Photocatalytic reduction of CO2 to renewable solar fuels is considered to be a promising strategy to simultaneously solve both global warming and energy crises. However, development of a superior photocatalytic system with high product selectivity for CO2 reduction under solar light is the prime requisite. Herein, a series of nature-inspired Z-scheme g C3N4/FeWO4 composites are prepared for higher performance and selective CO2 reduction to CO as solar fuel under solar light. The novel direct Z-scheme coupling of the visible light-active FeWO4 nanoparticles with C3N4 nanosheets is seen to exhibit excellent performance for CO production with a rate of 6 μmol/g/h at an ambient temperature, almost 6 times higher compared to pristine C3N4 and 15 times higher than pristine FeWO4. More importantly, selectivity for CO is 100% over other carbon products from CO2 reduction and more than 90% over H2 products from water splitting. Our results clearly demonstrate that the staggered band structure between FeWO4 and C3N4 reflecting the nature-inspired Z-scheme system not only favors superior spatial separation of the electron–hole pair in g-C3N4/FeWO4 but also shows good reusability. The present work provides unprecedented insights for constructing the direct Z-scheme by mimicking the nature for high performance and selective photocatalytic CO2 reduction into solar fuels under solar light.

In view of their ability to absorb visible light and their high surface catalytic activity, metal sulfides are rapidly emerging as promising candidates for CO 2 photoreduction, scoring over the traditional oxide-based systems. However, their low conversion efficiencies due to serious radiative recombination issues and poor stability restrict their real-life applicability. Enhancing their performance by coupling them with other semiconductor-based photocatalysts or precious noble metals as cocatalysts makes the process cost intensive. Herein, we report the single-phase ternary sulfide Cu 3 SnS 4 (CTS) as a robust visible-light photocatalyst for selective photoreduction of CO 2 to CH 4 . It showed a remarkable 80% selectivity for CH 4 evolution with the rate of 14 μmol/g/h, without addition of any cocatalyst or scavenger. The mechanistic pathway for catalytic activity is elucidated by first principle calculations and in situ ATR, which imply a formaldehyde pathway of hydrocarbon production. The Cu−Sn termination of the surface is shown to be the key factor for competent CO 2 absorption and activation as confirmed from our X-ray spectroscopy measurements and first principle calculations. This study provides a foundation and insights for the rational design of sulfide-based photocatalysts to produce renewable fuel.

A novel hybrid visible-light photodetector was created using a planar p-type inorganic NiO layer in a junction with an organic electron acceptor layer. The effect of different oxygen pressures on formation of the NiO layer by pulsed laser deposition shows that higher pressure increases the charge carrier density of the film and lowers the dark current in the device. The addition of a monolayer of small molecules containing conjugated π systems and carboxyl groups at the device interface was also investigated and with correct alignment of the energy levels improves the device performance with respect to the quantum efficiency, responsivity, and photogeneration. The thickness of the organic layer was also optimized for the device, giving a responsivity of 1.54 × 10(-2) A W(-1) in 460 nm light.

COMMUNICATION (1 of 8)improvement of efficiency and stability are required for the photocatalyst to meet the industrial requirements. To enhance the PEC activity of g-C 3 N 4 for water splitting, we report here a nanocomposite of 2D g-C 3 N 4 photocatalyst with a 2D co-catalyst in the form of titanium nitride (TiN) nanocrystals embedded N-doped graphene (TiN-NFG).Hydrogen generation using pristine g-C 3 N 4 suffers from faster recombination of photogenerated charge carriers before they could participate in redox reactions occurring on the surface. [9,10] Therefore, it is required to design a composite of g-C 3 N 4 with a co-catalyst material having a suitable band alignment to facilitate charge separation (transfer) at the interface. Toward this end, heterojunctions of g-C 3 N 4 with other semiconductors like TiO 2 , BiVO 4 , and CdS [8] have accelerated the charge separation through built-in electric field at the interface. [9] Also, heterojunctions of g-C 3 N 4 with expensive and less earth abundant noble metals (Pt, Pd, and Au) and noble metal oxides (IrO 2 and RuO 2 ) have been employed for water reduction and oxidation, respectively. [10] Cobalt-based nanomaterials are also coupled with g-C 3 N 4 to boost the water oxidation kinetics. [11] For example Wang and co-workers [11a] reported deposition of layered Co(OH) 2 on polymeric C 3 N 4 which boosted the oxygen evolution reaction almost seven times higher than pristine C 3 N 4 . In another report [12] CoSe 2 is proved to be a good co-catalyst for g-C 3 N 4 due to its lower anionic electronegativity. Also, Ni-based nanomaterials like NiO [13] and NiS [14] attached with g-C 3 N 4 have shown enhancement in reduction of water. In principle, the efficacy of charge transfer can be improved further by increasing the interfacial area per unit weight of the composite, and therefore, the possibilities of 2D co-catalyst with high surface area are also being explored. For example, Lu and co-workers [6b] showed that 2D/2D heterojunction of g-C 3 N 4 / graphdiyne significantly enhances the separation of photogenerated carriers because of excellent hole transfer nature of graphdiyne at the extended interface, eventually displaying a threefold enhancement in PEC activity. Liu et al. [15] reported almost ten times enhancement in PEC reduction of water to H 2 by loading of MoS 2 nanosheets on g-C 3 N 4 at 1 V versus RHE. Wei and co-workers [16] fabricated a heterojunction of g-C 3 N 4 Photoelectrochemical (PEC) water splitting is a sustainable pathway for solar to hydrogen conversion. Graphitic carbon nitride (g-C 3 N 4 ) nanosheets have the suitable bandgap and band-edge energies to act as a visible-light photocatalyst for water splitting, but the fast recombination of photoexcited electron-hole pair limits the efficiency. Herein, N-doped few-layer graphene (NFG) dressed with titanium nitride (TiN) nanocrystals (TiN-NFG) is introduced as an efficient co-catalyst which improved the water reduction activity of g-C 3 N 4 by 16 times. The 2D nanocomposite of g-C 3 N 4 :TiN-NFG...

NiS1.97, a sulfur-deficient dichalcogenide, in nanoscale form, is shown to be a unique and efficient photoelectrochemical (PEC) catalyst for H2 generation by water splitting. Phase pure NiS1.97 nanomaterial is obtained by converting nickel oxide into sulfide by controlled sulfurization method, which is otherwise difficult to establish. The defect states (sulfur vacancies) in this material increase the carrier density and in turn lead to favorable band line-up with respect to redox potential of water, rendering it to be an effective photoelectrochemical catalyst. The material exhibits a remarkable PEC performance of 1.25 mA/cm(2) vs NHE at 0.68 V in neutral pH, which is almost 1000 times superior as compared with that of the stoichiometric phase of NiS2. The latter is well-known to be a cocatalyst but not as a primary PEC catalyst.