Synthesis of iron oxide nanoparticles by the recently developed green approach is extremely promising because of its non-toxicity and environmentally friendly behavior. In this study, nano scaled iron oxide particles (α-Fe 2 O 3 ) were synthesized from hexahydrate ferric chloride (FeCl 3 .6H 2 O) with the addition of papaya ( Carica papaya ) leaf extract under atmospheric conditions. The synthesis of iron oxide nanoparticles was confirmed by systematic characterization using FTIR, XRD, FESEM, EDX and TGA studies. The removal efficiency of remazol yellow RR dye with the synthesized iron oxide nanoparticles as a photocatalyst was determined along with emphasizing on the parameters of catalyst dosage, initial dye concentration and pH. Increasing the dose of iron oxide nanoparticles enhanced the decolorization of the dyes and a maximum 76.6% dye degradation was occurred at pH 2 after 6 h at a catalyst dose of 0.8 g/L. Unit removal capacity of the photocatalyst was found to be 340 mg/g at dye concentration of 70 ppm and at a catalyst dose of 0.4 g/L. The synthesized nanoparticles showed moderate antibacterial activity against Klebsiella spp. , E.Coli , Pseudomonas spp. , S.aureus bacterial strains. Although the cytotoxic effect of nanoparticles against Hela, BHK-21 and Vero cell line was found to be toxic at maximum doses but it can be considered for tumor cell damage because it showed excellent activity against the Hela and BHK-21 cell lines.

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In this study, zinc oxide (ZnO) nanoparticle was synthesized by a novel route of microwave assisted method using ascorbic acid and PVA as capping agent and stabilizing agent. A prominent peak at 378 nm by UV absorption ensured the synthesis of ZnO nanoparticles. The crystalline property revealed that synthesized ZnO nanoparticle is highly crystalline having wurtzite structure. A significant band at ~ 498 to 557 cm −1 in FTIR was assigned to the characteristic stretching mode of Zn-O bond. EDX spectrum showed that ZnO nano particles were composed only with Zinc and oxygen. SEM image disclosed that ZnO nanoparticles were spherical in shape with an average particle size of 70-90 nm for the combined effect. The antimicrobial and ant-biofilm application of synthesized ZnO nanoparticle was studied against Salmonella typhi, Klebsiella spp. SK4, E. coli RN89, E. coli (gram-negative) and S. aureus-8a (gram-positive) bacteria and exhibited excellent activity against the strains. Prepared nanoparticle also found to possess outstanding photocatalytic activity against methylene blue degradation under sunlight with a T 50 and T 80 value of 71.44 and 165.87 min respectively.

Despite significant contributions to the national economy of Bangladesh, various urban developments, massive industrial and growing shipping activities are making the water of many urban rivers, including Karnaphuli River, extremely polluted. To find out the pollution sources and their possible health effects, 45 water samples were collected from 15 sampling stations. Investigation of six physicochemical parameters (pH, temperature, total dissolved solids, conductivity, salinity, and turbidity) through in-situ measurements and eight heavy metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) status using atomic absorption spectrophotometer (AAS) was carried out in this research. Both the physicochemical parameters and heavy metals exceeded the World Health Organization (WHO)’s permeable threshold limit. The calculated hazard quotient (HQ) and hazard index (HI) ingestion values indicate non-carcinogenic risk both for adults and children, but dermal exposure was within the safety limit. Carcinogenic risk analysis revealed that Cd could cause a risk of cancer in those using the river water for a long period. Spatial analysis and metal pollution index (MPI) results exhibit that downstream of the river water is more polluted than upstream of the river. Overall, the findings of this study imply that polluted water is a threat to human health and the results will also help to undertake proper management strategies and incorporate monitoring programs that study river water for the implementation of safety measures to protect human health.