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A-site doping of BaBi 2 NbTaO 9 by Ni 2+ was synthesized by chemical precursor solution decomposition method. The materials exhibited single-phase tetragonal structure. The crystallite size of the calcined powder exhibited 42 nm with high degree of tetragonality. Curie temperature ( T c ) was not found upto 600 °C that indicated higher T c of the material. Impedance spectroscopy showed non-Debye type of relaxation with semiconducting nature. The closeness of the activation energy for imaginary impedance relaxation and DC conductivity indicated same type of charge carriers. P–E hysteresis loop indicated ferroelectric properties of the material. Energy storage densities were calculated for charge and discharge. The highest energy efficiency was observed at 10 kV/cm electric field.

Waterbodies are day-by-day polluted by the various colored micropollutants, e.g., azo dyes enriched (carcinogenic, non-biodegradable) colored wastewater from textile industries. Water pollution has become a serious global issue as ~ 25% of health diseases are prompted by pollution as reported by WHO. Around 1 billion people will face water scarcity by 2025 and this water crisis is also a prime focus to the UNs’ sustainable development goal 6 (SDG6: clean water and sanitation). To prevent the water pollution caused by micropollutants, a mesoporous, 3D rod-like nano-oxide Ti/Al/Cr (abbreviated as TAC) has been synthesized via the solvothermal method. TAC degraded all classes of azo dyes (mono, di, tri, etc.) with > 90% efficiency under renewable energy source solar irradiation within the pH range 2–11. The detailed study was done on the photodegradation of carcinogenic di-azo dye Congo red (CR) which is banned in many countries. TAC showed 90.64 ± 2% degradation efficiency for CR at pH 7. The proposed photodegradation mechanism of CR was confirmed by the high-resolution liquid chromatography–mass spectroscopy (HRLC-MS) analysis obeying the Pirkanniemi path. The photodegradation obeyed the pseudo-1st-order kinetics and was reusable up to successive 5 cycles which can be an efficient tool to meet the UNs’ SDG:6.

Synthetic organic dyes which are produced > 10 6 tons throughout the globe per year commercially, are applied for several industrial purposes e.g., textile, tannery, cosmetic, food industries, pharmaceuticals, etc. causing several environmental hazards. About 5–50% of the dye type gets anchored to the fabrics and the rest becomes wastewater (~ 200 billion liters) which contaminates the waterbodies. As per the latest World Health Organization (WHO) report in 2018, ~ 844 million people lack basic drinkable water access worldwide. The degradation of these dyes using photocatalysts is a greener approach now-a-days than the previously reported remediation methods e.g., adsorption, precipitation, sedimentation, ion-exchange processes, etc. Carbonaceous biochar [BC] combined with metal nanoparticles called metal engrafted BC shows more than 90% photodegradation efficiency. These materials consist of promising physio-chemical properties e.g., higher surface area, porosity, lower bandgap, pH and thermal stability, etc. which lead to higher photodegradation ability towards colored wastewater treatment as compared to the pristine BC or the metal nanoparticles. This review focuses on the various contamination sources of dyes into waterbodies, soil, fishes, etc., and the efficiency of various BCs regarding the mineralization under solar irradiation. The toxicity parameters of various classes of dyes are also discussed in this review. The thermodynamic, kinetic, adsorption, pH, and mechanistic studies of the dye degradation processes in presence of BC have also been discussed with a proper mathematical approach. The various separation techniques of the BC materials from the reaction medium and the regeneration/reuse processes with the advantages and disadvantages along with some prospects for further modifications have been discussed in this review. It is expected that this review article will open up a new dimension to design more efficient metal-engrafted BC materials for the remediation of various toxic dyes under solar irradiation for upcoming use.

