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Highly active sulfated titania photocatalysts (SO42−/TiO2) were prepared using Ti(SO4)2 as precursor via a precipitation and peptization process. Precipitates obtained through adding NaOH solution into Ti(SO4)2 were peptized with HNO3, followed by calcination at varying temperatures to form SO42−/TiO2. The objective of the present work is to clarify the effect of calcination temperature on the structure and surface properties of SO42−/TiO2. A variety of characterization techniques, involving X-ray diffraction (XRD), Brunauer–Emmett–Teller analysis (BET), X-ray photoelectron spectroscopy (XPS), surface photovoltage spectroscopy (SPS), and electron spin resonance (ESR), were employed in this study. XRD revealed that well-crystallized titania was formed upon calcination at 300 °C (SO42−/TiO2-300). Owing to the stabilization effect of sulfate, SO42−/TiO2-300 exhibited small crystalline size and high surface area, which can account for its superior photocatalytic performance. Catalyst calcination at 600 °C (SO42−/TiO2-600) rendered rapid growth of crystalline size and drop of surface area. Meanwhile, such high-temperature calcination treatment gave rise to Ti3+ defects and oxygen vacancies. Although the photoactivity of SO42−/TiO2-600 was remarkably reduced as compared with SO42−/TiO2-300, it was still higher than that of Degussa P25 due very likely to the formation of Ti3+-oxygen vacancies-Ti3+ sites that are beneficial for the separation of photoinduced electrons and holes.

Significance A novel approach for ultra-deep desulfurization of diesel fuel was proposed, in which the original fuel was treated by light irradiation before adsorptive desulfurization (ADS) over the TiO2–CeO2/MCM-48 adsorbent under ambient conditions. A superior capacity of 95 cm3-fuel/g-adsorbent (32 times higher than that of the original fuel) was achieved. The promoting effect of light irradiation was likely through in situ peroxides generation in fuel under visible light/sunlight, which may oxidize organosulfur to form strongly adsorbed sulfones over the adsorbent.

This work was undertaken to systemically study the effect of various process parameters (solvent type, reaction temperature, hydrogen pressure, coal rank, and coal particle size) on the rheological properties of coal-derived liquids (CDLs). Among three investigated solvents (tetralin, a medium oil, and a heavy oil), only tetralin enhanced the coal conversion because of its superior hydrogen-donor capability. The viscosity of the CDLs exhibited a strong positive correlation with that of the solvent used. The increase of either reaction temperature or hydrogen pressure decreased the viscosity of the CDLs. A comparison of coal rank illustrated that a bituminous coal resulted in higher viscosity of the products than a subbituminous coal. The experiments performed with three different coal particle sizes (―60, ―100, and ―200 mesh) showed that coal with a smaller particle size distribution generated lower viscosity liquid products. It can be deduced that the coal liquefaction process parameters have a strong effect on the chemical compositions of CDLs and, therefore, their physical properties, such as viscosity. To accurately predict CDL viscosity, preliminary work was conducted to correlate the viscosities of CDLs generated at different conditions with other CDL physical properties [e.g., boiling point and American Petroleum Institute (API) gravity] using three commonly used petroleum viscosity correlations. The results showed that the predicted viscosities were much lower than the measured ones because of the presence of stronger hydrogen bonding in CDLs than in petroleum fractions. A simple correction could improve the viscosity prediction for the CDLs generated from tetralin by reducing an absolute average deviation from 65 to 28%.

Sulfate radical-based advanced oxidation technologies (SR-AOTs) are attracting considerable attention due to the high oxidizing ability of SRs to degrade organic pollutants in aqueous environments. This study was carried out to respond to current concerns and challenges in SR-AOTs, including (i) need of heterogeneous activation of sulfate salts using transition metal oxides, (ii) nanoscaling of the metal oxide catalysts for high catalytic activity and promising properties with respect to leaching, and (iii) easy removal and recovery of the catalytic materials after their applications for water and wastewater treatments. In this study, we report a novel approach of using Fe–Co mixed oxide nanocatalysts for the heterogeneous activation of peroxymonosulfate (PMS) to generate SRs targeting the decomposition of 2,4-dichlorophenol, and especially focus on some synthesis parameters such as calcination temperature, Fe/Co contents, and TiO 2 support. The physicochemical properties of the catalysts were investigated using porosimetry, XRD, HR-TEM, H 2 -TPR, and XPS. Ferromagnetic CoFe 2 O 4 composites formed by thermal oxidation of a mixed phase of Fe and Co exhibited significant implications for the efficient and environmentally friendly activation of PMS, including (i) the cobalt species in CoFe 2 O 4 are of Co(II), unlike Co 3 O 4 showing some detrimental effects of Co(III) on the PMS activation, (ii) CoFe 2 O 4 possesses suppressed Co leaching properties due to strong Fe–Co interactions (i.e. Fe–Co linkages), and (iii) Fe–Co catalysts in form of CoFe 2 O 4 are easier to recover due to the unique ferromagnetic nature of CoFe 2 O 4 . In addition, the presence of Fe was found to be beneficial for enriching hydroxyl group content on the Fe–Co catalyst surface, which is believed to facilitate the formation of Co(II)-OH complexes that are vital for heterogeneous PMS activation.

