Photocatalytic decomposition of orange II over TiO2-loaded on SBA-15 prepared using a microwave process

SBA-15 mesoporous material was prepared by microwave-hydrothermal method and was used as support in TiO₂-loaded SBA-15 photocatalysts. The physical properties of these particles were investigated. We also examined the activity of these samples as photocatalysts for the decomposition of orange II. Titania loaded on a silica matrix decreases the surface area of the support as expected for TiO₂ incorporation. For TiO₂-loaded SBA-15 photocatalysts, the IR absorption at ∼960 cm⁻¹ commonly accepted as the characteristic vibration of the Ti-O-Si bond. The photocatalytic activity increases with an increase of the TiO₂ loading.     

Functionalized SBA-15 and its Catalytic Applications in Selective Organic Transformations

Ordered, mesoporous SBA-15 functionalized with organic and inorganic moieties exhibits efficient catalytic activity in a variety of organic transformations. In this account, reviewing our own work, three-sets of surface-modified SBA-15 materials have been investigated. The first-set of materials consists of SBA-15 modified with organo-acidic (propyl thiol and propyl sulfonic acid) and basic (propyl amine and propyl adenine) moieties. The second-set of materials was prepared by grafting Mn complexes to the organo-functionalized SBA-15. The third-set composes of nanocrystalline metal oxides supported on SBA-15. All these catalysts have been characterized by structural and spectroscopic techniques. Catalytic activities of the first-set of solid materials have been investigated in acid/base-catalyzed reactions viz., ring-opening of epoxides with amines (producing β-amino alcohols), esterification, three-component-Mannich reactions and cycloaddition of CO₂ to epoxides. The Mn complexes grafted on organofunctionalized SBA-15 are efficient catalysts for the chemo-, regio- and stereoselective aerial oxidation of monoterpenes at ambient conditions. TiO_x, VO_x, MoO_x and WO_x supported on SBA-15 catalyzed biomimetic oxyhalogenation of aromatic compounds. In all these reactions, the functionalized SBA-15 showed high selectivity.     

Sol–gel immobilization of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> on hydrophobic clay and its removal of methyl orange from water

In this study, SiO₂/TiO₂–organoclay hybrids with high adsorption capability and high photocatalytic activity were synthesized by immobilizing mixed silica and titanium dioxide nanoparticles on organically modified clay via a hydrothermal sol–gel method. Addition of negatively charged silica particles enhanced the uniform dispersion of titanium dioxide nanoparticles on organoclay layers by decreasing the system tension, which resulted in high photocatalytic activity of SiO₂/TiO₂–organoclay hybrids. The high adsorption capability endowed by organically modified clay enriched the organic compounds around the photoactive sites, and thus greatly improved the photodegradation efficiency. Combining the high adsorption capability of organoclay with the high photocatalytic activity of TiO₂ nanoparticles, SiO₂/TiO₂–organoclay hybrids were promising and cost-effective photocatalysts in removal of pollutants from wastewater.     

Enhanced Photocatalytic Activity of Titanium Dioxide Supported on Hexagonal Mesoporous Silica at Lower Coverage

The photocatalytic activities of titanium dioxide (TiO₂) supported on hexagonal mesoporous silica (HMS), zeolite Y (NaY) were investigated by using the photodegradation of 2,4,6-trichlorophenol (TCP) as test reactions. It was found that the photocatalytic activity of TiO₂ on HMS was much higher than that of TiO₂ powders, and that of TiO₂ on NaY. It was also found that TiO₂/HMS had maximal photocatalytic activity at a lower Ti content. The larger the pore size of HMS used as the support of TiO₂, the better the photocatalytic activity of TiO₂ for degradating of organic pollutant. These observations suggested that the supported structure was a main factor responsible for enhancement of the photocatalytic activity of TiO₂. Characterization of the samples by TEM, XRD, BET, and UV-vis diffuse reflectance spectra indicated that the structures of HMS and TiO₂ were confirmed and TiO₂ did not enter into the HMS framework and was formed as nanoparticles on all supports.     

