Minimizing CO2 emissions by photocatalytic CO2 reduction to CH3OH over Li2MnO3/WO3 heterostructures under visible illumination.

Photocatalytic CO2 reduction to valuable fuels has proved to be a favourable process to produce renewable energy and reduce CO2 emissions, which mostly depends on designing effective photocatalysts with the rapid separation rate of charge carriers. In this contribution, mesoporous n-n heterojunction Li2MnO3/WO3 nanocomposites were designed via a simplistic sol-gel process for CO2 reduction utilizing visible illumination (λ > 420 nm). XRD and TEM measurements confirmed the synthesized Li2MnO3/WO3 nanocomposite is a monoclinic structure, and its particle size is 25 ± 5 nm. The obtained Li2MnO3/WO3 exhibited narrower bandgap energy (1.74 eV), larger surface area (212 m2g-1), exceedingly visible absorbing, and lower recombination of electron and hole. The yield of CH3OH was determined about 198, 871, 1140, 1550 and 1570 mmolg-1 for bare WO3 and 5%, 10%, 15% and 20% Li2MnO3/WO3 nanocomposites, respectively. These results evidenced that the 15% Li2MnO3/WO3 photocatalyst exhibited the best reduction ability compared to other nanocomposites. The CO2 reduction over 15% Li2MnO3/WO3 photocatalyst achieved a maximal CO2 conversion with the substantially boosted CH3OH, i.e., 1550 mmolg-1 after 9 h, which was enhanced 7.8 folds great than of WO3 NPs. Mesoporous Li2MnO3/WO3 nanocomposites, in comparison with bare WO3 NPs, created more active sites for facilitating CO2 and had a specific electric field to more effectively separate charge carriers. The Li2MnO3/WO3 photocatalyst has superior photostability during the continuous reduction of CO2 for 45 h with no remarkable decrease. The possible direct S-scheme mechanism for electron transfer over Li2MnO3/WO3 photocatalyst with the enhanced CO2 reduction ability was discussed. The present work demonstrates an avenue for building highly effective heterostructure photocatalysts in solar-energy-induced potential applications.

Impact of reaction parameters for photodegradation pharmaceuticals in wastewater over gold/titania photocatalyst synthesized by pyrolysis of NH2-MIL-125(Ti).

The efficient remediation of pharmaceuticals, including wastewater, remains a remarkably challenging issue for water regeneration. Herein, porous Au/TiO2 synthesized by pyrolysis of NH2-MIL-125(Ti) was utilized to be an efficient photocatalyst for mineralization of trimethoprim (TMP) and Metronidazole (MNZ) as the parent compound. The effects of different factors, including TMP and MNZ concentrations, light intensity, H2O2 concentration, Au/TiO2 dosage, and pH value of reaction solution on the degradation and mineralization performances during UV and visible light (VIS), were addressed. The porous Au/TiO2 photocatalyst exhibited superior photocatalytic degradation of TMP and MNZ under UV and VIS illumination. The optimum pH values were 4; the optimum dosage of Au/TiO2 was 1.5 g/L, H2O2 concentration was 9.8 mM, TMP and MNZ concentrations was 10 ppm, and their photodegradation efficiency was 100% after 30 min illumination time and mineralization efficiency 98.2% after 3 h illumination for TMP and MNZ, respectively under UV illumination, however, the photodegradation efficiency was 100% after 50 min illumination and mineralization efficiency 96.3% after 4.5 h illumination time for TMP and MNZ, respectively under VIS illumination. The real wastewater matrix with 10 mg/L of TMP and MNZ were subjected to 60 min of illumination under similar optimum conditions of synthetic solution. The results indicated that photodegradation efficiency was determined to be 100% after 70 min illumination time for removal of both TMP (k = 3.4 × 10-2 min-1) and MNZ (k = 2.87 × 10-2 min-1). This is ascribed to the incorporation of Au NPs onto TiO2, reducing the photoinduced electron-hole recombination, thus promoting the photocatalytic performance. The possible mechanism for photodegradation of antibiotics was also discussed. The demonstration of photocatalysis mechanism over Au/TiO2 photocatalyst can provide some directing in the enhancement of novel photocatalysts based on MOFs doped by noble metal.

S-scheme mesoporous Li2MnO3/g-C3N4 heterojunctions as efficient photocatalysts for the mineralization of trichloroethylene in aqueous media.

Novel mesoporous Li2MnO3/g-C3N4 heterostructures were prepared for the first time by utilizing the sol-gel route in the presence of a nonionic surfactant. TEM and XRD measurements showed that Li2MnO3 (5-10 nm) with monoclinic structures was uniformly distributed onto porous g-C3N4 for the construction of Li2MnO3/g-C3N4 heterojunctions. The obtained photocatalysts were assessed for mineralization and removal of trichloroethylene (TCE) in aqueous media under visible light exposure. Complete degradation of TCE over a 3 %Li2MnO3/g-C3N4 heterostructure within 120 min was achieved. The degradation rate over Li2MnO3/g-C3N4 heterostructures was significantly enhanced, and the 3% Li2MnO3/g-C3N4 heterostructure exhibited a large degradation rate of 7.04 µmolL-1 min-1, which was enhanced by 5 and 3.8 fold compared to those of pristine g-C3N4 (1.39 µmolL-1 min-1) and Li2MnO3 (1.85 µmolL-1 min-1), respectively. The photocatalytic efficiency of the Li2MnO3/g-C3N4 heterojunction was outstandingly promoted because integrating Li2MnO3 with g-C3N4 could create close interfaces with well-matched band potentials for easy mobility and low recombination of photoinduced carriers. The coexistence of Li2MnO3/g-C3N4 interfaces led to a synergic effect, which is considered the key factor in photoinduced electron-hole separation. The synthesis procedure that was employed here is a promising process for the preparation of effective g-C3N4-based photocatalyst systems for photocatalysis applications.

Doping Strontium into Neodymium Manganites Nanocomposites for Enhanced Visible light Driven Photocatalysis.

Nd1-xSrxMnO3 nanocomposites perovskites were synthesized using sol gel method at different Sr content x = 0.3, 0.5, 0.7, and 0.9. The photocatalytic performance of the Nd1-xSrxMnO3 nanocomposites for photodegradation of Acridine orange dye (AO) was evaluated over visible light illumination. The single phase of orthorhombic pbnm was formed for x = 0.3 and 0.5; however monoclinic and orthorhombic were observed at x = 0.7 and 0.9. The Energy gap of the Nd1-xSrxMnO3 nanocomposites were estimated for all concentrations to be in the range of 3 ± 0.05 eV. The photocatalytic efficiency of Nd0.3Sr0.7MnO3 nanocomposite was 95% of the initial AO dye concentration within 3 h illumination time. The linear increase of the photodegradation rate was found in our samples as a result of the increase of Sr contents from 0.3 to 0.7wt %. Interestingly, the Nd0.3Sr0.7MnO3 content has the highest degradation rate of AO which is two times faster than undoped NdMnO3. This superior behavior in photocatalytic activity of Nd0.3Sr0.7MnO3 nanocomposite emerges from large surface area, structural anisotropy, and small particle size. These findings shows convincingly that the Nd1-xSrxMnO3 photocatalysts possess great promise for visible light driven photodegradation of AO dye.