Full Spectrum Light Irradiation Research Articles

Surface oxygen vacancies induced by cu-doping in hexagonal ZnMn2O4 nanoplates for high efficiency photothermocatalytic oxidation of toluene

The exploitation of efficient and stable photothermal catalyst for the deep mineralization of volatile organic compounds (VOCs) is crucial and challenging. Herein, a photothermal catalyst with abundant oxygen defects was prepared for the first time via Cu-doped ZnMn2O4 hexagonal nanoplate. Experimental characterization results reveal that Cu doping enhances not only the ZnMn2O4 defect contents but also the light absorption and thermal conversion ability of ZnMn2O4. Compared to the undoped ZnMn2O4 (ZMO), the ZnMn2O4 with optimal Cu doping amount (ZMO-4Cu) exhibits excellent photothermal catalytic performance (94% toluene conversion and 87% toluene mineralization) and good resistance to low concentration SO2 under full-spectrum light irradiation. Experimental characterizations and theoretical calculations jointly demonstrated that the oxygen vacancies of ZMO-4Cu surface are more conducive to the adsorption of O2, effectively reduce the oxygen dissociation energy of ZMO-4Cu, thus generating abundant active oxygen species and improving the photothermal catalytic activity for toluene oxidation. In situ IR experiments disclosed that photothermal catalysis is more conducive to the toluene deep oxidation than thermal catalysis. This work provides new insights for the design of high efficiency photothermal catalysis for the deep oxidation of VOCs.

Steering Photooxidation of Methane to Formic Acid over A Priori Screened Supported Catalysts.

Efficient methane photooxidation to formic acid (HCOOH) has emerged as a sustainable approach to simultaneously generate value-added chemicals and harness renewable energy. However, the persistent challenge lies in achieving a high yield and selectivity for HCOOH formation, primarily due to the complexities associated with modulating intermediate conversion and desorption after methane activation. In this study, we employ first-principles calculations as a comprehensive guiding tool and discover that by precisely controlling the O2 activation process on noble metal cocatalysts and the adsorption strength of carbon-containing intermediates on metal oxide supports, one can finely tune the selectivity of methane photooxidation products. Specifically, a bifunctional catalyst comprising Pd nanoparticles and monoclinic WO3 (Pd/WO3) would possess optimal O2 activation kinetics and an intermediate oxidation/desorption barrier, thereby promoting HCOOH formation. As evidenced by experiments, the Pd/WO3 catalyst achieves an exceptional HCOOH yield of 4.67 mmol gcat-1 h-1 with a high selectivity of 62% under full-spectrum light irradiation at room temperature using molecular O2. Notably, these results significantly outperform the state-of-the-art photocatalytic systems operated under identical condition.

Photocatalytic performance of Au/Bi4Ti3O12 composite improved by synergistic piezoelectric effect and exciton-plasmon

Bi4Ti3O12 (BiTO) is a typical bismuth-layered Aurivillius ferroelectric material for its potential application in photocatalysis. In this study, Au/BiTO hybrid was fabricated by precipitating Au nanoparticles onto BiTO nanoflake using a sodium citrate reduction route. This integration has led to a remarkable enhancement in the photocatalytic efficiency, which is attributed to the synergistic coupling of piezoelectric effect of BiTO with the localized surface plasmon resonance (LSPR) of Au nanoparticles. The incorporation of Au nanoparticles onto the BiTO matrix has significantly boosted the light absorption and charge carrier separation, thereby augmenting the photocatalytic activity. Notably, Au/BiTO-2 composite exhibits exceptional photocatalytic performance, demonstrating the complete degradation of RhB within 40 min under full-spectrum light irradiation. Moreover, Au/BiTO-2 displays a robust photocatalytic action against other organic pollutants, including methyl orange (MO), ofloxacin (OFLX) and tetracycline hydrochloride (TC). Further enhancement of photocatalytic process is achieved when combing light irradiation with ultrasonic excitation. The ultrasonic waves break the static spontaneous polarization through alternating piezoelectric potential, which accelerates the catalytic reaction. The photocatalytic action rate of Au/BiTO-2 toward RhB reaches a value as high as 0.0984 min−1, which is nearly 2.3 folds increasement compared to that of pristine BiTO. The possible synergistic mechanism caused by piezoelectric effect and exciton-plasmon effect is discussed in detail. The work not only enriches our understanding of the underlying principles but also supply a new strategy to design high-performance catalysts in the field of environmental remediation and energy conversion.