In order to generate sulfate radicals (SRs) as oxidizing species for the degradation of 2,4-dichlorophenol (2,4-DCP) in water, we explored heterogeneous activation of peroxymonosulfate (PMS) by supported cobalt catalysts. More attention was given to the effect of support materials (Al2O3, SiO2, TiO2) and cobalt precursors (Co(NO3)2, CoCl2, CoSO4) on cobalt–support interaction, cobalt leaching, and reactivity of the catalysts. Especially, the feasibility of simultaneous generation of SRs and hydroxyl radicals (HRs) in PMS-Co/TiO2 systems was first studied under ultraviolet (UV) radiation. Much lower cobalt leaching was observed in Co/Al2O3 and Co/TiO2 systems than that of Co/SiO2 most probably due to their relatively strong cobalt-support interaction. Co/TiO2 catalyst prepared with Co(NO3)2, compared to CoCl2 or CoSO4 (where Cl− and SO42−, respectively, were not completely removed upon heat treatment at 500 °C), showed strong cobalt–support interaction, and thereby exhibited negligible cobalt leaching. Under UV radiation, Co/TiO2 at Co/Ti molar ratio of 0.001 showed significant improvement in the degradation of 2,4-DCP due to HRs. The effective generation of HRs in the system can be explained with Co(III)-mediated charge transfer from the photoinduced electrons to PMS, inducing facilitation of photoinduced electron-hole separation. However, high cobalt loading (i.e., Co/Ti molar ratio of 0.1) on TiO2 surface exhibited negligible enhancement of 2,4-DCP transformation under UV radiation since the penetration of UV light to TiO2 was prohibited by the cobalt.

The photolytic degradation of chlorinated aromatics namely pentachlorophenol (PCP) in 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF 6 ] room temperature ionic liquid (RTIL) has been investigated using UV radiation of 253.7 nm. At low concentrations (less than 1.57 mM), PCP could be degraded in this RTIL following pseudo-first-order kinetics. Addition of H 2 O 2 at different concentrations in the presence of UV 253.7 nm radiation showed an inhibition effect on the PCP degradation rate. The degradation of PCP was also studied using a radical-enhanced degradation process using Fe(II)/UV activation of Oxone. Initial studies showed that the enhancement of reaction rate in this case was approximately 72% when compared to only UV at a high PCP concentration of 0.225 mM. However greater Oxone concentrations exhibited an inhibition effect similar to H 2 O 2 addition. Quenching studies with tertiary butyl alcohol (TBA) suggested the generation of hydroxyl radicals in the ionic liquid. In situ degradation of PCP extracted from soils, namely, montmorillonite (MT) and glacial till (GT), using [BMIM][PF 6 ] showed enhanced reaction rates compared to those of the samples prepared by dissolving the compounds directly in the ionic liquid solvent. It is suggested that some species co-extracted with the target compound could facilitate the photodegradation reaction. This technique has shown potential for further development into a method for the removal of organic compounds from solid surfaces in the laboratory or in industry. This would involve the extraction of organic compounds using RTILs followed by in situ photodegradation of extracted compounds in the ionic liquid phases and recycling the extractants used.

A simple and efficient approach has been set up for fabricating highly active sulfated titania-silica (SO(4)(2-)/TiO(2)-SiO(2)): Ti(SO(4))(2) was hydrolyzed in the presence of silica, making it possible to sulfate titania and form titania-silica mixed oxide in one step. This study was focused on investigating the roles of sulfate species and silica in improving the physicochemical properties and photoactivity of SO(4)(2-)/TiO(2)-SiO(2) through comparison with sulfated titania (SO(4)(2-)/TiO(2)) and sulfate-free catalysts (TiO(2) and TiO(2)-SiO(2)). Various characterization methods, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and surface photovoltage spectroscopy (SPS), were employed to test these materials. The results revealed that for SO(4)(2-)/TiO(2) and TiO(2)-SiO(2) the sole presence of either sulfate species or silica imposes negative effects on the photocatalysis behavior of titania, leading them to have negligible photoactivities. On the contrary, in the case of SO(4)(2-)/TiO(2)-SiO(2), sulfate species and silica were proved to act in a cooperative manner; therefore, the following enhanced structure and surface properties of SO(4)(2-)/TiO(2)-SiO(2) were obtained: (i) relatively well-crystallized and smaller-size (15.4 nm) anatase-phase titania was formed upon 500 degrees C calcination without forming rutile phase and (ii) the formation of active surface sulfate species promotes the separation of photoinduced electron-hole pairs and therefore accelerates the photocatalysis reaction. Therefore, its photoactivity is enhanced as a result of the favorable synergic effects between sulfate species and silica due to their simultaneous presence.

