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The singlet oxygen could be generated over a novel Fenton-like CeO2/CN catalyst via Ce4+/Ce3+ redox for the first time in dark and was utilized to efficiently degrade the emerging pollutant of TCH in a wide pH value (1.20–11.20).

Electrospinning technology is regarded as a simple, versatile, and cost-efficient approach in fabricating one-dimensional (1D) nanomaterials in a large scale. The prepared 1D fiberous materials by electrospinning technology possess the merits of large specific surface area, tunable chemical composition, morphology, fiber diameter and high porosity, causing them to be extensively applied in the field of catalysis. In this review, we firstly have a brief introduction to the working principle of electrospinning technology and the influence factors to the electrospun materials. Then, we highlight the investigations of various 1D electrospun fiberous catalytic materials in the applications of photocatalysis, thermocatalysis, electrocatalysis, and the relations between catalytic properties with composition, unique 1D structure and morphology as well as related catalytic mechanisms are summarized and discussed. Finally, a conclusion is presented and future work is prospected.

A multi-dimensional (1D/2D/3D) carbon/g-C3N4 composite photocatalyst (CCN) was successfully prepared by a facile method with carbon from cheap absorbent cotton wool. The activities and stabilities of CCN were evaluated by photo-degrading Rhodamine B (RhB) under visible light irradiation. The effect of carbon content in composite on the catalytic activities was investigated. The results show that a good interfacial contact can be observed between g-C3N4 and carbon materials in CCN. It reveals an enhanced photocatalytic activity in photocatalytic decomposition of RhB compared with g-C3N4. The carbon content has obvious effect on the performance of CCN, and the optimal carbon content in CCN is 1 wt% (CCN1.0). The first-order rate constant (k) of CCN1.0 is approximately 5.5 and 3.4 times those of g-C3N4 and AC1.0/g-C3N4. The CCN1.0 catalyst also shows the excellent photocatalytic stability in the recycling experiments. The enhanced catalytic performance of CCN is mainly due to an increase in electron-hole pair separation efficiency and visible light adsorption after coupling carbon. The hole and •O2– radicals are the main active species, and •O2– plays a more important role than h+. The photocatalytic mechanism over CCN1.0 was proposed. This work will provide a new insight to prepare highly-efficient g-C3N4-based photocatalysts.

Miscanthus is regarded as a desired bioenergy crop with enormous lignocellulose residues for biofuels and other chemical products. In this study, the effect of different pretreatments (including microwave, NaOH, CaO, and microwave + NaOH/CaO) on sugar yields was investigated, leading to largely varied hexose yields at 4.0-73.4% (% cellulose) released from enzymatic hydrolysis of pretreated Miscanthus residues. Among them, the highest yield of 73.4% for hexoses was obtained from 12% NaOH (w/v) solution pretreatment, whereas 1% CaO (w/w) and microwave pretreatment resulted in a lower hexose yield than the control (without pretreatment). The sugar yield from microwave followed with 1% NaOH pretreatment was 4.3 times higher than that of microwave followed with 1% CaO. However, the enzymatic hydrolysis efficiencies of the sample were 15.2% and 58.5% under microwave pretreatment followed by 12% NaOH or 12.5% CaO, respectively, which were lower than those of the same concentration of alkali (NaOH and CaO) pretreatments. To investigate the mechanism of varied enzymatic saccharification under different pretreatments, the changes in the surface structure and porosity of the Miscanthus-pretreated lignocelluses were studied by means of Fourier transform infrared, Congo red staining, and scanning electron microscopy analysis. The results show that the different pretreatments destroy the cell wall cladding structure and reduce the bonding force between cellulose, hemicellulose, and lignin to different degrees, therefore increasing the accessibility of cellulose and enhancing cellulose digestion.

A flexible Pt/TiO2/γ-Al2O3 nanfiber paper (PTA) was successfully prepared by an electrospinning-coating-NaBH4 reduction method. The catalytic performance for formaldehyde (HCHO) oxidation over PTA with different Pt contents was investigated at room temperature. The results show that PTA exhibits higher catalytic activity and stability than Pt/γ-Al2O3. The TiO2 coating can promote the transformation of intermediate species and the desorption of CO2. The PTA1 with 1 wt% Pt shows the best catalytic activity and good stability. In the view of activity and cost, 0.5 wt% Pt is the optimal Pt content. The TiO2 coating not only plays an important role in improving the activity and stability of PTA, but also acts as a protective shell of γ-Al2O3 fiber, which greatly reduces the risk of alkali etching during preparation and maintains the good flexibility of PTA. The dioxymethylene (DOM), formate/carbonate species, CO are the intermediate species in HCHO oxidation over PTA. In addition, PTA exhibits good filtration performance for fine particles as well as good fluid permeability. Because of the high efficiency and flexibility of PTA composite catalytic material for HCHO oxidation with good filtration performance for fine particles, it will be a promising candidate in air purification.

