The study was designed to collect water samples over two seasons-wet-monsoon season (n = 96) (March-April) and dry-monsoon season (n = 44) (September-October)-to understand the seasonal variation in anion and cation hydrochemistry of the coastal rivers and estuaries contributing in the spatial trend in salinity. Hydrochemical examination of wet-monsoon season primarily revealed Ca-Mg-HCO type (66%) and followed by Na-Cl type (17.70%) water. In the dry-monsoon season, the scenario reversed with primary water being Na-Cl type (52.27%) followed by Ca-Mg-HCO type (31.81%). Analysis of Cl/Br molar ratio vs. Cl (mg/L) depicted sampling area affected by seawater intrusion (SWI). Spatial analysis by ordinary kriging method confirmed approximately 77% sample in the dry-monsoon, and 34% of the wet-monsoon season had shown SWI. The most saline-intruded areas in the wet-monsoon seasons were extreme south-west coastal zone of Bangladesh, lower Meghna River floodplain and Meghna estuarine floodplain and south-eastern part of Chittagong coastal plains containing the districts of Chittagong and Cox's Bazar adjacent to Bay of Bengal. In addition, mid-south zone is also affected slightly in the dry-monsoon season. From the analyses of data, this study could further help to comprehend seasonal trends in the hydrochemistry and water quality of the coastal and estuarine rivers. In addition, it can help policy makers to obligate some important implications for the future initiatives taken for the management of land, water, fishery, agriculture and environment of coastal rivers and estuaries of Bangladesh.
To examine the groundwater quality a total of 120 groundwater samples were collected from two southern districts; Barguna (27 points) and Patuakali (33 points) of Bangladesh in two seasons viz., pre-monsoon (60 samples) and post-monsoon (60 samples) in 2012. A comprehensive analysis has been conducted to explore the groundwater hydrochemistry and effects of major ions on the suitability for potable water and agricultural uses. Geochemical analyses have clearly shown that the seasonal effect does change the order of abundance of major ions in the groundwater, while principal component analysis confirmed the reasons of extreme salinity and hardness. Piper diagram showed that the predominant hydrochemical facies for the groundwater were Na ? -Cl --SO 4 2-and Na ? -K ? -HCO 3 -types. The chloroalkaline index confirmed that the ion exchange was governed mainly in water phase. Equiline diagram explained the relationship among the alkali with total cations and anions where cations were more dominant than anions at 1:1 ratio. The Gibb's diagram illustrated the chemical composition of water mainly influenced by precipitation from the water sources. The molar ratio Cl -/Ranions and Na ? /Na ? ?Cl -indicated that the groundwater of the study area was affected by seawater intrusion. In addition to unsuitable salinity ([5000 ls/cm), Kelly's ratio, total hardness, sodium absorption ratio, residual Sodium carbonate, and Na % clearly indicated that the groundwater in the study area were not suitable for drinking, irrigation, and domestic uses. Moreover, the spatial distribution maps were drawn to observe the spatial extent of EC, TDS, SAR, and SSP using IDW technique. Thus, considering all the above findings this area needs special attention to ensure the supply of potable water and to maintain sustainable agricultural activities.
In this study, we report the synthesis of SiO2@TiO2 core-shell nanocomposite particles by ultrasound irradiation of a mixture of dispersed SiO2 nanoparticles, titanium-tetra-n-butoxide (TBOT), and ammonia in an ethanol-water solution medium. The resulting core-shell nanocomposite particles were characterized by SEM, TEM, FT-IR, XPS, XRF, zeta potential measurements, XRD, and UV-visible spectroscopy. Results showed that TiO2 nanoparticles coated on the surface of SiO2 were 6–10 nm in size and retained an anatase crystalline phase. Zeta potential measurements confirmed that the surface property of the SiO2 changed after TiO2 coating. SiO2@TiO2 core-shell particles demonstrated better decolorization of methylene blue dye compared to commercial TiO2 in aqueous solution under UV light. After treatment, the catalysts were separated with low-speed centrifugation and successfully reused four times without loss of activity. This study may provide some inspiration for the synthesis of other metal oxide-metal oxide core-shell nanocomposite materials through ultrasound irradiation.
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