Usability, durability and regeneration of Ag/ZnO coated microreactor for photocatalytic degradation of methylene blue

A critical review on applications of microreactors for the treatment of polluted water with organic dyes

The scale-down of reaction processes by microreactors enables significant benefits over the applications of conventional reactors due to the intensification of reaction which become an emerging prospect in the environmental engineering. In the last decades, there has been a rapid pollution increase connected with various industries, in particular due to the dye and textile industries, which generate huge amounts of wastewater containing organic dyes. The abatement of dyes in wastewater using microreactors therefore has great potential. This paper reviews a rapidly emerging area of microreactors applications in the removal of dyes from polluted water and describes a survey on recent advances in the development of microreactors in this area. With respect to the nature of the treatment technique, the scope of the literature was divided into several categories - Fenton reaction, ozonation, photocatalytic degradation, reductive degradation, biotreatment, and separative sequestration. This review focusses on summarizing different configurations of reaction conditions of the respective treatment techniques, their efficiency, and, mainly, the characteristics including design, construction materials, and fabrication of microreactors applied. The evaluation and evolution of treatment techniques have also been critically analyzed, and future perspectives are proposed in this work. From the present study, it can be concluded that several treatment methods can be applied for removal of organic dyes in a wide range of microreactor designs. Furthermore, this work showcases how microreactor technology may improve mass transfer as well as treatment efficiency. A novelty of the this review article lies in (i) data analysis with emphasis on reaction conditions as well as microreactor designs, and, based on this, in (ii) the proposition of decision-making algorithm which can facilitate a designing of the dyes removal in microreactors.

Antibacterial and Photocatalytic Activity of ZnO/Au and ZnO/Ag Nanocomposites

The use of a combination of nanoparticles as antimicrobial agents can be one strategy to overcome the tendency of microbes to become resistant to antibiotic action. Also, the optimization of nano-photocatalysts to efficiently remove persistent pollutants from wastewater is a hot topic. In this study, two composites ZnO/Au (1% wt.) and ZnO/Ag (1% wt.) were synthesized by simple aqueous solution methods. The structure and morphology of the r nanocomposites were analyzed by structural and optical characterization methods. The formation of AuNPs and AgNPs in these experiments was also discussed. The antimicrobial properties of ZnO, ZnO/Au, and ZnO/Ag nanomaterials were investigated against Gram-negative bacteria (Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus). The results showed an increase of 80% in the antimicrobial activity of ZnO/Au against Pseudomonas aeruginosa compared with 30% in the case of ZnO/Ag. Similarly, in the case of the S. aureus strain tests, ZnO/Au increased the antimicrobial activity by 55% and ZnO/Ag by 33%. The photocatalytic tests indicated an improvement in the photocatalytic degradation of methylene blue (MB) under UV irradiation using ZnO/Au and ZnO/Ag nanocomposites compared to bare ZnO. The photocatalytic degradation efficiency of ZnO after 60 min of UV irradiation was ∼83%, while the addition of AuNPs enhanced the degradation rate to ∼95% (ZP2), and AgNP presence enhanced the efficiency to ∼98%. The introduction of noble metallic nanoparticles into the ZnO matrix proved to be an effective strategy to increase their antimicrobial activity against P. aeruginosa and S. aureus, and their photocatalytic activity was evaluated through the degradation of MB dye. Comparing the enhancing effects of Au and Ag, it was found that ZnO/Au was a better antimicrobial agent while ZnO/Ag was a more effective photocatalyst under UV irradiation.