Heterogeneous Fenton-like reaction has been extensively investigated for degradation of organic pollutants for waste treatment due to the formation of highly aggressive hydroxyl radicals from hydrogen peroxide. However, most heterogeneous Fenton-like catalysts still worked well under acid conditions/or with the help of light irradiation/ electrical field, which limits their applications. Here, a novel Fenton-like catalyst of Ag3PO4/g-C3N4 was used for degradation of tetracycline hydrochloride (TCH, a typical emerging aqueous pollutant) for the first time in a wide pH value range (4.04–9.08) in dark. The results showed that it could effectively activate H2O2 to generate ⋅OH and ⋅O2– radicals in dark, which could oxidize the target pollutant in the all testing pH value range. It also showed a good stability in repeating test. The results of characterizations and theory calculation revealed a strong electronic interaction between Ag3PO4 and g-C3N4 improving the electron densities around Ag and O atoms in Ag3PO4 on the interface, which benefited the formation of active species. This work is expected to provide an insight for the design and fabrication of the novel highly-efficient Fenton-like catalysts for purification of waste water in a wide pH range.

A multi-dimensional (1D/2D/3D) carbon/g-C

Development of nonprecious metal-based catalysts highly active for complete oxidation of CH4 at a temperature ≤600 °C is significant for removing unburned CH4 at exhaust of engines of vehicles using natural gas or liquefied petroleum gas. CeO2 is active for complete oxidation of CH4. Co3O4 has been identified as a promising catalyst for this reaction. A Co3O4/CeO2 nanocomposite catalyst consisting of ceria nanorods supported on Co3O4 nanoparticles was prepared through a modified deposition precipitation method. The Co3O4/CeO2 nanocomposite exhibits high activity for complete oxidation of methane with an apparent activation energy of 43.9 kJ/mol, which is obviously lower than 95.1 kJ/mol of pure CeO2 and 89.7 kJ/mol of pure Co3O4, suggesting a synergetic effect between Co3O4 and CeO2. Surface of the Co3O4/CeO2 nanocomposite during complete oxidation of CH4 in the temperature range of 200–500 °C and potential stable intermediate of this catalysis were identified with ambient pressure X-ray photoelectron spectroscopy (AP-XPS).

Hierarchically porous SiO2/C hollow microspheres (HPSCHMs) were synthesized by a hydrothermal and NaOH-etching combined route. The adsorption performance of the prepared HPSCHMs was investigated to remove Congo Red (CR) in aqueous solution. The results show that the synthesized composite possesses a hollow microspherical structure with hierarchical pores and a diameter of about 100–200 nm, and its surface area is up to 1154 m2 g−1. This material exhibits a remarkable adsorption performance for CR in solution, and its maximum adsorption amount for CR can reach up to 2512 mg g−1. It shows faster adsorption and much higher adsorption capacity than the commercial AC and γ-Al2O3 samples under the same conditions. The studies of the kinetics and thermodynamics indicate that the adsorption of CR on the PHSCHM sample obeys the pseudo-second order model well and belongs to physisorption. The adsorption activation energy is about 7.72 kJ mol−1. In view of the hierarchically meso–macroporous structure, large surface area and pore volume, the HPSCHM material could be a promising adsorbent for removal of pollutants, and it could also be used as a catalyst support.

The macro/mesoporous NiO/LaNiO3 composite catalysts were prepared by a combined citric acid combustion and acetic acid (AA) in-situ treatment method. The results show that the NiO/LaNiO3 composite has bigger surface area and enhanced methane catalytic oxidation performance than LaNiO3 obtained only by a citric acid combustion method. Besides the bigger surface area, the enhanced catalytic performance is mainly attributed to the formation of more NiO particles on the surface of catalysts, which is helpful to activate the C H bond.