A novel inorganic–organic nanohybrid material SBA-15@triazine/H<Subscript>5</Subscript>PW<Subscript>10</Subscript>V<Subscript>2</Subscript>O<Subscript>40</Subscript> as efficient catalyst for the one-pot multicomponent synthesis of multisubstituted pyridines

A novel inorganic–organic nanohybrid material SBA-15@triazine/H₅PW₁₀V₂O₄₀ (SBA-15@ADMPT/H₅PW₁₀V₂O₄₀) was prepared and used as an efficient, eco-friendly, and highly recyclable catalyst for the one-pot multicomponent synthesis of multisubstituted pyridines from the reaction of aldehydes, cyclic ketones, malononitrile, and ammonium acetate with good to excellent yields (77–97%). The nanohybrid catalyst was prepared by the chemical anchoring of Keggin heteropolyacid H₅PW₁₀V₂O₄₀ onto the surface of SBA-15 mesoporous silica modified with 2-APTS -4,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1,3,5-triazine (ADMPT) linker. Standard characterization data such as FT-IR, XRD, SEM, TEM, BET, EDX, and DTA-TGA spectroscopy confirmed that the heteropolyacid H₅PW₁₀V₂O₄₀ is well dispersed on the surface of the solid support and its structure is preserved after immobilization on the SBA-15 mesoporous silica modified with ADMPT. Furthermore, the nanocatalyst can be recovered easily and reused five times without considerable loss of catalytic activity. In general, these advantages highlight this protocol as an attractive and useful methodology, among the other methods reported in the literature, for the eco-friendly and rapid synthesis of biologically active multisubstituted pyridines.     

Comparison of low crystallinity TiO2 film with nanocrystalline anatase film for dye-sensitized solar cells

Dye adsorption and microstructure of TiO₂ film are important properties when it is used as photoelectrode of dye-sensitized solar cells (DSCs). This study investigated the application of a low crystallinity TiO₂ film in DSCs. The low crystallinity TiO₂ film is composed of interconnected spherical particles with an average size of 20 nm and has homogeneous mesoporous inner structure. A DSC based on the anatase nanocrystalline mesoporous film prepared by P25 was used for comparison purpose. It is shown that although loaded with much less dye, the DSC based on the low crystallinity TiO₂ film generated I_sc (short circuit photocurrent) as much as the one based on the conventional anatase nanocrystalline film does and obtained higher V_oc (open circuit photovoltage) as well as ff (fill factor). The overall light-to-electricity efficiency (η) of the DSC based on the low crystallinity TiO₂ film reached 5.37%, while the η of the DSC based on anatase nanocrystalline film was 4.69% in this work condition. It is suggested that a low crystallinity TiO₂ mesoporous film with a proper microstructure is as efficient as the anatase nanocrystalline mesoporous film when used in DSCs.     

SiO2/TiO2-xCx/C的制备、表征及其吸附和可见光催化性能

以SiO2为成核中心,钛酸四丁酯为钛源,分别以多羟基化合物乙二醇、丙三醇、葡萄糖和聚乙烯醇为联接剂,采用水解沉淀法制备了碳掺杂和包覆的多孔SiO2/TiO2-xCx/C可见光响应型光催化剂。采用X-射线衍射(XRD)、透射电子显微镜(TEM)、X-射线光电子能谱(XPS)、傅里叶变换-红外光谱(FTIR)、比表面积(BET)和紫外-可见(UV-Vis)漫反射光谱对样品进行表征。对不同结构样品的形成机理进行了分析。以次甲基蓝(MB)溶液为模拟废水,对样品的吸附性能和可见光催化性能进行了评价。结果表明,多羟基化合物对材料的结构和性能有重要影响。碳的掺杂和包覆使材料的吸收光谱包含了整个可见光区,而多孔结构使材料的吸附性能得到提高。以聚乙烯醇为原料所得样品吸附性能最好,30 min内吸附率达到70%;而以丙三醇为原料所得样品具有最好的可见光催化性能,40 min内次甲基蓝的降解率达到95%。     

Microstructure of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> hybrid electrospun nanofibers and their application in dye degradation

SiO₂/TiO₂ hybrid nanofibers were prepared by electrospinning and applied for photocatalytic degradation of methylene blue (MB). The phase structure, specific surface area, and surface morphologies of the SiO₂/TiO₂ hybrid nanofibers were characterized through thermogravimetry (TG), X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), etc. XRD measurements indicated that doping of silica into TiO₂ nanofibers can delay the phase transition from anatase to rutile and decrease the grain size. SEM and BET characterization proved that silica doping can remarkably enhance the porosity of the SiO₂/TiO₂ hybrid nanofibers. The MB adsorption capacity and photocatalytic activity of the SiO₂/TiO₂ hybrid nanofibers were distinguished experimentally. It was found that, although increased silica doping content could enhance the MB adsorption capacity, the intrinsic photocatalytic activity gradually dropped. The SiO₂ (10 %)/TiO₂ composite nanofibers exhibited the highest MB degradation rate, being superior to SiO₂ (20 %)/TiO₂ or pure TiO₂.     