A nonmetallic plasmonic catalyst for photothermal CO2 flow conversion with high activity, selectivity and durability

The meticulous design of active sites and light absorbers holds the key to the development of high-performance photothermal catalysts for CO2 hydrogenation. Here, we report a nonmetallic plasmonic catalyst of Mo2N/MoO2-x nanosheets by integrating a localized surface plasmon resonance effect with two distinct types of active sites for CO2 hydrogenation. Leveraging the synergism of dual active sites, H2 and CO2 molecules can be simultaneously adsorbed and activated on N atom and O vacancy, respectively. Meanwhile, the plasmonic effect of this noble-metal-free catalyst signifies its promising ability to convert photon energy into localized heat. Consequently, Mo2N/MoO2-x nanosheets exhibit remarkable photothermal catalytic performance in reverse water-gas shift reaction. Under continuous full-spectrum light irradiation (3 W·cm−2) for a duration of 168 h, the nanosheets achieve a CO yield rate of 355 mmol·gcat−1·h−1 in a flow reactor with a selectivity exceeding 99%. This work offers valuable insights into the precise design of noble-metal-free active sites and the development of plasmonic catalysts for reducing carbon footprints.

Enhanced photocatalytic properties of MWCNTs-decorated SrTiO3–SrCO3 hierarchical structures achieved by efficient charge transfer

Cr (VI) is a heavy metal ion that cannot be ignored in industrial wastewater and is highly toxic, posing a serious threat to the health and safety of natural organisms. In order to remove Cr (VI) ions in the wastewater, photocatalysis is currently employed and becomes a promising and effective way but the photocatalytic rate still needs further improvement. In this work, multi-walled carbon nanotubes (MWCNTs) modified SrTiO3–SrCO3 microspheres with a three-dimensional porous structure were prepared by a facile solvothermal method. When the dosage of MWCNTs was 0.55 wt%, the obtained sample exhibited the highest photocatalytic efficiency, with approximately 100 % removal of Cr (VI) within 6 min and the photocatalytic rate constant (k) can reach 0.52 min−1 under full-spectrum light irradiation. The enhancement in the photocatalytic performance is probably attributed to the large surface area for more adsorption of Cr (VI) ions on the sample and effectively transfer of photo-generated carriers via the hetero-structures for the reaction of Cr (VI) ions with more carriers. Therefore, this work can provide a facile method for the preparation of photocatalysts with good performance for the removal of Cr (VI) in the wastewater.

“One stone four birds” design atom co-sharing BiOBr/Bi2S3 S-scheme heterojunction photothermal synergistic enhanced full-spectrum photocatalytic activity

The rational design of heterostructure photocatalysts holds significant scientific and technical importance for maximizing the utilization of solar energy. In this study, a full spectrum-responsive S-scheme BiOBr/Bi2S3 heterojunction with co-sharing Bi atoms had been successfully constructed using an ion exchange approach accompanied by an in-situ growth process. Theoretical calculations and advanced techniques analysis demonstrate that the interfacial co-sharing of Bi atoms and the internal electric field (IEF) between BiOBr and Bi2S3 can greatly enhance S-scheme charge transfer, leading to effective spatial charge separation and the maintenance of maximum redox capacity. Additionally, the incorporation of Bi2S3 and the formation of oxygen vacancies (OVs) significantly increased NIR absorption and enhanced the photothermal property, further improving charge separation and utilization. As a result, the optimal photoreduction of Cr(VI) performance in BiOBr/Bi2S3 reached 100% within 10 min of full-spectrum light irradiation, and the CO yield was 20.32 µmol∙g–1 after 5 h of irradiation, which were 31.97 and 3.07 times higher than those of BiOBr, respectively. Furthermore, we elucidated the mechanism of Cr(VI) removal using DFT. This work provides valuable guidance for the rational design and construction of Bi-based S-scheme heterojunction photocatalysts with high-efficiency photocatalytic performance and effective solar light utilization.