Here, NiFe2O4 with an inverse spinel structure exhibits high activity for a complete oxidation of methane at 400 °C–425 °C and a higher temperature. The surface of the catalyst and its adsorbates were well characterized with ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and in situ infrared spectroscopy (IR). In situ studies of the surface of NiFe2O4 using AP-XPS suggest the formation of methoxy-like and formate-like intermediates at a temperature lower than 200 °C, supported by the observed vibrational signatures in in situ IR studies. Evolutions of C1s photoemission features and the nominal atomic ratios of C/(Ni + Fe) of the catalyst surface suggest that the formate-like intermediate is transformed to product molecules CO2 and H2O in the temperature range of 250–300 °C. In situ studies suggest the formation of a spectator, – Olattice – CH2 – Olattice –. It strongly bonds to surface through C–O bonds and cannot be activated even at 400 °C.

Formaldehyde (HCHO) is one of the major pollutants in indoor air and long-term exposure to HCHO even at very low concentrations is harmful and may cause health problems including nasal tumors and skin irritation. Removal of HCHO is necessary to improve the quality of indoor air. Catalytic oxidative decomposition of HCHO at room temperature is regarded as the most promising strategy for the removal of HCHO because it is environmentally friendly and energy-saving. In this review, the reported catalytic materials for room-temperature catalytic oxidative decomposition of HCHO are discussed. In addition, the development and performance of catalysts for HCHO oxidative decomposition, the mechanism of this catalytic process, the surface chemistry and structure factors influencing catalytic performances, existing challenges in the development of catalysts with low cost and high activity and perspectives for important topics of future research in this area were reviewed.

Hierarchically porous SiO

The activity of the Pt catalyst toward room-temperature catalytic oxidation of formaldehyde (HCHO) known as a common indoor air pollutant can be remarkably improved by the addition of some alkali metal salts. The resulting enhancement in the catalytic activity of the Pt catalyst is generally attributed to the introduction of alkali metal ions. Theoretical simulations and experimental studies presented here show that the OH− ions provided by alkali metal salts make a major contribution to the enhanced activity of Pt catalysts toward the room-temperature catalytic oxidation of HCHO instead of additional alkali metal ions. This is because Cl− ions from the Pt precursor (H2PtCl6) are easily chemisorbed on prepared Pt catalysts, leading to their deactivation. The OH− ions provided by some alkali metal salts can effectively substitute surface adsorbed Cl− ions and contribute to the dual dehydrogenation of the HCHO molecule, which promotes the regeneration of Pt catalysts and activation of the O2 molecule. These findings are significant for optimizing the surface structure of Pt catalysts and further preparing high-performance Pt catalysts for room-temperature catalytic oxidation of HCHO.

Hierarchically macro-mesoporous flowerlike NiO microspheres (NiO-F) were first prepared by a hydrothermal method using Ni(NO3)2 and ethylenediamine as the precursors, and then Pt nanoparticles (NPs) were deposited onto the surface of NiO-F to obtain the Pt/NiO-F composite catalyst by a NaBH4 reduction method. The prepared Pt/NiO-F sample was used for oxidative decomposition of formaldehyde (HCHO) at room temperature. The results indicate that the Pt/NiO-F composite catalyst shows higher catalytic activity than the Pt/NiO catalyst using NiO particles as the support (Pt/NiO-P), which is due to its high surface area, high-dispersion and accessible Pt NPs as well as hierarchically macro-mesoporous structure facilitating diffusion of reactants and products. The Pt/NiO-F catalyst also exhibited good catalytic stability in recycled experiments. This work may contribute to the development of high-performance catalysts for indoor air purification and related catalytic processes.

Hierarchically meso-macroporous γ-Al 2 O 3 hollow microspheres were synthesized at 180 °C for 40 min for the first time by a microwave-assisted hydrothermal (MAH) followed by calcination at 600 °C for 2 h route, using KAl(SO 4 ) 2 and urea as raw materials. The results show that the obtained γ-Al 2 O 3 hollow microspheres are about 0.8–1.2 μm in diameter with a shell thickness of approximately 200 nm and the high surface area of 242 m 2 /g. The prepared γ-Al 2 O 3 hollow microspheres also exhibit an enhanced adsorption performance for Cu 2+ in solution than those prepared by hydrothermal (HT) method and commercial γ-Al 2 O 3 .

