A generation of reactive oxygen species (ROS) from TiO2 under solar light has been long sought since the ROS can disinfect organic pollutants. We found that newly developed crystalline/amorphous reduced TiO2 (rTiO2) that has low energy bandgap can effectively generate ROS under solar light and successfully remove a bloom of algae. The preparation of rTiO2 is a one-pot and mass productive solution-process reduction using lithium-ethylene diamine (Li-EDA) at room temperature. Interestingly only the rutile phase of TiO2 crystal was reduced, while the anatase phase even in case of both anatase/rutile phased TiO2 was not reduced. Only reduced TiO2 materials can generate ROS under solar light, which was confirmed by electron spin resonance. Among the three different types of Li-EDA treated TiO2 (anatase, rutile and both phased TiO2), the both phased rTiO2 showed the best performance to produce ROS. The generated ROS effectively removed the common green algae Chlamydomonas. This is the first report on algae degradation under solar light, proving the feasibility of commercially available products for disinfection.

A band gap tuning of environmental-friendly graphene quantum dot (GQD) becomes a keen interest for novel applications such as photoluminescence (PL) sensor. Here, for tuning the band gap of GQD, a hexafluorohydroxypropanyl benzene (HFHPB) group acted as a receptor of a chemical warfare agent was chemically attached on the GQD via the diazonium coupling reaction of HFHPB diazonium salt, providing new HFHPB-GQD material. With a help of the electron withdrawing HFHPB group, the energy band gap of the HFHPB-GQD was widened and its PL decay life time decreased. As designed, after addition of dimethyl methyl phosphonate (DMMP), the PL intensity of HFHPB-GQD sensor sharply increased up to approximately 200% through a hydrogen bond with DMMP. The fast response and short recovery time was proven by quartz crystal microbalance (QCM) analysis. This HFHPB-GQD sensor shows highly sensitive to DMMP in comparison with GQD sensor without HFHPB and graphene. In addition, the HFHPB-GQD sensor showed high selectivity only to the phosphonate functional group among many other analytes and also stable enough for real device applications. Thus, the tuning of the band gap of the photoluminescent GQDs may open up new promising strategies for the molecular detection of target substrates.

Visible-light-driven photocatalytic CO2 reduction using TiO2 that can absorb light of all wavelengths has been sought for over half a century. Herein, we report a phase-selective disordered anatase/ordered rutile interface system for visible-light-driven, metal-free CO2 reduction using a narrow band structure, whose conduction band position matches well with the reduction potential of CO2 to CH4 and CO. A mixed disordered anatase/ordered rutile (Ad/Ro) TiO2 was prepared from anatase and rutile phase-mixed P25 TiO2 at room temperature and under an ambient atmosphere in sodium alkyl amine solutions. The Ad/Ro TiO2 showed a narrow band structure due to multi-internal energy band gaps of Ti3+ defect sites in the disordered anatase phase, leading to high visible light absorption and simultaneously providing fast charge separation through the crystalline rutile phase, which was faster than that of pristine P25 TiO2. The band gap of Ad/Ro TiO2 is 2.62 eV with a conduction band of −0.27 eV, which matches well with the reduction potential of −0.24 VNHE of CO2/CH4, leading to effective electron transfer to CO2. As a result, the Ad/Ro TiO2 provided the highest CH4 production (3.983 μmol/(g h)), which is higher than that of even metal (W, Ru, Ag, and Pt)-doped P25, for CO2 reduction under visible light.

We performed a band modulation of the phase-selectively disordered rutile P25 TiO2 and disordered anatase P25 TiO2 and their band structures were confirmed by transient absorption spectroscopy.

A novel gas sensor consisting of porous, non-stacked reduced graphene oxide (NSrGO)-heaxfluorohydoroxypropanyl benzene (HFHPB) nanosheets was successfully fabricated, allowing the detection of dimethyl methyl phosphonate (DMMP), similar to sarin toxic gas. The HFHPB group was chemically grafted to the NSrGO via a diazotization reaction to produce NSrGO-HFHPB. The NSrGO-HFHPB 3D film has a mesoporous structure with a large pore volume and high surface area that can sensitively detect DMMP and concurrently selectively signal the DMMP through the chemically-attached HFHPB. The DMMP uptake of the mesoporous NSrGO-HFHPB was 240.03 Hz, 12 times greater than that of rGO-HFHPB (20.14 Hz). In addition, the response rate of NSrGO-HFHPB was faster than that of rGO-HFHPB, an approximately 3 times more rapid recovery due to the mesoporous structure of the NSrGO-HFHPB. The NSrGO-HFHPB sensor exhibited long-term stability due to the use of robust carbon and resulting high resistance to humidity.

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