Oyster shell-derived CuFe2O4-Hap nanocomposite for healthy houses: Bacterial and formaldehyde elimination

Bacterial infections and the threat of volatile organic compounds (VOCs) to human beings have attracted increasing concerns over the years. The simultaneous and effective eradication of bacteria while purifying indoor air has become an urgent issue. Herein, a biomass-based CuFe2O4-Hap was prepared via an ion-exchange method by loading CuFe2O4 with flower-shaped hydroxyapatite (Hap) obtained from oyster shells. Based on the experimental results and theoretical basis, the introduction of CuFe2O4 reduced the work function of hydroxyapatite and inhibited the recombination of photogenerated carriers. After irradiated for 15 min (300 W xenon lamp), the CuFe2O4-Hap photocatalysts exhibited excellent antibacterial efficiencies against Staphylococcus aureus (99.6 ± 0.35) % and Escherichia coli (99.7 ± 0.23) %, respectively. In addition, the functional coating prepared with CuFe2O4-Hap as the active material exhibited approximately 100 % HCHO conversion rate within 10 min under the full-spectrum light irradiation. The excellent photocatalytic decomposition performance could be attributed to the large specific surface area of nano-flower-shaped hydroxyapatite and the fast separation efficiency of photogenerated carriers. Overall, the proposed strategy is expected to stimulate further research into the biomass valorization for a healthier and environment-friendly lifestyle.

In-situ construction of Schottky junctions by highly dispersed Ni co-catalysts supported on mesoporous defective t-TiO2 for boosting photocatalytic H2 evolution

Designing photocatalysts with interfacial design and defect engineering are crucial to improved H2-evolution efficiency of photocatalytic water splitting. Herein, mesoporous tablet-like x-wt% Ni/t-TiO2 catalysts with Schottky junction and oxygen vacancies (Oν) were constructed using metal–organic framework (namely MIL-125(Ti)) as template. It is demonstrated that the optimal composition of 1 wt% Ni/t-TiO2 achieves a H2 production rate of 4276.13 μmol/g/h without using noble metal Pt. It was ∼129 times higher than MIL-125(Ti) derived pure TiO2 (t-TiO2) and showed fair durability after least four consecutive cycles test under full spectrum light irradiation. Particularly, its apparent quantum efficiency (AQE) at 350 nm reaches 12.09 %. Our results show that the synergetic effect of Schottky junction and oxygen vacancies (Oν) contribute significantly to the high catalytic performance. Meanwhile, the mesoporous structure provides a large specific surface area which is crucial for further enhancement of the reaction rate. This work opens an effective and low-cost strategy for preparing novel heterojunction photocatalysts with abundant oxygen vacancies and improving the hydrogen generation rate of MOF-derived photocatalysts without using noble metal.

An effective strategy to improve the photothermocatalytic activity of Co3O4 for VOCs degradation: Specifically enhancing the surface lattice oxygen activity

Co3O4 catalysts with active surface lattice oxygen were constructed via a simple solvothermal method by adopting isopropyl alcohol (IPA) or tert-butyl alcohol (TBA) as solvent. The obtained Co3O4-IPA and Co3O4-TBA exhibit flower-like structures with (112) planes exposed on the surface. Due to abundant unsaturated Co3+ sites existing on the (112) plane, the content and activity of surface lattice oxygen on Co3O4-IPA and Co3O4-TBA are much higher than that on Co3O4-MA and Co3O4-EA, which prepared with methyl alcohol or ethyl alcohol as a solvent. The robust surface lattice oxygen on Co3O4-IPA and Co3O4-TBA facilitates the ring-opening process during photothermocatalytic oxidation of toluene, significantly promoting the catalytic performance. In the static atmosphere, about 98% of toluene conversion and 80% of CO2 yield can be achieved on Co3O4-IPA and Co3O4-TBA under full-spectrum light irradiation of 325 mW/cm2, much higher than 89% and 73% of conversion, 50% and 26% of CO2 yield on Co3O4-EA and Co3O4-MA, respectively.

Biomaterial-based metal-phthalocyanine/metal oxide microspheres for photocatalytic degradation of organic pollutants under visible light

Developing new eco-friendly photocatalytic materials and improving their performance under visible light are key areas of research in organic pollutant photodegradation. In this study, photocatalytic materials containing metal phthalocyanines (MPc) and metal oxides were prepared through a sol-gel process using gellan gum (GG) as the carrier. The adsorption capabilities of these new photocatalytic materials and their efficiency at decomposing Rhodamine B (RhB) under full-spectrum light irradiation were measured using UV spectroscopy and synchronous fluorescence spectrometry. The biomaterial with CoPc/CoO exhibited a higher photocatalytic effectiveness than that with TiO2, and has potential as a substitute for TiO2. Although the photocatalytic effect of GG composited with FePc/FeO was weaker than that of Co-containing materials, it still exhibited some photocatalytic activity. The superior photocatalytic degradation of RhB was attributed to the good adsorption properties of gellan gum, the fine light absorption properties of CoPc material, and the significant synergy and cooperation of the Fenton effect and photocatalysis within the microspheres. Furthermore, the CoPc/CoO/GG microspheres exhibited good photocatalytic degradation effects on nitrobenzene, acetophenone, flurofloxacin, and other organic matters. The good photocatalytic performance proved that the biomaterial-based metal-phthalocyanine/metal oxide microspheres have great potential as a promising photocatalytic candidate for removing organic pollutants.