Spherically shaped trimetallic MnAl 2 O 4 (MAO) nanoadsorbent was prepared in an one-pot synthesis process for the removal of excess fluoride from water. The adsorbent was characterized by thermogravimetric analysis (TGA), X-ray diffraction study (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), etc. The adsorption property for fluoride on the MAO was analyzed by batch experiments varying the adsorbent dose, pH, contact time, and initial fluoride concentration. The results showed that the fluoride uptake behavior of the samples could precisely be fitted by the Freundlich model, and the maximum adsorption capacity was estimated to be 39.21 mg/g at room temperature. The pseudo-second-order models accurately described the adsorption kinetics data. The regenerated sample showed excellent reusability along with high removal capacity on real water sample also. The underlying fluoride adsorption mechanism via ion-exchange and electrostatic interaction was established from X-ray photoelectron spectroscopy (XPS) and zeta potential studies. The sample showed excellent luminescence with blue emission with a band gap of 2.6 eV. The materials also showed good elastic behavior exhibiting the Poisson’s ratio ( σ ) 0.32 and excellent latent figure print detection capacity distinguishing the clearly the ridge and furrow regions under UV light. The magnetic behavior was also found to be in long range with antiferromagnetic characteristics.

A 3D flower-shaped bimetallic nanocomposite zirconium magnesium oxide (ZMO) was prepared first time by the controlled solution combustion method using triethanolamine (TEA) as a fuel and chelating agent. The composite material was used to remove excess fluoride via adsorption. The thermal stability of the adsorbent was characterized by thermogravimetric analysis (TGA). Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD) were used to characterize the adsorbent. The surface charge of the nano adsorbent was determined by Zeta Sizer. The surface area and pore volume of the adsorbent were determined by Brunauer–Emmett–Teller (BET) isotherm and Barrett-Joyner-Halenda (BJH) methods. The adsorption behavior of fluoride was studied systematically varying the pH, contact time, adsorbent dose, and initial fluoride concentration. The adsorption followed the Langmuir isotherm model with a maximum adsorption capacity of 42.14 mg/g. The pseudo-second-order kinetic model was confirmed by the adsorption study. The maximum adsorption efficiency was in the 6–10 pH range. The reaction mechanism was mainly based on ion exchange between hydroxy and fluoride ions which was proven by X-ray photoelectron spectroscopy (XPS). Real water tests indicated that ZMO could be used as a potential defluoridation agent for fluoride containing groundwater treatment.

The majority of people on the earth bank largely on groundwater to quench their thirst. In the era of rapid population growth, the over-exploitation of groundwater gives rise to water scarcity, and people find themselves in distress to manage safe drinking water. In this backdrop, the present study is carried out in the terrain of Pre-Cambrian igneous and high- to low-graded metamorphic rocks, to assess the groundwater potential zones (GWPZs) and evaluation of groundwater quality. The map of GWPZ is produced employing the multi-criteria decision-making model and geospatial technology. It unveils that around 29% area of the watershed enjoys good GWPZ, whereas around 43% area experiences low GWPZ. The overall accuracy of the simulated model is 92%. The water quality index indicates that 68% of water samples belong to excellent to good water quality. A significant proportion of water samples (24%) are found to be unsuitable for drinking, which may be due to groundwater contamination by the process of leaching of mineral-rich weathered rocks. The presence of fluoride (F − ) beyond the maximum permissible limit (1.5 mg L − 1 ) of WHO is recorded among 18% samples of the watershed, where 24,963 souls including 3457 children aged between 0 and 6 years lived and might have ingested F − through drinking water. Hence, the health risk of those people is quite high. Children are at a more non-carcinogenic health risk of F − than adults. The study also confirms no statistically significant difference ( p ˃ 0.05) is observed between low and high GWPZ with respect to groundwater quality. The study recommends adopting a sustainable outlook to explore GWPZ, and an assessment of drinking water quality must be done before drinking.

In this article, the multifunctional behavior of novel, efficient, and cost-effective humic acid–coated nanoceria (HA@CeO 2 NPs) was utilized for the sorptive removal of U(VI), Cr(VI), and F − ions at different conditions. The production cost of HA@CeO 2 was $19.28/kg and was well characterized by DLS, FESEM, HRTEM, FTIR, XRD, XPS, and TGA. Batch adsorption study for U(VI) (at pH ~ 8), Cr(VI) (at pH ~ 1), and F − (at pH ~ 2) revealed that the maximum percentage of sorption was > 80% for all the cases. From the contact time experiment, it was concluded that pseudo-second-order kinetics followed, and hence, the process should be a chemisorption. The adsorption study revealed that U(VI) and Cr(VI) followed the Freundlich isotherm, whereas F − followed the Langmuir isotherm. Maximum adsorption capacity for F − was 96 mg g −1 . Experiments in real water suggest that adsorption is decreased in Kaljani River water (~ 12% for Cr(VI) and ~ 11% for F − ) and Kochbihar Lake water (25.04% for Cr(VI) and 20.5% for F − ) because of competing ion effect. Mechanism was well established by the kinetic study as well as XPS analysis. Because of high adsorption efficiency, HA@CeO 2 NPs can be used for the removal of other harmful water contaminants to make healthy aquatic life as well as purified drinking water. Graphical Abstract

