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The separation, transfer and recombination of charge often affect the rate of photocatalytic reduction of CO2. Schottky junctions can promote the rapid separation of space charge. Therefore, in this paper, Pd nanosheets were grown on the surface of DUT-67 by a hydrothermal method, and a Schottky junction was constructed between DUT-67 and Pd. Under the action of the Schottky junction, the CO yield of 0.3-Pd/DUT-67 reached 12.15 μmol/g/h, which was 17 times higher than that of DUT-67. Efficient charge transfer was demonstrated in photochemical experiments. The large specific surface area and the increased light utilization rate also contributed to the increase in the CO2 reduction efficiency. In addition, the mechanism of Pd/DUT-67 photocatalytic reduction of CO2 was proposed.

Photocatalytic conversion of CO2 into hydrocarbon fuels is an ideal technology of mitigating greenhouse effect caused by excessive emission of CO2. However, the high recombination rate of electron-hole pairs and limited charge carriers transport speed constrained the catalytic performance of many semiconductor catalysts. In this contribution, a series of carbon nitride (g-CN) samples with intramolecular donor-acceptor (D-A) system were successfully prepared by introducing organic donor into their structures. Characterization results confirmed that carbazole was successful connected to the structure of g-CN via chemical bond. The formation of intramolecular D-A system greatly enlarged the light response region of g-CN-xDbc. In addition, a new charge transfer transition mode was formed in g-CN-0.01Dbc due to the incorporation carbazole, which enable it to use light with energy lower than the intrinsic absorption of g-CN. Meanwhile, the D-A structure led to the spatial separation of electrons and holes in g-CN-xDbc and significantly decreased the recombination rate of electron-hole pairs. The g-CN-0.01Dbc presented the best catalytic performance and the CO evolution rate was 9.6 times higher than that of g-CN. Moreover, the reaction was performed in water without any additive, which made it green and sustainable. DFT simulation confirmed the D-A structure and charge carrier migration direction in the prepared samples.

Defect structure is one of the crucial factors for enhancing the catalytic activities of photocatalysts. However, rational design and construction of defect structures in catalysts to meet the aim of enhancing photocatalytic performance in a simple and cost-effective way is still a challenge. In this contribution, we report a strategy to construct defect structures in graphitic carbon nitride (g-CN) by simple copolymerizing of urea with polyethyleneimine (PEI). Among the prepared catalysts, u-0.05PEI presents the best photocatalytic activity for CO2 reduction, with CO and CH4 yields of 32.86 and 1.68 μmol g-1 in 4 h, which is about 3.2 and 2.5 times higher than that of g-CN, respectively. Characterization results show that both C and N defects are formed in the newly prepared catalysts. The C defects on the surface of u-xPEI result in the formation of more amino groups which are beneficial for CO2 adsorption. Meanwhile, the N defects inside the samples lead to the generation of midgap states between the valance band and conduction band of u-xPEI. The midgap states greatly enlarge the light absorption extent, and enable the use of light with energy lower than the intrinsic absorption of g-CN in the photoreduction of CO2. As confirmed by DRS, EPR, PL analysis, the excellent catalytic activity of u-0.05PEI is mainly attributed to the remarkably improved light utilization efficiency and fast charge transfer. Moreover, the reaction is performed in water without any additive or organic solvent, which makes it environmentally friendly.

Photocatalytic technology provides a new strategy for the treatment of water pollution and energy crisis. Developing photocatalytic materials with high efficiency and stable visible light response has always been the direction of scientific researchers in the photocatalytic field. In this paper, we designed and prepared an efficient and stable rGO-modifited type-I Ag2S/g-C3N4 heterojunction photocatalyst (rGO/Ag2S/CN). The TEM (Transmission electron microscope) technology shows that the morphology of rGO/Ag2S/CN is a sandwich-like structure. UV–Vis DRS (UV–visible diffuse-reflectance spectrum) shows that the loading of Ag2S NPs and the modification of rGO effectively enhance the light response performance of nanocomposite materials in visible light. PL (Photoluminescence) and PEC (Photoelectrochemical) results prove that the photogenerated carriers transport and separation efficiency of rGO/Ag2S/CN have been improved. The photodegradation of RhB and the photoreduction of CO2 results confirmed that this ternary nanocomposite has great photocatalytic activity. The photodegradation efficiency of the RhB aqueous solution is about 98.5% after 30 min under the visible light irradiation. The photoreduction experiments showed that the yields of CO and CH4 are 178.05 μmol/g and 121.11 μmol/g, respectively after 8 h under the UV light irradiation. The results of cyclic photocatalytic experiments and the XRD pattern after those processes further revealed that the modification of rGO not only enhanced the photocatalytic performance of the nanocomposite photocatalyst, but also effectively improved the stability of Ag2S in the photocatalytic process. The possible photocatalytic reaction mechanisms were discussed in detail.

Photocatalytic conversion of CO

Defect structure is one of the crucial factors for enhancing the catalytic activities of photocatalysts. However, rational design and construction of defect structures in catalysts to meet the aim of enhancing photocatalytic performance in a simple and cost-effective way is still a challenge. In this contribution, we report a strategy to construct defect structures in graphitic carbon nitride (g-CN) by simple copolymerizing of urea with polyethyleneimine (PEI). Among the prepared catalysts, u-0.05PEI presents the best photocatalytic activity for CO

Photocatalytic technology provides a new strategy for the treatment of water pollution and energy crisis. Developing photocatalytic materials with high efficiency and stable visible light response has always been the direction of scientific researchers in the photocatalytic field. In this paper, we designed and prepared an efficient and stable rGO-modifited type-I Ag