Reinforced charge separation via Fe-doped Bi12O17Cl2 nanotube with UV–Vis and Near-Infrared responsive photocatalytic properties

Full-spectrum responsive and effective charge separation efficiency are still important factors for enhanced photocatalytic activity. Herein, a one-dimensional Bi12O17Cl2 nanotube (Fe-Bi12O17Cl2) has been synthesized successfully, which could simultaneously expand the ability of light absorption and charge separation. As the results, Fe-Bi12O17Cl2 could realize the degradation of rhodamine B (RhB) pollutants under near-infrared and full-spectrum light irradiation, and compared with Bi12O17Cl2 nanotube, the photocatalytic performance was improved by 3.49 and 1.93 times, respectively. Mechanism studies have shown that the Fe-doped strategy could introduce variable valence Fe3+, forming a Fe2+/Fe3+ cycle, which promotes efficient charge transfer and further enhances the activity of the photocatalytic reaction. Overall, this work provides new sight into the design of high-performance photocatalysts.

W18O49/MnWO4 heterojunction for highly efficient photocatalytic reduction of CO2 under full spectrum light

Solar-energy-driven CO2 reduction for chemical reagents production, such as CH3OH, CH4 and CO, has tremendous potential for carbon neutrality in the energy industries. However, the low reduction efficiency limits its applicability. Herein, W18O49/MnWO4 (WMn) heterojunctions were prepared via one-step in-situ solvothermal process. Through this method, W18O49 tightly combined with the surface of MnWO4 nanofibers to form nanoflower heterojunction. It was found that under full spectrum light irradiation for 4 h, the yields of photoreduction of CO2 to CO, CH4 and CH3OH by 3–1 WMn heterojunction were 61.74, 71.30 and 18.98 μmol/g, respectively, which were 2.4, 1.8 and 1.1 times that of pristine W18O49, and ca.20 times that of pristine MnWO4 towards CO production. Furthermore, even in the air atmosphere, the WMn heterojunction still performed excellent photocatalytic performance. Systematic investigations demonstrated that the catalytic performance of WMn heterojunction was improved by superior light utilization and more efficient photo-generated carrier separation and migration as compared with W18O49 and MnWO4. Meanwhile, the intermediate products of the photocatalytic CO2 reduction process were also studied in detail by in-situ FTIR. Therefore, this study provides a new way for designing high efficiency of heterojunction for CO2 reduction.

Facet tailoring and Cu doping promoted photo-assisted peroxymonosulfate activation by oxygen-deficient α-MnO2 for efficient mineralization of bisphenol a

Revealing the synergistic mechanism between facets and metal doping during catalytic processes is an efficient approach to improve the catalytic performance. Herein, the synergetic effects between Cu doping and crystal facets over α-MnO2 on the peroxymonosulfate (PMS) activation towards bisphenol A (BPA) degradation under full-spectrum light irradiation were studied in details for the first time. The Cu-doped α-MnO2 with (100), (110), and (310) facets were synthesized by hydrothermal method. The Cu-doped (110)/PMS/Light system presented the highest BPA removal efficiency with high 1O2 generation and selectivity, being superior over the Cu-doped (100), Cu-doped (310) and pristine (110) counterparts. The corresponding mechanism showed that Cu doping for α-MnO2 enhanced the absorption of light, the formation of oxygen vacancies and electronic conductivity as well as PMS activation, especially for the (110) facet, as compared to the (100) and (310) facets. In addition, density functional theory (DFT) calculations and characterizations indicated that the synergetic effect between facet and oxygen vacancies played an important role in 1O2 generation. Moreover, oxygen vacancies accelerated the complexation of PMS with surface Mn(IV) and improved the generation of 1O2, different to that due to Mn(III). Toxicity assessment showed that BPA was partially decomposed into highly toxic intermediates during the degradation process. However, Cu doping and light synergistically improved the mineralization rate of pollutants, removing 95% of the total organic carbon (TOC) and reducing the toxicity of the intermediates. The ultrahigh TOC removal was attributed to the joint effect of 1O2, O2− and electron transfer. This work therefore provides an efficient and highly selective PMS catalyst for 1O2 generation, and reveals the synergistic mechanism between metal doping and crystal facets of the catalyst in advanced oxidation processes.