Formaldehyde (HCHO) is a major indoor air pollutant and long-term exposure to HCHO may cause health problems including nasal tumors and skin irritation. Room-temperature catalytic oxidation decomposition of HCHO is considered as the most promising strategy for the removal of HCHO due to its environmental-friendly reaction conditions and energy-saving consideration. In this work, surface-fluorinated anatase TiO 2 nanosheets with dominant {0 0 1} facets (FTiO 2 -NS) were first prepared by a hydrothermal method using Ti(OC 4 H 9 ) 4 and HF as precursors. Then, Pt/FTiO 2 -NS catalyst with 0.5 wt% Pt loadings was obtained by a combined NaOH-assisted impregnation of titania with Pt precursor and NaBH 4 -reduction route. The catalytic activity was evaluated by catalytic oxidation decomposition of HCHO vapor at room temperature. Fluoride poisoning (F-poisoning) phenomenon of Pt/FTiO 2 -NS was first observed for oxidative decomposition of HCHO. The mechanism of F-poisoning is mainly due to blocking of Pt catalytic active sites by strong interactions between Pt and highly electronegative F. In order to recover the catalytic performance, a simple regeneration method for the deactivated Pt/FTiO 2 -NS catalysts was proposed by NaOH washing.

Formaldehyde (HCHO) is a major air pollutant that may cause health problems such as eye irritation, skin irritation, and nasal tumors. 2] Therefore, the removal of HCHO becomes an important task to improve the quality of indoor air. Many strategies have been developed to remove HCHO, such as adsorption, photocatalytic oxidation, and thermal catalytic catalysis. Among them, room-temperature thermal catalytic oxidative decomposition of HCHO to CO2 and H2O is regarded as one of the most promising techniques for the removal of HCHO because this technique is energy saving and environmentally friendly. To date, various supported noble-metal catalysts (such as Pt/TiO2, [8–10] Pt/Al2O3, [11] Pd/TiO2, [12] Au/Co3O4 CeO2, Pt/MnOx–CeO2, [14] and Pt/Fe2O3 ) have been developed for room-temperature HCHO oxidation. Among them, the Pt-supported catalysts are the best candidates for actual application because they can completely oxidize HCHO into CO2 and H2O at room temperature and exhibit higher catalytic performances than other noble-metal catalysts. However, most of them were synthesized by using conventional nanoparticles (NPs) as the supports of noble metals. In practical applications, such conventional-NP-supported catalysts have the drawback of high air resistance, so they often need to be pressed into tablets or attached to other big-block supports, which would also bring shortcomings of a more complicated process and the reduction of the number of active Pt NPs because of particle overlap or sticking to the surface of the support. Furthermore, the catalytic performance of those catalysts must be further improved from the viewpoint of actual applications. Therefore, the development of high-performance catalysts with low air resistance and less particle loss for the complete oxidative decomposition of HCHO at room temperature is highly desired. In addition, the production rate, cost, and simplicity of the setup for the preparation of catalysts also should be considered. Electrospinning is a new and efficient approach to fabricate continuous well-defined 3D mats with a large surface area and controlled porous structure. Furthermore, the technique of electrospinning has the merits of a high production rate, low cost, and simplicity. Recently, the fabrication of hierarchically porous nanofiber materials by electrospinning has received considerable attention from both fundamental studies and practical applications. Hierarchical porous nanofiber materials obtained by electrospinning have also been used as catalyst supports. For example, Fang et al. reported a facile approach to immobilize gold NPs onto electrospun poly(ethyleneimine)/poly(vinyl alcohol) nanofibers for catalytic application. Zhao et al. fabricated a Pt/WO3 hybrid system by electrospinning and a galvanic replacement reaction and they found that the synthesized sample exhibited exceptional catalytic activity for methanol oxidation. If the mats obtained by electrospinning are used as the supports for noble metals to prepare supported catalysts, which can overcome the shortcoming of the loss of powder catalysts because of their sufficient To overcome the drawbacks of high air resistance and the need to be pressed into tablets or attached to other big-block supports for powder catalysts in the application of air purification, a mat-like hierarchically porous TiO2 nanofibers (TF) decorated with Pt nanoparticles (NPs) catalyst (Pt/TF) was synthesized by dipping the hierarchically porous TF mat fabricated by electrospinning into an H2PtCl6 solution followed by NaBH4 reduction. Such a mat-like catalyst has a smaller air resistance than a powder catalyst because of its hierarchical macro-/ mesoporous structure and can be used directly in air-purification systems because of its larger size. In addition, the as-prepared Pt/TF catalyst showed enhanced catalytic activity compared to a Pt-NP-decorated commercial TiO2 (P25) catalyst in the decomposition of formaldehyde at room temperature because of its accessible Pt NPs and hierarchical porous structure that facilitates the diffusion of reactants and products. This work will provide some new insights into the design and fabrication of advanced catalysts for indoor air purification.

