In this work, we first have prepared graphene doped with different amounts of N through a one-pot ammonia-modified hydrothermal process and then successfully coupled them with nanocrystalline α-Fe2O3 by a common wet-chemical method. On the basis of the atmosphere-controlled surface photovoltage spectra, time-resolved surface photovoltage responses, and photoinduced hydroxyl radical amount measurements, it is confirmed that the photogenerated charge separation of α-Fe2O3 could be enhanced in N2 or in air atmosphere after coupling with a certain ratio of graphene. It is especially obvious with the graphene doped with a proper amount of nitrogen. This is responsible for the obviously improved visible activities of α-Fe2O3 for photoelectrochemical water oxidation to produce O2 and photocatalytic degradation of gas-phase acetaldehyde and liquid-phase phenol after coupling graphene doped with a proper amount of N species. It is suggested for the first time, mainly by means of N1s XPS data, electrochemical impedance spectra, O2 temperature-programmed desorption curves, surface acidity-related pyridine-adsorbed FT-IR spectra, and electrochemical O2 reduction measurements, that the increased amount of doped quaternary-type N would be quite favorable for photogenerated charge transfer and transportation and for O2 adsorption. As a result, photogenerated charge separation of the resulting N-doped graphene–Fe2O3 nanocomposite is greatly promoted. In addition, the enhanced O2 adsorption of α-Fe2O3 results mainly from the increased surface acidity after coupling with graphene, especially with quaternary-type N-doped graphene. This work would help us to better understand the important roles of doped N in graphene in the fabricated nanocomposites and also provide us with a feasible route to improve visible photocatalytic activities of α-Fe2O3 greatly.

The photocatalytic activity for degrading gas-phase acetaldehyde and liquid-phase phenol by graphitic carbon nitride could be greatly improved after modification with phosphoric acid, which is attributed to the clear increase in adsorbed O2 which prolongs the lifetime and enhances the separation of photogenerated charge carriers. This is based on O2 temperature-programmed desorption curves, steady-state surface photovoltage spectra, and time-resolved surface photovoltage responses.

In this work, it is clearly demonstrated that the visible photocatalytic activity for degrading colorless gasphase acetaldehyde and liquid-phase phenol of nanocrystalline a-Fe 2 O 3 , which is synthesized by a phaseseparated hydrolysis-solvothermal method, is greatly enhanced by coupling with an appropriate amount of unfunctionalized and phosphate-functionalized graphene, especially the latter. It is suggested that the enhanced activity can be attributed to the obviously increased amount of adsorbed O 2 so as to promote photogenerated charge separation, as verified mainly by means of atmosphere-controlled surface photovoltage spectra, transient state surface photovoltage responses, O 2 electrochemical reduction measurements, and O 2 temperature-programmed desorption curves. The coupled graphene is favorable for photogenerated electrons to transfer and then separate in space. This work provides a feasible route to improve photocatalytic activity for degrading pollutants using composites of nanostructured carbon and oxides.

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.

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