Boosting full-spectrum light driven surface lattice oxygen activation of ZnMn2O4 by facet engineering for highly efficient photothermal mineralization of toluene

To improve the catalytic activity of photothermal catalysts for efficient mineralization of volatile organic compounds still keeps challenge. Herein, ZnMn2O4 with controllably exposed {010} facets (ZMO-H), {11−1} facets (ZMO-R), and {1−1−1} facets (ZMO-C) were firstly synthesized and used to unveil an essential role of facet-dependent activation of surface lattice oxygen for toluene mineralization under full-spectrum light irradiation. The experimental studies and theoretical calculations together evidenced that as compared to ZMO-R and ZMO-C, ZMO-H is favorable for activating surface lattice oxygen, owing to its relatively stronger light absorption, higher surface lattice oxygen content, and lower oxygen dissociation energy. The theoretical calculations further confirmed that toluene is more easily adsorbed by ZMO-H than by ZMO-R and ZMO-C. All these advantages have substantially afforded the toluene photothermal oxidation activity of ZMO-H. This finding confirms that surface lattice oxygen activation of catalyst by facet engineering is crucial on the photothermal oxidation of toluene.

Piezoelectric effect enhanced plasmonic photocatalysis in the Pt/BaTiO3 heterojunctions

The use of piezoelectric internal field to assist in photocatalysis is important for inexpensive and high-efficiency catalytic techniques. In this study, novel Pt/BaTiO3 heterojunctions were prepared via decoration of Pt nanoparticles (PtNPs) on the surface of piezoelectric BaTiO3 nanocubes through a facile photoreduction process. The photocatalytic, piezo-catalytic, and piezo-photocatalytic activities of the Pt/BaTiO3 heterojunctions for methyl orange (MO) degradation were investigated under ultrasonic excitation and/or full-spectrum light irradiation. The weight percentage of PtNPs, piezoelectric internal field of BaTiO3, and plasmonic effect have been proven important for the photocatalytic activity of the heterojunctions. The Pt0.25/BaTiO3 with 0.25 wt% PtNPs exhibited an optimum photocatalytic degradation performance of 92.5% for MO in 50 min under full-spectrum light and ultrasonic co-excitation, and this value was about 1.35 times higher than the degradation rate under full-spectrum light irradiation alone. Well-dispersed PtNPs in the Pt/BaTiO3 heterojunction can be excited by incident light to generate an electromagnetic field caused by the surface plasmon resonance (SPR) effect, which drives the collective oscillation of electrons and generate hot electron–hole pairs. The piezoelectric internal field generated in BaTiO3 due to ultrasonic excitation can improve the separation efficiency of SPR-induced hot charge carriers and contribute to the production of highly reactive oxidation radicals, thereby enhancing the catalytic capability of the heterojunction to oxidize organic dyes. This study introduces the piezoelectric effect of BaTiO3 into plasma photocatalysis to enhance the photocatalytic activity of Ptx/BaTiO3 heterojunction, and this effect can be extended to other piezoelectric material systems to provide an effective technology for environmental purification.

Photothermal effect of carbon dots for boosted photothermal-assisted photocatalytic water/seawater splitting into hydrogen

Herein, carbon dots were loaded on the surface of hollow tubular carbon nitride (CDs/TCN) via a two-step route of hydrothermal and calcination processes for photothermal-assisted photocatalytic water/seawater splitting into hydrogen full spectrum light irradiation. The introduction of CDs promotes the separation and transfer rate of photogenerated carriers, and provides active sites for the hydrogen precipitation reaction. Most importantly, with the assistance of the thermal insulation effect of TCN, the photothermal effect of CDs can greatly increase the surface temperature of CDs/TCN composite system, thus enhancing the photocatalytic H2 production performance. All the synthesized CDs/TCN composites exhibited efficient photocatalytic H2 production rates, the highest of which reached 12.94 mmol h−1 g−1 and 11.92 mmol h−1 g−1 from water and seawater splitting, respectively. This study provides a new idea for enhancing the photothermal-assisted photocatalytic water splitting into hydrogen using CDs with photothermal effect.

