantum efficiency, and the photo-induced charge separation of the electron–hole pair in the samples were demonstrated by the XPS, FTIR, UV–vis, and PL spectroscopy. The α-Fe2O3 showed higher catalytic activity than the other two samples for photocatalytic oxidation of gaseous toluene. This may be attributed to the phase transformation-induced crystal plane effect of the α-Fe2O3 micropine dendrite, which has relatively more reactive crystal planes {001} and {110} exposed on the surface of α-Fe2O3.

Photocatalytic performances and activities of ZnAl2O4 nanorods loaded with Ag towards toluene

In this study, photocatalysts of ZnAl2O4 nanorods were obtained by adjusting pH values of the solution through hydrothermal routes, and then the Ag/ZnAl2O4 catalysts under pH=6 were synthesized via loading different amounts of silver. Their structural properties were systematically investigated by SEM, TEM, XRD, BET, DRS, XPS and FTIR techniques. The photocatalytic performances and activities of the prepared samples and commercial P25 were comparatively studied by the degradation of gaseous toluene under UV irradiation in in situ FT-IR reactor. The results revealed that the prepared Ag/ZnAl2O4 nanorods with loading 1wt.% Ag were more active than other prepared samples and commercial P25 in photocatalytic oxidation of gaseous toluene. Hydroxyl groups on the surface of Ag/ZnAl2O4 nanorods are able to react with photo-produced benzaldehyde, which is then retained on the catalyst surface leading to the progressive deactivation of the catalyst in the gas–solid system. The photocatalytic oxidation of gaseous pollutant over UV-illuminated Ag/ZnAl2O4 nanorods is a promising technique for air purification.

FT-IR study of the photocatalytic degradation of gaseous toluene over UV-irradiated TiO2 microballs: enhanced performance by hydrothermal treatment in alkaline solution

In this study, photocatalysts of TiO2 microballls were obtained via a hydrothermal treating of commercial P25 in alkaline solution, and then characterized with SEM, XRD, BET, DRS and surface photovoltage spectroscopy (SPS) techniques. The photovoltage response of the prepared TiO2 microballs on spectrum features a quantum size effect brought about by the reduced grain size with respect to the precursor. The UV-assisted photodegradation of gaseous toluene over P25 and the prepared TiO2 microballs was monitored by an in situ infrared technique. The results demonstrated that the prepared TiO2 microballs in anatase form were more active than commercial P25 in photocatalytic oxidation of gaseous toluene. The promoted activity of the hydrothermal-treated TiO2 is attributed to the increasing specific surface area and larger band gap induced by the reduced crystallite size.

Photocatalytic oxidation of gaseous toluene on titania/mesoporous silica powders in a fluidized-bed reactor

The photocatalytic degradation of toluene was carried out on titania/mesoporous silica photocatalysts in a self-constructed gaseous fluidized-bed photoreactor equipped with UVA light source. The powder photocatalysts were synthesized by incorporation of aqueous titania sol (as a photoactive component), into silica mesoporous materials (as a high-surface-area support), via the sol–gel impregnation method. SBA-15 was used as an ordered and KIL-2 as a disordered mesoporous silica support. The Ti/Si nominal molar ratio was adjusted to 1/2, 1/1 and 2/1. The photocatalysts were characterized by X-ray diffraction (XRD), nitrogen sorption (BET), UV–vis–NIR diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FT-IR) and high-resolution transmission electron microscopy (HR-TEM). The effects of Ti/Si molar ratio and of the mesoporous silica structure were investigated measuring adsorption capacity and photocatalytic degradation of toluene. The rates of photocatalytic degradation reactions were found to be similar for photocatalysts with the same Ti/Si molar ratio independently of the mesoporous structure of silica. The adsorption capacity was decreasing as a function of the increasing Ti/Si molar ratio in the case of both types of mesoporous silica support. However, the photocatalytic degradation proceeded faster for the Ti/Si molar ratio 1/1 while, in the case of the other investigated Ti/Si molar ratios 1/2 and 2/1, the degradation rates were lower. In general, the photocatalytic activity was considerably improved by using supported titania–silica catalyst compared to an unsupported titania powder prepared from the same nanocrystalline titania sol.

Fourier Transform Infrared Study of the Performance of Nanostructured TiO2 Particles for the Photocatalytic Oxidation of Gaseous Toluene

Thermal and hydrothermal treatments have been applied to an amorphous TiO2 precursor for obtaining nanosized TiO2 particles (P11t and P11h, respectively) of different photocatalytic properties. The activity of these catalysts has been tested by performing the toluene oxidation in gas phase in a continuous photoreactor. A Fourier transform infrared (FTIR) investigation of the catalysts under conditions prevailing during the test photoreaction has also been carried out. The photoreactivity results showed that CO2 was the main oxidation product and benzaldehyde a stable intermediate. Anatase P11t photoactivity was similar to that observed for commercial photocatalysts, while anatase P11h presented a marked improvement. The FTIR study on these samples indicate that P11h has a higher number of hydrogen-bonded hydroxyl groups that are more stable under RT outgassing than P11t. The higher photoactivity of P11h is attributed to the participation of these hydrogen-bonded hydroxyls in the toluene conversion to CO2. FTIR spectra also suggest that benzaldehyde, the minor oxidation product, originates from toluene adsorbed on isolated hydroxyls. Benzaldehyde is more strongly adsorbed on P11h than on P11t; the presence of water vapor in the reacting mixture, however, facilitates its desorption and/or photooxidation.

Photocatalytic oxidation of gaseous toluene on anatase TiO 2 catalyst: mechanistic aspects and FT-IR investigation

Photo-oxidation of toluene has been carried out in gas–solid regime by using polycrystalline anatase TiO 2 as the catalyst. The reacting gaseous mixture was toluene, air and water in various molar ratios. A pyrex fixed-bed continuous photoreactor irradiated by a medium pressure Hg lamp was used for performing the photoreactivity experiments. The main oxidation product was benzaldehyde but benzene, benzyl alcohol and traces of benzoic acid, phenol and unidentified compounds were also detected. The molar conversion to benzaldehyde with respect to the initial amount of toluene was ca. 20% in the best experimental conditions. Benzene was produced only as a transient product during the first 3–4 h of irradiation. The dependence of feed composition and flow rate on the toluene fractional conversion was investigated. Selected experiments were performed by using N 2 or CO 2 instead of air. The presence of oxygen was essential for the occurrence of the photoreaction while water played an important role in order to maintain the catalyst activity. Moreover, a Fourier-transform infrared spectroscopy (FT-IR) investigation was carried out simulating the experimental conditions used during the photoreactivity experiments. The results indicated that toluene is weakly stabilised on the hydrated TiO 2 particles by hydrogen-bonding with surface hydroxyl groups, and that it is photo-oxidised to benzaldehyde only in the presence of surface OH groups.