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The promotion of O2 adsorption on semiconductor surfaces for effectively capturing photogenerated electrons in the photocatalytic degradation of pollutants is highly desired. In this study, the targeted co-modification of residual chlorine rutile TiO2 nanorods with phosphoric and boric acids has been accomplished for the first time by simple wet chemical processes. The key to targeted co-modification is to connect –P–OH and –B–OH to the Cl-residual TiO2 surfaces by –Ti–OH and –Ti–Cl, respectively, consequently forming –Ti–O–P–OH and –Ti–Cl:B–OH ends. By means of the atmosphere-controlled surface photovoltage spectroscopy, the degrees for capturing photogenerated electrons by the adsorbed O2 as receptors on the resulting TiO2 nanorods are quantitatively analyzed. It is confirmed that the targeted co-modification could greatly promote the capture of the photogenerated electrons compared to the phosphate and borate modification alone. This is attributed to increased amounts of adsorbed O2 based on electrochemical O2 reduction and O2 temperature-programmed desorption measurements, further leading to the enhanced separation of photogenerated charges, characterized by an increase in the amount of produced hydroxyl radicals. This is responsible for the obviously enhanced photocatalytic activity of TiO2 nanorods towards the degradation of colorless gas-phase acetaldehyde and liquid-phase phenol. This work would provide us a feasible route for the co-modification with inorganic acids to synthesize efficient nanosized TiO2-based photocatalysts. [ABSTRACT FROM AUTHOR]

In general, an increase in O2 adsorption is highly desirable for efficient photocatalysis. Herein, commercial P25 TiO2 is modified with an F127-containing SiO2 sol, and post-treated with phosphoric acid. It is confirmed, on the basis of O2 temperature-programmed desorption measurements, that the O2 adsorption of commercial P25 TiO2 is greatly promoted through its modification with porous SiO2, especially in the phosphate-treated case. The promotion of O2 adsorption is attributed to the introduction of SiOH and POH as surface ends, and to the slightly increased surface area. Interestingly, it is concluded that the promotion of O2 adsorption is favorable for the separation of photogenerated charge carriers, as seen from the steady-state surface photovoltage spectra, transient-state surface photovoltage responses, and measurements of the hydroxyl radicals produced. This is responsible for the clear enhancement in the photocatalytic activity of modified TiO2 for the degradation of gas-phase acetaldehyde and liquid-phase phenol as colorless pollutants. This work provides a feasible route for improving the photocatalytic activity of TiO2. [ABSTRACT FROM AUTHOR]

In general, an increase in O2 adsorption is highly desirable for efficient photocatalysis. Herein, commercial P25 TiO2 is modified with an F127-containing SiO2 sol, and post-treated with phosphoric acid. It is confirmed, on the basis of O2 temperature-programmed desorption measurements, that the O2 adsorption of commercial P25 TiO2 is greatly promoted through its modification with porous SiO2, especially in the phosphate-treated case. The promotion of O2 adsorption is attributed to the introduction of SiOH and POH as surface ends, and to the slightly increased surface area. Interestingly, it is concluded that the promotion of O2 adsorption is favorable for the separation of photogenerated charge carriers, as seen from the steady-state surface photovoltage spectra, transient-state surface photovoltage responses, and measurements of the hydroxyl radicals produced. This is responsible for the clear enhancement in the photocatalytic activity of modified TiO2 for the degradation of gas-phase acetaldehyde and liquid-phase phenol as colorless pollutants. This work provides a feasible route for improving the photocatalytic activity of TiO2. [ABSTRACT FROM AUTHOR]

N-doped nanocrystalline TiO2 is synthesized successfully through a simple ammonia-modified hydrolysis-solvothermal process. It is demonstrated that the resulting TiO2 doped with an appropriate amount of N exhibits high visible photocatalytic activities for the degradation of gas-phase acetaldehyde and liquid-phase phenol, which is attributed to its increased visible adsorption, appropriate crystallinity, and good dispersibility, whereas its UV activity is decreased. On the basis of the atmosphere-controlled surface photovoltage spectra, it is found that the doped N species can capture the photogenerated holes so as to be favorable for photogenerated charge separation, so it is suggested that its decreased UV activity results from its weak adsorption of O2 compared with that of undoped TiO2, as shown by the O2 temperature-programed desorption curves. Interestingly, the photocatalytic activity of the resulting N-doped TiO2 under visible or UV irradiation can be improved further by promoting O2 adsorption after modification with an appropriate amount of phosphoric acid. [ABSTRACT FROM AUTHOR]