Optimization of photothermal conversion and catalytic sites for photo-assisted-catalytic degradation of volatile organic compounds

Solar energy conversion is a promising strategy to enhance the elimination of volatile organic compounds (VOCs) and minimize power consumption. Herein, non-noble metal WC@WO3 as cocatalyst was composited with CeO2 to optimize photochemical and photothermal conversion for the catalytic ozonation of toluene and acetone. The photothermal conversion efficiencies of visible and infrared lights on 20%WC@WO3–CeO2 were 2.2 and 10.4 times higher than those on CeO2, respectively, which indicates that the equilibrium temperature of the catalyst remarkably increased under full-spectrum light irradiation. Moreover, WC@WO3 transferred electrons to CeO2 in 20%WC@WO3–CeO2 and thus remarkably improved the activity of catalytic sites. The synergy factor of light and O3 on 20%WC@WO3–CeO2 was 5.8, and the reaction rate of toluene and acetone reached 9274.5 and 35779.0 mg/(m3∙min), respectively. This work provides a low-cost and high-efficient catalyst for the utilization of solar energy for VOC control.

Visible-near-Infrared Light-Driven Photocatalytic Characteristics of Er3+/Yb3+-Codoped BiOBr Upconverting Microparticles for Tetracycline Degradation.

To settle the unsatisfying efficiency and insufficient light harvesting ability of photocatalysts, we report on the development of Er3+/Yb3+-codoped BiOBr (BiOBr:Er3+/xYb3+) microparticles that were synthesized by a rational high-temperature solid-state reaction method. The prepared microcrystals exhibit high visible upconversion (UC) emissions with maximum intensities at x = 0.01 when excited by a 980 nm laser. Remarkably, the corresponding UC emission process is attributed to a two-photon absorption route. Furthermore, the photocatalytic activities of as-synthesized compounds were further evaluated through analyzing the visible-near-infrared light-triggered tetracycline degradation. Compared with BiOBr:Er3+ microparticles, BiOBr:Er3+/xYb3+ microparticles present superior photocatalytic properties and the optimal status is achieved when x = 0.05, in which h+, ·O2-, and ·OH active species contribute to the photocatalytic mechanism. Additionally, the designed microparticles exhibit better photocatalytic abilities than previously reported photocatalysts (i.e., TiO2, SnO2) upon full-spectrum light irradiation. These results reveal that Yb3+ codoping is able to not only enhance the UC emission properties of BiOBr:Er3+ microparticles but also reinforce their photocatalytic activities. Our findings may put forward a facile strategy to regulate the photodegradation capacity of photcatalysts.

Construction of Carbon Dot-Modified g-C3N4/BiOIO3 Z-Scheme Heterojunction for Boosting Photocatalytic CO2 Reduction under Full Spectrum Light

In this study, we successfully constructed a Z-scheme BiOIO3/CQDs/g-C3N4 (BCCN) composite modified with carbon quantum dots (CQDs) for photocatalytic CO2 reduction. A series of characterization approaches and testing technologies were carried out to investigate the components, morphologies, and optical properties of the fabricated photocatalysts. The 0.015B0.01CCN displayed an efficient photocatalytic CO2 reduction activity within 7 h full spectrum light irradiation, producing CO with a rate of 117.88 μmol gcat–1. The enhanced photocatalytic CO2 reduction of the BCCN composite can be attributed to the synergistic effects of CQDs and the Z-scheme heterojunction. This work presents a new insight into integrating CQDs with g-C3N4 and BiOIO3 for the positive synergetic effect to obtain a high-efficient photocatalyst.

Elevating Photooxidation of Methane to Formaldehyde via TiO2 Crystal Phase Engineering

Photocatalytic conversion of methane to value-added products under mild conditions, which represents a long sought-after goal for industrial sustainable production, remains extremely challenging to afford high production and selectivity using cheap catalysts. Herein, we present the crystal phase engineering of commercially available anatase TiO2 via simple thermal annealing to optimize the structure-property correlation. A biphase catalyst with anatase (90%) and rutile (10%) TiO2 with the optimal phase interface concentration exhibits exceptional performance in the oxidation of methane to formaldehyde under the reaction conditions of water solvent, oxygen atmosphere, and full-spectrum light irradiation. An unprecedented production of 24.27 mmol gcat-1 with an excellent selectivity of 97.4% toward formaldehyde is acquired at room temperature after a 3 h reaction. Both experimental results and theoretical calculations disclose that the crystal phase engineering of TiO2 lengthens the lifetime of photogenerated carriers and favors the formation of intermediate methanol species, thus maximizing the efficiency and selectivity in the aerobic oxidation of methane to formaldehyde. More importantly, the feasibility of the scale-up production of formaldehyde is demonstrated by inventing a "pause-flow" reactor. This work opens the avenue toward industrial methane transformation in a sustainable and economical way.