A novel porous spherical-shaped magnesium zinc binary oxide (MZO) was successfully prepared for the first time using a chemical process for fluoride removal and photocatalytic methylene blue (MB) and Congo red (CR) dye degradation. XRD, FESEM, and TEM were studied for phase formation, topographic, crystallographic, and detailed structural information. The surface charge and optical properties of the adsorbent were studied by zeta potential and photoluminescence spectra. The synthesized nano-adsorbents showed high fluoride removal capacity (43.10 mg/g) and photocatalytic activity with a degradation efficiency of 97.83% and 78.40% for MB and CR, respectively. The adsorption was strongly pH-dependent and worked well in the range 6–9. The kinetic studies were performed for both fluoride removal and dye degradation and were found to follow pseudo-second-order and first-order rate law, respectively. The samples were found to be extremely reusable and selective for fluoride removal in presence of co-ions such as NO 3 - , SO 4 2- , and Cl - . The basic fluoride adsorption process of the samples can be related to ion exchange and electrostatic interactions, according to XPS and FTIR data. The detailed mechanistic study of photocatalytic dye degradation showed that the reaction occurred via OH radicals. Thus, MZO could be considered an effective and quick adsorbent for water purification in fluoride-containing groundwater and industrial dye wastewater.

Perovskite nanocomposite electrodes, which are made of activated carbon (AC) and lanthanum nickel oxide (LaNiO 3 ), have unique electrical and chemical properties. LaNiO 3 was synthesized using the sol–gel method, whereas the LaNiO 3 @AC nanocomposite was generated by the ultrasonication process several times, keeping LaNiO 3 and AC in a solvent of 1-methyl-2-pyrrolidone (NMP). Examine the electrochemical performance after making a supercapacitor cell by coating electrode materials on Ni foam with a 4 mg/cm 2 mass loading. The pure LaNiO 3 electrode exhibits moderate specific capacitance (C s ) of 136.82 F/g at 0.5 A/g current density with cyclic stability of 62.09% capacitance retention after 10000 cycles, including energy density and power density of 19.00 W h/kg and 1.55 kW/kg, respectively. However, the LaNiO 3 @AC nanocomposite electrode produced a high C s of 260.45 F/g at 0.5 A/g current density and exhibited remarkable cyclic stability, maintaining around 80.78% of the specific capacitance retention after 10,000 cycles. It also demonstrated an exceptional energy density of 36.17 W h/kg and a high-power density of 1.58 kW/kg. Further investigation on the storage contribution has been conducted with b-fitting, Dunn’s, and Randles Sevcik’s models. The DFT investigation provides more insight into the stability and electrochemical characteristics of the LaNiO 3 material.

Nanocrystalline layered perovskite Sr 0.5 A 0.5 Bi 2 Nb 2 O 9 (A = Co 2+ , Ni 2+ , Cu 2+ ) ferroelectric ceramics were synthesized through chemical process. The synthesized compounds were found to have tolerance values 0.90, 0.865 and 0.872 which are well within its limit. The electrical behaviour was thoroughly studied through impedance analysis within the temperature range between 400 °C and 500 °C after sintering the pressed pellet at 750 °C for 4h. Strong relaxation behaviour was found for Sr 0.5 Co 0.5 Bi 2 Nb 2 O 9 and Sr 0.5 Cu 0.5 Bi 2 Nb 2 O 9 . The ac activation energy was calculated from the relaxation behaviour. All the studied samples showed grain conductivity behaviour only. The binding energy and density of states were studied with respect to temperature and frequency. The hopping behaviour was also studied and established a correlated barrier hopping model.