Highly efficient visible light active ZnO/Cu-DPA composite photocatalysts for the treatment of wastewater contaminated with organic dye

Abstract Industrial effluents are a leading major threat for water contamination, subsequently which results in severe health associated risks. Hence, purifying wastewater before releasing into the water resources is essential to avoid contamination. In this study, ZnO/Cu-DPA nano-composites were prepared by altering the percentage of Cu-DPA (20%, 30%, 40%, and 50% which are denoted to be ZnO/20%Cu-DPA, ZnO/30%Cu-DPA, ZnO/40%Cu-DPA and ZnO/50%Cu-DPA) using a simple mechanical grinding process. Several spectroscopic studies were employed such as electron paramagnetic analysis (EPR), powdered X-ray diffractometer (PXRD), UV–Vis absorbance spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscope to characterize these nano-composites. The photo-catalytic activities of the prepared nano-composites were studied by degrading MB under visible light irradiation. ZnO, ZnO/20%Cu-DPA, ZnO/30%Cu-DPA, ZnO/40%Cu-DPA and ZnO/50%Cu-DPA degradation efficiencies were determined to be 71.8, 78.5, 77.1, and 66.1%, respectively. Among the composite catalysts, the ZnO/20%Cu-DPA coupled system are demonstrated the best efficiency (87%) for photo-degradation of MB within 80 min when exposed to visible light. The ZnO/Cu-DPA nano-composites had a greater MB photodegradation efficiency than pristine ZnO owing to p-n heterojunction in the linked system. Under visible light irradiation, the ZnO/20%Cu-DPA catalysed the conversion of dissolved O2 to hydroxyl radicals (OH·), triggering the reduction of MB. This suggests that ·OH is the primary specific active radical involved in the photo-catalytic decomposition of MB. Furthermore, EPR analysis indicates the existence of ·OH in the photo-catalytic system. The proposed nano-composites (ZnO/20%Cu-DPA) reusability was investigated across three cycles as the most efficient photo-catalyst. The results show that, the ZnO/Cu-DPA nano-catalyst is a potential candidate for the remediation of dirty water

Site Activity and Population Engineering of NiRu-Layered Double Hydroxide Nanosheets Decorated with Silver Nanoparticles for Oxygen Evolution and Reduction Reactions

Developing efficient and durable bifunctional electrocatalysts for oxygen reduction and evolution reaction (ORR/OER) is highly desirable in energy conversion and storage systems. This study prepares nickel−ruthenium layered double hydroxide (NiRu-LDHs) nanosheets subjected to decoration with conductive silver nanoparticles (Ag NP/ NiRu-LDHs), which interestingly induce their multivacancies associated with catalytic site activity and populations. The as prepared Ag NP/NiRu-LDH shows excellent catalytic activity toward both OER and ORR features with low onset overpotentials of 0.21 V and −0.27 V, respectively, with a 0.76 V potential gap between OER potential at 10 mA cm−2 and ORR potential at −3 mA cm−2 , demonstrating that it is the preeminent bifunctional electrocatalyst reported to date. Compared with pristine NiRu-LDHs, the resulting Ag NP/NiRu LDHs nanosheets require only an overpotential of 0.31 V to deliver 10 mA cm−2 with excellent durability. The superb bifunctional performance of Ag NP/NiRu-LDH is ascribed to the formation of multivacancies, mutual benefits of synergistic effect between metal LDHs and silver nanoparticles, and increased accessible active sites together with site activity are the key to the perceived performance. This work provides a new strategy to decorate LDHs and to engineer multivacancies to enhance site activity and populations simultaneously as ORR/OER bifunctional electrocatalysts

Green synthesis of Co-doped ZnO via the accumulation of cobalt ion onto Eichhornia crassipes plant tissue and the photocatalytic degradation efficiency under visible light

Nowadays, water pollution is a major concern to the globe. For this reason, various research works has been done to access pure water thereby minimizing the effect of pollutants. In this work, the cobalt doped ZnO (Co-doped ZnO) via the accumulation of cobalt ion onto Eichhornia crassipes plant tissue for different days and combined with zinc precursor was synthesized. The resulting catalyst powder samples were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), and Ultraviolet–vis (UV–vis) spectroscopy, and microwave plasma atomic emission spectrometer (MP-AES). The catalysts were also tested for the photocatalytic degradation of methylene blue (MB) in the presence of H _2 O _2 under visible light irradiation. The best catalytic activity was gained by the 8th-days accumulation of cobalt ion onto the Eichhornia crassipes plant tissue and 99.6% of the dye was degraded within 45 min. However, 69.6, 65.7, 73.6, and 94.8% of MB dye was degraded by 1, 2, 4, and 6 days accumulations. Hence, removal of toxic heavy metal by using Eichhornia crassipes plant and recycling in the wastewater treatment gain is highly appreciated. Moreover, the Co-doped ZnO photocatalysts could enhance the photocatalytic activities due to suppressing of the electron and hole recombination and the porosity of the catalysts resulted from the Eichhornia crassipes plant after calcination