Aqueous photodegradation of methyl orange and antimicrobial activity against E. coli and S. aureus bacteria using pH modified MgO nanomaterials

A review on degradation of organic dyes by using metal oxide semiconductors

The discharge of organic dye pollutants in natural water bodies has put forward a big challenge of providing clean water to a large part of the population. As the population is increasing with time, only underground water is not sufficient to complete the water requirements of everyone everywhere. Purification of wastewater and its reuse is the only way to fulfill the water needs. Nanotechnology has been used very efficiently for wastewater treatment via photocatalytic degradation of dye molecules. In the past few years, a lot of investigations have been done to enhance the photocatalytic activity of metal oxide semiconductors for water purification. In this review, we have discussed the different methods of synthesis of various metal oxide semiconductor nanoparticles, energy band gap, their role as efficient photocatalysts, radiations used for photocatalytic reactions, and their degradation efficiency to degrade the dye pollutants. We have also discussed the nanocomposites of metal oxide with graphene. These nanocomposites have been utilized as the efficient photocatalyst due to unique characteristics of graphene such as extended range of light absorption, separation of charges, and high capacity of adsorption of the dye pollutants.

V. Metal peroxides as potential photocatalysts for environmental remediation

Inorganic oxide materials such as TiO₂ and ZnO have been extensively studied for environmental remediation, that operates through photo generated Reactive Oxygen Species (ROS) such as H₂O₂, ·OH and O₂ ^- to decontaminate waste water. However, inorganic solid oxidants such as metal peroxides capable of generating ROS in aqueous solutions have not been studied for environmental remediation. Towards this objective, we have synthesized peroxides of Zn, Mg, and Ba and characterized these by powder X-ray diffraction, Transmission Electron Microscopy, UV-visible spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic activity of these wide band gap semiconductors has also been investigated. The novelty of the work is in the use of these peroxides as chemical sources of ROS in aqueous suspensions in addition to their photochemical generation. Hence, these peroxides, in particular Ba, exhibit high photocatalytic activity, better than the well-known ZnO. The mechanisms of ROS generation and subsequent dye degradation are elucidated. ROS has been estimated and is correlated to the photocatalytic activity. This work reports for the first time BaO₂ as potential photocatalyst.

Antibacterial activities against Staphylococcus aureus and Escherichia coli of extracted Piper betle leaf materials by disc diffusion assay and batch experiments

The use of contaminated water by bacteria may cause many diseases, and thus clean water is needed. Chlorine is normally used for the disinfection of wastewater treatment; however, it produces unwanted odors. Using extracted Piper betle (P. betle) is an interesting choice because it is a good chemical compound for bacterial inhibitions. This study attempted to extract P. betle leaf and synthesize P. betle beads (PBB) to characterize materials and investigate antibacterial efficiencies by disc diffusion assay, batch tests, adsorption isotherms, kinetics, and material reusability. The results demonstrated the successful extraction and synthesis of the materials of P. betle. P. betle powder (PBP) had porous and rough surfaces, whereas PBB had a spherical shape with a coarse surface. The four main chemical elements and functional groups of PBP and PBB were carbon, oxygen, calcium, chlorine, and O–H, C–H, N–H, C–O, respectively. The extraction yield and total phenolic, flavonoid, and tannin contents of P. betle were 11.30%, 201.55 ± 0.31 mg GAE per g, 56.86 ± 0.14 mg RE per g, and 41.76 ± 1.32 mg CE per g, respectively. The six main compounds of eugenol, quercetin, apigenin, kaempferol, ascorbic acid, and hydroxychavicol were detected by HPLC analysis. The results of the disc diffusion assay confirmed antibacterial efficiencies of PBB, and the batch tests examined high antibacterial efficiencies of PBB for 100% on Staphylococcus aureus and Escherichia coli. The adsorption isotherms and kinetics of PBB corresponded to Freundlich model and pseudo-second order kinetic model, and the desorption experiments confirmed the reusability of PBB. Therefore, PBB can be possibly applied for an antibacterial purpose in wastewater treatment systems.

The alternative antibacterial material (PBB) is presented with high efficiency and reusability to apply for the disinfection of wastewater systems.