Deep oxidative desulfurization of fuels catalyzed by molybdovanadophosphoric acid on amino-functionalized SBA-15 using hydrogen peroxide as oxidant

This study reports the usage of molybdovanadophosphoric acid catalyst on amino-functionalized SBA-15(PMoV₂/SBA-15-NH₂) for the removal of sulfur from model oil (dibenzothiophene dissolved in n-hexane). To increase the tendency for adsorption of heteropoly acids, mesoporous SBA-15 silica was functionalized with amino groups by postsynthesis grafting, using 3-aminopropyltrimethoxy silane as the coupling agent. Immobilization of molybdovanadophosphoric acid on pure SBA-15 (PMoV₂/SBA-15) was also studied for comparison and the catalysts were characterized by physicochemical and spectroscopic methods. It was found that the catalysts exhibit high catalytic activities and PMoV₂/SBA-15-NH₂ is more durable than PMoV₂ impregnated on unmodified mesoporous SBA-15 silica. The results may bring about improvement for oxidative desulfurization of transportation fuels.     

Preparation and characterization of highly photoactive nanocrystalline TiO<Subscript>2</Subscript> powders by solvent evaporationinduced crystallization method

Highly photoactive bi-phase nanocrystalline TiO₂ photocatalyst was prepared by a solvent evaporation-induced crystallization (SEIC) method, and calcined at different temperatures. The obtained TiO₂ photocatalyst was characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM) and BET surface areas. The photocatalytic activity was evaluated by the photocatalytic oxidation of acetone in air. The results show that solvent evaporation can promote the crystallization and phase transformation of TiO₂ at 100°C. When calcination temperatures are below 600°C, the prepared TiO₂ powders show bimodal pore size distributions in the mesoporous region. At 700°C, the pore size distributions exhibit monomodal distribution of the inter-aggregated pores due to the collapse of the intra-aggregated pores. At 100°C, the obtained TiO₂ photocatalyst by this method shows good photocatalytic activity, and at 400°C, its photocatalytic activity exceeds that of Degussa P25. This may be attributed to the fact that the prepared TiO₂ photocatalyst has higher specific surface areas, smaller crystallite size and bimodal pore size distribution.     

Preparation, phase transformation and photocatalytic activities of cerium-doped mesoporous titania nanoparticles

Cerium-doped mesoporous TiO₂ nanoparticles with high surface area and thermal stable anatase wall were synthesized via hydrothermal process in a cetyltrimethylammonium bromide (CTAB)/Ti(SO₄)₂/Ce(NO₃)₄/H₂O system. The obtained materials were characterized by XRD, FESEM, HRTEM, FTIR spectroscopy, nitrogen adsorption and DRS spectra. Experimental results indicated that the doping of cerium not only increased the surface area of mesoporous TiO₂ nanoparticles, but also inhibited the mesopores collapse and the anatase-to-rutile phase transformation. Moreover, the undoped, doped anatase mesoporous nanoparticles exhibit higher photocatalytic activity than commercial photocatalyst (Degussa, P25), but the maximum photodegradation rate corresponds to the undoped mesoporous TiO₂ nanoparticles. The lower photocatalytic activities of cerium-doped samples compared with undoped one may be ascribed to that the doped cerium partially blocks titania's surface sites available for the photodegradation and absorption of Rhodamine B (RB).     

Metallic nickel supported on mesoporous silica as catalyst for hydrodeoxygenation: effect of pore size and structure

Catalytic hydrodeoxygenation (HDO) of anisole, a methoxy-rich lignin-derived bio-oil model compound, was carried out over a series of Ni-containing (5, 10, 20, and 30 wt%) catalysts with commercial silica and ordered mesoporous silica SBA-15 as support. Both supports and catalysts were characterized by N₂ adsorption–desorption isotherms, X-ray diffraction, CO chemisorption, and transmission electron microscopy (TEM). Catalytic reaction was performed at 250 °C and 10 bar H₂ pressure. Depending on the catalyst support used and the content of active metal, the catalytic activity and product distribution changed drastically. Increase of the nickel loading resulted in increased anisole conversion and C₆ hydrocarbon (benzene and cyclohexane) yield. However, loading more Ni than 20 wt% resulted in a decrease of both conversion and C₆ yield due to agglomeration of Ni particles. In addition, Ni/SBA-15 samples exhibited much stronger catalytic activity and selectivity toward C₆ hydrocarbon products compared with Ni/silica catalysts. The differences in catalytic activity among these catalysts can be attributed to the effect of the pore size and pore structure of mesoporous SBA-15. SBA-15 can accommodate more Ni species inside channels than conventional silica due to its high pore volume with uniform pore structure, leading to high HDO catalytic activity.     