Titania–silica mixed oxide (TiO 2 –SiO 2 ) was prepared from the alkoxides: titanium tetrabutoxide (TBOT) and tetraethyl orthosilicate (TEOS), by using an ammonia–water solution as the hydrolysis catalyst. Variables included synthesis route, aging time, the type of alcohol, and calcination temperature. The materials were then evaluated as photocatalysts for the decomposition of n -heptane. Experimental results revealed: (1) the photoactivity of TiO 2 –SiO 2 prepared via the route that Ti sol and Si sol were simultaneously and slowly added, was significantly enhanced due to its good homogeneity. However, for pure TiO 2 the route that Ti sol was slowly added into ammonia–water solution was effective in inhibiting the growth of crystalline size and therefore improving the photoactivity; (2) longer aging time promoted the hydrolysis of TEOS. As a result, the intimate interaction between titania and silica (Ti–O–Si hetero linkages) were strengthened and the photoactivity was increased; (3) TiO 2 –SiO 2 prepared by using ethanol as the solvent had the best combination of crystalline size, crystallinity, and homogeneity, thus, it exhibited the best photoactivity among the mixed oxides prepared via different alcohols; (4) 600 °C calcined TiO 2 –SiO 2 possessed excellent photoactivity as compared with that calcined at 400 or 800 °C due to the good crystallinity and the synergism between Ti–O–Si hetero linkages and surface hydroxyl groups.

Two different synthesis routes were applied to prepare TiO2–XSiO2 (X denotes mol% of silica in titania–silica mixed oxides) with different silica concentrations by using ammonia water as hydrolysis catalyst. Through comparing the photocatalytic performance of two sets of mixed oxides, we found that the photocatalytic activity of mixed oxides prepared via the route which can promote homogeneity, was significantly enhanced as compared with that of counterparts prepared via the another route, and the highest photocatalytic activity obtained by adding about 9.1 mol% silica into titania was much higher than that of pure TiO2. The mixed oxides were investigated by means of XRD, thermal analysis, UV–vis, FT-IR and XPS. The characterization results suggest that, in comparison with pure TiO2, the mixed oxides exhibit smaller crystallite size and higher thermal stability which can elevate the temperature of anatase to rutile phase transformation due to the addition of silica. Furthermore, Bronsted acidity, which is associated with the formation of Ti O Si hetero linkages where tetrahedrally coordinated silica is chemically mixed with the octahedral titania matrix, may be a very important contribution to the enhanced photocatalytic activity of titania–silica mixed oxides as well.

Gas–solid heterogeneous photocatalytic oxidation (PCO) of heptane and toluene over UV-illuminated pure titania, titania–silica mixed oxides and sulfated titania was investigated at room temperature in a batch reactor. By comparing the photocatalytic activities of the different catalysts, we draw the following two conclusions: (1) there is no clear relationship between the crystalline phase and photocatalytic activity; (2) larger surface area is not always effective in the photocatalytic process and its effects on the photocatalytic activity strongly depend on the nature of the reactant used. In addition, the study on the behavior of catalyst deactivation and regeneration shows that titania–silica mixed oxide is deactivated more slowly than pure titania and sulfated titania, and for sulfated titania the regeneration temperature can be lowered due to the presence of SO42−.

Highly active sulfate-promoted rutile titania (SO(4)(2-)/TiO(2)) with smaller band gap was prepared by an in situ sulfation method, that is, under moderate conditions, sulfate-promoted rutile titania was directly obtained via precipitating Ti(SO(4))(2) in NaOH solution followed by peptizing in HNO(3) without the phase transformation from anatase to rutile. Thus, the negative impacts of phase transformation from anatase to rutile on the structure, surface, and photoactivity properties of the catalysts due to higher calcination temperature can be avoided. The catalysts were characterized by means of thermal analysis, Brunauer-Emmett-Teller analysis (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), UV-visible spectroscopy, FT-IR pyridine adsorption, and temperature-programmed desorption (TPD). The results show sulfate species are sensitive to the variation of calcination temperature. In the process of peptizing, sulfate species are homogeneously dispersed throughout the bulk of catalysts, allowing sulfate species to penetrate into the network of TiO(2) effectively. After being calcined at 300 degrees C, sulfate species occupy oxygen sites to form Ti-S bonds, as evidenced by XPS results. As calcination temperature is further increased to 600 degrees C or above, the active sulfate species on the catalyst surface are destroyed, and the sulfate species in the network of TiO(2) are expelled out onto the surface to form inactive sulfate species. Thus, Ti(3+) defects will be produced on the catalyst surface. Accompanying this process, surface area is decreased promptly, and crystalline size is greatly increased via two fast growth phases due to the decomposition of sulfate species with different binding forces. Most importantly, the band gap of SO(4)(2-)/TiO(2) is remarkably shifted to the visible light region due to the formation of Ti-S bonds, and with increasing calcination temperature the visible light absorption capability is reduced due to breakage of Ti-S bonds. The excellent photoactivity of 300 degrees C calcined SO(4)(2-)/TiO(2) can be explained by its small crystalline size, high surface area, loose and porous microstructure, and the generation of Bronsted acidity on its surface.