S-scheme heterojunctions based on novel Sm2CeMnO6 double perovskite oxide and g-C3N4 with excellent photocatalytic dye degradation performances.

It has become of utmost importance to preserve marine life and human health by protecting aquatic environments from contaminants. Therefore, using photocatalytic materials in treatment of contaminated water is a promising and innovative technique. Novel double perovskite Sm2CeMnO6 was synthesized through a modified Pechini sol-gel method. Also, urea and melamine were utilized to synthesize graphitic carbon nitride (g-C3N4). Combination of Sm2CeMnO6 and g-C3N4 produced several S-scheme heterojunction materials in diverse components ratios. Average crystallite sizes of Sm2CeMnO6 and Sm2CeMnO6/g-C3N4 (20:80) samples were calculated by Debye-Scherrer and Williamson-Hall methods to be 19.77, 22.72 nm and 42.01, 43.73 nm, respectively. The coexistence of g-C3N4 (002) with a d-spacing of 0.325 nm and Sm2CeMnO6 planes of (222), (111), and (400) with spacing values of 0.314, 0.302, and 0.294 nm, respectively, was depicted in the HR-TEM image of the Sm2CeMnO6/g-C3N4 (20:80). The estimated bandgaps for the g-C3N4, Sm2CeMnO6, and Sm2CeMnO6/g-C3N4 (20:80) were 2.70, 2.60, and 2.65 eV, respectively. Their application was investigated in photocatalytic degradation of methylene blue (MB) dye as typical pollutant. The estimated degradation pathway of MB was also provided through LC-MS analysis. Under the identical conditions, the best photocatalytic performance was found for Sm2CeMnO6/g-C3N4 (20:80) composite. Using response surface methodology (RSM), operational parameters of the photocatalytic degradation were modeled and optimized by the best composite through central composite design approach. Applying optimized parameters led to 96% degradation of MB (8 mg/L) at pH 10 under 120 min visible light irradiation (λ > 365 nm) using 0.15 g of Sm2CeMnO6/g-C3N4 (20:80) composite in 100 mL aqueous solution. Due to low intrinsic charge transfer resistance, modified Eg, and good performance in e‒/h+ pairs production, Sm2CeMnO6/g-C3N4 (20:80) nanocomposite was introduced as a promising S-scheme photocatalyst.

Delafossite CuCoO2/ZnO derived from ZIF-8 heterojunctions as efficient photoelectrodes for dye-sensitized solar cells.

To achieve high-performance dye-sensitized solar cells (DSSCs), it is essential to establish new and effective photoelectrode materials. Herein, we report the successful synthesis of heterojunctions including Cu-based delafossite oxide CuCoO2 and ZnO derived from zeolitic imidazolate framework-8 (ZIF-8). The layered polyhedral nanocrystals of CuCoO2 produced through a feasible low temperature hydrothermal process and the faceted nanocrystals of ZnO were achieved by heat treatment of ZIF-8. The composite heterostructures were applied as photoelectrodes in DSSCs assembled using dye N719 and a Pt counter electrode. The physicochemical characteristics (XRD, FESEM, EDAX, mapping, BET, DRS), dye loading, and photovoltaic properties (J-V, EIS, IPCE) of the fabricated materials were studied and fully discussed. Results revealed that addition of CuCoO2 to ZnO significantly improved the Voc, Jsc, PCE, FF, and IPCE. Among all cells, CuCoO2/ZnO (0.1 : 1) showed the best performance (PCE = 6.27%, Jsc = 14.56 mA cm-2, Voc = 687.84 mV, FF = 62.67%, IPCE = 45.22%) and acted as a promising photoanode in DSSCs.

Rational modification of TiO2 photoelectrodes with spinel ZnFe2O4 and Ag-doped ZnFe2O4 nanostructures highly enhanced the efficiencies of dye sensitized solar cells.

To develop effective photoelectrode nanomaterials for dye-sensitized solar cells (DSSCs), spinel ZnFe2O4 (2.5, 5, 7.5, 10 wt%) and Ag-doped ZnFe2O4 (AgxZn1-x/2Fe2O4, x = 0.1, 0.2, 0.3, 0.4 mmol) nanomaterials were added into the TiO2 photoanodes. It was found that the DSSC fabricated with TiO2 + 5 wt% ZnFe2O4 exhibited the most improved efficiency of 3.89 % among the ZnFe2O4 containing devices. Furthermore, the power conversion efficiency (PCE) values were boosted when the Ag+ cations were doped into the ZnFe2O4 crystalline lattice. The greatest PCE = 5.75 % was achieved for the solar cell assembled using TiO2 + 5 wt% Ag0.2Zn0.90Fe2O4 photoanode indicating 47.81 % improved performance relative to that of the reference DSSC containing TiO2 + 5 wt% ZnFe2O4 photoelectrode. The electrochemical impedance spectra (EIS) approved that the DSSC with the TiO2 + 5 wt% Ag0.2Zn0.90Fe2O4 photoelectrode nanomaterial had the lowest charge transfer resistance but the greatest e-h recombination resistance at the interfaces of photoanode/dye/electrolyte. Hence, it had the quickest electron transport rate, and the greatest electron collecting efficiency in addition to the highest dye loading capacity and least photoluminescence (PL) intensity (charge recombination) which were all prominently beneficial for improvement of the DSSC performance.