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The enrichment of heavy metals and mixing with groundwater resources, which makes a serious threat to human health and the environment. The present study was conducted to determine the enrichment of heavy metals in groundwater, geochemical modelling, and to estimate the probable health risks (non-carcinogenic and carcinogenic) of a coal mining region, in eastern India. The relative abundance of mean heavy metal concentration was in the order of Fe > Zn > Al > Ba > Mn > Sr > Ni > Ag > Cu > Pb > V > Cr > Co > Cd, and are within the WHO standards limits for drinking water values. Groundwater shows pH values as generally acidic to alkaline in nature, while Eh values indicate an oxidising environment. Principal component analysis indicates, metal concentration in the groundwater to be mainly derived from the geogenic sources and in-situ leaching of mine overburden materials. Hydrogeochemical modelling indicates heavy metals are in supersaturation to near neutral state in the groundwater with oxide and carbonate mineral phases. Based on (HPI), and (HEI) values, the majority of groundwater samples are low to moderately contaminated. The health risk assessment model based on hazard quotient (HQ) and hazard index (HI) values show few groundwater samples as crossing the reference limit and have non-carcinogenic health risks for both children and adults. The study identifies the chemical characterisation and potential health risks due to the presence of heavy metals in the groundwater of the coal mining region. [ABSTRACT FROM AUTHOR]

Quaternary metal oxides, particularly those of pyrochlore-type, form a rapidly emerging class of new functional materials for photocatalytic applications in environmental purification and water splitting because of their intriguing structural and photocatalytic properties. In this work, pyrochlore structured compositions with the general formula K3MTe3O12 (M = Cr, Fe, Ga) were synthesized by a solid-state method and their photocatalytic properties are reported. The synthesized materials were subjected to X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM–EDS), transmission electron microscopy-selected area electron diffraction (TEM-SAED), N2 adsorption–desorption, Fourier transform infrared (FT-IR), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) techniques. All the compositions were crystallized in a cubic system with the Fd3m space group. All the compositions were evaluated for the photocatalytic degradation of methylene blue (MB), a toxic aromatic cationic dye, under visible light irradiation. Among the materials tested, K3CrTe3O12 offers the highest photocatalytic activity with a 96% degradation over 180 min of irradiation. Scavenger experiments were performed to find out the role of reactive oxygen species during the photocatalytic degradation of MB. The ·OH radicals were found to play a major role in the MB degradation. Furthermore, the recyclability and the chemical stability of K3CrTe3O12 were also presented. [ABSTRACT FROM AUTHOR]

The fabrication of composite photocatalysts with the surface plasmon resonance (SPR) concept has received more research interest in wastewater treatment in recent years. In this regard, an efficient composite photocatalyst, Ag/AgBr/LaAl0.5Cr0.5O3 (Ag/AgBr/LACO), was fabricated through the deposition–precipitation followed by the photoreduction method. The parent LACO was synthesized by a gel-burning method. The photocatalysts were characterized by XRD, FT-IR, FESEM-EDS, TEM-HRTEM, N2 adsorption–desorption, UV–Vis DRS, XPS, and PL techniques. The powder XRD results of LACO suggest a rhombohedral lattice with an R3c space group. The sizes of the nanoparticles are in the range of 5–45 nm. The photocatalytic activity of the samples was evaluated using the degradation of methylene blue (MB) and 4-chlorophenol (4-CP) under visible light irradiation. The Ag/AgBr/LACO composition exhibited better photocatalytic activity with 83% MB degradation and 77% 4-CP decomposition compared to that of LACO (70 and 57% of MB and 4-CP, respectively) in 180 min of irradiation. The higher photocatalytic performance of Ag/AgBr/LACO could be attributed to (a) the formation of heterojunction between Ag/AgBr and LACO, which enhanced the charge separation of photogenerated e–h pairs as indicated by PL measurements, and (b) larger surface area as reflected in N2 adsorption–desorption analysis. The trapping experiments identified •OH, and •O2− as the main reactive species involved in the photocatalytic degradation of MB. The stability and reusability of the Ag/AgBr/LACO composite were examined by five photocatalytic runs. A possible mechanism of the degradation process is proposed based on the results examined from trapping experiments. [ABSTRACT FROM AUTHOR]

Non-metal doping is a promising approach to enhance the visible light absorption of wide bandgap materials. Visible light active C and S-doped K2Ta2O6 photocatalysts were prepared by the hydrothermal method and studied. The as-prepared catalysts were well characterized by PXRD, UV–Vis DRS, FESEM-EDS-elemental mapping, carbon–sulphur analysis, TEM-SAED, XPS and BET surface area analysis. Parent K2Ta2O6 is UV-active material, while C and S-doped K2Ta2O6 exhibit visible light absorption. The photocatalytic activity of all samples was assessed by examining the photocatalytic degradation of methylene blue (MB), methyl orange (MO) dyes and a colourless pollutant 4-chlorophenol (4-CP) in the presence of visible light. The percentage of degradation of MB (MO, 4-CP) in the presence of KTO, C-KTO and S-KTO is 52 (41, 45), 84 (73, 76) and 65 (53, 56), respectively. All samples exhibit activity for MB, MO and 4-CP degradation and C-doped K2Ta2O6 showed enhanced photocatalytic performance compared to other catalysts. Scavenger studies were conducted to identify the active reactive species which degrade the MB dye molecules. Moreover, photogenerated charge carrier separation was compared for all catalysts using photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) measurements. The chemical stability and reusability of the C-doped K2Ta2O6 were tested. Furthermore, a photocatalytic mechanism is proposed for the degradation of MB over C-doped K2Ta2O6. [ABSTRACT FROM AUTHOR]

Defect pyrochlore‐type oxide, KGe0.5Te1.5O6 (KGTO) and its Ag+, Cu2+ and Sn2+ doped compositions were prepared by solid state and ion‐exchange methods respectively. The XRD results suggest that both parent KGTO and Ag+, Cu2+ and Sn2+ doped KGTO have crystallized in cubic lattice. The morphology of all compositions was obtained from SEM‐EDS and TEM‐SAED measurements. The textural properties were obtained from N2 adsorption‐desorption measurements. The FT‐IR and Raman spectra of all compositions are comparable. Surface elemental composition and electron‐hole recombination rate were deduced from XPS and PL measurements respectively. The photocatalytic performance of these materials was tested in the degradation of methylene blue (MB) and methyl orange (MO) dyes. The doping of Ag+, Cu2+ and Sn2+ into the KGTO lattice improved optical characteristics and photocatalytic activity significantly. Among the compositions investigated, Sn‐KGTO shown highest photocatalytic performance with 82 % for MB and 67 % for MO in 180 min. Trapping experiments were conducted to identify the active species participated in the MB degradation over Sn‐KGTO. The generation and participation of ⋅OH and O2−⋅ radicals were studied by terephthalic acid and potassium bromate experiments respectively. The reusability and chemical stability of Sn‐KGTO against MB degradation were also examined. A possible reaction mechanism was proposed to understand the MB degradation in the presence of Sn‐KGTO. [ABSTRACT FROM AUTHOR]