Environmentally Sustainable Synthesis of a CoFe2O4-TiO2/rGO Ternary Photocatalyst: A Highly Efficient and Stable Photocatalyst for High Production of Hydrogen (Solar Fuel).

Herein, a magnetically separable reduced graphene oxide (rGO)-supported CoFe2O4-TiO2 photocatalyst was developed by a simple ultrasound-assisted wet impregnation method for efficient photocatalytic H2 production. Integration of CoFe2O4 with TiO2 induced the formation of Ti3+ sites that remarkably reduced the optical band gap of TiO2 to 2.80 eV from 3.20 eV. Moreover, the addition of rGO improved the charge carrier separation by forming Ti-C bonds. Importantly, the CoFe2O4-TiO2/rGO photocatalyst demonstrated significantly enhanced photocatalytic H2 production compared to that from its individual counterparts such as TiO2 and CoFe2O4-TiO2, respectably. A maximum H2 production rate of 76 559 µmol g-1 h-1 was achieved with a 20 wt % CoFe2O4- and 1 wt % rGO-loaded TiO2 photocatalyst, which was approximately 14-fold enhancement when compared with the bare TiO2. An apparent quantum yield of 12.97% at 400 nm was observed for the CoFe2O4-TiO2/rGO photocatalyst under optimized reaction conditions. This remarkable enhancement can be attributed to synergistically improved charge carrier separation through Ti3+ sites and rGO support, viz., Ti-C bonds. The recyclability of the photocatalyst was ascertained over four consecutive cycles, indicating the stability of the photocatalyst. In addition, it is worth mentioning that the photocatalyst could be easily separated after the reaction using a simple magnet. Thus, we believe that this study may open a new way to prepare low-cost, noble-metal-free magnetic materials with TiO2 for sustainable photocatalytic H2 production.

Correction to "Environmentally Sustainable Synthesis of CoFe2O4-TiO2/rGO Ternary Photocatalyst: A Highly Efficient and Stable Photocatalyst for High Production of Hydrogen (Solar Fuel)".

[This corrects the article DOI: 10.1021/acsomega.8b03221.].

Oxygen-Functionalized and Ni+x (x=2,†3)-Coordinated Graphitic Carbon Nitride Nanosheets with Long-Life Deep-Trap States and their Direct Solar-Light-Driven Hydrogen Evolution Activity.

Graphitic carbon nitride, a 2 D layered photocatalyst coupled with transition metal oxides often shows promising photocatalytic hydrogen evolution activity. However, low surface area and poor charge separation greatly hinder its photocatalytic efficiency. A Ni+x (x=2, 3)/O-g-C3 N4 photocatalyst with a very high specific surface area (199 m2 g-1 ) has been prepared by thermal condensation and wet-impregnation methods. The oxygen-functionalized and Ni+x (x=2, 3)-coordinated g-C3 N4 produced 1664 µmol g-1 of hydrogen evolution from water under direct solar light irradiation in 4 h, which is 23 times higher than that over O-g-C3 N4 . This significant enhancement results from the combined effects of large surface area, the formation of long-life deep-trap states, effective charge carrier separation, and extended visible light absorption. The separation and transport behavior of the charge carriers are investigated by photoluminescence, time-resolved photoluminescence, photocurrent and Mott-Schottky measurements. Additionally, the interaction between Ni+x (x=2, 3) and O-g-C3 N4 is studied by X-ray photoelectron spectroscopy, X-ray diffraction, and FTIR spectroscopy. The Ni+x (x=2, 3)/O-g-C3 N4 photocatalyst shows remarkable reusability over a period of two months (six cycles). This study may provide a pathway to simultaneously overcome the challenges of low surface area and poor charge separation in g-C3 N4 -based photocatalysts.

Ultrasound assisted synthesis of reduced graphene oxide (rGO) supported InVO4-TiO2 nanocomposite for efficient hydrogen production.

Herein, a ternary nanocomposite, comprising metal oxide (InVO4 and TiO2) photocatalysts supported on rGO sheets was prepared via the hydrothermal method in the presence and absence of ultrasound irradiation. The photocatalytic performance of the prepared rGO/InVO4-TiO2 nanocomposites was evaluated for H2 evolution activity from water splitting with glycerol as a sacrificial agent. Interestingly, a synergistic effect (6-fold) was observed with rGO/InVO4-TiO2 nanocomposite prepared with the help of ultrasound compared to the samples prepared without ultrasound. The optimized nanocomposite (rGO/InVO4-TiO2) exhibited a maximum H2 evolution of 1669 µmol h-1, a ∼13-fold enhancement compared to the bare TiO2. This remarkable enhancement is mainly due to the synergistic effect induced by ultrasonic irradiation along with the shifting of the optical band gap of TiO2 from 3.20 eV to 2.80 eV by loading of InVO4 and rGO and also strong chemical bonding between metal (Ti) and C through Ti-C bond formation, as identified by UV-vis DRS spectra and XPS spectra, respectively. Moreover, a significant quenching of PL emission intensity and smaller radius arc of the Nyquist plot in the EIS were observed when the rGO and InVO4 were loaded in TiO2, indicating the efficient charge carriers separation and transfer in the presence of rGO sheet, resulting in enhanced photocatalytic activity. Thus, application of ultrasound has played significant and important roles in substantially enhancing hydrogen evolution along with rGO and InVO4 acting as support and co-catalyst, respectively.