Photocatalytic degradation of organic compounds by Au-TiO2/sepiolite composites as the highly efficient catalysts

Photocatalytic oxidation of methyl orange (MO) and Congo red (CR) as typical model organic contaminants was investigated in aqueous solution within a cooperating Au/TiO₂/sepiolite heterostructure system under UV light irradiation. The Au/TiO₂/sepiolite composites with a single-crystalline (anatase) framework was synthesized by a facile sol-gel method using titanium tetrachloride as a TiO₂ precursor and depositing metal Au on the surface of TiO₂ nanostructures via a facile chemical reduction process. The crystal structure, surface area, light adsorption and the photoinduced charge separation rate of the photocatalyst prepared were characterized in detail. As compared with the pristine TiO₂, the Au/TiO₂/sepiolite hybrid material exhibited good photocatalytic efficiency (90%) for the UV-light photooxidation of methyl orange, which is four-fold of that of reference TiO₂. In addition, Au/TiO₂/sepiolite hybrid material also shows a good photodegradation performance toward Congo red removal. The highly efficient photocatalytic activity is associated with the strong adsorption ability of sepiolite for aromatic dye molecules, fast photogenerated charge separation due to the formation of Schottky junction between TiO₂ and metallic Au. This work suggests that the combination of the excellent adsorption properties of sepiolite and the efficient separation effect of noble metallic nanoparticles provides a versatile strategy for the synthesis of novel and highly efficient photocatalysts.     

Preparation,Characterization and Photocatalytic Activity of Lanthanum Doped Mesoporous Titanium Dioxide

Lanthanum doped mesoporous titanium dioxide photocatalysts with different La content were synthesized by template method using tetrabutyltitanate (Ti(OC₄H₉)₄) as precursor and Pluronic P123 as template. The catalysts were characterized by thermogravimetric dif-ferential thermal analysis, N₂ adsorption-desorption measurements, X-ray diffraction, and UV-Vis adsorption spectroscopy. The effect of La³⁺ doping concentration from 0.1% to 1% on the photocatalytic activity of mesoporous TiO₂ was investigated. The characterizations indicated that the photocatalysts possessed a homogeneous pore diameter of about 10 nm with high surface area of 165 m²/g. X-ray photoelectron spectroscopy measurements in-dicated the presence of C in the doped samples in addition to La. Compared with pure mesoporous TiO₂, the La-doped samples extended the photoabsorption edge into the visible light region. The results of phenol photodecomposition showed that La-doped mesoporous TiO₂ exhibited higher photocatalytic activities than pure mesoporous TiO₂ under UV and visible light irradiation.     

Template‐free Fabrication of ZnS/TiO2 Photocatalyst with Macrochannels

Constructing a porous structure in photocatalysts is an effective strategy for improving the photocatalytic activity because of its enhanced molecule transfer capability and light capturing efficiency. In this work, a hierarchical macro‐/mesoporous ZnS/TiO₂ composite with macrochannels was successfully synthesized without using templates by the simple dropwise addition of an ethanol solution of tetrabutyl titanate and zinc acetate into a sodium sulfide aqueous solution, which was then calcined at 450°C. Compared with pure TiO₂, the ordered porous ZnS/TiO₂ composite exhibited an enhanced photocatalytic activity on methylene blue removal under UV‐light irradiation. The results indicate that the macro‐/mesoporous structure, the large specific surface area, and the heterostructure combination between ZnS and TiO₂ play a synergistic effect on the enhanced photocatalytic activity via improving the light absorption and the diffusion of organic molecules, providing more reactive sites for the photocatalytic reaction and improving the separation of photogenerated electron–hole pairs, respectively. Radical trapping experiments demonstrated that holes (h⁺) and superoxide anion radicals (O₂⁻) play an important role in the photocatalytic oxidation process.     