As research continues, the control on the polymorph and morphology of calcium carbonate (CaCO3) becomes a hot topic because its application is limited by these parameters. The polymorph and morphology control of CaCO3 was successfully achieved via temperature and PEG (Mw = 6000) during the decomposition of Ca(HCO3)2, which has rarely been employed to prepare precipitated CaCO3. As-prepared CaCO3 was characterized using XRD and SEM. In the case of no PEG, rhombohedra calcite, lamellar vaterite, rod- and needlelike aragonite are observed, and calcite is the major phase at all samples and it increases with temperature, whereas vaterite and aragonite decrease with temperature. The addition of PEG restrains the formation of vaterite and promotes the emergence of needlelike aragonite particles at 70°C, and prevents the generation of calcite and encourages the production of rodlike aragonite particles at 80°C and 90°C. This work not only provides a new way on the preparation of CaCO3 powder but also presents the feasible control method in this route.

Pt/honeycomb ceramic (Pt/HC) catalysts with ultra-low Pt content (0.005–0.055 wt%) were for the first time prepared by an impregnation of honeycomb ceramics with Pt precursor and NaBH4-reduction combined method. The microstructures, morphologies and textural properties of the resulting samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The obtained Pt/HC catalysts were used for catalytic oxidative decomposition of formaldehyde (HCHO) at room temperature. It was found that the as-prepared Pt/HC catalysts can efficiently decompose HCHO in air into CO2 and H2O at room temperature. The catalytic activity of the Pt/HC catalysts increases with increasing the Pt loading in the range of 0.005–0.013 wt%, and the further increase of the Pt loading does not obviously improve catalytic activity. From the viewpoint of cost and catalytic performance, 0.013 wt% Pt loading is the optimal Pt loading amount, and the Pt/HC catalyst with 0.013 wt% Pt loading also exhibited good catalytic stability. Considering practical applications, this work will provide new insights into the low-cost and large-scale fabrication of advanced catalytic materials for indoor air purification.

Room temperature catalytic oxidation by noble metals is considered to be the most promising strategy for the removal of HCHO, which is one of the major indoor air pollutants. Hierarchically macro-mesoporous structured Pt/γ-Al2O3 hollow spheres with open and accessible pores were synthesized and used for catalytic oxidative decomposition of HCHO at room temperature. The prepared composite hollow spheres showed higher catalytic activity than the conventional nanoparticle supports, which is mainly due to their hierarchical macro-mesoporous structure facilitating diffusion of reactants and products, and the high dispersion of accessible catalytic Pt nanoparticles. This work may contribute to the development of hierarchically structured materials and high-performance catalysts for indoor air purification and related catalytic processes.

Herein, we for the first time report the production of H2 using Degussa P25 TiO2 powder (P25) from a mixed aqueous solution of methanol and Ni(NO3)2. The effect of the amount of Ni(NO3)2 on the photocatalytic H2-production activity of TiO2 was investigated and discussed. The results indicate that the photocatalytic H2-production activity of TiO2 is significantly enhanced in the presence of Ni(NO3)2. The optimal Ni(NO3)2 amount (the molar ratio of Ni(NO3)2 to TiO2 and Ni(NO3)2) was found to be 0.32 mol%, giving a H2-production rate of 2547 μmol h(-1) g(-1) with a quantum efficiency (QE) of 8.1% at 365 nm, exceeding that of pure TiO2 by 135 times. This high photocatalytic H2-production activity is due to the adsorption of Ni(2+) on the surface of TiO2. The potential of Ni(2+)/Ni (Ni(2+) + 2e(-) = Ni, E(o) = -0.23 V) is slightly lower than the conduction band (CB) of anatase TiO2 (-0.26 V), but higher than the reduction potential of H(+)/H2 (2H(+) + 2e(-) = H2, E(o) = -0.00 V), which favors electron transfer from TiO2 to Ni(2+) and reduction of Ni(2+) to Ni(0). The role of metallic Ni is to help charge separation and to act as a co-catalyst for H2 production, thus enhancing the photocatalytic H2-production activity of TiO2.