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For white light-rendering research activities, interpretation by using colored emitting materials is an alternative approach. But there are issues in designing the white color emitting materials. Particularly, differences in thermal and decay properties of discrete red, green, and blue emitting materials led to the quest for the search of a single-phased material, able to emit primary colors for white light generation. The current study is an effort to design a simple, single-phase, and cost-effective material with the tunable emission of primary colors by a series of Mg 1-x Ba x Al 2 O 4 :Mn 2+ nanopowders. Doping of manganese ion (Mn 2+ ) in the presence of the larger barium cation (Ba 2+ ) at tetrahedral-sites of the spinel magnesium aluminate (MgAl 2 O 4 ) structure led to the creation of antisite defects. Doped samples were found to have lower bandgaps compared with MgAl 2 O 4 , and hybridization of 3d-orbitals of Mn 2+ with O(2p), Mg(2s)/Al(2s3p) was found to be responsible for narrowing the bandgap. The distribution of cations at various sites at random results in a variety of electronic transitions between the valance band and oxygen vacancies as well as electron traps produced the antisite defects. The suggested compositions might be used in white light applications since they have three emission bands with centers at 516 nm (green), 464 nm (blue) and 622 nm (red) at an excitation wavelength of 380 nm. A detailed discussion to analyze the effects of the larger cationic radius of Ba 2+ on the lattice strain, unit cell parameters, and cell volumes using X-ray diffraction analysis is presented., (© 2024 John Wiley & Sons Ltd.)

Background: The current article is about the water treatment in which colored water contaminated by methyl orange has been used for adsorption assisted photocatalysis. Coupling of photocatalysis with the traditional water treatment processes has been in practice since last couple of years for the improvement of degradation efficiencies, for example, photocatalysis coupled with ultrafilteration, adsorption, flocculation, biological methods, photolysis, membrane distillation, etc. Among all these coupling approaches, adsorption assisted photocatalysis being a very simple and highly efficient approach is suffering from few drawbacks on the account of high cost, low stability and surface area of the adsorbent support. The present study is a contribution towards improvement in this coupling approach. A low cost, highly stable spinel magnesium aluminate (MgAl2O4) material synthesized at nanoscale is used for composite formation with antimony sulphide (Sb2S3) material having high absorption coefficient in the visible light of solar spectrum. A review of recent patents shows that the field of photoctalysis is dominated by the traditional TiO2 catalyst. The modification of TiO2 by either composite formation or by doping is the main focus., Methods: Coprecipitation method is used for the synthesis of spinel in which the desired precursors in the respective molar ratios were mixed and annealing of the resulting precipitates was carried out at 800oC for 8 h. Sb2S3 was synthesized by the hydrothermal method in which the required molar solution of precursors was mixed with urea solution and the whole mixture was maintained at 105oC for 6 hrs in a Teflon lined autoclave. The resulting suspension was then annealed at 37oC for 3 hours. The composite of Sb2S3 and MgAl2O4 has been synthesized by mixing both the materials in 1:1 and heat treated in an oven at a temperature of 200oC., Results: Peaks in X-ray diffraction pattern correspond to both the Sb2S3 and spinel phase. All the peaks corresponding to the Sb2S3 and spinel phase were found to be shifted to higher d-spacing values. This indicates the expansion of unit cells of the Sb2S3 and MgAl2O4 phases. Thermal studies show that only 3% weight loss is observed at a temperature of 200-1000oC which may be due to the loss of surface water from the sample. Surface area, pore volume and pore size obtained from N2 adsorption were 143m2/g, 0.21cc/g and 23.26Å, respectively. The removal efficiency of 0.1g catalyst for methyl orange solution of 5mg/L concentration after reaction in dark conditions for the time of one hour was calculated to be 24% owing to the adsorption. The visible light degradation efficiency of the 0.1g catalyst for 1, 5, 19, 25 and 50 mg/L concentrations of MO solutions were 97, 93, 75, 72 and 62% respectively. The dosage of the catalyst was found to have a direct relationship with the degradation efficiency. Lower pH was found suitable for the degradation owing to better interaction of catalyst surface and the adsorbed dye. Percent degradation increased with the increase in the time and temperature of reaction. The degradation kinetics followed pseudo first order rate equation; the calculated value of rate constant was 0.0102 min-1., Conclusion: The mechanism involves the excitation of electrons in the valence band of Sb2S3 to the conduction band by the absorption of visible and UV light. The electrons and holes participate in the surface reactions resulting in the formation of superoxide and hydroxyl radicals which degrade the targeted polluted. Lower concentration of MO solutions, acidic pH, higher catalyst dosage and greater reaction times were found suitable for the degradation efficiency.