Samarium-doped mesoporous TiO2 nanoparticles with improved photocatalytic performance for elimination of gaseous organic pollutants

Mesoporous TiO₂ doped with different amounts of Sm were prepared via a sol-gel route with Pluronic P123 as template. The materials were characterized by X-ray diffraction, transmission electron microscopy, and N₂ sorption experiments, etc. The photocatalytic activity of the mesoporous TiO₂ was tested in elimination of gaseous methanol and acetone. The Sm doped mesoporous TiO₂ have higher activity than those of the commercial photocatalyst (Degussa, P25) and Sm doped TiO₂ counterparts without mesopore structure under ultraviolet light irradiation. A possible mechanism was proposed to account for the high photocatalytic activity of the Sm doped mesoporous TiO₂. The superior activity of the Sm doped mesoporous TiO₂ may be attributed to the synergic effect of the high surface area, mesopore structure and doped Sm species.     

Mesoporous SBA-15 materials modified with PW or W active species as catalysts for the epoxidation of olefins with H<Subscript>2</Subscript>O<Subscript>2</Subscript>

Five catalysts containing PW or W active species that anchored onto aminosilylated mesoporous silica SBA-15 by a post-grafting route were prepared and the resulting PW or W/APTES/SBA-15 hybrid materials were characterized by XRD, N₂ adsorption/desorption, surface area analysis, TEM, FT-IR, and ICP (inductively coupled plasma atomic emission spectroscopy). The names of these catalysts have been abbreviated as SBA-15m-a, SBA-15m-b, SBA-15m-c, SBA-15m-d, and SBA-15m-e according to the different active species. The PW or W active species were highly dispersed in the channels of the modified mesoporous materials. The interaction between PW or W species and amino groups grafted on the channel surface of SBA-15 led to the immobilization of PW or W species. Their catalytic activity in the epoxidation of cyclooctene with H₂O₂ as oxidant was investigated. Among them, SBA-15m-a showed the best performance, with 98.9% conversion and 98.4% selectivity. The catalyst could be reused for six times with a little decrease in activity.     

Constructing Ordered Three‐Dimensional TiO2 Channels for Enhanced Visible‐Light Photocatalytic Performance in CO2 Conversion Induced by Au Nanoparticles

As a typical photocatalyst for CO₂ reduction, practical applications of TiO₂ still suffer from low photocatalytic efficiency and limited visible‐light absorption. Herein, a novel Au‐nanoparticle (NP)‐decorated ordered mesoporous TiO₂ (OMT) composite (OMT‐Au) was successfully fabricated, in which Au NPs were uniformly dispersed on the OMT. Due to the surface plasmon resonance (SPR) effect derived from the excited Au NPs, the TiO₂ shows high photocatalytic performance for CO₂ reduction under visible light. The ordered mesoporous TiO₂ exhibits superior material and structure, with a high surface area that offers more catalytically active sites. More importantly, the three‐dimensional transport channels ensure the smooth flow of gas molecules, highly efficient CO₂ adsorption, and the fast and steady transmission of hot electrons excited from the Au NPs, which lead to a further improvement in the photocatalytic performance. These results highlight the possibility of improving the photocatalysis for CO₂ reduction under visible light by constructing OMT‐based Au‐SPR‐induced photocatalysts.     

Template‐free Fabrication of Hierarchical Macro‐/mesoporous N‐doped TiO2/graphene Oxide Composites with Enhanced Visible‐light Photocatalytic Activity

Hierarchical macro‐/mesoporous N‐doped TiO₂/graphene oxide (N‐TiO₂/GO) composites were prepared without using templates by the simple dropwise addition mixed solution of tetrabutyl titanate and ethanol containg graphene oxide (GO) to the ammonia solution, and then calcined at 350 °C. The as‐prepared samples were characterized by scanning electron microscopy (SEM), Brunauer‐Emmett‐Teller (BET) surface area, X‐ray diffraction (XRD), Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), and UV‐Vis absorption spectroscopy. The photocatalytic activity was evaluated by the photocatalytic degradation of methyl orange in an aqueous solution under visible‐light irradiation. The results show that N‐TiO₂/GO composites exhibited enhanced photocatalytic activity. GO content exhibited an obvious influence on photocatalytic performance, and the optimal GO addition content was 1 wt%. The enhanced photocatalytic activity could be attributed to the synergetic effects of three factors including the improved visible light absorption, the hierarchical macro‐mesoporous structure, and the efficient charge separation by GO.