The benefits of increasing the number of surface hydroxyls on TiO2 nanoparticles (NPs) are known for environmental and energy applications; however, the roles of the hydroxyl groups have not been characterized and distinguished. Herein, TiO2 NPs with abundant surface hydroxyl groups were prepared using commercial titanium dioxide (ST-01) powder pretreated with alkaline hydrogen peroxide. Through this simple treatment, the pure anatase phase was retained with an average crystallite size of 5 nm and the surface hydroxyl group density was enhanced to 12.0 OH/nm2, estimated by thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Especially, this treatment increased the amounts of terminal hydroxyls five- to six-fold, which could raise the isoelectric point and the positive charges on the TiO2 surface in water. The photocatalytic efficiency of the obtained TiO2 NPs was investigated by the photodegradation of sulforhodamine B under visible light irradiation as a function of TiO2 content, pH of solution, and initial dye concentration. The high surface hydroxyl group density of TiO2 NPs can not only enhance water-dispersibility but also promote dye sensitization by generating more hydroxyl radicals.

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Gold nanoparticles (NPs) and nanorods (NRs) were synthesized by chemical reduction in the aqueous micellar solution of ionic surfactants. Their surfaces were subsequently modified by cysteine. In the cationic cetyltrimethylammonium bromide (CTAB) solution, the linear cross‐assembly of gold NRs with NPs in alternate order was observed and could be related to the size‐dependent densities of their surface charges. The irregular aggregation of gold NRs (and NPs) appeared in the anionic sodium dodecyl sulfate (SDS) solution. Micellar electrokinetic capillary chromatography (MEKC) showed that cysteine‐binding gold NRs resulted in the decrease of their negative surface charge in the SDS solution. Experimental results indicated that the ionic surfactant which stabilized both gold NPs and NRs has the extraordinary effect on not only the location of the surface modification but also the interaction of the assembly for these NPs and NRs. Mechanism on the assembly of gold NPs and NRs in the ionic solutions will be discussed.