In this work, commercial P25 TiO2 is modulated by post-treatments with different acidic substances, and the effects of residual acidic substances on the photogenerated charge separation of TiO2 and its photocatalytic activity are investigated in detail. It is demonstrated by means of atmosphere-controlled surface photovoltage spectroscopy that an increase in acid surface modification is favorable for improving the photogenerated charge separation of TiO2. As a result, its photocatalytic activity for the degradation of gas-phase acetaldehyde is enhanced greatly. On the basis of measurements of O2 temperature-programmed desorption of untreated and treated TiO2, it is confirmed that an increased amount of acid surface modification promotes the adsorption of O2 on TiO2. Hence, it is suggested for the first time that an increase in surface acidity through post-treatment with an appropriate amount of acidic substance leads to a clear enhancement of the photocatalytic activity of TiO2 by promoting O2 adsorption, and thus, improving the photogenerated charge separation of TiO2. This work provides a feasible route for the synthesis of high-activity oxide-based semiconductor photocatalysts through surface modification with stable inorganic acids. [ABSTRACT FROM AUTHOR]

Effectively contacted multiwalled carbon nanotube (MWCNT)-titanium dioxide nanocomposites and phosphate-functionalized MWCNT-TiO2 composites have been successfully synthesized by simple one-pot phase-separated hydrolysis-solvothermal processes. The key to this synthetic strategy is to disperse MWCNTs uniformly in Ti(OBu)4 in advance and then to put them into the toluene organic phase. The as-prepared nanocomposites between TiO2 and the correct amount of MWCNT exhibits higher activity in the photocatalytic degradation of rhodamine B than that with the resulting TiO2, although the activity in the photocatalytic degradation of gas-phase aldehyde and liquid-phase phenol is lower. Interestingly, the functionalization of MWCNTs with an appropriate amount of phosphoric acids prior to the synthesis could greatly improve the activity of the MWCNT-TiO2 nanocomposites for the degradation of aldehyde and phenol, even superior to that of commercial P25 TiO2. Based on the measurements of atmosphere-controlled surface photovoltage spectra and O2 temperature-programmed desorption, it is suggested that MWCNTs are favorable to increase rhodamine B adsorption on the composite to promote the photosensitization oxidation reactions, whereas it is unfavorable for the adsorption of O2 and responsible for the low photocatalytic activity for the degradation of colorless pollutants. Phosphate functionalization greatly enhances the amount of O2 adsorbed on the MWCNT, which leads to significant charge separation, and thus, to significant photoactivity for the degradation of colored and colorless pollutants of the nanocomposites. [ABSTRACT FROM AUTHOR]

In this work, commercial P25 TiO2 is modulated by post-treatments with different acidic substances, and the effects of residual acidic substances on the photogenerated charge separation of TiO2 and its photocatalytic activity are investigated in detail. It is demonstrated by means of atmosphere-controlled surface photovoltage spectroscopy that an increase in acid surface modification is favorable for improving the photogenerated charge separation of TiO2. As a result, its photocatalytic activity for the degradation of gas-phase acetaldehyde is enhanced greatly. On the basis of measurements of O2 temperature-programmed desorption of untreated and treated TiO2, it is confirmed that an increased amount of acid surface modification promotes the adsorption of O2 on TiO2. Hence, it is suggested for the first time that an increase in surface acidity through post-treatment with an appropriate amount of acidic substance leads to a clear enhancement of the photocatalytic activity of TiO2 by promoting O2 adsorption, and thus, improving the photogenerated charge separation of TiO2. This work provides a feasible route for the synthesis of high-activity oxide-based semiconductor photocatalysts through surface modification with stable inorganic acids. [ABSTRACT FROM AUTHOR]

Efficient N-containing TiO(2) nanoparticles with high anatase thermal stability were synthesized via a hexamethylenetetramine (HMT)-modified sol-hydrothermal process. The results showed that modification with proper amounts of HMT is effective in increasing the onset temperature of the phase transformation of TiO(2) from anatase to rutile. The enhancement of the anatase thermal stability of the modified TiO(2) was attributed to ammonia produced slowly by hydrolysis of the HMT molecules in the sol-hydrothermal process and, additionally, to the residual nitrogen species after the thermal treatment at high temperatures, as indicated by the XPS examination. Compared with the unmodified TiO(2), the modified TiO(2) obtained by a thermal treatment at high temperatures exhibited good photocatalytic performance under UV light and was found to even be superior to the commercially available P25-TiO(2). It was suggested that the residual N species (Ti-O-N), formed after the thermal treatment at high temperatures, along with the mixed phase composition, large surface area and the increase in the thermal stability, were responsible for the enhanced photocatalytic activity of modified TiO(2). It was demonstrated, by means of the surface photovoltage responses of the modified TiO(2) in different atmospheres along with the aid of an outer electric field, that the residual N species could effectively capture the photoinduced holes, which was favorable for the effective separation of the photoinduced charges. This work provides a feasible route to fabricate high-performance TiO(2)-based functional nanomaterials with high anatase thermal stability.